GB2366757A

GB2366757A - Cutting mechanism

Info

Publication number: GB2366757A
Application number: GB0120334A
Authority: GB
Inventors: Leonard John Dawkin
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-08-25
Filing date: 2001-08-21
Publication date: 2002-03-20
Anticipated expiration: 2021-08-21
Also published as: GB0120334D0; GB0021192D0; GB2366757B

Abstract

A frame 10, 12 carries a housing 11. A bar assembly 14 is mounted on guide pins 9, which are slidable into housing 11 against the force of spring 13. Roller 23 is mounted on the frame and rotates about axis 25. The bar assembly has mounted at one end lever 19, pivoting about axis 26 and interacting with roller 23 via jaw 22 to provide a cam effect. The lower end of lever 19 is pivotally attached to blade 17, which is further pivotally attached to bar assembly 14 by lever 18. Also attached to the bar assembly is blade guard 20. Movement of bar assembly 14 causes rotation of lever 19 (and consequently lever 18), via the cam mechanism 22,23 moving the blade outwardly of the guard. The bar assembly then returns to its rest position under the influence of spring 13, thereby positively retracting the blade via the cam mechanism. The cutting mechanism may be used in a clothes bagging device, bar assembly 14 further including heater elements to seal the edges of a plastic web to form the bag, which is subsequently severed from the web by blade 17.

Description

<Desc/Clms Page number 1> Cutting Mechanism This invention relates to a cutting mechanism having a shielded blade, and particularly to a cutting mechanism for use in a sealing device for plastic film.

Enrobing of garments in transparent plastic film is well known. Typically a reel of tubular film is provided on a frame on which the garment is suspended, for example by a conventional clothes hanger. The open end of the film is drawn over the garment, and cut off when the garment is sufficiently covered. The upper end of the film is sealed to provide an enclosure which protects the garment from dirt and moisture, optionally the lower end of the film may be sealed as well.

Sealing is accomplished by pressing opposite sides of the film together in the vicinity of a heater bar, which melts and fuses the film to form a seam. After sealing, the bag is cut free from the remaining film on the reel.

The sealing/cutting mechanism is usually mounted on a skeletal steel frame which carries the reel of film, and the mechanism may be actuated by, for example, a treadle. Such device may typically be found in dry cleaning establishments.

In cases where a cutter is provided, there must be adequate safeguard to ensure that the blade is not inadvertently exposed, or left exposed after the mechanism has been actuated. The present invention provides such a mechanism.

According to the invention there is provided a blade assembly comprising a frame having a blade carrier movable linearly with respect thereto from an outward condition to inward conditions, and carrier return means operative between said frame and carrier to urge the carrier to the outward condition, the carrier having a blade provided thereon by substantially parallel links for movement from an advanced to a retracted condition, wherein one of the frame and links has a cam and the other of the frame and links has a cam follower, the cam and cam follower being operatively separate in the outward

condition, and operatively engaged in the inward conditions, whereby the blade is driven from the retracted to the advanced condition, and from the advanced to the retracted condition. The return means may be a coil spring.

Preferably the cam comprises a recess of one of said links, and the cam follower comprises a roller rotatable about a fixed axis on said frame. In the preferred embodiment the cam comprises an open rectangular jaw of one of said links, a light return spring being operable on a second of said links. Preferably two only of said links are provided.

The operative separation of cam and cam follower provides lost motion which permits a work part to be clamped between said blade carrier and a substrate, and prior to movement of said blade to the advanced condition. The interaction of the cam and cam follower ensure that the blade is driven in both directions; this is especially important in movement to the retracted condition in order that the blade is not accidentally exposed. The mechanism is particularly suitable for use in a sealing and cutting device for plastic film.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompany drawings, in which: Fig. I is a partially cut away front elevation of a mechanism according to the invention; and, Fig. 2 is an elevation of the right end of Fig. I on an enlarged scale.

