# Hardware-in-the-Loop Test of a Prosthetic Foot
###### Abstract  
For a targeted development process of foot prostheses, a profound understanding of the dynamic interaction between humans and prostheses is necessary. In engineering, an often employed method to investigate the dynamics of mechanical systems is Hardware-in-the-Loop (HiL). This study conducted a fundamental investigation of whether HiL could be an applicable method to study the dynamics of an amputee wearing a prosthesis. For this purpose, a suitable HiL setup is presented and the first-ever HiL test of a prosthetic foot performed. In this setup, the prosthetic foot was tested on the test bench and coupled in real-time to a cosimulation of the amputee. The amputee was modeled based on the Virtual Pivot Point (VPP) model, and one stride was performed. The Center of Mass (CoM) trajectory, the Ground Reaction Forces (GRFs), and the hip torque were qualitatively analyzed. The results revealed that the basic gait characteristics of the VPP model can be replicated in the HiL test. Still, there were several limitations in the presented HiL setup, such as the limited actuator performance. The results implied that HiL may be a suitable method for testing foot prostheses. Future work will therefore investigate whether changes in the gait pattern can be observed by using different foot prostheses in the HiL test. hardware-in-the-loop; prosthetic feet; prostheses testing; virtual pivot point model; real-time hybrid substructuring; real-time hybrid simulation +
Footnote †: journal: Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical Engineering, Medical, Engineering, Medical Engineering, Medical, Engineering, Medical, Engineering, Medical, Engineering, Medical, Engineering, Medical, Engineering, Medical, Engineering, Medical, Engineering, Medical,,,,,,,,,,,,,,  
the interaction between the prosthesis and the user, i.e., how certain properties benefit a user. Further testing methods commonly applied can be classified into model-based, human-based, and robot-based testing [7]. While model-based testing can be performed in the early development stage, the modeling process is complex and the validation of the models is difficult [1,8]. Human-based testing offers a great insight into the gait dynamics of amputees and the dynamic interplay between a user and the prosthesis [7,9]. However, the drawbacks of human-based testing are that the results are subjective and not repeatable [10,11]. In addition, the safety of the subjects is always paramount, leading to a limitation of possible testing scenarios. Robot-based testing is an objective and repeatable approach to test prosthetic feet [10]. These tests do not take the dynamic interplay between the prosthesis and the amputee into account, however. This means that the loading trajectory of the robot does not adapt depending on the resulting forces of the prosthesis, which a human would do (posture, walking speed, etc.). All of these test methods have their advantages and shortcomings. Ideally, a testing procedure is robot-based--due to the objectivity, the possibility to measure different quantities easily, the test repeatability and because no test subjects are required--while still emulating the dynamics of the prosthesis wearer.