Pneumatic cylinder slides or rodless cylinders, are designed to provide power and linear motion while supporting a load. Standalone pneumatic cylinders are suitable for providing power and motion, but are not designed to provide support for a load. Many cylinders have no way of holding the position of the piston rod, due to the rod’s ability to rotate. Pneumatic cylinder slides provide the load capability and a stable, non-rotating platform on which to mount tooling or other actuators. This is especially important when a cylinder is moving in a horizontal direction where side load is a major issue—common in automation devices used for picking and placing of parts.
Cylinder slides are popular choices when longer distances of travel are required, or when the overall length must be minimized due to space constraints
Typical uses for these slides include conveyor stops, part ejection and positioning, opening and closing safety doors, gates or curtains. In many of these applications, the need for side load capacity and non-rotating capability is critical.
The idea of applying a load to a linear actuator is very common and there are a number of types of cylinder slides that can be used for these applications. The first basic style of powered slide is commonly known as a “thruster” or cantilever type unit. This type of powered slide is typically powered by a pneumatic cylinder, which is attached to the body of the slide, or may be integral to the slide. In either case, the cylinder piston rod is attached to a tool plate providing power and motion. The tool plate is supported by a bearing mechanism, and together they are able to carry any loads that are attached, rather than transferring the load to the cylinder rod. This type of slide is designed to carry an overhung load known as a cantilevered load.
The second basic type of cylinder slides is called a saddle slide or base slide. In this case, the pneumatic cylinder is attached to a saddle that supports the bearing system on each end of the slide’s travel. This type of powered slide can be used for longer travels with less deflection based on the bearing system being supported on each end. Like the thruster style slide, the saddle carries the load verses the cylinder’s piston rod.
The types of bearing systems can vary on both the thruster slides and the saddle slides. The most common type of bearing system on cylinder slides uses round shafts with linear bearings. The bearings can be precision reciprocating ball bushings or a variety of composite bushings. The precision ball bushings provide low friction and more 200 million in. of travel life. Composite bushings are typically lower in cost and can be used in harsh environments. These have more friction and do not have the life expectancy of the reciprocating ball bushings.
Other pneumatic cylinder slides use profile rails with reciprocating ball carriage bearings. The profile rail bearing systems provide long life with minimum deflection. These can be incorporated in both thruster and saddle type slides.
There are several considerations when selecting the best type of pneumatic cylinder slides. These include:
- Load capacity required. The total payload must be calculated in order to start the selection process.
- Life required from the slide. The bearing system selected will have an impact on the expected life of the unit along with the required speed and payload.
- Speed required. The slide speed is a critical component including the ability of the slide to handle the kinetic energy as the load stops at the end of travel. Cylinder shock pads, cylinder cushions or shock absorbers may be required based on the load and speed of the slide.
- Accuracy needed. The amount of deflection will vary based on the bearing system and the payload being carried. This deflection will affect the positional accuracy of the slide.
- Many manufacturers of pneumatic cylinder slides provide specification and sizing software to allow the proper selection of the slide required for various applications.