JP2019150548A - sewing machine - Google Patents

Abstract

To provide a sewing machine including a thread tension detection device which does not hinder sewing and which can detect needle thread tension with good accuracy.SOLUTION: A sewing machine 1 includes a sewing needle 10, a balance 23 and a main thread tension unit 27. The balance 23 is provided in a needle thread path from a thread supply source to the sewing needle 10, moves vertically according to the vertical movement of the sewing needle 10, and pulls up a needle thread 6. The main thread tension unit 27 is arranged in the needle thread path between the needle supply source and the balance 23, and capable of controlling tension to be applied to the needle thread 6. The sewing machine 1 including this constitution also includes a thread tension detection device 30. The thread tension detection device 30 can detect tension applied to the needle thread 6. The thread tension detection device 30 is arranged in the needle thread path between the main thread tension unit 27 and the balance 23. Therefore, when the balance 23 pulls up the needle thread 6, there is no resistance between the balance 23 and the sewing needle 10. Therefore, since the thread tension detection device 30 does not hinder sewing of the sewing machine 1, high quality seams can be formed on a cloth.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a sewing machine.

  The sewing machine includes a bed portion and an arm portion. The arm portion is disposed above the bed portion and has a head at the tip. The needle bar is provided on the head so that it can move up and down. The sewing needle is attached to the lower end of the needle bar. The sewing machine described in Patent Document 1 includes a yarn tension detector. The thread tension detector is provided in front of the head of the sewing machine and is located between the sewing needle and the balance. The thread tension detector has three threaders arranged in order from the top, and a strain gauge is provided at the center threader. The yarn tension detector detects the tension of the yarn with a strain gauge and converts it into an electric signal.

JP 2007-159705 A

  Since the thread tension detector described in Patent Document 1 is located between the sewing needle and the balance, when the balance pulls up the upper thread, the thread tension detector becomes a resistance, which may interfere with sewing. It was. Since the thread tension detector is located in the vicinity of the sewing needle, there is a possibility that it may interfere with sewing.

  An object of the present invention is to provide a sewing machine provided with a thread tension detection device that can accurately detect an upper thread tension without interfering with sewing.

  The sewing machine according to claim 1, further comprising a sewing needle that holds the upper thread and is movable up and down, is provided in an upper thread path from a thread supply source to the sewing needle, and moves up and down as the sewing needle moves up and down. In the sewing machine comprising: a balance for pulling up a balance; and a thread tensioner that is disposed between the thread supply source and the balance in the upper thread path and is capable of controlling a tension applied to the upper thread. A yarn tension detecting device capable of detecting a tension applied to the upper thread is disposed between the thread tensioner and the balance in the middle. The sewing machine of this aspect includes a yarn tension detecting device between the yarn tensioner and the balance in the upper yarn path. Therefore, when the balance pulls up the upper thread, there is no resistance between the balance and the sewing needle. Therefore, since the thread tension detecting device does not interfere with sewing, the sewing machine can form high-quality stitches on the cloth. Since the balance does not pull the upper thread portion where the thread tension detection device detects the tension, the thread tension detection device can detect the original tension applied to the upper thread.

  The thread tension detection device for a sewing machine according to claim 2, wherein the sewing machine includes a mounting base attached to the sewing machine, a fixing part that is detachably fixed to the mounting base, connected to the fixing part, and the thread tensioner and the balance. A tension member that includes a yarn contact portion that extends in a direction intersecting with the upper yarn path and generates distortion in itself by contact with the upper yarn, and the distortion generated in the yarn contact portion directly or A sensor that detects indirectly and outputs a signal according to the detection result, and is fixed to the mounting base, and is provided at a position where the upper thread enters from the thread tensioner side with respect to a predetermined position of the thread contact portion. A first hole through which the upper thread passes, and a second hole through which the upper thread passes from the predetermined position to the balance side, and the upper thread passes through the upper hole at the predetermined position. Guide the upper thread so that the thread passes through That may comprise a guide member. The yarn tension detection device includes a mounting base, a tension member, a sensor, and a guide member. The yarn tension detecting device can be detachably attached to the sewing machine with a mounting base. Since the tension member detachably fixes the fixing portion to the mounting base, it can be appropriately replaced according to the model of the sewing machine. The upper thread contacts the thread contact portion of the tension member. The yarn contact portion is distorted by contact with the upper yarn. The sensor directly or indirectly detects distortion generated in the yarn contact portion, and outputs a signal according to the detection result. The guide member includes a first hole and a second hole. The first hole is provided at a position where the upper thread enters from the thread tensioner side with respect to a predetermined position of the thread contact section. The second hole is provided at a position where the upper thread comes out from the predetermined position of the thread contact section toward the balance. Therefore, the yarn tension detecting device has a function of guiding the upper yarn in the upper yarn path from the yarn tensioner to the balance. Therefore, since the sewing machine can always contact the predetermined position of the thread contact portion of the tension member without shifting the upper thread, the upper thread tension can be detected with high accuracy. The sewing machine can detect the upper thread tension with high accuracy by the thread tension detecting device, so that a tension abnormality can be detected immediately during sewing and a sewing failure can be detected. For example, the sewing operation can be stopped immediately. Therefore, the sewing machine can improve sewing product quality and work efficiency.

  The sensor of the sewing machine according to claim 3 may be a strain detection sensor that detects the strain generated in the yarn contact portion and outputs a signal according to the degree of the strain. Therefore, the yarn tension detection device can directly detect the strain generated in the yarn contact portion using the strain detection sensor.

  The strain detection sensor of the sewing machine according to claim 4 may be fixed to the back surface of the yarn contact portion opposite to the contact surface with which the upper yarn contacts. Therefore, the thread tension detecting device can prevent the upper thread passing in contact with the thread contact portion from being obstructed when sewing with the sewing machine.

  The strain detection sensor of the sewing machine according to claim 5 is fixed to one end side in the length direction of the yarn contact portion from a position corresponding to the predetermined position on a contact surface of the yarn contact portion with which the upper thread contacts. The first distortion detection sensor and a second distortion detection sensor fixed on the one end side of the back surface opposite to the contact surface rather than the position corresponding to the predetermined position may be provided. The first strain detection sensor is fixed to one end side in the length direction of the yarn contact portion from the position corresponding to the predetermined position on the contact surface of the yarn contact portion. The second strain detection sensor is fixed to one end side of the back surface opposite to the contact surface of the yarn contact portion, rather than the position corresponding to the predetermined position. Therefore, the strain detection sensor detects the strain of the yarn contact portion at the same position on the contact surface and the back surface, thereby making it difficult to be affected by a change in temperature, and accurately detecting the strain of the yarn contact portion.

  The sewing machine according to claim 6 is a magnet fixed to the back surface of the yarn contact portion opposite to the contact surface with which the upper thread contacts, and the sensor, and the sensor changes according to distortion of the yarn contact portion. A magnetic sensor that detects a change in magnetic flux density of the magnet and outputs a signal according to the change, and a sensor holder that is fixed to the mounting base and supports the magnetic sensor via a gap with respect to the magnet. Good. The magnet is fixed to the back surface of the thread contact portion. The sensor holder supports the magnetic sensor via a gap with respect to the magnet. When the yarn contact portion is distorted by the upper yarn tension, the magnetic flux density passing through the magnetic sensor changes. The magnetic sensor detects a change in magnetic flux density and outputs a signal according to the change. Therefore, the thread tension detecting device can detect the upper thread tension with high accuracy. Since the yarn tension detecting device uses a magnet and a magnetic sensor, the configuration can be made compact and inexpensive.

  The sensor holder of the sewing machine according to claim 7 may support the magnetic sensor via the gap in a predetermined direction in which the thread contact portion is distorted by contact with the upper thread with respect to the magnet. Therefore, the magnetic sensor can accurately detect a change in magnetic flux density that changes in accordance with the distortion of the yarn contact portion.

  The sensor holder of the sewing machine according to claim 8, wherein the sensor holder is formed in a plate shape having a surface direction in a direction intersecting the predetermined direction, is opposed to the back surface side of the yarn contact portion, and a support surface that supports the magnetic sensor; A mounting surface that is opposite to the support surface and is attached to the mounting base, the mounting base facing the back side of the thread contact portion, and the mounting surface of the sensor holder. A holder attachment surface to be attached; a step provided on the holder attachment surface; projecting to the back side of the yarn contact portion; and abutting against one end of the attachment surface of the sensor holder; and A holder fixing portion for fixing the sensor holder to the mounting base in a state in which one end portion is abutted and a gap is formed between the holder mounting surface and the region excluding the stepped portion, and is parallel to the predetermined direction. Direction, the sensor ho It may comprise at least the adjustable holder position adjustment portion the position of the part supporting the magnetic sensor of da. The holder fixing portion can fix the sensor holder to the mounting base in a state where a part of the mounting surface of the sensor holder is applied to the stepped portion and a gap is left between the holder mounting surface and the region excluding the stepped portion. The holder position adjustment unit can adjust the position of at least a portion of the sensor holder that supports the magnetic sensor. Therefore, the yarn tension detecting device can appropriately adjust the gap between the magnet and the magnetic sensor. For example, the user can adjust the target value of the gap while observing the output of the magnetic sensor, thereby eliminating variations in the output of the magnetic sensor and stably detecting the needle thread tension.

  The said holder fixing | fixed part of the sewing machine of Claim 9 is provided in the said area | region among the said holder attachment surfaces, and the opposite side to the opening of the said holder attachment surface side with respect to the hole penetrated orthogonally to the said area | region A fastening screw that is inserted through the opening of the sensor holder and is fastened to a holder-side screw hole provided in the region of the mounting surface of the sensor holder. The adjustment portion is provided in a position corresponding to the magnetic sensor in the predetermined direction, spaced apart from the step in the region of the holder mounting surface, and orthogonal to the region. The height of the tip portion protruding from the opening on the holder mounting surface side of the screw hole can be adjusted by rotation by a tool, screwed into the screw hole penetrating, and the sensor holder Cover provided on the mounting surface It may comprise a can abut rod-shaped adjustment screw contact portion. The user touches a part of the mounting surface of the sensor holder against the stepped part, leaving a gap between the holder mounting surface and the area excluding the stepped part, and then the sensor through the hole provided in the mounting base. The sensor holder can be fixed to the mounting base by fastening to the holder side screw hole of the holder. The user can appropriately adjust the gap between the magnet and the magnetic sensor by adjusting the height of the adjusting screw.

  A hole into which the tip of the adjustment screw can be inserted is provided at a position facing the tip of the adjustment screw on the attachment surface of the sewing machine according to claim 10, and the contacted portion is a bottom of the hole. There should be. The tip of the adjustment screw is inserted into a hole provided on the mounting surface of the sensor holder, and abuts against the bottom provided on the back side of the hole. Therefore, the tip of the adjustment screw can be brought into contact with the hole without being displaced.

  The magnetization direction of the magnet of the sewing machine according to claim 11 is a direction along the predetermined direction, and the adjustment screw is preferably a magnetic body. The magnetizing direction of the magnet is along a predetermined direction in which the yarn contact portion is distorted by the upper yarn tension. The adjustment screw is screwed into a screw hole provided in the mounting base. Since the screw hole is provided at a position corresponding to the magnetic sensor in the predetermined direction, the position of the adjusting screw screwed into the screw hole is also a position corresponding to the magnetic sensor in the predetermined direction. The adjusting screw is a magnetic material. Therefore, the magnetic flux of the magnet can pass through the magnetic sensor and go to the adjusting screw.

  The magnet of the sewing machine according to claim 12, wherein the magnet has a cylindrical shape having an axis in the predetermined direction, and one end surface in the axial direction of the magnet is a circular fixed surface that is fixed to the back surface of the yarn contact portion. Good. Since the magnet has a cylindrical shape and the fixing surface fixed to the back surface of the thread contact portion is circular, the frictional force distribution with the fixing surface due to distortion of the thread contact portion is not concentrated on one pole and is continuous. Therefore, it is difficult to peel off from the back surface of the yarn contact portion.

