JPH10281719A - Method for detecting border line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a highly accurate measurement even when objects having different reflectance are delivered sequentially by arranging the planes including, respectively, the light projecting axis and the light receiving axis of a reflective photoelectric sensor for detecting variation in the center of gravity of a reflected light on a light receiving element in parallel with each other in the moving direction, subtracting a light receiving signal and controlling the moving speed or the interval from the difference of detection time of a border line. SOLUTION: An LED 2 and a split-half PD 5 are provided and a light receiving signal of the split-half PD 5 is passed through a dividing circuit 11 at a processing circuit section 10 before being outputted. The LED 2 and the split-half PD 5 are arranged in parallel in the moving direction. Since a signal rising/ falling steeply is produced after division, a highly accurate positioning is realized. In order to position a border line, a divided signal is inputted to a comparator and compared with a threshold value. The waveform of a divided output may fluctuate in level due to combination of reflectance of the objects but the shift of positional intersecting the threshold is small when the waveform is steep and the positioning error is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boundary line detection method for detecting, with high accuracy, a boundary line generated by a difference in reflectance on a moving body by a reflection type photoelectric sensor.

[0002]

2. Description of the Related Art Conventionally, as a technique for detecting a linear mark, one using two light-receiving elements and taking the difference between the outputs of the light-receiving elements, or using a two-division photodiode and receiving light output from each of the divided photodiodes It is known to take the difference of

[0003]

In the above-described conventional method for detecting a boundary line of a mark or the like, in the method based on the output difference between two light receiving elements, the optical system is so arranged that the reflected light straddles a plurality of light receiving elements. Must be set, so that the light receiving beam needs to be enlarged. Since a plurality of light receiving elements are used, the optical system head is greatly complicated. Since the linear mark is detected from the difference, the rising or falling characteristics of the difference output depend on the reflectance of the object. Therefore, there is a problem that high-precision positioning cannot be performed in an application in which objects having different reflectivities are sequentially sent. In addition, the above-mentioned problem also occurs in a method of obtaining the output difference between the two-part photodiodes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a boundary line detection method capable of detecting a boundary line with high accuracy even when objects having different reflectances are sequentially sent. And

[0005]

According to a first aspect of the present invention, there is provided a method for detecting a boundary line, comprising the steps of: detecting a moving object having a boundary line caused by a difference in reflectance; A plane including the light projecting axis and the light receiving axis of the reflective photoelectric sensor that detects a change in the center of gravity of the reflected light is arranged in parallel to the moving direction,
The moving speed or the interval is controlled based on the detection time difference of the boundary line by dividing the light receiving signal.

According to a fifth aspect of the present invention, there is provided a method for detecting a boundary line, comprising:
A parallel structure is arranged on the surface of the moving object so that the boundary line caused by the difference in the reflectivity of the line is orthogonal to the moving direction, and the boundary line includes the light emitting axis of the photoelectric sensor and the normal to the light receiving surface of the light receiving element. The detection method of the light receiving element is set to be parallel to the moving direction of the moving body.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a sectional view of a sensor head of a reflection type photoelectric sensor which is a displacement sensor used in a linear mark detection method according to an embodiment of the present invention. In FIG. 1, light from an LED 2 serving as a light projecting element housed in a case body 1a is applied to an object 3 moving in a direction perpendicular to the light projecting axis (the direction of arrow P in the figure), and reflected light thereof Are provided through a slit 4 provided in an upper portion of the case body 1a, and are provided as light receiving elements 2 provided in the case body 1a.
The light is received by the divided PD (photodiode) 5. This 2
The split PD may be a PSD element.

The sensor head 1 determines the distance of the object 3 from the change in the center of gravity on the light receiving element in a plane (parallel to the paper) including the normals of the light projecting axes A and B and the light receiving surfaces a and b. Detection is performed based on the principle of triangulation, that is, based on triangle abO and triangle ABO. In this case, it is a condition for outputting an accurate distance that the light source has a uniform reflectance within the projected spot diameter on the target 3.

However, as shown in FIG. 2, if there is a portion Q having a different reflectivity (here, low reflection) within the projected spot diameter on the object 3, a change in the center of gravity on the light receiving element 5 will occur. And the output changes even though the distance is constant. For this reason, the accuracy of boundary line detection deteriorates. The boundary line detection method of this embodiment detects the boundary line such as a linear mark with higher accuracy in consideration of this phenomenon than in the case of using the conventional reflection type photoelectric sensor.

For this reason, in this embodiment, the circuit shown in FIG. 3 is used as post-processing of the sensor head section in FIG. 3, an LED 2 and a two-part PD 5 are provided in the sensor head unit 1 as in the case of FIG.
The light receiving signal of D5 is divided by the division processing circuit 11 of the processing circuit unit 10.
Is output after being subjected to division processing. Note that transistor 1
Reference numeral 2 denotes a transistor for driving LED2.

