TechArchive

Original article date: January 1999

A redesigned slit-type rodless cylinder is thin and short enough to compete with magnet types down to much smaller stroke lengths. DEREK ESSAM of Koganei UK explains

Generally in the case of conventional cylinders with a piston rod the operating space consists of the stroke space and cylinder volume. But a rodless type needs only the cylinder space. It is also easy to match a rodless cylinder with a linear guide making it easier to manufacture actuators with high rigidity. Rodless cylinders are used where there is a danger of the piston rod buckling because of large strokes and where limited mounting space is available. Typical application areas include insertion displacing opening closing lifting door operation transporting feeding of parts.

The main problem however is price. The price of a rodless cylinder cylinder is several times that of conventional cylinders limiting the applications. Rodless cylinders can be of three types – slit type (slotted tube) magnet type and the cable or belt type (see panel). One disadvantage of the slit-type rodless cylinder is that it needs a longer envelope than a magnet type. Also it cannot be directly mounted and the sensors will protrude from the cylinder body.

Now the ORV series of slit-type rodless cylinder overcomes these disadvantages. It is compact the sensors are mounted within the body envelope and it is available at lower cost. By comparison with current products it is claimed that the ORV is 40% thinner and 35% shorter. It almost meets the envelope space of a magnet type rodless cylinders. A stainless steel seal band is used which has longer life and minimum leakage compared with conventional plastic seal bands. This helps to save the height of the cylinder. Furthermore an oval piston gives a thinner body than conventional slit type rodless cylinders that have a circular shaped piston. Air cushioning at the end of stroke is eliminated and a rubber bumper with energy absorbing capabilities is used instead. This design modification enables the length to be reduced.

Generally conventional slit type rodless cylinders are only competitive with other types of cylinders with strokes of 100mm or over. The ORV series is now competitive down to strokes of only 25mm or over.

Compared to conventional designs the weight has been reduced by using lighter materials along with a reduced number of parts. This means that using ORV as a Y and/or Z axis apply less load onto the base X axis cylinder.

• By minimising height differentials between the table and the direct acting guide compact and simple machine designs are possible
• Light compact construction do not put stress on the main unit even if they are used in a Y axis or Z axis configuration
• Stainless steel band gives long life with minimum leakage compared with a conventional plastic seal band
• Bore sizes 16 to 40mm
• Stroke lengths 25 to 2000mm
• Shock absorber unit is standard equipment
• Direct mounting at the end plate. A T-slot on the bottom surface improves mounting flexibility
• A selection of chock absorbers will accommodate speeds of 1000mm/s and 2000mm/s

Varieties of rodless cylinders

With slotted cylinder tube and lateral force delivery

Piston fastening can take high torques and high transverse forces

Good guidance over the whole stroke

Equal piston area on both sides giving the same force in both directions

With force transmission using a magnet

Transmission of force is limited by the magnetic force

Closed system therefore protected

With cable or belt as piston rod

Short overall length

No buckling

Large strokes possible

Sealing is critical

• Koganei UK
• Derek Essam
• 01424 221144

January 1999