Servo and stepper motors have different basic technologies and histories because they've served different applications. However, recent efficiency gains and innovations are causing the line between servos and steppers to blur, especially as faster, cheaper and more powerful data processing analyzes motor feedback data, and enables new levels of servo motor performance.
"One of the main trends we see has been a shift to direct-drive technology, and the elimination of mechanical transmissions, gearboxes and timing belts," says Tom England, director of global product planning at Kollmorgen (www.kollmorgen.com). "Electromagnetic drives are being coupled to drive loads directly, and more are getting adopted because they cost less than before and are simpler to implement. Also, related electronics are being integrated nearer or directly onto servo motors, which saves space in control cabinets."
Jay Schultz, product manager for motors at Parker Hannifin (www.parker.com), adds that a lack of rare-earth metals, which come mainly from China, and resulting high prices will continue to cause problems for servo motor builders and their users. "We'll have tumult until the rest of the world revives production of rare earths," he says. "Until then, everyone is redesigning servo motors to use less material, even as some of our servo motors are used in more new industrial and transportation applications."
In addition, servo motors are moving beyond high-end motion applications and into regular-velocity, basic motor settings, reports Jesse Henson, manager for motion and PLCs at Baldor Electric (www.baldor.com). "These users want the same advantages that servos can provide of being able to vary speed and gain efficiency," Henson says. To ease this transition, some of Baldor's servo motors even have a rounded body to look like regular ac induction motors.
"We're also seeing growth in the use of high-pole-count, high-speed servo motors with two, four or six poles on the motor," says Don Labriola, PE, president of QuickSilver Controls (www.quicksilvercontrols.com). "This gives them better torque capacity, and the ability to drive many different kinds of loads without needing traditional gearheads. Also, servos are less likely to lose operational steps because their loads are electrically controlled, and so they're better able to give users increased performance, throughput and quality."
For example, QuickSilver's DSP-based servo motor combines its drive, servo controller, indexer and PLC in one package. "It takes 9 ms to ramp up, 10 ms of slewing to reach constant speed, and another 9 ms to ramp to a stop," Labriola says. "This can help users, such as semiconductor machine builders, who want to shrink their devices, but still have more capabilities with fewer embedded chips. In general, servos can be reduced in size, increase efficiency, or use less power depending on what each application demands."
In the past five years, it's become more common for servo motors to have continuously updated autotuning during a machine's normal operations, according to Joe Kimbrell, product manager for drives, motors and motion control at AutomationDirect (www.automationdirect.com). AutomationDirect's servo motors and drives use an adaptive, auto-tuning capability to change parameters based on what they're experiencing. "For a long time, we've had two worlds—those who adopted servos 20 years ago and those who still used drive shafts—and this was partly because it took a lot of education and programming to apply servos, especially in multi-axis applications," Kimbrell says. "Now, software does a lot of this work for users, and you don't have to be as much of an expert to program a motion system and use servos."
Likewise, Beckhoff Automation (www.beckhoffautomation.com) makes servo drives and controls to operate mostly small, 48 V servo motors in simple applications, rather than the usual stepper motors and pneumatics. "More recently, servos are getting easier and more economical to use, and so they also can be scaled up for some larger and more complex applications," says Graham Harris, Beckhoff's president. To get further into the act, Beckhoff formed a joint venture with Fertig Motors, headquartered in Marktheidenfeld, Germany, to launch its own line of servo motors in 2012.
