Rodless cylinder smooths sensor tracking

Hamel, MN--Boxes--big ones, little ones, brightly colored, and dull brown. Most people don't think twice about these ubiquitous objects. But Bruce Taylor, vice president of Qualitek (Columbus, OH), and associates are staging a quiet revolution of the corrugated board industry (cardboard as it's known in layman's terms) with the help of a rodless-band pneumatic cylinder from Tol-O-Matic (Hamel, MN).

QualiScan, an on-line measurement and process-control device developed by Qualitek, traverses a large skein of paper as it rolls through a corrugating machine. Three rolls of paper are fed through the device--a center fluted sheet, molded into a sinusoidal wave pattern, is sandwiched between two flat sheets. These are glued, cut, slit, and stacked. A sensor package measures moisture content and monitors temperature. Proprietary control strategies automatically adjust pre-heater wraps, doublebacker settings, speed, glue gaps, and auxiliary moisturizing devices based on pre-programmed quality targets.

To shuttle the scanning sensor package across the corrugated board, Qualitek chose the Tol-O-Matic BC3 Rodless Band Cylinder. "The Tol-O-Matic is the sturdiest pneumatic cylinder around," says Taylor. The company tested various pneumatically operated devices. Cable cylinders, though reliable and able to handle the high moisture conditions normal to corrugated converting, produced intermittent motion surges in the system. This resulted in flawed finished board. Other rodless cylinders delivered a smoother cycle, but because of their entirely plastic bearing system design, fell short of the high life-cycle requirements. Electrically powered rail/ball bearing systems proved quite capable of performing the necessary task, but were too expensive.

The Tol-O-Matic's BC3 design incorporates an internal, recirculating, steel ball bearing system that runs through an extruded aluminum tube. "This creates a frictionless system," says Phil Poeschl, project engineer for Tol-O-Matic, "and provides a consistently smooth tracking of the sensor package."

Because the BC3 is a rodless cylinder, it saves space. "If you had a regular rod-style and wanted 10 inches of movement, you would need 20 inches of space because of dead length," says Poeschl. With a rodless system, 10 inches of movement requires only 12 inches of space because the supporting structure is directly under the carriage. The carrier runs on precision rails attached to the inside of the cylinder tube with T-nuts. This design keeps the bearing way firmly in place for smooth motion and low breakaway force. "This is the whole reason for rodless cylinders," says Poeschl. They save space, weight, and costs by simplifying the final assembly and eliminating external guides or support rails.

Of a particular challenge to the Tol-O-Matic engineers was the wet environment involved in the Qualitek application. "We had to create a corrosive-free system," says Poeschl. "We flash chromed the ball ways, used stainless-steel balls, and changed to nickel-plated coating for the aluminum parts." Seals also protect the bearing from contaminants.

T-slots on three cylinder sides allow easy insertion of the T-nuts for easy mounting. This design makes repositioning the cylinders quite simple, a major advantage in applications where future design changes may be important. The large side-loading and bending-moment capacity BC3 ensures smooth movement with minimal play, even with the unbalanced loads. Motion is continuous, from side-to-side, although the stroke can be stopped anywhere along its typical 8-ft length. Shock absorbers cushion the stops. The cylinder operates with conventional air supply in the 10- to 100-psi range. An additional advantage of the BC3 cylinder for the corrugated industry is that its prelubricated, fully enclosed design tolerates the moist corrugator environment without maintenance or downtime, even in three-shift manufacturing settings.

"We are creating a new market," says Taylor, "Our missionary work is providing process control for web-fed or sheet-fed processes such as corrugated paper, extruded film, and metal-rolling mills."

Initially, the three-year-old company is focusing on the corrugated paper industry. "The demand for boxes is an indication of a healthy economy," says Taylor. "And a lot more material is being printed on a corrugated board background, primarily because of wholesale stores such as Sam's Club, Cosco, and BJ's." This increased demand has led to the need for shorter production runs, high-quality printability, and increased strength requirements.

"Our precise, continuous measurements and advanced control strategies ensure improved quality at all speeds," says Taylor. "Board is consistently flatter with less variability from order to order. There's also enhanced convertibility and virtual elimination of cracked scores and board delamination." Qualitek's system platform uses standard hardware and software components, databases, and networks. Windows makes it easy to maintain at the plant level.

The QualiScan sensor package weighs approximately 20 pounds and is offset 7 inches from the scanner's centerline, producing 150 inch-lbs of moment load. The Tol-O-Matic BC3 has a direct load capacity exceeding 1,091 lbs with maximum moment load capacity of 859 inch-lbs (rms). It moves the sensing package at 6 to 12 inches/sec over a typical 8-ft span.

The scanning system is not exclusive to the corrugating industry, says Taylor. Any type of sensor may be incorporated into the technology. All that is needed is to incorporate the proper number of wires into Qualitek's unique telescoping flex coil--the cables that extend and contract as the sensor moves back and forth across the sheet. The flex coil concept uses a spiral plastic tube through which electrical wires for sensor power and signal are passed, along with compressed air if it is needed to cool or purge sensor package. "We could use a laser sensor to continuously measure the roughness of a surface, or have a temperature sensor traverse hot steel sheets looking for cold spots," says Taylor. The corrugated paper industry is just the beginning of their process control revolution.