JPH05212183A - Automatic tension adjusting device of sewing machine - Google Patents

Abstract

PURPOSE:To make sewing in good tension balancing, which is made controllable, by comparing the actually consumed amount of needle thread with the required amount of needle thread determined previously through calculation, thereupon reading the correction data, correcting the pressing force given by a tension adjuster to the needle thread, and performing thread tightening for stitch forma tion in the next cycle. CONSTITUTION:By reference to a correction data memory means ROM2, a CPU reads the correction data from the difference between the actually consumed amount of needle thread and the required amount of needle thread which was determined through calculation and is stored in a needle thread requisite amount memory means RAM1, accommodates the read data in a temporary memory means RAM2, and corrects the pressing force of a tension adjuster prior to thread tightening for stitch formation in the next cycle. Thereby automatic correction is made so that the tension of the needle thread converges always in good condition, and sewing can be carried out with good tension balancing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic thread tension device for a sewing machine.

[0002]

2. Description of the Related Art Conventionally, as a technique of automatic thread tension of a sewing machine, there is a technique disclosed in Japanese Utility Model Publication No. 60-18223. According to the prior art, the necessary needle thread required amount is obtained by taking into consideration factors such as the type of the pattern based on the amplitude data of the needle and the cloth feed data, and further the cloth thickness, the thickness of the thread and the type, This is a technique for comparing the required amount of the upper thread and the estimated value of the upper thread consumption amount actually consumed by sewing with a comparator, and automatically adjusting the pressing force to the thread of the thread tension adjuster based on the comparison result. ..

According to the prior art, the upper thread consumption is measured by detecting the rotational speed of the rotary roller around which the upper thread drawn from the supply source mounted on the machine frame of the sewing machine is wound, and from this rotational speed. It is designed to estimate the needle thread consumption.

In actual sewing, the upper shaft phase range in which the upper thread is pulled from the thread tension device to the balance side is almost the entire thread tightening phase range in which a stitch is formed at the needle entry point by the sewing machine. It has been confirmed that in the upper axis phase range before that, there is almost no movement of the upper thread between the upper thread supply source and the thread tension regulator.

Therefore, it is technically impossible to detect or estimate the upper thread consumption amount or the estimated value thereof which cannot be detected unless the thread tightening is completed before the thread tightening phase range. However, there is a problem that it cannot be put to practical use.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an automatic thread tensioning device which solves the technical inconsistency of the above-mentioned prior art and enables controllable threading with a good thread tension. ..

[0007]

SUMMARY OF THE INVENTION In order to solve the problems of the prior art, the present invention provides, in a sewing machine, upper shaft phase detecting means for detecting a plurality of upper shaft phases of the sewing machine, and detection by the detecting means. A sewing machine having an upper thread consumption detecting means for detecting the upper thread consumption in the upper thread consumption detection phase and a thread tensioner capable of controlling the pressing force applied to the upper thread, the sewing machine being selected. Needle thread necessary amount calculation storage means comprising upper thread necessary amount calculation means for calculating the necessary amount of upper thread between needle drops in advance based on pattern data etc. of the pattern and means for storing the calculation result in the required upper thread amount storage means. And a comparison calculation means for calculating the difference between the upper thread consumption amount and the required upper thread amount, and thread tension correction for reading the corresponding correction data from the correction data storage means based on the calculation result and storing it in the correction data temporary storage means. Preparation means and the upper axis phase detection Sewing machine automatic thread tensioning device for correcting and controlling the pressing force of the thread tensioner based on the temporarily stored correction data for forming the next stitch in the next thread tensioner control phase range detected by the means. Is provided.

[0008]

According to the present invention, by comparing the required upper thread amount calculated in advance with the actual upper thread consumption amount, the appropriate correction data is read from the correction data storage means. The pressure applied to the needle thread of the thread tension regulator is corrected based on the correction data, and the needle thread tension is used to tighten the thread for stitch formation in the next cycle. Therefore, the needle thread tension is always good. It is automatically corrected so that it can be converged into a proper state, and there is an effect that sewing can be performed with a good thread tension.

