JPS5811787B2 - optical information sensing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to reduce the thermal influence of a light source, extend the life of the light source, and provide an optical system that can operate reliably even in the face of deterioration of the light source and fluctuations in the optical characteristics of the paper surface. Relating to an information sensing device.

Conventionally, this type of device irradiates a paper surface with a light source driven by a constant drive value, uses a scanning means to obtain an electrical signal corresponding to optical information on the paper surface using a photoelectric conversion element, and processes the electrical signal. Display white and black.

In this specification, a drive value refers to a drive voltage value or a drive current value.

In such devices, when optical information is not being input, that is, when information is being received, the light source illuminates the paper surface with an amount of light suitable for reading, so heat radiation from the light source is generated. This poses a problem in that the temperature of the entire device increases, and heat dissipation must be taken into consideration.

Furthermore, light sources such as incandescent lamps and light emitting diodes have a short lifespan compared to other electronic components, and their lifespan can be extended by lowering their driving value below the rated value.

This property is particularly noticeable in the case of incandescent lamps.

However, if the light source is operated at a drive value below the rated value in order to extend the life of the light source, the electrical signal from the photoelectric conversion element
This has the disadvantage that the N ratio deteriorates, making reliable signal detection impossible.

The purpose of the present invention is to drive the light source with a constant small drive value when the peak value of the white level (electrical signal output corresponding to white optical information) is lower than a constant value, and to maintain a constant value. By providing a means for driving the light source so that the peak value of the white level becomes a certain constant value when the degree of whiteness becomes higher than the value of This reduces the effects of deterioration of the light source, etc., and will be explained in detail below.

FIG. 1 is a block diagram of an optical information sensing device showing a first embodiment of the present invention.

In FIG. 1, a lamp 1, a lens 2, a photoelectric conversion element 3
is housed in an integrated case 4 with an opening, and the opening of the case 4 is directed toward the paper surface 5, and the paper surface 5 is opened by hand.
Scan above.

The light from the lamp 1 emitted from the opening illuminates the paper surface 5, and the reflection from the paper surface 5 enters from the opening, passes through the lens 2, and enters the photoelectric conversion element 3.

The lamp 1 is lit by a lamp lighting circuit 6 and emits light in response to the output of a light source driver T supplied to the lamp lighting circuit 6.

The photoelectric conversion element 3 converts the optical information written on the paper surface 5 into an electrical signal corresponding to the optical information, and the electrical signal is input to the preamplifier 8.

For convenience of explanation, the output signal from the preamplifier 8 is always positive with respect to ground, and the greater the amount of light incident on the photoelectric conversion element 3, that is, the higher the degree of white seen by the photoelectric conversion element 3. It is assumed that the output of the amplifier 8 becomes positive.

The output of this preamplifier 8 is input to a white level detector 9 which maintains the maximum input level.

The output of this white level detector 9 is the output of the reading area start detector 1.
0, which is supplied to the reading zone end detector 11 and the light source driver 7.

Reading area start detector 10 and reading area end detector 11
The flip-flop 12 is controlled by the output signal of .

The flip-flop 12 is set by the output of the read zone start detector 10 and reset by the output of the read zone end detector 11.

Further, the output signal of the flip-flop 12 is supplied to the light source driver 7, and the light source driver 7 is controlled to alternately perform a first operation and a second operation, which will be described later.

The output of the preamplifier 8 is also input to a comparator circuit 13 to detect white and black optical information.

Next, the operation of this embodiment will be specifically explained.

FIG. 2 is a waveform diagram of each part in FIG. 1, where a is the output waveform of the preamplifier 8, b is the output waveform of the light source driver 7, and C
is the output waveform of the white level detector 9, d is the output waveform of the reading area start detector 10, e is the output waveform of the reading area end detector 11, f is the output waveform of the comparison circuit 13, and g is the output of the flip-flop 12. It shows the waveform.

First, when the case 4 is moved away from the paper surface 5 and approaches the paper surface 5 with its opening toward the paper surface 5, and is scanned in contact with the paper surface 5, the output of the preamplifier 8, which is proportional to the output of the photoelectric conversion element 3, A signal shown in waveform S1 in FIG. 2a is obtained.

