JPH1120991A - Medium detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the existence of a medium for a long period of time. SOLUTION: A medium detecting device is provided with a sensor output storing means 34 for storing electric signals V01 and V02 outputted form a photosensor 10 when a medium P exists or does not exist; comparing and determining means 31 and 32 for determining whether a difference between the electric signals stored in the sensor output storing means 31 is smaller or not than a set value Vs; dynamic range increasing means 31 and 32 for changing, when the difference between the electric signals is determined to be smaller than the set value, the resistance value of the limit resistance section 15 or a light emitting side and/or the load resistance section 16 of a light receiving side and increasing the difference between the electric signals more than the set value; and threshold setting means 31 and 32 for setting, when the difference between the electric signals is larger than the set value, a threshold value Vth based on the sizes of the electric signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a medium detection device capable of determining the presence or absence of a medium by comparing an electric signal output from a photosensor with a threshold.

[0002]

2. Description of the Related Art For example, a medium detection device for detecting a medium is provided on a conveyance path for conveying a medium (paper or the like) to a printing unit of a printer.

FIG. 3 shows a conventional example of such a medium detecting device. In the figure, reference numeral 10 denotes a transmission type photosensor, and reference numeral 20 denotes a medium presence / absence determination circuit. The transmission type photo sensor 10
It includes a light emitting unit (photodiode) 11 and a light receiving unit (phototransistor) 12, and has a size according to the presence or absence of a medium (paper P) that blocks light emitted from the light emitting unit 11 from being incident on the light receiving unit 12. It is formed so that different electric signals (voltages) can be output.

[0006] The medium presence / absence determining means 20
It is formed such that the presence or absence of the medium (P) can be determined by comparing the electric signal output from 0 with a preset threshold value.

For example, when there is a medium (P) between the light emitting section 11 and the light receiving section 12, the amount of light entering the light receiving section (phototransistor) 12 is minimized and does not turn on, so that a large electric signal is output. You. On the other hand, when there is no medium (P) between the light emitting unit 11 and the light receiving element 12, the amount of light entering the light receiving unit 12 is maximized and turned on, so that a small electric signal is output.

In this manner, the electric signal output from the photosensor 10 according to the presence or absence of the medium (P) is compared with a threshold in the medium presence / absence determination circuit 20. If the electric signal is smaller than the threshold, the medium (P) is not present. If it is larger, it is determined that the medium (P) is present.

Here, the threshold value, which is a medium presence / absence determination criterion, is set at the time of manufacture, and its value is a fixed value.

[0008]

By the way, in the above-mentioned medium detecting device, the characteristics of the photosensor 10 change due to contamination or deterioration over time, and the size of the photosensor 10 is large or small when the medium is present or absent.
A situation in which the difference between the two electrical signals (voltages) becomes small may occur.

When such a situation occurs, it is difficult to accurately detect the presence or absence of a medium. For example, if the electric signal (voltage) when there is no medium exceeds the threshold, it is erroneously detected that there is a medium. Note that the erroneous detection also occurs when a reflective photosensor is used.

An object of the present invention is to provide a medium detecting device capable of accurately detecting the presence or absence of a medium over a long period of time.

[0011]

According to the present invention, there is provided a photosensor for outputting an electric signal having a different magnitude depending on the presence or absence of a medium for preventing light emitted from a light emitting section from being incident on a light receiving section;
A medium detection device comprising: a medium presence / absence determination unit capable of determining the presence / absence of a medium by comparing an electric signal output from the photosensor with a preset threshold value, wherein the resistance value is changed by being connected to the light emitting unit. A possible limiting resistance section, a load resistance section connected to the light receiving section and capable of changing a resistance value, and sensor output storage means for storing electric signals respectively output from the photosensors with and without a medium, A comparison determination unit that can determine whether a difference between the two electric signals stored in the sensor output storage unit is smaller than a set value, and a limiting resistor unit when the difference between the two electric signals is smaller than the set value; And / or a dynamic range increasing means for increasing the difference between the two electric signals to a set value or more by changing the resistance value of the load resistance section, and increasing the difference between the two electric signals when the difference between the two electric signals is more than the set value. Characterized by providing a threshold value setting means capable of setting said threshold value based on the.

