Servomotors and drives speed robot performance

Feb. 7, 2001
Eliminating the gearbox means fast starts and high reliability.

A new controller and motor configuration allows high-speed handling of injection-molded parts.


High output torque in a compact, low-inertia design allows G400 Series motors to accelerate and decelerate rapidly, speeding part removal.


When it comes to high-speed handling operations, time is money. In plastic injection-molding operations, for instance, high productivity often depends on a fast, reliable robot to remove parts from the mold. Shaving a tenth of a second off the removal time can impact productivity significantly.

That was the focus for Automated Assemblies Corp., Clinton, Mass., in designing a new three-axis robot to remove parts from injection-molding machines. The company sought high-performance servocontrols to speed production and improve system reliability. The resulting design, leveraging high-speed brushless servomotors and digital servodrives from Moog Industrial Controls, East Aurora, N.Y., has reduced the part-removal time on a 50-in. vertical round-trip cycle (including a simultaneous 2-in. strip-stroke move) to 0.22 sec — a 21% improvement over previous designs.

To accelerate end-of-arm tooling that can weigh as much as 7 lb to more than 15 g, engineers used a direct-drive rack-and-pinion configuration for the vertical axis. Eliminating the gearbox allows designers to take full advantage of the servosystem's high-acceleration capabilities while boosting overall reliability. Also, without the backlash inherent with mechanical gearing, the system benefits from higher control-loop gains to minimize settling time. The direct-drive configuration cuts total system cost as well.

A motor with a custom winding and a high-power T200 Series digital servodrive control the vertical axis. Standard catalog motors and the L180 digital servodrive power the less-demanding traverse axes, further reducing system costs.

In this high-speed application, vertical movements are most critical to overall system performance. The vertical axis executes a triangular motion profile — switching from maximum acceleration to maximum deceleration. With a fully laminated low-inertia rotor, high-pole-count design, and high-grade SmCo magnets, the G400 Series motor features a high peak torque-to-inertia ratio which, in turn, delivers fast positioning. The vertical axis operates at a relatively low duty cycle (less than 10%) compared to the entire process, providing high overload capability and permitting the motor to deliver intermittent torque levels three times the continuous torque rating. The motors are available with integral holding brake and include a lightweight design to reduce loads on the X and Y axes.

The T200 includes digital control loops with high bandwidth response and advanced signal-processing algorithms to deliver high dynamics. A conservative thermal-management design, next-generation IGBT switching modules, and a multitiered fault-protection scheme combine to offer reliable operation in harsh industrial environments. Integral motion control, servoamplifier, brake relay, EMC filters, and fieldbus connectivity — all integrated within the compact enclosure — reduce wiring costs and free up valuable cabinet real estate. The Windows-based interface includes automated self-tuning, virtual oscilloscope, data logger, and system-diagnostics support to simplify setup and commissioning.

G400 Series motor specs
 
X, Y AXES
Z AXIS
Continuous stall torque (Nm)
2.6
26
Peak stall torque (Nm)
6.50
78.2
Nominal power (kW)
0.95
5.1
Maximum speed (rpm)
8,000
4,300
Inertia (kg-cm 2 )
1.55
19.4*
Mass (kg)
3.6
17.4*
* Data includes integral holding brake.

Information for this article was provided by Automated Assemblies, Clinton, Mass., and Moog Industrial Controls Div., East Aurora, N.Y.

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