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Miniature power transmission range offers novel encoder options

08 December 2013

Across Rotalink's wide and modular range of miniature dc brushed and brushless gearmotors, customers can specify dual-channel incremental, or single- and multi-turn absolute encoders as part of integrated assemblies.

These compact assemblies offer machine builders and OEMs closed loop position and velocity control at extremely competitive cost, especially when used in combination with Rotalink’s low-cost Red Drive motion controller.

Sandwiched between the front shaft of the motor and the gearbox input for both ovoid and in-line gearbox types, Rotalink’s dual channel incremental encoder replaces the traditional and more expensive ‘kit encoder’ approach where a rear shaft (often a special) must be used.

Available in two standard diameters of 28 and 42mm, its minimal length (just 7.4 and 9mm respesctively) allows off-the-shelf single shaft motors to be adapted for motion feedback applications. Moreover, the incremental encoder forms part of the planetary gearbox endplate, reducing its axial length even further.

The new single and multi-turn absolute encoders, for use with Rotalink’s ovoid style gearboxes, are mounted directly on the rear side of the gearbox output shaft, providing position feedback at the actual load point where gearbox backlash or lost motion can be nulled by the control system - particularly for unidirectional motion.

The single-turn version has an axial length of less than 15mm, snugly fitting around the motor and well within the overall motor length and gearbox footprint for most applications. At just under 43mm in length the multi-turn version maintains the narrow motor/gearbox footprint which is critical in many applications.

Both of these feedback types are based on contactless, electro-magnetic technologies for maximum durability and long service life. They also include integrated custom ASICs that take care of signal amplification and directly drive the respective encoder outputs, making installation straightforward.

The incremental encoder features a capacitive design with a 48-line quadrature output (196 pulses per revolution) at 5V TTL levels with a frequency range that suits motor speeds up to 10,000rpm.  When multiplied through the gearbox ratio, extremely fine angular resolution is achieved.

The single-turn absolute encoder provides a linear 0 to 5Vdc analogue output, 10-bit per 360º positional data output via synchronous serial interface (SSI). This translates to a positioning resolution of ± 0.18º with accuracy to ± 1.5º.

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