Counter Rotation and Synchronization
We manufacture a complete line of vibratory equipment. The product line includes a variety of vibratory table configurations including the flat deck, FA, vibratory grid tables, GT, BT, and vibratory belt tables, along with Electro-mechanical feeders (EMF) and Electro-mechanical screeners (EMS). Many of these units are of the general “Brute force” design type. This broad design category is based on the principles of counter-rotation and synchronization when two electromechanical rotary electric vibrators are applied.
Counter Rotation – Brute force units require the use of two rotary electric vibrators. When mounted to a rigid structure the two vibrators will “sense” the presence of the other vibrator and make an effort to run together at the same speed. To produce linear force with two vibrators, which when operated alone produce a rotational or centrifugal force vector, the pair must run together and Counter Rotate. When mounted side-by-side and viewed from the end, one vibrator must run clockwise and the other vibrator must run counter-clockwise. In typical applications, it isn’t important which vibrator runs in which direction, it’s just critical that they run in different directions. When running properly and in opposite directions, the forces produced by the two vibrators cancel each other except for two times in a cycle with the eccentric weights of the vibrator both pointing in the same direction. With the Cleveland Vibrator line of three-phase powered rotary electric vibrators, changing the direction of vibrator with rotation on one of the vibrators is as simple as “flipping” two of the power legs of the vibrator. Check out the diagram below regarding counter-rotation and force cancellation!
For the sake of completeness, let’s take a moment to discuss in very basic terms the design of the rotary electric vibrator. Very broadly, the rotary electric vibrator is a through shaft motor with bearings on each end of the shaft. Outside of the bearings, there are two eccentric weights that produce an “unbalanced” condition when the motor runs. This unbalanced condition is what produces the vibration used to move, screen, or compact a variety of products. These eccentric weights are more or less “pie” shaped and are clamped onto the shaft with a bolt. The eccentricity or unbalanced condition of the vibrator can be varied from 0 – 100% based on the relationship of these weights.
To access the eccentric weights, you must remove the four bolts that hold the weight cover in place, and then remove the weight cover. To adjust the unbalanced condition, the outer weight, the one furthest from the center of the vibrator on each end of the vibrator, can be rotated to a new location changing its relationship to the inner weight thereby increasing or decreasing the force output of the vibrator. As outlined in the rotary electric user’s manual, only the outer weight is adjusted, never changing the location of the inner weight. It is critical to remember that if one outer weight is changed then ALL outer weights on both vibrators must also be moved to the new location.
On each end of the motor shaft, you’ll see a dial with increments between 0 and 100 percent. The outer eccentric weight has a small “punch mark” or “dot” on the face of the weight. This punch mark is aligned with the desired weight setting on the dial. The photo to the left showcases this “punch mark” with the dial being set to 40%.
For example: if the goal is to reduce the force produced by a vibratory table, the customer might decide to “turn the weights back”. In other words, change the position of all outer weights to say 40%. All four outer weights are rotated so that their punch marks align with the 40% mark on the dial at the end of the shaft. By changing the relationship of the inner to outer weights, the unbalance of the vibrator is reduced and with it the force it can produce at any given speed.
On a piece of equipment, it is critical to the success of the operation and the serviceable life of that unit that all out weights on each end of both vibrators are set in the same location. Again, refer to the rotary electric manual or call us if there are any questions on the positioning of the outer weights. It’s critical that all weights be set properly.