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Method of distance evaluation of a machine tool from a workpiece | Verfahren zur Abstandsbestimmung zwischen Werkzeugmachine und Werkstück | Procédé d'évaluation de la distance entre machine outil et pièce à usiner

Patentnummer:EP2546598B1
IPC Hauptklasse:G01B000714
Anmelder:
Erfinder:
Anmeldung:12.12.11
Offenlegung:14.07.11
Patenterteilung:20.11.19

Abstract / Hauptanspruch
This invention relates to a capacitive method of distance evaluation of a machine tool (2) from an electrically conductive workpiece (1), wherein a capacitive sensing electrode (3) is mounted on a machine tool (2) by a holder (4), which is moved towards the workpiece (1) by a driver, wherein a processing electronics (8) senses a resonance frequency of the oscillating circuit (6) non-linearly depending on the distance of a sensing electrode (3) from the workpiece (1), wherein the sensing electrode (3) is connected to the input of the oscillating circuit through a selectable impedance circuit (5), wherein each value read out of the oscillating circuit (6) is converted into the absolute value of the distance of the sensing electrode (3) from the workpiece (1) by applying a linearizing function of the processing electronics (8) that is defined by three parameters of balanced setting such as the gain K, the low limit frequency fo and the upper limit frequency fr of the oscillating circuit (6) or the gain K, the upper limit frequency fr of the oscillating circuit (6) and the period To of oscillation of difference frequency; and the distance of the endpoint of a machine tool (2) from a workpiece (1) is defined by measuring the distance of the sensing electrode (3) from the workpiece (1) and by the measured movement of the electrode (3) to the endpoint of a machine tool (2) in the initial calibration, and the low limit frequency fo, or the period To of oscillation of difference frequency as a parameter of balanced setting of the linearizing function of the processing electronics (8) is measured in the calibration in conductive connection of the sensing electrode (3) with the workpiece (1) by means of a contact of selectable impedance (5) controlled by two-step selected electrical signal (7).

The invention further relates to a circuit arrangement for implementing the method, consisting of a machine tool, a sensing electrode, a holder, a selectable impedance circuit, an oscillating circuit and a processing electronics including a data processing and control unit, an adjustable oscillator, a frequency mixer, a low-pass filter, an adjustable integer frequency divider, and a period to digital converter, wherein the sensing electrode (3) is connected to the input of the oscillating circuit (6) by means of selectable impedance circuit (5), wherein the oscillating circuit (6) and the selectable impedance circuit (5) are connected with the processing electronics (8 ).

EP2546598B1


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