For purposes of explanation, it is assumed that the higher the degree of white, the more positive it is with respect to ground.

First, when the case 4 is away from the paper surface 5, there is almost no light incident on the photoelectric conversion element 3, so the output of the white level detector 9 is also small, and the flip-flop 12 is reset.

The light source driver 7 performs the first operation based on the output signal of the flip-flop 12, and outputs a constant output signal as shown in FIG. .

is supplied to the lamp lighting circuit 6.

The lamp lighting circuit 6 lights the lamp 1 at a constant drive value.

As the case 4 approaches the paper surface 5, the output of the preamplifier 8 increases, and accordingly, the output of the white level detector 9, which maintains the peak value of the maximum input level, also increases as shown in FIG. 2C. come.

At a time t1 when the output of the white level detector 9 exceeds the reference value v1, the reading zone start detector 10 generates an output signal pulse as shown in FIG. 2d.

This read zone start pulse sets the flip-flop 12.

The light source driver I starts the second operation based on the output signal of the flip-flop 12, and lights the lamp 1 so that the output of the white level detector 9 becomes a constant reference value V2, as shown in FIG. A signal D8 as shown is supplied to the lamp lighting circuit 6, and the lamp 1 is lit at a drive value corresponding to the signal.

Waveforms S2 and S3 in Figure 2a are signal waveforms obtained as the output of the preamplifier 8 when the lamp is lit at a constant drive value.
Waveform S3 is the signal waveform obtained when scanning is carried out in close contact with the object, when scanning is carried out in a floating state without contact, or when scanning a paper surface with a lower reflectance than in S2, and the reading area is After the start pulse is generated, as the case 4 approaches the paper surface 5, the output of the preamplifier 8 tries to increase as shown in waveform S2 or S3, and the output of the white level detector 9 also tries to increase along with this. As shown in FIG. 2, the light source driver 7 supplies a signal to the lamp lighting circuit 6 to lower the driving value of the lamp 1, and even if the case 4 is in contact with the paper surface 5 at the time t2 when it is closer to the paper surface 5, Even in a slightly floating state, the output of the white level detector 9 becomes a constant value V2 as shown in FIG. 2C.

Next, even if the case 4 is scanned while touching the paper surface 5 or floating slightly, and the output of the preamplifier 8 decreases due to the optical information written on the paper surface, the output of the white level detector 9 will remain the same as the previous white level. Maintains state level V2.

Therefore, a signal having a constant white level peak value is obtained at the output of the preamplifier 8, as shown in waveform S1 in FIG. 2g.

Next, at time t3, when the case 4 finishes scanning the paper surface 5 and begins to move away from the paper surface, the output of the preamplifier 8 begins to decrease, and the output of the white level detector 9 also corresponds to the retention time of the peak value. However, the light source driver 7 outputs a signal to increase the driving value of the lamp 1 as shown in FIG. 2, and the output of the white level detector 9 is kept at V2.

However, finally at time L4, the light source driver 7 is saturated with the output DM corresponding to the maximum drive value of the lamp 1, and from then on,
The output of the preamplifier 8 decreases and the output of the white level detector 9 also begins to decrease with the time constant.

At time t5 when the output of the white level detector 9 falls below the reference level V3, the reading zone end detector 11 generates an output pulse as shown in FIG. 2e.

This reading zone end pulse resets the flip-flop 12 and controls the light source driver I to perform the first operation from the second operation.

The output of the light source driver 7 returns to a constant value from the maximum value DM at t5, the lamp 1 is lit at a constant drive value below the rated value, and the output of the preamplifier 8 decreases. The output of the white level detector 9 also decreases faster and eventually becomes less than the reference value V1.

The output signal of the preamplifier 8 has the waveform S1 in Fig. 2g,
This signal is compared with the reference value VT in the comparator circuit 13, and the second
As shown in FIG. f, a binary output representing a white state when the output of the preamplifier 8 is greater than the reference value VT, and a black state when it is smaller than the reference value VT is obtained as the output of the comparator circuit 13.

The output of the flip-flop 12 is as shown in FIG. 2g,
In the set state from time t1 to time t5, this period is taken as a reading area and the lamp 1 is lit by the second operation of the light source driver 7.

FIG. 3 is a specific circuit diagram of the embodiment shown in FIG. 1.

