An encoder for detecting the angular position of a shaft of an electric motor comprises an encoder disc (101) having tracks (515) sensed by detectors in reading heads (106a, 106b). Analog position signals from the detectors are sampled in sampling circuits (1701-1704) at times given by sampling pulses issued by a device such as a counter (506). The sampled analog values are converted to digital values by a converter (1706) and provided to a local processor (1707) calculating position values. The local processor sends commands to the device (506) to issue sampling pulses at accurately defined times, normally regularly spaced in time. The local processor also receives, from a central processor, read command signals commanding to it provide position values. These read command signals normally arrive rather regularly but are not synchronised. In order to provide positions values at suitable times after receiving the read command signals, the local processor can send its commands earlier or later, in relation to the normal regular rate.

An angle measuring system that includes a drive shaft that rotates about an axis of rotation, an encoder and an encoder attachment system that has a Belleville disk spring that generates a radial pressure with respect to the axis of rotation so as to attach the encoder to the drive shaft.

In order to provide multiple resolution capabilities in an encoder device with the fewest number of parts, a single circuit board platform is provided with multiple chip buses electrically connected in parallel. Each bus is located adjacent a different code disc track wherein the code disc includes multiple concentric tracks of different resolution. The chip buses are compatible with either a surface mounted or a plug-in mounted encoder module assembled to a printed circuit board platform having alternate disc track read locations provided by separate encoder module bus ports. To change resolution the encoder module chip is simply moved from one bus to an alternate resolution bus on the PC board that lies adjacent a different code disc resolution track. In one embodiment, the PC board is mounted to the housing and the electric motor and the code disc is mounted on the rotary motor shaft in order to provide shaft angle position for electrically controlling the operation of the motor.

A system and method of measuring a rotational motion of a code wheel measures a rotational movement of the code wheel including an error component due to a non-rotational movement of the code wheel; measures the non-rotational movement of the code wheel; and produces an error-corrected measurement of the rotational movement of the code wheel by using the measured non-rotational movement of the code wheel to cancel the error component of the measured rotational movement of the code wheel. A signal can be produced indicating a need for maintenance when the non-rotational movement of the code wheel exceeds a threshold.

A system and method for sensing position and/or displacement of a moving, substrate, ram, target, piston, encoder wheel or the like. The system includes a plurality of transducers for generating two sinusoidal signals in quadrature related to the position and displacement of the substrate, ram or the like. Alternatively, the sinusoidal signals may be generated by other well-known devices, such as by an optical encoder or the like. The two sinusoidal signals in quadrature are processed to provide enhanced resolution compared to conventional quadrature systems. The system is also capable of self-calibration in order to accommodate fluctuations in the two sinusoidal signals in quadrature.