Multiturn Absolute Optical Encoders

  • High Reliability
  • High Rotational Speed
  • Low Intertia
  • Low Torque
  • Compact and Light-Weight

This modular encoder can be constructed with any number of lay-shafts, each one increasing the maximum count by a factor of ten. The basic encoder is designed for instrument use and is 38mm in diameter. Heavy duty versions with larger, sealed shafts and strong casings can also be provided. The 0.125" diameter input shaft, carried on very low torque, precision ballraces, is fitted with a two track code wheel which provides five bit Coles codes for two decades. The inner track generates a sequence of 20 uniquely defined codes as the shaft rotates through one turn. The outer track contains ten similarly coded sectors giving a resolution of 1/200 of a turn. Each lay-shaft carries a single track code wheel and is geared to the preceding shaft with a 10:1 ratio. When the decade inputs are energised one at a time, the outputs can share a five-line bus to reduce the number of output wires and connections required. A code converter can be built-in to present the output in binary, Grey-code or BCD.

For Critical Applications
Designed for use in remotely controlled systems and electrically noisy environments where trouble-free operation is essential, this encoder gives an absolute readout which cannot be permanently corrupted by spikes on. or interruptions of, the supply.

The correct output code becomes available as soon as the encoder is switched on, so there is no need to drive the system to a base position for zeroing. Unlike systems controlled by stepping motors or incremental encoders. the zero position is not lost when the system is mechanically stalled or noise signals are picked up on the output lines.


Motorised Encoders
The size 15 encoder can be built together with a servo or stepping motor. The motor can be single or double ended. i.e. the encoder can be built onto one end and the drive taken from the other. or the motor can drive through the encoder making use of the encoder's gearing instead of using an additional gearhead.


Easy to Use
When the decades are multiplexed only five output leads are required, however many decades are in use. One input line is required per decade as well as the supply and ground lines. Outputs from several encoders may use the same output bus. As standard the inputs and outputs are HCMOS compatible but other levels can be accommodated, if required. Connection is normally by flying leads 450mm long. Connectors can be fitted on request.


Applications Support
Applications engineering support is available to assist in the implementation of systems.


All photographs and text copyright Crystal Structures Limited 1996 to 2002