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100-Percent Duty-Cycle Actuator
All-in-one actuator incorporates programmable digital drive and servo performance
Al Presher, Contributing Editor -- Design News, July 15, 2009
As a replacement for air cylinders, while also offering advanced linear motion capabilities, new integrated actuators are utilizing servos to guarantee a 100-percent duty cycle, enhanced performance and reliability.
The ICR Plus SmartActuator from Tolomatic offers machine designers a programmable, linear rod-style actuator for complex industrial applications. The unit integrates a digital drive, servomotor and actuator into a compact package for low- to medium-force applications. Designed to compete with air cylinders and traditional electric systems, the actuator can be built to order and ready to ship in five days from factory order.
"The heart of the ICR Plus is an integrated digital drive that provides the brains for the motor-actuator system," says Aaron Dietrich, electric products manager for Tolomatic. "It provides the user with flexible tools for programming a wide range of complex motion profiles, along with options for network communications including CANopen and DeviceNet."
Use of a servomotor, versus a stepper motor, was a design choice to achieve a 100-percent continuous duty cycle and better performance characteristics. The design also uses ballscrew technology rather than a solid nut or Acme screw to reduce friction. Dietrich says those solutions typically only provide duty cycles in the 30- to 40-percent range. Using stepper motor technology would result in an operating duty cycle of 50 percent or less, and problems generating the amount of force required for applications operating at higher speeds.
To compete against air cylinders and stepper-based systems, the design team looked carefully at costs and "design for manufacturing." The high thrust bearing that is normally part of the rod-style actuator is directly integrated into the servomotor, and the screw couples directly to the motor shaft. This approach reduces costs by eliminating the motor coupler and motor mount.
Two ball screw selections are available for the ICR Plus, providing up to 80 lbs of continuous force (150 lbs peak) for speeds up to 23 inch per sec, or up to 200 lbs continuous force (400 lbs peak) for speeds up to 9 inch per sec. Maximum stroke length is 24 inch.
To produce long service life, designers carefully analyzed the RMS or average thrust of target applications to predict expected life of the actuator in millions of inches. With the five-turn-per-inch ball screw operating at 400 lbs peak thrust, the estimated life of the unit is ten million inches. As the application requirements become smaller than the 400-lb peak thrust, the estimated life increases exponentially.
Dietrich says the peak thrust target was chosen to compete with two- to three-inch bore pneumatic cylinders. A three-inch bore cylinder at 80 psi can theoretically drive a 550-lb load but pneumatics typically build a 25- to 50-percent safety margin into their sizing calculations, which is close to the ICR design goal of 400 lbs.
Tolomatic also offers an ICR Basic model designed with dedicated functionality to complete as a direct replacement for pneumatic cylinders. Dietrich says the ICR Basic is unique because the servo drive is pre-tuned (no motor tuning required) and pre-programmed with limited dedicated functionality for simple air cylinder applications. No programming or software interface is required to integrate the unit into the machine.
Three potentiometers are used to independently adjust the actuator's extend speed, retract speed, and force output for push-and-hold applications. Acceleration and deceleration parameters are pre-programmed to create smooth controlled motion versus the typical "bang-bang" operation of an air cylinder extending and retracting against a mechanical stop. Dietrich says with most programmable actuators, users need a laptop computer to program the unit. If the air cylinder application requires very simple out and back motions, users can implement an electric actuator solution with the ICR Basic and not be required to learn new software.
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100-Percent Duty-Cycle Actuator
