Servo amplifiers designed for ultra-high-resolution motion control

Paul Boughton
Aerotech is launching a new digital servo amplifier with a linear power stage for ultra-high-resolution brushed or brushless linear and rotary motion control systems. The new compact ML series amplifier is intended for lower power use but maintains the very high performance characteristics required for nanometre and microradian level precision positioning applications that are acutely susceptible to electrical noise, and where PWM servo amplifiers become unusable. The DSP-based ML range is designed for minimal radiated noise to allow the servo system to provide exceptional levels of speed control and in-position stability for ultra-smooth motion profiles, and to ensure negligible interference for sensitive processing and measuring equipment.
Aimed at motion systems applications such as those found in non-destructive testing (NDT), micro-electrical mechanical systems (MEMS), vision systems and microscopy - but with less dynamic performance requirements - the new amplifier is available in three versions: as the Ndrive ML option for Aerotech's A3200 software-only motion controller; as an entry-level version of the Soloist ML integrated single-axis position controller range; and as a low-cost linear drive stage for the multi-axis Ensemble ML, a networkable and panel-mount motion control system.
The basic specifications for the ML series linear amplifiers in all configurations includes 5A continuous/10A peak current rating with a customer-supplied DC bus voltage of +/- 40V and a control supply requirement of 18-36V DC. A single 16-bit +/-10V analogue input is used for direct interfacing to the motion controller with an emergency stop input included.
Furthermore, the ML features primary and secondary incremental encoder interfaces that are optionally equipped with Aerotech's MXH hardware-based multiplied encoder technology for up to 65536 times quadrature output. Using a 1V p-p sinusoidal encoder that does not require a costly power supply, this level of multiplication has a 2MHz analogue input frequency that allows nanometre or microradian level resolution across Aerotech's wide range of high-precision direct-drive positioning mechanics, without compromising on top speed.
The MXH encoder option also enables the single-axis Position Synchronised Output (PSO) feature to be implemented at the highest level. Aerotech's PSO is a powerful algorithmic software tool that precisely co-ordinates the real-time position from a linear or rotary encoder with high-speed output pulses from the controller, which are used to trigger external events. This feature is widely used in applications such as laser micromachining or position-critical NDT where exacting, no-compromise synchronisation is required between laser firing or sensor reading and the axis path position.
For the software-based MXU encoder version, the encoder interfaces have a 4096 multiplication factor and both MXU and MXH encoder options include end-of-travel limits and home inputs on the primary feedback encoder. An optional I/O expansion board is also available to equip the ML drive with eight opto-isolated digital inputs and eight digital outputs (sinking or sourcing) in addition to single 16-bit analogue inputs and outputs, and a brake relay output.
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