AU592234B2 - Automatic needle thread supply control system - Google Patents

Description

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592234 S F Ref: 41004 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class t £4 t C* S Complete Specification Lodged: Accepted: Published: Priority: Related Art: liniT_ -'e pp, I

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Ii 11 Name and Address of Applicant: Brother Kogyo Kabushiki Kaisha 35, 9-chome, Horlt;-dori Mizuho-ku, Nagoya-shi Aichi-ken

JAPAN

Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Address for Service: 1.

t Complete Specification for the invention entitled: Automatic Needle Thread Supply Control System The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/4 <2 I TITLE OF THE INVENTION Automatic Needle Thread Supply Control System BACK GROUND OF THE INVENTION

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F C FFf F F The present invention relates to a sewing machine capable of automatic needle thread supply 'control, and more particularly, to improvement in the sam6 which \include a pair of thread clamp members that make a needle thread free to pass and clamped with predetermined timings between a thread supply source and a thread take-up lever in a path leading from the thread supply source to a needle, and a thread passage control means which controls so that at least one of releasing speed and clamping speed may be in proportion to a rotational speed of an arm shaft.

15 Generally, the take-up lever driven vertically in timed with rotation of the arm shaft performs supplying a needle thread toward a bobbin when the lever descends and also performs tightening a needle thread loop made at a needle eye and supplementing a predetermined amount of the needle thread from a thread supply spool when the lever ascends.

Within a thread supply path between the thread supply spool and a thread holding portion of the take-up lever, there is provided generally a thread controller that provides the needle thread with passage resistance to enable tightening of the needle thread loop. This needle thread -2 controller has a pair of thread cont-ol discs contacting each other under pressure of a compression spring and exerts a frictional resistance on a needle thread passing through between the pair of the thread control discs.

However, in the needle thread controllers of this kind, the needle thread is supplied under interaction of tension that acts on the needle thread following the thread controller and resistive force of thread controller, therefore it is difficult to exactly control the force of tightening the needle thread and supply quantity of the needle thread and it is also difficult to adjust the needle thread control of

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stitches in response to thicknesses and types of work fabrics (that is, thickness and type of the needle thread to be selected according to these factors) Therefore, as disclosed in Japanese Patent Publication (examined) No. 53-41580, an electrically actuated needle thread passage control device has been proposed which comprises, in place of the above mentioned spring actuated thread controller, a pair of the thread control discs that contact under pressure of a solenoid actuator, and which allows the needle thread to pass at a predetermined timing r during a given time period and does not allow to pass during a period except the above by driving the actuator in timed with the arm shaft rotation.

In the needle thread passage control device described 3 3 in the above publication, it can only control the thread passage in synchronism with the arm shaft rotation speed regardless of thicknesses and types of the work fabrics, that is, regardless of the thicknesses of 'the needle thread. Further, operation speeds when this control device release or regulates the thread passage are set independent of the armshaft rotation speed (sewing speed).

Therefore, this control device performs the same tightening of the needle thread and supplies the same quantity of the thread regardless of a thick or thin thread and can not tighten the thread so as to generate tension corresponding to the thread thickness. This results in unstable thread control.

0 00 Further, because a supply amount of the needle thread varies O a o delicately as the arm shaft rotation speed varies, the thread control aQ varies according to the sewing speed.

o 5 It is the object of the present invention to provide a sewing machine capable of automatic needle thread supply control.

In one broad form the Fresent invention provides an automatic needle 1 thread supply control system for use in a sewing machine having a needle act thread supply source, an endwise reciprocatory needle with an eye, a feed member operating in synchronism with the reciprocation of the needle for imparting a feed motion to a work fabric, a take-up member movable between a first position where the needle thread is slackened to a maximum thread a slack amount and a second position where the needle thread is taken up to a 4* maxlumum thread take-up amount, and a needle thread supply path extending from the needle thread supply source through the take-up member to the eye of the needle, said automatic needle thread supply control system comprising; thread securing means operative in synchronism with the reciprocation of said needle for securing said maximum thread take-up amount of the 6" needle thread during a specific period which starts at a time determined so as to at least pril:ly overlap with the period of said feed motion and terminates at a time when the eye of said needle Is lowered near the surface of a bed, thread supply stopping means operative to permit and check the supply of the needle thread which is drawn out from said needle thread supply ;e as said fabric is fed by said feed member, and

