GB2027074A - Method of Controlling the Relative Spacing of Tools, for Example Sewing Needles - Google Patents

Abstract

A method of controlling the relative spacing of tools, for example sewing needles 12, which are engageable with a workpiece which is movable in a plane. The tools are mounted in laterally spaced relationship relative to an axis 7 extending normally to the plane, the workpiece is moved along a predetermined path in said plane, and the tool carrier is rotated about said axis so as to selectively position the successive operating localities of the tools on the workpiece relative to the predetermined path. Means for selectively inactivating the needles and for pulling back the associated thread are provided. <IMAGE>

Description

SPECIFICATION Method of Controlling the Relative Spacing of Tools, for Example Sewing Needles This invention concerns a method of controlling the relative spacing of the operating paths of tools which are engageable with a workpiece which is movable in a plane. The invention also concerns a sewing machine in which the relative spacing of the operating paths of sewing needles are controlled.

When multi-needle sewing machines or other multi-tool machines are employed on a workpiece which is movable in a plane, a component of the workpiece feeding movement along a line interconnecting the tools alters the spacing of the operating paths of the tools producing unsightly results. To avoid this the workpiece can be rotated but this creates difficult feeding and workpiece clamping problems and it is an object of this invention to avoid these problems.

The invention provides a method of controlling the relative spacing of the operating paths of tools which are engageable with a workpiece which is movable in a plane, the method comprising mounting the tools on a tool carrier in laterally spaced relationship relative to an axis extending normally to the plane, and moving the workpiece along a predetermined path in said plane, wherein as the workpiece is moved in said plane, the tool carrier is rotated about said axis independently of the movement of the workpiece so as to selectively position the successive operating localities of the tools on the workpiece relative to the predetermined path.

In order to enable the production of decorative effects on the workpiece, one of the tools is rendered inoperative during one or more intervals in the operation of the machine.

In order to carry out the above described method where the tools are sewing needles, the invention provides a sewing machine arranged to operate on a workpiece which is movable in a plane, the machine comprising a tool carrier reciprocable towards and away from the workpiece, moving means operable to move the workpiece in the plane, and control means operable to control the operation of the moving means to cause the workpiece to move along a predetermined path, wherein the tool carrier is arranged to carry at least two needles and is rotatable independently of the movement of the workpiece about an axis which is normal to said plane, and the machine comprises rotating means operable under the control of the control means to rotate the tool carrier about said axis in a predetermined manner.

A sewing machine which embodies the invention is represented in the drawings and is described in greater detail below.

In the drawings: Figure 1 is a perspective view of the sewing machine; Figure 2 is a diagrammatic perspective view of rotating means of the sewing machine; Figure 3 is an enlarged side elevational view, with parts broken away, of the sewing head of the sewing machine; Figures 4 and 4a are, respectively, exploded perspective views of upper and lower portions of the sewing head; Figure 5 is an enlarged perspective view of thread control means of the sewing machine; Figure 6 is a side elevational view of the thread control means shown in Figure 5; Figures 7 and 8 are plan views of the thread control means showing, respectively, its inoperative and operative conditions; Figures 9 and 10 show stitching patterns of the sewing machine; Figure 11 isa diagrammatic view of control means of the sewing machine;; Figure 12 is a detailed diagrammatic view of a portion of the control means shown in Figure 11; Figure 13 is a diagram of the signals which occur in the control means of Figures 11 and 12; Figure 1 4a shows the sewing of a circular pattern by the sewing machine; Figure 1 4b shows the sewing of a circular pattern by a conventional sewing machine; Figures 1 5a to 15d show sewing patterns of the sewing machine.

The sewing machine shown in the drawings is a lockstitch machine arranged to operate on a workpiece W which is movable in a plane. The machine comprises a stationary head 8 which houses a tool carrier 10 which is reciprocal towards and away from the workpiece W. The workpiece W is held between clamps 1 3 and is moved in its plane by X and Y stepping motors.

