WO1997007275A1

WO1997007275A1 - Needlebar positioning system

Info

Publication number: WO1997007275A1
Application number: PCT/GB1996/001976
Authority: WO
Inventors: Roy Winstanley; David Haworth
Original assignee: Danley Engineering Services Limited
Priority date: 1995-08-16
Filing date: 1996-08-13
Publication date: 1997-02-27
Also published as: AU6747796A; GB9516809D0

Abstract

A needlebar positioning system for a tufting machine is disclosed which comprises a first hydraulic cylinder (44) driven directly or indirectly from the tufting machine main drive shaft (30), by the cylinder being connectable to a needlebar (10) actuating cylinder (16, 14) characterised in that the relative capacities of the two cylinders are chosen so that a given displacement of the first hydraulic cylinder (44) moves the needlebar (10) a precisely known amount. Preferably, the first hydraulic cylinder is not connected directly to the drive shaft (30) but is driven from an eccentric drive (38) which is in turn driven by the needlebar drive shaft (30) of the tufting machine. A gearbox (36) or other drive is preferably interspersed between the two with a one-to-two step-up ratio so that the eccentric drive revolves twice for each complete revolution of the needlebar drive shaft.

Description

NEEDLEBAR POSITIONING SYSTEM

This invention relates to a needlebar positioning system for a multiple needle tufting machine.

In the production of tufted fabrics, for example tufted carpets, patterns have been formed in the backing fabric by transversely or laterally shifting the needlebar with respect to the backing fabric between stitches. One way of doing this is by means of a pattern cam continuously rotated in synchronism with the rotary drive of the tufting machine, wherein the pattern cam engages a cam follower connected to the laterally reciprocal needlebar. However, this system has a number of disadvantages, not least in that there is considerable wear on both the cam surfaces and the cam followers together with the necessity for a long change over period when patterns of different designs are required, among others.

An improved form of needlebar positioning apparatus is disclosed in US-A-4173192 in which an electro-hydraulic positioning system includes a hydraulic actuator coupled to the needlebar (or the backing fabric support) . The hydraulic actuator is controlled by an electronic control circuit in which the particular stitch pattern information is stored, and the output of which generates a position command signal. This system includes, associated with the hydraulic actuator, a feed-back transducer which produces a feed-back signal corresponding to the actual position of the actuator or needlebar. The feed-back signal is compared with the command signal and the resulting electrical output drives an electrically controlled hydraulic valve causing the hydraulic actuator to move the needlebar to its new transverse position corresponding to the stitch pattern.

While this is an improvement over the earlier cam operated system, it nevertheless requires a hydraulic pump, which increases the power requirement of the tufting machine, and also requires constant tracking of the actuator, or needlebar, position.

The invention seeks to provide a needlebar positioning system improved in the above respects.

According to the present invention there is provided a needlebar positioning system for a tufting machine which comprises a first hydraulic cylinder driven directly or indirectly from the tufting machine main drive shaft, the cylinder being connectable to a needlebar actuating cylinder, characterised in that the relative capacities of the two cylinders are chosen so that a given displacement of the first hydraulic cylinder moves the needlebar a precisely known amount.

As with earlier proposals, rather than actuating the needlebar, the backing fabric support can be moved to achieve the desired aim of relative movement between the backing fabric and the needlebar in the transverse or lateral direction.

Preferably, the first hydraulic cylinder is not connected directly to the drive shaft but is driven from an eccentric drive which is in turn driven by the needlebar drive shaft of the tufting machine. A gearbox or other drive is preferably interspersed between the two with a one-to-two step-up ratio so that the eccentric drive revolves twice for each complete revolution of the needlebar drive shaft.

Conveniently, a further hydraulic cylinder, which may be of twice the capacity of the first, is also operatively connected to the eccentric drive and which can, therefore, move the needlebar twice the distance of the first cylinder. When both cylinders are actuated simultaneously, the needlebar may be moved three times its single actuation distance. In a preferred embodiment of the invention, the hydraulic cylinders are arranged in pairs such that one "pushes" hydraulic fluid as the other "pulls" it by suitable valves connecting the two, and a closed loop is formed whereby a push/pull effect is obtained giving very precise movement without possibility of overrun.

