Sewing machine with

Abstract

To accurately acquire the height of a presser foot.SOLUTION: The sewing machine includes a detection device 30 that detects a height of a presser foot 21 that is supported by a support member 22 so as to be movable up and down and that presses an object to be sewn on a needle plate 114 from above, the detection device including a detection target body 31 that moves up and down together with the presser foot and a first sensor 3 and a second sensor 3 that increase a signal output in accordance with approach of a distance to the detection target body, the first sensor being disposed below the second sensor. And a detection processing part 911 which is arranged so that the object to be detected is at the same height as the first sensor or at a height between the first sensor and the second sensor when the presser foot is at the lowest height, and acquires the height of the presser foot by a difference value between a signal output of the first sensor and a signal output of the second sensor.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a sewing machine capable of detecting the height of a presser foot. [Background technology]

[0002] Conventional sewing machines detect the height of the presser foot that presses down on the sewing object from above using a sensor, such as a Hall element, whose signal output increases or decreases depending on the distance from the object (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-111527 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the height of the presser foot is detected by a single Hall element, the accuracy is insufficient to detect minute fluctuations due to changes in the thickness of the sewing material. Furthermore, since sewing machines use motors that generate noise, there are cases where the presser foot height cannot be detected properly due to the influence of noise.

[0005] An object of the present invention is to properly detect the height of the presser foot. [Means for solving the problem]

[0006] The present invention provides a detection device that detects the height of a presser foot that is supported by a support member so as to be able to rise and fall and that presses down on an object to be sewn on a needle plate from above; the detection device includes a detection object that moves up and down together with the presser foot, and a first sensor and a second sensor whose signal output increases as the distance between the detection object and the first sensor decreases, the first sensor is disposed below the second sensor, and when the presser foot is at its lowest height, the detected object is disposed at the same height as the first sensor or at a height between the first sensor and the second sensor; The presser foot height sensor further includes a detection processing unit that acquires the height of the presser foot based on the difference between the signal output of the first sensor and the signal output of the second sensor. [Effects of the Invention]

[0007] According to the present invention, it is possible to properly detect the height of the presser foot. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view of a sewing machine according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing a side portion of the sewing machine. [Figure 3] FIG. 2 is a perspective view showing the side of the sewing machine with the presser foot detached. [Figure 4] FIG. 4(A) is a left side view of the detector that detects the height of the presser foot, and FIG. 4(B) is a left side view of the detector when the presser arm is swung upward. [Figure 5] FIG. 2 is a block diagram showing a control system of the sewing machine. [Figure 6] 10 is a diagram showing an approximate straight line of the characteristics of the signal output of the first sensor versus the distance from the first sensor to the permanent magnet in the Z-axis direction. [Figure 7] 10 is a diagram showing an approximate straight line of the characteristics of the signal output of the second sensor versus the distance from the first sensor to the permanent magnet in the Z-axis direction. FIG. [Figure 8] 10 is a diagram showing an approximate straight line of the characteristic of the difference value between the signal output of the first sensor and the signal output of the second sensor versus the distance in the Z-axis direction from the first sensor to the permanent magnet. [Figure 9] 10 is a diagram showing changes in the signal outputs of the first sensor and the second sensor relative to the distance from the first sensor to the permanent magnet in the Z-axis direction. FIG. [Figure 10]10 is a diagram showing changes in the signal outputs of the first and second sensors with respect to changes in the distance of the permanent magnet when the presser foot is released to the left from the first sensor. FIG. [Figure 11] 10 is a flowchart showing sewing operation control performed by a CPU. [Figure 12] 10 is a diagram showing another example of an approximate straight line of the characteristic of the difference value between the signal output of the first sensor and the signal output of the second sensor with respect to the distance in the Z-axis direction from the first sensor to the permanent magnet. FIG. [Figure 13] 10 is an explanatory diagram showing the positional relationship between a magnet, a first sensor, and a second sensor in the acquisition control of characteristic values. FIG. [Figure 14] 10 is a diagram showing a change in the signal output voltage of the first sensor when the presser foot is raised during control to obtain characteristic values. FIG. [Figure 15] 10 is a diagram showing a change in the signal output voltage of the second sensor when the presser foot is raised during control to obtain characteristic values. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Outline of the embodiment] An embodiment of the present invention will be described with reference to the drawings. The sewing machine 100 of this embodiment is exemplified by a so-called chain stitch sewing machine. FIG. 1 is a perspective view of a sewing machine 100, and FIGS. 2 and 3 are perspective views showing the side portion of the sewing machine 100. FIG. In the following description, when the sewing machine 100 is placed on a horizontal plane, the direction that coincides with the vertical direction is referred to as the Z-axis direction, one direction that is perpendicular to the other on the horizontal plane is referred to as the X-axis direction, and the other direction is referred to as the Y-axis direction. The X-axis direction is parallel to the feed direction of the workpiece, and the downstream side in the feed direction may be referred to as the "front" and the upstream side as the "rear." One end side in the Y-axis direction (the left-hand side when facing forward) may be referred to as the "left," and the other end side in the Y-axis direction (the right-hand side when facing forward) may be referred to as the "right."

[0010] The sewing machine 100 comprises a sewing machine frame 110, a needle up-and-down movement mechanism for moving the sewing needle up and down, a lower looper mechanism having a lower looper for passing the lower looper thread through the loop of the needle thread, an upper looper mechanism having an upper looper for passing the upper looper thread through the loop of the lower looper thread, a feed mechanism for feeding the sewn material, a knife mechanism for cutting the side end (for example, the right end) of the sewn material to trim the sewing end, a thread tension device 12, and a presser mechanism 20 for pressing the sewn material on the needle plate 114 from above.

[0011] The sewing machine frame 110 houses or supports the entire configuration of the sewing machine. The sewing machine frame 110 has a bed portion 111 located at the bottom, an upright body portion 112 standing upright from the right side of the bed portion 111, and an arm portion 113 extending leftward from the top of the upright body portion 112. The bed 111 has a horizontal and flat upper left surface on which a sewing object is placed and sewn. A needle plate 114, where a sewing needle penetrates, is provided flush with the upper surface of the bed 111 on the rear upper left surface of the bed 111.

