DE69510204T2 - Shaped shoulder for a device for manufacturing bags and method for the production thereof. - Google Patents

Description

This invention relates to a forming shoulder for a bag maker and to a method for producing such a forming shoulder. This invention also relates to packaging machines having such a forming shoulder.

A bag making packaging machine, such as a vertical pillow type form-fill-seal packaging machine described, for example, in U.S. Patent 5,237,798, issued August 24, 1993, uses a component commonly referred to as a forming shoulder to bend an elongated flexible bag making material into a cylindrical shape and generally consists of a vertically extending tubular member and a so-called shoulder member (sometimes referred to as a skirt member) having an inclined planar guide portion. The bag-making material, for example in the form of a web, is longitudinally fed horizontally in a flat shape to the forming shoulder, moves over and along this inclined planar guide portion of the shoulder part, sharply changes its direction of movement when it crosses the connecting line where the tubular part and the shoulder part are connected to each other to move into the tubular part, and is pulled axially downward along the inner surface of the tubular part. In other words, the bag-making material is first pushed upward over the inclined planar guide portion of the shoulder part, sharply changes its direction of movement at the connecting line when it is folded into a tubular shape, and is then pulled not only by the force of the articles fed to be packed in the formed bag but also by a pull-out belt or the like (not shown) for causing the movement of the bag making material. Thus, it is crucial that the joint line where the bag making material is forced to sharply change its direction of travel is a continuous smooth curve that is correctly shaped because if it is not correctly shaped or has even a small unevenness, the material will easily become wrinkled or develop small longitudinal lines on the surface.

Farm shoulders of this type are usually manufactured by molding, with a master mold then used to perform an accurate copying operation to correctly form the joint line. However, this requires a long time of hard work by a skilled worker in addition to the manufacturing cost and results in variations and unevenness in the shape of the mold shoulders, making them irreplaceable. Furthermore, many mold shoulders are usually required to produce bags of different sizes. Even when bags of the same size are produced, different mold shoulders are usually required depending on where and how the side edges of the elongated bag-making material are to overlap to be sealed or joined in the longitudinal direction. The angle of the inclined planar guide portion of the shoulder part must also be changed depending on the physical properties of the bag-making material such as its thickness. In short, the cost of equipping a bag maker with a sufficient number of forming shoulders of different types is considerable when using conventional technology.

US-A-3 636 826 describes a forming shoulder according to the preamble of claim 1 and has a folding shoe which, when unfolded, has a neck curve with a segment defined by the equation

where W and F are constants and X and Y are location coordinates.

GB-A-913114 and DE-A-40 38 888 describe alternative forming shoulders. GB-A-913 114 further describes a packaging machine according to the preamble of claim 16.

According to one aspect of the present invention, a forming shoulder for forming an elongated planar bag-making material into a tubular shape comprises a hollow cylindrical tubular member having an inner surface defining an axial direction and a shoulder member having a planar guide portion and connected to the tubular member along a connecting line surrounding the tubular member so that the material is guided over the planar guide portion of the shoulder member, sharply changes the direction of movement to the axial direction at the connecting line and is formed into a tubular shape along the inner surface of the tubular member, wherein the angle between the tangent to the connecting line and a plane perpendicular to the axial direction changes at a constant ratio.

According to a second aspect of the present invention, a method of manufacturing a forming shoulder adapted to form an elongated planar bag-making material into a tubular shape and having a hollow cylindrical tubular member defining an axial direction and a shoulder member having a planar guide portion connected to the tubular member along a connecting line so that the material is conveyed over the planar guide portion of the shoulder member, the direction of movement changes sharply to the axial direction at the connecting line and is formed into a tubular shape along the inner surface of the tubular member, comprises the steps of: cutting a tube-forming member and a shoulder-forming member from a flat blank, each of the members having a specific geometric shape with a certain distance between side edges and a curved edge portion, bending the tube-forming part into the tubular shape to form the tubular part by bringing the side edges together, bending the shoulder-forming part to form the shoulder part by forming the planar guide portion and to match the curved edge portion of the shoulder-forming part with the curved edge portion of the tube-forming part, and connecting the bent parts to each other along the curved edge portions to form the connecting line, the connecting line being shaped such that the angle between the tangent to the connecting line and a plane perpendicular to the axial direction changes at a constant ratio.

This invention provides a method for the accurate and automatic production of forming shoulders of various types.

This invention further provides forming shoulders produced by such a method, the tubular parts and shoulder parts of which are produced by bending parts cut from a blank by means of a numerically controlled cutting machine.

