MECHANISM FOR EFFECTING GUIDE BAR LAPPING MOVEMENT IN WARP KNITTING MACHINES

Abstract: A mechanism for effecting guide bar lapping movement in warp knitting machines comprises a double-acting piston-in-cylinder servo arrangement connected directly to the guide bar. The piston l3 of the arrangement ll may be connected by a rigid yoke arrangement l5 to a rod l6 slidable in linear bearings l7 and connected to the guide bar l2.

Description: This invention relates to mechanism for effecting guide bar lapping movement in warp knitting machines. The conventional mechanism for effecting the lapping movements of the guide bars of warp knitting machines is the pattern wheel or, in the case of long-repeat patterns, the pattern chain, in which cams of different heights corresponding to the amount of lapping movement required in terms of needle spacings, are attached in desired sequence to the peripheries of pattern wheels, or to chains that run on the peripheries of sprocket wheels. The cams, as they index round the wheels, push the guide bars, perhaps through the intermediary of a lever mechanism, against the action of a return spring that holds a cam follower on the guide bar or lever mechanism against the cams. Various mechamisms have been proposed to avoid the disadvantages of such cam arrangements. A principal disadvantage is the investment, in terms of preparation and fitting time in the pattern wheel or chain, with the associated machine downtime and concomitant uneconomic nature of short e.g. sampling or trial runs. FR-2 219 670 discloses stepper motor mechamism in which stepper motors act via rack and pinion arrangements on the guide bars. The advantage of this is that the pattern information can be supplied electronically and therefore substantially instantaneously. No commercial warp knitting machine has appeared to date, however, and it must be supposed that this advantage is countered by disadvantages not found in the more robust and - once set up - trouble-free pattern wheel or chain mechanism. Hydraulic guide bar lapping arrangements of varying degrees of complexity have also been proposed which can also be programmed electronically and which are also more robust than stepper motor arrangements. To date, however, no hydraulic arrangement has been commercially available. One problem with hydraulic arrangements is that, unlike the pattern wheel or chain mechanism or even the rack and pinion arrangement of FR-2 219 670, a sufficiently robust arrangement requires quite a large piston area to generate the forces required to move the guide bar. This presupposes a large diameter cylinder. However, the guide bars on a warp knitting machine are located, of necessity, very close together. Large diameter cylinders cannot be correspondingly closely spaced. One arrangement for dealing with this problem appears in DE-3 213 663-A1 of Karl Meyer Textil-Maschinen-Fabrik GmbH, an internationally-renowned warp knitting machinery manufacturer. Here, the arrangement is not hydraulic, rather a complicated summing gear. However, it will of necessity be of large cross-section as compared to the guide bar spacing. The working end of the summing gear is shown to be connected to the guide bar by a connecting rod which is held in spherical bearings, and this evidently allows the summing gear to be offset with regard to its guide bar. This solution could be readily adopted in the case of large diameter piston-in-cylinder arrangements, with the piston ends of the connecting rods being widely spaced apart while the guide bar ends are closely spaced. However, this seemingly simple arrangement would be found to give rise to problems of wear on the bearings of the expensive piston-in-cylinder arrangements which would lead to failures in operation and high machine downtime and repair costs, not to mention spoiled fabrics. This problem is solved by the present invention. The invention comprises a mechanism for effecting guide bar lapping movement in warp knitting machines having a plurality of guide bars, the mechanism comprising, for each guide bar, a double-acting piston-in-cylinder servo arrangement connected to said guide bar through a connecting rod, characterised in that the piston-in-cylinder arrangements have a substantial width by comparison with the spacing of the guide bars and have associated yoke arrangements more closely aligned with the guide bars than are the pistons of the piston-in-cylinder arrangements, the yoke arrangements and the guide bars being held to the connecting rods by spherical bearings which accommodate the swinging movements of the guide bars as they pass between the needles but give an essentially zero play in the direction of the lapping movement. Said piston-in-cylinder arrangement may comprise a double ended piston. A displacement transducer may also be connected to the piston-in-cylinder arrangement. Said displacement transducer may comprise a linear differential voltage transducer - such a transducer is inexpensive but adapted to give a reproducible output - the output is not necessarily as linear as may be required, but the invention further provides that the output of such a transducer can be calibrated for linearity. The mechanism may further comprise electrically operated valve means for the piston-in-cylinder arrangement. Said valve means may comprise a four port, torque motor valve. An electrical control signal driving the valve open to admit pressure fluid to one side of the piston (and simultaneously open to permit fluid to exhaust from the other side of the piston) may be balanced by an amplified signal from the displacement transducer when the measured displacement corresponds to the desired displacement. The mechanism may also comprise an hydraulic accumulator connected to supply hydraulic fluid to said piston-in-cylinder requirements during any period when the said supply arrangement might be inadequate, for example when other mechanisms moving