JP2007139495A - Photoelectric sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a useful value by avoiding a specific detected value when a peak hold value or bottom hold value is the specific value like glass. <P>SOLUTION: In this transmission type photoelectric sensor 1, the OFF signal is switched to the ON signal when glass 4 of a workpiece begins to pass a detection area and the amount of received light decreases and becomes less than a first threshold. The amount of received light after a lapse of a predetermined time T is obtained with reference to the value at the time of generating the ON signal, and this is stored as a sample hold value. The sample hold value is displayed on a display section 20 of the photoelectric sensor 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric sensor that detects the presence or absence of a workpiece by comparing the amount of received light with a threshold value.

  Photoelectric sensors are classified into reflective and transmissive types, but the basic function of the photoelectric sensor is to change the amount of light received as the work passes through the work detection area formed by the projected light. The presence or absence of is determined.

  Patent Document 1 discloses that a photoelectric sensor having two screens is used to display a margin value and a maximum value (peak hold value) and a minimum value (bottom hold value) of the margin and the amount of received light. is doing. The margin is expressed as (current received light amount / threshold) × 100 (%), and it can be determined whether or not the photoelectric sensor is in a stable operation state by looking at the margin.

The peak hold value or the bottom hold value is, for example, the highest received light amount or the smallest received light amount during a predetermined sampling period, and a threshold value is set between these values using the peak hold value and the bottom hold value. It is used for automatic setting, and as disclosed in Patent Document 1, the stability of the operation of the photoelectric sensor can be known by displaying the margin of the peak hold value and the bottom hold value. Here, the margin of the peak hold value and the bottom hold value is represented by (peak hold value or bottom hold value / threshold) × 100 (%).
JP 2002-324465 A

  FIG. 7 shows a transmissive photoelectric sensor 1, reference numeral 1 is a projector, and 3 is a light receiver. FIG. 7 also illustrates the case where the object to be detected (workpiece) 4 is glass. FIG. 8 shows a change in the amount of received light when the glass 4 passes between the projector 2 and the light receiver 3, that is, through the detection area.

  As can be seen from FIG. 8, the glass 4 has a high light shielding property at the edge 4a. Accordingly, when the edge 4a passes through the detection area, the amount of light received decreases instantaneously, and this minimum value is displayed as the bottom hold value.

  For this reason, for example, when the photoelectric sensor is applied to the glass 4, there is no meaning to display the peak hold value or the bottom hold value, or the automatic threshold setting function using the peak hold value or the bottom hold value cannot be used. There was a problem.

  An object of the present invention is to provide a photoelectric sensor that can detect a useful value by avoiding the specific detection value when the peak hold value or the bottom hold value shows a specific value like glass. It is in.

According to the present invention, the above technical problem is
A photoelectric sensor for detecting the presence or absence of a workpiece by receiving transmitted light or reflected light associated with the workpiece passing through a detection area formed by the projected light and comparing the received light amount with a first threshold value. Because
Time measuring means for measuring an elapsed time from a reference signal from inside or outside the photoelectric sensor;
Detection value acquisition means for acquiring the amount of received light when the time measured by the time measurement means has passed a predetermined time;
This is achieved by providing a photoelectric sensor comprising storage means for storing the detection value acquired by the detection value acquisition means as a sample hold value.

  For example, as illustrated in FIG. 3 showing the transition of the amount of received light when the workpiece is glass, a transmissive photoelectric sensor avoids a large drop 22 in the amount of received light when the edge 4a of the glass 4 passes the detection area. Thus, the predetermined time T is set based on the time point when the photoelectric sensor generates the ON output so that the amount of received light of the portion 23 showing a substantially constant value when the main body portion of the glass 4 passes can be acquired. .

  The user can confirm the stability of the operation of the photoelectric sensor by displaying the sample hold value. In addition, using this sample hold value, if it is a transmissive photoelectric sensor, the value between the maximum received light amount (peak hold value) and the sample hold value (for example, the intermediate value) is automatically set as a threshold value. You may make it do.