In one example, a forming shoulder according to the present invention may be characterized not only by being composed of a hollow cylindrical tubular member defining an axial direction and a shoulder member having a planar guide portion and being attached to the tubular member along a closed three-dimensional line or curve (referred to as the connecting line) so that an elongated bag-making material conveyed over the inclined planar guide portion of the shoulder member can be formed into a tubular shape when it crosses the connecting line to move into the tubular member, but that the aforementioned connecting line between the tubular member and the shoulder member is shaped such that the angle between its tangent and a plane perpendicular to the axial direction of the tubular part varies with a constant ratio with respect to the change in the position of the point of contact of the tangent with the connecting line, for example in the direction perpendicular to the axial direction of the tubular part or along the connecting line itself.

To produce such a forming shoulder according to the present invention, parts to be made into the tubular part and the shoulder part are cut out from a blank or sheet metal having certain geometric shapes, appropriately bent and folded into predetermined shapes of the tubular part and the shoulder part and joined, for example, by welding along the aforementioned joining line. The geometric shapes into which the blank is cut are determined such that when these parts are bent, folded and joined together as previously described, the joining line therebetween will satisfy the conditions set by this invention as described above with respect to the change ratio of their pitch.

Depending on the type of sealing desired, side strips of different widths can be provided along the side edges of the parts to be cut out of the blank.

The accompanying drawings, which are incorporated in and constitute 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 view of a forming shoulder according to the present invention as part of a vertical pillow type bag making packaging machine;

Figures 2A and 2B are plan views of sections of blank material cut, respectively, to form a shoulder portion and a tubular portion of a forming shoulder according to this invention;

Fig. 3A and 3B are perspective views of second tube-forming parts shortly before they are made into a tubular part of a forming shoulder;

Fig. 4 is a graph showing the curved edge portions of Figs. 2A and 2B;

Fig. 5 is a projection of the forming shoulder according to this invention onto the ξ-plane;

Fig. 6A, 6B, 6C and 6D are sketches of different ways of producing a longitudinal seal for producing bags; and

Fig. 7 is a schematic view of a portion of a form-fill-seal type packaging machine incorporating the forming shoulder of Fig. 1.

Fig. 1 shows at 10 an example of forming shoulders according to the present invention, which is substantially similar to a conventional forming shoulder, consisting of a funnel 15, a tubular part 20 and a shoulder part 30, which are connected to one another. The three-dimensional curved closed line along which the tubular part 20 and the shoulder part 30 are connected is referred to as a connecting line 40 (and also designated by the letter Q).

To form the tubular part 20 and the shoulder part 30, a plate-shaped tubular material is cut into specific geometric shapes as shown in Fig. 2A and 2B, which are bent and joined together. For the purpose of description, the parts thus cut from a blank Parts referred to here as the tube-forming part 52 and the shoulder-forming part 53 respectively.

Fig. 3A shows how the tube forming part according to Fig. 2B can be bent into a tubular shape to form the tubular part 20. It should be noted that both the tube forming and shoulder forming parts 52 and 53, respectively, have a curved edge portion 54. When the tube forming and shoulder forming parts 52 and 53, respectively, are bent to form the tubular part and shoulder parts 20 and 30, their curved edge portions 54 become the connection line 40 along which the tubular part and shoulder parts 20 and 30 are connected to one another. The desired shape of the joint line 40 and the problem of how to determine the shape of the curved edge portion 54 when the tube forming part and the shoulder forming part 52 and 53 are cut out will be discussed next.

Roughly described, the tubular member 20 has the shape of a cylinder cut along an inclined plane as shown in both Fig. 1 and 3A. For the description, it is assumed that the tubular member 20 stands vertically upright or has a vertical axial direction as shown in Fig. 3A, with the highest and lowest points of the connecting line Q designated by the letters O and A, respectively. For convenience, a three-dimensional rectangular coordinate system having mutually perpendicular ξ, η, and axes is defined as shown in Fig. 3A, with the origin at 0, the axis extending vertically downward, and the lowest point A of the connecting line Q on the ξ plane. The ξη plane is also referred to as the horizontal plane, and the projection of the cylindrical shape of the tubular member 20 onto the horizontal plane is referred to as the cross-sectional curve. Cross-sectional curves that are symmetrical with respect to the ξ-axis, such as a circle, and connecting lines that symmetric with respect to the ξ -plane are contemplated throughout, although this is not intended to limit the scope of the invention.