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r 4 control means operative in synchronism with the reciprocation of said needle for controlling the timing and the period of operation of said thread supply stopping means according to the thickness of said fabric being sewn or the thickness of the needle thread being used so that said thread supply stopping means permits the supply of the needle thread during said specific period.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic perspective view of a sewing machine incorporated an embodiment of the present invention; Figure 2 is a perspective view of the essential portion of the internal mechanism built in the head of the sewing machine of Fig. 1; o oo Figure 3 is a side elevation of the internal mechanism of Fig. 2; oo: o Figure 4 is a front elevation of the internal mechanism of Fig. 2; o 0 00 o 0 06 o 0 4 000 0 09 4 oa To S N/62b 1 /7 1 ii

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Figure 5 is a time chart showing the respective motions of the mechanisms of the sewing machine of Fig. 1; Figure 6 is a sectional view taken on line VI--VI in Fig. 4; s.

99O 9 9 99 o o a 9 00 0 99 99 99 9 £f 0 b F 9 9 #9 0*C OCe eI.

C CC Figure 7 is a sectional view taken on line VII-VII in Fig. 3; Figures 8 to 11 are schematic illustrations showing modifications of the thread clamping members shown in Fig.

7; 10 Figure 12 is block diagram showing the electrical constitution of a modification of the thread passage control unit of the embodiment; and Figure 13 is a time chart showing the variation of the gap of the thread path in relation to a timing singa' and a phase signal and the variation of the solenoid driving current in the modification shown in Fig. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

Fig. 1 illustrates an electronic lock stitch sewing machine M incorporating a embodiment of the present invention. Illustrated in Fig. 1 are bed 102, a standard 104 extending upright from the right end of the bed 0Q2, and an c., C e r C C C arm 106' horizontally extending from the upper end of the standard 104, overhanging the bed 102 and having a head 108 at the left end thereof. A needle bar 110 and a presser bar 118 are provided in the head 108. A needle 112 is attached to the lower end of the needle bar 110. The needle bar 110 is driven for vertical ripcarymotion and for lateral jogging motion by the arm shaft 128 of the sewing machine.

A presser foot 120 is attached to the lower end of the presser bar 118. The presser bar 118 is raised or lowered 10 by means of an operating member (not shown).

A throat plate 122 is provided on the bed 102, and a feed dog 123 is provided in the bed 102 so as to be moved upward through slots formed in the throat plate 122 by a feed mechanism. Predetermined stitches are formed in a work fabric through the cooperative operation of the needle bar 110 and the. feed mechanism including the feed dog 123.

Since the feed mechanism is of an ordinary know constitution, the description thereof will be omitted.

Fig. 2 to 4 illustrate internal mechanisms disposed, withini the head 108 and part of the arm 106 near the hear 108 of the sewing machine M.

As illustrated in Figs. 2 to 4, the needle 112 is at-, t~ached to the lower end of the needle bar 110, while -the neodle bar 110 is supported vertically movably by a needle bar support 124. Thc, needle bar support 124 is supported C C (1:7 4

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'-7 pivotally at the upper end thereof with a pin 126 on the frame so as to jog laterally. The needle bar 110 is driven by the arm shaft 128 and a needle bar crank 130 secured to the free end of the arm shaft 128 for vertical motion relative to the needle bar support 124.

The presser foot 120 is attached detachably to the lower end of the presser bar 118, while the presser bar 118 is secured to the frame by a mechanism (not shown) so as to be moved between an upper position and a lower position.

When the presser bar 118 is moved to the lower position, the presser foot 120 presses a work fabric against the throat plate 122.

A, take-up lever mechanism will be described hereinafter with reference to Figs. 2 to 4.

