Active datum for coordinate reference in a numerically controlled machine tool

摘要

A datum is disclosed for use as a coordinate reference in a numerically controlled machine tool. The datum which is active, consists of an elongated member, typically one half wavelength in length, supported at its center (and antinode) by a plate, and including electromechanical transducers for exciting resonance in a desired fundamental longitudinal mode. The datum is operated by an operational amplifier having the transducers connected in the amplifier feedback path. Assurance against the excitation of undesired modes is achieved by limiting the gain of the operational amplifier throughout the response band of the transducers, by use of an inductor for resonating the input capacitance of the driving transducer at the frequency of the desired mode and by gain bandwidth limits of the operational amplifier. The datum is active at an ultrasonic frequency suited to touch sensing and thus produces a response in a touch sensing system when the cutter is touched to the datum. The response provides an accurate indication of the cutter position referenced to the coordinate system of the machine tool as well as a test signal for a system test calibration.