Automation Design Tips: Transferring with Rollers Part 2

In the previous Automation Design Tips on Transferring with Rollers, it was explained that the three-row independent feed roller configuration would be more efficient. Here are a few more tips to consider with this configuration and how to improve the design.

One issue that can occur is the item/substrate not remaining in a straight path on the rollers. The frictional force must be equalized at all contact points between the item and rollers. In order to eliminate possible effects of unstable force for transport due to any deflected substrates, consideration may be given to increase the number of substrate support points, thereby ensuring stabilized loading and frictional force at each point of contact with a roller. In practice, however, this solution alone cannot necessarily equalize the frictional force at all points of contact.

To guide the loads being transported to move straight on the line, the direction of action of frictional force for transport must be made straight. There is no correlation between increasing the number of roller support points for substrates and making the direction of action of frictional force for transport straight. If the frictional force acting on the feed rollers becomes unbalanced, the loads being transported fail to move straight but their transport direction changes, resulting in transport problems.

Figure 1 below illustrates the possible movement of materials being transported when the frictional force acting on the feed rollers differs between roller positions; the frictional force is largest at the leftmost position followed by the middle and rightmost positions.

Figure 1: Curved transport of the material

Here are a few possible reasons why the frictional force becomes different:
1 – A bent shaft connecting the feed rollers
2 – Partially or unevenly worn feed rollers
3 – Inclined horizontal reference for the transfer machines

Therefore, in addition to the adoption of the three-row independent feed roller configuration, proper provisions must be made to equalize the frictional force on the feed rollers supporting the substrates.

In order to achieve the optimum frictional arrangement of rollers. Optimal allocation of the frictional force acting on individual rollers should be considered based on the concept of making the direction of action of frictional force easy to become straight even if the substrate support positions vary, by controlling the friction coefficient at each substrate support point of a roller.

One way to accomplish this is to use rollers made with O-rings and plastic.  If these types of rollers are arranged alternately, the varying degrees of friction of each roller will assist in ensuring that the material/substrate stays straight. The rollers will support a flat plate at a total of 9 points, and at 5 or 4 of the 9 points, the frictional force is transmitted, thus ensuring stable transfer.

The plan of arrangement of rollers with O-rings (Fig.2-Pattern A) provides agreement with the points for measurement of the thickness of flat plates, showing a fundamental pattern for flat plate support.

The relation between substrates and roller positions in Pattern B, different from Pattern A, in which substrates move on the transfer line, is shown (in Fig.2-Pattern B).

Combined adoption of two roller arrangement patterns, A and B, facilitates linear movement of each substrate under the well-balanced distribution of frictional force.

Figure 2: An Example Optimal Roller Placement

It is all a balancing act to keep materials/substrates straight on a transfer path with rollers. Thus concludes our automation design tips series on transferring with rollers! Be sure to read about Types of Rollers and How They are Used and our first post on Transferring with Rollers.

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