Digital servo `will run in 15 minutes`

Engineers at Parker EMD in Poole have developed a compact digital servo drive that, they contend, sets a new price-performance standard for the low-to-medium power market. The ViX drive, which can operate in position, velocity or torque control modes, uses auto-configuring software which, Parker claims, allows a fully tuned system to be running within 15 minutes of the drive being taken out of its box.

The drive uses an advanced field-oriented control (FOC) strategy to derive the power stage control signals. The approach is said to overcome limitations with conventional servo amplifiers which use independent low-pass filters and integrators to remove offsets and accommodate motor phase mismatches. Transient torque demands can cause imbalances in the motor phase currents resulting in poor response, increased heating and additional harmonic generation.

The FOC approach controls the torque magnitude directly and is said to ensure optimum performance at all speeds, as well as quiet motor operation. The ViX drive optimises the FOC system according to parameters that are entered either directly or using Parker`s Easi-V software.

The company claims that the drive can accommodate a wide range of motors and offers a significantly improved bandwidth (2kHz with most motors) and dynamic performance, allowing higher usable torques over a wide speed range. Dave Buckingham, Parker EMD`s business development manager, says that the 50µs current loop is "as fast as anything in its class".

When teamed with a high-performance servo motor, the drive can accelerate to 5,000 rpm and back to rest in less than 6ms. Both encoder and resolver feedback are built in.

The drives are housed in cases measuring just 125mm by 42m by 85mm that can be rail or panel mounted. They provide a choice of 250VA or 500VA outputs and can accommodate motor bus voltages up to 80V.

Parker, which has spent a year developing the ViX drive, is planning other variants including, possibly, analogue, CanBUS and direct-on-line versions. Buckingham hopes that the new family with its sub-$500 pricetag, will help Parker to capture 5% of the European servo market within three to five years.