JPH0654355U - Scanner - Google Patents

Abstract

(57) [Abstract] [Purpose] To suppress the change of the light emission amount of the LED due to the voltage change. [Structure] When R light is generated, a high level signal is applied to the R port 21. This turns on the FET 27 and the analog switch 40, and further turns on the NPN transistor 46. As a result, FET27, LED17,
A current flows through the path of the NPN transistor 46 and the resistor 47, and the LED 17 emits R light. Since the voltage corresponding to the current flowing through the LED 17 is detected by the resistor 47 and is fed back to the differential amplifier 44, the NPN transistor 46.
Operates as a constant current circuit.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a scanner suitable for use when illuminating a document with an LED as an illumination light source and reading characters or figures drawn on the document.

[0002]

[Prior art]

 When a document is read by the scanner, R, G, and B LEDs are prepared, and the R, G, or B light is sequentially applied to the document. Then, the R, G, or B light reflected by the original or transmitted through the original is detected by a sensor such as a CCD.

[0003]

[Problems to be solved by the device]

 Conventionally, a constant voltage circuit has been used to emit light from this LED. For this reason, when the power supply has a lot of noise, the light emission amount of the LED may change corresponding to the noise of the power supply.

When the light amount of the LED changes in this way, for example, when an image is captured line-sequentially, unevenness occurs in the captured image for each line, and there is a problem that the image quality deteriorates.

The present invention has been made in view of such a situation, and makes it possible to read an image of an original evenly.

[0006]

[Means for Solving the Problems]

 The scanner of the present invention is provided with LED 17, 18 or 19 for R, G or B for generating R, G or B light for irradiating a document to be scanned, and any one of LED 17, 18 or 19. A first constant current circuit 62 that supplies a constant current, a second constant current circuit 63 that supplies a constant current to the other two or one of the LEDs 17, 18 or 19, and LEDs 17, 18 or. The selection circuit 61 selects any one of the nineteen.

This scanner can be further provided with analog switches 40, 41 or 42 for selectively operating the constant current circuit 62 or 63 so as to correspond to the selection of the selection circuit 61.

Further, in this scanner, the selection circuit 61 and the constant current circuits 62 and 63 are connected to the LEDs 17, 18 or 19 by the _{first to} third three lines L ₁ , L ₂ or L _3. The first line L ₁ is connected to the anode of the LED 17 and the cathodes of the LEDs 18 and 19, the second line L ₂ is connected to the cathode of the LED 17 and the anode of the LED 18, and the third line L 1 is connected. ₃ can be connected to the anode of LED 19.

[0009]

[Action]

 In the scanner having the above-mentioned configuration, when the selection circuit 61 selects the LED 17, the constant current circuit 62 supplies a constant current to the LED 17. When the LED 18 or 19 is selected by the selection circuit 61, a constant current is supplied to each by the constant current circuit 63. Therefore, it is possible to suppress the change in the amount of light emitted from the LED due to the noise of the power supply, and as a result, it becomes possible to read the original evenly.

[0010]

【Example】

 FIG. 1 is a block diagram showing the configuration of an embodiment of the scanner of the present invention. The LED block 1 incorporates three LEDs 17, 18, and 19 (FIG. 2) for R, G, and B, and any one of them is driven by the LED drive circuit 5, and R, G, and B are driven. The light is generated independently. The R, G, or B light emitted from the LED block 1 is applied to the original 3 placed on the carriage 2, and the reflected light (or transmitted light) is detected by the CCD 4. . The stepping motor drive circuit 6 drives the stepping motor 7 to move the carriage 3 a fixed amount (one line at a time).

The CCD 4 is driven by the CCD driving circuit 11 and outputs a signal corresponding to incident light to the A / D converter 10. The A / D converter 10 is adapted to A / D convert the input signal, output it to the memory 12, and store it. The CPU 13 reads and processes the data stored in the memory 12 in response to a command supplied from the host computer 15 via the SCSI interface 14, and at the same time, transmits the data via the SCSI interface 14 to the host computer 15 It is designed to output to. Further, the CPU 13 controls the A / D converter 10 and the CCD drive circuit 11, and also controls the LED drive circuit 5 or the stepping motor drive circuit 6 via the input / output interface (I / O) 8 or 9. It is done like this.

Next, the operation will be described. The CPU 13 drives the stepping motor 7 through the I / O 9 and the stepping motor drive circuit 6 when the scan operation is instructed by the host computer 15 to move the carriage 2 to a predetermined position. As a result, the original 3 placed on the carriage 2 is placed at a predetermined position with respect to the LED block 1 and the CCD 4.