The arm'k shaft 128 is supported rotatably in a bearin bush 132 or the like on the frame. An auxiliary shaft 134 is disposed, W-ove and behind the arm shaft 128 so as to extend in parallel to the same. The auxiliary shaft 134 is journaled on the frame. A swing lever 136 is supported swingably at one end thereof on the auxiliary shaft 134.

The swing lever 136 extends from the auxiliary shaft 134 to the left side of a take-up lever crank 138 fixedly mounted on the arm shaft 128. The crank pin 140 of the take-up lever crank, 138 extend through, a slot cam 142 formed in, the swing lever 236. A connecting plate 144 is fixed to the left end of the crank pin 140. The needle bar crank 130 is connected rotatably to the connecting plate 144 with a pin 146 extending leftward from the connecting plate 144. The needle bar crank 130 is connected at the lower end thereof to the middle part of the needle bar 110.

The upper part of the swing lever 136 is bent in a zigzag shape to form a take-up lever 148 (take-up member) ce which extends upward. A thread guide hole 148a is formed at rIC r C S' the free end of the take-up lever 148.

As illustrated in Figs, and 3, the slot cam 142 of the swing lever 136 consists of a circular arc section 142a having a radius of curvature coinciding with the radius of the circular locus of the crank pin 140 and permitting the rotation of the crank pin 140 through an angle of approximately 740 in a range about the uppermost position of the crank pin 140, and short straight sections 142b extending from the opposite ends of the circular arc section 142a, respectively. The slot cam 142 is reinforced along the pilriphery thereQo with a reinforcement 136a.

When the take-up lever crank 138 and the crankpin 140 A4i 1 are turned around the arm shaft 128 with the crankpin 140 engaging the slot Cam 142 of the swing lever 136, the swing lever 136 is driven for reciprocatory swing motion about the auxiliary shaft 1,34 between an uppermost position indicated by continuous, lilnes (Fig. 3) and a lowermost position n indicated by imaginary lines (Fig. 3) by the crankpin 140, while the needle bar 110 is driven for vertical reciprocatory motion through the needle bar crank 130 and the crankpin 140 by the arm shaft 128 in phase with the arm shaft 128.

Since the slot cam 142 of the swing lever 136 has the Se6 circular arc section 142a, the take-up lever 148, the needle C' 112 attached to the lower end of the needleb ar 110 and the C' feed dog 123 of th feed mechanism perform motions representi 10 ed by motion curves MA, MB and MD as functions as the phase Sangle of the arm shaft 128 as a parameter in Fig. 5, respectively.

The take-up lever 148 is held at the uppermost position from a time after the arm shaft 128 has turned through an angle of approximately 400 from the start of the feed motion to a time when the eye of the needle 112 arrives at the upper surface of the throat plate 122. Accordingly, the take-up lever 148 is held at the upper most position substantially during the feed motion except the initial stage of the feed motion. The swing lever 136 may be designed so that the take-up lever 148 is held at the upper most position from the start of the feed motion. In either case, the swing lever 136 of the second embodiment is comparatively simple in construction and is able to operate smoothly and silently.

A thread supply control mechanism will be described hereinafter with reference to Figs. 2 to 7.

A plate member 150 forming part of the frame is disposed near and on the left hand side of the needle bar crank 130 disposed on the left hand sidr 4 I of the arm shaft 120.

The plate member 150 extends at right angles to the arm 0 00 a shaft 12R. As illustrated in Figs. 2 and 3, a pre-tension 0 0 4 00 0 device 152 for exerting a tension to the needle thread 114 is provided, when necessary, on the left side of the plate member 150 slightly before the arm shaft 128.