In this case, two electric signals having different magnitudes output from the photo sensor when the medium is present and when the medium is not present are stored in the sensor output storage means. The comparison determination means determines whether or not the difference between the two electric signals stored in the sensor output storage means is smaller than a set value. If the comparison and determination means determines that the difference between the two electric signals is smaller than the set value, the dynamic range increasing means changes the resistance value of the limiting resistance part on the light emitting part side and / or the load resistance part on the light receiving part side. As a result, the difference between the two electric signals is increased to the set value or more.

The threshold setting means sets a threshold based on the magnitude of the electric signals when the difference between the electric signals is equal to or larger than a set value. For example, the median of both electric signals is set as the threshold.

As described above, when the difference between the electric signals output from the photo sensor with and without the medium becomes smaller than the set value due to deterioration or the like, the electric signal is adjusted to be equal to or larger than the set value. Since the threshold value is set based on both electric signals, extremely reliable and stable medium presence / absence detection can be performed over a long period of time.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. The present medium detection device is applied to a printer (not shown), and as shown in FIGS.
The basic configuration is the same as that of the conventional example (FIG. 3). However, the limiting resistance unit 15, the load resistance unit 16, the sensor output storage unit (34), the comparison determination unit (31, 32), A range increasing unit (31, 32) and a threshold setting unit (31, 32) are provided, and an electric signal (voltage V0) output from the photo sensor 10 when a medium (paper P) is present.
1) and the output electric signal [voltage V02 (<V0
1)] [Dynamic range; (V01−V0)
2)] is greater than or equal to the set value (Vs), and the threshold (Vth) can be set based on the adjusted electric signals (V01 ′, V02 ′).

The same components as those in the conventional example (FIG. 3) are denoted by the same reference numerals, and description thereof will be simplified or omitted.

First, in FIG. 1, reference numeral 30 denotes a control unit of the printer, which includes a CPU 31, a ROM 32, a RAM 3
3, EEPROM 34, keyboard 35, display 36,
An input / output port (I / O) 37 is formed. Each component (1) of the medium detection device is connected to the input / output port 37.
0, 15, 16, 20).

The medium presence / absence determination circuit 20 as the medium presence / absence determination means has a threshold value (Vth) that can be set arbitrarily.
A / A conversion circuit 21 and a comparator 22 for comparing an electric signal (V01, V02) output from the photosensor 10 with a threshold value (Vth) are formed so that the presence or absence of the medium (P) can be determined. .

Here, a limiting resistor 15 is connected to the light emitting section 11 of the photo sensor 10. The limiting resistance section 15 includes two resistors Rf1 and Rf2 connected in parallel.
And an analog switch SW connected in series to the resistor Rf2.
1, and the resistance value of the light emitting unit 11 can be changed by turning on / off the analog switch SW1 according to a control signal from the control unit 30.

On the other hand, a load resistance section 16 is connected to the light receiving section 12 of the photo sensor 10. Load resistance section 16
Are two resistors R1 and R2 connected in parallel and a resistor R2
And an analog switch SW2 connected in series with the control unit 30. The analog switch SW2 is turned on / off by a control signal from the control unit 30 so that the resistance value of the light receiving unit 12 can be changed.

The sensor output storage means (34) outputs electric signals (V01, V0) having different magnitudes output from the photo sensor 10 when the medium (paper P) is present and when it is not.
This is means for storing 2). In this embodiment, the sensor output storage means is formed from the EEPROM 34, and is executed in step ST10 in FIG.

The comparing and judging means includes a sensor output storing means (3
This is means for determining whether or not the difference (V01-V02) between the two electric signals (V01, V02) stored in 4) is smaller than a set value (Vs). In this embodiment, the comparison and determination means includes the ROM 32 storing the comparison and determination program
It is formed including the PU 31, and is executed in step ST11 of FIG. Further, as the set value (Vs), for example, +
3 volts have been selected.

The dynamic range increasing means changes the resistance value of the limiting resistance unit 15 and / or the load resistance unit 16 when it is determined that the difference between the two electric signals (V01, V02) is smaller than the set value (Vs). And the two electric signals (V
01, V02) can be increased to a value equal to or larger than the set value (Vs). In this embodiment, the dynamic range increasing means is formed from the ROM 32 storing the dynamic range increasing program and the CPU 31, and is executed in ST12 of FIG.

