EP0107374A1 — Displacement measuring apparatus

Claim 1

Independent Claim 271 words

Apparatus for measuring displacement between a fixed and a movable member (11,10), comprising an elongate mark-space grid (13) secured to the fixed member (11), a reading head (12) secured to the movable member (10) and adapted to traverse the grid (13) along the length thereof during movement of the movable member (10), the reading head (12) having two input stations (251,261), each adapted to receive radiation emanating from said grid in the form of a wave signal (A or B) corresponding to said marks and spaces thereof, the two stations (25,26) being spaced apart in the direction of the length of the grid (13) by a distance p(n + a) where p is the pitch of the marks, n is a whole number, and a is a value of approximately 1/4p so that during movement of the reading head (12) the two wave signals (A,B) are out of phase by approximately 90°, means (40) for counting the periods or fractions thereof of at least one of the wave signals (A or B) thereby to determine the relative displacement of the reading head (12) and the grid (13) during the said movement, and means (42) for detecting which of the two wave signals (A or B) is leading the other thereby to determine the sense of direction of said displacement, characterised in that the detecting means (42) is situated on the fixed structure (11) in a position remote from the said reading head (13) and is connected thereto by an elongate flexible radiation guide (14) adapted to transmit said wave signals (A,B) from said reading head (13) to said detecting means (42).

Claim 2

Dependent Claim 271 words

Apparatus for measuring displacement between a fixed and a movable member (11,10), comprising an elongate mark-space grid (13) secured to the fixed member (11), a reading head (12) secured to the movable member (10) and adapted to traverse the grid (13) along the length thereof during movement of the movable member (10), the reading head (12) having two input stations (251,261), each adapted to receive radiation emanating from said grid in the form of a wave signal (A or B) corresponding to said marks and spaces thereof, the two stations (25,26) being spaced apart in the direction of the length of the grid (13) by a distance p(n + a) where p is the pitch of the marks, n is a whole number, and a is a value of approximately 1/4p so that during movement of the reading head (12) the two wave signals (A,B) are out of phase by approximately 90°, means (40) for counting the periods or fractions thereof of at least one of the wave signals (A or B) thereby to determine the relative displacement of the reading head (12) and the grid (13) during the said movement, and means (42) for detecting which of the two wave signals (A or B) is leading the other thereby to determine the sense of direction of said displacement, characterised in that the detecting means (42) is situated on the fixed structure (11) in a position remote from the said reading head (13) and is connected thereto by an elongate flexible radiation guide (14) adapted to transmit said wave signals (A,B) from said reading head (13) to said detecting means (42).

Claim 3

Dependent Claim 61 words

Apparatus according to claim 1, wherein said radiation guide (14) is a single such guide, said radiation insofar as it is derived from said stations (251,261) has different frequencies, said reading head (12) has means (23) for combining said frequencies for transmission by said single guide (14), and said detecting means (42) include means (27B,28B) for discriminating between said two frequencies.

Claim 4

Dependent Claim 61 words

Apparatus according to claim 2 comprising a source of radiation (20) connected to said guide (14) at the end thereof adjacent said detecting means (42) to transmit incident radiation via said reading head (12) to said grid (13) for reflection therefrom, the resulting reflected radiation constituting said radiation emanating from said grid (13) to be received by said input stations (251,261).

Claim 5

Dependent Claim 158 words

Apparatus according to claim 1, wherein said radiation guide (14) is a single such guide, said radiation insofar as it is derived from said stations (251,261) has different frequencies, said reading head (12) has means (23) for combining said frequencies for transmission by said single guide (14), and said detecting means (42) include means (27B,28B) for discriminating between said two frequencies, a source of radiation (20) is connected to said guide (14) at the end thereof adjacent said detecting means (42) to transmit incident radiation via said reading head (12) to said grid (13) for reflection therefrom, the resulting reflected radiation constituting said radiation emanating from said grid (13) to be received by said input stations (251,261), and wherein said guide (14) and said input stations (251,261) are arranged for the incident radiation to pass from the guide (14) through said stations (251,261) and, on reflection from said grid, return through said stations (251,261) to said guide (14).

Claim 6

Dependent Claim 55 words

Apparatus according to claim 3 or claim 4 wherein said guide (14) is connected, at the end thereof adjacent said detecting means (42), to first optical means (21,121) for transmission of said incident radiation to said guide (14) and to second optical means (22,122) for transmission of said reflected radiation to said detecting means (42).

Claim 7

Dependent Claim 78 words

Apparatus according to claim 5 wherein said first optical means (21,121) comprise lens means for converting radiation from said source (20) into a convergent beam (121A) having a narrow end positioned to direct said incident radiation into the adjacent end of said guide (14), means (27,28) provided in position clear of said beam (121A) for receiving reflected radiation emanating from said adjacent end of the guide (14) at angles clear of said narrow end of said convergent beam.

Claim 8

Dependent Claim 144 words

Apparatus for measuring displacement, comprising a scale (13), a radiation source (20), a single flexible light guide (14) having a first end adapted to receive incident radiation from said source (20), a photo- electronic scale reading head (12) optically connected to a second end of said guide (14) for transmission of the incident radiation to said scale (13), said head (12) having means (251,261) for receiving reflected radiation from said scale (13) at stations which are mutually out of phase relative to the scale and which is adapted to transmit the reflected raditation from said stations to said second end of the guide (14), and means (22,122) provided at or near said first end of the guide (14) for separating the reflected radiation from the path of the incident radiation and for discriminating (27B, 28B) between the radiation from the respective said stations (251,261).

Claim 9

Dependent Claim 144 words

Apparatus for measuring displacement, comprising a scale (13), a radiation source (20), a single flexible light guide (14) having a first end adapted to receive incident radiation from said source (20), a photo- electronic scale reading head (12) optically connected to a second end of said guide (14) for transmission of the incident radiation to said scale (13), said head (12) having means (251,261) for receiving reflected radiation from said scale (13) at stations which are mutually out of phase relative to the scale and which is adapted to transmit the reflected raditation from said stations to said second end of the guide (14), and means (22,122) provided at or near said first end of the guide (14) for separating the reflected radiation from the path of the incident radiation and for discriminating (27B, 28B) between the radiation from the respective said stations (251,261).

Displacement measuring apparatus

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