[0012] The needle up-down movement mechanism, lower looper mechanism, upper looper mechanism, feed mechanism, knife mechanism, and thread tension device 12 have the same configuration as well known in chain stitch sewing machines, so detailed description will be omitted. Here, only the needle up / down movement mechanism and the feed mechanism will be briefly explained.

[0013] The needle up-down movement mechanism is built into the rear left end of the arm portion 113 and moves the sewing needle through a needle hole (not shown) in the needle plate 114 . The needle up-down movement mechanism has a sewing machine motor 51 (see Figure 5) as a drive source, and applies up-and-down movement to the needle bar and sewing needle via a transmission mechanism that converts the rotation of the sewing machine motor 51 into up-and-down reciprocating motion. The sewing machine motor 51 is a motor such as an AC motor or a DC motor whose rotation speed (rotational speed) can be controlled.

[0014] The feed mechanism has a feed dog that moves back and forth while appearing up and down through an opening in the needle plate 114 . The feed mechanism has a forward / backward movement mechanism that uses the power of the sewing machine motor 51 to impart a forward / backward reciprocating movement to the feed dog, and a vertical movement mechanism that imparts an up / down reciprocating movement to the feed dog. The feed dog is given a combination of back and forth reciprocating motion and up and down reciprocating motion in synchronization with the needle up and down movement mechanism, and the tooth tip protrudes from the opening of the needle plate 114, thereby feeding the workpiece on the needle plate 114 forward.

[0015] The forward and backward movement mechanism of the feed mechanism is provided with an adjuster that increases and decreases the amplitude of the forward and backward reciprocating movement of the feed dog, and a feed adjustment motor 52 that operates the adjuster. The feed adjustment motor 52 is, for example, a stepping motor, and the control device 90, which will be described later, controls the operation of this feed adjustment motor 52 to arbitrarily adjust the amplitude of the back and forth movement of the feed dog, i.e., the stitching pitch.

[0016] [Press mechanism] As shown in FIGS. 1 to 3, the presser foot 21 presses down on the sewing object on the needle plate 114 from above, a presser arm 22 as a support member that supports the presser foot 21 at its rear swinging end, a base end support portion 23 that supports the front base end of the presser arm 22, a pressing member 24 that presses the swinging end of the presser arm 22 downward, and a presser adjustment motor 25 as an actuator that raises the presser foot 21 against the pressing member 24.

[0017] The presser foot 21 has a so-called boat-shaped presser body 211 with a curved rear portion, and a connecting portion 212 that supports the presser body 211 so that it can rotate around the Y axis. The upper end of the connecting portion 212 is connected to the swing end of the pressing arm 22 by embracing it.

[0018] The presser arm 22 extends generally in the X-axis direction, is inclined slightly downward toward the rear, and supports the presser foot 21 at its rear end. The base end portion on the front end side of the pressing arm 22 is connected by a base end support portion 23 so as to be rotatable about an axis whose upper side is inclined slightly rearward with respect to the Z-axis direction.

[0019] The base end support portion 23 supports the base end portion on the front end side of the pressing arm 22, has a shaft portion along the Y-axis direction, and is supported by the upright body portion 112 so as to be rotatable around the Y-axis. Therefore, the base end support portion 23 and the presser arm 22 swing around the Y axis with the base end side of the presser arm 22 as the center, and the rear end of the presser arm 22 and the presser foot 21 can be moved up and down.

[0020] Pressing member 24 abuts against the vicinity of the rear end of presser arm 22 from above, and applies a downward pressing force to presser foot 21 by means of a built-in pressing device. Pressing member 24 is supported at the lower front end of arm portion 113 so as to be able to move up and down, and its lower end protrudes downward to abut against presser arm 22. A stopper provided inside arm portion 113 determines the lower limit position of pressing member 24 so that it does not protrude too far downward. A recess is formed at the lower end of the pressing member 24, and fits onto the swinging end of the pressing arm 22. However, this fitted state can be released by manually pressing down the swinging end of the pressing arm 22 while holding down the pressing member 24.

[0021] 1 denotes a presser foot lifting lever 26. The presser foot lifting lever 26 extends diagonally upward toward the front, and its base end is connected to the support shaft of the base end support portion 23 of the presser arm 22. By manually pushing the tip of the presser foot lifting lever 26 downward, the presser foot 21 at the rear end of the presser arm 22 can be raised against the pressure of the pressing member 24. In other words, by rotating the presser foot lifting lever 26, the sewing material held down by the presser foot 21 on the needle plate 114 can be released.

[0022] The pressing device has a presser pressure adjusting actuator 27 that arbitrarily adjusts the pressing force (not shown) of the pressing member 24. The actuator 27 adjusts the pressing force of the pressing member 24, thereby adjusting the pressure with which the presser foot 21 presses the material to be sewn on the needle plate 114. The actuator 27 is controlled by the control device 90.

[0023] Base end support portion 23 is supported by upright body portion 112 so as to be rotatable about the Y axis, and the rotation axis of base end support portion 23 is connected via a connecting link to height adjustment motor 25, which imparts rotational motion to base end support portion 23. Height adjustment motor 25 can adjust presser foot 21 to any height via base end support portion 23 and presser arm 22. The connecting link transmits only torque from the height adjustment motor 25 in the direction of raising the presser foot 21. Therefore, the presser foot 21 can be raised above the height set and adjusted by the height adjustment motor 25, which allows the presser foot 21 to be pushed up by a step or the like of the sewing material during sewing. The height adjustment motor 25 is a motor capable of rotating an output shaft with a predetermined resolution, such as a stepping motor, and the control device 90 can raise and lower the presser foot 21 to any height in predetermined distance units, and can also adjust the pressure applied to the presser foot. The presser foot height adjustment is not limited to a motor, and a solenoid or linear motor, etc., whose movement amount can be controlled arbitrarily, may also be used.

[0024] As described above, the base end of the presser arm 22 is connected to the base end support portion 23 so as to be rotatable about an axis whose upper side is inclined slightly rearward with respect to the Z-axis direction, as shown in Fig. 3. Therefore, by moving the presser arm 22 away from the pressing position of the pressing member 24 and rotating it relative to the base end support portion 23, the swinging end of the presser arm 22 and the presser foot 21 can be pulled out to the left. In other words, the presser foot 21 is supported so as to be rotatable in a direction away from the path along which the lifting and lowering motion takes place.