[0009]

【Example】

(1) Configuration Hereinafter, the present invention will be described with reference to examples. First, the outline of the upper yarn path will be described with reference to FIG. The needle thread T pulled out from the thread spool 1 as the source of the needle thread set on the sewing machine head is guided by the guide portions 2 and 3, the thread tension adjuster 10, the detection wheel 22 of the needle thread consumption detecting means 20, and the bending. Information section 4
The thread take-up spring (not shown), the balance 5, the thread guide portion 6, the needle bar thread hook 7 and the like are guided to the needle hole 8a of the sewing machine needle 8.

Next, the configurations of the thread tension regulator and the upper thread consumption amount detecting means will be described with reference to FIG. In FIG. 3, the thread tension device 10 includes a thread tension shaft 11 and a fixed thread tension disc 1.
2 and the movable thread tension tray 13 are arranged, and the movable thread tension tray 1 is provided.
3 is pressed against the fixed thread tension disc 12 by a spring 14 arranged on the thread tension shaft 11. In the thread tension shaft 11,
An adjusting member 15 having a pin portion 15a is slidably arranged, and the pin portion 15a is a pulse motor TM for thread tension control.
Slot 17 of the control link 17 fixed to the output shaft 16 of the
engaged with a. The stop member 18 is fixed to the thread tension shaft 11 and limits the movable range of the adjusting member 15.

The pressing force applied to the needle thread T of the thread tension regulator 10 is controlled by rotating the output shaft 16 and controlling the compression length of the spring 14 via the control link 17 and the adjusting member 15. This is performed by controlling the pressing force of the movable thread tension disc 13 against the thread tension disc 12.

The upper thread T pulled out from the thread spool 1 is guided to the thread tensioner 10, and is guided to the guide pin 21, the groove 22a of the detection wheel 22 of the upper thread consumption amount detecting means 20 and the guide pin 23, and further. As described above, it is guided by other necessary guide members and the like, and is guided to the balance 5 and the sewing machine needle 8.

The detection wheel 22 of the upper thread consumption amount detecting means 20 is
It is fixed to a shaft 25 that is rotatably supported by the machine frame of the sewing machine together with the light shielding plate 24, and can be rotated by a slight torque. The torsion coil spring 26 disposed on the shaft 25 causes the timepiece of FIG. When the detection wheel 22 is biased in the direction and no external force is applied to the detection wheel 22, the light shielding plate 24 is locked by the pin 27 arranged on the machine frame of the sewing machine as shown by the two-dot chain line in the figure.

The thread tension device 10 applies a pressing force to the upper thread T above a certain level necessary for sewing, and the balance 5 is raised to tighten the thread for forming a stitch, and the upper thread T is thread tensioned. When it is pulled over 10 to the side of the balance 5, the detection wheel 22 moves to the groove 2
Due to the frictional force of the upper thread T guided by the 2a, the light shielding plate 25 is rotated counterclockwise against the biasing force of the torsion coil spring 26.

In the thread loosening phase of the cycle next to the thread tightening start phase A, which will be described later with reference to FIG. 5, when the thread tension controller 10 controls the thread loosening and the pressing force on the upper thread T becomes a certain value or less,
The frictional force between the detection wheel 22 and the upper thread T becomes weak, and the spring 26
Due to the clockwise urging force of the
Accordingly, the light shielding plate 24 is brought into an initial state in which it is locked by the pin 27.

A light emitting element 30 is arranged in front of the light shielding plate 24, and a light guide member 31 is arranged with the light shielding plate 24 interposed therebetween. The light guide member 31 is configured by densely inserting the tips of the thin glass fibers 32 into a plurality of guide holes 31a in a flocked shape. The glass fiber 32 drawn out from the light guide member 31 is guided to the converging member 33 that bundles the glass fiber 32 at the rear end, and the light from the light emitting element 30 is received by the light receiving element 35 via the condenser lens 34. There is.

At the initial position of the detection wheel 22, the light shield plate 24 is locked to the pin 27, and at this position the light shield plate 2 is held.
No. 4 completely shields the light of the light emitting element 30, and at the time of tightening the thread for forming the stitch, the light shielding ratio of the light shielding plate 24 to the light guide member 31 changes according to the consumed upper thread consumption amount. , The light-receiving element 35 extracts the change with a current, converts it into a voltage and amplifies it, and an A / D converter (not shown)
The central processing unit C is used as digital data for the upper thread consumption.
Send to PU. Light guide member 3 by upper thread consumption and light shield 24
The relationship with the ratio of shading to 1 has been obtained in advance by many experiments, and the upper thread consumption amount can be detected from the ratio of shading.

