FIELD OF INVENTION:

The invention relates to packaging machines where belts with adjustable frictional force are used.

BACKGROUND OF THE INVENTION:

Various types of packaging machines are already known as the state of the art. These packaging machines are designed to fill different items into pouches, packets or in cartons. Some of the packaging machines are used to pack or fill food items into packets. In such machines there is a continuous packaging material moving along a tube or a guide. The packaging material is cut into proper size, closed at one end; food item is filled from the other end and then sealed.

The packaging material which is used to make pouches or packets needs to move along a guide or a pipe. For this purpose 2 belts are used to impart motion to the packaging material along the guide or pipe. The belts are driven by a drive assembly. The surface of each belt is in contact with the outer surface of the packaging material and it is necessary to maintain a constant frictional force between these two surfaces. If the required force is not maintained, there may be slippage or uneven movement of the packaging material causing uneven packet or even damaging the packet.

There are different assemblies to maintain the required frictional force between the surface of the packaging material and the surface of the belt.

The US patent 3946861 discloses a conveyor assembly having a spring loaded belt tension sliding plate. The assembly provides automatic adjustment of an endless belt to maintain optimum tautness.

ADVANTAGES OF THE INVENTION:

The main advantage of the invention is that due to the spring loaded construction, tolerances can be compensated. The invention proposes a simple assembly to guarantee maximum and equal friction contact on both sides between the belts and the tube.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1: Shows the Vertical Form Fill Seal (VFFS) packaging machine

Figure 2: Shows friction belt with spring loaded sliding arrangement

Figure 3: Details of spring loaded sliding plate arrangement

DESCRIPTION OF THE INVENTION:

Shown in figure 1 is a typical VFFS packaging machine which is, in this figure, an intermittent running, vertically forming, filling & closing machine. The film is drawn from a film reel 100 by friction plates supported friction belts 102 and is guided over the tension arm 104 as well as the moveable tracking frame, over the adjustable roller 106 and the shoulder 108 so that a film tube is formed along the forming tube 110. A hot longitudinal jaw 112 closes the film tube when the film is stationary. The cross jaws 114 close synchronized with the long jaw 114 and the cross seal is achieved.

The dosing system above the machine drops a complete bag charge through the forming tube 110 in to the bag 116 on the closed cross jaws 114. A knife in the cross jaws 114 separates the completed bag 116 from the film tube. Two cross seams are formed across the width of the film tube. The upper half of the jaws forms the lower seal of the filled bag 116.

The friction belts 102 are also referred as belts in this document.

Shown in fig. 2 is the part of the machine where the spring loaded sliding plates are used.

The spring loaded sliding plates act as moveable compensation plates explained above.

The spring loaded sliding plates are referred as sliding plates in this document.

In fig. 2 same numerals are used to represent same parts as explained in Fig. 1.

The fig .2 shows the friction belts 102 which are endless. The friction belts 102 are driven and guided by 4 teethed wheels 200. Two teethed wheels 200 are located on the above side and other two are located on the below side and the friction belts form endless loop over the teethed wheels 200. When the friction belts 102 move in the direction shown by arrows, the friction belts draw the film along with them over the forming tube 110.

Normally, the parts and assemblies suffer due to manufacturing tolerances. Because of this fact, even the expensive parts with high accuracy will suffer due to tolerances of other parts. Hence, under normal circumstances, it is not possible to provide a uniform contact between friction belts and forming tube.

There are different techniques in the prior arts to provide uniform contact between the friction belts and the film over the forming tube. One of the techniques may be using vacuum belts. In the construction of the system working with vacuum belts, there is no contact between belts and forming tube (normally there is a gap which is adjustable).

With this gap it is possible to have some tolerance variations. But using the vacuum belts may involve a complex construction and are expensive.

The invention proposes the spring loaded sliding plates 202 to maintain uniform contact between the friction belts 102 and the forming tube 110.

Shown in Fig.3 are the assembly details of spring loaded sliding plates 202.

On each side of the forming tube 110 there is a block 300. Within this block there are several functions; one of them is the spring loaded sliding plates 202. The sliding plates 202 are held in position with the help of the screws 302 which are coupled to the block 300. The block 300 has a pair of reliefs to accommodate the two springs 304. The springs are free floating in the reliefs. The belt 102 moves over the sliding plates 202 thereby moving the film along with it.

The sliding plates act like floating parts controlled by the springs on one side and supported by the T nuts 306 with threads on the other side.

The sliding plates 202 which are supported by springs on one side guarantee that the contact of friction belts 102 against forming tube 110 is uniform over whole length in vertical direction to make the bag 116 uniform. If the contact of friction belts 102 against forming tube 110 is not uniform, the bag 116 may attain an uneven shape or the bag may get damaged.

As the spring loaded sliding plates 202 act like floating parts with the support of the springs 304, the spring loaded sliding plates 202 absorb any uneven frictional force between the friction belt 102 and the forming tube 110 thereby providing a uniform frictional force between the belt and the forming tube. As the film is placed between the belt and the forming tube, the film experiences the uniform frictional force while belt is moving. Hence the film moves uniformly over the sliding plate thereby forming uniform bags which contain the filled material inside.

The main advantages of the invention is that, due to the spring loaded sliding plates construction, tolerances can be compensated till a certain limit. Which is defined by the gap between T-nut and sliding plate. The 2 helical compression springs on each side will compensate the tolerances in one way and at the same time compensate the average pneumatic pressure. The pressure, results in a load of the friction belts against the tube.

So in the end there is a uniform contact between belt (102) and forming tube (110), and this again results in a better bag length variation quality.

The invention proposes a simple assembly to maintain the uniform friction between the surfaces of the belts and the film.

WE CLAIM:

1. A spring loaded sliding plate assembly for a packaging machine, the said spring loaded sliding plate assembly comprising :

a drive assembly (200) driving a pair of friction belts (102), the friction belts (102) being in endless loop

a forming tube (110) in between the said two friction belts (102)

at least one sliding plate (202) supporting the inner surface of the friction belt (102) which is in contact with the forming tube (110)

a block (300) disposed inside of the said loop to support the sliding plate (202)

a relief in the block to place a spring (304), one end of the spring (304) being in contact with the sliding plate (202)

2. A spring loaded sliding plate assembly according to claim 1 wherein the said springs (304 provide uniform contact between the friction belts (102) and the forming tube (110)

3. A spring loaded sliding plate assembly according to claim 1 wherein the said spring loaded sliding plates (202) are coupled to the block (300) with the help of screws (302)

4. A spring loaded sliding plate assembly according to claim 1 wherein the said springs (304) are free floats

5. A spring loaded sliding plate assembly according to claim 1 wherein the sliding plates 202 compress the springs (304) in perpendicular direction with reference to the direction of the motion of the friction belts (102) when the spring plates (202) experience uneven contact with the forming tube (110).

6. A spring loaded sliding plate assembly according to claim 1 wherein the springs absorb any uneven frictional force between the sliding plates and the forming tube thereby providing the uniform contact between the friction belt and the forming tube.