Controller makes motors follow the leader

Minnetonka, MN--Ever notice wavy patterns in the ceiling cloth of your car? If you own an expensive one, probably not. But for those of us who drive the lower-end models, the alternating light and dark bands are often distinguishable. Although they could be considered part of the decor, the moire pattern is the result of uneven rolling of the headliner cloth prior to dying.

Mack Johnson, field service and installation engineer for D.R. Kenyon (Bridgewater, NJ), solved the problem using a precise motor speed control device, Microspeed, from Drive Control Systems, a unit of Electro-Sensors. Microspeed acts as a "smart speed-pot," or potentiometer, for ac and dc variable-speed drivers to trim tension. This closed-loop system is especially useful for wind and unwind applications where specific parameters, such as line speed, web tension, and roll diameter, need to be monitored and the data used as inputs to determine the correct following speed.

The dyeing of headliner material is one such application. Textile manufacturers wind the uncolored material onto hollow, perforated cores. After winding, dye is forced into the core and out through the material. If the fabric isn't wound at a constant tension, the finished product looks like a tie-dyed tee shirt. The take-up roll, a large metal cylinder, resembles an empty toilet paper roll. Without fabric, it may be only 18 inches in diameter. After taking up the cloth, the roll expands to 48 inches. To maintain correct tension and surface speed, the winding speed of the core must slow as the fabric roll diameter increases.

"It is difficult to maintain tension Bona center hyperbolic winder when the core is slowing down as more fabric is added," says Richard Sabol, head electrical engineer at D.R. Kenyon. "We found an easy way to do something very difficult with the Microspeed."

"We can make a motor precisely follow another motor anywhere," says Brad Slye, president and CEO of Electro-Sensors Inc. Microspeed acts like the cruise control in a car with one major difference: Cruise control works only in the master mode while Microspeed typically works in a follower mode. "Instead of setting the cruise control at a set speed, the cruise is programmed to match the exact speed of the car in front. If it slows down, you slow down. If it speeds up, you speed up, while maintaining a constant distance of two car lengths," says Slye.

The web tension required by the headliner fabric will vary depending on material thickness, weight, and type of fabric. "We chose Microspeed because of the diversity and ease of changing parameters," says Johnson. "Microspeed allows the operator to change up to 50 different input variables with the touch of a keypad. Other systems are more difficult for in-house people to operate."

The Microspeed is easily programmed just like your microwave oven, with a color-coded keypad and displays that feature both numbers and names. Slye says, "I knew we had it right when my four-year-old could program the device, and he can't read." There is also an additional display that shows what variable is being changed, with arrows to scroll through all possible parameter changes.

Usually fabric wind-up machinery requires a smart drive, plus a tension control as well as a load cell to maintain speed and web tension. "[Microspeed] gives all start and stop features in one unit," says Johnson. "I don't know of another device on the market that is a closed-loop system with tension control."

"Our biggest engineering challenge," says Slye, "was trying to integrate all of the solutions into one box."

To wind the headliner material at the proper tension, the Microspeed uses encoder feedback to obtain the line speed and surface speed of the core. These encoders are similar to the magnetic wheel speed sensors used in the cruise control of a car. The lead encoder, by definition, is the one to follow. It provides the actual line speed, or how fast the cloth is entering the process; typically measured in feet/minute or yards/minute. The feedback encoder gives the surface speed of the building core, which should closely track the incoming lead line speed of the material. The Microspeed monitors the lead encoder and controls the speed of the motor that drives the wind-up roll to match the line speed. The Microspeed verifies the roll is winding at the correct speed using feedback from the surface speed encoder on the roll. A shaft mounted on load cells is used to measure the tension of the cloth web. The load cells translate the tension in the web to a 0 to 10V analog signal. The signal is fed to the Microspeed. An operator programs the desired tension into the motor control device. As the fabric is wound, the Microspeed simultaneously examines the lead line speed, the web tension, and the surface speed of the roll and adjusts the rate of the take-up core to maintain the programmed tension.

The Microspeed replaces the manually operated potentiometer used for setting the desired speed of the drive. A 16-bit controller from Intel serves as the microprocessor. Because the system is completely digital, it is not DSP based. No analog conversion is required.

Additional details...Contact Brad Slye at Drive Control Systems, (800) 323-0504

Other Applications

- Extrusion

- Metal processing

- Textile processing

- Wire drawing and traverse wind-up

- Sheet rock curing lines