Bag making machine

Abstract: According to the invention, there is provided a bag making machine including feeding means for feeding two or more superposed layers of plastic film (2) longitudinally thereof and intermittently for a length, the layers of plastic film having void area means such as notch hole means (4), and a cutter (13) for cutting the layers of plastic film crossly thereof along a line predetermined with respect to the void area means whenever feeding the layers of plastic film are temporarily stopped, to thereby succesively make plastic bags. A detector (8) is disposed near the cutter for recognizing the contour of the void area means as an image data immediately before or when the layers of plastic film are temporarily stopped. A computer is connected to the detector for calculating the difference between the position of the predetermined line of the layers and the position of the cutting edge means of the cutter in accordance with the image data of the detector. Drive means is connected to the computer for moving the cutter parallel to the layers feeding direction in response to the output signal from the computer to thereby compensate and eliminate the difference between the position of the predetermined line of the layers and the position of the cutting edge means of the cutter.

Description: FIELD OF THE INVENTION The invention relates to a bag making machine for successively make plastic bags. PRIOR ART There has been generally used a bag making machine which includes feeding means such as feeding rollers rotated by a servo motor for feeding two or more superposed layers of plastic film 1 longitudinally thereof and intermittently for a length, as shown in Fig. 14. Longitudinal and cross sealers are operated to heat seal the layers of plastic film 1 longitudinally and crossly thereof whenever feeding of the layers of plastic film 1 are temporarily stopped so that longitudinal and cross sealed areas 2 and 3 are formed on the layers of plastic film 1. The longitudinal sealed areas 2 extend parallel to the feeding direction X of the layers of plastic film 1. The cross sealed areas 3 extend perpendicularly to the feeding direction X. Notch holes 4 may then be punched in the intersection between the longitudinal and cross sealed areas 2 and 3 of the layers whenever the layers of plastic film 1 are temporarily stopped. A slitter slits the layers of plastic film 1 along longitudinal lines Y0 extending through the centers of the notch holes 4. A cutter is operated to cut the layers of plastic film 1 crossly thereof along a cross line X0 extending through the centers of the notch holes 4 whenever the layers of plastic film 1 are temporarily stopped, the thereby successively make plastic bags. Each of the plastic bags has four bevelled or round corners formed by the notch holes 4. In the bag making machine, it is required to cut the layers of plastic film 1 precisely along the cross line X0 extending through the centers of notch holes 4, otherwise protrusions 5 are formed at the corners of plastic bags, as shown in Fig. 12. In this connection, a cutting apparatus for precisely cutting is disclosed in Japanese Laid-Open Patent Publication No. 160231 of 1987, the applicant of which is Totani. In the apparatus in the publication, a light source and a detector are disposed near the cutter on the upper side of the layers feeding path. The light source directs a light toward the layers of plastic film around the notch hole when the layers of plastic film are temporarily stopped. The light passes through the notch hole, a portion of the light reflecting from the layers of plastic film around the notch hole. The detector includes a series of elements arranged along a line extending crossly of the layers of plastic film the elements receive the light reflecting from the layers of plastic film to thereby measure the width of the notch hole on the line along which the elements are arranged. The apparatus compares the measured value of the width of the notch hole on the line with a reference value which corresponds to the width of the notch hole at the center thereof, to thereby calculate the difference between the position of the cross line extending through the centers of the notch holes and the position of the cutting edge of the cutter. Drive means moves the cutter parallel to the layers feeding direction to thereby compensate and eliminate the difference between the position of the cross line extending through the centers of the notch holes and the position of the cutting edge of the cutter. The cutter then cut the layers of plastic film crossly thereof. The layers of plastic film can therefore be cut precisely along the cross line extending through the centers of notch holes. The protrusions 5 are not formed at the corners of plastic bags. However, the apparatus has a problem that the layers of plastic film 1 may spread out after slitting the layers along the longitudinal line Y0 to widen the notch hole 4. This affects the measured value of the width of the notch hole 4, resulting in miscalculation of the difference between the position of the cross line X0 extending through the center of the notch holes 4 and the position of the cutting edge of the cutter. A dust may be adhered to the periphery of the notch hole 4. This also affects the measured value. The notch holes 4 