(2) Sewing Machine Control Unit Next, the structure of the sewing machine control unit will be described with reference to FIG. The central processing unit CPU is provided with a pattern selecting means 40 for selecting a sewing pattern of the sewing machine and a start / stop switch 4 for instructing the operation and stop of the sewing machine.
1, upper shaft phase detecting means 42 for detecting a plurality of rotational phases, which will be described later, of the upper shaft of the sewing machine, and upper thread consumption detecting means 20 for detecting the upper thread consumption at the time of sewing are connected.

Further, the central processing unit CPU has a manual switch 4 which can be manually operated according to the thickness of the cloth to be sewn.
3 is connected. That is, the automatic thread tension device of the present embodiment is intended for a work cloth having a standard cloth thickness, and when the manual switch 43 is not operated, the thread tension control assuming the standard cloth thickness is performed, When the resulting work cloth is thicker than the standard and vice versa, it is for manually designating them to perform more preferable thread tension control.

Further, the central processing unit CPU has a lead
Only memory ROM and random access memory RAM are connected.

The read-only memory ROM is provided with a plurality of storage areas. For convenience of description, these are shown as independent components, and they are stored with a control program for controlling the entire sewing machine including thread tension control. Correction program storage means ROM1 and correction data storage means RO in which correction data for controlling the thread tension device 10 are stored.
M2, pattern data storage means ROM3 in which sewing pattern data for sewing patterns of the sewing machine are stored, display data storage means ROM4 in which sewing pattern display data is stored, and the like.

The random access memory RAM is provided with a plurality of storage areas, and for convenience, they are shown as independent components, which are based on the pattern data of the selected sewing pattern and the cloth thickness prepared in advance. Necessary needle thread amount storing means RAM1 for storing the calculated necessary needle thread amount data between the respective needle drops, and correction data temporary storage for temporarily storing the correction data corresponding to the condition read from the correction data storing means ROM1 at the time of sewing. It comprises a means RAM 2 and a work memory RAM 3 for temporarily storing various data and the like generated during the control program execution processing.

The central processing unit CPU further has a liquid crystal display unit LCD as a display means via a display control circuit LCDC.
Is connected and various displays related to sewing are displayed.

The amplitude pulse motor XM, the feed pulse motor YM, the sewing machine motor ZM and the thread tension control pulse motor TM are respectively in this order the amplitude pulse motor driver XDV, the feed pulse motor driver YDV, the sewing machine motor driver ZDV and the thread. It is connected to the central processing unit CPU via a driver TDV of a tension motor controlling pulse motor TM (hereinafter, thread tension motor TM).

The pulse motor XM for amplitude and the pulse motor YM for feed are synchronized with the upper shaft pulse from the upper shaft phase detecting means during the operation of the sewing machine by the sewing machine motor ZM, and the driving means of the sewing machine and the respective driving means of the feeding device are controlled. The thread tension motor TM is controlled by the upper shaft phase detecting means 4 as described later.
The thread loosening control and the pressing force control of the thread tension regulator 10 are performed at each phase detected in 2.

(3) Calculating Method of Needle Needle Needle Next, a method of calculating the required needle thread will be described. First, the sewing pattern is divided into a sewing pattern group for the purpose of sewing strength such as straight line stitching and a sewing pattern group for decorative purposes such as one-point stitching and letter stitching to join the cloths together. Assuming a cloth, for sewing pattern groups for the purpose of sewing strength, make sure that the upper thread and the lower thread intersect in the vicinity of the center of the cloth and the sewing pattern group for decoration purposes. On the other hand, the upper thread consumption amount is calculated so that the upper thread intersects with the lower thread near the back surface of the cloth.

That is, for the sewing pattern of the sewing pattern group for the purpose of sewing strength, first, the upper thread necessary amount calculation formula is the feed amount 2 for the straight stitch portion and the feed amount 2 for the zigzag stitch portion. This is an expression in which the square root of the sum of the square of the square and the amplitude amount is obtained, and the value of the cloth thickness is added to each of these values.

Similar to the above, the arithmetic expression of the needle thread required amount for the sewing pattern of the sewing pattern group for the purpose of decoration is as follows: first, the feed amount for the straight stitch portion, the square of the feed amount and the amplitude for the zigzag stitch portion. This is an equation in which the square root of the sum of the squares of the quantities is obtained, and a value twice the cloth thickness is added to each of these values.