  The sensor holder of the sewing machine according to claim 13 may be a non-magnetic material. Since the sensor holder is a non-magnetic material, it does not affect the magnet fixed to the back surface of the yarn contact portion.

  The magnetic sensor of the sewing machine according to claim 14 may be a Hall element. Since the magnetic sensor is a Hall element, a change in the magnetic flux density of the magnet can be detected with high accuracy.

  The fixing portion of the sewing machine according to claim 15 is preferably provided at both ends in the length direction of the tension member, and the yarn contact portion is provided between the pair of fixing portions. The two fixing portions provided at both ends of the tension member are fixed to the mounting base, respectively. The yarn tension detection device can stably support the yarn contact portion by fixing both ends of the tension member. Therefore, the yarn tension detecting device can suppress the vibration generated in the yarn contact portion when the sewing machine is driven.

  In a mode in which the sensor is a strain detection sensor, if only one end portion of the tension member is fixed, the yarn contact portion vibrates and low frequency vibration is generated as noise. In the signal output from the strain detection sensor, it becomes difficult to distinguish between the low vibration frequency generated in the tension member and the period in which the needle thread tension varies, and it is difficult to extract only the needle thread tension from the signal. In this aspect, by fixing both ends of the tension member, the natural frequency of the tension member can be increased as compared with the case where only one end of the tension member is fixed. Therefore, it is easy to identify the upper thread tension in the signal output from the strain detection sensor, so that only the upper thread tension can be extracted from the signal.

  In a mode in which the sensor is a magnetic sensor, the yarn tension detecting device fixes both ends of the tension member to the mounting base, so that the yarn contact portion does not tilt. Therefore, the magnet fixed to the back surface of the yarn contact portion can move to face the magnetic sensor that is always supported by the sensor holder through the gap.

  The predetermined position of the sewing machine according to claim 16 is preferably an intermediate position in the length direction of the yarn contact portion. Since the predetermined position where the upper thread contacts in the thread contact portion is an intermediate position of the thread contact portion, distortion can be formed in the entire thread contact portion. Therefore, the yarn contact portion can be distorted in accordance with the upper yarn tension, so that the upper yarn tension can be widely detected.

  The predetermined position of the thread contact portion of the sewing machine according to claim 17 may be located on the opposite side of the mounting base from an imaginary straight line connecting the first hole portion and the second hole portion. The predetermined position of the yarn contact portion is located on the opposite side of the mounting base from the virtual straight line connecting the first hole portion and the second hole portion. The yarn contact portion comes into contact with the upper yarn passing between the first hole portion and the second hole portion from the side. Therefore, the upper thread is bent with respect to the virtual straight line between the first hole and the second hole. Therefore, the yarn tension detection device can generate a force that pushes the yarn contact portion of the tension member toward the mounting base at a predetermined position by the upper yarn tension, and can easily distort the tension member.

  19. The predetermined position of the sewing machine according to claim 18, wherein the tension member applies the tension to the upper thread, the first tension being a vector from the predetermined position toward the first hole side, and the predetermined position. The predetermined position, the first hole portion, and the second hole portion may be arranged so that the second tension, which is a vector from the first to the second hole portion side, has the same magnitude as each other. In the state where the upper thread is in contact with a predetermined position of the thread contact portion, a first tension from the predetermined position toward the first hole side and a second tension from the predetermined position toward the second hole side are generated in the upper thread. Then, the resultant force of the first tension and the second tension becomes a force that pushes the yarn contact portion. Since the first tension and the second tension have the same magnitude, the direction in which the upper thread pushes the thread contact portion is a direction perpendicular to the thread contact portion. Therefore, the yarn tension detecting device can regulate the direction in which the tension member is distorted and can hardly detect the upper yarn tension to be detected.

  The thread contact portion of the sewing machine according to claim 19, comprising a contact surface that contacts the upper thread in parallel at the predetermined position, and one end portion of the contact surface on the first hole side and the second hole The other end portion on the portion side is provided with a guide portion that projects obliquely toward the mounting base with respect to a direction orthogonal to the length direction of the yarn contact portion and guides the upper yarn to the predetermined position. Good. The upper thread contacts the contact surface of the thread contact portion. The tension member is provided with guide portions at one end portion on the first hole side of the contact surface and the other end portion on the second hole side, respectively. The guide part protrudes inclining toward the mounting base. The guide part on the first hole side guides the upper thread passing through the first hole part to a predetermined position on the contact surface. The guide part on the second hole side guides the upper thread from the predetermined position toward the second hole part. The upper thread is bent at the thread contact portion, but can be reasonably contacted with the contact surface by the two guide portions. Therefore, since a large load is not applied to the upper thread, it is possible to prevent the upper thread from being cut at the thread contact portion.

  The guide part of the sewing machine according to claim 20, wherein the guide part includes a first wall part and a second wall part respectively arranged on both end sides in a direction along the upper thread path, and the first wall part includes the first wall part, A first hole guide, a first thread guide groove formed from an outer edge of the first wall toward the mounting base toward the first hole, and the second wall includes the second hole, And a second thread guide groove formed from an outer edge portion of the second wall portion on the mounting base side toward the second hole portion. The upper thread passes through the first hole provided in the first wall portion of the guide member, contacts the yarn contact portion of the tension member, and then passes through the second hole portion provided in the second wall portion. Prior to the sewing operation by the sewing machine, the operator can easily pass the upper thread from the first thread guide groove to the first hole and from the second thread guide groove to the second hole. Therefore, the thread tension detecting device can improve workability when passing the upper thread through the first hole and the second hole.

  The mounting base of the sewing machine according to claim 21, further comprising a wall portion facing the tension member with a gap, wherein the first thread guide groove and the second thread guide groove are more than the wall section in plan view. It should be located on the sewing machine side. The upper thread passing through the first hole and the second hole is unlikely to enter the first thread guide groove and the second thread guide groove by the wall. Therefore, the sewing machine can prevent the upper thread from coming off from the thread tension detecting device.

  The mounting base of the sewing machine according to claim 22, comprising an insertion hole that is long in a direction parallel to a length direction of the tension member, a fastening hole that is provided in the sewing machine and that faces the insertion hole, and is inserted through the insertion hole. And a fastening member fastened to the fastening hole. The yarn tension detecting device can change the attachment position in a direction parallel to the length direction of the tension member within the range of the insertion hole. By changing the attachment position of the yarn tension detecting device, the sewing machine can adjust the amount of pulling when the balance pulls up the upper thread. The sewing machine can easily perform the adjustment only by changing the attachment position of the yarn tension detecting device within the range of the insertion hole.

  The inventions of claims 1 to 22 described above can be arbitrarily combined. For example, not all or a part of claim 1 but also at least one of the other claims 2 to 22 may be provided. However, in particular, the configuration of claim 1 may be provided, and at least one of the configurations of claims 2 to 22 may be provided in combination. Further, any constituent elements of claims 1 to 22 may be extracted and combined. The applicant of the present application intends to obtain a patent right for such a configuration.

1 is an overall perspective view of a sewing machine 1. FIG. The elements on larger scale of the front surface of the head 5 shown in FIG. The elements on larger scale around the thread tension detection device 30 shown in FIG. FIG. 3 is a front view of the yarn tension detection device 30. FIG. 5 is a cross-sectional view taken along the line I-I in FIG. 4. The figure which shows the resultant force V3 which an upper thread presses the tension board 50. FIG. FIG. 3 is an exploded perspective view of the yarn tension detection device 30. The perspective view of the mounting base 40. FIG. The perspective view of the tension board 50. FIG. The perspective view of the guide member 60. FIG. The perspective view of the thread tension detection apparatus 130. FIG. The front view of the thread tension detection apparatus 130. FIG. The disassembled perspective view of the yarn tension detecting device 130. FIG. 3 is a bottom view of the yarn tension detection device 130. FIG. 3 is a plan view of the yarn tension detection device 130. Sectional view taken along the line II-II in FIG. FIG. 13 is a cross-sectional view taken along the line III-III shown in FIG. Sectional drawing of the yarn tension | tensile_strength detection apparatus 130 when adjusting a gap small. Sectional drawing of the yarn tension | tensile_strength detection apparatus 130 when adjusting a gap large. The table | surface which showed the relationship between the displacement amount of the tension board 50 with respect to needle thread tension, and the output of a Hall sensor.

  A first embodiment of the present invention will be described with reference to FIGS. In the following description, left, right, front, back, and top and bottom indicated by arrows in the figure are used. In the present embodiment, when the operator inputs a sewing start instruction, the sewing machine 1 sews a cloth (not shown).

  The structure of the sewing machine 1 will be described with reference to FIGS. The sewing machine 1 includes a bed portion 2, a pedestal column portion 3, and an arm portion 4. The bed 2 is attached to an opening of a work table (not shown) and extends in the left-right direction. The bed portion 2 is provided with a needle plate 7 on the upper surface. An operator places cloth on the bed 2 and the needle plate 7. The needle plate 7 includes a needle hole 8 and a feed dog hole 14. The needle hole 8 has a circular shape in plan view. The feed dog hole 14 has a long diameter in the front-rear direction and is located on the left side, the rear side, the right side, and the front side of the needle hole 8, respectively. The pedestal 3 extends upward from the right end of the bed 2. The arm portion 4 extends leftward from the upper end of the pedestal portion 3 and faces the upper surface of the bed portion 2. The arm unit 4 includes three operation buttons 24 and a display unit 25 at a substantially central portion in the front left-right direction. The operator operates the operation buttons 24 while looking at the display unit 25 to input various instructions. The arm portion 4 includes a thread stand bar 20 that protrudes upward on the left side of the upper surface. The thread stand 20 is inserted with the upper thread 6 fed from a thread spool (not shown). A thread spool is an example of a thread supply source.

  The arm unit 4 includes an upper shaft and a main motor (not shown) inside. The upper shaft extends in the left-right direction and is connected to the main motor via an upper shaft pulley (not shown). The upper shaft pulley is fixed to the right end of the upper shaft. The arm unit 4 includes a head 5 at the left end. The head 5 projects downward from the arm 4 and faces the needle plate 7 from above. The head 5 supports the needle bar 16 so as to be movable up and down. The lower end portion of the needle bar 16 protrudes downward from the head 5. The needle bar 16 is connected to the upper shaft via a vertical movement mechanism (not shown). The needle bar 16 moves up and down above the needle plate 7 as the upper shaft rotates. The needle bar 16 has a sewing needle 10 attached to its lower end. The sewing needle 10 holds the upper thread 6 inserted through the eye hole. The sewing needle 10 moves up and down together with the needle bar 16.

  The bed unit 2 includes a rotary hook, a thread trimming mechanism, and a cloth feeding mechanism (not shown). The rotary hook is provided below the needle plate 7 and accommodates a bobbin around which a lower thread is wound. The rotary hook rotates with the power of the main motor and captures the upper thread 6 held by the sewing needle 10 in the vicinity of the needle lower position. The thread cutting mechanism includes a fixed blade, a movable blade, and a thread cutting solenoid. The movable blade is connected to the thread trimmer solenoid. When the thread cutting solenoid is driven, the movable blade moves relative to the fixed blade, and the thread cutting mechanism cuts the upper thread 6 and the lower thread by the cooperation of the movable blade and the fixed blade.

