Clamping device for a back or bottom thread of a sewing machine

Description

[0001] The invention relates to a clamping device for temporarily clamping a back thread or bobbin thread in a sewing machine. The invention also relates to a needle plate with such a clamping device and a sewing machine with such a needle plate.

[0002] Sewing machines are used, for example, in the production of passport documents, where the individual passport book pages are sewn together. The production of such documents is highly automated, so it must be ensured that the bobbin thread or back thread is always available during the sewing process. Sewing machines that are not used for such passport documents have a metal spring on the needle plate that passively clamps the sewing thread temporarily. However, such metal springs are not usually used in sewing machines for the production of passport documents because the clamping of the bobbin thread or back thread cannot be actively controlled. The use of a passive metal spring leads to uneven sewing behavior and an increased amount of waste.

[0003] DE 10 2011 102 928 A1 describes a seam-forming device for a sewing machine with a thread guide. This guides at least one thread for seam formation. Furthermore, the sewing machine has a thread clamping device provided with a thread clamp that can be closed by a controllable actuating means for clamping and / or opened by the actuating means.

[0004] DE 901 860 C describes a method and a machine for attaching objects to a workpiece. In particular, a method and a machine for attaching objects to a workpiece by means of a plurality of unconnected groups of stitches.

[0005] It is therefore the object of the present invention to provide a clamping device, a needle plate and a sewing machine which overcome these disadvantages.

[0006] This object is achieved with a clamping device for temporarily clamping a bobbin thread or back thread having the features of claim 1, with a throat plate having the features of claim 8 and with a sewing machine having the features of claim 9. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0007] The clamping device according to the invention comprises a clamp and an adjustment device for actively adjusting the clamp, wherein the adjustment device is configured to adjust the clamp between a clamping position and a release position. In the clamping position, the clamp rests against a needle plate of the sewing machine or is moved toward the needle plate, thus clamping a back thread or bobbin thread between the needle plate and the clamp. In the release position, the clamp is moved away from the needle plate and thus mounted non-contact with it, leaving the back thread or bobbin thread unclamped.

[0008] This design enables active control of the clamping and the clamping force exerted. This makes the sewing process more stable and drastically reduces the amount of waste due to faulty sewing. This design is therefore characterized by increased process reliability.

[0009] Since a sewing machine typically has very limited space available for the components of the clamping device, the invention provides that the clamp is attached to a pivotably mounted rod, and that the adjustment device is configured to rotate the rod between different rotational positions in order to pivot the clamp between the clamping position and the release position. By using such a rod, the force application for adjusting the clamp can be offset relative to the clamp itself, thus effectively utilizing the available space.

[0010] In this context, it is also advantageous to have a rotary lever connected to the rod for rotational stability, which can be actuated by the adjustment device. The use of such a rotary lever has proven advantageous, as it allows an actuator to be used to adjust the rotary lever together with the rod, and thus the clamp.

[0011] It is advantageous if the adjustment device is formed by a linear actuator with an actuating rod that is coupled to the rotary lever via a pivot joint. This allows the actuating rod to engage the rotary lever and pivot the clamp between the clamping and release positions.

[0012] A simple actuation option for the linear actuator is provided by the fact that it comprises pressure medium connections in order to adjust a piston guided in a cylinder and coupled to the actuating rod between two end positions by means of a pressure medium.

[0013] To ensure that the document components are not contaminated by the units used in passport document production, it has proven advantageous to use pneumatically operated linear actuators. This prevents fluids or similar substances from getting onto parts of the documents or even into the passport document production units in the event of a leak – for example, at the pressure fluid connections.

[0014] In order to retrofit existing sewing machines with an actively adjustable clamping device, it has proven advantageous if a mounting plate is available and designed to be detachably attached to the needle plate of the sewing machine, and if the adjustment device is attached between the legs of a double angle attached to the mounting plate.

[0015] In order to be able to carry out compensating movements during the adjustment process between the clamping position and the release position, it has proven advantageous if the adjustment device is pivotably mounted between the legs of the double angle.

