WO1996038240A1

WO1996038240A1 - Methods and means for forming spring coils

Info

Publication number: WO1996038240A1
Application number: PCT/GB1996/001274
Authority: WO
Inventors: Jeremias Daniël WILKINS; Bruno Schostar; Ockert Jacobus Henning; Errol James Tyrer
Original assignee: Afcol Manufacturing Limited; Copley, Richard, William
Priority date: 1995-05-31
Filing date: 1996-05-30
Publication date: 1996-12-05
Also published as: AU5828596A

Abstract

The invention concerns an apparatus and method for forming a spring coil (45). The apparatus (1), which carries out the method, comprises feeding means (15, 16, 30) for feeding a predetermined length of wire through a guide to bring the wire to bear against forming means (40, 43) arranged to act on the wire in first and second, transverse, directions. Means (42) are provided for automatically controlling movement of the forming means (40) in the first direction to cause the wire to be formed into a predetermined number of convolutions of predetermined size. Means (44) are further provided for automatically controlling movement of the forming means (43) in the second direction to form successive convolutions of the wire into a predetermined pitch. Cutting means (50) are provided for cutting the wire once it has been formed into a coil by the forming means (40, 43).

Description

METHOD AND MEANS FOR FORMING SPRING COILS

FIELD OF THE INVENTION

This invention relates to an apparatus and method for forming spring coils such as those used in mattresses.

BACKGROUND TO THE INVENTION

Coils of this kind are made from steel wire which comes in rolls from the mill, a normal size being capable of being handled by two men. The wire is placed on a dispensing device known as a swift, which is essentially a vertical spindle about which the wire is unrolled as it is required.

The wire is then threaded through a wire straightening device, usually a set of small rollers or pins that will bend the wire in the opposite direction to that of the lay, so straightening the wire to a suitable degree.

The wire is dragged through the straightener by the pulling action of the feed rollers, which are usually hardened metal wheels having grooves on their periphery and clamped together with the wire nipped in between them. Feed rollers typically vary in diameter from about 80mm to 150mm, and number two or four, thus providing one or two points of nip on the wire. The length of wire required to form a coil is fed by clamping the rolls tightly together and releasing the pressure when enough of the wire has been forced through. The clamping action is done by means of a cam which forces a lever to press the shafts of the rollers together. The length of wire fed is adjustable to a certain degree by increasing the running length of the cam surface. The centres of the shafts that bear the feed rollers usually lie in a vertical plane. The drive to the feed rollers is maintained continuously, that is, they spin all the time.

After leaving the nip of the rollers the wire is forced through a wire guide which serves as an anvil on which to band the coil to shape. The idea is to provide a support that is sharper than the feed roller about which to bend the wire. Tubular guides or grooved pins are the most convenient way of doing this.

The actual bending is done by a roller or a grooved pin which is moved so as to vary the distance between the roller or pin and the wire guide. By varying the distance the waist of the coil is obtained. This action is also achieved by means of an adjustable cam, the cam being shaped to suit the profile of the coil being formed and a small amount of adjustment is provided to enable fine tuning.

The wire is then cut off at the critical point by a shear knife, again powered by a cam. The critical point is important to the final shape of the coil, and the ends of the wire in the coil must be in the correct relative position, especially if the ends are to be knotted. The position of the cut point is fixed in relation to the rest of the machine.

The newly cut coil is transferred to a grabber before it falls free, there being two ways of grabbing the coil. One is to grab one of the convolutions of the coil, usually somewhere near the centre of the coil, with a small hook pulling the wire on to a holder. Another is to grab the outer surface of the coil between two hands.

The coil is then transported to the knotter or forming heads, where the heads of the coil are formed to the required shape and condition. The coil is finally heat-treated to relieve the stresses set up during forming by subjecting it to an electrical short circuit for part of a second. It is then either stacked on a delivery tray or transported to an automatic assembler for assembly into a spring unit.

