Design of An Assist Device for... Repositioning of Bedridden Patients

Design of An Assist Device for Automated Rolling and Repositioning of Bedridden Patients by Arin Basmajian B.S., Mechanical Engineering Massachusetts Institute of Technology, 2000 Submitted to the Department of Mechanical Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Engineering BARKER OF TECHNOLOGY

at the Massachusetts Institute of Technology June 2002

OCT 2 5 2002 LIBRARIES

@ Massachusetts Institute of Technology, 2002. All Rights Reserved.

Author ............................... Depaarennte0 Mechanical Engineering May 6, 2002 Certified by ..........................

Ilaruhiko H. Asada Ford Professor Of Mechanical Engineering Thesis Supervisor

Certified by ..............................

Emesto E. Blanco

Adjunct Professor of Mechanical Engineering Thesis Supervisor Accepted by ................................ Ain A. Sonin Chairman, Department Committee on Graduate Students

2

Design of An Assist Device for Automated Rolling and Repositioning of Bedridden Patients by Arin Basmajian Submitted to the Department of Mechanical Engineering on May 6, 2002 in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering A novel design for rolling and repositioning a bedridden patient is presented. A pair of actuated rollers are attached to both sides of the bedsheet in order to lift and manipulate the patient body. The patient is gently supported on a hammock-like active bedsheet, creating virtually no shear forces on the patient body. Therefore, the patient can safely and easily be maneuvered with minimal physical assistance by the caregiver. This prevents development of painful bedsores and of pneumonia. In this thesis, functional requirements and design issues are addressed, followed by basic design concept, mechanism, and control strategy. A simple kinematic model is built to create trajectories for generation of desired body motion. A prototype is built and initial experiments demonstrate that a human body is rolled and manipulated by the assist device, providing proof of concept. Extended functionalities including bed-tochair and bed-to-bed transfers, are described at the end.

Thesis Supervisor: Haruhiko H. Asada Title: Ford Professor of Mechanical Engineering Thesis Supervisor: Ernesto E. Blanco Title: Adjunct Professor of Mechanical Engineering

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4

Acknowledgements

I would like to thank my grandfather who told me that I had to follow my dream. I wish he could be here to see it come true. I would like to thank my parents and brother, who contributed greatly to my being here today; without their unconditional love -- even during times when I was driving them crazy -- I could not have made it through. Thanks also to my aunt, Houry, for her endless support and patience. A warm thank you goes to both Professor Harry Asada and Professor Ernesto Blanco for giving me such an opportunity to work on a truly exciting project and especially for teaching and guiding me along the way. I would also like to thank Professor Sarma for taking time out and being a mentor to me during this eventful year. This thesis would not have been written without the support of my roommates, Kavita and Janelle. You were my strength when I ran out of my own. Thank you. A big thank you to all my friends, you know who you are, who reminded me of life beyond work, who believed in me, and who stood by the various decisions I made this year, yes, Jomaldo and Dinesh, that goes to you in particular.

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Thanks to Petros, for his help, both in the formatting of this thesis and otherwise. I would be very ungrateful if I did not thank my labmates in the d'Arbeloff Lab, in particular, KyuJin -- for his intense dedication to research and for heading the camera crew -- Binayak, Eric, Mikii, Phil and everyone else for being labmates, friends, advisors, critics. Oh, and for tolerating my out-oftune singing! Thanks to the machinists in the Central Machine Shop, and Steve in the Pappalardo Lab, for instructing me not just on machining and the art of painting but for all their work and support too. I truly appreciate it. I may have typed this thesis on my own but getting here was a team effort. Thank you!!!

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Table of Contents

11

CHAPTER 1

Introduction and Background .....................

CHAPTER 2

FunctionalRequirements and Design Concept ........ 15 (1) Functional Requirements ........

..........................

(2) Design Concept ...............

. ..

(3) Operation..................... Airborne Rolling................ Pivotal Rolling ................. Horizontal Translation ............. Changing Bedsheets ...............

CHAPTER 3

. 15

....... 16 ........... ........... ....... 19 . . . . . . ..... ..... 1. 20 ..... ...... ....... 21 ........... ........... ....... 21 ........... ........... ....... 22 ..

..

..

. . ..

..

..

..

.

System Modeling and Analysis .................... Modeling the Problem ................................. Determining Location of Patient............................

25 ....... .......

25 29

7

CHAPTER 4

Motion Planning..............................

33 ... 33 .... 33 .... 36 .... 38

Trajectory Generation .................................... Rolling ................................................... Bed-Bed/Chair Transfer...................................... Control ofActuators.........................................

CHAPTER 5

Implementation of FirstPrototype ..........

.. . . . . 41 41

(1) Mechanical Design and Electronics .......................... Selection of Materials and Determination of Design.................... Choosing the drive shaft ....................................... Electronics ....................................................

43 43 47

(2) Verification of Concept................................

50

(3) Verification of System Model...............................

55

System Verification..............................................56 PatientTranslation..............................................59

CHAPTER 6

(4) Control Software Implementation ...........................

60

Control Code for Rolling and Transfer ..............................

63

Conclusion and Future Work .....................

65

Discussion .............................................. Future Work............................................. Future Work regardingDesign and Structure of Device .............. Future Work with respect to Reinforcing Bedsheets.................. Future Work regardingElectrical Circuitry........................

.. 65

.. 66 ... 66 ... 68 ... 69

References....................................71 APPENDIX A

8

HistoricalRecord of Approaches ..................

73

Chronology of Designs ....................................

.. 73

Honeycomb M otion........................................... Belt and Belt................................................

... 73 ... 76

Tilt and belt................................................... Tilt and tilt.................................................... ChangingBedsheets ............................................

76 78 81

Axial Positioning...............................................

82

APPENDIX B

Assembly Drawings............................

85

APPENDIX C

PartDrawings and Listing........................

89

Part Info...................................................89

APPENDIX D

Hardware,Software and Common Operation Tips ....

123

Tips on Using the Hardware and Software of Machine..............123 To Improve Performanceof Gearboxes............................. HardwareConsiderations ...................................... Operation Considerations.......................................

123 125 125

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10

CHAPTER 1

Introduction and Background

As people get older, their mobility becomes impaired and they need assistance performing everyday tasks. In many instances, they are bedridden and may develop, in particular, bedsores and pneumonia. Bedsores are formed due to the continuous application of pressure on a person's body part. Therefore, redistribution of pressure applied to the body may be taken as a preventive measure. Also, a patient's own motion helps to reestablish blood flow and so prevents cell death. Repositioning the patient is not only advantageous for prevention of bedsores but also for preventing pneumonia. Pneumonia is an infection of one or both lungs in which fluid and damaged lung cells fill the air spaces in the lungs, making it difficult to breathe. Viral pneumonia, generally milder than the bacterial form, is the result of lower respiratory infection and has been the cause of more than 90% of deaths for individuals over 65 [1]. Stagnant mucus in the lower airways is a medium for bacterial growth, should pathogens reach

11

Introduction and Background

the lower airways. Routine turning and positioning assists in mobilization of secretions. Patients having breathing difficulties may find relief by being turned slightly on their side [3]. Caregivers move patients manually, a highly labor-intensive task. According to a survey by Garg et al [6], a nursing assistant performs over 50 such tasks per eight-hour shift. This results in alarmingly high numbers of back injuries that cost $24 billion each year [8]. In this thesis, a new methodology will be developed to assist patients in turning and repositioning. Both patients and nursing personnel will benefit from the proposed design. Bedsheets - with the aid of the marionette device presented in this paper - may be used to roll patients. Turning helps prevent bedsores. The patient is turned with almost no physical exertion or risk of injury. Only one caregiver will be able to turn the patient easily. By tilting a sheet laterally, rolling a patient becomes an easy task. It not only causes a change in the person's position, thereby altering the pressure but also stimulates blood flow. The patient may be moved to either edge of the bed. Bedsheets can easily be changed and nursing personnel no longer need to pull patients on the bed so reducing their own backache. There are a few commercially available beds that fulfill some requirements of patient and nursing personnel. Hill-Rom [4] and Kinetic Concepts Inc. (KCI) [5] are some of the companies that make hospital beds. Beds range from manually-operated to electrical ones, some even equipped with fluidized therapy units that provide pressure relief. However, their cost is exceedingly high and the beds are big and bulky. The device designed has the main advantage of having almost no set-up time. The hoists that are currently on the market, such as the Sara-Lift', often remain unused in hospitals and nursing

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homes. Nursing personnel complain that the setup time is too long. Caregivers do not wish to go through the trouble of setting up the equipment, which can sometimes take up to 20 minutes when the actual task would take a fraction of that time. Furthermore, patients feel unsafe being completely airborne when using these lifts. This thesis explores a new approach and presents a device that uses bedsheets to maneuver the human body. Using the bedsheet is beneficial to the patient because it does not produce large stress concentrations across the body, and it reduces the harmful shear forces. In addition, it is flexible so it adheres to the shape of the person. The remainder of this thesis is organized as follows. Chapter 2 deals with the methodology of the approach and the actual design. Chapter 3 presents a kinematic model. Chapter 4 introduces the analysis and control of the machine. Chapter 5 illustrates its implementation. Chapter 6 suggests extended functionalities with varying configurations of the design, and summarizes the important aspects of the design and how it may be improved respectively.