The pre-tension device 152 has a pair of tension discs 152a which, exert a tension to the needle thread passing therebetween. The tension of the needle threaI is adjusted by regulating spring for., applied to: the tension discs 152a I~ S y operating a dial. The pre-tension device 152 may be omitted, A thread, suipply control device 154 which clamps or releases the needle thread 114, in synchronism with the rotation of the armt shaft 128 is provided in a thread, path between a thread supply spool 116 and the thread guide hole 148a of the take-up. lever 14R, The t-hread supply control device 1,54 comprises, a thread guide plate 156, and a swing leverL 158 provided, with a thread clamping wheel 164, The thread guide: plate, 156 (thread clamping member) is secured to the: left side of the, plate- member 150 at a position below if

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the pre-tension device 152. The swing lever 158 is disposed Ad1jacent to the l~eft side of the thread guide plate 156 and is, pivotally attached to the plate member 150 with a hinge screw 1 A link plate 160 also is pivotally attached at the lower end thereof to the plate member 150 with the hinge screw 162. The thread clamping wheepl 164 (thread clamping member) held on the swing lever 158 engages the thread clamping, edge 156a of the -thread guide plate 156 to clamp the Aee4le thread~ 114 between the thread clamping edge 156a and the thread clamping wheel 164. The swing lever 158 is Jbiased resiliently by a spring 166 having one end connected to the frame and the other end connected to the Swing lever 158 so that the thread clampaIng wheel 164 ig pressed Ogaifit the thread 0lamping~ edge 156a, A contact wheel 168 aittached to the u~pper' Sri oP the, arm 158a of the awing lever 1-58 is In contact with the fronat aurfaoe oI a contaot 160a formwed teaf the: lower end of the link p14ate 100, As illustrated in~ Pigs. 2r 3 and 7, an annul1ar ,e groovor 164a is; formed -in the aii=&fddthci of the throgid a0oclamping wheel 164t While, the thtdad clam i edge 156a of the thread guide pl~te_ 1,5 is formwed in a Vbshaned. Ourve opehinq downward, i3'n a sidei View and in a U, ahdpe in rev6tion.

The- '(-haped groove -164a. of- the throod olmitpin1 16T4 and the U-shaped thtoad. glamping, edga ISO#, )j '--fr gtii-0, plate Onqggo W clamp the 4 41 ~p~v K k

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0 0 0 0 C. -<2 therebetwoen.

After passing the pre-tension device 152, the needle thread 114 is turned by the U-shape thread clamping edge 25~6a off the thread guide plate 156, and is guided via the thread guide hole 148a off the take-up lever 148 -to the needle 112, When the thread clamping edge 156a and the V"shaped groove 164a are engaged, the nee'dle thread 114 is clamped firmly between the thread clamgirig edge 156a and the V-shape groove 164a at two points. Parti cularly, since the thread clamping wheel 164 is moved in parallel to a plane including the thread supply path returned at the thread clamping edge 156a and the thread clamping wheel 164 clamps the needle thread 114 across the same, a Very high clamping pressui~o is applied the the needle thread 114. That is, if" the thread clamping wheel 1,64 is pressed with a small force ,against the thread clamping edge 156a the noedle thread 114 can firmly be clamped.

'To drive the thread clamping wheel 164 in phase with the rotation of the arm shaft 128 at a speed proportional to the rotating ripeed of the -arm shafft 128 toward and away from the thread clamping edge 156a to clamp and release the.

needle thread 114 alternately at predetermined phase angles of the &rm shaft 128, a rotary cam 170 (proportional control means) having an elliptic, cam groove 172 is fixedly mounted.

on the arm shaft 128 at a position opposite the right end of

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the auxiliary shaft 134, and a cam follower 174a attached to the free end of a first arm 174 engages the cam groove 172.

On, the other hand, a second arm 176 is fixedly mounted to the auxiliary shaft 134 at the left end cf the same. A pin 176a, attached to the free end of the second arm 176 is received in a slot 160b formed in the upper end of the link plate 160 to interconnect the second arm 176 and the link plate 160.