may be rugged by the malfunction of the punching means to affect the measured value. Accordingly, the apparatus can not always cut the layers of plastic film 1 precisely along the cross line X0 extending through the center of notch holes 4. JP-A-03227228 discloses a bag making machine which includes a cutter with cutting edge means for cutting a plastic film material along a predetermined line. A light source is disposed upstream of the cutter on a first side of a material feeding path. A detector is opposed to the light source on a second side opposite from the first side of the material feeding path for receiving light passing through a through-hole, where by the quantity of that light is detected. SUMMARY OF THE INVENTION It is an object of the invention to provide a novel and improved bag making machine, in which the above problems are overcome, namely in which the layers of plastic film are precisely cut along the predetermined line thereof. This object is solved by the features of the independent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a preferred embodiment of the invention. Fig. 2 is a schematic plan view showing the recognizing range of the detector in Fig. 1. Fig. 3 is a schematic plan view showing other recognizing range of the detector in Fig. 1. Fig. 4 is a schematic plan view showing other recognizing range of the detector in Fig. 1. Fig. 5 is a schematic plan view showing other recognizing range of the detector in Fig. 1. Fig. 6 is a side view of other embodiment of the invention. Fig. 7 is a side view of other embodiment of the invention. Fig. 8 is a side view showing the position of the notch hole when the layers of plastic film are temporarily stopped in Fig. 7. Fig. 9 is a schematic plan view showing the recognizing range of the detector in Fig. 7. Fig. 10 is a schematic plan view showing the recognizing range of the detector in Fig. 8. Fig. 11 is a schematic plan view showing notch holes formed in the intersection between the longitudinal and cross sealed areas of the layers of plastic films. Fig. 12 is a schematic plan view showing protrusions formed at the corners of plastic bags. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, there is shown a bag making machine which includes feeding means such as feed rollers rotated by a servo motor for feeding two superposed layers of plastic film 1 longitudinally thereof and intermittently for a length, as described above. The bag making machine further includes longitudinal and cross sealers operated by a servo motor to heat seal the layers of plastic film 1 longitudinaly and crossly thereof whenever feeding of the layers of plastic film 1 are temporarily stopped so that longitudinal and cross sealed areas 2 and 3 are formed on the layers of plastic film 1. The longitudinal sealed areas 2 extend parallel to the feeding direction X of the layers of plastic film 1. The cross sealed areas 3 extend perpendicularly to the feeding direction X. Notch holes 4 are then punched in the intersection between the longitudinal and cross sealed areas 2 and 3 of the layers whenever the layers of plastic film 1 are temporarily stopped. A slitter slits the layers of plastic film 1 along longitudinal lines Y0 extending through the centers of the notch holes 4. In the embodiment, the notch hole 4 is rectangular having an upstream end A, two central ends B and a downstream end C, the slitting line Y0 extending through the upstream and downstream ends A and C of the notch hole 4, shown in Fig. 2. Accordingly, the layers of plastic film 1 have void area means comprising the notch holes 4. The bag making machine further includes a cutter 6 operated by the servo motor common to the sealers and the cutter 6 to cut the layers of plastic film 1 crossly thereof along a line predetermined with respect to the void area means whenever the layers of plastic film 1 are temporarily stopped, to thereby succesively make plastic bags. In the embodiment, the predetermined line comprises a cross line X0 extending through the centers or central ends B of the notch holes 4. Each of the plastic bags has four bevelled or round corners formed by the notch holes 4. A light source 7 is disposed near and upstream of the cutter 6 on one side of the layers feeding path. A detector 8 is opposed to the light source 7 on the other side of the layers feeding path. In the embodiment, the layers of plastic film 1 are fed along a path extending horizontally, the light source 7 being positioned on the lower side of the layers feedig path, the detector 8 being positioned on the upper side of the layers feeding path. The detector 8 comprises a video camera including an electronic shutter. The light source 7 is intended to direct a light toward the layers of plastic film 1 and the cutter 6 when the layers of plastic film 1 are fed at a low speed and the notch hole 4 reaches the position of the light source 7, as shown in Fig. 1, immediately before the layers of plastic film 1 are temporarily stopped. The detector 8 is adapted to receive the light passing through the notch hole 4, the cutter 6 intercepting a portion of the light passing through the notch hole 4. The electronic shutter is clicked instaneously so that the detector 8 recognizes the contour of the notch hole 4 as an image data in a range R at least between the predetermined line X0 of the layers