JPH08188298A - Drive circuit for optical type sensor - Google Patents

Abstract

PURPOSE: To provide the drive circuit of an optical sensor which is constituted to automatically regulate an amount of light emitted from a light emission element and form a device in a compact manner and stably maintain detecting sensitivity of the sensor. CONSTITUTION: The drive circuit of an optical type sensor has a variable resistance part 8 and by changing the resistance value of the variable resistance part 8, a voltage applied on a light emission element 9 is changed to control a light emission amount. Based on the output voltage of a light receiving element 8 detected by an output detecting part, the resistance value of the variable resistance part 8 is changed by a computer. The variable resistance part 8 comprises a plurality of resistance parts R0-R7 having respective different resistance values; and a resistance switching part 7 connecting in a switching manner a part of a plurality of the resistance parts R0-R7 to the light emission element 9, and switching is effected by an output input interface part 7a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an optical sensor used in a printer, and more particularly to a drive circuit for an optical sensor used to detect the presence or absence of print paper in a printer and the home position of a print head. Regarding the circuit.

[0002]

2. Description of the Related Art Conventionally, a printer used in a computer, a word processor, etc., comprises a light emitting element such as a light emitting diode and a light receiving element such as a phototransistor in order to detect the presence or absence of print paper and the home position of the print head. Optical sensors are used. For example, when detecting the presence or absence of print paper, the light receiving element is based on that the light receiving element receives the light from the light emitting element reflected on the surface of the paper, or the light traveling from the light emitting element to the light receiving element is blocked by the paper. The presence or absence of the paper is detected by the change of the output level of. In this case, in general,
The former method is called a reflective sensor and the latter method is called a transmissive sensor.

[0003]

However, in the case of the above-mentioned optical sensor, there is a problem in that the detection sensitivity changes due to the aging of the light receiving element and the light emitting element, the adhesion of dirt, etc., and a detection error occurs. In addition, since an error occurs due to a variation in the mounting position of the sensor and the detection sensitivity, it is necessary to adjust the detection sensitivity of the light receiving element in advance in the assembly process. Therefore, in order to solve the above-mentioned problems, JP-A-64-
Japanese Patent No. 68686 discloses a method of providing a reflection reference member, irradiating the reflection reference member with light, and adjusting the amount of light emission from the amount of light received. However, in the above method, it is difficult to reduce the size of the device because a place for providing the reflection reference member is necessary, and it is difficult to apply the method to a transmission type sensor.

An object of the present invention is to provide a drive circuit for an optical sensor which can automatically perform an adjusting operation and is compact and which can stably maintain the detection sensitivity of the sensor. .

[0005]

The present invention relates to a drive circuit for an optical sensor. The target optical sensor is provided with a light emitting element that emits light when supplied with electric power, and a light receiving element that changes its output voltage upon receiving light, and the light emitting element that emits light from the light emitting element varies depending on the object to be detected. The output voltage of the light receiving element changes when the light irradiation is blocked or when the light is emitted from the light emitting element reflected by the object, and the presence of the object is detected based on the change in the voltage. To be done. The driving circuit is characterized by having the following requirements in order to solve the above problems. Light emission amount control section: equipped with a variable resistance section,
By changing the resistance value of the variable resistance portion, the voltage applied to the light emitting element is changed to control the light emission amount of the light emitting element. Output detector: Detects the output voltage of the light receiving element. Control instruction means: Change the resistance value of the variable resistance portion of the light emission amount control portion based on the output voltage of the light receiving element detected by the output detection portion.

The variable resistance section of the light emission amount control section includes a plurality of resistance sections each having a different resistance value, and a resistance switching section for connecting a part of the plurality of resistance sections to the light emitting element in a switchable manner. It can be provided. In this case, the drive circuit drives the light emitting element at a constant voltage.

The light emission amount control section can be configured to connect the resistance section to the light emitting element while switching the resistance section from a large resistance value to a small resistance value or from a small resistance value to a large resistance value.

Further, the resistance switching section is provided with an input / output interface section having an input port for receiving a control signal from the control command means and an output port to which a plurality of resistance sections are respectively connected. Based on the control signal from the control command means input from the port, among the resistance units connected to the output port, the resistance unit to be connected to the light emitting element has a different level from the other resistance units. It can be configured to apply a voltage.

The control command means outputs the output voltage of the light receiving element
The resistance value of the variable resistance portion is changed so as to approach the reference value from the larger side or the smaller side with respect to a predetermined reference value, and when the output voltage of the light receiving element is equal to or higher than or equal to the reference value, The change in resistance value may be stopped.

Specifically, the light emitting element can be configured by a light emitting diode. Further, the light receiving element can be composed of a phototransistor. The optical sensor may be provided in the printer to detect the presence or absence of print paper or the home position of the print head.

