Sewing machine presser foot

Abstract

This invention provides a sewing machine presser foot device that reduces costs while also allowing for accurate measurement of fabric thickness. [Solution] A magnet 9 is attached to the presser foot 2 midway along its longitudinal direction via a bracket 10. A Hall sensor unit 5 is attached to the left side of the sewing machine frame 1 via a bracket 8, and the Hall sensor 6 is positioned opposite the magnet 9. The Hall sensor 6 is a Hall effect linear sensor, and the magnet 9 is positioned so that its magnetic poles, corresponding to the polarity of the Hall sensor 6, face the Hall sensor 6.

Description

Technical Field

[0001] The present invention relates to a presser device for a sewing machine, and more particularly to a presser device for a sewing machine capable of measuring the thickness of a fabric to be sewn. In the present invention, front-back, left-right refer to the front-back and left-right directions when the sewing machine is viewed from the front. Also, up-down refers to the up-down direction of the sewing machine.

Background Art

[0002] As this type of presser device for a sewing machine, a device that measures the thickness of a fabric using a magnet and a Hall sensor has been conventionally known (for example, see Patent Document 1). Patent Document 1 discloses a presser foot of a presser device for an overlock sewing machine, and the presser foot is mainly composed of a holder and a presser plate. The presser plate is a substantially plate-shaped member, and is supported by a holder so as to be rotatable around an axis along the left-right direction in the middle of the front-back direction. A magnet is erected at the rear part of the presser plate. A Hall sensor is provided at a position of the holder facing the magnet, and a sensor device including the Hall sensor is connected to a control unit.

[0003] During sewing, the fabric is sent backward while being sandwiched between the presser plate of the presser foot and the needle plate. When the thickness of the fabric changes during sewing, for example, when a portion with a large fabric thickness such as a stepped portion is fed under the presser plate, the front side of the presser plate rises and the rear side of the presser plate falls. Then, the vertical relative position between the magnet attached to the presser plate and the Hall sensor attached to the holder changes, and the voltage value output from the Hall sensor changes. When the change in the above voltage value is input to the control unit, it is determined that the thickness of the fabric has changed, and a signal is output from the control unit to control the behavior of each mechanism of the sewing machine to obtain an appropriate stitch. What is controlled by the control unit includes the operating speed of the sewing machine, the feed pitch of the feed mechanism, the force (pressing pressure) for pressing the fabric downward by the presser foot, the tension applied to the thread, and the like.

[0004] [Patent Document 1] Chinese Utility Model Publication No. 209602763 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Since presser feet are generally used differently depending on the type of fabric and sewing conditions, adopting the presser foot device of the sewing machine described in Patent Document 1 would require equipping all presser feet with magnets or sensor units, which would lead to increased costs for the presser feet. Furthermore, the shape of the presser foot plate varies depending on the sewing conditions mentioned above, which presents a problem as the position where the magnets are attached cannot be standardized. Therefore, while it is possible to detect changes in fabric thickness, such as in stepped areas, it is difficult to accurately measure the fabric thickness.

[0006] This invention has been made in view of the above circumstances, and aims to provide a sewing machine presser foot device that can reduce costs and accurately measure the thickness of the fabric.

[0007] To achieve the above objective, the invention of claim 1 provides a presser foot device for a sewing machine comprising: a presser bar arranged on the sewing machine frame so as to be vertically movable and biased downward by a biasing means; a presser base arranged below the presser base so as to be horizontal in its longitudinal direction and front to back, with its upper part abutting against the lower end of the presser bar; and a presser foot attached to the front end of the presser base, characterized in that it comprises a magnet attached midway along the longitudinal direction of the presser base and a Hall sensor arranged opposite the magnet and attached to the sewing machine frame.

[0008] The invention of claim 2 is characterized in that, in the presser foot device of a sewing machine according to claim 1, the Hall sensor is a Hall effect linear sensor, and the magnet has magnetic poles corresponding to the polarity of the Hall sensor that are directed toward the Hall sensor.

[0009] The invention of claim 3 is characterized in that, in the presser foot device of a sewing machine according to claim 1 or claim 2, the vertical center height of the Hall sensor is positioned lower than the vertical center height of the magnet. [Effects of the Invention]

[0010] According to the present invention, since there is no need to provide magnets or Hall sensor units on the retaining plate, the cost of the retaining plate can be reduced. Furthermore, since the mounting positions of the magnets and Hall sensor units remain unchanged even when the type of presser foot is changed, the thickness of the fabric can be measured with high accuracy. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic partial cross-sectional view of the main part of the presser foot device of a sewing machine according to the present invention, viewed from the front. [Figure 2] A schematic diagram of a graph showing the relationship between the distance between the magnet and the Hall sensor and the voltage value output from the Hall sensor. [Figure 3] A magnified view of a portion of Figure 1. [Best Mode for Carrying Out the Invention]

[0012] The presser foot device for a sewing machine according to the present invention will be described below with reference to the drawings. The lower part of the presser foot bar 11 protrudes from the lower part of an arm (not shown) that forms part of the sewing machine frame 1 of the overlock sewing machine. The presser foot bar 11 is constantly biased downward by a biasing means (not shown). A spring, an air cylinder, or the like can be used as the biasing means.