The CPU 13 also controls the LED drive circuit 5 via the I / O 8 to turn on the R LED of the LED block 1. The R light emitted from the LED block 1 is applied to the original 3, and the reflected light or the transmitted light is incident on the CCD 4. The CCD 4 is driven by the CCD drive circuit 11 and outputs a signal corresponding to the incident R light to the A / D converter 10. The A / D converter 10 A / D converts the input signal, supplies the signal to the memory 12, and stores the signal.

As described above, when the R component data of a predetermined one line of the original 3 is read, the CPU 13 then controls the LED block 1 via the I / O 8 and the LED drive circuit 5, G light is generated. As a result, the G light is emitted to the same position of the original 3 where the R light is emitted. Then, the light of the G light from the original 3 is detected by the CCD 4, and its output is supplied to the memory 12 via the A / D converter 10 and stored therein.

Next, the CPU 13 causes the LED block 1 to emit B light. The B light is also applied to the same position where the R light and G light of the original 3 are applied, and the light from there is incident on the CCD 4. Then, the signal output from the CCD 4 is supplied to the memory 12 via the A / D converter 10 and stored therein.

When the reading of the data for one line is completed as described above, the CPU 13 then controls the stepping motor 7 via the I / O 9 and the stepping motor drive circuit 6 to drive the carriage 2. Move one line. Then, similarly to the case described above, the R, G, and B lights are sequentially emitted from the LED block 1, and the signal output from the CCD 4 is stored in the memory 12 via the A / D converter 10.

By repeating the above processing, the entire area of the original 3 is read.

Then, the CPU 13 outputs the data stored in the memory 12 to the host computer 15 via the SCS I interface 14 as needed.

FIG. 2 shows a configuration example of the LED block 1 and the LED drive circuit 5. In this embodiment, the LED block 1 is composed of an LED 17 that emits R light, an LED 18 that emits G light, and an LED 19 that emits B light. The anode of LED 17 and the cathodes of LEDs 18 and 19 are connected to line L ₁ . The cathode of LED 17 and the anode of LED 18 are connected to line L ₂ . Further, the anode of the LED 19 is connected to the line L ₃ .

The lines L _{1 to} L ₃ are connected to the selection circuit 61 and the constant current circuits 62 and 63, respectively. In the present embodiment, the selection circuit 61 is composed of FETs 27, 28, 29 and buffer amplifiers 24, 25, 26 connected to the gates of the respective FETs. One end of the FET 27 is connected to a predetermined voltage source (for example, 5V), and the other end is connected to the lines L ₁ , L ₂ and L ₃ , respectively.

The constant current circuit 62 is composed of a differential amplifier 44 and an NPN transistor 46 to which the output of the differential amplifier 44 is applied to its base via a resistor 45. The collector of the NPN transistor 46 is connected to the line L ₂ , its emitter is grounded through the resistor 47, and is also connected to the inverting input terminal of the differential amplifier 44. The non-inverting input terminal of the differential amplifier 44 is connected to a predetermined voltage source via the resistor 43.

The constant current circuit 63 is connected to the differential amplifier 49, the NPN transistor 51 to which the output of the differential amplifier 49 is applied to the base via the resistor 50, the NPN transistor 51, and Darlington connection. It is composed of an NPN transistor 52. The collectors of NPN transistors 51 and 52 are both connected to line L ₁ . The emitter of the NPN transistor 52 is grounded via the resistor 53 and is also connected to the inverting input terminal of the differential amplifier 49. The non-inverting input terminal of the differential amplifier 49 is connected to a predetermined voltage source via the resistor 48.

A high-level or low-level control signal is input to each of the R port 21, the G port 22, and the B port 23 via the I / O 8. This control signal is applied to the gate of the FET 27, 28 or 29 via the buffer amplifier 24, 25 or 26 and turns on or off the analog switch 40, 41 or 42, respectively. .

The positive voltage regulator 31 having the smoothing capacitors 32 and 33 outputs a positive voltage of a predetermined potential. This voltage is divided into a predetermined voltage by the resistors 34 and 35 and supplied to the non-inverting input terminal of the differential amplifier 44 via the switch 40. The voltage is divided by the resistors 36 and 37 and is supplied to the non-inverting input terminal of the differential amplifier 49 via the switch 41. Further, the output voltage of the positive voltage regulator 31 is divided by the resistors 38 and 39 and supplied to the non-inverting input terminal of the differential amplifier 49 via the analog switch 42.

