Abstract: The voltage between a work instrument and a workpiece varies with the distance between them. A microcoded controller is used to compare the voltage between the work instrument and the workpiece when the instrument moves relative to the workpiece, to generate a correction signal. The correction signal is the sum of a proportional term, a derivative term and an integral term. A servo means responds to the correction signal to correct the distance between the work instrument and the work piece so as to maintain the voltage between them at a set level. A battery-backed memory is used to store crucial parameters necessary for operating the automatic control system to prevent loss of the parameters from the controller memory caused by power interruptions. A stepper motor operating in either the full of half step mode may be used to move the work instrument away from or towards the work piece in response to the correction signal.

Abstract: The optical tracker of this invention tracks a boundary on the surface where the light reflectivity of the surface changes at the boundary. The optical tracker includes a sensing means for sensing light reflected from an elongated portion of the surface defining a window. When the sensing means is moved over the surface it will receive consecutively light reflected from a sequence of windows that ir passes over and generates a set of electrical signals indicative of the intensity of light reflected from locations along the length of the window. A microprocessor control means derives from the signals provided by the sensing means secondary sets of signals useful for serving as a template and for finding the boundary when the window includes a selected portion of the boundary. The microprocessor control means can be activated to record a secondary set of signals as a template.