Abstract:
A pair of pull-down belts pulls longitudinally a tubularly formed elongated bag-making film along a filling cylinder of a bag maker-packaging machine. A pair of members supporting the pull-down belts can move towards or away from each other depending on the size of the former, and elastic springs for providing each of the pull-down belts with a force which depends on their relative positions with respect to the corresponding belt-supporting members. An adjustment motor moves the pull-down belts initially to specified reference positions separate from the tubularly formed film and therefrom towards the filling cylinder. The distance traveled by the pull-down belts from their reference positions towards the filling cylinder is monitored. The distance by which the pull-down belts must be moved for each of different kinds of former is measured and stored in a memory device. Thus, whenever a particular former is selected and installed, the pull-down belts can be automatically moved to optimum positions for pulling down the film effectively by controlling the adjustment motor.

Description:
This is a continued prosecution application of application Ser. No. 08/887,360, filed Jul. 2, 1997, which is a continuation-in-part application of application Ser. No. 08/678,638, filed Jul. 10, 1996 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus, generally referred to as a pull-down belt, for pulling a cylindrically formed bag-making material for a bag maker-packaging machine. More particularly, this invention relates to such a bag maker-packaging machine having an improved positioning mechanism for its pull-down belts. 
     A bag maker-packaging machine, for example, of a so-called vertical pillow type, is generally adapted to bend an elongated web of a thermoplastic flexible bag-making material (hereinafter referred to as “the film”) into a cylindrical form around a filling cylinder by means of a component known as the former, to simultaneously seal together its mutually overlapping side edge parts and to use a pair of pull-down belts to pull it further down to a transverse sealer for sealing the cylindrically formed film transversely to the direction of its motion. The filling cylinder is for the purpose of dropping articles therethrough to be packaged, and a plurality of formers with different sizes are usually made available for handling films with different widths and different ways of sealing. Most pull-down belts which have been used for this purpose are of the type which will forcefully compress the film between the belt and the filling cylinder while the film is being pulled downward. Pull-down belts of this type have the disadvantage that a roller or a slidable plate is required to be buried inside the filling cylinder, thereby narrowing the available passage for the articles dropped therethrough. With pull-down belts of this type, furthermore, it has been difficult to programmatically adjust the contact pressure. 
     The present inventor has disclosed, in Japanese Patent Publication Tokkai 5-4609, another type of pull-down belt adapted to pull down a film while causing it to be pulled toward the belt surface by creating a negative pressure condition. Pull-down belts of this type are able to overcome the problems of the kind described above, but they have different problems such as not being able to pull the film effectively if the gap between the belt and the film is either too large or too small because the suction force by the negative pressure may weaken, or cause a zigzag motion of the film if the gaps between the film and the pair of belts on opposite sides thereof are not equal. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to overcome all these problems of prior art pull-down belts, by providing a new apparatus capable of transporting a cylindrically formed film while pressing the film evenly and lightly such that the friction force generated thereby with the film will not be strong enough to pull it down. 
     It is another object of this invention to provide an improved bag maker-packaging machine capable of causing its pull-down belts to come into contact with the film every time in an optimum condition on the basis of the measured distance between specified reference positions for the belts and the surface of the film. 
     It is a further object of this invention to provide such an improved bag maker-packaging machine capable of causing its pull-down belts to come into contact with the film every time in an optimum condition by an effect of learning. 
     An apparatus embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a pair of pull-down belts for pulling a cylindrically formed film along a filling cylinder, a pair of belt-supporting members adapted to move towards or away from each other depending on the size of the former, and elastic springs for providing each of the pull-down belts with a force which depends on the relative positions of the pull-down belts with respect to the corresponding belt-supporting members. An adjustment motor is adapted to move the pull-down belts initially to specified reference positions and therefrom towards the filling cylinder. The distance traveled by the pull-down belts from their reference positions towards the filling cylinder is monitored. The distance to be moved for each of different kinds of former is measured and stored in a memory device. Thus, whenever a particular former is selected and installed, the pull-down belts can be automatically moved to optimum positions for pulling the film down effectively by controlling the adjustment motor. 
