52results about "Tensioning devices" patented technology

The invention relates to the technical field of sewing machines, in particular to a multi-thread-trapper thread tension adjusting device which is characterized in that a driving motor drives a rotating shaft to rotate; the plurality of adjusting mechanisms are arranged in one-to-one correspondence with the adjusting nuts of the plurality of wire trappers; the adjusting mechanism comprises a friction wheel arranged opposite to the adjusting nut, a transmission piece connected with the rotating shaft and the friction wheel so as to drive the friction wheel to rotate, and a clutch piece connected with the friction wheel and driving the friction wheel and the adjusting nut to be pressed or not pressed. The invention further relates to a multi-yarn-trapper yarn tension adjusting method which adopts the device and comprises automatic adjustment and manual adjustment. The automatic adjustment is that the adjusting nuts of all the wire trappers or one or more of the wire trappers are compressed with the friction wheel, the driving motor drives the friction wheel to rotate through the rotating shaft and the transmission piece, and the friction wheel compressed with the adjusting nuts drives the adjusting nuts to rotate; the manual adjustment is that the adjusting nut of the wire clamp and the friction wheel are not tightly pressed, and the adjusting nut is manually rotated. Automatic synchronous or independent adjustment of the tension of the multi-thread-trapper thread can be achieved.

This invention relates to the field of sewing machine technology, and discloses a thread-releasing and presser foot lifting mechanism for a sewing machine and a sewing machine. The mechanism includes a thread-releasing assembly for opening the thread clamp and a presser foot lifting assembly. The thread-releasing assembly includes a top plate rotatable around a pivot and a thread-releasing pin. The top plate is driven to rotate around the pivot by the presser foot lifting assembly, thereby causing the thread-releasing pin to open the thread clamp and perform a thread-releasing action. The presser foot assembly includes a presser foot rod and a presser foot. The presser foot lifting assembly includes an adjusting block fixedly mounted on the presser foot rod and a manual presser foot lifting component. A toggle block is provided on the rear side of the adjusting block. The presser foot assembly also includes an adjusting component for adjusting the presser foot lifting height and pressure. By using the top plate and the thread-releasing pin, when the presser foot is lifted by the presser foot lifting assembly, it is driven to rotate around the pivot, thereby causing the thread-releasing pin to open the thread clamp and perform a thread-releasing action. This ensures that the thread clamp automatically completes the thread-releasing action during the presser foot lifting process, thus simplifying the structure and improving working accuracy.

The invention relates to the technical field of sewing machines, in particular to a thread tension adjusting device for multiple thread trappers, a driving motor drives a transmission mechanism to drive an adjusting motor to linearly move along the arrangement direction of the multiple thread trappers, the adjusting motor drives a friction wheel to rotate, and a clutch drives the friction wheel to be compressed or not compressed with adjusting nuts of the thread trappers. The invention further relates to a thread tension adjusting method of the multi-thread trapper, and the thread tension adjusting method adopts the device and comprises automatic adjustment and manual adjustment. The automatic adjustment is that an adjusting motor is opposite to a certain wire clamp, a friction wheel and an adjusting nut of the friction wheel are pressed tightly, and the adjusting motor drives the friction wheel to drive the adjusting nut to rotate; the manual adjustment means that the adjusting motor is not opposite to the wire trapper to be manually adjusted, or the friction wheel is not tightly pressed with an adjusting nut of the wire trapper to be manually adjusted, and the adjusting nut is manually rotated. And automatic and high-precision adjustment of the tension of the threads of the multiple thread trappers can be realized.

The utility model relates to sewing machine technical field discloses a thread unwinding device for sewing machine, including mounting panel, the first threaded rod that has the screw engagement in mounting panel, the bottom fixed mounting of first threaded rod has first knob, this thread unwinding device for sewing machine, rotates first knob to make first threaded rod drive fixed plate to move upwards to make fixed plate and mounting panel cooperation to install thread unwinding device, the friction layer that is provided on fixed plate simultaneously, therefore this can better increase the friction between fixed plate and sewing machine desktop, after rotating third knob to make bidirectional threaded rod rotate, when bidirectional threaded rod rotates can drive moving block to adjust distance in the sliding slot to make the tension of guide coil to sewing thread unwinding to adjust to can better prevent thread unwinding device sewing thread tight or too loose when unwinding appears the situation, and influence the sewing effect of sewing machine.

