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Low-cost digital servo drive

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article image High-performance control of resolver-based ac brushless servomotors.

AUSTRALIAN Baldor has released a low-cost digital servo drive for use with brushless rotary ac servomotors using resolver feedback. The drive provides a cost-effective means of increasing the speed and smoothness of existing automation through the application of digital control technology, without having to replace the servomotor.

It is suitable for OEMs and machine builders designing servo-based systems for use in challenging environments. Resolvers are generally considered more mechanically and electrically robust than encoders, especially at elevated temperatures.

MicroFlex servo drives are all-digital control solutions, using digital signal processor (DSP) technology to maximise performance and minimise cost. The resolver input model uses a resolver-to-digital-converter (RDC) IC to convert the analogue motor feedback signal into digital data immediately before processing. The drive's DSP enables users to optimise system performance via software-configurable anti-resonance filters. Instead of employing soft servo loop gains to eliminate noise and vibration by detuning the system users can set up the filters to optimise dynamic performance and minimise settling times.

Advanced space vector modulation (SVM) techniques are used to control the insulated gate bipolar transistor (IGBT) power devices in the drive's output stage, resulting in significantly reduced switching losses and harmonics. Compared to conventional drives with a pulse width modulated (PWM) output stage, MicroFlex units enable servomotors to run more smoothly and up to 15% faster - equating to greater control flexibility, improved accuracy and increased machine throughput.

The drive is capable of operating in torque or velocity control mode. It uses sinusoidal, resolver-based commutation to minimise torque ripple, making it suitable for precision motion control applications. It has a simulated encoder output for connection to an external motion controller. Like all MicroFlex drives, it is available with a choice of 3A, 6A and 9A continuous power ratings to simplify application matching. It accommodates peak currents of 200% to maximise dynamic performance.

The drive operates from any single or three-phase 50Hz/60Hz supply in the 115V to 230V ac range, enabling it to be used virtually anywhere in the world. It generates a nominal bus supply of 160V to 325V dc. It incorporates dc bus undervoltage and overvoltage monitoring, and is protected against conditions such as overcurrent, overtemperature and motor short-circuits. A built-in regenerative braking IGBT, in association with an external dump resistor, facilitates dissipation of braking energy.

MicroFlex drives are configured using Baldor's Windows software environment, Mint WorkBench. The same tool is used across the company's range of servo drives, intelligent drives and motion controllers, providing OEMs who build a variety of machines with a familiar configuration environment, supported by a choice of hardware with common features. Mint WorkBench includes an auto-tuning tool to help users install MicroFlex drives rapidly and efficiently, together with intuitive Fast Fourier Transform (FFT) analysis tools and automated frequency response tests to facilitate creation of custom anti-resonance filters.

Baldor offers a range of complementary products for use with MicroFlex drives, including NextMove motion controllers in PCB and packaged forms, and rotary and linear brushless ac servomotors.

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