[0025] The sewing machine 100 requires maintenance of the structure below the needle plate 114, and in that case, the presser foot 21 must be removed from above the needle plate 114. However, since the presser foot 21 can be detached to the left, it is possible to improve the workability during maintenance.

[0026] [Detection device] 4(A) and 4(B) are left side views of a detector 30 that is provided in addition to the presser mechanism 20 and detects the height of the presser foot 21. FIG. As shown in Figures 2 to 4(B), the detection device 30 has a permanent magnet 31 as a detected object that moves up and down together with the presser foot 21, and a first sensor 32 and a second sensor 33 whose signal output (voltage) increases as the distance between them and the permanent magnet 31 decreases. The first sensor 32 and the second sensor 33 are each formed of a Hall IC equipped with a Hall element.

[0027] The permanent magnet 31 is fixedly supported on the right side surface of the presser arm 22 at the longitudinal middle portion thereof. The first sensor 32 and the second sensor 33 are both disposed on the right side of the pressing arm 22 so as to be closely opposed to each other on the right side surface of the pressing arm 22 . The first sensor 32 and the second sensor 33 are arranged vertically, with the first sensor 32 being located below the second sensor 33.

[0028] When the presser foot 21 is at a height (minimum height) at which it abuts the upper surface of the needle plate 114, the first sensor 32 is positioned so as to be closely opposite (closest to) the permanent magnet 31 provided on the presser arm 22 at the same height as the permanent magnet 31, as shown in Figure 4(A). Then, when the presser foot 21 rises to press down on the workpiece on the needle plate 114, the permanent magnet 31 provided on the presser arm 22 moves away from the first sensor 32 and approaches the second sensor 33, as shown in FIG. 4(B). The installation position of the second sensor 33 in the Z-axis direction is set within a range in which the permanent magnet 31 will not be above the second sensor 33 even when the presser foot 21 presses down on a sewing object of the maximum thickness permitted for sewing by the sewing machine 100. However, it is preferable that the first sensor 32 and the second sensor 33 are not too far apart.

[0029] [Sewing machine control system] 5 is a block diagram showing the control system of sewing machine 100. As shown in the figure, sewing machine 100 is equipped with a control device 90 that controls the operation of each component. Sewing machine motor 51, feed adjustment motor 52, and height adjustment motor 25 are connected to this control device 90 via respective motor drive circuits 51a, 52a, and 25a. Encoders 511, 521, and 251 that detect the shaft angles of the output shafts are also provided in the sewing machine motor 51, feed adjustment motor 52, and height adjustment motor 25. These encoders 511, 521, and 251 are also connected to the control device 90 via motor drive circuits 51a, 52a, and 25a. The control device 90 is also connected to an actuator 27 for adjusting the pressure via a drive circuit 27a.

[0030] The control device 90 is also connected to a first sensor 32 and a second sensor 33 via interfaces 32a and 33a. Furthermore, an operation input unit 96 serving as a setting input device is connected to the control device 90 via an interface 96a. A pedal 95, which is depressed to start and stop sewing and input other commands, is also connected to the control device 90 via an interface 95a.

[0031] The control device 90 includes a CPU 91, a ROM 92, a RAM 93, and a data memory 94, and executes various operational controls described below. The ROM 92 stores a basic system program and various programs for implementing software modules of the CPU 91, which will be described later. The data memory 94 also stores various setting information for sewing, such as sewing speed, stitch pitch, etc. The data memory 94 is made up of a nonvolatile semiconductor memory such as a flash memory, EEPROM, or EPROM, but may also be a storage such as an HDD. The CPU 91 executes the above programs to control the sewing operation. The RAM 93 is a memory that serves as a work area for the CPU 91.

[0032] The CPU 91 also includes software modules such as a detection processing unit 911, a detachment determination unit 912, a presser control unit 913, and a stitching pitch control unit 914. Note that some or all of these software modules may be configured from hardware.

[0033] [Detection processing section] The detection processing unit 911 executes a process for determining the height of the presser foot 21 from the difference between the signal output of the first sensor 32 and the signal output of the second sensor 33 . Figure 6 is a diagram showing an approximate straight line of the characteristics of the signal output (voltage) of the first sensor 32 versus the separation distance in the Z-axis direction from the first sensor 32 to the permanent magnet 31, and Figure 7 is a diagram showing an approximate straight line of the characteristics of the signal output (voltage) of the second sensor 33 versus the separation distance in the Z-axis direction from the first sensor 32 to the permanent magnet 31.

[0034] As shown in FIG. 6, the first sensor 32 has a characteristic that the signal output voltage is V11 when the permanent magnet 31 is closest to the first sensor 32 (distance 0), and the signal output voltage is V12 when the permanent magnet 31 is separated from the first sensor 32 by a maximum distance K2 (a predetermined value, for example, the maximum height of the presser foot 21). For example, distance 0 may correspond to the lower limit of the measurement range of the height of presser foot 21 (the minimum height of presser foot 21), and distance K2 may correspond to the upper limit of the measurement range of the height of presser foot 21 (the maximum height of presser foot 21). Distance K2 is, for example, the distance between first sensor 32 and permanent magnet 31 that occurs when presser foot 21 is positioned at a height that sufficiently exceeds the maximum thickness of a sewing material that can be sewn by sewing machine 100. However, distance K2 is not limited to the above numerical value, but it is preferable that it does not deviate significantly from the above numerical value. Distance K2 may be equal to the distance between the centers of first sensor 32 and second sensor 33, or may be equal to or less than the distance between the sensors. The signal output voltages V11 and V12 and the distance values ​​of the distances 0 and K2 can be obtained by actual measurement or the like, and are registered in the data memory 94 as characteristic values.

[0035] According to the characteristics shown in FIG. 6, the signal output voltage V1x of the first sensor 32 and an arbitrary separation distance Kx from the first sensor 32 to the permanent magnet 31 in the Z-axis direction satisfy the relationship of the following equation (1). Kx=K2×(V11-V1x) / (V11-V12) …(1)

[0036] Also, as shown in Figure 7, the second sensor 33 has a characteristic that the signal output voltage is V21 when the permanent magnet 31 is closest to the first sensor 32 (distance 0), and the signal output voltage is V22 when the permanent magnet 31 is separated from the first sensor 32 by the maximum distance K2 (default value). The values ​​of the signal output voltages V21 and V22 can also be obtained by actual measurement or the like, and are registered in the data memory 94 as characteristic values.