[0011]

The driving circuit of the present invention receives the light emitted from the light emitting element reflected by the object or the light emitted from the light emitting element being blocked by the object to be detected. It is applied to an optical sensor that detects the presence of an object based on the output voltage of a light receiving element, and is provided with a light emission amount control section having a variable resistance section, and by changing the resistance value of the variable resistance section. The amount of light emitted from the light emitting element is controlled by changing the voltage applied to the light emitting element. Then, the control command means changes the resistance value of the variable resistance portion based on the output voltage of the light receiving element detected by the output detection portion. The drive circuit of the present invention as described above can automatically perform the operation of adjusting the light emission amount of the light emitting element and is compact, and can stably maintain the detection sensitivity of the optical sensor. Further, the invention is not limited to the reflection type sensor, but can be applied to a transmission type sensor that detects an object by blocking light.

The variable resistance section may include a plurality of resistance sections each having a different resistance value, and a resistance switching section that connects a part of the plurality of resistance sections to the light emitting element in a switchable manner. If so, the light emission amount control unit can be downsized. Particularly, according to the configuration in which the resistance switching unit includes the input / output interface unit having the input port for receiving the signal from the control command means and the output port to which the resistance unit is connected, the switching of the resistance unit is made non-contact. Therefore, the drive circuit can be downsized and the reliability can be improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of an optical sensor drive circuit of the present invention. The optical sensor drive circuit (hereinafter, also simply referred to as a drive circuit) 1 includes a CPU 3 and a RAM.
4, a ROM 5, a I / O port 6 and the like, and a computer 2 as a control command means, and a variable resistor section 8 and the like connected to the computer 2. The optical sensor 13 connected to the drive circuit 1 is configured as a photocoupler including a light emitting diode 9 as a light emitting element and a phototransistor 10 as a light receiving element, and the light emitting diode 9 is connected via a variable resistance section 8. Computer 2
Connected to the I / O port 6 of. On the other hand, the phototransistor 10 is connected to the I / O port 6 via the voltage detection unit 11 as an output detection unit and the A / D converter 12. The optical sensor 13 is mounted as a reflective or transmissive sensor together with the drive circuit 1 at a predetermined location in the printer and detects the presence or absence of printer paper and the home position of the print head. For example, when the sensor 13 is a reflection type, the object P is detected by the phototransistor 10 receiving the irradiation of the light L from the light emitting diode 9 reflected by the object P to be detected. When the sensor 13 is of a transmissive type, an object is detected by blocking the light emitted from the light emitting diode 9 to the phototransistor 10. here,
The computer 2 may be the one provided for controlling the printer, or may be the one provided separately from it. Here, the computer 2 and the variable resistance part 8 constitute a light emission amount control part of the light emitting diode 9.

FIG. 2 is a block diagram showing details of the variable resistance section 8. The variable resistance unit 8 includes a plurality of input ports D0-
An input / output interface unit 7a having D7 and output ports Q0 to Q7 corresponding to them, and each output port Q0
To Q7 through the buffer 15 connected to the resistors R0 to R
Equipped with 7. In the input / output interface unit 7a, the input ports D0 to D7 receive control signals from the I / O ports 6 of the computer 2 via the corresponding buses B0 to B7, and the output ports corresponding to the input ports receiving the control signals. Is L, and the output of the output port corresponding to the input port not receiving the control signal is H. On the other hand, the resistor section R0 connected to the output ports Q0 to Q7
The resistors R7 to R7 have different resistances, and are connected to the light emitting diode 9 on the side opposite to the input / output interface unit 7a.

The light emitting diode 9 is driven at a constant voltage of a predetermined voltage Vcc, and its current flows from the light emitting diode 9 side to the resistor portions R0 to R7 side. On the other hand, the buffer 15 connected to the input / output interface unit 7a outputs a voltage that substantially cancels the driving voltage Vcc of the light emitting diode 9 when receiving the output of H from the output ports Q0 to Q7, and outputs the output of L. When received, the current is allowed to flow from the light emitting diode 9 side to the resistor portions R0 to R7 side. Therefore, the input / output interface unit 7a has the buffer 15
At the same time, when a control signal is given to any of the input ports D0 to D7, it functions as a resistance switching unit 7 for selectively connecting any one of the resistance units R0 to R7 to the light emitting diode 9. .

