Abstract: An incremental encoder apparatus including: a scale including a series of periodic features defining an optical incremental scale, and at least one magnetic reference mark; and a readhead. The readhead includes at least one incremental sensor configured to detect light from the optical incremental scale and to output at least one signal dependent thereon, and at least two analogue Hall sensors, each including at least two output terminal pairs, and each configured to switch repeatedly between each output terminal pair so as to reduce any inherent offset in the output of the analogue Hall sensor. The apparatus is configured to determine the presence of the reference mark from the outputs of the at least two analogue Hall sensors.

Abstract: An encoder apparatus comprising a readhead moveable relative to a scale, configured to produce a position signal, as well as to produce a reference mark signal when the readhead passes over a reference mark on the scale, configured such that the process for producing the reference mark signal adapts automatically in response to a change in circumstance so as to at least pursue maintenance of a given relationship between the position and reference mark signals.

Abstract: A method of operating a measurement device such as position measurement encoder comprising a scale comprising a series of features and a readhead for reading the scale's features and supplying position signals, the readhead operable in a plurality of different modes of operation. The method comprises the measurement device such as a readhead outputting on at least one signal channel to an external device at least one mode of operation signal indicating the measurement device's (e.g. the readhead's) mode of operation.

Abstract: A scale reading apparatus includes a readhead that is moveable relative to a scale. The readhead includes an incremental channel from which a series of reference mark pulses are produced as the readhead is moved relative to the scale. A reference mark channel is also provided that produce a reference mark gating pulse when the readhead passes a predetermined (absolute) position mark on the scale. An alignment detection unit monitors during use, phase alignment of the reference mark gating pulse and reference mark pulses. The alignment detection unit is arranged to monitor the phase of the leading and trailing edges of said reference mark gating pulse relative to the phase of the reference mark pulses. The apparatus may be used in position encoders and the like.

Abstract: A method of calibrating a scale measurement apparatus. A scale has scale markings arranged to form an incremental pattern and at least one scale mark. A readhead has an incremental detector means which produces an output signal and a scale mark detector means for producing a signal having a zero crossing. The readhead is moved relative to the scale. The output from the incremental detector is used to determine a predetermined phase in the output signal and the value of the signal from the scale mark detector corresponding to the predetermined phase in the output signal from the incremental detector on either side of the zero crossing is determined. These values are used to define the width of the scale mark pulse.

Abstract: Scale reading apparatus is described that comprises a readhead (12) that is moveable relative to a scale (10). The readhead (12) comprises an incremental channel from which a series of reference mark pulses (56) are produced as the readhead (12) is moved relative to the scale (10). A reference mark channel is also provided that produce a reference mark gating pulse (58) when the readhead (12) passes a predetermined (absolute) position mark (22) on the scale. Alignment detection means monitor, during use, phase alignment of the reference mark gating pulse (58) and reference mark pulses (56). The alignment detection means is arranged to monitor the phase of the leading and trailing edges (68) of said reference mark gating pulse (58) relative to the phase of the reference mark pulses (56). The apparatus may be used in position encoders and the like.

Abstract: A method of calibrating a scale measurement apparatus. A scale has scale markings arranged to form an incremental pattern and at least one scale mark. A readhead has an incremental detector means which produces an output signal and a scale mark detector means for producing a signal having a zero crossing. The readhead is moved relative to the scale. The output from the incremental detector is used to determine a predetermined phase in the output signal and the value of the signal from the scale mark detector corresponding to the predetermined phase in the output signal from the incremental detector on either side of the zero crossing is determined. These values are used to define the width of the scale mark pulse.

Abstract: A scale for a scale reading apparatus has a scale track with scale marks which form an incremental scale. The scale also has a set of reference marks. The scale has at least one additional track and different combinations of markers in the at least one additional track have different functions, for example reference mark enablers and right and left limit switches.