JP3235736B2 - Lighting control device for arc tube of lighting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminator suitably used for a color image input device such as an image scanner, a digital copying machine, a facsimile, etc., and more particularly to lighting control of an arc tube of the illuminator.

[0002]

2. Description of the Related Art As a system for reading a color image, there is a system using a plurality of mercury fluorescent lamps having different spectral characteristics as disclosed in, for example, Japanese Patent Application Laid-Open No. 54-81715. FIG. 8 is a schematic sectional view of a color image input device according to the above-mentioned prior art.

[0003] A blue fluorescent lamp 11 emitting a blue color, a green fluorescent lamp 12 emitting a green color, and a red fluorescent lamp 13 emitting a red color are periodically turned on sequentially, and the glass table 6 is turned on.
Reading line S of the color image 200 placed on
The light is irradiated around the center. The reflected light L1 from the image 200 is
The light is reflected by the mirror 300 and is imaged by the imaging lens 40 on the one-dimensional array of storage type photoelectric conversion elements (CCD) 50. An electric signal corresponding to the reflected light L1 is output from the CCD 50 and converted into a digital signal by a processing unit (not shown) to obtain color information of the color image 200.

The operation of the color image input device will be described with reference to FIG. In FIG. 9, A, B, and C indicate the lighting timings of the blue fluorescent lamp 11, the green fluorescent lamp 12, and the red fluorescent lamp 13, respectively. D, E, F
Indicates the time change of the amount of light emitted from each fluorescent lamp. G indicates an electrical output from the CCD 50. H indicates a shift pulse that determines the accumulation time of the CCD 50.

As shown in FIG. 9A, the blue fluorescent lamp 11 is periodically turned on for a certain period of time to obtain a light output having a light quantity change shown in FIG. 9D. This light output enters the CCD 50 via the mirror 300 and the lens 40. And CCD
From 50, an output signal corresponding to the blue color image 200 as shown in FIG.

As shown in FIG. 9B, the green fluorescent lamp 12 is periodically turned on for a certain period of time to obtain a light output having a light quantity change shown in FIG. 9E. This light output enters the CCD 50 via the mirror 300 and the lens 40. And CCD
From 50, an output signal corresponding to the green color of the color image 200 as shown in FIG.

Further, as shown in FIG. 9C, the red fluorescent lamp 13 is periodically turned on for a certain period of time to obtain a light output having a light quantity change shown in FIG. 9F. This light output is mirror 300
And enters the CCD 50 through the lens 40. Then, a color image 20 as shown in FIG.
An output signal corresponding to a red color of 0 is obtained.

[0008]

SUMMARY OF THE INVENTION Each mercury fluorescent lamp 1
When lights are turned on as shown in FIGS. 9A, 9B, and 9C, the lights 1, 12, and 13 do not turn off instantaneously even after the lighting timing. As a result, light output including the afterglow time as shown in FIGS. 9D, E, and F is obtained from each fluorescent lamp.

For example, when magnesium germanate is used as the red phosphor, the afterglow time is about 5 milliseconds.

Here, the afterglow time is a time from the time when the lighting operation is completed to the time when the light amount becomes 10%.

Since the CCD 50 is a storage-type photoelectric conversion element, an output proportional to the integral amount of the light applied to the CCD 50 is output from the CCD 50 within the storage time determined by the shift pulse in one section shown in FIG. 9H. can get.

For this reason, in a color image input apparatus of a system for reading a color image by irradiating a plurality of illuminating lights having different spectral characteristics independently and sequentially and periodically to an image to be read, it is determined by a shift pulse in one section. The light applied to the CCD 50 within a given storage time must be monochromatic light.

Therefore, it is necessary to delay the start of lighting of the next green fluorescent lamp 12 for a time corresponding to the afterglow time of the blue fluorescent lamp 11. Similarly, the lighting start of the next red fluorescent lamp 13 needs to be delayed for a time corresponding to the afterglow time of the green fluorescent lamp 12.

The presence of afterglow hinders an increase in the reading speed of the color image input device. For example, a color image of A4 size (width 21.6 cm, height 30 cm) is 400
Consider reading at a resolution of dpi (= 64 microns) in 1 minute.

In order to obtain 4,800 lines of color information in the vertical direction, each color lamp must be sequentially turned on 4800 times per minute. The lighting time per line of each lamp is 4.2 milliseconds (= 60 / (4800 *
3)), and the above-mentioned red phosphor having an afterglow time of 5 milliseconds cannot be used.

However, the afterglow time of a fluorescent lamp that emits light by enclosing mercury is a characteristic peculiar to the phosphor used. In particular, the afterglow time of green and red is long, and the afterglow time is several milliseconds or less. There is no fluorescent lamp with a light time.