13

Introduction and Background

14

CHAPTER 2

Functional Requirements and Design Concept

(1) FunctionalRequirements Caregivers roll patients from one side of the bed to the other when changing bedsheets because rolling patients is less laborious for nursing personnel than pulling or lifting. Rolling is also used to reposition patients every few hours. The patient may be positioned on one side and may then be rolled onto his back and onto his other side to change the pressure being applied to him. Therefore, rolling is a common practice that has been widely used in caring for bedridden patients. The objective of the project was to replace this manual operation by a robotic device to assist nursing personnel in rolling and repositioning patients. The design must satisfy the following requirements whilst maintaining patient comfort: * Patients must be repositioned to redistribute the pressure applied to their bodies

15

Functional Requirements and Design Concept

* Patients must be transported from side to side to allow the bedsheets to be changed easily Shear forces applied to patients' bodies must be minimized. Patients may accidentally get sheet burns as caregivers may pull them from one side of the bed to the other to transport them. One of the laborious tasks caregivers have to face is that of changing bedsheets. Another desirable function of the device is the transfer of a patient from his/her current location to another one, that is, from the bed he/she is lying on to another bed or chair. Some of the important factors that should also be taken into consideration are quick setup times, safety and acceptability. The setup time of the device should be small because caregivers may not wish to spend too much time setting up a machine for doing a task that requires a fraction of the time required to set it up. Patients' safety is a priority. Therefore, the device should conform to safety standards. It should also be deemed acceptable by patients and caregivers in particular in terms of its appearance and function.

(2) Design Concept Figure 1 shows the basic design concept for rolling and translating the patient. It consists of a pair of powered rollers to which the bedsheet is attached on top of which the patient lies upon. The patient is suspended and supported between bedsheets as on a stretcher. Unlike a stretcher, the bedsheets are automatically wound off the rollers.

16

(2) Design Concept

FIGURE 1.

Patient suspended on Hammock-like Sheet

The design consists of a pair of parallel, independently-actuated rollers that are positioned above the bed. The rollers may be positioned using rods or arms that may be moved in two-dimensional vertical planes. The structure may either be part of the bed itself or may form a separate portable system. Each end of a bedsheet will be attached to a roller.

R2

Al

FIGURE 2.

A2

Hammock Skeleton

17

Functional Requirements and Design Concept

It was determined that arms with one degree of freedom causing rotary motion would be sufficient for the required set of tasks that are previously mentioned. Figure 2 shows a schematic of two crossed arms supporting rollers onto which the sheet is attached. The arms would be actuated at AIA 2 and the rollers at R1 R 2. The system has four degrees of freedom, the rotation of the arms, 01 and 02, and the rotation of the rollers, $1

01

FIGURE

3.

and 02-

1'0

Person lying flat waiting to be rolled.

The trajectory caused by the rotation of the arms is represented by the dashed arc shown in Figure 3 which is a side view of the bed system. The arms will be independently actuated so the horizontal and vertical distances between the rollers may vary, from almost touching one another to being at the ends of the bed. There are two modes of operation: rolling - airborne and pivotal and horizontal translation of the patient for both repositioning and transfer.

18

(2) Design Concept

(3) Operation Rolling Refer to Figures 4 and 5 for sketches of rolling and how it would occur.

P

FIGURE

4.

Person tilted by sheet action

Initially, the person lies flat on the bed. The bedsheets on either side of the person are attached to the rollers. This may be accomplished by attaching strips of VelcroTM to the ends of the sheets and the rollers. Once the sheets are attached to the respective rollers, then say the left one, is actuated in the counter clockwise direction. See Figure 4. This allows the sheet to be wrapped and the left end of the sheet decreases in length causing the person to tilt and pivot about point P as shown in Figure 4. As the roller is actuated, the sheet wraps further and the person is tilted at a greater angle.

19

Functional Requirements and Design Concept

FIGURE

5.

Person rolled by motion of left roller towards the right.

In order to roll the person completely, the left roller may be moved towards the right as shown in Figure 5. This results in the patient lying on his side. Further motion of the left roller towards the right would allow complete rolling of the patient. It would require coordination with the right roller that would have to unwind, providing slack in the sheet so the patient would be able to roll onto it. Figures 4 and 5 show that rolling and repositioning of the patient may be accomplished. Airborne Rolling: This is the case when the person is completely lifted off the bed surface. No contact is made by the person onto the bed surface at point P unlike Figures 4 and 5. Airborne rolling allows the person to be lifted and transported to either edge of the bed if either of the rollers is translated. The lifting motion eliminates harmful shear forces exerted on a patient's back as compared to him being dragged from one edge of the bed to the other. However, airborne rolling is scary for patients even though it allows complete control due to the cradling effect of the bedsheets. Airborne rolling may also be used to roll the patient in place, that is, he would not need to be translated to create space for rolling. Even if his initial position lies close to the edge of

20

(2) Design Concept

the bed, he may roll in place since the rolling action will take place off the bed surface and he would then be lowered to his original position on the bed. Pivotal Rolling: Pivotal rolling may be more acceptable for patients. It is demonstrated in Figure 4. During pivotal rolling, the patient pivots about a shoulder which remains in contact with the bed surface. Patients feel comforted by the fact that they are not completely airborne though they will experience normal and shear forces. Furthermore, using the bedsheet as the "tilting agent" results in the forces exerted on the body being distributed over a larger surface area thereby lowering the stress concentration. Supporting the patient in the sheet accounts for patient comfort and safety. The concept allows the device to be on casters hence making it portable and allowing a single module to be used for a number of hospital beds.

Horizontal Translation Horizontal translation of the patient is achieved by coordinating the movement of the arms and the rollers. Figure 6 shows the patient initially positioned on the left edge of the bed and finally translated to the right through coordination of both roller and arm motions. The angles through which the arms rotate are controlled by the actuators at the base of the bed. Assuming the initial lengths of the sheet on either side of the person are known, then the lengths of the sheets are known at every instant in time since the roller rotations are controllable. Thus, four parameters are controlled: 0,

02,

P1 and 02 The position of the rollers is uniquely

21

Functional Requirements and Design Concept

P1

FIGURE 6.

P2

Horizontal Translation of the Patient.

determined as is the location of the patient. The actuators at the rollers alone can cause rolling of the patient. If the arms are long enough to be positioned at the edge of a chair that is in line with the bed, then combining the motion of the arms may allow transfer of the patient to either edge of the bed and then onto the awaiting chair. The sequence of events is described in the next section where a preliminary model is introduced to obtain an understanding of the combination of actuator motions required to yield the desired motions of the patient.

Changing Bedsheets An added functionality of the device is that it may be used to change bedsheets. The rolling actions described above may be used to change them. The new bedsheet may be loaded onto a roller. The old sheet would be lifted and attached via VelcroTM strips to the new sheet. The rollers would be actuated in the same direction, either both clockwise or both anticlockwise. This would enable the patient to be continuously rolled a few times until the old sheet is removed and he is lying on top of the new sheet. At this instant, the

22

(2) Design Concept

rollers would slowly be brought to rest, resulting in the patient lying on top of the new sheet.

23

Functional Requirements and Design Concept

24

CHAPTER 3

System Modeling and Analysis

Modeling the Problem The kinematic model developed will be used to analyze the behavior of the system and obtain relationships between actuator movements and patient motion. As shown in Figure 7, the reference axes are fixed at the center of the bed, at the height where the actuators to control the arms are placed. As mentioned in a previous chapter, the rotation of the arms are given by 01 and 02, and the roller rotations by $ and 02-

25

--

I

-

-

-

-.---~

-

System Modeling and Analysis

D 9P2

(P

I 2

S

FIGURE 7.