  As shown in FIG. 2, the head 5 has a secondary thread tensioner 26, a main thread tensioner 27, and a thread guide in order from the upstream side of the path of the upper thread 6 (hereinafter referred to as the upper thread path) fed out from the thread spool. 28, a yarn tension detecting device 30, a balance 23, and a guide hook 29 are provided. The secondary thread tensioner 26 is provided in the upper right part of the front surface of the head 5. The main thread tension device 27 is provided below the sub thread tension device 26 and on the front surface of the head 5. The secondary thread tension device 26 and the main thread tension device 27 respectively apply tension to the upper thread 6. The secondary thread tensioner 26 gives the upper thread 6 a tension necessary for cutting the upper thread 6 and the lower thread by the thread trimming mechanism. The main thread tensioner 27 optimizes the tension acting on the upper thread 6 as the sewing machine 1 is sewn. The balance 23 is provided on the left side of the auxiliary thread tensioner 26. The balance 23 moves up and down as the main motor is driven. The yarn guide 28 is provided below the balance 23. The thread guide 28 guides the upper thread 6 that has passed through the main thread tensioner 27 by turning it back toward the balance 23.

  The yarn tension detecting device 30 is fixed to a recess 5A provided on the front surface of the head 5 with a screw 90. The recess 5 </ b> A is provided between the secondary thread tensioner 26 and the main thread tensioner 27. The concave portion 5A is a portion that is long in the left-right direction when viewed from the front and is recessed backward from the front surface of the head 5. The recess 5A includes a fastening hole 12 (see FIG. 5) on the right end side. The screw 90 is fastened to the fastening hole 12. The yarn tension detecting device 30 fixed to the recess 5A is located between the balance 23 and the main yarn tensioner 27. The thread tension detection device 30 can detect the tension applied to the upper thread 6. The guide hook 29 is provided on the left side of the yarn tension detecting device 30. The guide hook 29 guides the upper thread 6 that has passed through the balance 23 toward the needle bar 16.

  The structure of the yarn tension detecting device 30 will be described with reference to FIGS. In the present embodiment, for convenience of explanation, front and rear, left and right, and top and bottom will be described in the direction of the yarn tension detecting device 30 fixed to the sewing machine 1. As shown in FIG. 3 and FIG. 4, the yarn tension detection device 30 is a composite body that is long in the left-right direction when viewed from the front and is formed by assembling a plurality of members. The yarn tension detecting device 30 is arranged in the left-right direction so as to be orthogonal to the upper yarn path that is folded upward from the yarn guide 28 and extends upward toward the balance 23.

  As shown in FIG. 7, the yarn tension detecting device 30 includes a mounting base 40, a tension plate 50, a pair of strain gauges 71 and 72, a guide member 60, and the like. The attachment base 40 is a metal base that attaches the yarn tension detection device 30 to the recess 5 </ b> A of the head 5 of the sewing machine 1. The tension plate 50 is a metal member that is stretched over and fixed to the front surface of the mounting base 40 and that is distorted by contact with the upper thread 6. The pair of strain gauges 71 and 72 are attached to both surfaces of the tension plate 50. The pair of strain gauges 71 and 72 is a well-known electric resistance type sensor and detects the strain of the tension plate 50. The guide member 60 is made of metal that guides the upper thread 6 so that the upper thread 6 contacts and passes through a predetermined position on the contact surface of the tension plate 50 with the tension plate 50 sandwiched between the front surface of the mounting base 40. It is a guide member.

  The structure of the mounting base 40 will be described with reference to FIGS. The mounting base 40 includes a pedestal portion 41 and a mounting portion 42. The pedestal portion 41 functions as a pedestal that supports the tension plate 50, the guide member 60, and the like. The attachment portion 42 attaches the pedestal portion 41 to the sewing machine 1 so as to be detachable, and moves in the left-right direction so as to be positioned. Various materials, such as metal and resin, can be used as the material of the mounting base 40, for example.

  The pedestal portion 41 is formed in a substantially rectangular shape that is long in the left-right direction when viewed from the front, and has a thickness in the front-rear direction. The pedestal portion 41 includes a front wall portion 411 on the front surface. The pedestal portion 41 includes a pair of right support portion 412 and left support portion 413 on the left and right sides of the front wall portion 411. The right support part 412 and the left support part 413 are formed in a substantially rectangular parallelepiped shape protruding forward from the front wall part 411. The right support portion 412 includes a fixing hole 415 in the center of the front surface. The left support part 413 includes a fixing hole 416 in the center of the front surface. The front wall portion 411 is located behind the front surfaces of the right support portion 412 and the left support portion 413.

  The attachment portion 42 is formed in a substantially rectangular ring shape that is long in the left-right direction when viewed from the front. The attachment portion 42 includes an insertion hole 421 at the center. The insertion hole 421 is a long hole that is long in the left-right direction when viewed from the front, and penetrates in the front-rear direction. The corner of the insertion hole 421 is preferably tapered. The shaft portion of the screw 90 can be inserted into the insertion hole 421 from the front, and can move along the length direction inside the insertion hole 421. The head of the screw 90 has a diameter larger than the short diameter of the insertion hole 421 and can be locked to the edge of the insertion hole 421 from the front.

  The shape of the tension plate 50 will be described with reference to FIGS. The tension plate 50 extends in the left-right direction when viewed from the front. The material of the tension plate 50 is preferably a metal, and in consideration of distortion and durability, for example, a spring steel material such as carbon tool steel material or bainitic steel may be used. The tension plate 50 includes a thread contact portion 51 and fixing portions 52 and 53.

  The thread contact portion 51 is provided in an intermediate portion excluding the left and right sides in the length direction of the tension plate 50, and is formed in a thin plate shape extending in the left-right direction when viewed from the front. The length in the left-right direction of the yarn contact portion 51 is substantially the same as the length in the left-right direction of the front wall portion 411 of the mounting base 40. Although the thickness of the yarn contact portion 51 is not limited, it may be set to, for example, 0.5 mm in consideration of durability. The front surface of the thread contact portion 51 is a contact surface with which the upper thread 6 contacts. The intermediate position in the length direction of the contact surface is a predetermined position where the upper thread 6 contacts. The yarn contact portion 51 includes a guide portion 55 at an intermediate position in the length direction of the upper end portion, and includes a guide portion 56 at an intermediate position in the length direction of the lower end portion. The guide portions 55 and 56 face each other with the yarn contact portion 51 therebetween. The guide portions 55 and 56 protrude obliquely rearward (on the mounting base 40 side) with respect to the direction orthogonal to the length direction of the yarn contact portion 51. The guide part 55 is formed in a substantially trapezoidal shape in front view that tapers upward. The guide part 56 is formed in a substantially trapezoidal shape in a front view that tapers downward.

  The fixing portion 52 is provided on the right end side of the yarn contact portion 51. The fixing portion 53 is provided on the left end side of the yarn contact portion 51. The fixing parts 52 and 53 are formed in a substantially rectangular shape when viewed from the front. The shapes of the fixing portions 52 and 53 are substantially the same as the front shapes of the right support portion 412 and the left support portion 413 of the mounting base 40, respectively. The fixing portions 52 and 53 are provided with circular fixing holes 521 and 531 at substantially central portions thereof. The fixing holes 521 and 531 correspond to the fixing holes 415 and 416 of the right support portion 412 and the left support portion 413 of the mounting base 40, respectively. The fixing hole 521 is a long hole having a long diameter in the left-right direction.

  The pair of strain gauges 71 and 72 will be described with reference to FIG. For example, the strain gauges 71 and 72 are obtained by attaching a metal foil as a resistance material and gauge leads 71A and 72A as lead lines on a resin base as an electrical insulator. In the present embodiment, the strain gauge 71 is fixed to the left portion from a predetermined position on the contact surface (front surface) of the yarn contact portion 51 of the tension plate 50 with an adhesive. The strain gauge 72 is fixed to the left side portion from a predetermined position on the surface (back surface) opposite to the contact surface of the yarn contact portion 51 of the tension plate 50 with an adhesive. The strain gauges 71 and 72 are at the same position with the yarn contact portion 51 in between.

  The strain generated in the yarn contact portion 51 is transmitted to the metal foil through the bases of the adhesive and the strain gauges 71 and 72. The electric resistance value of the metal foil changes when strain is transmitted. A signal of the electrical resistance value of the metal foil is output to the control unit (not shown) of the sewing machine 1 through the gauge leads 71A and 72A. Based on the signals received from the strain gauges 71 and 72, the control unit of the sewing machine 1 calculates the change in the electric resistance value of the metal foil in each of the gauge leads 71A and 72A, and uses the contact surface of the yarn contact part 51 as a reference. And the distortion based on the back surface are detected. That is, the sewing machine 1 according to the present embodiment can detect the distortion generated in the yarn contact portion 51 on both the contact surface and the back surface so that it is not easily affected by the temperature change, and the distortion generated in the yarn contact portion 51 can be accurately detected. Can be detected. Therefore, the sewing machine 1 can detect the tension of the upper thread 6 with high accuracy.

  The structure of the guide member 60 will be described with reference to FIGS. The guide member 60 is formed in a substantially rectangular shape that is long in the left-right direction in plan view and that opens toward the rear in the side view (sewing machine 1 side). The guide member 60 includes a lower wall portion 61, an upper wall portion 62, a right connection wall portion 63, a left connection wall portion 64, and the like. The lower wall portion 61 and the upper wall portion 62 are spaced apart from each other in the vertical direction and arranged in parallel. The separation distance between the lower wall portion 61 and the upper wall portion 62 is slightly longer than the vertical length of the pedestal portion 41 of the mounting base 40.

  The lower wall portion 61 is formed in a thin plate shape that is long in the left-right direction when viewed from the bottom. The lower wall portion 61 includes a lower thread guide portion 66 at a substantially central portion in the left-right direction of the front end portion. The lower thread guide portion 66 is formed in a substantially U shape when viewed from the bottom, protrudes forward from the front end portion of the lower wall portion 61, and its distal end portion is bent rightward and further bent rearward. The lower yarn guide portion 66 includes a hole portion 661 at the center inner side. The hole 661 penetrates in the vertical direction. The upper thread 6 enters and passes through the hole 661 from the main thread tensioner 27 side. The front end portion that is bent rearward of the lower thread guide portion 66 is spaced forward from the front end portion of the lower wall portion 61, and a yarn guide groove 662 is formed in the gap. The thread guide groove 662 has a width through which the upper thread 6 can pass, and communicates with the hole 661.

  The upper wall portion 62 is formed in a thin plate shape that is long in the left-right direction in plan view, and faces the lower wall portion 61. In the left-right direction of the guide member 60, the position of the left end portion of the upper wall portion 62 corresponds to the position of the left edge portion of the lower thread guide portion 66 of the lower wall portion 61. The upper wall portion 62 includes an upper thread guide portion 67 at the left front end portion. The upper thread guide portion 67 has the same shape as the lower thread guide portion 66 and is formed in a substantially U shape in plan view, protrudes forward from the left front end portion of the upper wall portion 62, and its tip end portion is bent to the right. Furthermore, it bends backward. The upper thread guide part 67 is provided with a hole 671 inside the center. The hole 671 penetrates in the vertical direction. The hole 671 is provided at a position where the upper thread 6 comes out from the predetermined position of the thread contact portion 51 of the tension plate 50 to the balance 23 side. The upper thread 6 that comes out from the predetermined position toward the balance 23 enters and passes through the hole 671. The tip portion that bends rearward of the upper yarn guide portion 67 is spaced forward from the front end portion of the upper wall portion 62, and a yarn guide groove 672 is formed in the gap. The thread guide groove 672 has a width through which the upper thread 6 can pass, and communicates with the hole 671.

  The right connection wall portion 63 is formed in a substantially U shape in a side view opening toward the rear (sewing machine 1 side), and is between the right front end portion of the lower wall portion 61 and the right front end portion of the upper wall portion 62. Link. The right connecting wall portion 63 includes a fixing portion 63A at the center. The fixing portion 63A is arranged with the surface direction facing the front-rear direction. The fixing portion 63A includes a circular fixing hole 631 at the center. The fixing hole 631 corresponds to the fixing hole 415 of the right support part 412 of the mounting base 40 and the fixing hole 521 of the fixing part 52 on the right side of the tension plate 50 (see FIG. 7).

