Thread cutting device of sewing machine

Abstract

 The invention relates to a thread cutting device (10) of a sewing machine. The thread cutting device (10) includes a moving knife and a stand-by knife (3). The thread cutting device (10) is configured to cut a thread by a cooperation of the moving knife (2) and the stand-by knife (3) when the moving knife (2) is retreated to a cutting position. The thread cutting device (10) further includes a cam mechanism (40) configured to give a back and forth turning movement to the moving knife (2), an actuator (51) configured to connect and disconnect a power transmission between the cam mechanism (40) and the moving knife (2), and to advance the moving knife (2) from the most retreated position and retreat the moving knife (2) to the most retreated position, an interlocking mechanism (60) configured to interlock the stand-by knife (3) with the advancing movement of the moving knife (2) until the stand-by knife (3) reaches its most advanced position, a stand-by mechanism (70) configured to hold the stand-by knife (3) to prevent the stand-by knife (3) from retreating when the moving knife (2) retreats, a releasing means (24) for releasing the stand-by knife (3) from the stand-by mechanism (70) when the moving knife (2) has passed the cutting position, and a returning means (12, 12A) for returning the stand-by knife (3) to its most retreated position.

Description

[0001] The present invention relates to a thread cutting device of a sewing machine. The thread cutting device is configured to cut a thread by a cooperation of a moving knife and a stand-by knife.

[0002] Conventionally, as described in JP 2008-068004 A for example, a thread cutting device includes a moving knife configured to move back and forth between a most advanced position and a most retreated position, a stand-by knife configured to advance toward the most advanced position to a cutting position to stand by until the moving knife moves back toward the most retreated position to a cutting position where the thread is cut between the moving knife and the stand-by knife, a coupling mechanism having a cam mechanism configured to give a back-and-forth movement to the moving knife in conjunction with a lower shaft, and an air cylinder configured to connect or disconnect the cam mechanism and the lower shaft.

[0003] A projection (indicated by the reference numeral 21 in JP 2008-068004A) is provided on the moving knife, and the projection is brought into contact with the stand-by knife so that the moving knife is moved together with the stand-by knife in the advancing direction.

[0004] When cutting the thread, the air cylinder turns the stand-by knife in the advancing direction from its initial position, and accordingly, the projection provided on the moving knife is pressed by the stand-by knife and the advancing movement is also applied to the moving knife.

[0005] As a result, a cam roller that moves together with the moving knife enters a groove of a grooved cam, and the advancing movement of the moving knife is succeeded by the cam mechanism. The cam mechanism turns the moving knife in a reciprocating manner by rotation of a cam shaft, and captures and pulls the thread to the cutting position when the moving knife retreats.

[0006] At that time, the stand-by knife is held at the cutting position by the air cylinder, and when the moving knife reaches the cutting position, the thread is cut between the cutting edges of the respective knives.

[0007] However, in the thread cutting device of JP 2008-068004 A, the air cylinder functions to advance the stand-by knife to the cutting position, to guide the cam roller into the grooved cam by advancing the moving knife via the stand-by knife, and also to hold the stand-by knife at the cutting position.

[0008] The moving knife has the projection to move together with the stand-by knife. Thus, when retreating the moving knife, the air cylinder is actuated at to retreat the stand-by knife in order to avoid collision of the projection with the stand-by knife which would otherwise cause an operation failure.

[0009] However, the air cylinder also functions to hold the stand-by knife at the cutting position, and if the stand-by knife is retreated too early, it would cause a cutting failure. Therefore, it has been difficult to appropriately adjust the actuating timing of the air cylinder for retreating the stand-by knife to achieve a reliable thread cutting operation.

[0010] Further, depending on the type of the thread, friction may occur when retreating the stand-by knife after the cutting, and delay the timing of the retreating movement of the stand-by knife, which makes it even more difficult to appropriately adjust the actuating timing of the air cylinder

[0011] It is an object of the present invention to enable a reliable thread cutting operation.

[0012] According to a first aspect of the present invention, a thread cutting device of a sewing machine includes a moving knife configured to move back and forth between a most advanced position and a most retreated position, and a stand-by knife supported such that the moving knife contacts the stand-by knife in a sliding manner and such that the stand-by knife turns back and forth. The thread cutting device is provided on a shuttle shaft base of a horizontally rotating shuttle or near the shuttle shaft base, and is configured to cut a thread by a cooperation of the moving knife and the stand-by knife when the moving knife is retreated to a cutting position.

[0013] The thread cutting device is characterized in that it further includes:

a cam mechanism having a cam driver configured to rotate by obtaining power from a lower shaft, and a cam follower configured to give a back and forth turning movement to the moving knife;

an actuator configured to connect and disconnect a power transmission between the cam mechanism and the moving knife, and to advance the moving knife from the most retreated position and retreat the moving knife to the most retreated position;

an interlocking mechanism configured to interlock the stand-by knife with the advancing movement of the moving knife until the stand-by knife reaches its most advanced position;

a stand-by mechanism configured to hold the stand-by knife to prevent the stand-by knife from retreating when the moving knife retreats;

a releasing means for releasing the stand-by knife from the stand-by mechanism when the moving knife has passed the cutting position; and

a returning means for returning the stand-by knife to its most retreated position.

[0014] According to a second aspect of the present invention, the stand-by mechanism may be a latch mechanism having a pawl configured to lock the stand-by knife to prevent the stand-by knife from retreating when the moving knife reaches the most advanced position, and the releasing means may have a protrusion configured to retreat together with the moving knife to move the pawl in a releasing direction when the moving knife has passed the cutting position.

[0015] According to a third aspect of the present invention, the protrusion of the releasing means may be a separate part from the moving knife and may be detachable from the moving knife.