and a portion of the cutter 6, as shown in Fig. 2, immediately before the layers of plastic film 1 are temporarily stopped. The layers of plastic film 1 are further fed a length L (about 8 mm) and then temporarily stopped by the feeding rollers driven by the servo motor. The bag making machine further includes a computer 9 connected to the detector 8. The computer 9 calculates the distance D1 between the position of the predetermined line X0 of the layers and the position of the side X2 of the cutter 6 at the image data recognizing point in accordance with the image data of the detector 8. The computer 9 add that distance D1 to the distance D2 between the position of the side X2 of the cutter 6 and the position of the cutting edge X1 thereof, the distance D2 being previously recognized by the computer 9, to thereby calculate the distance D1 + D2 between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6 at the image data recognizing point. In addition, the computer 9 measures or computes the feed length L of the layers of plastic film 1 from the image data recognizing point to the layers temporarily stopping point. In the embodiment, the computer 9 counts the number of pulses which are sent from the servo motor driving the feeding rollers to the computer 9 after the image data recognizing point, to measure the feed length L. The computer 9 then compares the distance D1 + D2 at the image data recognizing point with the feed length L from the image data recognizing point to the layers temporarily stopping point, to thereby calculate the difference L - (D1 + D2) between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6 at the layers temporarily stopping point. The bag making machine further includes drive means connected to the computer 9 for moving the cutter 6 parallel to the layers feeding direction X. The drive means comprises a servo motor 10 connected to the computer 9, a feeding screw 11 extending parallel to the layers feeding direction X and operatively connected to the servo motor 10, and a nut member 12 threadedly engaged with the feeding screw 11 and mounted on a frame 13, the cutter 6 being supported on the frame 13. The servo motor 10 rotates the feeding screw 11 in response to the output signal from the computer 9, after calculating the difference L - (D1 + D2). The feeding screw 11 and the nut member 12 therefore move the cutter 6 and frame 13 parallel to the layers feeding direction X in response to the output signal from the computer 9, to thereby compensate and eliminate the difference L - (D1 + D2) between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6 at the layers temporarily stopping point. The cutter 6 is then operated by the servo motor common to the sealers and the cutter 6 to cut the layers of plastic film 1 crossly thereof. The layers of plastic film 1 can therefore be cut precisely along the cross line X0 extending through the centers of the notch holes 4. The protrusions 5 shown in Fig. 19 are not formed at the corners of plastic bags. Accordingly, in the bag making machine, it is not required to measure the width of the notch hole 4 but recognize the contour of the notch hole 4 as an image data, unlike the apparatus disclosed in Japanese Laid-Open Patent Publication No. 160231 of 1987. Accordingly, it does not result in miscalculation. For example, the layers of plastic film may spread out after slitting along the longitudinal line Y0 to widen the notch hole 4, as shown in Fig. 3. In this case, the computer 9 compares the image data of the detector 8 with the previous image data to judge the unusualness in the image data so that the detector 8 recognizes only an usual image data in a range R1 and cancell the other image data. The computer 9 then calculates the difference between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6 in accordance with the image data in the range R1. If the dust is adhered to the periphery of the notch hole 4, the detector 8 recognizes only an usual image data in a range R2 and cancell the other image data, as shown in Fig. 4. If the notch hole 4 is rugged, the detector 8 recognizes only an usual image data in a range R3 and cancell the other image data, as shown in Fig. 5. Accordingly, the bag making machine can compensate and eliminate the difference between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6 without miscalculation, to thereby cut the layers of plastic film 1 precisely along the predetermined line thereof. Referring to Fig. 6, there is shown a bag making machine for feeding transparent layers of plastic film 1. The bag making machine includes two polarizing screens 14 and 15 disposed the opposite sides of the layers feeding path. The light source 7 is covered by the polarizing screen 14. The detector 8 is covered by the polarizing screen 15. The light source 7 therefore directs a light to the polarizing screen 14, the light penetrating through the polarizing screen 14 by which the light is polarized. The light then passes through the notch hole 4 and penetrates through the layers of plastic film 1 around the notch hole 4 to reach the polarizing screen 15 by which the light is again polarized. The polarizing screens 14 and 15 have orientations perpendicular to each other. Accordingly, as to the light passing through the notch hole 4, it does not penetrate through the polarizing screen 