JPS5931357B2 - Lower thread breakage detection device for sewing machines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bobbin thread breakage detection device for a sewing machine that stops operation of the sewing machine when the bobbin thread of the sewing machine breaks.

Conventionally, thread breakage detection devices for sewing machines have been equipped with a lever that intermittently contacts the bobbin thread, which alternately tightens and relaxes as the thread take-up moves up and down. There are devices that detect bobbin thread breakage, no bobbin thread on the bobbin, poor condition of the bobbin thread, etc. by operating a limit switch or a proximity switch that is activated by an increase in the amount of movement.In this case, the lever must be rotated. There is a drawback that the biasing force of the spring is applied to the bobbin thread and damages the bobbin thread.In order to eliminate this problem, if the biasing force of the spring is weakened, the swinging of the lever will not be able to follow the rotation of the sewing machine. Further, even if the biasing force of the spring is increased, when the sewing machine is rotated at high speed, the lever resonates at a certain rotation speed of the sewing machine and cannot follow the rotation of the sewing machine.

As a countermeasure against this problem, for example, there is a method that uses a photoelectric element to detect the horizontal deflection of the bobbin thread in the direction perpendicular to the center of the needle hole due to the rotation of the outer hook, but in this case, this detection function is lost due to bobbin thread fluff floating around the needle hole. There was a drawback that it could be damaged.

As a method for eliminating the above-mentioned drawbacks, the present inventor has applied for a thread breakage detection method using a piezoelectric element (Patent Application No. 54-100578).
However, the present invention provides a method for controlling the sewing machine when the bobbin thread breaks, in which the bobbin thread initial detection signal obtained by the method of the above application can be freely used as a sewing machine stop signal and a sequence information signal. The object of the present invention is to provide a stop signal generation circuit.

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

First, before explaining the electric circuit of this embodiment, the mechanical structure of the invention already filed by the inventor of the present application will be summarized and explained.

That is, in FIGS. 1 to 3, the back surface of the throat plate 1 contacts the fin 3 of the outer hook 2 when the outer hook rotates twice, and comes into contact with the bobbin thread 5 that is displaced in a direction perpendicular to the center of the needle hole 4. A piezoelectric element 6, in this case a bimorph type piezoelectric element 6 in which a silver electrode 8 is vacuum-deposited on a ceramic 7 made of lead zirconate titanate, is attached via a rubber 9 and a bracket 10, and in this attached state the outer pot is 2 rotates, the bobbin thread 5 moves laterally on the groove 12 of the inner hook 11 between the bottom surface of the groove 12 and the thread shedding surface of the fin 3 as shown in FIG. There is a displacement from distance L2 to L3 between the two.

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. It makes temporary contact with the element 6 and repeats this operation.

However, as mentioned above, the signal obtained by this type of thread breakage detector outputs a signal with a certain period when the thread is not broken, and when the thread breaks, the signal with the certain period disappears. Since this is an information signal, such a signal cannot be easily used as a sewing machine stop signal as it is.

An example of an electric circuit for converting the above information signal into a normal stop signal, that is, a signal generated only when the thread breaks, is shown in the fourth embodiment.
The series of waveforms is shown in FIG.

That is, in FIG. 4, OP is, for example, TC-7063p.
VC is a voltage comparator such as M-51202, MV is a multivib break such as NS-121, and NAND is a NAND such as NS-7400.
The gate and NOR are NOR gates such as NS-7402, R is a resistor, C is a capacitor, and Tr is a transistor. Identical circuit elements in the figures are given serial numbers after each element code.

In the above circuit diagram, the rotary plate 15 mounted in relation to the rotating shaft (not shown) of the sewing machine rotates the light rays of opposing light emitting elements, such as light emitting diodes LED, and light receiving elements, such as photodiodes PD, as the shaft rotates. intermittently,
Output of a pulse waveform corresponding to the rotational speed of the shaft (Fig. 5A)
) is obtained at the input terminal T1.

However, as shown in the figure, the same waveform (Fig. 5A) is higher than the O level and exceeds the threshold voltage of the TTL IC connected to the next stage, making the above IC inoperable. In order to prevent this problem, by outputting a pulse waveform from the emitter of the transistor Tr1, the timing signal can be brought almost to the O level as shown in FIG. 5B.

This timing signal is input to a time constant circuit composed of NAND4 and NoR1, and this time constant circuit is a circuit that generates a pulse in the positive direction only when the input waveform falls from positive to negative, and the pulse width is equal to the time constant RXC. This pulse (waveform E in FIG. 5) becomes a stop signal when there is no thread breakage detection signal, that is, a cancellation pulse caused by a signal from the piezoelectric element 6.