other guide bars are also demanding pressure fluid. A mechanism for driving a plurality of guide bars in a warp knitting machine may comprise a plurality of piston-in-cylinder arrangements with associated yoke arrangements and rods connected thereby to the pistons, the piston-in-cylinder arrangements having a substantial width by comparison with the epacing of the guide bars intended to be driven thereby, the said rods being more closely located together than the piston-in-cylinder arrangements can be, because of their width, so that they can be more closely aligned with the said guide bars than could the piston-in-cylinder arrangements. A piston-in-cylinder arrangement with a maximum stroke of about 0.05m will be adequate for most warp knitting machines, but some special machines might require maximum strokes of 0.l0m or even longer. It will be appreciated that any single displacement of a piston will usually be over only one or a small number of needle spaces, but during a pattern repeat a piston may need - as in the case of an Atlas construction - to move over longer distances. Although in general the piston will act intermediate the ends of the cylinder it might nevertheless on occasion come up against one or other end wall and it is preferred to relieve the piston or the cylinder in the case of a side-ported cylinder so as to avoid the possibility of the piston becoming jammed through there being no path for the fluid to pass from the port to the piston face. Shaft encoder means, which may be magnetic or optical, may respond to the operation of the main shaft of the knitting machine whereby the movements of the guide bars may be synchronised with the movements of other knitting elements. Dynamic response of the surface is important particularly at high operational speeds which are usually required in warp knitting and means may be provided activating said mechanism in accordance with the said movments of said other elements so as to compensate for changes in the speed of the knitting machine. Thus a delay of lms between valve actuation and piston movement corresponds to guide bar movement lagging 3.6° behind main shaft position at 600 r.p.m. as compared to inching speed and 7.2° at l200 r.p.m. It can be arranged that the signals for valve actuation are given correspondingly earlier the higher the main shaft speed. Automatic means determining the operation of said piston-in-cylinder arrangement may comprise a computer or data processor programmable with the required lapping movment of the guide bar and operable to cause said piston-in-cylinder arrangement to effect such movement of said guide bar. A mechanism for effecting guide bar lapping movement in warp knitting machines according to the invention will now be described with reference to the accompanying drawings in which:- Figure l is a part-sectional side elevation of a mechanism showing its connection to a guide bar, Figure 2 is a side elevation of a four guide bar arrangement, Figure 3 is a plan view of the arrangement shown in Figure 2, Figure 4 is a block diagram of the servo arrangement, and Figure 5 is a block diagram of the hydraulic arrangement. The mechanism for effecting guide bar lapping movement in warp knitting machines illustrated in Figure l comprises a double-acting piston-in-cylinder servo arrangement ll connected directly to the guide bar l2. By "connected directly" is meant that there is a substantially rigid connection between the piston-in-cylinder arrangement ll and the guide bar l2, and by double-acting in this context is then meant also that the piston-in-cylinder arrangement positively moves the guide bar in both directions. The piston l3 of the piston-in-cylinder arrangement ll is double ended having rod parts l3a, l3b projecting from cylinder l4 of the arrangement ll. The piston l3 is connected by these rod parts l3a, l3b through a rigid yoke arrangement l5 to a rod l6 slidable in linear bearings l7 in a block l8, and connected to said guide bar l2. The connection to said guide bar l2 is through a connecting rod l9 that accommodates movements of said guide bar l2 transverse to the axis of the piston-in-cylinder arrangement ll. Said connecting rod l9 is joined to the rod l6 at one end and to the guide bar l2 at the other end by spherical bearings 2l that permit the front and back swing movements of the guide bar l2 while holding a rigid, substantially no play, connection so that movements of the piston l3 are reflected precisely in lapping movements of the guide bar l2. A displacement transducer 22 is arranged with its cylinder 22a fixed in the machine and its piston 22b fixed to the yoke l5. Such transducers are relatively inexpensive and give highly reproducible output, without necessarily being precisely linear. However, any non-linearity can be calibrated out electronically or by computer programming. Electrically operated valve means 23, comprising a four port, torque motor valve, are attached to the piston-in-cylinder arrangement ll, two ports being inlet ports to opposite sides of the piston l3, the other two being outlet ports. A hydraulic accumulator 24 is connected to the valve means 23. Figures 2 and 3 show how four piston-in-cylinder arrangements lla, llb, llc, lld as described with reference to Figure l may be mounted at one side of a warp knitting machine to effect the lapping movements of four guide bars l2a, l2b, l2c, l2d. The guide bars are necessarily located close together, whereas the piston-in-cylinder arrangements have, by comparison, substantial width. They are accommodated by arranging them in upper and lower pairs, lla, llb and llc, lld respectively, of which pairs one of said arrangements, lla, llc respectively, is arranged axially displaced from the other, llb, lld respectively. The upper and lower arrangements are also inverted with respect to each other so that the attached hydraulic accumulators extend outwardly away from each other. The rods l6 