S

Preliminary Model

The difference in height between the rollers is defined as H, and the horizontal distance between them is D. The angles made by the sheet on either side of the patient are respectively a and P . His angle of tilt is y with his width given by w. L, and L 2 are the lengths of the sheet on either side of the patient and T, and T2 are the tensions in the sheet. Point M is the point where the forces, that is, the weight of the patient and the tensions in the sheet, pass through.

26

--- ~-

.-

-

Modeling the Problem

The following table summarizes the parameters used. TABLE 1. List of Parameters

Symbol

Description

cc

angle made by left edge of person with left roller

P

angle made by right edge of person with right roller

LI

length of bedsheet from right edge of person to right roller

L2

length of bedsheet from left edge of person to left roller

01

angle made by left arm with the horizontal

02

angle made by right arm with the horizontal

T,

tension in left sheet

T2

tension in right sheet

1

length of each arm

Ws

width of sheet

w

total width of person

y

tilting angle of person

XRR

x-coordinate of right roller

YRR

y-coordinate of right roller

s

horizontal distance from pivot point of either arm to center of bed

D

center-to-center horizontal distance between rollers

H

center-to-center vertical distance between rollers

01

rotation of left roller

02

rotation of right roller

27

System Modeling and Analysis

Symbol

Description

XCM

x-coordinate of patient's center of mass

YCM

y-coordinate of patient's center of mass

z

height from origin, to meeting point, M, of the three forces Although the problem is actually three-dimensional, it has been

reduced to a two-dimensional problem by taking a vertical cross-section. A limitation is that if the patient is positioned diagonally across the bed, then the model does not hold as the force distribution is altered. The model is based on a number of assumptions. It is assumed that the patient suspended by the bedsheets is in quasi-static equilibrium, that is, the acceleration of the person is so small that inertial force is considered to be negligible. It is also assumed that the person is airborne. Both normal and shear forces acting by the bed on the body are equal to zero as the body is suspended by the bedsheets alone. This assumption will later be relaxed to obtain patient reassurance as some contact between the patient and the bed is established. Bedsheet elongation is assumed to be negligible. The final assumption is the initial knowledge of the values for the lengths LI, L 2 , and the width w. The geometry of the given problem results in the following kinematic relations. Considering the vertical distance between rollers, H = wsiny+L 2 sinf-Ljsin c

,

(1)

where H is a known value given by the geometry to be H =

28

l(sinO 1 - sinO2 )

,

(2)

Modeling the Problem

and 1, 01 and

02

are known variables. Considering the horizontal distance

between rollers, we obtain the relation D = wcosy + L 2cosP+ L, cosa

,

(3)

where D is known in terms of known variables as D = l(cos0 1 + cos02 )-2s

.

(4)

The y-coordinate of the person's center of mass is given by:

YCM = -Lisinca+

Wsiny

(5)

Determining Location of Patient If the location of the patient is known at every instant, then we can control the trajectory of the patient and position him as desired. Two variables would be enough to define the patient's location. The position of his center of mass, yCM, and his angle of tilt, y, would fully define his position. Taking moments about point P, the following equation is obtained:

T 1wsin(cc-y)-MgwcosF = 0,

(6)

A force balance in the vertical direction gives Tisina+ T 2 sinp = Mg,

(7)

A force balance in the horizontal direction yields Ticosa = T2 cos$.

(8)

29

System Modeling and Analysis

Given three equations, that is, Equations (6), (7), and (8), and three unknowns, the unknowns may be solved for. The known parameters are M, w, TI, and T2. The latter two parameters will be known as they will be measured using sensors and they will be estimated as a fraction of the person's weight. They will alter as functions of the angles made by the person with either side of the sheet which is how they help to obtain these values for different instances in time. The unknowns are, a,

P, and y. The most important infor-

mation is the value of y which is thus obtained. In terms of the given variables, the x-coordinate for the center of mass of the patient is obtained by the following equation,

XCM

=

xRR(

L 2 COSP+

(9)

WCOSIJ,

where XRR, the x-coordinate of the right roller, is known to be

XRR =

(10)

lcosO 1 - s

due to the positioning of the arms which depend on the angles

01 and 02-

Since the y-coordinate of the right roller is also known given as

YRR

=

lsinO,

(11)

then the length, L 2 , may be obtained from the equation,

L2 =

sin@

.

(12)

Therefore, two additional equations, Equations (9) and (12), are obtained with two additional unknowns, L 2 and xCM. They may be solved for and the location of the person's center of mass is defined.

30

Modeling the Problem

The overall equations used are rearranged as follows: wsiny +

L, sinox =

YRR -

WCosy + YRRT + L, ST2,

l(sin0,

- sin0 2 )

coscx = (CosOI+Cos02) - 2s

a = asin MgWCosY +y

(13) (14)

(15)

2T

where T, is a function of y and is also a fraction of the patient's weight. The equations obtained are non-linear. Therefore, they may be solved by either numerical analysis or by iterative methods for angle, y, and length L, in terms of known parameters, 01 and

02.

Since L, and L2 will be known, then the

rotation of the rollers are related using the following equation

+02+

L, + L2 = Ws --

,(16)

where wS is the width of the sheet. The equations shows that, to control the device, it is necessary to have only three degrees of freedom. The roller rotations are coupled. Therefore, there exists an additional -- redundant -- degree of freedom. This analysis allows the complete monitoring of the patient and determination of his position. The model is rather simplistic, in particular since it does not take into account shear forces that are experienced by the patient at the pivoting contact area as well as the normal forces acting against the patient's body when he is in contact with the bed surface. However, it will be shown in Chapter 5 that this model does indeed come close to the actual posi-

31

System Modeling and Analysis

tioning of the patient. The system model developed here will be modified to accommodate for a more empirical model in Chapter 5. The additional degree of freedom provided by the design may be useful as a controllable parameter may be altered to provide greater accessibility of the patient by nursing personnel. It may also be used to improve the efficiency of the system, that is, the line of force for one of the sheets may act along the corresponding arm thereby decreasing the torque applied by the sheet to zero, and minimizing the energy required for the system. There are two modes of operation, namely rolling and horizontal translation. Horizontal translation of the patient will be used to position the patient on the bed for rolling to occur. The patient must be accurately positioned on the bed in order to avoid tipping him over the edge of the bed when rolling occurs. Rolling is desired. This too, may be subdivided into two parts - complete rolling and half-rolling. The former is when the person is rolled through 180 degrees, that is, from lying on his back to lying on his stomach or vice versa, and the latter is when the person is rotated by 90 degrees and is positioned on his side. Horizontal translation requires the use of all four actuators that will be coordinated together to achieve the desired motion. Rolling only requires the use of the actuators at the rollers, that is, the control of 01 and 02. The parameters may be mapped using the Jacobian matrix to relate the controllable parameters,

[01

02 01

2] '

to the coordinates of the desired ones [XCM y c L2] . The fol-

lowing chapter discusses the planning of the motion based on the model presented here.

32

CHAPTER 4

Motion Planning

Trajectory Generation A number of programs have been written in order to control the sequence of motion. The two main types are either for complete rolling of the patient or to transfer a patient from the bed he is laying on to another bed or chair. The programs may have their values adjusted for different patients. The following sketches show the sequence of events in each mode of operation upon which the formulated trajectory is based.

Rolling Initially, the device is at rest. The arms are positioned in their home or zero position, that is, they are extended to the maximum.

33

Motion Planning

I

z

~

p1

FIGURE 8.

p2

Arms at Home Position.

Then, the arms are positioned according to the location of the patient on the bed as well as his width.

i-a---

Pi

FIGURE 9.

P2

Arms Positioned

The actuators controlling the bedsheet motion are switched on. They rotate in the same direction causing the patient to be slowly pivoted about one shoulder. As shown in Figure 10, both the rollers rotate clockwise.

34

Trajectory Generation

P1

P2

FIGURE 10. Rollers actuated in the same direction. The sheet is taut at the right edge of the person and correspondingly, slack is introduced in the left end of the sheet to allow the person to roll over onto the left end. The next figure shows that while the right roller causes tension in the sheet, the left continues introducing slack and meanwhile, the right arm may move left to aid the cradling effect for the patient and allow slow yet precise rolling of the patient.

FIGURE 11. Person begins to tilt

35

Motion Planning

The program would then command the entire system, that is, all four actuators to come to a complete stop to allow caregivers to detach the bedsheets from the rollers. The arms then return to their home positions.

Bed-Bed/Chair Transfer As in the case of rolling, initially, the arms are placed in their home positions.

P

P2

FIGURE 12. Patient at "Home" Position Then, one arm sweeps out to the edge of the bed/chair to which the patient will be transferred. See Figure 13. The rollers rotate in the same direction. This causes translation of the patient. The sketches show that the rollers move clockwise, causing the patient to move rightwards.

