For over 10 years, Ever Elettronica has flanked the open loop stepper drive line with a family of servo-drives for the vectorial control of the stepper motor, similar to the same Brushless motor control techniques. Thanks to these drives, the stepper motor can be seen as a 50-pole Brushless synchronous motor: as a matter of fact, by checking the position of the motor shaft in real time, the step loss problem is solved by delivering in the motor phases only the current required for the execution of the movement, reducing the heating, vibrations and noise emitted by the motor. Even in the presence of highly inertial loads, the stepper motor is thus able not to lose the synchronism, adapting current, ramps and maximum speed according to the load to be moved. The advantages of this technology, compared to the use of Brushless servo-drives, can be summarised in the following points:
- advantages of Closed Loop Control compared to an open loop stepper solution:
• stable maintenance and automatic recovery of the original position in case of positioning error caused by external factors such as mechanical vibrations;
• reliable positioning without loss of synchronism;
• recise torque control even without gearboxes;
• 100% exploitation of the motor torque;
• ability to operate at high speeds according to the current control regulated according to load variations, where normal open loop systems use constant current control at all speeds without
considering load variations:
• significantly lower cost of the control electronics by backfeeding the motor with a simple incremental encoder;
• simplified mechanics with the same performance.
- advantages compared to a servo-controlled Brushless solution:
• no need for power adjustment (automatic current regulation according to load variations);
• position held stably without fluctuations after completing the positioning;
• rapid positioning favoured by the independent control of the integrated DSP;
• continuous and rapid execution of short-stroke movements thanks to the short positioning time.