Abstract:
Sewing machine with a control for the movement of a workholder. For the formation of edge parallel seams when sewing on labels with seam sections extending parallel to the movement axes of a cross slide system carrying the work holder, there are arranged at uniform distance from the stitch hole four transmitted light sensors, of which always only the one which can recognize the crosswise extending following edge of a seam section is switchable into readiness for operation. After a signal has been given by a sensor, the respective drive motor of the cross slide system is controlled by means of a microcomputer in such a way that the respective seam section ends exactly in the intended corner. Because of the work related feed control, a sewing program is not needed. Besides, the control automatically adapts itself to different label dimensions.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     This invention refers to sewing machines and in particular to a new and useful control for a sewing machine for the motion of a workholder. 
     From U.S. Pat. No. 4,444,734 a sewing machine with a cross slide guide workholder driven by two step motors is known. The motors are operated by a control unit which comprises, among other things, a microcomputer. By X-and Y-axis scale switches the basic seam program contained in the memory can be varied in X and/or Y direction. This type of seam size variation can be carried out relatively easily and quickly. However, if this sewing machine is used for sewing cloth parts, e.g. labels, on a workpiece, it would take too much time, despite the easy variability, to make a size adaptation for every cloth part that differs in size from the cloth part sewn on before, so as to obtain a uniform seam distance at all edges. Besides, in this case the cloth part must be exactly centered in the workholder, because otherwise the seam would be shifted relative to the edges of the cloth part and thus irregular seam distances would occur. 
     U.S. Pat. No. 4,073,247 discloses a sewing machine with a cross slide guided workholder for the edge parallel sewing of workpieces. The sewing machine comprises a work edge scanner with light source disposed below the workpiece and a camera disposed above the workpiece. The camera contains a linear arrangement of a plurality of photo diodes and can be rotated through a positioning drive about a vertical axis in X and Y directions of the cross slide system of the workholder, the diode row being aligned substantially crosswise to the work edge to be scanned. The photodiodes illuminated during the scanning process emit a proportional number of pulses which, depending on the rotational position of the camera, are supplied to a corresponding input of a signal processing system containing a microcomputer. As soon as the previously scanned workpiece is in the working position, the signal processing system calculates from the signals received from the camera and from additionally entered sewing parameters the control commands for the drive motors of the cross slide system. As this sewing machine does not operate with a given basic seam program but automatically determines for each workpiece the specific control data for the forward movement of the workholder, it is suitable in particular for the treatment of workpieces which successively differ in size and/or form. This advantage, however, is offset by a considerable technical effort. 
     SUMMARY OF THE INVENTION 
     The invention provides a sewing machine for the sewing on of cloth parts, e.g. labels, on a workpiece by means of a seam consisting of seam sections determined as to direction, where the cloth part is scanned directly during the sewing for the formation of control commands for the motors. 
     By the measure of arranging one sensor spaced from the stitch hole for each movement direction of the workholder that occurs during a sewing cycle in order to recognize the cloth part edge extending substantially crosswise to the respective sewing direction, and switching into readiness for operation by the control system always only the sensor which precedes the stitch hole in a forward direction of the workholder, there is scanned for each individual seam section the cloth part edge extending substantially crosswise and determining the end of this seam section. Based on the sensor signal and in consideration of the size of the seam distance entered in a memory of the control unit and in consideration of the preselected stitch length, the microcomputer of the control unit now calculates the number of residual stitches still required before the seam corner is reached. 
     If it is found in the calculation that the last of the residual stitches still to be formed would not coincide with the desired seam corner, depending on whether the last residual stitch would go beyond the desired seam corner, with a smaller or with a larger distance, the stitch length of the residual stitches still to be sewn after the sensor signal is reduced or respectively, omitting one stitch, increased to such an extent that the last residual stitch lies exactly in the desired seam corner. Being that the stitch/length correction value is divided over several residual stitches, the length of the residual stitches sewn after the sensor signal differs very little from that of the previously formed residual stitches, so that all in all a very uniform seam pattern is obtained. 
