Thursday, May 6, 2010

Design Case Study : A Recumbent Bike For Patients With Cerebral Palsy

It is quite often that we observe cycles becoming a platform for design and study ideas, especially at universities. Perhaps it is the simplicity and access to the structures and parts of cycles that make it popular for such use. Students choose bikes to explore the physics of riding, or torque and power relationships; they like to mount motors on them to establish drive capabilities, or generate electricity using pedal power, or automate it using various mechanisms and so on to put it to different uses.

Last year, I wrote about Alfred University alumni creating a hotdog launcher using a bicycle. In February, you may recall how I wrote a bit about Yale students building a spokeless wheeled bike. Keeping with the theme of bikes for design projects, this week we explore the work of a team of students from Michigan State University who took a recumbent bike and engineered it for the use of patients with cerebral palsy. The work was sponsored by GM and the MidMichigan Medical Center.

Senior mechanical engineering students Spiros Kakos, Eric Wickenheiser, Drew Darling and Marshall Mendoza were inspired by the Nu-step exercise machine and desired to mimic it's design elements into their bike. That said, their engineering time was predominantly devoted towards creating an electromechanical steering system in order to present a safe and convenient interface for patients.

15 weeks of hard work later, they had a successful design. Just last week, it was publicized by a local TV station and unveiled on the school's 'Design Day'. They were all smiles as they presented their mobile recumbent bike to Peggy Essex, a physical therapist assistant and their liason at MidMichigan Medical Center.

Obviously, creating designs for physically challenged people is not an easy task as these are not your everyday users. I had a chance to chat with Spiros and shoot him a few questions about the bike and what their work comprised of. In reply, the team was quite forthcoming in sharing information.

Presented below are lots of pictures and tables to look at along with material to read !

1. This rehab bike project was for a senior design class I take it?

SK : Yes.

2. But how is it that you were working on it for four years?

SK : Our design team hasn't been working on this project for four years. We are just the fourth team to work on project. The teams before us have failed in completing the recumbent cycle. Each generation of the cycle has gotten better, however; our team has successfully completed it this year.

3. Forgive my ignorance. Now this bike of yours has a solid clinical purpose behind it. How did you define this purpose at the initiation of the project?

SK : The purpose of the cycle is to help patients with neuro-muscular diseases perform cardiovascular exercise outside rather than inside the rehabilitation center. The goal was to provide these patients with a more fulfilling and enjoying workout.

Engineering projects typically involve outlining a set of goals and ranking desired features, materials and other details based on distinct attributes.

4. What objectives did you want the bike to achieve and were you inspired by something in your journey to make it?

SK : Our main goal on the project was to design a functional steering system that would allow the patients control the cycle with ease. We chose a rack and pinion design because we were impressed with its reliability.

5. Great! For readers here, talk a little about the highlighting features of the bike such as source of motive power, brake systems, controls, and so on.

SK : Well to highlight some of the features, it has electric steering. A battery powers a motor to turn the rack and pinion a certain direction once a button on the arm handles is pressed. The cycle is powered by the arms and legs of the patient in a "push and pull" motion.

From just talking with Peggy Essex from MidMichigan Health Center, it was found that children with cerebral palsy have decreased muscle strength, muscle spasms, decreased range of motion, and poor or altered posture control. This suggested that the design of the recumbent cycle needs to be efficient in generating propulsion from the energy exerted by the patient. Also, a push pull system gives a better advantage to the patient rather than a rotational propulsion system, because of the limited range of motion in the patient’s extremities.

The Nu-Step propulsion system helps utilize energy from both arms and legs simultaneously.

Previous teams had standard lever arm steering. Integrated rack and pinion improved functionality and durability.

The input power is transmitted to a couple of gears that have one directional bearings which then rotates the chain to propel the cycle forward. There are disk brakes on the two front wheels which are applied through a cable after squeezing the arm handles. Unfortunately we only had access to the previous teams' design reports and pictures so it is hard to describe the changes from before that. But the "re-design" in steering basically encompasses a much more reliable and stronger system. The design of steering in the previous year contained a servo motor that was insufficient and a motor that did not have enough power to turn the wheels. This caused the teeth on the motor to skip and grind down.