Next, the operation will be described. When generating R light, a high level voltage is applied to the R port 21 from the I / O 8. This high level voltage is inverted by the buffer amplifier 24 and then applied to the gate of the FET 27 to turn on the FET 27.

When the R port 21 outputs a high level voltage, the analog switch 40 is turned on. As a result, the voltage output from the positive voltage regulator 31 is divided into a predetermined value by the resistors 34 and 35 and then supplied to the non-inverting input terminal of the differential amplifier 44 via the analog switch 40. As a result, the differential amplifier 44 outputs a current, the current is supplied to the base of the NPN transistor 46 via the resistor 45, and the NPN transistor 46 is turned on.

Therefore, current flows through the path of the FET 27, the LED 17, the NPN transistor 46, and the resistor 47, and the LED 17 emits R light.

Now, if the voltage of the predetermined voltage source increases for some reason, the voltage of the inverting input terminal of the differential amplifier 44 increases, and its output current decreases. As a result, the collector-emitter impedance of the NPN transistor 46 increases and its emitter current decreases. When the emitter current of the NPN transistor 46 decreases, the voltage drop of the resistor 47 decreases, and the potential at the connection point between one end of the resistor 47 and the emitter of the NPN transistor 46 drops.

On the other hand, when the voltage of the predetermined voltage source decreases and the input voltage of the inverting input terminal of the differential amplifier 44 decreases, the output current of the differential amplifier 44 increases. As a result, the base current of the NPN transistor 46 increases and the emitter current of the NPN transistor 46 also increases. Therefore, the terminal voltage of the resistor 47 rises, and the input voltage of the inverting input terminal of the differential amplifier 44 also rises.

As described above, the current flowing between the collector and the emitter (resistor 47) of the NPN transistor 46, that is, the current flowing through the LED 17 is a constant current. As a result, even if the predetermined voltage source changes due to noise or the like, the amount of light generated by the LED 17 is not affected by this and remains substantially constant.

When the R light is generated, low level signals are applied to the G port 22 and the B port 23, respectively. As a result, the FETs 28 and 29 are turned off, and the analog switches 41 and 42 are also turned off. When the analog switches 41 and 42 are off, a voltage of 0V is applied to the non-inverting input terminal of the differential amplifier 49 via the resistor 48. As a result, the output voltage of the differential amplifier 49 becomes low and the base voltage applied via the resistor 50 also becomes low, so that the NPN transistor 51 is turned off. Therefore, the NPN transistor 52 connected to the NPN transistor 51 and Darlington is also turned off. Therefore, the LEDs 18 and 19 are turned off and only R light is emitted.

Next, when G light is generated, a high level signal is applied to the G port 22. As a result, a low level signal is applied to the gate of the FET 28 via the buffer amplifier 25, and the FET 28 is turned on. Further, since the analog switch 41 is turned on, the output voltage of the positive voltage regulator 31 is divided into a predetermined value by the resistors 36 and 37, and then the non-inverting input terminal of the differential amplifier 49 is connected via the switch 41. Supplied. As a result, the output voltage of the differential amplifier 49 increases, the NPN transistor 51 whose output voltage is applied to the base via the resistor 50 turns on, and the NPN transistor 52 also turns on. As a result, a current flows through the path of the FET 28, the LED 18, the NPN transistor 52, and the resistor 53, and the LED 18 generates G light.

When the voltage supplied from the predetermined voltage source increases for some reason, the emitter currents of the NPN transistors 51 and 52 increase. When the emitter current of the NPN transistor 52 increases, the terminal voltage of the resistor 53 also increases, and the voltage of the inverting input terminal of the differential amplifier 49 also increases. As a result, the output current of the differential amplifier 49 decreases, and the base current of the NPN transistor 51, and thus the emitter current also decreases. As a result, the base current of the NPN transistor 52 decreases and the emitter current of the NPN transistor 52 decreases.

Conversely, when the voltage of the predetermined voltage source decreases, the emitter currents of the NPN transistors 51 and 52 decrease. As a result, the terminal voltage of the resistor 53 decreases and the voltage of the inverting input terminal of the differential amplifier 49 decreases. As a result, the output current of the differential amplifier 49 increases, and the base current of the NPN transistor 51, and thus the emitter current thereof, also increases. As a result, the base current of the NPN transistor 52 rises and its emitter current increases.

