Linear slides and stages provide smooth, precision linear motion and positioning for many different types of automated machinery. They use one of several linear bearing methods to reduce friction, stick-slip and energy expenditure. Linear slides are simple linear motion devices composed of a stationary base and a moving carriage. Linear stages are slides with a drive mechanism that provide controlled, precise positioning along a linear axis. Linear slides and linear stages use a linear bearing to reduce friction and guide the slide.

Common linear bearing types used in linear slides include:

• Air bearings
• Ball slides
• Crossed rollers bearings
• Dovetail ways
• Hardened ways (or box ways)
• Linear ball bushings
• Linear motion guides
• Linear needle roller bearings (or M/V ways)
• Sleeve bearings

The rail or stationary member of the linear bearing is assembled to a base and a carriage is assembled to the moving member of the bearing. The linear bearing provides a low-friction, smooth and accurate linear motion for the carriage.

Linear slides typically use a ball screw or lead screw supported by rotary bearings as a drive mechanism to move the carriage. The screw is attached to the fixed base, and the nut assembly is attached to the moving carriage. As the screw rotates, the nut and carriage move linearly along the screw. The screw is turned by a handwheel or electric motor (which may or may not be included with the slide). Alternative drive mechanisms may also be used that do not require a ball screw or lead screw, such as linear motors, pneumatic cylinders and hydraulic cylinders. In a linear motor driven slide, the linear motor directly moves the carriage along the slide. Pneumatic cylinders and hydraulic cylinders may also be used. The cylinder body is attached to the slide base and the cylinder rod is attached to the carriage.

Components of Linear Slides

The base is usually stationary and can be mounted to a machine or other surface. The base usually supports the slide linear bearing, motor and screw components, if present. The base is typically made of cast iron, steel or aluminum.

The carriage is usually the moving component to the slide and mounts to the moving member of the linear bearing or driver. The carriage supports a spindle, machine subassembly or other component that requires linear movement. The carriage is typically made of cast iron, steel, or aluminum.

The linear bearing may be incorporated into the base (dovetail slide or box way slide) or may be a purchased bearing used in the slide assembly.

Ball screws and lead screws are used to provide precise and repeatable motion to a linear slide. The screw is usually mounted to the base, supported by a rotary bearing assembly and the screw nut is mounted to the carriage. As the screw is rotated (either by hand or motor) the nut and carriage move along the screw.

Linear motors are used to provide precise positioning of the carriage. Linear motors can generate high forces, as well as high acceleration rates and speeds.

Pneumatic or hydraulic cylinders use a gas or liquid pressurized piston to determine the linear placement of the carriage.

Specifications

Number of axes - Single-axis systems have only one carriage or saddle and move along the X-axis. By contrast, vertical lift devices move along the Z-axis. Some stacked or coupled units, referred to as multi-axis positioning systems, move along two--usually orthogonal--axes in the X-Y plane. Others include one carriage that moves along the X-axis and another carriage that moves along the Z-axis. Three-axis systems provide motion in three orthogonal axes. Important travel specifications for linear slides and linear stages include X-axis linear travel, Y-axis linear travel and Z-axis linear travel.

Slide accuracy is mainly determined by the bearing or way system used. Linear bearings can provide extremely accurate and repeatable motion.

Linear travel is the total stroke of the slide from one end to the other.

The load capacity is the total load that the slide can carry without suffering any permanent damage.

The linear speed refers to the maximum velocity the carriage can move along the positioning axis.

Load, moment and stiffness ratings - the construction of the slide and the bearing or way system determines the load capacity, moment rating and stiffness of the slide.

Drive mechanism type - very stiff, repeatable slides may require a ball screw drive with a motor. Manual positioning applications are better suited with a ball or lead screw and a handwheel. Pneumatic and hydraulic drives can be used for fast actuation that does not require the accuracy and repeatability of a motor driven slide.

Types

Features

A linear slide or stage may include one or more of the following features:

• A brake/lock assembly for slowing or stopping the linear motion, or a lock for maintaining the carriage position.
• A clutch assembly for connection or disconnection of the drive mechanism.
• A combination brake/clutch assembly for slowing or stopping the linear motion (brake) and connection or disconnection of the drive mechanism (clutch).
• The double carriage slide or stage is equipped with two sliding carriages.
• A rotary axis where the last axis (Y or Z) is capable of rotary motion.
• A stackable slide or stage that can be stacked (one on top of another) to provide linear motion in more than one axis.
• A side motor or side motor mount is offered to fit in smaller spaces.
• Way covers, which are sometimes referred to simply as bellows, cover the rails/guides for protection from dust and dirt.
• The unit is equipped with wipers or scrapers for cleaning the surface of the rails/guides.

Applications

Linear slides are used in many applications requiring a linear motion. Some examples include machine tools, packaging equipment, metrology equipment, processing equipment, pick and place and other material equipment, and many others.

Some linear slides are suitable for unique work environments

Cleanroom Rated - The unit is certified for use in cleanroom environments. Cleanroom requirements are typically specified in orders of magnitude of 1, 10, 100, 1000, 10,000, relating the particles per million and defining the particle size.

Vacuum Rated - The unit is vacuum qualified for use inside chambers.

References

Del-Tron Precision Inc. - Linear Slides

Milwaukee Machine Tool Corp.

RT Gilman

Setco Precision Slides

Image credit:

PBC Linear