[0037] 7, the signal output voltage V2x of the second sensor 33 and the distance Kx satisfy the relationship shown in the following equation (2), where Kx is a value equal to or less than the distance from the first sensor 32 to the second sensor 33. Kx=K2×(V21-V2x) / (V21-V22) …(2)

[0038] It is also possible to determine the position of the permanent magnet 31 in the Z-axis direction based on the above formula (1) or (2) from the signal output of either the first sensor 32 or the second sensor 33, but the detection processing unit 911 determines the difference between the signal output of the first sensor 32 and the signal output of the second sensor 33, and derives the position of the permanent magnet 31 in the Z-axis direction from this difference value.

[0039] FIG. 8 is a diagram showing an approximate straight line characteristic of the difference value between the signal output (voltage) of the first sensor 32 and the signal output (voltage) of the second sensor 33 versus the separation distance from the first sensor 32 to the permanent magnet 31 in the Z-axis direction. As shown in FIG. 8, the difference value (hereinafter referred to as composite voltage V31) between the voltage of the signal output of the first sensor 32 at a distance of 0 and the voltage of the signal output of the second sensor 33 at a distance of 0 can be expressed by the following equation (3): Similarly, the difference between the voltage of the signal output of the first sensor 32 at the maximum distance K2 and the voltage of the signal output of the second sensor 33 at the maximum distance K2 (hereinafter referred to as composite voltage V32) can be expressed by the following equation (4). V31=V11-V21 …(3) V32 = V12 - V22 … (4)

[0040] Furthermore, if the difference between the signal output voltage V1x of the first sensor 32 and the signal output voltage V2x of the second sensor 33 is defined as a composite voltage V3x, then based on the characteristics shown in FIG. 8, the relationship of the following equation (5) holds between the composite voltages V31, V32 and the distance Kx. Kx=K2×(V31-V3x) / (V31-V32) …(5)

[0041] As described above, the signal output voltages V11, V12, V21, and V22, which are preset values, and the value of the distance K2 are all registered as setting information in the data memory 94. Therefore, the detection processing unit 911 can calculate the distance Kx once the signal output voltage V1x of the first sensor 32 and the signal output voltage V2x of the second sensor 33 are detected.

[0042] Although the separation distance Kx in the Z-axis direction from the first sensor 32 to the permanent magnet 31 is different from the actual value of the height of the presser foot 21, there is a certain correlation between the distance Kx and the height of the presser foot 21, so the detection processing unit 911 is essentially equivalent to determining the height of the presser foot 21. The detection processing unit 911 may further derive the height of the presser foot 21 from the calculated distance Kx. In this case, the detection processing unit 911 may determine the height of the presser foot 21 by calculation from the dimensions of each part of the presser arm 22, or may prepare table data that indicates the correlation between the distance Kx and the height of the presser foot 21 and refer to the table data to determine the height of the presser foot 21.

[0043] [Detachment determination unit] The detachment determination unit 912 determines whether or not a state has occurred in which the presser arm 22 has rotated in the direction shown in FIG. 3 and the presser foot 21 has detached from the path along which the presser foot 21 moves up and down. FIG. 9 is a diagram showing the change in the signal output (voltage) of each of the first sensor 32 and the second sensor 33 with respect to the distance from the first sensor 32 to the permanent magnet 31 in the Z-axis direction. In contrast, Figure 10 is a diagram showing the changes in the signal output (voltage) of each of the first sensor 32 and the second sensor 33 relative to the change in distance to the permanent magnet 31 when the presser arm 22 rotates in the direction shown in Figure 3 and the presser foot 21 separates from the first sensor 32 to the left. 9 and 10, a line L1 indicates the signal output of the first sensor 32, and a line L2 indicates the signal output of the second sensor 33.

[0044] As shown in Figures 9 and 10, the correlation between the signal outputs of the first sensor 32 and the second sensor 33 and the change in position of the permanent magnet 31 when the presser foot 21 has not detached from the path along which it moves up and down is significantly different from the correlation between the signal outputs of the first sensor 32 and the second sensor 33 and the change in position of the permanent magnet 31 when the presser foot 21 has detached from the path along which it moves up and down. When the presser foot 21 is not detached from the path along which it moves up and down, the signal output of the first sensor 32 satisfies the above-mentioned formula (1), and the signal output of the second sensor 33 satisfies the above-mentioned formula (2). In other words, if the presser foot 21 is not detached from the path along which it moves up and down, the distance Kx calculated from the signal output voltage V1x of the first sensor 32 according to equation (1) and the distance Kx calculated from the signal output voltage V2x of the second sensor 33 according to equation (2) should be approximately the same. In other words, the value obtained by dividing the right side of equation (1) by the right side of equation (2) should be close to 1, as shown in the following equation (6). 1={(V11-V1x) / (V11-V12)} / {(V21-V2x) / (V21-V22)} …(6)

[0045] Therefore, when the detachment determination unit 912 receives the signal outputs of the first sensor 32 and the second sensor 33, it performs a calculation according to the above formula (6) and determines whether or not the detached state of the presser foot 21 has occurred based on whether or not the calculated value is close to 1. However, because the first sensor 32 and the second sensor 33 output analog signals, a certain amount of error is included, and so the determination using the above formula (6) should take this error into consideration. For example, assuming an error of ±10% is possible, if the value calculated using the above formula (6) is between 0.9 and 1.1, it can be determined that the presser foot 21 has not come off, and if the value falls outside this range, it can be determined that the presser foot 21 has come off. The numerical range of the error is not limited to the above, and may be arbitrarily set through the operation input unit 96.

[0046] The detachment determination unit 912 periodically performs the above determination during sewing, and when it detects that the presser foot 21 has been detached during sewing, it executes a notification process. Examples of the notification process include a notification operation to notify the user that the presser foot 21 has come off by displaying a screen on the display unit 961 or the like, and control to stop sewing urgently.