The movement of the workpiece W is carried out as a series of discrete movements. The carrier 10 carries two needles 12 which are each offset from a vertical axis Z-Z of the carrier 10 by substantially the same distance. The carrier 10 is reciprocated by a crank 1 4 and a motor 1 6 connected to the crank 14 by a shaft 18 to cause the needles 1 2 to move towards the workpiece W to penetrate the workpiece W and away from the workpiece W to release it for movement. The tool carrier 10 is thus reciprocated to bring the needles 1 2 into intermittent operative contact with the workpiece W in timed relation with the movement of the workpiece W.

The machine also comprises a stitch-forming assembly 20 beneath the workpiece W. The assembly 20 comprises two hooking devices 21 which co-operate with the needles 1.2. A drive belt 22 operates off the shaft 1 8 and rotates a gear 23 which meshes with a gear 24. The gear 24 meshes with a gear 25 on a shaft 26. A gear 27 also on the shaft 26 meshes with a gear 28 fixed to a vertical shaft 29. Thus, rotation of the gear 23 causes rotation of the shaft 29 about the Z-Z axis. A gear 30 mounted at the top of the shaft 29 meshes with a gear 31 fixed to a horizontal shaft 32 rotatablyjournalled in a housing of the assembly 20. Two gears 33 fixed to the shaft 32 mesh with two gears 34 fixed to the ends of two vertical stub shafts 35 fixed to the hooking devices 21.The stub shafts 35 are rotatively mounted within support arms 36 of the housing. The hooking devices 21 rotate about their respective axes in response to rotation of the shaft 32 and this rotation causes the devices 21 to carry out their thread hooking function.

The carrier 10 is rotated about the Z-Z axis by rotating means in the form of a motor 37 (Figure 2) which rotates a shaft 38 via a drive belt 39. The motor 37 is controlled by control means 60 of the sewing machine to cause rotation through an angle 0 when the needles 12 are out of the workpiece W. Like the movement of the workpiece W, the angular rotation of the tool carrier 10 is carried out as a series of discrete angular rotations but the rotation of the tool carrier 10 is independent of the movement of the workpiece W. Furthermore, the reciprocation of the tool carrier 10 is in timed relation with both the movement of the workpiece W and the rotation of the carrier 10.

The shaft 38 has gears 40 and 41 fixed at opposite ends thereof to transmit motion to shafts 42 and 43 via gears 44 and 45. The shaft 42 has a gear 46 mounted thereon which meshes with a gear 47 fixed on a shaft 48. A gear-49 is mounted on the shaft 48 to transmit rotary motion to a member 50 by meshing with a spline gear 51 formed thereon. The member 50 is journalled in the head 8 and imparts rotary motion to the carrier 10 thereby rotating the needles 1 2 about the Z-Z axis. The shaft 43 has a gear 52 mounted thereon which meshes with a gear 53 fixed to the housing of the assembly 20 so that the assembly 20 and therefore the hooking devices 21 rotated about the Z-Z axis.

The gear 41 also meshes with a gear 54 fixed on a shaft 55 which via gears 57, 58 and 59 imparts rotation to a shaft 56 which is freely rotatable in a bore through the gear 23. The gear 24 is mounted on the shaft 56 and meshes with the gear 25 so as to rotate the shaft 26. Rotation of the shaft 26 rotates the shaft 29 and the shaft 32 so as to counteract epicyclic movement of the hooking devices 21 about their own axes caused by movement of the shaft 32 about its own axis.

The motors 1 6 and 37 are connected to the control means 60 by lines 62 and 64, respectively, and a needle position sensor 66 is connected to the control means 60 by a line 68.

The carrier 10 comprises two needle bars 70 and 72 (Figures 3, 4 and 4a) each arranged to reciprocate one of the needles 12. The crank 14 carries a vertically guided connecting rod 74 having an annular wrist pin 76 which is received in a groove of a lifting rotatable collar 78 fixed by a set screw 80 to a partially tubular member 82.

