Sewing machine and control method thereof

Abstract

A sewing machine includes a thread take-up lever that supplies an upper thread to a needle from a thread supply source, a hook which catches the upper thread inserted in the needle, and which intertwine the upper thread with a lower thread, and a control unit that controlling a hook release phase at which the hook releases the upper thread in such a way that a hook/upper-thread necessary amount that is necessary when the upper thread is intertwined with the lower thread becomes smaller than a thread-take-up-lever/upper-thread supply amount that is supplied by an operation of the thread take-up lever. The control unit controls the hook release phase at a plurality of timings.

Claims

1. A sewing machine comprising: a thread take-up lever supplying an upper thread to a needle from a thread supply source; a hook catching the upper thread inserted in the needle, and intertwining the upper thread with a lower thread; a rotatable upper shaft driving a needle bar that supports the needle, and the thread take-up lever; a rotatable lower shaft driving the hook; an upper-shaft pulley provided at the upper shaft; a lower-shaft pulley provided at the lower shaft; a belt coupling the upper-shaft pulley and the lower-shaft pulley and synchronizing respective rotations; a belt adjusting mechanism contacting the belt and changing a belt length at a tensioned side where the belt is drawn in; and a control unit controlling a hook release phase, at which the hook releases the upper thread, in such a way that a hook/upper-thread necessary amount that is an upper thread length being required when the upper thread goes around an inner hook in which the lower thread is retained and corresponding to an outer circumference of the inner hook becomes smaller than a thread-take-up-lever/upper-thread supply amount that is supplied by an operation of the thread take-up lever, wherein the control unit controls and changes a timing at which the belt adjusting mechanism changes the belt length at the tensioned side and controls the hook release phase at a plurality of timings.

2. The sewing machine according to claim 1, wherein the control unit controls, at a timing before the hook release phase, the hook release phase so as to advance the hook release phase.

3. The sewing machine according to claim 1, wherein: the belt adjusting mechanism comprises at least one idler contacting the belt at the tensioned side; and the belt length at the tensioned side is changed by swinging the idler.

4. A control method of a sewing machine comprising a thread take-up lever supplying an upper thread to a needle from a thread supply source, a hook catching the upper thread inserted in the needle, and intertwining the upper thread with a lower thread, a rotatable upper shaft driving a needle bar that supports the needle, and the thread take-up lever, a rotatable lower shaft driving the hook, an upper-shaft pulley provided at the upper shaft, a lower-shaft pulley provided at the lower shaft, a belt coupling the upper-shaft pulley and the lower-shaft pulley and synchronizing respective rotations, and a belt adjusting mechanism contacting the belt and changing a belt length at a tensioned side where the belt is drawn in, the method comprising: controlling and changing a timing at which the belt adjusting mechanism changes the belt length at the tensioned side and controlling, at a plurality of timings, a hook release phase at which the hook releases the upper thread in such a way that a hook/upper-thread necessary amount that is an upper thread length being required when the upper thread goes around an inner hook in which the lower thread is retained and corresponding to an outer circumference of the inner hook becomes smaller than a thread-take-up-lever/upper-thread supply amount that is supplied by an operation of a thread take-up lever.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an explanatory diagram illustrating an example general structure of a sewing machine according to a first embodiment;

(2) FIG. 2 is a functional block diagram illustrating an example structure of a control unit C of the first embodiment;

(3) FIG. 3 is an explanatory diagram illustrating how a needle and a hook tip form a stitch;

(4) FIG. 4 is an explanatory diagram illustrating a change in the position of the needle, and a change in a relative operation between the needle and the hook tip in accordance with the change in the needle position;

(5) FIG. 5 is an explanatory diagram illustrating a change in the position of an idler unit, and a change in a relative operation between the needle and the hook tip in accordance with the change in the idler unit position;

(6) FIG. 6 is an operation diagrammatic drawing indicating a change in a loosened upper thread caused by the operation of a thread take-up lever and that of the hook when straight sewing is performed without a needle/hook intersecting phase control;

(7) FIG. 7 is an operation diagrammatic drawing illustrating a change in the loosened upper thread caused by the operation of the thread take-up lever and that of the hook when straight sewing is performed at a right base line position where a needle/hook intersecting phase is controlled by a phase difference ;