[0047] [Presser height control section] The presser control unit 913 detects a change in the thickness of the workpiece from the value of the distance Kx derived by the detection processing unit 911 or the height of the presser foot 21, and by controlling the height adjustment motor 25, can change the height of the presser foot 21 so as to follow the change in the thickness of the workpiece. For example, if the presser foot 21 is pushed up above the set height by a stepped portion of the sewing material, the operation of the height adjustment motor 25 can be controlled so as to maintain the set height.

[0048] [Stitch pitch control section] The stitching pitch control section 914 controls the operation of the feed adjusting motor 52 based on the value of the distance Kx or the height of the presser foot 21 derived by the detection processing section 911 . The sewing machine 100 allows the width of the stitch pitch, which is the distance between stitches, to be set numerically from the operation input unit 96, and the feed adjustment motor 52 operates to adjust the stitch pitch determined by the feed adjustment body so that it becomes the set stitch pitch. However, if the height of the presser foot 21 fluctuates depending on the thickness of the workpiece, etc., the meshing state between the feed dog and the workpiece may change, causing the stitching pitch to fluctuate.

[0049] Therefore, the stitching pitch control unit 914 controls the operation of the feed adjusting motor 52 to increase or decrease the stitching pitch so as to maintain the set stitching pitch in accordance with the value of the distance Kx derived by the detection processing unit 911 or the increase or decrease in the height of the presser foot 21. For example, if the value of the distance Kx derived by the detection processing unit 911 or the height of the presser foot 21 indicates an increase from the immediately preceding value, the feed adjusting motor 52 is controlled to reduce the increased stitch pitch corresponding to the amount of increase. Furthermore, if the value of the distance Kx derived by the detection processing unit 911 or the height of the presser foot 21 indicates a decrease from the previous value, the feed adjusting motor 52 is controlled to compensate for the decrease in the stitch pitch that has decreased in accordance with the amount of decrease.

[0050] [Sewing machine operation] The sewing operation control performed by the CPU 91 of the sewing machine 100 will be described with reference to the flowchart of Fig. 11. This sewing operation control is repeatedly executed in short cycles.

[0051] When the pedal 95 is depressed to input a command to start sewing, the CPU 91 starts the sewing machine motor 51 to start sewing. The detachment determination unit 912 then performs a calculation based on the signal output voltage V1x of the first sensor 32 and the signal output voltage V2x of the second sensor 33 in accordance with the aforementioned equation (6), and determines whether or not the detached state of the presser foot 21 has occurred based on whether or not the calculated value is within the range of 1±10% (step S1).

[0052] If the presser foot 21 has not come off, the detection processing unit 911 performs calculations using the signal output voltage V1x of the first sensor 32 and the signal output voltage V2x of the second sensor 33 according to the above-mentioned equations (3) to (5) to calculate the distance Kx in the Z-axis direction from the first sensor 32 to the permanent magnet 31 (step S3). The height of the presser foot 21 may also be determined based on the distance Kx.

[0053] Next, the presser control unit 913 may control the operation of the height adjustment motor 25 so that the set height is followed based on the distance Kx or the height of the presser foot 21 derived by the detection processing unit 911 (step S5). Furthermore, the stitching pitch control section 914 controls the operation of the feed adjusting motor 52 so as to optimize the stitching pitch based on the distance Kx or the height of the presser foot 21 derived by the detection processing section 911 (step S7). It should be noted that either the process of step S5 or the process of step S7 may be performed first.

[0054] Then, the CPU 91 determines whether the pedal 95 has been returned to the stopped state, and if the input of the drive state continues, returns the processing to step S3, and if the pedal 95 has been returned to the stopped state, stops the sewing machine motor 51 and ends sewing.

[0055] Furthermore, if the detachment determination unit 912 determines in step S1 that a detached state has occurred, it executes a notification process (step S11). As the notification process, the detachment determination unit 912, for example, causes the display unit 961 of the operation input unit 96 to display a notification screen that notifies the user that the presser foot 21 has detached. Then, the detachment determination unit 912 stops driving the sewing machine motor 51 (step S13) and ends the operation control.

[0056] [Technical effects of sewing machines] The sewing machine 100 is arranged so that the permanent magnet 31 is at the same height as the first sensor 32 when the presser foot 21 is at its lowest height (height above the needle plate 114), and is equipped with a detection processing unit 911 that obtains the height of the presser foot 21 from the difference between the signal output of the first sensor 32 and the signal output of the second sensor 33. Therefore, compared to when the height of the presser foot 21 is detected by a single sensor, the range of change in signal potential in response to a change in position can be increased by up to two times, making it possible to detect the height of the presser foot 21 with high accuracy. Furthermore, the sewing machine 100 may generate noise from the motor, etc., and the signal outputs of the first sensor 32 and the second sensor 33 may be affected by the noise simultaneously. However, by using the difference between the signal outputs of the first sensor 32 and the second sensor 33, the effect of the noise is sufficiently reduced, making it possible to accurately derive the height of the presser foot 21.

[0057] Furthermore, the sewing machine 100 controls the operation of the height adjusting motor 25 by the presser foot control unit 913 based on the height of the presser foot 21 derived from the signal outputs of the first sensor 32 and the second sensor 33 . For this reason, although the configuration of sewing machine 100 described above illustrates an example in which encoder 521 is provided in addition to height adjustment motor 25, it is also possible to omit encoder 521 from the configuration. In other words, it is possible to simplify the configuration of sewing machine 100.

[0058] In addition, the control device 90 of the sewing machine 100 is equipped with a data memory 94 as a storage unit that stores the signal output voltages V11, V12, V21, V22 and the distance K2 obtained by actual measurement as characteristic values ​​for determining the distance characteristics of the signal outputs of the first sensor 32 and the second sensor 33. Therefore, a measurement value measured in advance can be used as the characteristic value, and the detection processing unit 911 can obtain the height of the presser foot 21 by referring to the characteristic value. This makes it possible to obtain the height of the presser foot 21 with high accuracy while minimizing the effects of individual differences in the signal output of the sensor and installation errors.

