Device and method for influencing the position of knots between the upper thread and the lower thread when sewing with a sewing machine

Abstract

A device and the method for influencing the position of the knot (31) between the upper thread (23) and the lower thread (17) when sewing with a sewing machine (1) using a computer (37), which calculates for every sewing stitch to be formed a control value for an actuator (39), by which a braking force of the thread tension regulator (23) is controlled.

Claims

1. A device for controlling a position of knots (31) between an upper thread (21) and a lower thread (17) when sewing a material (15) with a sewing machine (1), comprising a thread tension regulator with an actuator (39), the actuator (39) being configured to influence a tensile force F.sub.AR applied upon the knot (31) during tightening of the knot (31) of the upper thread (21) and the lower thread (17), a computer (37) to control the actuator that individually predetermines a guide parameter for the actuator (39) for every sewing stitch or for every group of several successive sewing stitches.

2. The device according to claim 1, further comprising a thread tension regulator and a thread lever (27) located successively between a storage site for an upper thread supply (21) and a needle bar (9) in a direction of removal of the upper thread (21), the thread tension regulator (23) acting as a friction brake for the upper thread (21), and the thread lever (27) being adapted to tighten the upper thread (21), and a braking force of the thread tension regulator (23) is at least one of adjustable or controllable by the actuator (39).

3. The device according to claim 2, wherein the computer (37) comprises a program memory (38) and a reference memory (36), with processing stipulations in the program memory (38) for processing being dependent at least on one reference value saved in the reference memory (36) for a guide parameter of the actuator (39) and on values of at least one input parameter (58), which the knot position L1 is dependent upon during a sewing process, in order to form a guide value for addressing the actuator (39).

4. The device according to claim 3, wherein each of the input parameters (58) comprises a value of one of the following parameters, which is effective at a time of formation of the actual sewing stitch or a previous sewing stitch or a subsequent sewing stitch: a pivotal position of the needle bar (9), a width of the stitch, a length of the stitch, an amount of the change of the pivotal position of the needle bar (9) in reference to the pivotal position during the execution of the previous sewing stitch, an direction of the change of the pivotal position of the needle bar (9) in reference to the pivotal position during the execution of the previous sewing stitch, a sewing speed, or control parameter of a foot control (47).

5. The device according to claim 4, wherein saved reference value represents a value for the control parameter of the actuator (39), which under predetermined reference conditions together with a predetermined value of at least one parameter of the input parameters result in a deviation of the knot position L1, L1, L1 during the sewing process being minimal compared to a predetermined reference position L0, L0, L0.

6. The device according to claim 5, wherein for every one of the sewing stitches to be formed a target value is predetermined for the respective knot position L1, L1, L1 compared to the reference position L0, L0, L0.

7. The device according to claim 6, wherein several successive ones of the sewing stitches are combined into groups, and that for every one of the sewing stitches within said group of sewing stitches, a target value is predetermined for the respective knot position L1, L1, L1 compared to the reference position L0, L0, L.

8. The device according to claim 1, further comprising a device for limiting a maximally permitted sewing speed depending on an adjustment time of the actuator (39).

9. A method for influencing a position of knots (31) between an upper thread (23) and a lower thread (17) when sewing with a sewing machine (1) using a device according to claim 1, comprising the computer (37) determining for every one of the sewing stitches to be executed a value for the guide parameter to control the actuator (39), and coordinating the actuator (39) when executing said sewing stitch with a motion of the needle bar (9), at least during a tightening of the knot (31), with a calculated value of the guide parameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is explained in greater detail based on some figures. Shown are:

(2) FIG. 1 a sewing machine, shown schematically,

(3) FIG. 2 a schematically shown cross-section of the sewing machine in the area of the needle plate when sewing a material,

(4) FIG. 3 a cross-section of the material while sewing with moderate upper thread tension,

(5) FIG. 4 a cross-section of the material while sewing with a low upper thread tension,

(6) FIG. 5 a cross-section of the material while sewing with a high upper thread tension,

