Limit Switch System for Robot Use

Balluff, Inc.ot Base Limit is designed to allow employees to work safely alongside their automated mechanical counterparts. The new system fits to the base of the robot, monitoring the robot's angular position about its vertical axis. Used in conjunction with an employee-monitoring safety mat or light curtain, it cuts power to the robot only if the robot attempts to move outside its user-defined workzone when operators are present, and mutes the safety devices while the robot operates within its designated workzone.

Adaptable to a wide variety of robots, the base limit system can monitor up to three zones and is adjustable to provide 15° to 180° of robot workzone. An alternative to robot-sensing light curtains, the system is designed to withstand the rigors of industrial applications for robots used in manufacturing, assembly, and welding operations. The system implements dynamic restricted envelope per ASME R15.06-1992.

The system features a mechanical limit switch assembly that mounts to the stationary base of the robot, a slotted aluminum circular cam tray that attaches to the robot's rotating flange, and switch-actuating circular cams that mount on the trays at rotation boundary locations. The cams, adjustable in 7.5° increments, trip the mechanical switch if the robot rotates beyond the defined workzone.

The mechanical limit switch assembly is a double-changeover switching system made up of six limit switches actuated by stainless steel plungers. Each limit switch has a repeatability of ±0.02-mm. Positive-break, force-guided contacts are rated for five million operations. The switch assembly has an anodized aluminum housing sealed to IP65 and can tolerate temperatures ranging from -5° to 80° C.

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