As described above, in a color image input apparatus of a type in which a color image is read by irradiating a plurality of illumination lights having different spectral characteristics independently and sequentially and periodically to an image to be read, a fluorescent lamp remains. Light time has been an obstacle to increasing the reading speed of the color image input device.

Accordingly, the present invention solves the above-mentioned problems, and an object of the present invention is to provide a lighting control device for controlling lighting of a light emitting tube of a lighting device so as to shorten the afterglow time. Is to do.

[0019]

SUMMARY OF THE INVENTION The present invention relates to a lighting device which irradiates an object to be excited provided in each of a plurality of arc tubes with an electron beam to emit light sequentially and periodically independently. In the lighting control device of the arc tube, during a predetermined light emitting period,
And an electron flow control unit for supplying an electron flow to each of the excitable bodies, wherein the control unit immediately before the end of the light emitting period, adjusts the density of the electron flow supplied to each of the excitable bodies to a value other than the light emitting period. And a lighting control device for the arc tube of the lighting device, characterized in that the lighting control device has an increasing means for increasing the lighting period.

[0020]

An electron flow having a predetermined density is supplied to an object to be excited for a certain period to emit light. Subsequently, an electron flow having a density higher than the predetermined density is supplied to the excitation target for a period shorter than the predetermined period to emit light.

[0021]

FIG. 1 shows a schematic structure of an arc tube 20 of a lighting device. Inside the front plate 7 constituting the arc tube 20,
0.1 to 100 milligrams per square centimeter,
Optimally, 4 milligrams of the phosphor 4 for cathodoluminescence is applied in stripes in the longitudinal direction. Phosphor 4
Is covered with an anode 3 formed by vacuum evaporation of aluminum to a thickness of 0.1 to 0.4 μm.

Inside the back plate 6 constituting the arc tube 20, a back electrode 8 made of aluminum is formed in the longitudinal direction by vacuum deposition or the like. The cathode 1 is stretched directly above the back electrode 8. The cathode 1 is made of a fine wire of tungsten having a diameter of 5 to 100 microns.

A grid 2 is provided at a position blocking between the anode 3 and the cathode 1, and the grid 2 is formed of a slit-shaped or net-shaped metal plate perforated by punching, electroforming or the like.

Anode 3, grid 2, cathode 1, back electrode 8
Can be electrically connected to a lighting circuit 30 to be described later by a terminal drawn out of the arc tube 2.

The luminous tube 20 forms a vacuum cavity sealed by a glass container, evacuates the exhaust tube 5 from a vacuum degree of minus 10 Pascal to about 10 minus 6 Pascal, and then heats by gas combustion heating. The vacuum inside the arc tube 20 is maintained by melting and sealing the tube 5.

FIG. 2 is a block diagram showing a lighting control device 30 for controlling lighting of the arc tube 20 shown in FIG. 1 together with a schematic sectional view of the arc tube 20.

In FIG. 2, the lighting control device 30 includes a power source E1 for applying a voltage V1 to the cathode 1 of the arc tube 20, a power source E2 for applying a high voltage to the anode 3, and an appropriate positive voltage for the back electrode 8. And a power source E3 for applying the voltage.

Further, the lighting control device 30 includes a lighting control unit 31 for generating control signals CTL1 and CTL2 described later,
The lighting drive unit 32 receives the both control signals and generates a control signal CTL3 for controlling the grid 2 of the arc tube 20.

Referring to FIG. 2, the operation until the arc tube 20 emits light will be described. When a voltage V1 is applied to the cathode 1 by the power supply E1, electrons 9 are emitted from the surface of the cathode 1 by Joule heat. The electrons 9 are accelerated by the power supply E2 toward the anode 3 to which a high voltage of about 8 kV is applied. The electrons 9 applied to the anode 3 penetrate the thin-film aluminum anode 3, excite the phosphor 4, and emit visible light L5 toward the outside of the arc tube 20 based on the principle of cathodoluminescence.

An appropriate positive voltage is applied to the back electrode 8 by the power supply E3, and plays a role of efficiently guiding the electrons 9 emitted from the cathode 1 to the anode 3.

Here, the grid 2 serves to adjust the amount of electrons 9. For example, the electrons 9 can be completely cut off by applying a control signal CTL3 applied to the grid 2 to the voltage V1 applied to the cathode 1 or equal to or a negative voltage. Also, the control signal CTL3
Then, when a positive voltage is applied to the voltage V1 applied to the cathode 1, the electrons 9 pass through the slit-shaped opening of the grid 2 and are irradiated to the anode 3. Further, the control signal CTL3
When the voltage is increased, the number of electrons 9 applied to the anode 3 increases in accordance with the voltage. That is, the current density applied to the phosphor 4 can be adjusted by the voltage applied to the grid 2.