The member 82 axially and slidably receives the lower ends of the needle bars 70 and 72. An upper forked end of the member 82 is formed with spaced holes 84 for removably receiving ends of socket pins 86 which extend transversely one through a bore 88 in the bar 70 and the other through a bore 90 in the bar 72. The socket pins 86 have a driving connection to the member 50 and each is connected to one of two dual acting air motors 92 and 94 which operate to enable or disable vertical reciprocation of the needles 12.

Each of the pins 86 has a socket 96 which receives the lower end of one of two vertical rods 98 (Figure 4a) which extend through elongated radial slots 100 in the member 50 so that the rods 98 form a driving connection between the pins 86 and the member 50. The upper ends of the rods 98 are screwed by screws 102 to blocks 104 and 106. A forked clip 108 bears on the blocks 104 and 106 to hold the carrier 10 up when the pins 86 are disengaged from the holes 84. Springs 1 09 secured to the inside of the head 8 urge the rods 98 towards radially inward ends of the slots 100. Thus, the pins 86 through the rods 98 turn the bars 70 and 72 with the member 50.

Means of the illustrative machine for rendering either of the needles 12 inoperative at predetermined localities on the workpiece will now be described. The blocks 104 and 106 (Figures 4 and 4a) have radially spaced conical faces 110 and 112 engageable by correspondingly conical outer and inner faces 114 and 116 formed one on each of two coaxial tubular plungers 118 and 120. The air motors 92 and 94 are mounted on a cross pin 122 in the upper end of a bracket 124 (Figures 1 and 4) fixed to the head 8. Heightwise movement of either of the plungers 11 8 and 120 by operation of piston rods 126 and 128 of the air motors 92 and 94 causes radial movement of one of the rods 98 and axial movement of the pin 86 in its bore 88 or 90 hence breaking operative engagement of the pin 86 with the wall of the hole 84.This is because the blocks 104 and 106 have holes 107 and are axially slidable on bearing pins 130 and 132 therein (Figure 4a). The pins 130 and 132 are radially disposed in a bridge portion 136 of the member 50 and in a block 138 mounted on the member 50.

Downward movement of the piston rod 126 lowers the inner plunger 120 by pressing on a block 140 slidably fitted in a slot 142 formed in the outer plunger 118, the block 140 being secured to the plunger 120 by a screw 144.

Downward movement of the piston rod 128 lowers the outer plunger 11 8 by pressing a block 146 screwed to the plunger 11 8 by screws 148.

A guide pin 1 50 (Figures 3 and 4) extends through the bracket 124 and aligned slots 1 52 and 1 54 in the plungers 118 and 120. Return springs 156 suspended from a support 1 58 fixed to the bracket 124 oppose lowering of the plungers. A lower end portion of one of the springs 1 56 is connected to a tab 160 mounted on the block 146 and a lower end portion of the other spring is connected to a tab 1 62 mounted on the block 140.

Thread take up and pull back means 170 of the illustrative machine is shown in Figures 5 to 8.

Thread T is supplied from spools (not shown) to the needles 12 via the means 1 70 and extends downwardly through bores 172 in a plug 174 mounted on the bridge portion 1 36. Thence the thread T runs downwardly through axial holes 176 in the bars 70 and 72 to the needles 12. In order to eliminate the excess of thread T caused when either of the needles is disabled, a thread pull-back stepper motor 1 78 mounted on a frame 188 rotates a friction roll 180. The friction roll 1 80 co-operates with one or both of two idler rollers 1 82 carried by upper and lower levers 1 84 mounted on a bracket 186 on the main frame 1 88 of the machine.Each lever 1 84 engages at one end an adjustable thread-engaging friction means 1 89 and has its opposite end arranged to be engaged by one of a pair of piston rods 190 respectively operated by two spring return air motors 1 92. The thread T- passes between the bracket and the means 1 89 and compression springs 1 94 (Figure 8), adjustably confined on screws 1 96 projecting from the bracket 1 86 by nuts 198, act to tension the thread T.

The air motors 192 and the motor 178 are controlled by the control means 60. When an air motor 1 92 is operated it causes its idler roller 1 82 to move thread in contact therewith against the friction roller 180 and the motor 1 78 will rotate the roller 180 to pull back the thread.