Here, a division circuit is used for processing the received light signal.
The reason for using will be described. FIG. 4A shows a light receiving element.
FIG. 4 (b) is an explanatory view in the case of using a PSD as an example.
FIG. 4 is an explanatory diagram when a two-segment PD is used as an optical element;
In either case, the output current is I ₁, I_Two, Element width L, figure
4 (a), the position of the center of gravity is x, on the light receiving element of FIG.
Is the beam diameter at Bw, and the incident light beam enters the center
The distance from the inside of the split PD to the beam spot end
x, each output current I₁, I_TwoRemove with
In the case of the PSD shown in FIG.

[0012]

(Equation 1)

And the two-divided PD shown in FIG.
in the case of,

[0014]

(Equation 2)

In any case, the position of the center of gravity can be obtained without depending on the amount of reflected light. In the case shown in FIG. 2, as shown in FIG. 5A, when the light beam width Bw is fixed and the object moves from right to left, the differential processing is performed as in the related art. FIG. 5B shows the output of FIG. 5 when the division processing is performed as in the embodiment of the present invention. In FIG. 5B and FIG. 5C,
As shown in FIG. 6, the positions of,... Indicate when the boundary reaches the end of the projection beam, when the boundary reaches the center of the projection beam, and when the boundary passes through the projection beam. I have.

As shown in FIG. 5B, when the division processing is performed, the rising and falling of the signal become steeper than in the case of the differential processing shown in FIG. 5C. Therefore, positioning can be performed with high accuracy. The reason why the steeper the waveform is, the more accurate the positioning can be described. In order to position the boundary line, finally, the signal subjected to the division processing is input to a comparator, and it is determined whether the signal is above or below a certain threshold. It is conceivable that the waveform of the decalculation force may move up and down in a level depending on the combination of the reflectances of the target object.However, if the waveform is steep, the position crossing the threshold is slightly shifted even if the waveform is moved up and down, Low positioning error. That is, the positioning accuracy is good. in this case,
If the difference between the reflectances is small, ΔV becomes small in the differential processing, so that the signal rises slowly. However, if the division processing is performed, the rise of the signal is affected.
Since the fall is steep, positioning can be performed with high accuracy as described above. However, the description in FIGS. 5 and 6 is based on the case where the size W of the object is equal to or larger than the light projection beam diameter Bw.

Next, a case where the size W of the target object is smaller than the diameter Bw of the projection beam will be described with reference to FIGS. FIG. 7A shows a case where an object having a width W moves from right to left with respect to a projected beam having a beam diameter Bw, and FIG. 7B shows a process of dividing a received light signal. FIG. 7C shows the output when the received light signal is subjected to the differential processing. In addition, (b) of FIG.
And (c) of FIG. 7, the position of...
As shown in FIG. 8, the position at which the boundary 1 of the object reaches the front end of the projection beam, the position at which the center of the object reaches the front end of the projection beam, and the object at the front end of the projection beam Is the position at which the center of the object reaches the center of the projection beam, is the position at which the boundary 1 of the object reaches the rear end of the projection beam, and The case where the center of the object has reached the rear end indicates the position where the boundary 2 of the object has reached the rear end of the projection beam.

In this case, the steepness of the rise and fall of the signal appears to have no difference, but in the case of the differential processing, it is difficult to determine because the change ΔV in the amount of reflected light is extremely small. Difficult in practice. Further, when the reflectance difference is reduced, ΔV is further reduced, so that it becomes more difficult to determine the boundary line. On the other hand, in the case of the division processing, the waveform shown in FIG. 7B can be maintained even if the reflectance difference is small, so that the positioning can be performed with high accuracy.

FIG. 9 is a diagram showing an application example in which the position of toner on a drive belt in a copying machine is detected by using a reflection type photoelectric sensor comprising the optical head shown in FIG. 1 and the circuit of FIG. It is. Yellow, magenta, cyan, and black transfer positions 22, 23, 24, and 25 on transfer belt 21
Is the reflection type photoelectric sensor 2 due to the movement of the transfer belt 21.
6 outputs the signal waveforms shown in FIG. 10 from the division processing circuit 11, respectively, and it is possible to perform high-precision positioning using these signals. That is, the detection time difference of the boundary line is obtained from the signal indicating the boundary line, and thereby the moving speed or the interval between the boundary lines is controlled. 27, 28, 29, 30
Are transfer drums for yellow, magenta, cyan, and black.

FIG. 11 is a schematic diagram showing an example of a reflection type photoelectric sensor used in a boundary line detecting method according to another embodiment of the present invention. In FIG. 11, a boundary line 31 generated by a linear reflectance difference is arranged on the surface of the moving body 3 in a direction orthogonal to the moving direction. The reflection-type photoelectric sensor 32 is configured such that a plane including a light-projecting axis from the LED 33 and a light-receiving surface normal of a two-divided PD (or a PSD) 34 as a light-receiving element is parallel to the boundary line. ing. The two-divided PD 34 is composed of two moving objects 3
Are arranged in a direction parallel to the surface.

