TechArchive

Original article date: June 1999

Like all products in the machine safety field, light curtains are developing fast and dragging legislation along with them. Alan Quinn talks to some of the major UK suppliers about recent news

As with all developing technologies, standards inevitably struggle to keep pace with capabilities. One concern expressed by many suppliers in the safety field at the moment is that the bureaucracy and inertia of standards committees means that the drafting of standards to cover technically advancing features will increasingly lag behind the capability to provide them.

Safety equipment is necessarily more complex than other industrial equipment because of the control reliability requirements. To achieve certification with the required regulations can be a long and costly exercise. Recent harmonisation of standards across Europe however, has made the process somewhat easier.

But what are the other changes going on in the market at the moment? A trend noted by MTE Turck is that more customers are now requiring suppliers to provide not just the light curtain, but also fixed guards, switches, two-hand control devices, emergency stop devices and interlocks, as well as installation. This will inevitably lead to a shake-up of the market.

According to Guardscan, the most rapid area of change currently is in the development of networked systems. Increasingly, at both machine and plant level, we are seeing the use of bus connected sensors, for both control and safety. Guardscan is active in the development of open system, safety bus protocols and standards, which are accessible to all manufacturers. The company believes that it is only through the development of internationally accepted, open (as opposed to proprietary) systems and standards, that the interests of the system supplier and end user will be best served.

The newest Guardscan light curtains handle demanding machine guarding applications with standard functions easily extended to provide important programmable features such as muting, beam blanking and reduced resolution. Such features allow for safeguarding areas where it is necessary to allow obstruction of the light curtain under controlled circumstances. For example, reduced resolution will enable work-piece ejection through the curtain, whilst maintaining body presence sensing.

Similarly, Smartscan has set up an option for multiple muted areas within the detection zone which can be defined by use of the Smartscan 6000 serial interface program Smartgram. In addition to the muted area, users can have floating blanking, which allows workpieces to move through the detection zone without halting the process. This can be of advantage on machines such as press brakes and wire-bending machines, where bending occurs and parts of the workpiece can pass through the light curtain

Erwin Sick’s view, as expressed by safety systems manager Graham Tarry, is that assessment of the application in order to determine the exact type of guard needed in each application is one of the many recommendations laid down by HSG 180. This, along with circuit interface and commissioning support ensures compliance with all relevant legal requirements. To ensure the integrity of an application, Sick provides application advice, circuit design, commissioning and stop time measurement of the installation free of charge.

Sick agrees that centralised monitoring and control is fast becoming an increasing requirement and has available a simulation CD showing the “obvious advantages” of fieldbus and its application to opto-electronic protection devices.

Sick’s FGS range of light curtains provides true finger or hand protection. “Host and Guest” options provide both trip functions and presence sensing. Also based on the FGS housing, perimeter protection is provided by the MSL range of guards. The range provides a rugged perimeter guard for up to 70m in distance, with beam options available as well as housing length. Once again, muting can be provided for entry/exit systems by external Din rail modules or integral to the light guard housing.

MTE Turck’s George Perkins also notes that the Health and Safety Executive’s guidance note HS(G) 180 has made it much easier and clearer for the end user and the supplier to determine the correct product for installation. In the past few years, this has been left wide open and the guidance should help in risk assessment.

Turck was also a pioneer of fieldbus and all its equipment is network-ready, making installation simpler and more reliable. Cabling is reduced and should modifications be required later, these are also easier. A major feature of Turck’s controllers is that they are “diverse redundant”. This means that, as well as providing self-checking control reliability, the different construction of duplication items ensures that a common fault cannot occur.

On the other hand, the Smartscan view is that none of the fieldbus protocols are safe enough for the control and interface of a safety light curtain or other Annex 4 safety devices. The company feels that the role of fieldbus is in control, status and monitoring of production processes rather than safety control. The company goes on to argue that no combination of fieldbus, PLC and I/O has been developed which can meet the safety integrity required of Type 4 light curtains as specified in the Light Curtain Standard IEC 6146, which has now been adopted as the norm as required in the Machinery Directive. Others may disagree. Smartscan also asserts that the only bus system suitable for light curtains is its own proprietary Smartscan 6000, although there are other major safety buses appearing, as Tommy Miller has been reporting in Safety First in this magazine each month.

OEM Automatic now has a stock of the new category 4 photoelectric safety barriers from Italian manufacturer Reer. The Argolux AS4 range is aimed at guarding presses and forming equipment, punching machines, shears and automated machine handling systems. Useful features include alignment indicators on the barriers and status LEDs on the barriers and controllers to assist with installation and indicate system status. The range comprises three resolutions of barrier ¡ 35mm, 55mm and multibeam for pedestrian access ¡ in protection heights varying from 185 to 1645mm.

Keyence has launched an expandable safety light curtain that allows the user to build up exactly the curtain coverage needed to provide optimal safety and adapt the system to meet changing conditions. The modular design of the PJ-V safety curtain means that elements can be snapped together to provide detection coverage zones from 140 to 1260mm. The optimal detection zone can be configured with up to seven expansion units in increments of 80mm to create a system with up to 15 levels. Operating range is up to 7m.

An incorporated LED bar indicator is used to provide an alignment guide. The number of illuminated LEDs confirms the signal strength and a colour change from red to green indicates optimal alignment. Cleverly, in operation, the same LED indicators are used to inform operators of the detection status in real time.

Honeywell has introduced the FF-SY A Series type 4 safety light curtain. This device offers a variety of safety sensing and control options. Typical applications include presence sensing, point of operation guarding and zone/perimeter guarding on metal forming, plastic forming, materials handling and light electronic assembly machinery and equipment.

Installation and troubleshooting are made easier thanks to a small size (42 x 55mm) and diagnostics which include signal strength, output status, failure and cross-talk indicators. The integrated cross-talk reduction system allows the scanning range to be adjusted for the application distance if emissions from other systems are detected.

Finally, Siemens has a new family of safety products under the Siguard banner, which includes light barriers. The company highlights extremely compact design as one of the key features.

• Erwin Sick: 01727 831121
• Guardscan: 01257 249777
• Honeywell: 01344 656000
• Keyence: 01908 696900
• MTE Turck: 01702 525186
• OEM Automatic: 0116 284 9900
• Siemens: 0161 446 5308
• Smartscan: 01536 401313

June 1999