JPS635152Y2 - - Google Patents

Description

[Detailed Description of the Invention] <<Field of the Invention>> This invention relates to an improvement in the mounting structure of a photoelectric switch, and particularly relates to a mounting structure that improves the noise resistance of the light receiving circuit portion.

<Prior art and its problems> A typical small photoelectric switch that integrates a light emitting element, its driving circuit, a light receiving element and its output signal processing circuit, etc., receives light emitted from the light emitting element. The level of light received by the element is often weak, and therefore the level of the light-receiving signal of the light-receiving element is also weak, and it is necessary to significantly amplify the light-receiving signal during signal processing.

In conventional photoelectric switches of this kind, the light-emitting element, the light-receiving element, and the electric circuit section including the drive circuit and signal processing circuit are mounted on separate boards, and a pre-amplifier for amplifying the output signal of the light-receiving element is mounted on separate boards. The amplifier and the signal processing circuit were mounted on an electric circuit board (printed circuit board) separate from the light receiving element, and the preamplifier and the light receiving element were connected via lead wires. As a result, the lead wires through which weak signals are transmitted are susceptible to external noise, and the normal operation of the photoelectric switch is easily disturbed by induced noise. This type of photoelectric switch is often used in places with poor electromagnetic environments, and is expected to operate accurately even in such environments without being affected by induced noise. In this respect, conventional photoelectric switches have been inadequate.

《Purpose of the invention》 This invention was devised in view of the above-mentioned conventional problems.The main purpose of this invention is to improve the noise resistance of the photodetector and preamplifier circuit, and to improve the noise immunity of the photodetector and preamplifier circuit. The object of the present invention is to provide a mounting structure that can realize a highly reliable photoelectric switch that operates normally even when the switch is operated normally.

<Configuration and Effects of the Invention> In order to achieve the above object, this invention includes a light emitting element, a light receiving element, a drive circuit for driving the light emitting element, and a preamplifier for amplifying the light receiving output of the light receiving element. A circuit, a signal processing circuit that obtains a binarized output signal as a predetermined signal processing based on the output signal of this preamplifier circuit, and a control output circuit that responds to the output signal of this signal processing circuit are housed in the same case. In the built-in photoelectric switch, a first printed circuit board on which the light emitting element, light receiving element, and preamplifier circuit are mounted, and a second printed circuit board on which the drive circuit, signal processing circuit, and control output circuit are mounted. a first ground conductor provided on the element mounting surface side of the first printed circuit board excluding the element mounting section; and a first ground conductor provided on the side of the first printed circuit board opposite to the element mounting surface side, a second ground conductor provided between the light emitting element, the light receiving element and the preamplifier circuit, the light emitting element and the light receiving element being attached to the element mounting surface side of the first printed circuit board; , the preamplifier circuit is mounted on a side of the first printed circuit board opposite to the element mounting side and corresponding to the light receiving element side.

That is, in the present invention, a light emitting element and a light receiving element are placed on one surface of the first printed circuit board,
By placing a preamplifier circuit on the other surface facing the light-receiving element side of the above-mentioned one surface, and providing a first ground conductor on the part of the printed circuit board excluding the element mounting part. , it is possible to electromagnetically shield the photodetector and preamplifier circuit parts that handle the weakest signals without the need for additional parts such as a shield case, which prevents malfunctions due to external noise, and without the need for additional parts such as a shield case. Since this type of photoelectric switch is not particularly required, this type of photoelectric switch can be manufactured at low cost.

(b) Also, since a second ground conductor is provided on the other surface of the first printed circuit board between the light emitting element, the light receiving element, and the preamplifier circuit, it is possible to drive the light emitting element to emit light. It is possible to avoid noise generated from the output of the circuit from being superimposed as noise on the light receiving element and the preamplifier circuit that handle the weakest signals.