The utility model discloses a sewing thread clamping device of a sewing machine. The sewing thread clamping device comprises a driving motor, a buffering piece, a connecting rod, a pull rod, a thread clamping piece and a fixing block. The driving motor is connected with a fixed shaft sleeve, the connecting rod is linked with the fixed shaft sleeve, the buffer piece is respectively connected with the connecting rod and the fixed shaft sleeve, the other end, far away from the fixed shaft sleeve, of the connecting rod is movably connected with one end of the pull rod, and the other end of the pull rod is connected with the thread clamping sheet; the thread clamping piece comprises a thread clamping connecting part and a thread clamping clamping part, a rotating shaft is arranged between the thread clamping connecting part and the thread clamping clamping part, the fixing block is arranged below a machine needle and is adjacent to the thread clamping piece, and the thread clamping clamping part rotates around the rotating shaft and abuts against the fixing block to clamp a sewing thread. According to the utility model, the sewing stability can be effectively improved, and the sewing off-line and bird nest phenomena are reduced.

The utility model discloses an integrated thread trapper and a sewing machine in the technical field of sewing machines. The integrated thread trapper comprises a thread passing plate, an outer switching sleeve and an inner switching shaft. An outer reset spring and an inner reset spring are arranged on one side of the wire passing plate, the outer switching sleeve is in sliding connection with the wire passing plate in the axis direction, the inner reset spring is connected between the wire passing plate and the outer switching sleeve, the inner switching shaft is sleeved with the outer switching sleeve in an axial moving mode, and the outer reset spring is connected between the wire passing plate and the inner switching shaft; a thread clamping piece, an outer supporting pad and an inner supporting pad are arranged on the other side of the thread passing plate, the thread clamping piece and the outer supporting pad are arranged on the outer switching sleeve in a sleeving mode, and the inner supporting pad is arranged on the inner switching shaft in a sleeving mode. According to the sewing machine clamping device, free adjustment and gear adjustment of the sewing thread clamping force are achieved, a user can directly use fabric conforming to the preset clamping force for sewing according to needs, the clamping force of the clamping device can also be freely adjusted, and the adjusting efficiency of the sewing thread clamping force is improved.

The invention discloses a flat seaming machine presser foot lifting air suction thread clamping device and aims to provide a flat seaming machine presser foot lifting air suction thread clamping device which is simple in structure and convenient to manufacture. The presser foot lifting air suction thread clamping device of the flat seaming machine can effectively solve the problem that after the flat seaming machine cuts threads every time, when sewing is started next time, due to the fact that the thread clamping force of upper threads is insufficient, the sewing is prone to loosing. The device comprises a fixed part which is fixedly arranged on a machine head of the flat seaming machine and comprises a fixed thread pressing part which is located between a sewing needle and a presser foot rod of the flat seaming machine; the air suction pipe comprises an air suction port which is located between the sewing needle and the fixed thread pressing part; the elastic element is arranged on the fixed part and comprises an elastic arm and a thread pressing part arranged on the elastic arm, the thread pressing part and the sewing needle are located on the same side of the fixed thread pressing part, and the thread pressing part abuts against the fixed thread pressing part under the action of the elastic arm; the push plate is fixed on the presser foot rod; when the presser foot rod drives the presser foot to ascend, the push plate abuts against the elastic arm and enables the line pressing piece to be separated from the fixed line pressing part.

The invention discloses a thread tension adjusting device and a sewing machine, relates to the technical field of sewing equipment, and aims to solve the problems that an existing electromagnet-driven thread tension adjusting device is low in response speed, thread tension is reduced due to long-time operation, and the thread loosening speed lags behind. The motor is arranged on one side of the supporting structure; the wire clamping mechanism and the motor are oppositely arranged on the other side of the supporting structure, the wire clamping mechanism comprises a cam and a wire passing wheel, the cam is connected with a motor shaft of the motor, and the outer edge of the cam is attached to a wire passing groove of the wire passing wheel; by means of the arrangement, high-precision, quick-response and long-term stable thread tension control is achieved through motor driving, meanwhile, the thread loosening performance is optimized, and the overall performance of the sewing machine is remarkably improved.

