VANDERBILT UNIVERSITY



Continuous Passive Motion Hand Rehabilitation

Group 10: Matthew Byrne, Aaron Hadley, Jennifer Hornberger, Jonathan Webb

Advisors:

Bert Lariscy, Electrical Engineering, Vanderbilt University Graduate School

Crystal Bates, Occupational Therapist, Mercy Medical

Dr. Paul King, Department of Biomedical Engineering, Vanderbilt University

Table of Contents

I. Abstract………………………………………………………………….……....Pg. 3

II. Introduction

Literature Review…………………………………………………….……...Pg. 3

Design Goals…………………………………………………………..…….Pg. 6

III. Methodology

Design Ideas………………………………………………………..………..Pg. 6

Prototype Progress:

Alpha…………………………………………………………..……..Pg. 10

Beta………………………………………………………..…………Pg. 10

Gamma……………………………………………………..…...…...Pg. 11

Power Control……………………………………………………….Pg. 12

IV. Results

Discussion……………………………………………………………..…….Pg. 14

Safety Issues…………………………………………………………..….…..Pg. 15

Economic Analysis………………………………………………….………..Pg. 16

Innovation Workbench………………………………………………....…….Pg. 17

V. Conclusions………………………………………………………………..…….Pg. 18

VI. Recommendations…………………………………………………………...…Pg. 19

VII. References……………………………………………………………....…...…Pg. 20

VIII. Appendixes

Appendix A (Innovation Workbench/Concept Map)…….……….…...……...Pg. 21

Appendix B (DesignSafe)…..................................................................……...Pg. 26

I. Abstract

Continuous Passive Motion (CPM) is used in the rehabilitation of joints after surgery in order to increase the range of motion of the joint to its initial capacity. CPM devices prevent the buildup of scar tissue around these joints through passive movement of the body part, which is less painful than an active movement of the joint. CPMs reduce the overall costs associated with injuries by decreasing the length of hospital stay, the time in physical therapy, and the duration that one is out of work due to the injury. Hand CPM devices are used by a large target market including the 1 million people who are treated at a hospital per year with work related hand injuries (Sorock). However, the devices on the market fail to allow a customizable therapy process due to their limitations. These devices do not have individual finger control and force all fingers through the same range of motion, increasing rehabilitation time of stronger fingers because of the limitation of weaker fingers. These devices also do not incorporate both the thumb and fingers into one device, are heavy and bulky, are intimidating to patients, and are difficult to put on. This article outlines the goals, process, and results of the proposed solution to these design specifications. Included is the progress of designs from the use electromagnetic forces to a string and pulley design. Also, the successes and further recommendations to the final string and pulley prototype are discussed.

II. Introduction

Literature Review

Continuous Passive Motion (CPM) devices are used in rehabilitation, following surgery, in order to restore the entire range of motion of injured joints. CPM is invaluable during the first phase of recovery, which involves controlling post-operative pain and inflammation and protecting the healing process. It is used to prevent intra-articular adhesions and extra-articular contractures, which can lead to stiffness and loss of motion, and promotes faster healing and the growth of articular cartilage (Stroud). More generally, CPM devices prevent the buildup of scar tissue and joint stiffness related to reconstructive surgery by limiting the pain to the user though passive use of muscle. By controlling the movement of the affected joints, the pain associated with rehabilitation is limited while the correct ranges of motion in the flexion and extension directions are established.  These devices can be set to allow motion to regulated amounts, which increase over time until the joint is able to extend through its entire range of motion. CPMs reduce the overall costs associated with injuries by decreasing the length of hospital stay, the time in physical therapy, and the duration that one is out of work due to the injury. Also, the productivity of the physical therapy sessions is increased and allows more time for therapists to focus on active motion activities, the second phase of recovery (Schuster). CPMs are available for hands, knees, elbows, toes, ankles, and shoulders, allowing rehabilitating patients the ability to function in society while still recovering. The focus of this project is in the hand CPM market. Hand CPM devices are typically used for the following conditions: ankylosis of hand joints, dislocation of the fingers and wrist, sprain and strain of the wrist joint, and tissue replacement at hand joints. These devices are used within 48 hours post-surgery and are used up to 6 weeks after surgery, with therapy sessions lasting eight hours daily (Otto Bock HealthCare). Hospitals treat about 1 million people for work-related hand injuries annually, of which 13% are crush injuries (Sorock). Also, according to the American Burn Association (ABA), 500,000 people are treated for burn injuries each year, and a majority will have severe burns to the hands. Recovery from these two injuries is accelerated through continuous passive motion, and these statistics alone indicate the market power of hand CPM devices. This market consists of two primary users, physical therapy clinics and post-operative individuals. Also, the typical rental fee of a hand CPM device is $600 for one month, while ownership costs range from $3,000 to $7,000.

