Device for detecting amount of bobbin thread remaining in sewing machine

Abstract

The present invention addresses the problem of detecting, by means of a simplified structure, the amount of bobbin thread remaining in a vertical rotary hook housed in a cylindrical bed (cylinder bed). The cylinder bed (1) extends forward from a sewing machine body and houses a vertical rotary hook (5) in a tip section. An operation part (12) has a detection piece (12a), is disposed in the vicinity of the vertical rotary hook (5) in the cylinder bed (1), and causes the detection piece (12a) to enter and exit the vertical rotary hook (5). A drive part (11) for driving the operation part (12) is provided on the side of the sewing machine body part, and a transmission part (13) for transmitting a driving motion of the drive part (11) to the operation part (12) is provided inside the cylinder bed (1). The amount of bobbin thread remaining in the bobbin thread bobbin (22) is detected on the basis of causing the detection piece (12a) to enter the vertical rotary hook according to the driving motion of the drive part. The transmission part (13) is composed of a rotary shaft extending into the cylinder bed (1), and pivots the detection piece (12a).

Description

Bobbin thread remaining amount detection device in sewing machines

[0001] The present invention relates to a lower thread remaining amount detection device suitable for detecting the remaining amount of lower thread in a lower thread bobbin stored in a vertical rotating hook, in a sewing machine equipped with a cylindrical bed (cylinder bed) having a vertical rotating hook at its tip.

[0002] Embroidery machines have been known for some time in which a cylindrical bed (cylinder bed) with a vertical rotating hook housed at its tip is extended forward from the main body of the sewing machine (for example, Patent Document 1). Embroidery machines equipped with such a cylindrical bed are suitable for embroidering cylindrical workpieces such as T-shirts and hats, and have a slender cylindrical structure to accommodate small diameter workpieces such as golf club covers and armbands. Patent Document 1 also shows a structure in which a cylindrical workpiece is set in a cylindrical frame (such as a hat frame or cylindrical frame), and the cylindrical frame is rotated around the cylindrical bed (X drive) and linearly driven along the axis of the cylindrical bed (Y drive) to automatically sew a desired embroidery pattern. In such a structure in which the cylindrical frame is automatically driven around the cylindrical bed, the components for supporting the cylindrical frame so that it can move are arranged around the cylindrical bed, so there is no extra space around the cylindrical bed in which any other device could be installed.

[0003] On the other hand, in a sewing machine that arranges a bed having a vertically rotating bobbin below a flat sewing table (sewing machine table) and sews a fabric (plain fabric) spread on the upper surface of the sewing table, a lower thread remaining amount detection device for detecting the remaining amount of the lower thread wound around a lower thread bobbin housed in the vertically rotating bobbin is known (for example, Patent Document 2 or 3). Such a conventionally known lower thread remaining amount detection device arranges a detection mechanism including an air cylinder (actuator) and a detection pin etc. on the side (lateral) of the vertically rotating bobbin, and linearly strokes the detection pin by the air cylinder to make it enter / exit the vertically rotating bobbin, and detects the remaining amount of the lower thread based on the amount of entry of the detection pin when it abuts on the lower thread wound around the lower thread bobbin. In such a lower thread remaining amount detection device, since the detection mechanism including components that linearly stroke in the lateral direction is arranged on the side (lateral) of the vertically rotating bobbin, it is essential that there is room to arrange a detection mechanism that tends to be bulky around the vertically rotating bobbin. Assuming that such a conventionally known lower thread remaining amount detection device is applied to a vertically rotating bobbin housed in the above-mentioned cylindrical bed, it is substantially impossible to install such a detection mechanism beside the vertically rotating bobbin in the slender cylindrical bed. Due to such circumstances, conventionally, there has been no lower thread remaining amount detection device suitable for a cylindrical bed (cylinder bed).

[0004] Japanese Patent Application Laid-Open No. 2017-169599, Patent No. 6092965, Japanese Patent Application Laid-Open No. 2001-178980

[0005] The present invention has been made in view of the above points, and aims to provide a lower thread remaining amount detection device with a simplified structure suitable for a cylindrical bed (cylinder bed).

