Pneumatics have always played an important role in achieving maximised productivity for manufacturing automation applications and the technology is constantly evolving to solve engineering challenges.
One such evolution is the development of rodless cylinders.
The disadvantages of rod-type cylinders
The limitations of conventional rod-type cylinders are widely recognised, particularly where long strokes are required. Being unsupported, the cylinder rod has a tendency to flex in the extended position which can cause excessive wear on rod seals and bearing leading to the need for additional engineering to avoid premature wear.
Space constraints may also limit the use of rod-type cylinders with the overall length being more than double the stroke length. This can cause problems when designing or mounting cylinders to machinery. In long travel situations, rod-type cylinders can also sag under its own weight and this misalignment can cause the cylinder rod to bind or buckle.
The disadvantages of rod-type cylinders are:
- Overall length is more than double the stroke length.
- Risk of the piston rod bending, resulting in excessive wear.
- Bad positioning features due to two different piston areas.
- Unequal velocities in forward and return strokes.
- Designed for short stroke length.
The development of slot-type rodless cylinders was designed to eliminate all of these disadvantages.
The construction of rodless cylinders
The rodless pneumatic cylinder has been engineered to be a self-contained linear actuator with a unique design that offers greater design flexibility. With a unique design that uses only four main components, rodless cylinders, such as Parker's OSP range, offer a robust and reliable solution in operation that is simple to maintain; providing long trouble free service. Operated by compressed air, rodless cylinders combine controlled and precise movement with integral support and guidance in any plane.
The rodless cylinder consists of four main parts:
- The cylinder barrel of extruded anodized aluminium has a slot along its entire length.
- A flexible hardened stainless steel inner band running the entire length of the bore and passing through the piston provides a metal to metal seal. An outer band of the same material acts as a cover over the slot preventing foreign particles from entering into the cylinders interior.
- The aluminium piston is fitted with synthetic bearing rings. The power transmission outwards takes place through a positive, physical connection through the slot to the external piston mounting. This solid guide permits the acceptance of external forces and moments and minimizes frictional losses.
- End caps providing connections to the air supply, and housing cushioning adjustment screws.
When to use rodless cylinders
The double acting operation of pneumatic rodless cylinders is advantageous in applications where space is limited.
This is because the installation length of a rodless cylinder is only slightly longer than the cylinder’s stroke. For example, 25mm diameter rodless cylinder with 1000mm stroke would only occupy 1200mm of space, opened or closed.
When specifying, a pneumatic rodless cylinder would be the ideal choice over a pneumatic rod-type cylinder to meet the following requirements:
- A source of repetitive linear movement is needed.
- Cleanliness and minimal risk of contamination from lubricants must be assured.
- Space savings are a major design consideration, e.g. long stroke applications.
- Reliability and minimal component maintenance is needed to safeguard against downtime.
- Overall length can present problems when designing or mounting cylinders to machinery.
- Automated manufacturing
- Processing and packaging, e.g. bottling and canning
- Textiles and ceramics
- Pharmaceuticals and chemicals
- Food production
- Test, inspecting and quality control
Specifying a rodless cylinder solution can deliver substantial savings in engineering and greater design flexibility when compared to the use of a rod-type cylinder.
See the OSP-P in action in our application video, where the rodless cylinder is being utilised in an assembly line for modular steering kits.
Article contributed by Dieter Winger, product manager for rodless cylinders, Pneumatic Division Europe