(8) FIG. 8 is an operation diagrammatic drawing illustrating a change in the loosened upper thread caused by the operation of the thread take-up lever and that of the hook when zig-zag sewing is performed without the needle/hook intersecting phase control;

(9) FIG. 9 is an operation diagrammatic drawing illustrating a change in the loosened upper thread caused by the operation of the thread take-up lever and that of the hook when zig-zag sewing is performed and the needle/hook intersecting phase is controlled by the phase difference ; and

(10) FIG. 10 is an operation diagrammatic drawing illustrating a change in the upper thread caused by the operation of the thread take-up lever and that of the hook when the present invention is applied to the case in FIG. 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

1. First Embodiment

(11) [1-1. Structure]

(12) An embodiment of the present disclosure will be explained with reference to the accompanying drawings. In the following explanation, a structure that adjusts a timing at which a needle and a hook in a sewing machine intersect will be mainly explained. The explanation for a detailed structure of a sewing machine will be omitted, but the embodiment of the present disclosure is applicable to all sewing machines available currently or in future like a zig-zag stitching sewing machine. FIG. 1 illustrates an example general structure of a sewing machine of this embodiment.

(13) (1) General Structure

(14) The sewing machine includes a needle bar 1 and a hook. The needle bar 1 supports a needle 1b that has a needle hole 1a into which an upper thread is inserted. The upper thread is supplied to the needle 1b from a thread supply source through a thread take-up lever 8. The thread take-up lever 8 changes the amount of the upper thread to be supplied to the needle 1b. The hook includes an unillustrated inner hook that retains therein a bobbin around which a lower thread is wound, and an outer hook 2 that catches the upper thread. The outer hook 2 catches the upper thread through a tip 2a.

(15) The sewing machine of this embodiment includes a control unit C that controls a hook release phase, at which the hook releases the upper thread, in such a way that the hook/upper-thread necessary amount becomes smaller than the thread-take-up-lever/upper-thread supply amount. The control unit C controls the hook release phase at plural timings. The hook/upper-thread necessary amount means a necessary amount of upper thread when the upper thread inserted in the needle 1b is intertwined with the lower thread retained in the inner hook. The thread-take-up-lever/upper-thread supply amount means an amount of the upper thread to be supplied to the needle 1b by the thread take-up lever 8 that operates up and down at a predetermined timing.

(16) (2) Needle/Hook Operation Mechanism

(17) The needle bar 1 and the thread take-up lever 8 are linked with an upper shaft 3 through a crank mechanism. The hook is linked with a lower shaft 4 through a gear mechanism. The upper shaft 3 and the lower shaft 4 are supported rotatably by respective unillustrated bearings fixed in the sewing machine. Drive force from an unillustrated sewing machine motor is transferred to the upper shaft 3.

(18) The crank mechanism of the upper shaft 3 converts the rotation of the upper shaft 3 into a reciprocal motion, thereby moving the needle bar 1 and the thread take-up lever 8 up and down. The upper shaft 3 is provided with a swing mechanism 5 that swings the needle bar 1. When the swing mechanism 5 swings the needle bar 1 with the drive force by a swing motor 5a in a direction intersecting with a cloth feeding direction, zig-zag stitches are formed.

(19) The upper shaft 3 is fixed with an upper-shaft pulley 3a that has a predetermined number of teeth. In addition, the lower shaft 4 is fixed with a lower-shaft pulley 4a that has the same number of teeth as that of the upper-shaft pulley 3a. The upper-shaft pulley 3a and the lower-shaft pulley 4a are coupled with each other through a toothed belt 6. The length of the toothed belt 6 is set so as to produce a predetermined slack when the toothed belt 6 is hung between the upper-shaft pulley 3a and the lower-shaft pulley 4a.

(20) When the upper shaft 3 rotates, the upper-shaft pulley 3a also rotates. This rotation is transferred to the lower-shaft pulley 4a through the toothed belt 6, and thus the lower shaft 4 rotates at the same speed as that of the upper shaft 3. The gear mechanism of the lower shaft 4 rotates the hook 2 together with the rotation of the lower shaft 4.

(21) (2) Belt Adjusting Mechanism

(22) A belt adjusting mechanism contacts the toothed belt 6 to adjust the belt length of the toothed belt 6 at the tensioned side A. The belt adjusting mechanism changes the timing of the rotation of the lower shaft 4, thereby correcting a needle/hook intersecting phase that is a timing at which the needle 1b and the hook 2 meet each other. In this embodiment, an explanation will be given of an idler unit 7 as an example. The idler unit 7 includes idlers 7a, 7b that contact the toothed belt 6 at the tensioned side A and a loosened side B, respectively. It is appropriate if the idler unit 7 has at least one idler at the tensioned side A.

