End-point sensing and load-adaptive control of a flexible robot arm

The use of lightweight flexible links in robot manipulators is desirable from the point of view of achieving robot arms which are faster and less expensive than the typical robot arms in use today. The disadvantages of light, flexible arms are (1) that they require a means for accurate end-point sensing and feedback to compensate for static load errors, and (2) that the feedback control system must also suppress the vibrational transients in the flexible arm during rapid arm movements. Since the arm load affects the transient and steady-state behavior of the flexible arm, the control strategy must be adaptive to load changes. This paper describes a method using an on-line estimator to provide periodic updates of load mass estimates to a parametric optimal controller which then adjusts the control gains to maintain the desired arm response. The method appears to offer a promising means for achieving rapid, smooth, and accurate motion of flexible robot arms under varying load conditions.