Safety with Flexibility  
Dynamic envelope restriction gives the robot cell designer the freedom to allow coordination between robots and humans within the same physical space. This flexibility can help improve workflow and reduce floor space requirements while maintaining the highest degree of personnel safety. The key is diverse complementary redundant operation.

Function
The Zone Limit System provides a control-reliable means to interlock light curtains and safety mats with the angular position of the robot. While the robot is clear of the operator area, the cell controller mutes the output of safety sensors, allowing workers to access part of the robot cell without stopping the robot. When the robot enters the operator zone, the light curtains and safety mats are re-enabled. If a worker is present in the operator area, robot servo power is interrupted until the person leaves the area. If no worker is present in the operator area, the robot is free to move about and perform tasks in that area until someone re-enters the controlled space.
 
Features

• Monitors up to three independent work zones with a six-channel cam system
• Robot work zones configurable from 15° to 345° in 15° increments
• Implements dynamic restricted envelope per ANSI/RIA R15.06-1999
• Addresses need for Category 4 control reliability
• Safety limit switches designed to VDE 0113
• Limit switch housing sealed to IP67
• Conforms to General Motors’ Global Common Technical Specification for Production Robots RS-1, Section 3.10.3 "Zone Limit Switches/Dynamic Limiting Devices“

Design
The system is composed of a heavy-duty mechanical cam switch assembly that mounts to the stationary base of the robot, a rugged circular cam tray that attaches to the robot’s rotating flange, and hardened circular cams that mount on the cam tray at rotation boundary locations.

Each zone is monitored by a pair of switches tripped by a pair of complementary cams covering the full 360° of the robot’s range of motion. A single point fault in any part of the system will not compromise the safety function:

• Missing cam(s)
• One cam overlapping the other
• Open/short circuit
• Welded contact
• Stuck plunger
• Switch disconnected

The long-life mechanical cam switch assembly is a double-changeover switching system made up of six limit switches actuated by solid stainless steel plungers with high-speed ball-bearing rollers. Positive-break, force-guided contacts to VDE 0113 are rated for five million operations. The switch assembly has an anodized aluminum housing sealed to IP67 and can tolerate temperatures ranging from -5 to 80°C. Connector options range from rectangular Harting to circular Brad Harrison styles.

Precision-manufactured, hardened and hard chrome plated cams are designed for long-wearing durability.

Contact Balluff Applications to discuss your requirements. Balluff has pre-engineered, kitted solutions for many popular robots from Fanuc, Motoman, and Nachi.