This paper describes an adaptive feedforward controller to let the output of a plant with stable and unstable zeros track a time varying desired output. The dynamics of the closed loop system consisting of the plant and the feedback controller are assumed unknown or slowly varying due to changes on the plant parameters. In the control scheme proposed in this paper, the feedforward controller is adaptive while the feedback controller is fixed under the assumption that the closed loop system remains stable at all times. With a few samples of future reference input data available, the preview action of the adaptive feedforward controller cancels the phase lag caused by the closed loop dynamics and attains the zero phase error tracking performance (i.e., the plant output is in phase with any sinusoidal desired output) asymptotically.
Lmear motion electric motors have shown promising potential for use as next generation machine tool feed drives since they can increase machining rates and improve servo accuracy by eliminating gear related mechanical problems. TO combat chatter instability, large dynamic stiffness is desirable in the servo control loop.This paper investigates the use of optimal H , control to design for large stiffness.Position feedback alone is first considered, with cutting force feedback later added to augment closed loop stiffness. Optimal position feedback is experimentally seen to achieve up to a 46% stiffness improvement over that achievable with propaionalderivative control. The addition of force feedback to the servo loop resulted in a further 70-100% stiffness improvement over the position feedback alone values.
Using linear motors as machine tool feed drives has the potential of enhancing machining performance by eliminating gear related mechanical problems and increasing speed and accuracy, but introduces a stability concern due to a strong dynamic feedback interaction between the machining process and the drives. This paper investigates the stability aspect of this dynamic interaction and the use of active damping to achieve machining stability in turning. Various necessary and sufficient conditions for stability at all cutting speeds are derived, and have been used to study the effect of damping and gear reduction in system stability. The interaction of the cutting process with the tool servo loop is seen to have significant instability consequences in systems with small drive gear reductions. Both theoretical stability and experimental cutting results are presented for PD and PID regulation. Results show that actively controlled linear motors can provide sufficient dynamic stiffness for stable turning operation.
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