JPS5936547B2 - Lower thread breakage detection device for sewing machines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for stopping a sewing machine when a bobbin thread breakage is detected in the sewing machine.

Conventionally, as a bobbin thread breakage detection device for a sewing machine, for example, a lever is provided that intermittently contacts the bobbin thread, which alternately tensions and relaxes following the vertical movement of the thread take-up, and detects when the bobbin thread breaks. There are methods of detecting bobbin thread breakage, no bobbin thread on the bobbin, or poor condition of the bobbin thread by operating a limit switch or +b contact switch that is activated by increasing the amount of movement of the lever. In this case, the biasing force of the spring to rotate the lever is applied to the bobbin thread, damaging the bobbin thread. Therefore, even if the biasing force of the spring is strengthened, resonance will occur due to the high-speed rotation of the sewing machine, and the lever will no longer be able to follow the rotation of the sewing machine. There was a drawback.

On the other hand, as a method for detecting bobbin thread breakage without contacting the bobbin thread, there is a method in which the horizontal runout of the bobbin thread in the direction perpendicular to the needle hole center due to the rotation of the outer hook is detected using a photoelectric element. There is a drawback that the detection function is lost due to bobbin thread fuzz, dust, etc. floating around.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thread breakage detection device for a sewing machine that detects bobbin thread breakage by intermittently and repeatedly contacting the fin of the outer hook and displacing the bobbin thread in a direction perpendicular to the center of the needle hole when the outer hook rotates. The object of this invention is to eliminate the above-mentioned conventional drawbacks.

Next, the configuration of an embodiment of the present invention will be explained with reference to the drawings.

On the back surface of the throat plate 1, a contactor 6 (described later) that contacts the fin 3 of the outer hook 2 and the lower thread 5 displaced perpendicular to the center of the needle hole 4 when the outer hook rotates 200 times is attached to a soft rubber 9 and a bracket. 10
When the outer hook 2 rotates in this state, the bobbin thread 5 moves horizontally on the groove 12 of the inner hook 11 between the bottom of the groove 12 and the thread shearing surface of the fin 3 as shown in FIG. 2 L1. distance L2 to L3 between needle hole 4 of throat plate 1
Displaced as follows.

As a result, each time the outer hook 2 rotates once, the lower thread 5 pulled out from the thread guide 14 of the bobbin 13 is displaced as shown by the two-dot chain line in FIG. Contact with 6.

Next, the structure of the contactor 6 is shown in FIG. 4, and the electric circuit of this embodiment is shown in FIG.

The contactor 6 has a structure in which the inductance changes due to the contact of the thread.The yoke 13 is made of a magnetic material with high magnetic permeability (for example, permalloy, etc.) and is wound with a wire 14. A movable piece 15 made of the same (high permeability magnetic material) is provided opposite the yoke 13 with a gap in between, and an insulating piece 17 and a spacer 18 made of an elastic material such as butyl rubber are used to maintain the gap. is attached to the movable piece 15, and an actuator 19 with which the bobbin thread 5 contacts is fixed to the movable piece 15.
The contact causes a change in the gap, and therefore winding 1
The inductance of 4 also changes.

Next, FIG. 5 shows an electric circuit according to an embodiment of the present invention.
An inductance bridge is formed by R, and on the other hand, the input/output terminals of the tuning fork TF are connected to the non-inverting input of a normal OP amplifier OP1 and the output side of the amplifier OP1, respectively, to form a tuning fork oscillation circuit. ,
The output of the circuit is connected to the bridge circuit described above via a matching transformer T.

Variable resistor BVR forming each side of the bridge circuit above
The movable contact of is connected to the inverting input terminal of the OP amplifier 0P20, and the variable resistor VRI for offset voltage adjustment is connected to the OP amplifier OP2, and the output of the OP amplifier P2 is connected to the next stage. It is connected to the non-inverting input terminal of the connected OP amplifier OP3, and the inverting input terminal is connected to the Zener diode ZD.
It is connected to the output side of the amplifier OP3 through a resistor R1 and to the base of an NPN transistor Tri.

The emitter of the transistor Tri is grounded through the resistor R2, and the collector is connected to the + side power supply VC through the relay RY.
In addition to being connected to C, the normally closed contact RYb of the same relay RY
is connected to an external stopping member (not shown) via terminal TA, and in the figure, R is a resistor, C is a capacitor, D is a diode, and ZD is a Zener diode. A serial number is attached after each element code.

Next, the operation of this embodiment will be explained.

When the power is on, the oscillation circuit including the tuning fork TF oscillates a stable low wave (1564KH2 in this example) that is less affected by power supply hum (harmonics of 50H2 or 60H2). , a frequency impedance matched by a matching transformer T is applied to the bridge circuit.