The voltage applied to the grid 2 is usually about 5 V, but when it is lower than this, the afterglow time tends to be longer. The reason will be explained with experimental results.
When, for example, ZnS (Cu, Al as an activator) is used as the material of the phosphor 20, the afterglow time becomes shorter as the current density increases.

FIG. 3 is a diagram showing the measurement results of the afterglow time with respect to the current density. The current density applied to the phosphor is 10 microamps per square centimeter to 100
When changed to microamps, the afterglow time is 0.
It was found to decrease from 45 milliseconds to 0.15 second millimeters.

FIG. 4 is an explanatory diagram of the afterglow time. (A)
Represents the light output of the phosphor, and (b) represents the lighting control signal CTL.
Represents When the light amount immediately before the lighting control signal CTL is changed from ON to OFF is set to 100%, the remaining light amount is 10%.
The time that elapses before is called the afterglow time. In this experiment, the light output was sufficient and the output of a photodiode with a short time constant on the order of nanoseconds was observed using an oscilloscope.

FIG. 5 shows a comparison of the light output of the phosphor at two typical current densities, 40 and 100 microamps per square centimeter. In FIG. 5A, I and II indicate the light output when the current density is 40 microamps per square centimeter and the light output when the current density is 100 microamps, respectively.

From FIG. 5, it can be seen that the curves of the afterglows after the light is turned off reverse after about 1.2 milliseconds. For example, at 40 microamps of afterglow per square centimeter of current density, the total integrated value of afterglow after 0.18 milliseconds is 1 per square centimeter of current density.
In the afterglow of 00 microamps, it is equal to the value obtained by totally integrating the afterglow after 0.09 millisecond.

Accordingly, by setting the current density to 40 to 100 microamps per square centimeter, the waiting time for removing the effect of afterglow can be reduced by 0.09 millisecond.

However, when the current density applied to the phosphor is increased, the decrease in luminous efficiency is promoted due to an increase in the temperature of the phosphor.

Therefore, in the present invention, the phosphor is turned on and emits light at a low current density for a certain period of time, and the current density is increased just before the light is turned off.

FIG. 6 is a diagram for explaining that the above-described control is performed by the lighting control device 30 shown in FIG.

From the lighting control section 31 shown in FIG. 2, the voltage is normally 5 V, and becomes 0 V only during the time t1.
The control signal CTL1 shown in (b) is output. Further, the voltage is usually 0 V, and the time t2 from the start of lighting of the arc tube 20.
6C, the control signal CTL2 shown in FIG.
Is output. The lighting drive unit 32 outputs a control signal CTL3 shown in FIG. The control signal CTL3 has a voltage V4 during a time t1 from the start of lighting, and a time t4 corresponding to a difference between t1 and t2.
The lighting signal having the voltage V5 is between three.

Since the voltage applied to the grid 2 is a two-step voltage, the electrons 9 applied to the phosphor 4
Also has a two-stage step-like temporal change. As a result, the light emitted from the phosphor, that is, the light output of the arc tube 20 shown in FIG.

The lighting control section 31 is constituted by a known signal generating circuit. The lighting drive unit 32 that receives the control signals CTL1 and CTL2 generated by the lighting control unit 31 and generates the control signal CTL3 will be described.

FIG. 7 shows a circuit configuration of the lighting drive unit 32 that generates the control signal CTL3 supplied to the grid 2 of the arc tube 20. The base of the transistor Tr1 is connected via a base resistor R1 to one input terminal IN1 of the lighting drive unit 32 to which the control signal CTL1 is input from the lighting control unit 31. The voltage V5 is applied to the collector of the transistor Tr1 from the power supply E5 via the collector resistor R2. The emitter of the transistor Tr1 is grounded.
The control signal CTL3 is provided to the collector of the transistor Tr1.
Is connected to an output terminal OUT.

The base of the transistor Tr2 is connected via a base resistor R3 to the other input terminal IN2 of the lighting drive unit 32 to which the control signal CTL2 is input from the lighting control unit 31. The base of the transistor Tr3 is connected to the collector of the transistor Tr2 via the collector resistor R5. The emitter of the transistor Tr2 is grounded.

The power supply E is connected to the collector of the transistor Tr3.
4 provides a voltage V4. A diode D1 and a resistor R4 are connected between the collector of the transistor Tr1 and the collector resistor R5. When the transistor Tr1 is turned on, the voltage V4 is reverse-biased, and the current flows from the transistor Tr3 to the transistor Tr1.
To prevent the water from flowing to

In the above configuration, the control signal CT
When L1 is supplied to the input terminal IN1, in the high-level section of FIG. 6B, a + 5V control signal CTL1 is supplied to the base of the transistor Tr1 via the resistor R1,
The transistor Tr1 turns on. Then, a current flows from the power supply E5 to the transistor Tr1 via the resistor R2.
Therefore, the collector voltage of the transistor Tr1 becomes approximately 0V, and the voltage of the control signal CTL3 output from the output terminal OUT becomes approximately 0V.