As described above, the current flowing between the collector and the emitter of the NPN transistor 52 (current flowing through the resistor 53), and hence the current flowing through the LED 18, becomes a constant current.

When G light is generated, a low level signal is applied to the R port 21 and the B port 23. Therefore, the FETs 27 and 29 are turned off. Also, the analog switches 40 and 42 are turned off. When the analog switch 40 is turned off, a low level voltage is applied to the non-inverting input terminal of the differential amplifier 44 via the resistor 43, so that the output current of the differential amplifier 44 also decreases. As a result, the NPN transistor 46 is also turned off. Therefore, at this time, the LEDs 17 and 19 remain off.

Next, when the B light is generated, a high level signal is applied to the B port 23, the FET 29 is turned on, and the analog switch 42 is also turned on. When the analog switch 42 is turned on, the voltage output from the positive voltage regulator 31 is divided by the resistors 38 and 39 and then applied to the non-inverting input terminal of the differential amplifier 49 via the analog switch 42. Therefore, the NPN transistor 52 is turned on in the same manner as when a high level voltage is applied to the G port 22. As a result, a current flows through the path of the FET 29, the LED 19, the NPN transistor 52, and the resistor 53, and B light is generated.

In this case, the fact that the current flowing through the NPN transistor 52 (hence the LED 19) becomes a constant current is the same as in the case where the G light is generated.

Further, at this time, since the low level voltage is applied to the R port 21 and the G port 22, the FETs 27 and 28 are turned off, and the analog switches 40 and 41 are also turned off. Therefore, the LEDs 17 and 18 do not generate light.

As described above, the R LED 17 is driven by one NPN transistor 46, and the G LED 18 and the B LED 19 are driven by two Darlington-connected NPN transistors 51 and 52. . This is for the following reason. That is, since the R LED 17 has a higher luminous efficiency than the G and B LEDs 18 and 19, it is possible to generate the same amount of light as that of the G or B LED 18 or 19 with a smaller driving current. Therefore, the R LED 17 having good light emission efficiency is driven by one NPN transistor 46, and the G and B LEDs 18 and 19 having poor light emission efficiency are driven by two NPN transistors 51 and 52 (R It is driven by a larger current than the LED 17) to generate the same amount of light.

In the above embodiment, the anode of LED 17 and the cathodes of LEDs 18 and 19 are connected to line L ₁ , the cathode of LED 17 and the anode of LED 18 are connected to line L _2, and the anode of LED 19 is connected to line L ₃ . It is connected. Therefore, the three LEDs 17, 18, and 19 can be driven by the _three lines L ₁ , L ₂ , and L ₃ . Normally, to drive three LEDs independently, four lines are required even if the cathode is shared, but by connecting in this way, one line can be reduced. it can.

[0042]

[Effect of device]

 As described above, according to the scanner of the present invention, since the R, G, and B LEDs are driven by the constant current circuit, it is possible to always generate a constant amount of light regardless of the noise of the power source. It is possible to read an even image.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a scanner of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of an LED block 1 and an LED drive circuit 5 in FIG.

[Explanation of symbols]

 1 LED Block 2 Carriage 3 Document 4 CCD 5 LED Drive Circuit 10 A / D Converter 12 Memory 13 CPU 17 to 19 LED 27 to 29 FET 31 Positive Voltage Regulator 40 to 42 Analog Switch 44, 49 Differential Amplifier 61 Selection Circuit 62 , 63 constant current circuit

Claims (3)

[Scope of utility model registration request] 1. An R, G, or B LED for generating R, G, or B light for irradiating an original to be scanned, and a constant current for any one of the R, G, or B LEDs. A first constant current circuit for supplying a constant current, a second constant current circuit for supplying a constant current to the remaining two one or the other of the LEDs for R, G or B, and the R, G or B And a selection circuit for selecting any one of the LEDs for use in the scanner. 2. Corresponding to the selection of the selection circuit,
The scanner according to claim 1, further comprising an analog switch that selectively operates the first or second constant current circuit. 3. The selection circuit and the first and second
In the constant current circuit of, the R, G
Alternatively, the first line is connected to the anode of the first LED of the R, G or B LEDs and the cathode of the second and third LEDs, The second line is connected to the cathode of the first LED and the anode of the second LED, and the third line is connected to the anode of the third LED. Item 3. The scanner according to Item 1 or 2.