Cranfield Precision's Friction Drive Range - linear drive systems for ultra smooth, backlash free linear motion.
Cranfield Precision has developed a range of friction drive units which are totally backlash free offering higher levels of accuracy than achievable with conventional linear drive systems. The friction drive unit's main advantage is in the positioning accuracy, which is not affected by backlash like conventional ballscrews or rack and pinion systems. Backlash can be modelled as pure time delay in a mechanical system and combined with mechanical resonances, restricts the ability to extend the position loop band-width. Accuracy with the friction drive is such that it can fully exploit the resolution attainable from a position sensor, such as a laser interferometer to less than 2.5 nanometres.
Friction drive units are most suited to applications which require extremely smooth motion and nanometer repeatability. Typical applications are; Scanning Machines, Precision Feed Drives (for turning and grinding machines) and High Accuracy Co-ordinate Measuring Machines.
Friction drive units can be built to suit various applications with varying requirements. The profile and size of the "drive bar" and "drive roller" can give different charcterisitcs for traction, acceleration and maximum velocity. Cranfield Precision has used friction drives on small in-feed carriages to large 26 tonne bridges used as seen on the Large Off Axis Grinding Machine.