[0001] The present invention relates to a sewing machine capable of automatic needle thread
supply control, and more particularly, to improvement in the same which includes 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.
[0002] 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.
[0003] 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 controller has a pair of thread control 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.
[0004] 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 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).
[0005] 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 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.
[0006] In the needle thread passage control device described 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 thicknesses
of the needle thread. Further, operation speeds when this control device releases
or regulates the thread passage are set independent of the arm shaft rotation speed
(sewing speed).
[0007] 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 a thin thread
and can not tighten the thread so as to generate tension corresponding to the thread
thickness. This results in unstable thread control.
[0008] Further, because a supply amount of the needle thread varies delicately as the arm
shaft rotation speed varies, the thread control varies according to the sewing speed.
SUMMARY OF THE INVENTION
[0009] It is therefore an object of the present invention to provide an automatic needle
thread supply control system capable of accurately controlling the supply of the needle
thread so that the point of interlock of the needle thread and the bobbin thread is
always located within the fabric being sewn irrespective of the variation of the thickness
of the fabric being sewn.
[0010] It is another object of the present invention to provide an automatic needle thread
supply control system capable of controlling the needle thread tension at an optimum
level according to the thickness of the fabric being sewn.
[0011] It is a further object of the present invention to provide an automatic needle thread
supply control system capable of releasing and clamping the needle thread silently
and surely.
[0012] The foregoing objects are attained according to the principle of the present invention.
The present invention is an invention in combination with a sewing machine having
a needle 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 slack amount and a second
position where the needle thread is taken up to a maximum 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, by providing an automatic needle thread
supply control system comprising: thread securing means operative in synchronism with
the reciprocation of the needle for securing the maximum thread take-up amount of
the needle thread during a specific period which starts at a time determined so as
to at least partly overlap with the period of the feed motion and terminates at a
time when the eye of the needle is lowered near to 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 the needle thread supply source as the fabric is fed by the feed
member; and control means operative in synchronism with the reciprocation of the needle
for controlling the timing and the period of operation of the thread supply stopping
means according to the thickness of the fabric being sewn or the thickness of the
needle thread being used so that the thread supply stopping means permits the supply
of the needle thread during the specific period.
[0013] The present invention also is an invention in combination with a sewing machine having
the same constitution as that of abovementioned aspect of the invention, by providing
an automatic needle thread supply control system comprising: driving means for timing
the start of holding the take-up member at the second position so that the period
of holding the take-up member at the second position at least partly overlaps with
the period of the feed motion, holding the take-up member at the second position until
the eye of the needle is lowered near to the surface of a bed, and moving the take-up
member in sychronism with the reciprocation of the needle after the eye of the needle
has been lowered near to the surface of the bed; thread supply stopping means operative
to permit and check the supply of the needle thread which is drawn out from the needle
thread supply source as the fabric is fed by the feed member; and control means operative
in synchronism with the reciprocation of the needle for controlling the timing and
the period of operation of the thread supply stopping means according to the thickness
of the fabric being sewn or the thickness of the needle thread being used so that
the thread supply stopping means permits the supply of the needle thread while the
take-up member is held at the second position.
[0014] According to the present invention, the control means determines the timing of actuation
and the period of operation of the thread supply stopping means according to the
thickness of the fabric or the thickness of the needle thread every vertical movement
of the needle and, while being actuated, the thread supply stopping means permits
the free supply of the needle thread from the thread supply source to the take-up
member. During the free supply of the needle thread, the take-up member is held at
the maximum thread take-up position (second position), and thereby the fixed length
of the thread stored by the loop taker is secured without being used for forming a
stitch. Consequently, an optimum length of the needle thread spontaneously determined
according various stitching conditions, such as the type of fabric and stitch length,
is supplied from the thread supply source. After the period of actuation of the thread
supply stopping means has elapsed the take-up member starts its motion in phase with
the vertical reciprocatory motion of the needle upon the arrival of the eye of the
needle at a position near the surface of the bed. As the take-up member moves toward
the maximum thread slackening position (first position), the needle thread is supplied
to the loop taker, and then the needle thread and the bobbin threads are interlocked
through the known motion of the loop taker. The point of interlock of the needle thread
and the bobbin thread is completed at a moment when the take-up member arrives at
the maximum thread take-up position after the needle thread and the bobbin thread
has been interlocked.
