Impedance control with energy regeneration in advanced exercise machines

This paper shows how a controls-oriented approach can be used to improve the functionality, energy efficiency and bulk/weight requirements of advanced exercise machinery. Exercise devices for the space environment are the motivation for this research, but other applications are certainly possible. The paper introduces a design concept involving a user force/velocity port, a mechanical transmission, a DC motor/generator a regenerative servo amplifier and an ultracapacitor as the sole electric energy storage device. The intrinsic capability of the design concept to realize any desired force/velocity relationship at the user port (controllability of port impedance) is verified first using an inverse model approach. As an example, design parameters are selected to match the force/velocity characteristic of a typical gym rower. A feedback implementation is then developed based on the author's semiactive virtual control strategy. The validity of the approach is demonstrated with a laboratory prototype of a scaled rowing machine. The results show that the system can be operated entirely on human power, while simultaneously attaining the impedance control objective.