Encoders provide motion feedback for linear measurement by generating pulses in response to linear displacement of the material or object to be measured. Then the encoder sends those pulses to a controller, which converts those pulses into distance.
A common method uses a measuring wheel with the encoder. The wheel either has direct contact with the surface to be measured (direct feedback), or it has contact with a shaft that moves in conjunction with the material (indirect feedback). For this type of application, EPC's Tru-Trac® encoders are all-in-one solutions that include an encoder, measuring wheel, and spring-loaded torsion arm. They make for fast and easy installation. Another option is a thru-bore or hollow bore encoder attached to a roller shaft, such as a conveyor head-roll.
For reciprocating linear measurement, a measuring wheel may not be the best choice because of the potential for slippage during start/stop cycles. Solutions that eliminate or limit backlash, include a belt and pulley, a chain and sprocket, rack-and-pinion gear. Another solution is a draw wire, where a spring-driven retractable cable spool is attached to a shaft encoder.
Electrically, incremental encoders are most often specified for linear measurement, with some specialized applications requiring absolute positioning. For applications with frequent start/stop or bi-directional travel, quadrature output is required.
Environmental considerations are important when specifying your encoder. Take into account the encoder's exposure to liquids, fine particulates, extreme temperatures, and washdown requirements. An IP66 or IP67 seal protects against moisture ingress, while a stainless steel or polymer composite housing to mitigate the effects of harsh cleaning chemicals and solvents. EPC's Models TR1 and TR3 Tru-Trac® come with a housing made of a durable, conductive composite material that minimizes static build up.
Examples of Motion Feedback in Linear Measurement