[0016] According to a fourth aspect of the present invention, the interlocking mechanism may be configured to interlock the stand-by knife only with the advancing movement of the moving knife by pushing the stand-by knife or a member that turns back and forth together with the stand-by knife with the moving knife or a member that turns back and forth together with the moving knife.

[0017] According to a fifth aspect of the present invention, the actuator may include an actuation part configured to move back and forth and coupled to the moving knife. The actuator may be controlled such that the actuation part is movable in accordance with an external force while the back and forth movement is applied to the moving knife from the cam mechanism.

[0018] According to the first aspect of the present invention, switching between connection and disconnection of the power between the moving knife and the cam mechanism is performed by directly applying a forward and backward movement not to the stand-by knife but to the moving knife by the actuator. Therefore, operational restriction that the application of a retreating movement by the actuator needs to be after completion of thread cutting as in the case of the conventional technique is eliminated, interference between the cam mechanism and the actuator is reduced by appropriately adjusting the retreating movement start timing of the actuator, and an excellent cutting operation without troubles can be realized.

[0019] Further, switching is performed by applying the forward and backward movement not to the stand-by knife but to the moving knife by the actuator, so that an influence of a movement delay of the stand-by knife depending on the type of the thread is reduced, and therefore, an excellent cutting operation can be realized.

[0020] According to the second aspect of the present invention, the stand-by mechanism is a latch mechanism, and the protrusion which retreats together with the moving knife releases the pawl of the latch mechanism, so that unlike the case where the moving knife and the stand-by knife are operated by individual drive sources and synchronized at a predetermined timing, a release timing in the retreating movement of the moving knife can always be fixed, and a more excellent cutting operation can be realized.

[0021] According to the third aspect of the present invention, the protrusion of the releasing means is formed of a separate member that is detachable from the moving knife, so that the position of the moving knife can be adjusted without changing the timing to release the stand-by knife by the protrusion.

[0022] According to the fourth aspect of the present invention, by pressing and contact between the knives or members, the moving knife and the stand-by knife are interlocked in the advancing direction, so that a configuration of the interlocking mechanism in which the moving knife and the stand-by knife are interlocked only in the advancing direction and are made free from each other in the retreating direction can be realized by a simple structure.

[0023] According to the fifth aspect of the present invention, while the back and forth movement is applied to the moving knife by the cam mechanism, the actuator is controlled so that the actuation part of the actuator becomes freely movable in accordance with an external force, and the movement application by the cam mechanism can be performed without being influenced by the actuator while making a means for switching interlock of the moving knife and the actuator or the moving knife and the cam mechanism unnecessary.

[0024] Other aspects and advantages of the present invention will be apparent from the following description, the drawings and the claims.

[0025] The following description of a preferred embodiment of the invention serves to explain the invention in greater detail in conjoint with the drawings. These show:

Fig. 1:

a perspective view of a thread cutting device according to an embodiment of the invention;

Fig. 2:

a perspective view of a moving knife and a moving knife support mechanism;

Fig. 3:

a plan view in which a part of a tip end portion of the moving knife is cut away;

Fig. 4:

an exploded perspective view of a stand-by knife support means;

Fig. 5:

a plan view around the stand-by knife;

Fig. 6:

a perspective view of a cam mechanism and an air cylinder mechanism;

Fig. 7:

a sectional view of the cam mechanism and the air cylinder mechanism, illustrating a cross section along center lines of a moving knife shaft and a moving knife link shaft of the cam mechanism;

Fig. 8:

a perspective view of the thread cutting device, without a shuttle shaft base;

Fig. 9:

a perspective view of the shuttle shaft base from below;

Fig. 10A:

an explanatory view of a thread cutting operation;

Fig. 10B:

another explanatory view of the thread cutting operation following Fig. 10A;

Fig. 10C:

another explanatory view of the thread cutting operation following Fig. 10B;

Fig. 11A:

another explanatory view of the thread cutting operation following Fig. 10C;

Fig. 11B:

another explanatory view of the thread cutting operation following Fig. 11A;

Fig. 11C:

another explanatory view of the thread cutting operation following Fig. 11B;

Fig. 12A:

another explanatory view of the thread cutting operation following Fig. 11C;

Fig. 12B:

another explanatory view of the thread cutting operation following Fig. 12A;

Fig. 12C:

another explanatory view of the thread cutting operation following Fig. 12B;

Fig. 13:

a perspective view of another example of a returning means; and

Fig. 14:

a plan view showing an example in which a stand-by knife adjusting structure is added.

[0026] In an embodiment described hereinafter, various limitations technically preferred for carrying out the present invention are provided, however, they do not limit the scope of the invention to the embodiments described hereinafter and shown examples. In the present embodiment, based on X, Y, and Z axes shown in the drawings, the directions of the respective components of the thread cutting device 10 of a sewing machine are described. The Z-axis direction is the vertical direction, and the X-axis direction and the Y-axis direction are horizontal directions orthogonal to each other. The sewing machine is installed on a horizontal plane, and on the assumption that the longitudinal direction of the sewing machine bed portion is parallel to the Y-axis direction, the thread cutting device 10 installed inside a sewing machine will be described.

[0027] Sewing machine

[0028] In the present embodiment, the sewing machine is not especially limited, however, here, an example in which the thread cutting device is installed in a general feed sewing machine will be described. The general feed sewing machine (hereinafter, referred to as sewing machine, simply) is a sewing machine which feeds a thick workpiece (for example, leather) while a sewing needle is stuck into the workpiece by synchronizing a needle feeding operation in which an up-down movement of the sewing needle by a needle up-down movement mechanism and needle oscillation by a needle oscillation mechanism are synchronized and a feeding operation by an upper feed mechanism and a lower feed mechanism in order to prevent displacement of the workpiece according to the feeding operation.