Fig. 4 shows the shape of the curved edge portion 54, i.e., the portion of the tube-forming part 52 which, when bent, will form the connecting line Q. In other words, Fig. 4 shows the curve obtained in accordance with the connecting line Q when the tubular part 20 shown in Fig. 3A is bent and unrolled. This two-dimensional curve representing the aforementioned curved edge portions 54 is hereinafter referred to as the edge curve, and a two-dimensional rectangular coordinate system with mutually perpendicular x and z axes is defined for convenience as shown in Fig. 4, where the z axis coincides with the -axis and the origin O is at the same location as shown in Fig. 3A.

Roughly speaking, the object of this invention is to properly design the edge curve so that a bag-making material (denoted by letter f in Fig. 1) will smoothly change its direction of movement when it is drawn over the connecting line Q. It is thus clear that the edge curve in Fig. 4 should be a smoothly curved curve. However, this condition alone is not sufficient to determine the shape of the curve. According to this invention, the connecting line Q must change its slope smoothly. More specifically, the angle between the tangent to the connecting line Q and the horizontal plane should change at a constant ratio.

According to an embodiment of the invention, the aforementioned constant ratio refers to the x-coordinate of the point of contact at which the connecting line Q and its tangent touch each other. In other words, the slope of the tangent of the connecting line Q must be constant Ratio related to the vertical component of the change in the location of the contact point between the connecting line Q and its tangent with respect to the axial direction of the tubular part 20. If an arbitrary point on the connecting line Q is designated as P, the slope at the point P determined above is the tangent with the angle γ shown in Fig. 4. Thus, since the tan = dz/dx when z = z(x) is the equation of the edge curve shown in Fig. 4, the condition established according to the first embodiment of the invention can be written as follows:

d(dz/dx)/dx = a(constant). (1)

Because the connecting line Q must be smooth or continuous and symmetrical with respect to the ξ -plane, tan = 0 when x = 0 and one therefore obtains by simple integration of (1):

dz/dx = ax. (2)

If the height difference between the points O and A or the distance between them along the -axis is denoted by H and the width of the bag to be formed by the forming shoulder is denoted by B, as shown in Fig. 2A and 2B, by integrating (2) we obtain:

z = (H/W²)x², (3)

i.e. the edge curve shown in Fig. 4 should be a parabola.

If the cross-sectional curve is a circle with radius r (= B/π) as a special example, the ξ-coordinate and the x-coordinate of the arbitrary point P on the connecting line Q through

ξ = r(1 - cos(x/r)) (4)

in relationship and consequently

d /dξ = (dz/dx)(dx/dξ) = - (2Hx/B²) /sin (x/r). (5)

Consequently, the angle between the ξ-axis and the projection of the connecting line Q at the highest point O of the connecting line Q is

tan-¹(2Hr/B²) = tan-¹(2H/π²r) (6)

certainly.

According to another embodiment of this invention, the aforementioned constant relationship exists along the connecting line Q itself. If the distance of the arbitrary point P from the origin O along the connecting line Q (or the edge curve) is denoted by s as shown in Fig. 4, this condition can be expressed as follows:

d(tan γ)/ds = d(dz/dx)/ds = a(constant). (7)

Because ds = {1 + (dz/dx)²}1/2dx, (7) can be written as follows if one sets y = dz/dx:

dy/ds = (dy/dx)(dx/ds) = (dy/dx)/(1 + y²)1/2 = a. (8th)

If (8) is integrated with the condition that y = 0 when x = 0,

log {y + (1 + y²)1/2} = ax. (9)

This has the following solution:

y = dz/dx = sinh(ax). (10)

If (10) is integrated with the condition that z = 0 when x = 0, the following is obtained as the equation of the edge curve:

z = (cosh(ax) - 1) /a. (11)

This result is also independent of the shape of the cross-sectional curve.

The portion of the shoulder part 30 that coincides with the connecting line Q is identically shaped. This must be so because each piece of the bag-making material f must travel the same path before and after it is formed into a tubular shape.

As shown in Fig. 1, the shoulder part 30 has an inclined planar guide portion 33 over which the bag-making material f must slide upwards before the direction of its movement is suddenly changed downwards when it reaches the connecting line 40. The angle of this planar guide portion 33 with the horizontal direction is designated ρ in Fig. 5. Fig. 5 also shows the projection of the connecting line Q onto the ξ plane.

If the cross-sectional curve is a circle, the angle δ between this inclined planar guide section 33 of the shoulder part 30 and the projection of the connecting line Q onto the �xi -plane from (6) is given by

δ = ? - ρ - tan&supmin;¹(2H/π²r) (12)

given.

