JPH0362231B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the detection characteristics of a paper detection device used in printers and the like to detect the presence or absence of recording paper.

[Conventional technology]

Some paper detection devices emit light from a light emitting diode onto the recording paper feeding path, receive the reflected light with a phototransistor, and detect the presence or absence of recording paper based on the amount of light received. . Hereinafter, such a device will be referred to as a paper detection device using a reflective optical sensor.

An example of the configuration of a conventional paper detection device using a reflective optical sensor is shown in FIG.

In FIG. 6, 10 is a light emitting diode, 20 is a phototransistor, and 30 is a reflective surface.

The light emitting diode 10 irradiates light onto the reflective surface 30.

The phototransistor 20 receives the reflected light from the reflective surface 30 and generates a voltage e at both ends of the resistor R _L in accordance with the amount of received light. One end of the resistor R _L is connected to the emitter of the phototransistor 20, and the other end is connected to ground.

The reflective surface 30 is arranged on the recording paper feeding path. This reflective surface 30 is the recording paper surface when there is recording paper, and is the surface on which the recording paper is placed when there is no recording paper, for example, a platen surface made of black rubber. The surface on which the recording paper is placed has a lower light reflectance than the surface of the recording paper.

In such a device, if the base current and collector current generated in the phototransistor 20 by incident light of intensity I are I _D and I _L , the relationship between these currents is as follows.

I _L = h _FE · _ID where, h _FE : Current amplification factor of the phototransistor From this, the voltage across the resistor R _L is as follows.

e= _RL・_IL =h _FE・R _L・_ID By comparing this voltage e with a comparator, the presence or absence of recording paper is detected.

[Problem that the invention seeks to solve]

Here, the collector current I _L is affected by changes in parameters such as the amount of light emitted from the light emitting diode, the distance between the sensor and the recording paper, the reflectance of the recording paper, and the current amplification factor _hFE . Therefore, in the apparatus shown in FIG. 6 which detects the presence or absence of recording paper based on the collector current I _L , the threshold level of the comparator must be adjusted when each of the above parameters changes. This led to the problem that it was not suitable for mass production.

The present invention was made to eliminate the above-mentioned problems, and there is no need to adjust the threshold level of the comparator even in response to changes in the amount of light emitted from the light emitting diode, the reflectance of the recording paper, etc. ,
The purpose is to realize a paper detection device suitable for mass production.

[Means for solving problems]

The present invention provides a paper detection device that irradiates light from a light emitting diode onto a recording paper feed path, receives reflected light from a phototransistor, and detects the presence or absence of recording paper based on the amount of received light. While the light emitting diode is emitting light, the phototransistor is driven with a pulse voltage, and the charge accumulated by the light received while the pulse voltage is at a low level is transferred to the phototransistor when the pulse voltage is at a high level. A control circuit that discharges when the phototransistor reaches the level, a peak output generation circuit that generates a signal with a level corresponding to the maximum output voltage when discharging the phototransistor, and A/D conversion of the output of the peak output generation circuit. and an A/D converter that outputs the information, and the control circuit determines the presence or absence of recording paper based on the output of the A/D converter.

〔Example〕

The present invention will be explained below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a paper detection device according to the present invention. Components in FIG. 1 that are the same as those in FIG. 6 are given the same reference numerals.

In FIG. 1, 40 is an inverter, 50 is a peak output generation circuit, 60 is an A/D converter, and 70 is a control circuit.

The inverter 40 inverts a constant periodic pulse signal generated from the control circuit 70 and sends it to the phototransistor 20. The accumulation mode is detected by driving the phototransistor 20 with a pulse signal of a constant period.

Here, the operation of detecting the power storage mode of the phototransistor will be explained.

FIG. 2 is a circuit diagram of a phototransistor.

In FIG. 2, phototransistor TR is irradiated with light. In this state, the phototransistor
When the driving voltage _Vcc of TR changes as shown in FIG. 3a, the voltage e across the resistor R _L changes as shown in FIG. 3b.

That is, the pulse signal in Fig. 3a is “Low”.
During the accumulation period T _i at "Level", charge is accumulated in the phototransistor TR by the received light.

During the readout period _Ts in which the pulse signal of FIG. 3b is at "High Level", the charges accumulated during the accumulation period _Ti are discharged. As a result, a current flows through the resistor R _L , and the voltage e across the resistor R L has a waveform with a peak as shown in FIG. 3b. The height V _p of this peak is given by the following equation.

V _p = T _i · I _L /C _BC ...(1) Here, T _i : Length of storage period C _BC : Junction capacitance when reverse bias is applied between the base and collector of the phototransistor Again, the first Return to the diagram, peak output generation circuit 50
consists of a diode D, a resistor R and a capacitor C. The diode D has one end connected to the emitter of the phototransistor 20 and the other end connected to the A/D converter 60. Resistor R and capacitor C
is connected at one end to the A/D converter 60 and at the other end to ground.

