Abstract:
A method and the device for minimizing stitching faults in embroidery devices ( 1 ) is provided, which includes a drive for moving the material holder ( 13 ), with an article to be sewn ( 11 ) being stretched therein, based on the knowledge that such stitching faults frequently can be explained by oscillations of the article to be sewn ( 11 ) and the material holder ( 13 ) due to rapid accelerations. Various effects, such as different types of articles to be sewn, changing weights, and friction ratios can cause a change of the oscillation behavior. One or more sensors ( 29, 43, 44 ) are provided and arranged such that they can detect the oscillation of the article to be sewn ( 11 ) and/or the material holder ( 13 ). The control of the drive and/or the sewing needle ( 23 ) occurs depending on the detected oscillations such that deviations of the stitching site from the predetermined target value is minimized.

Description:
BACKGROUND  
       [0001]     The invention is directed to a method and a device for minimizing stitching faults in embroidering devices.  
         [0002]     In embroidering devices, such as e.g., embroidering machines or sewing machines with an attachable embroidering module, the article to be embroidered is stretched into a frame. The device is arranged below the stitch forming device and/or the sewing needle and can be displaced and/or positioned in the sewing plane using a driving device. A control unit controls both the movement of the sewing needle as well as the one of the driving device for the embroidery frame. For each individual stitch, the embroidery frame with the stretched article to be sewn is displaced into the position required, in order for the stitching site of the needle in the article to be sewn to be equivalent to a predetermined target position. Conventionally for this purpose, common x-y-drives with two stepper motors are used, which can be addressed independent from one another. Here, for example, toothed belts can be provided to perform a transfer of the movement from the motors to the corresponding carriage, which can be displaced in a guided manner.  
         [0003]     In such conventional embroidery devices the embroidery frame and thus the article to be sewn can be excited into vibrations based on inertia. This particularly applies to high stitch frequencies and/or to fast changes of direction and the rapid accelerations connected therewith. As a consequence, the actual stitching position of the needle in the article to be sewn can deviate from the predetermined target position. When very large forces or accelerations affect the embroidery frame, it can result not only in contouring errors but also in a skipping of individual steps, when stepper motors are used, and thus in permanent contouring errors (until the subsequent reference point is taken for the stepper motors.) Various effects, such as differences in the types of articles to be sewn, the weight to be moved, or the friction ratios result in the fact that the vibration behavior cannot be calculated precisely and thus it cannot be eliminated a priori.  
       SUMMARY  
       [0004]     Therefore, the object of the present invention is to provide a method and a device, by which stitching faults caused by vibrations of the embroidery frame can be minimized in embroidery devices.  
         [0005]     This object is attained in a method and a device for minimizing stitching faults in embroidery devices according to the present invention.  
         [0006]     According to the invention, sensors are provided, which directly or indirectly detect characteristic features of vibrations of the embroidery frame and/or the article to be sewn stretched therein.  
         [0007]     In order to reduce and/or minimize stitching faults, in a preferred embodiment of the invention the drive motor or drive motors for the embroidery frame are controlled such that the amplitudes of the oscillations, namely the vibrations of the embroidery frame developing during the approach of the individual stitching positions caused by the inertia and the accelerations occurring, amount to values below a predetermined minimum. Here, preferably the speed and/or movement progression between the individual stitching positions is optimized and/or controlled or adjusted such that the accelerations developing in the predetermined stitching frequencies each are minimal.  
         [0008]     As an alternative to minimizing the vibrations of the frame, the movement of the sewing needle may also be controlled and/or modified such that the stitching time occurs precisely at the time the target position for stitching into the article to be sewn is directly below the sewing needle.  
         [0009]     In a further development of this alternative embodiment, the target positions can each be adjusted such that the stitches entering the article to be sewn are each positioned at the inversion points of the oscillating movements detected.  
         [0010]     The detection of the oscillations preferably occurs via an optical sensor in proximity of the stitching site of the sewing needle, with the optical sensor being equivalent to a laser mouse sensor, in principle, which detects images of the surface of the article to be sewn with a high spatial and temporal resolution and uses said information to calculate the respective position or speed or acceleration of the article to be sewn. This method is advantageous in that the sensor can also be used for controlling the article to be sewn and/or the movement of said article during the formation of the stitch.  
