- June 28, 2019
- POSITAL - Fraba Inc.
June 28, 2019 – POSITAL introduced absolute multi-turn kit encoders for stepper motors.
Stepper motors are brushless DC motors that turn their shaft by a small fixed amount (step) in response to a control signal. However, this is an open loop control system: if the motor fails to complete a step (e.g. due to unexpected mechanical resistance) system accuracy is degraded. This can be overcome by adding an incremental encoder to provide feedback as to whether step motions have occurred. POSITAL’s magnetic encoders take this a step further by providing absolute position feedback. (With incremental feedback, control system needs to keep an accurate count of the number of steps in order to track the absolute rotary position of the motor shaft. If this count is lost or corrupted – e.g. due to a power interruption – knowledge of the position of machine components is also lost. It is usually necessary to return the machinery to a known starting position and re-initiate the step count. By contrast, with absolute measurement systems, complete position measurements are available whenever the control system queries the encoders.)
POSITAL’s absolute kit encoders are available with multi-turn measurement ranges, which can be useful when a motor is connected to a screw shaft, cable drum or gear reduction system. The multi-turn rotation counter is self-powered, using POSITAL’s Wiegand energy harvesting technology.
POSITAL’s encoders for stepper motors are “kit” or modular devices, designed to be integrated into a motor housing, measuring the rotary position directly from the drive shaft. Kit packages are available with the same mounting form factor as incremental encoders for NEMA-standard stepper motors. The magnetic measurement module is 37 mm diameter, 23 mm deep and resistant to dust, moisture and shock/vibration loading. Shields are available to protect the measurement module from external magnetic fields. SSI and the more advanced "BiSS C" communication interfaces have been implemented. Both are open-source interfaces that are compatible with a wide range of PLC’s and computers.