Operation of the cylinders is through valves which are electrically controlled in accordance with a stored programme as described more fully hereinafter.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation of one form of needlebar positioning system in accordance with the invention;

Figure 2 is a diagrammatic representation similar to Figure 1 of a second embodiment of the system;

Figure 3 is a graph of the operation curve of a typical solenoid valve;

Figure 4 is a similar view to Figure 3 of a valve operated in accordance with the invention;

Figure 5 is a block diagram of a circuit for operation of the solenoid; and

Figure 6 is a diagrammatic illustration of the needlebar drive shaft.

Referring to the drawings, and in particular Figure l, a tufting machine (not shown) which is otherwise conventional and therefore need not be described in detail comprises one or more needlebars (10) carrying tufting needles (12) in a manner known per se in the art. As illustrated, the needlebar (10) is connected to a pair of hydraulic cylinders (14) , (16) which can move it laterally in order to effect pattern changes. Cylinder (14) is connected hydraulically to port (18) , and cylinder (16) to port (20) of a valve (22) . The valve (22) is a five-way valve controllable by a solenoid. The solenoid within the valve (22) is connected by an electrical connection (24) via an interface (26) to a computer control system (28) . The computer control system (28) controls the power supply to the solenoid within the valve (22) and thus controls its opening and closing as will be described more fully hereinafter.

The tufting machine has a main needlebar drive shaft (30) driven by an electrical motor (32) and associated speed control (34) as is conventional with this type of machine. In the system of the invention, the drive shaft (30) is connected by a two-to-one reduction gearbox (36) to an eccentric shaft (38) . A push rod (40) connects the eccentric to the piston actuator rod (42) of a first hydraulic cylinder (44) . The cylinder (44) is hydraulically connected to a relief valve (46) and a three-way valve (48) . The valve (48) is also actuated by a solenoid controlled via the electrical line (24) to the computer control system (28) and can be switched so that port (50) connects with port (52) or port (54) . Port (54) is connected by a non-return valve (56) to a tank or reservoir (58) of hydraulic oil. A non-return valve (60) is also located in the hydraulic input to the relief valve (46) .

Port (52) of valve (48) is connected to the valve (22) . The valve (22) also has ports (62, 64, and 66).

Connected to the needlebar drive shaft (30) is an encoder unit (68) which senses the angular position and speed of the shaft (30) and is connected to the computer control system (28) .

Operation of the device is as follows. The electric motor (32) drives the shaft (30) at a speed set by the speed control (34) . This in turn drives the eccentric (38) at double the speed of the needlebar drive shaft. Thus, for a quarter turn of the drive shaft (30) the eccentric moves through 180°, which corresponds to the full stroke of the first cylinder (44) . The capacity of the cylinder (44) is precisely known and is related to the capacity of cylinders (14) and (16) . The ratio is chosen such that a stroke of cylinder (44) will cause the cylinders (14) or (16) to move the needlebar (10) transversely by exactly the pitch of the needles, i.e. one stitch width. The position of the push rod connection on the eccentric (38) is adjustable for fine control. It enables the stroke length, and thus displacement, of the cylinder (44) to be adjusted.

When the valve (48) is in the "off" position port (50) is connected to port (54) and as the piston (42) reciprocates within the cylinder (44) as eccentric (38) rotates, fluid is drawn into the cylinder through the relief valve (46) and non¬ return valve (60) and back, on the opposite stroke, through the valve (48) and the non-return valve (56) to the tank (58) . That is, in this mode, no movement is transmitted to the needlebar (10) .

When it is desired to move the needlebar one stitch width to the left, for example, valve (48) is energised by a signal from the computer system (28) via the interface (26) to its solenoid causing port (50) to be connected with port (52) . At the same time the valve (22) is also energised and oil from valve (48) entering port (62) is connected to port (20) thereby causing the right-hand cylinder (16) to be actuated moving the needlebar (10) to the left. As the cylinder (16) "pushes", the cylinder (14) is "pushed" and oil from it is vented through the port (18) of valve (22) and out of port (64) back to the reservoir (58) . As mentioned above, a single stroke of the cylinder (44) delivers a precisely known amount of hydraulic oil to the cylinder (16) causing the needlebar (10) to move exactly one stitch to the left. The valve (48) is then closed again. Should two stitches to the left be required, a second cylinder (44) will be provided (not shown) so that twice the hydraulic fluid is diverted to the valve (16) thus moving the needlebar (10) twice as far.