In the aboveinentioned thread supply control device 154, when the arm, shaft 128 is rotated to swing the first arm 174 by the eJliptic cam groove 172. of the rotary canm 170, the link plate 160 is reciprocated through the auxiliary shaft 134 and the second arm 176 on'crie hinge screw 162, When the contact wheel 168 is pushed forward by the contact lug 160a of the link plate 160 as the link plate 160 is driven. by the second arm 176, the swing lever 158 is turxed- against the resilient force of the sprinig 166, so that the, thread clamping wheel 164 is separated from the thread clamping edla 156a of the thread guide. plate 156 to release the needle thread 11.4. When the contact, lug 160a of the link plate 160 is moved backward, the swing~ lever 158 is turned in the opposite direction by the sjpring 166, sQ that the thread clamping wheel 164 engages that, thread clat:,oing edge 156a to clamp the needle thr~ead 114, Thus, the needle thread 114 is clamped and released alternately at 1 r r ir i 1 it i r ct. C ~r P C C;~

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r i'r O i it Ili(i predetermined phase angles, respectively. The needle thread clamping and releasing motion is represented by a motion curve MC in Fig. As is apparent from Fig. 5, during the upward movement of the take-up lever 148 from the lowermost position to the uppermost position for tightening the needle thread 114, the needle thread 114 is clamped between the thread guide plate 156 and the thread clamping wheel 164 so that the needle thread 114 is surely tightened. After the needle thread 114 1Q has completely been tightened, the swing lever 158 is driven in phase with the feed motion to release and supply the needle thread 114. While the needle thread 114 is thus released free, the feed motion and the needle jogging motion are accomplished, ard then the needle thread 114 is clamped ]5 again before the aeedle 112 arrives at the throat plate 122.

While the needle thread 114 is clamped, the stitching motion is carried out to form a needle thread loop by the shuttle.

Accordingly, the needle thread of an amount necessary for feeding the work fabric and for jogging the needle 112 is 20 surely supplied, while the needle thread 114 is not supplied uselessly while a loop of the needle thread 114 is formed, because the needle thread 114 is clamped during the loop forming period.

As is apparent from the motion curve MC shown in Fig.

5, owing to the needle thread clamping characteristics $1

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i r -e~L 7 1 determined by the shape of the elliptic cam groove 172 of the rotary cam 170, when the thickness of the needle thread 114 is small, the needle thread 114 is released and is clamped at a point F 1 and at a point C 1 respectively. When the thickness of the needle thread 114 is large, the needle thread 114 is released at a pint F 2 after the point F 1 and I'e: is clamped at the pint C 2 before the point C 1 Accordingly, thin needle threads and thick needle threads are tightened w" properly at a low tension and at a high tension, respective- I 10 ly.

tot S' Since the cam groove 172 of the rotary cam 170 serving as the proportional control means has an elliptic can sur- S face, the respective speed of the upward swing and downward swing of the first arm 174 are proportional to the rotating ,o 15 speed of the arm shaft 128, so that the needle thread clampl ing wheel 164 is moved toward and away from the thread ite clamping edge 156a at a speed proportional to the rotating S speed of the arm shaft 128, Thus, a substantially fixed amount of the needle thread 114 is supplied in every stitching cycle regardless of the rotating speed of the arm shaft 128, and hence the tension of the needle thread in forming stitches is not affected by the stitching speed.

A needle thread supply mechanism 178 which draws out the needle thread 114 from the thread supply spool 116 by a predetermined amount and stores the same while the take-up taip. T. 17 I', e 4 lever 148 is moved downward and the needle thread 114 is clamped between the needle thread clamping wheel 164 and the needle thread guide plate 156 will be described hereinafter with reference to Figs. 2 to 4.

A sleeve 180 is fitted rotatably on the auxiliary shaft 134 near a position where the auxiliary shaft 134 supports the swing lever 136 at one end, and the end of the swing lever 136 on the auxiliary shaft 134 is fixed to the sleeve 180. An L-shaped arm 182 having a thread catching hook 182a at the free end thereof is fixed to the sleeve 180. A thread guide member 184 substantially of a U-shape in front view is disposed on top of the left end of the arm 106 of the sewing machine M. The thread guide member 184 has a top wall 1,84a, a first guide wall 1840" and a second guide wall 15 184c. The first guide wall 184b and a second guide wall 184c extend vertically downward from the opposite sides of the top guide wall 184a, respectively. The second guide wall 184c of the thread guide member 184 is fixed to the upper end of the plate member 150 with a screw 186. The thread guide member 184 is disposed near and above the Lshape arm 182. The first guide wall 184b and the second guide wall 184c are disposed opposite to each other with a predetermined distance therebetween. A first guide slit 188a and a second guide slit 188b are formed laterally opposite to each other in the first guide wall 184b and the I

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second guide wall 184c, respectively. The respective rear ends of the first guide slit 188a and the second guide slit 188b are open to receive the needle thread 114 therein. A third guide slit 190 is formed in the upper part of the front end of the second guide wall 184c.