(23) In this case, the tensioned side A of the toothed belt 6 means a side where the upper-shaft pulley 3a is newly meshed upon rotation of the upper-shaft pulley 3a, i.e., a side where the belt is drawn in. In addition, the loosened side B means a side where the upper-shaft pulley 3a is disengaged upon rotation of the upper-shaft pulley 3a, i.e., a side where the belt is drawn out. In the following explanation, the tensioned side A and the loosen side B are referred to as right and left, respectively in some cases.

(24) The idlers 7a, 7b are disposed at the tensioned side A and the loosened side B so as to hold the toothed belt 6 therebetween from the outer circumference of the toothed belt 6. The idlers 7a, 7b are coupled with a motor 7d through an arm 7c. The idlers 7a, 7b swing, by the drive force from a motor 7d, in accordance with an operation instruction from the control unit C. The motor 7d is connected with a motor drive unit 16 to be discussed later. When the idler unit 7 is operated, the slack of the toothed belt 6 is moved to the tensioned side A and the loosened side B. Hence, the belt length of the toothed belt 6 at the tensioned side A is changed in accordance with the swing of the needle bar 1. Accordingly, the timings of the respective rotations of the upper shaft 3 and the lower shaft 4 are controlled, and thus a timing at which the needle 1b and a tip 2a of the hook 2 meet is adjusted.

(25) (3) Control Unit

(26) The control unit C controls the hook release phase, at which the hook releases the upper thread, in such a way that the hook/upper-thread necessary amount becomes smaller than the thread-take-up-lever/upper-thread supply amount. The control unit C employs plural timings of changing the hook release phase. FIG. 2 is a functional block diagram illustrating a structure of the control unit C. More specifically, the control unit C is constructed by a computer or an exclusive electric circuit which includes a CPU, a memory, etc., connected with an input unit 11 and an output unit 12, and which is operated in accordance with a predetermined program. In this case, the program physically utilizes the hardware resources of the computer, etc., thereby executing the processes to be explained below.

(27) A method of executing each process explained below, a program, and a recording medium having stored therein the program are also aspects of this embodiment. In addition, how to set a range processed by hardware resources and a range processed by software resources that include the program is not limited to any particular way. For example, any one of the following units may be constructed as a circuit that executes each process.

(28) In this embodiment, the control unit C controls the timing at which the idler unit 7 that is the belt adjusting mechanism changes the belt length at the tensioned side A. The control unit C includes a stitch data memory 13, a needle/hook control timing memory 14, and a timing determining unit 15. In addition, the control unit C is connected with a motor drive unit 16 that drives the motor 7d in accordance with a control signal from the timing determining unit 15.

(29) The input unit 11 includes an input device that receives inputting of information by an operator, and an interface that notifies the control unit C of the input information. For example, the input unit 11 is input device for the operator to input an operation request and a change in set values to the sewing machine. Example input devices are operation buttons of the sewing machine, and a touch panel (including the touch panel placed on the display device of the output unit 12).

(30) The output unit 12 includes an interface that outputs information from the control unit C, and the display that displays, in accordance with the output information, screens for the operator to check and select the details of operation. The output unit 12 is to, for example, indicate an operation setting for the sewing machine, and display an alert for an operation given by the operator. An example display device is a display that includes a display screen like a liquid crystal display panel.

(31) The stitch data memory 13 stores pieces of stitch data corresponding to various stitch patterns including zig-zag stitches. Arbitrary stitch data can be selected through an operation button of the input unit 11. In addition, the output unit 12 may display pieces of stitch data upon operation given to the operation button of the input unit 11 to enable the operator to select the stitch data. The stitch data selected by the operator is input to the timing determining unit 15.

(32) The needle/hook control timing memory 14 stores plural timings of swinging the idler unit 7 relative to the swing of the needle bar 1. Hence, in this embodiment, a timing at which the idler unit 7 changes the belt length at the tensioned side A, i.e., the needle/hook control timing is changeable.