One of the problems of the apparatus used to carry out the method described above is the mechanical complexity of the apparatus. It consists of numerous cams, shafts, gears, strikers and other elements which are combined together. A considerable degree of skill is necessary to set a machine of this kind to run properly and to keep it running. The wire used in the method is hard and unkind to softer metal and the whole machine accordingly as to be kept well lubricated with grease and oil. Not only does this make the machine messy but despite the lubrication the amount of wear on the moving parts of the machine remains substantial and they require regular and expensive maintenance to keep them functional. Another problem is a lack of flexibility in the adjustment of the machines, a problem which is exacerbated by the tendency of the strength of the wire used in the method to vary in quality. The actual value of the tensile strength of the wire in a spring is not as important as the need for the value to be constant. When wire is bent the elastic limit of the material must be exceeded for the wire to retain the shape required of it. The wire will tend to spring back to its original shape unless the elastic limit is exceeded. The extent to which any desired angle has to be exceeded is a function of the tensile strength of the wire. The coiling machines also exceed the elastic limit of the wire in order to obtain a permanent set, but if the tensile strength were to vary, the resulting coils would be of different shapes.

OBJECT OF THE INVENTION

It is accordingly an object of the present invention to provide an apparatus and method for forming spring coils which endeavour to overcome or at least to diminish the problems associated with the prior art. SUMMARY OF THE INVENTION

According to the invention apparatus for forming a spring coil comprises;

- feeding means for feeding a predetermined length of wire through a guide to bring the wire to bear against forming means arranged to act on the wire in first and second, transverse, directions;

means for automatically controlling movement of the forming means in the first direction to cause the wire to be formed into a predeter¬ mined number of convolutions of predetermined size;

means for automatically controlling movement of the forming means in the second direction to form successive convolutions of the wire into a predetermined pitch; and

cutting means for catting the wire once it has been formed into a coil by the forming means. The forming means may comprise first and second forming means controlled separately by first and second linear servo actuators respectively, the servo actuators being controlled by first and second electronic drives respectively and being linked to a motion controller which is programmed to control the first and second electronic drives and hence movement of the first and second forming means.

The feeding means may comprise first and second rollers of which the first roller is driven by an electric servo motor controlled by an electronic drive. The electronic drive may be linked to the motion controller which is programmed to control the servo motor and hence the length of wire drawn through the rollers. The second roller may have a shaft carrying an encoder which is linked to the electronic drive of the servo motor to compensate for slippage of the wire.

Preferably, the first roller is fixed and the second roller is displaceable relative to the first and carried on a pneumatic cylinder adapted to clamp the wire between the rollers. The cylinder may be connected to a digital valve linked via a solid state relay to a programmable logic controller which is programmed to activate the pneumatic cylinder and hence to displace the displaceable roller to clamp the wire.

The apparatus preferably includes a swift adapted to carry a wire roll from which wire is fed to the feeding means, the swift being driven by an electric motor controlled by an electronic drive switched by the programmable logic controller which is programmed to control the length of wire fed from the swift.

The cutting means preferably comprises a knife mounted on a pneumatic cylinder connected to a digital valve linked via a solid state relay to the programmable logic controller which is programmed to activate the pneumatic cylinder and hence the knife to cut the wire.

The invention also concerns a method of forming a spring coil in a coil forming apparatus comprising the steps of; feeding a predetermined length of wire through a guide to bring the wire to bear against forming means arranged to act on the wire in first and second, transverse, directions;

- automatically controlling movement of . the forming means in the first direction to cause the wire to be formed into a predetermined number of convolutions of predetermined size;

simultaneously therewith automatically controlling movement of the forming means in the second direction to form successive convolutions of the wire into a predetermined pitch; and

cutting the wire once it has been formed into a coil by the forming means.

The wire is preferably brought to bear against first forming means to act on the wire in the first direction and against second forming means to act on the wire in the second direction, the first and second forming means being controlled separately by first and second linear servo actuators respec¬ tively, the servo actuators being controlled by first and second electronic drives respectively and being linked to a motion controller which is programmed to control the first and second electronic drives and hence movement of the first and second forming means.