Here, the resistance values of the resistance portions R0 to R7 are sequentially reduced in the order of, for example, R0, R1, ... R7. On the other hand, the clock circuit 14 is connected to the input / output interface unit 7a, and by receiving the clock, the input ports for receiving the control signals from the computer 2 are switched sequentially in the order of, for example, D0, D1 ... D7. And the output port whose output is L is also Q
Switches in the order of 0, Q1 ... As a result, the resistance part becomes R
0, R1, R2, ... R7 are sequentially switched in this order to be connected to the light emitting diode 9, and the divided voltage applied to the light emitting diode 9, that is, the light emission level of the light emitting diode 9 is switched while being connected to each of the resistor parts R0 to. It will increase stepwise according to the resistance value of R7. Here, the resistance part R0
The range of the resistance value covered by R7 to R7 is such that the current flowing through the light emitting diode 9 by switching the resistance part is the maximum current If that can be conducted from the minimum current If (MIN) at which light emission starts substantially.
It is set to fit within (MAX).

Next, as shown in FIG. 1, the phototransistor 10 is provided at a position where it can receive the light from the light emitting diode 9 or its reflected light, and as shown in FIG. Is connected to the resistor portion R8, and the same driving voltage of Vcc as that of the light emitting diode 9 is applied,
The output voltage V0 is detected by the voltage detector 11,
After being / D converted, it is sent to the computer 2. Then, the ROM 5 of the computer 2 stores a control program 5a for controlling switching of the resistance units R0 to R7 based on the value of the output voltage V0 sent.

FIG. 4 shows a resistance portion R for the light emitting diode 9.
7 is a graph showing the relationship between the current value flowing through the light emitting diode 9 when 0 to R7 are connected, that is, the light emission level of the light emitting diode 9 and the output voltage V0 of the phototransistor 10. If (0), ... If (7) on the horizontal axis of the graph
Is a current value when the connected resistance portions are R0, ..., R7, and the current value, that is, the light emission level of the light emitting diode 9 becomes higher toward the right side of the horizontal axis. The output voltage V0 of the phototransistor 10 sharply decreases when the light emitted from the light emitting diode 9 reaches a certain level (hereinafter, also referred to as a threshold irradiation level), and an object is detected based on the decrease in the output. Will be done.

Here, the threshold irradiation level may change with age of the phototransistor 10. On the other hand, if the surface of the light emitting diode 9 or the phototransistor 10 is covered with dirt, dust, or the like, the light from the light emitting diode 9 is blocked, so that the threshold irradiation level can be obtained unless the light emission output of the light emitting diode 9 is increased. Sometimes you can't. Therefore, when the divided voltage applied to the light emitting diode 9 is constant, the irradiation level of light to the phototransistor 10 may be insufficient due to the above reason, and the sensor may not operate normally. However, in the drive circuit 1 of the present embodiment, the divided voltage can be adjusted by appropriately selecting the resistor portions R0 to R7 connected to the light emitting diode 9, and thus the phototransistor 10 is not excessively deficient. The light irradiation level can be obtained. The operation will be described below.

The computer 2 (FIG. 1) of the drive circuit 1 is
While monitoring the output V0 of the phototransistor 10,
Input / output interface unit 7 (FIG. 2) input port D0
To D7 are sequentially applied to sequentially switch the resistance portions R0 to R7 connected to the light emitting diode 9 in order from the one having a larger resistance value, thereby stepping the level of light emitted from the light emitting diode 9 to the phototransistor 10. The output voltage V0 from the photo transistor 10 is compared with a reference value Vr stored in advance in the RAM 4 or the like. Then, when the output voltage V0 becomes equal to or lower than the reference value Vr, the switching of the resistance units R0 to R7 is stopped, and the circuit control is performed so that the resistance unit connected to the light emitting diode 9 at that time continues to be connected thereafter. I do. In addition, the resistance part R0-
R7 may be switched in ascending order of resistance value. In this case, when the output voltage V0 becomes equal to or higher than the reference value Vr, switching of the resistance units R0 to R7 is stopped, and light is emitted immediately before the final switching. The circuit is controlled so that the diode 9, which was connected to the diode 9, is finally connected.

The above-mentioned control is executed based on the control program 5a stored in the ROM 5. The control flow will be described below with reference to the flowchart of FIG. First, in S1, a control signal is transmitted to the input port D0 of the input / output interface 7a to connect the corresponding resistor R0 to the light emitting diode 9, and in S2, the output voltage V0 of the phototransistor 10 is less than the reference value Vr. Check if If V0 <Vr, the processing is terminated and the resistance portion R0 is kept connected to the light emitting diode 9. On the other hand, when V0 ≧ Vr, S3
Then, the control signal is applied to the input port D1 and the output V0 of the phototransistor 10 is checked at S4. If V0 <Vr in S5, the state in which the resistance portion R1 is connected to the light emitting diode 9 is maintained, and if V0 ≧ Vr, the process proceeds to S5. Thereafter, similarly, the control signal is sequentially given in the order of D2 and D3, and the output V0 of the phototransistor 10 is given each time.
Is checked and the same processing as S2 is performed (S6 to S16). Then, even if a control signal is given to D7, the phototransistor 1
When the output voltage V0 of 0 does not fall below Vr, an alarm is displayed on the alarm display unit 17 such as a display and a lamp connected to the computer 2 (S17). Here, the reference value Vr can be stored as a fixed value in the ROM 5 or the like in advance, or may be input from the input unit 16 such as a key operation unit connected to the computer 2.