With reference to the drawings a generally horizontal frame member 10 is mounted on a fixed support (not shown). Laterally spaced on the member 10, and fixed thereto by e.g. welding, are two housings I I containing a bushing of e.g. nylon. A sealing bar 0 assembly 14 is horizontally disposed below the member 10, and guided with respect thereto by upstanding guide pins 9 slidable through the respective housings 11. Coil

springs 13 have lower ends housed in respective spring housings 8, mounted on the assembly 14, and serve to urge the member 10 and assembly 14 apart. Thus the sealing bar assembly 14 is guided for up and down movement only, with respect to the frame member 10, At the left end of the frame member 10 (as viewed in Fig. 1) a depending limb 3 has spacers 4 welded thereto. An upstanding limb 12 carries relatively fixed spacers 5, 6 to the outermost of which is mounted a roller 23 rotatable about a fixed axis 25. Member 10 and limb 12 may form two sides of a large box-section support.

At the left end of the sealing bar assembly 14 (as viewed in Fig. 1), a lever 19 is provided about an axis 26. The lever has a rectangular jaw 22 open to one side and in which the roller 23 is located with vertical play. The upper side of the jaw 22 constitutes a stop limiting relative downward movement of the sealing bar assembly 14 away from the frame member 10, by abutment with the top side of the roller 23.

Relatively upward movement of the sealing bar assembly 14, against the springs 13, is permitted by the clearance in the jaw 22, until the lower side of the jaw contacts the roller 23. Further upward movement of the sealing bar results in anticlockwise pivoting of the lever to the position shown in dotted outline and marked 19a.

The lower end of the lever 19 has a generally horizontal blade 17 pivoted thereto about axis 27. A slave lever 18 is similarly pivoted to the sealing bar assembly about axis 28, and carries the right hand end of the blade 17 about axis 29.

The levers 18, 19 are symmetrical with respect to the axes 26-29 and ensure that the blade remains substantially horizontal. As illustrated, pivoting of the lever 19 (and consequently lever 18) causes the blade 17 to move rightwards and downwards with respect to the sealing bar 14. A single tooth 17a is shown in the extended position. A light return spring 21 operable between the slave lever 18 and the sealing bar assembly 14 urges the blade to the uppermost (retracted) condition.

A cover 20 shields the blade, and has the blade 17 and levers 18, 19 mounted thereon, thus constituting a replaceable sub-assembly. This sub-assembly is secured relative to the sealing bar by e.g. screws 7 which engage the spacers 4 (Fig. 2). The cover has an inturned lower edge 30 which with the sealing bar 14 defines a slot 31 through which the blade 17 protrudes on anticlockwise pivoting of the levers 18, 19, A pressure frame 15 is mounted on the fixed support for movement against the sealing bar 14. This movement may be substantially vertical (arrow 32) or radial (arrow 33) depending on the kind of linkage utilised. The frame 15 carries rubber strips 34 which in operation extend along either side of the slot 3 1, and which contain one or more heating elements.

The pitch of the teeth of the blade 17 is just less than the stroke thereof (compare tooth l7b and tooth 17a). This arrangement gives a smooth efficient action. As illustrated, the teeth have spaces therebetween approximately as long as an individual tooth, and the blade angle is about 45'.

Operation of the mechanism is as follows: A tubular film represented by chain-dot line 16 is drawn under the sealing bar 14, and, when in the desired position, the pressure frame 15 is brought into contact from below. At this stage the film is squeezed between the rubber strips 34 and the underside of the sealing bar assembly 14. The heating elements may seal the film one or both sides of the cutter, as desired.

From the position shown in Fig, 2, further upward movement of the pressure frame 15 causes relative upward movement of the sealing bar 14 against the effect of springs 13. When the lower side of jaw 22 contacts the underside of the roller 23, the levers 18, 19 pivot to cause the blade 17 to move down with respect to the sealing bar 14, and thereby cut through the film 16 between the strips 34.

