5DOF Myoelectric Arm

Employer: Shirley Ryan AbilityLab / RIC

Role: Research Engineer III

This project was motivated by trying to understand the needs of people who reject the use of a prosthesis. While traditional users wanted more strength or speed, manufacturers were not satisfying the untapped market. Through our reserach we discovered:

• It doesn't matter how strong the device is if it is not being worn

• The device should weigh less than the anatomical counterpart. It is not attached via a bone or connective tissue, so the user experiences the weight of the device differently than their anatomical limb.

• Available devices are too large. These are designed for the 50th percentile male which is too large for 72% of adults. Not only is this bulky and burdensome, but it removes visual symmetry. It becomes obvious that the user is wearing a device.

• Dexterity is lacking. Commercial devices had a thumb that moved in prehension and no wrist flexion ability. We use our thumbs to locate and oppose our grasps, it doesn't move in prehension. This design chocie forces users to more cognitively engage with grasping movements due to the unnatural actuation of the digits.

Key Design Features of the RIC Arm

• Wrap around fingers which utlize an optimized 4-bar linkage design*

• Independently controlled, non-backdriveable thumb which utilizes a single axis of rotation to accomplish 3 distinct grasping patterns *

• Wrist flexion with dart thrower's angle which allows users to better reach their midline and wrist behaves more like anatomical counterpart *

• Universal, electromechancial quick disconnect which was the first of it's kind being able to support passive and active rotation in a tiny package *

• Wrist rotation. Coupled with our wrist flexion unit, this was the first 2DOF wrist available to users. This 2DOF wrist allows for 95% of anatomical motions and manevuers.

• Elbow flexion with biomemetic carrying angle which flexes toward the midline, which allows users to better perform activities of daily living.

• Design for the 25th percentile female in mass and size (covers ~87% of the population)

• Match other benchmarks in terms of force and speed

• State of the art pattern recognition control. This technolgoy became the first spin out from the resarch group and is now Coapt.

This project was the effort of a multi-disciplinary team of researchers, engineers, and clinicians. Items with * are projects where I was the lead design engineer, however this was a highly collaborative project built by small 5 person team of engineers.

2015 Presentation by project principle investigator Jon Sensinger on the status of the project.