Manual Linear Stage Basics

This article will help you learn the basics of manual linear stages, learn how to select the best stage for your application and link you to a list of stages from the leading manufacturers so that you can compare products.

QUICK NAVIGATION:

• What is a Manual Linear Translation Stage?
• What are the Main Types of Linear Stages Available?
• What are the Differences in Capabilities and Cost of Manual Linear Stages?
• How is the Position of Linear Stages Controlled?
• Do I have to Use an Actuator with a Manual Linear Stage?
• What is a Differential Micrometer Screw?
• What are the Most Important Factors to Consider when Choosing a Linear Translation Stage?
• Where can I select Manual Linear Stages?

Manual Linear Stage Basics

If you are working on almost any laser based development application, you have already determined that you will need some sort of motion translation stage for small incremental movement of focusing optics and other components. While it may seem simple to move an object from point A to an optimal point B, there are important factors you should take under consideration that will determine which translation stage best fits your application. These factors will also contribute to the cost effectiveness, efficiency, throughput and maintenance or technical support of your motion control system.

What is a Manual Linear Translation Stage?

At first glance, you will see that a linear translation stage is a simple enough looking device consisting of a moving carrier or rail where a load is attached, such as an optical mirror or lens, a fixed base which supports the carrier plate, a bearing interface allowing the carrier to slide on or against the base and an actuator for precise positional control of the carrier. Although these stages can be simple in appearance, there are a lot of design criteria in developing linear translation stages. These include material selection, bearing and flexure mechanisms, and drive options such as actuators and screws. More information on linear stage design elements can be found in a technical note titled Linear Translation Stage Technology Guide by Newport Corporation.

Why are they Important?

Linear stages are the most common optical system elements that provide precise, repeatable and stable positioning of an optical element or other device in many optical alignment systems at laser manufacturer's around the world. In a paper by Anees Ahmad from the Center for Applied Optics optical systems can have 10 to 15 mirrors and lenses that must be axially positioned relative to one another and centered on a common optical axis with tolerances of a few microns. It is impractical and cost prohibitive to manufacture the optical components to micron level machining accuracies. It is much more practical and economical to fabricate the optics and mounts to standard machining tolerances and then to provide adjustment mechanisms to align the optical elements.

What are the Main Types of Linear Stages Available?

There are several types of manual translation stages determined by the type of movement between the moving plate or carrier and fixed plate or base. They are dovetail slide, ball bearing, crossed-roller bearing and flexures.

Edmund Optics has posted a short video titled Important Concepts for Selecting Manual Translation Stages that briefly discusses these and other considerations.

There are also more specialized stage types for environments which require extremely low friction. These are not typically used in optical alignment systems. There stages incorporate hydrostatic bearings using air or a clean gas and are much more expensive due to the complexity of the design and the system needed to supply the air or gas.

What are the Basic Differences in Capabilities and Cost of Linear Translation Stages?

The dovetail slide is the most common and cost effective stage capable of the highest loads and longest length of travel. But, it also has the highest friction and so is the most inaccurate in positioning. These are used where coarse positioning is sufficient.

Ball bearing stages are common for general purpose precision, moderate load capability and have very low friction but are more expensive than dovetail stages. Roller bearing stages have a higher load capacity and offer increased repeatability and load carrying capacity than ball bearings. They are also higher cost compared to ball bearing stages.

In more complex alignment systems where there are multiple mirrors, lenses and other components a combination of these stages may be required depending on the factors such as load, travel and sensitivity of the device being moved.

How is the Position of Linear Stages Controlled?

You have no doubt run across the term actuator by now. Actuators for a linear translation stage are used for adjusting the carrier to a precise point in your system. These actuators can be fine adjustment screws or micrometer heads, the difference between the two types being capability of position read-out for micrometer heads.

Do I have to Use an Actuator?

Fine adjustment screws are the simplest and most cost-effective and consist of a fine pitch screw with a nut that is attached to the stage carrier. Micrometer heads allow for accurate position read-out in where position repeatability is required such as in a beam line where position of a pump laser position is critical in relation to a laser rod for example. Position resolutions of 1 μm is possible with micrometer heads.

What is a Differential Micrometer Screw?

If your system requires finer positioning, a differential micrometer can be used. These devices use the difference between two fine-pitch threads combined on one micrometer resulting in positioning of less than 1 μm. Any manufacturer of linear translation stages offers a wide variety of actuators for precise positioning.

What are the Most Important Factors to Consider when Choosing a Linear Translation Stage?

Hopefully, you are now a bit more familiar with the terminology so that you can speak more accurately about translation stages. There are important factors to consider when selecting the translation stage for your alignment system. The most important of these are load on the stage, range of travel and positional accuracy, repeatability and sensitivity. Other factors you should consider are the environment the alignment system will be used in such as a clean room, sensitivity to vibration, and thermal environment, these will help determine the construction material of the stage. Vibration, temperature variations and contamination (on the optics) could have a large impact on the stability and repeatability of your alignment system. Understanding these factors will help determine what type of stage you will need. A good reference describing these factors and the types of stages is a paper by Katie Schwertz and J. H. Burge of the University of Arizona titled Cost and Performance trade-offs for commercially available linear stages.

Where do I Begin?

Hopefully you now uderstand the basic terminology and concepts underlying linear stages. Trying to link all of the concepts together with your need to develop an alignment station for your application. We suggest you start with the three most basic requirements - the travel range, sensitivity and load that you will be moving from point A to B. With these three parameters in mind, you can visit our list of manual linear stages which are available from top suppliers around the World to compare specifications and get pricing information.