(7) FIG. 6 a principle diagram of a sewing machine with elements of a thread tension regulator, and

(8) FIG. 7 a material with knots arranged along a curve between the lower thread and the upper thread.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) FIG. 1 shows schematically a sewing machine 1 with a frame 2, with the arm bed 3 laterally projecting at the bottom and spaced apart therefrom a top arm 5 at the top. The exterior edge section of the top arm 5 is embodied as a machine head 7. At the bottom of the machine head 7 a needle bar 9 projects with a sewing needle 11 arranged therein in an exchangeable fashion. In order to execute sewing stitches the needle bar 9 is supported such that it can move up and down in the direction of the axis A of the sewing bar (double arrow A) and in order to execute zigzag stitches additionally pivotally about a pivotal axis B perpendicular to the sewing direction N and/or in the longitudinal direction of the top arm 5 in the machine head 7 (double arrow B). Below the needle bar 9, a needle plate 13 is arranged at the top of the arm bed 3. It comprises an oblong hole 14, through which during the sewing process the bottom section of the sewing needle 11 after piercing a material 15 resting on the needle plate 13 can penetrate the frontal section of the arm bed 3. Here, the supply of bottom thread 17 is stored, spooled in a bobbin case 19.

(10) The spooled supply of upper thread 21 rests on a mandrel at the top arm 5. From this supply area the upper thread 21 is guided successively over a thread tension regulator 23, a deflection means 24, and a thread lever 27 towards the sewing needle 11, and through the eye of said needle 29.

(11) During the sewing process the sewing needle 11 pierces through the material 15 and the oblong hole 14 near the bobbin case 19 into the arm bed 3, where a hook (not shown) engages a loop of the upper thread 21 and guides it around the lower thread 17. In a manner coordinated thereto, the thread lever 27 is lowered and thus releases a sufficient length of the upper thread 21 so that it can unhindered be guided about the bobbin case 19 with the supply of the lower thread 17. When the needle bar 9 is pulled upwards the thread lever 27 also moves back upwards, coordinated with the motion of the needle bar 9.

(12) FIG. 2 shows schematically a cross-section of the sewing machine in the area of the arm bed during the sewing process with straight stitches. During the execution of a sewing stitch cycle the upper thread 21 in the last section of the upwards motion of the sewing needle 11 is tightened between the wrapping site with the lower thread 17 and/or the knot 31 and the thread tensioning regulator 23 acting as a friction brake. The lower thread 17 is tightened between the previous knot 31 and a lower thread tension regulator 33, embodied as a friction brake at the outlet from the bobbin case 19. In the area of the knot 31 the lower thread 17 applies a tensile force F.sub.A1 of the upper thread 21 upon the upper thread 21, at this point opposite the force F.sub.B1. Due to the forces acting in the area of the knot 31 during the stitch formation upon the upper thread 21 the knot 31 is tightened. Here, the defined knot position L.sub.1 shows, in reference to a neutral reference position L.sub.0 at a corresponding piercing site of the sewing needle 11, a considerable dependency on the forces and/or the projection of the resulting force F.sub.AR during the tightening of the knot 31. The neutral reference position L.sub.0 may be predetermined, e.g., by its distance from the needle plate 13. In particular, this neutral reference position L.sub.0 may be predetermined in the machine control in a material 15 in the form of a planar formation with two material layers 15a, 15b, as shown in FIG. 2, as the central position between the two material layers 15a, 15b. Without moving the material 15 and without any pivotal motion of the needle bar 9 the effective direction of the resulting force F.sub.AR is essentially predetermined by the direction of the axis of the needle bar A. In general, the progression of the amount and the direction of the resulting force F.sub.AR are dependent on various parameters. They include particularly the following parameters: the friction coefficients of the upper thread 21 and the lower thread 17, the brake forces applied by the thread tension regulator 23 and the lower thread tension regulator 33 perpendicular to the tensile direction upon the upper thread 21 and/or the lower thread, additional friction forces acting upon the threads 17, 19, such as at the eye of the needle 29, the thread lever 27, or the deflection means 25 upon the upper thread 21, knot type (rotary or knotting thread connections), geometric tensile components and/or directions of the lower thread and the upper thread at the contact sites, tensile forces acting upon the upper thread 21 and/or the lower thread 17, which are caused by the transportation of the material 15 in the sewing direction N and/or a pivotal motion B of the needle bar 9 perpendicular to the sewing direction N and/or by a motion of the needle bar 9 in the direction of the axis of the needle bar A and/or by the motion of the thread lever 27.