The needle thread 114 pulled out from the thread supply T' C spool 116 is extended sequentially through the first guide V slit 188a, the second guide slit 188b, along the left side Sc of the second guide wall 184c, via the third guide slit 190, 0 c I 10 the pre-tension device 152, the thread clamping edge 156a of the thread guide plate 156, where the needle thread 114 is returned upward, and then further through the thread guide Shole 148a of the take-up lever 148, and thread guides 192 and 194 to the eye of the needle 112.

Both the L-shape arm 182 and the swing lever 136 are fixed to the sleeve 180, and hence the L-shaped arm 182 and the swing lever 136 are driven for swing motion by the take- S\ up lever crank 138 in phase with the rotation of the arm shaft 128. As illustrated in Fig. 3, while the take-up lever 148 ,s held at the uppermost position as indicated by continuous lines, the L-shaped arm 182 is located, as indicated by dotted lines, behind the needle thread 114 passing the respectively front ends of the first guide slit 188a and the second guide slit 188b. On the other hard, when the take-up lever 148 is moved downward the lowermost :^i f e I~ g C C t t 4 t~ position as indicated by imaginary lines, the swing lever 136 swings on the auxiliary shaft 134 and the L-shape arm 182 swings forward as indicated by imaginary lines on the auxiliary shaft 134, so that the thread catching hook 182a is moved forward and engages the needle thrbad 114 extending between the respective front ends of the first guide slit 188a and the second guide slit 188b, and thereby the needle thread 114 is pulled by the thread catching hook 182a by a predetermined distance. Since the needle thread 114 is 10 clamped between the thread clamping wheel 1(64 and the threadI guide plate 156 while the needle thread 114 is pulled by the thread catching hook 182a, a predetermined amount of the needle thread is surely pulled out from the thread supply spool 116.

Thus, while the take-up lever 148 is located. at the lowermost position, the needle thread 114 is pulled out from the thread supply spool 116 by the, L-shaped arm 18,2 of the needle thread supply mechanism 178, so that the needle thread 114 between. the thread supply spool 116 and the thread clamping edge of the, thread guide plate 156 is slackened. After the. needle thread 114 has thus been slackened, the take-up lever 148 is moved upward to tighten the needle thread 114, then the needle thread 114 is released from the restrain of the thread guide p~lat 156 and the thread clamping wheel 164, t4nd then the needle thread 114 of a necessary

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amount is supplied via the take-up lever 148 to the needle 112 as the feed dog 123 performs the feed motion and the needle 112 is jogged.

Although the feed motion of the feed dog 123 is started before the needle thread 114 is released, the amount of the needle thread 114 required for such a mode of feed motion is supplemented by the elastic extension of the needle thread 114, and the needle thread 114 is recovered from the elastic I extension as the same is supplied after being released.

Thus, the phases of the needle thread clamping and releasing operations are controlled automatically according to the thickness of the needle thread 114, and the needle thread 114 of a necessary amount dependent on the feed stroke and the needle jogging stroke is surely supplied for every stitching cycle. Accordingly, an optimum tension according to the thickness of the needle thread 114 is exerted to the needle thread 114.

In the thread supply control device 154, a U-shaped groove 164b may be formed in the circumference of the thread clamping. wheel 164, as illustrated in Fig. 8, the thread M clamping wheel 164 may be moved obliquely relative to the thread guide plate 156 as illustrated in Fig. 9, or the needle clamping wheel 164 may have a cylindrical circumference as illustrated in Fig. 10. Furthermore, although not shown, a member secured to the swing lever 158 may be mL] Z C: ~r.

