Modulation unit for an encoder

A method of determining an absolute position of an encoder, the encoder comprising:

• a receiver configured to detect electromagnetic radiation and convert it into an output signal;
• an emitter configured to emit electromagnetic radiation in the direction of the receiver;
• a data processing apparatus;
• and
• a modulation configured to be movably supported between the and the emitter, the modulation unit comprising:
• a code section comprising alternating opaque and transparent segments, the opaque segments being configured, in use, to interrupt emitted electromagnetic radiation between the emitter and the receiver and the transparent segments being configured, in use, to permit emitted electromagnetic radiation to impinge on the receiver according to the position of the modulation unit;
• and a plurality of index segments, wherein each index segment is uniquely identifiable in dependence on the output signal, and wherein each pair of index segments is arranged in a distinctive spatial relationship with respect to other pairs of index segments;
• wherein the method comprises:
• determining, by the data processing apparatus, when a first index segment passes between the emitter and receiver in dependence on a first variation to the output signal;
• determining, by the data processing apparatus, when a second index segment passes between the emitter and receiver in dependence on a second variation to the output signal;
• determining, by the data processing apparatus, a spatial relationship between the first and second index segments based on the output signal between the first and second variations to the output signal;
• and,
• determining, by the data processing apparatus, an absolute position of the modulation unit based on the spatial relationship between the first and second index segments.

An encoder comprising:

• a receiver configured to detect electromagnetic radiation and convert it into an output signal;
• an emitter configured to emit electromagnetic radiation in the direction of the receiver;
• a modulation unit configured to be movably supported between the and the emitter, the modulation unit comprising:
• a code section comprising alternating opaque and transparent segments, the opaque segments being configured, in use, to interrupt emitted electromagnetic radiation between the emitter and the receiver and the transparent segments being configured, in use, to permit emitted electromagnetic radiation to impinge on the receiver according to the position of the modulation unit;
• and a plurality of index segments, wherein each index segment is uniquely identifiable in dependence on the output signal, and wherein each pair of index segments is arranged in a distinctive spatial relationship with respect to other pairs of index segments;
• a data processing apparatus;
• and,
• a non-transitory processor-readable data carrier communicatively coupled to the data processing apparatus and which stores processor-executable instructions which, when executed by the data processing apparatus, cause the data processing apparatus to perform a method, the method comprising:
• determining, by the data processing apparatus, when a first index segment passes between the emitter and receiver in dependence on a first variation to the output signal;
• determining, by the data processing apparatus, when a second index segment passes between the emitter and receiver in dependence on a second variation to the output signal;
• determining, by the data processing apparatus, a spatial relationship between the first and second index segments based on the output signal between the first and second variations to the output signal;
• and,
• determining, by the data processing apparatus, an absolute position of the modulation unit based on the spatial relationship between the first and second index segments.