It has been found experimentally that good results are obtained when δ is about 110º or 11π/18. Substituting this into (12) we obtain:

H = (π²r/2)tan{(7π/18) - π}. (13)

If the angle ρ of the inclined plane guide portion 33 is set equal to t/4 as a typical example, H = 0.233π²r. Thus, it becomes possible to design standardized forming shoulders.

After the longitudinally elongated bag-making material f is bent into a tubular shape by the forming shoulder, its side edges are overlapped and joined, glued or welded together. However, as shown in Figs. 6A, 6B, 6C and 6D, there are many different ways to perform this longitudinal sealing operation. Fig. 6A shows a standard ridge seal, where the inner surfaces of both side edges of the material are joined together and the two side edges are then folded in one direction. Fig. 6B shows a lap seal, also sometimes referred to as an envelope seal, where the inner surface of one side edge is joined to the outer surface of the other edge. Depending on the type of seal desired, both the positions and the widths of the joined areas must be determined differently. Fig. 6C shows a type of offset sealing wherein the overlapped edges are folded in one direction so that either the fold line or the outer edges are in the middle in the width direction of the bag. In this case too, both the positions and the widths of the areas for making the connection vary depending on the type of sealing. Fig. 6D shows still another sealing wherein the edges are folded in the reverse direction after a ridge seal has been made. When the tube-forming member is bent to form the tubular member, its side edge parts are either overlapped as shown in Fig. 3A or made to form a flat part 34 as shown in Fig. 3B so that a pair of mutually opposed vertical sealers (not shown) to form a ridge seal. In summary, the width W of the narrow strip for forming an overlap when cutting a blank as shown in Figs. 2A and 2B should be determined depending on what type of seal is desired when making bags at a later stage after the bag making material f has been bent into a tubular shape by the forming shoulder.

After the width W of the overlap is thus determined and the constants in (3) or (11) for the connecting portion are determined, for example, on the basis of the size of the bags to be produced, the shape shown in Figs. 2A and 2B in which the blank is to be cut is determined. Accordingly, a CAD/CAM system can be used to generate a numerical control program automatically on the basis of such determinations as well as physical properties of the blank plate such as its thickness. A numerically controlled laser cutter is operated by such a program to cut a blank plate as shown in Figs. 2A and 2B in individual lines and obtain parts to be bent to make the tubular part and the shoulder part. These parts are positioned together along their connecting lines and welded together to form a forming shoulder shown in Fig. 1.

The invention has been described above with reference to only two examples, where the constant change ratio of the slope of the connecting line Q was either with respect to the x-axis or along the connecting line Q itself (or with respect to the variable s), but these examples are not intended to limit the scope of the invention. In the case of the examples explained, however, the shape of the edge portion of the tube-forming and shoulder-forming part can be described in a closed form with a known function, and this makes it easier to carry out the numerical To accurately generate control program for the equipment, such as a laser cutter, to cut a blank plate to obtain the tube forming and shoulder forming part.

Regarding the cross-sectional shape of the tubular member, it need not be circular. For example, for producing relatively large bags, a somewhat elongated circular shape such as a shape consisting of two semicircles connected to each other by two straight side lines or an elliptical cross-sectional shape may be advantageous. Because the condition set for the shape of the connecting line according to this invention does not depend on the cross-sectional shape of the tubular member, the present invention is applicable to tubular members having various cross-sectional shapes as described above.

Fig. 7 shows a vertical pillow type form-fill-seal packaging machine 90 as an example of a packaging machine which can include a forming shoulder according to the invention. The flexible thermoplastic bag-making material f (or film) is initially in the form of a web roll 92 which is held around a shaft 95 (serving as a web holding means). The film f drawn from the web roll 92 is guided by a plurality of guide rollers (including tension rollers) 105 to the forming shoulder 10 described above with reference to Fig. 1. After the film f is thereby formed into a tubular shape by sliding on the shoulder part 30 and changing the direction of its movement at its connecting line 40 with the tubular part 30, it is pulled downward by means of a film pulling unit 100 having a pair of pulling belts 101 running parallel to each other and a longitudinal sealer in the form of a heating belt 102 for sealing or welding together the mutually overlapping edge portions of the film f. The film f, which now has a cylindrical shape, is sealed horizontally (i.e., transversely to its downward direction of movement) by a transverse sealer 110 when articles to be packaged are dropped from the hopper 15. The transverse sealer 110 may have a design which provides a fixed sealing jaw 112 and a movable sealing jaw 114, both of a known construction, and may be arranged below the film drawing unit 100. In Fig. 7, reference numeral 113 denotes a blade for cutting the film f transversely between the bags into which the film f has been formed.