  The left connecting wall portion 64 is formed in a substantially L shape in a side view, protrudes forward from the left front end portion of the lower wall portion 61, and its distal end side is bent upward and extends. The left connecting wall portion 64 includes a fixing portion 64A on the distal end side that extends and bends upward. The fixing portion 64A is arranged with the surface direction facing the front-rear direction. The fixing portion 64A includes a circular fixing hole 641 at the center. The fixing hole 641 corresponds to the fixing hole 416 of the left support part 413 of the mounting base 40 and the fixing hole 531 of the fixing part 53 on the left side of the tension plate 50 (see FIG. 7).

  An example of an assembly method of the yarn tension detection device 30 will be described with reference to FIGS. The operator fixes the strain gauges 71 and 72 on both sides of the tension plate 50. The operator places the right fixing portion 52 of the tension plate 50 on the right support portion 412 of the mounting base 40 and the left fixing portion 53 on the left support portion 413 of the mounting base 40. The tension plate 50 is bridged between the right support portion 412 and the left support portion 413 of the mounting base 40. The front wall portion 411 of the mounting base 40 faces the yarn contact portion 51 of the tension plate 50 with a gap (see FIGS. 3 and 5).

  The operator places the guide member 60 on the mount 40 on which the tension plate 50 is placed. The pedestal 41 of the mounting base 40 is inserted between the lower wall 61 and the upper wall 62 of the guide member 60. The operator arranges the fixing portion 63 </ b> A of the right connection wall portion 63 of the guide member 60 with the fixing portion 52 of the tension plate 50 sandwiched between the right support portion 412 of the mounting base 40. The operator arranges the fixing portion 64 </ b> A of the left connecting wall portion 64 of the guide member 60 with the fixing portion 53 of the tension plate 50 sandwiched between the left support portion 413 of the mounting base 40.

  The operator inserts a screw 91 into the fixing hole 631 of the fixing portion 63A of the right connection wall 63 and the fixing hole 521 of the fixing portion 52 of the tension plate 50, and the fixing hole on the upper surface of the right support portion 412 of the mounting base 40. Fasten to 415. The operator inserts a screw 92 into the fixing hole 641 of the fixing portion 64A of the left connecting wall portion 64 and the fixing hole 531 of the fixing portion 53 of the tension plate 50, and the fixing hole on the upper surface of the left support portion 413 of the mounting base 40. Fasten to 416. The guide member 60 and the tension plate 50 are fixed to the mounting base 40. The assembly of the yarn tension detecting device 30 is completed.

  As shown in FIGS. 3 and 4, the yarn tension detecting device 30 fixes the left and right end portions of the tension plate 50 to the right support portion 412 and the left support portion 413 of the mounting base 40. Therefore, since the yarn tension detecting device 30 can stably support the yarn contact portion 51 of the tension plate 50, unnecessary vibration generated in the yarn contact portion 51 when the sewing machine 1 is driven can be suppressed. If only one end of the tension plate 50 is fixed, the yarn contact portion 51 vibrates as the sewing machine 1 is driven, and low frequency vibration is generated as noise. In the signals output from the strain gauges 71 and 72, it becomes difficult to distinguish between the low vibration frequency generated in the tension plate 50 and the period in which the tension of the upper thread 6 varies, and only the tension of the upper thread 6 is extracted from the signal. Have difficulty. In the present embodiment, by fixing both the left and right ends of the tension plate 50, the natural frequency of the tension plate 50 can be made higher than when only one end of the tension plate 50 is fixed. Therefore, since the sewing machine 1 can easily identify the tension of the upper thread 6 in the signals output from the strain gauges 71 and 72, only the tension of the upper thread 6 can be extracted from the signal.

  In the present embodiment, the tension plate 50 is detachably fixed to the mounting base 40 with screws 91 and 92. Therefore, depending on the model of the sewing machine 1, the material, thickness, tension, and the like of the upper thread 6, for example, the thread contact portion It can be easily replaced with other tension plates with different thicknesses.

  With reference to FIG. 3, an example of a method for fixing the yarn tension detecting device 30 to the sewing machine 1 will be described. The operator arranges the attachment portion 42 of the yarn tension detection device 30 inside the concave portion 5 </ b> A on the front surface of the head 5 with the orientation being the right side of the pedestal portion 41. An operator arrange | positions so that the fastening hole 12 (refer FIG. 5) provided in the right side of the recessed part 5A may oppose the inner side of the insertion hole 421 of the attaching part 42. FIG. The attachment portion 42 is positioned in the left-right direction of the sewing machine 1 so that the predetermined position of the yarn contact portion 51 of the tension plate 50 is located on the upper yarn path. The operator fastens the screw 90 to the screw hole of the recess 5 </ b> A through the insertion hole 421 of the attachment portion 42. The attachment portion 42 is fixed to the recess 5A. Fixing the yarn tension detecting device 30 to the sewing machine 1 is completed.

  The yarn tension detecting device 30 can move the attachment portion 42 along the length direction of the recess 5 </ b> A within the range of the insertion hole 421 by loosening the screw 90. Therefore, the thread tension detection device 30 can change the attachment position in the left-right direction parallel to the length direction of the tension plate 50 within the range of the insertion hole 421. By changing the attachment position of the yarn tension detecting device 30, the sewing machine 1 can adjust the amount of pulling up when the balance 23 pulls up the upper thread 6. Therefore, the sewing machine 1 can easily perform the adjustment only by changing the mounting position of the yarn tension detecting device 30 within the range of the insertion hole 421.

  In the conventional sewing machine, a guide hook for guiding the upper thread 6 via the main thread tensioner 27 and the thread guide 28 toward the balance 23 is fixed to the recess 5A provided on the front surface of the head 5 of the sewing machine 1. The sewing machine 1 of the present embodiment can fix the yarn tension detection device 30 instead of the guide hook fixed to the recess 5A.

  An example of a method for passing the upper thread 6 through the thread tension detection device 30 will be described with reference to FIGS. The operator passes the upper thread 6 from the front with respect to the thread tension detecting device 30 fixed to the recess 5 </ b> A of the head 5. The operator passes the upper thread 6 through the hole 661 of the lower thread guide part 66 of the guide member 60 and the hole 671 of the upper thread guide part 67. At this time, the operator passes the upper thread 6 through the front side with respect to the thread contact portion 51 of the tension plate 50. The operator can easily pass the upper thread 6 from the thread guide groove 662 to the hole 661 and from the thread guide groove 672 to the hole 671. Therefore, the sewing machine 1 can improve the workability when the upper thread 6 is passed through the holes 661 and 671. The operator brings the upper thread 6 into contact with a predetermined position on the contact surface of the thread contact portion 51 of the tension plate 50. If the predetermined position of the thread contact portion 51 is shifted with respect to the upper thread 6, the screw 90 may be loosened and the position of the thread tension detecting device 30 may be adjusted in the left-right direction. Installation of the upper thread 6 to the thread tension detecting device 30 is completed.

  As shown in FIGS. 3 and 5, in the yarn tension detection device 30, the yarn guide grooves 662 and 672 are located on the sewing machine 1 side (the recessed portion 5 </ b> A side) with respect to the front wall portion 411 of the mounting base 40 in plan view. Therefore, the upper thread 6 passing through the holes 661 and 671 is difficult to enter the thread guide grooves 662 and 672 by the front wall part 411. Therefore, the sewing machine 1 can prevent the upper thread 6 from coming off from the thread tension detecting device 30.

  The upper thread 6 contacts a predetermined position on the contact surface of the thread contact portion 51. The guide portions 55 and 56 of the tension plate 50 are curved and protrude toward the mounting base 40 (see FIG. 3). The guide portion 55 guides the upper thread 6 passing through the hole portion 661 to a predetermined position on the contact surface. The guide portion 56 guides the upper thread 6 from a predetermined position on the contact surface toward the hole portion 671. As shown in FIG. 5, the upper thread 6 is bent at the thread contact portion 51, but can be reasonably contacted with the contact surface by the two guide portions 55 and 56. Therefore, since a large load is not applied to the upper thread 6, the thread tension detecting device 30 can prevent the upper thread 6 from being cut at the thread contact portion 51. Therefore, the upper thread 6 can come into contact with the predetermined position of the thread contact portion 51 so as to slide smoothly.

  The guide portions 55 and 56 position the upper thread 6 at a predetermined position of the yarn contact portion 51. As described above, since the predetermined position is an intermediate position of the yarn contact portion 51, the entire yarn contact portion 51 can be distorted. Therefore, since the yarn contact portion 51 can be distorted according to the tension of the upper thread 6, the yarn tension detecting device 30 can widely detect the tension of the upper thread 6.

  The force with which the upper thread 6 pushes the tension plate 50 will be described with reference to FIG. When passing through the guide member 60 and the tension plate 50, the upper thread 6 comes into contact with the inner edge of the hole 661, the predetermined position P of the contact surface of the thread contact portion 51 of the tension plate 50, and the inner edge of the hole 671. The predetermined position P of the contact surface of the yarn contact portion 51 is located on the opposite side of the mounting base 40 from the virtual straight line L connecting the hole portion 661 and the hole portion 671. The yarn contact portion 51 contacts the upper yarn 6 passing between the hole portion 661 and the hole portion 671 from behind. Therefore, the upper thread 6 is bent with respect to the virtual straight line L between the hole 661 and the hole 671. Therefore, the yarn tension detection device 30 can generate a force that pushes the yarn contact portion 51 of the tension plate 50 toward the mounting base 40 at the predetermined position P due to the tension of the upper yarn 6, and can easily distort the tension plate 50. .

  The upper thread 6 has a first tension V1, which is a vector of force from the upper end position toward the hole 661 in the predetermined position P, and a force vector from the lower end position toward the hole 671 in the predetermined position P. The second tension V2 is generated. An intersection of a line in which the first tension V1 is extended from the upper end position to the center side in the predetermined position P and a line in which the second tension V2 is extended from the lower end position to the center side in the predetermined position P is defined as a Q point. . A vector of force from point Q in a direction perpendicular to the contact surface of the yarn contact portion 51 is a resultant force V3 of the first tension V1 and the second tension V2. The resultant force V3 is a force that pushes the yarn contact portion 51 toward the sewing machine 1 side. In the present embodiment, the positional relationship between the yarn contact portion 51 and the hole portions 661 and 671 is determined so that the first tension V1 and the second tension V2 have the same magnitude. Since the first tension V <b> 1 and the second tension V <b> 2 are the same magnitude, the direction of the resultant force V <b> 3 in which the upper thread 6 pushes the thread contact part 51 is a direction perpendicular to the contact surface of the thread contact part 51. Therefore, the yarn tension detecting device 30 can regulate the direction in which the tension plate 50 is distorted, so that it is difficult to vary the tension of the upper thread 6 to be detected.

  Although this embodiment does not limit each magnitude | size of the 1st tension | tensile_strength V1 and the 2nd tension | tensile_strength V2, and the magnitude | size of the resultant force V3, it is good to set it as a 2: 1 relationship, for example. The angle θ1 between the first tension V1 and the second tension V2 is not limited, but may be 145 °, for example. At this time, due to the tension of the upper thread 6, the thread contact part 51 of the tension plate 50 can be pushed to the sewing machine 1 side without difficulty, and the thread contact part 51 can be distorted according to the magnitude of the tension of the upper thread 6.