[0006] The present invention relates to a sewing machine comprising a cylindrical bed extending forward from the main body of the sewing machine and housing a vertical rotary hook at its tip, and a lower thread remaining amount detection device for detecting the remaining amount of lower thread wound on a lower thread bobbin housed in the vertical rotary hook, comprising a drive unit, an operating unit having a detection piece and positioned near the vertical rotary hook in the cylindrical bed and configured to move the detection piece into and out of the vertical rotary hook, and a transmission unit provided in the cylindrical bed and transmitting the drive motion of the drive unit to the operating unit, thereby enabling the detection of the remaining amount of lower thread wound on the lower thread bobbin by moving the detection piece into the vertical rotary hook in response to the drive motion of the drive unit.

[0007] According to the present invention, the only component positioned near the vertical rotating bobbin in the cylindrical bed is an operating unit configured to move the detection piece into and out of the vertical rotating bobbin. Since the operating unit only needs to have a simple structure that allows the detection piece to move in and out, it can be easily positioned near the vertical rotating bobbin within a slender cylindrical bed without being positioned outside the cylindrical bed. Furthermore, the transmission unit only needs to have a motion transmission function, so it can also have a simple structure and can be easily positioned within a slender cylindrical bed. This makes it possible to provide a simple bobbin thread remaining amount detection device suitable for cylindrical beds (cylinder beds).

[0008] A perspective view showing an example of a multi-needle sewing machine equipped with a bobbin thread remaining amount detection device according to one embodiment of the present invention. A perspective view showing an extracted cylinder bed (cylindrical bed) in the sewing machine shown in Figure 1, and showing the arrangement of the bobbin thread remaining amount detection device according to one embodiment of the present invention. A right side view of the cylinder bed (cylindrical bed) and the bobbin thread remaining amount detection device shown in Figure 2. An enlarged front view showing the relationship between the cylinder bed (cylindrical bed) and the sewing needle in the sewing machine shown in Figure 1, showing the state with the cover provided at the tip of the cylinder bed removed. An exploded perspective view of the vertical rotary hook. A front view showing the operation of the operating part in the bobbin thread remaining amount detection device shown in Figures 2 and 3. A perspective view showing an example of a sensor provided in relation to the drive part in the bobbin thread remaining amount detection device shown in Figures 2 and 3. A block diagram showing an outline of the control system related to the bobbin thread remaining amount detection device according to one embodiment of the present invention. A perspective view showing an embodiment of the present invention in a multi-head sewing machine with respect to the part related to the cylinder bed. A right side view showing the arrangement of the bobbin thread remaining amount detection device in the cylinder bed shown in Figure 9.

[0009] Figure 1 is a perspective view showing an example of a multi-needle sewing machine equipped with a bobbin thread remaining amount detection device 10 according to one embodiment of the present invention. Figure 2 is a perspective view showing an excerpt of the cylinder bed (cylindrical bed) 1 in this multi-needle sewing machine, and the arrangement of the bobbin thread remaining amount detection device 10 within the cylinder bed 1 is shown in perspective. Figure 3 is a right side view of the cylinder bed 1 and the bobbin thread remaining amount detection device 10. Figure 4 is an enlarged front view showing the relationship between the cylinder bed 1 and the sewing needle 2 in this multi-needle sewing machine, and shows the state with the cover provided at the tip of the cylinder bed 1 removed in order to show the structure inside the cylinder bed 1. This multi-needle sewing machine is, as an example, a single-head sewing machine equipped with a single sewing head H, and the sewing head H is provided on the upper front of the sewing machine body F. A needle bar case 3 equipped with multiple needle bars and sewing needles 2 is arranged to slide laterally on the front of the sewing head H.