Next, when the control signal CTL1 falls to 0 V in the section t1 of FIG.
r1 turns off, and its collector voltage becomes substantially equal to the supply voltage V5 from the power supply E5. At the same timing as the fall of the control signal CTL1, the control signal CTL2 of +5 V is supplied to the input terminal IN2 via the resistor R3 to the base of the transistor Tr2, and the transistor Tr2 is turned on. Therefore, the collector voltage of the transistor Tr2 becomes approximately 0V.

Then, the transistor Tr3 is turned on, and operates so that the collector voltage of the transistor Tr1 becomes substantially equal to the supply voltage V4 from the power supply E4. Since the voltage drop of the difference between the voltage V5 and the voltage V4 is consumed by the resistor R2,
In a section t2 of FIG. 6D, the control signal CTL3 has a voltage substantially equal to the voltage V4.

The section t2 of FIG.
When the control signal CTL2 falls to 0V,
The transistor Tr2 turns off, and the transistor Tr3 also turns off. The collector voltages of the transistor Tr1 and the transistor Tr2 become substantially equal to each other, and become substantially equal to the voltage V5. Therefore, the control signal CTL3 having a voltage substantially equal to the voltage V5 is output from the output terminal OUT.

In FIG. 6B, when the control signal CTL1 goes high after the section t3 has passed, the transistor T
r1 turns on, and the control signal CTL3 output from the output terminal OUT returns to approximately 0V again.

As described above, the input terminals IN1, 2
Therefore, when the control signals CTL1 and CTL2 having the waveforms shown in FIGS. 6B and 6C are given to the lighting drive unit 32,
As shown in FIG. 6D, a control signal CTL3 having a step-like waveform having a voltage substantially equal to V4 in the section t2 and a voltage substantially equal to V5 in the section t3 are output from the output terminal OUT. You.

When the control signal CTL3 having such a waveform is given to the grid 2 of the arc tube 20, the arc tube 20 outputs
An optical output as shown in FIG. This is because the light emission is performed at a large current density during the period t3 immediately before the light is turned off, compared with the case where the light emission is performed at the small current density during the light emission period t1 as in the period t2. Moreover, if the period of the high current density is set to a sufficiently short period immediately before turning off, there is no danger of shortening the life of the phosphor.

[0054]

As described above, the lighting control device of the present invention turns on and emits light from the phosphor of the arc tube at a low current density for a certain period of time, and raises the current density immediately before the light is turned off, thereby increasing the temperature of the phosphor. Since the rise can be suppressed low, the luminous efficiency does not decrease and the afterglow time can be shortened. Therefore, image reading can be performed at high speed in the color image input device.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic structure of an arc tube of a lighting device.

FIG. 2 is a diagram showing both a block diagram of a lighting control device of the present invention and a schematic sectional view of an arc tube.

FIG. 3 is a diagram showing a measurement result of an afterglow time with respect to a current density.

FIG. 4 is a diagram showing a light output of a phosphor and a time chart of a lighting control signal.

FIG. 5 is a diagram showing a light output of a phosphor at two types of current densities and a time chart of a lighting control signal.

FIG. 6 is a diagram illustrating the operation of the lighting control device of the present invention.

FIG. 7 is a diagram illustrating a circuit example of a lighting drive unit of the lighting control device of the present invention.

FIG. 8 is a schematic sectional view of a conventional color image input device.

FIG. 9 is a time chart illustrating a lighting control operation of the conventional color image input device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode 2 Grid 3 Anode 4 Phosphor 5 Exhaust pipe 6 Back plate 7 Full plate 8 Back electrode 11 Blue fluorescent lamp 12 Green fluorescent lamp 13 Red fluorescent lamp 20 Light emitting tube 30 Lighting control device 31 Lighting control unit 32 Lighting drive unit 40 Lens Reference Signs List 50 photoelectric conversion element 60 glass base 300 mirror Tr1 transistor Tr2 transistor Tr3 transistor R1 resistance R2 resistance R3 resistance R4 resistance R5 resistance D1 diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-98076 (JP, A) JP-A-3-112093 (JP, A) JP-A-59-181499 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H05B 37/02-37/03 H05B 41/30-43/02 H01J 63/06 H04N 1/04-1/20 G03B 27/52-27/56

Claims (1)

(57) [Claims] 1. A lighting control device for an arc tube of an illumination device, wherein an electron beam is applied to an object to be excited provided in each of a plurality of arc tubes to emit light sequentially and periodically. An electron flow control unit that supplies an electron flow to each of the excited bodies during a predetermined light emission period, and the control unit controls an electron flow supplied to each of the excited bodies immediately before the end of the light emission period. A lighting control device for an arc tube of a lighting device, further comprising increasing means for increasing a density from that of another period of the light emitting period.