U.S. patent application number 11/630114 was filed with the patent office on 2007-11-08 for foot controller for sewing machine and sewing machine.
This patent application is currently assigned to Brother Kogyo Kabushiki Kaisha. Invention is credited to Eiichi Hamajima.
Application Number | 20070256618 11/630114 |
Document ID | / |
Family ID | 35786037 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256618 |
Kind Code |
A1 |
Hamajima; Eiichi |
November 8, 2007 |
Foot Controller for Sewing Machine and Sewing Machine
Abstract
A foot controller for a sewing machine includes a drive start
switch (18) provided in a drive circuit (17) of a sewing machine
motor (10) and a speed adjusting circuit (25) having a variable
resistor (26) for adjusting a speed of the sewing machine motor
(10) and a switching element (28) cooperating with the variable
resistor (26), characterized by an interruption circuit (19)
interrupting the drive circuit (17) of the sewing machine motor
(10) when the switching element (28) is short-circuited while the
drive start switch (18) is in an off-state.
Inventors: |
Hamajima; Eiichi;
(Aichi-ken, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Brother Kogyo Kabushiki
Kaisha
15-1, Naeshiro-cho
Nagoya-shi
JP
467-8561
|
Family ID: |
35786037 |
Appl. No.: |
11/630114 |
Filed: |
May 10, 2005 |
PCT Filed: |
May 10, 2005 |
PCT NO: |
PCT/JP05/08511 |
371 Date: |
December 20, 2006 |
Current U.S.
Class: |
112/277 |
Current CPC
Class: |
H02P 27/024 20160201;
D05B 69/18 20130101 |
Class at
Publication: |
112/277 |
International
Class: |
D05B 41/00 20060101
D05B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 28, 2004 |
JP |
2004-219917 |
Claims
1. A foot controller for a sewing machine, which comprises a start
switch (18) provided in a drive circuit (17) of a sewing machine
motor (10) and a speed adjusting circuit (25) provided with a
variable resistor (26) for adjusting a speed of the sewing machine
motor (10) and a switching element (28) cooperating with the
variable resistor (26), characterized by an interruption circuit
(19) interrupting the drive circuit (17) of the sewing machine
motor (10) when the switching element (28) is short-circuited while
the drive start switch (18) is in an off-state.
2. The foot controller according to claim 1, wherein the
interruption circuit (19) has a thermal fuse (20) connected in
series to the drive circuit (17) of the sewing machine motor (10)
and an electrical resistance (21) provided to be capable of
applying heat to the thermal fuse (20) and connected in parallel
with the drive start switch (18).
3. The foot controller according to claim 2, wherein the
interruption circuit (19) comprises a cement resistor (19) with the
built-in thermal fuse (20).
4. The foot controller according to claim 1, wherein the switching
element (28) comprises a triac (28) switched by a diac (30)
connected to the variable resistor (26).
5. A sewing machine which comprises a needlebar driving mechanism
vertically moving a needlebar (5) having a lower end to which a
sewing needle (6) is attached, a feed-dog vertically moving
mechanism, a feed-dog horizontally moving mechanism, a thread loop
taker accommodating a lower thread bobbin and cooperating with the
sewing needle (6), a drive start switch (18) provided in a drive
circuit of a sewing machine motor (10), and a foot controller (15)
having a speed adjusting circuit (25) provided with a speed
adjusting variable resistor (26) of the sewing machine motor (10)
and a switching element (28) cooperating with the variable resistor
(26), characterized in that the foot controller (15) includes an
interruption circuit (19) interrupting the drive circuit (17) of
the sewing machine motor (10) when the switching element (28) is
short-circuited while the drive start switch (18) is in an
off-state.
6. The foot controller according to claim 2, wherein the switching
element (28) comprises a triac (28) switched by a diac (30)
connected to the variable resistor (26).
7. The foot controller according to claim 3, wherein the switching
element (28) comprises a triac (28) switched by a diac (30)
connected to the variable resistor (26).
Description
TECHNICAL FIELD
[0001] The present invention relates to a foot controller for a
sewing machine and a sewing machine, and more particularly to such
a foot controller for a sewing machine which can detect and prevent
a condition where failure of a foot controller conventionally
results in abnormal rotation of a sewing machine motor, at a stage
prior to start of sewing.
BACKGROUND ART
[0002] Various types of sewing machines such as embroidery sewing
machines and lock-stitch sewing machines conventionally comprise a
needlebar driving mechanism provided in a sewing arm for vertically
moving a needlebar to which a sewing needle is attached and a
thread loop taker such as a full-rotary hook provided in a sewing
bed. When a user sets a sewing speed by a speed adjusting knob and
then operates a start/stop switch, a sewing machine motor starts
and the needlebar driving mechanism, thread loop taker and the like
are driven via a main shaft of the sewing machine synchronously so
that utility stitches, embroidery patterns and the like are formed
on workpiece cloth placed on the bed at a previously adjusted
sewing speed.