    
    
     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 diagonal view of a portion of a film transporting mechanism embodying this invention; 
     FIG. 2 is a plan view of a portion of the film transporting mechanism of FIG. 1; 
     FIG. 3 is a diagonal external view of a vertical pillow type packaging machine incorporating the mechanism embodying this invention; 
     FIG. 4 is a block diagram of the control unit for the packaging machine of FIG. 3; 
     FIG. 5 is a plan view of a portion of another film transporting mechanism embodying this invention; and 
     FIG. 6 is a flow chart of the operation of the packaging machine of FIG. 4 according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 shows schematically a bag maker-packaging machine of a vertical pillow type, which incorporates the present invention. A flexible, elongated thermoplastic bag-making material (the film S) is originally in the form of a web roll  92  supported around a shaft  95  (serving as web supporting means). The film S is pulled out of the web roll  92  by a pair of pull-down belts  4  and guided by a plurality of guide rolls (including dancer rollers)  105  to a former  2  disposed below a hopper  1 . The function of the former  2  is to bend the film S into a tubular shape, and the tubularly shaped film S is then pulled downward along the peripheral surface of a filling cylinder (sometimes also referred to as a former tube)  3  towards a transverse sealer  110 . The transverse sealer  110  is for horizontally (that is, transversely to the downward motion of the film S) sealing the film S such that a batch of articles which is dropped simultaneously through the hopper  1  can be sealed inside the bag being formed. Each of the pair of pull-down belts  4  is provided with a suction chamber  5  connected to a negative pressure source (not shown) while longitudinal seal parts of the film S are sealed together by means of a longitudinal sealing jaw  8  (shown somewhat removed from the filling cylinder  3  for clarity). There is also provided an adjustment mechanism  10  for causing the pair of pull-down belts  4  to move towards or away from each other according to the size of the former  2  which is currently installed. The adjustment mechanism  10  comprises a pair of elongated mutually parallel belt-supporting members  13 , disposed in a side-by-side relationship, each supporting a corresponding one of the pull-down belts  4  and being supported so as to be horizontally slidable along a guide rod  12  having both its ends supported by main frames  11  (only one of them shown) of the apparatus. This pair of belt-supporting members  13  can be moved towards or away from each other in a mutually coordinated manner by means of a turnbuckle  16  adapted to be driven by an adjustment motor  15  disposed on one side of the main frames  11 . 
     As shown in FIGS. 1 and 2 in detail, there is a fine-adjustment mechanism at one end of the supporting members  13 . Each pull-down belt  4  and a belt-driving motor  6  therefor are both supported by a belt-supporting plate  18 , and an L-shaped (when seen from above, as shown in FIG. 2) block  19  is attached to its back surface (away from the belt  4 ). This assembly is referred to below as “the pull-down belt unit”. This L-shaped block  19  and one end part of a corresponding one of the pair of belt-supporting members  13  are connected to each other by means of a parallelogram linkage mechanism formed with a pair of elongated connectors  20  connected so as to remain parallel. A forward protrusion  21  is formed from each belt-supporting member  13 , and a weak elastic spring  22  is inserted between this protrusion  21  and the L-shaped block  19  such that the pull-down belt  4  is normally supported at its neutral (unloaded) position. 
     There is a position-indicating rod  23  attached to the L-shaped block  19 , penetrating through and protruding to one side of the belt-supporting member  13 . A limit switch  25  is attached to the belt-supporting member  13  for detecting the distance of this protrusion and outputting a stop signal for stopping the adjustment motor  15  according to this distance of protrusion. The position-indicating rod  23  and the limit switch  25  may be together also referred to as the position-indicating means. 
     FIG. 4 shows a control unit  30  for the adjustment mechanism  10  including a memory device  33 , comparing means  34 , data selecting means  32  and a counting means  35 . The counting means  35  is for counting the number of rotations of the adjustment motor  15 , on the basis of outputted pulse from an encoder  17  attached to its shaft, representing the distance travelled by the pull-down belts  4  from their reference positions, which are pre-specified positions for the pull-down belts  4  separate from the filling cylinder  3 , until a stop signal is received from the limit switch  25 . The memory device  33  is for storing data received from the counting means  35  counted for each type of former. The data selecting means  32  is for receiving signals from an external input means  31  such as a keyboard or a touch panel through which necessary data can be inputted by the user, selectively retrieving data which are stored in the memory device  33  for each former and transmitting them to the comparing means  34 . The comparing means  34  is for comparing data received from the data selecting means  32  with the count data from the counting means  35  and outputting a deceleration signal to a motor control device  36  immediately before their coincidence to thereby cause the adjustment motor  15  to decelerate and a stop signal at the time of their coincidence to thereby stop the motion of the adjustment motor  15 . 
     Operations of the apparatus thus structured will be explained next with reference to the flow chart shown in FIG.  6 . 
     First, a former  2  and a film roll appropriate for the packages to be produced are selected and installed on the machine and the film S is pulled out of the roll to the filling cylinder  3 . The identification of this selected former  2  is inputted through the input means  31  (say, by key operations) to the memory device  33  (Step Sl), and a start switch (not shown) is thereafter switched on (Step S 2 ) to activate the adjustment motor  15  and to move the pair of belt-supporting members  13  engaged with the turnbuckle  16  such that the pull-down belts  4  go back to their specified reference positions (Step S 3 ). 