  As described above, the sewing machine 1 according to the first embodiment includes the sewing needle 10, the balance 23, and the main thread tension device 27. The sewing needle 10 holds the upper thread 6 and can move up and down. The balance 23 is provided in the upper thread path from the thread supply source to the sewing needle 10, and moves up and down with the vertical movement of the sewing needle 10 to pull up the upper thread 6. The main yarn tensioner 27 is disposed between the yarn supply source and the balance 23 in the upper yarn path, and can control the tension applied to the upper yarn 6. The sewing machine 1 having the above configuration further includes a yarn tension detecting device 30. The thread tension detection device 30 can detect the tension applied to the upper thread 6. The yarn tension detecting device 30 is disposed between the main yarn tensioner 27 and the balance 23 in the upper yarn path. Therefore, when the balance 23 pulls the upper thread 6, there is no resistance between the balance 23 and the sewing needle 10. Further, the thread tension detecting device 30 is not near the sewing needle 10. Therefore, since the thread tension detecting device 30 does not interfere with the sewing of the sewing machine 1, high-quality stitches can be formed on the cloth. Since the balance 23 does not pull the portion of the upper thread 6 where the thread tension detection device 30 detects the tension, the thread tension detection device 30 can detect the original tension applied to the upper thread 6.

  The yarn tension detection device 30 of the first embodiment includes a mounting base 40, a tension plate 50, a pair of strain gauges 71 and 72, a guide member 60, and the like. The mounting base 40 can be attached to the front surface of the head 5 of the sewing machine 1 with screws 90. The tension plate 50 includes a thread contact portion 51 and two fixing portions 52 and 53. The fixing parts 52 and 53 are detachably fixed to the mounting base 40 with screws 91 and 92. The yarn contact portion 51 is connected between the fixing portions 52 and 53, extends in a direction intersecting the upper yarn path between the main yarn tensioner 27 and the balance 23, and is distorted by contact with the upper yarn 6. Produce. The strain gauges 71 and 72 detect the strain generated in the yarn contact portion 51 and output a signal according to the degree of strain. The guide member 60 is fixed to the mounting base 40 with screws 91 and 92. The guide member 60 includes holes 661 and 671. The hole 661 is provided at a position where the upper thread 6 enters from the main thread tensioner 27 side with respect to a predetermined position of the thread contact section 51. The hole 671 is provided at a position where the upper thread 6 comes out from the predetermined position to the balance 23 side. The yarn tension detecting device 30 having the above-described configuration can be detachably attached to the sewing machine 1 with the mounting base 40. Since the tension plate 50 removably fixes the fixing portions 52 and 53 to the mounting base 40, the tension plate 50 can be appropriately replaced according to the model of the sewing machine 1. The guide member 60 guides the upper thread 6 so that the upper thread 6 contacts and passes at a predetermined position. Therefore, since the sewing machine 1 can always contact the predetermined position of the thread contact portion 51 of the tension plate 50 without shifting the upper thread 6, the tension of the upper thread 6 can be detected with high accuracy. The thread tension detecting device 30 can detect the tension abnormality immediately during sewing by detecting the tension of the upper thread 6 with high accuracy, can detect a sewing failure, and can feed back to the sewing machine 1. Therefore, when a tension abnormality is detected during sewing, the sewing machine 1 can immediately stop the sewing operation, for example. Therefore, the sewing machine 1 can improve sewing product quality and work efficiency.

  In the above description, the secondary thread tensioner 26 and the main thread tensioner 27 are examples of the thread tensioner of the present invention. The tension plate 50 is an example of the tension member of the present invention. The strain gauges 71 and 72 are examples of the strain detection sensor of the present invention. The hole 661 of the guide member 60 is an example of the first hole of the present invention, and the hole 671 of the guide member 60 is an example of the second hole of the present invention. The lower wall portion 61 and the lower thread guide portion 66 of the guide member 60 are an example of the first wall portion of the present invention. The yarn guide groove 662 is an example of the first yarn guide groove of the present invention. The upper wall portion 62 and the upper thread guide portion 67 of the guide member 60 are an example of the second wall portion of the present invention. The yarn guide groove 672 is an example of the second yarn guide groove of the present invention. The front wall portion 411 of the mounting base 40 is an example of the wall portion of the present invention. The screw 90 is an example of the fastening member of the present invention.

  A second embodiment of the present invention will be described with reference to FIGS. The sewing machine according to the second embodiment includes a yarn tension detecting device 130 shown in FIG. The yarn tension detecting device 130 detects the upper yarn tension by indirectly detecting the distortion generated in the tension plate 50 by the upper yarn tension using the magnet 58 and the hall element 105. The yarn tension detection device 130 is a modification of the yarn tension detection device 30 of the first embodiment, and has a part of the configuration changed. Therefore, in 2nd embodiment, it demonstrates centering on a different part from the yarn tension | tensile_strength detection apparatus 30, and attaches | subjects the same code | symbol about a common part, and simplifies or abbreviate | omits description. The configuration of the sewing machine is the same as that of the sewing machine 1 of the first embodiment.

  The configuration of the yarn tension detection device 130 will be described with reference to FIGS. As shown in FIGS. 11 and 12, the yarn tension detection device 130 is a composite body that is long in the left-right direction in front view and is constructed by assembling a plurality of members, like the yarn tension detection device 30 of the first embodiment. The yarn tension detecting device 130 is arranged on the sewing machine in the same manner as the yarn tension detecting device 30 of the first embodiment (see FIG. 2).

  As shown in FIG. 13, the yarn tension detecting device 130 includes a mounting base 140, a tension plate 50, a magnet 58, a sensor holder 80, an FPC 100, a Hall element 105, a temperature sensor 106, a fastening screw 95, an adjusting screw 96, a guide member 160, and the like. Is provided. The tension plate 50 is the same component as in the first embodiment. The mounting base 140 and the guide member 160 are obtained by modifying a part of each of the mounting base 40 and the guide member 60 of the first embodiment.

  The structure of the mounting base 140 will be described. As shown in FIG. 13, the mounting base 140 includes a pedestal portion 410 and a mounting portion 42. The pedestal portion 410 functions as a pedestal that supports the tension plate 50, the guide member 160, and the like. The pedestal portion 410 is formed in a substantially rectangular shape that is long in the left-right direction when viewed from the front, and has a thickness in the front-rear direction. The pedestal 410 has a front wall 431 on the front surface. The front wall 431 is formed in a substantially rectangular shape that is long in the left-right direction when viewed from the front. The pedestal 410 includes a pair of right support 412 and left support 413 on the left and right sides of the front wall 431. The right support portion 412 and the left support portion 413 protrude forward from the front wall portion 431 and are formed in a substantially rectangular parallelepiped shape. The right support portion 412 includes a fixing hole 415 in the center of the front surface. The left support part 413 includes a fixing hole 416 in the center of the front surface.

  The front wall portion 431 is located behind the front surfaces of the right support portion 412 and the left support portion 413. The front wall portion 431 includes a step portion 432, a through hole 435, a screw hole 436, and the like. The step portion 432 is provided at the left end portion on the left support portion 413 side of the front wall portion 431. The step portion 432 projects forward from the front wall portion 431 and is formed in a substantially rectangular parallelepiped shape. The through hole 435 is provided close to the right side of the step part 432 and penetrates the front wall part 431 in the front-rear direction. The through hole 435 inserts a fastening screw 95 described later. The screw hole 436 is provided close to the right side of the through hole 435, and an adjustment screw 96 described later is screwed inward. The attachment part 42 has the same structure as that of the first embodiment.

  The magnet 58 will be described. As shown in FIG. 13, the magnet 58 is fixed to the middle portion in the left-right direction on the back surface opposite to the contact surface (front surface) of the yarn contact portion 51 of the tension plate 50 with an adhesive. Since the middle portion of the yarn contact portion 51 includes the guide portions 55 and 56, the magnet 58 is hidden inside the guide portions 55 and 56. Therefore, the upper thread 6 can be prevented from being caught by the magnet 58. The middle portion of the back surface of the yarn contact portion 51 is bent in a circular arc shape by the guide portions 55 and 56, and therefore has high rigidity and is difficult to bend. Therefore, the magnet 58 is difficult to peel from the back surface intermediate portion of the yarn contact portion 51.

  The shape of the magnet 58 is not limited, and any shape such as a columnar shape, a square shape, or a cylindrical shape is possible, but a columnar shape is preferable. The columnar magnet 58 has one end surface as a fixed surface and is fixed to the back surface of the thread contact portion 51 with an adhesive. Since the fixed surface is circular, the frictional force distribution due to the bending of the yarn contact portion 51 of the fixed surface is continuous and does not partially deviate. On the other hand, the fixed surface of the square magnet is polygonal and has a plurality of corners, so that the frictional force distribution due to bending of the yarn contact portion 51 of the fixed surface is concentrated on the corners and is discontinuous. Therefore, the columnar magnet 58 has an advantage that it is difficult to peel off from the back surface of the yarn contact portion 51 compared to the square magnet. The magnetizing direction of the magnet 58 is a height direction passing through the cylindrical magnet 58 along the axial direction.

  The size of the magnet 58 is preferably small so as not to affect the natural frequency of the tension plate 50. For example, when the magnet 58 is Φ1 or 1.5 and about 1 mm in length and 1/20 or less of the mass of the tension plate 50, the tension plate 50 provided with the magnet 58 and the tension plate 50 not provided with the magnet 58 The coincidence ratio of the natural frequency of is 95%. Since the mass of the magnet 58 is extremely smaller than the mass of the tension plate 50, the natural frequency of the tension plate 50 is not greatly reduced. Therefore, the tension plate 50 can avoid resonance with the magnet 58 in use. However, the size of the magnet 58 is preferably sufficiently larger than the area of a detection unit (not shown) that detects the magnetic field of the Hall element 105. In this case, the yarn tension detecting device 130 can reduce the influence of the mutual displacement between the magnet 58 and the Hall element 105 described later.

  The material of the magnet 58 is not limited. For example, any of ferrite, alnico, samarium cobalt, neodymium, and the like can be applied, but neodymium is preferable. Neodymium has a higher magnetic flux density than other materials, and is advantageous in that it is inexpensive and readily available.

  The structure of the sensor holder 80 will be described. As shown in FIGS. 13 and 16, the sensor holder 80 is attached to the front wall 431 side of the mounting base 140. Although the material of the sensor holder 80 is not limited, it is preferably formed of a non-magnetic material. For example, aluminum can be adopted. The sensor holder 80 has a plate shape having a surface direction in a direction orthogonal to a direction (rear direction) in which the yarn contact portion 51 is distorted, and is formed in a substantially trapezoidal shape whose vertical width becomes narrower toward the front in a side view. The sensor holder 80 includes a support surface 81, a mounting surface 82, and an outer surface 83. The support surface 81 is the front surface of the sensor holder 80 and is a surface that supports a sensor support portion 101 of the FPC 100 described later. The support surface 81 includes a left part 81A and a right part 81B. The left portion 81A is provided on the left side of the support surface 81 and is formed in a substantially rectangular shape when viewed from the front. The right part 81B is formed in a substantially rectangular shape extending rightward from the central part of the left end part of the left part 81A and having a narrower vertical width than the left part 81A. The vertical width of the support surface 81 matches the vertical width of the sensor support portion 101 of the FPC 100 described later.

  The attachment surface 82 is a back surface of the sensor holder 80 and is a surface attached to the front wall portion 431 of the attachment base 140. The attachment surface 82 is formed in a substantially rectangular shape in rear view. The area of the attachment surface 82 is larger than the area of the support surface 81. The outer side surface 83 is a side surface that surrounds the outer periphery of the sensor holder 80, and is formed in a tapered shape that smoothly spreads from the outer edge portion of the support surface 81 toward the outer edge portion of the mounting surface 82.

  The sensor holder 80 further includes a screw hole 85 and a hole 86. The screw hole 85 is provided substantially at the center of the left portion 81A of the support surface 81 and penetrates between the mounting surface 82 (see FIG. 15). When the sensor holder 80 is attached to the mounting base 140, the screw hole 85 corresponds to the position of the through hole 435 provided in the front wall portion 431 of the mounting base 140. The hole 86 is provided on the right side of the screw hole 85 in the mounting surface 82. The hole 86 is a dead-end hole having a bottom on the back side, and does not penetrate the support surface 81 (see FIG. 16).

