Treadmill motor current based real-time estimation of anteroposterior force during gait

We have been developing a new vehicle, "Tread-Walk 2", which supports walking for elderly. A control algorithm to improve the operability has been constructed. As the first step, we accurately estimated the user's anteroposterior force from the motor current value without the force sensor. This method is to develop a new mechanical model that considers the friction forces of the treadmill and remove the modeled friction losses from the output. However, we need the vertical force in order to develop a mechanical model. Thus, we proposed the new method to estimate the vertical force without the force sensor. This paper describes the new method to approximate the waveforms of the vertical forces as square waves by adding the user's weight as a parameter to the stance phase. By comparing the estimated anteroposterior force using the new method with the measured one using the force plate, the waveform pattern of the estimated one was similar with that of the measured one in two young subjects whose physical characteristics were different. This showed that the proposed method might possibly be useful for estimating the anteroposterior force in real-time.