Currently, a number of hand CPM devices exist but a wide range of problems occur with their use. Firstly, the devices do not allow for individual finger motion and force all four fingers into the same mechanical movement, limiting the extent of the rehabilitation of all of the fingers. For example, if the pointer finger is able to move to 40% of its motion while the index finger moves only 10% of its motion, the device closes both the pointer finger and the index finger to only 10% of their motion. Therefore, the pointer finger is unable to use its entire range of motion and the rehabilitation of this finger does not progress. Secondly, devices on the market either focus on the rehabilitation of the fingers or the thumb but do not incorporate both aspects into their designs. This forces patients with injuries to both fingers and thumb to use multiple devices for rehabilitation, creating and inconvenience that causes some to neglect their therapy (Crystal Bates, Bert Lariscy). Thirdly, the weight and bulk of the hand CPM restricts the patient’s daily activity and comfort. And lastly, the devices are difficult to attach to the hand and to setup the initial movement criteria. It often requires two people to complete the setup and the mechanical complexity is intimidating to the user (Crystal Bates, Bert Lariscy). These problems with the hand CPMs that currently exist on the market lead to their improper use and ineffectiveness.

Design Goals

The primary goal of the hand CPM senior design project is to discover a method to provide controllable and programmable motion to the individual fingers of a patient. This will create a more customizable rehabilitation process. A secondary focus resides in creating a device that incorporates the use of both the thumb and fingers into one hand CPM. Furthermore, the CPM system is to be lightweight (less than 1 lb) and portable, so that it can be easily used at home without restricting daily activities, and should be able to adjust to the hand size of differing users, providing for a reusable device. In keeping with the industry standard, the CPM must offer a full range of motion extending from 270o of flexion to -15o of extension. Also with this standard, the speed of the mechanism must adjust from a minimum of 2o per second to a maximum of 54o per second. Other factors have been considered in the design but are less important that those stated above. These issues include: the battery life of the CPM should last 1 day, the device should allow for simple control by user, the system should be easily put on and setup, the CPM should be inexpensive compared to the market, and the mechanism should not be intimidating to the patient. Inherent in all of the goals presented is the overall need to provide a safe mechanism for rehabilitation.

II. Methodology

Design Ideas

Past models of CPMs functioned by using a series of gears behind the hand to push and pull the fingers in the desired motion. These devices are bulky and would only become more so if independent functionality was added for each finger. For this reason, it was determined that a new method for generating the forces should be developed. Using our list of design goals mentioned above, we brainstormed new methods of forming the desired finger motion while reducing the size of the device. Through discussing mechanisms and processes that cause movement, we came up with a list of possible methods to provide the needed motion. These methods include memory metals, magnetism, fluid-filled bladders, and strings and pulleys. Each of these possibilities was then researched further to discover its productivity and applicability to our device.

Memory metals, also known as shape metal alloys, are types of metals that have the ability to return to an original shape after being mechanically deformed. This ability to return to an original shape is activated on response to a stimulus, such as electricity or heat. Our design would incorporate memory metals on the front and back of each finger, with activation of the palm side causing a regulated amount of flexion, and activation of the reverse side causing the extension of the fingers. Research into shape metal alloys showed that the precision necessary for the CPM would be difficult to obtain with the types of memory metal available. Memory metals would not provide the necessary strength to move the fingers, and also the metals will not retain their desired shape over the life cycle needed for rehabilitation. Memory metals of improved quality and size necessary for the design are expensive as well. Because of these many reasons, memory metals were rejected as a viable option, but in the future as memory metals become more advanced and cheaper, this could be a functional idea.

