The invention is directed to a method and a device for minimizing stitching faults in embroidering devices.
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.
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.
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.
This object is attained in a method and a device for minimizing stitching faults in embroidery devices according to the present invention.
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.
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.
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.
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.
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.
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.
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.
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.
In the following, the invention is explained in greater detail using the drawing figures. In the drawings:
In
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 (
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.
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.
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
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
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 (
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In drives using servomotors, usefully optimized control parameters can be determined.
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.
Number | Date | Country | Kind |
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01047/05 | Jun 2005 | CH | national |