The output from the photoelectric conversion element 3 is supplied to a preamplifier 8.

The output of preamplifier 8 charges capacitor C1 through diode DI.

Even if the potential of terminal 31 falls below the potential of terminal 32, terminal 3
2 holds the peak potential.

The time constant formed by capacitor C1 and resistor R1 is set to have a sufficient length to maintain the peak potential during the period when the black area of the optical information is being scanned.

When the potential of the terminal 32 is lower than the reference potentials V1 and V2,
The flip-flop 12 has been reset, and the output terminal 33 is outputting a positive potential.

On the other hand, the holding output of the terminal 32 is supplied to the differential amplifier A1, and the potential of the output terminal 34 is a potential obtained by amplifying the difference between the reference potential V2 and the terminal 32, and the potential V2 is larger than the potentials V1 and V3, and the amplification degree is also sufficiently large. Therefore, the terminal 34 is lower than the potential DM supplied to the anode of the diode D2, and the diode D2 is in a non-conductive state.

Since the positive potential output of the terminal 33 is greater than the emitter potential VC of the transistor T1, the transistor T is in a conductive state.
The potential of the terminal 35 becomes approximately Vc.

The output potential of the terminal 35 drives the transistor T2 forming the lamp lighting circuit, and a constant current determined by the resistor R2 and the potential of the terminal 35 flows through the lamp 1 to light the lamp 1.

Next, when the peak holding potential of the terminal 32 becomes greater than the reference potential V1, the reading zone start detector consisting of the differential amplifier A2 is activated, and the terminal 36 goes from the ground potential to a positive potential, and the terminal 36 consists of the capacitor C2 and the resistor R3. It is differentiated by a differentiating circuit, and a rising portion of the pulse output is generated at the terminal 37 by the diode D3.

This pulse sets the flip-flop 12,
The terminal 33 changes from positive potential to ground potential, and the transistor T
1 becomes non-conductive.

Since the terminal 34 remains higher than the potential vM, the diode D
2 is non-conductive.

When transistor T1 and diode D2 are non-conductive,
Transistor T2 will be driven by supply potential VM.

Since the potential VM is higher than the potential ■c that had previously driven the transistor T2, the current in the lamp 1 increases compared to before, and the output of the preamplifier 8 also increases accordingly.
The peak holding potential of 2 is also increased.

When the potential of this terminal 32 reaches the reference potential v2, the potential of the output terminal 34 of the differential amplifier A1 decreases, and when it becomes lower than the supply potential VM, the diode D2 becomes conductive, and the potential of the terminal 35 changes to the potential V8 of the terminal 34. (G is the amplification degree of the differential amplifier A1), and if the amplification degree G is very large, it becomes almost equal to V2.

Next, when the potential of the terminal 32 tries to rise, the potential of the terminal 34 falls, and the current of the lamp 1 due to the transistor T2 decreases, so that the potential of the terminal 32 eventually changes from the potential V8 to the potential V8.
When it is smaller than M, the value is equal to the voltage potential V2.

Next, when the potential of the terminal 32 tries to fall, the potential of the terminal 34 rises, increasing the current of the lamp 1, and the potential of the terminal 32 hardly changes. However, when the potential of the terminal 34 becomes 7M or higher, the diode D2 becomes non-conducting, the transistor T2 is driven with the supply potential VM, and the lamp 1 is connected to the potential VM and the resistor R
2, and is not driven above this current, the output of the preamplifier 8 no longer increases, and as the case 4 moves further away from the plane of the paper 5, the output of the preamplifier 8 decreases.

The potential at the terminal 32 begins to decrease with the time constant of the capacitor C1 and the resistor R1, and when it becomes smaller than the reference potential V3, the output terminal 38 of the reading area end detector consisting of the differential amplifier A3
changes from the ground potential to a positive potential, and is differentiated by a differentiator circuit consisting of a capacitor C3 and a resistor R4, and a rising portion of the pulse output is generated at the terminal 39 by the diode D4, and this pulse returns the flip-flop 12 to the reset state.
The potential of the terminal 33 changes from ground potential to positive potential, the transistor T1 becomes conductive, the current of the lamp 1 decreases, the output of the preamplifier 8 also decreases, the potential of the terminal 32 also decreases faster, and finally the terminal 31 and the potentials of the terminal 32 become equal.

