JPH04102499A - Skip stitch detecting device for sewing machine - Google Patents

Abstract

PURPOSE:To detect a skip stitch by the change of frictional sound at the time of running a needle thread by bringing the needle thread in contact with a sound detecting sensor to detect the length of the frictional sound of the running needle thread generated every rotation of a sewing machine. CONSTITUTION:A sound detecting sensor 1 for detecting the frictional sound of a needle thread has such a constitution, for example, as passing a needle thread 4 in a channel 3 provided on one surface of a piezoelectric element 2. When the needle thread 4 is pulled at the time of thread feed, it is rubbed with the piezoelectric element 2 to generate the frictional sound, which is detected by the piezoelectric element 2. The frictional sound signal thus detected by the sound detecting sensor 1 is amplified by an amplifier 5. The following thread feed data transmitted from a time measuring circuit 10 and the thread feed data read out from a data temporary memory device 11 are inputted to an arithmetic circuit 12, in which the difference between the both is calculated. When the needle thread 4 is normally sent at the time of constant-speed rotation of a sewing machine, the difference between the successively inputted thread feed data is zero, and no skip stitch signal is outputted. When the difference between a signal and the next signal is large, a skip stitch signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a skipped stitch detection device for a sewing machine that detects skipped stitches by measuring the feeding length of upper thread for each stitch using contact sound.

[Prior Art] Conventionally, as a means for detecting skipped stitches, a differential spatial filter is constructed in which one comb-shaped slit is inserted between the other comb-shaped slits, and this differential spatial filter is A device has been proposed in which a photodetector detects the upper thread through the thread (see Japanese Patent Application Laid-open No. 37082/1982).

In this device, when feeding the upper thread, the shadow of the upper thread is detected by a differential spatial filter, and the traveling thread length is detected by the movement of this shadow.

In addition, as another skipped stitch detection device, a device that detects the tension of the needle thread using a strain gauge has been proposed (Japanese Patent Laid-Open No. 55
(Refer to Publication No.-22115).

[Problems to be Solved by the Invention] However, in the former device, since the measurement is based on the shadow of the upper thread projected on the differential spatial filter, detection is extremely difficult depending on the thickness and type of the thread. There is a drawback that cotton dust tends to adhere to the differential spatial filter, thereby causing malfunction.

Further, in the latter device, there is a problem in that it is difficult to accurately detect skipped stitches because the needle thread tension fluctuates greatly even when it is normal.

The present invention detects the length of the fricative sound that occurs during each rotation of the sewing machine by bringing the upper thread into contact with a sound detection sensor, thereby detecting stitch skipping due to changes in the fricative sound when the upper thread is running. It is an object of the present invention to provide a stitch skipping detection device for a sewing machine that can detect stitch skipping.

[1 [Means for Solving the Problem] In order to achieve the above object, the present invention brings the upper thread of the sewing machine into contact with a sound detection sensor, and measures the yarn feeding length of each stitch of the upper thread by measuring the needle thread. This is detected by contact sound during running, and skipped stitches are detected from changes in the contact sound.

In addition, the upper thread of the sewing machine is brought into contact with a sound detection sensor, and the thread feeding length of each stitch of the upper thread is detected based on the generation time of the contact sound when the upper thread runs for each rotation of the sewing machine. The generation time of the contact sound is compared with the generation time of the contact sound measured previously, and skipped stitches are detected from the difference in the generation time of the contact sound.

Further, the upper thread of the sewing machine is brought into contact with a sound detection sensor, and the yarn feeding length of each stitch of the upper thread is detected based on the time during which a contact sound is generated when the upper thread runs per rotation of the sewing machine. This method detects skipped stitches by comparing the generation time of the contact sound with the previously measured generation time of the contact sound, and comparing the difference in the generation time of the contact sound with a change in the rotational speed of the sewing machine.

[Function] According to the present invention, when a sound detection sensor is attached to the upper thread path of the sewing machine and the upper thread is brought into contact with this sound detection sensor to drive the sewing machine, when the upper thread is fed for each needle, this Friction noise is generated by the movement of the upper thread.

This fricative sound is detected by a sound detection sensor, and this detection signal is outputted as a signal in a necessary frequency range by a bandpass filter, and this signal is waveform-shaped. This waveform-shaped signal is time-measured in a time measurement circuit using a signal from a rotational speed sensor and a clock per unit output from a timing generation circuit, and the time-measured data is stored in a temporary storage device. Then, the difference between the time-measured data of the detection signal due to the next fricative sound detected in the same manner and the time-measured data of the stored detection signal is calculated by the arithmetic circuit and outputted to the error detection comparison circuit. On the other hand, the rotation speed detector outputs a rotation speed signal based on the signal from the rotation detection sensor.

This rotational speed signal is temporarily stored in a temporary storage device.

When the next rotational speed signal is output from the rotational speed detector, it is compared with the rotational speed signal stored at - time, and if there is a difference, the error data due to this rotational speed variation is determined as R.
Store in OM. This error data is read from the ROM and input to the error detection and comparison circuit, where it is compared with data on the difference between the detection signals due to the fricative sound, and a skipped stitch signal is output.