36

Trajectory Generation

P, P2 FIGURE 13. Roller Actuation causes Translation. As the patient nears the edge of the bed, the right arm moves further right to cause cradling of the patient and to enable transfer onto the bed/chair.

See Figure 14.

P,

P

2

FIGURE 14. Coordination of Roller and Arm motion allows Translation. The right roller continues to turn clockwise, pulling the patient. This motion is coordinated with the motion of the arm which travels further

37

Motion Planning

towards the right and aids the transfer of the patient from the bed he was originally laying on to the new bed/chair.

Control of Actuators Each roller and arm is assigned to an actuator. The actuators may be separately controlled in manual mode. Or, a pre-programmed file may be executed for the simultaneous motion of both arms and rollers. If a program sequence is to be used, then all the actuators are first initialized. Equations (13), (14), and (15) have been differentiated with respect to time and the velocities are given by the following relations.

(-LI)cosa

cosina-+y) Cos(a-Y)

sina

wcosy

-sin

-wsiny

coscc

-cos(c-y)+Mg

Wcosy

0

_

0

+L

(7Cos) cosy

For different values of the angle of tilt where the weight is assumed to be evenly distributed, that is, T,

=

T 2 , a number of data points have been theo-

retically obtained. They illustrate that the coupled roller rotations yield a magnitude in the range of 6 to 8 inches for a subject of width, 15 inches, and the positioning of the arms equally at 600. Sample trajectory has been generated.

38

Trajectory Generation

Sample Trajectory for Rolling, Arms Fixed at Specified Angle

7

6 0

W

-3 0

2

1

u'

1

2

3 4 5 Rotation of Right Roller, Phil

6

7

8

FIGURE 15. Sample Trajectory for Rolling Patient If AC,, corresponds to the amount of sheet wrapped on either roller, then initially, AC 1 and AC

2

are positive to enable the sheets to be taut on either

side of the patient. Once the sheet is tight, the patient is firmly supported, then AC 1 increases whereas AC

2

decreases. As sheet is wrapped around one roller,

slack is introduced in the other. Slack introduction appears as a negative amount of wrap. Figure 16 gives a simplified version of bed transfer where it is assumed that if both arms are kept horizontal and the rollers are actuated, then the sheet wrapping acts almost as a conveyor belt along the width of the bed.

39

Motion Planning

Sample Trajectory for Translation, Arms Fixed at Specified Angle

20

*

18

* *

16 14

* *

12 10 16 00

*

8

*

0f

6 *

4

*

2

0

2

4

6

8 10 12 Rotation of Right Roller, Phil

14

16

18

20

FIGURE 16. Sample Trajectory for Transferring Patient The graph shows that as the sheet is wrapped around one roller, it is correspondingly unwrapped from the other exhibiting a simple linear relationship. For a more interactive version of this prototype, communication between the sensors and the program commands will be established to enable response to various actions of the patient.

40

CHAPTER 5

Implementation of First Prototype

This chapter will consist of the following sections: (1) Mechanical Design and Electronics (2) Verification of Concept (3) Verification of System Model (4) Control Software Implementation

(1) Mechanical Design and Electronics An initial prototype of the device has been built and tested. It does indeed allow rolling of patients. It has almost no setup time, only requiring the sticking of the bedsheet onto the roller via VelcroTM. It demonstrates both the ease with which the device may be set up above the bed and with which the patient may be transported.

41

Implementation of First Prototype

5 7

(2y

1 Frame 2 Gearmount 3 Roller 4 Arm, Type 1 5 Arm, Type 2 6 Gearbox, LP-90 7 Gearbox, LP- 155 8 McMC Spur Gears 9 Bottom Joi ner 10 Edge Joiner 1 1 Leg, Type 1 12 Leg, Type 2 FIGURE 17. Design of Rolling Bed.

42

(1) Mechanical Design and Electronics

The design shown in the figure above has been chosen because it allows variation in both width and height without a significant increase in the cost of actuation. See Appendices B and C for complete assembly and part drawings. When the arms are rotated, not only do they change the height between the rollers and the patient but they also vary the width between the rollers. The former facilitates bed-bed or bed-chair transfer and the latter accommodates for different-sized patients.

Selection of Materials and Determination of Design A box frame is built for this prototype to demonstrate how the machine would work on a regular bed. The frame is made in order to have a box-spring and mattress placed upon it. It is made up of square hollow steel tubes welded to one another to cover the drive tube, support its load via a bushing, and prevent any objects from either jamming or interfering in any manner with the driving of the arms. The final prototype could have the machine on casters so that it may be portable and may be wheeled around different beds. Choosing the drive shaft: The drive shaft is made of hollow stainless steel tube with either end welded to a solid steel shaft having the same diameter, 1.75 in, but different lengths. The front and back solid steel shafts have keyways to allow transmission of torque to either of the arms as well as to the follower gears. Both the arm ends and the gears have set screws to locate the position of the arms and gears on the drive shaft. The hollow steel drive shaft was chosen to minimize deflection at the furthest end. The values were determined using the following equation,

43

Implementation of First Prototype

0 =

GJ

,

(18)

where 0 is the deflection measured in radians, T is the torque, I is the length of the shaft, G is the modulus of rigidity of the material, and J, the moment of inertia is given by the equation

=

-

.

(19)

DOWt is the outer diameter of the tube and Din is the inner diameter of

the tube. A hollow tube is chosen instead of using a solid shaft because a hollow tube has a larger moment of inertia than a solid one. Steel is chosen for the tube because its properties suit the application. It has a large modulus of rigidity. Hardened steel would be ideal to minimize deflection. However, due to the large difference in cost, stainless steel was decided upon as a more reasonable option. The deflection equation yields a range of deflection between 1-2*. Given that the length of the arm is 41.60 in, then, using the tangent of the deflection gives the deflection of one arm with respect to the other resulting in

an absolute deflection in a range of 0.7-1.4 in. This amount of deflection, and hence misalignment between either end of the rollers, is deemed acceptable. It is expected to be absorbed by the limited elasticity of the aluminum rollers, the self-aligning bearings, as well as the flexible couplings. Sleeves may be placed on the end of the drive shaft on the gearmount side to prevent the shaft from slipping away. Sleeves will not be placed on the other side of the shafts so as not to overconstrain it.

44

(1) Mechanical Design and Electronics

Hollow rectangular steel tube is used for the arms to minimize both torsion and weight in the arms. The lower ends of the arms are made of steel and are welded to the hollow rectangular steel arms. The upper ends are also made of steel for welding. However, care is taken to ensure that they weigh as little as possible. This is to minimize the torque at the base of the structure. Even a small weight difference would cause a significant increase in the torque because, when multiplied by a large moment arm, the torque value shoots up. On the gearmount side, the upper ends of the arms, shaped as cubes, have access windows cut out, both as slots and as squares. This is done to decrease the weight and also keeping assembly in mind. The access window is necessary because the flexible coupler consists of three separate pieces. One end of the coupler attaches to the gearbox shaft and the other to the shaft extending out of the roller. The gearbox shaft is not long enough to drive the roller itself. The access window allows one to attach the flexible coupler to the extending shaft easily. The upper ends of the arms that are not on the gearmount side only contain the bearings for the roller to roll on. The arms are staggered from one another to prevent interference during their motion. The arms are maintained at the staggered distance by locating set-screws. Holes may be drilled at the top of the hollow arms to allow electrical cables into the tube. The cables run from the gearbox and motors placed for roller actuation to the controller. Inserting the cables into the tubes would house the cables and significantly reduce chances of operators/ patients tripping or getting caught in the cables.

