Conceptual Considerations

What is the motivation for this project?

We had one two group members interested in lower-body kinematics and two members currently enrolled in a class concentrating on lower-body exoskeletons. It made sense to combine the interests and experience of all group members to tackle a problem relating to lower-body motion.  Additionally, a cheap exoskeleton knee has never really been attempted.  All prior art in this area has been done with massive budgets and lots of time.  The technology to tackle this project is maturing such that home-grown projects now have a chance at success.

What are some kinematic challenges you have faced?

We had to put a lot of thought into constructing the most effective linkage for the actuated knee joint. We considered every type of linkage that we studied in class before choosing a linkage that would be possible to machine and mesh with the actuator. The linkage had to accommodate the widest range of motion possible without causing harm to a human leg. We were also required to operate within the constraints of the knee brace that was ordered as the basis of our mechanism.  We settled on a 5-bar-geared mechanism because it fit well with the knee brace, but also allowed for the most straight forward actuation.  The kinematic analysis of the 5-bar-geared linkage revealed a very smooth velocity throughout the entire range of motion, which is very important in ordre to mesh with the human body.  

What went into the selection of your motor?

We had to consider the following when choosing a motor:

• torque requirements
• mounting logistics
• cost
• controllability
• attachment to linkage

We were not able to actually select the motor we wanted due to budget and time constraints.  Our project really needs a specialty motor with a specific (large) gear reduction in order to extract the most amount of power despite a very small range of motion.  We are using the motor provided in class as a baseline, with the assumption that future development of this project would incorporate the correct motor needed.

What programming challenges have you encountered?

No team member has worked with the Arduino software before, so we are currently learning how to control our motor using that system. We also had to consider and plan how to move the knee both forward and backwards, planning our design according to our programming experience. The design that we came up with seemed to stretch our boundaries to an achievable limit during the time constraint. 

There was some difficulty in configuring the EMG sensors to acquire usable data, which mostly stemmed from the fact that no one had worked with this kind of equipment before. We worked to employ the appropriate sample rate and analysis technique and were able to use the sensors for our robot, but the sensors are not of the highest quality.

What do you have left to do to in order to have a successful presentation?

• Attach the motor to the linkage/brace
• Program the Arduino device
• Test the system

What are the most important skills and/or lessons you have taken from this project?

Becca

• This was my first time to take a product the all the way through the conception, development, manufacturing, and testing process - an experience that will certainly help me in my research and career.
• I got to brush up on my machine shop skills.
• I was fortunate enough to wind up in a group where each member had different, complimentary strengths. It was interesting (in a good way) to see how everyone fit into their roles and how we all learned from one another and built upon each other.
• Design is definitely an iterative process.