(33) That is, as a timing at which the idler unit 7 is moved to shorten the belt length at the tensioned side A and to retard the phase of the hook, a timing after the hook release phase may be applied, and as a timing at which the idler unit 7 is moved to elongate the belt length at the tensioned side A and to advance the phase of the hook, a timing before the hook release phase may be applied. The needle/hook control timing memory 14 also stores a constant timing of swinging the idler unit 7 in synchronization with, for example, the swing of the needle bar 1 by the swing mechanism 5.

(34) The timing determining unit 15 determines the timing of swinging the idler unit 7 based on the stitch data input from the stitch data memory 13. The timing determining unit 15 reads the determined timing from the needle/hook control timing memory 14, and outputs the read timing to the motor drive unit 16. When, for example, the width of zig-zag sewing in the input stitch data is the maximum, the timing determining unit 15 outputs the control signal to the motor drive unit 16 so as to control the idler unit 7 at plural needle/hook control timings. This is because when the width of zig-zag sewing is the maximum and the hook release phase comes at a timing at which the hook is retarded, the hook/upper-thread necessary amount exceeds the thread-take-up-lever/upper-thread supply amount, causing an abnormal noise or a thread breakage.

(35) When there is no possibility that, in the input stitch data, the hook/upper-thread necessary amount exceeds the thread-take-up-lever/upper-thread supply amount, the timing determining unit 15 determines a constant timing of, for example, swinging the idler unit 7 in synchronization with the needle bar 1. The timing determining unit 15 outputs the determined timing to the motor drive unit 16. The motor drive unit 16 controls the motor 7d in accordance with a control signal from the timing determining unit 15.

(36) [1.2 Operation]

(37) An example operation of the above-explained sewing machine will now be explained.

(38) (1) Stitch Formation

(39) With the upper thread inserted in the needle hole 1a of the needle 1b, and the bobbin around which the lower thread is wound being retained in the inner hook, when the upper shaft 3 is driven, stitches are formed. More specifically, when the upper shaft 3 is driven by the sewing machine motor, the crank mechanism converts the rotation of the upper shaft 3 into a reciprocal motion, and thus the needle bar 1 and the thread take-up lever 8 are moved up and down. In addition, the rotation of the upper shaft 3 is transferred to the lower shaft 4 through the upper-shaft pulley 3a, the toothed belt 6, and the lower-shaft pulley 4a. When the lower shaft 4 is rotated by the rotation of the upper shaft 3, the hook is rotated.

(40) In such operations, the needle 1b passes completely through a cloth, and reaches a needle bottom dead center. When the needle 1b is raised to some level, the upper thread cannot be pulled out to the top face of the cloth due to a friction therewith, and thus a thread loop is formed below the cloth. When the tip 2a of the outer hook 2 passes through the thread loop, the bobbin around which the lower thread is wound passes through the thread loop, and the upper thread and the lower thread are intertwined with each other, and thus a stitch is formed.

(41) (2) Thread Loop Formation

(42) The size of the thread loop depends on the level of the needle 1b is raised from the bottom dead center. In FIG. 3, the raised level of the needle 1b from the bottom dead center is indicated as a needle displacement . 1 indicates an under-displacement of the needle 1b. When the displacement of the needle 1b is too small like 1, it is difficult to form a thread loop, or even if the thread loop can be formed, the thread loop is too small, and the tip 2a cannot enter the thread loop. Conversely, 4 indicates an over-displacement of the needle 1b. When the displacement of the needle 1b is too large like 4, the thread loop becomes too large, and is collapsed by the self-weight of the thread or by twisting, and thus the tip 2a cannot enter the thread loop. As explained above, if the needle displacement is too small or too large, it is difficult to form a stitch.

(43) Hence, in order to form an appropriate stitch, the needle displacement should be set so as to enable the formation of the thread loop and to cause the tip 2a of the hook 2 to enter the thread loop. In FIG. 3, a necessary minimum displacement is indicated as 2, and an allowable maximum displacement is indicated as 3. In order to form an appropriate stitch, it is necessary to set the needle displacement to be equal to or larger than 2 but equal to or smaller than 3.

