sewing machine

Abstract

Sewing machine (10) with a vertical shuttle (20) and a center shuttle presser (22) arranged on a front side of the vertical shuttle (20), the sewing machine (10) comprising: a presser frame (30) which is movably held between a press position in which the center shuttle presser (22) is pressed and a retract position which is separate from the press position; an optical upper thread detector (60) which is provided on the presser frame (30) and is configured to detect the passage of an upper thread using detection light which passes through passage areas formed in the center shuttle presser (22) and crosses a front side of a bobbin case (24) of the vertical shuttle (20);and a stitch exit detection processor (90) which is configured to determine, based on an amount of light received from the detection light by the upper thread detector (60), whether the passage of the upper thread is present.

Description

BACKGROUND OF THE INVENTION Field of invention The present invention relates to a stitch skip detection of a sewing machine, which optically detects whether an upper thread, which is picked up by an upper thread loop formed by a sewing needle via a shuttle point of a shuttle, passes through the shuttle, and which thereby detects a stitch skip in which no stitch is formed. State of the art Sewing on a sewing machine is accomplished by an upper thread and a bobbin thread forming stitches as needed. Specifically, a sewing needle, its eye threaded through the upper thread, pierces the fabric, emerging from beneath it, and then rises upwards. As the needle reaches its bottom dead center, the upper thread loosens beneath the fabric, forming a loop. Simultaneously, a shuttle, rotating in sync with the needle's up-and-down motion, catches the looped upper thread at a point where the needle has moved slightly beyond its bottom dead center.When a thread take-up lever rises to a position where the shuttle is rotating and the shuttle point passes a given position, the shuttle is caused to pass through the loop of the upper thread, and the lower thread, which comes from a bobbin case to reach the fabric being sewn, is intertwined with the upper thread to form a stitch. The conventional sewing machine detects whether the loop passes across the bobbin case when the shuttle is caused to pass through the loop of the upper thread caught by the shuttle, projects light onto a front of the bobbin case from a direction which is inclined with respect to a rotational center line of the shuttle, optically detects a change in the light intensity of the reflected light by means of a photoelectric detector and detects the creation of a stitch skip, thus preventing knot formation between the upper thread and the lower thread (see for example JP 2000 - 197 786 A ). However, in a conventional sewing machine, the light is projected onto the bobbin case from the front. Since the bobbin case is made of metal and usually shiny, the reflected light is significantly altered by even slight vibrations or rattling during sewing. This increases interference and makes it difficult to detect the thread's passage with high accuracy. DE 10 2014 220 209 A1 discloses a sensor assembly for a sewing machine. DE 10 2016 107 761 A1 describes a sewing machine. DE JP 2006 - 262 978 A deals with a device for detecting skipped stitches and empty sewing for lockstitch sewing machines. One object of the present invention is to detect a stitch omission with higher accuracy. SUMMARY (1) A sewing machine comprises a vertical shuttle and a central shuttle presser. The central shuttle presser is arranged on the front side of the vertical shuttle. The sewing machine includes a presser frame, an optical upper thread detector, and a stitch exit detection processor. The presser frame is movably mounted between a pressing position, in which the central shuttle presser is pressed, and a retraction position, which is separate from the pressing position. The optical upper thread detector is provided on the presser frame and is configured to detect the passage of an upper thread using detection light, which passes through openings formed in the central shuttle presser and crosses the front side of a bobbin case of the vertical shuttle.The stitch exit detection processor is designed to determine, based on the amount of light received from the upper thread detector, whether the upper thread has passed through. (2) In the sewing machine according to (1), an uneven structure is provided for positioning between the presser frame and the shuttle presser. (3) In the sewing machine according to (2), the uneven structure includes a pin and a hole that allows the pin to be inserted into the hole. (4) In the sewing machine according to any of points (1) to (3), the shuttle presser has a circumferential wall area that surrounds a periphery of the vertical shuttle. Through holes are formed in the circumferential wall area, which act as the passage areas.A portion of each through-hole has a shape configured to fit a recessed form of a concave area formed in a front of the vertical shuttle. (5) The sewing machine according to any one of points (1) to (4) further comprises a toggle lever mechanism. The toggle lever mechanism is configured to apply a pressing force to the presser frame in the pressing position in the direction of the center shuttle presser. The presser frame is rotated to move between the pressing position and the retraction position. (6) In the sewing machine according to (5), the toggle lever mechanism comprises an input lever and an operation detector. The input lever is configured to apply and release the pressing force to the presser frame. The operation detector is configured to detect an operating state of the input lever. (7) The sewing machine according to any one of points (1) to (6) further comprises an air delivery mechanism.The air delivery mechanism is designed to blow air through a detection light passage path to remove dust. (8) In the sewing machine according to (7), the air delivery mechanism is provided on the presser frame and has nozzles which blow air through the passage areas of the center shuttle presser from one end and from the other end of the center shuttle presser in one direction. (9) In the sewing machine according to either point (7) or (8), the air delivery mechanism is provided on the presser frame and has nozzles which blow air through the light-receiving and light-emitting areas of the upper thread detector. (10) The sewing machine according to either point (7) to (9) further comprises a cleaning control unit. The cleaning control unit is designed to control the air delivery mechanism to periodically blow out air at intervals of a predetermined number of stitches or at a predetermined timing. The present invention is provided with an optical upper thread detector, which is equipped for a presser frame that presses a shuttle presser and detects the passage of an upper thread by means of detection light, which passes through passage areas formed in the shuttle presser and crosses a front side of a bobbin case of a vertical shuttle, and with a stitch exit detection processor, which determines, on the basis of an amount of received light of the detection light caused by the upper thread detector, whether the passage of the upper thread is present. Therefore, the upper thread can be detected by the detection light, which passes through the openings in the center shuttle presser and crosses the front of the bobbin case. Because the detection light is not projected onto the front of the bobbin case, variations in the detection light caused by vibration are inhibited. Since interference is reduced, the passage of the upper thread can be accurately detected, and the creation of a skipped stitch can also be accurately detected. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a front view showing the area surrounding a shuttle of a sewing machine according to an embodiment of the present invention; Fig. 2 is a perspective view showing the area surrounding the shuttle of the sewing machine according to an embodiment of the present invention; Fig. 3A is a front view of a bobbin case and Fig. 3B is a side view of the bobbin case; Fig. 4A is a left side view of a center shuttle presser and Fig. 4B is a right side view of the center shuttle presser; Fig. 5 shows a left side of the center shuttle presser in a partially enlarged view; Fig. 6 is a top view of a frame holding mechanism, wherein a presser frame is arranged in a pressing position; Fig. 7 is a top view of the frame holding mechanism, wherein the presser frame is arranged in a retracted position; Fig. 8 is a block diagram showing a control system of the sewing machine; and Fig.Figure 9 is a flowchart showing the control of a sewing process depending on a control unit. DETAILED DESCRIPTION [Sewing machine complete configuration] A sewing machine 10 according to an embodiment of the present invention will now be described in more detail with reference to the drawings. Fig. 1 is a front view of the area surrounding a shuttle of the sewing machine 10 and shows a configuration of a lower region of a plate-shaped needle plate auxiliary cover 11, which is arranged around a needle plate on the same plane as the needle plate. Fig. 2 shows the same configuration in a perspective view. As shown in Fig. 1, the sewing machine 10 is provided with a sewing machine frame, which is a housing. A sewing machine bed 12 is arranged below the sewing machine frame. At one end of the sewing machine bed 12, a large shuttle 21 of a vertical semi-rotary shuttle 20 is provided in a projected position in a horizontal direction. In the following description, a direction that is horizontally oriented and parallel to the direction in which the large shuttle 21 projects from the sewing machine bed part 12 is defined as an X-axis direction. Here, the side on which the large shuttle 21 lies (front of the sheet in Fig. 1) is defined as "front" and an opposite direction is defined as "back". Furthermore, a direction that is horizontally oriented and perpendicular to the X-axis direction is defined as a Y-axis direction. One endpoint (the left side in Fig. 1) of this direction is defined as "left"; the other endpoint (the right side in Fig. 1) of this direction is defined as "right". Furthermore, a direction perpendicular to both the X-axis and the Y-axis is defined as a Z-axis direction. One end face (the upper face in Fig. 1) of this direction is defined as "top" and the other end face (the lower face in Fig. 1) is defined as "bottom". The sewing machine 10 is provided with a sewing machine motor 14, with which a typical sewing machine is equipped, a top shaft, a needle bar up-and-down movement mechanism, a workpiece transport mechanism, a thread take-up lever, a thread tensioner, a thread cutting device, etc. These are identical to well-known components; therefore, a representation and description of them is omitted. The present sewing machine 10 is provided with characteristic configurations including a presser frame 30, which presses a center shuttle presser 22, which is arranged on a front side of the vertical semi-rotary shuttle 20, a frame holding mechanism 40, which holds the presser frame 30, an upper thread detector 60, which detects an upper thread that crosses a bobbin case 24 of the vertical semi-rotary shuttle 20, an air release mechanism 70, which performs an air blowing process to remove dust in the vicinity of the vertical semi-rotary shuttle 20, and a control unit 90, which controls the operation of each part of the sewing machine 10. The front of the vertical semi-rotary shuttle 20 is referred to as a surface on which the spool capsule 24 is arranged with respect to a central shuttle 23, which is described below. [Vertical semi-rotating boat] The vertical semi-rotary shuttle 20 is provided with the large shuttle 21, which has an approximate cylindrical shape, a middle shuttle 23, which is rotatably held inside the large shuttle 21, the bobbin case 24, which is housed inside the middle shuttle 23, a bobbin (not shown) which is housed in the bobbin case 24, and with a middle shuttle press 22, which holds the middle shuttle 23 housed in the large shuttle 21. The large shuttle 21 has an approximate cylindrical shape and is held firmly in place by a front end of the sewing machine bed part 12 in a state in which a center line of the same runs parallel to the X-axis direction. A central region of the front end of the large boat 21 is circularly wide open, and the middle boat 23 is housed inside the large boat 21. A sliding contact region is formed inside the large boat 21 along a circumference around an X-axis, is in sliding contact with an outer circumference of the middle boat 23, and holds the middle boat 23 in such a way that it is rotatable about the X-axis. The middle shuttle 23 is provided with a spindle which is inserted into the bobbin and bobbin case 24 at an inner rotation center position thereof, and with a shuttle point for catching the upper thread on an outer circumference thereof. Together with this central shuttle 23, a driver (not shown) is provided, which is given a reciprocating rotational movement centered on the X-axis by a sewing machine motor, which acts as a drive source for the sewing operation. The central shuttle 23 performs this X-axis-centered reciprocating rotational movement together with the driver. Due to this reciprocating rotational movement, the central shuttle 23 catches the loop of the upper thread from the sewing needle when the shuttle point is at its highest position and rotates downwards to pull the loop of the upper thread out. After the loop of the upper thread has been caused to pass through a lowest part of the central shuttle 23, the central shuttle 23 can change direction to reverse its rotation and return to the shuttle point at its highest point.Since the loop of the upper thread, which is pulled out to a position where it is caused to pass through the lowest part of the middle shuttle 23, is raised by lifting a thread take-up lever, the loop of the upper thread is lifted upwards, despite being separated from the shuttle point, and a knot can be formed between the upper thread and the lower thread. [Vertical semi-rotary boat: bobbin case] Fig. 3A is a front view of the coil capsule 24 and Fig. 3B is a side view of the coil capsule 24. As shown, the coil capsule 24 is provided with a cylindrical outer circumferential area 241 in which the coil is housed, and with a front area 242 which blocks a front end of the outer circumferential area 241.The bobbin case 24 is provided with a circular hole area 243 formed in the middle of the front area 242, into which the spindle of the middle shuttle 23 is inserted, a locking lever 244 which locks a circumferential groove formed at a tip of