The illustrative machine comprises thread supply means and thread cutting means (not shown) of conventional construction and a presser foot 200 formed with a hole which can encircle both needles 12 when the foot 200 is raised by conventional means (not shown).

Figure 9 shows an example of a stitching pattern sewn by the illustrative machine. This pattern comprises a dotted centre-line path 206 which traces the successive positions of the pattern relative to the Z-Z axis. Each successive position is reached by X and Y movements. P0 is the initial position and movements of X, and Y, reach positions P, and so on. The angular rotation of the needles 12 about the Z-Z axis of 0, between the positions P0 and P. By successive X and Y movements and rotations about the Z-Z axis two stitching paths 208 and 210 which make up the pattern are formed.

Figure 10 shows a corner stitching pattern comprising an outer corner path 221 and an inner corner path 222 sewn on to the workpiece W.

The pattern is defined by two dotted straight-line centre-line paths 212 and 214 and an arcuate centre-line path 21 5. A first of the needles 12 is operated along the outer stitch path 221 while the second needle 12 is operated along the inner stitch path 222. When the second needle 12 reaches the apex 21 6 of the inner corner (position P4 on the centre-line 212), the second needle 12 is rendered inoperative by operation of one of the motors 92 and 94. The movement along the line 212 continues with only the first needle 1 2 operating until the first needle 12 reaches the apex 21 8 of the outer corner (position P10 on the line 212). The second needle 12 is next rotated about the apex 218, along an arc 219 from the point 220 which it has reached, while the first needle 12 is maintained at the apex 218.This rotation is achieved by a combination of movements of the workpiece W and rotation of the tool carrier 10. P" to P15 show progressive centre-line positions along the arcuate centre-line path 215. This arcuate movement about the apex 218 ensures that the first needle will not have any appreciable thread pulling therethrough. The amount of angular rotation B is equal to 1800 minus (x where u is the corner angle to be negotiated. As the rotation about the apex 21 8 takes place, both needles 1 2 are inoperative.

When the position P15 is reached on the centreline path 214, the first needle 1 2 is re-activated and the needles 12 are moved in the new direction of movement until the second needle 12 again reaches the apex 216 of the inner corner (position P20). An amount of thread substantially equal to the amount of thread pulled out by the second needle 1 2 since it was rendered inoperative is pulled back through the second needle 12 by operation of the motor 178. This amount of thread should be substantially equal to the distance L marked in Figure 10. The thread is pulled back in five increments 6 as the movement between positions Ps and P20 takes place. At the apex 216, the second needle is re-activated and sewing continues either side of the centre-line path 214.The control means 60 controls X, Y, O, (i)and the operation of the motors 92 and 94.

Figure 11 shows the control means 60 which comprises a memory 230 having addressable storage locations which are twenty-seven bits wide (Bo to B26). The bits are organised as follows: B0-B5 magnitude of X movement B6 direction of X movement B7-B12 magnitude of Y movement B,3 direction of Y movement B.4B.8 magnitude of 0 movement Bag direction of 0 movement (clock wise or anti-clockwise) B20-B22 magnitude of Ql'movement B23 direction of movement B24 engage/disengage first needle B25 engage/disengage second needle B26 end of pattern Each addressable storage location is addressed by an address register 232 connected to the memory through an address bus 234. The register 232 is a ten bit register capable of addressing at least one thousand individual storage iocations in the memory 230.

The ten bit address in the register 232 is advanced in response to a change in state of an AND gate 236 caused by a plurality of signal conditions being present at its input. The output of the AND gate 236 gives an "address advance" signal to the register 232 which then addresses the next twenty-seven bit storage location in the memory 230. The bits B0 to B25 are applied to a drive system 238 via a bus 240. The drive system 238 executes the movements and signals via a bus 242 to the input of the AND gate 236 when they have been accomplished.