A movement to the right takes place in an entirely an analogous manner except that the oil entering valve (22) via port (62) is ducted to port (18) thus actuating the left-hand cylinder (14) and in this case the excess fluid from the cylinder (16) is ducted via port (66) back to the reservoir (58) .

Figure 2 illustrates a second, and currently preferred, embodiment of the system of the invention. Like numbers will be used for like parts. In this embodiment, a pair of cylinders (44, 44') are connected to the eccentric (38) such that one is on a "push" stroke while the other is on a "pull" stroke. A pair of three-way valves (48 and 48') are connected respectively to the cylinders (44 and 44'). In the "off" position of the valves (48, 48') they are connected to one another and so the hydraulic fluid forms a closed loop. Unlike the system illustrated in Figure 1, hydraulic fluid is not taken from and vented back to a tank or reservoir and instead it is a closed system.

On actuation of the valves (48 and 48') (from the computer control system as before) cylinder (44) is connected via the five-way valve (22) to the cylinder (14) (for movement to the right, or to cylinder (16) for movement to the left) and the cylinder (16) is connected by the three-way valve (48') to the cylinder (44') .

As the eccentric shaft 38 revolves, fluid will be "pushed" by one of the cylinders (44, 44') and "pulled" by the other. As before the precise volume of the cylinders (44, 44') is known (and the same for each) and is predetermined in relation to the volume of cylinders (14, 16) so as to provide a single pitch lateral movement of the needlebar (10) . However, the "push/pull" effect is such that very precise movement is obtained and the presence of a closed hydraulic loop system prevents any overrun of the needlebar (10) . Moreover, because the motion imparted by the eccentric (38) is essentially sinusoidal, rapid accelerations and decelerations are avoided.

The second eccentric (38') in Figure 2 is connected to a pair of hydraulic cylinders (70, 75) which are exactly of twice the capacity of the cylinders (44, 44'). These are connected to three-way valves (48'' and 48'''). When not required to be used the valves (48'' and 48'''), are connected together to form a closed loop as described above. If a movement of two stitch widths is required rather than one stitch, the cylinders 44, 44') are not actuated but instead the cylinders (70 and 70') which, having twice the capacity, move the needlebar (10) by twice the amount. If a movement of three stitches is required both sets of cylinders are switched into circuit simultaneously providing three times the fluid output of the cylinders (44, 44') on their own. Since very few patterns require at any one time a movement of more than three stitches, the whole range of patterning can be accommodated by this embodiment of the invention.

The computer control system (28) is set up in a manner which in many ways is conventional. The carpet pattern may first be designed, for example on a computer aided design work station, where yarn colours, number of stitches, needlebar step data and other relevant information is entered. The computer then formats the data into a suitable form for the tufting machine and for subsequent needlebar movement control.

Connected to the needlebar drive shaft (30) is the encoding unit (68) which gives information as to the angular position and speed of the shaft. This data is processed so that the hydraulic valve solenoids can be switched on at the correct time. Owing to the fact that solenoid actuation of hydraulic valves takes a finite time, it is necessary to take steps to ensure that the valve is fully open (or fully closed) at the correct point in the cycle.

A common type of hydraulic valve typically takes 50ms to operate. Since tufting speeds in the order of 1500 stitches per minute may be required from a tufting machine including the system of the invention, this translates into the needlebar drive shaft (30) rotating once every 40ms. Clearly a 50ms delay in operation of the hydraulic valves is unacceptable. In the system of the invention this is overcome in two ways.

Figure 3 illustrates a typical current/time diagram of the operation of a solenoid actuated hydraulic valve. The valve tends to open (or close) when the current reaches 66% of maximum, the points P and D on the curve in Figure 3. Since the inductive impedance of the solenoid slows the build-up in current, the pull-in time and drop-out time are significant, in the order of 50ms as indicated earlier.

