How Does a CNC Servo Motor Work? Full Working Explained | The Edge Cutter

Utilizing brushless servo motors for industrial-footprint machines that use planetary drive systems is a good motor-driver combination to bring a closed-loop response technology and develop a compact-design solution. This contrast technical components tend to be the best fit for CNC plasma applications and regular CNC routing works.

Also read 10 Best Stepper Motors for CNC in 2022: Reviews and Buying Guide

With the increase in the size and speed of the CNC machine, the demand for more power (to work more efficiently) also rises. This is where the need for servo motors steps in.

Closed-loop Feedback Systems

AC servo motors follow a closed-loop feedback system, meaning that the servo drive is always aware of the process happening during the operation and so, it can respond quickly and accordingly whenever required.

Just try to relate the concept of a GPS navigation system to the closed-loop feedback system of a servo motor. When you use GPS service while driving, the system automatically updates showing you a newer route to your destination if you have already missed the route that the GPS displayed previously. As a result, the system ensures that you ultimately reach the destination even if you missed the turn initially. 

If this rerouting facility was not there, then you probably would have driven the wrong route all the way. This is almost exactly how a stepper motor operates. Since a stepper motor does use include encoders, the motor has no means to deliver back a positional data to the motor drives. This phenomenon is called  “losing a step”, and once it happens, the next move of the motor can be totally a random one, delivering a catastrophic project output.  

Almost every closed-loop drive system comes with an absolute encoder. This econder helps in delivering data signals to the motor drive (Servo motor drive), enabling the system to identify an issue and act accordingly, ensuring instant corrections during the ongoing machine operation. 

Let’s understand the above with an example: say, a block of wood was to fall off and jam between the table and CNC gantry, thereby raising a mechanical issue. But, closed-loop feedback motors (like Servo motors) can immediately recognize this technical abnormality in the system and check on the other motors. Once such abnormality takes place, the entire process halts to avoid further functional error.

Absolute Encoder

The primary reason behind the above example is the availing of absolute encoder in the system. Encoder is a device situated at the edge of the servo. This encoder directly sends back data to the motor drive upon which the servo drive gets to know about the exact positioning of the motor shaft and working of the motor in the CNC system. 

Quick Tip: It is always better to use a glass encoder as it does not react to changes in the surrounding temperature. If you privacy running on a tiger budget or want an affordable encoder option, go for the plastic encoders. But, remember that plastic encoders do not  exhibit accuracy in determining the functional status of the CNC servo motor. Since plastic has a tendency to change with the temperature fluctuations, if the motor gets too much heated up, the encoder size changes which can significantly affect the data accuracy of the motor shaft position.


Considering the utility value of a servo motor, it is widely used in the manufacturing industries where improved precision in positioning and resolution are the two primary requirements. A servo motor generally runs at a speed of several thousands RPM which is higher than a stepper motor. Moreover, the torque generated by a servo is more consistent across the overall limit of the machine.

Quick Recommendation

If you are already looking for an internationally reputed servo motor manufacturer to buy one for your CNC machine, Mitsubishi AC servo motors are one of the most used servos by the finest machine tool manufacturers across the globe. 

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