[0059] Furthermore, the control device 90 of the sewing machine 100 is provided with a detachment determination unit 912 that determines whether the presser foot 21 has detached from the sewing machine 100 based on the signal output of the first sensor 32 and the signal output of the second sensor 33, thereby eliminating the need for a specific sensor such as a microswitch for detecting the detached state of the presser foot 21. Furthermore, since it is possible to detect the occurrence of accidental detachment of the presser foot 21 or forgetting to return the presser foot 21 after maintenance, it is possible to prevent errors from occurring during sewing.

[0060] The detachment determination unit 912 also determines whether the presser foot 21 is detached by comparing the height of the presser foot 21 determined from the signal output of the first sensor 32 with the height of the presser foot 21 determined from the signal output of the second sensor 33. Therefore, the sensor arrangement of the first sensor 32 and the second sensor 33 can be made suitable for detecting the height of the presser foot 21, making it possible to easily detect both the height of the presser foot 21 and determine whether the presser foot 21 is detached.

[0061] [others] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. For example, in the embodiments, a component integrally formed from a single member may be replaced with a component divided into multiple members that are connected or fixed to each other. Furthermore, a component formed by connecting multiple members may be replaced with a component integrally formed from a single member. In addition, the details shown in the embodiments may be modified as appropriate without departing from the spirit of the invention.

[0062] For example, although a Hall IC including a Hall element is exemplified as the first sensor 32 and the second sensor 33, the present invention is not limited to this and any sensor that outputs an electrical signal corresponding to the distance to the object to be detected can be used. For example, a sensor including a magnetoresistive element may be used as the first sensor 32 and the second sensor 33.

[0063] In addition, in the sewing machine 100, an example of an arrangement in which the permanent magnet 31 as the detected object is at the same height as the first sensor 32 when the presser foot 21 is at the lowest height in contact with the needle plate 114 has been exemplified, but this is not limited to this. When the presser foot 21 is at its lowest height, the permanent magnet 31 as the object to be detected may be located at a height between the first sensor 32 and the second sensor 33. In this case, it is preferable that the permanent magnet 31 as the object to be detected be closer to the first sensor 32.

[0064] In addition, in the above embodiment, an example was given of the case where the detection processing unit 911 acquires the separation distance Kx in the Z-axis direction from the first sensor 32 to the permanent magnet 31, but the detection processing unit 911 may also acquire the separation distance (referred to as K2x) in the Z-axis direction from the second sensor 33 to the permanent magnet 31 (the premise remains the same that the movable range of the permanent magnet 31 in the Z-axis direction is between the first sensor 32 and the second sensor 33). In this case, the characteristic of the signal output (voltage) of the second sensor 33 with respect to the separation distance K2x will be a characteristic that shows a downward gradient as shown in Figure 6, and the characteristic of the signal output (voltage) of the first sensor 32 with respect to the separation distance K2x will be a characteristic that shows an upward gradient as shown in Figure 7. However, from these characteristics and the characteristic values ​​described above, it is possible to determine the correlation between the difference between the signal output of the first sensor 32 and the signal output of the second sensor 33 and the separation distance K2x, so it is possible to obtain the separation distance K2x from the signal output of the first sensor 32 and the signal output of the second sensor 33.

[0065] Furthermore, the signal output voltages of the first sensor 32 and the second sensor 33 at multiple separated positions are recorded as characteristic values, but the component voltage consisting of the difference between the signal output voltages of the first sensor 32 and the second sensor 33 at multiple separated positions may also be used as the characteristic value.

[0066] Furthermore, although a chain stitch sewing machine has been exemplified as a sewing machine for detecting the presser foot height, the detection device 30 can be applied to any sewing machine that has a presser foot that can be raised and lowered. In this case, if the sewing machine is one in which the presser foot is supported so as to be rotatable in a direction away from the path along which the presser foot moves up and down, the detection device 30 can be applied more preferably.

[0067] [Other configurations for obtaining presser foot height] Furthermore, as characteristic values ​​for determining the distance characteristics between the first sensor 32 and the permanent magnet 31 with respect to the differential value of the signal outputs of the first sensor 32 and the second sensor 33, the values ​​of two separation distances 0 and K2 in the Z-axis direction between the first sensor 32 and the permanent magnet 31, the respective signal output voltages V11 and V12 of the first sensor 32 at the two separation distances 0 and K2, and the respective signal output voltages V21 and V22 of the second sensor 33 at the two separation distances 0 and K2 have been exemplified, but this is not limited to this, and for example, the characteristic values ​​may be three or more separation distances in the Z-axis direction between the first sensor 32 and the permanent magnet 31 and the signal output voltages of the first sensor 32 and the second sensor 33 at each separation distance (or the differential value of the signal output voltages of the two sensors at each separation distance).

[0068] 8, the above-described detection processing unit 911 has been illustrated as being configured to calculate the distance Kx in the Z-axis direction from the first sensor 32 to the permanent magnet 31 based on a single approximate straight line that indicates the characteristics of the difference value between the signal output voltage of the first sensor 32 and the signal output voltage of the second sensor 33 with respect to the distance in the Z-axis direction from the first sensor 32 to the permanent magnet 31. However, the calculation of the distance Kx by the detection processing unit 911 is not limited to the above.

[0069] The approximate straight line L3 shown in Figure 12 shows the characteristics based on the composite voltages V31, V32, which are the difference between the signal output voltage of the first sensor 32 and the signal output voltage of the second sensor 33, relative to the distance in the Z-axis direction from the first sensor 32 to the permanent magnet 31, as determined by the detection processing unit 911 described above. In contrast, the actual measurement curve Lr, which is obtained by plotting the difference values ​​based on the actual measurement signal outputs of the first sensor 32 and the second sensor 33 at each distance at minute intervals over the entire range from distance 0 to maximum distance K2, deviates from the approximate line L3 in many places. This deviation directly results in an error in the height of the presser foot 21 that is obtained.

[0070] Therefore, the target characteristic values ​​for determining the distance characteristics of the differential value of the signal output of the first sensor 32 and the second sensor 33 may be increased from just two points, distance 0 and distance K2 from the first sensor 32 to the permanent magnet 31, to three or more points. For example, as shown in Figure 12, points with distances K3, K4, and K5 may be added between distance 0 and distance K2, and the numerical values ​​of each distance K3, K4, and K5 and the actual measured values ​​of the signal outputs of the first sensor 32 and the second sensor 33 at each distance K3, K4, and K5 or the difference between the actual measured values ​​of the signal outputs of the first sensor 32 and the second sensor 33 at each distance K3, K4, and K5 may be added as characteristic values ​​and registered in the data memory 94. The numerical values ​​of the distances K3, K4, and K5 may be set so that the intervals between the distances 0, K3, K4, K5, and K2 are uniform.