[0029] The sewing machine includes the known needle up-down movement mechanism inside the sewing machine arm portion, and a horizontally rotating shuttle below the throat plate inside the sewing machine bed portion although these are not shown. To the needle up-down movement mechanism, power of a sewing machine motor is transmitted via a main shaft, and to the horizontally rotating shuttle, the power of the sewing machine motor is transmitted via a lower shaft and a shuttle shaft. The main shaft and the lower shaft are disposed in parallel to the Y-axis direction, and the shuttle shaft is disposed in parallel to the Z-axis direction. Both of the lower shaft and the shuttle shaft are provided with bevel gears which engage with each other to transmit power.

[0030] Other various components to be generally installed in the sewing machine are known, so that description thereof is omitted here.

[0031] Thread Cutting Device

[0032] Next, a configuration of a thread cutting device 10 in the present embodiment will be described in detail.

[0033] In Fig. 1, the thread cutting device 10 includes a shuttle shaft base 11 which supports a shuttle shaft inside the sewing machine bed portion, a moving knife 2 configured to turn back and forth, a moving knife support mechanism 20 supporting the moving knife 2 such that the moving knife can be turned back and forth with respect to the shuttle shaft base 11, a stand-by knife 3 which comes into sliding contact with the moving knife 2 and turns back and forth, a stand-by knife support means 30 supporting the stand-by knife 3 such that the stand-by knife 3 can turn back and forth with respect to the shuttle shaft base 11; a cam mechanism 40 as a first movement application mechanism configured to give the back and forth turning movement to the moving knife 2, an air cylinder mechanism 50 as a second movement application mechanism configured to give the back and forth turning movement to the moving knife 2, an interlocking mechanism 60 configured to interlock the stand-by knife 3 with the advancing movement from a predetermined position before the most advanced position to the most advanced position of the moving knife 2 (direction of the black arrow in Fig. 1), a stand-by mechanism 70 configured to hold the stand-by knife 3 so as not to allow the stand-by knife 3 to retreat (in the direction of the white arrow in Fig. 1) when the moving knife 2 retreats, a protrusion 24 as a releasing means for releasing the stand-by knife 3 from the stand-by mechanism 70 when the moving knife 2 has passed a cutting position, and a return spring 12 as a returning means for returning the stand-by knife 3 to its most retreated position.

[0034] Shuttle Shaft Base

[0035] The shuttle shaft base 11 is fixed and installed below a feed dog not shown inside the sewing machine bed portion, and supports substantially all components of the thread cutting device 10. Further, in the lower portion of the shuttle shaft base 11, a through hole along the Y-axis direction through which the lower shaft 1 is inserted and a through hole adjacent to the above-described through hole and along the Z-axis direction through which a shuttle shaft is inserted are formed. Power is transmitted from the lower shaft 1 to the shuttle shaft via bevel gears, and a torque is applied to the horizontally rotating shuttle provided on an upper end portion of the shuttle shaft (just above the shuttle shaft base 11). The moving knife 2 described later is disposed so as to turn back and forth on the side just above the horizontally rotating shuttle.

[0036] Moving Knife and Moving knife Support Mechanism

[0037] In Fig. 2, the moving knife support mechanism 20 includes a moving knife shaft 21 which becomes a central axis of a turning movement of the moving knife 2, a support plate 22 formed integrally on an upper end portion of the moving knife shaft 21, and a moving knife base 23 fitted by screwing to the upper surface of the support plate 22, and the moving knife base 23 retains the base end portion of the moving knife 2 by screwing.

[0038] The moving knife shaft 21 is supported rotatably with respect to the shuttle shaft base 11 via a hollow stand-by knife shaft 31 described later while being parallel to the Z-axis direction. Accordingly, the moving knife 2 turns back and forth around the Z axis, and the turning end portion of the moving knife 2 moves along the X-Y plane.

[0039] The support plate 22 has a tabular shape along the X-Y plane, and includes a protrusion 24 and an input portion 25 which are extended toward the outer side in the radial direction around the moving knife shaft 21.

[0040] The protrusion 24 has a tip end portion which interlocks with retreat-turning (in the direction of the white arrow in Fig. 1) of the moving knife 2 to release a stand-by state (retreat preventing state) of the stand-by knife 3 caused by the stand-by mechanism 70 described later at a predetermined timing, and an operation of the protrusion will be described in detail in the description of the structure of the stand-by mechanism 70.

[0041] On the upper surface of the input portion 25, a block 46 of the cam mechanism 40 described later is provided turnably around the Z-axis direction due to a shoulder screw, and transmits power for a turning movement to the moving knife 2 according to the cam mechanism 40 via the support plate 22.

[0042] On the lower surface of the support plate 22, an interlock pin 61 of an interlocking mechanism 60 described later is provided adjacent to the moving knife shaft 21 while proj ecting downward.

[0043] On the upper surface of the support plate 22, a positioning pin 26 of the moving knife base 23 is provided while projecting upward. This positioning pin 26 is provided concentrically with the moving knife shaft 21 described above.

[0044] The moving knife base 23 has a retaining groove 27 formed for retaining the base end portion of the moving knife 2, and by moving the base end portion of the moving knife 2 along the horizontal groove 27 and fixing it with fixation screws 28, position adjustment is enabled in this direction. The retaining groove 27 is provided on the axis line of the moving knife shaft 21, and enables adjustment of the turning radius of the tip end portion of the moving knife 2.

[0045] On the lower surface side of the moving knife base 23, a fitting hole not shown which fits the positioning pin 26 described above is formed. The moving knife base 23 is attached to the support plate 22 via through holes slightly larger than the outer diameters of fixation screws 29, and by turning the moving knife base 23 around the positioning pin 26 and fastening it with the fixation screws 29, the angle of the moving knife 2 around the moving knife shaft 21 is made adjustable. By this angle adjustment, the most advanced position and the cutting position of the moving knife 2 can be adjusted.

