Abstract:
A form-fill-seal packaging machine has a pull-down mechanism for advancing an elongated bag-making film, a longitudinal sealer for sealing the film in the longitudinal direction to make a tube and a transverse sealer for sealing the film transversely to form the bottoms and the tops of the bags, and is controlled such that the longitudinal sealer is activated for a specified length of time whenever a ready signal is outputted to the weigher to request a discharge of articles to be packaged but the operations of the pull-down mechanism and the transverse sealer are not started unless a signal is received from the weigher, indicating that it has discharged articles as requested.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a form-fill-seal packaging machine. More particularly, this invention relates to a control device for the longitudinal sealer of such a packaging machine. 
     Such a packaging machine of the so-called vertical pillow type transports an elongated thermoplastic bag-making material (the “film”) along the outer surface of a filling cylinder while bending it into a tubular form by means of a former and to seal the mutually overlapping side edges of the film by means of a longitudinal sealer and simultaneously both the top edge of the bag which has been filled and the bottom edge of the next bag to be filled by means of a transverse sealer. For the longitudinal sealing, a sealer employing a heat belt is commonly used. 
     A packaging machine of this type is usually operated without stopping except in the case of a trouble, transporting the film continuously. In the case of a packaging machine of the type forming a system with a weigher, the packaging machine serving as the “main” and the weigher serving as the “slave” such that the weigher will serve to supply articles to be packaged in response to a “ready” signal outputted from the packaging machine, the packaging machine may be designed to stop the transport of the film temporarily when no articles are supplied from the weigher for whatever reason and to remove the heater belt so as to separate it from the film. If no articles are supplied in the next cycle, however, the heater belt will heat the same portions of the film in preparation for the next packaging operation, thereby damaging the film and producing a defective bag. 
     If the mechanism for transporting the film and the heater belt are controlled so as to be activated together, however, the longitudinal sealing will not be effected sufficiently on the beginning portion of the film, again producing a defective bag which can easily break after transversely sealed. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention, in view of the problems described above, to provide an improved packaging machine which will not produce any defective package even when it is reactivated after the supply of articles is once stopped and then restarted. 
     A packaging machine embodying this invention, with which the above and other objects can be accomplished, may be characterized as having a control unit adapted to control the operations of the packaging machine as a whole such that the longitudinal sealer is operated for a specified period of time when a first ready signal is outputted to the weigher and the mechanism for the film transport and the transverse sealers are activated after waiting until a signal is received from the weigher, indicating that a discharge of articles has been completed. With a packaging machine thus structured, longitudinal sealing is carried out for a specified length of time required for the type of film being used when a ready signal is outputted to the weigher to request a discharge of articles to be packaged, but the operations of the mechanisms for advancing the film and transverse sealing are started only after a signal is received from the weigher, indicating that the requested discharge of articles has been carried out. 
     The invention provides packaging machines with the advantage that properly sealed bags can be produced even after the weigher failed to discharge articles to be packaged. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is a schematic presentation of a packaging machine embodying this invention with a portion shown as a block diagram; 
     FIG. 2 is a partially sectional plan view of the longitudinal sealer of FIG. 1; 
     FIG. 3 is a timing chart for explaining the delay time in the operation of the packaging machine; 
     FIG. 4 is a timing chart for the operation of a packaging machine of this invention; 
     FIG. 5 is another timing chart for the operation of a packaging machine of this invention with a different type of film; and 
     FIGS. 6 and 7 are still other timing charts for the operation of a packaging machine of this invention under different situations. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described next by way of an example. In FIG. 1, numeral  1  indicates a weigher such as a combinational weigher with a large number of weighing heads. A hopper  2  for receiving articles weighed by and discharged from the weigher  1  is disposed therebelow, and a former  3  for bending an incoming film  100  into a tubular form and a pull-down mechanism  5  for transporting the tubularly formed film  100  to a transverse sealer  7 . A longitudinal sealer  6  for longitudinally sealing together the mutually overlapping side edges of the tubularly formed film  100  is disposed below the hopper  2 . 