[0010] In the sewing machine body F, a needle bar drive mechanism (not shown) is provided behind the sewing head H, which moves up and down in accordance with the rotation of the main shaft motor (not shown). Below the sewing head H, a cylinder bed 1 is provided, extending forward from the sewing machine body F. As is well known, a needle plate 4 having a needle hole is provided on the upper surface of the tip of the cylinder bed 1, and a vertical rotary hook (bobbin hook) 5 that rotates in synchronization with the main shaft motor is housed below the needle plate 4. Between the sewing head H and the cylinder bed 1, an embroidery hoop 6 is positioned so as to be movable in two dimensions in the X-Y direction. As is well known, the embroidery hoop 6 stretches and holds the workpiece (e.g., fabric), and is detachably held by a pair of holding arms 6a, and is driven horizontally in two dimensions in the X-Y direction in accordance with the movement of the pair of holding arms 6a, which are driven by a hoop drive device (not shown) provided on the sewing machine body F side.

[0011] As shown in Figure 1, a thread stand TS is provided extending from an appropriate location on the sewing machine body F, and multiple thread spools (not shown) are detachably installed on the thread stand TS. A thread introduction section TI is also installed at a position extending upward from the sewing machine body F. The thread introduction section TI includes components (omitted from the illustration for convenience) for introducing each color thread (upper thread) drawn upward from each thread spool of the thread stand TS, and is configured to guide the introduced color threads to the sewing head H.

[0012] An adjustment stand 7 is positioned on the upper part of the needle bar case 3, and the adjustment stand 7 slides and displaces integrally with the needle bar case 2 in the left-right direction (lateral direction). The adjustment stand 7 is equipped with a thread tension control and thread break detection device that applies tension to the upper thread passing through each needle and adjusts the tension. Each upper thread, guided from the thread introduction section TI to the sewing head H, is set in the thread tension control and thread break detection device on the adjustment stand 7, and then passed through the corresponding balance before being passed through the sewing needle 2. When one needle bar selected by sliding the needle bar case 3 is driven up and down by the needle bar drive mechanism, the sewing needle 2 attached to the selected needle bar moves up and down through the needle hole of the needle plate 4 of the cylinder bed 1. As is well known, a presser foot 8 is provided corresponding to each sewing needle 2, and the presser foot 8 moves up and down in synchronization with the up and down movement of the selected needle bar, pressing down the workpiece held in the embroidery hoop 6 near the needle drop position. Through the cooperation of the vertically moving sewing needle 2 and the vertically rotating bobbin (lower thread bobbin) 5 provided in the cylinder bed 1, a main stitch operation is performed using the upper thread threaded through the sewing needle and the lower thread drawn out from the vertically rotating bobbin (lower thread bobbin) 5, thereby performing embroidery stitching or other sewing on the workpiece held in the embroidery hoop 6.

[0013] Furthermore, the sewing machine according to this embodiment is designed to allow the attachment of a rotary frame drive unit (cylindrical frame drive unit) capable of setting a cylindrical frame (such as a hat frame or cylindrical frame) instead of the embroidery hoop 6 that moves horizontally in the X-Y direction, as is conventionally known (for example, as mentioned in Patent Document 1). In other words, it has a structure that allows either the embroidery hoop 6 that moves horizontally in the X-Y direction or the rotary frame drive unit (cylindrical frame drive unit) to be arbitrarily attached and detached. When the rotary frame drive unit (cylindrical frame drive unit) is attached, the cylindrical frame set in the rotary frame drive unit is rotated (X-driven) around the cylinder bed 1 and linearly driven (Y-driven) along the axis of the cylinder bed 1, thereby sewing the desired embroidery pattern onto the cylindrical or curved workpiece held in the cylindrical frame.

