Classifications

• • D—TEXTILES; PAPER
  • D05—SEWING; EMBROIDERING; TUFTING
  • D05B—SEWING
  • D05B69/00—Driving-gear; Control devices
  • D05B69/22—Devices for stopping drive when sewing tools have reached a predetermined position
  • D05B69/24—Applications of devices for indicating or ascertaining sewing-tool position

Definitions

• the invention relates to a method and an arrangement for detecting a workpiece edge carrying out a relative movement with respect to a detection location according to the preamble of claim 1 and claim 7, respectively.
• a method and an arrangement of this type is known from US Pat. No. 4,829,194 and can be used in sewing machines can be used to feel the edge of a fabric layer and to control the operation of the machine accordingly.
• the preferred but not exclusive field of application of the present invention is also
• a problem with the automatic detection of workpiece edges using optical measuring devices such as light barriers are the changing boundary conditions of the measurement. In addition to interference such as ambient light, this also includes the different initial conditions before the workpiece edge appears at the detection location. If, for example, the end edge of a substance is to be detected, it will be on before the substance arrives
• the location of the light measured depends very much on the nature of the material such as density and color.
• an adjustment device which optimally adjusts the measuring range of the light measuring device and / or the threshold value at which the edge sensing signal is to be triggered during an adjustment phase before the workpiece edge is expected to arrive.
• the adjustment process during the adjustment phase consists in bringing the measurement signal to a certain reference value above a minimum value by computer-controlled gain control and then setting a display threshold by a certain amount above this reference value. The end edge sensing signal is emitted when the measurement signal exceeds this display threshold.
• the one workpiece part (for example the one for one Transmitted light measurement "lighter” single-layer section of the fabric package) is moved over the detection location, and the extreme values of the fluctuations in the measurement signal, ie maximum and minimum, are determined and stored in a first pair of memories. Then the other part of the workpiece (e.g. for
• Transmitted light "darker" two-layer section of the material package is moved over the detection location in order to determine the extreme values of the measurement signal and to store them in a second pair of memories.
• the "darkest" value of the lighter workpiece part and the “lightest” value of the darker workpiece part are then selected for further processing in order to use these values to calculate a threshold which lies between the two values and is defined by an upper and a lower threshold value.
• These two threshold values are set on a comparison device, which receives the measurement signal in the detection phase and generates the edge sensing signal whenever the measurement signal crosses both threshold values in succession.
• the object of the present invention is to reduce the effort to be carried out for the implementation of the edge detection method.
• This object is achieved according to the invention by method features as characterized in claim 1.
• the essential features of an arrangement for performing the method according to the invention are listed in claim 7.
• the invention is based on the knowledge that it is sufficient for the usual cases of edge detection in practice to take into account only the (inhomogeneity-related) brightness extremes of the workpiece part lying in front of the edge and to only consider the lighting conditions behind the edge to the extent that the detection threshold is determined they provide information about the direction of change of the measurement signal when the edge is crossed, for which purpose no extreme value determination is required for this workpiece part.
• the extreme value in the opposite direction is also included in the threshold calculation algorithm.
• the extreme values deflecting in the opposite direction are also determined in the known method, but they are not included in the threshold calculation itself, but only serve to find out the other extreme value deflecting in the predetermined direction by comparing sizes.
• the method according to the invention brings several advantages over the prior art.
• the omission of the extreme value analysis of the workpiece part lying behind the edge shortens and also simplifies the adjustment phase as a whole.
• the workpiece does not have to be moved back and forth during the adjustment phase, because since the extreme value detection is limited to the workpiece part lying in front of the edge, the workpiece movement required during the adjustment phase can be rectified and continuous with the workpiece movement during the subsequent detection phase.
