Estimation of Solid Friction in a Servomotor Mechanism Using an Adaptive Observer and Its Application to Positioning Control

In many mechanisms, sold friction has a bad effect on motion. Therefore, to realize faster and more accurate positioning, it is important to compensate for nonlinear solid friction acting on a positioning mechanism. From this point of view, this paper discusses a design method for an adaptive observer which can estimate solid friction in addition to state variables, as well as a compensation method for solid friction incurred in positioning control. First, a kind of adaptive observer for a servomoter system is introduced. When considering the nonlinear characteristics of solid friction, the adaptive observer changes its parameter values according to three signs (plus, minus and zero) of velocity. It is experimentally confirmed that the adaptive observer exhibits superior properties in contrast to other observers, whose designs ignore solid friction or regard it as a constant disturbance, etc. Moreover, an approximate compensation method for solid friction using the abovementioned adaptive observer is proposed. It is also shown that this compensation method enables high-speed positioning for a servomotor system with solid friction.