Instrumented Pyramid Adapter for Amputee Gait Analysis and Powered Prosthesis Control

Novel advanced prostheses aim to improve the ambulation ability of lower-limb amputees by adapting the prosthesis mechanical behavior online during ambulation. Accurate force/torque sensing is necessary to measure the physical interaction between the user, the prosthesis, and the environment. Most available solutions consist of retrofitting an off-the-shelf load cell, which leads to suboptimal designs regarding weight and size, ultimately reducing the prosthesis usability. To address this limitation, we propose to instrument an existing prosthesis component, namely, a pyramid adapter, with force/torque sensing and an inertial measurement unit. Magnetic sensing of large structural deformations is used to improve system reliability and reduce costs. Testing shows that the proposed sensor prototype can sense up to 120 Nm and 2500 N of torque and force and has 2.1% and 8.3% nonlinearity, respectively, during walking. The total weight is 150 g-only 66 g more than a standard pyramid adapter without force/torque instrumentation. Amputee testing with robotic leg prosthesis is conducted to validate the instrumented pyramid in a case scenario.