• the adjustment phase and the subsequent transition to the detection phase can even take place during the machining of the workpiece without interruption or other influencing of the workpiece feed.
• the arrangement can optionally be switched between a transmitted light measurement and a reflected light measurement.
• the measurement of reflected light is e.g. B. more advantageous for the detection of the end edge of a very dense material such. B. leather, or the edge of a fabric that is on a very dense layer of fabric.
• the measurement that brings the stronger measurement signal during the adjustment phase is always switched on.
• Fig. 1 shows two layers of fabric lying partially one above the other, which have a pronounced inhomogeneity, and below that a diagram of the light transmitted at the different locations of the two layers;
• FIG. 2 shows in the form of a block diagram an embodiment of an arrangement according to the invention
• Fig. 3 shows the basic structure of a combined transparent / reflective light barrier.
• the layers of fabric 1 and 2 shown in the upper part a) have a pronounced inhomogeneity in the form of alternating light and dark areas A and B. This inhomogeneity can e.g. B. by a color pattern or by changing the structure of the fabrics.
• the upper fabric layer 1 ends with a pronounced edge 3.
• the output-side measurement signal of the light barrier takes a course as it does in lower part b) of FIG. 1 is shown.
• the measurement signal amplitude is relatively low; it fluctuates between a maximum U j , caused by the bright areas A, and a minimum U £, caused by the dark areas B.
• the intensity of the transmitted light and thus the amplitude of the measurement signal changes to higher values, because from now only the lower layer of fabric 2 is penetrated.
• the measurement signal fluctuates between a much higher minimum U ' j and a far higher maximum U ⁇ «
• the diagram in FIG. 1b is run through from right to left.
• the measurement signal U thus initially fluctuates between the lower extreme value U ' ] _ and the upper extreme value U ⁇ , in order then to drop even lower than the previous lower extreme value U' 2 when the edge 3 appears. After this, the measurement signal fluctuates between the lower extreme values U j and U £.
• a light barrier which contains a light source in the form of a light-emitting diode 13 and a light sensor in the form of a photodiode 14.
• the workpiece whose edge is to be detected is moved between the light emitting diode 13 and the photodiode 14.
• the light barrier consisting of light-emitting diode 13 and photodiode 14 can also be moved relative to the stationary workpiece in order to determine the position of the workpiece edge.
• the workpiece consists of the inhomogeneous material 1 on a further inhomogeneous layer of material 2, as already shown in more detail in FIG.
• the photodiode 14 captures that portion of the light emitted by the light-emitting diode 13 that penetrates through the workpiece and leaves a corresponding one at the output of a measuring amplifier 15
• the light emitting diode 13 is modulated via a driver amplifier 12 by an oscillator 11 at a predetermined frequency, and the output signal of the measuring amplifier 15 is passed via a bandpass filter 16 tuned to this frequency to a synchronous rectifier 17 which is synchronized with the oscillator frequency.
• a delay element 18 inserted between the oscillator 11 and the synchronous rectifier 17 serves as a runtime compensation so that the synchronizing signal appears with exactly the right phase on the synchronous rectifier.
• the light modulation and subsequent synchronous rectification serve to suppress external influences.
• a downstream low-pass filter 19 smoothes the rectified measurement voltage, which then passes through a changeover switch 20, the function of which is described below, to an analog / digital converter 21 in order to display the measurement signal U in the form of successive digital samples.
• this measurement signal changes approximately as shown in FIG. 1b.
• the measurement signal U reaches a first input of a digital comparator 25, which receives a threshold value 3 at a second input.
• the comparator 25 supplies a signal K on the output side which is intended to indicate the appearance of a workpiece edge in the light barrier (edge detection signal).
• a comparison device which contains an extreme value detection device 22 and a threshold value setting device 23 and can be activated by a program switching device 26 during an adjustment phase before the workpiece edge appears.
• the extreme value detection device 22 receives the successive samples of the measurement signal U and a direction signal R which indicates the direction of the measurement signal change occurring at the expected edge.
• the extreme value detection device 22 determines the extreme value U j , which deflects in the direction indicated by the direction signal, and the extreme value U 2 , which deflects in the opposite direction, from the samples of the measurement signal U that arrive during the adjustment phase.
