JPS6031516B2 - Presser foot device in sewing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a sewing machine which has an extremely simple structure and which is independent of changes in the thickness of the fabric to be processed or the shape of the presser foot.
This invention relates to a cloth presser device that presses a workpiece cloth against a feed dog or the like with a constant force at all times.

When sewing work is performed using a sewing machine, for example, if the fabric to be processed is a thick material such as jeans, the stepped portions such as hems where the fabric is layered in multiple layers will be considerably thick. If such a step exists, the step 1 comes into contact with the lower surface of the presser foot 2 to rotate the presser foot 2 around the pin 3 and raise the presser foot 4, as shown in FIG. In this case, a vague gap is formed between the lower surface of the presser foot 2 and the upper surface of the feed dog 5, and the presser foot pressure increases rapidly, making it difficult for the feed dog 5 to transfer the work cloth 6. This may cause the seams to become clogged or create lumps in the seams, which may interfere with sewing. A similar problem occurs when sewing a thick workpiece fabric starting from the edge of the fabric. In order to solve the above-mentioned problems, for example, Japanese Patent Application Laid-Open No. 54-133943 discloses a step sewing device in which the presser foot can be forcibly rotated until it becomes horizontal when the stepped portion of the fabric is reached. ing. surely,
If the presser foot is horizontal, it will be easier for the fabric to pass through, but this will complicate the structure of the device, and it is inevitable that the presser foot pressure will increase and deviate from the optimum value. On the other hand, the above-mentioned drawbacks can be solved by an automatic presser foot pressure adjustment device disclosed in Hakama Kaisho 54-150244, for example.

In this device, the set load of the presser spring, which is manually set prior to sewing, is corrected according to the fabric thickness of the sewing part.
This is because a substantially constant presser foot pressure is always applied regardless of changes in fabric thickness during sewing work. However, this requires an electric servo device or the like, making the structure complex and the manufacturing cost high. The present invention has been made against this background, and aims to solve the drawbacks of the above-mentioned prior art by simple measures.

More specifically, it has a simple structure, does not require any adjustment operations, and can be processed with a substantially constant pressing force regardless of the vertical movement of the presser bar as the thickness of the fabric changes. It is an object of the present invention to provide a cloth presser device capable of pressing cloth. The gist of this is that the spring means for biasing the presser bar downward includes a tightly wound coil portion and a pair of arm portions extending outward from both ends of the coil portion. The free ends of the parts are rotatably connected to the presser bar and the sewing machine frame, respectively, and are bent coil springs having an arcuate shape as a whole. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in more detail based on the drawings.

In FIGS. 2 and 3, 11 is a hollow arm that extends laterally above the bed 12. In FIG.

The upper part of the hollow arm 11 is covered by a top cover 13, and a face plate 16 is pivoted to the mounting plate 14 of the head so that it can be opened and closed rearward. The two presser rods extend vertically through the head of the hollow arm 11, and the intermediate and upper end portions thereof can slide into through holes 21 and 23 formed in the hollow arm 11 and its extension 18. A presser foot holder 26 is removably attached to the lower end with a tightening screw 22.

A presser foot 27 is attached to the presser foot holder 26 via a pin 28, and the presser foot 27 can rotate around the pin 28 within a certain angle range with respect to the presser foot holder 26. A bending coil spring 40, which is a constant load spring, is installed between the extending portion 18 and the presser bar 20.

This bent coil spring 40 consists of a coiled main body portion 41 and arm portions 42 at both ends. The tip of the arm part 42 is curved into an annular shape to form a stop part 43, and the extension part 18 and the presser foot 2 are rotatably connected. That is, the flat hanging plate 46 attached to the extension part 18 and the hanging plate 48 with an L-shaped cross section attached to the block 47 fixed to the presser bar 20 are arranged so that their vertical positions match. Pins 51 and 52 are erected, and each locking portion competes with each pin. When the bent coil spring 4 is in its natural state, the main body 41 is in close contact with each other and forms a straight line;
The arm part 42 forms a predetermined angle with respect to the main body part 41, but as is clear from FIG. ing. A presser bar holder 31 is fixed to a position below the block 47 of the presser foot holder 20, and a cam surface of a presser foot lifting lever 32 pivotally connected to the hollow arm 11 can be engaged with the extending portion 33 of the presser bar holder 31. The presser bar 20 can be raised and lowered by rotating the elongated bar 32. Said bed 1
A throat plate 56 is attached to a position facing the presser foot 27 on the presser foot 2.

A feed dog 57 is disposed below the throat plate 56 so as to protrude and retract from the upper surface of the throat plate to perform a feed motion. The upper end of a needle support frame 62 is pivotally attached to a pivot 61 fixed to the extension part 18, and the lower end thereof is guided by a guide slot 63 formed in the hollow arm 11 and swings from side to side. I'm starting to get it.

A needle bar 66 is attached to the needle support frame 61 so as to be movable up and down, and a needle 67 is fixed to the lower end of the needle bar 66. When performing sewing work with the sewing machine configured as described above, if there is a step in the fabric to be processed, the presser foot 27 rotates around the pin 28 and tilts, while the presser foot 20 is moved upward as described above. (See Figure Y).

