Control means for a plastic bag making machine

Abstract: A plastic bag making machine is disclosed, and includes a dancer assembly (203) that receives film (201) from which the bags are to be made. The film travels from the dancer assembly to a drum-in nip (205,206) and then to a sealing drum (208). After the sealing drum, the film travels to a drum-out nip (210,211). Then the film travels to a device-in nip (215,216), vertically through a processing device (218), and then to a device-out nip (219,220). A controller (221) is connected to and controls the drum-in nip, the drum-out nip, the device-in nip, the device out nip, the dancer assembly and the sealing drum (including the seal bars and/or the sealing blanket drives). The controller includes a memory in which at least one set of operating parameters used to control the machine is stored.

Description: FIELD OF THE INVENTION The present invention relates generally to the art of bag making machinery. More specifically, it relates to a bag making machine according to the preamble of claim 1. BACKGROUND OF THE INVENTION Many different types of plastic bag making machines are known in the art of producing plastic bags for industrial and individual consumers for many different applications (e.g. small sandwich bags and trash bags). A discussion of the history and operation of these machines can be found in US-A-4,642,084 entitled "Plastic Bag Making Machine", assigned to the present assignee. The US-A-4,642,084 discloses a bag machine which includes a rotary drum with seal bars attached thereto. Prior art machines maintain the position of the seal bars (at the drum periphery) using air cylinders. Improvements made to that design are described in other patents assigned to the present assignee, including US-A-4,934,993, US-A-5,518,559 and US-A-5,587,032. Generally, the machines implementing these inventions have been well received. A prior art bag making machine constructed generally in accordance with the descriptions of the above referenced patents is shown in Figure 1. The major elements of such a prior art bag making machine 10 include a dancer and idler assembly 12, a sealing drum and blanket assembly 14, a chill roll 16, a controller 15, a punching station 17, a folding station 18, a pull roll system 20, a perforator/cutting station 22 and a phase variator assembly 24. Film 11 is fed in the direction of the arrows from a source of plastic tubing 13 through a dancer roll 12a and an idler roll 12b into the sealing drum and blanket assembly 14. Source 13 may be any source for plastic material such as an extruder, a roll of plastic film, or a printer on which the plastic is imprinted. Dancer roll 12a exerts a known tension on the film by pulling it in a downward direction. The position of dancer roll 12a is used to determine the actual speed (by determining the difference from a nominal speed). The nominal tension is adjusted pneumatically. The adjustment may be difficult for the user because the adjustments are counter-intuitive: increasing pressure on the dancer cylinder decreases film tension. The sealing drum and blanket assembly 14 includes a cylindrical drum 28, which is capable of being varied in diameter. That feature is illustrated by the dotted circle illustrating a smaller diameter. A number of sealing bars 30 are also shown and periodically form cross seals across the flattened film tube 11. Sealing bars 30 are of conventional design and are disclosed in detail with respect to construction and operation in the US-A- 4,642,084. A blanket 32 is mounted on rollers 34, 35, 36 and 37 for surrounding a portion of drum 28 in such a way that the film 11 passes between blanket 32 and drum 28 while seals are being formed. Rollers 34 and 35 are mounted to an elongate frame 39 which is pivotable between the solid and dotted line positions shown in Figure 1. Frame 39 includes a perpendicular plate 40 near its midsection, the latter being coupled to an air cylinder 42 having an extensible rod 43. It will be appreciated that extension of rod 43 causes rollers 34 and 35 to move to the dotted line position when the drum diameter decreases, thereby maintaining tension of blanket 32 against drum 28. Roller 37 is driven from a gear motor 44 by belt 45 to drive blanket 32, and in turn blanket 32 will rotate drum 28 due to the tension between these components. Motor 44 includes an encoder 47 which generates a position signal each revolution of motor 44. Alternative encoder locations are on roller 37 or roller 38. A detector 23, such as an electric eye or magnetic sensor is positioned directly above drum 28 and generates a signal when a small metal or magnetic protrusion 26 on drum 28 passes, i.e. each revolution of drum 28. From the output of encoder 47 and detector 23 the circumference of drum 28 and the linear travel of film 11 bag are determined by controller 15. In an alternative embodiment encoder 47 may be mounted via a pulley to roller 37 or roller 36. After passing chill roll 16, the film 11 next passes through an optional punching station 17 which punches preselected hole and handle configurations in the film. Thereafter, the film may be further processed as shown or in any other appropriate manner. Variator system 24 is driven from a gear box 63 by belt 64. Gear box 63 is driven by drum 28 through belt 65. Variator system 24 also includes a pair of gears 66 and 67, used to vary the phase of the perforator/cutting station 22 and punching station 17, respectively, or any other type of downstream device. GB A-A-2283837 describes a plastic bag making machine comprising a sealing drum and control means for storing at least one set of operating parameters used to control the machine, and wherein the control means are connected to the sealing means. Prior art rotary sealing drums in general perform better when the film is not under tension when it is sealed. However, as the film travels through