Electromagnets are coils of wire that generate a magnetic field when a current travels through the wire. The strength of this field is related to the size of the coil and the number of coils of wire. Electromagnets are incorporated into a CPM by connecting them to each of the finger tips, on the front of the palm, and on a column extending from the back of the hand. The force of the electromagnets could be adjusted by controlling the current through the wires, resulting in the control of the desired motion of the hand. Research into the strength of electromagnets showed us that the force of a magnetic field relates to the square of the distance away from other fields, making precision difficult with the magnets. The size of the electromagnets necessary to generate a strong enough field negates our goal of a compact, lightweight design, and the current necessary generates an additional hazard of electrocution. Because of the necessary size, safety issues, and imprecision, electromagnets were rejected as a possibility for our design.

Inflatable bladders were also investigated as a means of controlling the individual motion of the fingers. Each finger would be attached to one of five individual compartments to allow a different range of motion for each finger, and the inflation rate would be variably controlled via strain gages and/or pressure sensors. Initial inflation of the air/fluid-filled bladder must be adjustable to fit all hand sizes comfortably, and small enough to not inhibit movement. Some of the major drawbacks involve creating a system for feedback to stop the device if there is too much resistance, and the fact that the range of motion would not reach the design specifications in -15o extension. The largest hindering factor is the large bulk and weight of air compressors need to act as an air supply for the inflatable bladders. This option does not fit the design specification of portability and therefore was not used.

The fourth method we considered during our brainstorming session was the use of a system of strings and pulleys to pull the hand through flexion and extension. This method is meant to replicate the system of tendons and muscles within the hand that is naturally used to move the fingers. The Mechanical Engineering department at Vanderbilt University is developing an artificial hand which uses a similar technique, indicating the viability of a string and pulley system. Figure (1) shows the initial design which would allow the precise control of each joint but would require the use of three strings on each side of the finger. The design would cause, for example, the second joint of the finger to flex while retaining full extension of the other joints. This degree of precision would be useful for a hand model designed to obtain full control of the hand, but for the simple flexion and extension required for a CPM, this could be simplified to one string for the palm side and one for the reverse of each finger.

Figure (1): Initial string and pulley design with three string joint attachments

Prototype Progress

The string and pulley design fit the design criteria we hoped to satisfy and a model was set out to develop in order to discover any problems. Using paper clips and solder, a draft form-fitting model was made and placed onto a hand. The metal pieces wrapped around the bone of the finger and extended outward on the palm and reverse side to a small loop, where a piece of wire was thread through. Three pieces like this were made and attached to one another at an attached joint where the fingers have their joints. When the wire was pulled from the palm, the hand exhibited the desired motion, and the same happened when the wire on the reverse side was pulled. This desired motion indicated that using strings and pulleys would provide a functional design and decrease the size and weight of the device. However, the metal paper clips rubbed directly onto the skin and caused some painful pressure, which showed that some form of padding would be necessary around the pieces, leading to the use gloves in the future to protect the hand.

This first prototype, the Alpha model, was constructed using a soft, black knit glove, which had copper tubing attachments at each bone shaft of the finger for anchor points. This prototype is seen in Figure (2). Small plastic tubing pieces which guide a

Figure (2): Alpha Prototype

metal wire, used to pull the finger, were adhered to these points. The heavy wire was chosen to create the motion for the finger, and to be robust enough to stand up to plenty of wear. Unfortunately, the wire was not deformable enough, as it tended to stay curved even when the finger was extended. Also, the plastic guiding tubes were too long and hit each other while the hand was in flexion. The glove was found to be too stretchy, and the copper mounting tubes were too heavy and did not allow for much customization.