[0016] The clamp itself can be formed from a spring sheet or a sheet metal angle, preferably comprising two clamp legs whose free leg ends are connected to each other via a clamp bar. The leg ends attached to the mounting plate or the rod can include an angle to provide elasticity for the clamp.

[0017] The advantages, configurations, and effects described in connection with the clamping device according to the invention apply equally to a throat plate according to the invention equipped with such a clamping device. The clamping device is attached to a surface of the throat plate facing away from the fabric support side.

[0018] The advantages, configurations and effects mentioned in connection with the clamping device according to the invention and the throat plate according to the invention apply equally to a sewing machine according to the invention which is equipped with such a throat plate.

[0019] Further features, properties, and advantages of the present invention are described in more detail below using embodiments with reference to the accompanying figures. All features described so far and below are advantageous both individually and in any combination. The embodiments described below are merely examples and do not limit the subject matter of the invention. They show: Figure 1a perspective view of a clamping device mounted on the throat plate, in which the clamp is in the release position, Figure 2a side view of the clamping device mounted on the throat plate from Figure 1 , in which the clamp is in the release position, Figure 3 a perspective view of the throat plate and the clamping device from Figure 1 , in which the clamp is in the clamping position, Figure 4 a side view of the throat plate and the clamping device from Figure 1 , in which the clamp is in the clamping position, and Figure 5 is a further perspective view in which the clamp is in the clamping position.

[0020] The figures show a needle plate 200 to which a clamping device 100 is fixed. The clamping device 100 is fixed to a surface of the needle plate 200 facing away from the fabric support side. The clamping device 100 is fixed by means of a mounting plate 126, which is screwed to the needle plate 200. The clamping device 100 serves to temporarily clamp a back thread or bobbin thread in a sewing machine with a clamp 102. The clamp 102 is formed from two clamp legs 122, the free leg ends of which are connected to one another via a clamp web 124. The clamp web 124 has a bevel that facilitates the insertion or removal of the thread. The two clamp legs 122 are also each formed with an angle that is arranged at a distance from the clamp web 124. In this way, the clamp 102 provides elasticity to clamp the sewing thread.The clamp 102 is attached to a rod 106. In this case, the two clamp legs 122 are screwed to the rod 106. For this purpose, the rod has a flattened section so that the clamp 102 can be securely attached to the rod 106. In the areas away from the clamp 102, the rod 106 has a circular cross-section. The rod 106 is mounted in the mounting plate 114 with limited rotation. In this way, the clamp 102 can be pivoted when the rod 106 is rotated.

[0021] In order to actively adjust the clamp 102, an adjustment device 104 is also provided, wherein the adjustment device 104 is configured to adjust the clamp 102 between a clamping position and a release position. In the clamping position, the clamp 102 rests against the needle plate 200 of the sewing machine or is at least moved toward it, whereby a back thread or bobbin thread is clamped between the needle plate 200 and the clamp 102. In the release position, the clamp 102 is moved away from the needle plate 200 and thus mounted without contact with it, whereby a back thread or bobbin thread is not clamped, in other words, is unclamped.

[0022] The adjusting device 104 is configured here to rotate the rod 106 between different rotational positions in order to pivot the clamp 102 between the clamping position and the release position. For this purpose, a rotary lever 108 is provided, which is connected to the rod 106 in a rotationally fixed manner and extends through a recess 120 in the mounting plate 120 to act on the rod 106. In the present case, the adjusting device 104 is formed by a linear actuator with an actuating rod 110, which is coupled to the rotary lever 108 by means of a rotary joint 112. The linear actuator comprises two pressure medium connections 114 in order to adjust a piston, which is guided in a cylinder and coupled to the actuating rod 110, between two end positions using a pressure medium. These two end positions therefore also correspond to the positions that bring about the clamping position and the release position of the clamp 102.The linear actuator is operated pneumatically to avoid contamination from liquid pressure media. Compressed air, for example, is used here.