[0003] A foot controller is provided on the sewing machines in
order that the user may instruct sewing start or sewing speed
adjustment without use of his/her hands when sewing is carried out
while the user is putting both his/her hands on the workpiece cloth
to be sewn. In this case, a plug disposed on a distal end of a
connecting cord extending from the foot controller is connected to
a jack of a sewing machine body, the user can instruct sewing start
by pressing the foot controller, and moreover, the sewing speed can
be changed according to an amount of pressing.
[0004] For example, a safety gear described in patent document 1 is
arranged so that when a user presses a pedal of a speed instructing
unit, a resistance value of an internally provided variable
resistor varies, and a speed control unit receives speed command
voltage which is a speed command signal according to a resistance
value of the variable resistor, and a sewing machine motor is
controlled so that a sewing speed takes a value according to the
speed command voltage.
[0005] The speed control unit controlling the sewing machine motor
comprises a trigger control circuit, paired thyristors
(silicon-controlled-rectifiers (SCRs)) or the like. Each thyristor
is triggered when a pulse signal generated by the trigger control
circuit based on a command signal from the variable resistor of the
speed command unit is supplied to a gate thereof. AC current
supplied from an AC power source is supplied via the paired
thyristors to the sewing machine motor.
Patent document: JP-A-S55-71186
DISCLOSURE OF THE INVENTION
Problem to be Overcome by the Invention
[0006] The electrical arrangement of the foot controller has
recently been simplified. For example, as shown in FIG. 4, a speed
adjusting circuit 125 provided in a foot controller 115 comprises a
variable resistor 126, capacitor 127, resistance 129, diac 130,
triac 128 and the like which are wired as shown in the figure. The
foot controller 115 further comprises a drive circuit 117 and a
drive start switch 118 closed when pressed by the user. The drive
circuit 117 supplies current of an AC power source 111 to the
sewing machine motor 110 in phase with trigger voltage applied to
the gate of the triac 128, driving the motor 110.
[0007] When the triac 128 is normal, the drive start switch 118 is
closed upon press of the foot controller 115 by the user. The
trigger phase of impulses supplied from the diac 130 to the gate of
the triac 128 is controlled based on a resistance value of the
variable resistor 126 varied according to an amount of pressing.
Since the phase-controlled current is supplied to the sewing
machine motor 110, the motor is rotated at a speed according to the
amount of pressing of the foot controller 115.
[0008] The above-described foot controller 115 has such a circuit
arrangement as to be composed of the drive circuit 117 provided
with only the drive start switch 118. Accordingly, in the case
where the triac 128 fails thereby to be short-circuited, large
current is supplied via the short-circuited triac 128 to the sewing
machine motor 110 irrespective of phase control of the speed
adjusting circuit 125 when the drive start switch 118 is closed
concurrently with pressing of the foot controller 128 by the user.
Consequently, the sewing machine motor 110 is rotated at high
speeds concurrently with pressing of the foot controller 128 and
furthermore, the speed control on the basis of an amount of
pressing of the foot controller 115 is rendered ineffective.
[0009] The present invention was made in view of the foregoing
circumstances and an object thereof is to prevent abnormal
high-speed rotation of the sewing machine motor forcibly during
start of sewing when a switching element provided in the foot
controller has failed thereby to be short-circuited.
MEANS FOR OVERCOMING THE PROBLEM
[0010] A foot controller for a sewing machine of the present
invention comprises a drive start switch (18) provided in a drive
circuit (17) of a sewing machine motor (10) and a speed adjusting
circuit (25) provided with a variable resistor (26) for adjusting a
speed of the sewing machine motor (10) and a switching element (28)
cooperating with the variable resistor (26), characterized by an
interruption circuit (19) interrupting the drive circuit (17) of
the sewing machine motor (10) when the switching element (28) is
short-circuited while the drive start switch (18) is in an
off-state.
[0011] Furthermore, a sewing machine which comprises a needlebar
driving mechanism vertically moving a needlebar (5) having a lower
end to which a sewing needle (6) is attached, a feed-dog vertically
moving mechanism, a feed-dog horizontally moving mechanism, a
thread loop taker accommodating a lower thread bobbin and
cooperating with the sewing needle (6), a drive start switch (18)
provided in a drive circuit of a sewing machine motor (10), and a
foot controller (15) having a speed adjusting circuit (25) provided
with a speed adjusting variable resistor (26) of the sewing machine
motor (10) and a switching element (28) cooperating with the
variable resistor (26), characterized in that the foot controller
(15) includes an interruption circuit (19) interrupting the drive
circuit (17) of the sewing machine motor (10) when the switching
element (28) is short-circuited while the drive start switch (18)
is in an off-state.
