WO1992003292A1

WO1992003292A1 - Sack printing mechanisms

Info

Publication number: WO1992003292A1
Application number: PCT/GB1991/001377
Authority: WO
Inventors: Duncan Clark Rye
Original assignee: Tropic Shipping Co Ltd.
Priority date: 1990-08-16
Filing date: 1991-08-13
Publication date: 1992-03-05
Also published as: GB9018030D0

Abstract

In a method of printing a filled bag or sack (10) being carried on a continuously moving conveyor (11), a print head (19) is positioned in the path of the bag or sack and allowed to pivot about a predetermined axis in response to engagement with the bag or sack. The orientation of the print head (19) is therefore dependent on the particular portion of the bag or sack (10) passing beneath the head at any instant, and a printing fluid is discharged through at least one nozzle in the print head as the bag or sack passes beneath the head.

Description

SACK PRINTING MECHANISMS

This invention relates to the printing of bags or sacks filled with granules, powder or other particulate materials, such as sugar, flour and grain.

When importing and exporting large quantities of these products, it is frequently desirable that the bags or sacks should be labelled or marked with some identification, such as the country of origin. At present the filled bags or sacks can be marked in the dockside warehouse using, say, stencil or other contact printing methods, or the empty bags can be pre-printed before being filled. The former method is too slow and laborious, while the latter method involves a substantial delay between the bags being printed and the bags being received at the warehouse.

It would be an advantage if the filled bags could be printed while being conveyed on a continuously moving conveyor from or to the warehouse.

According to the present invention there is provided a device for printing a filled bag or sack carried on a continuously moving conveyor, the device comprising a print head having a plurality of nozzles through which a printing fluid is selectively discharged on to a sack or bag passing beneath the head; and support means disposed in the path of the moving bag or sack for supporting the print head a predetermined distance from the surface of the bag or sack, the support means being pivotable about a predetermined axis in response to engagement with the moving bag or sack such that the orientation of the print head is dependent on the particular portion of the bag or sack passing beneath the head at any instant.

The predetermined axis can be fixed, but it is preferably a floating axis which can rise and fall with the contour of the bag or sack as the bag or sack passes beneath the print head. In this manner, the print head is able to follow or track the contour of the bag or sack more closely. The print head may therefore have a downward orientation relative to its pivot axis as the leading sloped portion of the bag passes beneath the head, progressivel increasing to a generally flat horizontal orientation as the flatter middle portion of the bag passes beneath the head, and finally assuming a reverse upward orientation as the trailing portion of the bag passes beneath the head.

To smooth the motion of the print head as it follows the contour of the bag or sack, and to prevent undue wear, a damper mechanism is preferably incorporated in a linkage between the print head support means and a fixed support member bridging the conveyor.

In the accompanying drawings, by way of example only : Fig 1 is a schematic side view showing a bag or sack passing beneath a printing device embodying the invention,

Fig 2 is a schematic side view of a device embodying the present invention.

Fig 3 is a schematic side view similar to Fig 2 showing the print heads in a second orientation.

Fig 4 is a top plan view of the device shown in Fig 1 and 3, and

Fig 5 is a bottom plan view.

Referring to these drawings, filled bags 10 containing sugar, flour, grain or like particulate products, are carried along a predetermined path by a continuously moving conveyor 11. The conveyor may extend, for example, from a dockside warehouse to an articulated arm extending over the cargo hold in a ship berthed at the dockside. The conveyor runs between parallel guide rails 12.

A mechanism for printing the bags with identification markings is pivotally mounted on a support bar 14 bridging the guide rails 12. The bar 14 is supported by legs 13 at each end, the legs being releasab y secured to the respective guide rails. The heigr_:. of the legs is preferably adjustable.

The mechanism comprises a pair of spaced parallel links 15,15a which pivot about respective bearings 32,32a carried by support members 31,31a clamped to the bar 14, and a holder 17 for an array of print heads 19, the holder 17 pivoting about bearings 18,18a carried at the free ends of the links 15,15a. The holder 17 comprises a pair of side plates 20,20a and a base plate or skid 21 which slides over the bags 10 as the bags pass successively beneath the holder 17.

The pivotal motion of the l nks 15,15a and the holder 17 is constrained by additional links 22,22a each having one end pivotal about respective bearings 30,30a carried by the supports 31,31a at respective points spaced above the pivotal connections 32,32a to the links 15,15a, and the other end pivotally connected to the respective side plates 20,20a at a point spaced above the pivotal connection to the links 15,15a. In addition, a further link 23 is connected from a point mid-way across the bar 14 to the mid-point of a cross-member 16 interconnecting the links 15,15a.

Each of the links 22,22a and 23 incorporates a respective air cylinder 24,24a and 25 with a slidable piston to act as a damping mechanism. The length of each link 22,22a,23 thus varies as the piston moves in and out of the cylinder, the rate of movement being controlled by adjusting the rate at which a r is exhausted from, or drawn into, the cylinder. This in turn controls the rate at which the holder 17 responds to changes in the slope of the bag as it passes beneath the skid plate 21, and prevents abrupt changes in the orientation of the holder which might otherwise occur. Fig 2 shows the links 22,22a and 23 in their extended state, and Fig 3 shows the same links in their contracted state.