In accordance with the invention, however, a greater voltage is applied in the initial stages, as illuεtrated in Figure 4 this considerably reduces the pull-in time and drop-out time. The voltage is then reduced to the correct operating voltage to prevent burn out of the solenoid. The circuit for controlling this is illustrated in Figure 5. A signal is received from the computer control and is simultaneously applied to inputs A and B. Input A switches one side of the solenoid coil to the zero volts reference potential. Input B switches the other side of the solenoid firstly to a voltage V2 (which is higher than the voltage VI) for a period of time determined by the timer and then automatically switches it to VI. VI is the normal operational voltage of the solenoid. This action produces the voltage wave-form illustrated in the lower half of Figure 4. The negative pulse is provided by rectifying the back EMF produced by the inductance of the solenoid. This method of operation significantly reduces the pull-in time to about 25% of the normal time, provided that the amplitude and width of the pulse are carefully adjusted. Although the above reduces significantly the pull-in and drop¬ out time of the hydraulic valve solenoids, they are not reduced to zero. They can, however, be reduced to approximately 20ms. It is therefore necessary to εtart the actuation of the solenoid in advance of when the valve is actually required to open. If we assume that the solenoid of the hydraulic valves will take 20ms to operate, and that a speed of operation of the machine of 1500 stitches per minute is required, then the drive shaft (30) completes one revolution every 40ms. It iε therefore necessary to energise the relevant solenoid 20ms sooner than otherwise would be necessary. Referring to Figure 6, if S represents the point at which the needlebar should start moving, and F represents the point at which it should finish moving, then it would be necessary to εtart energiεing the εolenoid at point T, 180° in advance.

At a εpeed of 750 εtitcheε per minute, the time for revolution increases to 80ms while the solenoid operating time remains the same at 20ms. The operating point must therefore be moved in a clockwise direction by 90° which is only 90° in advance of point S. At a further reduced speed of 375 stitches per minute, the time for revolution increases to 160ms and the operating point iε reduced by a further 45°. In order to achieve ε ooth control over the whole speed range of the machine, the encoder (68) is fitted to the needlebar drive shaft (30) so that the speed and revolutions per minute can accurately be measured in time and the angular displacement from a reference point is also measured. The data from the encoder is then procesεed to produce a signal which will energise the solenoid of the relevant valve at the correct amount of advanced timing with respect to the speed of the machine. It will be appreciated that the needlebar (10) should only be moved laterally when the needles (12) are out of the backing fabric. The points S and F are 45° on either side of Top Dead Centre (where the needlebar is furthest away from the backing fabric) and the quadrant between these points corresponds to the portion of the machine cycle during which the needles are at their furthest point from the backing fabric.

The system of the invention produces a simple, accurate and re¬ producible way of positioning the needlebar of a tufting machine. The use of accurately known hydraulic cylinder capacities enables the needlebar to be moved at precise amount without monitoring its position. Moreover, the use of cylinderε connected directly or indirectly to the machine drive εhaft obviateε the need for a hydraulic pump.

Claims

1. A needlebar positioning system for a tufting machine which comprises a first hydraulic cylinder driven directly or indirectly from the tufting machine main drive shaft, the cylinder being connectable to a needlebar actuating cylinder, characterised in that the relative capacities of the two cylinders are chosen so that a given displacement of the first hydraulic cylinder moves the needlebar a precisely known amount.

2. A system as claimed in claim 1 in which the first hydraulic cylinder is not connected directly to the drive shaft but is driven from an eccentric drive which is in turn driven by the needlebar drive shaft of the tufting machine.

3. A system as claimed in either of claims 1 or 2 in which a gearbox or other drive is interspersed between the two cylinders with a one-to-two step-up ratio so that the eccentric drive revolves twice for each complete revolution of the needlebar drive shaft.

4. A system as claimed in any of claims 1 to 3 in which a further hydraulic cylinder, which may be of twice the capacity of the first cylinder, is also operatively connected to the eccentric drive and which can, therefore, move the needlebar twice the distance of the first cylinder.

5. A system as claimed in any of the previous dims in which the hydraulic cylinders are arranged in pairs such that one "pushes" hydraulic fluid as the other "pulls" it by suitable valves connecting the two, and a closed loop is formed whereby a push/pull effect is obtained giving very precise movement without possibility of overrun.

6. A system as claimed in any of claims 1 to 5 wherein operation of the cylinders is through valves which are electrically controlled in accordance with a stored programme.