# Rotary Stage

A rotary stage refers to a component contained within a motion system that is set up such that when an object is on a rotation, it is restricted to a single axis of rotation. Sometimes, people interchange rotation stage and rotary table when using the terms. Every rotary stage is made up of a base and a platform and gets joined with a guide that puts some restriction to the rotation about that axis.

Operating Principle

When dealing with three-dimensional spaces, there are three axes that an object may translate along, or rotate about. At that point, it can be said that the object making the movement is going through what is referred to as “6 degrees of freedom”, and these degrees of freedom are divided into two- 3 translational, and 3 rotational. However, the rotary stage does not exhibit the 6 degrees of freedom, rather its function is based on only 1 degree of freedom, and that is rotation about an axis. This is indicative of the fact that rotary stages function by creating a physical restriction of 2 rotational axes and 3 translational axes.

In order for this system to function as effectively as expected, their movement which is relative to their bases is dependent on bearings. The base of the system and the platform are joined with the aid of bearings that are fashioned such that they bring some restriction to motion, and limits it to just the single axis. There are different bearing styles used in creating a rotary stage, and each of these styles come with their unique pros and cons, and that in turn makes some bearings better for some functions than for other applications. Two types of bearings that are prominent in the rotary stage are:

• Rolling Element Bearing

This bearing consists of crossed roller bearing stages, ball bearing stages, etc. There is the possibility of employing the use of any other type of rolling element bearing. In this style of bearing, a pair of bearings gets used, and then has a preloading system in place, to deal with any slack that may occur and cause some lifting motion to happen to the stage platform, as a function of the base.

• Plain Bearing

Basically, a plain bearing refers to two surfaces that arranged to slide against each other. By default, there is a circular step that is present on the platform that is designed to mate perfectly with the circular depression of similar design in the base, making it possible for free rotation to happen, while also minimizing the chances of a side to side motion. When a rotary stage is created with the plain bearing, it is normally employed to facilitate coarse positioning, and then gets a manual adjustment via the process of turning the platform. Furthermore, the bases of the platforms are usually provided with index marks; hence, they allow for the positioning to be repeatable, as a function of the base.

Methods for Position Control

There are different position control techniques to facilitate the rotary stage’s functions, and these methods include:

• Manual Worm Drive

This is usually used for increased precision. It involves affixing a worm wheel to a platform that is rotating and then connects with a worm that is located at the base of the system. When the worm is rotated with a manual knob, the platform begins to rotate, as a function of the base.

• Manual direct

There are rotary stages that get operated manually, by turning the platform with your hand.

• Stepper Motor

The manual control now used in the worm drive can be replaced with a stepper motor, which in turn automates the function of the rotary stage.

• Linear Actuator

If you require a rotary stage that will give you an angular positioning about a small angle, you can employ the use of a linear actuator that can wither be motorized or manual. However, the motion’s range is a rotation of 10 degrees to 20 degrees.

• DC Motor

This is an option to replace the manual control knob. It is important to note that the movement is not in fixed increments. The stage position can be determined via an alternate means.