The utility model discloses an electronic thread trapper for a sewing machine, which relates to the field of sewing machine components, solves the problem of weak magnetic attraction force caused by direct attraction of an existing electromagnetic coil seat, and adopts the following scheme that the electronic thread trapper comprises a lower seat component and an upper seat component assembled on the top side of the lower seat component, a spiral cylinder is fixedly installed at the bottom of the inner side of the shell, an electromagnetic coil seat is sleeved with an inner cavity of the shell, the input end of the electromagnetic coil seat is electrically connected with a wire, a spacer ring is arranged between the top side of the electromagnetic coil seat and the upper seat assembly in a cushioned mode, and sewing machine threads are clamped between the upper supporting plate and the lower supporting plate; according to the electronic thread trapper for the sewing machine, the distance ring is arranged between the lower base assembly and the upper base assembly, the magnetic circuit of the coil can be increased through the distance ring, the efficiency and the stability of an electric appliance are improved, and due to the fact that iron has good magnetic permeability, magnetic field lines can be attracted, and the magnetic flux in the coil is enhanced.

The invention provides an upper thread anti-off sewing method of a sewing machine and the sewing machine. A thread passing notch and a first clamping part are arranged on a first thread trimmer of the sewing machine, a clamping assembly is further arranged, and the clamping assembly is provided with a second clamping part; comprising the following steps that before a first needle is sewed, a first thread trimmer stops at a working position A, and a thread passing notch is located under a machine needle; starting to sew a first needle, enabling a machine needle to move downwards, and driving an upper thread to pass through a thread passing notch and a sewing material; then the rotating shuttle hooks the upper thread, the machine needle ascends to the position above the first thread trimmer, and the upper thread is located in the thread passing notch; the first thread trimmer moves towards the clamping assembly to a working position B, the thread passing notch drives the upper thread in the thread passing notch to reach a second clamping part of the clamping assembly, the first clamping part and the second clamping part clamp the upper thread between the first clamping part and the second clamping part, and the first thread trimmer stops at the working position B; the machine needle completes follow-up sewing starting actions of a plurality of needles; when the first thread trimmer moves to the working position C, the first clamping part and the second clamping part loosen the upper thread.

The utility model discloses a sewing machine technical field's electronic thread clamp and sewing machine, including mounting panel, drive motor is set up in one side of mounting panel, guide seat is set up in the other side of mounting panel, and guide seat includes guide axle section, transmission screw, transmission screw is worn in the axle hole of guide axle section, and one end of transmission screw is passed through mounting panel and is connected with drive motor transmission, thread clamp piece, two thread clamp pieces are set on the guide axle section face to face, pressure regulating nut is screwed on the other end of transmission screw and is connected with guide axle section along the axle direction sliding, pressure regulating spring, pressure regulating spring is set on the guide axle section, and pressure regulating spring is butt joint between thread clamp piece and pressure regulating nut. The utility model discloses the mode of electrically adjusting instead of mechanical adjustment, realized the automatic regulation of thread clamp and clamping force, not only can improve the regulation efficiency of thread clamping force, can also get rid of the experience level requirement to the debugging personnel.

The utility model discloses a thread loosening device for a sewing machine, and relates to the field of sewing machines. The thread loosening device comprises an installation plate and a thread clamping disc, a thread loosening mechanism is installed on the installation plate, the thread loosening mechanism comprises two sets of brackets and an installation frame, and a plurality of supporting pieces are fixedly arranged on the inner sides of the brackets. The bracket and the supporting pieces on the bracket are driven to move relatively, the moving process directly acts on the wire clamping discs, so that gaps between the wire clamping discs are gradually enlarged, the wire loosening effect is achieved, meanwhile, in the wire loosening process, the bracket stably supports the wire clamping discs, multi-point shifting operation on the wire clamping discs is achieved through movement of the bracket, and the wire loosening effect is improved. Compared with the traditional single-point shifting, the multi-point shifting has the advantages that the two groups of thread clamping discs can be separated more comprehensively, the probability of thread breakage is effectively reduced, and the use convenience and the working efficiency of the sewing machine are remarkably improved.