The bridge circuit is an inductance bridge, and the inductance of the contactor 6 and the inductor SL wound around the toroidal core are connected as proportional selection thereof, and the resistors of the above two inductances are made equal to each other, and the inductance is connected to the toroidal core. The bridge circuit is balanced by the variable resistor BVR so that the potential at the operating point P shows zero potential when the inductance of the child 6 is free (the thread is not in contact) (of course, before adjusting the balance, (The offset is adjusted by the variable resistor vR1), and in this state, as described above, the bobbin thread 5 is displaced in the direction perpendicular to the center of the needle hole 4.
When the contactor 6 contacts the actuator 19 of the contactor 6, the gap between the yoke 13 and the movable piece 15 shown in FIG. 4 closes, and the inductance of the contactor 6 increases.

This increase in inductance causes the bridge to become unbalanced, causing the oscillation frequency of the oscillator to be proportional to the change in inductance between the OP amplifier 0P20 inverting terminal and ground.
64KH2 is generated and input to the inverting input terminal of OP amplifier 0P20, and after being amplified, it is input to the OP amplifier OP3 of the next stage.
is input.

In some cases, it may be effective to insert an appropriate bypass filter between the OP amplifier 0P20 input terminal and the bridge in order to avoid the influence from the commercial power supply, but in this case, the gist of the present invention will not be changed in any way. It's not a thing.

The OP amplifier OP3 is a normal time integrating circuit, and outputs the signal (thread presence signal) from the contact 6 as a DC potential at a constant level, and connects the transistor Trl via the resistor R1. In order to make the transistor conductive, the relay RY connected to the collector of the transistor Trl is activated to turn off the normally closed contact RYb and open the stop member (not shown) of the sewing machine, and the sewing machine continues to rotate normally. I can do it.

On the other hand, if there is no intermittent signal from the contactor 6 (thread breakage signal), the bridge circuit is balanced and the
The input signal to the amplifier OP2 disappears, the output side of the integrating circuit also becomes negative level, the conduction of the transistor Tri is canceled, the relay RY is cut off, the normally closed contact RYb is turned on, and the stop member is activated. The sewing machine will stop rotating immediately.

Note that there is no problem in using a normally closed contact as the relay RY contact in order to stop the function of the thread breakage stop device for a certain period of time when the sewing machine is started.

Next, the effects of the present invention will be explained.

The present invention relates to a contactor of a variable inductor that is attached between the back surface of the throat plate and the outer circumference of the outer hook so as to be able to come into contact with the lower thread that is displaced perpendicular to the center of the needle hole by contacting the fin of the outer hook when the outer hook rotates, and the contactor. a bridge circuit that has a variable inductor on one side and outputs zero potential when the bobbin thread is not in contact with the contactor; an oscillation circuit that supplies alternating current power to the bridge circuit; A relay circuit that outputs a sewing machine stop signal when the bridge circuit loses contact at a period corresponding to the operation of the sewing machine and the output from the bridge circuit becomes zero potential continuously, such as a transistor Tri, a relay RY, and resistors R1 and R2.
There is a bobbin thread breakage detection device in the sewing machine, which is equipped with a relay circuit and a lower thread breakage detection device, respectively.

As a result, the present invention forms a bobbin thread breakage detection device with a simple and compact structure between the back of the needle plate and the outer periphery of the outer hook, where the needle passes and the thread is repeatedly tensed and relaxed, and the device does not damage the bobbin thread. It has the effect of being able to sufficiently follow the high-speed operation of the sewing machine, without causing malfunctions due to mechanical vibrations during machine operation, and generating a thread breakage signal when the bobbin thread breaks to reliably stop the sewing machine. be.

[Brief explanation of drawings]

FIG. 1 is a front view of one embodiment of the present invention, FIG. 2 is a plan view thereof, FIG. 3 is a cutaway side view thereof, FIG. 4 is a perspective view of the contactor 6, and FIG. It is an electrical circuit diagram. 1... Throat plate, 2... Outer hook, 3...
...fin, 4...needle eye, 5...bobbin thread,
6...Contactor, OP...OP amplifier,
R...Resistor, C...Capacitor, S
L...Inductor, ZD...Zener diode, Tr---1-) transistor, RY...
····relay.

Claims (1)

[Claims] 1. A contactor of a variable inductor installed between the back of the throat plate and the outer circumference of the outer hook so as to be able to come into contact with the lower thread which contacts the fin of the outer hook and is displaced perpendicular to the center of the needle hole when the outer hook rotates, and the variable inductor of the contactor. a bridge circuit whose output is zero potential when the inductor is on one side and the bobbin thread is not in contact with the contact; an oscillation circuit that supplies alternating current power to the bridge circuit; and a relay circuit that outputs a sewing machine stop signal when the output from the bridge circuit becomes zero potential continuously. Bottle thread breakage detection device.