Delayed-reference control (DRC) applied to machining operations

This paper deals with a non-time based control for machining operations. Such a control can be implemented in most of the CNC centers in a practical way. Basically, in this control, which belongs to the category of non-time based controllers, the desired input reference is a function of the time and of a variable which plays the role of a time delay: xd(t−T). Indeed, the proposed controller is called delayed-reference control (DRC). It is recalled that in a time-based control, the desired input reference is described as a function of time only, which is referred to as reference time: xd(t). The calculation of this function is usually implemented off-line by means of the so called path-planning process. According to this traditional approach, during the task execution, at each instant, the control module is required to track an input reference. What is relevant is that such a reference can never be modified by any event or circumstance. The DRC control differs from time-based controllers in the sense that time delay is properly calculated on-line according to the measured force signals in such a way to improve the interaction during the cutting process. In fact, the DRC consists in an outer force feedback loop around an inner position feedback loop. The effectiveness of the controller has been proven by means of its implementation on a three axes CNC center for wood machining. Eventually, experimental results are presented.