US 4,586,260 A · Capacitive displacement measuring instrument

Abstract

A scale and slider in a linear displacement measuring instrument have spaced opposed parallel surfaces bearing aligned patterns of thin flat conductive elements. The scale pattern consists of equally spaced parallel bars transverse to displacement with enlarged aligned central portions which form collectively a single set of coupling electrodes. A pair of aligned sensor electrodes are fixed on the surface of the slider opposite the coupling electrodes of the scale and matching arrays of transmitter elements are arranged on opposite sides of the sensor electrodes and grouped axially in space quadrature. Alternate interdigitated sets of the transmitter electrodes on the slider are excited with oppositely phased square wave signals. The signals picked up by the sensor electrodes on the slider are fed to separate coarse plate counting and fine plate interpolation circuits. In the fine count circuit, the displacement-dependent amplitude of the signals from first one and then the other of the sensor electrodes is amplitude demodulated and digitally converted by a dual slope integrator. The reference signal for the return slope is furnished by placing cophase signals on the transmitter electrodes. Battery life is prolonged by staged power down modes which remove bias voltages from selected analog components while retaining limit values.

Claims22

Dependent claims

A capacitive displacement transducer, comprising

a scale member bearing a transducer surface,
a slider member bearing a transducer surface,
means for mounting said members for relative movement over a displacement interval throughout which said transducer surfaces are in predetermined spaced opposition,
a pattern of spaced elongated conductive elements fixed on said transducer surface on said scale member extending over said displacement interval arranged transversely to the direction of relative movement between said members,
a pattern of conductive elements fixed on said transducer surface of said slider member including two elongated coupling electrodes in spaced alignment parallel to the direction of movement opposite said elements on said scale member, and at least one array composed of two interdigitated sets of transmitter electrodes arranged parallel to said coupling electrodes, said array being divided lengthwise into two parts in space quadrature with each other at least coextensive respectively with said coupling electrodes in the direction of the length of said coupling electrodes,
means for furnishing electrical connections to said slider electrodes including means for electrically connecting said transmitter electrodes, respectively, in an external circuit and means for electrically connecting said two coupling electrodes respectively in an external circuit.

3 more elements

A capacitive displacement transducer system, comprising

a scale member bearing a transducer surface,
a slider member bearing a transducer surface,
means for mounting said members for relative movement over a displacement interval throughout which said transducer surfaces are aligned in predetermined spaced opposition,
a pattern of spaced conductive elements fixed on said transducer surface of said scale member extending over said displacement interval,
a pattern of spaced conductive elements fixed on said transducer surface of said slider member in alignment with said pattern of conductive elements on said scale element, said pattern of conductive elements on said slider member being divided lengthwise into X and Y groups arranged in space quadrature with each other,
means for applying multiphase high frequency excitation signal to said spaced elements on said slider member,
means for producing an X signal indicative of the signal capacitively coupled from the X group of conductive elements to the subjacent conductive elements of said scale member,
means for generating a Y signal indicative of the signal capacitively coupled from the Y group of conductive elements to the subjacent conductive elements on said scale member,
coarse counting means including
first demodulator means for sampling the relative polarity of said X and Y signals for producing outputs indicative thereof, and
logic means responsive to the outputs of said demodulator means for keeping a count proportional to the number of conductive elements on said scale member traversed by said slider member indicative of gross displacement, and
fine counting means for converting the analog amplitude of said X signal to a digital value.

9 more elements

Dependencies are inferred from the claim text.

Capacitive displacement measuring instrument

Life of this patent

Capacitive displacement measuring instrument

Life of this patent

Abstract

Claims22