Presser device for covering chain stitch sewing machine

Abstract

To provide a presser device for a covering chain stitch sewing machine which solves the problem in which, compared with conventional ones, the seam pitches apparently change due to the change of the thickness of a fabric and this damages beautiful appearance.SOLUTION: A presser device 13 includes a presser mechanism 2, and a pressing pressure conversion mechanism 4. The presser mechanism 2 includes a presser bar 21, a presser bar holder 24 for holding the presser bar 21, and an upper side spring 27. The pressing pressure conversion mechanism 4 includes a pressing pressure conversion crank 41 whose two action ends are arranged between the upper side spring 27 and the presser bar holder 24, and which oscillates. Therefore, even when the thickness of a fabric changes during sewing, the change in a frictional force generating between the upper surface of the fabric and the bottom surface of the presser can be suppressed, the amount of feeding the fabric is stabilized, and the seam pitches can be made apparently uniform, so that beautiful appearance can be maintained.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a presser foot device for an interlock stitch sewing machine. In the present invention, "front and rear" refers to the front and rear direction in the fabric feed direction, "left and right" refers to the left and right direction when the sewing machine is viewed from the front, and "up and down" refers to the up and down direction of the sewing machine. [Background technology]

[0002] A known conventional presser foot device for a sewing machine includes a needle plate that is installed on the sewing machine body and supports the fabric from below, a presser foot that presses down and supports the fabric from above, a presser bar that has the presser foot installed at its lower end and can move up and down, a presser bar holder that grips the upper end of the presser bar, a presser bar holder guide that is installed on the sewing machine body and clamps the left and right sides of the rear part of the presser bar holder to prevent the presser bar from rotating, and a compression coil spring that presses down on the presser bar holder from above to press down on the presser foot (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Publication No. 50-146759 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, when fabric sandwiched between the needle plate and presser foot is fed backward during stitch formation, the feed dog rising from below the needle plate lifts the fabric upward and moves backward while pressing it against the bottom of the presser foot. At this time, the presser foot also rises in accordance with the height to which the fabric rises above the needle plate, and the compression coil spring pressing the presser foot from above contracts, applying a greater force to the presser foot than before it rose. This generates a frictional force between the top surface of the fabric and the bottom of the presser foot, which opposes the force of the feed dog to feed the fabric.

[0005] When the thickness of the fabric is constant, the frictional force during sewing is stable with each stitch, the amount of fabric fed is stable, and the stitch pitch is consistent. However, when there is tape or overlapping fabric in a portion of the fabric, which increases the thickness, the compression coil spring contracts significantly in the thicker portion, increasing the frictional force, reducing the amount of fabric fed and causing the stitch pitch to become noticeably finer, a phenomenon known as "stitch jamming." Conversely, in areas where the thickness decreases, the amount of fabric fed increases, causing the stitch pitch to become noticeably coarser. A consistent stitch pitch is required for aesthetic purposes, and any change during sewing is considered to be aesthetically distorting.

[0006] To provide a presser foot device for an interlock stitch sewing machine which suppresses a change in frictional force occurring between the top surface of the fabric and the bottom surface of the presser foot due to a change in the thickness of the fabric during sewing and stabilizes the amount of fabric feed, thereby eliminating the problem of a visible change in stitch pitch and a loss of aesthetic appeal. [Means for solving the problem]

[0007] In order to achieve the above object, the invention described in claim 1 provides a presser foot device for an interlock stitch sewing machine comprising: a needle plate mounted on the sewing machine body and supporting the fabric from below; a presser foot supporting the fabric from above; a presser bar with the presser foot attached to its lower end and capable of moving up and down; a presser bar bushing mounted on the sewing machine body and inserted through it to support and guide the presser bar so that it can move up and down; a presser bar upper support member mounted on the sewing machine body and inserted through it to support the presser bar from above; a presser bar holder that grips the upper end of the presser bar; a presser bar holder guide mounted on the sewing machine body and clamping the sides of the presser bar holder; and an upper spring that is positioned above the presser bar holder and applies pressure, and is characterized by comprising a presser foot pressure conversion mechanism positioned between the upper spring and the presser bar holder.

[0008] In order to achieve the above object, the invention described in claim 2 is a presser foot device for a flat stitch sewing machine described in claim 1, characterized in that the presser foot pressure conversion mechanism comprises a presser foot pressure conversion crank having one support end that serves as the center of oscillation and two acting ends that are positioned between the upper spring and the presser bar clamp.