45

Implementation of First Prototype

The rollers are made out of hollow aluminum tubing. This ensures that they are lightweight yet their diameters are large enough to allow easy wrapping of the sheet. The roller has a cap - gudgeon - at either end of it and a steel shaft going through it. The cap is long enough to drive the roller and a shaft extends out of it in order to go into the coupler. A rolled pin holds the cap and shaft in place. Yaskawa motors were selected to be placed at the base for maximum torque. Gearbox LP-155 (Alpha Gear Manufacturers) with a ratio of 100:1 is compatible with Yaskawa motors to increase torque. Also, gearbox LP-90, with a ratio of 50:1 is compatible with Yaskawa motors. Actual gears were chosen from the McMaster Carr catalogue to effectively double the torque output at the gearbox shaft. Cost-effective and easily available gears were chosen. The base spur gear ratio was 2.38:1. This, along with the gearbox, results in a total gear reduction at the base of 238:1. The gearmount - used to mount both LP-155 and the gears from McMaster Carr - is made of aluminum, strong enough to bear the load of the gearbox, yet light so as not to increase the overall weight of the machine. Bottom and edge joiners are welded to the box frame and then attached by bolts to the gearmount to minimize twisting when the forces between the drive and follower gears act to push them away from one anther. The bolt attachment allows for minor misalignments that may occur due to imprecision either in parts and machining, or during assembly. The gearbox, LP- 155, has a spacer between it and the gearmount which serves a dual purpose. First, it positions the output shaft of the gearbox far enough away so as not to interfere with the motion of the arms without

46

(1) Mechanical Design and Electronics

causing a significant increase in the weight of the gearmount. Also, the spacer has a shoulder to allow the gearbox to rest onto it and to locate the gearbox with its location holes. The gearbox, LP-90, is mounted onto the arms on the side of the gearmount, which is where the drive shaft is driven to minimize flexure at the end of the shaft. Adjustable feet are attached to the bottom of the box frame to account for any misalignments that may be present on the floor. Also, the feet accommodate imprecision in either the legs or the attachment of the gearmount. This reduces the cost since high precision is not needed during machining and assembly.

Electronics Software, ServoWorks40 and the MCQuad Package, was obtained from Soft Servo Systems, Inc. It allows 4 axes actuator control and may be extended to 16 axes. This would be beneficial for when the system is extended to various functionalities, having a larger number of actuators for additional control of the patient and also for patient monitoring.The following figure more clearly illustrates the architecture of the ServoWorks software. The FP-50 is a dual-link VersioBus Master Board inserted into a host CPU and used to communicate with both the Servo and 1/0 Network. The DC-120 is a servo interface module that controls 4 axes, and upto four DC120s may be daisychained to increase the control capacity to 16 axes. The IM200 us a general 1/0 module that provides 64 points of 1/0. It too may be daisychained with a total of 4 IM-200s.

47

Implementation of First Prototype

ISA Bus FP-50 VersioBuTM Servo Network

FIGURE 18.

j

VersioBuTM 1/O Network

DC-1201

IM-200

Servo Drives

1/0 Devices

ServoWorks Architecture

Additional circuitry was designed to enable the control of the device in case of emergencies such as loss of control by the ServoWorks controller or by computer failures. Limit switches were purchased to ensure that the arms did not crush the gearmount if the controller lost control. The following circuit was designed using a series of relays and switches as shown in Figure 19. It is currently being implemented.

48

(1) Mechanical Design and Electronics

FIGURE 19. Electrical Circuit designed for Limit Switches

An external circuit connected to the motor supply with relays was used to control the power to the motors. If either of the limit switches is activated, then both motors at the base of the bed will be switched off. Therefore, the relays are connected in series. The switching of both motors may, at first glance, seem unnecessary since the arms are never supposed to cross. However, they are not allowed to cross if they are under the controller's control. If this is lost, then the right roller may actually try and travel towards the left limit switch. It may collide with the left roller, thereby causing a very unpleasant situation. So, if one limit switch is reached by either roller, the power to both motors is switched off preventing further mishap. When a limit switch is

49

Implementation of First Prototype

pressed, then the circuit is broken, the relay loses contact and the power to the motors is lost. The limit switches used are normally closed (NC) switches to allow detection of any breaks in the circuit. If normally open switches were used, then, if there did exist another break in the circuit, one would not know about it unless a limit switch was activated and it did not cut the power to the motors. This, however, would defeat the purpose of the limit switch because we would only know that it was not working after it did not work. A "start", normally open (NO) switch is used to manually restart the system once the limit switches are cleared. If the limit switches are not cleared, then pressing the start switch will not turn the motors on because the circuit would still be open by the limit switch. An additional emergency stop "mushroom" switch could be included in this circuit design but it currently is not because the handwheel device provided by Soft Servo Systems contains an emergency switch, that if needed, stops all the motors from functioning.

(2) Verification of Concept Implementation of the first prototype verified the proposed and designed concept.

50

.

-------...... --.... ........ ........... ............ .. .........

(2) Verification of Concept

The photographs illustrate the device in action. Initially, the machine is at its home position with the arms almost horizontal as shown.

FIGURE 20. Machine at Rest Position

51

.

.. ............. ......... ... .....

Implementation of First Prototype

The patient lies on the bed as shown and the arms are actuated to position the rollers above the patient.

FIGURE 21. Patient lying on back in Bed

52

.

............

.

... ......... ............ .....................

(2) Verification of Concept

The patient is lying on her back and the sheets are attached on either

FIGURE 22. Arm Positioned side to the rollers via VelcroTM. The right roller - as viewed from the foot of the bed - is rotated clockwise. Figure 23 shows the person slowly beginning to roll onto her side.

53

Implementation of First Prototype

FIGURE 23. Patient beginning to tilt.

Since the left bedsheet has so far remained stationary, the patient tends to lean onto it. Therefore, as slack is introduced in the left bedsheet the patient rolls completely - with the aid of the momentum gained - onto her

stomach.

54

(3) Verification of System Model

FIGURE 24. Patient Completes a Full Roll onto Stomach

The steps show that the device does indeed cause the patient to roll. If patients are cooperative, then rolling is easily achieved. However, uncooperative patients, especially those with dementia, may require a modified approach wherein the rollers are translated in the direction of rolling as discussed in Chapter 2, Figure 5.

(3) Verification of System Model The assumptions made in the model presented in Chapter 3 were rather crude and may have caused error in the system modeling phase. How-

55

Implementation of First Prototype

ever, as will be demonstrated, the errors are allowable and patient trajectory may be obtained. Quasi-static equilibrium was assumed. This is the point when the person just becomes airborne. This assumption will need to be relaxed because the patient is never totally raised from the bed as patients tend to feel unsafe when completely airborne. Therefore, there will be shear and normal forces acting on the patient that are currently ignored. The patient is modeled as a rigid body. This simplifies the analysis. However, it does not take into account the elasticity of patients. In fact, during rolling, one must realize that the patient appears to contract in width. This is due to the cushioning effect of human tissue and fat that flows and is partially compressible. The model presented does not take into account the elongation of the bedsheet as it helps roll the patient. Measurements were estimated for certain sheet lengths and distances. Taking accurate measurements was relatively difficult. In addition to this, determining the "width" of the person was an issue. The patient was measured at the shoulders and the hips and an average of the two values were taken. There are inevitable errors in measuring because the rollers themselves are assumed to be points. The sheet does not really meet the roller at its center, rather there is the distance that is actually the radius of the roller.

System Verification Prior to the start of verifying the system model, the apparatus was calibrated to determine the torque constant, k,. The motor manufacturers did provide a value for this. However, it was for an AC motor but for my purposes, the motor becomes DC. A Hall effect sensor was placed at the motor and

56

(3) Verification of System Model

readings were obtained with (a) no weight applied to the roller, and (b) with a mass of 18.9kg attached to the roller. The following was obtained:

Mass

Input Current (Peak Value)

No Mass

I, = 0.3 A

18.9kg

12 =

A

Using the following equation, , = kI

(20)

where T is the torque, and I is the current provided to the motor, two equations may be obtained. They are Fir = kJ11

(21)

(F 1 + F)r = k,1 2

(22)

where F1 is the weight of the system with no additional weight, F is the added weight to the overall weight of the system, and r is the radius of the roller which is 1 in. Subtracting one from the other and rearranging the above equations gives

k,

Fr

(23)

I2(-11

Therefore, k, is determined to be 6.72Nm/A. So, the tension, TI, may be written as T, = 2651

(24)

57

Implementation of First Prototype

The theoretical value of T, is expected to be 490N -- when T2 is equal to zero -- which is the weight of the author, the test subject used. The experimental value obtained at the moment of rolling of the subject was measured to

be 424N. TI, experimental

=

0.87Ti, theoretical

(25)

This shows that there is a close correspondence of the experimental value obtained to the theoretical prediction!! Furthermore, a sharp drop in T was observed at the moment of roll during experimentation. This gave clear indication that the person had indeed shifted weight from the left to the right. Verification of the model allows the trajectory generation for patients given their weights and widths. A larger data set will be obtained. Currently, the model verified the concept, and demonstrated that the model obtained is satisfactory. It allows the building of a generic control program to generate trajectory motion. However, this needs to be perfected and an extended model should be designed. Furthermore, additional human subject testing will help in verification. L, was expected to increase as slack is introduced. L 2 appears to decrease because it is measured from the right end of the patient who, while turning, moves closer to the right roller as it is lifted off the bed surface. Rollers are placed as close to the width of the patient as possible. This was not predicted prior to the implementation of the first prototype. However, it was realized that placing the rollers with minimal horizontal distance between them helps in caressing the patient between the sheets and in placing

58

(3) Verification of System Model

him wherever desired. It enables the patient to easily be placed on his side. The sheets act to provide greater stability while being placed in this position. As demonstrated by experimentation, the angle, a , reaches 900 when the person is tilted towards a side. This is to be expected. Since the rollers are placed as close as possible, then, as the patient is turned onto his side, the left sheet meets the patient in an almost parallel direction. Corresponding to the 900 value reached by angle, ux,

P drops signifi-

cantly in my calculations. This is because the angle is measured from the patient's right end that is closer to the right roller thereby decreasing the angle. However, this value was never really verified because obtaining a measurement for L 2 was not a simple task. There was too much slack in the sheet. Also, it would be too subjective a decision to take as to where the sheet ended - at the right end of the patient or underneath him. The motor torques at the base may be monitored by the current input into the system. The torques would provide further information with respect to obtaining an extended model that accounts for shear and normal forces acting on the body.