The drive system 238 is shown in Figure' 1 2 and comprises drive systems for X, Y, 6 and . The magnitudes of the parameters are applied to counters within the drive system viz. an X counter 244, a Y counter 246, a 6 counter 248 and a counter 250. The magnitudes of movement are loaded into the respective counters by a pulse generator 252 triggered by the address advance signal from the AND gate 236 via a line 253.

A set of flip-flops 254 and 256 are ålso loaded at the same time as the counters 244 to 250 and receive the bits B24 and B25. A pulse created by the pulse generator 252 triggers the loading of the counters 244 to 250 and the flip-flops 254 and 256 to which it is connected via an inverter 258. Outputs 255 and 257 of the flip-flops 254 and 256 are arranged to control the air motors 92 and 94 to make the second and first needles 12, respectively, operative and further outputs are connected to an AND gate 260 the output of which is connected to a line 358 which carries a signal when neither of the needles 1 2 is to be operative.Since the X and Y rates of movement require to be different depending on whether or not a stitch is to be formed, when no stitch is to be formed, these rates are defined by a clock 264 and, when a stitch is to be formed, these rates are defined by a clock 262. Similarly the 6 rate of movement is defined by a clock 266 when a stitch is to be formed and a clock 268 when no stitch is to be formed. The clocks 262, 264, 266 and 268 are multi-vibrator circuits which produce trains of pulses at prescribed frequencies.

The signals from the clocks 262 and 264 are applied to a clock selection circuit 270 and the signals from the clocks 266 and 268 to a clock selection circuit 272. The clock selection circuits 270 and 272 also receive the signal on the line 358 and are operative to select the clocking signals from either the clocks 262 and 266 or the clocks 264 and 268 depending on the signal on the line 358.

In the clock selection circuit 270, an AND gate 274 receives signals from the clock 262 and from the line 358 via an inverter 278 and an AND gate 276 receives signals from the clock 264 and the line 358. The outputs of the gates 274 and 276 are connected to an OR gate 280. If there is a signal on the line 358 indicating no stitch, the gate 276 will pass the signals from the clock 264 to the gate 280 and, if there is no signal on the line 358, the signals from the clock 262 are passed to the gate 280. The output of the OR gate 280 is applied to both an AND gate 282 and an AND gate 284. The gate 282 is enabled for an X movement and the gate 284 for a Y movement.

The X counter 244 is loaded with a non-zero count when an X movement is to occur and the Y counter when a Y movement is to occur. These non-zero counts are detected by an X-count detector 286 and a Y-count detector 288. When they detect a non-zero count, the count detectors 286 and 288 generate logically low signals which are passed via invertors 290 and 292 to the AND gates 282 and 284 so as to enable them.

The clock selection circuit 272 functions in the same manner as the circuit 270 but in relation to the 6 counter 248, an AND gate 294, a count detector 296 and an inverter 298. The AND gate 294 is enabled when a 6 movement is to occur.

The X, Y and 6 clocking signals are also respectively applied to direction selection circuits 300, 302 and 304. These circuits also each receive a bit from the memory 230 via the bus 240 indicating positive or negative or clockwise or anti-clockwise movement. The circuits 300, 302 and 304 respectively receive the bits B6, B13, and B19 which indicate the direction of movement.

The circuit 300 has a positive direction output 301 and a negative direction output 303 both connected to an X stepping motor control 306, the circuit 302 has two similar outputs connected to a Y stepping motor control 308, and the circuit 304 has two similar outputs connected to a 6 stepping motor 310 control which controls the stepping motor 37.

The direction selection circuit 300 comprises an AND gate 314 whose output is the output 301 and an AND gate 316 whose output is the output 303. The signal on the bit B6 is applied directly to the gate 314 and through an inverter 31 8 to the gate 316. Thus, the circuit 300 signals the direction of movement and passes the number of pulses corresponding to the required amount of movement, since each pulse from the counter 244 is passed via either the output 301 or the output 303 to the control 306. When all the pulses have been passed to the control 306, the X count detector 286 passes a signal through the inverter 290 to disable the AND gate 282. The X count detector 286 also passes a signal to a line 320 which forms part of the bus 242.