The threshold value setting means outputs the electric signal (V0
1, V02) is equal to or greater than the set value (Vs), the threshold value (V) is determined based on the magnitude of the electric signals (V01, V02).
th). In this embodiment, the threshold setting means is a ROM 32 storing a threshold setting program.
And the CPU 31 and are executed in ST13 of FIG.

Next, the operation of this embodiment will be described with reference to the flowchart shown in FIG. The electric signals (V01, V02) respectively output from the photo sensor 10 with and without the medium (P) are measured [D / A conversion circuit 2
1, the threshold (Vth) is sequentially changed to V01 (V
02) is obtained by searching for a place having the same value. ]. Both measured voltages (V01, V02) are stored in the EEPROM 34 of the control unit 30 as a sensor output storage unit.
(ST10).

Next, both measured voltages (V0 and V0) stored in the EEPROM 34 are compared by the comparing and judging means (31 and 32).
It is determined whether or not the difference of (1, V02) is smaller than the set value (Vs) (ST11). Both measurement voltages (V01, V02)
Is smaller than the set value (Vs) (S
In T11 (YES), the limiting resistor unit 15 on the light emitting unit 11 side by the dynamic range increasing means (31, 32).
And / or the resistance value of the load resistance section 16 on the light receiving section 12 side is changed, and the difference between the two measurement voltages (V01, V02) is increased to a set value (Vs) or more (ST12).

When the difference between the two voltages (V01, V02) is equal to or greater than the set value (Vs), the threshold setting means (31, 32) sets the threshold (Vth, Vth) based on the magnitude of the two voltages (V01, V02). ) Is set. For example, both voltages (V01,
The median of [V02) [(V01 + V02) / 2] is set as the threshold value.

As described above, the voltage (V0) output from the photosensor 10 when the medium (P) is present and when it is not present, respectively.
If the difference of (1, V02) becomes smaller than the set value (Vs) due to deterioration or the like, the difference is adjusted to be equal to or more than the set value (Vs), and the threshold (Vth) is set based on both voltages after the adjustment.
Is set, extremely reliable and stable medium presence / absence detection can be performed over a long period of time.

Although the transmission type photosensor 10 is used as the photosensor, a reflection type photosensor may be used. Further, the present medium detection device is applied to a printer, but may be applied to other electronic devices.

[0030]

According to the present invention, a limiting resistance section, a load resistance section, a sensor output storage section, a comparison / determination section, a dynamic range increasing section, and a threshold setting section are provided. Sometimes, the difference between the electric signals output from the photo sensor is adjusted to be equal to or greater than the set value, and the threshold value can be set based on the adjusted electric signals. Can be detected.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation.

FIG. 3 is a diagram illustrating a conventional configuration of a medium detection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Transmissive photosensor 11 Light emitting part 12 Light receiving part 15 Limiting resistance part 16 Load resistance part 20 Medium presence / absence determination circuit (medium presence / absence determination means) 31 CPU (threshold setting means, comparison determination means, dynamic range increasing means) 32 ROM (threshold) Setting means, comparison determining means, dynamic range increasing means) 34 EEPROM (sensor output storage means)

Claims (1)

[Claims] 1. A photosensor that outputs an electric signal having a different magnitude according to the presence or absence of a medium that blocks light emitted from a light emitting unit from being incident on a light receiving unit, and an electric signal output from the photosensor. A medium detection device comprising: a medium presence / absence determination unit capable of determining presence / absence of a medium by comparing with a preset threshold value; a limiting resistance unit connected to the light emitting unit and capable of changing a resistance value; and the light receiving unit A load resistance unit connected to the power supply unit, a resistance value changeable, a sensor output storage unit for storing electric signals output from the photosensor in the presence and absence of the medium, and both of the electric signals stored in the sensor output storage unit. A comparison determining means for determining whether the difference between the signals is smaller than a set value, and changing the resistance value of the limiting resistor and / or the load resistor when it is determined that the difference between the two electric signals is smaller than the set value. I Dynamic range increasing means capable of increasing the difference between the two electric signals to a set value or more, and threshold setting means capable of setting the threshold based on the magnitude of the two electric signals when the difference between the two electric signals is equal to or more than the set value And a medium detection device.