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.
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