METHOD AND APPARATUS FOR TRANSFERRING AND BUNDLING PLASTIC BAG SHEET MATERIAL

Abstract: A method and apparatus for transferring and bundling plastic bag sheet material wherein bag cycle speed is automa­ tically slowed, but not stopped, during a bundle transfer opera­ tion and cycle speed is resumed after one slow speed bag pro­ duction cycle.

Description: BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for making thermoplastic bags. More specifically, this invention relates to a method and apparatus for transferring and bundling thermoplastic bags of the type used to sack consumer goods in a grocery store, convenience store, drug store and the like. Thermoplastic convenience bags have gradually gained more acceptance by the retail industry and have completely replaced the utilization of paper bags in many market areas. A typical plastic bag includes a heat sealed bottom and integral carrying handles adjacent a top opening portion prompting some to descriptively refer to the bags as plastic tee-shirt bags. In the past, tee shirt and other plastic bags have been manufactured by high speed processing machines wherein a roll of tubular thermoplastic stock is mounted upon one end of the machine and stack or bundles of completed bags exit from an opposite end of the machine. More specifically, the tubular plastic is unreeled by a pair of opposing drive or nip rolls which are coupled to an electric motor through a clutch and brake mechanism. The drive rolls are thereby suitable to be intermittently stopped and started to advance the plastic tubular stock at a predetermined rate and pattern of control. A cutting and sealing station is positioned downstream from the drive rolls and includes a first heat sealing strip, and intermediate heated cutting knife and a parallel bottom heat sealing strip. Actuation of the sealing and cutting mechanism is synchronously controlled with the advancement of the tubular stock so that the stock is stopped during a cutting and sealing operation, where the bag is sealed and cut and then advanced a predetermined length. The process is repeated in a rapid manner at a rate of approximately 120 to 150 bags per minute. Downstream of the cutting and sealing station is a stack or bundle forming mechanism wherein a plurality of bags are stacked into a neat arrangement until a predetermined number is formed into a bundle for further transfer, processing and packing. One previously known thermoplastic bag making machine, of the type generally described above, is illustrated in United States Patent No. 3,580,142. In this patent disclosure, sheet material, which is flattened synthetic resin tubing, is transferred in specific lengths to a sealing and cutting station. Production of a single bag is referred to as a bag making cycle. After each cycle the completed bag is stacked to form a bundle, when the number of the sheet material reaches a specified total, the bag making operation is temporarily stopped or interrupted and the bundle of plastic bags is then transferred by a transferring mechanism to an index conveyor where completed bundles are formed into a shingle array for further handling and packing. In accordance with the previously known device, the bag making operation was stopped for one cycle to permit operation of the transferring mechanism for each bundle. In another machine, the duration of the stoppage was selected to be independent of one bag making cycle to permit a bag making cycle to be faster than a bundle transfer operation. In both instances bag production is stopped to prevent the this sheet bag material from becoming jammed at the bundle station. As a result of this stopping to perform the transfer operation, production of the sheet material is suspended which results in a reduction in production efficiency, Although the production of thermoplastic bags in accordance with previously known techniques has achieved a degree of success and industry recognition. It has been found that production in accordance with conventional techniques is limited to approximately to 150 cycles per minute. Increasing the bag making cycle tends to increase a tendency for mis-alignment, wrinkling, and jamming of the relatively thin bags as well as increasing the wear on various moving components. In addition, it has been found that in operating machinery with a fixed bag production cycle, that operators have tended to remove damaged or jammed bags or material during the rapid bag making operation of the machine without stopping the bag making machine. Attempting to clear fouled material during full speed bag making presents a safety hazard. In addition, conventional plastic bag making machinery which runs at a constant speed can present setup problems in the sense that the machine produces bags at such a rapid rate that it is difficult to visually perceive and verify the correctness of a single bag making operation. The difficulties suggested in the proceeding are not intended to be exhaustive but rather are among many which tend to reduce the effectiveness and user satisfaction with prior methods and apparatus for transferring and bundling plastic bags. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that thin plastic bag making methods and apparatus appearing in the past will admit to worthwhile improvements. Representative prior art, including art of the above nature, would be DE 23 12 316, US 3,580,142, US 3,947,021, and US 4,040,618. OBJECTS OF THE INVENTION It is therefore a general object of the invention to provide a novel method and apparatus for transferring and bundling thermoplastic bags which will obviate or minimize difficulties of the type previously described. It is a specific object of the invention to provide a novel method and apparatus for transferring and bundling plastic bag sheet material wherein adjustments to the bag making operation may be effected without bringing the entire bag production operation to a halt. It is another object of the invention to provide a novel method and apparatus for transferring and bundling plastic bag sheet material wherein the bag making operation need not be terminated during bundle transfer. It is a related object of the invention to provide a novel method and apparatus for transferring and bundling plastic bag material wherein bundle transfer may be advantageously and achieved while concomitantly and economically