[0009] In order to achieve the above object, the invention described in claim 3 is a presser foot device for a flat stitch sewing machine described in claim 2, characterized in that the presser foot pressure conversion mechanism comprises an upper guide member arranged at the lower end of the upper spring and a lower guide member arranged at the upper end of the presser bar holder.

[0010] In order to achieve the above object, the invention described in claim 4 is a presser foot device for a flat stitch sewing machine described in claim 3, characterized in that the presser foot pressure conversion mechanism includes a presser foot pressure conversion crank having two working ends, one of which is guided in contact with the lower end of the upper guide member and the other of which is guided in contact with the upper end of the lower guide member. [Effects of the Invention]

[0011] The presser foot device of the present invention allows the stitch pitch of a sewing machine to appear consistent as follows. A presser foot pressure conversion mechanism is disposed between the upper spring and the presser bar support. The presser foot pressure conversion mechanism includes a presser foot pressure conversion crank having one support end serving as the center of oscillation and two working ends disposed between the upper spring and the presser bar support. The pressing force of the upper spring acts downward on one working end of the presser foot pressure conversion crank, which can be considered to be resolved into a component force toward the center of oscillation of the presser foot pressure conversion crank and a component force that acts as an oscillation action. These components are each smaller than the pressing force of the upper spring. The oscillation action component is transmitted to the other working end of the presser foot pressure conversion crank as torque, causing an oscillation action, and only the downward component acts on the up and down movement of the presser bar support. This downward component force is also smaller than the original oscillation action force transmitted to the other working end as torque. The former swinging force component and the latter downward force component change direction and the degree to which they become smaller as the positions of one working end and the other working end of the pressure conversion crank change due to the swinging motion.

[0012] Therefore, when the presser bar rises due to an increase in fabric thickness, compressing the upper spring and increasing the pressing force, the positions of the two working ends of the presser foot pressure conversion crank change as the presser bar rises. By selecting and configuring a positional relationship and shape that further reduces the two aforementioned component forces, the downward pressing force of the presser bar clamp can be prevented from increasing. Compared to conventional technology, this prevents the presser foot from increasing downward pressing force even when the presser foot rises and the upper spring compresses significantly in areas where the fabric thickness increases, and the friction between the top surface of the fabric and the bottom surface of the presser foot does not change significantly. Therefore, the stitch pitch does not become noticeably finer due to a decrease in fabric feed, and the stitch pitch remains consistent visually, maintaining a beautiful appearance. Similarly, in areas where the fabric thickness decreases, the stitch pitch does not become noticeably coarser due to an increase in fabric feed, maintaining a beautiful appearance. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view of a sewing machine applied to the present invention, viewed from the front left, in which the positive direction of the X axis indicates the right direction, the positive direction of the Y axis indicates the rearward direction, and the positive direction of the Z axis indicates the upward direction. [Figure 2] 1 is a perspective view of a presser foot device of a sewing machine to which the present invention is applied, viewed from the left front. [Figure 3] 1 is a left side view of a presser foot device of a sewing machine to which the present invention is applied; DETAILED DESCRIPTION OF THE INVENTION

[0014] An example of an embodiment of the present invention will be described below with reference to Figs. 1 to 3. Fig. 1 is a perspective view from the left front of a sewing machine to which the present invention is applied. Sewing machine 1 is equipped with presser foot 20 and needle plate 11 mounted on sewing machine body 10 above and below a sewing area, which is a region where sewing is performed by cooperation of needle 12 and looper (not shown). When sewing fabric, presser foot 20 is first raised to a height greater than the thickness of the fabric to place the fabric between presser foot 20 and needle plate 11, and after the fabric has been placed, it is lowered to press down on the fabric. Presser foot device 13 is equipped with presser foot mechanism 2 and presser foot lifting mechanism 3. In this embodiment, presser foot device 13 is equipped with presser foot pressure conversion mechanism 4.