[0012] According to the above arrangement, the drive circuit (17)
can be interrupted forcibly at a stage prior to start of sewing by
the user when the switching element (28) fails thereby to be
short-circuited. Accordingly, even when the user has pressed the
foot controller (15), electric current is not supplied to the
sewing machine motor (10) and consequently, high-speed rotation of
the sewing machine motor (10) can reliably be prevented.
Furthermore, since the sewing machine motor (10) is not driven even
when the user presses the foot controller (15), failure of the foot
controller can be recognized prior to sewing start by the user.
EFFECT OF THE INVENTION
[0013] According to the foot controller for sewing machine of the
present invention or the sewing machine of the present invention,
in the case where the switching element fails thereby to be
short-circuited, high-speed rotation of the sewing machine motor
can reliably be prevented even when the user has pressed the foot
controller. Furthermore, failure of the foot controller can be
recognized prior to sewing start by the user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a perspective view of an electronic sewing machine
of an embodiment of the present invention;
[0015] FIG. 2 is a circuit diagram showing an inner circuit of a
foot controller;
[0016] FIG. 3 is a view explaining phase control by a triac;
[0017] FIG. 4 is a view similar to FIG. 2, showing a prior art.
EXPLANATION OF REFERENCE SYMBOLS
[0018] M designates an electrically driven sewing machine, 10 a
sewing machine motor, 15 a foot controller, 17 a drive circuit, 18
a drive start switch, 19 an interruption circuit, 20 a thermal
fuse, 21 electrical resistance, 25 a speed adjusting circuit, 26 a
variable resistor, 28 a triac and 30 a diac.
BEST MODE FOR CARRYING OUT THE INVENTION
[0019] An embodiment of the present invention will be described in
the following with reference to FIGS. 1 to 3. Firstly, an
electrically driven sewing machine M capable of sewing various
utility stitches will be described in brief as shown in FIG. 1. The
sewing machine M has a bed 1, a pillar 2 standing on a right end of
the bed 1 and an arm 3 which extends from an upper end of the
pillar 2 so as to be opposed to the bed 1. In the bed 1 are
provided a feed dog vertically moving mechanism moving a feed dog
vertically, a feed dog horizontally moving mechanism moving the
feed dog horizontally, a thread loop taker (a horizontally rotating
shuttle, for example) accommodating a lower thread bobbin and
cooperating with a sewing needle 6, a thread cutting mechanism and
the like (none of which are shown).
[0020] In the arm 3 are provided a needlebar driving mechanism
vertically moving a needlebar 5 having a lower end to which the
sewing needle (6) is attached, a needlebar swinging mechanism
swinging the needlebar 5 in the direction perpendicular to a
direction in which workpiece cloth is fed, a needle thread take-up
driving mechanism moving a needle thread take-up vertically in
synchronization with the vertical movement of the needlebar 5 and
the like (none of which are shown). A sewing machine motor 10 is
provided for driving via a main shaft of the sewing machine the
feed dog vertically moving mechanism, feed-dog vertically moving
mechanism, needlebar vertically moving mechanism and needlebar
swinging mechanism.
[0021] A pattern display window 8 is provided in a front of the arm
3. Stitch patterns of various utility stitches are displayed on the
pattern display window 8. A pattern selecting dial which is not
shown is provided on a right side of the arm 3. The pattern
selecting dial is turned so that a desired one of a plurality of
types of patterns is selectable.
[0022] A foot controller 15 which can be pressed by a user is
connectable via a connecting cord 16 to a jack provided in the
right side of the pillar 2. Once the foot controller 15 is
connected to the sewing machine M, the user can instruct start of a
sewing operation only by pressing the foot controller 15 and
moreover, a sewing speed can be changed according to an amount of
pressing.
[0023] Next, the foot controller 15 will be described with further
reference to FIG. 2. The foot controller 15 has a lower case 15a
and an upper case 15b as shown in FIG. 1. The upper case 15b has
one end pivotally supported on the lower case 15a and the other end
which is vertically movable. A drive circuit 17, speed adjusting
circuit 25 and the like as shown in FIG. 2 are arranged on a
printed circuit board (not shown) provided in the lower case 15a.
