Light curtain apparatus

In a three dimensional cartesian space having mutually orthogonal x, y and z directions, a light curtain apparatus for generating a relatively broad, relatively thin light curtain, lying in a single plane, from a relatively narrow, relatively thick light curtain, and for directing said generated light curtain through a monitored region, the apparatus comprising:

• means for projecting a light curtain in the x direction, said light curtain having a width extending in the z direction and a thickness extending in the y direction;
• a plurality of strip mirrors, arranged one strip mirror behind another in the x direction at an angle to the x direction, each strip mirror being laterally displaced in the y direction relative to a preceding strip mirror, each strip mirror reflecting a full width of the projected light curtain but only a portion of the thickness thereof through an angle of substantially 90 degrees into said z direction, forming thereby a plurality of reflected light curtain portions arranged in a row extending in the x direction, each said reflected light curtain portion being laterally displaced in the y direction relative to a preceding reflected light curtain portion, a total width of a row of reflected light curtain portions in the z direction corresponding to a width of said projected light curtain multiplied by the number of said strip mirrors;
• a plurality of strip-like deflecting mirrors, each said deflecting mirrors extending in the x direction;
• a respective strip-like deflecting mirror being associated with each said strip mirrors;
• said strip-like deflecting mirrors being arranged in planes parallel to one another and displaced in the y direction in the manner of said strip mirrors, said striplike deflecting mirrors having no displacement in the z direction;
• each said deflecting mirror having a normal to its surface, each said normal forming a respective angle of 45 degrees with the z direction, and in a plane parallel to a plane defined by said y and z directions;
• and
• whereby said deflecting mirrors deflect individual reflected light curtain incident thereon, which are displaced in accordance with the displacement of the first said strip mirrors, into a common plane parallel to a plane defined by the x and y directions, for transmission through said monitoring region as said relatively broad and relatively thin light curtain, thereby eliminating displacement of the reflected light curtains resulting from said lateral displacement of said first strip mirrors.