Basics of Motion Control

Synchronizing Motion Control Systems

Master-slave motion control systems are common in web presses where one or more axes must follow the speed and acceleration of a master axis. Motion control systems require synchronization to keep the web from stretching, tearing, or bunching as it winds through the machinery.

The conventional way of synchronizing axes in these motion control systems is with mechanical drive shafts. A master axis turns all other axes on the machine through connections such as gearboxes and universal joints. A problem with some applications is that the drivetrain may twist appreciably, introducing position error in rolls from the master axis. Such torque buildup causes axes located farther away to increasingly lag the master axis. A result is that jerks and oscillations can take place as the web comes up to speed, so that remote roller stands do not come up to speed at the same time as the master. Web material produced during such intervals may be unusable.

For these and other reasons, electronic motion control systems are increasingly used to provide perfect synchronization between the master motor and remote rollers. Feed-forward control is a well-known means of providing such behavior. Here, a preprogrammed feed-forward signal is applied to the master motor during acceleration intervals. This signal is added to the motor command generated by the position feedback. The feed-forward signal reduces the amount of position error needed to generate a given output voltage to the motor.

In motion control systems that use this method, one axis typically serves as a master. An encoder monitors the position of this axis. The signal from this encoder is used as a master position signal. The signal is sent both to the processor controlling the master axis and to the processors controlling other slaved axes in motion control systems.

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Motion Control Systems: Introduction to Motion Control Systems

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