[0046] The movable end portion 2a extending straight to the moving knife 2 is retained on the moving knife base 23, and on a tip end portion 2b largely curved and extended from the base end portion 2a, a cutting edge 2c which cuts a thread is formed. The moving knife 2 is supported turnably by the above-described moving knife support mechanism 20, and by advance-turning (in the direction of the black arrow in Fig. 1) of the moving knife 2, the tip end portion moves to approach a stitch point, and by retreat-turning (in the direction of the white arrow in Fig. 1) of the moving knife 2, the tip end portion moves to separate from the stitch point.

[0047] On the lower surface side of the tip end portion 2b of the moving knife 2, a latching portion for capturing a thread is formed, and the most advanced position of turning is set at a position at which the latching portion of the moving knife 2 slightly passes over the stitch point.

[0048] In Fig. 3, the tip end portion 2b of the moving knife 2 is sharp-pointed and extended so that its longitudinal direction is along an arc centered on the moving knife shaft 21. Near the tip end of the moving knife 2, a through hole 2d is opened from the outer side surface to the inner side surface. The through hole 2d is formed aslant with respect to the outer side surface, and a portion closer to the tip end portion on the end edge portion of the through hole 2d becomes a cutting edge 2c. The cutting edge 2c has an acute angle due to the aslant form of the through hole 2d, and a thread is cut when it is sandwiched between the cutting edge 2c and the cutting edge 3a of the tip end portion of the stand-by knife 3.

[0049] Stand-By Knife and Stand-By Knife Support Means

[0050] In Fig. 4 and Fig. 5, the stand-by knife support mechanism 30 includes a stand-by knife shaft 31 as a central axis of the turning movement of the stand-by knife 3, an arm-shaped stand-by knife base 32 provided on and fixed to the upper end portion of the stand-by knife shaft 31, and a metal bearing 33 fitted to an opening formed along the Z-axis direction on the upper surface of the shuttle shaft base 11 and supports the stand-by knife shaft 31 rotatably.

[0051] As described above, the stand-by knife shaft 31 is formed to be hollow, and structured so as to support the moving knife shaft 21 inserted in the hollow rotatably.

[0052] The stand-by knife base 32 has a base end portion attached to the upper end portion of the stand-by knife shaft 31 by holding it, and has a turning end portion to which the stand-by knife 3 is fitted.

[0053] To the stand-by knife base 32, a return spring 12 which always energizes turning in the retreat-turning direction (direction in which the stand-by knife 3 separates from the stitch point: the direction of the white arrow in Fig. 1) is joined, and unless an external force in the advance-turning direction is applied, the stand-by knife base stands by at the most retreated position (position of Fig. 5) at which it comes into contact with a stopper 34.

[0054] Alongside the metal bearing 33, a height adjust screw 37 which adjusts the vertical heights of the stand-by knife shaft 31 and the moving knife shaft 21 via the bearing 33 is provided (see Fig. 1 and Fig. 7). The height adjust screw 37 penetrates through the shuttle shaft base 11 along the X-axis direction and is supported rotatably, and on its tip end portion, an eccentric projection is provided and inserted into a recess provided on the outer peripheral surface of the metal bearing 33. When the height adjust screw 37 is operated to rotate, the eccentric projection on the tip end changes in position vertically, so that according to this change, the metal bearing 33 is also adjusted in height vertically, and the moving knife 2 and the stand-by knife 3 are also adjusted in height in the same manner.

[0055] The stand-by knife 3 has a tabular shape along the outer side surface of the moving knife 2, and has a tip end portion formed as a cutting edge 3 a. The cutting edge 3a of the stand-by knife 3 is disposed so as to come into sliding contact with the cutting edge 2a of the moving knife 2 according to relative turning movements of the moving knife 2 and the stand-by knife 3, and a thread is cut at a cutting position at which the cutting edge 2a and the cutting edge 3a face each other as described above.

[0056] By moving the stand-by knife 3 to the most advanced position (cutting position) close to the stitch point by advance-turning of the stand-by knife base 32, the length of the extra end portion of the thread from a workpiece after cutting can be made as short as possible.

[0057] On the outer side of the stand-by knife 3, a thread guide 35 is provided alongside the stand-by knife 3. The tip end portion of the thread guide 35 guides a thread so as to prevent the thread from being sandwiched and cut between the cutting edge 3a of the stand-by knife 3 and a portion other than the cutting edge 2c of the moving knife 2.

[0058] As shown in Fig. 1, a clamp spring 36 is attached to the shuttle shaft base 11 via a clamp spring base 38. The clamp spring 36 is provided so as to come into pressure contact with the inner side surface of the moving knife 2, and a cut end portion of the thread extending from the horizontally rotating shuttle side is sandwiched and retained between the inner side surface of the moving knife 2 and the clamp spring 36.

[0059] Cam Mechanism

[0060] The cam mechanism 40 will be described based on Fig. 6 to Fig. 9.

[0061] The cam mechanism 40 is provided on and fixed to the lower shaft 1 and includes a cam member 41 (a cam driver) which has a cam groove 41a formed on the outer peripheral surface, a moving knife link shaft 42 supported rotatably along the Z-axis direction by the shuttle shaft base 11, a moving knife drive arm 43 fixed to and fitted to the lower end portion of the moving knife link shaft 42 by holding it, a cam roller 44 (a cam follower) directed upward and provided on the turning end portion of the moving knife drive arm 43, a moving knife link arm 45 provided on and fixed to an upper end portion of the moving knife link shaft 42, and a block 46 which engages with the moving knife link arm 45 and transmits a turning movement to the support plate 22 and the moving knife 2.