Return movement of the mechanism corresponds, the blade firstly retracting, and then the sealing bar moving down until the upper side of the jaw contacts the roller 23.

The film is thus sealed and severed, and the mechanism is ready for a repeat operation. The roller 23 is illustrated in several positions in order to show the different relationships with the jaw 22. In practice, the roller is fixed and the jaw moves relative thereto.

The jaw 23 and roller 22 constitute the important feature of the invention. If by any chance the return spring 21 does not retract the blade 17, the inner side of the jaw 23 will force the lever 19 clockwise by virtue of the contact with the roller 22. A positive mechanical return of the blade 17 is thus ensured whilst retaining the light return spring 21, and there is consequently less chance that the blade will remain in the protruding condition, perhaps due to friction in the mechanism due to inadequate lubrication. The lost motion in the jaw 23 also ensures adequate gripping of the film prior to cutting.

The effective length of lever 18 may be varied by movement of one of the pivots thereof. In this way, the blade may not move in a truly parallel fashion, and thus is advantageous if it is desired that the individual teeth cut sequentially. The blade may, for example, slope slightly downwardly from left to right in the rest position, but be horizontal when the teeth are fully exposed.

Although the device has been described in conjunction with a sealing mechanism, the blade return mechanism is suitable for use in a simple guillotine. Actuation of the pressure frame 15 may be by hand, or by powered mechanism, such as a pneumatic cylinder. A serrated blade has been illustrated, for use with plastic film, but a straight blade may be equally suitable with other materials. Although an open jaw 23 has been described, a slot or other opening in the lever 19 would be suitable. The jaw could alternatively be provided on the fixed member and the roller mounted on the lever 19.

In an alternative embodiment (not illustrated), the sealing bar assembly may be pivoted on a relatively fixed frame member, for example one or more upright side plates of a machine frame. The sealing bar assembly is urged to a return condition by one or more tension springs, equivalent to the coiled compression springs 13.

An operating arm, typically pivoted about the same axis as the sealing bar assembly is operable to urge this assembly towards a pressure frame, and a tubular film is located between the assembly and the pressure frame. In operation the film is squeezed between the sealing bar assembly and the pressure frame, and is sealed and sheared in the manner described above. Two stage operation of the sealing bar assembly, by which the blade is positively advanced and retracted, is as described above. Accordingly this variant merely uses one of a variety of different possible means of mounting and actuating the mechanism, but the principle of positive blade withdrawal is common.

Other means of mounting the sealing bar assembly are of course possible within the scope of the appended claims.

Claims

Claims 1. A blade assembly comprising a frame having a blade carrier movable linearly with respect thereto from an outward condition to inward conditions, and carrier return means operative between said frame and carrier to urge the carrier to the outward condition, the carrier having a blade provided thereon by substantially parallel links for movement from an advanced to a retracted condition, wherein one of the frame and links has a cam and the other of the frame and links has a cam follower, the cam and cam follower being operatively separate in the outward condition, and operatively engaged in the inward conditions, whereby the blade is drivable from the retracted to the advanced condition, and from the advanced to the retracted condition.
2. A blade assembly according to claim I and further including a blade return spring operable to return said blade from the advanced to the retracted condition.
3. A blade assembly according to claim 1 or claim 2 wherein said cam comprises a recess of one of said links, and the cam follower comprises a roller rotatable about a fixed axis on said frame.
4. A blade assembly according to claim 3 wherein said cam comprises an open rectangular jaw of one of said I inks.
5. A blade assembly according to claim 2 wherein said blade return spring is operable on one of said links.
6. A blade assembly according to any preceding claim and having two only of said links.
7. A blade assembly according to any preceding claim wherein the edge of said blade is serrated.

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8. A blade assembly according to any preceding claim wherein the edge of said blade moves arcuately between the advanced and retracted condition.
9. A blade assembly substantially as described herein with reference to the accompanying drawings.