maintaining bag production. It is a related object of the invention to provide a novel method and apparatus for transferring and bundling plastic bag sheet material wherein bag production may be accurately monitored to permit minor adjustments with visual confirmation. It is yet another objects of the invention to provide a novel method and apparatus for transferring and bundling thermoplastic bag sheet material wherein control of the tubular sheet material feeding operation is advantageously monitored and maintained without stopping the bag making process. BRIEF SUMMARY OF THE PREFERRED EMBODIMENT OF THE INVENTION One preferred embodiment of the invention which is intended to accomplish the foregoing objects includes a method and apparatus wherein drive rolls for a thermoplastic bag making machine are monitored and upon reaching a predetermined number of bag making cycles, the drive rolls are slowed, without stopping, to permit a bundle transfer operation to be synchronously performed. Since the drive rolls and bag production is not stopped during the transfer operation, but rather is merely slowed to a "creep speed", bag production can be visually monitored, wrinkle producing phenomena identified and the time spent in machine production down time during bundle transfer minimized. The preferred method according to the invention for transferring and bundling plastic bag sheet material includes the steps of feeding a plastic tubing to be processed into plastic bags from a feed roll, advancing this plastic tubing through a drive roll for controllably advancing the tubing to a station for sealing and cutting, intermittently cutting the tubing into pre-selected lengths and concomitantly sealing the bottom of a next adjacent bag, temporarily storing a predetermined number of bags in a bundle, tranferring a bundle of completed bags away from the means for temporarily storing, and during the step of tranferring, controlling the drive roll for maintaining a desired speed of advancement of the plastic tubing to be processed into plastic bags, by controlling the timing of intermittent cutting and sealing, reducing the speed of the drive roll for one bag making cycle, without stopping the drive roll means and, upon reaching completion of a predetermined period of one bag making cycle, resuming the speed of the drive roll mechanism. THE DRAWINGS Other objects and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein: Figure 1 is a schematic illustration of a thermoplastic bag making apparatus in accordance with the subject invention wherein a pair of opposing nip or drive rolls are electronically monitored and controlled to slow bag production, without stopping production during a plastic bag bundle transfer sequence; and Figures 2A through 2K disclose timing charts for bag making production and the control state of various components. DETAILED DESCRIPTION Structure Referring now to the drawings and initially to Figure 1, there will be seen a schematic illustration of a thin plastic bag making machine in accordance with the subject invention. More specifically, a relatively large role of sheet material 1 is produced, in an independent operation, in a continuous tubular length. The sheet material is rolled into flattened tubular stalk for processing into plastic bags. The tubular stack is composed of conventional synthetic resins such as a thermoplastic material. As further shown in Figure 1, the role of plastic tubular stock is unwound and fed into a transferring mechanism 2 which comprises a pair of opposing nip rollers 3 which operably hold the sheet material between the roles. The roles are driven by an electric servo motor 4 which is mechanically attached to the rollers. The motor 4 in turn is controlled by a servo driver 5. A sealing and cutting mechanism 6 is mounted downstream of the nip rolls and comprises a servo motor 8 which is connected to a heated cutter bar 7. The cutting bar cuts the sheet stock material in a conventional manner. A servo driver 9 is connected to the cutting motor 8 and operably controls the same. A bundling mechanism 11 is mounted adjacent to the sealing and cutting station and provides a mechanism for stacking of accumulated bags. The bundling mechanism 11 includes a sheet receiving table 12 which is operable to swing from a horizontal posture as shown in Figure 1 to a downward inclined position as represented in phantom lines in Figure 1. The bags are stacked upon a pair of needles 14 which are controlled by solenoids 13 in a conventional manner. A transferring mechanism 15 includes a holding nail 16 which is able to move forward and backward and assist in a conventional manner in transferring a completed bundle of bags away from the stacking station upon withdrawal of the stacking pins 14. The subject apparatus advantageously includes an electronic control unit 21 which includes a sequence module 22 and a positioning unit 23 attached to the sequence module. The control unit 21 further includes a length position and bundle setting counter 24 which is connected to both the sequencing device 22 and positioning unit 23. As seen in Figure 1, the positioning 23 is attached to the servo drivers 5 and 9 to input signals to the transferring motor 4 and cutting motor 8 respectively. Sequence of Operation Turning to Figure 2, and in cooperation with the elements discussed in Figure 1, a sequence of operation of the subject invention may be appreciated. More specificallyn an operation switch is thrown, not shown, and a signal is sent to the positioning device 23 from the sequence module 22 of the control unit. The positioning device 23 sends a driving signal to the servo driver 5 and the servo driver 5 actuates the transferring motor 4, note Figure 2(A). The sheet material is thus transferred by drive rollers 3 at a standard speed, note Figure 2(C). A feedback signal pulse is sent to the positioning device 23 from the transferring motor 4 and the positioning device 23 drives rollers 3 to specific value which is by length specifying switch, not shown. Pulses are counted up to a specified set value by the length specifying switch and the transferring rollers 3 are stopped to terminate advance of the sheet material when the specified value is counted. At the same time, that the transferring motor 4 sends a transfer completion signal to the positioning device 23, note Figure 2(E), the