Stepper motors, while still commonplace, have seen their popularity erode a bit over the past few years as servo motors boomed amidst falling prices and a rising high-tech appeal. But now, steppers seem to be gaining some ground against servo motors in low- and medium-speed applications — those up to 900 rpm — according to Rich Lenzing, Danaher Motion product manager.
Control options based on I/O systems are another thing giving steppers new life. These systems eliminate the need for separate amplifiers, reducing the installed costs of steppers and making them attractive in applications that may have favored small servos over the past few years. What's more, automation software suites allow steppers and servos to be programmed in the same environment, further reducing engineering costs in mixed servo-and-stepper environments. “We're seeing a big resurgence in stepper motors,” says Joey Stubbs, an applications and support engineer for Beckhoff Automation. Helmut Kirnstoetter, international sales manager for B&R Industrial Automation, has seen the same thing. “Stepper motors have always been a good choice for simple auxiliary axes,” Kirnstoetter says, explaining they produce lots of torque from relatively little power. He cites pick-and-place and semiconductor applications, where machine builders are up against intense price pressures, as two places where steppers are gaining ground.
Danaher boosts stepper torque
Danaher Motion has developed a series of high-torque hybrid stepper motors with magnetic design and thermal management improvements. These new CT Series motors offer a 20 to 50 percent torque improvement compared to previous motor designs, according to Rich Lenzing, Danaher Motion's product manager for stepper motors. The CT Series motors also feature a new front-bearing design allowing them to support two to three times the shaft loads than in previous models, potentially eliminating the need for separate shaft supports. The new motors have a step size of 1.8 degrees and come in NEMA flange sizes 17, 23 and 34. A variety of lengths are available for each flange size.
B&R's newest stepper motor module
B&R Industrial Automation displayed its latest take on stepper motor control with the stepper motor control modules for its X20 I/O system. Intended for two-phase stepper motors, two of these X20 stepper motor modules are available. One of them handles motors with 1A current ratings, while the other handles motors with 3A current ratings. Each can resolve motor steps into 256 microsteps. Additional features include automatic motor and stall detection, four digital inputs for limit switches or encoders and integrated counter function. Helmut Kirnstoetter, B&R's international sales manager, says the modules allow servos to be operated as single axes or in groups, with or without coordinated motion. The modules are also compatible with B&R's “Soft” CNC system, which can support up to 100 axes.
Beckhoff steps up
Beckhoff Automation has had a line of stepper motors and stepper I/O terminals available for more than a year. Its I/O stepper module terminal was honored as a Design News best product finalist in 2006. But recently, these stepper products have picked up steam, according to Application Engineer Joey Stubbs. Beckhoff's motor offering include the AS Series stepper motors, which have a current rating from 1 to 5A and torques from 0.38 to 5 Nm. One of the company's related stepper motor I/O bus terminals, the KL 2541, offers a peak current of 5A/phase and a supply voltage from 8 to 50V dc, allowing it to generate up to 5 Nm of torque. “That's comparable with a small servo drive,” Stubbs says.