The Art of Manufacturing by Ninad Deshpande & Sivaram Pothukuchi

Author:Ninad Deshpande & Sivaram Pothukuchi
Language: eng
Format: epub
Publisher: Packt
Published: 2023-11-15T00:00:00+00:00

Figure 5.5 – A conveyor run by a VFD

A servo motor and a servo drive are deployed when the application demands high accuracy and precision. A user cannot demand accuracy and precision from a servo using a VFD. Servo drives and motors provide the application with its high acceleration and deceleration needs. They are able to follow the exact motion path, whereas a VFD provides velocity control.

An induction motor reduces speed (RPM) as the torque delivered (in other words, load) increases. This drop in speed as load increases is called droop. A graph that depicts this relationship is called the speed characteristic of the motor. A servo motor has a flat speed-torque relation, which means that at any speed it can deliver the same torque. A servo motor is, by construction, a brushless DC motor (BLDC), where the magnetic field is provided by powerful permanent magnets.

Figure 5.6 describes a motion application such as a machine that is responsible for labeling bottles (beverages, medicines, etc.). In this case, instead of using a VFD or an induction motor, a servo is preferred, as the conveyor acts as the primary position, and the labeler follows the primary axis to label the bottles based on the position received from the primary axis. This works in tandem with the bottle presence sensor on the conveyor. These labeling applications are operating at high speeds, which results in the need for higher synchronization among all the motion components. In this case, a synchronization between the VFD and the servo motor. Moreover, it needs a high degree of precision and accuracy for labeling, hence the use of servo motors and drives:

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