Mechatronics Device Innovation
By: Po-Ting Chen
Tags: Prototyping, Mechanical Design, Mechatronics, Medical Devices, Mechanical Engineering

Mechatronics Device Innovation

Introduction

Mechatronics Device Innovation was one of the courses in my master's degree, and this was a project-based course. At the beginning of the course, our professor, Troy McDaniel, introduced 15 real-world problems and let us choose which one we were interested in. All the problems were provided by therapists in ASU Barrow Neurological Institute. Then, in the following course, we collaborated with a therapist to design a mechatronics device to solve the problem.

Problem Statement

The problem statement was to design an EMG sensor/Feedback glove for stroke patients to provide robotic assistance for gross grasp during daily life, for example, holding a hairbrush or cup, etc. The glove should be easy to clean, easy and quick setup, at least bulky as possible, and water-resistant. Even though there already exist several current products, for instance, Bionesss H200 which uses electrical stimulus to trigger motions, it makes patients feel uncomfortable and can only be controlled by therapists.

Background

It is common for individuals to suffer decreased hand function and strength after a stroke. In the United States, 171 for every 100,000 individuals, approximately 500,000 people every year, experience a stroke. The stroke patient suffers impairments in hand function with different aspects of motor performance. This includes reduced strength, loss of individuated finger control, and abnormal force control at the level of the fingers. However, this dysfunction can be rehabilitated by motor-skill exercises that can improve muscle strength and coordination. Based on the background and knowledge, we started brainstorming and prototyping the mechatronic device for assisting stroke patients to rehabilitate their hand functions.

Brainstorm

After clarifying the problem statement, background researching, and having several meetings with our client, we moved to the next stage, brainstorming ideas. We built the combination table and listed the requirements. After that, we depended on the combination table to generate, discuss, and select the final five ideas.

Table 1: Combination Table

This was one of the final ideas which is the first choice for the prototype. This idea was generated by me. The concept was building an Exo-skeletal device, including linkages as finger bones and joints. The strip with the EMG sensor was attached to the forearm to detect the EMG signals for interpreting whether the stroke patients want to close or open their hands.

Prototype

After the brainstorming stage, we started building 3D CAD, 3D printing, purchasing materials, and testing EMG sensors.

3D CAD & 3D Print

There were several points I considered when I drew the 3D CAD. First of all, I considered how to assemble the parts. For example, if I designed all the mechanisms in one part, there was no space for plugging in the Chicago screws. Therefore, I separated each finger as one part for assembling with Chicago screws. After that, there were mortises and tenons at fingers and a palm to connect. Secondly, I considered the thickness of the part because of the strengthness, weight, and limit of 3D printers.

This was the final version of the 3D CAD of hand device design.

In the 3D printing process, geometric dimensioning and tolerancing are rather important. Every 3D printer has a slight error; therefore, the actual dimension is sometimes smaller or larger than the 3D CAD. In addition, the feasibility of 3D printing should be considered. To build a practicable hand mechanism, I spent a lot of time testing and consulting with different experts.

The left picture showed the first version of the hand device, that was failed because the joints’ structures were not easy to make by 3D printers. The right picture showed the second version, that was failed because GD&T was not good enough.

EMG Sensors

The electrical system with EMG sensors was attached to the forearm for detecting the EMG signals. Our method was very simple to predict whether the stroke patients want to open or close their hands. We depended on the value of the signal to observe the muscle groups on the forearm are active or not. If the muscle group is active, the signal will show a spike immediately. Then, the electrical system will start controlling the mechanical system.

Final Prototype

After 3D printing the hand mechanism and testing the EMG sensor, we started to integrate all the parts together. There is always a distance between ideal and reality. We found that the strings cannot be collected smoothly and totally. Therefore, we changed the degrees of the motors and added small caps on the shafts. After improving the design, at least the device operated smoothly. Indeed, this was not as complete as those current products. However, for the prototype, that was good enough.

In this video, we tested holding a water bottle with this mechatronic device.

Conclusion

This was a very interesting project, and I definitely learned a lot from that. First of all, how to lead a team. Even though I have some experience in leading a team in Taiwan, I was still nervous when I said that I want to be a team leader, because English is not my native language. I was afraid of my teammates being unable to understand what I was saying. However, my worry is redundant, and I was able to have a great conversation and discussion with my team. Secondly, being positive is very important to a leader. For me, I always believe that we are building the best product in the world. I even told to my teammates that our project was the best in the class. Thirdly, I learned how to generate the product from brainstorming with the teammates to building the prototypes. Those were what I get from this course project. Thanks to my professor, Troy McDaniel, and also my teammates for completing this project together.