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igus® inc.

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drylin® W - Design Notes

Reduce misalignment errors with floating bearings - only necessary for individual rails

drylin® WQ square profile linear guides are useful as floating bearings which compensate for misalignment errors in all directions (+-1 mm) between rails. This includes jamming, which can only otherwise be prevented by time-consuming parallel alignment.

Although drylin® W is a profile rail system, it can compensate for rotational errors around the x-axis. An angle of +/- 7° is possible. This effectively eliminates the problems known to occur when fitting to sheet metal.

Floating bearing, selectable in all directions (+/- 0.03937 inch (1 mm)), compensate for misalignments and parallelism errors.

System assembly: rails

1. Fixed bearing, 2. Floating bearing
1. Fixed bearing, 2. Floating bearing
1. Fixed bearing, 2. Floating bearing

Available floating bearing blocks

LL - round (dimension mm)
LLY - angular (dimension mm)
LLZ - angular (dimension mm)
Rotating - angular

Fixed and floating bearings

When using systems with two parallel rails, one side must be designated as the “fixed” rail, and the opposite side as the “floating” rail.

Why use floating bearings?

- promotes smooth gliding performance and maximizes bearing life

- prevents binding caused by parallelism and misalignment errors

- decreases necessary drive force and wear by minimizing friction-forces

- enhances the precision of the system over the bearings’ lifetime

- reduces assembly time and cost

Fixed Bearings
The “fixed” bearing rail should be positioned closest to the drive force. This rail will determine the precision of the system; no system should contain more than two “fixed” bearings.

Floating/Self-Aligning Bearings
The “floating” rail should be the rail located furthest from the drive force. It is to act only as a guide, and will compensate for any misalignments or errors in the system ensuring proper functionality.

Mounting Surfaces
The mounting surfaces for rails and bearings should have a very flat surface (e.g. milled surface) in order to enhance performance. Variations in these surfaces may be compensated for by using floating bearings.

Automatic adjustment of parallelism errors,
1. Floating bearing, 2. Fixed bearing

Eccentric forces - The 2:1 Rule

When using maintenance-free drylin® linear bearings, it is important to ensure that the acting forces follow the 2:1 Rule (see drawing). If either the load or the drive force (F) is greater than twice the bearing length (1X), then a binding or interrupted motion may occur.

If the location of the drive force can not be changed, simply increase the distance between the bearings, or create a counterbalance to move the center-of-gravity back within the 2 to 1 ratio.

The 2:1 rule,
1. Floating bearing, 2. Fixed bearing