[0015] Fig. 2 is a perspective view of a sewing machine presser foot device applied to the present invention, seen from the front left. Fig. 2(a) shows the entire presser foot device of the sewing machine, and Fig. 2(b) shows an excerpt. The presser mechanism 2 comprises a presser bar 21, which is axially shaped with an upper portion bored to a certain depth and hollow, a stepped shaft-like lower portion, and a presser foot 20 fixed to the lower end by a screw; a presser bar bushing 22, which is installed in the sewing machine body 10 and through which the presser bar 21 is inserted to support and guide the presser bar 21 so that it can move up and down; a presser bar upper support member 23, which has a cylindrical body portion and a long shaft portion in the center, a male screw portion on the outer periphery of the body portion, and is screw-fastened to the sewing machine body 10 so that its vertical position can be adjusted; and a presser bar support member 23, which is inserted around the outer periphery of the upper end of the presser bar 21 and is screw-fastened to the sewing machine body 10 so that the lower part of the long shaft portion is inserted from the top of the presser bar 21 into the hollow portion. The sewing machine includes a presser bar holder 24 that is gripped by a screw and has a guide portion with an extended rear portion and guide surfaces on its left and right sides, a presser bar holder guide 25 that is installed in the sewing machine body 10 and supports and guides the left and right sides of the guide portion of the presser bar holder 24, a lower spring 26 that is a compression coil spring that is disposed in the hollow portion of the presser bar 21 and has its lower end in contact with the inside of the presser bar 21 and its upper end in contact with the lower end of the long shaft of the presser bar upper support member 23 to press the presser bar 21 downward, and an upper spring 27 that is a compression coil spring that has its upper end in contact with the body of the presser bar upper support member 23 and is inserted into the long shaft. In the prior art described above, the lower end of the upper spring 27 contacts and presses the upper surface of the presser bar holder 24, thereby pressing the presser bar 21 and the presser foot 20. The lower spring 26 presses the presser bar 21 and presser foot 20 in cooperation with the upper spring 27, and the spring forces act in parallel. The lower spring 26 is installed to mitigate the effects of surging at normal rotation speeds, and can be omitted if not necessary.

[0016] The presser foot lifting mechanism 3 is configured to include: a plate-shaped presser bar clamping link 32 that is connected to the presser bar clamp 24 at the bottom end of a long hole that extends vertically at the bottom; a presser bar lifting crank 31 that is connected to the presser bar clamping link 32 and swings upward, thereby moving the presser bar clamping link 32, the presser bar clamp 24, the presser bar 21, and the presser foot 20 upward; a shaft clamp (not shown) that is located at the center of the swing of the presser bar lifting crank 31 and is gripped by a screw near the right end of the shaft that extends to the right (in the positive direction of the X-axis); a presser lifting plate (not shown) that is rotatable and inserted into the shaft of the presser bar lifting crank 31, and has a portion that comes into contact with the shaft clamp and swings together with it; a presser lifting plate link (not shown) that is connected to the presser lifting plate; and a presser lifting lever 30 that is connected to the presser lifting plate link and swings to swing the presser lifting plate. As a result, presser foot lifter lever 30 swings downward, causing the presser foot lifter plate to swing downward and the shaft clamp with which it is in contact to swing, causing presser bar lifting crank 31 to swing upward, causing presser bar connecting link 32 to move upward, which in turn causes presser bar connecting link 24 to move upward and raise presser foot 20. When presser foot lifter lever 30 is not operated, presser foot 20 is pressed downward as described above, and when there is no fabric, it comes to rest in contact with the top surface of the needle plate or the top surface of the feed dog (not shown). When presser foot 20 is directly lifted to raise it from the top surface of the needle plate, presser bar connecting link 24 rises and separates from the bottom end of the elongated hole at the connection point with presser bar connecting link 32, so presser bar connecting link 32 does not move upward and presser bar lifting crank 31 does not swing.

