Pressure sensitive safety edges and safety bumpers are machine safeguarding devices that sense changes in pressure. They are made of flexible materials and attach to the edges of moving parts such as machine tables or powered doors. When a moving part that includes a safety edge or safety bumper strikes an operator, conductive plates touch and the output relays in the controller are de-energized. In turn, a stop signal is sent to the machine. Safety edges usually consist of an aluminum rail, safety contact, and rubberized contact strip. The contact strip protects the safety contact from damage and allows actuation angles to exceed 90°. Safety bumpers are similar to safety edges, but are coated with polyurethane to protect objects that come into contact with the bumper. Pressure sensitive safety edges and safety bumpers are used mainly in applications where a machine operator or setup person requires easy, continuous access to an e-stop device. 

Types of Contact

Pressure sensitive safety edges and safety bumpers use two basic types of contacts: normally open (NC) and normally closed (NC). Most suppliers list contact specifications such as maximum current rating, maximum AC voltage rating, maximum DC voltage rating, and maximum power rating. Positive-break contacts are normally closed electrical contacts which, upon actuation, are forced open by a non-resilient, mechanical drive mechanism. In the event of a mechanical failure such as the breakage of a spring or weld, the contact point remains in an activated position. Some pressure sensitive safety edges and safety bumpers are chemical, moisture, or impact resistant. Others are certified by Underwriters Laboratories (UL) or bear the CE Mark. 

Selection

Selecting pressure sensitive safety edges and safety bumpers requires an analysis of performance specifications, mounting styles, physical dimensions, and terminal styles. Performance specifications include minimum actuation force, mechanical life, and response time. There are three basic mounting styles: flat channel, angle channel, and straight-flanged channel. Physical dimensions for pressure sensitive safety edges and safety bumpers include length, height from base, and width. Terminal type and terminal exit method determine the terminal style. Cable glands, wire leads, and wire terminals are common terminal types. Terminal exit methods extend a lead from each end, two leads from the same end, or both leads from the bottom of the device.


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