Q. I am shopping for an automatic press. I noticed that some models have servo drives and some are pneumatic. What are the differences that I should be aware of when choosing?
A. Roughly 50% of presses on the market have pneumatic drives and 50% are servo. The drive mechanism is what rotates the press around. A lot of people confuse the drive mechanism with registration. How well a press registers is independent of its drive mechanism.
Both drive systems use air cylinders to raise and lower the mechanical engagement of pallets to screens. Air cylinders do a good job of accelerating during the index, but have difficulty in the deceleration phase, most systems use some form of external mechanism to assist in the deceleration of the inertial load created by the weight of the pallet arms. How the drive handles the deceleration is the biggest difference between a pneumatic and a servo.
A pneumatic system uses less expensive hardware than a servo system so it costs less and it also is easier to repair. In fact, many printers can do the repairs themselves. A servo system is more expensive and generally requires a technician to repair it, so repair costs are higher. In most cases a servo drive costs anywhere from $3,000 to $5,000 more than a pneumatic drive.
The advantage of the servo drive over the pneumatic is performance. A servo drive adjusts to changes in conditions. You can change out the pallet from a sleeve size to a jumbo size with no mechanical adjustments. The servo automatically adjusts itself based on the pallet size selection. With a pneumatic drive, you would need to adjust the press to accommodate the different pallet and/or job weights. Although Pneumatic indexing has become more sophisticated over the years it still requires the turning of a knob or a screw.