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Integrated Motion in a Compact Package
Direct ac input delivers high force and torque
Karen Field, Editor-in-Chief -- Design News, September 10, 2009
Almost from the day Exlar introduced its Tritex DC
actuator, which is based on a patented concept of integrating roller-screw
technology into a servo motor to create linear motion and combining it with a
position controller into a compact package, the company says that design
engineers were asking for an ac version. In the general servo market,
approximately 90 percent of the drives are ac.
In April 2009, Exlar announced the Tritex II AC actuator. Available in a linear or rotary version, its designers say that the device delivers the highest power density and smallest footprint available in the market.
The actuator is available in 90 and 115-mm frame linear frames that allow forces up to 4,000 lbs continuous and 10,000 lbs peak and speeds up to 33.33 in/sec. Technical Services Manager Mike Wolfe says that comparable, rod-style versions of dc linear servo actuators are limited to light duty applications, typically under 500 lbf or speeds of less than 20 in/sec.
To achieve the high performance levels of the Tritex II, Exlar engineers took the 3-inch-frame dc actuator and integrated it into a 90-mm stator design (115-mm stator on the 4-inch frame). The fact that the ac unit is rated for 230V, which translates into a bus voltage of 325V dc (thereby requiring less amperage for the same power), was a major benefit, though design engineers wrestled with thermal management and size issues to optimize the design.
"Because we were building an amplifier that has three times the power of the Tritex DC, we had to increase the size of the bus capacitors and the ADC, and that took up a significant amount of the footprint," says John Walker, Exlar's VP of marketing and sales. Designers went through a number of iterations in the components to ensure there would be no waste from the power available from the 1.5 kW servo amplifier and components would be kept cool.
The Tritex II includes standard motion features, including analog following for position, torque or velocity, compound moves, move chaining and individual force/torque control for each move. Modbus communications is standard and gear ratios of 4:1 to 100:1 are available.