(13) By influencing and/or controlling the braking force of the thread tension regulator 23 and/or the lower thread tension regulator 33, at least during the phase of the knot tightening process, the knot position L.sub.1 can be influenced in reference to the predetermined reference position L.sub.0 by the thread lever 27 at this piercing site. An increase of the guide value for an actuator 39, by which the actuating value of the thread tension regulator 23 is controlled and the increase in braking force of the thread tension regulator 23 connected thereto causes in the knot 31 an increase of the thread tension and/or the regulating tensile force F.sub.AR of the upper thread 21. The final knot position L.sub.1 is here displaced towards the top of the material 15. Similarly, the final knot position L.sub.1 is displaced at a lower braking force of the thread tension regulator 23 towards the bottom of the material 15. The progression of the resulting force F.sub.AR and the final knot position L.sub.1 are also dependent on the feed of the material 15 in the sewing direction N and the pivotal motion B of the needle bar 9, which are implemented to execute the directly subsequent sewing stitch. The FIGS. 3 to 5 show schematically a cross-section of the material 15 when generating a straight seam. The actuating value of the thread tension regulator 23 is determined in the illustration of FIG. 3 such that the final knot position L.sub.1 is equivalent to the reference knot position L.sub.0. In the example of FIG. 4, based on a weaker braking force of the thread tension regulator 23, the final knot positions L.sub.1, L.sub.1, L.sub.1 are shifted downwards compared to the respective reference position L.sub.0, L.sub.0, L.sub.0 within the material 15, in the example of FIG. 5 upwards, due to a stronger braking force of the thread tension regulator 23.

(14) In the situations shown in FIGS. 3, 4, and 5 all knots 31 are located within the material 15, which shows a thickness D and/or at a height between 0 and D in reference to the top of the needle plate 13. With an additional increase of the actuating value for the braking force of the thread tension regulator 23 the knots 31 can be pulled completely through the material 15 during the tightening process.

(15) Depending on the respective braking force of the thread tension regulator 23 as well as the feed of the material and the change of the pivotal position of the needle bar 9 for the next sewing stitch to be executed the final knot position L1, L1, L1, with regards to the corresponding reference position L0, L0, L0, shows not only a component in the vertical direction and/or the piercing direction of the sewing needle 11, but also a horizontal component in the direction of the next following piercing site of the sewing needle 11. For zigzag stitches or generally for stitch sequences in which the pivotal position of the needle bar 9 is changed between successive sewing stitches, the knot position L.sub.1 at the top of the material 15 can be changed between respectively two successive sewing stitches by the braking force of the thread tension regulator 23, at least while tightening the knot 31. The actuating value for the thread tension regulator 23 is adjusted and/or controlled by the actuator 39, for example by a stepper motor, an actuator motor, or an electromagnet. Similarly, the knot position L.sub.1 at the bottom of the material 15 can also be adjusted and/or controlled by the actuator 39. The actuator 39 is controlled by the guide parameter, which is issued by the control 35 of the sewing machine 1. The value of this guide parameter is individually calculated by the computer 37 for every sewing stitch or at least for each group of two or more sewing stitches and provided for addressing the actuator 39.