     As the seam corner is reached, the motor that was in operation until then is stopped and the motor needed for the formation of the next seam section is started, whereupon this seam section is formed without interruption to the next seam corner. This second seam corner as well as all further seam corners are approached equally exactly in the same manner by means of the respective sensors. 
     Since the motors are controlled only by the given parameters of seam distance and stitch length and also by the sensor signals generated with the scanning of the respective cloth part edges; and since therefore they do not require a sewing program containing the geometric data of the seam, the control commands for the motors serving for the forward movement of the workholder are derived directly from the cloth piece to be sewn on, so that the seam is always formed matching the respective cloth part, and even in case of a cloth part arranged out of center in the work-holder, equal seam distances are obtained all around. 
     An especially simple construction of the sewing machine results if on it only seams with seam sections extending parallel to the cross slide axes are to be formed and for the formation of seals with seam sections extending parallel to the cross slide axes there are arranged in the stitch plate four transmitted light sensors to which at equal distance from the stitch hole, lie on a system of coordinates aligned with the cross slide axes and centered on the stitch hole. 
     The sewing machine according to the invention can be used advantageously also for the formation of seams where one or more seam sections extend at an angle of, e.g. 45°, to the other seam sections. In this case, both motors of the cross slide systems are operated simultaneously for the formation of the angularly extending seam sections, and the cloth part edges are scanned simultaneously possibly by two adjacent sensors. 
     Accordingly it is an object of the invention to provide an improved sewing machine construction in which the workpiece is advanced in respect to a reciprocating needle of the machine in accordance with signals from a plurality of sensors which advantageously include a single sensor located along each axis at which a seam is to be formed. 
     A further object of the invention is to provide a control system for moving a workpiece in association with a needle of a sewing machine which includes a microcomputer which is operated in consideration of a sensor located so as to recognize the starting edge of a piece to be sewn and to indicate the approach of a corner at which a following seam is to be formed and to control the movement of the needle in respect thereto so that the seams being sewn terminate at the precise edge at which they are intended to which further includes means for sensing before the edge is approached the number of stitches that would be required to terminate the stitch at the corner location. 
     A further object of the invention is to provide a sewing machine which is simple in design, rugged in construction and economical to manufacture. 
     A further object of the invention is to provide a method of effecting sewing of a seam which is to be directed along at least two seam lines which are arranged along axes which are at an angle to each other and which comprises using a sensor to locate the edge of an object to be sewn so that the needle will begin an initial seam, advancing the workpiece in respect to the needle to form the initial seam but before it is finished, sensing where the next seam is to begin and forming the remaining first seam with a required spacing of stitches to bring the end of the stitch formation to the corner at which the second seam is to be begun. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a front top perspective view of a part of a sewing machine constructed in accordance with the invention; 
     FIG. 2 is a block diagram of the control unit for the sewing machine of FIG. 1; and 
     FIG. 3 is a top view onto the stitch plate of the sewing machine of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular, the invention embodied therein comprises a sewing machine generally designated 1 which has a stitch plate 8 carrying a plurality of sensors 37,38,39 and 40 which are advantageously located in a spaced location from a stitch hole 9 through which a needle guiding the thread 7 is moved and along each axes of which a seam is to be formed. In the embodiment of the invention shown, the seam is to be formed along five separate stitch lines or seam lines N1 to N5. To effect the shifting of the workpiece W and a cloth part S which is to be affixed to the workpiece by a seam formation, the embodiment of the invention shown provides for the formation of the five stitch lines to secure the cloth part 5 to the workpiece 8. 
