Product category:
Machine Safety Components
News Release from: Schmersal UK | Subject: Man-machine safety systems
Edited by the Engineeringtalk Editorial
Team on 30 May 2000
Working safely with machines
In this article Terry Hayward, general manager of Schmersal UK Ltd, discusses man-machine safety and the options available.
The area around manufacturing robots, automated handling machines and machine tools will always be hazardous and a potential threat to operator safety To reduce the risk of accidents, it is essential that engineers analyse carefully the safety implications and specify the most appropriate protection measures
This article was originally published on Engineeringtalk on 30 May 2000 at 8.00am (UK)
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Traditionally, a mechanical fence with switches fitted to opening doors and gates, is the first solution to be considered.
However, it may also be the most expensive, take up a great deal of space and reduce operational flexibility.
Access to the various zones in modern processes or machines, cannot be categorised as simply 'allowed' or 'disallowed'.
The designer needs to allow for variables, dependent on the stage the machine or process has reached in its operating cycle.
To accommodate variables there are other, often more appropriate, safety solutions - such as safety mats, safety laser scanners, safety light barriers and safety light curtains - that should be considered as alternatives to mechanical switches.
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The following notes explain the functionality and features of the latest tactile and electro sensitive devices and should help plant engineers evaluate their performance against traditional mechanical components.
Safety Mats - Simple, reliable security without fences or doors: The safety mat is a tactile device that offers a simple yet flexible solution to machine safety.
Their robust design combines reliability and long mechanical life with a non-slip and chemical-resistant surface.
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Available in different sizes, safety mats are designed to provide operator protection around moving machinery such as industrial robots, stamping and woodworking machines.
They are sensitive enough to detect a single person and robust enough to carry the weight of a forklift truck, and either will be detected immediately.
Tactile safety mats consist of two separated electrodes (steel plates) which are held apart with insulating strips.
Electrode strips located between the two steel plates cause an electrical short circuit when the pressure sensitive mat is activated.
A safety-monitoring module evaluates the signal and switches off the machine movement.
Safety mats comply with safety requirements up to Category 3 of EN 954-1.
Opto-Electrical Devices - a non-intrusive approach to machine safety: The main advantage of most optical devices is that they can be programmed to allow access to machinery at specific times during the process and in specific areas.
This important facility allows designers to tailor a safety system to particular hazards, whilst allowing the machine or process to operate at its maximum capacity.
When compared to machines fitted with standard mechanical guarding, the increase in efficiency can greatly improve the profitability of the process.
Opto-Electrical safety devices fall into three main categories - laser scanners, light barriers and light curtains.
They provide the highest levels of safety without obstructing normal machine access or impeding productivity.
Safety laser scanner: Similar to a radar system, the laser scanner is a flexible and powerful device that is able to continuously scan a 180§ detection zone up to a maximum radius of 60 meters using a beam that is absolutely safe and harmless to the operator.
Safety zones and warning zones can be user-defined.
When a safety zone is entered, the scanner detects the person or object and machine motion is immediately stopped.
When a warning zone is entered, the scanner issues a warning signal to prevent inadvertent machine stops.
The laser scanner can also be used to detect objects or as the sensor for an automatic transport system.
Safety light barrier: Light barriers are designed for use as entry controls or movement detectors.
They are ideal for guarding: powered windows, doors and gates; danger zones in conveyor systems; printing, packaging and paper-processing machinery; storage equipment and machinery; elevator platforms; and palletising, stacking and production machinery.
Any interruption of the safety light barrier produces a signal, which stops dangerous machine operations.
Light barriers can be used as perimeter guards or as direct guards for smaller danger zones on a machine.
They ensure perfect safety without restricting the production process or reducing productivity.
Their small size means that light barriers can be installed almost anywhere without interfering with machine operations.
Light barriers comply with safety requirements up to Category 4 of EN 954-1 and their light beams are infrared and invisible.
Safety light curtains: Using a master/slave configuration, a series of cascading safety light curtains can be created to protect operators of equipment such as power presses, industrial robots, welding machines and many more.
Under normal circumstances, when the light beam of the curtain is interrupted a signal is triggered to switch off the machine.
However, where the process requires it, curtains can be programmed to allow the light beam to be interrupted without generating a stop signal.
Light curtains comply with safety requirements up to Category 4 of EN 954-1.
Schmersal specialise in man-machine safety systems and offer a range of approved safety products for applications described in this article.
Further information is available on interlock switches, safety limit switches, sensors, monitoring and control devices, safety mats, light curtains, light barriers and laser scanners, to allow process engineers to make an informed decision on individual installations or a comprehensive machine safety strategy.
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