Robocodo

Therapists often spend hours working with patients to loosen the elbow joint manually (through humeroulnar distraction) after surgery to help the elbow recover flexion and extension mobility. There is a need for a device that can do this automatically so that the therapist can be free to work on other parts of the rehabilitation process to decrease rehabilitation time and maximize recovery.

Problem Definition
Problem Statement We are tasked with developing a device that can perform a humeroulnar distraction on the elbow. Ideally, the device will be less than 1 kilogram (kg) and apply a 100 Newton (N) linear force and a 35-40 Newton meter (Nm) torsional force.

Design Goals and Deliverables   Document which solutions worked and which did not. Explain failures in detail so the company won’t waste time building something that we already tried.    The gadget should be: comfortable, easy to take on and off, weigh less than 1kg, and have a safety release mechanism. 

Specifications  Mobility: Keep arm rigid and allow for adjustment of different angles of pronosupination. The device should allow for a linear motion which will apply a force just distal to the elbow. It also allows for rotational motion, which will apply a torque to the forearm. Once the forearm is pronated to the correct position, the device should hold the arm rigidly in this position. Misalignment or rotation of the elbow during use of the device could cause injury. The primary opposition to holding the arm rigidly is skin slippage. The motion of the skin allows the underlying bone structure to become misaligned even though the arm is being held tightly. Work to develop a system that will minimize skin slippage.

 Strength/Motion: The device should be able to provide a linear force of 100 N and a torsional force of 35–40 Nm. The device will carryout the following motions:  A force of up to 100 N is placed just distally to the elbow. This is done to release the ulna from the humerus.    After the ulna is released a torque of 35-40 Nm is applied to rotate the forearm.</li> </ul>   In some cases it is necessary to bring the elbow to its full extension and oscillate back and forth. </li> </ul>

<p style="text-indent"> Weight:  Mass of entire device should not exceed 1 kg on the arm. The device should ideally be as light as possible. The goal is to maximize patient comfort. To accomplish this, an effort should be made to keep the majority of the weight of the device proximal to the shoulder or back. If the weight must be placed distally on the arm, it should not exceed 1kg.

<p style="text-indent">Safety:  Easy to activate quick release. There is always the possibility that a mechanical device can act in an unexpected way or a patient to react poorly to the procedure. For this reason, the device should have some sort of quick release mechanism, which will immediately release all pressure on the arm. The release mechanism should be easy to activate by both the therapist and the patient.

<p style="text-indent">Feedback: Position feedback for functional electrical stimulation (FES). In order for the FES system to activate at the right time, the mechanical system must be able to provide some sort of feedback which describes its current position.

<p style="text-indent">Power: Grid power using medical grade power supply Although the final device is intended to be powered by a lightweight and compact battery pack, it is sufficient for this project to power the device using power supply running off of mains power. If possible, the power supply should be medical grade. All of the wiring should be kept neat and should in no way inhibit the movement of the device or increase risk to the user.

Conceptual Design
Overall Look of the Design Our goal is to create a prototype similar to the ones illustrated below.

Orthoses
Arm and Wrist Orthosis

<p style="text-indent"> Use: for attaching the device to the forearm and to hand minimize skin slippage during use. <p style="text-indent"> Materials and Methods for Production: Low temperature thermoplastics can be molded directly onto the forearm and hand which allows for rapid prototyping. They also have adequate rigidity to support the arm while being low cost and easily customizable. We will fabricate an upperarm, forearm, and wrist orthosis from these thermoplastics.

Shoulder Orthosis

Frame
Layout

the Frame for the Device This is our current work in progress SolidWorks model of the frame for the device. Many of the parts in this project are sourced from Mc Master to sacrifice some of our budget for time. The load cell in the model has been adapted into an S-shaped load cell so that we will not need to buy a new load cell.



Electronic Development
Micro-Controler <p style="text-indent"> Use: for a feedback system. <p style="text-indent"> Controlled by Button or App: for starters we will test the circuit with the button. <p style="text-indent"> Cost: $200 for all sensors and microcontrollers. <p style="text-indent"> Description: A load cell has been placed in line with the linear actuator so that as well as positional feedback, it will also have force feedback. This was done because the actuator’s built in measurement of position does not give a good estimate of the force being placed on the arm. This load cell was a beam type load cell purchased from sparkfun.com. Spacers and plates were used to transform the load cell from a beam type load cell to an S-type load cell. This cell can take a maximum force of 200 Newtons before it loses its calibration. The load cell uses a HX711 amplifier which is sold as a breakout board on sparkfun.com. The cell is run and calibrated using the HX711 arduino library and the code provide by sparkfun.

Linear Actuator/DC Gear Motor We looked into several linear actuators but found that servos weighing under 100g cannot product more than 200N of force. Conversely, actuators that can produce over 200N of weigh between 800 to 1000 grams. For this project it is more ideal to use lighter weight motors than to compromise our weight goal of under 1kg by using the more powerful actuator.

Planetary Gear 12v DC Motor: This is a real workhorse of a motor put into a small package. This motor allows for high torque while keeping size and weight down. The actual purchased motor is the Servo City: 12 RPM HD Premium Planetary Gear Motor. Servo City offers the same motor with a rotary encoder installed. Instead of using the encoder version of the motor, which does not give a measurement of absolute position, a potentiometer was placed on the frame which turns with the forearm so that an absolute position measurement can be achieved.

Electrical Circuit Design