[0017] The presser foot pressure conversion mechanism 4 is disposed between the upper spring 27 and the presser bar holder 24. As a result, the upper spring 27 presses the presser bar holder 24 via the presser foot pressure conversion mechanism 4. In this embodiment, the presser foot pressure conversion mechanism 4 includes a base 40 that is fixed to the presser bar holder guide 25 or the sewing machine body 10, and a presser foot pressure conversion crank 41 that has a shaft (not shown) at one support end that serves as the center of oscillation, is inserted into a hole (not shown) in the base 40 so that it can oscillate, and has two working ends that serve as the force point and action point of the lever with the shaft as the fulcrum. The two working ends are disposed between the upper spring 27 and the presser bar holder 24. When the pressing force of the upper spring 27 acts downward on one working end of the presser pressure conversion crank 41, it is considered to be resolved into a component force toward the swing center of the presser pressure conversion crank 41 and a component force for swinging action, and this swinging component force is transmitted as torque to the other working end of the presser pressure conversion crank 41 to become a swinging force, and is further resolved so that only the downward component force acts on the up and down movement of the presser bar holder 24. In this embodiment, the presser pressure conversion crank 41 is shaped so that the lines connecting the fulcrum, force point, and point of action form an acute triangle, making it smaller in volume and lighter in weight than shapes such as an obtuse triangle. Furthermore, the pressure pressure conversion crank 41 is bifurcated with a recess that can be seen from a direction perpendicular to the shaft, and the long shaft of the presser bar upper support member 23 is located between the forks. Two upper pins 411 are installed on both sides of the upper left and right walls of the bifurcated wings as one working end (hereinafter referred to as one end), and two lower pins 412 are installed on both sides of the lower left and right walls of the bifurcated wings as the other working end (hereinafter referred to as the other end). However, the upper and lower surfaces of the pressure pressure conversion crank 41 may be one end and the other end, without using the upper pins 411 and the lower pins 412. Furthermore, the left and right walls of the bifurcated wings of the pressure pressure conversion crank 41 may not be bifurcated, but may be the walls of one wing.

[0018] In this embodiment, the presser foot pressure conversion mechanism 4 includes the aforementioned presser foot pressure conversion crank 41, a plate-shaped upper guide member 42 that is inserted through the long shaft of the presser bar upper support member 23 and has its upper end in contact with the lower end of the upper spring 27 and its lower end in contact with one end of the presser foot pressure conversion crank 41, and a plate-shaped lower guide member 43 that is inserted through the long shaft of the presser bar upper support member 23 and has its upper end in contact with another end of the presser foot pressure conversion crank 41 and its lower end in contact with the upper end of the presser bar holder 24. The lower end of the lower guide member 43 may also be in contact with the upper end of the presser bar 21. The upper guide member 42 and the lower guide member 43 are easier to manufacture than the presser foot pressure conversion crank 41, the upper spring 27, and the presser bar holder 24, making them easier to repair or replace when they wear out or are damaged over long periods of use. The upper guide member 42 has a square outer periphery and fits between the two prongs of the pressure conversion crank 41, restricting its rotation to the left and right. This also restricts the rotation of the upper spring 27 that presses it around its inner axis, thereby reducing wear on the spring.

[0019] In this embodiment, two upper pins 411 contact the lower end of the upper guide member 42 as one end of the presser pressure conversion crank 41, and two lower pins 412 contact the upper end of the lower guide member 43 as the other end. The upper guide member 42 receives the force of the upper spring 27 at its upper end and transmits the force to one end of the presser pressure conversion crank 41 at its lower end. The lower guide member 43 receives the force from the other end of the presser pressure conversion crank 41 at its upper end and transmits the force to the upper end of the presser bar support 24 at its lower end. The lower end of the upper guide member 42 and the upper end of the lower guide member 43 form guide surfaces that slide and guide the presser pressure conversion crank 41 as it swings and the contact portion moves back and forth. This reduces the frictional force generated by contact with the presser pressure conversion crank 41. Alternatively, the upper pins 411 and lower pins 412 may be rotating needle rollers or the like to provide rolling guidance.

[0020] Figure 3 is a left side view of the presser foot device of a sewing machine to which the present invention is applied. Figure 3(a) shows the state in which presser bar 21 is in the lowest position, Figure 3(c) shows the state in which presser bar 21 is in the highest position, and Figure 3(b) shows the positions in between. When presser bar 21 is in the lowest position, the bottom surface of presser foot 20 is in contact with the top surface of needle plate 11. When presser bar 21 is in the highest position, presser foot 20 has risen to a set height, for example by contacting a member (not shown) that restricts its rise.

[0021] In the following, in this embodiment, when the upper spring 27 is significantly compressed and the pressing force increases, the positions of the two working ends of the presser foot pressure conversion crank 41 change, thereby preventing the presser bar clamp 24 from increasing in downward pressing force. The numerical values ​​and units of the force magnitude, angle, magnification, length, etc. described below are those used in this embodiment, and these numerical values ​​and units will vary depending on the specifications of the sewing machine. Furthermore, the numerical values ​​are not precise, and because each numerical value is expressed with significant digits, there will be errors in the numerical values ​​after addition, subtraction, multiplication, and division. However, they are provided as an example for reference in understanding the figures.