The peak signal generation circuit 50 uses these elements to generate a signal at a level corresponding to the peak value of the output voltage e in the power storage mode.

The A/D converter 60 is a peak signal generating circuit 50
A/D converts the output.

The control circuit 70 drives the phototransistor 20 with a pulse signal, and also drives the A/D converter 60.
The presence or absence of recording paper is determined based on the signal sent from the printer.

Next, the operation of such a paper detection device will be explained.

FIG. 4 is a time chart for explaining the operation.

The light emitting diode 10 irradiates light onto the reflective surface 30.

In the power storage mode, the control circuit 70 outputs a constant cycle pulse voltage signal S shown in FIG. 4a. This signal is inverted by an inverter 40 to become a signal S as shown in FIG. 4b. The signal S is input from the collector of the phototransistor 20.
As a result, the emitter voltage _es of the phototransistor 20 changes as shown in FIG. 4c due to the above-described operation of detecting the storage mode of the phototransistor. The peak voltage V _p of the waveform in Figure 4c is:
It is given by equation (1).

Here, when there is recording paper on the reflective surface 30, the reflected light is strong, so the collector current I _L is large. As a result, the peak voltage V _p increases, and the emitter voltage e _s changes with a waveform as shown by the solid line in FIG. 4c. On the other hand, when there is no recording line on the reflective surface 30,
Since the reflected light is weak, the collector current I _L is small. As a result, the peak voltage V _p becomes low, and the emitter voltage e _s changes in a waveform as shown by the broken line in FIG. 4c.

The peak signal generation circuit 50 uses a diode D, a resistor R, and a capacitor C to perform pseudo peak detection on the voltage generated across the resistor R _L , as shown in FIG.
It outputs _a sawtooth voltage signal as shown in . The level of this signal corresponds to the value of the peak voltage V _p . Therefore, when there is recording paper on the reflective surface 30, the voltage _ed changes in a waveform as shown by the solid line in FIG. 4d. On the other hand, when there is no recording paper on the reflective surface 30, the voltage _ed changes with a waveform as shown by the broken line in FIG. 4d.

The A/D converter 60 A/D converts the voltage signal e _d .

The control circuit 70 determines the presence or absence of recording paper on the reflective surface 30 based on this A/D converted signal.

The operation in this power storage mode is performed at the beginning of the paper feeding operation. After that, normal phototransistor driving is performed with the signal S set to High Level. Once the presence or absence of the recording paper is detected, the value of the detection signal remains approximately constant thereafter, and if the presence or absence of the recording paper changes, the detection signal changes significantly.

In the embodiment, a case has been described in which the presence or absence of recording paper is detected, but various marks placed on recording paper may also be detected.

〔effect〕

According to the paper detection device according to the present invention, the following effects can be obtained.

That is, as can be seen from equation (1), detection sensitivity can be increased simply by changing the length of the accumulation period T _i without being affected by variations in the current amplification factor h _FE of the phototransistor.

By the way, when the detection sensitivity is increased, the peak voltage
V _p increases, but is limited by the output voltage of buffer 40. Therefore, the relationship between the amount of incident light I and the output voltage _ed is as shown in FIG. Here, the amount of incident light I is influenced by changes in parameters such as the amount of light emitted from the light emitting diode, the distance between the sensor and the recording paper, and the reflectance of the recording paper.

Therefore, by increasing the detection sensitivity (by lengthening the accumulation time T _i ) and utilizing the characteristics of the flat region of the graph in FIG. 5, it becomes less susceptible to the changes in each of the parameters. This eliminates the need to adjust the threshold level of the comparator even if each parameter changes, making it suitable for mass production. Additionally, recording paper with a wider range of reflectance can be used.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the paper detection device according to the present invention, FIGS.
FIG. 5 is a graph showing the relationship between the amount of incident light and the output of the device; FIG. 6 is a configuration diagram of a conventional paper detection device. DESCRIPTION OF SYMBOLS 10... Light emitting diode, 20... Phototransistor, 30... Reflection surface, 50... Peak output generation circuit, 60... A/D converter, 70... Control circuit.

Claims (1)

[Claims] 1. Paper detection in which the recording paper feed path is irradiated with light from a light emitting diode, the reflected light of this light is received by a phototransistor, and the presence or absence of recording paper is detected based on the amount of received light. In the device, the phototransistor is driven with a pulse voltage while the light emitting diode is emitting light, and the pulse voltage is applied to the phototransistor at a low level.
A control circuit that discharges the charge accumulated by light received while the pulse voltage is at High Level when the pulse voltage reaches High Level, and generates a signal whose level corresponds to the maximum value of the output voltage when the phototransistor is discharged. an A/D converter that A/D converts the output of the peak output generation circuit and outputs the A/D converter, and the control circuit converts the output of the A/D converter into A paper detection device characterized in that it determines the presence or absence of recording paper.