Abstract: Contact sensing probe apparatus includes a workpiece contacting stylus, a transducer mechanically coupled to the stylus and an oscillator for supplying an alternating current to the transducer to induce vibration of the stylus. A contact sensor is also provided for monitoring the phase difference between the voltage supplied to the transducer and the current flow to the transducer. The oscillator is arranged to supply the transducer with an alternating current of a first frequency during contact sensing. This first frequency is selected to induce mechanical resonance but to be away from the maximum of the mechanical resonance peak. The probe may be used with co-ordinate positioning machines, such as portable articulated measuring arms, co-ordinate measuring machines (CMM) and the like.

Abstract: Apparatus and method of determining drift for a surface measurement probe. The surface measurement probe has a housing, a surface contacting stylus, a vibration generator which causes vibration of the stylus, a sensing device for determining a parameter related to change in vibration of the stylus, and a comparator for determining the relationship of the parameter with a threshold. Readings of the parameter are taken when the stylus is not in contact with a surface and average over a time t, which is significantly larger than the transition time when touching a surface. The average of the readings of the parameter is compared to a reference parameter. The comparison is used to determine whether there has been significant drift of the parameters. Thus drift due to temperature change is corrected.

Abstract: Contact sensing probe apparatus includes a workpiece contacting stylus, a transducer mechanically coupled to the stylus and an oscillator for supplying an alternating current to the transducer to induce vibration of the stylus. A contact sensor is also provided for monitoring the phase difference between the voltage supplied to the transducer and the current flow to the transducer. The oscillator is arranged to supply the transducer with an alternating current of a first frequency during contact sensing. This first frequency is selected to induce mechanical resonance but to be away from the maximum of the mechanical resonance peak. The probe may be used with co-ordinate positioning machines, such as portable articulated measuring arms, co-ordinate measuring machines (CMM) and the like.