Tracer control system

A tracer control system in which the configuration of a model is detected by the motion of a tracer head with a stylus relative to the model surface being traced during a selected tracing, said system including a movable machine part moving along machine axes for providing said motion, and in which feed velocity components along said machine axes for providing the motion are obtained by arithmetic processing of data including displacement signals corresponding to the position of the end of said stylus with respect to the tracer head, said displacement signals having components corresponding to said machine axes, said motion of said tracer head selectively comprising sequential trace feed and pick feed steps, the tracer control system comprising:

• a memory for storing data for determining the limits of the range of a selected tracing of the surface of the model;
• a processor for reading out the stored data of the memory, for performing any necessary calculation of the limits of the range of the selected tracing from said stored data, and for performing control functions for performing said selected tracing over said range defined by said limits;
• and
• detecting means for detecting the current position of said movable machine part along each said machine axis;
• wherein each said limit of the selected tracing corresponding to a respective machine axis is compared with the current position along the respective machine axis, and when it is detected that the current position has reached a respective limit, during one of said trace feed steps, the trace feed step is switched to a pick feed step, and, after the pick feed step is performed for a respective predetermined distance, a predetermined subsequent trace feed step is performed, until said selected tracing is completed over said range.