Synchronisation of multi-axis automation processes using iterative learning control

It is often necessary to synchronise the actions of the various sub-systems involved in process applications. This is usually achieved through direct mechanical coupling, involving gears, drive belts and cams. Apart from the additional cost incurred, these are subject to wear, constrain the plant layout, and may have limited accuracy. It is shown that such a linkage may be replaced by instead implementing a control scheme comprising an iterative learning controller together with a supervisory control loop. To illustrate the approach, two types of iterative learning controller are first implemented on a gantry robot test facility to confirm the high levels of tracking accuracy that may be achieved. The supervisory control loop is then added to synchronise the `pick and place' action of the robot with a conveyor system moving at constant velocity. Experimental results confirm both the accurate tracking performance produced by the iterative learning controller, and the high level of synchronisation achieved by the overall scheme.