Our Beta prototype was created to eliminate the problems incurred through the Alpha model. The Beta prototype is seen in Figure (3). For this model, a newer glove was purchased, which fit more tightly over the hand, yet was still elastic along the sides. This elasticity is ideal for adjusting to swelling levels in patients while not putting too much pressure on the injured hand. In order to keep the string, which pulls the finger, along a Figure (3): Beta Prototype

steady path, a change was made from the prior idea of using tubing guides. Instead of specific mounting points along the finger, one strip of cloth was sewn into the palm of the glove, extending to the tip of the finger as a guide for the string, creating a long, flexible path to follow. The string used was a hard plastic line, typically used for hanging things. The major setback with this model was that the cloth was too elastic and pulled away from the finger during flexion. Also, this failed to give a flexion range of motion of 270o due to bunching of the cloth around the finger joints. Also, the plastic line was not suited for use, as it was too hard to adjust to the curvature of the fingers.

Finally, the Gamma model was created using the joint system in the alpha model and the glove idea in the beta model to gain the desired range of motion, and is seen in Figure (4). Simple fishing line proved to be the best material for the tensile string, as it carried a 5 lb load, is small and lightweight, and most importantly, highly flexible. Small plastic rings were sewn onto the long parts of the palm side of the glove and onto the joints of the reverse side, serving as hinges at which the string would pull the fingers into a fist. This did indeed achieve the desired flexion and extension, as the string is held very close to the hand while not digging into the hand. On the palm side of the hand, each finger has five rings, one on each finger bone and two on the palm to keep the string in a straight path. On the reverse side, there is a ring at the tip of each finger, on each of the

Figure (4): Gamma Model

three finger joints, and near the wrist to maintain control of the string. These rings allow for the string to create the desired motion and put the string in a place where it can be pulled by some form of motor system attached to the wrist.

Power Control

With the mechanics of the hand designed, a method for pulling the strings needed to be chosen. McKibben muscles, tubes that contract and expand when subjected to differing internal pressures, were initially considered as the driving source for the CPM, but several drawbacks were discovered upon more research (Shadow Robot Company, Vanderbilt Intelligent Robotics Lab). Though the air muscles are small enough and strong enough, they are rather difficult to control with variable exponential factors. Also, they must be attached to an air compressor to force the contraction of the muscle. Having ruled out linear actuators for size and cost restrictions, along with step motors for performance functionality, it was decided to use simple servomotors as the power source for CPM movement. For simplicity’s sake, a Futaba S3003 servo with 2-channel digital proportional remote control was purchased and subsequently altered for use. The adaptation of the original motor involved removing several plastic stoppers inside the casing which inhibited the motor from continuous rotation. The neutral position of the motor was also found and glued in place, so as to ensure a complete ceasing of movement when desired. The gearing was left unaltered, as it created sufficiently slow turning and satisfactory torque through the output shaft. The motor and radio receiver system is powered by 4 AA batteries, sufficiently small enough to place in one’s pocket. In any future designs, it would be desirable to replace this servomotor with a smaller model, and one that could be powered by a small, rechargeable source. Though this would indeed cost more, the overall cost would still be considerably lower than other products currently available.

The degree of flexion and extension desirable in each finger is somewhat problematic for a CPM system working inside the palm, rather than just from behind the fingers. Since strings must contract to pull the finger from both sides, the inner sting must move a distance of approximately 4 inches to cause full flexion, while the outer string need only move approximately 1 inch for full extension. It is advantageous to use only one motor for each finger, rather than two (one for the front, and one for the back) because this will reduce the weight and cost of the device. The varying changes in length of string required can be met with a simple rotating spool attachment on the output shaft of the servomotor. Following the 4:1 ratio previously measured, a spooling system was fabricated to pull the finger closed with one rotation of the motor, and open it with an opposite rotation. In doing so, the correct motion has been obtained as has the possibility to instantly stop the hand CPM for reasons of pain or other emergency. One need only stop the motor or turn it the other way to immediately reduce tension. In addition to the inner diameters of the spooling device, lips were added to guide the string and force it to wrap around the course designated for it. This way, there should be no slippage of the string or accidental crossing/knotting of the two strings.