  The FPC 100 will be described. FPC (Flexible printed circuits) 100 is an abbreviation for flexible printed circuit board. As shown in FIG. 13, the FPC 100 includes a sensor support portion 101, a horizontal direction portion 102, and a vertical direction portion 103. The sensor support portion 101 has a surface direction in the front-rear direction and is a portion that is fixed to the support surface 81 of the sensor holder 80 with an adhesive. The sensor support portion 101 is formed in the same shape as the support surface 81 and includes a left portion 101A and a right portion 101B. The left portion 101A corresponds to the left portion 81A of the support surface 81, and the right portion 101B corresponds to the right portion 81B of the support surface 81. The sensor support unit 101 includes a hall element 105 and a temperature sensor 106 on the upper surface. The hall element 105 is fixed to the upper surface of the right part 101B. The Hall element 105 is a known semiconductor that detects a magnetic flux density of a magnet and outputs an analog signal (voltage signal) proportional to the magnitude as a sensor value. The Hall element 105 of the present embodiment is a vertical detection Hall element that can detect the magnetic flux of the magnet 58 that passes perpendicularly to the Hall element 105. The temperature sensor 106 is fixed to the boundary portion between the left portion 101A and the right portion 101B. The temperature sensor 106 is, for example, a thermistor, and detects the ambient temperature using the resistance temperature characteristic of the semiconductor.

  The lateral direction portion 102 is formed in an elongated substantially rectangular shape extending from the rear end portion of the left portion 101 </ b> A of the sensor support portion 101 to the rear at a substantially right angle and extending rightward and extending in the left-right direction in plan view. The vertical portion 103 is formed in an elongated substantially rectangular shape extending vertically upward from the right portion of the rear end portion of the horizontal portion 102 and extending in the vertical direction when viewed from the front. The sensor support portion 101, the horizontal direction portion 102, and the vertical direction portion 103 are substrates on which electric circuits of the hall element 105 and the temperature sensor 106 are formed.

  The fastening screw 95 and the adjustment screw 96 will be described. As shown in FIG. 13, the fastening screw 95 is a general screw having a round bar-like portion having a screw thread on the outside and a head portion provided at one end in the axial direction of the rod-like portion and projecting radially outward. The fastening screw 95 is inserted into the through hole 435 from the rear side of the mounting base 140, and the tip side protruding from the opening on the front wall portion 431 side is fastened to the screw hole 85 provided in the mounting surface 82 of the sensor holder 80. Therefore, the sensor holder 80 is fixed to the front wall portion 431 side of the mounting base 140.

  The adjusting screw 96 is formed in a round bar shape having a thread on the outside. The adjustment screw 96 is screwed into the screw hole 436 of the mounting base 140 and protrudes from the front end side through the opening on the front wall portion 431 side. The adjustment screw 96 includes a tool groove 96 </ b> A at one end located on the back side of the mounting base 140. The groove 96A has a-(minus) shape. The operator inserts the tip of a tool (for example, a flat-blade screwdriver) into the screw hole 436 from the back side of the mounting base 140, inserts it into the groove 96A, and rotates in one direction or in the opposite direction. As the tool rotates, the adjustment screw 96 moves back and forth along the screw hole 436 in the front-rear direction. Therefore, the height at which the tip of the adjustment screw 96 projects from the opening on the front wall 431 side of the screw hole 436 can be adjusted with a tool.

  In a state where the sensor holder 80 is attached to the mounting base 140, the tip end portion of the adjustment screw 96 is inserted into the hole 86 provided in the attachment surface 82 of the sensor holder 80 and abuts against the bottom portion of the hole 86 (see FIG. 16). The sensor holder 80 is supported on the front wall 431 side of the mounting base 140 by the upper surface of the stepped portion 432 and the tip of the adjustment screw 96. The operator adjusts the height protruding from the front wall portion 431 of the adjustment screw 96 to fix the Hall element 105 supported by the sensor holder 80 via the FPC 100 and the back surface of the thread contact portion 51 of the tension plate 50. The gap with the magnet 58 is adjusted. A gap adjusting method using the adjusting screw 96 will be described later.

  The structure of the guide member 160 will be described. As shown in FIG. 13, the guide member 160 includes a lower wall portion 61, an upper wall portion 62, a right connection wall portion 63, a left connection wall portion 64, and the like. The distance between the lower wall portion 61 and the upper wall portion 62 is slightly longer than the vertical length of the pedestal portion 410 of the mounting base 140.

  As shown in FIGS. 13 and 14, the lower wall portion 61 includes a lower thread guide portion 166 at a substantially central portion in the left-right direction of the front end portion. The lower thread guide portion 166 is formed in a substantially U shape when viewed from the bottom, protrudes forward from the front end portion of the lower wall portion 61, and the tip portion of the protruding portion is bent rightward and further bent rearward. The lower thread guide portion 166 includes a hole 171 at the center inner side. The hole 171 penetrates in the vertical direction. The upper thread 6 enters and passes through the hole 171 from the main thread tensioner 27 (see FIG. 2) side. The tip portion that bends backward of the lower thread guide portion 166 is spaced forward from the front end portion of the lower wall portion 61, and forms a yarn guide groove 172 in the gap with the front end portion of the lower wall portion 61. The thread guide groove 172 has a width through which the upper thread 6 can pass, and communicates with the hole 171.

  As shown in FIGS. 13 and 15, the position of the left end portion of the upper wall portion 62 in the left-right direction of the guide member 160 corresponds to the position of the left edge portion of the lower thread guide portion 166 of the lower wall portion 61. The upper wall part 62 includes an upper thread guide part 167 on the left side of the front end part. The upper thread guide portion 167 is formed in a substantially U shape in plan view, protrudes forward from the left side of the front end portion of the upper wall portion 62, the tip end portion is bent rightward, and further bent rearward. The upper thread guide portion 167 includes a hole 181 at the center inner side. The hole 181 penetrates in the vertical direction. The hole 181 is provided at a position where the upper thread 6 comes out from the middle part of the thread contact part 51 of the tension plate 50 toward the balance 23 (see FIG. 2). The upper thread 6 that passes from the middle part of the thread contact part 51 to the balance 23 side enters and passes through the hole 181.

  As shown in FIG. 15, the upper wall 62 includes a recess 183 at the front end. The concave portion 183 is provided on the left side of the base end portion of the upper thread guide portion 167 and at a position facing the distal end portion that bends rearward of the upper thread guide portion 167. The recess 183 is a substantially semicircular groove when viewed from the bottom. The tip end portion of the upper thread guide portion 167 is formed in a substantially semicircular arc shape and is disposed inside the recess 183. The tip of the upper thread guide 167 is spaced forward from the inner edge of the recess 183, and an arcuate thread guide groove 182 is formed in the gap. The thread guide groove 182 has a width that allows the upper thread 6 to pass therethrough, and communicates with the hole 181. The guide member 160 can form the thread guide groove 182 in an arc shape along the inner edge of the recess 183 so that the upper thread 6 is more difficult to come out of the hole 181. Since the right connecting wall 63 and the left connecting wall 64 have the same structure as that of the first embodiment, description thereof is omitted.

  An example of an assembling method of the yarn tension detecting device 130 will be described with reference to FIGS. As shown in FIG. 13, first, in the sensor support portion 101 of the FPC 100, the worker fixes the hall element 105 at the center of the right portion 101B and the temperature sensor 106 at the boundary between the left portion 101A and the right portion 101B. The operator positions the sensor support portion 101 of the FPC 100 with respect to the support surface 81 of the sensor holder 80 and fixes it with an adhesive. At this time, the outer peripheral edge portion of the support surface 81 and the outer peripheral edge portion of the sensor support portion 101 are aligned. The operator screws the adjustment screw 96 into the screw hole 436 of the mounting base 140, and projects the tip of the adjustment screw 96 from the opening on the front wall portion 431 side of the screw hole 436 (see FIG. 16).

  The operator abuts the left end portion of the mounting surface 82 of the sensor holder 80 against the stepped portion 432 of the mounting base 140, and inserts the distal end portion of the adjustment screw 96 into the hole 86 provided in the mounting surface 82. The sensor holder 80 is supported on the front wall 431 side of the mounting base 140 by the step 432 and the tip of the adjustment screw 96. A gap is interposed between the mounting surface 82 of the sensor holder 80 and the front wall portion 431 of the mounting base 140. The operator inserts the fastening screw 95 into the through hole 435 from the back side of the mounting base 140, and fastens the tip portion to the screw hole 85 provided on the mounting surface 82 of the sensor holder 80. The sensor holder 80 is fixed to the mounting base 140. The adjustment screw 96 is positioned behind the Hall element 105 fixed to the sensor support portion 101 of the FPC 100 via the sensor holder 80.

  The operator fixes the fixing surface of the magnet 58 to the middle portion of the back surface of the thread contact portion 51 of the tension plate 50 with an adhesive. Since the tension plate 50 is a magnetic material (for example, a metal such as iron), the effective magnetic flux can be increased as a back yoke of the magnet 58. During the fixing operation of the magnet 58, the magnet 58 is attracted to the tension plate 50 by a magnetic force, so that the fixing operation can be facilitated. The operator places the right fixing portion 52 of the tension plate 50 on the right support portion 412 of the mounting base 140 and the left fixing portion 53 on the left support portion 413 of the mounting base 140. The tension plate 50 is bridged between the right support portion 412 and the left support portion 413 of the mounting base 140. The Hall element 105 fixed to the sensor support portion 101 of the FPC 100 faces the magnet 58 fixed to the middle portion of the back surface of the thread contact portion 51 of the tension plate 50 via a gap.

  The operator places the guide member 160 on the mounting base 140 on which the tension plate 50 is placed. The pedestal portion 410 of the mounting base 140 is inserted between the lower wall portion 61 and the upper wall portion 62 of the guide member 160. The operator arranges the fixing portion 63 </ b> A of the right connection wall portion 63 of the guide member 160 with the fixing portion 52 of the tension plate 50 sandwiched between the right support portion 412 of the mounting base 140. An operator arranges the fixing portion 64 </ b> A of the left connecting wall portion 64 of the guide member 160 with the fixing portion 53 of the tension plate 50 sandwiched between the left support portion 413 of the mounting base 140. The lateral portion 102 of the FPC 100 is disposed in a gap between the lower surface of the upper wall portion 62 of the guide member 160 and the upper surface of the mounting base 140 (see FIG. 17). The vertical portion 103 of the FPC 100 is disposed behind the right connection wall 63 of the guide member 160 so as to bend and extend upward from the right side of the rear end portion of the horizontal portion 102 (see FIGS. 12 and 13).

  As shown in FIG. 16, the operator inserts a screw 91 from the front into the fixing hole 631 of the fixing portion 63 </ b> A of the right connection wall portion 63 and the fixing hole 521 of the fixing portion 52 of the tension plate 50. Fastened to the fixing hole 415 on the upper surface of the right support portion 412. The operator inserts a screw 92 from the front into the fixing hole 641 of the fixing portion 64A of the left connecting wall portion 64 and the fixing hole 531 of the fixing portion 53 of the tension plate 50, and the upper surface of the left support portion 413 of the mounting base 140 is inserted. Fasten to the fixing hole 416. The guide member 160 and the tension plate 50 are fastened and fixed to the mounting base 140 with screws 91 and 92. The assembly of the yarn tension detecting device 130 is completed.

  An example of the gap between the magnet 58 and the Hall element 105 and a gap adjusting method will be described with reference to FIGS. As shown in FIG. 17, the gap between the magnet 58 and the hall element 105 (see G in FIG. 17) is such that the magnet 58 does not interfere with the hall element 105 even if the thread contact portion 51 of the tension plate 50 is deformed to the maximum. It should be as small as possible. The gap of the present embodiment may be set to a target value of, for example, 0.25 mm in consideration of the assemblability of the yarn tension detection device 130, component variations, and the like.

