Biomimetic Impedance Control of an EMG-Based Robotic Hand

The number of extremity amputations resulting from workplace mishaps, traffic accidents and other incidents has shown an increasing trend over time, although the importance of safety management and the prevention of such accidents is fully recognized. Since precise and complex motion may be very difficult in the daily activities of amputees, the development of prosthetic systems is necessary to support their lives and enable social integration. In particular, there is a mandatory requirement for the development of externally powered prosthetic hands with a natural feeling of control, since the role played by this part of the body is very important. However, the control of such hands is problematic, and they must be carefully designed in line with the amputee’s remaining functions. Many researchers have designed prosthetic limbs for amputees since the concept was proposed by N. Wiener in Cybernetics [1]. In previous research, electromyograms (EMGs) have been widely used as an interface tool for prosthetic hands because EMG signals contain information about the operator’s intended motion [2] – [8]. For example, an EMGprosthetic hand made in the USSR [2], the Waseda hand developed by Kato et al. [3], the Boston arm by MIT [4] and the Utha artificial arm by Jacobson et al. [5] were all pioneering steps in the field. Since EMG signals also include information on the force level and mechanical impedance properties of limb motion, Akazawa et al. [6] estimated the force of flexors and extensors from these signals and proposed a scheme to use them in controlling a prosthetic hand. Abul-haj and Hogan [8] also proposed prosthetic control based on an impedance model and analyzed its control characteristics. Most previous research, however, dealt only with on/off control for prosthetic arms depending on the results of EMG pattern discrimination [2], [3], [7], or controlled only a particular joint depending on the torque estimated from EMG signals [4], [5], [6], [8]. Multijoint control of prosthetic arms considering the variable viscoelasticity of flexors and extensors has not yet been realized. This chapter introduces a biomimetic control for an externally powered multi-joint prosthetic hand that considers the muscular contraction levels of flexors and extensors using 9