In the world of control and automation, technological milestones are not always recognised as they occur but become glaringly obvious with the passage of time, such is the power of hindsight. One such milestone occurred in the early 1970s when reliable and affordable photoelectric sensors and inductive proximity devices became the accepted replacements for mechanical switches.
These sensors offered faster, more reliable switching capabilities and, as is now widely recognised, played a significant part in revolutionising the automation industry. This concept of eliminating mechanical switches and all the inherent problems associated with them, though widely used in standard applications, was never developed for the machine safety market.
Now Turck Banner believes that its US parent company, Banner Engineering, is set to create a milestone that is as significant in the history of machine safety as mechanical switch replacement was for standard applications in the early 70s.
As part of their very comprehensive machine-guarding programme, Banner Engineering have introduced Pico-Guard, a new fibre-optic safety system that directly replaces mechanical safety interlock switches to safeguard potentially dangerous machines. This combination of control-reliable, non-contacting photoelectric and fibre- optic technologies provides a low-cost alternative to cumbersome and costly methods of machine safeguarding.
This new concept in safety systems is versatile, efficient and easy to install. It combines a controller and various plug-in, snap-lock Pico-Guard optical safety interlock switches and plastic fibre-optic cable to monitor doors, gates, and hard guards.
The system eliminates the need to run electrical wiring to the machine or hazardous area. Durable fibre optic-cables can be easily routed to multiple machine guard points or hazardous areas, making conventional copper wires that carry electrical current to the guarded points no longer necessary.
Especially significant, is the flexibility of the system thanks to its advanced optical controller. This includes four separate optical channels. Each of the four channels can control multiple optical safety interlock switches in the same optical network. Additional optical safety interlock switches can be instantly added to any channel simply by inserting them into the fibre-optic loop for that channel. If desired, each channel can control a separate zone of a machine such as doors, entry gates, guards, etc.
Regardless of the optical safety interlock switches used, when the system detects a break in the optical beam (absence of its signal) such as the opening of a door, or receives a safety stop request, it provides a stop signal to the machine control circuit to protect personnel from hazardous equipment.
However, the system does allow for some degree off mechanical tolerance in hinges, door alignment, etc, thus preventing nuisance tripping. In addition to personnel protection, the system can protect equipment, critical tooling, or other critical materials in process. The receiver has two solid-state safety outputs to control 24V dc loads alternatively it can control forced-guided relays to provide isolated contacts.
Additional flexibility is provided with the patent-pending Universal Safety Stop Interface (USSI). It allows two or more Pico-Guard controllers to be connected to control a single machine when required. In addition, this interface permits other safety devices such as light curtains, E-Stop buttons and rope pulls to be connected to the controller. Each controller has two of these useful input connections, one latching output with manual reset and a trip output with automatic reset.
Pico-Guard is ISO 13849-1 (EN954-1) Category 4 approved. This guarding method has been designed so that a single switch point per door will meet Safety Category 4 applications, an industry first. This is possible due to its patent pending, diverse-redundant, self-checking photoelectric engine specifically designed for use with plastic fibre-optic cable.
In addition, the hardware and firmware of the controller have been extensively tested via rigorous Failure Modes and Effects Analysis (FMEA) techniques to ensure that no single system component failure will create a fail to a dangerous condition. The product is approved to IEC 61496. Moreover, the fibre-optic light principle means that it is intrinsically safe and has ATEX approval for use in Zone 1 hazardous areas.
Pico-Guard 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.