| 摘要 |
784,328. Photo-electric protective devices. GENERAL ELECTRIC CO., Ltd. Dec. 9, 1955 [Dec. 10, 1954], No. 35835/54. Class 40 (3). A photo-electric machine guard arranged to prevent the machine being operated when any part of the operator's person is in danger comprises light curtains arranged to extend outwardly in front of the machine both above and below the danger zone, the machine being rendered inoperative only if both light curtains are interrupted. As described each curtain 2 comprises a plurality of beams of light arranged in a substantially flat horizontal plane extending outwardly from a point just in front of the machine. Each of the beams originates at a light source in support-member 4 on one side of the forward extension of the danger zone and is directed on to a photo-sensitive device in support-member 5 on the other side. The curtains are not necessarily parallel but may be flat or curved planes approaching each other in the direction away from the machine. The guard of the present invention is preferable to the provision of a vertical guard curtain immediately in front of the machine as described in Specification 717,399, where the work projects from the front of the machine. In the case of a machine operating on a projecting sheet of material movement of the sheet to interrupt either the upper or lower curtain of the guard according to the present invention does not stop the machine but interruption of both curtains by the operator's body does so. It may be arranged that the outermost light beam of one of the curtains acts as a master and that interruption of this beam alone renders the machine inoperative. In order that the operator may be reasonably near the machine when it has completed an operation the movement of the machine may progressively switch out of circuit the photo-cells associated with the parts of the curtains furthest from the machine. Guards according to the present invention and also as described in Specification 717,399 may be provided on the same machine and a changeover switch provided so that the operator may choose which is in use. Means as described in Specification 664,797 and 717,399 may be provided for checking the operation of the safety arrangements. |