positioning device 23 sends a transfer completion signal to the servo driver 9 of the cutting and sealing motor 8. The servo motor 8 then drives the cutting and sealing bar 7, note Figure 2(B) and the sheet material is cut to the specified length by the cutter 7. Upon completion of the cutting operation, a signal is sent from the cutting motor 8 to the positioning device 23, note Figure 2(D), and the transferring mechanism 2 is again driven and sequencing control is performed by the sequencing device 22. In accordance with the above, the operation is rapidly repeated and the transferring, cutting and sealing are performed to produce a plurality of identical plastic bags. As each bag is produced, the needles 14 pierce an upper edge of the bag and form a neat stack of formed bags on the receiving table 12. During the bag makin cycles, a bundle counter 24 counts the number of the sheet material advances and sends a counting signal to the sequence device 22 and positioning device 23 when the number reaches a specified value, note Figure 2(F). The sequence device 22 processes and sends a speed selection signal to the positioning device 23, note Figure 2(C), and a relatively slow speed instruction is sent to the servo driver 5 of the transferring device 2. The transferring motor 4 then rotates at a designated relative slow speed for 600 milliseconds, Figure 2(A). The stock sheet material is thus advanced at a creep speed which is reduced from the standard speed, note Figure 2(C). During bundle transfer, the count up signal drives the sheet receiving table 12 upward, note Figure 2(G), and the holding nail 16 closes to keep the bundle of the bag sheets at the upper limit of the table movement, Figure 2(H). When the holding nail 16 holds the bundle of sheet material the sequence device 22 sends a nail closing completion signal, which is not shown in the diagram, to the solenoid 13 and the needle 14 descends to pull the needle out from the bundle, Figure 2(J). A lower limit signal is then sent to the sequence device 22 when the needle journeys to the down limit, to remove the holding unit 16, Figure 2(K). Then the bundle of the sheet material is transferred to the right as shown in Figure 1. During this bundle transfer period, the succeeding sheet material which is advancing at creep speed becomes the first sheet of the next bundle. Upon transfer completion a signal is sent when the sheet material reaches a specified length, Figure 2(E). The creep speed of the transfer motor 4 is released and the cutting motor 8 is driven. The speed of the transferring motor 4 resumes a normal continuous operation speed and advances the sheet material at the standard speed. The following is an example of actual preferred operation. The operation period of the transfer motor 4 is 70 milliseconds (ms) for acceleration, 60ms for normal operation, 70ms for descending and thus a total time of 200 ms. The cutting motor operates for 120 ms with 40ms for transfer completion signalE and 40ms for cutting completion signalD for a total of 400ms per bag production cycle. These periods allow a production quantity of 150 bags per minutes. On the other hand, the period of operation at the creep speed, as instructed by the speed selection signal is 600ms. The response time of the solenoid 13 and the needle 14 is 10 milliseconds and the operation period of the plunger of the solenoid 13 is 71.5 milliseconds for a total operating time of 81.5. Thus 100 milliseconds is sufficient to retract and release the pins from a bundle of plastic bags. To compare the production efficiency of the subject invention to conventional bag making apparatus assuming a 24 hour operation for 25 days a month and that the stop period for each bundle transfer by convention apparatus is 2.5. By comparison, the creep speed transfer operation has been found to be facilely performed within 600 milliseconds for transferring a bag bundle and restarting normal speed bag making. With conventional methods and apparatus, producing 120 bags per minute the actual production rate is 115 sacks when the 2.5 second stop period is considered. In a given month therefore the number of plastic bags produced may be computed as follows: 115 (sack/min.) x 60 (min.) x24 (hours) x25 (days) =4, 140,000 (sacks/month) In accordance with the subject invention, however, a greater number of plastic bags per month may be produced as follows: 120 (sacks/minutes) x 60 (min.) x24 (hours) x25 (days) = 4, 320,000 (sacks/month) It will be noted by utilizing the subject continuous but creep mode of operation, the number of bags per month may be increased by 180,000. For a 150 bag per minute operation, a conventional machine will produce 5,184,000 (sacks/month) whereas the subject creep motion method and apparatus will produce 5,400,000 (sacks/month) which results in an increase in production of 252,000 (sacks/month). In a similar vein for a 200 sack per minute operation conventional apparatus will produce 6,912,000 (sacks per month) whereas the subject invention will produce 7,200,000 plastic bags per month for an increase of 288,000 sacks per month. In addition, to actuation of the creep motion of bag making during bundle transfer, the control unit 21 may be actuated by a manual switch, not shown, to selectively initiate one or more creep motion cycles to enable an operation to clear a jam, visually monitor misalignment problems, etc. as desired. SUMMARY OF ADVANTAGES OF THE INVENTION After reading and understanding the foregoing description of the invention, in conjunction with the drawings, it will be appreciated that several distinct advantages are obtained. Without attempting to set forth all of the desirable features of the instant method and apparatus for transferring and bundling plastic bags, at least some of the major advantages include the provision of a creep mode of bag making operation for 600 milliseconds to permit transfer and bundling of stacks of bags. In addition selective manual actuation of the creep mode of operation, by an operator, will permit safe removal of jammed sheets stock, as needed, without shutting down the line. Additionally during the creep mode of one bag production, and automatic transfer of a bundle of bags, an operator may visually inspect and verify proper bag making functions and identify for connection troubling indications, if any, before a jam occurs.