driven through the yokes l5 can thus be all arranged substantially aligned with their respective guide bars. The arrangement has several advantages over the principal one that the relatively bulky actuators can be accommodated in a relatively small space roughly equivalent to that ordinarily taken up by the conventional pattern wheel or chain equipment (but much less, clearly than is required when long pattern chains are used) and, despite the close spacing of the guide bars, directly drive the same, thereby avoiding the need for complicated linkages that would permit more or less play and hence inaccuracies and irregularites in operation and evential wear and even failure of pivot bearings. By providing the separate linear bearings l7 for the rods l6, side loads on the piston rod and hence on its bearings in the piston-in-cylinder arrangements ll are avoided, leading to increased life of the arrangements ll. Moreover, in the event that a piston-in-cylinder arrangement goes faulty, it is relatively easily replaced. The fluid pressure and the effective piston area of the piston-in-cylinder arrangement are such as to apply a force on the guide bar of the order of 2.5KN. If the fluid pressure is approximately 8000KN/m², then the effective piston area will be about 0.0003m². The stroke length of the piston is about 0.05m. In practice, the actual length of any one stroke of the piston l3 for a lapping movement of the guide bar will be very small, usually one or only a few needle spaces, which is to say one or a few millimetres. The arrangement may have to provide however for more substantial displacements as when an Atlas construction is being knitted. Occasionally, the piston l3 may be driven against one or other end wall 3l of the cylinder l4 and, since the cylinder has side ports 32 the piston l3 might stick against the end wall 3l. To avoid this possibility the cylinder l4 and the end bearings are relieved at 33 to permit fluid to flow from the port 32 to act against the piston face. Figure 4 shows a diagram of the servo circuit. A voltage V is input from a control arrangement, to be described further below, to the torque-motor valve 23 through a summing arrangement 42 and an amplifier 43. The valve 23 provides fluid pressure to the piston-in-cylinder arrangement ll which displaces the guide bar l2 and the piston of the displacement transducer 22. A displacement output voltage F is passed from the displacement transducer to the summing arrangement 42 so that in fact it is a voltage V-F that is fed from there to the amplifier 43. When V=F, the valve is shut. It should be understood of course that when the valve admits fluid to one side of the piston l3 the outlet port on the other side of the piston is open. Figure 5 shows a more comprehensive block diagram of the arrangement. Hydraulic fluid from a reservoir 5l is pumped by a pump 52 through a fine filter 53 to a distributor 54 which feeds four similar piston-in-cylinder arrangements, only one, ll, of which is shown. There will in practice of course be as many piston-in-cylinder arrangements as there are guide bars on the machine. The components associated with such arrangement ll are identified by the reference numerals used previously on Figures l to 3. Thus the distributor 54 supplies hydraulic fluid to the valve 23 with its connected accumulator 24. The double ended piston l3 drives the guide bar l2 through the connecting rod l9, and also displaces the piston 22 b of the displacement transducer 22 which feeds a displacement signal to the summing arrangement 42 which is connected to the torque motor of the valve 23 through the amplifier 43. Hydraulic fluid exhausted from the arrangement ll (and from the other similar arrangements) passes to a collector 55 which returns it to the reservoir 5l via a shock absorber 56, a coarse filter 57 and a cooler 58. Also connected to the summing arrangement 42 is a computer or data processor 59 programmed to give command signals as inputs to the amplifier which in turn actuates the valve 23 to effect movement of the guide bar l2. The processor 59 is connected to an optical or magnetic shaft encoder 6l connected to the main shaft of the knitting machine and which gives to the processor 59 precise information about the instantaneous position and the speed of the main shaft. The processor 59 is programmed to advance or retard the timing of its signals to the valve 23 in accordance with shaft speed to compensate for the dynamic response of the system. The computer or processor 59 can also monitor other variables such for example as hydraulic pressure and fluid temperature, and of course can be programmed to execute different guide bar movements for different fabric constructions, as well as being operable to control specific movements for example for maintenance and setting up purposes. Although guide bar movements will ordinarily be over distances corresponding to integral numbers of needle spaces, fractional movements may be required for initial setting up purposes and also to take account of needle bending under thread tensions especially when forming long underlaps. Because of the precision with which the guide bars can be controlled through a computer or other processor, knitting can be carried out at high speeds with less downtime for fault correction than at present. And, of course, the setting up operation for a change of pattern is simplified as compared to the conventional pattern wheel or chain arrangements. Moreover, because the number of moving and wearing parts is considerably reduced, maintenance requirements are reduced. Reference is hereby made to GB-A- 2l55507 which claims a mechanism for effecting guide bar lapping movement in warp knitting machines comprising a double-acting piston-in-cylinder servo arrangement, comprising a piston connected by a rigid yoke arrangement to a rod, slidable in linear bearings, said rod being directly connectible to said guide bar.