[0015] Preferably, the 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.
[0016] Preferably, the control means comprises proportional control means operatively connected
to the main shaft of the sewing machine to control the speed of at least either a
motion for engaging or a motion for disengaging the thread clamping member of the
thread supply stopping means in proportion to the rotating speed of the main shaft
of the sewing machine.
[0017] If need be, the proportional control means may comprise a rotary member operatively
connected to the main shaft of the sewing machine, a detector for generating a pulse
signal every predetermined angle of rotation of the rotary member, and actuating means
for varying the relative position of the thread clamping members in response to the
pulse signal at least either in engaging or in disengaging the thread clamping members.
[0018] The proportional control means engages and disengages the thread clamping members
through a smooth and continuous motion at a speed proportional to the rotating speed
of the main shaft of the sewing machine. Accordingly, the phase of clamping the needle
thread and the phase of the releasing the needle thread vary according to the thickness
of the needle thread. That is, a thick needle thread, as compared with a thin needle
thread, is clamped at an earlier phase and is released at a later phase, and hence
a thick needle thread of a less length is supplied for forming a stitch, so that a
higher tension is exerted on the loop to tighten the loop, where as a thin needle
thread of a more length is supplied and a lower tension is exerted to the thin needle
thread for tightening the loop. Thus, the tension of the needle thread is controlled
stably according to the thickness of the needle thread and the rotating speed of
the main shaft of the sewing machine.
[0019] The present invention is also an invention in combination with a sewing machine
having a needle thread supply source, an endwise reciprocatory needle with an eye,
a take-up member movable between a maximum thread slack position and a maximum thread
take-up position, and a needle thread supply path extending from the needle thread
supply source through the take-up member to the eye of the needle, by providing an
automatic needle thread supply control system comprising: a pair of thread clamping
members movable toward and away from each other for checking and permitting the supply
of the needle thread from the needle thread supply source toward the take-up; and
proportional control means for controlling the speed of at least either a motion for
engaging or a motion for disengaging the thread clamping members in proportion to
a sewing speed; whereby the timing and the period of checking and permitting the supply
of the needle thread are automatically changed according to the thickness of the needle
thread being used.
[0020] If need be, the proportional control means may comprise a cam member operatively
connected to the main shaft of the sewing machine and a cam follower engageable with
the cam member and operatively connected to one of the thread clamping members.
[0021] The present invention is also an invention in combination with a sewing machine having
a needle thread supply source, an endwise reciprocatory needle with an eye, and a
needle thread supply path extending from the needle thread supply source and to the
eye of the needle and including at least one bent portion, by providing an automatic
needle thread supply control system comprising: a pair of thread contacting members
located at the bent portion of the needle thread supply path and movable toward and
away from each other in a specific direction which is substantially parallel to a
plane including the needle thread supply path about the bent portion; and control
means for controlling the movement of the thread contacting members to vary an amount
of the needle thread to be supplied toward the eye of the needle.
[0022] The drawings are provided by way of example;in 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;
Figure 3 is a side elevation of the internal mechanism of Fig. 2;
Figure 4 is a front elevation of the internal mechanism of Fig. 2;
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;
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;
Figure 12 is a 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 singal and a phase signal and the variation of the solenoid driving current
in the modification shown in Fig. 12.
[0023] Preferred embodiments of the present invention will be described hereinafter with
reference to the accompanying drawings.
[0024] 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 102, and an 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 reciprocatory motion 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 by means of an
operating member (not shown).
[0025] 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.
[0026] Fig. 2 to 4 illustrate internal mechanisms disposed within the head 108 and part
of the arm 106 near the hear 108 of the sewing machine M.
[0027] As illustrated in Figs. 2 to 4, the needle 112 is attached to the lower end of the
needle bar 110, while the needle bar 110 is supported vertically movably by a needle
bar support 124. The needle bar support 124 is supported 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.
[0028] 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.
[0029] A take-up lever mechanism will be described hereinafter with reference to Figs.
2 to 4.
[0030] The arm shaft 128 is supported rotatably in a bearing bush 132 or the like on the
frame. An auxiliary shaft 134 is disposed above and beyond 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
136. 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.