With this configuration, the direction of detecting the change in the center of gravity caused by the reflectance difference, that is, the direction of detecting the boundary line is horizontal, and the direction of detecting the change in the center of gravity of the reflected light due to the fluttering of the object (moving body) is 90 degrees. Due to the difference, the boundary line can be detected stably even if the object flutters. Therefore, in order to detect the transfer position of the transfer belt of the copying machine in this boundary line detection method, it is not necessary to consider the fluttering of the belt so much, so that the reflective photoelectric sensor can be provided at any position of the belt. .

As still another embodiment of the present invention, a differential processing circuit may be provided after the division processing circuit of the circuit shown in FIG. 3, and the output of the differential processing circuit may be used to detect the boundary line. According to this method, the output of the division processing circuit is
In the case of 2 (a), the differential processing output becomes the signal waveform of FIG. 12 (b), and the output waveform becomes steeper, so that the positioning accuracy can be further improved. Further, the peak point of the divisional calculation force waveform can be stably detected by the differential output waveform.

[0023]

According to the first, second and third aspects of the present invention, the change in the center of gravity of the reflected light on the light receiving element is obtained by the division processing.
Since the optical system of the displacement sensor may be used, the optical system is simple. Even if the size of the object is smaller than the beam diameter, the center of gravity changes on the light receiving element, so that the size of the object can be less restricted. Even if the reflectance of the object is different, the signal can be normalized by the division process,
Signal rising or falling characteristics can be made uniform, and positioning can be performed with high accuracy.

According to the fourth aspect of the present invention, the differential processing is further performed after the division processing, so that the output signal waveform becomes steeper, and the peak point of the division calculation force waveform can be detected stably, thereby achieving higher accuracy. Can be detected. According to the fifth aspect of the present invention, the direction of detection of the center of gravity of the reflected light due to the flutter and the direction of detection of the boundary line differ by 90 °.
Even if the object flutters, the boundary can be detected stably without being affected by the flutter.

[Brief description of the drawings]

FIG. 1 is a sectional view of a sensor head of a reflection type photoelectric sensor used in a boundary line detection method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram in the case of detecting a boundary line of an object having non-uniform reflectance with the reflective sensor head.

FIG. 3 is a circuit diagram of a circuit unit which constitutes a reflective photoelectric sensor in combination with the sensor head of FIG. 1;

FIG. 4 is an explanatory diagram of a case where a boundary line is detected by a division process using the same reflection type photoelectric sensor.

FIG. 5 is a diagram illustrating a difference in output between a case where a division process is performed and a case where a differential process is performed when the width of the target object is equal to or larger than the light projection spot diameter.

6 is a waveform chart illustrating each timing of the waveform in FIG.

FIG. 7 is a diagram illustrating a difference between output waveforms when division processing and differential processing are performed when the width of the target object is smaller than the light projection spot diameter.

FIG. 8 is a waveform chart for explaining each timing of the waveform of FIG. 7;

FIG. 9 is a diagram illustrating an application example of the boundary line detection method according to the embodiment.

FIG. 10 is a diagram showing an output waveform of a reflection type photoelectric sensor in the application example.

FIG. 11 is a diagram illustrating a boundary line detection method according to another embodiment of the present invention.

FIG. 12 is a diagram showing output waveforms for explaining a boundary line detection method according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor head part 2 LED 3 Target object 5 2 division PD 11 Division processing circuit

Claims (5)

[Claims] 1. A surface including a light-projecting axis and a light-receiving axis of a reflection-type photoelectric sensor for detecting a change in the center of gravity of reflected light on a light-receiving element for a moving object having a boundary generated by a difference in reflectance. A boundary line detection method comprising: arranging in parallel with a moving direction, dividing a light receiving signal, and controlling a moving speed or an interval based on a detection time difference of the boundary line. 2. The boundary detection according to claim 1, wherein the boundary is formed by toner on a transfer belt of a copying machine, and a toner position interval is controlled based on a detection time difference of the boundary. Method. 3. The boundary line detection method according to claim 1, wherein the size of the object forming the boundary line is equal to or larger than the diameter of the projected beam. 4. The apparatus according to claim 1, wherein after the division of the light receiving signal, a differentiation process is further performed.
Or the boundary line detection method according to claim 3. 5. A boundary line formed by a difference in reflectance between lines is arranged on the surface of the moving body so as to be orthogonal to the moving direction, and the boundary line is a projection axis of the photoelectric sensor and a normal to a light receiving surface of the light receiving element. Wherein the detection method of the light receiving element is parallel to the moving direction of the moving body.