Optical grating with interpolator having multiplying means to produce quadrature signals

Claim 2

An interpolator for receiving quadrature input signals at a first frequency and producing quadrature output signals at a second frequency which is a multiple of the first frequency, comprising means for producing first and second signals at double said first frequency and substantially in quadrature if the input signals are in quadrature, said producing means comprising squaring means for squaring one only of said input signals to provide said first signal and multiplying means for multiplying said input signals together to provide the second signal.

Claim 3

An interpolator according to claim 1 wherein said squaring means uses the trigonometric identity sin 2 A=1/2-(cos 2A)/2.

Claim 4

An interpolator according to claim 1 wherein said squaring means uses the trigonometric identity cos 2 A=1/2+(cos 2A)/2.

Claim 5

An interpolator according to claim 1 wherein said multiplying means uses the trigonometric identity sinAcosA=(sin2A)/2.

Claim 6

An interpolator according to claim 1 comprising high pass filtering means for removing DC drift components.

Claim 7

An interpolator according to claim 5, wherein said high pass filtering means is arranged to filter said input signals prior to said squaring and said multiplication.

Claim 8

An interpolator according to claim 1 comprising further squaring means for squaring one of said first and further signals and second multiplying means for multiplying said first and second signals together, to provide output signals in quadrature at four times said first frequency.

Claim 9

An interpolator according to claim 7, comprising filtering means for high pass filtering said first and second signals, to remove DC components therefrom.

Claim 10

An interpolator according to claim 7 comprising means for amplifying said first and second signals, prior to said squaring and said multiplication applied to said first and second signals, to compensate for loss of gain relative to said input signals.

Claim 11

An interpolator according to claim 7, comprising means for high pass filtering said output signals to remove DC components therefrom.

Claim 12

An interpolator according to claim 1 comprising automatic gain control means for controlling the gain of said input signals.

Claim 13

An interpolator according to claim 1 in association with a zero-crossing detector which receives the signals output by the interpolator.

Claim 14

A movement detector comprising an optical grating, light sensor means for producing quadrature signals in response to relative movement between said grating and said light sensor means, and an interpolator for producing quadrature output signals at a frequency which is a multiple of the frequency of the signals produced by the light sensor means, said interpolator receiving quadrature input signals in accordance with the signals produced by the light sensor means and comprising means for producing first and second signals at double the frequency of said quadrature input signals and substantially in quadrature if the input signals are in quadrature, said producing means comprising squaring means for squaring one only of said input signals to provide said first signal and multiplying means for multiplying said input signals together to provide the second signal.

Claim 15

A movement detector comprising an optical grating, light sensor means for producing quadrature signals in response to relative movement between said grating and said light sensor means, and an interpolator for producing quadrature output signals at a frequency which is a multiple of the frequency of the signals produced by the light sensor means, said interpolator receiving quadrature input signals in accordance with the signals produced by the light sensor means and comprising means for producing first and second signals at double the frequency of said quadrature input signals and substantially in quadrature if the input signals are in quadrature, said producing means comprising squaring means for squaring one only of said input signals to provide said first signal and multiplying means for multiplying said input signals together to provide the second signal.

Claim 16

Metrological apparatus comprising a surface sensor, means for causing said sensor to traverse the surface of a workpiece, and sampling means for sampling the output of said surface sensor during said traversing, said sampling means comprising a position detector for producing first quadrature signals in response to said traversing, an interpolator for producing further quadrature signals at a frequency which is a multiple of the frequency of the first quadrature signals, and means to effect said sampling in response to a predetermined condition in each of said further quadrature signals, said interpolator receiving quadrature input signals in accordance with said first quadrature signals produced by said position detector, and comprising means for producing first and second signals at double the frequency of said quadrature input signals and substantially in quadrature if the input signals are in quadrature, said producing means comprising squaring means for squaring one only of said input signals to provide said first signal and multiplying means for multiplying said input signals together to provide the second signal.

Claim 17

Metrological apparatus comprising a surface sensor, means for causing said sensor to traverse the surface of a workpiece, and sampling means for sampling the output of said surface sensor during said traversing, said sampling means comprising a position detector for producing first quadrature signals in response to said traversing, an interpolator for producing further quadrature signals at a frequency which is a multiple of the frequency of the first quadrature signals, and means to effect said sampling in response to a predetermined condition in each of said further quadrature signals, said interpolator receiving quadrature input signals in accordance with said first quadrature signals produced by said position detector, and comprising means for producing first and second signals at double the frequency of said quadrature input signals and substantially in quadrature if the input signals are in quadrature, said producing means comprising squaring means for squaring one only of said input signals to provide said first signal and multiplying means for multiplying said input signals together to provide the second signal.

Claim 18

Apparatus according to claim 14, wherein said position detector comprises an optical grating and light sensor means.

Claim 19

Apparatus according to claim 14 including means for low pass filtering signals derived from the sensor for removing interpolation noise.