On many large machine tools, the performance of the vertical axis is often the limiting factor in the accuracy of the machine. Traditional ball screw methods have inherent backlash and a limited life. For large axes, a counterforce mechanism will be required. Pneumatic and hydraulic methods are used, but these are expensive, complex and all introduce hysteresis to the axis. Therefore, a new counterforce design was needed to allow higher speeds and accuracies, better dynamic performance, reduced mass and cost – particularly important where linear motors are desired.
Using CAD, FEA and test rigs, a new counterforce mechanism was designed. A slave axis uses a traditional ball screw to support the mass of the carriage but is mechanically decoupled from the carriage itself, through a spring system. For the master axis, linear motors and high resolution linear encoders are used to drive and position the axis, for high accuracy positioning. A position demand is sent to the master axis, simultaneously ‘followed’ by the slave axis to provide a counterforce to the carriage mass.
- A patented, high accuracy, high speed, counterforce solution for large axis mass
- Successfully implemented as an upgrade to existing customer machines, 25 years after the original machine was installed. As well as new, large optics grinders with freeform capability and sub-micron positioning accuracy