The wire is preferably fed from between first and second rollers of which the first roller is driven by an electric servo motor controlled by an electronic drive, the electronic drive being linked to the motion controller which is programmed to control the servo motor and hence the length of wire drawn through the rollers. The wire may be clamped between the rollers by displacing the second roller relative to the first roller by means of a pneumatic cylinder, the second roller being provided with a shaft carrying an encoder which is linked to the electronic drive of the servo motor to compensate for slippage of the wire. The pneumatic cylinder may be connected to a digital valve linked via a solid state relay to a programmable logic controller which is programmed to activate the pneumatic cylinder and hence to displace the displaceable roller to clamp the wire. The wire is preferably fed from a swift adapted to carry a wire roll from which wire is fed to the feeding means, the swift being driven by an electric motor controlled by an electronic drive switched by the programmable logic controller which is programmed to control the length of wire fed from the swift.

The wire may be cut by means of a knife mounted on a pneumatic cylinder connected to a digital valve linked via a solid state relay to the programmable logic controller which is programmed to activate the pneumatic cylinder and hence the knife to cut the wire.

BRIEF DESCRIPTION OF DRAWINGS A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which;

Figure 1 is a schematic perspective diagram of a coil forming apparatus arranged in accordance with the invention; Figure 2 is a front perspective view of an operational coil forming apparatus constructed in accordance with the invention;

Figure 3 is a rear perspective view of the operational coil forming apparatus of Figure 2;

Figure 4 is a block diagram further illustrat¬ ing the functioning of the apparatus of Figures 1-3; and

Figure 5 is a front view of the coil forming apparatus of Figures 2 and 3 showing a knotting apparatus used in conjunction therewith.

DESCRIPTION OF PREFERRED EMBODIMENT

Throughout the drawings, like numbers are used to denote like parts. In the drawings, coil forming apparatus 1 in accordance with the invention is shown diagramati- cally in Figure 1 and in an operational form^* in Figures 2 and 3.

The coil forming apparatus 1 includes a swift 2, driven by an electric motor 3, from which steel wire 4 is fed off a roll 5 (Figure 1). The motor 3 is controlled by an electronic drive 60 switched, via a sensor 6, by a programmable logic controller 61 (Figure 4), hereinafter referred to as a PLC.

The apparatus 1 comprises a main frame 12 on which is mounted a main electric servo motor 13 driving a motor shaft 14 carrying a roller 15. A second roller 16 is located adjacent the roller 15 on a stub shaft 17 which is mounted on an arm 13, itself mounted on a pneumatic pressure unit 19. The stub shaft 17 of the second roller 16 is connected to an encoder 20. When the pressure unit 19 is activated it displaces the roller 16 towards the roller 15 to clamp the steel wire 4 between the rollers 15, 16. The main electric servo motor 13, which may have a power rating of the order of 4kw, is controlled by an electronic drive 62 (Figure 4) with internal encoder (not shown) connected to the motor shaft 14. The electronic drive 62 is linked to a motion controller 63 which is programmed to control the motor 13 and hence the length of wire 4 drawn through the rollers 15, 16. Slippage is compen¬ sated for by means of the encoder 20, which is linked to the controller 63.

The motion controller 63 is preferably a 4-axis controller designed to control interlinked motion. An example of such a controller is an IMC S class controller supplied by the Allen-Bradley company.

The pneumatic pressure unit 19 is connected to a digital valve 21 supplied from a pneumatic supply (not shown) of approximately 6 bar pressure. The digital valve 21 is linked to the PLC 61 which is programmed to control the digital valve and hence the operation of the pneumatic pressure unit 19. In Figure 4 the combination of valve 21 and pressure unit 19 is indicated by the block 64 as the vice activator. The wire 4 is fed to the rollers 15, 16 via a wire censioning and straightening mechanism 30, consisting of a series of off-set rollers 31. The outer rollers 31' are adjustable by means of a rotatable knob 32 relative to the inner rollers 31" to adjust the resistance of the wire 4 passing through the wire path between the rollers. From the rollers 31 the wire 4 passes through tungsten sleeved wire guides 33, 34.