The rack and pinion was controlled by a DC servo motor that was mounted to the frame. The DC servo motor is operated with two push buttons that were installed atop the hand grips located on the handle bars. The location of the push buttons was determined with the help from Peggy Essex, the professional assistant at the Mid-Michigan Medical Center. It was important to place these buttons where they could be easily operated by the patients.

The two front wheels are connected to a rack and pinion. The shaft of the rack and pinion is attached to a motor. Rack and pinions are effortless to use, self steered, reliable, and allows smooth steering without interfering with propulsion.

Design using tools such as ANSYS helped increase torsional stiffness and overall strength on the frame. The frame was made from steel which made welding additional brackets and parts to the frame easier than aluminum and created a stronger bond. The frame was circular in shape and had dimensions of 35in. x 22in.

A new cam support was designed to allow for smooth propulsion at greater torsional stresses.

6. Now that this is over, would you consider the project successful?

SK : Yes definitely. We are very pleased with the outcome.

7. Your customers are the folks who have these physical challenges and indirectly, the medical staff as well. What do they have to say about it?

SK : We have only tested the prototype on fellow students so far but everyone seems very excited to try it out. The steering is so easy and everyone we talked to seems to like the overall aesthetics.

Since this cycle will be used for people of all shapes and sizes, a wide range of people were asked to use the cycle. The table below gives the results. The height and weight was recorded for these tests. The person was then asked about how comfortable they felt and how easy the cycle was to use once they adjusted the arms and seat to a position of their liking. These values were also recorded.

The electromechanical steering was one of the most challenging aspects of this project and testing its usability from the patient's standpoint was very important. With the help of our advisor, we were able to rank how easily a patient could operate the cycle. The table below displays these results. A ranking of 5 for Disease Case means a very extreme case of neuromuscular disease, while a rank of 5 in Ease means supreme functionality of the user and the push button on the handle grip.

The table shows that the very serious cases of neuro-muscular diseased patients have a harder time with the push button system our team incorporated. However, our design is still successful overall. Patients with less severe cases will still be able to enjoy their cardiovascular workout.

8. Time, money and materials. How many man-hours do you estimate you put on this, and what were the main tooling and processes you used?

SK : I would say that each member of the team put about 25 hours a week of work into the cycle. We used many different machines, but the main ones were band saws, belt sanders, and welding. We built the cycle in-house at a shop owned by Michigan State University. None of the work was outsourced.

Each of these machines served a purpose for the creation of each part used on the cycle. To minimize time spent on manufacturing each part through trial and error, a NX prototype served as a very useful tool in seeing how the assembly would mesh and operate without any manufacturing. This enabled the team to create parts once; mounting them to their position without any alterations after being initially fixed.

9. Give us an idea of the people and organizations that helped you in this project.

SK : The cycle was basically built by the team. General Motors was our project sponsor but they only supplied the budget for the project. We also had a faculty advisor who helped us in coming up with ideas and computer modeling. Otherwise, everything was completed by our team of four students.

10. What engineering lessons did you learn, if any, from this endeavor. Do you guys feel there is a future for the design?

SK : Personally I learned a lot about manufacturing and control systems. This project did cover a huge range of engineering principles and required all of the team to brush up on previous knowledge. I do believe there is a future for this design. It's a start. I'm sure there will be other ways to perfect the cycle in the future, but showing everyone the answer to a solution will hopefully spark some excitement in making it better.

11. As time goes, new needs come about. What suggestions do you have for future work?

SK : Some improvements would require a better belt tensioning system. It tends to come lose every now and then. Also, the arm handles are heavy and shifts the cycle's center of gravity from where it should ideally be. If it were made of aluminum instead of steel, I'm sure this could be resolved.

12. You guys were obviously inspired by a recumbent bike to help these patients out. What do you think of bicycling itself as activity for recovery and rehabilitation, compared to other impact bearing activities?

SK : Fortunately, I have never needed rehabilitation for an injury so far in my life, but I think cycling in general is a great way for someone to recover. The impact on joints, such as knees and ankles are minimized compared to jogging or weight lifting. Overall, it was a very fulfilling experience for the entire team.

13. Do you have anything personal to tell people with physical injuries and disabilities?

SK : Our team has gained respect for the people dealing with such a disabilities and how many hardships they must overcome within their life.

I would like to say that technology in this field is taking off so fast. From where I see it, there will be a solution to many disabilities in the near future. So I would like to tell people with physical challenges to be patient and always keep their heads up.

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