the inserted spindle of the middle shuttle 23 and prevents it from falling out, a thread tension spring 245 for applying a tensile force to the lower thread taken from the inner bobbin, an angular area 246 which extends upwards from the front area 242 and has an upper end on the inside which forms an insertion hole for the lower thread, and a concave area 247 which is formed in a lower area of ​​the front area 242 and recedes backwards. The outer circumference area 241 is wide open at one rear end, and the coil can be inserted into it from there. Additionally, the outer circumference area 241 is provided with a feed opening for the lower thread and can feed the wound lower thread of the inner bobbin to the outside. The thread tension spring 245 is a leaf spring, curved to follow a circumferential surface of the outer circumferential area 241, and positioned outside the outer circumferential area 241 to cover the thread feed opening. When the lower thread passes through a gap between the outer circumferential area 241 and the thread tension spring 245, a tensile force caused by sliding friction can be applied. As described above, the circular hole area 243 is formed in the center of the front area 242 and is equipped with the locking lever 244 such that it crosses the circular hole area 243. This locking lever 244 can be rotated relative to the front area to move up or down and locks the tip of the spindle of the central shuttle 23 by means of a rectangular opening which is formed at a position corresponding to the circular hole area 243. The angled section 246 extends from an upper side of the locking lever 244 at the front section 242 in a diagonal upward and rightward direction. This angled section 246 is bent backward at one upper end and has an insertion hole at one tip. The lower thread, taken from the bobbin, is guided through the insertion hole of the angled section 246, over the thread tension spring 245, to a needle hole in the needle plate. In Fig. 3A, the bobbin case 24 is shown in a state in which the upper end of the angular region 246 is located just above the center of the front region 242. However, as shown in Fig. 1, the bobbin case 24 is housed in the central shuttle 23 in a state in which it is tilted slightly to the left. The concave area 247 formed in a lower region of the front area 242 has an inclined surface 247a, which is inclined backwards from the front area 242, and a retreat surface 247b, which runs parallel to the front area 242 and is located behind the front area 242. In Fig. 3A, both the inclined surface 247a and the retraction surface 247b are shown as having a horizontal length. However, as shown in Fig. 1, the inclined surface 247a and the retraction surface 247b are inclined to a certain degree to the left when the bobbin case 24 is housed in the central shuttle 23. A valley in a downward-leftward inclined direction forms a boundary between these two planes. The formation of this concave area 247 in the lower area of ​​the front area 242 serves to reduce the sliding resistance of the upper thread, which passes through the lower area of ​​the front area 242 when the bobbin case 24 is caused to pass through the loop of the upper thread that is caught by the aforementioned shuttle point of the middle shuttle 23. If, as in an upper area of ​​the front area 242, a curved surface with a gentle backward curvature is also formed in the lower area of ​​the front area 242, then the upper thread moves in sliding contact with the entire curved surface and the sliding resistance increases. If, in contrast, the concave area 247 is formed, then the sliding resistance can be reduced by reducing the contact area, since only an upper edge of the inclined surface 247a and a lower edge of the retraction surface 247b come into sliding contact with the upper thread. It is therefore possible to advantageously allow the bobbin case 24 to pass through the loop of the upper thread; stitches can be formed stably. [Vertical semi-rotation boat: mid-boat presser] The center boat presser 22 is provided with a circumferential wall area 221, which has an approximate ring shape and surrounds a circumference of the center boat 23, and with a flange area 222, which extends from an outer circumference of the circumferential wall area 221 around it, excluding an upper area of ​​the circumferential wall area 221. The circumferential wall area 221 passes forwards and backwards in a state in which it is approximately circularly wide open and is provided with a sliding contact surface which slides in contact with a front surface of an outer edge of the middle boat 23 on its inner side. Since the circumferential wall area 221 is wide open, the bobbin case 24 can be inserted into and removed from an opening when the central shuttle presser 22 is attached to the large shuttle 21. Furthermore, an outwardly recessed, fitted concave region 221a is formed in a front inner circumferential region of the circumferential wall region 221, and the angular region 246 of the coil capsule 24 is fitted into the fitted concave region 221a. By fitting the angular region 246 into this fitted concave region 221a, rotation around the coil capsule 24 associated with the central shuttle 23 is prevented, and the coil capsule 24 can maintain a resting state. The flange area 222 of the center boat press 22 is formed with cutouts 222a and 222b, which are recessed to the left and right in the shape of a "U". Coupling elements 211 and 212 are arranged inside the cutouts 222a and 222b, which are equipped with the front area of ​​the large boat 21. Each of the coupling elements, namely the left and right coupling elements 211 and 212, is provided with a shaft section extending in the X-axis direction and with a plate-shaped handling lever located at one front end of the shaft section. The shaft section is inserted into a coupling hole (not shown) formed at the front of the large boat 21 and is rotatable and permanently locked in place. The operating lever extends radially from the front end of the shaft section, centered on the shaft section. The operating lever can be manually operated by a person to rotate the shaft. The coupling elements 211 and 212 do not interfere with the flange area 222 of the center boat press 22 when their respective operating levers are facing outwards, and can couple the center boat press 22 to or decouple it from the large boat 21. In the case of coupling, the center boat press 22 is positioned at the front of the large boat 21 by positioning the cutouts 222a and 222b relative to the coupling elements 211 and 212, and the operating lever of each coupling element 211 and 212 is rotated downwards. This brings the operating lever into contact with the front of the flange area 222 of the center boat press 22 and holds it in such a way that the center boat press 22 cannot detach from the large boat 21 by moving forwards. Because the handling lever of the right coupling element 212 is arranged to shield a light path for detection light of an optical element of the upper thread detector 60 (which will be described below), part of it becomes an opening 212a, which is cut out in a rectangular shape, and the detection light can pass through the opening 212a. Because the circumferential wall area 221 of the midship presser 22 is also arranged to shield the light path for the detection light of the optical element of the upper thread detector 60 (which will be described below), through holes 221b and 221c are formed in the left and right lower area of ​​the circumferential wall area 221, as shown in Fig. 4A and Fig. 4B, which function as passage areas allowed along the light path. The upper thread detector 60 (to be described below) is provided with an optical unit 61, which functions as a light-receiving area and a light-emitting area, receiving and projecting the detection light from a lower left side of the center shuttle presser 22 in a diagonally upward direction, and with a reflector 62, which reflects the detection light at a lower right side of the center shuttle presser 22. The detection light is designed to run parallel to a longitudinal direction of the concave area 247 of the aforementioned bobbin case 24 and to pass through the interior of the concave area 247. This means that, because - as with the concave area 247 - the light path of the detection light takes a direction that is inclined slightly downwards to the left with respect to the Y-axis direction, the left through-hole 221b is formed in a position that is slightly lower than the right through-hole 221c. As described above, the upper thread detector 60 has the optical unit 61 and the reflector 62 arranged in such a way that the detection light passes through the concave area 247 of the bobbin case 24 when the bobbin case is allowed to pass through the loop of the upper thread, the upper thread moves along the upper edge of the inclined surface 247a and the lower edge of the retraction surface 247b in order not to come into contact with the concave area 247, and part of the detection light is blocked to reduce the amount of light received, so that the upper thread detector 60 can detect that the upper thread is not skipping stitches and that the stitches are being formed. Therefore, at the through-hole 221b on the side of the optical unit 61, which receives the detection light, it is not desirable that a variation in the amount of received detection light occurs for reasons other than those caused by the upper thread. On the other hand, as shown in Fig. 4A, the through-hole 221b on the side of the optical unit 61 is formed in an approximate fan shape, without its shape being a circular shape like that of the through-hole 221c on the side of the reflector 62, thereby reducing the influence of the variation in the amount of received light of the detection light. This means that, since the central boat 23 performs a back-and-forth motion and a rotation around the coil capsule 24 at high speed, vibration in a forward / backward direction is particularly likely to occur. The cross-sectional shape of the concave region 247, through which the detection light passes and which lies along an XZ plane, is determined by the inclined surface 247a and the retraction surface 247b. When the detection light passing through this concave area 247 is received, and the shape of the through-hole 221b on the side of the optical unit 61—like the through-hole 221c in Fig. 4B—is approximately circular, a shielding area is formed within this approximately circular shape by the inclined surface 247a and the retraction surface 247b. When the bobbin case 24 vibrates back and forth, the shielding area also vibrates. This leads to variations in the amount of received detection light and reduces the detection accuracy of the upper thread. For this reason, as shown in Fig. 5, the through-hole 221b on the side of the optical unit 61 is formed in an approximate fan shape, and the formation of the shielding area caused by the inclined surface 247a and the retraction surface 247b is reduced or eliminated. This reduces the variation in the amount of received detection light due to the vibration of the bobbin case 24 and improves the detection accuracy of the upper thread. If the shape of the through-hole 221b on the side of the optical unit 61 has a form that is not shielded by the inclined surface 247a and the retraction surface 247b of the concave region 247, it may be a shape different from the approximate fan shape, for example a rhomboid shape, a parallelogram, a groove-shaped shape in which the through-hole is open, etc. In a front lower region of the flange area 222 of the center boat press 22, two pins 223 and 223 are formed, which are used for positioning and protrude in the form of a circular projection. These pins 223 and 223 form part of an uneven structure designed to perform positioning, which is formed between the press frame 30 (which is described below) and the center boat press 22; the pins 223 and 223 are inserted into two positioning holes 321 and 321 on the sides of the press frame 30, which form the uneven structure, and position the center boat press 22 and the press frame 30 in the correct positions relative to each other. [Press framework] The presser frame 30 is a frame which is held by the frame holding mechanism 40 (described below) in order to be movable between a pressing position (see Fig. 6) in which the center boat presser 22 is pressed from front to back and a retraction position (see Fig. 7) which is spaced apart from the pressing position. Unless explicitly stated otherwise, in the following description, orientation or direction and position information for each configuration is to be understood as referring to a pressing position of the press frame 30. This press frame 30 is provided with a plate-shaped main body 31, which extends along a YZ plane in the press position, and with a plate-shaped retaining plate 32, which is fixed to a rear side of the main body 31 and extends along the YZ plane together with the main body. The retaining plate 32 is held in place so that it can be connected at its lower end to the frame retaining mechanism 40. An arcuate concave region is formed at an upper end of the retaining plate 32, which is in contact with a lower end of the outer circumference of the circumferential wall region 221 of the center vane press 22. The two positioning holes 321 and 3221 are formed below the arcuate concave region of the retaining plate 32 in a passageway in the X-axis direction. As described above, these positioning holes 321 and 321 form part of the uneven structure designed to perform positioning, and which is formed between the presser frame 30 and the center boat presser 22; in this context, the positioning holes 321 and 321 fit around the pins 223 and 223 of the center boat presser 22 and position the center boat presser 22 and the presser frame 30 in correct positions relative to each other. The main body 31 is fixed to a front side of the retaining plate 32 and is subjected to a change of position as a body with the retaining plate 32 via the frame retaining mechanism 40. The main body 31 holds the optical unit 61 of the upper thread detector 60 firmly to a rear lateral area of ​​the same and the reflector 62 to a front right end of the same. The main body 31 holds a first and a second nozzle 71 and 72 of the air delivery mechanism 70 at a front left end of the same, a third and fourth nozzle 73 and 74 at a front central area of ​​the same and a fifth and sixth nozzle 75 and 76 at a rear right end of the same. [Upper thread detector] As described above, the upper thread detector 60 is provided with the optical unit 61, which is fixedly attached to a rear left end of the main body 31 of the presser frame 30, and with the reflector 62, which is fixedly attached to the front