(44) (3) Trajectory of Needle at the Time of Zig-Zag Sewing in Conventional Sewing Machines

(45) The swing mechanism 5 swings the needle bar 1 by the drive force from the swing motor 5a so as to intersect with the cloth feeding direction, zig-zag stitches are formed. FIG. 4 illustrates, in conventional sewing machines, a change in the relative operation of the needle 1b and the tip 2a of the hook 2 when zig-zag sewing is performed. The horizontal axis in FIG. 4 represents the phases of the upper shaft 3 and the lower shaft 4, while the vertical axis represents the simulated trajectories of the tip of the needle 1b and the tip 2a of the hook 2. The trajectory of the tip 2a is slightly different from an actual trajectory, but is illustrated with a continuous line for the purpose of explanation. In the example in FIG. 4, it is presumed that the hook rotates in a counterclockwise direction.

(46) In FIG. 4, the needle 1b and the trajectory illustrated by thick lines indicate that the swing mechanism 5 is not actuated and the needle 1b is located at a center base line that is the center. In addition, the needle 1b and the trajectory illustrated by dashed lines indicate that the needle 1b swings from side to side by the swing mechanism 5. At the needle/hook intersecting phase in the figure, the needle 1b and the tip 2a are coming close to each other maximally. In such a needle/hook intersecting phase, the tip 2a enters the thread loop of the upper thread.

(47) As explained above, in order to form a stitch, it is necessary to set the needle displacement to be equal to or larger than the necessary minimum displacement 2 but equal to or smaller than allowable maximum displacement 3. At the time of zig-zag sewing, however, the position of the hook 2 is constant, but the needle 1b swings from side to side from the center base line, and thus the relative position of the needle 1b to the hook 2 changes. A change in the positional relationship affects the needle displacement.

(48) When, for example, in conventional sewing machines, representing the needle displacement when the needle 1b is moved to the right as R1, R1 is smaller than the needle displacement in the center-base-line condition. In addition, representing the needle displacement when the needle 1b is moved to the left as L1, L1 becomes larger than the needle displacement in the center-base-line condition. That is, even if the needle displacement in the center-base-line condition is set to be an appropriate value, when the needle 1b swings from side to side, R1 becomes smaller than the minimum necessary displacement 2 or L1 becomes larger than the allowable maximum displacement 3, and thus it sometime becomes difficult to form an appropriate thread loop.

(49) A change in the needle displacement due to a position change of the needle 1b increases in proportional to a swing level Z of the needle 1b which swings side to side. Hence, according to conventional sewing machines, a stitch can be formed only when the needle displacement satisfies a condition 2<R1<<L1<3. Accordingly, the maximum swing level Z is automatically determined. Hence, even if there is a need for sewing of a pattern that needs a larger swing than the automatically determined value, it is technically difficult to meet such a need.

(50) (4) Change in Relative Operation of Needle to Hook when Belt Adjusting Mechanism is Applied

(51) The belt adjusting mechanism corrects the needle displacement by changing the belt length of the toothed belt 6 at the tensioned side A. FIG. 5 illustrates a change in the relative operation of the needle 1b to the tip 2a of the hook 2 when the idler unit 7 that is the belt adjusting mechanism is moved. The horizontal axis of FIG. 5 represents the phases of the upper shaft 3 and the lower shaft 4, while the vertical axis represents the simulated trajectories of the tip of the needle 1b and the tip 2a of the hook 2. The trajectory of the tip 2a is slightly different from an actual trajectory, but is indicated by a continuous line for the purpose of explanation. In the example case in FIG. 5, it is presumed that the hook 2 rotates counterclockwise.

(52) FIG. 5 illustrates respective changes in the hook-tip trajectory when the idler unit 7 is located at the center position, the left position, and the right position. In the needle/hook intersecting phase in the figure, the needle 1b and the tip 2a are coming close to each other maximally. In this needle/hook intersecting phase, the tip 2a enters the thread loop of the upper thread. When the idler unit 7 is moved, the motion trajectory of the tip 2a of the hook 2 changes. Hence, the needle/hook intersecting phase also changes, and thus the raised level of the needle and the needle displacement both in the needle/hook intersecting phase change. In this case, it is presumed that the needle/hook intersecting phase when the idler unit 7 is located at the center position is 0, and the needle displacement in this case is .

(53) When, for example, the idler unit 7 is moved to the left, i.e., when the idler unit 7 is moved in a direction in which the idler 7a pushes the tensioned side A of the toothed belt 6, the length of the toothed belt 6 at the tensioned side A becomes long. When the length at the tensioned side A becomes long, in comparison with a case in which the idler unit 7 is located at the center position, a phase difference is produced between the upper shaft 3 an the lower shaft 4, the needle/hook intersecting phase is changed to a position that is , and the needle displacement decreases by relative to .

