THE CLOSED-LOOP CONTROL OF STEPPING MOTORS IN CNC ROUTERS ,
Stepping motors have been used in open-loop mechanical positioning systems for many years, and are still the motor of choice in a wide range of applications. Their ability to move through fixed angular increments or steps means that stepping motors can be used without feedback and that interfacing to digital positioning systems is particularly easy. Stepping motors are also simple, robust and very reliable.
Below is a block diagram of a control system without feedback, which is widely used in CNC routers:
Under normal operating conditions the load torque will cause a small displacement of the rotor from its nominal position, but such displacements are not cumulative and do not lead to a loss of synchronization. However, synchronization will be lost if the load torque exceeds a critical value which is dependent on the motor speed. This can be the result of too-rapid acceleration of a high inertia load, excessive load friction or operation at a resonant step rate. In an open-loop positioning system this loss of synchronization can be neither detected nor corrected, and all subsequent absolute positioning operations will be in error.
Our company offers the upgrade kit “ERROR DETECTION” for your CNC machine, a block diagram is shown below:
Feedback system “ERROR DETECTION” defines the position of the axis by the rotary encoder and transmits the data to the software for verification, thus “closing” feedback of the tool. This is to prevent further damage to expensive works or materials. The feedback increases the reliability of the system in terms of accuracy and reliability of positioning the working tool.
The system “ERROR DETECTION” performs an emergency stop of the machine when it detects a fatal positioning error and is not a complete feedback system, which can correct positioning errors. These problems can be overcome by the used of positional feedback system “FULL FEEDBACK”, which our specialists can install on your CNC machine. In a closed-loop stepping motor system “FULL FEEDBACK” the position of the rotor is sensed and the information gained can be used to both detect and correct loss of synchronization. The excess torque capability that must be designed into open-loop systems is no longer necessary and it is possible to exploit fully the performance of the motor:
Upgrade kits “ERROR DETECTION” and “FULL FEEDBACK” include additional rotary encoders for each stepper motor, interface boards for connection with PC, expansion card LPT for a PC, LPT cables, software (driver for MACH3).
If you are interested in upgrading of your CNC systems by feedback, please contact us by e-mail firstname.lastname@example.org or call +38 (063) 375-95-24.