     The sewing machine comprises a housing 1, of which a support arm 2 and an arm 3 with a head 4 is illustrated. Mounted in arm 3 is an arm shaft 5, shown only symbolically in FIG. 2, which drives a needle bar 6 upwardly and downwardly. Secured in the needle bar 6 is a thread guiding needle 7 which cooperates with a shuttle (not shown) for the formation of stitches. The shuttle is located below a stitch plate 8 which is arranged in the support arm 2 and has a stitch hole 9 for the passage of the needle 7. 
     A guide bar 11 is arranged on both sides of the support arm 2 and is parallel to the longitudinal axis of the support arm. On the guide bars 11, a U-shaped slide 12 spanning the support arm 2 is mounted, on which a rack 13 is secured. Meshing with rack 13 is a pinion 15 driven by a step motor 14. The step motor 14 is disposed at a bracket 16 secured to the housing 1. 
     On two guide bars 17 sliding in slide 12 and extending crosswise to the longitudinal axis of support arm 2, a substantially U-shaped yoke 18 is fastened. Yoke 18 carries a rack 19 which meshes with a pinion 20. Pinion 20 is driven by a step motor 21 secured on the slide 12. At the free end of the yoke 18, a guide head 22 is disposed, in which a carrier 23 displaceable in vertical direction is received. The carrier 23 is pushed downward by a spring (not shown) arranged inside the guide head 22, and now comprises a cross pin 24 protruding through a slit in the guide head 22. 
     Arranged on carrier 23 is a holding mechanism 25 known from German Pat. No. 1,115,113 for a pressure plate 26. The holding mechanism 25 consists essentially of an intermediate piece 27 fastened to the carrier 23, a U-shaped crank 28 rotatably mounted in said intermediate piece, and a spring loaded slide block 29 movable relative thereto. A pin 30 fastened to crank 28 engages in a cutout 31 on slide block 29. An upwardly extending lug 32 is fastened on slide block 29. The structural elements 11 to 32 form a workholder 33 for the work W and a cloth part S to be sewn onto it, the movement directions of the slide 12 and of the yoke 18 constituting the Y axis and the X axis of a cross slide system. 
     In head 4, a lift bar 34 is arranged which is liftable by a drive mechanism not shown. Secured on the lift bar 34 are a finger 35 protruding crosswise and a stop 36 protruding downward and cooperating with lug 32. 
     Fastened in the stitch plate 8 at equal distance to the stitch hole 9 are four transmitted light sensors 37, 38, 39, 40 which lie with their upper end and the top side of the stitch plate 8 in a common plane. The sensors 37, 38, 39, 40 lie on a system of coordinates 41, the two axes of which are aligned with the X- and Y-axes of the cross slide system. The sensors 37, 38, 39, 40 are connected via line 42 to corresponding inputs of a microcomputer 43, which is a component part of a control unit 44 for the step motors 14 and 21 as well as for a motor 45 shown symbolically in FIG. 2. The motor 45 is in drive connection with the arm shaft 5 via a belt drive 46 and serves to drive the sewing machine. 
     On the arm shaft 5 a strobe disc 48 provided with a plurality of bar marks 46 is fastened; it cooperates with a pulse generator 49. Pulse generator 49 is connected via a line 50 to one input of the microcomputer 43. 
     To another input of microcomputer 43 an input device 51 is connected. The two step motors 14, 21 are connected via lines 52, 53 and control circuits (not shown) to two outputs of the microcomputer 43. Another output of microcomputer 43 is connected via a line 54 to the control circuit (not shown) of motor 45. 
     Secured on a bracket 55 disposed at heat 4 is a lighting fixture 56 which illuminates the area of the sensors 37, 38, 39, 40. 
     The sewing machine operates as follows: 
     For placing a workpiece W and a cloth part S to be sewn thereon on the support arm 2, the lift bar 34 is raised. The lift bar 34 engages by its finger 35 under the pin 24 and in so doing lifts the carrier 23 and the holding mechanism 25 together with the pressure plate 26. The workpiece W is then positioned on the support arm 2 and the cloth part S is aligned under the pressure plate 26. It suffices for the cloth part S to be aligned parallel to the edge. It need not be centered under the pressure plate 26 at the same time, whereby the aligning process is substantially simplified. Then the pressure plate 26 is lowered, whereupon it seizes the cloth part S and the workpiece W by frictional contact. The pressure plate 26 and crank 28 are then in the position shown in FIG. 1. 
