Anti-Maim

Fiber optics employed in interlock switch

Whether one sees OSHA as a hedge against spiraling employee insurance rates or as a bunch of meddle-some government busybodies, their efforts have at least contributed to a reduction of serious injuries in the workplace. They have also given rise to a segment of the switches and sensors markets, for components that prevent machine operation until hands and heads are out of harm’s way. These devices range from dead man switches and pressure-sensitive mats, to light curtains and interlock switches.

PICO-GUARD, recently unveiled by Banner Engineering, Minneapolis, MN, is a system designed as a direct replacement for the mechanical safety interlock switch. Besides removing the possibility of mechani-cal failure of a switch, PICO-GUARD also eliminates the need for electrical current to be routed into a ma-chine’s hazardous areas — instead, the system substitutes durable fiber optic cables, running from an opti-cal controller to one or more doors, gates or hard guards. The controller has four separate optical channels, which in turn can each control multiple optical switches in the same optical network. Additional interlock switches can be quickly added to any channel simply by inserting them into the fiber optic loop for that channel. On large complex machines, each channel can control a separate zone of doors, entry gates, guards, etc.

The operation of the optical system is similar to that of a mechanical interlock — when the system de-tects a break in the optical beam (absence of signal, which may occur with a guard or door movement) or when the system receives a safety stop request, it sends a stop signal to the machine’s control circuit. The system’s receiver has two solid-state safety outputs to control 24 VDC loads, or it can control forced-guided relays to provide isolated contacts. A Universal Safety Stop Interface (USSI) allows two or more PICO-GUARD controllers to be connected to control a single machine when required. In addition, the in-terface permits other safety devices such as light curtains, E-Stop buttons and rope pulls to be connected to the controller, making it easy to integrate many safety functions into one controller. Each controller has two of these very useful input connections — one latching output with manual reset and a trip output with auto-matic reset.

PICO-GUARD is designed to meet ISO 13849-1 (EN954-1) Category 4 requirements. Due to a diverse-redundant, self-checking photoelectric engine specifically designed for use with plastic fiber optic cable, a single switch point per door will meet Safety Category 4 applications. The optical safety interlock switches install instantly with a snap-lock connector, and are available in a variety of configurations including straight, right angle, and a dual lens model with a passive opposed actuator. The PICO-GUARD controller is also designed for fast installation using plug-on wiring terminals.

—RM