Patient Translation Patient translation was also verified. The arms were positioned at their rest, "home" position and the rollers were simultaneously actuated. The position of the person is located on the bed, as described by previous analysis and the person is translated laterally as in a conveyor belt system.

59

Implementation of First Prototype

When translating the patient sideways, the roller moves in the direction of translation and the fact that it moves upwards - in an arc - increases the tension in the sheet helping the person to be translated.

(4) Control Software Implementation The position loop gain and the smoothing time was tuned. PD control was used. The ServoWorks software and the handwheel device provided allows both the manual yet separate control of the motors. If desired, trajectories may be generated by programming in G-code using the system model developed and verified earlier. The NC files created for the programs allow the simultaneous control of all four actuators. The roller feedrates were adjusted to 1200mm/min. deemed to be a suitable rate to roll patients. Preliminary experiments showed that slow and steady motion was a priority in control so the positioning of the arms was also set to a relatively low speed of 1200mm/min. G-code was written for a person weighing 110 lbs and having an average width of 15 inches. The value for the program command of the roller, PCrollerwas determined using the equation:

PCroller =

s

27tr

x dpm x

GRroier,

(26)

where s is the amount of sheet wrapped around the roller, r is the radius of the roller, which is 1 in. for this prototype, dpm is the distance per motor revolution which is set to 8192 jm, and GRroller is the gear ratio which is 50 for the rollers. The program command for the arm, PCarm, is given as

60

(4) Control Software Implementation

PCarm =

x dpm x GRrm,

(27)

where a is the arc length that the arm travels, R is the radius of the circular trajectory, effectively the length of the arm which is 41.60 in. GRarm is the gear ratio which, as previously mentioned, is 238. Motor 1, X - right roller

Motor 2, Y - left roller

Motor 3, Z - left arm

Motor 4, A - right arm

(for right roller)

(for left roller)

The arms were initialized to home position. The length of arm travel and roller wrap was determined and input into a program which was then executed. The motions are defined as tabulated below. TABLE 2. Motion Definition Motion

Description

X positive

Clockwise rotation of right roller

Y positive

Clockwise rotation of left roller

Z positive

Clockwise rotation of motor, counterclockwise rotation of left arm (supporting right roller), that is, arm moves up

A positive

Clockwise rotation of motor, counterclockwise rotation of right arm (supporting left roller) that is, arm moves down

It was determined that the arms could be positioned at the given parameters in the program, that is, close to the width of the patient and then the rollers could be actuated. The preliminary code used to successfully roll the author is shown as follows. Initially, since the bedsheet used is a full-sized sheet, first the left end of the sheet is attached to the left roller which wraps up some of the sheet in order to have enough sheet to later introduce slack to. This is performed in the second line (N200) of the following code.

61

Implementation of First Prototype

Using the given software, the machine was taught a sequence of events. In fact, this was done inversely by first specifying the points in the code and then observing the behavior of the device. The desired coordinates were stored for use in generic programming. The home position was set to where the sheet would be attached to the roller. The left roller's home position was after two complete wraps of the sheet onto it. This allows enough sheet to introduce slack while rolling. The right roller's home position was set directly above the patient. The desired coordinates were recorded for when the sheet would be relatively tight at either end of the patient prior to commencement of rolling. This teaching was for patients ranging in widths of 15-19 inches. The code for rolling the patient includes positioning of the arms, and initial uptake of slack in the sheet on either side of the patient. The code for transferring the patient from one end of the bed to another assumes that the maximum length of translation of the patient will be half the width of the bed, from the center of the bed to either edge. Therefore, the maximum length of travel was assumed to about 20 in. The first line of code, however, is used to uptake any slack in the sheet prior to translation. The feedrate was increased to 4500mm/min because during testing, it was deemed that although slower is better for the skin on patients, an increase in the speed decreases a feeling of dizziness experienced by the author. This parameter may be left as a matter of preference and may be adjusted according to each person's wishes.

62

(4) Control Software Implementation

Control Code for Rolling and Transfer Codefor Rolling % Rolling (Generic) N100 G91 G01 Z202000 A-204000 F1500 N200 G01 X456270 Y-293316 F2500 N300 G04 P3000 N400 G01 X325907 Y114067 N500 G04 P2000 N400 G01 X325907 Y130363 N500 G04 P2000 N400 G01 X325907 Y195544 N500 G04 P2000 N600 G01 Y651814 M02 Codefor Translation %Translation N100 G91 G01 X570337 Y-407384 F2500 N200 G04 P5000 N300 G01 X-1271037 Y-1271037 F4500 M02

These programs were used to automatically and successfully control the implementation of the first prototype.

63

Implementation of First Prototype

64

CHAPTER 6

Conclusion and Future Work

Discussion The prototype built verified the proposed design concept. The device will indeed help to transport bedridden patients easily and comfortably. The benefits of using the bedsheet as the transport medium are manifold. First, patients experience lower stress concentrations. During initial pivotal rolling, the forces are distributed on a patient's body through the active sheet. This may be followed by a short period of airborne rolling helping patients to complete the roll as they lose contact with the bed surface. Second, shear forces exerted on patients, when moved from one edge of the bed to the other, are almost eliminated as they become airborne on the sheet and are moved over. Lifting does not introduce increased setup times as in currently available products. Since patients will scarcely be lifted off the bed surface, their fears are also reduced. Finally, the cradling aspect of the design ensures that the patient is transported both safely and comfortably.

65

Conclusion and Future Work

Additional actuated prototypes will be built. The design may be improved using the jointed arm configuration discussed below in order to test the proposed extended functionalities. Further experiments and in-depth analysis will be conducted to ensure safe and easy repositioning of patients.

Future Work Future Work regarding Design and Structure of Device The stiffness of the arms may be increased by adding a rib-like structure to the hollow rectangular steel arm in its weakest direction. In fact, the structure may be made such that the second arm does not collide with it and slides within it. Currently, strips of VelcroTM are used to attach the sheet to the bed. This may be extended to using a band of VelcroTM on either side of the sheet to ensure that it remains attached to the roller. A clamping mechanism or even eyelets may be used to hold the bedsheets instead of VelcroM. Patient transport has been accomplished in this paper. However, the concept and first prototype may be extended to include certain functionalities such as bed-to-chair transfer, and bed-to-bed transfer. The device may be made such that is easily adapted to accommodate different-sized beds and people. It may be portable. If so, then in order to minimize deflection, it may be mounted on solid rubber casters used to wheel it around. The device may be adapted to a U-shaped frame to allow it to be wheeled around the bed. It may have an attachable chain or flaps to anchor it

66

Future Work

to the ground on the open-ended side if necessary. If the device is indeed portable, then it also allows axial repositioning of patients by initially suspended the patient on the bedsheet and then wheeling the device to the desired axial location of the patient and then placing him back onto the bed. Figure 25 illustrates that the device can be adjusted by additional piv-

FIGURE

25. Jointed Arms for Easy Transfer.

oting about joints A and B. This allows it to be adjusted to beds of different widths. Roller motions are also independent. Since each side may be pivoted, the patient may be lifted off the bed and positioned where desired, for example near the edge of the bed. The device may also be used to transfer a patient from a bed to a chair. A reclined chair may be positioned next to the bed. The pivoting marionette configuration would allow the distance between the two rollers to encompass both the bed and the chair. This may be accomplished if, as shown in Figure 25, the right roller pivots about joint B. Coordination of roller actuation would allow patient transfer from the bed to the chair. Once the patient is transferred to a chair, the sheet needs to be tucked into the chair so that it may be used to return the patient to the bed. Using the bedsheet to transfer the

67

Conclusion and Future Work

patient is advantageous because it helps move the patient over discontinuities such as bed edges during transfer. The jointed arms would also allow the arms to be positioned underneath the bed. They would be "tucked in" to their home position as shown.

