Gait Emulator for Evaluation of Ankle–Foot Prostheses Capable of Turning

One of the challenges in the development of prostheses is the testing and tuning of the mechanism before testing with human subjects. It is a common practice in the industry to use testing platforms to tests new products for different properties such as strength and fatigue; however, few platforms have been developed for testing and tuning of ankle–foot prosthesis. Before testing the lower extremity prostheses with human subjects, the designers need to assure that the device would perform as designed, otherwise it may result in injury. Another issue that may arise is the lack of repeatability during evaluation experiments with human subjects. Humans have a remarkable ability to adapt to new environments; hence, studying the effects of any tuning in the prosthesis performance may not be conclusive, as it may not always be clear if the outcomes are due to the changes in the prosthesis, or due to the adaptation by the amputees. Richter et al. reported a testing apparatus to evaluate the lower extremity prostheses in the sagittal plane [1]. Sagittal plane testing of leg-prostheses meets the requirements for testing the currently available powered ankle–foot prostheses, which control the ankle only in the sagittal plane and focus on straight walking. However, depending on the activity, turning steps may account for up to 50% of the steps [2]. Turning steps require modulation of the torques and angular displacements of the ankle–foot mechanisms in both the sagittal and frontal planes resulting in increased lateral and propulsive impulses when compared to straight walking [3]. The need of a device to help in testing and development of ankle–foot prostheses with two DOFs (degrees of freedom) motivated the present work. A gait emulator that can be used with both standard and circular treadmills was developed (Fig. 1), allowing testing and tuning of different types of ankle–foot prosthesis, including active and passive, and working as an intermediate step between design and human trials. The gait emulator was used together with a custom-made circular treadmill to develop and tune an ankle–foot prosthesis with two DOFs in the frontal and sagittal planes. 2 Methods