In other words, the present invention overcomes the drawback of conventional photoelectric switches of this type, such as being susceptible to noise on the light emitting side and external noise, and is highly reliable and can operate accurately even in adverse electromagnetic environments. This has the advantage that a photoelectric switch can be obtained at low cost.

<<Description of Embodiments>> Embodiments of this invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing an outline of the electrical configuration of a photoelectric switch according to this invention, and FIG. 2 is a sectional view showing an overall outline of its mounting structure. This photoelectric switch includes a light emitting element 1 and a light receiving element 2.
A drive circuit 3 drives the light emitting element 1, for example, by pulse lighting; a preamplifier circuit 4 amplifies the light receiving output of the light receiving element 2; It has a signal processing circuit 5 that obtains a binary output signal, and a control output circuit 6 that sends an output signal to the outside in response to the output signal of the signal processing circuit 5, and these are housed in a case 7. There is.

The embodiment shown in FIG. 2 is an optical fiber type reflective photoelectric switch. The light from the light emitting element 1 is guided to the optical fiber 8 and exits from the end face of the detection head 9, and the light reflected from the object to be detected enters the end face of the detection head 9 and is guided to the optical fiber 10. The light is received by the light receiving element 2. The drive circuit 3, signal processing circuit 5, and control output circuit 6 are connected to the second printed circuit board 11A and 1 installed in the case 7.
It is implemented in 1B. Code 1 for external drawer
2 is coupled to one end of the case 7 via the cord cover 13, and is electrically connected to the first printed circuit board 11A. Supplementary explanation of the embodiment shown in FIG. 2 is as follows: 14 is a volume for adjusting the operating sensitivity in the signal processing circuit 5;
A light emitting element 16 is used to display the operation status of the switch, which is turned on or off depending on the output of the light emitting element 15, and is a window for confirming the operation display that guides the light from the light emitting element 15 to the outside.

The light emitting element 1, the light receiving element 2, and the preamplifier circuit 4 are connected to the first printed circuit board 11A and 1
It is mounted on a small first printed circuit board 17 different from 1B. Figure 3 shows the first printed circuit board 1
7 is an exploded perspective view showing the mounting structure of the light-emitting element 1, the light-receiving element 2, and the preamplifier circuit 4. Further, FIG. 4 is a wiring diagram showing an example of a specific circuit configuration of the light receiving element 2 and the preamplifier circuit 4. In FIG. The first printed circuit board 17 is made of a double-sided conductor board, and one surface has a surface on which the light-emitting/light-receiving elements 1 and 2 are mounted. A first ground conductor is formed on the side opposite to the element mounting surface of the first printed circuit board 17, and is connected to the light emitting element 1, the light receiving element 2, and the preamplifier circuit 4. There is a second
A ground conductor is formed. The light emitting element 1 and the light receiving element 2 are respectively attached to the first printed circuit board 17 via insulating plates 18 and 19 so as not to come into contact with the first ground conductor. A and B of the second ground conductor on the first printed circuit board 17 are pad portions connected to both terminals of the light emitting element 1, and lead wires 20 shown in FIG. 2 are soldered to the pad portions A and B. , through this lead wire 20
A drive circuit 3 mounted on printed circuit boards 11A and 11B and a light emitting element 1 are connected.

As shown in FIG. 4, a photodiode is used as the light receiving element 2. Preamplifier circuit 3
is provided on the back side of the first printed circuit board 17, that is, on the side opposite to the element mounting surface, and this circuit 4 includes a resistor R1 connected in parallel with the light receiving element 2.
The structure is such that a voltage generated in the light emitting element 2 is amplified by a transistor 21 biased by resistors R1 and R2, and a capacitor 22 is used for coupling to pass the high frequency component of the photocurrent of the light emitting element 2.