If the presser bar 20 rises, the bending coil spring 40 will be further bent. However, at this time, the magnitude of the biasing force applied to the presser bar 20, that is, the cloth presser pressure at which the presser foot 27 presses the work cloth (not shown in FIGS. 2 and 3) toward the feed dog 57, does not increase. This is because the bent coil spring 40 is used as the spring that urges the presser bar 20 downward. That is, according to an experiment conducted by the present applicant using the bending coil spring 40, as shown in FIG. It has been confirmed that if the angle is within the range of about 8 to 16 ribs, the variation in the load (biasing force) applied to the lower locking portion 43 is no more than 50 ta.

This amount of variation is insignificant compared to the set load (approximately 1.55k9) when the deflection is 8 Yanagi. Based on this experimental result, the bending coil spring 40 in this embodiment is suitable for use when the presser foot 20 is at the lowest layer (the presser foot 25 is at the throat plate 5).
6), the deflection is approximately 8 Yanagi. Furthermore, when the presser foot lifting lever 32 is rotated to raise the presser foot 20 to the uppermost layer for attachment and detachment of the work cloth, the amount of rise is approximately 7 degrees. In other words, this sewing machine can only sew fabrics with a thickness of less than 7 layers, and the presser foot pressure is approximately constant within this range, but when the fabric thickness exceeds 7 layers, it is normal to sew. This is almost impossible at work. Therefore, even if the presser foot 27 is initially inclined due to the stepped portion of the workpiece cloth, the magnitude of the biasing force applied to the presser foot 27 remains approximately the same as before, and thereafter, as shown in FIG. The situation is the same even in a state where the cloth 27 completely rides on the stepped portion 71 of the work cloth 70.

Approximately the same amount of presser foot pressure is applied when sewing the normal portion of the work cloth 70 (portion other than the stepped portion 71) and when sewing the stepped portion 71. Therefore, when sewing the stepped portion 71, there is no possibility that the feed by the feed dog 57 will be obstructed and the stitches will become clogged or knotted. For good sewing work, it is desirable to always apply a substantially constant presser foot pressure regardless of changes in the thickness of the work cloth, and the presser foot pressure automatic adjustment device disclosed in the above-mentioned Japanese Patent Application Laid-open No. 150244/1983 is desirable. The above can also be achieved by However, since a normal compression coil spring is used as a spring for applying presser foot pressure, the structure of the entire device becomes complicated and expensive. In order to achieve the above using a normal compression coil spring, an adjustment means is required to change the overall length according to the fabric thickness, which complicates the structure of the device. If this were to be done, an electromagnetic servo device or the like would be required, making the device expensive.
On the other hand, in the above embodiment, the same purpose is the bending coil spring 40 and the false stop plates 46 and 48 which are its attachment parts.
The structure is extremely simple and inexpensive.

This is made possible by employing the bent coil spring 40 as a spring that biases the presser foot pressure. In addition, by constantly applying a substantially constant pressure force regardless of the vertical movement of the presser foot 20, it becomes extremely easy to perform intermittent step stitch sewing and to start sewing from the edge of thick work cloth. When exchanging a presser foot for zigzag sewing and a presser foot for buttonhole stitching, use a presser foot that has a height from the bottom surface of the presser foot to the mounting part (corresponding to the position of the pin 28) that is different from that of a normal presser foot. Even when the presser foot is installed, there is no change in presser foot pressure, and a constant and good feed is always ensured.

As detailed above, in the presser foot device for the sewing machine according to the present invention, the bent coil spring 40, which is a constant force spring, is used as the spring that biases the presser bar downward.
Even if the thickness of the fabric to be processed changes and the presser foot moves up and down, the pressure applied to the fabric from the presser foot does not change, and sewing starts from the edge of the fabric when sewing steps or thick fabrics. Since the feed dogs are used to feed the sewing machine reliably, the stitches do not become jammed or knotted, and the sewing operation continues to work smoothly.

[Brief explanation of the drawing]

FIG. 1 is a front view (main part only) showing a state in which a conventional presser foot device is used to sew a stepped portion of a work cloth. Fig. 2 is a front view showing an embodiment of the present invention (however, the face plate has been removed), Fig. 3 is a view taken along the mm direction in Fig. 2, and Fig. 4 is a front view showing an embodiment of the present invention. FIG. 5 is a graph showing the characteristics of the bent coil spring, and is a front view showing the state when sewing a stepped portion according to the above embodiment. 11: Hollow arm,
12: Bed, 20: Presser foot, 27: Presser foot, 31: Presser bar holder, 32: Presser foot lifting lever, 40: Bending coil spring (constant force spring), 41: Main body, 42: Arm, 43:
Locking portion, 46, 48: Locking plate, 51, 52: Pin, 57
: Feed dog, 67: Needle. Figure 1 Figure 2 Figure 4 Figure 5 Figure 3

Claims (1)

[Claims] 1. A presser foot that is attached to the machine frame of the sewing machine so as to be vertically movable and has a presser foot attached to its lower end, and a feed dog that is located opposite to the presser foot and that protrudes and retracts from the upper surface of the sewing machine's throat plate to perform a feeding motion. and a spring means for applying a downward biasing force to the presser bar, and under the action of the biasing force of the spring means, the feed dog cooperates with the presser foot to move the work cloth located between them. In the sewing machine to be transferred, the spring means has a tightly wound coil portion and a pair of arm portions extending outward from both ends of the coil portion, and the free ends of the both arm portions are connected to the presser bar and the sewing machine mechanism. By using bending coil springs that are rotatably connected to each of the and have an arcuate shape as a whole, the presser foot always presses the work cloth with a substantially constant pressing force regardless of fluctuations in the vertical position of the presser bar. A cloth presser device characterized in that it presses the cloth.