Updated May 2015. || Positioning stages and tables are used in motion control systems to hold down a work piece or position it for some operation.
Stages or tables, whether linear or rotary, are most often complete motion sub-systems. That is, they are motion systems themselves comprised of components such as linear motion elements, motors or actuators, encoders, sensors and controllers. For instance, a typical positioning stage is made up of linear guides or carriages and some type of drive mechanism.
Because stages are basically motion assemblies, they continue to evolve as their components improve. Some key developments include improved mechanical components and innovations in feedback and control that are improving metrology, particularly in high-end stages.
As a result, today’s positioning stages can do many things including making moves with incredible accuracy, synchronizing complicated axis commands, and optimizing travel from coarse and fine drives in tandem, closing the loop on one common position feedback.
Stages and tables are used in a range of high-performance applications, such as industrial robots, fiber optics and photonics, vision systems, machine tools, semiconductor equipment, medical component laser machining, micromachining and electronic manufacturing.
Stages can provide one of several different types of motion. They can be linear, rotary or even lift types (Z-axis positioning stages). Among these, they can be configured in many different ways including movement in one direction (or axis) only, in multiple directions (X-Y positioning), or for extremely small and precise movements, as in nanopositioning applications where moves are in the micro- or nanometer range.
The drive mechanisms for positioning stages and tables can also vary significantly depending on a number of factors including cost and desired accuracy. For instance, stages can be direct-drive types driven by linear servomotors or by a combination of motors and gearing and couplings, and can be linear or rotary actuator driven (either using electric actuators, or even pneumatic or hydraulic actuation). Other methods can include belt and pulley systems, ballscrews or leadscrews.
Precision and accuracy requirements can also dictate design decisions such what components to use in assembling a positioning stage. One kind of component used in stages where reliability and high accuracy are desired are air bearings.
Air bearings support a load with a thin film of pressurized air between the fixed and moving elements. They are typically referred to as aerostatic bearings, because a source of pressure rather than relative motion supplies the film of air.
Unlike ordinary bearings, the surfaces of an air bearing do not make mechanical contact, so these systems do not need lubrication. Because the surfaces do not wear, the systems don’t generate particulates, which makes them suitable for clean-room applications. When supplied with clean, filtered air, the bearings can operate without failure for many years.