Allison Johnston, Syracuse University
Kendra Kyler, Taylor Carpenter, Loc Lam, Fadil Al-Ahmed, The University of Tulsa
The Cerebral Palsy Crawler is a device to assist a child with Cerebral Palsy learn to crawl. The machine reproduces patterning, a therapy whereby the arms and legs of a child are moved back and forth in a crawling motion. Patterning, usually requiring three adults, can be performed by a single adult with the Cerebral Palsy Crawler. The operator is only required to turn on the machine and rotate the child’s head during patterning. The machine runs is able to safely and accurately replicate the necessary patterning motions. Four actuators connect to the child’s arms and legs and move on a linear path in the homolateral patterning motion. The actuator motion is controlled by a custom designed microprocessor and the actuator position is limited by magnetic position switches.
A three year old boy Shane suffers from Cerebral Palsy, affecting his motor control functions and mental development. Cerebral Palsy has several causes, but in Shane’s case, a bleed in his brain shortly after birth caused his disease. Because he has Cerebral Palsy, Shane is unable to learn to crawl, and is currently at the developmental level of a 6-9 month old child.
In order to teach Shane to crawl, his family employs a form of therapy called patterning (1), whereby three adults manipulate Shane’s arms, legs and head to simulate a crawling motion. The particular type of patterning used is homolateral patterning, where the arm and leg from one side move forward at the same time as the arm and leg of the other side move backwards. The head is then rotated in the direction of the forward moving limbs.
The theory behind patterning is neuroplasticity. Neuroplastic theory suggests that over time a person’s external environment can affect their brain function and structure. Patterning is an environmental stimulation that, if done enough, can positively affect a child’s brain. Patterning has the potential to reestablish damaged connections in Shane’s brain and allow him to crawl.
In order to be effective, patterning much be done daily, and is recommended in fifteen minute increments four to five times per day. It is difficult to gather three adults for this amount of time in a day, and so Shane has not been patterned as regularly as necessary. His family is in need of a machine that can pattern Shane regularly so he can begin to reestablish damaged brain connections and learn to crawl.
The primary customer of this design is Shane’s immediate family. Their basic desires for the design are as follows:
– Replication of correct patterning motion
– Light and portable machine
– Easily operated by one person
– Aid Shane in learning to crawl
– Safe for Shane and the operator
In order to solve the problem described above, the quantitative engineering specifications described below were generated. They were formulated by the design team with help from Shane’s family.
– Machine weight less than 30 lbs
– Machine size less than 40” x 22” x 12”
– Pattern speed of 10 sec/cycle
– Machine force output of no more than 30 lbs
– Remove child from device within 5 seconds
– Stop machine motion within 0.25 seconds
DESIGN AND DEVELOPMENT
The final prototype for this project is a rectangular machine with a footprint of 40” x 22”. A custom designed microprocessor controls four actuators that move forward and backward to simulate the motion of crawling. Straps connect the child to the machine and move his arms and legs as needed. The machine has a foot pedal that must be depressed to operate the machine. Before being constructed, the machine was built in SolidWorks. An animation of the crawler can be seen below.
Guide Rails and Mounting Blocks
Linear guide rails and blocks were purchased to transfer the motion of the actuator to the child being patterned. A mounting block was designed to screw on top of the guide block in order to couple the actuator motion to that of the child. The material selected for the mounting block was high strength Aluminum alloy 2024. Engineering calculations were conducted to verify that this is an acceptable material and that the mounting block is adequately sized with a factor of safety of 2.27.
A steel rod is set into the mounting block, and this rod protrudes into the crawler base area. Custom designed gloves and leg attachments connect to these rods through a small bracket welded to the end of the rod. Padding then covers the rod to keep the operator and child safe. While most of the crawler is fabricated from Aluminum, these rods are steel. It was not possible to acquire an aluminum material with high enough yield strength to resist the bending stresses that Shane would be able to impose at the ends of the rods. It was therefore made from high strength carbon steel.
When in the machine, Shane lays stomach down on a pillow. This pillow is used to raise his chest off the ground and allow his arms and legs clearance to move on the machine. The pillow is fabricated from expanded polyethylene foam and bolted to the base.
There are two sets of straps on the crawler; one set that connects Shane’s limbs to the actuator motion, and other set that hold Shane down on the pillow to prevent him from moving during patterning. Gloves connect Shane’s hands to the arm rods. Similarly, leg straps connect his shins to the leg rods. The arm and leg straps have velcro loops that connect them to the steel rods. There are separate velcro sections connecting Shane to the straps and the straps to the rods so Shane can be easily removed from the machine without the need to take the gloves and leg straps off of him. A pair of belt buckle connections are used to secure Shane to the pillow. These straps constrain his torso and thereby force his hip, knee, shoulder and elbow joints to move. The straps allow quick connection and disconnection, so Shane can easily be removed from the machine in case of emergencies.