         [0011]     Alternatively, for example, one or more sensors for detecting force or torque can be provided, e.g., in the area of the mounting positions of the embroidery frame at the carriage of the driving device. In this case, the oscillations of the embroidery frame can be deducted from the measured signals of the sensors. Here, those signal components of the measuring signal, that can be purely deducted from the movement predetermined by the control without any elasticity-dependent excessive oscillation components, are filtered out of the measurement signals.  
         [0012]     Instead of stepper motors, preferably controllable servomotors can also be used for moving the embroidery frame, with the servomotors comprising, e.g., rotary sensors for detecting the actual rotary position of the motor. The detection of the contouring errors can also be used for analyzing the vibration behavior of the embroidery frame.  
         [0013]     Furthermore, it is possible to detect electric measurements, such as e.g., current or voltage consumption of the motor or motors and deduct information therefrom concerning the vibrations of the embroidery frame. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     In the following, the invention is explained in greater detail using the drawing figures. In the drawings:  
         [0015]      FIG. 1  is a side view of an embroidery device, comprising a sewing machine with a coupled embroidery module;  
         [0016]      FIG. 2  is a top view of a sewing machine with a coupled embroidery module;  
         [0017]      FIG. 3  is a view of a sewing foot, in a partial cross-section, with an integrated optic sensor;  
         [0018]      FIG. 4  is a detailed view of the connection point of a embroidery frame with a carriage of an x-y-drive; and  
         [0019]      FIG. 5  is a control arrangement diagram with an adaptive control. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     In  FIG. 1 , an embroidery device  1  is shown with a stitching module  5  coupled to a sewing machine  3 . The embroidery module  5  is connected to the sewing machine  3  via a connection wire  7  ( FIG. 2 ). The power supply of the embroidery module  5  is provided via the connection wire  7 , as well as an effective connection of the embroidery module  5  to a sewing machine control  9 . The embroidery device  1  can, e.g., also be provided as an embroidery machine with an enlarged support for articles to be sewn and with an integrated x-y-drive (not shown). For the embroidering process, the article to be sewn  11  is stretched in an embroidery frame and/or in a material holding device, in general. Subsequently, the holding device is mounted as stiff as possible to a holder  17 , e.g., using a clamp or fastening means  15 , in general, with a driving device  18  and/or an x-y-drive allowing the fastener to be moved back and forth in the two directions x and y of the sewing plane.  
         [0021]     The driving device  18  comprises a first slide or carriage  19 , which can be driven and/or displaced by a motor in the first sewing direction x, and a second slide or carriage  21 , which can be driven and/or displaced in a guided manner by a motor in the second sewing direction y in reference to the first carriage  19  ( FIG. 2 ). Preferably, adjustable servomotors are used as the motors (not shown) for the driving device  18 . Alternatively, sometimes stepper motors are used as well. In general, the first motor is connected in a fixed manner to the housing of the embroidery module  5  for the movement of the first carriage  19 , and the second motor is connected in a fixed manner to the movable first carriage  19  for the movement of the second carriage  21 . The transfer of the rotary motion into a linear motion can occur, e.g., via toothed belts  45  ( FIG. 4 ). In general, drives are arranged for adjusting the speeds between the motors and the toothed belt  45 . Guidance rods  22  or other guiding devices may be provided for guiding the carriages  19 ,  21 .  
         [0022]     A fastener  17  is provided at the second carriage  21 , protruding perpendicularly to a direction of movement y. The control  9  of the sewing machine adjusts, among other things, the upward and downward motion of the sewing needle  23 , which is held below the machine head  25  at a needle rod  27  that can be driven by a motor, and the movements of the two carriages  19 ,  21 .  
