Linear Slides

Some linear slides are motorized such as machine slides, XY tables, roller tables and some dovetail slides which are then able to handle heavy and cumbersome loads. Other slides such as drawer slides, ball bearing slides, telescopic slides and roller slides do not need the addition of a driver engine and rely on hand power, inertia or gravity to move the load through the linear guide. There are many applications in which linear slides are used including: clean room operating systems, robotic assembly machinery, automatic packaging equipment and CNC machining equipment such as drilling and grinding machines. Linear rails are also used in many other diverse industries, such as semiconductor, chemical processing, optical, textile and commercial. While basic linear slides are used to provide motion along a single plain and back and forth in one direction, advanced linear slides, such as positioning stages, XY tables, linear stages and machine slides may be designed and configured to provide movement along multiple axes. These systems are more complicated to manufacture and yet can be used to drastically cut back on operating procedure times.

Typically, linear slides are composed of a stationary base onto which a carriage, or moving platform or component, is attached along a linear rail of bearings. The carriage slides along the bearings from one end of the base to the other with minimal friction, offering a precisely restricted range of movement. This is ideal for many applications such as precision eyeglass assembly, robotic welding, instrumentation and other specialized processes. The precisely controlled automated equipment using linear slides provides an ideal solution to many operating needs for both large and small applications. While some applications rely on inertia or gravity to move the carriage, others are motor driven which further adds to the control of the motion process as the load or equipment can be moved at an exactly desired speed. However, linear slides are designed primarily for precision movement control, not for power. Although linear slide components are used to move thousands of pounds of weight, and ball bearing slides and crossed roller slides are both capable of handling heavy loads, this is done with minimal friction as the bearings provide a sliding mechanism. Therefore, only a relatively small amount of torque is required to move even massive loads. Roller slides tend to absorb less stress from weight as they offer a line of contact, rather than the point contact of a ball bearing.

Cast iron is commonly used to fabricate components of a linear system as it is a durable and strong material which is able to withstand a fair amount of wear and tear which linear systems, especially those designed for heavier load carrying, are susceptible to. Aluminum is another commonly used material as it is able to maintain its shape and structure even under stress. Stainless steel is used as the material for linear systems which are designed to be used in work environments in which humidity and corrosion may be factors.. For processes which have prolonged exposure to moisture, corrosion in the linear bearing system would result in system failure. Therefore, stainless steel is used as its corrosion resistant properties combined with its durability make it an ideal material choice. Linear slides are a cost-effective piece of operating machinery and tend to be low maintenance equipment. The bearings used in the linear system are the components that show deterioration soonest as they are the point of contact between the weight of the load and the linear rails. Roller slides tend to absorb less stress from weight as they offer a line of contact, rather than the point contact of a ball bearing. Ball bearings are most susceptible to wear and tear, even those made from cast iron, and will need to be periodically replaced to ensure the optimum running of the linear rail system.

Plant conditions are an important factor to consider when choosing linear systems. Bearing housings should be used to provide a protective barrier between the sensitive bearing systems and the possible contaminants of debris and dust. Covers or other shields should be used where it is possible to attach them to the slide system without interfering in the operations of the sliding mechanism. In machine slides, machine ways are used which are placed in front of the attached carriage to brush or wipe clean the railing before the carriage passes over it. This removes dirt particles which would speed up the rate of wear and tear on the complete system. Dovetail slides may require additional lubrication, but most linear slides should be able to maintain a low-friction, smooth movement without adding further lubrication. Precisely controlled automated equipment is costly and the procedures which use linear slides are often dependent upon accuracy, therefore it is important to maintain optimum working conditions of linear slide systems including regular maintenance and repair when needed.

Linear Slides Images Provided by Velmex, Inc.

Linear Slide Image Provided by Del-Tron Precision, Inc.

Linear Slide Types

• Ball bearing slides, also referred to as "ball slides," are the most common type of linear slide because of their self-lubricating qualities, which increase their reliability. Ball bearing slides, which perform with a smooth linear motion, typically use four hardened and ground shafts that surround the balls at four different points.
  
• Crossed roller slides utilize rollers that crisscross each other and usually move between a group of four semi-flat and parallel rods, which surround them. The design of crossed roller slides allows them to carry up to twice the load of ball bearing slides and to absorb larger impacts.
  