The application discloses a kind of servo type swing yarn leading and overlock device and method, device includes servo type yarn leading platform, swing yarn leading mechanism, tension compensation yarn supply mechanism and continuous overlock mechanism, the swing yarn leading mechanism and tension compensation yarn supply mechanism are installed on the servo type yarn leading platform, follow the current opening movement of servo type yarn leading platform with fabric;Continuous overlock mechanism and servo type yarn leading platform are respectively opposite to be arranged in the both sides of fabric, follow the yarn leading position along the width direction movement of fabric.The yarn leading platform can follow the current opening movement of fabric, the swing yarn leading mechanism is introduced from the long and narrow optimal opening position, and continuous overlock is completed via the continuous overlock mechanism, the whole process is yarned by the tension compensation yarn supply mechanism and controls yarn tension constant.The application solves the forming problem of the yarn leading, overlock of the large width, large thickness, high density of fabric, improves the production efficiency of fabric and the consistency of forming.

The utility model discloses a gear adjusting mechanism of a clamping device and a sewing machine, and belongs to the technical field of sewing machines. The adjusting rotating shaft is mounted on one side of the rack; the preset gear wheel is mounted on the adjusting rotating shaft, and a preset gear section and an adjusting matching section are formed on the working surface of the preset gear wheel; the adjusting hand wheel is installed at one end of the rack and fixedly connected with one end of the adjusting rotating shaft, and the adjusting hand wheel has a rotating state capable of driving the adjusting rotating shaft to rotate and a static state capable of enabling the adjusting rotating shaft to be fixedly connected with the rack. The cam transmission mode is adopted, and gear adjustment of the thread trapper on the thread clamping force is achieved.

The utility model provides a thread clamping adjuster capable of visually adjusting thread tension and a sewing machine, and belongs to the technical field of sewing equipment. The thread clamping adjuster comprises a thread clamping screw, a thread clamping piece, a pressure adjusting stop cover, a thread clamping spring and an adjusting knob, one end of the thread clamping screw sequentially penetrates through the thread clamping piece, the pressure adjusting stop cover and the thread clamping spring and is in threaded connection with the adjusting knob, the thread clamping spring is located between the pressure adjusting stop cover and the adjusting knob, the pressure adjusting stop cover is provided with a protruding edge, and a first notch is formed in the protruding edge. Scale marks are arranged on the edge of the first notch, and a scale ring opposite to the scale marks is arranged at the inner end of the adjusting knob. According to the thread clamping regulator, the thread tension is regulated by adopting a mechanical structure, the visual regulation of the thread tension is realized under the condition of lower cost, the regulation is convenient, and the working efficiency is high.

To provide a sewing machine contributing to improvement in operability of a workpiece when a user manually moves the workpiece in execution of free motion sewing.SOLUTION: A processor of the sewing machine drives a sewing machine motor in a state where an upper end of a feed dog is positioned below a throat plate, and executes free motion sewing processing for vertically moving a needle bar (S32, S35, S36). At least a part of a needle up period in which the lower end of the needle is above the throat plate is defined as a first period, and at least a part of a needle second half in which the lower end of the needle is below the throat plate is defined as a second period. The thread tension control processing includes adjusting a length of the spring in a pressure direction during a first period to a first length, and adjusting a length of the spring in the pressure direction during a second period to a second length shorter than the first length (S36).SELECTED DRAWING: Figure 9

The utility model discloses a sewing machine is with thread clamp assembly and sewing machine, sewing machine is with thread clamp assembly includes electromagnet, and electromagnet includes electromagnet body and moving iron core, and electromagnet body is fixed in one side of mounting panel, and the one end of moving iron core passes through mounting panel and is at the other side of mounting panel and is fixed with the thread passing joint axle, and the first thread clamp piece, second thread clamp piece and pressure -bearing cover of close -fit mounting panel are sequentially covered and are established on the thread passing joint axle, and the thread passing joint axle still is fixed with the stop ring of close -fit first thread clamp piece and is used for the location of first thread clamp piece, and the clearance between first thread clamp piece and second thread clamp piece is used for the setting of sewing thread, through the electrification of electromagnet body, make moving iron core drive stop ring first thread clamp piece and exert pressure to first thread clamp piece, and the sewing thread is clamped between first thread clamp piece and second thread clamp piece.

The utility model relates to the technical field of sewing equipment, and discloses a sewing machine stitch adjusting device which comprises a sewing machine and an installation table top, the top end of the installation table top is hollowed out and fixedly provided with the sewing machine, a stitch controller is arranged on one side of the sewing machine, and a thread trapper is driven by an internal rotating device to conduct fine adjustment. The device is specially provided with a thickness measurer, the thickness of the cloth is monitored in real time, accurate data support is provided for stitch adjustment, the leveling roller is ingenious in design, cloth friction is reduced, the flatness and passing efficiency are improved, intelligent control of a control computer is achieved, and the automatic and accurate stitch adjustment process is achieved. The device is compact in structure, easy and convenient to operate, capable of remarkably improving sewing efficiency and quality and ensuring uniform and attractive stitches, and suitable for various sewing scenes.

