Renishaw Plc

Renishaw Metrology Limited

Clifford W Archer

Peter Hajdukiewicz

David R McMurtry

A touch trigger probe for machine tools or coordinate measuring machines has three strain gauges SG1-3 which react to deflection of a stylus of the probe, causing a trigger signal to be generated in signal processing circuitry SP. To reduce power consumption, and thus to reduce thermal growth of the probe, the strain gauges are fed by constant current sources CS1-3. The sources CS1-3 are servo controlled from a reference resistance R.sub.ref and constant current source CS4, by an amplifier A4.

Sensing circuit for position-sensing probe

A touch trigger probe for machine tools or coordinate measuring machines has three strain gauges 10A-C, which respond to deflection of a stylus of the probe when it contacts a workpiece. The signals from the strain gauges are each rectified by precision rectifiers 18A-C, and then combined at a summing junction 20. A first comparator 28 compares the combined signal with a threshold voltage V.sub.ref1, to produce a sensitive trigger signal. A second comparator 30 compares the combined signal with a higher threshold voltage V.sub.ref2, which produces a confirmation signal. This confirms that the trigger signal is caused by a genuine workpiece contact, and not caused falsely by vibration or acceleration.

Signal processing circuit for trigger probe

A contact-sensing probe for measuring workpieces includes a body (16) for attachment to a machine and a workpiece contacting stylus (22) carried by a stylus holder (24) which is mounted within the body for movmeent relative thereto from a rest position to a displaced position when the stylus contacts the workpiece. Sensors are provided for sensing workpiece contact by the stylus. The sensors comprise a plurality of strain gauges (46) mounted on pillars (44) connecting two parts (36A,36B) of a support structure which supports the stylus holder on the body. The strain gauges are mounted with their principal axes lying at an angle to the axes of the pillars, and by optimizing the numbers, positions and dimensions of the pillars together with the angles of the strain gauges, high sensitivity can be achieved with minimum risk of false signals due to probe vibration, while at the same time minimizing the variation in pre-travel of the stylus.

Probe for measuring workpieces

The invention enables two-way communication to be established between a measuring probe on a machine spindle and the machine using only two wires between the probe and the machine. Communication from the probe to the machine is achieved by causing current changes in an electrical circuit within the probe (due to the probe circuit changing state when a workpiece is detected) to be sensed by a current sensing circuit on the machine to produce an output in the machine circuit indicative of workpiece detection. Communication from the machine to the probe is achieved by varying the voltage supplied to the probe circuit under the control of the machine controller, the change in voltage being sensed by components of the probe circuit to initiate different functions of the probe circuit e.g. re-setting the probe or changing the gain of a component.

Probe for measuring workpieces and electrical connections therefor

A contact-sensing probe for measuring workpieces includes a body (16) for attachment to a machine and a workpiece contacting stylus (22) carried by a stylus holder (24) which is mounted within the body for movement relative thereto from a rest position to a displaced position when the stylus contacts the workpiece. Sensing means are provided for sensing workpiece contact by the stylus. The sensing means comprise a plurality of strain gauges (46) mounted on pillars (44) connecting two parts (36A,36B) of a support structure which supports the stylus holder on the body. The strain gauges are mounted with their principal axes lying at an angle to the axes of the pillars, and by optimizing the numbers, positions and dimensions of the pillars together with the angles of the strain gauges, high sensitivity can be achieved with minimum risk of false signals due to probe vibration, while at the same time minimizing the variation in pre-travel of the stylus.

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Dursley, United Kingdom

Clifford W Archer