Why the Servo Motor Transformed (and Will Continue to Transform) the Converting Industry
Necessity is the mother of all invention, and the story of adding servo motors to converting machines serves as a perfect example.
What was once considered a big gamble has now become the standard for achieving extremely tight tolerances. To understand how servo motors revolutionized converting, we tapped the expertise of the pioneer Dave Schiebout, President and CEO of Delta ModTech.
What is a servo motor and why is it so beneficial to the converting industry?
For a straight-up servo motor definition, we turn to Wikipedia’s entry: “A servo motor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration.”
The “precise control” was what attracted Dave Schiebout to servo motors. Back in the early ‘80s, his company, Delta Industrial, was a retrofitter of small mills and lathes in the machine tool industry. The bulk of his work involved installing computer controls on manually-operated machinery.
One day, he received a call from a large materials converter. They were struggling to get a project through FDA approval, and needed some help achieving a tight tolerance. “I suggested we take off all the mechanics on the machine,” Dave recalled. “All that inaccuracy caused by mechanical tolerance, temperature changes, and wear in the mechanical drive system can affect the performance.”
Dave and his team stripped out all the mechanics, and installed servo motors. Accuracy improved by 25 times, even without a sophisticated control. The light bulb went off, and Dave realized there was a whole new world of opportunities for converters in search of tighter tolerances.
It’s the self-contained nature of the servo motor that allows for its success with tight tolerances. Schiebout knew that moving away from the mechanical approach, where the machine is driven with backshafts, gears, pulleys, and belts, would allow for improved accuracy. But no one believed him.
“They just didn’t think it would work to have a machine with individual servo motors,” he said. They also didn’t understand how a servo motor differs from a conventional motor.
Servo Motors Basics: The Difference Between a Motor and a Servo Motor
A DC (direct current) motor consists of two continuous rotation motors. When power is supplied, the DC motor will spin until the power is removed. The speed is controlled using pulse width modulation, and the cycling of the power controls how fast the motor spins.
A servo motor includes an electric motor and an encoder or position-sensor. Unlike the DC motor, the servo motor doesn’t rotate freely. A control signal provides an output position, and an amplifier applies power to the motor until the shaft finds the correct position based off of feedback from the encoder. Duration, not speed, of the positive pulse will determine the position of the shaft.
It’s noteworthy that once the servo motor is in position, it will hold the position, even if external forces push against it. That’s why Schiebout knew the servo motors would work as a solution for his customer.
For Converters, the Servo System Control Makes All the Difference
What is servo control? A servo motor has its own individual servo system control that allows you to control the motor independently of other motors.
In the converting process, where there can be multiple segments of a web run with different die cuts, the ability to adjust the modules independently of each other allows the cut location to be changed or corrected, quickly. The machine can make precise cuts even when the eyemarks are inconsistent.
The individual servo control at each die station also allows for another critical factor in web converting: Precise tension control. Each die, nip or print station can be set at a different speed ratio to allow for the creation of tension zones with the press of a button.
Servo Motor Accuracy Comes With Longevity Bonus
Schiebout’s reluctance to pursue a mechanical approach wasn’t just based on accuracy. It was also based on longevity and scalability.
Mechanics, over time, wear out. The gears wear. The quality of the big motor driving the crankshaft and the pulley that drives the rotary die degrades. With the servo motors, individual motor failures don’t affect the machine as a whole.
They also dramatically improves the lifespan of a machine. Some machines Delta ModTech installed back in the early ‘90s continue to hum along. In fact, because there are new updates to the software driving the servos and drive systems, the accuracy continues to improve.
Torque of Servo Motor Creating Future Opportunities
As the torque of the servo motor increases, so does the potential for the converting industry. Schiebout notes that every three or four years, new designs will emerge with better encoders or more pulse per revolutions.
“When we first started, servo motors would give us 20 percent more power. They had very high induction,” he said. “Now they will absorb 800 percent of power, so the performance is amazing.”
Yet every “improvement” in a servo motor shouldn’t be fully embraced until it has undergone rigorous testing. Whenever Delta ModTech switches brands or models of servo motors, it conducts two months of testing to see if the new servo motor measures up.
“We have our own testing that we put them through to see how they impact a rotary die cut,” he said. “We want to see if the servo motor can absorb the energy and keep the cut on the same path.”
Servo Motors Require a Human Counterpart
As much as servo motors have provided new opportunities in converting, it’s the engineers that know how to best apply the technology that make the difference.
It’s like any business. Everyone has access to the best tools, but the top performers are those that have the systems and the experience in place to implement effectively. Schiebout credits much of Delta ModTech’s success to focusing on supplying proven reliable systems and learning from mistakes.
With servo motors and technology in general evolving at a dizzying rate, the converting industry has both enormous opportunities and tremendous challenges. Let’s continue to push the envelope on innovation by seeing just where the miraculous servo motors can take us.