[0013] A retaining base 2 is positioned below the retaining bar 11. The retaining base 2 is positioned so that its longitudinal direction is horizontal and aligns with the front-to-back direction, and the upper surface of the retaining base 2 is in contact with the lower end of the retaining bar 11. A retaining plate 3 is attached to the front end of the retaining base 2. The retaining plate 3 mainly consists of a holder 3a and a retaining plate 3b. The retaining plate 3b is a plate-shaped member having a predetermined length in the front-rear direction, and is connected to the holder 3a so as to be rotatable around an axis by an axis (not shown) which is arranged along the left-right horizontal direction midway in the front-rear direction. A needle plate 4 is provided below the presser foot 3. The presser plate 3b of the presser foot 3 is biased downward by the biasing means of the presser bar 11 described above, pressing against the upper surface of the needle plate 4. In sewing fabric, the fabric is held between the presser plate 3b and the needle plate 4 and is pressed downward by the presser plate 3b while being fed backward by a known feed mechanism (not shown).

[0014] A magnet 9 is fixed to the right side of the longitudinal direction of the retaining base 2 via a bracket 10. The magnet 9 is a cylindrical neodymium magnet, positioned so that its south pole faces to the right. As the fabric is fed in and the presser foot 3 rises, the presser base 2 and the magnet 9 also rise.

[0015] A Hall sensor unit 5 is fixed to the left side of the sewing machine frame 1 via a bracket 8. A Hall sensor 6 is mounted on the circuit board 7 of the Hall sensor unit 5. The Hall sensor 6 is a Hall effect linear sensor that detects one magnetic pole of a magnet, and the output voltage value changes linearly in response to changes in magnetic flux density. In this embodiment, a type that detects the south pole is used.

[0016] The Hall sensor unit 5 is positioned so that the Hall sensor 6 is positioned opposite the magnet 9. As shown in Figure 3, when the presser foot plate 3b of the presser foot 3 is in contact with the upper surface of the needle plate 4, that is, when there is no fabric between the presser foot 3 and the needle plate 4, the Hall sensor 6 is positioned such that its vertical center height position (shown by the dashed line h2) is slightly lower than the vertical center height position of the magnet 9 (shown by the dashed line h1).

[0017] FIG. 2 is a schematic view of a graph showing the relationship between the distance between the magnet 9 and the Hall sensor 6 and the voltage value output from the Hall sensor 6. L1 in FIG. 2 is the distance between the magnet 9 and the Hall sensor 6 when the presser weight 3 is in the lowest position, and L2 is the distance between the magnet 9 and the Hall sensor 6 when the presser weight 3 is in the uppermost position. According to the presser device of the sewing machine configured as described above, an approximate linear relationship can be obtained between the distance between the magnet 9 and the Hall sensor 6 and the output voltage value of the Hall sensor 6 between L1 and L2 in FIG. 2. As a result, the thickness of the fabric under the presser weight 3 can be accurately measured.

[0018] The voltage value output from the Hall sensor 6 is input to a control unit (not shown) in the same manner as the presser device of Patent Document 1 to control each mechanism of the sewing machine to form appropriate stitches. During sewing, when the thickness of the fabric is measured as 0 (the distance between the magnet 9 and the Hall sensor 6 is L1 in FIG. 2), it is determined that the fabric has passed under the presser weight 3, and control is performed to reduce the pressing pressure by the presser weight or to lift the presser base 2 so that the presser plate 3b does not contact the needle plate 4. As a result, the noise generated by the intermittent contact between the feed teeth (not shown) that protrude and retract from the needle plate 4 and the presser plate 3b can be eliminated or reduced.

[0019] One Hall sensor 6 is provided in the Hall sensor unit 5, but another Hall sensor can also be added. For example, if a Hall effect switch sensor is provided above the Hall sensor 6, it can also function as a known presser base safety switch. In this case, the horizontal distance from the presser base 2 is monitored as the output voltage value, and control is performed such that the sewing machine cannot be driven when the presser base 2 moves a predetermined amount to the left.

[0020] The above-described embodiments are applied to the presser device of an overlock sewing machine, but are not limited thereto, and the same effects as those of the present embodiment can be obtained for sewing machines equipped with similar presser bars and presser bases. Also, the type of Hall sensor and the arrangement of the magnets are not limited to the above embodiments, and the Hall sensor can be of the N-pole detection type, and the side of the magnet facing the Hall sensor can be the N-pole. [Explanation of Symbols]

[0021] 1 Sewing machine frame 2. Pressing stand 3. Presser foot 4 Needle Plate 5 Hall sensor unit 6 Hall sensors 7 circuit boards 8 brackets 9 Magnets 10 brackets 11 Pressing rod

Claims

1. A presser foot device for a sewing machine comprising: a presser bar positioned on the sewing machine frame so as to be vertically movable and biased downward by a biasing means; a presser base positioned below the presser base so as to be horizontal in its longitudinal direction and front to back, with its upper part abutting against the lower end of the presser bar; and a presser foot attached to the front end of the presser base, characterized in that it comprises a magnet attached midway along the longitudinal direction of the presser base and a Hall sensor positioned opposite the magnet and attached to the sewing machine frame.

2. The presser foot device for a sewing machine according to claim 1, characterized in that the Hall sensor is a Hall effect linear sensor, and the magnet has magnetic poles corresponding to the polarity of the Hall sensor that are positioned toward the Hall sensor.

3. The presser foot device for a sewing machine according to claim 1 or claim 2, characterized in that the vertical center height of the Hall sensor is positioned lower than the vertical center height of the magnet.

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