[0031] The upper part of the swing lever 136 is bent in a zigzag shape to form a take-up
lever 148 (take-up member) which extends upward. A thread guide hole 148a is formed
at the free end of the take-up lever 148.
[0032] As illustrated in Figs. 2 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 74° 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 periphery thereof with a reinforcement 136a.
[0033] When the take-up lever crank 138 and the crankpin 140 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 134 between
an uppermost position indicated by continuous lines (Fig. 3) and a lowermost position
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.
[0034] Since the slot cam 142 of the swing lever 136 has the circular arc section 142a,
the take-up lever 148, the needle 112 attached to the lower end of the needleb ar
110 and the feed dog 123 of th feed mechanism perform motions represented by motion
curves MA, MB and MD as functions as the phase angle of the arm shaft 128 as a parameter
in Fig. 5, respectively.
[0035] 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 40° 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.
[0036] A thread supply control mechanism will be described hereinafter with reference to
Figs. 2 to 7.
[0037] 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 side of the arm shaft 120.
The plate member 150 extends at right angles to the arm shaft 128. As illustrated
in Figs. 2 and 3, a pre-tension 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.
[0038] 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 thread is adjusted
by regulating spring force applied to the tension discs 152a by operating a dial.
The pre-tension device 152 may be omitted.
[0039] A thread supply control device 154 which clamps or releases the needle thread 114
in synchronism with the rotation of the arm 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
148. The thread supply control device 154 comprises a thread guide plate 156, and
a swing lever 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 the pre-tension device 152. The swing lever 158 is disposed adjacent
to the left side of the thread guide plate 156 and is pivotally attached to the plate
member 150 with a hinge screw 162. 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 wheel 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 needle thread
114 between the thread clamping edge 156a and the thread clamping wheel 164. The swing
lever 158 is biased 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 clamping wheel
164 is pressed against the thread clamping edge 156a. A contact wheel 168 attached
to the upper end of the arm 158a of the swing lever 158 is in contact with the front
surface of a contact lug 160a formed near the lower end of the link plate 160.
[0040] As illustrated in Figs. 2, 3 and 7, an annular V-shaped groove 164a is formed in
the circumference of the thread clamping wheel 164, while the thread clamping edge
156a of the thread guide plate 156 is formed in a U-shaped curve opening downward
in a side view and in a U-shape in section. The V-shaped groove 164a of the thread
clamping wheel 164 and the U-shaped thread clamping edge 156a of the thread guide
plate engage to clamp the needle thread 114 therebetween.
[0041] After passing the pre-tension device 152, the needle thread 114 is turned by the
U-shape thread clamping edge 156a of the thread guide plate 156, and is guided via
the thread guide hole 148a of the take-up lever 148 to the needle 112. When the thread
clamping edge 156a and the V-shaped groove 164a are engaged, the needle thread 114
is clamped firmly between the thread clamping edge 156a and the V-shape groove 164a
at two points. Particularly, 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 pressure is applied the the needle thread 114. That is, if the
thread clamping wheel 164 is pressed with a small force against the thread clamping
edge 156a, the needle thread 114 can firmly be clamped.
[0042] To drive the thread clamping wheel 164 in phase with the rotation of the arm shaft
128 at a speed proportional to the rotating speed of the arm shaft 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 arm shaft 128, a rotary arm 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 the auxiliary shaft 134, and a cam follower
174a attached to the free end of a first arm 174 engages the cam groove 172.
[0043] On the other hand, a second arm 176 is fixedly mounted to the auxiliary shaft 134
at the left end of 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.
[0044] In the abovementioned thread supply control device 154, when the arm shaft 128 is
rotated to swing the first arm 174 by the elliptic cam groove 172 of the rotary cam
170, the link plate 160 is reciprocated through the auxiliary shaft 134 and the second
arm 176 on the hinge screw 162.
[0045] 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 turned against the resilient force of the spring 166, so that the thread clamping
wheel 164 is separated from the thread clamping edge 156a of the thread guide plate
156 to release the needle thread 114. 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 spring 166, so that the thread clamping wheel 164 engages that thread clamping
edge 156a to clamp the needle thread 114. Thus, the needle thread 114 is clamped and
released alternately at predetermined phase angles, respectively. The needle thread
clamping and releasing motion is represented by a motion curve MC in Fig. 5.
