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 a device for recognizing a sewing material edge by an optoelectronic sensor arranged on a sewing machine according to the preamble of patent claim 1 and of patent claim 6.
• Edge sensors which work in an optoelectronic manner in order to detect a material edge directly in front of the stitch formation point of the sewing machine when transporting the material are known.
• Common principle of action is the exploitation of the fact that the optical property of an upper layer of sewing material differs from that of a lower layer of sewing material, so that the lighting conditions at the detection location change suddenly as soon as the edge of the sewing material of the upper layer of sewing material appears at the detection location during the sewing process.
• the area immediately in front of the stitch formation point is illuminated and the output variable of a light receiver directed at this detection location is monitored in order to detect abrupt changes that indicate the appearance of a sewing material edge.
• This detection can be done in different ways, mostly by comparison with some kind of reference value, which is either set in a separate adjustment phase beforehand (German Offenlegungsschrift 3606208) or obtained by averaging the previous output signal (German Offenlegungsschrift 3224314) or from the output of a second one Light receiver originates, which is aimed at a point just before the detection location (German Patent 3323214).
• some kind of reference value which is either set in a separate adjustment phase beforehand (German Offenlegungsschrift 3606208) or obtained by averaging the previous output signal (German Offenlegungsschrift 3224314) or from the output of a second one Light receiver originates, which is aimed at a point just before the detection location (German Patent 3323214).
• the material, the edges of which are to be scanned, can be such that there is very little or no light passes on to the light receiver.
• the output signal of the light receiver can be too weak, even with the maximum setting of the illuminance and the measurement amplification, in order to enable reliable edge detection.
• the edge detectors described in the above-mentioned publications fail. In this case, the light receiver does not deliver any noteworthy output signal from which a reference value for the edge detection could be derived before the edge of the material to be sewn appears. Then there is also no possibility of bringing the output signal of the light receiver into the optimum measuring range for edge detection.
• the material to be sewn is one or more layers and at least one of the material layers is made of leather or dense felt, for example. If this layer of material also represents the base on which another layer of material is to be sewn, then neither the front edge nor the end edge of this other material can be detected, because there is no change in light on the receiver at any of these material edges.
• the object of the invention is to provide a method and a device for optoelectronic detection of sewing material edges so that the reliability of the exact detection can be less affected than before by the nature of the sewing material at the detection location. According to the invention, this object is achieved by the characterizing features of patent claim 1 and of patent claim 6.
• Intensity measurement value is generated and not, as in the case of the latter publication, at the location of the peak value of a symmetrical intensity distribution. Furthermore, transmitted light and reflection light are measured separately in the invention, and only one of these measurements is evaluated to generate the edge detection signal, while in the known case the total intensity of a superimposition of transmitted light and reflected light is evaluated.
• the decision as to whether the transmitted light measurement or the reflected light measurement is used for the generation of the edge signal depends, in the method according to the invention, on which measured value is expected to make the more distinguishable jump when the material edge to be detected is at
• Detection location appears. In many cases this can easily be predicted. It is preferable to select the measurement whose measured value has the higher amplitude when the material edge has not yet appeared. With this, the method can be easily automated, and preferably already by means of a pre-adjustment, in which the illuminance or the measurement signal amplification is increased from a low value for setting the measurement range, until the measurement signal falls within the desired measurement range. This comparison and thus also the decision about the measurement to be selected in each case can advantageously be carried out again after detection of a material edge in order to create the optimal conditions for the reliable detection of a subsequent material edge.
• FIG. 1 shows the front view of a sewing machine with a sewing material scanning device
• Fig. 2 shows the side view of the sewing machine with the basic structure of a combined transmitted light / reflex light barrier
• Fig. 3 is a block diagram of the circuit for the arrangement according to the invention.
• FIG. 1 shows a sewing machine 1 which has a stand, an upper arm and a head and a fabric support plate 1 a which is fastened in a cutout of a table top 2 a of a sewing machine frame 2 and by a sewing motor 3 fastened below the table top 2 a via a V-belt 4 is driven.
• the head of the sewing machine 1 has the usual presser bar 5 (FIG. 2) which carries a presser foot 6 which lies on the material to be processed and is arranged behind the usual needle bar 7 driven by the sewing motor 3. This carries a needle 8 which one through a tap hole 9a in the
• Fabric support plate la arranged stitch plate 9 cooperates with a thread catcher, not shown, also synchronously driven in a known manner to the needle bar 7.
• a light barrier is arranged in front of the working area of the needle bar 7, which has a light source in the form of a light-emitting diode 13, a first light sensor in the form of a photodiode 14 and a second light sensor in the form of a photo transistor 14a contains.
• the light-emitting diode 13 and the phototransistor 14a are arranged in a reflex button 10 attached to the head of the sewing machine 1 in front of the stitch-forming point, the light-emitting diode 13 and phototransistor 13a being closely aligned with the stitch plate 9, but against direct radiation from one another are shielded. Glass fiber optics or a reflex coupler can also be used as a reflex sensor.
• the distance between the reflex button 10 and the throat plate 9 is selected, for example about 5 mm, that the two layers of material N1 and N2 can be moved through well.
• the photodiode 14 is accommodated in a cutout 9b of the throat plate 9.
• the sewing material whose edge is to be scanned moves between the light-emitting diode 13 and the photodiode 14.
• the sewing material consists of two sewing material layers, an upper sewing material layer N1 and a lower sewing material layer N2, which are to be sewn together.
• the photodiode 14 captures that part of the light emitted by the light-emitting diode 13 which penetrates through the layers of material N1 and N2 and causes a corresponding voltage to appear at the output of a measuring amplifier 15.