)

A,

A2

0

FIGURE 26. Home Position of Jointed Arm Design One of the drawbacks of the current prototype is the noticeable vibration of the arms as they are positioned. This is attributed to the discretization of the motion due to the spur gears being used to drive the arms. The small discretization is amplified as the arm is long. For future prototypes, helical gears could be used to alleviate this problem.

Future Work with respect to Reinforcing Bedsheets The sheets that are currently being used for demonstration are standard off-the-shelf sheets with VelcroTM strips sewn along the length of either edge. For patients with larger weights than the inventor, the sheets may be

68

Future Work

reinforced laterally by having fibers sewn into them. Cotton strips may be attached along the width of the sheet. Other materials, such as a type of plastic filament may be sewn into the sheet. Cotton is preferable for now because, it is not yet clear how, say, kevlar-reinforced sheets would affect the skin of the patient. Furthermore, cotton strips would still allow the sheets to be easily washed. There is also another material that is currently under investigation -clothing used by people in the navy that is known for its strength. Bedsheets should constantly be inspected for holes. Appearance of holes could cause the design to not yield the desired results. When the sheet is under tension and a hole exists, then the sheet will tend to tear at the hole, the weakest point. In order to avoid this, the easiest solution would be to use new sheets at the onset of holes. Another option would be to use a patch or a clasp. These would allow the sheets to be used for a longer period of time. However, if there are holes in sheets, then it should anyway be a clear indication to caregivers that the time has arrived for new sheets!

Future Work regarding Electrical Circuitry Currently, an emergency switch is available on the handwheel controlling the device so the power may be immediately cut off during testing. Limit switches for the rollers will be provided for a second prototype. A beltpulley or gearing system may be used to control the limit switch. For every n turns of the roller, the follower gear or pulley will turn once and hit a limit switch at the end of its travel. The number of turns of the roller is chosen by determining a relatively "safe" number of turns for the roller, small enough so as not to totally wind the patient but also large enough so as not to interfere

69

Conclusion and Future Work

with the various motions required for rolling and repositioning the patient. This switch will also be easily reset manually to allow flexibility in operator control. Also, sensors may be mounted to determine the location of the gear or pulley and hence monitor the absolute position of the patient given the amount of sheet that is wrapped onto each roller. This work may be extended to make one arm of the device longer than the other. This would enable the arms to cross one another without colliding. It would also allow a patient to be transferred easily to another bed or chair without significantly increasing the workspace required by the device when it is in use.

70

References

[1] www.encyclopedia.com [2] Nursing Strategies to Prevent Ventilator-Associated Pneumonia, AACN Clinical Issues: Advance Practice in Acute and Critical Care, Vol. 9, No 1. February 1998. Shelby Hixson, RN, MSN, CCRN; Mary Lou Sole, RN, PhD, CCRN, FAAN; Tracey King, RN, BSN, CCRN [3]

http://seniors-site.com/copin2/sickdvin.html

[4] http://www.hill-rom.com

[5] http://www.kcil.com [6] A. Garg, B.D. Owen, B. Carlson, An ergonomic study of nursing assistants' job in a nursing home, Ergonomics, vol. 35, no. 9, 979995, 1992 [7] A. Garg, B. D. Owen, D. Beller, J. Banaag, A biomechanical and ergonomic evaluation of patient transferring tasks: bed to wheelchair and wheelchair to bed, Ergon omics, vol. 34, no. 3, 289-312, 1991

71

References

[8] Garrett, Singiser, and Banks, 1992. Back injuries among nursing personnel: the relationship of personal characteristics, risk factors, and nursing practices. AAOHN Journal,40 (11), 510-516. [9] Spano, J., Asada, H., 2000, Kinematic Analysis and Design of Surface Wave Distributed Actuators with Application to a Powered Bed for Bedridden Patients, accepted for publication in IEEE Transactions on Robotics and Automation, February 2000. [10] S.H. Crandall, N.C. Dahl, T.J. Lardner, An Introduction to the Mechanics of Solids, 2 nd Edition, McGraw-Hill Book Company. [11] Shigley, and Mischke, Mechanical Engineering Design, 5 th Edition, McGraw-Hill, Inc., 1989 [12] Machine Design - Power and Motion Control Reference Volume #12, Penton Publication, June 1989. [13] F.E. Giesecke, A. Mitchell, H.C. Spencer, I.L. Hill, and J.T. Dygon, Technical Drawing, 7 th Edition, Macmillan Publishing Co., Inc., NY 1980. [14] ServoWorksTM Documentation, Version 0.3, Soft Servo Systems,

72

APPENDIX A

Historical Record of Approaches

Chronology of Designs The conceptual phase of the design was crucial to arriving at the final design. This stage consumed a large amount of time and creative energy! This chapter presents the designs as they were arrived at chronologically. An attempt is made here to depict the evolution of concepts, without disguising the inevitable imperfections and wishful thinking that may have violated the laws of physics during conceptualization.

Honeycomb Motion Initially, flexible honeycomb structures were examined for twodimensional motion due to their ability to expand and contract in either direction. Honeycomb sheets for medical purposes are commercially available. Two methods of motion were considered using the honeycomb sheet. They were the inching and buckling motions. Figure 27 shows the inching motion.

73

Historical Record of Approaches

In this case, the length of the honeycomb structure would be contracted towards the fixed end, hence moving the person from his position in Figure 27(a) to that of Figure 27(b). Assuming that the contracted segment is small enough to leave the patient stationary at his newly acquired position, the contraction could be propagated underneath the person. Once the segment is propagated, as seen in Figure 27(d), the free end may be extended and the motion repeated.

FIGURE

27. Inching Motion The second approach considered was buckling motion, illustrated in

Figure 28, which would utilize the buckling nature of the honeycomb. Similar to the mechanism utilized in inching motion, the honeycomb would be contracted towards the fixed end, causing the patient to move. A buckle would develop which would then be propagated under the person and extended on the other (free) end allowing repetition of the cycle.

74

Chronology of Designs

FIGURE 28. Buckling Motion A person lying in the center of the bed could easily be at the edge just by contracting the honeycomb sheet. In this way, the person would not really move to the edge, instead, the edge would move to the person. Honeycomb sheets were found to be unsuitable for this application due to their lack of load bearing ability. Controlling the propagation of a contracted segment precisely was also an issue. A solution would be to insert rods into the honeycomb sheet and actuate the rods, either individually or as sets using linear actuators. Rods would also increase the load bearing capability of the sheets. However, they would cause discomfort to the patient. Tests were conducted and it was observed that not only were the rods uncomfortable but there existed too much friction between the rods and the honeycomb sheet during expansion and contraction. Also, for precise control of the propagated segment, many rods would need to be actuated resulting in too many actuators being used. Therefore, both the inching and buckling motions were reevaluated.

75

Historical Record of Approaches

Belt and Belt Use of modular conveyor belts was investigated.

FIGURE 29. Modular Belt Design Figure 29 illustrates a single conveyor belt in the y-direction with modules consisting of mini-conveyor belts in the x-direction. Each module is made up of a flexible material attached rigidly at the ends that are shown as bold lines in the figure above. The material for each module needs to be flexible to enable it to make the turns at the top and foot of the bed. In this manner, motion in two dimensions would be obtained but problems would arise in accessing the modules for actuation. Furthermore, the design did not satisfy the requirement of stimulating the patient - it only provided patient translation.

Tilt and belt An offshoot of "Belt and Belt" was developed into "Tilt and Belt", which consisted of two main modules, tilt and y-belt. See Figure 30. Tilting would occur both along the x-axis and the y-axis. Tilting the bed along the y-

76

Chronology of Designs

axis - plates 1 and 2 allow this in either direction - would aid in rolling the person from side to side. Tilting along the x-axis using plate 3 would allow the patient to be reconfigured into a sitting position, enabling him to get out of

bed easily.

FIGURE 30. Sketch of "Tilt-N-Belt" Bed. Additionally, the design includes a belt drive system in the y-direction, referred to as y-belt. The purpose of y-belt is to repeatedly position the patient longitudinally in the center of the bed'. Y-belt would be made up of a flexible material to allow tilting of the bed by plates 1, 2, and 3 in either direction without tearing it. As in regular beds, bedsprings would bear load but unlike regular beds, the springs may be activated to cause tilting when desired. The extra degree of freedom provided by y-belt allows positioning of the patient onto the actuated portion so that his center of mass coincides with the location of the actuated portion.

