Better drives and motors power lively competition

Sept. 5, 2008
Contributing Editor Sheila Kennedy reports that better motors, drivers, controllers and systems are powering a lively competition.

New stepper motors are smaller, quieter, easier to set up and network, and more cost-effective overall. They produce higher torque density and less noise, resonance and vibration. They remain particularly well suited to continuous-duty applications that have low speed and high torque requirements. Here are some highlights of where the technology is going.

Torque density and output: Portescap’s “stator-enhanced” version of its h3 Series Step Motors reportedly produces 25% more torque across the entire speed range than the original h3 models, which themselves deliver as much as 40% more torque than conventional hybrid step motors. The increased output and density is the result of the stator’s patented magnets. Rare-earth neodymium-iron-boron magnets inserted between the stator teeth force more of the magnetic field to flow through, rather than around, each tooth. This reduces leakage and produces more torque. The unit’s aluminum housing optimizes heat dissipation, which slows the temperature rise, provides greater torque and reduces power consumption.

In addition, the new h3 series runs quieter and exhibits minimal resonance. A bearing retainer and O-ring reduce motor noise and prevent bearing spin, and larger bearings handle higher axial and radial loads. The motor is smaller and lighter than a hybrid stepper, but delivers equivalent performance.

Position setup and control: Festo’s CMMS-ST stepper motor controller leverages encoder-based feedback to deliver servo-like functionality, high positional accuracy and cost effectiveness. Designed for use with standard two-phase hybrid stepper motors such as Festo’s EMMS-ST, the controller operates in full-step, half-step and micro-step (in open-loop mode), and in anti-resonance closed-loop mode. It offers full control of current, speed and position, and automatically compensates to maintain position tracking if the motor is overloaded. Closed-loop mode isn’t limited to stall detection or end position correction. The controller is continuously in closed-loop configuration, eliminating loss of step. Operation is smooth with low acoustic noise levels and no mechanical resonance.

Commissioning is simplified with Festo’s FCT software, and the variables and controller operating system can be stored on an SD card. When the controller is swapped out for a replacement, the original configuration can be restored using the SD card.

Smoothness: Microstepping provides smooth operation at low speeds. The new IP20-rated stepper motor controller from B&R Industrial Automation is designed for the X20 controller and I/O system. The controller can resolve each full step into 256 microsteps, providing positioning precision, less resonance and smoother operation by performing the maximum number of microsteps possible at a particular step frequency.

A stepper amplifier with built-in stall detection is part of the I/O system, which improves diagnostics of overloads or motor blockage. The X20 also boasts automatic motor detection when booting. An AB or ABR encoder can be connected for external feedback.

Shrinking size and costs: Smaller dimensions mean smaller cabinet and machine requirements. At just 63 mm wide, B&R’s ACOPOSmicro is a compact drive for stepper and servo motors operating in the lower performance range. It has a modular cooling design that eliminates the cost of switching cabinet climate control. Free space allows for conventional heat dissipation. Other cooling options include a feed-through cooler with IP65 protection that releases heat outside the cabinet, or cold-plate mounting that connects to an oil- or water-cooling circulation system.

Network connectivity: Nyden’s compact 5-Phase MLN50 Mechatrolink-II stepper and motor driver network series is said to deliver better performance than the company’s original MLINK-I series. Being fully compliant with the high-speed Mechatrolink II motion field network, system configuration is easier and more flexible, and less wiring is required, saving costs. Users also can develop their own motion field networks.

The MLN50 provides encoder and general-purpose inputs, alarm signal outputs and USB-type output connections to interface with other compliant devices. Variables are stored on the onboard serial EEPROM, which can be rewritten 100,000 times. The company’s pulse generator chip, MPG1032, allows operators to execute advanced operating functions such as fast-forward positioning, interpolation feed and home. Control signals can be transferred in real time.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].

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