A consolidated approach to sourcing AC drives has allowed Texwrap Packaging Systems to gain improved timing accuracy, reliable torque at low speeds, programming simplicity, and cost savings in its 1809 Series of shrink wrappers.
Previously, the firm used AC drives from as many as three different suppliers. Now all AC drives come from Hitachi. In the 1809 SS Model, for example, six Hitachi AC drives are used: four on the conveyor belts that feed product through the wrapping station, one on the film unwind, and one on the film scrap rewind. The Rockwell Allen-Bradley Contrologix controller that governs logic and motion throughout the machine sends an analog signal to the drives to coordinate the speed at which they drive their associated AC motors.
“The Hitachi drives deliver greater accuracy in keeping all the belts timed properly,” says Brian Stork, chief engineer at Texwrap. “From belt to belt, all the speeds are exactly the same.
“These drives are also better at maintaining torque at low speeds. Other drives operate on volts per hertz. They send a frequency to the motor, and ideally it follows that frequency. The problem with volts per hertz is that at low speeds, the motor can stall and slip, so it doesn’t maintain its torque.
“A Hitachi drive relies on sensorless vector control instead of volts per hertz, so it monitors the motor as it’s spinning and compares that speed to what the proper speed should be. If the drive sees the motor is lagging or stalling, it delivers more current to the motor to keep it at the accurate speed.”
Stork also says the switch to Hitachi drives has brought benefits on the software front. “Share-ware” software, he says, simplifies programming because readily available off-the-shelf programs “can be dumped in and we’re off and running.”
Simpler software brings cost savings, says Stork. Additional savings accrue, he adds, because buying of AC drives is now consolidated with one supplier.