[0062] The cam member 41 has a cylindrical shape around the lower shaft 1, and has a cam groove 41 a formed on the outer peripheral surface. The cam groove 41 a has an inlet and an outlet on one end face side, and the cam roller 44 enters the cam groove 41a from the inlet according to turning of the moving knife drive arm 43.

[0063] The cam roller 44 is a columnar body formed along the Z-axis direction, and when not cutting a thread, the cam roller 44 stands by at a position away from one end face of the cam member 41, and enters the cam groove 41a from the inlet when the moving knife drive arm 43 is turned to the cam member 41 side by the air cylinder mechanism 50 described later.

[0064] Then, the cam roller 44 which has entered the cam groove gives the back and forth turning movement to the moving knife drive arm 43 in accordance with the displacement of the cam groove 41a, and exits from the cam groove 41. After the exit, as in the case of entering, the moving knife drive arm 43 is turned in the direction of separating from the cam member 41 by the air cylinder mechanism 50, and the cam roller 44 is returned to the original standby position.

[0065] The moving knife drive arm 43 is extended toward the outer side in the radial direction around the moving knife link shaft 42, and retains the cam roller 44 on its extending end portion. The moving knife drive arm 43 has a function to apply a thread cutting movement to the moving knife 2 by means of back and forth turning via the moving knife link shaft 42 and the moving knife link arm 45, etc., when back and forth turning is applied to the moving knife drive arm 43 via the cam roller 44 according to displacement of the cam groove 41a. At the time of turning by the cam groove 41a, the moving knife drive arm 43 turns clockwise (the direction of the black arrow) and counterclockwise (the direction of the white arrow) in Fig. 6 in this order.

[0066] The moving knife link arm 42 is directly linked to the moving knife drive arm 43 by the moving knife link shaft 42, and turns in conjunction with the moving knife drive arm 43.

[0067] The moving knife link arm 45 has a long-groove-shaped notch 45a formed along a radial direction from its turning end portion toward the moving knife link shaft 42 side. The block 46 is fitted in the notch 45a, and is slidable along the longitudinal direction of the notch 45a. Therefore, when the moving knife link arm 45 is turned by the cam member 41, the block 46 moves along an arc-shaped locus centered on the moving knife shaft 21, so that the distance between the block 46 and the moving knife link shaft 42 changes, however, this distance change is absorbed by sliding of the block 46 along the notch 45a. Therefore, when the moving knife link arm 45 turns back and forth, the support plate 22 also turns back and forth around the moving knife shaft, so that a back and forth turning movement is smoothly transmitted to the moving knife 2.

[0068] The moving knife link arm 45 and the support plate 22 turn opposite to each other, so that the support plate 22 turns counterclockwise and clockwise in Fig. 6 in this order. Specifically, due to the cam groove 41a of the cam member 41, the moving knife 2 advances (the direction of the black arrow in Fig. 6) and then retreats (the direction of the white arrow in Fig. 6).

[0069] Air Cylinder Mechanism

[0070] The air cylinder mechanism 50 will be described based on Fig. 1 and Figs. 6 to 9. The air cylinder mechanism 50 includes an air cylinder 51 as an actuator attached by directing the actuation direction toward the Y-axis direction by a bracket 52 provided on and fixed to the lower portion of the shuttle shaft base 11, a joint 53 as an actuation part attached to the tip end of a plunger of the air cylinder 51 which advances and retreats, an input arm 54 having a base end portion fixed to the lower end portion of the moving knife shaft 21 by holding it, and a pin 55 which joins the turning end portion of the input arm 54 and the joint 53.

[0071] The input arm 54 is in a state where it is axially supported on the moving knife shaft 21, and has a turning end portion joined to the joint 53 of the plunger of the air cylinder 51. Specifically, the input arm 54 is structured to apply a turning movement to the moving knife shaft 21 according to an advancing and retreating actuation output of the air cylinder 51.

[0072] While the joint 53 of the air cylinder 51 moves linearly, the turning end portion of the input arm 54 moves on an arc-shaped locus, however, the air cylinder 51 is joined to the bracket 52 by a pin, so that displacement in the X-axis direction due to the arc movement of the input arm 54 is absorbed, and the input arm 54 smoothly turns according to driving of the air cylinder 54.

[0073] A major function of the air cylinder mechanism 50 is to switch the drive source of the turning movement of the moving knife 2 to the cam mechanism 40 by advancing the moving knife 2 at the most retreated position and making the cam roller 44 of the cam mechanism 40 interlocked with the moving knife 2 enter the cam groove 41a of the cam member 41, to retreat the moving knife 2 to the most retreated position after the back and forth turning of the moving knife 2 by the cam mechanism 40 ends and the cam roller 44 is discharged from the cam groove 41a, and further, to retain the moving knife 2 at the most retreated position.

[0074] As the air cylinder 51, a double-acting cylinder having individual air chambers for applying an advancing movement and a retreating movement to the plunger, respectively, is used. Specifically, when advancing, compressed air is supplied to the advance-side air chamber and the air in the retreat-side air chamber is released to the atmosphere, and when retreating, compressed air is supplied to the retreat-side air chamber and the air in the advance-side air chamber is released to the atmosphere. That is, the thread cutting device 10 has an air circuit capable of applying the above-described control to the air cylinder 51 although this is not shown, and a solenoid valve for supplying compressed air and releasing air to the atmosphere is controlled by a control circuit of the sewing machine.