This invention relates to an electronic thread tensioner and a sewing machine. The electronic thread tensioner includes a thread tension base, a first coil, and a thread tension plate. The thread tension base includes an iron core and a housing surrounding the iron core, forming a cavity between the iron core and the housing. The first coil is fitted onto the iron core and located within the cavity. A thread tensioning surface is provided at the end of the iron core, and the thread tension plate abuts against the thread tensioning surface. Both the thread tension base and the thread tension plate are made of ferromagnetic material, and when the first coil is energized, the thread tension plate is attracted to the thread tensioning surface of the thread tension base. The face thread of the electronic thread tensioner passes between the thread tension plate and the thread tensioning surface of the thread tension base. The electronic thread tensioner of this invention adjusts the tension of the face thread by controlling the input current of its first coil. It has a simple structure, fast response speed, and very low actual operating current, thus avoiding significant temperature rise.

This utility model discloses a built-in electronic thread clamp and sewing machine in the field of sewing machine technology, including a mounting plate; a guide seat disposed on one side of the mounting plate; a guide shaft disposed on the other side of the mounting plate; a thread clamping assembly disposed on the guide shaft; a top sleeve axially movable between the thread clamping assembly and the mounting plate; a drive motor disposed on one side of the mounting plate; a transmission screw, one end of which is connected to the drive motor; an adjusting nut threadedly connected to the transmission screw, and slidingly connected to the guide seat in the axial direction; and an adjusting spring, one end of which abuts against the adjusting nut, and the other end of which abuts against the top sleeve. This utility model uses electric adjustment instead of mechanical adjustment, which not only improves the adjustment efficiency of the thread clamping force but also eliminates the requirement for experience level of the adjustment personnel.

The overlock sewing machine (100) is provided with an adjustment input part (34) which pulls the midway part of the first operation thread (321) to move the needle thread adjusting part (24), and pulls the midway part of the second operation thread (331) to move the needle thread adjusting part (24). Linkage of the lower looping thread adjusting part (25) and the upper looping thread adjusting part (26) accompanying movement of the needle thread adjusting part (24) generated by the adjusting linkage part (27) is restrained or reduced.

The utility model discloses a thread channel capable of reducing upper thread tension and a sewing machine in the technical field of sewing machines. The thread channel comprises a machine head and a needle bar, a left thread hook is installed on one side of the machine head, a needle bar thread hook is installed at the bottom end of the needle bar, a lining thread hook is installed below the machine head, and the thread channel of the left thread hook, the thread channel of the lining thread hook and the thread channel of the needle bar thread hook are collinear. According to the utility model, the linear thread channel is adopted, so that the overall frictional resistance of the left thread channel to the upper thread is reduced, and the thread clamping force required by the large thread trapper in the right thread channel is reduced, thereby reducing the risk of thread breakage and improving the sewing effect.

The invention relates to an apparatus and a method for applying dots to a decorative component having a three-dimensional configuration.A stitching head for a decorative component having a three-dimensional configuration, comprising: a needle bar assembly functionally coupled to the head; a looper configured to cooperate with the needle bar assembly to perform a plurality of stitches on the decorative component, the looper rotating in a plane parallel to the decorative component; a rod assembly configured to drive the looper in a reciprocating motion in the plane, where the rod assembly is functionally coupled to a motor configured to drive the needle bar assembly in a reciprocating motion, the rod assembly being functionally coupled to the head via a cylinder arm assembly and a downshaft assembly; and where the cylinder arm assembly is rotated in a synchronized manner with a swing frame by a mechanical link connecting a swing frame drive shaft to the cylinder arm assembly.