• the determined extreme values U j and U 2 are processed in the threshold value setting device 23 in order to bring the threshold value ⁇ i- to a level which, on the one hand, is beyond the extreme value U- in the direction indicated by the direction signal R, but on the other hand is still close enough that it is surely achieved by the measurement signal deflection when the edge appears.
• m is a positive factor less than 1. It has been shown that a generally valid value can be determined statistically for this factor, which is equally satisfactory for a wide variety of conditions. This value is preferably 0.25.
• U j and U 2 are assigned to the two extreme values in the manner described above (U j for the extreme value deflecting in the indicated direction and U for the extreme value deflecting in the opposite direction) »
• a second light sensor in the form of a phototransistor 14a is shown, which receives the portion of the light emitted by the light emitting diode 13 that is reflected by the workpiece at the detection location.
• This phototransistor is also followed by a measuring amplifier 15a, a bandpass filter 16a, a synchronous rectifier 17a and a low pass filter 19a, the function of which is the same as the function of the elements 15, 16, 17, 19 behind the output of the photodiode 14.
• the output from the low pass filter 19a Signal that corresponds to the light reflected from the workpiece at the detection location may be better suited than the "transmitted light signal" provided by the low-pass filter 19, the edge of a workpiece such as. B. to detect the edge 3 of the fabric layer 1, for example when the layer 2 is opaque material such as leather and consequently the photodiode 14 receives light neither before nor after the edge. Even if layer 1 had little or no light transmission, edge detection by means of light measurement would be problematic at least if the end edge is to be detected. In such cases, you should switch to reflected light measurement.
• the Switching criterion can be obtained from an amplitude comparison of the transmitted light signal and the reflected light signal.
• An amplitude discriminator 30 serving this purpose which receives the output signals of the two low-pass filters 19 and 19a, can be activated at the beginning of the adjustment phase in order to set the changeover switch 20 to the output which delivers the measurement signal of higher amplitude.
• the switch setting can of course also be done manually when the operator is shown which measurement signal is the stronger, or when the operator has sufficient experience to look at the
• the decision about the direction signal R must also be made, because it also depends on the type of measurement in which direction the measurement signal is expected to deflect when the edge appears. This decision is not difficult, because it is easy to estimate with the eye whether the workpiece appears darker or lighter after the edge than before the edge for the relevant measurement type.
• the measurement type selected in each case is advantageously displayed.
• a further embodiment can consist in that the amplification factor of the driver amplifier 12 and / or the measuring amplifier 15 can be adjusted in order to bring the measuring signal U into the most favorable measuring range at the beginning of the adjustment phase. This is indicated by the control inputs S j and S M on the relevant amplifiers.
• the control signals S ⁇ and S M for the amplifiers can be supplied by a controller arrangement 27 which receives the measurement signal U as the actual value and a value representing the center of the desired measuring range as the setpoint.
• the extreme value detection circuit 22, the threshold value setting device 23, the comparator 25 are the Program switching device 26 and the controller arrangement 27 are shown as discrete assemblies, which can each be implemented by hard-wired circuits. The functions of some or all of these elements can, however, also be implemented by a digital microcontroller with appropriate software, as indicated by the dashed frame 40. Such a microcontroller is preferably used instead of discrete circuits.
• the workflow of the edge detector shown in FIG. 2 is described below, both in a first embodiment with "manual” adjustment and in a second embodiment with “automatic” adjustment, both using the example of a sewing machine where the end edge 3 of the fabric layer 1 to be detected over the cloth area 2. It is assumed that the light barrier is switched on, the direction is selected and only the light measuring section 14, 15, 16, 17, 19 is present and the analog / digital converter 21 receives the output signal from the low-pass filter 19. First, the operator places the lower fabric layer 2 at the detection location in the light barrier. Then the driver amplifier 12 and the
