Abstract: An opto-electronic scale reading apparatus comprises a light source (20) which projects light via an index grating (22) onto a reflective scale (10). Light is reflected from the scale (10), passes through an auxiliary grating (36) and is incident upon an analyser grating (28), at which a plurality of periodic light patterns are formed. Light from the light source (20) travels initially parallel to the scale plane, and is subsequently deflected through 90.degree. by a beam splitter cube (26); the light is thus incident upon and reflected and off the scale (10) at 90.degree. to the scale plane. This arrangement enables large movements of the readhead in a direction perpendicular to the scale.

Abstract: Apparatus for generating a quadrature signal for the purpose of determining the direction in which the scale is being read. There is provided a primary grating means defining spaced lines and adapted for generating orders of diffraction, secondary grating means defining spaced lines arranged at an angle to those of the primary grating means thereby to separate said orders of diffraction into differing phases, and tertiary grating means movable together with the secondary grating means relative to said primary grating means and adapted for detecting the respective said phases and for generating correspondingly phased light modulations which are detected by respective transducers connected to a quadrature-forming circuit.

Abstract: A scale for use with scale reading apparatus having grooves spaced along its length at a pitch P. Each groove is made with a shape or depth variation along its length to provide a scatter mechanism for breaking up the ordered diffraction pattern which would otherwise be generated by the grating structure defined by the grooves. Methods of making the scale involve applying a transverse vibration to the cutting tool during the groove cutting operation.

Abstract: The invention provides an opto-electronic scale reading apparatus comprising a read head in which a plurality of optical emitter and receiver pairs are arranged so that beams of collimated light generated by the respective emitters fall on a common region of a scale. Compared to arrangements where the light beams fall on separate regions of the scale, the apparatus according to the invention is relatively immune to the effects of certain misalignments between the scale and the read head.

Abstract: An optical electronic scale reading apparatus comprising a scale read by a read head to determine the relative displacement therebetween. The read head comprises reflective surfaces so arranged that light from a source is reflected therefrom and interacts with the scale at first, second and third positions. At the third position, a fringe field is developed which has the same pitch as the scale. A detector is provided to receive light modulations during relative movement of the scale and read head as the fringe field interacts with the scale at the third position. These modulations are counted to determine the relative displacement between the scale and read head.

Abstract: Optical scale reading apparatus in accordance with the invention includes an optical fibre 30 for directing light from a light source 22 on to a scale 10. Light from the scale is reflected into a readhead 12 of any suitable construction. The fibre is designed to reduce any non-uniformity in the light entering it and various embodiments of the invention are described for achieving the required effect. For example, the length to diameter ratio of the fibre is made to be at least 5:1. Alternatively, or in addition, one or more constrictions are formed in the fibre, and as a further alternative or addition, at least one end face of the fibre is roughened to cause diffusion of the light.

Abstract: An opto-electronic scale-reading apparatus comprising a scale defined by marks provided on one of two members, a read head provided on the other member and including diffraction means for producing interference fringes having movement relative to the read head responsive to a displacement between the scale and the read head, and detecting means for detecting the movement of the interference fringes. The scale marks may have periodicities differing from a nominal value, and the apparatus includes a spatial filter whereby scale periodicities, differing from the nominal value by more than a given maximum, are prevented from contributing to the production of said fringes.

Abstract: The invention provides an opto-electronic scale reading apparatus wherein a read head comprises a lens adapted to project a beam of collimated light through a spatial filter on to a scale having lines. Light reflected from the scale passes back through the filter and through the lens to a phase discrimination circuit. The filter comprises two gratings co-operating to produce light modulations corresponding to the scale lines. Since the light passes twice through the filter the latter has improved ability to exclude scale lines not having the periodicity demanded by the filter.