other parts of the machine it is desirable to place it under tension to control and drive it. Thus, prior art machines overspeed the film as it approaches the sealing drum. The roll where the film contacts the blanket is referred to as the lay on roll, and it assists in overspeeding the film. The blanket is driven at the speed of the machine. As the blanket moves around the lay on roll the outside of the blanket (relative to the lay on roll) travels faster than the inside of the blanket (which is at the machine speed). As the film passes around the lay on roll, it is on the outside of the blanket. Since film 11 is in contact with the outside of blanket 32, it too travels faster than the machine speed. An analogous effect occurs when the film's contact with the blanket ends. The prior art was thus limited in the ability to overspeed the film (i.e. it was determined largely by the blanket thickness. Additional control was obtained by an additional nip and the user needed to adjust the tension of the dancer rolls when adjusting the overspeed. Also, a mechanical adjustment was made when product size was changed. Another drawback was the blanket needed to be able to hold the film when oversped, yet it still needed to be slick enough to release the film after sealing. Prior art machines have a variety of controllable parameters, including dancer tension and the overspeeding of the lay on roll and chill roll (the roll following the drum). These adjustments were individually made, and required the user to make mechanical adjustments. The adjustments were made by observing the film being processed, and adjusting the settings. Thus, it is difficult for inexperienced operators to make the proper adjustments. Figure 1 shows a perforator or cutter 22 (a knife) used to perforate the location demarking the end of one bag and the beginning of the next. The film path through the knife is horizontal, which causes difficulty in threading. Also, the knife is mechanically driven with a variator. The user adjusts for tension using a magnetic particle clutch or an ac vector drive. These adjustments are also made by observing the process. According, a bag making machine that provides a dancer assembly exerting upward tension is desirable. Also, it will preferably have a sealing drum with infeed and outfeed nips, such as servo driven nips, that control the web speed to provide sealing with reduced or no tension. Such a machine will also have controls that allow an inexperienced user to operate the machine. SUMMARY OF THE PRESENT INVENTION Accordingly the present invention provides a plastic bag making machine comprising a sealing drum; a drum-in nip formed with at least one drum-in servo-drive roll, and wherein the speed of the drum-in roll is controlled by the controller, and further wherein, the film travels directly from the drum-in nip to the drum, a controller connected to the drum-in nip and the sealing drum; wherein the controller includes a memory in which at least one set of operating parameters used to control the machine is stored and, wherein the drum in nip overspeeds the film and wherein the film travels from the overspeed means to the drum. Preferably the machine further comprises a drum-out nip, wherein the film travels from the drum to the drum-out nip. The drum-out nip is formed with at least one drum-out servo-driven roll. The speed of the drum-out roll is controlled by the controller. The controller may include at least one input used to select one of a set of operating parameters and to enter the at least one set of operating parameters, and a memory that stores the at least one set, and at least one output for controlling the machine. The plastic bag making machine preferably includes a dancer assembly that receives a film from which the bags are to be made. An air cylinder is connected to the dancer assembly. The film travels from the dancer assembly to a sealing drum. The speed of the machine is dependent on the position of the air cylinder, and a controller senses the position of the air cylinder. An alternative provides the controller with an input used to select the air cylinder pressure, and/or used to store the pressure. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a prior art bag making machine with a rotary sealing drum. Figure 2 is a diagram of a portion of a bag making machine constructed in accordance with the preferred embodiment. Like reference numerals are used to indicate like components. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is illustrated with reference to a rotary drum sealer in a bag making machine, having particular servo drives and control inputs. Figure 2 shows the preferred embodiment of the present invention which processes a film 201 using a dancer assembly 203, a pair of drum-in rolls 205 and 206, a sealing drum 208, a pair of drum-out rolls 210 and 211, a sealing blanket 213, a pair of knife-in rolls 215 and 216, a knife 218 (which could be any other film processing device such as a perforator, knife, die cutter, punching station, or folding station), a pair of knife-out rolls 219 and 220, and a controller 221. Sealing drum 208 is, in the preferred embodiment, constructed generally in accordance with the prior art cited above, although it could be made using a different design. It has a variable diameter of from 96 to 152 inches. The particular type of drum is not important for the present invention. As shown in Figure 2, the processing device is located downstream of the drum, thus the film travels from the drum to the processing device. One change in drum 208 from the prior art is the provision of a retractable sealing bar. The bar may be retracted during operation so that the user can more readily correlate individual seals with individual sealing bars. This is useful in the event that one sealing bar is not functioning properly, and allows the user to identify the malfunctioning seal bar. The