right end of the main body 31. The optical unit 61 is provided with the light-emitting element, which projects the detection light towards the reflector 62, and with the light-receiving element, which receives the detection light reflected from the reflector 62. The light-emitting element and the light-receiving element are arranged adjacent to each other and directed towards the side of the reflector 62 where the light-projecting direction of the light-emitting element and the light-receiving direction of the light-receiving element are the same. That is, the light-emitting element and the light-receiving element are parallel to the longitudinal directions of the inclined surface 247a and the retracted surface 247b of the concave region 247 of the coil capsule 24, and they are positioned inside the concave region 247 in the direction in which the detection light passes. The reflector 62 has a reflective surface which extends to the rear, and the reflective surface lies on an optical axis of the detection light and has a direction perpendicular to the optical axis. With the above configuration of the upper thread detector 60, it follows that when the detection light is projected from the light-emitting element of the optical unit 61, the detection light passes through the through-hole 221b of the mid-shuttle presser 22, then past the concave area 247 of the bobbin case 24, which is provided inside the mid-shuttle presser 22, passes through the through-hole 221c of the mid-shuttle presser 22, is reflected from the reflective surface of the reflector 62 in a parallel and reverse direction, passes again through the through-hole 221c, the concave area 247 and the through-hole 221b and is received by the light-receiving element of the optical unit 61. During sewing, the optical unit 61 detects that the loop of the upper thread passes through the concave area 247 and that the amount of received light from the detection light is reduced at a given angle of harmonic; this detects the formation of a proper knot. If the optical unit 61 does not detect that the amount of received light from the detection light is reduced at the given angle of harmonic, this results in the formation of a stitch skip. [Frame holding mechanism] Fig. 6 is a top view showing a state in which the frame holding mechanism 40 holds the press frame 30 in a pressing position, and Fig. 7 is a top view showing a state in which the frame holding mechanism 40 holds the press frame 30 in a retraction position. As shown in Fig. 1, Fig. 2, Fig. 6 and Fig. 7, the frame holding mechanism 40 is provided with a base frame 41, which is held firmly by the needle plate auxiliary cover 11 and the sewing machine bed part 12, a rotating plate 42, which is rotatably held by the base frame 41 about a Z-axis, a retaining block 43, which is fixed at one rotational end of the rotating plate 42 and holds the presser frame 30, and with a toggle lever mechanism 50, which presses the presser frame 30, which is in a pressing position, against the side of the large shuttle 21 via the retaining block 43. The base frame 41 is an approximately U-shaped frame when viewed from the Y-axis direction, and by bending a long flat plate, an upright plate area running along the YZ plane, an upper plate area extending forward from an upper end of the upright plate area, and a lower plate area extending forward from a lower end of the upright plate area are formed. The upright plate area of ​​the base frame 41 is fixed to the front of the sewing machine bed part 12 by screws, and the upper plate area is fixed to a lower surface of the needle plate auxiliary cover 11 by screws. As shown in Fig. 6 and Fig. 7, the rotating plate 42 rotates within an angle of approximately 90° around the Z-axis; in a state where one end of its rotation is directed to the right, it holds the press frame 30 in a pressing position, while in a state where its end of rotation is directed forward, it holds the press frame 30 in a retraction position. In the press position, this rotating plate 42 has a crank shape when viewed from the X-axis direction, and by bending a long flat plate, an upright plate area which runs along the XZ plane, an upper plate area which extends to the left from an upper end of the upright plate area, and a lower plate area which extends to the right from a lower end of the upright plate area are formed. The upper plate area of ​​the rotating plate 42 is rotatably mounted relative to the upper plate area of ​​the base frame 41 by means of a spindle extending in the Z-axis direction, and the retaining block 43 is fixed by screws on a lower surface of the lower plate area of ​​the rotating plate 42. The retaining block 43 is a long block extending in the Y-axis direction. An upper surface of a left end of the retaining block 43 is fixed by screws to the lower surface of the lower plate area of ​​the rotating plate 42, and a lower area of ​​the retaining plate 32 of the press frame 30 is fixed by screws to a lower surface of a right end of the retaining block 43. [Frame holding mechanism: Knee lever mechanism] The toggle lever mechanism 50 is provided with a connecting link body 51, which is coupled at one of its ends to the retaining block 43 and is rotatably mounted at its other end via the lower plate area of ​​the base frame 41 about the Z-axis, an input lever 52, which actuates the application of a pressing pressure to the press frame 30 and the removal of the pressing pressure from it, and with an operation detector 53, which detects an operational state of the input lever 52. The connecting element body 51 is mounted on the lower plate area of ​​the base frame 41 via a spindle which lies on the same axis as the spindle of the rotating plate 42, allowing it to rotate about the Z-axis. Therefore, the connecting element body 51, the rotating plate 42, the retaining block 43, and the press frame 30 can be rotated about the Z-axis as a single unit. The input lever 52 is rotatably mounted on the left side of the connecting link body 51 via the lower plate area of ​​the base frame 41 about the Z-axis, and a connecting arm between the connecting link body 51 and an operating area, which inputs a rotation operation via a human hand, extends transversely to a rotation spindle of the input lever 52 to one side and to the other side. The connecting arm of the input lever 52 is connected to the connecting link body 51 in a manner that allows rotation around the Z-axis near a rotary spindle of the same. If the input lever 52 is rotated clockwise when viewed from above, the connecting link body 51 is given a counterclockwise rotation, and the press frame 30 can be rotated from the retraction position towards the pressing position. Furthermore, a mutual connection position between the input lever 52 and the connecting link body 51 is designed to become a dead center before the pressing position. As the mutual connection position approaches the dead center, elastic bending is generated between the links of the input lever 52 and the connecting link body 51. Until the mutual connection position passes the dead center, elastic forces on the input lever 52 and the connecting link body 51 act in a rotational direction towards the retraction position. When the mutual connection position passes the dead center, an elastic force caused by bending of the input lever 52 and the connecting link body 51 changes to a rotational