When the wire 4 emerges from the wire guide 34, it is brought to bear against a forming means in the form of a forming wheel 40, which is mounted on an arm 41 parallel with the direction of wire feed. The forming wheel 40 is movable in an arc to determine the size, or diameter, of a convolution formed in the wire. Movement of the forming wheel is effected by a linear servo actuator 42 connected to the arm 41.

Simultaneously with the forming wheel 40 controlling the diameter of the wire convolutions, the pitch of the convolutions is controlled by an inclined pitch t)ar 43 being moved horizontally into the path of the wire, causing it to bend sideways and thereby forming a coil 45. The movement of the pitch bar is controlled by a linear servo actuator 44.

The servo actuators 42, 44 are powered by electronic drives 65, 66 respectively, linked to the motion controller 63 which is programmed to control movement of the servo actuators 42, 44 and hence the profile of the coil 45.

The wire may be cut by a knife 50 mounted on an arm 51 operated by a pneumatic cylinder 52. The knife is activated to cut the wire against an anvil 53. The pneumatic cylinder 52 is connected to a digital valve 54 (Figure 3) supplied from the same pneumatic supply referred to above. Tne digital valve is linked to the PLC 61 which is programmed to control the valve and hence the operation of the knife 50. In Figure 4 the combination of digital valve 54 and cylinder 52 is indicated by the block 67 as knife activator.

A sensor (not shown) may be linked to the PLC 61 to indicate if the knife 50 is clear of the anvil 53. This is indicated in Figure 4 by the block 68 as knife position.

Thus, the wire length, diameter and pitch are controlled by the motion controller 63 through control of the servo motor 13 and servo actuators 42, 44.

The shape of the coil 44 is determined by the positions of the forming wheel 40 and pitch bar 43 as the wire is fed through the guide 34. These positions and wire length are controlled by a program in the motion controller 63 during program execution.

Conveniently, the positions of the forming wheel 40 and pitch bar 43 versus wire length are contained in look up tables in tne software and various tables can be stored to represent different coil profiles.

The program enables the operator to change the parameters of the coil, thus enabling a coil of any shape to be produced, as long as the sizes are within the physical capabilities of the apparatus and within the predetermined set of stored tables. When the apparatus is enabled, the program in the motion controller 63 reads a set of coil profile information from a file stored in memory. The program then gives the operator the opportunity to select the profile that he desires from the list of profiles available.

To form a coil, the forming wheel 40 is first pulled up to a home position near the top of its travel limit. This position is verified by sensors 55 on the actuator 42. The forming wheel 40 is then driven down to a position that corresponds to the size of the head of the coil. The pitch bar 43 is homed and zeroed in the same way.

The PLC 61 then signals the controller 63 to form a coil. To start the process of forming a coil, the main motor 13 under the control of the program of the controller 63 is advanced from a start to a stop position to draw a predetermined length of wire 4 through the guide 34 against the forming wheel 40 whilst the swift motor 3 runs simultane¬ ously to provide the required wire feed. The position of the forming wheel 40 and pitch bar 43 are changed by the motion controller according to the profile table in the controller program. The wire length, measured by encoder 20, is the table reference, thus eliminating errors due to wire slippage between the rollers 15, 16.

After the controller 63 signals the PLC 61 that the forming is complete, the coil is grabbed by a hand 70 mounted on an indexing arm 71. The cut command is then issued by the PLC. An indexing device 72 is then activated and the spring grasped by a hand 70 is moved around to a knotting station 73 (Figure 5).

In the knotting station, the coil 45 is positioned in front of a first knotting head 74, where the indexing arm 71 moves sideways to compress the coil 45 into the knotting head.

The head of the coil is clamped to the face of the knotting head where the wire end is wrapped around the adjoining convolution of wire to form a knot. The indexing arm 71 next returns to the central position to release the compressed coil. The indexing device 72 next moves the coil to the next knotting station (not shown) and repeats the above operation at the opposite end of the coil 45.

On completion of knotting, the indexing device 72 moves the coil to a heat treatment station 77where heat treatment by way of an electrical current flow is carried out.

On completion of heat treatment the indexing device moves the coil to the unload station 75 where the completed coil is pushed out onto a feed track.

The knotting apparatus and operation described above is known in the art.

