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.