The selection circuits 302 and 304 operate in similar manner to the circuit 300 but in respect of the Y stepping motor control 308 and the 6 stepping motor control 310 and output signals from the Y and 6 count detectors 288 and 296 are passed to lines 322 and 324 which form part of the bus 242.

The drive system 238 is also operable to implement a pull-back of threads when called for on the bits B20 to B23. The magnitude of the pullback is defined by bits B20 to B22 which are applied to the counter 250 and the direction of pull-back indicated by the bits B23 is applied to a direction selection circuit 326. The loading of a particular magnitude of pull-back into the (i) counter 250 will cause a (il count detection 328 to produce a logically low signal which is inverted by an inverter 330 to enable an AND gate 332.

Clocking pulses from a pull-back clock 334 are passed through the AND gate 332 and are applied to the (i) counter 250 and the selection circuit 326. The circuit 326 will have either its plus or its minus output enable to pass pulses to a (iistepping motor control 336 which controls the motor 1 78. When all the pulses have been passed, the Q) count detector 328 disables the gate 332 and passes a signal to a line 338 of the bus 242.

The signal on the line 338 is also fed through an inverter 340 to two AND gates 342 and 344.

When a pull-back is to take place, a logically low signal is inverted by the inverter 340 so as to enable the AND gates 342 and 344. The AND gates 342 and 344 also receive signals from the flip-flops 254 and 256 which will be logically high when the needle 1 2 associated therewith is to be inoperative. When the first needle 12 is inoperative, the gate 344 produces a signal on a line 341 and when the second needle 12 is inoperative, the gate 342 produces a signal on a line 343. Signals on the lines 341 and 343 activate the respective air motors 1 92 to bring the idler rollers 1 82 into contact with the friction roll 180 causing pull-back of thread.

In addition to the lines 320, 322, 324 and 338, the AND gate 236 (Figure 11) also receives a "start" signal from a start switch 350 in combination with a one-shot circuit 352 and an inverter 354 and a signal from an OR gate 356.

The or gate 356 receives signals on the line 358 from the drive system 238 and on a line 360 from a pulse generator 362. A signal will occur on the line 358 when no stitching is taking place but only movement and a signal will occur on the line 360 when stitching is taking place.

The timing of the generation of a pulse by the pulse generator 362 is controlled by a needle position detection circuit 364 which is operative to provide a logically high pulse to the pulse generator 362 via a line 366 whenever a needle 1 2 moves out of the workpiece W.

The actual stitching of the workpiece W is controlled by a sewing machine motor control 368 which controls the motor 1 6. The control 368 receives a signal from the needles position sensor 364 along a line 370 and signals from the line 358 along a line 372. The control 368 prevents needle movement when it receives logically high signals on the lines 370 and 372 indicating that the needles are out of the workpiece W and that no stitching is required.

Further needle movement is initiated if the signal on the line 372 goes logcially low indicating that stitching is to take place.

An operation of the illustrative machine continues until bit B26 indicates "end of pattern".

This gives a logically high signal on a line 374 which will trigger a negative pulse generator 376 which applies a negative pulse to an AND gate 378. The AND gate 378 also receives a normally logically high signal on a line 380 from a flip-flop 382 so that the negative pulse causes the output of the gate 378 to drop logically low. This output is connected to a reset terminal of the address register 232 to a line 384 so as to re-set the register 232.

The sewing of a pattern is initiated by pressing the start switch 350 which triggers the one-shot 352 which generates a pulse. This pulse normally does not have any effect on the flip-flop 382 but causes the AND gate 236 to activate the address register 232.

To start up the illustrative machine, a power supply circuit 385 generates a "power on" signal when power is supplied thereto. This signal resets the flip-flop 382 to a logically low state so that it applies a logically low signal to the AND gate 378 via the line 380. This causes the AND gate 378 to go logically low in turn holding the address register 232 at a memory address of zero. The logically low output of the flip-flop 382 is also applied to the drive system 238 via a line 386 which is connected to reset terminals of the X counter 244, the Y counter 246, the 0 counter 248, the (b counter 250 and the flip-flops 254 and 256 (Figure 12). The counters 244, 246, 248 and 250 now produce logically high signals on the lines 320, 322, 324 and 338.The flip-flops 254 and 256 will now produce logically high signals on their outputs to the AND gates 342 and 344 and to the AND gate 260 which passes a logically high signal to the line 358. The signal on the line 358 sets the output of the OR gate 356 logically high.