(16) FIG. 6 shows for example a basic circuit diagram of a sewing machine 1 with elements of a thread tension regulator, which can be used for controlling the knot positions L.sub.1 when sewing with a sewing machine 1. The control 35 comprises a computer 37 with a program memory 38 and a memory for reference data 36. The sewing machine 1 can be configured and controlled via the user interface 41 using operating elements 43 and preferably showing a graphic display 45. The predetermination of the sewing speed occurs via a foot control 47, which is effectively connected to the control 35.

(17) At the output side the control 35 is effectively connected to the primary engine 49, which serves to drive the cyclical up and downmotion of the needle bar 9 during the sewing process. Other motions, which occur synchronously with the cyclical motion of the needle bar 9, for example the movement of the feeder 51 to feed the material 13 in the sewing direction N, the motion of the grasper 53 to wrap the upper thread 21 about the lower thread 17 during the execution of the sewing stitch, and the pendulum motion of the thread lever 27 are generally also driven by the primary engine. The control 35 may be effectively connected to other actuators for adjusting and/or controlling sewing parameters, particularly an actuator 55a to control the pivotal position of the needle bar 9 and an actuator 55b for controlling the feeding component of the feeder 51 in the sewing direction N.

(18) The processing specifications are saved in the program memory 38 for calculating the guide values for the actuator 39, by which the pressure and braking force of the thread tension regulator 23 is controlled. At least one reference value for the guide parameter is saved in the reference data memory 36. This reference value is equivalent to a value of the guide parameter by which the actuator 39 must be addressed in order to cause, with predetermined reference conditions during the execution of a sewing stitch, that the actual position L.sub.1 of the knot 31 is equivalent to a predetermined reference position L.sub.0. This reference value is preferably determined in the initialization process individually for each sewing machine 1 and saved in a non-volatile fashion in the reference memory 36. Alternatively, the reference value may also be predetermined depending on a certain type of sewing machine.

(19) Alternatively, several reference values may be saved in the reference memory 36, each of which for different reference conditions respectively being equivalent to an optimized value of the guide parameter for the actuator 39. The reference conditions may differ by various values for one or more parameters. For example, the reference values for different stitching widths under otherwise identical conditions are saved in the reference memory 36. Similarly, a two-dimensional array of reference values depending on lengths of stitches and widths of stitches can be saved in the reference memory 36. During the sewing process, the actuator 39 is controlled with the particular value saved in the reference memory 36 for the respective combination of length and width of the stitch.

(20) In a similar fashion, reference parameters may be saved in the reference memory 36 for the additional or other combinations of parameters. In particular, the values may also be saved depending on the pivotal direction of the needle bar 9 in reference to the previous sewing stitch and/or values depending on the pivotal position of the needle bar 9 in the reference memory 36. The reference values saved this way represent information carriers, which must be selected as the guide parameter for the actuator 39 depending on one or more parameters in order for the position L.sub.1 of the knots 31 being equivalent as closely as possible to a predetermined reference position L.sub.0 during the sewing process.

(21) In addition to the saved reference value or values, the computer 37 is provided with values of one or more parameters as the input parameter and/or input parameters 58, influencing the knot position L.sub.1 during the sewing process. Such parameters are particularly the pivotal position of the needle bar 9 as well as the material feed in the sewing direction N between the previous sewing stitch and the one now to be executed. Optionally, such values for one or more sewing stitches may be temporarily saved in a memory of the computer 37, and this way considered when calculating the guide parameter. For example, the computer 37 may determine from the difference of the pivotal position of the needle bar 9 between the previous and the present sewing stitch the direction and the amount of the pivotal motion of the needle bar 9. These parameters also represent parameters influencing the knot position L.sub.1 during the sewing process.