[0046] 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 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,
and then the needle thread 114 is clamped again before the needle 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 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.
[0047] As is apparent from the motion curve MC shown in Fig. 5, owing to the needle thread
clamping characteristics 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 F₁ and at a point C₁, respectively.
When the thickness of the needle thread 114 is large, the needle thread 114 is released
at a pint F₂ after the point F₁, and is clamped at the pint C₂ before the point C₁.
Accordingly, thin needle threads and thick needle threads are tightened properly at
a low tension and at a high tension, respectively.
[0048] Since the cam groove 172 of the rotary cam 170 serving as the proportional control
means has an elliptic can surface, the respective speed of the upward swing and downward
swing of the first arm 174 are proportional to the rotating speed of the arm shaft
128, so that the needle thread clamping wheel 164 is moved toward and away from the
thread clamping edge 156a at a speed proportional to the rotating 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.
[0049] 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
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
herinafter with reference to Figs. 2 to 4.
[0050] 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 184a, a first guide wall 184b and a second guide wall
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 L-shape
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 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.
[0051] The needle thread 114 pulled out from the thread supply spool 116 is extended sequentially
through the first guide slit 188a, the second guide slit 188b, along the left side
of the second guide wall 184c, via the third guide slit 190, 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 hole 148a
of the take-up lever 148, and thread guides 192 and 194 to the eye of the needle 112.
[0052] 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-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 is 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 hand, when the take-up lever
148 is moved downward the lowermost 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 thread 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 clamped between the thread
clamping wheel 164 and the thread 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.
[0053] 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 182
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, when the needle thread 114 is
released from the restrain of the thread guide 156 and the thread clamping wheel
164, and then the needle thread 114 of a necessary 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.
[0054] 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 extension as the same is supplied
after being released.
[0055] 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.
[0056] 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 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 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 needle
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 circumference of the free wheel 156A to clamp the needle thread
as illustrated in Fig. 11.
[0057] A modification of the thread supply control device will be described hereinafter
with reference to Fig. 12 and Fig. 13.
[0058] The thread supply control device 154A comprises the thread clamping wheel 164, a
linear actuator 200 for driving the thread clamping wheel 164, a displacement sensor
201 for sensing 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.
[0059] 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 magnetic path, and a permanent magnet 207 forming a uniform magnetic field
around the moving coil 205. The vertical position of the moving coil is determined
according to the intensity of current supplied to the moving coil 205.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] The control unit 204 comprises a central processing unit (hereinafter abbreviated
to "CPU") 211, a read-only memory (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 supplied a driving current corresponding
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 given the same to the input-output interface 214.
The detection signals of the phase angle sensor 202 and the timing sensor 203 are
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.
[0064] The ROM 212 pre-stores a control program for controlling the linear actuator 200
in accordance with a timing signal S₁ given by the timing sensor 203, a phase angle
signal S₂ given by the phase angle sensor 202 and displacement signal given by the
displacement sensor 201 ro regulate the gap between the thread clamping wheel 164
and the thread clamping edge 156a of the thread guide plate 156.
[0065] Since the mode of controlling the linear actuator 200 is comparatively simple, the
same will be described characteristically hereinafter.
[0066] Referring to Fig. 11, a predetermined current is supplied to the moving coil 205
until a predetermined number of phase angle signals S₂ are given to the CPU 211 after
a timing signal S₁ has been given to the CPU 211, and thereby the thread clamping
wheel 164 is held in contact with the thread clamping edge 156a to clamp the needle
thread 114 therebetween.
[0067] Upon the reception of the predetermined number of phase angle signals S₂, 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 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.
[0068] The rotating speed of the arm shaft 128 is determined through computation on the
basis of the phase angle signals S₂. Various CP curves for various rotating speeds
are stored as a memory map in the ROM 212. The magnitude of the driving current is
controlled memontly through feedback control on the basis of the displacement signals
given by the displacement sensor 201 in a mode as represented by the curve IP.
[0069] Similarly to the manner of control in the foregoing embodiments, the curves 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 clamping edge 156a in proportion to the rotating speed of the arm
shaft 128.
[0070] The magnitude of the driving current is controlled in the same manner to decrease
the gao 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 counting the phase angle signals S₂, and then the magnitude of the driving current
supplied to the moving coil 205 is regulated through feed-back 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.