On the other hand, the output of the piezoelectric element 6 is input to the preamplifier OP via the variable resistor VR1, and is amplified to a value suitable for operating the voltage comparator VC connected to the next stage, and further increases the voltage. Comparator VC removes noise other than the signal,
The pulse waveform is shaped into a pulse waveform corresponding to the time when the bobbin thread 5 contacts the piezoelectric element 6 (FIG. 5C).

Note that the rising position of this waveform is synchronized with the timing signal described above (FIG. 5B).

The timing signal (FIG. 5B) and the signal from the piezoelectric element 6 (FIG. 5C) are matched by NAND2 and further inverted by NAND3 to become an input trigger for the multivibrator MV (FIG. 5F). The multi-by-break MV is activated to output the waveform shown in FIG. 5G, and the width of this waveform is adjusted by the time constant Ro X Co (ADJ in FIG. 5G).

Furthermore, the same waveform (Figure 5G) is inverted by NAND5, and the above-mentioned NOH output (Figure 5E) and NAND6 are inverted.
If there is a signal from the piezoelectric element 6 (if the thread is not broken), the timing signal (Fig. 5E
) and the yarn detection signal (G in Figure 5) are both at H level, the output of NAND6 is at L level (H in Figure 5), and therefore the output of NAND7 is at H level, transistor Tr1 is on, and relay RY is off when Tr2 is off. does not operate, and the piezoelectric element 6
When there is no signal from (in the case of thread breakage), the timing signal (E in Figure 5) is at H level and the thread detection signal (G in Figure 5) is at L level, so the output of NAND6 is at H level (in the case of thread breakage). As the figure becomes "), the above signal is transmitted by NAND7,
After inversion, the relay RY is activated via the transistors Tr1 and Tr2, and is output via the diode D as a stop signal or a sequential signal.

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

The present invention uses a lower thread contact signal from a piezoelectric element installed between the back surface of the throat plate and the outer circumference of the outer hook so that it can contact the lower thread that is displaced in a direction perpendicular to the center of the needle hole by contacting the fin of the outer hook when the outer hook rotates. A multivibrator whose trigger input is a signal that coincides with a timing waveform generated in response to the rotation of the sewing machine, and an output signal from the multivibrator and the falling edge of the timing waveform generated in response to the rotation of the sewing machine. In a sewing machine equipped with a relay circuit that outputs a sewing machine stop signal when the related pulse waveforms do not match, for example, a relay circuit consisting of NAND7, transistor Tr2, relay RY, and resistors R11 to R14. It is in the bobbin thread breakage detection device.

As a result, the present invention provides a simple and compact bobbin thread breakage detection device between the back of the needle plate and the outer periphery of the hook, where the needle passes through and the thread is repeatedly tensioned and relaxed, and also enables high-speed operation of the sewing machine. It has the effect of being able to sufficiently track the sewing machine and to generate a thread breakage signal when the bobbin thread breaks without damaging the bobbin thread, thereby reliably stopping the sewing machine.

Furthermore, by adjusting the pulse width of the cancel signal (Fig. 6G) mentioned above, there is no need to provide a timing device for each sewing machine even in multi-head sewing machines, and one timing device is required for all types of sewing machines. This has the effect of simplifying the construction of the entire sewing machine and ensuring more reliable timing for all types at the same time.

Furthermore, when a thread breakage occurs, a stop signal is output intermittently and continuously, which has the effect of reliably stopping the sewing machine.

[Brief explanation of the drawing]

Fig. 1 is a front view of an embodiment of the present invention, Fig. 2 is a plan view thereof, Fig. 3 is a side view thereof, Fig. 4 is an electric circuit diagram thereof, and Fig. 5 is a timing and waveform diagram thereof. . 1... Throat plate, 2... Outer hook, 3...
...fin, 4...needle eye, 5...bobbin thread,
6...Detector (piezoelectric element), 15...
Rotating plate, OP... Preamplifier, VC...
・Voltage comparator (comparator), NAND...
NAND gate, NOR...NOR gate, MV...multivibrator, R...
・Resistor, C... Capacitor, RY...
・Relay, LED...Light source, PD...
Photodiode.

Claims (1)

[Claims] 1. When the outer hook rotates, the lower thread contact signal from the piezoelectric element is installed between the back of the throat plate and the outer periphery of the outer hook so that it can come into contact with the lower thread that is displaced in a direction perpendicular to the center of the needle hole by contacting the fin of the outer hook, and the sewing machine. A multivibrator whose trigger input is a signal that coincides with a timing waveform generated in response to rotation, and an output signal from the multivibrator and a falling edge of the timing waveform generated in response to rotation of the sewing machine. and a relay circuit that outputs a stop signal for the sewing machine when the rising pulse waveforms do not match.