Adaptive control of a flexible manipulator with unknown changing loads

A new adaptive control scheme for the tip position control of a single link flexible manipulator handling unknown changing loads and its experimental verification is presented here.; The major portion of the new adaptive control scheme consists of a recursive control algorithm (RCA) combined with parameter estimate resetting; acting together, the RCA and the parameter estimate resetting eliminate undesirable transients. The parameter estimate resetting is to memorize the parameter estimate vector obtained from system identification before a payload is picked up and then to use this vector to reset the estimated parameters before the payload is released, so that a "ringing phenomenon" transient will not occur when the payload is released. If one were only to reset the parameter estimate vector, however, another undesirable transient would be introduced. This latter transient is successfully eliminated by the RCA, wherein the control signal does not respond to sudden changes in the control gains set by the parameter estimate vector.; Besides the RCA with parameter estimate resetting, the new adaptive control scheme has two other components, namely (i) a new modified Luenberger observer control structure for pole placement and (ii) the Fortescue's algorithm for system identification. The modified Luenberger observer control structure applies integral action on the Luenberger observer structure and is shown both in theory and in simulation to have better performance than the commonly used "error-driven control structure." The Fortescue's algorithm is used to suppress the transient when the setpoint is changed after the payload is picked up.; Experimental results show that the developed adaptive control scheme can satisfactorily maneuver the flexible manipulator with a reasonable speed and a large range of operation without any transients under changing load situations. Experimental results also show that this new adaptive scheme can handle a broad range of payloads without the requirement of prior knowledge of the payloads. This demonstrates that the developed adaptive control scheme can deal with "unknown" payloads.; Compared with a constant gain pole placement controller and a general self-tuning pole placement control scheme for a task with unknown changing loads, the new adaptive control scheme clearly demonstrates its superior performance.