[0022] In FIG. 3(a), upper spring 27, which is inserted through the shaft of presser bar upper support member 23, is compressed more than in its natural state, and presses downward on upper guide member 42, whose upper end is in contact with the lower end of upper spring 27. As a result, a downward force Fa1 (hereinafter, only Fa1) acts on upper pin 411, whose upper end is in contact with the lower end of upper guide member 42. Fa1 is generated in the same way even when upper guide member 42 is not used. Upper pin 411 is installed at one end of presser pressure conversion crank 41, and the oscillation center of presser pressure conversion crank 41 is located to the lower left of upper pin 411 as viewed in the figure. Fa1 can be considered to be decomposed into a force (not shown) directed toward the oscillation center of presser pressure conversion crank 41 and a force Fa2 (hereinafter, only Fa2) perpendicular to the force Fa1, which acts to oscillate upper pin 411. The direction of Fa2 is different from that of Fa1, and the magnitude of the force of Fa2 is smaller than that of Fa1. In Figure 3(a), there is an angle difference of about 37 degrees between Fa1 and Fa2, and Fa2 is about 0.80 times that of Fa1.

[0023] Fa2 is transmitted as torque to the lower pin 412 at the other end of the pressure conversion crank 41, and transmitted as a force Fa3 (hereinafter, only Fa3) in a direction that causes the lower pin 412 to swing. The upper pin 411 and the lower pin 412 of the pressure conversion crank 41 are arranged so that the lines connecting the fulcrum, force point, and point of action form an acute triangle. In FIG. 3A, the angle difference between the directions of Fa2 and Fa3 is approximately 32 degrees. Furthermore, when the distance between the oscillation center of the upper pin 411 and the pressure conversion crank 41 and the distance between the oscillation center of the lower pin 412 and the pressure conversion crank 41 are equal, the magnitudes of the forces Fa2 and Fa3 are equal. When these distances are different, the magnitudes of the forces Fa2 and Fa3 are different. In this embodiment, the latter is true, and the magnitude of the force Fa3 is approximately 1.15 times that of Fa2 and approximately 0.92 times that of Fa1. Fa3 can be considered to be decomposed into a downward force Fa4 (hereinafter, only Fa4 will be referred to) acting on the lower pin 412 so as to affect the up and down movement of the presser bar clamp 24 via the lower guide member 43, and a force (not shown) that is perpendicular to Fa4 and does not contribute to the up and down movement. The direction of Fa4 is different from that of Fa3, and the magnitude of the force of Fa4 is smaller than that of Fa3. In Figure 3(a), there is an angular difference of about 4.4 degrees, and because the angular difference is small, the difference in the magnitude of the forces is small, so Fa4 is about 1.00 times the magnitude of Fa3 and about 0.92 times the magnitude of Fa1.

[0024] In the prior art, the downward pressing force of the underside of presser foot 20 is the sum of Fa1, which is equal to the downward force of upper spring 27 in FIG. 3(a), and Fa5, the downward pressing force of lower spring 26 connected in parallel (hereinafter, only Fa5 will be referred to), i.e., Fa1 + Fa5. In this embodiment, due to differences in the compression state and spring constants of upper spring 27 and lower spring 26, Fa5 is set to approximately 0.25 times Fa1, and Fa1 + Fa5 is set to approximately 1.25 times Fa1. In this embodiment, the downward pressing force of the underside of presser foot 20 is Fa4 + Fa5, which is approximately 1.17 times Fa1. Thus, when presser bar 21 is at its lowest position in FIG. 3(a), the difference between Fa1 + Fa5 and Fa4 + Fa5 is less than 10%.

[0025] In this embodiment, the spring constants of the upper spring 27 and the lower spring 26 are set to approximately 0.4 kgf / mm and approximately 0.3 kgf / mm, respectively. In FIG. 3(a), the vertical position of the presser bar upper support member 23 fixed to the sewing machine body 10 is adjusted to compress the upper spring 27 and the lower spring 26 approximately 8.1 mm and approximately 2.7 mm from their natural positions, respectively, resulting in the magnitude of the forces Fa1 being approximately 3.2 kgf, Fa5 being approximately 0.8 kgf, and Fa1+Fa5 being approximately 4.1 kgf. In this case, Fa4+Fa5 is approximately 3.8 kgf. Thus, in FIG. 3(a), where the presser bar 21 is at its lowest position, the difference between Fa4+Fa5 and Fa1+Fa5 is less than 10%.