         [0023]     An optic sensor  29  is provided at the bottom of the sewing machine head  25 , which can detect and/or determine at least two dimensions of the space, and which preferably comprises a micro-camera. The optic sensor  29  is embodied and arranged such that it can detect a surface of the article to be sewn in an area of the stitching site of the needle  23  and/or parts of the material holding device  13 . A display optic (not shown), which is located in front of the sensor  29  or is a component of the sensor  29 , displays the area of the article  11  to be detected and/or the material holding device  13  onto the light-sensitive sensor area. Preferably, the sensor  29  comprises a light source for lighting the detection area with light in the visible or invisible range of the spectrum. The optic sensor  29  has a high local resolution, amounting approximately to 0.1 mm in two dimensions, and a high temporal resolution and/or scanning rate of 3000 Hz, for example. An image processing unit  30 , which e.g. can partially or entirely be integrated in the optic sensor  29  or in the machine control  9  is provided so that it can reliably detect oscillations of the article to be sewn  11  and/or the material fastening device  13 , even when the amplitudes of the oscillation are small and the frequency of the oscillation is high.  
         [0024]     Alternatively, the optic sensor  29  or parts thereof may also be integrated e.g., in the sewing and/or embroidery foot, which comprises for example an interchangeable sole  32  as shown in  FIG. 3 . The sensor  29  is shown in a partial cross-section in  FIG. 3 , so that essential elements on the inside are discernible. The design and operation of the sensor  29  are essentially equivalent to that of sensors used in laser computer mice. Such sensors have been developed, e.g., by the companies Logitech and Agilent, and are used in laser mice under the name “MX1000 cordless Laser Mouse”. A light source  33  in the form of a laser diode emits pulsed laser light. This light is radiated to the surface of the article to be detected via a display optic comprising a prism  35 . Using the display optic with the prism  35  and one or more lenses  37 , the surface of the article to be sewn, lit by the laser light, is imaged on an image sensor  39 . The sharpness of the imaging optic is high enough that the jumping motions of the sewing foot rod (not shown), at which the sewing foot  31  is fastened, developing during the embroidering process do not compromise the safe detection of the article  11  to be sewn. The sensor  29  can detect more than 6000 individual images per second. Using the movement and/or change in location of the structural features of images subsequently following one another, the image processing unit  30  calculates values, which characterize the oscillating behavior of the material  11  to be sewn and/or the material fastening device  13 , i.e., for example amplitude, frequency, and direction of oscillation components. For these calculations, advantageously an algorithm is used for a FFT (Fast Fourier Transformation). Alternatively, other calculations can be performed as well in order to yield data typical for the oscillation behavior. In these calculations, the portion of the measurement signals purely deductible from the predetermined target movement and not including any excessive oscillation components are filtered off. In general, sensors with light diodes can also be used as light sources  33  for detecting oscillations, similar to conventional optic mice. The scanning rate ranging from approximately 1000 Hz to 1500 Hz and the resolution of such sensors is at the lower range tolerable for a reliable detection of the oscillation. Better suitable are scanning ranges above 1500 Hz.  
         [0025]     The sewing or embroidery foot  31  can be connected to the machine control  9  via a connection wire  41  having a plug  42 , as shown in  FIG. 3 . Alternatively or in additional thereto wireless communication connections (radio, infrared light, etc.) and/or light conductors could be used as well.  
         [0026]     Instead or in addition to the optic detection of oscillations of the article  11  to be sewn or the material holding device  13  other physical measurements can also be used to characterize the oscillation behavior. Due to the fact that the cause of such oscillations is based on the acceleration of inert masses and/or the changes of the corresponding speed vectors and the elasticity of the materials used, such vibrations can also be detected indirectly via forces and/or torques. For example, force sensors  43  ( FIG. 4 ) can be arranged in the connection area of the fastener  17  and the material holding device  13 , which can detect dynamic pressure and/or tensile forces, preferably independent from their direction, thus for example piezo-elements or strain gauges. The forces measured are proportional in reference to the respective acceleration. When they occur periodically alternating in the opposite direction, the amplitude and frequency of said forces are equivalent to the amplitude and the frequency of the oscillation movement of the material holding device  13 .  