In order to provide reproducible motion to the hand CPM, the servo motor must be driven by a computer. Using LabVIEW, a program has been designed that controls the motion of the motor, but LabVIEW’s lack of the proper tools inhibits programming the complete set of capabilities that are desired for the CPM. The high sampling rate required for servomotors cannot easily be replicated with LabVIEW, resulting in a complex program and the ability to use only speeds programmed into the device, not a full range. The precision and range provided by the existing manual controller of the motor is superior to that capable with LabVIEW. Because of the inability to replicate the required signal, it was not possible to design a loop that allowed for a controlled cycling of the CPM through the range of motion for which a CPM is used. Though LabVIEW does not provide the desired output, other CPMs demonstrate the ability to perform the cyclical motion and required precision. Therefore, by exploring other motor circuitry and other programming languages, a suitable program can be found that will allow the duplication of the capabilities of existing CPMs. Because our goals were focused upon the improvement of the biomechanics of the hand CPM and not upon the existing power capabilities, it is not seen as a setback that the motor/CPU function was not reproduced.

III. Results

We have designed a single-finger CPM prototype which functions to passively flex and extent one finger of the hand. It can achieve 270o of flexion and -10o of extension as desired. In the design, the range of motion and speed are controlled using a remote radio frequency controller.

The string and pulley prototype meets most of our design goals. It begins in an open palm and provides the anatomically correct finger motion. The device can run at a variety of speeds and ranges of motion by controlling the direction, distance, and speed with which the controller knob is rotated. This model is also easy to put on, lightweight, and unrestrictive. The device, with the manufacture of additional gloves, is adaptable to both the left and right hand as well as to different hand sizes making it adjustable for different users. However, the methods for controlling the motor prevent portability. It has the potential to be made more portable by minimizing the computer motor control system. The current prototype only works for one finger but could be easily expanded with additional strings and motors. The thumb could be incorporated to the prototype as well. However, in this design controlled thumb motion would be achievable in only one axis of motion. The patient also has the ability adjust the speed and range of motion of the CPM as well as the ability to return the device to the starting position if too much pain is experienced.

Safety Analysis

A safety analysis was performed using Designsafe which can be found in Appendix B. During normal operation, there is a moderate risk that the user or things in the environment surrounding the user could be caught on the strings or motor that drives the motion. This is harmful to the user because it could affect the anatomical correctness of finger motion as well as to the person or thing being caught in the strings or motor. This problem could be addressed by enclosing the motor and strings. Also, there is a high risk that the strings will pull too hard, particularly when a patient reaches his or her limit in range of motion. To solve this problem, force sensors could be incorporated to detect resistance too motion and trigger return of the fingers to the resting position. There is a moderate risk that patients will begin to feel too much pain after using the device for a long period of time or that the device won't be used long enough to achieve desired results. In this case, the physician will be important in helping patient to determine optimal length of time for the treatment and helping the patient to learn the difference between normal pain associated with rehabilitation therapy and dangerous levels of pain. One suggestion is that doctors should help patients develop a threshold pain level beyond which they should stop the use of the device or adjust range and speed of motion. There is also a moderate risk that the patient will set the device up incorrectly. Extensive physician training and subsequent patient training will be important in teaching the correct way to put on the device and to program the device to run an appropriate speeds and ranges of motion. There is also a risk of injury when one is repairing or performing maintenance on the motors of the device. This will be resolved through training of those performing maintenance and a warning to the users not to open the area containing harmful equipment.