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employed instead of -the thread clamping wheel 164. still further, it is also possible to employ a grooved free wheel 156A instead of the thread clamping edge 156a. When the free wheel, 156A is employed., the nee( le thread 114 is wound around the half of the circumference of the free wheel 156A, and a clamping member 164A substituting the thread clamping wheel 164 is brought into point-contact with the circumnference of the free wheel 156A to clamp the needle thread as illustrated in Fig. 11.

A modification, of the thread supply control device will be described hereinafter with reference to Fig. 12 and Fig.

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The thread supply control device 154A comprises the thread clamping wheel 164, a linear actuator 200 for driving 15 the. thread clamping wheel 164, a displacement sensor 201 for sensinq the displacement of the thread clamping wheel 164, a phase angle sensor 202 for sensing the. phase angle of the arm shaft 128, at timing sensor 203, and a control unit 204.

The linear actuator 200 comprises a moving coil 205 connected to the thread clamping wheel 164, a metallic frame 206 vertically movably retaining the moving coil 205 and forming a magnetilc path, and a psprmanent magnet 207 forming a uniform magnetic field around the moving coil 205. The vertical position of the moving coiLl is determined according 2to the intensity of current supplied to the Moving coil 205.

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i I r r ~ur~ zl -'29 The displacement sensor 201 is a potentiometer comprising a contact 209 connected to the thread clamping wheel supporting member 208 of the moving coil 205, and electric resistor 210 connected to a reference voltage line.

The phase angle sensor 202 comprises, for example, a disc having a plurality of slits formed along the circumference thereof at regular angular intervals and fixed to the arm shaft 128, and a photoelectric detector comprising a light emitting element and a light receiving element for detecting the slits.

The timing sensor 203 is a limit switch or a contactless switch which detects the arrival of the needle bar 110 at the upper most position.

The control unit 204 comprises a central processing unit (hereinafter abbreviated to "CPU") 211, a read-only nemory (ROM) 212, a random access memory (RAM) 213, an input-output interface 214, a driving circuit 215 which receives control signals through the input-output interface 214 from the CPU 211 and supplies a driving current corre- 20 spending to the input signal to the moving coil 205, and AD converter 216 which converts an analog detection signal of the displacement sensor 201 into a digital signal corresponding to the analog detection signal and gives the same to the input-output interface 214. The detection signals of the phase angle sensor' 202 and the timing sensor 203 are sa t %4 -i i: C C~' C: C Ir

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given through the input-output interface 214 to the CPU 211.

The input-output interface 214, the ROM 212 and the RAM 213 are connected through an address bus and a data bus to the CPU 211.

The ROM 212 pre-stores a control program for controlling the linear actuator 200 in accordance with a timing signal S 1 given by the timing se;isor 203, a phase angle signal S 2 given by the phase angle sensor 202 and displacement signal given by the displacement sensor 201 to regulate 10 the gap between the. thread clamping wheel 164 and the thread clamping edge 156a of the thread guide plate 156.

Since the mode of controlling the linear actuator 200 is comparatively simple, the same will be described characteristically hereinafteri 15 Referring to Fig. 13, a predetermined current is supplied to the moving coil. 205 until, a predetermined number of phase angle Isignals S2 are, given to the CPU 211 after a timing signal S i has been given to the CPU 211t and thereby the thread clamping wheel 164 is. hel~d in contact with the thread clamping edge 156a to clamp the h(iedle thread 114, therebetween, Upon the reception of the predetermined number of phase angle signals S 2 f the CPU 211 controls the driving circuit 215 so as to reduce the driving current at a rate corresponding to the rotating speed of the arm shaft 128 as p represented by a curve IP; consequently, the moving coil 205 is lowered gradually to increase the gap between the thread clamping wheel 164 and the thread clamping edge 156a as represented by a curve CP.