15. On the other hand, as to the light penetrating through the layers of plastic film 1, the layers of plastic film 1 rotate the wave front of the light polarized by the polarizing screen 14 so that the light can penetrate through the polarizing screen 15. The detector 8 therefore receives not the light passing through the notch hole 4 but the light penetrating through the layers of plastic film 1 around the notch hole 4, to recognize the contour of the notch hole 4 as an image data. Accordingly, even if the transparent layers of plastic film 1, the computer 9 can calculate the difference L - (D1 + D2) , between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6, as described above. In a bag making machine shown in Fig. 7, the light source 7 direct a light toward the layers of plastic film 1 so that the detector 8 receives the light passing through the notch hole 4, or the light penetrating through the layers of plastic film 1 around the notch hole 4, immediately before the layers of plastic film 1 are temporarily stopped. The detector 8 recognizes the contour of the notch hole 4 as an image data in a range R at least between the predetermined line X0 of the layers and a reference portion of the layers, the reference portion comprising the upstream end A of the notch hole 4, which is positioned upstream of the predetermined line X0, as shown in Fig. 9. The computer 9 calculates the distance between the predetermined line X0 of the layers and the upstream end A of the notch hole 4 in accordance with the image data of the detector 8 immediately before the layers of plastic film 1 are temporarily stopped. The light source 7 then again directs a light toward the layers of plastic film 1 so that the detector 8 receives the light passing through the notch hole 4, or the light penetrating through the layers of plastic film 1 around the notch hole 4, when the layers of plastic film 1 are temporarily stopped, as shown in Fig. 8. The detector 8 recognizes the contour of the notch hole 4 as an image data in a range R including the reference portion of the layers, that is the upstream end A of the notch hole 4, as shown in Fig. 10. The computer 9 calculates the distance between the position of the upstream end A of the notch hole 4 and the position of the cutting edge X1 of the cutter 6 in accordance with the image data of the detector 8 when the layers of plastic film 1 are temporarily stopped. The computer 9 then compares the distance between the predetermined line X0 of the layers and the upstream end A of the notch hole 4 with the distance between the position of the upstream end A of the notch hole 4 and the position of the cutting edge X1 of the cutter 6, to thereby calculate the difference between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6. The servo motor 10 rotates the feeding screw 11 and moves the cutter 6 and the frame 13 parallel to the layers feeding direction X in response to the output signal from the computer 9, to thereby compensate and eliminate the difference between the position of the predetermined line X0 of the layers and the position of the cutting edge X1 of the cutter 6. Accordingly, the layers of plastic film 1 can be cut precisely along the cross line X0 extending through the centers of the notch holes 4.

Claims: A bag making machine for making plastic bags from a web material comprising two or more layers of plastic film (1), said material (1) having notch means such as notch holes (4) formed therein, said bag making machine including feeding means for feeding said material (1) intermittently for a length along a longitudinal material feeding path, a cutter (6) including cutting edge means for cutting said material (1) along a predetermined line which extends in a direction transverse to the longitudinal material feeding direction (X) and intersects said notch means (4) whenever feeding of said material (1) is temporarily stopped, to thereby successively make plastic bags, a light source (7) disposed upstream of said cutter (6) on a first side of said material feeding path for directing a light toward said material (1), and a detector (8) opposed to said light source (7) on a second side opposite from said first side of said material feeding path for receiving the light passing through said notch means (4), said bag making machine being characterized in that said light source (7) is disposed near said cutter (6) on said first side for directing the light toward said material (1) and said cutter (6), that said detector (8) is opposed to said light source (7) on said second side for receiving the light passing through said notch means (4) at a first point immediately before said material (1) is temporarily stopped, said cutter (6) being positioned to intercept a portion of the light passing through said notch means (4) at said first point, said detector (8) recognizing said light passing through said notch means (4) as an image data corresponding to the contour of said notch means (4) to detect the position of said predetermined line (X0) of said material (1) and the position of said cutting edge means (X1) of said cutter (6) in said material feeding direction (X) at said first point, said material (1) being then temporarily stopped at a second point after said feeding means further feeds said material (1) by a remaining length segment (L) fed from