Here's the progress we've made so far on this project...Enjoy!
Our team is designing a Pediatric Trainer add-on for a pediatric body-powered voluntary-close arm prosthetic device that will help children learn to use their prostheses faster. The add-on consists of a strain gauge attached to the cable on the terminal end of the prosthetic device; the strain measurements are converted to a voltage signal by Wheatstone bridge. This voltage signal is then fed into a circuit board, where it is converted from an analogue signal to a digital signal. An FPGA (Field-Programmable Gate Array) chip is then used to activate a specific sound chip according to the strain measured. The sound chip will then play a pre-recorded voice segment giving the child constant positive feedback when they use their prosthetic device; thereby aiding in the learning process of the toddler.
A. Statement of Problem
Learning to use a prosthetic device can be a challenge. It takes time, great effort, strength, patience and perseverance for both the child and the parents. Younger children have an easier time learning how to use prostheses because a child’s brain is still developing and able to accept new information more easily than adults. Therapists work with the toddlers in scattered therapy sessions to help them learn how to handle their new prostheses, but just like learning anything else new to them, toddlers need constant guidance and assistance.
Children require arm prostheses due to birth defects, accidents or amputations. Normally, toddlers learn to use their prosthetics through physical therapy sessions when adults give them positive feedback for doing the right thing. In physical therapy sessions the therapist utilizes toys that involve the usage of both arms and is appealing to them at the same time. This encourages the children to use their prosthetic device. Children need a reason to use their arm prosthesis otherwise they usually function without it. Therapy sessions are essential to learning; the quantity, quality, and promptness of feedback directly affect the development of a learned skill. The pediatric trainer prosthetic device add-on will allow the patient to receive constant reinforcement as they would in a therapy session, helping them learn how to operate their body-powered voluntary-close arm prosthesis more rapidly.
Children can be, and are encouraged to be, fitted for a prosthetic as early as possible. According to the article Impact of Prostheses on Function and Quality of Life for Children with Unilateral Congenital Below-the-Elbow Deficiency, when children are still in the crawling stage, approximately six months, they are typically fitted with a passive prosthesis. The terminal ends of passive arm prosthetic device do not have a gripping function; they are of equal length of the opposite arm and have a rubberized slit (act like two fingers slightly apart) where items can be held, but the object must be pushed, or pulled, into the slit to hold, or remove the item. Children can then advance to a body-powered arm prosthetic device as young as a year and a half, but aren’t able to achieve the control or coordination needed to operate their prosthesis until they are approximately five years old. It takes years for young children to learn how to control their body-powered arm prosthetic device due to the coordination required to isolate certain muscle movement within the trunk, scapula and shoulder.
The recordable sound chips will allow the parents to record their voices into the device. This is a crucial component of the design because toddlers are tuned in to their parent’s voices and will therefore respond most positively when they hear their parent’s encouragement. We will provide the parents with suggested sound segments to record on the device, but ultimately it is up to the parent and the child’s therapist to choose what their particular child will respond most positively to.
The inspiration behind this design is Michael Haag, who is a four year old boy, born without a fully developed left hand (unilateral congenital below-the-elbow deficiency). He is currently attending therapy sessions to learn how to use his body-powered voluntary-close prosthetic arm. These therapy sessions are short and sporadic throughout the year; therefore Michael does not receive constant reinforcement of how to use his new and unfamiliar prosthetic device. When children receive their prosthetic device it is crucial that they wear it as much as possible so that they begin to accept their prosthesis as part of themselves. This is achieved by very consistent practice as well as wearing the device constantly. Michael only practices using his prosthetic during the therapy sessions; if he were able to wear his prosthetic device all the time and still continue to receive constant reinforcement, similar to that provided in the therapy session, he would be able to develop a positive body image and think of the prosthetic device as part of him. Also, by receiving the constant “therapy” from the Pediatric Trainer, Michael will be able to learn how to use his new prosthetic device much more rapidly.
II. Scope of Work
We are designing an add-on to a pediatric body-powered voluntary-close prosthetic arm that would help children learn how to use their prostheses faster. The idea to create a Pediatric Trainer came from the Open Prosthetics Project Website. We will be posting our progress on the Open Prosthetics Forum throughout the duration of this project. This will be helpful because it will allow others to track our progress as well as offer suggestions to help us improve our design. The Pediatric Trainer device would be comprised of three major components: a strain gauge, circuit board and three sound chips. The add-on will be attached on the outside of the prosthetic device and near the terminal end. It ideally will be light weight and easily attached to the prosthesis. Depending on the amount of strain measured, a sound will be emitted from a particular sound chip providing encouraging phrases for positive reinforcement.