When the user presses the upper case 15b by his/her foot, the drive
start switch 18 is turned on and a rotational speed of the sewing
machine motor 10 is adjusted according to an amount of
pressing.
[0024] The drive circuit 17 is provided with a first connecting
line L1 connected directly to the sewing machine motor 10 and a
second connecting line L2 connected via an AC power source 11 to
the sewing machine motor 10. The drive start switch 18 and a
thermal fuse 20 are provided for instructing to start drive of the
sewing machine motor 10 and inserted in series to the first
connecting line L1. Furthermore, electrical resistance 21 is
inserted in parallel with the drive start switch 18.
[0025] The electrical resistance 21 is set at a relatively larger
resistance value (1.8 K.OMEGA., for example). An interruption
circuit 19 comprises the electrical resistance 21, thermal fuse 20
and the like. The electrical resistance 21 and the thermal fuse 20
are integrally covered with cement while disposed in proximity to
each other. More specifically, the interruption circuit 19 is
arranged as a cement resistor with a built-in thermal fuse 20. The
thermal fuse is adapted to be melted down when the electrical
resistance 21 heats up to or above about 100.degree. C., for
example.
[0026] Furthermore, the resistance value of the electrical
resistance 21 needs to be set at such a value, as maximum
resistance value (at which electrical current is small and an
amount of heat generated is rendered small), that an amount of heat
sufficient to melt down the thermal fuse 20 is generated even when
the ambient temperature is at 0.degree. C. The resistance value of
the electrical resistance 21 further needs to be set at such a
value, as minimum resistance value (at which the sewing machine
motor 10 is not rotated by current flowing through the electrical
resistance 21 and an amount of heat does not reach Tm (maximum
temperature limit) of the thermal fuse 20.
[0027] Tm is set at about 200.degree. C. Furthermore, a temperature
of the electrical resistance 21 in the melting of the thermal fuse
20 is set so as to be sufficiently larger than a melting
temperature of the thermal fuse in view of time lag between
generation of heat by the electrical resistance 21 and transfer of
heat to the thermal fuse 20 or melting time of the thermal fuse
20.
[0028] When the resistance value of the electrical resistance 21 is
excessively small, a temperature increased in the case of
overcurrent becomes far higher than a melting temperature of the
thermal fuse 20, exceeding Tm. As a result, the thermal fuse 20 has
a possibility of re-conduction thereof after the melting.
Accordingly, the resistance value of the electrical resistance 21
needs attention so as to be set in view of the current values
during the normal and abnormal occasions, the melting conditions of
the thermal fuse 20, drive conditions of the sewing machine motor
10.
[0029] The speed adjusting circuit 25 is provided with a third
connecting line L3 connected to the first connecting line 1 and a
fourth connecting line L4 connected to the second connecting line
L2. Between the third and fourth connecting lines L3 and L4 is
connected a parallel circuit of a triac 28 and a series circuit of
a variable resistor 26 (maximum resistance value of 200 K.OMEGA.,
for example) and a capacitor (0.1 .mu.F) 27.
[0030] Furthermore, a series circuit of a resistance 29 (10.OMEGA.,
for example) and a diac 30 is connected between a connection point
P between the variable resistor 26 and the capacitor 27 and a gate
G of the triac 28. When applied AC voltage exceeds a predetermined
value, the diac 30 generates and delivers sharp impulses to the
gate G of the triac 28.
[0031] Next, the operation of the foot controller 15 described
above will be described. However, the resistance value of the
variable resistor 26 takes a maximum value when the foot controller
15 is not pressed.
[0032] The drive start switch 18 is open when the user has not
pressed the foot controller 15. However, a slight amount of current
(no more than 1 mA) from the AC power source 11 flows to the drive
circuit 17 via the parallel-connected electrical resistance 21.
Such a small current results in a small amount of heat generated by
the electrical resistance 21 and moreover, an amount of charge to
the capacitor 27 is also small. As a result, the speed adjusting
circuit 25 is not operated, whereupon the sewing machine motor 10
is not rotated.
[0033] When the user presses the foot controller 15 in order to
start a sewing operation, the drive start switch 18 is switched to
a closed state. In this case, current from the AC power source 11
flows through the drive start switch 18 of the first connecting
line L1 and the thermal fuse 20, so that the capacitor 27 is
further charged with the current.
[0034] When the terminal voltage of the capacitor 27 rises to or
above a predetermined value, the diac 30 is rendered conductive
such that sharp impulses are supplied from the diac 30 to the gate
G of the triac 28. The triac 28 is then triggered to be operated.
As a result, the AC current is supplied to a closed circuit of the
first connecting line L1, third connecting line L3, triac 28,
fourth connecting line L4 and second connecting line L2
sequentially, whereupon the sewing machine motor 10 is rotated.