[0023] In the Figures 1 and 2 the piston is in one of its two end positions and thus the clamp 102 is in its release position, in which it does not rest on the needle plate 200 and thus cannot clamp any back or bobbin thread. This release position of the clamp 102 is particularly indicated by Figure 2 clearly, whereby it can also be seen that the actuating rod 110 of the linear actuator protrudes significantly from the housing.

[0024] If the pressure medium connections 114 are now pressurized in opposite directions with the pressure medium, the piston is moved to its other end position and the pressure in the Figures 3 to 5The situation shown is shown, in which the clamp 102 is in the clamping position. It can be seen that in this clamping position configuration, the adjustment unit 104 can also be pivoted, which promotes the flow of force during actuation. For this reason, a double bracket 118 is attached to the mounting plate 126. This bracket comprises two legs 116, between which the adjustment device 104, i.e., the pneumatic cylinder, is pivotably mounted.

[0025] Based on Figure 5The structure of one of the two clamp legs 122 becomes clear, which is formed with a guide angle 128 extending perpendicularly to the clamp leg 122. A constriction 130 on the respective clamp leg 122 is then connected to the guide angle 128. This illustration clearly shows that the two fixed clamp legs 122 of the clamp 102 are fixed to the partially flattened rod 106, in particular by means of a screw mounted on the rod 106.

[0026] The invention described above significantly increases process reliability in the production of passport documents and reduces the scrap rate. The selected design also ensures a flat construction and optimal utilization of the available space within a sewing machine. It is possible to supplement the throat plate 200 with such a clamping device 100, thus allowing older sewing machines to be retrofitted with the clamping device 100 or the new throat plate 200 with such a clamping device 100. LIST OF REFERENCE SYMBOLS

[0027] 100Clamping device 102Clamp 104Adjusting device 106Rod 108Rotary lever 110Operating rod 112Swivel joint 114Pressure medium connections 116Leg 118Double angle 120Recess 122Clamping leg 124Clamping web 126Mounting plate 128Guide angle 130Constriction 200Throat plate

Claims

1. A clamping device (100) for temporarily clamping a backing thread or bobbin thread in a sewing machine, having a clamp (102) and an adjustment device (104) for actively adjusting the clamp (102), the adjustment device (104) being configured to adjust the clamp (102) between a clamping position in which the clamp (102) is moved towards a needle plate (200) of the sewing machine or rests against it and thus clamps a backing thread or bobbin thread between the needle plate (200) and the clamp (102), and a release position in which the clamp (102) is moved away with respect to the needle plate (200) and is thus mounted without contact relative thereto, as a result of which the backing thread or the bobbin thread is unclamped, characterized in that the clamp (102) is fastened to a pivotably mounted rod (106), and in that the adjustment device (104) is configured to rotate the rod (106) between different rotational positions in order to pivot the clamp (102) between the clamping position and the release position.

2. The clamping device (100) according to claim 1, characterized in that there is a rotating lever (108) which is connected to the rod (106) in a rotationally fixed manner and which can be actuated by means of the adjustment device (104).

3. The clamping device (100) according to claim 2, characterized in that the adjustment device (104) is formed by a linear actuator with a push rod (110) which is coupled to the rotating lever (108) by means of a swivel joint (112).

4. The clamping device (100) according to claim 3, characterized in that the linear actuator comprises pressure medium connections (114) in order to adjust a piston guided in a cylinder and coupled to the push rod (110) between two end positions by means of a pressure medium.

5. The clamping device (100) according to claim 4, characterized in that the linear actuator is pneumatically actuated.

6. The clamping device (100) according to any one of claims 1 to 5, characterized in that a mounting plate (126) is provided and adapted to be detachably fixed to the needle plate (200) of the sewing machine, and that the adjustment device (104) is fixed between the legs (116) of a double bracket (118) fixed to the mounting plate (114).

7. The clamping device (100) according to claim 6, characterized in that the adjustment device (104) is pivotably mounted between the legs (116) of the double bracket (118).

8. A needle plate (200) for a sewing machine with a clamping device (100) according to any one of claims 1 to 7, which is fixed to a surface facing away from the fabric support side.

9. A sewing machine with a needle plate (200) according to claim 8.