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A safety light curtain can be used on a machine or in a production plant in the same way as a hatch or door. There are great differences though when it comes to the component installation and functionality. When a light curtain is mounted on a hazardous machine, we are not only concerned with the response times of the safety systems, but also the Depth Penetration Factors. It is possible for the operator's fingers or hands to pass through the light curtain a certain distance before being detected. This becomes the Depth Penetration Factor. This distance must also be entered into the Minimal Safety Distance Calculation for the machine.
It is also very important that the level of safety of the light curtain with dual supervised outputs be continued throughout the rest of the stopping control circuit. Even valves and contactors, which ultimately control dangerous movements, normally have to be redundant and monitored.
Automatic Machines
For light curtains on automatic machines there shall be a reset function which is active when the machine is set for automatic production, whether or not it is a passable protection. After an engagement one must first use a reset function, then the restart of the cycle should be made with a separate starting device. The same reset applies for machines with semi-automatic drives.
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Light Curtains on Presses
Light curtain applications are often categorized by the type of guarding required. Protecting an operator from the hazards associated with material positioning or where a process is performed is called Point of Operation Guarding. The point of operation is often called the Zone of Hazardous Operation or the Pinch Point. This type of guarding is associated with mechanical and hydraulic power presses, molding presses, stamping, forming, riveting, eyelet and automated assembly machinery. Light curtains used in these applications are typically selected for finger and hand protection.
Operator Protection during Manually Serviced Machines
With manually operated machines where one or more operators move parts in and out between every cycle. This type of application is the most risky because the number of engagements into the machine's dangerous area is often several times per minute.
Reset
On the servicing side (i.e. the side or sides where there is an operator who moves parts in and out) there shall be a separate reset function for the light curtain. If there are several light curtains (e.g. on the front and back) there shall be one for each. If the light curtain is actuated during a dangerous movement the press should not be able to restart without being reset. During engagement after the end of the cycle no reset is needed.
For a light curtain which is placed as protection on both sides which are not servicing sides, there shall be a reset button which always needs to be activated after an engagement.
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