Motion-system design often requires a drive selection of either servo or stepper motors. Servos tend to be more stable and inexpensive, while steppers are known for high power and efficiency. Recent designs show that servo and stepper-motor companies are constantly making the drawbacks less so, while keeping the advantages. For example, Pittman series 8000 brush-commutated DC motors feature a 7-slot skewed armature to minimize magnetic cogging (reluctance torque) and for smooth and quiet operation. The company says this family of servo motors offers performance, reliability, and long life for a wide range of power applications including medical and biotech.

The motors from Ametek Technical & Industrial Products, Kent, Ohio (www.ametektechnicalproducts.com) also show other improvements. For instance, designs are available in 2.070, 2.195, and 2.445-in. lengths and can reach peak torques of 16.8 oz-in and speeds to 9,020 rpm at continuous torque for standard motors at rated voltages. Speed, voltage, current, and torque characteristics can be varied to satisfy particular application needs.

Standard features include sintered bronze bearings, 2-pole stator, ceramic magnets, heavy gauge steel housing, silicon steel laminations, and copper graphite brushes. Commutators are diamond turned after armature assembly to promote optimum concentricity and long brush life.

Another recent servo comes from Beckhoff Automation, Burnsville, Minn., (www.beckhoffautomation.com). The company's AM3500 series features a high moment of inertia without requiring an additional gear unit in applications such as rotary tables. Flanges, connectors, and shafts are compatible with Beckhoff AM3000 motors. The new models are available with flange sizes 3 to 6, torques between 1.9 and 15 Nm, and rated speeds of 3,000 and 6,000 rpm. Resolvers or absolute encoders (single- or multi-turn) are available as a feedback system.

Based on new material and manufacturing technologies, the AM3500 series has the same features as the AM3000 series low-inertia servomotors, including a compact size from a pole-wound stator winding.

Stepper motors are also on the march. They are a component of the Piezo-Z-Stage from Physik Instrumente, Auburn, Mass., (www.physikinstrumente.com). The P-737 specimen Z-stage is a new member in a large family of products for microscope automation. Intended for biotech research microscopes, the Z-stage can move as little as 250 µm with millisecond responsiveness and nanometer precision motion under closed-loop control.

The P-737 stage is an addition to the PIFOC brand of high-speed piezo objective Z-steppers. The fast response of the stage fully uses the high throughput of the latest digital imaging systems and achieves 10 to 50 times faster response than conventional stepper motor focus drives.

Stepper drives from Applied Motion Products, Watsonville, Calif., (www.applied-motion.com) are said to be programmed with Windows-based software for stand-alone operation. The ST5-Si stepper drives deliver 24 to 48 Vdc with output current from 0.5 to 5.0 A. They are protected against over-voltage, under-voltage, over-temp and external output shorts, and provide 8 digital inputs and 4 digital outputs. Option boards are available to add encoder feedback and RS485. The encoder-feedback-option board detects motor stall, prevention, and position maintenance. The company says its Si Programmer software comes with tuning features, and a graphical point-and-click format combines motion, I/O and operator interface for simple machine sequencing.

Self-Test and Auto Setup features measure and configure motor parameters although users can create custom motor configurations, if useful. Additionally, MicroStep Emulation is said to provide smooth motion for systems that require low step resolutions.