Roller Bearings in Linear Motion
Linear motion applications are often found to have not only radial loads but also axial load requirements. For these applications, single or double row angular contact bearings are often used. Single row bearings offer the advantage of a slimmer profile and double row bearings offer the advantage of longer life and higher radial, axial and moment loads capability.
Some companies choose to use single row ball bearings. However, this limits the number of balls inside and also reduces the radial, axial and moment load supported by the bearing. Double row bearings have a thick outer ring which is often machined to match the raceway. For these reasons, PBC limits the use of single row bearings only to custom products where load is not the limiting factor, where a slimmer profile is critical, single row bearings are not used in any IVT products to provide greater load capacity.
Figure 1 - Schematic of double row angular contact construction
Figure 1 above illustrates a typical double ball roller construction. For example, a 90-degree V profile matches a 90-degree raceway, or a Gothic Arch profile matches round shafting which have a double-row angular contact construction inside, and also have either V profile or Gothic Arch profile for the outer ring. Illustrated below shows the contact area between the outer race of the cam roller and the track upon which it rides. In the case of the Gothic Arch design, the track is typically a linear shaft and in the case of the V roller, the track is a V profile.
As you can see from figures 2 and 3, Gothic Arch rollers have two contact points and the V profile has a line segment contact. This means that load will be transferred from the roller to the rail either via a point or a line segment. A line segment can be defined as a perfectly straight curve between two points which contains an infinite number of points. This essentially means that the load will be transferred between the roller and the race either via a very small point contact or via a much larger (in comparison) line segment contact.
Figure 2 - Schematic of V profile outer ring contact (line contact)
Figure 3 - Schematic of Gothic Arch profile outer ring contact (2 point contact)