said first point to said second point, that a computer (9) is connected to said detector (8) for calculating a distance (D1 + D2) between the position of said predetermined line (X0) of said material (1) and the position of said cutting edge means (X1) of said cutter (6) in said material feeding direction (X) at said first point in accordance with detected data received from said detector (8), measuring or computing said remaining length segment (L), and comparing said distance (D1 + D2) with said remaining length segment (L) to thereby calculate a difference (L - (D1 + D2)) between the position of the predetermined line of said material (1) and the position of said cutting edge means (X1) of said cutter (6) in said material feeding direction (X) at said second point, said computer (9) subsequently generating an output signal relating to said difference (L - (D1 + D2)), and that cutter drive means (10) is connected to said computer (9) for moving said cutter (6) parallel to said material feeding direction (X) in response to the output signal from said computer (9), to thereby adjust the position of said cutting edge means (X1) of said cutter (6) in said material feeding direction (X) and compensate for and eliminate said difference (L - (D1 + D2)) so that said material (1) can be cut precisely along said predetermined line by the cutting edge means of said cutter (6). A bag making machine for making plastic bags from a web material comprising two or more layers of plastic film (1), said material (1) having notch means such as notch holes (4) formed therein, said bag making machine including feeding means for feeding said material (1) intermittently for a length along a longitudinal material feeding path, a cutter (6) including cutting edge means for cutting said material (1) along a predetermined line which extends in a direction transverse to the longitudinal material feeding direction (X) and intersects said notch means (4) whenever feeding of said material (1) is temporarily stopped, to thereby successively make plastic bags, a light source (7) disposed upstream of said cutter (6) on a first side of said material feeding path for directing a light toward said material (1), and a detector (8) opposed to said light source (7) on a second side opposite from said first side of said material feeding path for receiving the light passing through said notch means (4), said bag making machine being characterized in that said light source (7) is disposed near said cutter (6) on said first side, that said detector (8) is opposed to said light source (7) on said second side for receiving the light passing through said notch means (4) at a first point immediately before said material (1) is temporarily stopped, and recognizing said light passing through said notch means (4) as an image data corresponding to the contour of said notch means (4) to detect the position of said predetermined line (XO) of said material (1) and the position of a reference portion (A) of the material (1) which is positioned upstream of said predetermined line in said material feeding direction (X), at said first point, said material (1) being then temporarily stopped at a second point after said feeding means further feeds said material (1) by a remaining length segment fed from said first point to said second point, said detector (8) further receiving the light passing through said notch means (4) at said second point and recognizing said light passing through said notch means (4) as an image data corresponding to the contour of said notch means (4) to detect the position of said reference portion (A) of the material (1) in said material feeding direction (X) at said second point, that a computer (9) is connected to said detector (8) for calculating a first distance between the position of said predetermined line (X0) of said material (1) and the position of said reference portion (A) of said material (1) in said material feeding direction (X) at said first point in accordance with detected data received from said detector (8), calculating a second distance between the position of said reference portion (A) of said material (1) and the position of the cutting edge means (X1) of said cutter (6) in said material feeding direction (X) at said second point in accordance with the detected data received from said detector (8), and comparing said first distance with said second distance to thereby calculate a difference between the position of the predetermined line (XO) of said material (1) and the position of said cutting edge means (X1) of said cutter (6) at said second point, said computer (9) subsequently generating an output signal relating to said difference, and that cutter drive means (10) is connected to said computer (9) for moving said cutter (6) parallel to said material feeding direction (X) in response to the output signal from said computer (9), to thereby adjust the position of said cutting edge means (X1) of said cutter (6) in said material feeding direction (X) and compensate for and eliminate said difference so that said material (1) can be cut precisely along said predetermined line by the cutting edge means of said cutter (6).

Inventors: TOTANI MIKIO, TOTANI, MIKIO
Applicants: TOTANI GIKEN KOGYO KK, TOTANI GIKEN KOGYO CO., LTD.
Application year: 1995
Main classification: B31B1
IPC codes: B31B1