[0075] Even after the drive source of the back and forth movement of the moving knife 2 shifts to the cam mechanism 40, the joint 53 of the plunger of the air cylinder 51 is left joined to the input arm 54, so that when a turning movement is applied to the moving knife shaft 21 by the cam mechanism 40, the plunger of the air cylinder 51 also moves forward and backward via the input arm 54. Therefore, during a period in which the moving knife 2 is driven to move back and forth by the cam mechanism 40, a control is performed to open both air chambers of the air cylinder 51 to the atmosphere and make the plunger free. Accordingly, the back and forth turning movement of the moving knife 2 by the cam mechanism 40 is smoothly performed without being influenced by the air cylinder 51. Then, when the back and forth turning by the cam mechanism 40 ends and the cam roller 44 is discharged from the cam groove 41 a, a control is performed to supply compressed air to the retreat-side air chamber and maintain the atmosphere opened state in the advance-side air chamber, and the moving knife 2 is returned to the most retreated position.

[0076] The timing to open both air chambers of the air cylinder 51 to the atmosphere and the timing to restart supply of compressed air are the timing at which the cam roller 44 enters the cam groove 41 and the timing at which the cam roller 44 is discharged, so that these timings are taken by monitoring the main shaft angle or the lower shaft angle. Therefore, by using a main shaft angle detection device usually installed in a sewing machine, the air cylinder 51 is controlled at proper timings.

[0077] Interlocking Mechanism

[0078] The interlocking mechanism 60 includes an interlock pin 61 provided on and fixed to the lower surface of the support plate 22, a fan-shaped stand-by knife fixed plate 62 disposed on an upper end portion of the stand-by knife shaft 31, and a fixation screw 63 which fixes the stand-by knife fixed plate 62 to the stand-by knife base 32 as shown in Fig. 1, Fig. 4, Fig. 5, and Fig. 8.

[0079] Specifically, the stand-by knife fixed plate 62 has a through hole into which the stand-by knife shaft 31 is inserted, and is turnable around the stand-by knife shaft 31. Further, a slot 62a along an arc centered on the stand-by knife shaft 31 is pierced through the stand-by knife fixed plate 62. When the fixation screw 63 is inserted through the slot 62a and screwed into a screw hole formed in the stand-by knife base 32, the stand-by knife fixed plate 62 is fixed to the stand-by knife shaft 31 and turns integrally with the stand-by knife shaft 31. By loosening the fixation screw 63, the angle of the stand-by knife fixed plate 62 with respect to the stand-by knife shaft 31 can be adjusted in the range of the slot 62a, and by this angle adjustment, the cutting position can be adjusted.

[0080] The interlock pin 61 is at a position away from the stand-by knife fixed plate 62 when the moving knife 2 is at the most retreated position, and comes into contact with the end edge portion of the stand-by knife fixed plate 62 when the moving knife 2 starts advance-turning and reaches a predetermined angle, and after this, the interlock pin 61 presses the stand-by knife fixed plate 62 to turn the moving knife 2 and the stand-by knife 3 concurrently while keeping the relative positions of these until the moving knife 2 reaches the most advanced position. Interlock of the knives is realized by pressing the stand-by knife fixed plate 62 by the interlock pin 61, so that when the moving knife 2 starts retreating from the most advanced position, the interlocked state is released.

[0081] When cutting a thread, the most advanced position of the moving knife 2 and the most advanced position of the stand-by knife 3 (in the case of the stand-by knife 3, the most advanced position is the cutting position) have a constant angle different from each other, and the position relationship between the interlock pin 61 and the stand-by knife fixed plate 62 in the interlocking mechanism 60 is set so that the moving knife 2 and the stand-by knife 3 turn in the advancing direction in conjunction with each other while maintaining this angle difference.

[0082] Stand-By Mechanism

[0083] The stand-by mechanism 70 includes, as shown in Fig. 1, Fig. 5, and Fig. 8, a stand-by knife stopper 71 provided on the shuttle shaft base 11 so as to become adjacent to the stand-by knife fixed plate 62, and a stopper spring 72 which energizes the stand-by knife stopper 71 in a direction of latching the stand-by knife fixed plate 62.

[0084] The stand-by knife stopper 71 has a base end portion axially supported turnably with respect to the shuttle shaft base 11 by a shoulder screw 73 along the Z-axis direction, and has a turning end portion provided with a lock pawl 74 projecting toward the stand-by knife fixed plate 62.

[0085] When the stand-by knife 3 is at the most retreated position, the protrusion 24 and the stand-by knife stopper 71 are mutually disposed so that the tip end portion of the lock pawl 74 of the stand-by knife stopper 71 comes into contact with and presses the arc-shaped end edge portion of the protrusion 24 provided on the support plate 22 by energization of the stopper spring 72 (refer to Fig. 10A). The attaching angle of the stand-by knife fixed plate 62 to the stand-by knife shaft 31 is adjusted so that the terminal end of the arc-shaped end edge portion of the stand-by knife fixed plate 62 passes through the lock pawl 74 of the stand-by knife stopper 71 when the stand-by knife 3 advance-turns to the most advanced position. Accordingly, the lock pawl 74 of the stand-by knife stopper 71 is latched on the terminal end corner portion of the arc-shaped end edge portion of the stand-by knife fixed plate 62 by energization of the stopper spring 72, and retains the stand-by knife 3 to prevent the stand-by knife 3 from turning in the retreating direction from the most advanced position (refer to Fig. 11B). Specifically, the stand-by mechanism 70 including the stand-by knife fixed plate 62 functions as a latch mechanism. The stand-by knife 3 is always energized in the retreat-turning direction by the return spring 12 via the stand-by knife base 32, however, due to retaining by the stand-by mechanism 70, even if the moving knife 2 turns in the retreat-turning direction and the interlocked state by the interlocking mechanism 60 is released, the stand-by knife 3 is held at the most advanced position.