[0071] In this case, the detection processing unit 911 subdivides the range from distance 0 to distance K2 into multiple ranges: a first range (distance 0 to K3), a second range (distance K3 to K4), a third range (distance K4 to K5), and a fourth range (distance K5 to K2), and obtains a formula equivalent to the above-mentioned formula (5) for each of the first to fourth ranges. Approximation lines L31 to L34 showing the distance characteristics of the difference values ​​between the signal outputs of the first sensor 32 and the second sensor 33 in FIG. 12 are approximation lines based on mathematical expressions equivalent to equation (5) corresponding to the first to fourth ranges, respectively.

[0072] When detecting the height of the presser foot 21, the detection processing unit 911 calculates the difference between the signal output voltages of the first sensor 32 and the second sensor 33 upon detection. Furthermore, the detection processing unit 911 identifies which of ranges 1 to 4 the detected difference value belongs to based on the difference between the actually measured values ​​of the signal outputs of the first sensor 32 and the second sensor 33 at distances 0, K3, K4, K5, and K2, which are prepared in advance as characteristic values, and calculates the distance Kx in the Z-axis direction to the permanent magnet 31 from a formula equivalent to equation (5) that corresponds to which of the identified ranges 1 to 4. The height of the presser foot 21 is determined from this distance Kx.

[0073] 12, the detection processing unit 911 divides the range from distance 0 to distance K2 into first to fourth ranges, and calculates the distance Kx by finding an equation equivalent to equation (5) for each range. Therefore, the distance Kx can be found based on four connected approximate straight lines L31 to L34 that have little deviation from the measured curve Lr. This reduces errors in the distance Kx, making it possible to obtain the height of the presser foot 21 with greater accuracy.

[0074] 12, an example was given in which the distances 0, K3, K4, K5, and K2 consisting of five numerical values ​​were introduced, but the number of numerical values ​​for the distances may be three or more. However, the more distances are introduced, the more subdivided the range between distance 0 and distance K2 becomes, and an approximate line showing the distance characteristics of the difference values ​​between the signal outputs of first sensor 32 and second sensor 33 can be obtained over a wider range. This reduces the deviation from the measured curve Lr, and makes it possible to obtain the height of presser foot 21 with greater accuracy.

[0075] Furthermore, the signal output voltages of the first sensor 32 and the second sensor 33 may be measured for each of the countless distance values ​​that divide the detection range from distance 0 to distance K2 into even finer intervals, and the mutual difference value may be calculated for each distance value. Table data that associates the difference value with each distance value in the range from distance 0 to distance K2 may be generated, and the data may be registered in the data memory 94 as a characteristic value for calculating the distance characteristic of the difference value of the signal output of the first sensor 32 and the second sensor 33. In this case, the detection processing unit 911 does not need to determine an equation equivalent to equation (5). That is, when the detection processing unit 911 detects the signal output voltages of the first sensor 32 and the second sensor 33 and obtains the difference between them, it references the table data and selects the distance associated with the closest difference value defined in the table data, thereby obtaining the distance Kx. This allows the height of the presser foot 21 to be obtained with even greater accuracy.

[0076] [Controlling acquisition of characteristic values] To detect the characteristic value of the height of the presser foot 21, it is necessary to measure multiple separation distances in the Z-axis direction between the first sensor 32 and the permanent magnet 31, and the signal output voltages of the first sensor 32 and the second sensor 33 at each separation distance, which is a very complicated measurement process. Therefore, the CPU 91 of the control device 90 may control the height adjustment motor 25 to automatically acquire the characteristic values ​​described above. This control is preferably executed while the sewing machine 100 is sewing. For example, it is assumed that height adjustment motor 25 is capable of rotating the output shaft in known output shaft angle units (resolution), and accordingly, is capable of raising and lowering presser foot 21 in known distance units. In this case, as an example, height adjustment motor 25 is preferably a stepping motor.

[0077] Under the above assumptions, as shown in Fig. 13, the detection processing unit 911 controls the height adjustment motor 25 to store the signal output voltage values ​​of the first sensor 32 and the second sensor 33 when the presser foot 21 is at its lowest height (the height at which the presser foot 21 abuts the needle plate 114). Then, the presser foot 21 starts to rise from its lowest height, and the number of operation steps of the height adjustment motor 25 from the start of the rise operation is counted. Reference symbol K11 in Fig. 13 indicates the separation distance from the first sensor 32 to the permanent magnet 31 along the Z axis direction when the permanent magnet 31 is closest to the first sensor 32 (distance 0), and reference symbol K12 indicates the separation distance from the first sensor 32 to the permanent magnet 31 along the Z axis direction when the permanent magnet 31 is closest to the second sensor 33.

[0078] It is preferable that the minimum height of the presser foot 21 is set so that the permanent magnet 31 is closest to (at the same height as) the first sensor 32, but it may also be arranged so that the permanent magnet 31 is slightly higher than the first sensor 32. Furthermore, if the height adjustment motor 25 is a stepping motor, it is preferable to set the presser foot 21 to be at its minimum height when it is at the origin position indicated by an origin sensor that is normally provided on the stepping motor. However, this is not essential. For example, without using the origin sensor of the height adjustment motor 25, it is possible to control the height adjustment motor 25 so that the presser foot 21 descends, and when the presser foot 21 descends to its minimum height and abuts against the needle plate 114, it is no longer able to descend any further. This can be detected by an increase in the drive current value that accompanies an increase in the torque of the height adjustment motor 25.