B. Plan of Implementation
1. Intended Market
Michael Haag is the motivation to design and build this device, but it will ultimately be marketed to toddlers and young children, specifically ages 2-4 years old, who use body-powered voluntary-close arm prosthetics. This design will provide constant, instantaneous positive voice feedback acting to enhance the learning experience of the child beyond what they receive in physical therapy sessions.
2. Design Components
a. Strain Gauge
1) Three strain gauges will be mounted on a methacrylate polymer cube which will be connected in line with the cable, near the terminal end of the prosthetic device. Three strain gages will be used to obtain accurate voltage output. A strain measurement will be taken every 3 seconds, regardless of whether the tension on the cable is increasing or decreasing.
2) The target force ideally will be approximately 2 lbs. for 2-year-olds and 4 lbs. for 3- to 4-year-olds. This is the minimum grip force required for a toddler to perform age-appropriate activities. The table below shows grip forces for voluntary close prehensors for children ages 2-4 years old. The target forces used for the pediatric trainer add-on device will be based off of data obtained from an article found in The Journal of Prosthetics and Orthotics (Source: Journal of Prosthetics and Orthotics 1995; Vol 7, Num 2, p 61. URL: http://www.oandp.org/jpo/library/1995_02_061.asp
a) Final target tension and tolerances will be confirmed during testing stages. The muscle strength of children at different ages will also be taken into account.
i) Ideal forces will be determined experimentally by attaching the strain gauge to a methacrylate polymer cube in line with the cable near the terminal end. Various weights ranging from approximately 50g to 850 grams will be hung from the opposite end of the cable to simulate the force a toddler would apply to the prosthetic device. The voltages produced by the strain gauge will be recorded which will allow us to calibrate the strain gauge to determine the ideal voltage ranges.
3) Strain Gauge Specifications
a) Strain gauges from Vishay, Appendix C.
i) Pattern: 015DJ
ii) Gauge Series: EA (strain range: +/- 3%)
iii) Dimensions: Gauge Length: 0.38mm, Overall Length: 2.54mm, Grid Length: 0.51mm, Overall Width: 0.51mm, Matrix Length: 5.8mm, Matrix Width: 3.0mm
b. Programming Component
1) Circuit board will be constructed in order to activate the correct sound chip according to the voltage measured from the strain gauge.
a) Analogue to Digital Converter- first the voltage signal from the strain gauge will be converted from an analogue signal to a digital signal
i) AD557JN will be used.
b) The main design of the board will include a combination of a FPGA Altera MAX EPM7128S chip, which will be programmed using Quartus software to lay out the digital gates and an analog to digital converter.
i) Gate 1: activated by lower threshold tolerances and will activate sound chip A.
ii) Gate 2: activated by target (ideal) voltage range and will activate sound chip B
iii) Gate 3: activated by upper threshold tolerances and will activate sound Chip C.
c) Circuit board and sound chips will be powered by a 9V battery.
d) Plan of Implementation
e) LabVIEW simulation of how the Pediatric Trainer device will function. The block diagram models how the FPGA chip should be programmed.LabVIEW pic.doc
f) The above screen shot is a rough idea of what we need/want to program our FPGA chip. The FPGA Altera MAX EPM7128S chip will be programmed using VHDL language and Quartus software.
c. Sound Modules
1) Three TAS recordable sound modules will be used to play predetermined verbal recordings according to the measured tension.
a) Chip A - If tension measured is above the lower limit but below the target tension range, then sound chip A will be triggered and an encouraging sound will play
b) Chip B - If tension measured is within target tension range, then sound chip B will be triggered and a “reward” sound will play
c) Chip C - If tension measured is between the target tension range and the upper limit then sound chip C will be triggered and a discouraging sound will play
2) TAS recordable sound module from AGC sound:
TAS-10C-Recordable Module-This module is ideal for prototyping. Up to 10 second message can be recorded. The diameter is 1 1/4" (3.2cm) and the height is 5/8" (1.6cm)
Required voltage needed: 4.5 V 3.0 – 1.5 V batteries
Expected voice output is ~ 50 decibels (dB)
C. Housing Unit
1. The ideal dimensions of the entire housed device will be approximately 4.0cm x 6.0cm x 2.0cm.
2. The ideal maximum weight will be approximately 20-40% of the total prosthetic device weight. The approximate weight of a pediatric prosthetic device for a toddler is 10 oz; therefore the approximate weight of the add-on will be 2-4 oz.
3. The circuit board will be mounted inside a protective polycarbonate plastic casing. This box will be mounted on a sheet of 1.0 cm thick memory foam to conform to the surface of the prosthetic device.
4. This device will be attached to the prosthetic arm using a Velcro wristband.