As the cloth thickness data used for the calculation, in addition to the standard cloth thickness data, the cloth thickness data for thin and thick materials are prepared. When the manual switch 43 is not operated, the standard cloth thickness data is the cloth thickness data. The data is used for calculation, and when the manual switch 43 is operated to specify a thin material or a thick material, cloth thickness data for the thin material or the thick material is used for calculation.

The correction data stored in the correction data storage means ROM2 is obtained from the value of the difference between the actually consumed upper thread consumption amount and the upper thread necessary amount stored in the upper thread necessary amount storage means RAM1. The corresponding correction data is read out by referring to the correction data storage means ROM2, stored in the correction data temporary storage means RAM2, and the pressing force control of the thread tension regulator 10 is performed prior to thread tightening for stitch formation in the next cycle. Used for correction.

With respect to the correction data stored in the correction data storage means ROM2, the difference between the actually consumed upper thread consumption amount and the required upper thread amount stored in the required upper thread required amount storage means RAM1 is calculated. If the value is, for example, on the positive side, it is assumed that the current upper thread tension is weaker than the lower thread tension, and the upper thread pressing force by the thread tensioner 10 is currently measured prior to thread tightening in the formation of stitches in the next cycle. If the correction data for controlling to be stronger than that is specified, and conversely the value of the difference is on the negative side, in order to control the pressing force of the upper thread by the thread tensioner 10 to be stronger than the present condition. Correction data is designated.

(4) Each upper shaft rotation phase Next, each upper shaft rotation phase of the lockstitch sewing machine will be described with reference to FIG. In the figure, the horizontal axis represents the upper axis rotation phase of the sewing machine, the curve a is a motion locus offset to the upper end position of the needle hole of the sewing machine needle 8 by the vertical amount of the needle bar, and the curve b.
Indicates the vertical amount of the balance. Both the vertical amount of the needle bar and the vertical amount of the balance are displayed by the dimension of the vertical axis in the figure, but the dimension of the vertical axis has a different reference point and magnification. Further, in the same figure, illustration of other trajectories such as feeding is omitted.

Here, the sewing process will be briefly described. When you start the sewing machine from the vicinity of the top dead center of the needle bar,
The needle bar descends, the balance 5 which once rises turns to descend, passes the thread loosening phase C described later, and the thread amount on the balance gradually increases, and the sewing machine needle 8 attached to the needle bar becomes the work cloth. , The needle bar starts to rise from the bottom dead center, the hook point of the hook catches the upper thread loop formed on the sewing machine needle 8, passes the thread tensioner control phase D described later, and the phase needle bar top dead center. After that, the balance 5 continues to move upward, and the balance 5 starts thread tightening from the thread tightening start phase A slightly before the top dead center of the balance, and the thread tightening is completed at a phase near the top dead center of the balance and the stitch It is formed.

At the time of forming a stitch by thread tightening after the second stitch in the thread tightening start phase A, the upper thread consumption detected in the upper thread consumption detection phase B after the thread tightening start phase A is calculated in advance. The difference from the required needle thread amount is calculated, and the corresponding correction data is read from the correction data storage means ROM2 based on the sign and the magnitude of this difference value, stored in the correction data temporary storage means RAM2, and sewn in the next cycle. It is used as correction data for the control of the thread tension regulator 10 prior to thread tightening for forming stitches.

When the upper shaft phase detecting means 42 detects the thread loosening phase C, the thread tension motor TM controls the thread loosening phase C.
Thread loosening control is performed, and the pressing force of the thread tension unit 10 on the upper thread T is controlled to be a certain value or less.

When this thread loosening control is performed, the thread tension controller 10 is operated from the upper thread supply source at the time of thread tightening for forming the stitch in the previous cycle.
The frictional force between the upper thread T and the detection wheel 22 that has been rotated counterclockwise by the upper thread T that has passed through the
The torsion coil spring 26 rotates the detection wheel 22 together with the light shield plate 24 in the clockwise direction in FIG. 3, and the light shield plate 24 returns to the initial position where it is locked by the pin 27.
Shuts off the light-guiding member 31 from the light emitting element 30, and the preparation for detecting the upper thread consumption amount at the time of thread tightening in the next cycle is completed.