These light receiving element 2, resistors R1 and R2, transistor 21, and capacitor 22 are connected to the first
are soldered to the first and second ground conductors of the printed circuit board 17, respectively. Preamplifier 4-2
Pad portions C and D corresponding to the two terminals are provided at the end of the first printed circuit board 17, and these pad portions C and D are directly soldered to one end of the second printed circuit board 11A. The amplifier circuit 4 and the signal processing circuit 5 are electrically connected. That is, as shown in FIG. 2, the first printed circuit board 17 is joined to one end of the second printed circuit board 11A so as to be perpendicular thereto, and the pad portions C, D of the first printed circuit board 17 and the second The printed circuit board 11A is directly connected to the second ground conductor of the signal processing circuit 5 by solder 30. Note that the first printed circuit board 17 is mechanically fixed to the case 7 by means such as screws.

As described above, the light receiving element 2 and the preamplifier circuit 4 for amplifying its output are mounted on the first printed circuit board 11.
Since it is mounted very close to the front and back sides of the second printed circuit board 17 other than A and 11B, the input side of the preamplifier circuit 4 that is most affected by external electromagnetic noise, that is, the transistor 21 The circuitry on the base side is densely mounted with no additional geometric distance. Therefore, the light receiving element 2 and the preamplifier circuit 4, which handle weak signals, are less susceptible to external noise. In addition, since the output side of the preamplifier circuit 4 is a part to which a relatively large amplified signal is transmitted, it is originally a part that is relatively unaffected by external noise, but as in the embodiment shown in FIG. Furthermore, since the first printed circuit board 17 is directly connected to the second printed circuit board 11A by soldering, it is further resistant to external noise. In addition, the wide-area ground conductor formed on the element mounting surface side of the first printed circuit board 17 acts as a shield plate to protect the preamplifier circuit 4 mounted on the opposite side from external noise. Therefore, it becomes even more resistant to external noise.

As explained in detail above, according to the mounting structure of the photoelectric switch according to this invention, the photodetector and preamplifier circuit parts that handle the weakest signals are densely mounted and electromagnetically shielded, making it possible to It is possible to overcome the drawback of this type of photoelectric switch that it is susceptible to external noise, and to realize a highly reliable photoelectric switch that operates accurately even in a bad electromagnetic environment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the electrical configuration of a photoelectric switch according to this invention, FIG. FIG. 4 is an exploded perspective view showing the details of the mounting portion of the light receiving element and the preamplifier circuit, and FIG. 4 is a wiring diagram showing a specific circuit example of the light receiving element and the preamplifying circuit portion. 1... Light emitting element, 2... Light receiving element, 4... Preamplifier circuit, 5... Signal processing circuit, 11A, 11B
... Second printed circuit board, 17 ... First printed circuit board, 18, 19 ... Insulating board, 21 ... Transistor, 8, 10 ... Optical fiber, 9 ... Detection head, A to D ... Pad Department.

Claims (1)

[Claims for Utility Model Registration] A light-emitting element, a light-receiving element, a drive circuit for driving the light-emitting element, a preamplifier circuit for amplifying the received light output of the light-receiving element, and an output signal of the preamplifier circuit. In the photoelectric switch, the photoelectric switch has a signal processing circuit that performs predetermined signal processing based on the signal processing signal to obtain a binary output signal, and a control output circuit that responds to the output signal of this signal processing circuit, built in the same case. a first printed circuit board on which the element, a light receiving element, and a preamplifier circuit are mounted; a second printed circuit board on which the driving circuit, the signal processing circuit, and the control output circuit are mounted; and the elements of the first printed circuit board. A first grounding conductor provided on the mounting surface side excluding the element mounting part; and a first grounding conductor provided on the side of the first printed circuit board opposite to the element mounting surface side, the light emitting element, the light receiving element, and the preamplifier. a second ground conductor provided between the circuit and the light emitting element and the light receiving element, the light emitting element and the light receiving element are attached to the element mounting surface side of the first printed circuit board, and the preamplifier circuit is connected to the first printed circuit board. A mounting structure for a photoelectric switch, characterized in that the photoelectric switch is mounted on the side opposite to the element mounting side of the printed circuit board, corresponding to the light receiving element side.