Posted to News on 29th Nov 2007, 16:55
Stepper motors synchronised with closed-loop control
Festo demonstrated its recently launched EMMS-ST series stepper motor at the 2007 SPS/IPC/Drives show. These stepper motors, when used with encoders, are said to be an affordable alternative to synchronous servo motors, especially for applications where the high performance available from a servo motor is not required.
The new EMMS-ST stepper motors are the latest additions to the Festo range of electrical drives and, together with encoders and the matching CMMS-ST controller, form a 'Servo Lite' offering. They provide fully regulated movement, optimum operational precision and the ability to control torque, position and power.
CMMS-ST controllers operate in closed-loop mode, just as a full servo-drive package does. By regulating power, torque and position, it keeps the stepper motors well under control. Moreover, if the 'master' motor stops due to a fault, the position synchronisation within the controller immediately stops the 'slave' motor as well. The stepper motors are therefore fully synchronised at all times.
CANopen, Profibus and DeviceNet
CMMS-ST controllers may be connected to a CANopen system and retrofitted to Profibus or DeviceNet networks. Network filters and brake resistance are fully integrated, and an SD card provides portable parameter storage. Combined with the EMMS-ST stepper motor and Festo axis modules, the CMMS-ST controller is suitable for price-sensitive applications with a torque range of up to 6.5Nm.
During normal operation, the controller compares the actual and specified motor position across the full number of revolutions travelled in relation to the feedback from the encoder and corrects any deviation within the closed loop – thereby producing a complete servo system. And because the encoder is an absolute device, if power is lost and then restored, the correct position is ensured.