direction towards the pressing position. This allows the toggle lever mechanism 50 to impart a pressing pressure towards the side of the center boat presser 22 to the presser frame 30 in the pressing position via the connecting link body 51 and the retaining block 43. When the presser frame 30 is rotated by the toggle lever mechanism 50 over the connecting link body 51 and the retaining block 43 towards the side of the center boat presser 22, the two positioning holes 321 and 321 of the presser frame 30 coincide positionally with the pins 223 and 223 of the center boat presser 22 and the links are joined together such that the pins 223 and 223 are inserted into the positioning holes 321 and 321. Furthermore, the tips of pins 223 and 223 have tapered or rounded shapes. Even if a slight positional deviation occurs, pins 223 and 223 are designed to be guided into the positioning holes 321 and 321. The operational detector 53 is a proximity sensor and is positioned closest to the input lever 52 when the press frame 30 is moved upwards into the pressing position. This allows the operational detector 53 to detect that the press frame 30 is in the pressing position based on the approach of the input lever 52. [Air delivery mechanism] The air delivery mechanism 70 is provided with an air pressure generator (not shown) which uses a pneumatic pump or the like, and with nozzles, which are a first to sixth nozzle 71 to 76, which are connected to the air pressure generator via an electromagnetic valve and deliver air. All nozzles, namely the first to sixth nozzles 71 to 76, are held above the main body 31 of the press frame 30. Each nozzle, at a given position, performs an operation of blowing air and removing dust when the press frame 30 is in the pressing position. The first nozzle 71 is directed towards the light-emitting and light-receiving element of the optical unit 61 of the upper thread detector 60, is held at one tip of the same, and removes dust adhering to the optical unit 61. The second nozzle 72 is held at a tip of the outer side of the circumferential wall area 221 of the central boat presser 22 and is directed towards the through-hole 221b, and removes dust which adheres to the periphery of the through-hole 221b on the outer circumferential surface of the circumferential wall area 221 and the inside of the through-hole 221b. The third nozzle 73 is held at a tip of the inner side of the circumferential wall area 221 of the central boat presser 22 and is directed towards the through-hole 221b, and removes dust which adheres to the periphery of the through-hole 221b on the inner circumferential surface of the circumferential wall area 221 and the inner side of the through-hole 221b. The fourth nozzle 74 is held at a tip of the inner side of the circumferential wall area 221 of the central boat presser 22 and is directed towards the through-hole 221c, and removes dust which adheres to the periphery of the through-hole 221c on the inner circumferential surface of the circumferential wall area 221 and the inner side of the through-hole 221c. The fifth nozzle 75 is held at a tip of the outer side of the circumferential wall area 221 of the central boat presser 22 and is directed towards the through-hole 221c, and removes dust which adheres to the periphery of the through-hole 221c on the outer circumferential surface of the circumferential wall area 221 and the inside of the through-hole 221c. The sixth nozzle 76 is directed towards the reflective surface of the reflector 62 of the upper thread detector 60, is held at one tip of the same, and removes dust which adheres to the reflective surface of the reflector 62. [Sewing machine control system] As shown in Fig. 8, the sewing machine 10 has a drive circuit 14a for driving the sewing machine motor 14, a counter circuit 15a for a detected signal from an encoder 15 which detects a harmonic angle, the operation detector 53, the optical unit 61 of the upper thread detector 60, a drive circuit 78 of an electromagnetic valve 77 which controls an air blow operation of the air delivery mechanism 70, and an operating panel 91 which inputs start or set information regarding a sewing operation and displays given information, connected via (not shown) interfaces. The Encoder 15 outputs two types of phase signals that indicate the harmonic angle. An Encoder-A phase signal, output by the Encoder 15, is a smallest-unit signal and outputs one pulse each time the harmonic angle changes by 1 degree. An Encoder-Z phase signal, output by the Encoder 15, is a pulse signal that uses one revolution of the harmonic as one cycle. The control unit 90 can detect the harmonic angle by counting the number of pulses of the encoder-A phase signal using the encoder-Z phase signal as a starting point. The control unit 90 is a microprocessor which is provided with programs for executing various processes and controls, and with a (not shown) memory in which data used by the programs is stored, and executes the various controls based on these programs. The control unit 90 executes the programs and thereby performs a sewing work start determination process, a stitch exit detection process and a cleaning control. During the sewing work start determination process, when the sewing work start is entered via the control panel 91, the operation detector 53 detects whether the input lever 52 is present, and the control unit 90 starts the sewing work by driving the sewing machine motor 14 only if the approach of the input lever 52 is detected. This means that if the input lever 52 is not detected by the operation detector 53, the drive of the sewing machine motor 14 is regulated for itself – because there is a possibility that the presser frame 30 is not in a usable position and the center shuttle presser 22 is not pressing the center shuttle 23. When the input lever 52 is detected by the operation detector 53, a "sewing work permitted" state is set, and the sewing work, which is effected by driving the sewing machine motor 14, is initiated – because this means that the presser frame 30 is still pressing the center shuttle presser from the front in a usable position. The stitch omission detection process is a process of detecting the generation of a stitch omission using the upper thread detector 60 during sewing work and is performed repeatedly in a given cycle during sewing work. This means that, as described above, the upper thread detector 60 can detect the appropriate passage of the upper thread through the lower part of the bobbin case 24 due to a reduction in the intensity of the received detection light generated by the optical unit 61. Because the timing at which the upper thread passes through the lower part of the bobbin case 24 is a nearly constant harmonic angle, the control unit 90 monitors the output of the encoder 15 and determines whether the reduction in the intensity of the received detection light generated by the optical unit 61 is detected within a given harmonic angle range, including the harmonic angle in question.Therefore, if the reduction in the intensity of the received light does not occur, then the upper thread does not pass through the bobbin case 24, and it can thus be detected that the stitch skip is being created. Therefore, the control unit 90 functions as "a stitch exit detection processor to determine whether the passage of the upper thread is present, based on an amount of received light