  In order to give a degree of freedom in setting the timing for acquiring the sample hold value, it is preferable to further include a setting unit that allows the user to set the predetermined time.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the transmissive photoelectric sensor 1 described above with reference to FIG. 8, and can be similarly applied to the reflective photoelectric sensor 25 described later with reference to FIG.

  FIG. 1 is a block diagram of the photoelectric sensors 1 and 25. The photoelectric sensors 1 and 25 have, for example, a light projection processing unit 10 and a light projection unit 11 for causing a light emitting element made of a light emitting diode (LED) to emit light, and are connected to a light receiving element made of a photodiode or the like. The light receiving unit 12 and the amplification unit 13, and the A / D conversion unit 14 that digitally converts the light reception signal amplified by the amplification unit 13 and outputs the light reception data.

  The main control unit 15 that controls the light projecting unit 11 and the light receiving unit 12 is basically composed of, for example, a gate array or a CPU. The main control unit 15 transmits and receives signals to and from the outside through the external input / output unit 16. Give and receive. The main control unit 15 is supplied with signals from the operation unit 17 including various operation switches or buttons, as well as the detected light reception amount and threshold values (in this example, the first and second thresholds). Value), and data is exchanged with the storage unit 18 that stores a sample hole value acquisition time T, which will be described later. Also, the setting values required for the processing of the main control unit 15, such as the first and second threshold values and the sample hold value acquisition time T described above, are set by the setting unit 19, and the first and second values are set. The threshold value, the amount of received light, and the like are supplied from the main control unit 15 to the first and second display units 20 as disclosed in, for example, Patent Document 1, and various information corresponding to the selected display mode is provided. It is displayed on the first and second display units 20.

  In the basic operation mode, the photoelectric sensors 1 and 25 acquire the received light amount acquired by the light receiving unit 12 (step S1) and use the detected received light amount (detected value) as a threshold value as shown in FIG. In comparison, the presence or absence of an object to be detected is determined based on the size (step S2), and the result is output (step S3). In this operation mode, typically, the current received light amount (current value) acquired by the light receiving unit 12 and, for example, the first threshold value set for detecting the presence or absence of the detection object T, Simultaneously displayed on the first and second display units 20 described above.

  The photoelectric sensors 1 and 25 are based on a predetermined reference signal generated outside or inside, typically a signal that inverts the output determination of the photoelectric sensors 1 and 25, and when a predetermined time T has elapsed from the reference signal. The received light amount can be displayed on the display unit 20 by user selection, for example.

  This additional function will be described with reference to FIG. FIG. 3 shows the received light amount (detection amount) and the ON / OFF output associated therewith when the glass 4 described in FIGS. 7 and 8 passes through the detection area of the transmissive photoelectric sensor 1. As described above, the amount of received light is greatly reduced at the edge 4a of the glass 4, but the amount of received light is substantially constant when the central portion of the glass 4 passes. A significant drop in the amount of light received when the edge 4 a passes is indicated by reference numeral 22, and the amount of light received at the central portion of the glass 4 is indicated by reference numeral 23. Taking such characteristics into consideration, the amount of received light that falls when the glass 4 passes through the detection area of the transmissive photoelectric sensor 1 falls below a threshold value, and the transmissive photoelectric sensor 1 generates an ON signal from the OFF signal. Time measurement is started by the time measuring means of the main control unit 15 with reference to the time (FIG. 4, step S10) (FIG. 4, step S11), and the received light amount (detection) when a predetermined time T (FIG. 3) has passed. Value) is acquired (FIG. 4, steps S12 and S13). The acquired detection value is stored in the storage unit 18 as a sample hold value. The sample hold value can be displayed on the first or second display unit 17 or 20 according to the user's selection.

