Posted to News on 3rd Dec 2013, 00:00
Encoder options save space and lower the price barrier for motion control feedback
Rotalink has continually developed an innovative design-led approach to its miniature power transmission and motion control product line and its feedback technology is no exception. Across its 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 that minimise the installed space, ensure fast time to market with standard options, and significantly reduce the price point for position and velocity feedback when compared to other manufacturer's products.
>For motion feedback requirements as diverse as medical dosing pumps to labelling machines, ticketing equipment to CCTV pan and tilt mechanisms, these compact solutions 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; for miniature brushed or brushless DC motors up to 200 Watts and featuring straightforward drag-and-drop flow chart programming for servo motion control.
>Rotalink's dual channel incremental encoder design is distinctively unique. Sandwiched between the front shaft of the motor and the gearbox input for both ovoid and in-line gearbox types, it 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 42 mm, its minimal length (just 7.4 and 9 mm resp.) allows off the shelf single shaft motors to be adapted for motion feedback applications. Rotalink's incremental encoder has been designed as a part of the planetary gearbox endplate, reducing its axial length even further.
>The new single and multi-turn absolute encoders are equally innovative. For use with Rotalink's ovoid style gearboxes, the encoder is 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 15 mm, snugly fitting around the motor and well within the overall motor length and gearbox footprint for most applications. At just under 43 mm 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 around robust contactless non-optical technologies for maximum durability and long service life. They also both 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 rev) at 5V TTL levels with a frequency range that suits motor speeds up to 10000 rpm. When multiplied through the gearbox ratio, extremely fine angular resolution is achieved.
>The single-turn absolute encoder employs a contactless electro-magnetic technology that provides a linear 0 to 5 V DC 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.
>The multi-turn version supplements the single-turn output with a 32000 revolution capacity and also includes an integral rechargeable battery that will power the device to maintain full position monitoring for up to 100 hours if main power is lost. The use of an extended 16 bit SSI interface with the multi-turn version also allows the option of programming of datum position and minimum/maximum rotation limits.
>Rotalink's innovative incremental and absolute encoders are available for use across its full range of DC brushed and brushless gear motors which offer motor powers up to 200W with peak gearbox torque to 26 Nm. Rotalink's own manufactured range of planetary and ovoid style gearboxes are also characterised by their uniqueness. They include a choice of standard or enhanced polymer gears with combinations of sintered or ball bearings, making an exact price and performance match easy for each application. Further benefits include extremely high torque levels in space restricted envelopes that suit applications where product design miniaturisation or maximising power to actuator size is important.