     FIG. 2 shows more in detail the longitudinal sealer  6 , as disclosed by the present inventor in Japanese Patent Publication Tokkai 6-239318. The longitudinal sealer  6  is disposed, like pull-down belts  51  for pulling the film  100  downward, proximally to a filling cylinder  4  through which articles to be packaged are dropped from the hopper  2  and includes a longitudinal sealer unit  63  which can be moved away from the filling cylinder  4  by means of a swing arm  62  rotatable around a support pin  61  when, for example, the filling cylinder  4  is exchanged. It also includes a positioning motor  64  for positioning a longitudinal seal belt  66  at an appropriate position according to the diameter of the filling cylinder  4  and an air cylinder  67  which operates by means of an electromagnetic valve  65  to release the compressive pressure by the seal belt  66  from the surface of the film  100  when the operation of the packaging machine has been stopped. In FIG. 2, numeral  68  indicates a knob for changing the seal position and numeral  69  indicates a sleeve for changing the angle of the seal belt  66  at which the film  100  is contacted. 
     In FIG. 1, numeral  10  indicates a control circuit forming a part of a host computer adapted to control the packaging machine as a whole, or the entire package-making system inclusive of the weigher  1 . As schematically shown in FIG. 1, the control circuit  10  includes ready signal outputting means  11 , discharge-end signal inputting means  12 , a timer  13 , calculating means  14 , and valve operating signal outputting means  15 . The ready signal outputting means  11  is for outputting a ready signal to the weigher  1 , when the user presses a ready button (not shown), to indicate that the packaging machine is ready to receive articles to be packaged, thereby causing the weigher  1  to discharge a weighed batch of articles. The discharge-end signal inputting means  12  is for receiving a discharge-end signal which is outputted by the weigher  1  when it finishes discharging a batch of articles to the packaging machine and responding to it by outputting a signal to the timer  13 . The timer  13  is for counting a specified delay time T 1  (to be explained below) from the moment when it receives the signal from the discharge-end signal inputting means  12  and then outputting a start signal to a pull-down motor  52  of the pull-down mechanism  5  and an arm-driving motor  72  of the transverse sealer  7 . The calculating means  14  is for subtracting time length T 2  (the “longitudinal seal time”) required for the longitudinal sealing from the aforementioned delay time T 1 , when an operation-starting switch (not shown) is pressed, and transmitting a signal indicative of the result of this calculation to the valve operating signal outputting means  15 . The valve operating signal outputting means  15  serves to output an operating signal to the electromagnetic valve  65  in the beginning in response to an output signal from the calculating means  14  and later in response to a signal from the timer  13 . An input device  16  through which the longitudinal seal time T 2  is inputted to the calculating means  14  for each selected kind of film  100  may also be considered a part of the control circuit. 
     The aforementioned delay time T 1  will be explained next with reference to FIG. 3 which is a timing chart for the operation of the seal jaws  71  with respect to the other components. Detailed accounts of how a transverse sealer of the type shown at  7  in FIG. 1 have been available, say, in U.S. Pat. No. 5,753,066, and hence will not be repeated here. When the weigher  1  starts to discharge a batch of articles in response to a ready signal from the packaging machine, the motion of the seal jaws  71 , which are waiting at their specified starting positions  710 , is started with this delay time T 1  such that the seal jaws  71  come to engage each other with the film  100  in between when the dropped articles have passed the position of the engagement of the seal jaws  71 . In other words, the delay time T 1  is determined by the speed of motion of the seal jaws  71 . As explained above, the downward motion of the film  100  by the pull-down belts  51  is also started after this delay time T 1 . The longitudinal seal time T 2 , on the other hand, is dependent on the kind of the film  100  and is determined such that the longitudinal sealing can be accomplished securely and dependably over the entire distance between the pulleys for the seal belt  66 . 
     The operation of the packaging machine structured as described above will be explained next with reference to FIG. 4 as well as FIG.  3 . The longitudinal seal time T 2 , dependent on the type of the film  100  as explained above, is preliminarily inputted to the calculating means  14  through the input device  16 . When the operating switch (not shown) is pressed thereafter, a ready signal is transmitted (at time t a ) from the ready signal outputting means  11  of the packaging machine to the weigher  1 , requesting that articles for packaging be discharged. At the same time, the calculating means  14  subtracts the inputted longitudinal seal time T 2  from the delay time T 1 . Let us assume now that the weigher  1  did not output any discharge-end signal for a specified length of time T 3  after the output of the ready signal (at time t a ). At time t b  after time period T 1 -T 2  has farther elapsed, the electromagnetic valve  65  is activated by a signal outputted from the valve operating signal outputting means  15  so as to operate the air cylinder  67 , causing the longitudinal seal belt  66  to be pressed onto the mutually overlapping side edges of the film  100  for the inputted seal time T 2  and thereby carrying out the longitudinal sealing. 