of the detection light caused by the upper thread detector". The cleaning control is a control for carrying out a process of blowing air from the first to sixth nozzle 71 to 76 of the air delivery mechanism 70 during sewing work and for removing dust at any position of the optical path of the detection light. In principle, during cleaning control, when the completion of the sewing work is detected, for example by entering the execution of the thread cutting via the control panel 91, the electromagnetic valve 77 is opened via the control unit 90 in order to carry out the process of blowing air from each of the nozzles 71 to 76 for a given time. However, in the case of sewing machine 10, if the needle localization frequency according to the sewing work exceeds a value of 1000 times, the amount of adhering dust in the vicinity of the vertical semi-rotary shuttle 20 is increased, and the detection accuracy of the upper thread by the optical unit 61 of the upper thread detector 60 is reduced. Therefore, the control unit 90 opens the electromagnetic valve 77 not only at the end of the sewing operation, but also to control the blowing of air from each of the nozzles 71 to 76 for a given time at intervals of 500 revolutions of the shaft from the start of the sewing operation. The number of revolutions of the shaft is detected by means of the encoder 15. The control unit 90 thus functions as "a cleaning control unit for controlling the air delivery mechanism to perform air blowing at intervals of a specified needle localization frequency or a specified time." The air blowing interval can be freely changed by a user, and thus the blowing at intervals of a given time can also be modified. [Sewing operation] Based on the flowchart of Fig. 9, a sewing operation control is described which includes the sewing start determination process, the stitch exit detection process and the cleaning control and is carried out by the control unit 90. When the sewing start is entered via the control panel 91, the control unit 90 first determines, using the operation detector 53, whether the input lever 52 of the knee lever mechanism 50 is in an operating position as a press position in which the presser frame 30 is pressed (step S1). In this process, if the operation detector 53 detects that the input lever 52 is not in the operating position (NO in step S1), an error indicating the failure of pressing is displayed on the control panel 91 as an error that the failure of pressing of the center boat presser 22, caused by the presser frame 30, occurs (step S3). On the other hand, if the operation detector 53 detects that the input lever 52 is in the operating position (YES in step S1), then the control unit 90 starts the drive of the sewing machine motor 14 (step S5) and starts counting the number of revolutions of the upper wave from the Z-phase signal of the encoder 15 (step S7). Furthermore, the control unit 90 determines from the A-phase signal of the encoder 15 whether the harmonic reaches a harmonic monitoring start angle, which is a start angle of the harmonic angular range to detect that the upper thread caught by the middle shuttle 23 passes correctly through the lower area of ​​the bobbin case 24 (step S9). If the harmonic does not reach the harmonic monitoring start angle (NO in step S9), the determination is repeated. If the harmonic does reach the harmonic monitoring start angle (YES in step S9), the control unit 90 determines from the output of the light-receiving element of the optical unit 61 whether a reduction in the intensity of the received light is detected according to the passage of the upper filament (step S11). If the upper thread is not detected (NO in step S11), the control unit 90 determines from the A-phase signal of the encoder 15 whether the harmonic reaches a harmonic monitoring end angle, which is an end angle of the harmonic's angular range to detect that the upper thread caught by the middle shuttle 23 passes correctly through the lower part of the bobbin case 24 (step S13). If the harmonic does not reach the harmonic monitoring end angle (NO in step S13), the control unit 90 reverses the process and determines again, based on the output of the light-receiving element of the optical unit 61, whether a reduction in the intensity of the received light is detected according to the passage of the upper thread (step S11). If, on the other hand, the passage of the upper thread is not detected and the upper wave reaches the upper wave monitoring end angle (YES at step S13), then it is determined that the stitch omission is generated, and the control unit 90 reports the generation of the stitch omission to the control panel 91 (step S15), stops the sewing machine motor 14 (step S17) and ends the sewing operation control. If, on the other hand, the passage of the upper thread is detected in step S11 (YES in step S11), then the control unit 90 determines whether a value obtained from counting the number of revolutions of the overtone using the encoder 15 reaches 500 revolutions (step S19). If the value obtained by counting the number of revolutions of the harmonic does not reach 500 revolutions (NO in step S19), the process proceeds to step S23. If the value obtained by counting the number of revolutions of the harmonic reaches 500 revolutions (YES in step S19), the control unit 90 opens the electromagnetic valve 77 of the air delivery mechanism 70 to blow air from each of the nozzles 71 to 76 for a given time (step S21). Next, the control unit 90 determines whether the thread cutting operation is initiated via the control panel 91 (step S23). If the thread cutting operation is not initiated (NO in step S23), the control unit 90 returns the process to step S9 and determines whether the harmonic angle reaches the harmonic monitoring start angle. When the thread cutting operation is entered (YES in step S23), the control unit 90 stops the drive of the sewing machine motor 14 (step S25) and the thread cutting operation is carried out via the thread cutting device (step S27). The control unit 90 opens the electromagnetic valve 77 of the air delivery mechanism 70 to continue the blowing of air from each of the nozzles 71 to 76 for a given time (step S29), resets the value obtained by counting the number of revolutions of the harmonic (step S31) and ends the sewing operation control. [Technical effects of the embodiment of the invention] The above sewing machine 10 is provided with the optical upper thread detector 60, which is equipped for the presser frame 30, which presses the center shuttle presser 22 and detects the passage of the upper thread by means of the detection light, which passes through the through holes 221b and 221c of the center shuttle presser 22 and crosses the front of the bobbin case 24 of the vertical semi-rotary shuttle 20, and with the control unit 90, which functions as a stitch exit detection processor, which determines, on the basis of the amount of light received from the detection light caused by the upper thread detector 60, whether the passage of the upper thread is present. This allows the upper thread to be detected by the detection light, which crosses the front of the bobbin case 24, due to the through-holes 221b and 221c formed in the center shuttle presser 22, and the detection light is not projected onto the front of the bobbin case 24. It is therefore possible to inhibit vibration-induced variations