The principal use of ball screw assemblies is to mechanically convert rotary motion into linear motion. They can serve for table positioning or linear actuator applications. A rotary encoder, when attached to the end of the ball screw shaft or the drive motor, provides feedback used to determine linear speed, direction, rate and position.
Mechanically, both shaft and thru-bore encoders can be applied to ball screws, depending what design is most readily integrated into the system. However, hollow bore or thru-bore encoders tend to be used more prevalently.
Electrically, variables such as resolution, output type, channels, voltage, etc, all should be specified to meet the individual application requirements. Due to the reciprocating motion typical of ball screw assemblies, quadrature output is required to determine direction of travel. Additionally an index pulse should be specified to ensure the ability to find a home position. Both incremental and absolute encoders are suitable for X-Y positioning. In situations where position is needed during power-off scenarios without cycling back to a known home position, a multi-turn absolute encoder is required.
Environmentally, proximity of the encoder to potential exposure to liquids, fine particulates and extreme temperatures will dictate specification. In applications with wash down requirements, an IP66 or IP67 seal can offer protection against moisture ingress. However, consider a stainless steel or polymer composite housing or shielding the encoder to mitigate the effects of harsh cleaning chemicals and solvents.
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