[0014] As shown in Figures 2 and 3, the bobbin thread remaining amount detection device 10 comprises a drive unit 11, an operating unit 12 having a detection piece 12a and positioned near the vertical rotary hook 5 in the cylinder bed 1, configured to allow the detection piece 12a to enter and exit the vertical rotary hook 5, and a transmission unit 13 provided in the cylinder bed 1 and configured to transmit the drive motion of the drive unit 11 to the operating unit 12. The drive unit 11 is provided on the side of the sewing machine body F. As an example, the drive unit 11 consists of a rotary motor, and the transmission unit 13 consists of a long shaft (long member) coupled to the rotating shaft of the rotary motor and rotated in accordance with the rotation of the rotary motor. As is well known, a lower shaft 9 is housed within the cylinder bed 1, extending in the longitudinal direction of the cylinder bed 1 from a drive source (not shown) on the side of the sewing machine body F to the vertical rotary hook 5 at the tip. The rotational motion from the drive source is transmitted to the vertical rotary hook 5 via the lower shaft 9, and the outer hook 20 (Figure 5) of the vertical rotary hook 5 rotates accordingly. The shaft acting as the transmission unit 13 is positioned below the lower shaft 9 that extends within the cylinder bed 1 and extends parallel (or approximately parallel) to the lower shaft 9.

[0015] The operating unit 12 is fixed to the tip of the shaft, which serves as the transmission unit 13, via a mounting portion 12b, and is configured to rotate / rotate integrally with the shaft. More specifically, the operating unit 12 includes a connecting piece 12c connected to the mounting portion 12b, and a substantially L-shaped (or substantially right-angled) detection piece 12a connected to the connecting piece 12c (see Figures 2 to 4). More specifically, the detection piece 12a includes a horizontal portion at one end connected to the connecting piece 12c, and a vertical portion extending upward from the other end of the horizontal portion, with the tip (upper end) of the vertical portion being configured to enter or exit the vertical rotating bobbin 5. In the standby state when the lower thread amount detection operation is not performed, as shown in Figures 2 to 4, the tip (upper end) of the vertical portion of the detection piece 12a is located to the right of the transmission unit (shaft) 13 (outside the rotation trajectory of the outer bobbin) in a front view. As will be explained later, when detecting the remaining amount of bobbin thread, the transmission unit (shaft) 13 rotates counterclockwise in a front view in accordance with the rotation of the drive unit (motor) 11, and the vertical portion of the detection piece 12a rotates counterclockwise around the axis of the transmission unit (shaft) 13 in accordance with this. In other words, the operating unit 12 is configured to pivot the detection piece 12a in accordance with the driving motion of the drive unit (motor) 11 transmitted via the transmission unit (shaft) 13.

[0016] Thus, the components of the bobbin thread remaining amount detection device 10, which is positioned near the vertical rotary hook 5 within the cylinder bed 1, consist only of an operating unit 12 configured to move the detection piece 12a into and out of the vertical rotary hook 5. The drive unit 11 for driving the operating unit 12 is provided on the side of the sewing machine body F (the side of the base opposite to the tip of the cylinder bed 1). Here, the operating unit 12 only needs to have a simple structure (12a, 12b, 12c) that allows the detection piece 12a to move in and out, so it can be easily positioned near the vertical rotary hook 5 within the slender cylinder bed 1 without being positioned outside the cylinder bed 1. Also, the transmission unit 13 only needs to have a motion transmission function, so it can have a simple structure (rotating shaft) and can be easily positioned within the slender cylinder bed 1. This makes it possible to provide a bobbin thread remaining amount detection device 10 with a simple structure suitable for the cylinder bed 1. Furthermore, since the movement of the detection piece 12a in the operating unit 12 is a pivot motion, there is no need to secure bulky space for linear stroke motion as seen in known detection mechanisms based on linear stroke motion, and in this respect as well, the lower thread remaining amount detection device 10 can be made more compact.

