A scale includes a base material, scale patterns arranged at a predetermined periodicity on a main surface of the base material, and a fluorine film that covers the scale patterns and is at least partly a monomolecular fluorine compound.

A position detecting member includes a base portion including a light-receiving surface having a black color tone and a back surface located on an opposite side to the light-receiving surface. A surface layer portion including at least the base portion is made of ceramic. An average value of root mean square slopes (RΔq) on the light-receiving surface in a roughness curve is larger than an average value of root mean square slope (RΔq) on the back surface.

A rotary encoder for a valve comprises a rotatable code plate and an optical detector module comprising one or more optical detectors. The code plate defines a set of voids arranged along a set of one or more concentric circular arcs about an axis of rotation. The voids define an angle-dependent pattern over the set of arcs, the pattern comprising a plurality of distinct sectoral elements (A-O, X). At least two of the sectoral elements, located in non-adjacent sectors of the code plate, are identical, but the pattern is non-repeating over a single full rotation of the code plate about the axis. Each optical detector is aligned with a respective concentric circular arc of the code plate. A controller processes time-varying output signals from the optical detectors to determine successive positions of the rotatable code plate.

There is provided an optical encoder including an encoding medium, a substrate, a light source and a light sensor. The encoding medium includes an index track and a position track. The light source is arranged at a first surface of the substrate to emit light toward the index track and the position track. The light sensor is arranged at a second surface of the substrate, and has a first light sensing region and a second light sensing region for receiving reflective light respectively from the index track and the position track.

An index grating of an optical encoder provided by the invention has a main technical feature of increasing a ratio of light-transmissible area of a grating per unit area, thereby increasing a light source utilization efficiency and a signal intensity, and reducing light-blocking ratio caused by dust and other foreign matters, thereby reducing a degree of influence on light intensity, so as to improve a sensing precision of the optical encoder.

There is provided a displacement measuring apparatus capable of being used in a vacuum environment. The displacement measuring apparatus includes a scale and a detection head part disposed in such a manner as to be relatively displaceable to the scale and as to face the scale with a predetermined gap. The detection head part detects a displacement or position relative to the scale. The scale is disposed in a vacuum. The detection head part is housed in a housing holder separating an atmospheric environment side from a vacuum environment side. In a gap between the detection head part and the scale, the housing holder includes a relay means for passing a detection signal between the detection head part and the scale,

There is provided an optical encoder including a photodiode array and a code disk opposite to each other. The photodiode array includes at least three sets of position photodiodes and two index photodiodes arranged transversally. The two index photodiodes are adjacently arranged at the same side of the at least three sets of position photodiodes. A first set of position photodiodes and a last set of position photodiodes of the at least three sets of position photodiodes are partially covered to alleviate the total harmonic distortion. The rest position photodiodes of the at least three sets of position photodiodes other than the first and last sets of position photodiodes are not covered.

A scale includes: a substrate that is made of low expansion glass of which a thermal expansion coefficient is 1×10.sup.−7/K or less; and scale gratings having a plurality of gratings that are arranged on a first face of the substrate at a predetermined interval and are made of a transparent inorganic material of which a thermal expansion coefficient is more than 1×10.sup.−7/K.

A life detection device of an encoder is used for the encoder including a scale and a head. The scale is housed in a scale frame. The head relatively moves along the scale to detect an amount of relative movement with the scale. The life detection device includes environmental condition detection means, life determination means, and informing means. The environmental condition detection means is configured to detect an environmental condition related to life detection in the encoder. The life determination means is configured to determine a life of a component constituting the encoder based on a detection result by the environmental condition detection means. The informing means is configured to inform the life based on a determination result by the life determination means.

A position-measuring device includes a scale having first and second measuring graduations, which each include graduation structures that respectively extend parallel to first and second directions. A first scanning unit is associated with the first measuring graduation, and second and third scanning units are associated with the second measuring graduation. A fourth scanning unit is associated with the first or second measuring graduation. In the former case, a first straight connecting line running through scanning locations of the first and fourth scanning units and a second straight connecting line running through scanning locations of the second and third scanning units are parallel or form a predetermined angle therebetween that is not equal to a sum of the angles of the first and second directions. In the latter case, the scanning locations of the second, third and fourth scanning units do not lie on a common straight connecting line.