The output of the preamplifier 8 obtained by the above operation is compared with the reference potential VT in a comparator circuit consisting of a differential amplifier A4, and the output terminal 40 has a binary level displaying white and black (see Fig. 2 f). ) is output.

As explained above, in this embodiment, case 4 is
When the lamp is away from the paper surface 5, the lamp 1 is lit with a small current, so there is less heat radiation from the lamp 1, which has the advantage of reducing the temperature rise of the device. Furthermore, even if the reflectance of the base of the paper surface 5 is different, the photoelectrically converted output corresponding to the white background is constant, so there is an advantage that the optical information written on the paper surface can be reliably detected.

In the first embodiment, by setting the reference value V3 larger than the reference value V1, the influence of hysteresis in the ratio of the amount of light emitted by the light source to the amount of light received by the photoelectric conversion element (in the case where the lamp, lens, and photoelectric conversion element are housed) However, in cases where such hysteresis is not a problem, the fourth
As shown in the second embodiment of the figure, the reference value V1 and the reference value V3
If the functions of the reading area start detector, reading area end detector, and flip-flop in the first embodiment are provided by a level detector made of a single differential amplifier, the circuit can be further simplified. There is.

In FIG. 4, an output holding the peak value of the white level is supplied to an input terminal 41 of a level detector consisting of a differential amplifier A5 and compared with a reference value V4.

When the potential of the terminal 41 is smaller than the reference value V4, the output terminal 42 outputs a positive potential, and when the potential of the terminal 41 is larger than the reference value V4, the output terminal 42 outputs the ground potential.

The output of this terminal 42 is input to the light source driver I to control the light source driver 7.

It should be noted that although the above description relates only to preferred embodiments of the present invention, without departing from the scope of the present invention,
Numerous variants, for example replacing the light source with a light emitting diode,
Needless to say, it is possible to use a device in which photoelectric conversion elements are arranged one-dimensionally or two-dimensionally, and to transfer the paper surface by a roller instead of scanning by hand.

As detailed above, according to the present invention, the light source is driven below the rated value when optical information is to be read, and the photoelectric conversion output corresponding to the white level of the paper surface is constant during reading. Therefore, it is possible to prevent a temperature rise due to heat radiation from the light source, and there is an advantage that optical information can be reliably detected even when there are differences in the reflectance of the paper surface and differences in the scanning state.

The effect is particularly great when used in barcode readers and character readers using band scanning, which require the sensing section to be housed in an integrated case.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the first embodiment of the present invention, and FIG. 2 is a configuration diagram of the first embodiment of the present invention.
3 is a circuit diagram of the embodiment of FIG. 1, and FIG. 4 is a circuit diagram of a second embodiment of the present invention. 1... Lamp, 2... Lens, 3...
...Photoelectric conversion element, 4...Case, 5...
...Paper, 6...°Lamp lighting circuit, 7...
...Light source driver, 8...Preamplifier, 9.
...White level detector, 10...Reading area start detector, 11...Reading area end detector, 1
2...Flip-flop, 13...Comparison circuit.

Claims (1)

[Scope of Claims] 1. A light source that illuminates a paper surface, a photoelectric conversion means that converts optical information written on the paper surface into an electrical signal corresponding to the density of the optical information, and a peak of a white level from the electrical signal. a white level detector that detects a value and holds this peak value by a decay time constant; a first operation that drives the light source at a preset drive value; and a first operation that drives the light source within a predetermined maximum drive value. a second operation of driving the output of the white level detector to a preset first reference value V2; When the degree of whiteness reaches a value higher than the second reference value V1 set in advance to detect the start, the second light source driver
The light source driver is controlled so that the operation is performed, and the output of the white level detector becomes a value lower than a third reference value V3 preset for detecting the end of the reading area. means for controlling the light source driver so that the first operation of the light source driver is performed at certain times; and means for controlling the light source driver so that the first operation of the light source driver is performed at certain times; An optical information sensing device comprising: a comparison circuit that outputs a binary level. 2. The optical information sensing device according to claim 1, wherein the second reference value V1 and the third reference value V3 of the means for controlling the light source driver are equal.