[0035] Next, when an amount of pressing against the foot controller
15 by the user 15 is increased, the resistance value of the
variable resistor 26 is reduced. Accordingly, a charging time for
the capacitor 27 is shortened such that the time for trigger of the
triac 28 is accelerated. Then, the time when the triac 28 is
rendered conductive is accelerated, whereupon the current supplied
to the sewing machine motor 10 is increased such that the
rotational speed of the sewing machine motor 10 is increased. Thus,
the resistance value of the variable resistor 26 is varied
according to an amount of pressing against the foot controller 15
and the trigger time of the triac 28 is changed accordingly,
whereby the phase control is carried out.
[0036] On the other hand, in a case where the triac 28 is
short-circuited due to failure when the foot controller 15 is not
pressed by the user, that is, when the drive start switch 18 is
open, an amount of the current flowing through the electrical
resistance 21 and thermal fuse 20 is increased to a maximum value
and accordingly, an amount of heat generated by the electrical
resistance 21 is increased. However, the AC current flowing in this
case is insufficient to rotate the sewing machine motor 10. Since
the electrical resistance 21 heats up to the maximum by this
current, the thermal fuse 20 efficiently receives the heat
generated by the electrical resistance 21.
[0037] As described above, an amount of heat generated by the
electrical resistance 21 is increased, and the thermal fuse 20
provided in proximity to the electrical resistance 21 is heated in
subjection to the heat generated by the electrical resistance 21.
When the temperature of the thermal fuse 20 reaches a predetermined
temperature (about 110.degree. C., for example) or above, the
thermal fuse 20 melts down. As a result, since the drive circuit 17
is interrupted by the interruption circuit 19, the AC current is
not supplied to the sewing machine motor 10, and the drive circuit
17 can forcibly be interrupted at a stage prior to start of sewing
by the pressing of the foot controller 15.
[0038] Accordingly, no current is supplied to the sewing machine
motor 10 even when the user presses the foot controller 15 in order
that sewing may be started, whereupon the sewing machine motor 10
can reliably be prevented from inadvertent high speed rotation.
Furthermore, since the sewing machine motor 10 is not driven even
when the user presses the foot controller 10, the user can
recognize the failure of the foot controller 10 before start of
sewing.
[0039] Furthermore, the interruption circuit 19 comprises the
thermal fuse 20 connected in series to the drive circuit 17 and the
electrical resistance 21 provided so as to be capable of heating
the thermal fuse 10 and connected in parallel with the drive start
switch 18. Accordingly, when the triac 28 serving as the switching
element is short-circuited due to failure, the current from the
drive current is supplied to the electrical resistance 21, which
heats up. Since the thermal fuse 20 melts down by the resultant
heat, only the provision of an inexpensive thermal fuse 20 can
forcibly and reliably interrupt the drive circuit 17.
[0040] Furthermore, since the interruption circuit 19 comprises the
cement resistor with built-in thermal fuse 20, the interruption
circuit 19 can be rendered small-sized and accordingly, resistance
to heat can be improved. Moreover, a work for mounting the
interruption circuit 19 on the printed circuit board can markedly
be simplified.
[0041] Furthermore, since the switching element comprises the triac
28 switched by the diac 30 connected to the variable resistor 26,
the phase control of AC current can be realized by a simplified
circuit arrangement while reduction in size of the switching
element is achieved.
[0042] The present invention can be modified or expanded as
follows:
[0043] 1) Various switching elements such as a silicon controlled
rectifier (SCR; or thyristor), field effect transistor (FET) or the
like can be employed, instead of the triac 28.
[0044] 2) When the cement resistor with built-in thermal fuse 20 is
used as the interruption circuit 19, the resistance value of the
electrical resistance 21, the distance between the electrical
resistance 21 and the thermal fuse 20, the meltdown temperature of
the thermal fuse 20 and the like may be changed according to the
magnitude of AC current flowing into the drive circuit 17, a type
of the cement resistor, a type of the foot controller 16 or the
like. In short, the temperature of heat generated by the electrical
resistance 21 and the meltdown time of the thermal use 20 may be
changed arbitrarily.
[0045] 3) The present invention should not be limited to the
foregoing description of the embodiment and may be taken into
practice by adding various modifications to the foregoing
embodiment without departing from the gist of the invention.
Accordingly, the invention involves these modified forms.
INDUSTRIAL APPLICABILITY
[0046] As obvious from the foregoing, the present invention is
applicable to a foot controller for controlling a rotational speed
of a sewing machine motor.
* * * * *