Balancing by Feedback

Control takeups following all but one of several drives on a conveyor provide means to operate a feedback signal to synchronize the drives. Any difference in speed between two drives will cause the takeup between to move. This movement, coupled to a potentiometer or rheostat slider, provides signal to correct the speed of the drive feeding chain into the takeup to stop movement. A rheostat in series with the motor shunt field can be used with d-c motors. A potentiometer, in parallel with an adjustable tap resistor in control panel, provides a signal between slider and tap for electronic servomotor speed control with mechanical speed changer. Movement of control takeup need not be more than 3 or 4 in. Limit switches operated by extreme travel of takeup are recommended in drive control circuits and are provided with signals on a central panel. This ensures stopping the conveyor and trouble point indication before damage if a conveyor jams or a control component fails.

A long travel takeup should be used after the one uncontrolled drive. This is called a slack chain takeup and accepts all the elongation of chain due to wear or heat expansion. It must have sufficient travel to compensate for movement of control takeups to synchronize drives, temperature change length, and wear elongation for a reasonable time.

Location of control takeups are important to ensure that movement will be due to speed difference only. Takeups may be operated by counterweights or air cylinders with adjustable pressure regulator. Takeup tension need only be sufficient to keep chain stripped from drive. As long as control takeup is neither fully open or closed, tension is just right. The control takeups may be built into either 90 0 or 180 0 turns. This method is fully automatic and controls drive speeds regardless of variations in speed or load. Minimum chain pull is developed since each drive pulls its section of conveyor only. Drive loads can be unequal and different sized drives may be synchronized. Since no manual adjustment of individual drives is required, production supervisors can be permitted to make speed changes.

Follower drives must be capable of running both faster and slower than the master at extremes of production speed. Rheostats for d-c drives have value to raise base speed of motors by 200/0. The master drive has manual field rheostat to raise its base speed by 100/0. Control rheostats, by field control, can make follower drives run up to 100/0 faster or more slowly. The layout of some types of conveyors do not permit use of control takeups. These conveyors then must use one of the force methods with manual adjustment.