[0026] FIG. 3(b) shows the state in which the presser foot 20 has risen to a certain height from FIG. 3(a). In this embodiment, the presser foot 20 and presser bar 21 have risen approximately 3.0 mm. The compression distance of the upper spring 27 does not match the lift distance of the presser foot 20 because it passes through the presser foot pressure conversion crank 41, decreasing to approximately 2.5 mm. The compression distance of the lower spring 26 is approximately 3.0 mm, the same as the lift distance of the presser foot 20. In FIG. 3(b), the presser bar 21 rises, compressing the lower spring 26, raising the lower guide member 43, causing the presser foot pressure conversion crank 41 to swing counterclockwise as viewed in the figure, raising the upper guide member 42, and compressing the upper spring 27. At this time, the downward force Fb1 (hereinafter referred to as Fb1 only) acting on the upper pin 411 is greater than Fa1. Since the spring constant of the upper spring 27 is about 0.4 kgf / mm and the compression distance is about 2.5 mm, Fb1 is about 1.0 kgf larger than Fa1, and is about 4.2 kgf.

[0027] As with Fa2, the force Fb2 (hereinafter referred to only as Fb2) in the direction that causes the upper pin 411 to swing is directed in a different direction than Fb1, and the magnitude of the force Fb2 is smaller than Fb1. In FIG. 3(b), the swinging of the pressure-changing crank 41 has progressed, and the degree of decrease in the force Fb2 is greater than that in Fa2. There is an angular difference of approximately 50 degrees between Fb1 and Fb2, and Fb2 is approximately 0.64 times Fb1. The force Fb3 (hereinafter referred to only as Fb3) in the direction that causes the lower pin 412 to swing is transmitted in the same manner as Fa3, and Fb3 is approximately 1.15 times Fb2 and approximately 0.73 times Fb1. The downward force Fb4 (hereinafter, referred to only as Fb4) acting on the lower pin 412 differs in direction from Fb3, as in the case of Fa4, and the magnitude of the force Fb4 is smaller than that of Fb3. As in the case of Fb2, the degree to which the force Fb4 decreases is greater than that of Fa4. In FIG. 3(b), there is an angular difference of approximately 18 degrees, and the magnitude of the force Fb4 is approximately 0.95 times that of Fb3 and approximately 0.70 times that of Fb1. The downward force Fb5 (hereinafter, referred to only as Fb5) due to the pressure of the lower spring 26 is determined in the same manner as in the case of Fa5, and is approximately 0.37 times that of Fb1. As a result, Fb1 + Fb5 is approximately 1.37 times that of Fb1, and Fb4 + Fb5 is approximately 1.07 times that of Fb1.

[0028] In the prior art, when the presser foot 20 is raised by approximately 3.0 mm, the downward pressing force of the underside of the presser foot 20 is greater than Fb1+Fb5. This is because the compression distance of the upper spring 27 is reduced to approximately 2.5 mm at Fb1, while the presser foot 20 is raised by approximately 3.0 mm. The difference in distance of approximately 0.5 mm and the spring constant of the upper spring 27 of approximately 0.4 kgf / mm result in a downward pressing force of approximately 0.2 kgf greater than Fb1+Fb5. The magnitudes of the forces Fb1 and Fb5 are approximately 4.2 kgf and 1.5 kgf, respectively, and Fb1+Fb5 is approximately 5.7 kgf. Therefore, in the prior art, the downward pressing force of the underside of the presser foot 20 is approximately 5.9 kgf. In this embodiment, the magnitudes of the forces Fb4 and Fb4+Fb5 are approximately 2.9 kgf and 4.4 kgf, respectively. In this way, the downward pressing force of the lower surface of the presser foot 20 is approximately 5.9 kgf when the presser foot 20 is raised by approximately 3.0 mm, compared to approximately 4.1 kgf (Fa1+Fa5) before the presser foot 20 is raised, which is an increase of more than 40% compared to before the presser foot 20 was raised. In this embodiment, the downward pressing force is approximately 4.4 kgf, which is an increase of only about 15% compared to approximately 3.8 kgf (Fa4+Fa5) before the presser foot 20 was raised.

