JPS6020005Y2 - photo sensor - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a photosensor comprising a light emitting element and a light receiving element.

Automated equipment often uses photosensors to detect the position of objects or movable parts.

FIG. 1 shows an example of a photosensor that is frequently used for such purposes.

In the figure, 1 is a light emitting diode, and 2 is a phototransistor.

The light emitting diode 1 is connected to the power supply (+
Vo), and emits light with an amount of light according to the value of the drive current 6.

When the light emitted from the light emitting diode 1 is blocked by the object to be detected 5, the phototransistor 2 is turned off and the photocurrent 7 is turned off.

When the light is not blocked by the object to be detected 5, a photocurrent 7 having a value corresponding to the amount of received light flows.

The amplifier 4 binarizes the photocurrent 7 at a certain threshold value and outputs a digital signal to the output terminal 8.

By the way, even if the value of the drive current 6 of the light emitting diode 1 is maintained correctly, malfunction may occur due to deterioration of the characteristics of the light emitting diode 1 or the phototransistor 2, dirt on the light emitting/receiving surface, or the like.

In particular, when the amount of light emitted and the light receiving sensitivity decrease and the photocurrent value in the non-light-shielded state decreases to around the threshold value, sporadic malfunctions are likely to occur.

Therefore, it is necessary to perform regular maintenance.

Conventionally, when performing this maintenance work, the method of measuring the value of the photocurrent 7 with a current calculator or the like or actually moving the detected object 5 to check the operation has been taken, which requires a considerable amount of maintenance work. It required a lot of time and equipment.

Therefore, an object of the present invention is to provide a photosensor with improved maintainability.

However, the features of the photosensor of the present invention are that a switch for turning on and off the drive current of the light emitting element is provided in the drive current path of the light emitting element, and a switch with a constant voltage element or an impedance element connected in parallel is installed in the drive current path of the light emitting element. It is inserted in series with the path.

FIG. 2 shows an embodiment of the photosensor according to the present invention.

The difference between this embodiment and the conventional example shown in FIG. 1 is that switches 9 and 10 are provided in series in the drive current path of the light emitting diode 1, and a diode 11 is connected in parallel to one switch 10.

During normal operation, switch 10 is closed to short-circuit both ends of diode 11, and switch 9 is closed.

Therefore, under exactly the same conditions as before, the light emitting diode 1
is driven.

Perform maintenance according to the following procedure.

First, the switch 9 is opened to turn off the drive current of the light emitting diode 1.

In other words, the state is equivalent to when light is blocked by an object to be detected.

Check the signal at the output terminal 8 at this time.

Next, switch 9 is closed and switch 10 is opened.

Since the diode 11 (which can be regarded as a constant voltage element) enters the drive current path of the light emitting diode 1 in series, the value of the drive current 6 decreases.

If the amount of decrease in this current value, that is, the value of the forward voltage drop of the diode 11, is appropriately selected, the degree of contamination or characteristic deterioration of the light emitting diode 1 and phototransistor 2 can be detected by checking the signal at the output terminal 8. By knowing this, you can determine whether replacement or cleaning is necessary.

This embodiment will be further explained with reference to FIG.

At time point a, the switch 9 is opened, and after confirming that the output signal 8 has reached the "0" level, the switch 9 is closed (the switch 10 is closed in advance), and the photosensor is brought into operation.

The output signal 8 is at the 1 level.

When the light is already blocked by the object 5 to be detected, the photocurrent 7 decreases below the threshold value (ItH), the output signal 8 becomes "off," and the object 5 to be detected is normally detected.

When the light shielding state is removed, the photocurrent 7 rises again and the output signal (8) returns to 1.

Switch 10 at time C to check for maintenance needs.
open.

Although the photocurrent 7 decreases, it remains above the threshold value, so the output signal 8 remains at "1P".

In other words, no maintenance is required. Then, at time d, switch 1
Reopen 0.

In this case, the photocurrent 7 falls below the threshold value, and the output signal 8 is inverted to "0".

In other words, the operating margin of the photosensor is reduced, and it is necessary to perform maintenance work such as cleaning and replacing the light emitting diode 1 and the phototransistor 2.

As described above, according to the present invention, it is possible to easily check whether or not maintenance of the photosensor is necessary just by operating a switch, and maintenance time can be shortened.

Note that the switches 9 and 10 described above are not limited to mechanical ones;
Relays, semiconductor switches, etc. can also be used.

In the latter case, it is possible to automatically and periodically open and close these switches without human intervention, and also to automatically check the output signal 8 at that time.

Further, the number of diodes 11 is not limited to one,
It is also possible to connect any number in series to optimize the reduction in drive current.

Further, as the diode 11, a pure constant voltage element such as a Zener diode may be used.

Furthermore, an impedance element such as a resistor may be used.

In short, it is sufficient if the purpose of changing the drive current of the light emitting diode 1 to a predetermined value in accordance with the opening and closing of the switch 10 can be achieved.

Furthermore, in the photosensor according to the present invention, the light emitting element and the light receiving element are of course not limited to light emitting diodes and phototransistors.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional photosensor, Figure 2 is a circuit diagram showing an embodiment of the photosensor according to the present invention, and Figure 3 is a circuit diagram showing an embodiment of the photosensor according to the present invention.
The figure is a time chart for explaining the operation of the above embodiment. 1... Light emitting diode, 2... Phototransistor, 3... Resistor, 4... Amplifier, 5... Object to be detected, 9 ,10...
Switch, 11...Diode.

Claims (1)

[Scope of utility model registration request] A light emitting element, a first switch for turning on and off a driving current provided in a drive circuit of the light emitting element, a light receiving element disposed at a position to receive light from the light emitting element, and an output current of the light receiving element. A photosensor comprising a circuit that outputs a signal indicating the presence or absence of an object between the light-receiving element and the light-emitting element by comparing them with a predetermined threshold value. A second switch that is normally kept closed is provided with a voltage element or an impedance element connected in parallel, and while the first switch is in the on state, the second switch is temporarily opened and closed to weaken the amount of light emitted. A photosensor characterized in that the deterioration state of the light-emitting element or the light-receiving element can be checked from the change in the state of the output signal when the light-emitting element or the light-receiving element changes.