  As shown in FIG. 16, in a state where the sensor holder 80 is fixed to the mounting base 140 with the fastening screw 95, the operator rotates the adjustment screw 96 in one direction or the reverse direction with a tool, The protruding height of the adjusting screw 96 is adjusted. For example, in this embodiment, the basic posture of the sensor holder 80 is a posture in which the mounting surface 82 of the sensor holder 80 is parallel to the front wall portion 431 of the mounting base 140. When the protrusion height of the adjustment screw 96 from the front wall portion 431 is increased from the state in which the sensor holder 80 is in the basic posture, the tip end portion of the adjustment screw 96 pushes up the hole bottom of the hole 86 of the sensor holder 80. At this time, as shown in FIG. 18, the sensor holder 80 is lifted on the right end side with the left end portion contacting the stepped portion 432 and the screw hole 85 portion where the fastening screw 95 is fastened as a base point. Since the Hall element 105 approaches the magnet 58, the gap becomes small.

  On the other hand, as shown in FIG. 19, when the height of the protrusion of the adjustment screw 96 from the front wall portion 431 is lowered from the state in which the sensor holder 80 shown in FIG. The screw hole 436 is moved downward. Accordingly, the sensor holder 80 is inclined so that the right end side is lowered with the left end portion in contact with the stepped portion 432 and the screw hole 85 portion to which the fastening screw 95 is fastened as a base point. Since the Hall element 105 moves in a direction away from the magnet 58, the gap increases. Note that the sensor holder 80 shown in FIG. 19 is shown larger than the actual tilt so that the tilted state can be easily understood.

  The operator adjusts the protruding height of the adjustment screw 96 from the front wall portion 431 by the above method, and adjusts the gap to a target value (for example, 0.25 mm) while checking the sensor value (voltage signal) of the Hall element 105. . Therefore, the sewing machine can obtain a stable output of the Hall element 105. The gap adjustment is complete. Since the sensor holder 80 is a non-magnetic material, the effect of changing the gap due to the attractive force of the magnet 58 fixed to the back surface of the thread contact portion 51 of the tension plate 50 can be suppressed.

  The operation of the yarn tension detector 130 will be described as shown in FIGS. Also in the yarn tension detection device 130, the upper thread 6 contacts the contact surface (front surface) of the yarn contact portion 51 of the tension plate 50, as in the yarn tension detection device 30 of the first embodiment. Due to the upper thread tension, the thread contact portion 51 is distorted backward. In accordance with the distortion of the yarn contact portion 51, the magnet 58 moves in the front-rear direction. As the magnet 58 moves, the magnetic flux density of the magnet 58 passing through the Hall element 105 changes. The Hall element 105 detects a change in magnetic flux density and converts it into a voltage signal. The sewing machine calculates the needle thread tension based on the sensor value output from the hall element 105. In the present embodiment, the magnetic flux density detected by the Hall element 105 when the tension plate 50 is loaded with the upper thread tension is linear with respect to the magnetic flux density detected by the tension element 50 when the upper thread tension is not loaded. It is preferable to change greatly.

  The Hall element 105 has temperature characteristics. Therefore, the sensor value of the Hall element 105 may change due to the environmental temperature, the temperature rise of components, and the like. The yarn tension detection device 130 of this embodiment fixes the temperature sensor 106 to the sensor support portion 101 of the FPC 100. The temperature sensor 106 is located in the vicinity of the hall element 105. Therefore, the sewing machine detects the temperature around the hall element 105 with the temperature sensor 106 and corrects the sensor value of the hall element 105 according to the detected temperature, thereby obtaining a stable sensor value that does not affect the temperature change.

  In the yarn tension detecting device 130, the magnetizing direction of the magnet 58 is a direction along a predetermined direction in which the yarn contact portion 51 of the tension plate 50 is distorted by contact with the upper yarn 6. The sensor holder 80 supports the Hall element 105 with respect to the magnet 58 through a gap in a predetermined direction. Therefore, the Hall element 105 can accurately detect a change in magnetic flux density that changes according to the strain of the yarn contact portion 51. The position of the adjustment screw 96 screwed into the screw hole 436 of the sensor holder 80 is a position corresponding to the hall element 105 in a predetermined direction. The adjusting screw 96 is a magnetic material. Therefore, the magnetic flux of the magnet 58 can pass through the Hall element 105 toward the adjusting screw 96. The magnetic flux passes through the mounting base 140 that is a magnetic body from the adjusting screw 96 and returns to the tension plate 50 to be able to circulate well.

  The relationship between the needle thread tension and the sensor value of the hall element 105 will be described with reference to FIG. In the present embodiment, the amount of movement of the middle portion of the thread contact portion 51 of the tension plate 50 when the upper thread tension is changed (hereinafter referred to as the amount of movement of the tension plate 50) and the sensor value of the Hall element 105 are shown. The upper thread tension (N) applied to the thread contact portion 51 is obtained when the upper thread 6 is pulled downward from the hole 171 of the lower thread guide section 166 of the thread tension detecting device 130 and pulled with various strengths. Show. The amount of movement of the tension plate 50 is 0 when the upper thread tension is not applied to the tension plate 50. In the present embodiment, the movement amount (mm) of the tension plate 50 when the upper thread tension is changed and the sensor value (V) from the Hall element 105 are shown in the chart.

  In FIG. 20, the straight line A indicates the relationship between the needle thread tension and the amount of movement of the tension plate 50. A straight line B shows the relationship between the needle thread tension and the sensor value of the hall element 105. As shown by the straight line A, the amount of movement of the tension plate 50 is proportional to the change in the needle thread tension. Therefore, this embodiment can detect the upper thread tension with high accuracy by detecting the movement amount of the tension plate 50. On the other hand, as indicated by the straight line B, the sensor value of the Hall element 105 is proportional to the change in the needle thread tension. Therefore, in this embodiment, the upper thread tension can be detected with high accuracy based on the sensor value of the hall element 105.

  As described above, since the yarn tension detecting device 130 fixes both ends of the tension plate 50 to the mounting base 140, even if the yarn contact portion 51 of the tension plate 50 is deformed by the upper thread tension, the yarn contact portion 51 The middle part does not tilt. Since the magnet 58 is fixed to the middle portion of the back surface of the yarn contact portion 51, the magnet 58 can always move facing the hall element 105. Therefore, the yarn tension detecting device 130 can ensure linearity between the upper yarn tension and the sensor value of the hall element 105.

  With reference to FIG. 12, FIG. 13, and FIG. 17, the thread damage prevention effect and the thread drop prevention effect when the upper thread 6 is violated by the thread tension detector 130 during sewing will be described. The yarn tension detecting device 130 reduces the width of the right portion 81B of the support surface 81 of the sensor holder 80 and the width of the right portion 101B of the sensor support portion 101 of the FPC 100, and reduces the width of the yarn contact portion 51 of the tension plate 50 in front view. It hides in the guide parts 55 and 56 (refer FIG. 12, FIG. 13). Therefore, even when the upper thread 6 is violated during sewing, the thread tension detecting device 130 can prevent the upper thread 6 from being caught on the sensor holder 80 and the sensor support portion 101 of the FPC 100. Therefore, the yarn tension detecting device 130 can prevent the upper yarn 6 from being damaged.

  As shown in FIG. 13, the width of the right portion 81B of the support surface 81 of the sensor holder matches the width of the right portion 101B of the sensor support portion 101 of the FPC 100, and the outer surface 83 of the sensor holder 80 is It is formed in a tapered shape that smoothly spreads from the outer edge portion toward the outer edge portion of the mounting surface 82. Therefore, even when the upper thread 6 is violated during sewing, the upper thread 6 is not easily caught on the outer surface 83 of the sensor holder 80. Therefore, the yarn tension detecting device 130 can prevent the upper yarn 6 from being damaged.

  As shown in FIG. 17, the yarn tension detecting device 130 includes a gap K1 between the upper end portion of the sensor holder 80 and the upper yarn guide portion 167 of the guide member 160 opposed thereto, the lower end portion of the sensor holder 80, and a guide opposed thereto. The gap K2 with the lower thread guide portion 166 of the member 160 is narrowed together. Therefore, the yarn tension detecting device 130 can suppress the ramp of the upper yarn 6 in the gaps K1 and K2. Therefore, the yarn tension detecting device 130 can prevent the upper yarn 6 from coming out from the holes 171 and 181 through the yarn guide grooves 172 and 182 to the outside.

  As described above, the sewing machine according to the second embodiment includes the yarn tension detecting device 130. The yarn tension detection device 130 includes a mounting base 140, a tension plate 50, a magnet 58, a sensor holder 80, a hall element 105, and the like. The magnet 58 is fixed to the back surface of the yarn contact portion 51 of the tension plate 50. The sensor holder 80 is fixed to the mount 140 and supports the Hall element 105 with respect to the magnet 58 through a gap. When the yarn contact portion 51 is distorted by the upper yarn tension, the magnetic flux passing through the Hall element 105 changes. The Hall element 105 detects a change in magnetic flux density and outputs a signal in accordance with the change. Therefore, the thread tension detecting device 130 can detect the upper thread tension with high accuracy. Since the yarn tension detecting device 130 uses the magnet 58 and the hall element 105, the configuration can be made compact and inexpensive.

  In the above description, the hole 86 provided in the mounting surface 82 of the sensor holder 80 is an example of the hole of the present invention. The bottom part on the back side of the hole 86 is an example of the contacted part of the present invention.

  The present invention can be variously modified in addition to the first and second embodiments.

(Modification common to the first and second embodiments)
The yarn tension detection devices 30 and 130 of the first and second embodiments fix the left and right ends of the tension plate 50 to the pedestal 41 of the mounting base 40 and the pedestal 410 of the mounting base 140, respectively. You may fix only one end part of one side among both ends.

  The thread contact portion 51 of the tension plate 50 is disposed so as to extend in the left-right direction perpendicular to the upper thread path between the main thread tensioner 27 and the balance 23, but intersects the upper thread path. Should be arranged.

  In the first embodiment, the strain generated in the tension plate 50 is directly detected using a strain gauge, and in the second embodiment, the strain generated in the tension plate 50 is indirectly detected using the magnet 58 and the Hall element 105. Detect. The yarn tension detecting device may detect distortion generated in the tension plate 50 by a method other than the first and second embodiments, for example, using a sensor such as an infrared sensor or a laser displacement meter. Good.

  The guide portions 55 and 56 of the tension plate 50 are formed in a substantially trapezoidal shape when viewed from the front, but may have other shapes.

  In the tension plate 50, the predetermined position for contacting the upper thread 6 is an intermediate position in the length direction of the thread contact portion 51. However, if it is at least in contact with the contact surface of the thread contact portion 51, the predetermined position is not the intermediate position. Also good.

(Modification of the first embodiment)
The guide member 60 includes a lower yarn guide portion 66 and an upper yarn guide portion 67. The front end portion of the lower thread guide portion 66 may be connected to the front end portion of the lower wall portion 61. The front end portion of the upper thread guide portion 67 may be connected to the front end portion of the upper wall portion 62. The yarn guide grooves 662 and 672 may be omitted. The holes 661 and 671 may be circular holes.

  The two strain gauges 71 and 72 are fixed to both surfaces of the thread contact portion 51 of the tension plate 50, respectively, but may be fixed to the same surface. For example, the strain gauges 71 and 72 may be fixed to the left and right sides of the same surface with a predetermined position in between. In this case, the yarn tension detecting device 30 can widely detect the distortion of the entire yarn contact portion 51 generated with the predetermined position as an intermediate portion. Further, one strain gauge or two or more strain gauges may be fixed to the tension plate 50, but it is preferable to fix a plurality of strain gauges. In this case, the yarn tension detection device 30 can accurately detect distortion generated in the yarn contact portion 51. Further, the strain gauge may be fixed to the back surface opposite to the contact surface of the yarn contact portion 51. In this case, the thread tension detecting device 30 can prevent the strain gauges 71 and 72 from interfering with the upper thread 6 passing through the thread contact portion 51 when sewing with the sewing machine 1.