(54) In addition, when the idler unit 7 is moved to the right, i.e., when the idler unit 7 is moved in a direction in which the idler 7b pushes the loosened side B of the toothed belt 6, the length of the tensioned side A of the toothed belt 6 becomes short. When the length at the tensioned side A becomes short, in comparison with a case in which the idler unit 7 is located at the center portion, a phase difference is produced between the upper shaft 3 and the lower shaft 4, the needle/hook intersecting phase is changed to a position that is , and the needle displacement increases by relative to .

(55) The increase/decrease in the needle displacement due to the movement of the idler unit 7 is determined based on the position of the idler unit 7 regardless of the movement of the needle bar 1 by the swing mechanism 5. Hence, by swinging the idler unit 7, a decrease by or an increase by can be arbitrarily given to the needle displacement .

(56) As explained above, in conventional sewing machines, it is necessary to set the maximum value of the swing level Z to satisfy, for the needle displacement that changes in proportional to the swing level Z, a condition 2<R1<<L1<3. Conversely, according to the advantageous effects of the sewing machine of this embodiment, an increase/decrease in the needle displacement by the movement of the idler unit 7 can be determined based on the position of the idler unit 7 regardless of the movement of the needle bar 1 by the swing mechanism 5. Hence, when a setting is made so as to cancel the increase/decrease in the needle displacement by the movement of the needle bar 1 by the increase/decrease in the needle displacement by the movement of the idler unit 7, a condition 2<(R2+)<<(L2)<3 is satisfied. In this case, R2 is a needle displacement when the needle bar 1 swings maximally to the right in the sewing machine of this embodiment. Also, L2 is a needle displacement when the needle bar 1 swings maximally to the left in the sewing machine of this embodiment.

(57) When the needle displacement at the time of maximum swing to the right/left is compared between conventional sewing machines and the sewing machine of this embodiment, R1=R2+, and L1=L2 are satisfied. R2 can be reduced by relative to R1, while L2 can be increased by relative to L1. In this case, a difference between the needle displacement when the needle falls at the right side and the needle displacement when the needle falls at the left side is proportional to the swing level Z, i.e., according to the sewing machine of this embodiment, the maximum value of the swing level Z can be set larger than that of conventional sewing machines.

(58) Control of Idler Unit 7 by Control Unit C

(59) First, prior to the explanation for a control by the control unit C, a detailed explanation will be given to a relationship between the hook/upper-thread necessary amount and the thread-take-up-lever/upper-thread supply amount in plural sewing conditions.

(60) (a) Straight Sewing at Center Base Line

(61) FIG. 6 illustrates a relationship between the hook/upper-thread necessary amount and the thread-take-up-lever/upper-thread supply amount in a case of straight sewing. The vertical axis represents an amount of thread that increases as coming close to the origin. In addition, the horizontal axis represents a phase. The thread-take-up-lever/upper-thread supply amount that is supplied larger than the hook/upper-thread necessary amount is indicated by hatching in the figure as the loosened upper thread. In this graph, the tip 2a catches the upper thread at the needle/hook intersecting phase, and the upper thread goes through the inner hook at the hook release phase.

(62) It is not illustrated in FIG. 6, but the needle 1b moves up and down that has a motion trajectory of passing through the top dead center at the phase of 0 degree, and also passing through the bottom dead center at the phase of 180 degrees. At a needle/hook intersecting phase 1 subsequent to the bottom dead center, the needle 1b passes completely through a cloth and forms a thread loop of the upper thread below the cloth, and, this thread loop is caught by the tip 2a. In this case, in conjunction with the operation of the hook, the caught upper thread goes through the inner hook that retains therein the lower thread. At this time, the upper thread temporarily needs a length by what corresponds to the portion of the upper thread that goes through the inner hook. Hence, after the needle/hook intersecting phase 1, the hook/upper-thread necessary amount gradually increases, and becomes the maximum right before a hook release phase 2 where the inner hook releases the upper thread.

(63) The thread take-up lever 8 goes down in accordance with the increasing hook/upper-thread necessary amount. Hence, the thread-take-up-lever/upper-thread supply amount gradually increases. Accordingly, the operation of the thread take-up lever 8 supplies the hook/upper-thread necessary mount at the hook release phase 2, and thus a sufficient loosened upper thread L is maintained. The thread-take-up-lever/upper-thread supply amount becomes the maximum right before the hook release phase 2, but after the hook release phase 2 at which the upper thread goes through the hook, the hook/upper-thread necessary amount remarkably decreases. Accordingly, the loosened upper thread increases rapidly.