[0029] FIG. 3(c) shows the state in which the presser foot 20 is in its uppermost position, as seen from FIG. 3(a). In this embodiment, the presser foot 20 and presser bar 21 are raised approximately 6.0 mm. The compression distance of the upper spring 27 does not match the lift distance of the presser foot 20 because it passes through the presser foot pressure conversion crank 41, resulting in a reduction to approximately 4.6 mm. The compression distance of the lower spring 26 is approximately 6.0 mm, the same as the lift distance of the presser foot 20. In FIG. 3(c), the presser bar 21 is raised, the lower spring 26 is compressed, the lower guide member 43 is raised, the presser foot pressure conversion crank 41 swings counterclockwise as viewed in the figure, the upper guide member 42 is raised, and the upper spring 27 is compressed. At this time, the downward force Fc1 (hereinafter referred to as Fc1) acting on the upper pin 411 is greater than the forces Fa1 and Fb1. Since the spring constant of the upper spring 27 is approximately 0.4 kgf / mm and the compression distance is approximately 4.6 mm, the magnitude of Fc1 is approximately 1.8 kgf larger than Fa1, and is approximately 5.1 kgf.

[0030] As with Fa2 and Fb2, the force Fc2 (hereinafter referred to only as Fc2) in the direction that causes the upper pin 411 to swing differs from that of Fc1, and the magnitude of the force Fc2 is smaller than that of Fc1. In FIG. 3(c), the swinging of the pressure-changing crank 41 has progressed, and the degree of decrease in force is greater than that of Fa2 and Fb2. There is an angular difference of approximately 65 degrees between Fc1 and Fc2, and Fc2 is approximately 0.42 times Fc1. The force Fc3 (hereinafter referred to only as Fc3) in the direction that causes the lower pin 412 to swing is transmitted in the same manner as Fa3 and Fb3, and Fc3 is approximately 1.15 times Fc2 and approximately 0.48 times Fc1. The downward force Fc4 (hereinafter, referred to as Fc4 only) acting on the lower pin 412 differs in direction from Fc3, as in the cases of Fa4 and Fb4, and the magnitude of the force Fc4 is smaller than Fc3. As in the case of Fc2, the degree to which the force Fc4 decreases is greater than that in the cases of Fa4 and Fb4. In FIG. 3(c), there is an angular difference of approximately 33 degrees, and Fc4 is approximately 0.84 times Fc3 and approximately 0.41 times Fc1. The downward force Fc5 (hereinafter, referred to as Fc5 only) due to the pressure of the lower spring 26 is determined in the same way as in the cases of Fa5 and Fb5, and is approximately 0.44 times Fc1. As a result, Fc1 + Fc5 is approximately 1.44 times Fc1, and Fc4 + Fc5 is approximately 0.84 times Fc1.

[0031] In the prior art, when the presser foot 20 is raised by approximately 6.0 mm, the downward pressing force of the underside of the presser foot 20 is greater than Fc1+Fc5. This is because the compression distance of the upper spring 27 is reduced to approximately 4.6 mm at Fc1, while the presser foot 20 is raised by approximately 6.0 mm. The difference in distance, approximately 1.4 mm, and the spring constant of the upper spring 27, approximately 0.4 kgf / mm, result in a downward pressing force of approximately 0.6 kgf greater than Fc1+Fc5. The magnitudes of the forces are approximately 5.1 kgf and 2.2 kgf for Fc1 and Fc5, respectively, and Fc1+Fc5 is approximately 7.4 kgf. Therefore, in the prior art, the downward pressing force of the underside of the presser foot 20 is approximately 8.0 kgf. In this embodiment, the magnitudes of the forces are approximately 2.1 kgf for Fc4 and approximately 4.3 kgf for Fc4+Fc5. In this way, the downward pressing force of the lower surface of the presser foot 20 is approximately 8.0 kgf when the presser foot 20 is raised by approximately 6.0 mm, compared to approximately 4.1 kgf (Fa1+Fa5) before the presser foot 20 is raised, which is more than 90% of the force before the presser foot 20 is raised. In this embodiment, the force is approximately 4.3 kgf, which is an increase of approximately 15% compared to approximately 3.8 kgf (Fa4+Fa5) before the presser foot 20 is raised.