• Dovetail slides are used in high load applications that require long travel distances and/or damping. Dovetail slides consist of a saddle or flaring tenon and a fixed base. 
• Drawer slides are a specific type of linear slide used to mobilize drawers for easier access.
• Linear guide are used to support and guide the rolling elements, typically rollers or balls, of a linear bearing.
• Linear rails consists of a smooth, flat base that is used to support and guide the motion of linear bearings.
• Linear positioners consist of a drive that is attached to a fixed slide base and two extended springs that pull the slide top toward the screw end, against which it is firmly held. As the screw is turned clockwise, it moves the slide top forward along the linear axis, and because of the spring pressure, the screw retracts when turned counter-clockwise, resulting in a smooth linear rotation.
  
• Linear stages are reliable single- or multi-axis mechanical systems that position a payload and consist of few components, including a linear motor, bearings, encoder, limit switches, cable carrier and bellows. Linear motor positioning stages move payloads vertically or horizontally without mechanical transmission devices and at varying rates of acceleration and speed.
  
• Machine slides are precision products used in CNC machining.
• Positioning stages are linear slides with the addition of a drive mechanism that allows them to be used to provide both low-friction linear movement and controlled, precision positioning along a linear axis.
• Precision slides consist of a carrier, a base and ways fitted together with a gib and gib screws, which allow for adjustment to ensure accurate movement. Precision slides are basically motion guides that are used to feed and retract parts, tools or fixtures on all kinds of equipment.
  
• Roller slides use perpendicular rollers and have a higher load capacity than ball bearings.
• Roller tables are the quietest type of bearing table.
• Rotary stages rotate on an axis, typically positioned in the center, and provide rotary motion used in positioning and moving objects. Rotary stages are utilized to adjust the roll, pitch and yaw of objects, as opposed to linear stages, which position objects in space.
  
• Standard slides integrate roller or ball guides to permit the engineering of complete systems easily and with a minimum of assembly time.
• Telescopic slides are linear motion devices that are capable of compaction and extension as a result of concentric parts that slide inside of each other.
• XY tables are motorized linear slides, with linear motion based in bearings and driven by a drive mechanism, typically a linear motor.

Linear Slides Terms

Actuator - A mechanism used for controlling or moving an object indirectly, as opposed to manually.
 
Auxiliary Carrier - An optional carrier for linear slides that increases the load capacity.
 
Axial Loading - A load with a force moving along a shaft or another type of axis.
 
Base Mount - To attach linear slides by either fastening directly to "T" slot nuts located in the slide base or by using the base mounting.
 
Bearing - A device whose support allows smooth, low friction motion between two loaded surfaces moving against each other.
 
Breakaway - The minimum amount of force or pressure needed to actuate movement of a device, such as a cable, cylinder or rotary actuator, through a complete stroke.
 
Carrier - A device attached to the linear slide, commonly with a bearing system, and responsible for supporting and moving the load.
 
Center of Gravity (COG) - A single point at which the weight of an object is most concentrated. The object would remain in equilibrium if supported at the COG.
 
Coefficient of Friction - A measurement of resistance of a single object sliding across another.
 
Dead Length - The part of a linear slide or band cylinder that is necessary for mechanisms and mounting. Dead length plus stroke length equals the total length of the linear slide or band cylinder.
 
Deflection - The amount of bend under a specific weight load.

Gib - A wedge-shaped piece of metal or wood designed to hold structural parts in place and/or provide a bearing surface.  

Inertia - The amount of resistance of an object to change velocity. If a linear slide has a large inertia, more torque will be required to move it.
 
Leadscrew - A device that changes rotary motion into linear motion.
 
Proximity Sensor - A device that senses the end of a stroke on a linear slide. Proximity sensors supply signal to any of various controllers.
 
Rotary Actuator - An actuator that provides rotational movement.
 
Rotor - The shaft on a rotary actuator that rotates on its own axis.
 
Shock Absorber - A device implemented with linear slides to decelerate heavy loads at high speeds.
 
Stroke Length - The distance the carrier and its load move on the linear slide.
 
Tenon - A finger-shaped projection that fits into a corresponding hole.
 
Torque - The twisting or turning force that produces rotation.