The crawler is controlled by a custom designed microprocessor. The microprocessor takes in information from limit switches to determine the position of the four actuators, and sends signals to control the actuator direction of travel. Each actuator includes a motor, and motor controllers send the correct current and voltage to the actuators when told to by the microprocessor. A 12V power supply is used to power the crawler, and plugs directly into a standard outlet.
Also included in the design is a small servo motor mounted at the front of the crawler. A small shaft on the motor rocks back and forth in time with the motion of the actuators, and is meant to be a pace keeping device for the machine operator who turns the child’s head. A photograph of Shane’s head is fastened to the shaft in the prototype so the photographic head rocks back and forth to indicate which direction Shane’s head should be moved.
Shrouds and Bellows
Polycarbonate shrouds were used to cover the electronics and avoid injury to the child or operator. The outer shroud is a shell with tabs to bolt to the extruded Aluminum frame. The inner shroud is a u-channel with two slots machined into the wide face. The steel rods connecting Shane to the actuators fit through the slots and are free to move back and forth with the motion of the actuators.
In order to avoid pinch points between the steel rods and the shroud slots, a vinyl bellows material is used to act as a barrier. Two polycarbonate tabs are adhered perpendicular to the face of the inside shrouds at the outside edge of each slot. The vinyl bellows are bolted to these tabs. A central hole is located in the bellows and secured with a metal eyelet. The rod runs through this eyelet to contract and expand the bellows as it moves through its cycle of patterning.
The testing conducted on the crawler was mostly for safety. There were very few design specifications for general function of the machine, and this section is short. Test results are given as either passing or failing the test.
Tests for Safety
All tests for safety passed. The actuators are not able to generate more the 30 lbs force, the patterning speed is set at 10 seconds per cycle, and the machine stops instantly with loss of contact with the foot switch. The child is able to be removed from the machine in 4 seconds, which is a second better than the goal.
Table 1: Safety tests and engineering specifications
|Customer Wants||Engineering Specification||Test||Testing Result|
|Safe for Child||No force greater than 30 pounds||Use load cell to measure forces on arms and legs. Pick safe actuator||Passed|
|Safe for Child||Pattern Speed – 10 sec/cycle||Measure speed of actuator with a stopwatch||Passed|
|Safe for Child||Put foot pedal to stop action within 0.25 seconds||Measure seconds to stop after letting off pedal||Passed|
|Easy and quick removal||Remove Child from prototype within 5 seconds||Time the removal of a dummy with a stopwatch||Passed|
|Safe for all||Crevices that shrink to less than 1 inch must be covered||Measure each crevice||Passed|
|Safe for all||Center of gravity must be low enough to prevent tipping in normal operation||Measure center of gravity using SolidWorks||Passed|
|Safe for all||Current must be within manufacturing specifications||Measure current and be sure the electronics are grounded||Passed|
Test for Functionality
The machine passed three of the four tests for general design constraints, as seen in Table 2. It is the correct size, and the patterning motion reproduced is acceptable. However, the machine is heavier than anticipated. The goal was 30 lbs, while the actual machine weights approximately 40 lbs. This is due to the poor selection of the power supply, as this adds the most weight. The machine is still functional, and can be transported when desired, but the weight is more than ideal, and this test failed.
Table 2 shows a comparison of the initial budget to the final prototype cost. The final cost of the prototype was underestimated by approximately $850. This was caused by a combination of unforeseen purchases. The seamstress who sewed the gloves was not budgeted for, nor were the shrouds. These purchases account for $500 of the over-budget cost.
Table 2: Crawler Budget Comparison
The Cerebral Palsy Crawler design project has been completed successfully in the time allotted as defined and approved by Shane’s family. The machine is capable of patterning Shane with the assistance of a single adult helper, and is still light enough to be transported if desired. Except for the weight specification, all of the design criteria have been met. In particular, all of the safety criteria have been verified as being passed, which is critical for a machine used by a child.
The family has stated its excitement over this project, and has been present for testing as well as the final design review. They agree that the weight could be reduced, but as a machine for teaching Shane to crawl, it is as much as they wanted.
1. Doman, Glenn J. What to Do About Your Brain Injured Child. Garden City Park, NY: Avery Publishing Group, 1994.
The Cerebral Palsy Crawler design project wants to acknowledge the assistance of the following individuals: Zach Carpenter, Erna-Grace, Terry Hutson, David Jones, and Drs. Tipton, Henshaw, and Stratton.