Economic Analysis

The total cost of this project was about $130. However, a large portion was spent on the development of the prototype. The materials for the final prototype alone were about $105. We estimate the extension of this prototype to include the 3 other fingers would add an additional $225. Making the total cost $330. This value does not include the cost of the program to control the motors as we have used the control which came with the servo motor or LabVIEW which was available at no cost. Assuming a 40% markup, the product could be sold for $465. Modifications of this prototype for commercial sale would include addition of force sensors, goniometers, smaller motors, and a portable control for the motors. Additionally the cost of labor would need to be considered. Even taking into consideration the costs of modifications to upgrade the prototype, the device should still be able to be sold for well under $2500, half the price of existing hand CPM devices. There is a large portion of the potential market that does not choose the use of hand CPM as treatment option. The estimated 50% decrease in the cost of hand CPMs should make this therapy available to more patients, particularly those whose insurance does not cover the full length of their treatment or those have no insurance at all (ABA, ). The increased patient compliance predicted with the use of this new design is expected to decrease the length, and therefore, the cost of treatment (Schuster). Increased efficacy along with decreased cost should make this treatment option more attractive to doctors, patients, and insurance providers. The decreased cost of this new design would be very beneficial to the existing market and should result in the continued growth of the market as more people begin to use the device. Investing in the further development would be a wise idea for a company wanting to invest in the future of continuous passive motion market. Not only would this company receive almost all new customers, but existing customers are likely to choose this new device because many therapists are looking for the ability to customize therapy.

Innovation Workbench

Innovation workbench helped to define the specific design problems and objectives of the hand CPM project. The resulting innovation workbench is found in Appendix A. The design team was able to determine the resources that were available to them through this program. It also helped to define the allowable modifications and limitations associated with redesigning a hand CPM device. IWB also assisted us in the prioritization of our goals. As a result, independent finger motion of the fingers and portability were placed above incorporation of the thumb.

IV. Conclusions

While the design team has not made a readily marketable prototype, it has demonstrated through the construction of a single-finger model that the hand CPM design can produce anatomically correct motion. This design will be easily modified to accommodate all fingers and potentially one axes of motion for the thumb. This model can accommodate both the left and right hands and a range of hand sizes with the simple exchange of gloves, and additional modifications made by a company desiring to use this idea will make the model safer and easier to use and more portable. Suggested modifications are discussed in the recommendations section.

This prototype is an improvement on existing hand CPM devices. It provides the much needed ability to control the speed and range of motion in the movement of individual fingers. This will enable better customization of rehabilitation therapy, allowing patients to maintain the range of motion in less injured or non-injured fingers. Increased comfort, ease of use, and decreased weight will help to increase patient compliance and decrease the patient’s recovery time. It will also reduce the amount of money patients and insurance providers spend on physical therapy and enable patients to return to their normal lives more quickly (Schuster). The generously-estimated 50% decrease in cost will make CPM therapy an option for more patients, resulting in a larger market. Therefore, we have reached the immediate design goal to provide individual finger motion and created a portable, lightweight, safe, inexpensive device that is easily attached to the arm.

VI. Recommendations

This prototype has great potential in the continuous passive motion market because it provides the ability to adjust the range and speed of motion of individual fingers without removal and reassembly of the device. However, there are several improvements and modification that must be made to make a more marketable prototype.

The first and most essential change is that additional fingers and thumb if possible need to be incorporated. These additions will require at least three separate motors, or four, if the thumb is included. It is not certain if correct anatomical motion can be attained in same manner as with the other fingers. This motion was not tested in the design of the single-finger prototype.

Additionally, it is desirable that the motors as well as the system used to control the motors be condensed. The motors and control would ideally fit on the forearm of the hand being controlled. The user-interface of the motor control should be user-friendly and enable the patient or doctor to program the desired exercise protocols. The precision of the motors and control system also needs to be improved by incorporating goniometers to detect joint angles and accelerometers to detect force and speed. Additional safety measures should be included. For example, a stop button which would trigger return to starting position and force sensors which would determine if there is too much resistance to motion and trigger return to start. The strings and motors should be covered to prevent them from getting caught on the user or surrounding objects. The length of the strings should also be adjustable to accommodate the use of different glove sizes as well as left- and right-handed gloves. Finally, the string should be made of more durable material which will not deform and deteriorate upon repetitive use.