The control as described above can be automatically executed by the computer 2 when the printer is started up, for example. As a result, not only can the optical sensor 13 be operated in a good condition at all times, but also its adjustment work is substantially unnecessary. In addition, when the optical sensor 13 is not used, if the drive circuit 1 is configured so that the current does not flow in the light emitting diode 9 and the phototransistor 10, the life of the sensor can be extended.

Here, the driving circuit 1 can be configured so that a current flows from the resistance portion R0 side to the light emitting diode 10 side as shown in FIG. In this case, the light emitting diode 9 is connected in the opposite direction to that shown in FIG.
The output of the buffer 15 of the inverter 15 is Vcc when the input is L, and the output is small when the input is H.
Has been replaced by. That is, when the output of the output port is H, no current flows through the resistor units R0 to R7 and the light emitting diode 9, and when the output of the output port is L, no current flows through the resistor units R0 to R7 and the light emitting diode 9. Flow, the same effect as the above-described embodiment can be obtained.

The resistance switching unit 7 may have a structure including the input / output interface unit 7a, or may have a structure including a switching mechanism using a thyristor.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a drive circuit of an optical sensor of the present invention.

FIG. 2 is a circuit diagram showing details of a variable resistance portion thereof.

FIG. 3 is a flowchart of a control program

FIG. 4 is a graph showing the relationship between the output voltage of the phototransistor and the value of the current flowing through the light emitting diode when the resistance portions having different resistance values are connected to the light emitting diode.

5 is a circuit diagram showing a modified example of the drive circuit of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 drive circuit 2 computer (control command means) 7 resistance switching section 7a output / input interface section D0 to D7 input port Q0 to Q7 output port 8 variable resistance section R0 to R7 resistance section 9 light emitting diode (light emitting element) 10 phototransistor (light receiving element) Element) 13 Optical sensor

Claims (7)

[Claims] 1. A light-emitting element that emits light when supplied with electric power, and a light-receiving element that changes its output upon receiving light, and the light emitted from the light-emitting element is irradiated by an object to be detected. By being blocked, or by receiving irradiation of light from the light emitting element reflected by the object,
An optical sensor that detects the presence of the object based on a change in the output of the light receiving element and a change in the voltage, comprising a variable resistance part, and changing the resistance value of the variable resistance part to cause the light emission. A light emission amount control unit that controls the light emission amount of the light emitting device by changing the voltage applied to the device, an output detection unit that detects the output of the light receiving device, and a light receiving device of the light detection device that the output detection unit detects. A drive circuit for an optical sensor, comprising: a control command unit that changes a resistance value of a variable resistance unit of the light emission amount control unit based on an output. 2. The variable resistance section of the light emission amount control section has a plurality of resistance sections each having a different resistance value, and a resistance for switchably connecting a part of the plurality of resistance sections to the light emitting element. 2. The optical sensor drive circuit according to claim 1, further comprising a switching unit, wherein the light emitting element is driven at a constant voltage. 3. The light emission amount control unit connects to the light emitting element while sequentially switching the resistance unit from one having a large resistance value to one having a small resistance value or from one having a small resistance value to a large resistance value. Optical sensor drive circuit. 4. The resistance switching section includes an input / output interface section having an input port for receiving a control signal from the control command means and an output port to which the plurality of resistance sections are respectively connected, Based on the control signal from the control command means input from the port, among the resistance units connected to the output port, for the resistance unit to be connected to the light emitting element, another resistance unit and The drive circuit for the optical sensor according to claim 2 or 3, wherein different levels of voltage are applied. 5. The control command means changes the resistance value of the variable resistance portion so that the output voltage of the light receiving element approaches the reference value from a larger side or a smaller side with respect to a predetermined reference value. The drive circuit for the optical sensor according to claim 1, wherein the change in the resistance value is stopped when the output voltage of the light receiving element becomes equal to or higher than or equal to the reference value. . 6. The light emitting device is a light emitting diode,
The drive circuit for an optical sensor according to claim 1, wherein the light receiving element is a phototransistor. 7. The driving of the optical sensor according to claim 1, wherein the optical sensor is provided in a printer to detect the presence or absence of print paper and the home position of the print head. circuit