It should be noted that forming shoulders according to this invention can be incorporated into many other types of packaging machines and bag makers where it is necessary to bend a longitudinally running flexible bag making material into a tubular shape.

Claims (16)

1. A forming shoulder for forming an elongated planar bag-making material (f) into a tubular shape, the forming shoulder comprising: a hollow cylindrical tubular member (20) having an inner surface defining an axial direction; and a shoulder part (30) which has a flat guide section (33) and is connected to the tubular part along a connecting line (40) which surrounds the tubular part so that the material is conveyed over the flat guide section of the shoulder part, changes the direction of movement sharply at the connecting line to the axial direction and is converted into a tubular shape along the inner surface of the tubular part, characterized in that the angle between the tangent to the connecting line and a plane perpendicular to the axial direction changes with a constant ratio. 2. The forming shoulder according to claim 1, wherein the constant ratio exists with respect to the vertical change component of the position of the contact point between the connecting line (40) and the tangent with respect to the axial direction. 3. The forming shoulder according to claim 1, wherein the constant relationship with respect to the change in position of the contact point exists between the connecting line and the tangent along the connecting line (40). 4. The forming shoulder according to claim 1, wherein the connecting line becomes a parabola when the tubular part (20) is cut along a line parallel to the axial direction and developed. 5. The forming shoulder according to claim 1, wherein the connecting line becomes the curve of a hyperbolic function when the tubular part (20) is cut and developed along a line parallel to the axial direction. 6. The forming shoulder according to claim 4, wherein the shape of the parabola is determined in part by a specific height difference between the highest (O) and the lowest (A) point on the connecting line (40) measured in the axial direction. 7. The forming shoulder of claim 5, wherein the shape of the curve of the hyperbolic function is determined in part by a specific height difference between the highest (O) and lowest (A) points on the connecting line, measured along the axial direction. 8. A method of manufacturing a forming shoulder designed to form an elongated planar bag-making material (f) into a tubular shape, and having a hollow cylindrical tubular member (20) defining an axial direction and a shoulder member (30) having a planar guide portion (33) connected to the tubular member (20) along a connecting line so that the material is guided over the planar guide portion of the shoulder member, changes the direction of movement sharply at the connecting line to the axial direction and is formed into a tubular shape along the inner surface of the tubular member, the method comprising the steps of: Cutting a tube-forming part (52) and a shoulder-forming part (53) from a flat blank plate, each of the parts having a specific geometric shape with a specific width between side edges and a curved edge portion (54); Bending the tube forming part (52) into the tubular shape to form the tubular part by bringing the side edges together; Bending the shoulder forming part (53) to form the shoulder part by forming the flat guide portion and fitting the curved edge portion of the shoulder forming part with the curved edge portion of the tube forming part; and Attaching the bent parts to each other along the curved edge portions to form the connecting line (40), the connecting line being shaped such that the angle between the tangent to the connecting line and a plane perpendicular to the axial direction changes at a constant ratio. 9. The method of claim 8, wherein the constant relationship is with respect to the vertical component of change of the position of the contact point between the connecting line and the tangent with respect to the axial direction. 10. The method of claim 8, wherein the constant relationship regarding the change in position of the contact point exists between the connecting line and the tangent along the connecting line. 11. The method of claim 8, wherein the curved edge portions are a parabola. 12. The method of claim 8, wherein the curved edge portions are the curve of a hyperbolic function. 13. The method of claim 11, further comprising the step of partially determining the shape of the parabola by specifying a height difference between the highest and lowest points on the connecting line, measured in the axial direction. 14. The method of claim 12, further comprising the step of partially determining the shape of the curve of the hyperbolic function by specifying a height difference between the highest and lowest points on the connecting line, measured in the axial direction. 15. The method according to claim 8, wherein the cutting step includes obtaining a numerical control program based on the shape of the curved edge portion and operating a laser cutter by the numerical control program. 16. A packaging machine comprising: a web holding device (95) holding a web roll (92) having a web of bag making material wound around a core shaft; a forming shoulder for forming the web into a tubular shape; a web guide device (105) for guiding the web from the web roll to the forming shoulder and the tubularly formed web in a longitudinal direction; a longitudinal sealer (102) for sealing side edges of the tubular-shaped web together in the longitudinal direction; a transverse sealer (110) having a pair of sealing means for pressing and sealing portions of the tubular-shaped web together transversely to the longitudinal direction to thereby form a bag, characterized in that the forming shoulder is in accordance with any one of claims 1 to 7 or is manufactured in accordance with any one of claims 8 to 15.