     Since in a non centered position of the cloth part S its edge K1 can have any distance from the stitch hole 9, provision must be made before sewing is begun that the edge K1 has a distance from the stitch hole 9 which corresponds to the intended seam distance. For this purpose the workholder 33 is first moved to the left by the step motor 14 according to FIG. 2 until the sensor 38 recognizes the edge K1. Thereafter the step motor 14 moves the workholder 33 to the right again, the microcomputer 43 controlling the number of steps of the step motor 14 and hence the displacement path of the workholder 33 as a function of the value of the seam distance entered via the input device 51, in such a way that thereafter edge K1 is at the intended seam distance from the stitch hole 9. 
     The sewing cycle is started with the motor 45 being turned on, whereupon the first stitch of the seam section N1 is formed in the region of the crank throw below the pivot axis of crank 28. After formation of the first stitch, step motor 21 displaces the workholder 33 by the amount of the stitch length set at the input device 51. The timing of the forward movement is controlled by means of the pulses generated by the pulse generator 49 as a function of the position of the arm shaft 5 in such a way that the workholder 33 is displaced always only during the time that the needle 7 is above the cloth part S. During formation of the seam section N1, only the sensor 38 nearest the edge K2 subsequently to be worked, that is, the one preceding the stitch hole 9 parallel to the forward direction of the work holder 33 is switched by computer 43 into readiness for operation. 
     As soon as sensor 38 has recognized the edge K2 of cloth part S through the workpiece W, microcomputer 43 calculates, on the basis of the sensor signal as well as the size of the set stitch length and of the seam distance from the edges K1 to K4 of the cloth part S, the number of residual stitches still required before the seam corner lying at seam distance from the edge K2 is reached. If it is established in the calculation that the last of the residual stitches still to be formed would not coincide with the desired seam corner, the stitch length of the residual stitches still to be sewn after the sensor signal is decreased or, omitting one residual stitch, increased, depending on whether the last residual stitch would go beyond the desired seam corner with a smaller or larger distance, to such an extent that the last residual stitch lies exactly in the desired seam corner. Being that the stitch length correction value can be distributed over several residual stitches, the stitch length of the residual stitches sewn after the sensor signal differs very little from the stitch length of the previously formed stitches, so that all in all a very uniform seam pattern is obtained. 
     After the seam corner has been reached, the microcomputer 43 causes the step motor 21 to stand still and the step motor 14 to be actuated instead for the formation of the seam section N2. At the same time the sensor 38 is disconnected and sensor 39 switched to readiness for operation. Approach of the seam corner of seam section N2 and of the remaining seam sections N3 and N4 occurs in the same manner as described above for seam section N1. 
     In the formation of seam section N5, the lug 32 strikes against the stop 36 protruding into its movement path, whereby the slide block 29 is retained, which until then had been moving jointly with the intermediate piece 27. By the then occurring relative movement between the intermediate piece 27 and the slide block 29, crank 28 is pivoted into the position shown in FIG. 2. 
     The end point of seam section N5 does not coincide with a seam corner but lies at the point of the first stitch of seam section N1, seam section N5 having the same length as the seam section N1. Since in this case none of the sensors 37 to 40 can be used for the approach of the end point of seam section N5, previously the number of steps to be executed by step motor 21 required for the production of seam section N1 is totaled and later step motor 21 is controlled by means of the stored value in the formation of seam section N5. In this manner the last stitch of seam section N5 is formed in the place of the first stitch of seam section N1, with the stitch formation again occurring in the region of the crank throw below the pivot axis of crank 28. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.