[0079] The detection processing unit 911 monitors changes in the signal output voltages of the first sensor 32 and the second sensor 33 while raising the presser foot 21. Fig. 14 is a diagram showing changes in the signal output voltage of the first sensor 32 when the presser foot 21 is raised, and Fig. 15 is a diagram showing changes in the signal output voltage of the second sensor 33 when the presser foot 21 is raised. 15, when the presser foot 21 rises and the permanent magnet 31 reaches the separation distance K12, the signal output voltage of the second sensor 33 changes from rising to falling. This allows the detection processing unit 911 to detect that the separation distance K12 has been reached. The detection processing unit 911 then stores the signal output voltage values ​​of the first sensor 32 and the second sensor 33 at this time. If the amount of lifting and lowering movement of the presser foot 21 in one step of the height adjustment motor 25 is known, the detection processing unit 911 multiplies the amount of lifting and lowering movement of the presser foot 21 in one step by the cumulative number of operating steps of the height adjustment motor 25 when the separation distance K12 is reached, and thereby obtains the height of lift of the presser foot 21 from the start of driving of the height adjustment motor 25 until it reaches the separation distance K12, i.e., the distance in the Z-axis direction from separation distance K11 to separation distance K12. The distance in the Z-axis direction from the separation distance K11 to the separation distance K12 may be obtained from known design information regarding the placement of the first sensor 32 and the second sensor 33, or may be pre-registered in the data memory 94. Then, through the above processing, the detection processing unit 911 can obtain the distance numerical values ​​of the separation distance K11 and the separation distance K12, and the signal output voltage values ​​of the first sensor 32 and the second sensor 33 at the separation distance K11 and the separation distance K12, and store these in the data memory 94 as characteristic values.

[0080] During sewing, the detection processing unit 911 can calculate the distance Kx using the above characteristic values ​​by the same calculation method as the above-mentioned formulas (1) to (5). This eliminates the need for the operator to measure the signal output voltages of the first sensor 32 and the second sensor 33 at the distance values ​​of each separation position as characteristic values ​​and manually register them in the data memory 94, thereby reducing the burden of advance preparation work.

[0081] Furthermore, when control for automatically acquiring characteristic values ​​is executed, the signal output voltage values ​​of the first sensor 32 and the second sensor 33 are recorded for each predetermined number of operating steps from the time when the presser foot 21 starts to move until it reaches the separation distance K12. This makes it possible to acquire three or more separation distances, such as the aforementioned distances 0, K3, K4, K5, and K2, and the signal output voltage values ​​of the first sensor 32 and the second sensor 33 at each separation distance as characteristic values, thereby making it possible to acquire the distance Kx with even greater accuracy. Furthermore, when executing control to automatically obtain characteristic values, by reducing the number of predetermined operation steps for recording the signal output voltage values ​​of the first sensor 32 and the second sensor 33 (for example, every step or every few steps) from the start of driving the presser foot 21 until it reaches the separation distance K12, it is also possible to generate table data in which difference values ​​are associated with each distance value in the range from distance 0 to distance K12.

[0082] In addition, the control by the detection processing unit 911 to automatically acquire the characteristic value may be repeated multiple times, and the signal output voltages of the first sensor 32 and the second sensor 33 (or their difference values) may be averaged to determine the numerical value. [Explanation of symbols]

[0083] 20 Presser mechanism 21 Presser foot 22 Holding arm (support member) 23 Proximal support part 24 Pressing member 25 Height adjustment motor 30 Detection device 31 Permanent magnet (detection object) 32 First Sensor 33 Second Sensor 51 Sewing machine motor 52 Feed adjustment motor 90 Control device 91 CPU 94 Data memory (storage section) 100 sewing machines 114 Needle plate 911 detection processing unit 912 Detachment determination unit 913 Presser control section 914 Stitch pitch control unit K2 Maximum distance (characteristic value) Kx distance V11, V12, V21, V22 signal output voltage (characteristic value) V1x signal output voltage V2x signal output voltage V31, V32 composite voltage (differential value) V3x Composite voltage (difference value)

Claims

1. a detection device that detects the height of a presser foot that is supported by a support member so as to be able to rise and fall and that presses down on an object to be sewn on a needle plate from above; the detection device includes a detection object that moves up and down together with the presser foot, and a first sensor and a second sensor whose signal output increases as the distance between the detection object and the first sensor decreases, the first sensor is disposed below the second sensor, and when the presser foot is at its lowest height, the detected object is disposed at the same height as the first sensor or at a height between the first sensor and the second sensor; a detection processing unit that acquires the height of the presser foot based on a difference between the signal output of the first sensor and the signal output of the second sensor;

2. a storage unit configured to store a characteristic value for determining a distance characteristic of the object to be detected relative to the first sensor or the second sensor from a difference value of the signal output of the first sensor and the second sensor, The sewing machine according to claim 1 , wherein the detection processing unit acquires the height of the presser foot by referring to the characteristic value.

3. The sewing machine according to claim 2, characterized in that the characteristic values ​​are distance numerical values ​​from the first sensor or the second sensor to each of a plurality of distance positions of the object to be detected, and signal output values ​​of the first sensor and the second sensor at each of the plurality of distance positions or differential values ​​between the signal outputs of the first sensor and the second sensor.

4. 4. The sewing machine according to claim 3, wherein the plurality of spaced apart positions are three or more spaced apart positions.

5. The detection processing unit 5. The sewing machine according to claim 4, wherein the height of the presser foot is obtained by calculating the distance characteristic for each section divided by the three or more separation positions.

6. an actuator capable of raising and lowering the presser foot in known distance increments; a control device that controls the actuator to be driven in units of the distance; Equipped with the control device controls the actuator to raise and lower the presser foot so that the detection object is at the plurality of separate positions, and reads the signal output of the first sensor and the signal output of the second sensor at each of the plurality of separate positions; The sewing machine according to any one of claims 3 to 5, characterized in that the signal outputs of the first sensor and the second sensor at the plurality of spaced positions or the differential value of the signal outputs of the first sensor and the second sensor are stored in the memory unit as the characteristic value.

7. The presser foot is supported so as to be rotatable in a direction away from the path for the lifting operation, 2. The sewing machine according to claim 1, further comprising a detachment determination unit that determines whether the presser foot has been detached based on the signal output of the first sensor and the signal output of the second sensor.

8. 8. The sewing machine according to claim 7, wherein the detachment determination unit determines whether the presser foot is detached by comparing the height of the presser foot determined from the signal output of the first sensor with the height of the presser foot determined from the signal output of the second sensor.

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