VII. References

1. Otto Bock HealthCare.

2. Stroud, Ruth. "CPM Therapeutic Benefits".



3. American Burn Association.



4. Sorock, G S, Lombardi, D A, Hauser, R, Eisen, E A, Herrick, R F, Mittleman, M A

”A case-crossover study of transient risk factors for occupational acute hand injury” Occup. Environ Med 2004 61: 305-311

5. Schuster, Edward. "Hand Rehabilitation Utilizing a Continuous Passive Motion Device following a Tenolysis, Athrolysis, Capsular Release, or Post-Traumatic Stiffness”; A Review.



6. Crystal Bates. Occupational Therapist. Mercy Medical. Interview

7. Bert Lariscy, Vanderbilt University EE graduate. Interview

7. Goldfarb, M and Fite, K. Transhumeral Prosthesis.

8. Shadow Robot Company.

9. Vanderbilt Intelligent Robotics Lab. Erdemir, E. and Gordon, S. Interview.

Appendix A

Innovation Workbench

Ideation Process

Project Initiation

Project name: Continuous Passive Motion Devices

Project timeline: Nov 2006-April 2007

Project team: Matthew Byrne, Aaron Hadley, Jennifer Hornberger, Jonathan Webb

 

Innovation Situation Questionnaire

Brief description of the situation

Continuous Passive Motion (CPM) devices are used in rehabilitative surgery to allow joints to relearn movement, but without the chance of hyperextension or motion in improper directions. These devices can be set to allow motion to regulated amounts which can be increased over time until the joint is able to extend through its entire range of motion, and their use instead of a cast prevents the buildup of scar tissue and stiffness in the joint. Problems with the devices include size, bulkiness, individuality of the fingers, and that there is not a method developed for controlling the thumb.

Reduce cost

Reduce weight

Make the device smaller and more friendly

Improve functional efficiency

Separate to individual fingers

Apply to thumb

Detailed description of the situation

Input - Process - Output

Functioning of the system

Device flexes and extends the hand to move joints

System inputs

User programs desired ranges of motion and speed

System outputs

Device causes fingers to move at the rate and range defined by the user

Cause - Problem - Effect

Problem to be resolved

Range of motion of the individual fingers cannot be changed with out taking apart the device and reassembling it.

Undesirable consequences if the problem is not resolved

Rehabilitation process will be less efficient

Other problems to be solved

Bulky, hard to put on

Resources, constraints and limitations

Available resources

Burt Lariscy and Crystal Bates

Jim Lassiter at Therapeutic Center in MCN

Dr. Paul King

BME computer and instrumentation labs

Funding through BME Department

 

Allowable changes to the system

Completely changing the system is allowed

Constraints and limitations

Complete range of motion should not decrease

Criteria for selecting solution concepts

Should be novel change

Improved product appearance

More choice of finger motion

Safe

 

Problem Formulation and Brainstorming

 

CPM

[pic]

4/16/2007 1:55:54 PM.

Find a way to eliminate, reduce, or prevent no thumb motion under the conditions of Forces hand into a fist.

 

4/16/2007 1:55:35 PM.

Resolve the contradiction: The useful Forces hand into a fist should provides increased range of motion and reduced edema and scar tissue and avoids no thumb motion and range of motion limited by most injured finger.

 

4/16/2007 1:55:07 PM.

Find an alternative way to obtain Forces hand into a fist that offers the following: provides or enhances increased range of motion and reduced edema and scar tissue does not cause no thumb motion and range of motion limited by most injured finger.

 

 

Develop Concepts

Building bi- and poly-systems

Combine systems having opposite functions - one to open and one to close the hand

String and pulley system - each finger controlled by a single pulley

Evaluate Results

Meet criteria for evaluating Concepts

System is easier to use and unique to existing devices.

Reveal and prevent potential failures

Implement feedback system or stop button to shut off device or return to open palm position in the even that too much pain is experienced.

Apply Patterns/Lines of Evolution

Increasing controllability

Add goniometers and force sensors to more precisely control finger motion.

Use LabVIEW to program speeds and ranges of motion - later use more compact control.

Plan the implementation

What are the ideal ranges of motion and speeds necessary - expert to contact Crystal Bates

What can provide us with the necessary power and forces to run the system - expert to contact Bert Lariscy.

Concept Map

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Appendix B

DesignSafe

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