[0086] The retaining state by the stand-by mechanism 70 is released by a protrusion 24 provided on the support plate 22 described above. When the moving knife 2 turns in the retreating direction, thread cutting is performed at a position at which the cutting edge 3a of the stand-by knife 3 retained by the retaining mechanism 70 matches the cutting edge 2c of the moving knife 2 retreating (cutting position of the moving knife 2), and at least after the moving knife 2 passes through the cutting position, the protrusion 24 comes into contact with the lock pawl 74 of the stand-by knife stopper 71 and pushes-back the lock pawl 74 against the stopper spring 72. Accordingly, the retained state of the stand-by knife fixed plate 62 by the lock pawl 74 is released, and the stand-by knife 3 is energized by the return spring 12 and returned to the most retreated position.

[0087] Thread Cutting Operation by Thread Cutting Device

[0088] A thread cutting operation of the thread cutting device 10 configured as described above will be described with reference to the operation explanatory views of Figs. 10 to Figs. 12.

[0089] During sewing by the sewing machine, the moving knife 2 and the stand-by knife 3 stand by at their most retreated positions. Then, after sewing by the sewing machine, when a thread cutting signal is input, the air cylinder 51 is actuated to start advance-turning of the moving knife 2 (Fig. 10A). At this stage, the interlock pin 61 of the interlocking mechanism 60 has not reached the stand-by knife fixed plate 62 yet, and the stand-by knife 3 is still in the stand-by state.

[0090] Then, according to turning of the moving knife 2, the cam roller 44 of the cam mechanism 40 enters the inside of the cam groove 41a of the cam member 41, and a control to switch the plunger of the air cylinder 51 to free is performed. Then, when the moving knife 2 is switched to be actuated by the cam mechanism 40 and then the opening degree between the moving knife 2 and the stand-by knife 3 (the angle difference between their most advanced positions) reaches a predetermined opening angle, the interlock pin 61 comes into contact with and presses the stand-by knife fixed plate 62 (Fig. 10B), and accordingly, the stand-by knife 3 and the moving knife 2 are interlocked with each other and start advance-turning (Fig. 10C).

[0091] Then, the lock pawl 74 of the stand-by knife stopper 71 of the stand-by mechanism 70 latches the end portion of the stand-by knife fixed plate 62 (Fig. 11A), and the moving knife 2 and the stand-by knife 3 reach their most advanced positions (Fig. 11B). At this time, the tip end portion of the moving knife 2 enters a loop of a thread captured by the hook of the horizontally rotating shuttle at the final stitch.

[0092] The cam mechanism 40 switches to apply retreat-turning, and the moving knife 2 starts retreat-turning independently. Accordingly, the moving knife 2 captures the thread and pulls it to the side of the stand-by knife 3 standing by at the cutting position (most advanced position).

[0093] Then, when the moving knife 2 comes into contact with the stand-by knife 3 at the cutting position, the moving knife 2 cuts the thread in cooperation with the stand-by knife 3 (Fig. 11C).

[0094] When the moving knife 2 further continues retreating, the protrusion 24 comes into contact with the lock pawl 74 of the stand-by knife stopper 71 and pushes it back to the outer side (Fig. 12A).

[0095] As a result, the stand-by knife fixed plate 62 is released and the stand-by knife 3 is returned to the most retreated position by the return spring 12 (Fig. 12B).

[0096] Then, the cam roller 44 of the cam mechanism 40 is discharged from the cam groove 41 a, the free state of the plunger of the air cylinder 51 is released, and retreat driving is performed. Accordingly, the moving knife 2 is returned to the most retreated position, and the thread cutting operation is ended (Fig. 12C).

[0097] Advantageous Effects

[0098] The thread cutting device 10 performs switching between connection and disconnection of power between the moving knife 2 and the cam mechanism 40 by applying a forward and backward movement not to the stand-by knife 3 but to the moving knife 2 by the air cylinder 51, so that unlike the conventional technique, it becomes unnecessary to retreat the stand-by knife by the air cylinder at an exact timing with respect to the moving knife that is retreated by the cam mechanism, and therefore, interference between the cam mechanism 40 and the air cylinder 51 can be reduced by properly adjusting the retreating movement start timing of the air cylinder 51, and an excellent cutting operation without troubles can be realized.

[0099] Switching between power connection and disconnection is performed by applying a forward and backward movement not to the stand-by knife 3 but to the moving knife 2 by the air cylinder 51, so that an influence of a movement delay of the stand-by knife 3 due to the kind of the thread can be reduced, and for this reason as well, an excellent cutting operation can be realized.

[0100] Further, the stand-by mechanism 70 is configured as a latch mechanism which restricts turning of the stand-by knife 3 by using the lock pawl 74, and the protrusion 24 that retreats integrally with the moving knife 2 releases the lock pawl 74, so that different from the case where the moving knife 2 and the stand-by knife 3 are operated by individual drive sources and synchronized with each other at a predetermined timing, the release timing in the retreating movement of the moving knife 2 can always be fixed, and a still more excellent cutting operation can be realized.

[0101] Further, the support plate 22 including the protrusion 24 is formed of a separate member separable from the moving knife 2, so that without changing the timing to release the stand-by knife 3 by the protrusion 24, the position of the moving knife 2 can be adjusted.

[0102] Further, by pressing and contact between the interlock pin 61 that moves integrally with the moving knife 2 and the stand-by knife fixed plate 62 that moves integrally with the stand-by knife 3, the moving knife 2 and the stand-by knife 3 are interlocked with each other in the advancing direction, so that the configuration of the interlocking mechanism which interlocks the moving knife 2 and the stand-by knife 3 only in the advancing direction and makes them free from each other in the retreating direction can be realized by a simple structure.

[0103] While a back and forth movement is applied to the moving knife 2 by the cam mechanism 40, the air cylinder 51 is controlled so that the joint 53 of the air cylinder 51 is movable freely in accordance with an external force, and while the means for switching interlock between the moving knife 2 and the air cylinder 51 or the moving knife 2 and the cam mechanism 40 is made unnecessary, the cam mechanism 40 can apply a movement without being influenced by the air cylinder 51.