[0032] To summarize the above explanation, when the presser foot 20 is raised to 0.0 mm, 3.0 mm, and 6.0 mm, the downward pressing force of the lower surface of the presser foot 20 changes from approximately 4.1 kgf, to approximately 5.9 kgf, and to approximately 8.0 kgf in the conventional technology. In this embodiment, the downward pressing force changes from approximately 3.8 kgf, to approximately 4.4 kgf, and to approximately 4.3 kgf. In this way, the force is prevented from increasing, and therefore, compared to the conventional technology, the frictional force generated between the top surface of the fabric and the bottom surface of the presser foot does not change significantly and can be stabilized.

[0033] According to the presser foot device of the interlock stitch sewing machine described above, the presser foot device is equipped with a presser foot pressure conversion mechanism that is located between the upper spring and the presser bar clamp, and this makes it possible to suppress changes in the frictional force that occurs between the top surface of the fabric and the bottom surface of the presser foot even if the thickness of the fabric changes during sewing.As a result, the amount of fabric feed is more stable than before, and the stitch pitch appears consistent, maintaining an aesthetically pleasing appearance.

[0034] The present invention is not limited to the above-described embodiment, and those skilled in the art can make various modifications to the above-described embodiment without departing from the spirit of the present invention, and the present invention also encompasses such modifications. Furthermore, although this embodiment uses a flat stitch sewing machine, the present invention is not limited to this, and can also be implemented with, for example, a single-needle or multi-needle double chain stitch sewing machine equipped with a presser foot similar to that of a flat stitch sewing machine. [Explanation of symbols]

[0035] 1 sewing machine 2 Presser foot mechanism 3 Presser foot lifting mechanism 4 Presser foot pressure conversion mechanism 10 Sewing machine body 11 Throat plate 12 needles 13 Presser foot device 20 presser foot 21 Presser bar 22 Presser bar bush 23 Presser bar upper support member 24 Presser bar clamp 25 Presser bar guide 26 Lower spring 27 Upper spring 30 Presser foot lifter lever 31 Presser bar lifting crank 32 Presser bar holding link 40 Foundation 41 Presser foot pressure conversion crank 42 Upper guide member 43 Lower guide member 411 Upper pin 412 Lower pin Fa1: Downward force acting on the upper pin 411 Fa2: Force in the direction of swinging the upper pin 411 Fa3: Force in the direction of swinging the lower pin 412 Fa4: Downward force acting on the lower pin 412 Fa5 Downward force due to pressure from the lower spring 26 Fb1: Downward force acting on the upper pin 411 Fb2 Force in the direction of swinging the upper pin 411 Fb3 Force in the direction of swinging the lower pin 412 Fb4 Downward force acting on lower pin 412 Fb5 Downward force due to pressure from the lower spring 26 Fc1: Downward force acting on the upper pin 411 Fc2 Force in the direction of swinging the upper pin 411 Fc3 Force in the direction of swinging the lower pin 412 Fc4 Downward force acting on the lower pin 412 Fc5 Downward force due to pressure from the lower spring 26

Claims

1. a needle plate attached to the sewing machine body and supporting the fabric from below; a presser foot attached to the sewing machine body and supporting the fabric from above; a presser bar with the presser foot attached to its lower end and capable of moving up and down; a presser bar bushing attached to the sewing machine body and supporting and guiding the presser bar so that it can move up and down; a presser bar upper support member attached to the sewing machine body and supporting the presser bar from above; a presser bar holder that grips the upper end of the presser bar; a presser bar holder guide attached to the sewing machine body and holding the sides of the presser bar holder; and an upper spring that is positioned above the presser bar holder and applies pressure;

2. 2. The presser foot device of the interlock stitch sewing machine according to claim 1, wherein the presser foot pressure conversion mechanism comprises a presser foot pressure conversion crank having one support end serving as the center of oscillation and two acting ends disposed between the upper spring and the presser bar clamp.

3. 3. The presser foot device of the interlock stitch sewing machine according to claim 2, wherein the presser foot pressure conversion mechanism comprises an upper guide member disposed at the lower end of the upper spring and a lower guide member disposed at the upper end of the presser bar support.

4. 4. The presser foot device of the interlock stitch sewing machine according to claim 3, wherein the presser foot pressure conversion mechanism comprises a presser foot pressure conversion crank having two operating ends, one operating end of which is guided in contact with the lower end of the upper guide member and the other operating end of which is guided in contact with the upper end of the lower guide member.

Images