A Design For An Exoskeletal Device With Reduced Reliance On Joint Alignment

As robotic exoskeletons begin to find more use in the areas of medicine and rehabilitation, efforts to improve comfort and reduce the chance of injury for wearers have resulted in the development of joint mechanisms with extra passive degrees of freedom. The added redundancy in such mechanisms enables the system to accommodate for joint axis misalignments between the exoskeleton and the human skeleton, as well as deviations from ideal circular motion that are inherent in normal human body motion. However, proper measurement of joint positions and torques, and by extension proper position and impedance control of the exoskeleton still relies on the approximate alignment of these joint axes. This paper presents a method for such a system to calculate the pose and torque about a human elbow joint for a wider variety of possible mounting positions. Using the developed calibration procedure, the main joint of the exoskeleton can be located as much as 110 mm away from the elbow and still position the elbow to within 10 degrees of a given flexion angle and measure torques to within 13 percent of the actual value. An elbow exoskeleton was developed employing this system and tested for comfort. The wearer was able to comfortably move their elbow in any desired motions using the device’s passive mode. These results demonstrate the feasibility of using such a system on a robotic rehabilitation device and open up more possibilities for future exoskeleton designs not limited by joint placement.