(64) Conversely, the thread take-up lever 8 changes its operation to an operation of collecting the upper thread, and thus the loosened upper thread that has rapidly increased is quickly decreased. Through the above-explained successive operations, a sewing operation is performed while maintaining the certain loosened upper thread. When the loosened upper thread becomes insufficient, it causes a thread breakage, but when the loosened upper thread increases excessively, a thread breakage or a thread tightness failure is caused due to the excessive vibration of the thread and the snarl of the thread. Therefore, the loosened upper thread should be increased or decreased only in accordance with a need.

(65) (b) Straight Sewing with Needle/Hook Intersecting Phase Control

(66) When, for example, the needle 1b is moved to a right base line from the center base line, and a change in the needle displacement due to the movement of the needle 1b is corrected by a needle/hook intersecting phase control that moves the idler unit 7, as explained above, the idler unit 7 is moved in the direction in which the idler 7b pushes the loosened side B, and thus the length of the toothed belt 6 at the tensioned side A becomes short. When the length at the tensioned side A becomes short, the needle/hook intersecting phase is controlled by a phase difference . Hence, as illustrated in FIG. 7, in comparison with the hook release phase 1, a hook release phase 1 is retarded by the phase difference , and a loosened upper thread L2 at the hook release phase becomes shorter than L. In this case, however, the loosened upper thread is not insufficient.

(67) (c) Zig-Zag Sewing without Needle/Hook Intersecting Phase Control

(68) As explained above, when zig-zag sewing is performed, the needle bar 1 swings and moves from side to side in a swing phase while the outer hook 2 is catching the upper thread. That is, the upper thread inserted in the needle hole of the needle 1b moves from side to side. Hence, as illustrated in FIG. 8, the hook/upper-thread necessary amount increases by what corresponds to the swing level Z of the needle 1b. In this case, however, the hook/upper-thread necessary amount at the hook release phase 2 can be supplied by the operation of the thread take-up lever 8, and thus a sufficient loosened upper thread L3 is maintained.

(69) (d) Zig-Zag Sewing with Needle/Hook Intersecting Phase Control

(70) As explained above, the setting is made, in any conditions, such as straight sewing and zig-zag sewing at a constant swing level, so that the loosened upper thread does not become insufficient although the loosened upper thread decreases. Conversely, according to a sewing machine disclosed in JP 2008-264500 A which can set the maximum value of the swing level Z to be further large through a needle/hook intersecting phase control, the retard of a hook release phase 2 by the control of the needle/hook intersecting phase 1 illustrated in FIG. 7, and the decrease in the loosened upper thread at the hook release phase 2 originating from zig-zag sewing illustrated in FIG. 8 may simultaneously occur.

(71) As illustrated in FIG. 9, with the timing of the hook being retarded in zig-zag sewing employing a needle/hook intersecting phase control, if the phase progresses beyond the hook release phase 2 while the loosened upper thread is reduced by the swing of the needle 1b, the hook/upper-thread necessary amount exceeds the thread-take-up-lever/upper-thread supply amount by what corresponds to a loosened upper thread L4. That is, a condition in which L4<0 occurs, and the loosened upper thread becomes insufficient during sewing, causing a thread breakage or an abnormal noise.

(72) According to the sewing machine of this embodiment, however, when, for example, stitch data is input which has a possibility that the loosened upper thread becomes insufficient, such as the needle falling at the right side in zig-zag sewing which needs a needle/hook control and which has the swing level Z that is equal to or larger than a certain value, the control unit C controls the timing of changing the hook release phase in such a way that the hook/upper-thread necessary amount becomes smaller than the thread-take-up-lever/upper-thread supply amount. That is, the control unit C controls and changes a timing at which the idler unit 7 changes the belt length at the tensioned side A. FIG. 10 illustrates an example case in which needle/hook control timings A, B before and after the hook release phase are changed to control the hook release phase, thereby preventing the loosened upper thread from being insufficient.