Claims: 1. A method for transferring and bundling plastic bag sheet material (1) comprising the steps of: feeding plastic tubing (1) to be processed into plastic bags from a feed roll; advancing the plastic tubing (1) through a drive roll mechanism (3) for controllably advancing the tubing (1) to a station for sealing and cutting; intermittently cutting the tubing (1) into pre-selected lengths and concomitantly sealing the bottom of a next adjacent bag; temporarily storing a predetermined number of bags in a bundle; transferring a bundle of completed bags away from the means (11) for temporarily storing; and during said step of transferring, controlling said drive roll mechanism for maintaining a desired speed of advancement of the plastic tubing (1) to be processed into plastic bags, by controlling the timing of intermittent cutting and sealing, reducing the speed of said drive roll mechanism (3) for one bag making cycle, without stopping said drive roll mechanism (3), and upon reaching completion of a predetermined period of one bag making cycle resuming the speed of said drive roll mechanism (3). 2. A method for transferring and bundling plastic bag sheet material (1) as defined in claim 1 wherein said step for controlling further includes; counting the number of bag making cycles up to a predetermined number to complete a bundle; and reducing the speed of said drive roll mechanism (3), without stopping said drive roll mechanism (3), upon reaching a predetermined number of bag making cycles to permit removal of a completed bundle of plastic bags. 3. A method for transferring and bundling plastic bag sheet material (1) as defined in claim 2 and further comprising the step of: timing the duration of reduced speed of the drive roll mechanism (3) consistent with a predetermined time necessary to perform a transfer operation of a completed bundle of bags, and re-initiating full speed operation of the drive roll mechanism (3) upon completion of one complete bag making cycle at a reduced speed and the transfer operation. 4. A method for transferring and bundling plastic bag sheet material (1) as defined in claim 3 wherein said step of timing the duration of reduced speed of the drive roll mechanism (3) comprises: controlling the advancement of plastic tubing (1) to produce a single bag during a 600 millisecond period. 5. An apparatus for transferring and bundling plastic bag sheet material (1) comprising: drive roll means (3) for feeding plastic tubing (1) from a feed roll to a bag sealing and cutting station; means (7) for intermittently cutting the tubing into preselected lengths and concomitantly sealing the bottom of a next adjacent bag; means (11) for temporarily storing a number of bags in a bundle; means (15) for transferring a bundle of bags away from the means (11) for temporarily storing; and control means (21) for maintaining a desired speed of a said drive roll means (3) during normal bag making and for controlling said means (7) for intermittently cutting and sealing and for reducing the speed of said drive roll means (3), without stopping said drive roll means (3), upon reaching a predetermined completed bag count for a predetermined period of time while said means (15) for transferring removes a hundle of completed bags from said means (11) for temporarily storing. 6. An apparatus for transferring and bundling plastic bag sheet material (1) as defined in claim 5 wherein said control means (21) includes: means (24) for counting the number of bag making cycles; and means (22) for slowing, without stopping, said drive roll means (3) upon reaching a predetermined number of bag making cycles to permit removal of a bundle of bags. 7. An apparatus for transferring and bundling plastic bag sheet material (1) as defined in claim 5 and further including: means (22) for timing the duration of reduced speed of said drive roll means (3) for a period of 600 milliseconds for a single bag making cycle to perform a transfer operation of a completed bundle of bags.

Inventors: FUKUYAMA, YOSHIAKI
Applicants: NIPPON FLUTE CO. LTD.
Application year: 1987
Main classification: B31B1
IPC codes: B65H31, B31B19, B65H29, B65H43