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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