The rotating speed of the arm shaft 128 is determined through computation on the basis of the phase angle signals S Various CP curves for various rotating speeds are 2' SC 0 stored as a memory map in the ROM 212. The magnitude of the driving current is controlled memo ttyW through feedback 1Q control on the basis of the displacement signals given by the displacement sensor 201 in a mode as represented by the curve IP.

To the manner of control in Lhe foregoing embodiments, the ourves CP corresponding to the rotating speed of the arm shaft 128 are stored in the memory map of the ROM 212 to regulate the rate of increasing the gap between the thread clamping wheel 164 and the thread glamping edge 156a in proportion to the rotating speed of the arm shaft 128.

The magnitude of the driving current is controlle in the same manner to decrease the gap between the thread clamping wheel 164 and the thread clamping edge 156a in clamping the needle thread 114. The timing of driving the moving coil 205 is determined by colnting the phne angle signals S 2 and then the magnitude of the driving current 3' tc ~G C It

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supplied to the moving coil 205 is regulated through feedback control on the basis of the displacement signals according to a curve IQ so that the gap is decreased along a curve CQ stored in the memory map of the ROM 212.

Similarly to the curve MC for the second embodiment, a thin needle thread is released at a point EF 1 and is clamped at a point EC, while a thick needle thread is released at a point EF 2 and is clamped at a point EF 2 as shown in Fig. 13.

The linear actuator 200 employed in this embodiment may 10 be substituted by a stepping motor or the like.

Claims (9)

1. 2.1 An automatic needle thread supply control system according to claim 1, wherein said thread securing means includes a swing lever swingably supported on a machine frame and connected to said take-up member, and said swing lever has a slot cam engageable with a crankpin eccentrically connected to a main shaft of said sewing machine and consisting of a circular arc section having a radius of curvature coinciding with the radius of the circular locus of said crankpin and short straight sections extending from the opposite ends of said circular arc section.
2. 3. An automatic needle thread supply control system according to claim 1 wherein said thread securing means comprises means for timing the start of holding said take-up imber at said su-,ond position so that the period for holding said take-up member at said second position at least partly overlaps with the period of said feed motion, holding said take-up member at said seond position until the eye of the said needle is lowered near to the s--4eqof a bed, and moving said take-up member in synchronism with the reciprocation of said needle after the eye of said needle has been lowered near to the surface of said bed.
3. 4. An automatic needle thread supply control system according to claim 3, wherein thread securing means includes cam means for holding said take-up member at said second position.
4. 5. An automatic needle thread supply control system according to claim 3, wherein said thread supply stopping means comprises a pair of thread clamping members having clamping surfaces which engage in point contact to surely clamp the needle thread.
5. 6. An aut,)nmatic needle thread supply conrol system according to claim 3, wherein iaid thread supply stopping means comprises a pair of thread clamping n,:imbers and said control means comrises proportional control means fot controlling the speed of at least either a, motion for engaging or a motion for disengaging said thread clamping members In proportion to a sewing speed. cYl/1562b 27
6. 7. An automatic needle thread supply control system according to claim 6, wherein said proportional control means includes a cam member operatively connected to a main shaft of said sewing machine.
7. 8. An automatic needle thread supply control system according to claim 6, wherein said proportional control means includes a rotary member operatively connected to a main shaft of said sewing machine, a detector for generating aXphl signal every predetermined angle of rotation of said rotary member, and actuating means for varying the relative position of said thread clamping members in response to said pulse signal at least either In engaging or in disengaging said thread clamping members.
8. 9. An automatic needle thread supply control system for use in a sewing machine which system is substantially as hereinbefore described with reference to Figs. 1 to 8, Figs. 1 to 7 and 9, Figs. 1 to 7 and 10 or Figs. 1 to 7 and 11. An automatic needle thread supply control system for use in a sewing machine which system is substantially as herein described.
9. 11. An automatic needle thread supply control system for use in a sewing machine which system is substantially as herein described with S reference to Figs. 12 and 13, DATED this NINETEENTH day of SEPTEMBER 1989 Brother Kogyo Kabushlkl Kaisha .r :Patent Attorneys for the Applicant SPRUSON FERGUSON A- -tL i 562b