Detection of critical errors of locomotion mode recognition for volitional control of powered transfemoral prostheses

Combination of intrinsic control and volitional control that recognizes the user´s locomotion mode (LM) has been applied to powered prosthetic legs, which enables lower limb amputees to adapt to varying terrains seamlessly. However, errors in volitional control may disrupt the user´s walking balance. This study aimed to determine whether the critical errors in volitional control could be detected before they disturbed the user´s walking. The positive answer might lead to more robust volitional control for powered prosthetic legs. To achieve this goal, volitional control and intrinsic control were connected hierarchically to operate a powered transfemoral prosthesis. Critical errors for recognizing the user´s LM were introduced artificially when transfemoral amputees walked with the powered prosthesis. Intrinsic measurements from the prosthesis were explored first in order to select effective data sources for error detection. Then a phase-dependent outlier detector was designed and offline evaluated. The results demonstrated that the designed detector can detect the tested critical errors with a high sensitivity and a low false alarm ratio before the errors disrupted the amputees´ balance. Additional engineering efforts were still necessary to test the detector on more error types and design a control strategy that can make volitional control of powered lower limb prosthesis robust and safe to use.