Thus the invention provides a novel and useful method and apparatus for forming spring coils.

Many other embodiments of the invention may be made without departing from the scope of the invention described in the -appended claims.

Claims

1. Apparatus for forming a spring coil, comprising;

feeding means for feeding a predetermined length of wire through a guide to bring the wire to bear against forming means arranged to act on the wire in first and second, transverse, directions;

cutting means for cutting the wire once it has been formed into a coil by the forming means.

2. Apparatus as claimed in claim 1 in which the forming means comprise first and second forming means controlled separately by first and second linear servo actuators respectively, the servo actuators being controlled by first and second electronic drives respectively and being linked to. a motion controller which is programmed to control the first and second electronic drives and hence movement of the first and second forming means.

3. Apparatus as claimed in claim 2 in which the feeding means comprise first and second rollers of which the first roller is driven by an electric servo motor controlled by an electronic drive, the electronic drive being linked to the motion controller which is programmed to control the servo motor and hence the length of wire drawn through the rollers.

4. Apparatus as claimed in claim 3 in which the first roller is fixed and the second roller is displaceable relative to the first and carried on a pneumatic cylinder adapted to clamp the wire between the rollers, the second roller having a shaft carrying an encoder which is linked to the electronic drive of the servo motor to compensate for slippage of the wire.

5. Apparatus as claimed in claim 4 in which the pneumatic cylinder is connected to a digital valve linked via a solid state relay to a programmable logic controller which is programmed to activate the pneumatic cylinder and hence to displace the second roller to clamp the wire.

6. Apparatus as claimed in claim 5 in which the apparatus includes a swift adapted to carry a wire roll from which wire is fed to the feeding means, the swift being driven by an - electric motor controlled by an electronic drive switched by the programmable logic controller which is programmed to control the length of wire fed from the swift.

7. Apparatus as claimed in claim 5 in which the cutting means comprise a knife mounted on a pneumatic cylinder connected to a digital valve linked via a solid state relay to the programmable logic controller which is programmed to activate the pneumatic cylinder and hence the knife to cut the wire.

8. A method of forming a spring coil in a coil forming apparatus, comprising the steps of;

- feeding a predetermined length of wire through a guide to bring the wire to bear against forming means arranged to act on the wire in first and second, transverse, directions;

automatically controlling movement of the forming means in the first direction to cause the wire to be formed into a predetermined number of convolutions of predetermined size;

cutting the wire once it has been formed into a coil by the forming means.

9. A method as claimed in claim 8 in which the wire is brought to bear against first forming means to act on the wire in the first direction and against second forming means to act on the wire in the second direction, and in which the first and second forming means are controlled separately by first and second linear servo actuators respectively, the servo actuators being controlled by first and second electronic drives respectively and being linked to a motion controller which is programmed to control the first and second electronic drives and hence movement of the first and second forming means.

10. A method as claimed in claim 9 in which the wire is fed from between first and second rollers of which the first roller is driven by an electric servo motor controlled by an electronic drive, the electronic drive being linked to the motion controller which is programmed to control the servo motor and hence the length of wire drawn through the rollers.

11. A method as claimed in claim 10 in which the wire is clamped between the rollers by displacing the second roller relative to the first roller by means of a pneumatic cylinder, the second roller being provided with a shaft carrying an encoder which is linked to the electronic drive of the servo motor to compensate for slippage of the wire.

12. A method as claimed in claim 11 in which the pneumatic cylinder is connected to a digital valve linked via a solid state relay to a programmable logic controller which is programmed to activate the pneumatic cylinder and hence to displace the displaceable roller to clamp the wire.

13. A method as claimed in claim 12 in which the wire is fed from a swift adapted to carry a wire roll from which wire is fed to the feeding means, the swift being driven by an electric motor controlled by an electronic drive switched by the programmable logic controller which is programmed to control the length of wire fed from the swift.

14. A method as claimed in claim 12 in which the wire is cut by means of a knife mounted on a pneumatic cylinder connected to a digital valve linked via a solid state relay to the programmable logic controller which is programmed to activate the pneumatic cylinder and hence the knife to cut the wire.