On depression of the start switch 350, the oneshot 352 generates a pulse of which the leading edge sets the flip-flop 382 to a logically high state. The output of the flip-flop 382 is applied to the AND gate 378 releasing the address register 232 to accept pulses from the memory 230.

Returning to the pulse generated by the one-shot 352, it is inverted by the inverter 354 and applied to the AND gate 236 which is thereby enabled incrementing the address register 232 to receive information from the memory 230.

Figure 1 3 shows various waveforms of the machine for an exemplary operation of the machine. Waveform A is the output of the flip-flop 382, B is the output of the one-shot 352.

Waveforms C to F are the outputs of the counters 286, 288, 296 and 328. Waveforms G and H are the outputs of the AND gates 260 and 236 and waveform J is the load on the pulse generator 252. Waveforms K and L are the outputs of the flip-flops 254 and 256. Waveforms M, N, P and R are the outputs of the AND gates 282, 284, 294 and 332. The waveform Q is that of the needle position sensor 364. The waveforms S and T are those of the AND gates 342 and 344 and the waveform U is that of the negative pulse generator 376.

To in Figure 1 3 indicates the time when the power is switched on. At time T1 the start switch 350 is depressed causing a pulse from the oneshot 352, setting the flip-flop 382, and holding the address register at zero (waveforms B, A and H). When the output of the one-shot 352 goes logically low at time T2,the AND gate 236 goes high advancing the address register 232 and initiating a pulse from the pulse generator 252 (waveforms B, H and J).

At time T3 the trailing edge of the pulse in waveform J occurs and the memory 230 loads the counters 244, 246, 248 and 250 and sets the flip-flops 254 and 256. In Figure 13, at time T3 movement without stitching occurs so the X, Y and 0 clocking signals (waveforms M, N and P) are at the non-stitching clocking rate. At time T4, the 0 count reaches zero and, therefore, the 0 clocking signals (waveform P) cease. At time T5, the X count reaches zero and the X clocking signals (waveform M) cease. At time T6, the Y count reaches zero and the Y clocking signals (waveform N) cease.

At time T6 with all three counts at zero, the AND gate 236 is enabled (waveform H) and the address register 232 advances to the next memory address. The new memory address selects the second needle 12 as indicated by the flip-flop 254 going logically high at time T, (waveform K) and the AND gate 260 goes logically low (waveform G). The sewing motor 16 is turned on and the crank 14 rotates. When the crank 14 rotates to the up position, the sensor 364 gives a pulse (waveform Q) at time T8. This enables the AND gate 236 and the address register advances to the third memory address.

The third memory address contains data for X, Y, 0 and QI and selection of the first needle 12. The QI data is to achieve pull-back of the thread associated with the second needle 12 at time T9 which continues until time T10 (waveform F shows the QI count detector and waveform R shows the 01 clock 332). At time T11 the 0 count detector 296 goes logically high (waveform E) and 0 movement ceases. The Y movement ceases at time T,2 and the X movement at time T13. At time T14 a "needle up" pulse is generated by the needle position sensor 364 (waveform Q) enabling the AND gate 236 so that the address register 232 advances to the next memory address.

When a pattern has been completed, it may be necessary to return to the original starting position of the machine. This is accomplished by X and Y movements initiated at time T15. Both X and Y movements begin at time T16 and the movements terminate respectively at times T17 and T18. At time T16, the next memory address contains all zeros and a negative pulse is generated by the generator 376 (waveform U) resetting the address register 232 to zero and the machine stops at time Tl9.

