Engineers who deal with design of gear, feel that not enough emphasis is placed on the advantages of rack and pinion measuring systems, and explain here why this tried and tested technology should not be dismissed.
The companies which are long-standing suppliers of high performance rack and pinion measuring systems, and often find that this tried and tested technology is dismissed (because of the pinion error) in any discussion on the current state of the linear measuring market.
Engineers feel that not enough emphasis is placed on the following advantages of rack and pinion measuring systems:
a Long term stability over long lengths.
c Extremely low cost of the scale (racks).
d Ability to convert to absolute without additional scales.
e Non-catastrophic failure if damaged (totally incremental systems retain glitches and errors until switched off).
Expanding on these basic advantages, there is also the fact that the racks usually have a thermal expansion coefficient very similar to the host machine.
In addition, with use of laser measuring techniques the system can be calibrated to take account of inherent repeatable machine errors to accuracies of 25 microns over 10m.
Where the pinion errors are unacceptably large it is also possible to apply a straight edge and disc system combined with the rack and pinion.
The measuring advantages are not the only benefits of the system.
A very cost-effective light open loop actuation system can be designed using rack and pinion for accurate drives.
The ability to manufacture racks to these high standards does not come easily and has been progressively developed over the last thirty years by Reliance, using helicoidal rack tooth form and other proprietary techniques.