Patent GB-1447688-A (GB)
Title: Shearing of sheet material
IPC: B21D43/28
Filed: 1973-10-03
Abstract: 1447688 Shearing; turning sheets CREUSOT-LOIRE 3 Oct 1973 [26 Oct 1972] 46191/73 Headings B3W and B3M Apparatus for trimming sheet edges comprises an edge shear, a roller table adjacent shear feed means for moving a sheet perpendicularly into the cutting plane of the shear and means for turning the sheet adjacent the shear through 180 degrees after trimming a first edge. As shown, Fig. 3, disc cutter 71 is movable along cutting line 72 in co-operation with a fixed cutter 71A. A sheet is fed on to a driven roller table 8 from a driven roller feed table (not shown) to the left side of table 8 as seen in Fig. 1. The sheet is backed against a gauging stop at the entry end of table 8 and rollers 83 are raised by hydraulic jacks to lift the sheet off rollers 81. The sheet is fed into the shear by at least gripper units 1 and 2, gripper units 3 and 4 also being used if the sheet extends that far. Grippers 12-42 of the units 1-4 are reciprocable vertically. When the sheet is correctly positioned, the roller 83 and a hold down are lowered and the cutter shears off the sheet edge. After the cut, the rollers and hold down are raised and the gripper units draw the sheet back until its axis coincides with the pivot axis of a sheet turner 14. Vacuum ducts 144 are mounted in pairs on respective brackets 143 and the brackets are pivoted about a horizontal axis extending longitudinally of the sheet to turn the sheet over. The sheet is fed again into the shear and the second edge is trimmed. To shear to a desired width K a sheet P with concave edges and long enough to use all four gripper units, the apparatus is operated in the the following manner. The desired width K is fed into a numerical control. The grippers 12 and 42 of units 1 and 4 respectively are moved to engage the sheet edge at points e<SP>1</SP> and e respectively. Grippers 22, 32 are then moved to grip the sheet at points i<SP>1</SP> and i. Coders 17, 47 record in two numerical control the difference between the distance from the cutting line 72 of gripper 12 and gripper 22 i.e. A-B, Fig. 5, and of gripper 42 and gripper 32, i.e. D-C, representing the divergence of the edge II from a straight line. The grippers 22, 32 are retracted. The grippers 12, 42 move the sheet forward, the coders 17, 47 recording in the numerical control the difference in the distances between the coders and the cutting line when the edge I passes over first detectors 19, 49 and then detectors 29, 39 i.e. E-F and H-G representing the divergence of the edge I from a straight line. The detectors are spaced from the cutting line by a safety distance r. The sheet is then withdrawn and feeding for the shearing operation starts. The positions of points e<SP>1</SP> and e relative to the cutting line 72 for shearing the edge I are calculated thus. The maximum widths L<SP>1</SP>, L of the sheet, Fig. 10, are determined by subtracting r from E and H. The values for the divergence from the straight of edge I, d<SP>1</SP>l, dl, and of edge II, d<SP>1</SP>2, d2, are subtracted from the widths L<SP>1</SP>, L to give the sheet width U<SP>1</SP>, U which it is possible to cut from the sheet P. The known desired width K is subtracted from the possible width to give values 2c<SP>1</SP>, 2c. Point e<SP>1</SP> is therefore correctly positioned for shearing of edge I when it is spaced from the cutting line by a distance I+c<SP>1</SP>+d<SP>1</SP>2 or L<SP>1</SP>-c<SP>1</SP>-d<SP>1</SP>l and point e when it is spaced by I+c+d2 or L - c - d2 If the sheet is only long enough for grippers 12 and 22 to operate no calculation is made of the divergence of the edges from a straight line. Grippers 12 and 22 move the sheet to a position in which the coders 17, 27 are ¢ (the desired width + the maximum width) from the cutting line. If the sheet to be trimmed has parallel sinuous edges the sheet widths can be determined solely from the divergence of edge II from a straight line.