Three rail features make smoother motion in machine tools

When it comes to linear motion, machine-tool applications are often the most demanding.

Just consider how motion-controller manufacturers have improved their components in recent years with the latest processors to boost the precision of machine tools. Or consider how Heidenhain (maker of linear encoders) addresses the relatively small effect of thermal drift on mechanical components in typical machine-tool setups.

Now in its own effort to boost precision, Bosch Rexroth is helping machine-tool operators reduce a problem called pulsation on mechanical linear-motion devices. Pulsation is a sustained series of impacts when load-bearing rollers inside the carriage come into and out of a loaded condition as they travel around their circuit.

In traditional setups, rollers enter loading while circulating through the end of the bearing and round a critical radii. But their smooth rolling can hiccup if they hit sudden bends or areas of surface roughness inside the circuit.

Once loaded, roller motion is fairly consistent, but there’s another problem when the rollers exit the load zone …

The balls tend to shoot out and then accumulate. Such impulses even happen at low speeds, and in turn make the carriage rock and jump.

So, the Bosch Rexroth carriage reduces pulsation with two features.

1. The ball track has a super-smooth steel insert.

2. Relief zones that damp ball-entry forces at the carriage-bearing’s ends.

Here, the track loads the cylindrical rollers according to a harmonic bending line — so the runner block gets to maximum load smoothly. That evens out the motion about the carriage axes.

In fact, here’s an illustrated PDF on the problem of pulsation and Bosch Rexroth’s runner block to reduce the issue … and a competitive linear-rail product with low pulsation.

In addition, the rail design sports subcomponents to better contain lubrication and keep out contaminants.

3. A universal lubrication system extends lubrication intervals by roughly 20% and reducing lubricant consumption.

Here, resistance-optimized lubrication channels distribute lubricant in precise doses. If overloading occurs, bypass channels bleed off lubricant to protect mechanical parts. The lube fittings are metal so are less likely to detach during the actual application of lubricant.

A longitudinal seal inside the runner block retains lubricant; a modular sealing with a double-lip seal at each end (standard) plus an optional seal made of fluororubber protect the bearing; for machine-tool applications, there’s also a scraper if the for machines that make extra-large chips.

Bonus: The lubrication system lets machine builders use one runner-block type for myriad applications, reducing block types by 2/3 in some industries.