1.

Patients have a tendency to slip to the foot of the bed while lying down.

77

Historical Record of Approaches

This design causes motion in two dimensions by repositioning and hence stimulating the patient. However, one of the key assumptions of the design is that the y-belt will be extremely flexible which may not really be the case. Controlling the flexible belt would be imprecise due to the formation of

a hyperbolic paraboloid.

Tilt and tilt A two-way folding bed was designed. Independently-actuated plates, with n number of rows by m number of columns, would be used to cause both lateral and longitudinal tilting of the bed. The plates would be able to slide past each other for axial repositioning of patients. Rollers could be used to assist in changing bedsheets by moving the patient from one end of the bed to the other. Tilting would aid the patient to roll off the used bedsheet and onto a new one. The photographs shown below illustrate how the concept would work. Initially, the person would be lying on top of the sheet to be changed. See Figure 31. The sheet would then be pulled with the person lying on top of it towards the edge. See Figure 32.

78

Chronology of Designs

FIGURE 31. Patient on sheet to be removed.

FIGURE 32. Sheet and Patient translated towards edge. The mattress is exposed and the person is only on a fraction of the sheet to be changed. The bed is now tilted to release the remaining portion of the sheet.

79

Historical Record of Approaches

FIGURE 33. Bed tilted to release bedsheet Therefore, the person is off the old bedsheet and if a new one is attached to the ends of the old one, then he will be lying on the new sheet. In the figure, he is shown finally to be lying just on top of the mattress.

FIGURE 34. Bedsheet removed with Patient on new sheet The bed could be reconfigured into a sitting position as shown below.

80

Chronology of Designs

FIGURE 35. Bed reconfigured into Chair.

Changing Bedsheets Bedsheets could be changed using rollers attached along the length of the bed. Prior to use, the patient would be rolled over to one edge of the bed to free up a portion of the sheet. This would be accomplished by tilting the bed. The sheet would then be inserted between the rollers that would be pressed together. The bottom roller would be actuated causing the bedsheet to be rolled through it. This would result in pulling the patient lying on top of the sheet to the edge. Once the patient reached sufficiently close to the edge of the bed, the bed would be tilted laterally allowing the patient to roll towards the opposite edge, freeing the remaining portion of the sheet. In this way, changing bedsheets would be easier. Nursing personnel would no longer need to drag the patient towards any side because the tilting would aid in rolling the patient and the rollers in any pulling that may be necessary.

81

Historical Record of Approaches

Axial Positioning Axial motion would be obtained by positioning the patient say, on the right side of the bed, as shown in Figure 36. The right side then slides forward and tilts. The patient will be on the left side and the right plate may slide back to its original position. In this manner, the patient could be repositioned axially on the bed..

FIGURE 36. Sliding Motion for Axial Repositioning of Patient The preliminary design is shown below.

FIGURE 37. Lateral Tilt of Two-Way Folding Bed. The figure shows one side of the bed frame tilted laterally. The design shows that the plates can be tilted either laterally or longitudinally. The plates

82

Chronology of Designs

may be tilted about the y-axis as shown above because they are attached to rollers. This also gives the advantage of allowing the plates to slide past one another along the y-direction. The sliding rollers, can translate the plates thus enabling axial positioning of the patient as described previously in Figure 36. The figure shows the plates moved as a unit. The patient would have been positioned onto the moving plates, translated axially "higher" on the bed, and, as Figure 38 shows, the plates would be tilted and the patient would be positioned in the desired axial location back onto the stationary plates. The moving plates would then slide back to their original position.

FIGURE

38. Sliding and Tilting Motions for Axial Repositioning

83

Historical Record of Approaches

84

APPENDIX B

Assembly Drawings

The following views of the overall design are given: isometric, top and side.

85

THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF MIT. ANY REPRODUCTION IN PART OR WHOLE WITHOUT WRITTEN PERMISSION IS PRONIBITED.

3

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Part Drawings and Listing

The table below gives the listing of the parts that were puchased. TABLE 3. Off-the shelf Parts List

Name of Part

Part Number

Manufacturer/Supplier (if any)

Qty.

Gearbox, R1:50

LP-90

Alpha Gear/Northeast Motion

2

Gearbox, R1:100

LP-155

Alpha Gear/Northeast Motion

2

Roller Motors

SGMAH-02

Yaskawa/Soft Servo Systems

2

Base Motors

SGMPH-15

Yaskawa/Soft Servo Systems

2

Bearings

60355K19

McMC

4

Adjustable Feet

62805K42

McMC

4

Drive Gear

6867K76

McMC

2

Follower Gear

6867K84

McMC

2

Flexible Couplers

59985K25

McMC

2

Aluminum Rollers

9056K166

McMC

2

Square Bearings

6664K13

McMC

2

McMC = McMaster Ca:

Some of the parts labeled in the figure were machined out of stock that was purchased from the MIT Central Machine Shop. A description is provided as to how the parts were made, what they consisted of. A listing is given of different parts that are labeled as forming part of the machine. Detailed drawings of each part are available. The listing helps keep track of the type and number of parts. Note that though in the prototye that is built, both roller and basemotors used were the same

120

Part Info

due to the short lead times of Yaskawa motor, part number SGMAH-02, the base motors, Yaskawa motor, part number SGMPH-15 arrived and is in the process of being tested as this thesis is being docmented. TABLE 4. Machined Parts List Part Name

Description

Quantity

Box Base

3x3 steel tube @ 7 ft.

2

Joining Bar

3x3 steel tube

2

Arms, Type 1

2x1 hollow steel tubes

2

Arms, Type 2

2x1 hollow steel tubes

2

Gearmount

4 sided aluminum box extrusion

1

Edge Joiner

steel attachment

2

Bottom Joiner

steel attachment

2

Bushing

bronze bushing for drive tube

2

Drive Tube

hollow stainless steel tube

2

Back Drive Shaft

solid steel shaft

2

Front Drive Shaft

solid steel shaft

2

Legs

hollow square steel tube

4

Steel Shaft

steel shaft to drive rollers

4

Gudgeon

aluminum insert for rollers

4

Spacer

aluminum spacer for LP- 155

2

121

Part Drawings and Listing

122

APPENDIX D

Hardware, Software and Common Operation Tips

Tips on Using the Hardwareand Software of Machine To Improve Performance of Gearboxes Lower Jog Feedrate Default Value: 2000 Try 500-1000 Goto Parameter Mode Goto tab NC Params.

Increase Smoothing Time Default Value:60 Try 600 Do NOT exceed 5000ms

123

Hardware, Software and Common Operation Tips

Goto Servo Params.

Increase Position Loop Gain Default Value: 5 Hz Increase gradually by increments of 5 Hz

Do NOT exceed 20-30 Hz Goto Servo Params

Tune the Amps There are 4 black round little buttons on Amp. When just powered, display should show "bb" Push the "Mode/Set" button (1st from the left) twice. It shows PNOOO.

Change to PN1 10 Hold down data button Make sure the 4th digit is "2". This is the control register and disables autotuning. Hold down data button till you get back to PN display.

Change to PN103 Hold down data button. You may see 100-150. Increase it to 200-300. This is the inertia ratio of the gearbox to the motor shaft as a %. Hold down data button The current settings for the motors controlling the rollers is 500 and

124

Tips on Using the Hardware and Software of Machine

for those controlling the arms is 1000.

Change to PN100 Hold down data button Default value is either 25-40. This is the velocity loop gain. Make it

40.

To exit, push the "Mode/Set" button twice and you see the "bb" dis play again.

Hardware Considerations Check that the emergency button is not pressed on the handwheel. This would cause the system to not respond to any commands from the PC. Check that the power cables connected to the amps are still in place. Loose connections are terrible!!! Make sure that you are turning the arms in the correct direction. Failure to do so would result in the arms colliding with the gearmount thus either activating the limit switches or causing an emergency shutdown of the software as the amps go into torque overload failure mode.

Operation Considerations Ensure that the arms are initialized as soon as the software is loaded. Since the encoders for the motors used are incremental, the software does not store the absolute home position which is the almost horizontal position. Failure to do so will cause the arms to be initialized at an incorrect location.

125

Hardware, Software and Common Operation Tips

Therefore, when the program is loaded, this error will be propagated and the desired motion of the patient will not be obtained. Ensure that the sheet is wrapped one wrap around the roller prior to the introduction of slack otherwise, as slack is introduced, the sheet will tend to peel off the roller.

126

(4CVjC~ Q~A