         [0027]     Pressure, force, or torque sensors  43  can also be mounted at other sites, at which forces equivalent to the vibrations of the material holding device  13  are to be expected, i.e. for example at the toothed belts  45 , which transfer the movement of the motors to the carriages  19 ,  21  or at the encircling wheels for the toothed belts.  
         [0028]     In another embodiment, electric measurements, such as e.g., current consumption or motor output, are controlled. Contouring errors and the corresponding forces can be deducted therefrom. In particular, the affecting forces can be determined indirectly and conclusions can be drawn from their cause.  
         [0029]      FIG. 4  shows a possible arrangement of force sensors  43  in the area of the connection site of the embroidery frame  13  to the second carriage  21  of the x-y-drive and/or at the connection site of the second carriage  21  with the corresponding toothed belt  45 . In  FIG. 4 , the embroidery frame  13  is shown separated from the carriage  21 . The fastening means  15  comprise two guiding grooves  47  and a spring-loaded fixing device  48 . When being placed onto the fastener  17 , the fixing device  48  is compressed against the effecting spring force. This way, the guiding grooves  47  are released and can be pushed over two holding pins  49  with protruding stops  49  embodied correspondingly. Here, the guiding groove  47  or the spring-loaded bar (not shown) of the fixing device  48  come into contact with the holding pins. Subsequently the fastening device  15  with the embroidery frame  13  is fixed at the fastener  17  in a form-fitting and/or force-fitting manner.  
         [0030]     During embroidering, the carriage  21  is moved from one stitching position to another in rapid succession. The accelerations and changes in direction, occurring in rapid sequences, of the embroidery frame and/or the material holding device  13  and the article  11  stretched therein can lead to undesired oscillations of the embroidery frame  13  interfering with the predetermined target movement. By evaluating the measurement signals of pressure, force, or torque sensors  43 , characteristic values can be calculated, which perhaps correspond to a certain phase lag of the mechanical oscillations of the embroidery frame  13 .  
         [0031]     Alternatively or in addition to the force sensors  43 , acceleration sensors  44  could also be used for detecting oscillations at the material holding device  13  and/or other elements mechanically coupled to the material holding device  13  of the embroidery device  1 . Preferably, such acceleration sensors  44  are mounted at the material holding device  13  at a distance as great as possible from the second carriage  21  of the driving device  18 . Based on the elasticity of the material holding device  13 , the greatest oscillation amplitudes can be expected here and the acceleration sensors  44  react most sensitively to these oscillations, here. Ideally, micro-mechanical acceleration sensors  44  are used. They can be produced in very small dimensions and do not hinder the embroidery process. Thanks to the low weight they hardly affect the oscillation behavior of the material holding device in a negative way. Due to the low power consumption it is possible to supply power to such micro-mechanical acceleration sensors  44  via small batteries, so that an electric connection to the driving device  18  and/or to the machine control  9  is not mandatory. Processing the measured signals can directly occur via the integrated sensor chip and the transmission of signals to the control  9  can occur via radio, for example. Of course, conducting connections for the power supply of the sensor  44  and for transmitting signals to the machine control  9  are possible, as well.  
         [0032]     The machine control  9  evaluates the measurement signals generated by the sensor(s)  29 ,  43 ,  44  and controls or adjusts the movements of the x-y-drive and the sewing needle  23  in a manner that the stitching positions of the sewing needle  23  are equivalent to the predetermined values saved. Here, the oscillations of the frame  13  and/or the article to be sewn  11  are determined and minimized and/or the stitching movements of the sewing needle  23  are temporally optimized, so that the stitching position can coincide as well as possible with the predetermined values even in vibrating frames  13 . The material holding device  13  with the article  11  stretched therein is an oscillating system based on the weight and the elasticity of the article  11  to be sewn. It is a component of a complex overall oscillation system, which sequentially comprises the following components: first motor, first transmission, first toothed belt  45 , first carriage  19 , second motor, second transmission, second toothed belt  45 , second carriage  21 , material holding device  13 , article to be sewn  11 . Therefore, the detection of the oscillations of the article to be sewn  11  in the immediate environment of the stitching site of the sewing needle  23  is the method least subjected to incidental or systematic faults.  