(73) FIG. 10 is a diagram illustrating a relationship between the thread-take-up-lever/upper-thread supply amount and the hook/upper-thread necessary amount when zig-zag sewing is assumed. The first cycle (0 to 360 degrees) indicates a needle falling at the left side, and the second cycle (360 to 720 degrees) indicates a needle falling at the right side. By repeating the first cycle and the second cycle alternately, zig-zag stitches can be formed. In this case, the control unit C performs a needle/hook control at different phases which are the needle/hook control timing A and the needle/hook control timing B before and after the hook release phase, thereby controlling the hook release phase.

(74) According to this embodiment, in the second cycle, a needle/hook control is performed which moves the idler unit 7 in a direction in which the loosened side A is pushed at the timing A that is before the hook release phase, and which advances the phase of the hook. Hence, the hook release phase in the second cycle is advanced by what corresponds to an addition of phase differences and in comparison with a case in which a control is performed so as to retard the phase by . Accordingly, the hook/upper-thread necessary amount becomes smaller than the thread-take-up-lever/upper-thread supply amount, and a sufficient loosened upper thread L6 is ensured. Therefore, unlike the loosened upper thread L4 in FIG. 9 which is caused when the swing is increased and a needle/hook control is performed, an abnormal noise or a thread breakage originating from abnormal tension applied to the upper thread due to insufficient loosened upper thread can be prevented.

(75) [1.3 Effects of Embodiment]

(76) The sewing machine of this embodiment which employs the above-explained structure can accomplish the following advantageous effects.

(77) (1) The control unit C controls the hook release phase in such a way that the hook/upper-thread necessary amount becomes smaller than the thread-take-up-lever/upper-thread supply amount. The control unit C controls the hook release phase at plural timings. Hence, when an operation is performed in which the hook/upper-thread necessary amount exceeds the thread-take-up-lever/upper-thread supply amount, a needle/hook control timing can be changed. Accordingly, a sufficient loosened upper thread can be ensured. Therefore, an occurrence of a thread breakage or an abnormal noise can be prevented.

(78) (2) The control unit C controls the phase of the hook so as to be advanced at a timing before the hook release phase. When the width of zig-zag sewing is the maximum and the hook release phase comes while the phase of the hook is being retarded, the hook/upper-thread necessary amount exceeds the thread-take-up-lever/upper-thread supply amount, but through the control by the control unit C, the phase of the hook is advanced at a timing before the hook release phase. Accordingly, a sufficient loosened upper thread can be ensured, thereby preventing an occurrence of a thread breakage or an abnormal noise.

(79) (3) The sewing machine is provided with the idler unit 7 which is the belt adjusting mechanism and which changes the belt length of the toothed belt 6 at the tensioned side A. Hence, a timing of the needle 1b and that of the hook can be controlled as needed. Therefore, a difference in timing between the needle and the hook which is caused by the swing of the needle bar can be stably controlled, and a sufficient loosened upper thread can be ensured.

2. Other Embodiments

(80) The present invention is not limited to the above-explained embodiment, and various changes can be made thereto as needed.

(81) (1) According to the above-explained embodiment, the belt adjusting mechanism is constructed by the idler unit 7 that includes the two idlers 7a, 7b which contact the tensioned side A of the tooled belt 6 and the loosened side B thereof, respectively. However, the structure including the two idlers is employed in view of the safeness, and it is appropriate if at least one idler is provided at the tensioned side A of the toothed belt 6. According to this structure, the number of parts can be reduced, and the same advantageous effects as those of the above-explained embodiment can be still accomplished.

(82) According to the above-explained embodiment, when, for example, stitch data is input which has a possibility that the loosened upper thread becomes insufficient, such as the needle falling at the right side in zig-zag sewing which needs a needle/hook control and which has the swing level Z that is equal to or larger than a certain value, the control unit C controls the timing of changing the hook release phase in such a way that the hook/upper-thread necessary amount becomes smaller than the thread-take-up-lever/upper-thread supply amount. However, a simpler control method which is carried out before the hook release phase in the case of, for example, a control of advancing the hook release phase, and is carried out after the hook release phase in the case of a control of retarding the hook release phase can also accomplish the same advantageous effects as those of the above-explained embodiment.

(83) (3) The embodiments of the present invention were explained above, but various omissions, replacements, and modifications can be made without departing from the scope of the present invention. Such embodiments and modified embodiments thereof are within the scope of the present invention, are also within the scope of the invention as recited in appended claims and within the equivalent range thereto.