     Let us assume firstly that data on the former  2  which has just been installed were not stored in the memory device  33  (NO in Step S 4 ). In this situation, the pull-down belts  4  are moved from their reference positions towards the filling cylinder  3  (Step S 5 ), while the distance travelled by them are monitored by counting the number of pulses received from the rotary encoder  17  (Step S 6 ). As the pull-down belts  4 , attached to the belt-supporting members  13  through the aforementioned linkage mechanism and hence movable with respect thereto, come lightly into contact with the film S moving along the outer surface of the filling cylinder  3 , they are each against the elastic force of the associated one of the springs  22 , and the film S can be easily pulled down by the pull-down belts  4  because it is being adsorbed to their inwardly-facing surfaces, not because of friction between the pull-down belts  4  and the film S. After the pull-down belts  4  are thus positioned, the limit switch  25  on either of the supporting members  13  will detect the protruding position-indicating rod  23  and output a detection signal to the counting means  35  to stop its counting and to the adjustment motor  15  to stop its rotation (YES in Step S 7 ), causing the adjustment motor  15  to stop and hence also the motion of the pull-down belts  4  towards the filling cylinder  3  (Step S 8 ). The number of the counted pulses, representing the distance between the reference positions of the pull-down belts  4  and where they are thus stopped, is then stored in the memory device  33  (Step S 10 ). 
     Although not separately shown, a manually adjusting mechanism may be employed, in addition to the adjustment motor  15 , to move the pull-down belts  4  forward and backward in a step-wise fashion. If such a mechanism is incorporated, the pull-down belts  4  may be manually pulled back (Step S 9 ), after they come into contact with the film and their motion is stopped in Step S 8 , to optimum positions for supporting the film S by the suction force. 
     If data on the installed former  2  are already stored in the memory device  33  (YES in Step S 4 ), the number of pulse counts representing the distance travelled to such a lightly contacting position in the case of this former  2  is retrieved from the memory device  33  to the comparing means  34 . As the pull-down belts  4  are moved towards the filling cylinder  3  (Step S 11 ), the count numbers of the pulses transmitted from the rotary encoder  17  are sequentially received by the comparing means  34  (Step S 12 ). When the received count number matches this retrieved value corresponding to the former  2  (YES in Step  13 ), a match signal is outputted from the comparing means  34 . The motor control device  36 , upon receiving this match signal from the comparing means  34 , stops the adjustment motor  15  and hence the motion of the pull-down belts  4  towards the filling cylinder  3  (Step S 14 ), thereby causing the pull-down belts  4  to lightly contact the film S around the filling cylinder  3  by a learning effect and allowing the film S to be pulled down by the suction force of the pull-down belts  4  towards the transverse sealer  110  shown in FIG. 3, as explained above. 
     This routine is repeated for each available former  2  with a different size such that an optimum position of the pull-down belts  4  corresponding to each former  2  can be preliminarily stored by a learning process in the memory device  33  in terms of pulse counts counted by the counting means  35 . After all these data are stored in the memory device  33 , the operator has only to specify the former  2  (or its size), say, on a touch panel serving as the input means  31 . The data selecting means  32  thereupon retrieves from the memory device  33  a corresponding data item for the specified former and transmits it to the comparing means  34 . Based on this data item and the number counted by the counting means  35 , the control unit  30  outputs a signal immediately before their coincidence will occur and another signal at the time of their coincidence, as explained above, to decelerate and stop the adjustment motor  15  without relying on the outputs from the limit switch  25  such that the two pull-down belts  4  are correctly positioned. When an operation is once interrupted and then restarted, the pull-down belts  4  are first returned to their reference positions and can then be automatically and reliably set at their optimum contact positions with the film S. 
     The invention has been described above with reference to only one example, but this example is not intended to limit the scope of the invention. Many modifications and variations are possible within the scope of the invention. For example, this invention is applicable also to the type of bag maker-packaging machine having no filling cylinder to keep the tubularly formed film open such that articles dropped from above can easily pass therethrough. The tubularly formed film in such a case is kept open by adsorption onto pull-down belts each provided with a suction chamber connected to a negative pressure source, and a longitudinally elongated backing plate may be provided such that the longitudinal sealing jaw can press the film against it for effecting the longitudinal sealing. Although a linkage mechanism with a weak elastic spring was disclosed above as an example of fine-adjustment mechanism, this may be replaced by a simple structure using a pair of simple plate springs, as shown at  28  in FIG. 5, in which other components which are substantially similar to those shown in FIG. 2 are indicated by the same numerals. Numeral  29  indicates an elongated member adapted to move with the belt-supporting plate  18  and to activate the limit switch  25  for controlling the deactivation of the adjustment motor  15 . The contact pressure between the pull-down belts  4  and the filling cylinder  3  may be adjusted by providing proximity switches where their contacts are to occur and reversing the direction of rotation of the adjustment motor  15  after a detection signal is outputted from them. Moreover, the invention is applicable also to the kind of bag maker-packaging machine having only one pull-down belt (instead of a pair facing each other and at a 90 degree position from the longitudinal sealing jaw  8 , as shown in FIG. 2) disposed opposite the longitudinal sealing jaw  8 . In summary, all such modifications and variations that may be apparent to a person skilled in the art are intended to be within the scope of this invention.