preferred embodiment provides a valve on the air cylinder of one seal bar. The valve is used to vent the cylinder, thus retracting the seal bar. The position of the valve is controlled by controller 221. Controller 221 causes the bar to be retracted when the user makes an appropriate input to controller 221. Dancer assembly 203 includes a plurality of upper rolls 225 and lower rolls 226. Rolls 225 and 226 are mounted on arms 227 and 228, which are pivotally interconnected. An air cylinder 229 is used to adjust the tension applied to film 201. The vertical distance between rolls 225 and 226 is determined by the tension applied to film 201 (and is related to the speed of film 201). As may be seen, increasing the air pressure moves upper rolls 225 farther from rolls 226 and increases the tension on film 201. Thus, the control is intuitive: more pressure moves the rolls up and thus increases tension. Air cylinder 229 is controlled with an air regulator, which is controlled by controller 221. Because an air cylinder and air regulator are used, and controlled by controller 221 (or in operative association therewith), adjustments may be made easily, and operating parameters stored for a number of different products (types of film, bag length, etc.). Also, the position of dancer rolls 225, as sensed by controller 221, is used by controller 221 to determine the speed of the film 201. The operation and use of controller 221 will be described in greater detail below. Alternative embodiments include using a different number of dancer rolls, other arrangements to control the position of the dancer rolls (including pneumatics and mechanical drives), and using a dancer that increases tension by moving a roll downward. After leaving dancer assembly 203 film 201 is directed to drum-in rolls 205 and 206. As used herein drum-in rolls mean rolls preceding the drum. Roll 205 is a servo-driven roll, and roll 206 is an idler roll in the preferred embodiment. Rolls 205 and 206 are rubber wrapped. Of course, other roll arrangements may be used as well. Figure 2 shows that only film 201 passes through the drum-in nip (between rolls 205 and 206). A blanket 213 is used to hold the film to the sealing drum, but the film does not contact blanket 213 until after the drum-in nip. Servo-driven roll 205 is used to overspeed the film. Controller 221 causes roll 205 to be driven at a speed greater than the machine speed (and the speed of the film through dancer assembly 203) by a user selected percentage. The speed of roll 205 is thus linked electronically, rather than mechanically, to the machine speed. The user selects the percent overspeed based on observation, or from a set of control parameters stored by controller 221. Thus, controller 221 uses the nominal (or base) speed, the position of rolls 225 of dancer assembly 203 and the user entered overspeed to set the speed of roll 205. Thus, the film may be sealed under little or no tension. The overspeed is not limited by blanket thickness, and may be made as large as the user desires (and the film will tolerate). Alternatively, controller 221 could be used to sense tension, and determine an appropriate overspeed (rather than the users percentage input overspeed). Drum-out rolls 210 and 211 are used to slow down film 201, and reintroduce tension. As used herein drum-out roll means a roll downstream of the drum. Roll 211 is a servo driven roll and is driven at an underspeed equal to the overspeed of roll 205. Thus, the film will be returned to the same tension, and the same speed, that it was at prior to sealing. Rolls 210 and 211 are both rubber wrapped rolls, and roll 211 is an idler roll. Alternatively, the user could input an underspeed independent of the overspeed, or select only the underspeed and have the controller determine the overspeed. Also, the alternatives discussed above may be implemented for rolls 210 and 211. The over and under speed arrangement of the present invention is thus easily controlled, performed by servo-driven rolls, and occurs when blanket 213 is not in contact with the film. Film 201 is only in contact with blanket 213 when they are against drum 208. Accordingly, blanket 213 to drive film 201 only when film 201 is sandwiched between drum 208 and blanket 213, and it may be possible to choose a surface of blanket 213 that more easily releases film 201, such as a cross linked urethane. After film 201 leaves drum 208 and drum-out rolls 210 and 211, it is directed to knife 218. Knife 218 is disposed such that the film path therethrough is vertical. This allows for easier threading of the knife than if it were disposed horizontally. The threading will be easier so long as the path is predominantly vertical (more than a 45 degree angle to horizontal), although substantially vertical is preferred. Knife-in rolls 216 and 215 are provided to more accurately control the speed of film 201 as it passes through knife 218. At least one of rolls 215 and 216 is servo driven and controlled by controller 221. Similarly, at least one of rolls 219 and 220 is servo driven and controlled by controller 221. The user inputs a percent over/under speed into controller 221, and the knife-in and knife-out rolls are driven to the selected speed. As used herein knife-in and knife-out rolls refer to rolls upstream and downstream of the knife. It may be desirable for the film to be under more or less tension when being cut, so the user can select either. Alternatively, the user could select the speed of the knife-in rolls, and controller 221 could assign a speed to the knife-out rolls that returns the film to the original speed. Controller 221 has control outputs (not shown) connected to the various servo and other driven rolls, the air regulator that controls air cylinder 229, dancer assembly 203, drum 208 (which includes outputs to the seal bars and/or the blanket drives), knife 218 to control these elements. Alternatives