[Embodiment] Referring to FIG. 1, in a skipped stitch detection device according to an embodiment of the present invention, a sound detection sensor 1 that detects the friction sound of the upper thread is connected to one of the piezoelectric elements 2, for example, as shown in FIG. It is constructed so that the upper thread 4 is passed through a groove 3 provided on the surface, and when the upper thread 4 is pulled during yarn feeding, it rubs against the piezoelectric element 2 and generates a frictional sound. Detected by element 2.

The fricative sound signal detected by the sound detection sensor 1 in this way is amplified by the amplifier 5, and only the necessary frequencies of the fricative sound signal pass through the band pass filter 6, and time can be measured by the waveform shaping circuit 7. The signal is shaped into a waveform signal (see FIG. 2(c)). Also, a clock signal is generated from the timing generation circuit 9 according to the timing from the rotation detection sensor 8 (see FIG. 2(, )).
) is input to the time measuring circuit 10. The clock signal input to this time measurement circuit 10 is passed only during the signal sent from the waveform shaping circuit 7.

The number of clock signals that have passed (see FIG. 2(d)) is stored in the data storage device 11 as yarn feeding data. Similarly, the next yarn feeding data sent from the time measuring circuit 10 and the yarn feeding data read out from the data storage device [11] are input to the calculation circuit 12, and the difference between them is calculated. If the upper thread 4 is being fed normally when the sewing machine is rotating at a constant speed, the difference between the thread feeding data that is inputted one after another is zero, and no skipped stitch signal is output.

Here, a skipped signal is issued when the difference from the next signal is large.

Note that the number of rotations varies due to mechanical variations in the sewing machine. This variation in rotation speed can be detected by detecting the rotation speed per minute (rpm) with a rotation speed detector 13 based on a timing signal from a rotation detection sensor 8, and temporarily storing this rotation speed signal in a rotation speed-hour storage device 14. Then, the calculation circuit 15 calculates the difference between the rotation speed signal detected by the rotation speed detector 13 and the rotation speed signal read from the rotation speed-time storage device 14.
is calculated and stored in advance in the ROM 16 as error data. The error signal read from the ROM 16 is input to the error detection comparison circuit 17, and this error signal is compared with the difference signal of the yarn feeding data output from the arithmetic circuit 12. An error signal is output from the error detection comparison circuit 17 as a jump signal.

This embodiment detects the friction noise when feeding the upper thread in this way,
It compares the signals caused by fricative sounds that are sent one after another, and outputs a skipped stitch signal when the difference is large.

Further, since this skipped stitch signal can be determined based on a change in the rotational speed, accurate skipped stitches can be easily detected.

[Effects of the Invention] Since the present invention is configured as described above, the running of the upper thread during feeding is detected by the friction sound, the timing at which the friction sound is generated is detected for each rotation of the sewing machine, and Since it is also possible to correct deviations in the generation of fricative sounds during acceleration or deceleration, there is an advantage that skipped stitches can be detected accurately and easily.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a skipped stitch detection device according to an embodiment of the present invention, Fig. 2 is a perspective view of a piezoelectric element used as a sound detection sensor in Fig. 1, and Fig. 3 is a waveform of each part in Fig. 1. It is a diagram. 1... Sound detection sensor, 2... Piezoelectric element, 3... Groove. 4... Needle thread, 5... Amplifier, 6... Bandpass filter, 7... Waveform shaping circuit, 8... Rotation detection sensor. 9... Timing generation circuit, 10... Time measuring circuit, 11... Data time storage device, 12... Arithmetic circuit, 13... Rotation speed detector, 14... Rotation speed-hour storage Device, 15... Arithmetic circuit, 16... ROM, 17.
...Error detection comparison circuit.

Claims (1)

[Scope of Claims] 1. The upper thread of the sewing machine is brought into contact with a sound detection sensor, and the yarn feeding length of each stitch of the upper thread is detected by the contact sound when the upper thread runs, and the change in the contact sound is detected. A skipped stitch detection device for a sewing machine characterized by detecting skipped stitches. 2. Bring the upper thread of the sewing machine into contact with a sound detection sensor, and detect the yarn feeding length of each stitch of the upper thread based on the time during which the contact sound occurs when the upper thread runs for each rotation of the sewing machine. A skipped stitch detection device for a sewing machine, characterized in that a skipped stitch detection device for a sewing machine is characterized in that skipped stitches are detected from the difference in the generation time of a contact sound by comparing the generation time with a previously measured generation time of a contact sound. 3. Bring the upper thread of the sewing machine into contact with the sound detection sensor, and detect the thread feeding length of each needle of the upper thread based on the generation time of the contact sound when the upper thread runs per rotation of the sewing machine. The method is characterized in that skipped stitches are detected by comparing the generation time with the generation time of the contact sound measured previously, and comparing the difference in the generation time of the contact sound with a change in the rotational speed of the sewing machine. Skip stitch detection device for sewing machines.