[0017] Furthermore, as shown in Figure 4, the pivot axis of the detection piece 12a (i.e., the axis of the rotating shaft of the transmission unit 13) should be positioned on approximately the extension of the straight line connecting the needle drop position in the cylinder bed 1 and the rotation axis of the vertical rotary hook 5 (i.e., the axis of the lower shaft 9) (i.e., below the lower shaft 9). This arrangement only requires securing the necessary space in the vertical direction to house the lower thread remaining amount detection device 10 within the cylinder bed 1, and does not require expanding the size of the cylinder bed 1 in the left-right direction (lateral direction), thus making it possible to house the lower thread remaining amount detection device 10 within the frame size of an existing cylinder bed. In addition, by positioning the pivot axis of the detection piece 12a on approximately the extension of the straight line connecting the needle drop position and the rotation axis of the vertical rotary hook 5 (i.e., the axis of the lower shaft 9) (i.e., below the lower shaft 9), the detection piece 12a can be positioned in the space on the lower right side of the cylinder bed 1 when viewed from the front (see Figure 4). In existing cylinder beds, the bobbin cover support shaft is located directly below the vertical rotating bobbin, leaving an empty space to the lower right. In this embodiment, it is possible to use a cylinder bed 1 with the same external dimensions as existing cylinder beds to house the bobbin thread remaining amount detection device 10. In that case, the bobbin cover support shaft, which was previously located directly below the vertical rotating bobbin, can be redesigned to be located in the space to the lower left (or lower right) of the cylinder bed 1 when viewed from the front. Even in that case, the space to the lower right (or lower left) of the cylinder bed 1 when viewed from the front remains an empty space, allowing the detection piece 12a to be placed there. In this sense, it is possible to house the bobbin thread remaining amount detection device 10 within the frame size of an existing cylinder bed without the need to secure extra space for the detection piece 12a. Therefore, the arrangement of the pivot axis of the detection piece 12a (arranged to be below the lower shaft 9) as seen in this embodiment is advantageous. Thus, according to this embodiment, the lower thread remaining amount detection device 10 can be compactly housed within the cylinder bed 1 without increasing the frame size of the cylinder bed 1 (especially the horizontal size).

[0018] Figure 5 is an exploded perspective view of the vertical rotary hook 5. The vertical rotary hook 5 includes an outer hook 20 and an inner hook 21, as is commonly known, and a bobbin case 23 containing a lower thread bobbin 22 is set in the inner hook 21. The central hole 22a of the lower thread bobbin 22 is inserted into a support shaft 21a protruding from the inner hook 21, so that the lower thread bobbin 22 can rotate freely around the support shaft 21a. During sewing, the inner hook 21 is fixed and the outer hook 20 rotates. The lower thread T becomes entangled with the upper thread caught by the rotation of the outer hook 20, and as the sewing needle 2 rises, the lower thread T is pulled out from the lower thread bobbin 22, and the lower thread bobbin 22 can also rotate freely as appropriate. In this embodiment, openings 21b and 23a are provided at predetermined positions on the sides of the inner bobbin 21 and bobbin case 23, respectively, to allow the detection piece 12a of the operating unit 12 to enter the vertical rotating bobbin 5 during the lower thread remaining amount detection operation. When the bobbin case 23 is set in the inner bobbin 21, the openings 21b and 23a are aligned so as to follow the rotational trajectory of the vertical portion of the detection piece 12a. An opening 20a is originally present on the side of the outer bobbin 20. Furthermore, the rotation angle of the outer bobbin 20 is predetermined so that the openings 20a and 21b and 23a are aligned with the rotational trajectory of the vertical portion of the detection piece 12a of the operating unit 12 during the lower thread remaining amount detection operation. In other words, when detecting the remaining amount of bobbin thread, by positioning the outer bobbin 20 of the vertical rotary bobbin 5 at such a predetermined rotation angle, the detection piece 12a (its vertical portion), which rotates counterclockwise in a front view, can enter the vertical rotary bobbin 5 through the openings 20a and 21b and 23a. The tip of the detection piece 12a that has entered the vertical rotary bobbin 5 through the openings 20a and 21b and 23a comes into contact with the surface of the bobbin thread T wound on the bobbin thread bobbin 22, and its movement is stopped.

[0019] Figure 6 is a front view showing the operation of the operating unit 12 in the lower thread remaining amount detection device 10 as described above. Figure 6(a) shows the state of the operating unit 12 (detection piece 12a) in a standby state when the lower thread remaining amount detection operation is not performed, similar to Figure 4 described above, and (b) shows the state of the operating unit 12 (detection piece 12a) when the lower thread remaining amount detection operation is performed (in particular, the state when the tip of the detection piece 12a is in contact with the outermost part of the lower thread T wound on the lower thread bobbin 22). In the standby state shown in (a), the detection piece 12a is outside the vertical rotary hook 5, and the vertical rotary hook 5 rotates without being buffered by the detection piece 12a. At an appropriate time when the sewing operation is stopped (i.e., when the rotation of the vertical rotary hook 5 is stopped) (for example, after stopping the rotation of the vertical rotary hook 5 and cutting the lower thread at the end of sewing), the lower thread remaining amount detection operation is performed by the lower thread remaining amount detection device 10.