• the light emitting diode 13 is preferably switched on by a driver amplifier 12
• Oscillator 11 modulated with a predetermined frequency, and the output signal of the measuring amplifier 15 is passed through a bandpass filter 16 tuned to this frequency to a synchronous rectifier 17 which is synchronized with the oscillator frequency.
• a bandpass filter 16 tuned to this frequency to a synchronous rectifier 17 which is synchronized with the oscillator frequency.
• Synchronous rectifier 17 inserted delay element 18 serves as a runtime compensation so that the synchronization signal appears with exactly the right phase on the synchronous rectifier.
• the light modulation and subsequent synchronous rectification serve to suppress external influences and make complex optics unnecessary.
• a downstream low-pass filter 19 smoothes the rectified measuring voltage, which is then switched to a switch 20, the function of which is described below
• Analog / digital converter 21 arrives in order to display a measurement signal U in the form of successive digital samples.
• the digitized measurement signal U arrives at an input of a processing device 40 which e.g. can be realized by a digital microcontroller.
• This processing device 40 monitors the temporal course of the signal U and, in the event of a sudden change in this signal, which indicates the appearance of a material edge W, on the output side an edge detection signal K.
• the processing method used for this can be arbitrary and therefore does not need to be described in more detail; some possible examples from the prior art have already been indicated above. However, it is always a prerequisite that the jump in the measurement signal U is sufficiently pronounced when a material edge W appears to distinguish it from other measurement signal fluctuations.
• the phototransistor 14a of the light barrier is arranged in such a way that it receives the portion of the light emitted by the light source 13 which is reflected by the upper layer of material N1.
• This phototransistor is also followed by a measuring amplifier 15a, a bandpass filter 16a, a synchronous rectifier 17a and a lowpass filter 19a, the function of which is the same as the function of the elements 15, 16, 17 and 19 behind the output of the photodiode 14.
• the output from the lowpass filter 19a Signal which corresponds to the light reflected from the upper layer of material Nl may be better suited than the "transmitted light signal" provided by the low-pass filter 19 to detect the edge of the material W of the layer of material Nl if the material N2 is made of an opaque material, e.g. B. consists of leather and consequently the photodiode 14 receives light neither before nor after the material edge W.
• An edge detection by means of transmitted light measurement would be at least then even if the layer of material N2 has little or no light transmission problematic 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 comparator 30 serving for this purpose which receives the output signals of the two low-pass filters 19 and 19a, can be activated before the possible appearance of the material edge W in order to set the changeover switch 20 to the output that delivers the measurement signal of higher amplitude.
• the switch setting can of course also be carried out manually if the operator is shown which measurement signal is the stronger, or if the operator has sufficient experience to decide for himself which type of measurement is to be preferred when considering the nature of the material to be processed.
• the measurement type (transmitted light or reflected light) can also be selected in connection with a measurement range setting in which the illuminance at the detection location and / or the measurement signal gain are adjusted in a preparatory adjustment process so that the measurement signal falls within the most favorable measurement range.
• the gain factor of the driver amplifier 12 and / or the measuring amplifier 15, 15a can advantageously be set. This is indicated by the control inputs Sy and S M on the relevant amplifiers in FIG. 3.
• Control signals S- j * and S M for the amplifiers can be supplied by a controller arrangement which receives the measurement signal U as the actual value and a value in the desired measuring range as the setpoint.
• a corresponding control mechanism is preferably implemented using special software in the processing direction 40.
• the control signals S - * - and S- j can be supplied in digital form to corresponding digital setting devices in the driver amplifier 12 or in the measuring amplifiers 15 and 15a.
• the changeover switch 20 can first be set to any of the two measuring sections 14-19 and 14a-19a, for example to the transmitted light measuring section 14-19 (shown position of the changeover switch 20).
• the driver amplifier 12 and the measuring amplifier 15 are initially set to minimal 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 started up to reach the measuring range. All of this can be done fully automatically with the aid of the processing device 40.
• the same procedure can then be carried out with the changeover switch 20 also with the other measuring section, for example if it turns out that the measuring range cannot be reached with the transmitted light measuring section.
• This switchover can also take place automatically.
• Both measuring sections can also be tried out independently of one another in order to then select the one in which the measuring range is reached earlier (i.e. lower gain).
• this takes place automatically if the amplitude comparator 30 always sets the changeover switch 20 to the measuring section which supplies the stronger output signal.
• a common measuring channel can be used, the input of which can be switched between the two light sensors 14 and 14a.
• a measurement value memory can be provided in the processing device 40, possibly with associated display devices. The two types of measurement would then be tried out in succession or quasi-parallel in a kind of time-division multiplex.
• two separate light barriers each with its own light source, can be used. These two light barriers would then preferably be arranged next to one another transversely to the relative movement of the object and, if desired, could be operated with different light change frequencies.
• two light transmitters it is also possible to have two light transmitters on opposite sides of the object
• Provide light receiver that receives the transmitted light from one light source and the reflected light from the other light source.
• one of the light transmitters must be switched on and the other switched off for separate measurement of transmitted light and reflection.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Textile Engineering (AREA)
• Sewing Machines And Sewing (AREA)
• Length Measuring Devices By Optical Means (AREA)

Applications Claiming Priority (4)

Publications (2)

Family

ID=25886276

Family Applications (1)

Country Status (3)

Cited By (1)

Family Cites Families (5)

• 1990
  • 1990-09-29 DE DE19904030854 patent/DE4030854A1/de active Granted
  • 1990-10-19 JP JP2514737A patent/JP2960777B2/ja not_active Expired - Fee Related
  • 1990-10-19 WO PCT/EP1990/001771 patent/WO1991005902A2/de unknown

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