     If no discharge-end signal from the weigher  1  is received by the discharge-end signal inputting means  12  although the ready signal has been transmitted, the timer  13  is not allowed to start operating and hence the pull-down mechanism  5  and the transverse sealer  7  remain inactive. 
     FIG. 4 shows a situation where the weigher  1  still fails to output a discharge-end signal in response to the second ready signal transmitted from the ready signal outputting means  11  of the packaging machine to the weigher  1  after a period for one cycle has elapsed (that is, in the second cycle, indicated by numeral “ 2 ” in FIG.  4 ). If a discharge-end signal is received only at time t c  in the nth cycle (indicated by letter “n” in FIG.  4 ), the timer  13  begins to count time, as shown in FIG.  3  and after a time period equal to the delay time T 1  has been counted, or at time td, the electromagnetic valve  65  and the motors  52  and  72  are activated such that air begins to be supplied to the air cylinder  67 , the pull-down belts  51  begin to pull the film  100  downward and the seal jaws  71  of the transverse sealer  7  begin their motion. Since the tubularly formed film  100  is already sealed longitudinally during the first cycle of operations, the making of a bag is thus completed and the bag is discharged as a finished product. Let us now assume that the weigher  1  does not fail to output a discharge-end signal in response to a ready signal in the (n+1)st cycle and thereafter. The electromagnetic valve  65  and the motors  52  and  72  for the pull-down mechanism  5  and the transverse sealer  7  will go into a continuous mode of operations to operate the longitudinal seal belt  66 , the pull-down belts  51  and the seal jaws  71 , respectively. 
     FIG. 5 shows a timing chart for the operation when the type of the film  100  is such that the required longitudinal seal time T 2  is longer than the delay time T 1 . When the operation-starting switch (not shown) is pressed in such a case, the valve operating signal outputting means  15  activates the electromagnetic valve  65  at time t b ′ earlier by |T 1 -T 2 | (or T 2 −T 1 ) than the time by which the aforementioned specified time period T 3  has elapsed since a ready signal was outputted. Other than that, the timing chart in this case is the same as shown in FIG.  4 . 
     Only situations wherein the weigher  1  fails to output a discharge-end signal in response to the ready signal in the first cycle of its operation have been described above. Let us now consider situations wherein the weigher  1  does not fail to output a discharge-end signal in the first cycle of its operation in response to a ready signal. In such a situation, the timer  13  is started before or after the electromagnetic valve  65  is activated, as shown in FIGS. 6 and 7, respectively, depending on whether the longitudinal seal time T 2  is shorter or longer than the delay time T 1 , and the operations of the pull-down mechanism  5  and the transverse sealer  7  are started after the elapse of the delay time T 1 . 
     FIGS. 6 and 7 show situations wherein the weigher  1  continues not to fail to output a discharge-end signal in response to the ready signal but does fail to do so in the third cycle of its operation. As the discharge-end signal is outputted in the second cycle, FIGS. 6 and 7 show that the electromagnetic valve  65  and the pull-down and arm-driving motors  52  and  72  of the pull-down mechanism  5  and the transverse sealer  7  operate the longitudinal seal belt  66 , the pull-down belts  51  and the seal jaws  71  in a continuous mode of packaging operations. In the third cycle, however, as the weigher  1  fails to output a discharge-end signal even after waiting for the specified wait period of T 3  after the ready signal is outputted, the electromagnetic valve  65  is deactivated to remove the longitudinal seal belt  66  from the overlapping edge portions of the film  100 , the arm-driving motor  72  is stopped such that the seal jaws  71  will rest at their starting positions  710 , and the pull-down motor  52  is decelerated and stopped such that the upper end of the longitudinally sealed portion of the film  100  will come to a position somewhat above the lower end position of the seal belt  66  and stop after the delay time T 1  has further elapsed. By this time, the articles which were discharged in response to the ready signals in the first and second cycles are already packaged. 
     The operations in the fourth and subsequent cycles are the same as explained above with reference to FIGS. 4 and 5. In FIGS. 4,  5 ,  6  and  7 , ready signals are outputted automatically and periodically to the weigher  1  from the second cycle onward. 
     Although not separately illustrated, it goes without saying that the present invention is applicable to packaging machines adapted to be operated in the so-called intermittent mode of film transportation in which the film is transported not in a continuous manner but in an intermittent manner.