[0020] When starting the bobbin thread remaining amount detection operation, first, the outer bobbin 20 of the vertical rotary bobbin 5 is positioned at the predetermined rotation angle and its rotation is stopped, setting the tip of the detection piece 12a to be able to enter the vertical rotary bobbin 5 through the openings 20a and 21b and 23a. Next, the motor of the drive unit 11 is slowly rotated (with low torque) counterclockwise when viewed from the front. In response, the transmission unit (shaft) 13 rotates counterclockwise, and the operating unit 12 (detection piece 12a) rotates counterclockwise around the axis of the transmission unit (shaft) 13, causing the tip of the detection piece 12a to enter the vertical rotary bobbin 5 through the openings 20a and 21b and 23a. When the tip of the detection piece 12a that has entered the vertical rotary bobbin 5 comes into contact with the surface of the bobbin thread T wound on the bobbin thread bobbin 22, its movement is stopped. Figure 6(b) illustrates the state in which the movement of the detection piece 12a is stopped in this manner. The amount of time the detection piece 12a enters the vertical rotary bobbin 5 when its movement is stopped corresponds to the amount of lower thread T used from the lower thread bobbin 22. The amount of lower thread T used is inversely correlated with the amount of lower thread T remaining wound on the lower thread bobbin 22. Therefore, the remaining amount of lower thread can be detected by detecting the amount of time the detection piece 12a enters the vertical rotary bobbin 5 using an appropriate detection means. Magnetic, optical, or mechanical detection means can be arbitrarily adopted for this purpose. If there is sufficient space in the cylinder bed 1, such detection means can also be placed near the vertical rotary bobbin 5 within the cylinder bed 1. However, in a preferred embodiment, such detection means can be placed outside the cylinder bed 1, for example, on the side of the drive unit 11 as shown in Figure 7. By placing the detection means on the side of the drive unit 11 in this way, it is possible to prevent the structure inside the cylinder bed 1 from becoming complicated. After the detection of the remaining amount of bobbin thread is completed, the motor of the drive unit 11 is rotated in the reverse direction (clockwise) to remove the detection piece 12a from the vertical rotary bobbin 5, returning it to the standby state shown in Figure 6(a).

[0021] Figure 7 is a perspective view showing an example in which a detection means 14 for detecting the amount of entry of the detection piece 12a into the vertical rotary hook 5 is provided on the side of the drive unit 11. This detection means 14 includes a magnetic body 14a (rotor) attached to the rotating shaft of the drive unit 11, which is an electric motor, and a rotation sensor 14b (stator) fixed to the sewing machine body via a bracket 14c. The magnetic body 14a (rotor) and the rotation sensor 14b (stator) are in close, non-contact proximity and facing each other, and the rotation sensor 14b is configured to generate an output signal corresponding to the rotation angle (rotation position) of the magnetic body 14a. The amount of entry of the detection piece 12a into the vertical rotary hook 5 corresponds to the rotation angle of the transmission unit (shaft) 13 when the detection piece 12a stops, that is, the motor rotation angle of the drive unit 11. Therefore, by detecting the motor rotation angle of the drive unit 11 with the detection means 14, the amount of entry can be detected, and based on this, the remaining amount of bobbin thread can be detected.