  It is preferable that the user can set an arbitrary value for the predetermined time T using the setting unit 19 (FIG. 1). As can be seen from FIG. 3, the detection value (light reception amount) is determined according to the characteristics of the detected object. A portion 23 where the amount of received light becomes a substantially constant value is set in the process of passing through the central portion of the glass 4 while avoiding the large sagging portion 22.

  Since the sample hold value can be displayed on the first or second display unit 20 as described above, the user can confirm the stability of the operation of the transmissive photoelectric sensor 1 by confirming the sample hold value. . Further, a margin may be calculated using this sample hold value, and this margin may be displayed on the first or second display unit 20, or a threshold value may be automatically set using the sample hold value. You may make it perform.

  Further, the sample hold value can be used, for example, to determine the state of a specific part of the workpiece having an uneven upper surface. This will be described with reference to FIGS. 5 and 6. FIG. 5 illustrates the reflective photoelectric sensor 25. As is well known, the reflection type photoelectric sensor 25 detects the presence or absence of the work 26 by receiving the light reflected by the projected light hitting the work 26.

  For example, as shown in FIG. 5, when the workpiece 26 has a convex portion 26a and a concave portion 26b on the surface thereof, for example, the detection acquired at the predetermined time T to detect the state of the concave portion 26b. You can use the value.

  For example, an ON signal is generated when the amount of received light becomes equal to or greater than a first threshold value, and time measurement is started by the time measuring means of the main control unit 15, and the amount of received light when a predetermined time T has elapsed ( (Detection value) is obtained, and the state of the recess 26b can be known by comparing the obtained detection value with the second threshold value.

It is a block diagram of the photoelectric sensor of an Example. It is a flowchart for demonstrating the procedure of the basic workpiece | work detection function of a photoelectric sensor. It is a figure for demonstrating the reference point for detecting the sample hold value and the function which simulates the light-receiving amount at the time of predetermined time having passed from the reference point as the minimum value. It is a flowchart for demonstrating the procedure which acquires the light reception amount at the time of the predetermined time T having passed from the reference point. It is a figure for demonstrating the example of a reflection type photoelectric sensor to detect the state of the specific site | part of a workpiece | work using the light reception amount at the time of predetermined time passing from a reference point. It is a figure for demonstrating that the state of the specific site | part of a workpiece | work is detectable using the two threshold values of the reflective photoelectric sensor shown in FIG. It is a figure for demonstrating the workpiece | work detection using a transmissive photoelectric sensor. It is a figure for demonstrating the problem at the time of detecting the presence or absence of glass for a transmissive photoelectric sensor as an example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission type photoelectric sensor 2 Emitter 3 Light receiver 4 Glass (workpiece)
4a Glass edge 20 Display unit 25 Reflective photoelectric sensor 26 Workpiece 26a Convex part of work surface 26b Concave part of work surface T Predetermined time

Claims (6)

A photoelectric sensor for detecting the presence or absence of a workpiece by receiving transmitted light or reflected light associated with the workpiece passing through a detection area formed by the projected light and comparing the received light amount with a first threshold value. Because
Time measuring means for measuring an elapsed time from a reference signal from inside or outside the photoelectric sensor;
Detection value acquisition means for acquiring the amount of received light when the time measured by the time measurement means has passed a predetermined time;
A photoelectric sensor comprising storage means for storing the detection value acquired by the detection value acquisition means as a sample hold value.   The photoelectric sensor according to claim 1, further comprising a setting unit that allows a user to set the predetermined time.   The photoelectric sensor according to claim 2, wherein the reference signal is an ON or OFF signal that causes the photoelectric sensor to invert its output.   The photoelectric sensor according to claim 3, further comprising a display unit that displays the sample hold value.   The photoelectric sensor according to claim 1, further comprising a function of detecting a partial state of a workpiece by comparing the sample hold value with a second threshold value.   The photoelectric sensor according to claim 1, further comprising a function of automatically setting a threshold value using the sample hold value.

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