in the reflected light and to reduce interference. Thus, the passage of the upper thread and the generation of the skipped stitch can be precisely detected. Because the upper thread detector 60 is mounted on the presser frame 30, the upper thread detector 60 can be retracted along the presser frame 30 in the event of maintenance or replacement, cleaning work, etc. of the shuttle, while easily ensuring an installation space around the vertical semi-rotary shuttle 20, and improving usability. Since the pins 223 and 223 and the positioning holes 321 and 321 are provided between the presser frame 30 and the center shuttle presser 22 to serve as uneven structures for performing the positioning, the relative position between the presser frame 30 and the center shuttle 23 can be easily established by simple structures. As a consequence, because the upper thread detector 60 can also be precisely positioned for the vertical semi-rotary shuttle 20, the passage of the upper thread can be accurately detected. Because part of the through-hole 221b, which is provided in the circumferential wall area 221 of the center shuttle presser 22, has a shape (an approximate fan shape) that assumes the concave shape of the concave area 247, which is formed in the front of the vertical semi-rotary shuttle 20, the variation in the intensity of the received light of the detection light can be reduced, even when the bobbin case 24 vibrates forwards and backwards, and the passage of the upper thread can be detected more accurately even when vibration occurs at the vertical semi-rotary shuttle 20. Based on the configuration in which the presser frame 30 can be rotated between the pressing position and the retraction position by means of the frame holding mechanism 40 and the toggle lever mechanism 50 is provided to impart the pressing pressure to the presser frame 30, which is in the pressing position, in the direction of the center shuttle presser 22, the presser frame 30 can be fixed to the center shuttle presser 22 and the upper thread detector 60 can also be fixed in place. If necessary, the compressed state caused by the press frame 30 can also be easily lifted. Because the toggle lever mechanism 50 has the operation detector 53, which detects the operational state of the input lever 52, the failure of pressing caused by the presser frame 30 during sewing can be detected, and the execution of sewing in a state in which the center shuttle presser 22 is not pressed by the presser frame 30 can be prevented and reduced. Because the sewing machine 10 has the air delivery mechanism 70, which blows air along the detection light's passage path to remove dust, the dust can be removed from any area along the detection light's passage path, for example, from the passage holes 221b and 221c of the center shuttle presser 22, the optical unit 61 and the reflector 62 of the upper thread detector 60, and the like, and the influence of the dust can be reduced to detect the passage of the upper thread with higher accuracy. By controlling the air delivery mechanism 70, the control unit 90 ensures that the air blowing caused by the air delivery mechanism 70 is carried out at intervals of the specified needle localization frequency (for example, at a value of 500), allowing the air blowing process to be performed with a sufficient and correct frequency before a reduction in detection accuracy occurs. [Further] The example given is the case in which the sewing machine 10 has the vertical semi-rotary shuttle 20; however, a vertical full-rotary shuttle may also be provided, for example. The number of revolutions of the upper shaft, on the basis of which the air blowing process caused by the air delivery mechanism 70 is carried out under the cleaning control, is not limited to a value of 500. Furthermore, the number of revolutions of the upper shaft can be set as desired using setting devices, for example with the help of the control panel 91.

Claims

Sewing machine (10) with a vertical shuttle (20) and a center shuttle presser (22) arranged on a front side of the vertical shuttle (20), the sewing machine (10) comprising: a presser frame (30) which is movably held between a press position in which the center shuttle presser (22) is pressed and a retract position which is separate from the press position; an optical upper thread detector (60) which is provided on the presser frame (30) and is configured to detect the passage of an upper thread using detection light which passes through passage areas formed in the center shuttle presser (22) and crosses a front side of a bobbin case (24) of the vertical shuttle (20);and a stitch exit detection processor (90) which is configured to determine, based on an amount of light received from the detection light by the upper thread detector (60), whether the passage of the upper thread is present. Sewing machine according to claim 1, wherein an uneven structure is provided for positioning between the presser frame (30) and the center shuttle presser (22). Sewing machine according to claim 2, wherein the uneven structure comprises a pin (223) and a hole (321) which allows the pin (223) to be inserted into the hole (321). Sewing machine according to one of claims 1 to 3, wherein the central shuttle presser (22) has a circumferential wall area (221) which surrounds a periphery of the vertical shuttle (20); through holes (221b, 221c) are formed in the circumferential wall area (221) which act as the passage areas; and wherein a part of each through hole (221b, 221c) has a shape which is designed to fit a recessed shape of a concave area (247) which is formed in a front of the vertical shuttle (20). Sewing machine according to one of claims 1 to 4, further comprising: a knee lever mechanism (50) which is configured to apply a pressing pressure to the presser frame (30) in the pressing position in the direction of the center shuttle presser (22), wherein the presser frame (30) is rotated to move between the pressing position and the retraction position. Sewing machine according to claim 5, wherein the knee lever mechanism (50) comprises: an input lever (52) configured to apply and remove pressing pressure from the presser frame (30); and an operation detector (53) configured to detect an operating state of the input lever (52). Sewing machine according to one of claims 1 to 6, further comprising: an air delivery mechanism (70) which is configured to blow air into a passage path of the detection light to remove dust. Sewing machine according to claim 7, wherein the air delivery mechanism (70) is provided on the presser frame (30) and has nozzles (71, 72, 73, 74, 75, 76) which blow air into the passage areas of the center shuttle presser (22) from one end area and from the other end area of ​​the center shuttle presser (22) in a passage direction. Sewing machine according to claim 7 or 8, wherein the air delivery mechanism (70) is provided on the presser frame (30) and has nozzles (71, 72, 73, 74, 75, 76) which blow air onto light-receiving and light-emitting areas of the upper thread detector (60). Sewing machine according to one of claims 7 to 9, further comprising: a cleaning control unit (90) which is configured to control the air delivery mechanism (70) in order to periodically blow out air at intervals of a predetermined number of stitch formations or at a predetermined timing.

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