[0022] Figure 8 is a block diagram illustrating the schematic control system related to the bobbin thread remaining amount detection device 10. The electronic control device 15 includes a microprocessor and memory, and is configured to execute a program related to the bobbin thread remaining amount detection operation, and performs functions such as determination means 15a and calibration means 15b. The determination means 15a determines the bobbin thread remaining amount based on the output signal of the detection means 14 (i.e., the rotation angle corresponding to the amount of insertion). As an example, the determination means 15a may have a function to convert the output signal of the detection means 14 (i.e., the rotation angle corresponding to the amount of insertion) into data or information indicating the bobbin thread remaining amount. For example, it may convert the bobbin thread remaining amount into a percentage, with 100% representing a full state and 0% representing an empty state, and output determination information that expresses the detected current bobbin thread remaining amount as a percentage. Alternatively, it may compare the output signal of the detection means 14 (i.e., the rotation angle corresponding to the amount of insertion) with a predetermined reference value and output determination information that notifies of a shortage of bobbin thread remaining amount when it falls below the reference value. This bobbin thread remaining amount information can be displayed, for example, on a general-purpose display device 30 (Figure 1) attached to the sewing machine and / or on a dedicated LED indicator light (not shown), and an alarm sound may also be emitted from a speaker if necessary.

[0023] [Correction based on Rule 91 15.04.2026] Due to subtle variations (or errors) in the mounting position of the operating part 12 relative to the transmission part (shaft) 13, variations (or errors) may occur in the relationship between the actual amount of insertion and the value of the output signal (rotation angle) of the detection means 14. Furthermore, individual differences in the lower thread bobbins 22 set in the vertical rotary hook 5, or individual differences in each type of lower thread T, may also cause variations in the relationship between the actual amount of insertion and the value of the output signal (rotation angle) of the detection means 14. To pre-calibrate such variations (or errors), a calibration means 15b may be provided. The calibration means 15b, for example, pre-measures the output value of the detection means 14 when the amount of lower thread in the lower thread bobbin 22 is approximately full and stores it as a first measurement value (A), and measures the output value of the detection means 14 when the amount of lower thread in the lower thread bobbin 22 is approximately zero and stores it as a second measurement value (B). Using the first and second measurement values ​​thus stored, it functions to calibrate (correct) the output value (C) of the detection means 14 during the actual lower thread remaining amount detection operation. As an example, a calibration formula of "Calibration value (%) = (C - B) ÷ (A - B) × 100" can be adopted. By undergoing calibration (correction) by this calibration means 15b, the determination process in the determination means 15a can be performed accurately.

[0024] It is also possible to modify the design so that the detection piece 12a is positioned on the opposite side from the example shown in Figure 4, etc., where the detection piece 12a is positioned in the space on the lower right side of the cylinder bed 1 when viewed from the front, that is, in the space on the lower left side of the cylinder bed 1. In that case, the vertical portion of the detection piece 12a is modified so that it rotates clockwise around the axis of the transmission part (shaft) 13, and the openings 21b and 23a on the sides of the inner casing 21 and bobbin case 23 are also modified so that they are positioned on the opposite side (i.e., the side facing the vertical portion of the detection piece 12a).

[0025] In the above embodiment, the elongated member functioning as the transmission unit 13 is a rotating shaft, but it is not limited to this. For example, the drive unit 11, located on the side of the sewing machine body F (or the base side of the cylinder bed 1), may be used to swing or slide the elongated member (transmission unit 13) from side to side by an appropriate amount in the lateral direction within the cylinder bed 1, thereby causing the detection piece of the operating unit 12 provided at the tip of the elongated member (transmission unit 13) to enter and exit the vertical rotary hook 5.

[0026] The present invention is not limited to single-head sewing machines as in the above embodiment, but can also be applied to multi-head sewing machines equipped with multiple sewing heads. Figure 9 is a perspective view showing an embodiment of the present invention in a multi-head sewing machine, relating to the cylinder bed 1. Figure 10 is a right side view showing the interior of the cylinder bed 1 shown in Figure 9 and the arrangement of the related bobbin thread remaining amount detection device 10. In a multi-head sewing machine, a cylinder bed 1 is provided below each sewing head, and the bobbin thread remaining amount detection device 10 according to this embodiment is also provided for each cylinder bed 1. In this case, the specific configuration of each bobbin thread remaining amount detection device 10 may be substantially the same as the configuration of the bobbin thread remaining amount detection device 10 in the single-head sewing machine described above. In the embodiment shown in Figures 9 and 10, the drive unit 11 is installed in the sewing machine body F so that its output rotation shaft points vertically upward, and the direction of its rotation axis is converted to the horizontal direction via bevel gears 11a and 11b and connected to a transmission unit (rotating shaft) 13 that extends horizontally inside the cylinder bed 1. The structure of the operating part 12, which is provided on the tip side of the transmission part (rotating shaft) 13, may be exactly the same as described above. Also, the detection means 14 is provided in relation to the rotating shaft of the drive part 11, as described above.