include having controller 221 control fewer or more components. Controller 221 includes a touch pad, in the preferred embodiment, that allows the user to input various control parameters. These parameters include dancer pressure (PSI), overspeed of the drum-in nip (%), underspeed of the drum-out nip (%), overspeed of the knife-in nip (%), underspeed of the knife-out nip (%), and the temperature of the seal bars on drum 208. Alternative embodiments include the use of other sets of control parameters. Controller 221 includes a Giddings & Lewis PIC 900 PLC. Other microprocessor or analog based controllers could be used. The PLC includes a memory in which sets of operating parameters are stored. Up to 50 sets of parameters are stored in the preferred embodiment Each set is intended to be used with a particular type of bag being made. Hopefully, a skilled operator initially chooses the parameters by observing the process (or they could be factory set). Thereafter, the user only needs to select the correct set for the bag being made, and thus does not need much experience to run the machine. The various parameter sets could be accessed by number, where the user knows that, for example, set 5 is to be used for bag A. Alternatively, controller 221 could store bag types, and the user need only identify bag type being made, or input bag parameters such as film width, thickness etc. Other embodiment provide for common types of bags to have default parameters that could be adjusted by the user. The default parameters could be factory set, or set by an experienced user. Alternatively, film parameters, such as width and thickness could be determined by controller 221 using sensors such as photocells, the tension on dancer assembly 203 could be sensed (and speed determined) and controller 221 could calculate a parameter set using a formula or look-up table. The calculated parameter sets could be implemented by the user, or altered as needed. Numerous modifications may be made to the present invention which still fall within the scope of the appended claims. Thus, it should be apparent that there has been provided in accordance with the present invention a method and apparatus for making plastic bags that fully satisfies the objectives and advantages set forth above. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.

Claims: A plastic bag making machine comprising: a sealing drum (208); a drum-in nip (205, 206) formed with at least one drum-in servo-drive roll (205), and wherein the speed of the drum-roll is controlled by a controller, and the controller (221) connected to the drum-in nip and the sealing drum, wherein the controller includes a memory in which at least one set of operating parameters used to control the machine is stored, characterised in that the drum in nip overspeeds the film (201) and wherein the film travels directly from the overspeed means to the drum. The apparatus as claimed in claim 1 further including a drum-out nip (210,211) wherein the film travels from the drum to the drum-out nip, and wherein the drum-out nip is formed with at least one drum-out servo-driven roll (211), and wherein the speed of the drum-out roll is controlled by the controller. The apparatus as claimed in claim 1 further including an underspeed means (211), wherein the film travels from the drum to the underspeed means. Apparatus as claimed in claim 1 wherein the controller includes at least one input used to select the one set of operating parameters from a plurality of sets of operating parameters, and to enter at least one set of operating parameters, and a memory that stores the at least one set, and at least one output for controlling the machine. The apparatus as claimed in claim 4 wherein the bag machine includes a dancer assembly (203), and wherein the sealing drum 208 and the dancer assembly (203) are each connected to an output of the controller. The apparatus as claimed in claim 1 further including a dancer assembly (203) that receives a film (201) from which the bags are to be made, wherein the film travels from the dancer through the drum-in nip and directly to the drum; an air cylinder (229) connected to the dancer assembly, wherein the position of the air cylinder is dependent on the speed of the film; and the controller is in operative association with the air cylinder, wherein the controller senses the position of the air cylinder. The apparatus as claimed in claim 6 wherein the controller includes an input used to select the air cylinder pressure. The apparatus as claimed in claim 6 or 7 wherein the controller includes an input used to enter the air cylinder pressure, and a memory for storing the pressure. The apparatus as claimed in claim 1 further including a processing device (218); a dancer assembly (203) that receives a film (201) from which the bags are to be made and which travels through the apparatus of claim 1 and then to a drum out nip (210,211) comprising at last one processing servo driven roll (211) controlled by the controller, a device-in nip (215,216) connected to the controller, wherein the film travels from the drum-out nip to the device-in nip, and then to the processing device wherein the speed of the drum-out nip is controlled by the controller; and a device-out nip (219,220) connected to the controller, wherein the film travels from the processing device to the device-out nip. Apparatus as claimed in anyone of claims 1 to 4 or 9 wherein the controller includes an input used to select a one of the at least one set of operating parameters. Apparatus as claimed in anyone of claims 1 to 4 or 9 or 10 wherein the controller includes an input used to enter the at least one set of operating parameters.

Inventors: CLEMONS EDWARD, SAUDER CHARLES, STICKNEY MICHAEL, CLEMONS, EDWARD, SAUDER, CHARLES, STICKNEY, MICHAEL
Applicants: CMD CORP, CMD CORPORATION
Application year: 1998
Main classification: B31B23
IPC codes: B31B19, B31B23