The invention relates to the technical field of sewing machines, in particular to a thread trapper device and a sewing machine comprising the thread trapper device. The front wire clamping disc, the inner elastic piece, the rear wire clamping disc, the outer elastic piece and the nut are sequentially arranged on the stud in a sleeving mode from front to back in the axial direction of the stud in a sleeving mode, the nut is connected with the rear end of the stud in a threaded fit mode, and the outer elastic piece elastically abuts against the position between the rear wire clamping disc and the nut. The rear wire clamping disc is provided with a wire clamping part and a cap part, the wire clamping part is attached to the front wire clamping disc to form a wire clamping position, the cap part is sunken towards the rear side relative to the wire clamping part, the wire clamping part is connected to the outer periphery of the front end of the cap part, the stud is sleeved with the cap part in a manner of moving in the axial direction, a containing cavity is formed between the cap part and the stud, and a stopping boss is arranged on the stud; the stopping boss and the inner elastic piece are both located in the containing cavity, and the inner elastic piece elastically abuts against the position between the stopping boss and the rear wire clamping disc. And a stable low-line tension or zero-line tension state can be realized.

The invention discloses an overedger, and relates to the field of sewing equipment. The overlock machine comprises a machine shell, a swing part, a thread passing sliding block and a cam, the swing part and the cam are rotationally arranged on the machine shell, and the cam is in rolling fit with the swing part and used for driving the swing part to swing; the thread passing sliding block is connected with the swing piece, and the thread passing sliding block is provided with a first thread passing hole for the upper looper thread to penetrate through and a second thread passing hole for the lower looper thread to penetrate through. The overlock machine can meet different tension requirements in the sewing process, fabric arching is prevented, and the sewing quality is improved.

The utility model discloses a thread tension adjusting system of a sewing machine and the sewing machine in the technical field of sewing machines, the thread tension adjusting system comprises a machine shell, a thread trapper, a driving electromagnet, a controller and a control panel, the thread trapper is arranged on one side of the machine shell, the driving electromagnet is arranged on the other side of the machine shell, and the driving electromagnet can drive the thread trapper to clamp or release an upper thread; the control panel can display and adjust wire tension parameters, the controller is electrically connected with the control panel and the driving electromagnet, and the controller can control the power-on current value of the driving electromagnet according to the wire tension parameters. According to the utility model, an electric adjusting mode is adopted, and the magnitude of the energizing current of the driving electromagnet is controlled, so that the rapid transplantation of thread tension parameters among a plurality of sewing machines is realized, and the style changing efficiency is improved.

The anti-winding device for the sewing machine head comprises a machine head body, an external plate is fixedly connected to the position, close to the center, of the front side of the machine head body, a fixing rod is fixedly connected to the front side of the external plate, a cylindrical roller is arranged on the outer side of the fixing rod in a sleeving and sliding mode, and the cylindrical roller is provided with a thread. A plurality of trapezoidal plates are arranged on the outer side of the cylindrical roller, and wire arranging grooves are formed in the outer sides of the trapezoidal plates. According to the anti-winding device for the sewing machine head, the external plate and the cylindrical roller fixedly connected with the external plate are arranged on the front side of the machine head body, and the trapezoidal plates and the wire arranging grooves are arranged on the outer side of the cylindrical roller, so that the movement path of a wire is effectively guided, and the wire can smoothly penetrate through the wire arranging grooves; according to the thread winding prevention device, the phenomena of drifting and knotting of threads in the sewing process are avoided, the thread management efficiency and stability are remarkably improved, the cylindrical roller and the trapezoidal plate are fixedly connected through the connecting strip, and a dynamically-adjusted thread winding prevention structure is formed.

The present invention provides a sewing machine and a bobbin thread judging method capable of accurately detecting that the bobbin thread is used up or that the bobbin thread is entangled with the thread even under any sewing conditions. The sewing machine includes a needle bar, a needle bar up-and-down movement mechanism, a bobbin, a bobbin mechanism, a tension detector, a rotation detector, and a bobbin thread judging section. The needle bar is equipped with a needle through which a thread is inserted. The needle bar up-and-down movement mechanism moves the needle bar up and down. The bobbin is provided below the needle bar and houses a bobbin spindle on which a bobbin thread is wound in a rotatable manner. The bobbin mechanism rotates the bobbin in synchronization with the up-and-down movement of the needle bar, catches a loop-shaped thread inserted through the needle, and entangles the thread with the bobbin thread to form a stitch. The tension detector detects the tension of the thread or the bobbin thread. The rotation detector detects whether the bobbin spindle is rotating. The bobbin thread judging section judges the presence or absence of the bobbin thread with respect to the stitch based on whether the tension detected by the tension detector is greater than a threshold value and the detection result of the rotation detector (S3-S7, S11-S19).