Figure 1 4a illustrates a pair of concentric circles 400 and 402 stitched by the illustrative machine whereas Figure 1 4b illustrates attempted circles 400' and 402' stitched by a conventional sewing machine. The illustrative machine made X and Y movements around a circular path 404 and 0 movements to maintain the line L joining the needles 12 normal to a tangent to the path 404 at each point P1 so that the stitches S, are always on the circles 400 and 402. Figure 1 4b shows that the lack of 0 movement makes the sewing of such circles very poor.

Figures 1 spa to 1 sod illustrate further examples of stitching by the illustrative machine. Figure 1 5a shows different spacing between stitch rows 406 and 408 which are attained by 6 movements as the Z-Z axis moves along the line 410. Figure 15b shows stitches first in a single row and then separated by 0 movement. Figure 1 sic shows row spacing with periodic disengagement of a needle to permit the other needle to sew an independent pattern. Figure 1 5d shows 8 movement through 3600 to form a cross containing a half twist.

Claims (12)

Claims

1. A method of controlling the relative spacing of the operating paths of tools which are engageable with a workpiece which is movable in a plane, the method comprising mounting the tools on a tool carrier in laterally spaced relationship relative to an axis extending normally to the plane, and moving the workpiece along predetermined path in said plane, wherein as the workpiece is moved in said plane, the tool carrier is rotated about said axis independently of the movement of the workpiece so as to selectively position the successive operating localities of the tools on the workpiece relative to the predetermined path.

2. A method according to Claim 1 wherein the movement of the workpiece and the angular rotation of the tool carrier are carried out as a series of discrete movements and angular rotations carried out simultaneously.

3. A method according to either one of Claims 1 and 2 wherein the tool carrier is reciprocated towards and away from the workpiece to bring the tools into intermittent operative contact with the workpiece in timed relation with the movement of the workpiece and the rotation of the carrier.

4. A method according to any one of Claims 1, 2 and 3 wherein one of the tools is rendered inoperative during one or more intervals in the operation of the machine.

5. A method according to Claim 4 wherein the tools are sewing needles and movement of the workpiece takes place in intervals of nonengagement of the needles therewith, wherein, in order to sew a corner pattern comprising an outer corner and an inner corner on to the workpiece, a first of the needles is operated along an outer stitch path while a second of the needles is operated along an inner stitch path, when the second needle reaches the apex of the inner corner, the second needle is rendered inoperative, the movement continues with only the first needle operating until the first needle reaches the apex of the outer corner whereupon the second needle is rotated about the apex of the outer corner while the first needle is maintained at the apex of the outer corner, the needles are moved in a new direction of movement until the second needle again reaches the apex of the inner corner, an amount of thread substantially-equal to the amount of thread pulled out by the second needle since it was rendered inoperative is pulled back through the second needle, and the second needle is again rendered operative.

6. A sewing machine arranged to operate on a workpiece which is movable in a plane, the machine comprising a tool carrier reciprocable towards and away from the workpiece, moving means operable to move the workpiece in the plane, and control means operable to control the operation of the moving means to cause the workpiece to move along a predetermined path, wherein the tool carrier is arranged to carry at least two needles and is rotatable independently of the movement of the workpiece about an axis which is normal to said plane, and the machine comprises rotating means operable under the control of the control means to rotate the tool carrier about said axis in a predetermined manner.

7. A sewing machine according to Claim 6, wherein the tool carrier is arranged to carry two needles each offset from said axis by substantially the same distance.

8. A sewing machine according to either one of Claims 6 and 7 wherein the tool carrier comprises means for rendering either or both of the needles inoperative at predetermined localities on the workpiece.

9. A sewing machine according to Claim 8, wherein pull back means is provided for pulling back thread under the control of the control means from an inoperative needle.

10. A sewing machine according to Claim 9, wherein the pull back means comprises a reversible motor which is also arranged to induce slack at the needle to facilitate thread snipping thereat.

11. A sewing machine according to any one of Claims 6, 7, 8, 9, and 10 wherein the machine also comprises a hooking device for each needle and means for rotating the devices about the axis so that they remain aligned with the needles.

12. A sewing machine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.