Bag making machine

A bag making machine for making plastic bags from a web material comprising two or more layers of plastic film, said bag making machine including feeding means for feeding said material intermittently for a length along a longitudinal material feeding path, said material having notch means such as notch holes formed therein, and a cutter including cutting edge means for cutting said material along a predetermined line which extends in a direction transverse to the longitudinal material feeding direction and intersects said notch means whenever feeding of said material is temporarily stopped, to thereby successively make plastic bags, said bag making machine comprising:

• a light source disposed near and upstream of said cutter (6) on a first side of said material feeding path for directing a light toward said material, said light indicating a contour of said notch means when said light passes through said notch means;
• a detector opposed to said light source on the a second side opposite from said first side of said material feeding path for receiving the light passing through said notch means at a first point immediately before said material is temporarily stopped, to detect a first position of said predetermined line of said material and a second position of a reference portion of the material which is positioned upstream of said predetermined line in said material feeding direction at said first point, said detector recognizing said light passing through said notch means as an image data corresponding to the contour of said notch means;
• said material being then temporarily stopped at a second point after said feeding means further feeds said material by a remaining length segment fed from said first point to said second point, to detect a third position of said reference point of the material in said material feeding direction and a fourth position of said cutting edge means of said cutter at said second point in accordance with the contour of said notch means indicated by the light passing through said notch means;
• a computer connected to said detector having means for calculating a first distance between the first position of said predetermined line of said material and the second position of said reference portion of said material in said material feeding direction at said first point in accordance with detected data received from said detector, means for calculating a second distance between the third position of said reference portion of said material and the fourth position of the cutting edge means of said cutter in said material feeding direction at said second point in accordance with the detected data received from said detector, means for comparing said first distance between the first position of said predetermined line of said material and the second position of said reference portion of said material at said first point with said second distance between the third position of said reference portion of said material and the fourth position of the cutting edge means of said cutter in said material feeding direction at said second point, and means for subsequently generating an output signal relating to said difference;
• and
• cutter drive means connected to said computer for moving a position of said cutter parallel to said material feeding direction in response to the output signal from said computer, to thereby adjust the position of said cutting edge means of said cutter in said material feeding direction and compensate for and eliminate said difference so that said material may be cut precisely along said predetermined line to form respective plastic bags without protrusions.