Step On It
Stepper motors are ideal for low-speed applications where the load and motion profile don’t change.Source: YASKAWAUnnecessary Feedback
Generally, servo motors are available in a much wider power range than stepper motors. We offer servo motors from 0.1 to 160 hp and stepper motors from 0.1 to 1.8 hp. As a result, servo motors offer more choices for a wide power range of applications.
A fairly new development in stepper control is to incorporate a rotor-position feedback—encoder or resolver—to optimize torque generation according to actual rotor position. This turns the stepper motor into a high-pole-count, brushless servo motor. An advantage of this technique is to normally run the motor in open-loop mode and only enter closed-loop mode if the rotor position error becomes too large.
The added encoder system feeds back the actual position to the drive to correct the number of steps performed if the motor loses some steps due to high load inertia and fast acceleration. However, it still does not position the motor between two steps. Hence, the added feedback does not improve the resolution and positioning accuracy of stepper motors. This typically is between 500 and 50,000 steps per revolution, while a servo motor with a sin/cos encoder offers a resolution of > 4 x 106 counts per revolution.
Ralph Baran, product manager,
Siemens Energy & Automation, www.sea.siemens.com
Servo Stepper Controller
Stepper motors and associated components have evolved, taking on new functionalities. An example would be our servo stepper controller that is equipped with encoder feedback capabilities to function as a closed-loop controller.
The torque is there with these servo stepper controllers; however, it’s also important to consider how well the component actually transmits that torque to your application. Select servo stepper controllers operate on a resolution of 64 microsteps, preventing step losses caused by acceleration and a finer step position. High resolutions prevent excessive wear on mechanical components. Furthermore, these servo steppers have current control, minimizing any power dissipation while increasing torque efficiency. Also consider vector control. When paired with the incremental encoder, vector control creates highly efficient rotational speeds.
Servo stepper controllers also offer six configurable inputs for start/stop, end-stop, reference, jog/tip, and can be processed directly via internal software. Two outputs can be linked with internal functions or used freely. This ensures servo stepper controllers can adapt easily to meet application needs via various acceleration ramps, command tables, auto reference and other event-driven characteristics while ensuring no position loss.
Mark DeCramer, product manager,
Wago, www.wago.us
September's Problem
Our printing machines consist primarily of discrete I/O with a small quantity of analog I/O. We ship these machines worldwide, and to reduce startup time and travel we plan to start doing more extensive shop testing. Right now, we test on-machine I/O to some extent. But some I/O cannot be tested easily as it’s either field-installed or requires actual production for responses to make sense. For those I/O points, is software simulation the answer? Or should we go with hardware simulation by wiring at least some outputs to devices and reading responses at the inputs?
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