Machine Safeguarding and Presence Sensing Devices

Machine safeguarding, presence sensing devices control machine operations and protect personnel by detecting the presence of objects that could interfere with or be harmed by machinery. Activating a machine safeguarding, presence sensing device sounds a warning, ends a process, initiates a different machine action, or stops the machine altogether. Several types of devices are commonly available. Area guarding systems are used to monitor large areas such as shop floors. By contrast, perimeter guarding devices are designed to monitor the edges of machines. Door and gate guarding devices prevent employees from entering restricted areas, typically during machine operation. Process protection devices are used to protect personnel during equipment service and maintenance. Machine protection devices are used to monitor and guard operators during normal machine operation. 

Machine safeguarding, presence sensing devices use many technologies. Contact strips and bumpers contain pressure-sensitive edges that stop the machine when contact is sensed. By contrast, emergency stop (e-stop) switches are activated by pushing a button or flipping a switch. Cable pull switches are also available. RF presence sensors transmit a high frequency signal that, when disturbed, stops the machine or process. Similarly, ultrasonic sensors use high frequency sound to monitor processes or machines. Laser presence sensors are used to sweep large areas and detect foreign objects. Safety mats are suitable for guarding the floor near a machine or robot. Light curtains use a photoelectric transmitter to generate multiple beams of light. When an opaque object interrupts one or more beams, the light curtain controller sends a stop signal to the guarded machine. Safety gates are movable barriers that protect operators before the machine cycle can be started. Intrinsic safety (IS) barriers are devices that limit the current, voltage, or total energy delivered to a sensor in a hazardous area or flammable environment. Safety relays differ from conventional relays in that they have force guided (positive driven) contacts. Safety interlock switches are available in a variety of form factors and with both contact and non-contact activation. 

Machine safeguarding, presence sensing devices are used with many different types of equipment. Examples include augers, presses, balers, cutters, crushers, rollers, mixers, drive shafts, conveyors, and feed systems. Some machine safeguarding, presence sensing devices meet machine safeguarding requirements from the U.S. Occupational Safety and Health Administration (OSHA). Other machine safeguarding, presence sensing devices comply with the B11 series of safety standards from the American National Standard Institute (ANSI). For example, the ANSI B.11.1.-2001 machinery safety standard covers mechanical power presses. 

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