The print heads 19 supported by the holder 17 are of the type in which pressurised ink is fed to a row of nozzles extending generally transverse to the direction of motion of the bag being printed, the ink flow to each nozzle passing through a respective valve which is computer controlled to open at the appropriate instant. A jet of ink is then discharged from each nozzle to produce a dot of ink on the bag, the dots from the various nozzles combining to produce dot matrix characters. The skid plate 21 has slots 26 aligned with the rows of nozzles, and maintains a substantially constant spacing between the bag and the nozzles equal to the thickness of the plate. The slots 26 extend to the rear edge of the plate to prevent the plate smudging the ink markings. Print heads of this type are sometimes known as ink jet coders. Rotation of the head changes the size of the characters being printed.

The supply of ink for the print heads 19 is contained in a separate ink reservoir which is conveniently located within the bar 14 if the bar is made hollow. The program controllers for the print heads are mounted on a support member secured to the bar 14 and extending alongside the guide rails 12. The controllers may be programmed such that the data printed on the bags includes production dates and/or expiry dates, as well as consecutively numbering each bag. This facility would not be available if the bags were pre-printed.

The mechanical operation of the print device is substantially as follows. As the sloped leading portion 10a of a bag engages the skid plate 21, the plate pivots about the shaft 18 to allow passage of the bag beneath the plate. The plate is thus inclined downwards for alignment with the slope of the leading portion 10a of the bag, as shown in Fig 1 and Fig 2. At the same time, the bearing shaft 18 is able to move upwards as the bulk of the bag beneath the plate 21 progressively increases. This ensures that the skid plate 21 is able to pivot about an axis which is constantly tracking the contour of the bag. In particular, as the plate 21 slides over the flat top section 10b of the bag, the linkage will be orientated as shown in Fig 3. At the tail end 10c of the bag, the slope of the bag reverses and the shaft 18 drops down as it follows the reverse slope before eventually moving off the bag. The plate 21 is then t lted upwards for alignment with the reverse slope, and remains in this orientation until the plate also clears the bag. The quality of the print is largely dependent on maintaining a constant uniform spacing between the print head nozzles and the surface of the bag or sack. With the above arrangement, the print head is aligned with a relatively small increment of the bag or sack equal to the length of the skid plate 21, and the successive increments follow the contour of the bag or sack. Provided there are no abrupt changes of contour within each increment, the nozzles will therefore remain a substantially constant distance from the surface of the bag or sack. In this manner, print quality is maintained over the length of the sack at conveyor speeds exceeding 80 metres per min.

Claims

1. A method of printing a filled bag or sack being carried on a continuously moving conveyor, the method comprising positioning a print head in the path of the moving bag or sack, allowing the print head to pivot about a predetermined axis in response to engagement with the moving bag or sack such that the orientation of the print head is dependent on the particular portion of the bag or sack passing beneath the head at any instant, and discharging a printing fluid through at least one nozzle in the print head as the bag or sack passes beneath the head.

2. A method according to claim 1 wherein the predetermined axis rises and falls with the contour of the bag or sack passing beneath the head.

3. A device for printing a filled bag or sack carried on a continuously moving conveyor, the device comprising a print head having at least one nozzle through which a printing fluid is discharged on to a sack or bag passing beneath the head; and means disposed along the path of the moving sack or bag for holding the print head a predetermined distance from the surface of the bag or sack, the holding means being pivotable about a predetermined axis in response to engagement with the moving bag or sack such that the orientation of the print head is dependent on the particular portion of the bag or sack passing beneath the head at any instant.

4. A device according to claim 3 in which the predetermined axis is a floating axis that rises and falls with the contour of the bag or sack.

5. A device according to claim 4 wherein the holding means is pivotally linked to fixed support means bridging the conveyor.

6. A device according to claim 5 in which the pivoted linkage comprises a pair of spaced parallel links, and the holding means is pivotally mounted about bearings carried at the free ends of the respective links.

7. A device according to claim 6 in which the pivotal motion of the holding means is constrained by an additional pair of links between the fixed support means and the holding means, the additional links being spaced above the first pair of links and extending generally parallel thereto.

8. A device according to clai... 7 wherein each of the additional links includes a damper mechanism for smoothing the motion of the print head over the contour of the bag or sack.

9. A device according to any one of the claims 3-9 in which the holding means comprises a base plate for slidably engaging the moving bag or sack passing beneath the print head, the base plate having an aperture aligned with a row of nozzles in the print head such that the nozzles are spaced from the surface of the bag or sack by a distance substantially equal to the thickness of the plate.

10. A device according to claim 9 in which the holding means holds a plurality of the print heads, and the base plate has a corresponding plurality of apertures aligned with the nozzles of the respective print heads.

11. A device for printing a filled bag or sack and substantially as herein described with reference to the accompanying drawings.