[0027] As another embodiment, the lower thread remaining amount detection device 10 according to this embodiment can also be applied to a sewing machine of the type in which sewing is performed by setting a cylindrical workpiece on the cylinder bed 1 and manually moving the workpiece, without using either an X-Y driven embroidery hoop 6 or a cylindrical workpiece hoop.

Claims

1. A sewing machine comprising a cylindrical bed extending forward from the main body of the sewing machine and housing a vertical rotary hook at its tip, wherein the remaining amount of lower thread wound around a lower thread bobbin housed in the vertical rotary hook is detected, comprising: a drive unit; an operating unit having a detection piece and positioned near the vertical rotary hook in the cylindrical bed and configured to move the detection piece into and out of the vertical rotary hook; and a transmission unit provided in the cylindrical bed and transmitting the drive motion from the drive unit to the operating unit, wherein the remaining amount of lower thread wound around the lower thread bobbin can be detected by moving the detection piece into the vertical rotary hook in response to the drive motion from the drive unit.

2. The lower thread remaining amount detection device for a sewing machine according to claim 1, wherein the operating unit is configured to pivot the detection piece in response to the driving motion of the drive unit transmitted via the transmission unit.

3. The lower thread remaining amount detection device for a sewing machine according to claim 1, wherein the transmission unit includes an elongated member that transmits the driving motion from the drive unit, and the elongated member extends parallel to or substantially parallel to a lower shaft that extends into the cylindrical bed for rotationally driving the vertical rotary bobbin.

4. The lower thread remaining amount detection device for a sewing machine according to claim 3, wherein the driving motion by the drive unit is rotational motion, and the long member of the transmission unit is a rotating shaft.

5. The lower thread remaining amount detection device for a sewing machine according to claim 2, wherein the pivot axis of the detection piece is located on substantially the extension of the straight line connecting the needle drop position on the cylindrical bed and the rotation axis of the vertical rotary hook.

6. The lower thread remaining amount detection device for a sewing machine according to claim 1, wherein the vertical rotating bobbin has an opening formed therein that allows the detection piece to enter and exit.

7. A lower thread remaining amount detection device for a sewing machine according to claim 6, wherein the remaining amount of lower thread is detected by introducing the detection piece into the vertical rotating bobbin through the opening when the rotation of the vertical rotating bobbin is stopped, and then the detection piece is removed from the vertical rotating bobbin.

8. A lower thread remaining amount detection device for a sewing machine according to any one of claims 1 to 7, further comprising: a detection means for detecting the amount of the detection piece that has entered the vertical rotating bobbin; and a determination means for determining the remaining amount of lower thread based on the amount of entry detected by the detection means.

9. A lower thread remaining amount detection device for a sewing machine according to claim 8, further comprising a calibration means for measuring the output value of the detection means when the amount of lower thread wound on the lower thread bobbin is approximately full and holding it as a first measured value, and measuring the output value of the detection means when the amount of lower thread wound on the lower thread bobbin is approximately zero and holding it as a second measured value, and calibrating the output value of the sensor using the first and second measured values.

10. The sewing machine is equipped with a detachable cylindrical frame drive unit that can set a cylindrical frame so as to be rotatable around the cylindrical bed and so as to be linearly movable along the cylindrical bed, and is capable of sewing on a workpiece held in the cylindrical frame, the lower thread remaining amount detection device for a sewing machine according to any one of claims 1 to 7.

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