Claims: A mechanism for effecting guide bar lapping movement in warp knitting machines having a plurality of guide bars (12),characterised by the mechanism comprising, for each guide bar, a double-acting piston-in-cylinder servo arrangement (11) connected to said guide bar through a connecting rod (19), the piston-in-cylinder arrangements having a substantial width by comparison with the spacing of the guide bars (12) and having associated yoke arrangements (15) more closely aligned with the guide bars (12) than are the pistons (13) of the piston-in-cylinder arrangements (11), the yoke arrangements (15) and the guide bars (12) being held to the connecting rods (19) by spherical bearings (21) which accommodate the swinging movements of the guide bars (12) as they pass between the needles but give an essentially zero play in the direction of the lapping movement. A mechanism according to claim 1, said piston-in-cylinder arrangement (11) comprising a double ended piston (13). A mechanism according to claim 1, in which a displacement transducer (22) is connected to the piston-in-cylinder arrangement (11). A mechanism according to claim 3, wherein said displacement transducer (22) comprises a linear differential voltage transducer. A mechanism according to claim 3 or claim 4, in which said displacement transducer (22) is calibrated for linearity. A mechanism according to claim 1, comprising electrically operated valve means (23) for the piston-in-cylinder arrangement (11). A mechanism according to claim 6, said valve means (23) comprising a four port, torque motor valve. A mechanism according to claim 1, comprising a hydraulic accumulator connected to supply hydraulic fluid to said piston-in-cylinder arrangement. A mechanism according to claim 1, in which the fluid pressure and the effective piston area of the piston-in-cylinder arrangement (11) are such as to apply a force of the order of 2.5KN. A mechanism according to claim 9, in which the fluid pressure is approximately 8000kN/m² and the effective piston area is approximately 0.0003m². A mechanism according to claim 1, in which the maximum stroke of the piston-in-cylinder arrangement (11) is approximately 0.05m. A mechanism according to claim 1, in which the piston-in-cylinder arrangement (11) is relieved at at least one end (31) whereby the piston (13) can be traversed up to the end wall (31) of the cylinder (14) and yet hydraulic fluid can flow through the relieved part to between the piston (13) and said end wall (31) to move said piston (13) away from said end wall (31). A mechanism according to claim 1, comprising shaft encoder means (61) responsive to the operation of the camshaft of a knitting machine whereby the movements of the guide bars (12) may be synchronised with the movements of the knitting elements. A mechanism according to claim 13, having an inertia, and means (59) activating said mechanism in accordance with the said movements of said elements so as to compensate for changes in the speed of the knitting machine. A mechanism according to claim 1, comprising automatic means (59) determining the operation of said piston-in-cylinder arrangement (11). A mechanism according to claim 15, said automatic means (59) comprising a computer or data processor programmable with the required lapping movement of said guide bar (12) and operable to cause said piston-in-cylinder arrangement (11) to effect such movement of said guide bar (12).

Inventors: PORAT, ITZCHAK ENGINEERING SECTION
Applicants: GUILFORD KAPWOOD LIMITED
Application year: 1985
Main classification: D04B27
IPC codes: D04B27