         [0033]      FIG. 5  shows schematically a control arrangement with an adaptive control  51  for controlling a motor M of the drive device  18 . The control  51  can be constructed, e.g., cascade-like. At the input side, the control  51  is fed, on the one side, with target values  53 , such as motor rotation or rotation angle of the motor, and, on the other side, the actual or measured dimension  55 , such as the motor rotation angle detected by a speed sensor, the position, and the acceleration of the article  11  to be sewn, or the forces determined by the force sensors  43 . At the exit side, adjustment values  57 , such as stepper-motor switches and phase and power values are forwarded to a power component  58  for controlling the motor M by the adaptive regulator  51 .  
         [0034]     Structural possibilities and effectiveness of the adaptive regulators are known, for example, from ISBN-3-527-25347-5 “Winfried Opelt: Kleines Handbuch der Regelungstechnik [Small Manual of Control Technology], chapter 65, pages 729-735 (automatic adjustments)”, or from the lectures “Einfuehrung in die adaptive Regelung [Introduction to the Adaptive Control], part I, “Parameteridentifikation” [parameter identification], 2003, by Dr. E. Shafal, Institut fuer Mess- und Regeltechnik of the Eidgenoessische Technische Hochschule.  
         [0035]     The control of current phase and switching points and/or the commutation of stepper motors with such adaptive controls is additionally advantageous in that the stepper motors can be operated under overload for a short period of time. Therefore, it is not necessary to size the motors to match individual extraordinary power peaks. In general, smaller and more cost effective stepper motors can be used.  
         [0036]     In an advantageous embodiment of the invention, a learning process is provided, by which connections and/or dependencies between certain motion patterns of the x-y-drives and the oscillation behavior of specific configurations of the material device  13  and an article to be sewn  11  are determined.  
         [0037]     Depending on the stretched article to be sewn  11 , the oscillation behavior can be different. Such learning processes are preferably performed with the sewing needle  23  being raised and inactive. For example, for both drives, certain sequences of alternating movements with one or more different amplitudes can be performed independent from on another and with a series of predetermined oscillating frequencies. When the control  9 , based on sensor signals, determines an excessive oscillation of the frame  13  and/or the article to be sewn  11 , one or more parameters of the control frequency are varied until the amplitude of the oscillation falls below a predetermined limit. A series of suitable control parameters results depending on the control frequency. In stepper motors, for example, such control parameters are the number of support sites used with the respective predetermined target values for the number of steps per time unit. The control parameters determined in this manner can be saved in a storage unit of the control  9  or in another storage medium.  
         [0038]     In a suitable embodiment of the storage unit, different sets of control parameters can be determined and saved for different types of articles to be sewn.  
         [0039]     In drives using servomotors, usefully optimized control parameters can be determined.  
         [0040]     Learning processes can alternatively occur directly during embroidering as well. Here, it is accepted that slightly higher deviations of the stitching positions from the predetermined target position can occur in individual points of the article to be sewn  11 .  
       List of Reference Characters  
       [0000]    
       
           1  Embroidery device  
           3  Sewing machine  
           5  Embroidery module  
           7  Connection wire  
           9  Sewing machine control  
           11  Article to be sewn  
           13  Material holding device (Embroidery frame)  
           15  Fastening means  
           17  Holder  
           18  Driving device  
           19  First carriage  
           21  Second carriage  
           22  Guiding rod  
           23  Sewing needle  
           25  Machine head  
           27  Needle rod  
           29  Optic sensor  
           30  Image processing unit  
           31  Sewing foot  
           32  Sole  
           33  Light source  
           35  Prism  
           37  Lenses  
           39  Image sensor  
           41  Connection wire  
           42  Plug  
           43  Force sensor  
           44  Acceleration sensor  
           45  Toothed belt  
           47  Guiding grooves  
           48  Fixing device  
           49  Holding pin  
           51  Adaptive control  
           53  Target values  
           55  Measurement values  
           57  Guiding values  
           59  Power component