(22) Values of input parameters 58, which are imported by the computer 37 and further processed, may be already provided within the control 35 or be determined via the user interface 41 by an operator. In particular, one or more of the following actions may be performed via the user interface 41: Defining groups of sewing stitches by stipulating the respective number of successive sewing stitches. Selecting, editing, and saving sewing patterns with several successive stitch positions. Determining a target value for the knot position L.sub.1 for each individual sewing stitch within a group of sewing stitches. Preferably here pattern templates saved in the control 35 may be selected, edited, scaled, and saved. The target value for every knot position L.sub.1 within a group may be individually altered. Adjusting parameter values, such as width and length of the stitch, friction coefficient of the upper thread 21 and/or the lower thread. Selecting and/or activating a type of stitching, a stitch pattern, or a group of several successive sewing stitches to be used in the subsequent sewing process. Selecting and/or activating a pattern template to predetermine the knot positions during the subsequent sewing process.

(23) Based on the processing instructions saved in the program memory 38 the reference value or values are processed together with at least one parameter influencing the knot position L.sub.1 during the sewing process in order to form a guide parameter for the actuator 39.

(24) The processing specifications comprise information regarding the fact how the knot position L.sub.1 changes depending on one or more parameter and/or how the guide parameter for the actuator 39 must be adjusted, starting with a saved reference value, depending on one or more parameters, in order for the knot position L.sub.1 to be equivalent as good as possible to the reference knot position L.sub.0. Such dependencies may be saved in the program memory 38, for example as functions, with the values of the guide parameter preferably being provided for support points, which are distributed evenly over the value range of the respective parameter. If only a few support points are provided, intermediate values may be interpolated.

(25) Optionally, information may be saved for calculating optimized control values for the actuator 39 as reference parameters in the reference memory 36 and/or as processing specifications in the program memory 38.

(26) A desired operating type may be predetermined and/or selected via the user interface 41. In a first operating mode the stitch insertion is optimized in every sewing stitch such that the position of L.sub.1 of the knots 31 is equivalent to a neutral central position and/or the reference position L.sub.0. In another operating mode the target position L.sub.1 for the knots 31 may be predetermined, deviating from the reference position L.sub.0. In particular, groups with different sewing stitches may be defined, in which the knot position L.sub.1 is adjusted according to selected stipulations individually for every sewing stitch.

(27) FIG. 7 shows schematically a top view of a material 15, in which the positions L.sub.1 of the knots 31 are arranged between the lower thread 17, shown as a thin line, and the upper thread 21, shown as a thicker line, during the sewing process of a zigzag seam along a curve at the top of the material. During the sewing process, the values of the guide parameters calculated for an optimized stitch insertion (positions L.sub.0, L.sub.0, L.sub.0, . . . ) are adjusted via correction values for generating the arched curve. In the piercing sites at the left side and/or at every other piercing site the correction value is zero, so that here the actual knot position L.sub.1 is equivalent to the target position and/or the reference position L.sub.0. In the piercing sites at the right side, however, the actual positions L.sub.1, L.sub.1 are offset compared to the corresponding reference positions L.sub.0, L.sub.0 at the desired position of the top of the material. During the sewing process the actuator 39 was addressed by the control 35 with values of the guide parameter adjusted for each individual sewing stitch.

(28) Of course, the guide parameter may also be varied for the sewing stitches at the left side, the knots 31 here too being arranged displaced towards the top or bottom of the material 15.

(29) Furthermore, the computer 35 may also monitor the reaction times of the actuator 39 and limit the sewing speed predetermined by the foot control 47 such that the reaction times are always shorter than the duration of the stitch cycles.

LEGEND OF THE REFERENCE CHARACTERS

(30) 1 Sewing machine 2 Frame 3 Arm bed 5 Upper arm 7 Machine head 9 Needle bar 11 Sewing needle 13 Needle plate 14 Oblong hole 15 (sewing) Material 17 Lower thread 17 Supply of lower thread 19 Bobbin case 21 Upper thread 21 Upper thread supply 23 Thread tension regulator 25 Deflecting means 27 Thread lever 29 Eye of the needle 31 Knot 31a Previous knot 33 Lower thread tension regulator 35 Control 36 Reference memory 37 Computer 38 Program memory 41 User interface 43 Operating elements 45 Display device 47 Foot control 49 Primary engine 51 Feeder 53 Grasper 55a, 55b Actuators 58 Input parameter