[0071] Similarly to the curve MC for the second embodiment, a thin needle thread is released
at a point EF₁ and is clamped at a point EC₁, while a thick needle thread is released
at a point EF₂ and is clamped at a point EF₂ as shown in Fig. 13.
[0072] The linear actuator 200 employed in this embodiment may be substituted by a stepping
motor or the like.
1. An automatic needle thread supply control system for use in a sewing machine having
a needle 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 slack amount and a second
position where the needle thread is taken up to a maximum 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 needle thread during a specific
period which starts at a time determined so as to at least partly overlap with the
period of said feed motion and terminates at a time when the eye of said needle is
lowered near to 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 source as said fabric is
fed by said feed member, and
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.
2. 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.
3. An automatic needle thread supply control system for use in a sewing machine having
a needle thread supply source, an endless 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 takeup member movable between a first position where
the needle thread is slackened to a maximum thread slack amount and a second position
where the needle thread is taken up to a maximum 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;
driving means for timing the start of holding said take-up member at said second position
so that the period of 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 second position until the eye of siad needle is lowered near to the surface of
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,
thread supply stopping means operative to permit and check the supply of the needle
thread which is drawn out from said needle thread supply source as said fabric is
fed by said feed member, and
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 while said take-up member is held at said second position.
4. An automatic needle thread supply control system according to claim 3, wherein
said driving means includes cam means for holding said take-up member at said second
position.
5. An automatic needle thread supply control system according to claim 3 or 4 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.
6. An automatic needle thread supply control system according to claim 3, 4 or 5 wherein
said thread supply stopping means comprises a pair of thread clamping members and
said control means comprises proportional control means for 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.
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.
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 a pulse 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.
9. An automatic needle thread supply control system for use in a sewing machine having
a needle thread supply source, an endwise reciprocatory needle with an eye, a take-up
member movable between a maximum thread slack position and a maximum thread take-up
position, 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;
a pair of thread clamping members movable toward and away from each other for checking
and permitting the supply of the needle thread from said needle thread supply source
toward said take-up member, and
proportional control means for 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,
whereby the timing and the period of checking and permitting the supply of the needle
thread are automatically changed according to the thickness of the needle thread being
used.
10. An automatic needle thread supply control system according to claim 9, wherein
said proportional control means comprises a cam member operatively connected to a
main shaft of said sewing machine and a cam follower engageable with said cam member
and operatively connected to one of said thread clamping members.
11. An automatic needle thread supply control system according to claim 10, wherein
said cam member is an elliptic cam for controlling the speed of both a motion for
engaging and a motion for disengaging said thread clamping members.
12. An automatic needle thread supply control system according to claim 9,10 or 11
further including a needle thread supply mechanism located between said needle thread
supply source and said thread clamping members and operative in synchronism with the
reciprocation of said needle for drawing out the needle thread from said needle thread
supply source by a predetermined amount while said thread clamping members are engaged
to clamp the needle thread.
13. An automatic needle thread supply control system according to claim 12, wherein
said needle thread supply mechanism includes a pair of thread guides and a thread
catching hook operatively connected to said take-up member for catching the needle
thread between said thread guides.
14. An automatic needle thread supply control system for use in a sewing machine having
a needle thread supply source, an endwise reciprocatory needle with an eye, and a
needle thread supply path extending from the needle thread supply source and to the
eye of the needle and including at least one bent portion, said automatic needle thread
supply control system comprising;
a pair of thread contacting members located at said bent portion of said needle thread
supply path and movable toward and away from each other in a specific direction which
is substantially parallel to a plane including said needle thread supply path about
said bent portion, and
control means for controlling the movement of said thread contacting members to vary
an amount of the needle thread to be supplied toward the eye of said needle.
15. An automatic needle thread supply control system according to claim 14, wherein
said thread contacting members comprises a thread guide plate secured to a machine
frame and a thread clamping member movable toward and away from said a thread guide
plate, and said thread guide plate is disposed at a fixed position in a bent direction
of said bent portion.
16. An automatic needle thread supply control system according to claim 14 or 15 wherein
said thread contacting members have contacting surfaces which engage in point contact
to surely clamp the needle thread.