Rotary stages are mechanical devices that are used to rotate objects in motion control applications. There are several basic types of products. Rotary positioning stages use rotating tables, shafts, or rings to move objects in a circular motion. Inclination positioning stages also rotate objects, but according to the angular attributes of a table or similar device. Cradle positioning stages or goniometers use an external axis of rotation. Instead of rotating around the center of the stage, these devices rotate around a point in space. By contrast, gimbal-mounted stages locate the axis of rotation on a yoke-like device which allows both rotation and inclination. Bare-slide rotary stages do not include a lead screw and are suitable for basic applications. Manually-powered devices use a screw or shaft and are actuated with a hand crank. Devices that are driven by an AC motor, stepper motor, brushed DC servo motor, or brushless DC servo motor are commonly available. Direct drives are used to couple tables to drive shafts or screws. Gears pass the drive mechanism through a gear train to the table drive. Belt and pulley drives are used to separate the drive mechanism from the output axis.
Specifications for rotary stages include operating temperature, maximum shock, load capacity or maximum load, maximum torque, speed, gear ratio, accuracy, resolution, travel distance, repeatability, and physical dimensions. Load capacity is usually measured in pounds (lbs). Maximum torque is usually measured in inch-pounds (in-lbs). Accuracy describes the precision with which a directed movement compares to a standard length. Resolution is the smallest possible length of travel. By contrast, travel distance is the maximum length of travel in one direction. Repeatability is measured in degrees and describes a stage’s ability to move repeatedly to the same position. In terms of physical dimensions, important specifications to consider are platter size, length, width, and height.
Features and Applications
Rotary stages differ in terms of features and applications. Some products provide positional feedback via home switches, limit switches, encoders, or resolvers. Others include brake/lock mechanisms or brake/clutch combinations. Rotary stages are used in a variety of manufacturing and testing applications. Examples include wafer inspection, DVD mastering, servo writing, and optical inspection. Rotary stages are also used in fully integrated automation systems that include linear positioning stages and machine or motion controls.