  The guide member 60 includes a lower yarn guide portion 66 and an upper yarn guide portion 67. The front end portion of the lower thread guide portion 66 may be connected to the front end portion of the lower wall portion 61. The front end portion of the upper thread guide portion 67 may be connected to the front end portion of the upper wall portion 62. The yarn guide grooves 662 and 672 may be omitted. The holes 661 and 671 may be circular holes.

(Modification of the second embodiment)

  The Hall element 105 and the temperature sensor 106 are fixed on the sensor support portion 101 of the FPC 100, and the sensor support portion 101 is fixed to the support surface 81 of the sensor holder 80. The Hall element 105 and the temperature sensor 106 are connected to the sensor holder 80. The support surface 81 may be directly fixed. The temperature sensor 106 may be omitted.

  In a state where the sensor holder 80 is fixed to the front wall 431 side of the mounting base 140 with the fastening screw 95, the height of the adjustment screw 96 protruding from the front wall 431 is adjusted to support the Hall element 105 of the sensor holder 80. By adjusting the position of the portion to be adjusted, the gap between the magnet 58 and the Hall element 105 is adjusted, but the gap may be adjusted by other methods. For example, the step portion 432 may be omitted from the front wall portion 431, and a plate-shaped spacer may be sandwiched between the mounting surface 82 of the sensor holder 80 and the front wall portion 431. Spacers with different thicknesses may be selected and sandwiched, or the number of spacers sandwiched may be adjusted. For example, a plate-shaped spacer is sandwiched between the right support portion 412 of the mounting base 140 and the fixing portion 52 of the tension plate 50, and between the left support portion 413 of the mounting base 140 and the fixing portion 53 of the tension plate 50. The gap between the magnet 58 and the Hall element 105 may be adjusted by inserting a plate-shaped spacer. Therefore, the yarn tension detecting device can adjust the position of the sensor holder 80 in a predetermined direction parallel to the direction in which the tension plate 50 is distorted, and can adjust the gap between the magnet 58 and the Hall element 105. In the second embodiment, the gap adjusting function by the adjusting screw 96 may be omitted. The method of fixing the sensor holder 80 to the mounting base 140 is not limited to the fastening screw 95, and may be fixed with a fixing pin or the like.

  The guide member 160 includes a lower yarn guide portion 166 and an upper yarn guide portion 167. The front end portion of the lower thread guide portion 166 may be connected to the front end portion of the lower wall portion 61. The front end portion of the upper thread guide portion 167 may be connected to the front end portion of the upper wall portion 62. The yarn guide grooves 172 and 182 may be omitted. The holes 171 and 181 may be circular holes.

  The magnetizing direction of the magnet 58 is a height direction passing through the columnar magnet 58 along the axial direction. For example, a columnar magnet through which magnetic flux passes in the radial direction may be adopted.

  The protruding tip end of the adjustment screw 96 is inserted into a hole 86 provided in the mounting surface 82 of the sensor holder 80 and abuts against the bottom of the hole 86 on the back side. The shape of the abutting portion may be any of a hole shape, a protruding shape, a planar shape, and the like. For example, the hole 86 of the mounting surface 82 may be omitted and the mounting surface 82 may be in direct contact. For example, a protruding portion that protrudes toward the front wall portion 431 of the mounting base 140 may be provided at a portion facing the leading end portion of the adjusting screw 96, and the leading end portion of the adjusting screw 96 may be brought into contact with the protruding portion.

  The yarn tension detecting device 130 detects the change in the magnetic flux density of the magnet 58 with the hall element 105, but may be detected with other sensors. For example, a magnetic impedance element, a magnetoresistive effect element, etc. Can be used.

DESCRIPTION OF SYMBOLS 1 Sewing machine 6 Upper thread 10 Sewing needle 23 Balance 26 Sub thread tensioner 27 Main thread tensioner 30, 130 Thread tension detection apparatus 40,140 Mounting stand 50 Tension plate 51 Thread contact part 52,53 Fixing part 55,56 Guide part 58 Magnet 60, 160 Guide member 61 Lower wall part 62 Upper wall part 66 Lower thread guide part 67 Upper thread guide part 71, 72 Strain gauge 80 Sensor holder 90 Screw 95 Fastening screw 96 Adjustment screw 105 Hall element 411 Front wall part 421 Insertion hole 661 Hole 662 Thread guide groove 671 Hole 672 Thread guide groove L Virtual straight line V1 First tension V2 Second tension

Claims (22)

It has a needle that holds the upper thread and can move up and down,
A balance that is provided in an upper thread path from a thread supply source to the sewing needle, moves up and down with the vertical movement of the sewing needle, and pulls up the upper thread;
In a sewing machine including a thread tensioner that is disposed between the thread supply source and the balance in the upper thread path and that can control a tension applied to the upper thread.
A sewing machine comprising: a thread tension detecting device capable of detecting a tension applied to the upper thread between the thread tensioner and the balance in the upper thread path. The yarn tension detecting device is
A mounting base attached to the sewing machine;
A fixing part that is detachably fixed to the mounting base, and is connected to the fixing part, extends in a direction intersecting the upper thread path between the thread tensioner and the balance, and contacts with the upper thread. A tension member provided with a yarn contact portion that causes distortion in itself,
A sensor that directly or indirectly detects the distortion generated in the yarn contact portion and outputs a signal according to the detection result;
Fixed to the mounting base, provided at a position where the upper thread enters from the thread tensioner side with respect to a predetermined position of the thread contact portion, a first hole through which the upper thread passes, and from the predetermined position A guide member provided at a position where the upper thread is pulled out to the balance side, and a second hole through which the upper thread passes, and guides the upper thread so that the upper thread contacts and passes at the predetermined position; The sewing machine according to claim 1, further comprising: The sewing machine according to claim 2, wherein the sensor is a strain detection sensor that detects the strain generated in the yarn contact portion and outputs a signal according to the degree of the strain. The sewing machine according to claim 3, wherein the strain detection sensor is fixed to the back surface of the yarn contact portion opposite to the contact surface with which the upper yarn contacts. The strain detection sensor is
A first strain detection sensor fixed on one end side in the length direction of the yarn contact portion from a position corresponding to the predetermined position on a contact surface of the yarn contact portion with which the upper thread comes into contact;
5. The sewing machine according to claim 3, further comprising: a second strain detection sensor fixed to the one end side of the back surface opposite to the contact surface with respect to the position corresponding to the predetermined position. . A magnet fixed to the back surface opposite to the contact surface with which the upper thread of the thread contact portion contacts;
A magnetic sensor that detects a change in magnetic flux density of the magnet that changes in accordance with distortion of the yarn contact portion and outputs a signal in accordance with the change;
The sewing machine according to claim 2, further comprising a sensor holder that is fixed to the mounting base and supports the magnetic sensor via a gap with respect to the magnet. The said sensor holder supports the said magnetic sensor through the said gap in the predetermined direction which is a direction where the said thread contact part is distorted by the contact with the said upper thread with respect to the said magnet. The sewing machine according to 1. The sensor holder is
Forming a plate having a surface direction in a direction intersecting the predetermined direction,
A support surface that faces the back side of the yarn contact portion and supports the magnetic sensor;
A surface opposite to the support surface, the mounting surface to be attached to the mounting base,
The mounting base is
A holder mounting surface facing the back surface side of the yarn contact portion, and mounting the mounting surface of the sensor holder;
Provided on the holder mounting surface, protruding to the back side of the yarn contact portion, and a stepped portion that contacts one end of the mounting surface of the sensor holder;
Holder fixing for fixing the sensor holder to the mounting base in a state in which the one end portion of the mounting surface is in contact with the stepped portion and a gap is formed between the holder mounting surface and a region excluding the stepped portion. And
The sewing machine according to claim 7, further comprising a holder position adjusting unit capable of adjusting a position of at least a portion of the sensor holder that supports the magnetic sensor in a direction parallel to the predetermined direction. The holder fixing part is
A hole provided in the region of the holder mounting surface and penetrating perpendicularly to the region;
Inserted from the opening opposite to the opening on the holder mounting surface side with respect to the hole, and provided with a tip portion protruding from the opening on the holder mounting surface side in the region of the mounting surface of the sensor holder A fastening screw for fastening to the holder side screw hole,
The holder position adjusting unit is
A screw hole that is provided in a position corresponding to the magnetic sensor in the predetermined direction at a position opposite to the step in the region of the holder mounting surface and opposite to the step portion, and penetrates perpendicularly to the region. When,
The height of the tip of the screw hole protruding from the opening on the holder mounting surface side of the screw hole can be adjusted by screwing into the screw hole and rotating by a tool, and the height of the tip provided on the mounting surface of the sensor holder can be adjusted. The sewing machine according to claim 8, further comprising a rod-shaped adjustment screw that can come into contact with the contact portion. A hole through which the tip of the adjustment screw can be inserted is provided at a position facing the tip of the adjustment screw on the mounting surface;
The sewing machine according to claim 9, wherein the contacted portion is a bottom portion of the hole. The magnetizing direction of the magnet is a direction along the predetermined direction,
The sewing machine according to claim 9 or 10, wherein the adjustment screw is a magnetic body. The magnet has a cylindrical shape having an axis in the predetermined direction,
12. The sewing machine according to claim 7, wherein one end surface of the magnet in the axial direction is a circular fixed surface that is fixed to the back surface of the yarn contact portion. The sewing machine according to claim 6, wherein the sensor holder is a non-magnetic material. The sewing machine according to claim 6, wherein the magnetic sensor is a Hall element. The fixing portions are provided at both ends in the length direction of the tension member,
The sewing machine according to any one of claims 2 to 14, wherein the yarn contact portion is provided between a pair of the fixing portions. The sewing machine according to any one of claims 2 to 15, wherein the predetermined position is an intermediate position in a length direction of the yarn contact portion. The predetermined position of the yarn contact portion is located on a side opposite to the mounting base with respect to a virtual straight line connecting the first hole portion and the second hole portion. The sewing machine according to 1. In the predetermined position, the tension applied by the tension member to the upper thread is a first tension that is a vector from the predetermined position toward the first hole, and from the predetermined position to the second hole. The sewing machine according to claim 17, wherein the predetermined position, the first hole portion, and the second hole portion are arranged so as to have the same magnitude as a second tension that is a vector directed to the side. . The yarn contact portion includes a contact surface that contacts the upper yarn in parallel at the predetermined position,
The one end portion on the first hole side of the contact surface and the other end portion on the second hole side are inclined toward the mounting base with respect to a direction orthogonal to the length direction of the yarn contact portion. The sewing machine according to any one of claims 2 to 18, further comprising a guide portion that protrudes and guides the upper thread to the predetermined position. The guide part is
A first wall portion and a second wall portion respectively disposed on both end sides in the direction along the upper thread path;
The first wall part is the first hole part, and a first thread guide groove formed from an outer edge part of the first wall part on the mounting base side toward the first hole part,
The second wall portion includes the second hole portion and a second thread guide groove formed from an outer edge portion of the second wall portion on the mounting base side toward the second hole portion. The sewing machine according to claim 19. The mount includes a wall portion facing the tension member with a gap therebetween,
21. The sewing machine according to claim 20, wherein the first thread guide groove and the second thread guide groove are positioned on the sewing machine side with respect to the wall portion in plan view. The mounting base includes a long insertion hole in a direction parallel to the length direction of the tension member,
A fastening hole provided in the sewing machine and facing the insertion hole;
The sewing machine according to any one of claims 2 to 21, further comprising: a fastening member that is inserted through the insertion hole and fastened to the fastening hole.

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