• Measuring signal amplifier 15 is initially set to minimum gain, and then the driver amplifier 12 is turned up until the measuring signal U falls within the desired measuring range. If this range is not reached even with the maximum gain setting of the driver amplifier 12, then the gain of the measuring amplifier 15 is then ramped up in order to reach the measuring range. All of this can be done fully automatically with the aid of the program switching device 26 and the controller arrangement 27 or by means of the microcontroller.
• the same procedure can also be carried out with this measuring section with the changeover switch 20, for example if it becomes apparent that the measuring range of the transparent measuring section cannot be reached.
• This switchover can also take place automatically.
• Both measuring sections can also be tried out independently of one another, in order then to select the one in which the measuring range is reached earlier (ie with less amplification).
• this takes place automatically if the amplitude discriminator 30 always switches the changeover switch 20 to the measuring section which supplies the stronger output signal.
• the extreme value detection circuit 22 supplies the two extreme values U j and U 2 'of the measurement signal U that has appeared until then to the threshold value setting device 23, which then in turn sets the threshold value U- at the comparator 25 according to the algorithm described above . This ends the adjustment process, and the extreme value detection circuit 22 is switched off and the threshold value setting device 23 is shut down.
• the operator can now start the sewing machine for sewing the two layers of fabric 1 and 2, the comparator 25 also being switched on at the same time, and as soon as the end edge 3 appears at the detection location, the edge sensing signal K is emitted, which can cause the sewing machine to start sewing on it End edge.
• the "automatic" adjustment differs from the manual adjustment described above essentially in that the operator does not have to move the fabric layers separately by hand before the sewing process and does not have to press a key.
• the operator puts on a single or two fabric layers 1, 2 aligned in the correct position and immediately starts sewing.
• the control command for inhomogeneity adjustment which activates the extreme value detection device 22 is triggered when the machine is started and at the same time starts a counter (not shown) which counts the sewing stitches carried out.
• the threshold value setting device 23 is activated in order to set the threshold value ⁇ ⁇ at the comparator 25 on the basis of the extreme values U ⁇ and U 2 or U ⁇ 'and U 2 ' determined up to that point.
• the comparator 25 is then switched on, and the threshold value setting device and the extreme value detection device are stopped, so that the edge feel signal K can be emitted in the further course of the sewing process when the fabric edge 3 appears at the detection location.
• the preset count value on the stitch counter is advantageously dimensioned such that it is at least equal to the number of stitches which corresponds to a feed over a period length of the inhomogeneities (e.g. repeat length).
• the direction signal transmitter is a bistable flip-flop, the state of which is changed by the edge-sensing signal. In this way it is also possible to grasp a large number of successive front and end edges of workpieces one after the other without any intermediate adjustments by hand or interruptions being necessary.
• FIG. 3 shows an embodiment of a combined transmitted light / reflex light barrier, as can be used in the arrangement according to FIG. 2.
• a photo receiver such as e.g. B. the photodiode 14 shown in FIG. 2
• a so-called reflex sensor 52 is arranged at a certain distance above the base 50, which emits and receives light.
• This reflex sensor can, for. B. the light emitting diode 13 and the phototransistor 14a, these two elements lying closely together are both aligned on the base 50, but are shielded from direct radiation from each other.
• Glass fiber optics or a reflex coupler can also be used as a reflex sensor.
• the distance between the reflex sensor 52 and the base 50 is chosen so that the material with the edges to be detected such as. B. the layers of fabric 1 and 2 can be moved through well (in the case of a sewing machine, for example, about 5 mm).

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Textile Engineering (AREA)
• Sewing Machines And Sewing (AREA)
• Cooling Or The Like Of Electrical Apparatus (AREA)
• Length Measuring Devices By Optical Means (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6391818

Family Applications (1)

Country Status (3)

Families Citing this family (7)

Family Cites Families (5)

• 1989
  • 1989-10-20 DE DE19893934933 patent/DE3934933A1/de active Granted
• 1990
  • 1990-10-19 WO PCT/EP1990/001770 patent/WO1991005901A2/de unknown
  • 1990-10-19 JP JP2514250A patent/JP2892830B2/ja not_active Expired - Fee Related

Also Published As

Similar Documents

Legal Events