When the thread tension control phase D is detected, the thread tension motor TM starts controlling the thread tension controller 10 based on the correction data stored in the correction data temporary storage means RAM2. The control data of the thread tension adjuster 10 for the stitches up to the second stitch, the correction data of which is not stored in the correction data temporary storage means RAM2, is given as default value data for applying a standard pressing force to the needle thread T.

(5) Control Procedure The control procedure of the automatic thread tension device of this embodiment will be described below with reference to FIG. In the figure, Sn (n =
, 1, 2, 3 ...) Indicate the processing steps of each control.

When the power of the sewing machines S1 and S2 is turned on, the program starts,
When a desired sewing pattern is selected by the pattern selecting means 40 in S1, the required needle thread amount between needle drop points is calculated from the pattern data of the sewing pattern selected in S2 and the standard cloth thickness data prepared in advance. The upper thread necessary amount storage means RAM1 is stored. This processing step is a needle thread required amount calculation storage means as a function realizing means by a program.

S3 Waiting for key input of the start / stop switch 41, and when there is a start command from the start / stop switch 41, the sewing machine starts operation.

S4, S5 When the upper shaft phase detecting means 42 reaches the thread loosening phase indicated by the symbol C in FIG. 5, the pressing force of the thread tensioner 10 on the upper thread T is controlled to a certain weak value in S5. .. Thread tension device 10
Is controlled by controlling the thread tension motor TM. This thread loosening control is performed prior to the formation of stitches, and is control for returning the detection wheel 22 of the needle thread consumption amount detecting means 20 to the initial state.

S6, S7 In S6, the thread tension regulator control phase D from the upper shaft phase detecting means 20.
Is determined. When the thread tensioner control phase shown by D in FIG. 5 is reached, the pressing force of the thread tensioner 10 is controlled by the control of the thread tension motor TM based on the correction data in S7. This control is performed after the seam of the second needle is formed and before the seam of the third needle is formed, and thereafter, the control of the pressing force is similarly continued. The thread tensioner until the stitch formation of the second needle is controlled such that the standard upper thread tension acts on the upper thread T by the default value.

S8, S9 At S8, it is judged if the thread tightening start phase A has been reached. When the thread tightening start phase indicated by the symbol A in FIG. 5 is reached, thread tightening is performed in S9 to form a stitch, and the upper thread T is threaded by the thread tension adjuster 10.
And is supplied to the balance 5 side, the friction force of the upper thread T acts on the detection wheel 22, and the detection wheel 22 turns the torsion coil spring 26.
The light-shielding plate 24 is rotated counterclockwise by an amount corresponding to the upper thread feeding amount against the biasing force.

S10, S11 At S10, it is judged if the upper thread consumption amount detection phase B has been reached. When the phase shown by the symbol B in FIG. 7 is reached, the upper thread consumption amount detection means 20 detects the upper thread consumption amount in S11.

S12 The difference between the detected upper thread consumption amount and the required upper thread amount stored in the upper thread required amount storage means RAM1 is calculated. This processing step is a comparison calculation means as a function realizing means by a program.

S13 The correction data of the corresponding thread tension regulator is read from the correction data storage means ROM2 based on the sign and the magnitude of the difference between the upper thread consumption amount and the upper thread consumption amount, and the read correction data is corrected. The data is temporarily stored in the data temporary storage means RAM2. This processing step is a thread tension correction preparation means as a function realizing means by a program. This correction data is used as correction data for controlling the thread tension regulator 10 prior to thread tightening for stitch formation in the next cycle.

S14 The processing from S4 is repeatedly executed until the stop command for stopping the operation of the sewing machine is executed, and the sewing is performed in a preferable intersecting state of the upper thread and the lower thread. When there is a stop command, this flowchart is exited.

[0048]

As described above, according to the present invention, by comparing the required amount of the upper thread obtained by the calculation in advance with the actually consumed amount of the upper thread, it is possible to determine the appropriate value from the correction data storage means. The correction data is read out, the pressing force to the needle thread of the thread tension regulator is corrected by the correction data, and the thread tension for the stitch formation of the next cycle is performed by the needle thread tension. However, it is automatically corrected so that it always converges to a good state, and the effect is obtained that sewing can be performed with a good thread tension.

[Brief description of drawings]

FIG. 1 is a block diagram of a control circuit

FIG. 2 is a perspective view of the main part of the sewing machine showing the path of the upper thread.

FIG. 3 is a perspective view showing the main parts of the thread tension regulator and the needle thread consumption amount detecting means.