[0104] Modifications

[0105] In the thread cutting device 10 described above, the return spring 12 is used as a returning means, however, without limiting to this, an actuator may also be used.

[0106] For example, as in the example shown in Fig. 13, an air cylinder 12A may be used as the actuator as the returning means. In this case, a joint attached to the plunger of the air cylinder 12A is joined to the turning end portion of the input arm 13A which is joined to the stand-by knife shaft 31 and turns together with the stand-by knife shaft 31, and the air cylinder 12A is controlled so that it is actuated to return the stand-by knife 3 from the most advanced position to the most retreated position when the stand-by state of the stand-by mechanism 70 is released. The moving knife 2 is driven by the air cylinder 12A joined to the turning end portion of the input arm 13A that is joined to the moving knife link shaft 42 and turns together with the moving knife link shaft 42.

[0107] Even in this configuration, it is preferable that the air pressure circuit is controlled so that the plunger becomes free while the stand-by knife 3 is making an advance-turn by the interlocking mechanism 60 (not shown in Fig. 13).

[0108] In the thread cutting device 10, during the period in which the moving knife 2 is supplied with power by the cam mechanism 40, a control is performed to make free the plunger of the air cylinder 51, however, without limiting to this, for example, it is also possible that the air cylinder 51 is controlled not to release air to the atmosphere at the retreated position and the advanced position of the plunger but to keep the positions. In this case, during the period in which the cam mechanism 40 applies a turning movement to the moving knife 2, it is preferable that the joint 53 and the input arm 54 are joined by an elastic member such as a spring to prevent the air cylinder 51 from obstructing the movement. Accordingly, during the period in which power is supplied by the cam mechanism 40, the input arm 54 is allowed to separate from the joint 53 and move while expanding the spring. Alternatively, it is possible that the joint 53 and the input arm 54 are joined by a magnet, etc., and are separable during the period in which power is supplied by the cam mechanism 40. In each case, after the period of power supply by the cam mechanism 40 ends, by driving and retreating the joint 53 of the air cylinder 51 again, the moving knife 2 can be returned to the most retreated position.

[0109] In the embodiment described above, an example in which the stand-by knife 3 is provided and fixed to the turning end portion of the stand-by knife base 32 is shown, however, as in the example shown in Fig. 14, it is also possible that a slot 3b substantially along the turning radial direction of the stand-by knife 3 is formed at the base end portion of the stand-by knife 3, and the stand-by knife 3 is fastened to the turning end portion of the stand-by knife base 32 by two fixation screws 3c via the slot 3b. With this structure, the movement of the stand-by knife 3 can be adjusted along its turning radial direction, and engagement between the stand-by knife 3 and the moving knife 2 can be adjusted.

Claims

1. A thread cutting device (10) of a sewing machine, the thread cutting device (10) comprising:

a moving knife (2) configured to move back and forth between a most advanced position and a most retreated position; and

a stand-by knife (3) supported such that the moving knife (2) contacts the stand-by knife (3) in a sliding manner and such that the stand-by knife (3) turns back and forth,

wherein the thread cutting device (10) is provided on a shuttle shaft base (11) of a horizontally rotating shuttle or near the shuttle shaft base (11), and is configured to cut a thread by a cooperation of the moving knife (2) and the stand-by knife (3) when the moving knife (2) is retreated to a cutting position,

characterized in that the thread cutting device (10) further comprises:

a cam mechanism (40) comprising a cam driver (41) configured to rotate by obtaining power from a lower shaft (1), and a cam follower (44) configured to give a back and forth turning movement to the moving knife (2);

an actuator (51) configured to connect and disconnect a power transmission between the cam mechanism (40) and the moving knife (2), and to advance the moving knife (2) from the most retreated position and retreat the moving knife (2) to the most retreated position;

an interlocking mechanism (60) configured to interlock the stand-by knife (3) with the advancing movement of the moving knife (2) until the stand-by knife (3) reaches its most advanced position;

a stand-by mechanism (70) configured to hold the stand-by knife (3) to prevent the stand-by knife (3) from retreating when the moving knife (2) retreats;

a releasing means (24) for releasing the stand-by knife (3) from the stand-by mechanism (70) when the moving knife (2) has passed the cutting position; and

a returning means (12, 12A) for returning the stand-by knife (3) to its most retreated position.

2. The thread cutting device (10) according to claim 1, wherein the stand-by mechanism (70) is a latch mechanism comprising a pawl (74) configured to lock the stand-by knife (3) to prevent the stand-by knife (3) from retreating when the moving knife (2) reaches the most advanced position, and
the releasing means (24) comprises a protrusion (24) configured to retreat together with the moving knife (2) to move the pawl (74) in a releasing direction when the moving knife (2) has passed the cutting position.

3. The thread cutting device (10) according to claim 2, wherein the protrusion (24) of the releasing means (24) is a separate part from the moving knife (2) and may be detachable from the moving knife (2).

4. The thread cutting device (10) according to any one of the preceding claims, wherein the interlocking mechanism (60) is configured to interlock the stand-by knife (3) only with the advancing movement of the moving knife (2) by pushing the stand-by knife (3) or a member that turns back and forth together with the stand-by knife (3) with the moving knife (2) or a member that turns back and forth together with the moving knife (2).

5. The thread cutting device (10) according to any one of the preceding claims, wherein the actuator (51) comprises an actuation part (53) configured to move back and forth and coupled to the moving knife (2), and the actuator (51) is controlled such that the actuation part (53) is movable in accordance with an external force while the back and forth movement is applied to the moving knife (2) from the cam mechanism (40).

Drawing