Servobrake hangs tough

Tuesday, September 14, 2000

Beaumont, TX--A designer and builder of robotic gantry systems, C&D Robotics Inc. once used only electric brakes, but they failed to meet emergency-stop and dynamic-braking requirements. So the company approached Nexen Group Inc. (www.nexengroup.com) for a solution. Nexen offered a solution with its Eclipse Servo Brake.

"Prior to installation"," explains Joey Glenn, C&D Robotics Director of Mechanical Engineering, "we needed to modify the brake flanges to accept Indramat MKD-series servomotors and mount onto a NEMA-flanged gear reducer. And we couldn't use our electric brake as a dynamic brake. Nexen sized an Eclipse brake for us to provide the dynamic braking we needed and accommodated our gearhead interface requirements."

One application is C&D Robotics' multi-line palletizer, which uses a gantry robot to service up to 24 pallet stations. Gliding along a three-axis gantry system, the robotic arm picks, moves, and stacks a variety of finished products onto pallets. C&D required the brake mounted between a servomotor and a 145TC-flanged gearbox to perform a dynamic stop within five seconds of the gantry moving in the x-axis. The 18-ft-long gantry travels at 120 inches/sec and carries a 3,500-lb load. The driving/stopping forces are driven through a 40-tooth, 14-mm pitch sprocket.

According to Nexen Senior Technical Representative Edd Brooks, electrically-released brakes would overheat and exhibit torque fade in this application because they must continuously expend 15-20W of power through the coil to pull the springs back and keep the brake disengaged.

"In contrast, the Eclipse brakes are a spring-engaged, air-released design unique to the marketplace," says Brooks. "It's the most efficient way to brake servos." The efficiency comes from a small amount of compressed air dead-ended into a cylinder which remains static until the air releases to engage the brake. Air is introduced again to disengage the brake.