FIG. 4 is a flowchart showing a control processing procedure.

FIG. 5 is a diagram showing a part of a motion diagram of the sewing machine.

[Explanation of symbols]

 8 needles 10 thread tensioner 20 needle thread consumption amount detecting means 40 pattern selecting means 42 upper shaft phase detecting means 43 manual switch B needle thread consumption amount detecting phase D thread tensioner control phase RAM1 needle thread necessary amount storing means RAM2 correction data temporary Storage means ROM2 Correction data storage means ROM3 Pattern data storage means S2 Needle thread required amount calculation storage means S12 Comparison calculation means S13 Thread tension correction preparation means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Sumiyoshi 3-1-1, Kyobashi, Chuo-ku, Tokyo Janome Sewing Machine Co., Ltd.

Claims (5)

[Claims] 1. A pattern data storage means for storing pattern data for a plurality of sewing patterns of a sewing machine, a pattern selecting means for selecting a desired sewing pattern, and a selected sewing pattern having needles that move up and down. In a sewing machine including a stitch forming mechanism that forms a stitch on a work cloth in synchronism with the upper axis rotation of the sewing machine based on the pattern data for the upper axis phase detecting means for detecting a plurality of upper axis phases of the sewing machine, A sewing machine comprising an upper thread consumption detecting means for detecting the upper thread consumption in the upper thread consumption detecting phase detected by the detecting means, and a thread tensioner capable of controlling a pressing force applied to the upper thread. The upper thread required amount calculation means for calculating the upper thread required amount between the needle drops in advance based on the pattern data of the selected sewing pattern and the means for storing the calculation result in the upper thread required amount storage means. Thread necessary amount calculation storage means, and Comparing calculation means for calculating the difference between the consumption amount and the required needle thread amount, and thread tension correction preparation means for reading the corresponding correction data from the correction data storage means based on the calculation result and storing it in the correction data temporary storage means In the next thread tensioner control phase detected by the upper shaft phase detecting means, the pressing force of the thread tensioner is corrected and controlled by the temporarily stored correction data for thread tightening in the next cycle. Automatic thread tension device for sewing machines. 2. The upper thread necessary amount calculating means calculates the upper thread necessary amount based on the pattern data of the selected sewing pattern and standard cloth thickness data prepared in advance. An automatic thread tension device for a sewing machine according to Item 1. 3. A pattern data storage means for storing pattern data for a plurality of sewing patterns of a sewing machine, a pattern selecting means for selecting a desired sewing pattern, and a selected sewing pattern having vertically moving needles. In a sewing machine including a stitch forming mechanism that forms a stitch on a work cloth in synchronism with the upper axis rotation of the sewing machine based on the pattern data for the upper axis phase detecting means for detecting a plurality of upper axis phases of the sewing machine, A sewing machine including upper thread consumption detecting means for detecting the upper thread consumption at the upper thread consumption detecting phase detected by the detecting means, and a thread tensioner capable of controlling the pressing force applied to the upper thread. , The manual switch that can specify the cloth thickness according to the thickness of the work cloth by manual operation, and the needle thread required to calculate the needle thread required amount between each needle drop in advance based on the selected sewing pattern data etc. Amount calculation means and calculation result Needle thread required amount calculation storage means including means for storing in the required amount storage means, comparison calculation means for calculating a difference between the upper thread consumption amount and the required upper thread amount, and correction data storage means based on the calculation result. And thread tension correction preparation means for reading out the corresponding correction data from the above and storing it in the correction data temporary storage means for tightening the thread in the next cycle at the next thread tensioner control phase detected by the upper shaft phase detection means. An automatic thread tension device for a sewing machine, which corrects and controls the pressing force of the thread tension device based on the temporarily stored correction data. 4. When the manual switch is operated, the required needle thread amount is calculated based on the cloth thickness data for a thin material or the cloth thickness data for a thick material prepared in advance, in addition to the sewing pattern data in accordance with the operation. The automatic thread tension device for a sewing machine according to claim 3, wherein: 5. A sewing pattern is divided into a sewing pattern group for the purpose of sewing strength and a sewing pattern group for the purpose of decoration, and the needle thread required amount calculating means is different for the two types of sewing pattern groups. The automatic thread tension device for a sewing machine according to any one of claims 1 to 4, wherein the required amount of the upper thread is calculated by an arithmetic expression.