CN107666759B

CN107666759B - Discharge lamp lighting device and image forming apparatus including the same

Info

Publication number: CN107666759B
Application number: CN201710628336.6A
Authority: CN
Inventors: 水岛明洸; 福田稔; 松本茂义
Original assignee: Ushio Denki KK
Current assignee: Ushio Denki KK
Priority date: 2016-07-28
Filing date: 2017-07-28
Publication date: 2020-05-19
Anticipated expiration: 2037-07-28
Also published as: CN107666759A; JP2018018722A; JP6673081B2

Abstract

The invention provides a discharge lamp lighting device, which can maintain stable illumination intensity for a discharge lamp used as a light source for an image forming device with a color wheel no matter what application environment. The discharge lamp lighting device includes a pulse generating unit that receives a synchronization signal synchronized with a timing at which a color region of a subject to be irradiated with light from the discharge lamp is switched, and generates a pulse wave whose polarity is inverted in accordance with the synchronization signal. The pulse generating unit executes a control pattern including a first step of reversing the polarity of the pulse wave and a second step of maintaining the polarity of the pulse wave for a predetermined number of revolutions of the color wheel and repeatedly executes the control pattern for a predetermined number of revolutions of the color wheel. The predetermined number of turns is set to a first number of turns when the frequency of the synchronization signal is a frequency belonging to a first frequency band, and is set to a second number of turns larger than the first number of turns when the frequency of the synchronization signal is a frequency belonging to a second frequency band higher than the first frequency band.

Description

Discharge lamp lighting device and image forming apparatus including the same

Technical Field

The present invention relates to a discharge lamp lighting device suitable for use as a light source for a projector or the like. The present invention also relates to an image forming apparatus including the lighting device.

Background

Data projector apparatuses using a discharge lamp as a light source are roughly classified into two types of apparatuses. One is a liquid crystal system, in which light emitted from a high-pressure discharge lamp is projected onto liquid crystal panels of three colors of RGB. Another method is to project light emitted from a high-pressure discharge lamp onto a DMD (digital micromirror Device) by means of a DMD color wheel.

As such a discharge lamp, a discharge vessel made of transparent glass and sealed therein with a volume of, for example, 0.2mg/mm³And mercury above the discharge lamp, wherein the pressure in the container during lighting is 200 atm or more. By increasing the mercury vapor pressure, light in the visible waveform region can be obtained with high output.

Fig. 8A and 8B are schematic cross-sectional views of discharge lamps. Fig. 8B is an enlarged schematic sectional view of the vicinity of the electrode tip of fig. 8A.

As shown in fig. 8A, the discharge lamp 10 has a substantially spherical light emitting portion 11 formed by a discharge vessel. In the light emitting section 11, a pair of

electrodes

20a and 20b are arranged to face each other at a very small interval of 2mm or less.

Further, sealing portions 12 are formed at both ends of the light emitting portion 11. The conductive metal foil 13 is hermetically embedded in the sealing portion 12, and one end of the metal foil 13 is joined to the shaft portions (30a, 30b) of the

electrodes

20a, 20 b. The other end of the metal foil 13 is joined to an external lead 14, and electric power is supplied from a power supply unit not shown.

In such a discharge lamp 10, during lighting, the projections 21 are formed on the distal end surfaces of the pair of electrodes 20a and 20B, respectively, and the discharge arc 22 is held between the projections 21, whereby a stable lighting state is maintained, and the pair of electrodes 20a and 20B are arranged to face each other in the light emitting portion 11 of the arc tube (see fig. 8B and 9A).

On the other hand, when the discharge lamp 10 is lit in the same state for a long period of time, a large number of fine protrusions 23 are formed due to a high temperature, and fine irregularities are generated on the tip surface portion of the electrode (see fig. 9B). These fine protrusions 23 and irregularities are generated by the aggregation of compounds generated by melting of the material (e.g., tungsten) constituting the

electrodes

20a, 20b and by the combination with the gas enclosed in the light-emitting section 11, and the presence thereof changes the shape of the surface portion of the electrode tip. It is known that the starting point of the arc moves, the discharge position becomes unstable, and the illuminance decreases and flickers occur.

In order to solve such a problem, patent document 1 below discloses a lighting system of a discharge lamp (see fig. 10) in which a current waveform of a pulse wave P1 of a predetermined frequency (fundamental frequency) is supplied to the discharge lamp, and a current waveform of a pulse wave P2 of a lower frequency than the fundamental frequency is intermittently or periodically inserted into the pulse wave of the fundamental frequency. More specifically, the fundamental frequency is a frequency selected from the range of 60 to 1000Hz, and the low frequency is a frequency selected from the range of 5 to 200 Hz.

By setting the pulse wave to a low frequency, a period in which one electrode is fixed as an anode and the other electrode is fixed as a cathode is extended, that is, a period in which a high voltage is applied unidirectionally between the both electrodes is extended. As a result, the degree of heating of the electrode is increased, and heat can be transferred not only to the electrode tip but also to a portion distant from the tip. Therefore, even while the low-frequency pulse wave is applied, heat can be transferred to a portion away from the electrode tip, and the minute projections and projections generated at the portion can be melted and evaporated. This makes it possible to eliminate projections and irregularities other than the electrode tip portion, which are not intended to serve as arc starting points but rather are likely to have adverse effects.

Patent document 2 below describes a lighting device that corresponds to a system using a DMD. In the method using the DMD, it is described that the polarity of the pulse wave is inverted in synchronization with the timing of switching the color region (sector) of the color wheel. The polarity inversion of the pulse wave in synchronization with the switching timing of the sector has an advantage of preventing flicker.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4416125

Patent document 2: japanese patent No. 5141703

Disclosure of Invention

Problems to be solved by the invention

The present inventors have studied to control a discharge lamp lighting device corresponding to a projector having a color wheel so as to stabilize the position and shape of a projection of an electrode by using the techniques of

patent documents

1 and 2. That is, the lighting device is controlled such that the timing for inverting the polarity of the pulse wave corresponds to the rotation frequency of the color wheel, and a low-frequency pulse wave is intermittently or periodically inserted into the pulse wave of the fundamental frequency. However, when an image is continuously displayed by using light from the discharge lamp while such control is performed, it is known that there is a difference in brightness of the displayed image depending on the place and application of the application.

In view of the above-described problems, an object of the present invention is to provide a lighting method that can maintain stable illuminance regardless of an application environment of a discharge lamp used as a light source for an image forming apparatus having a color wheel. That is, an object of the present invention is to realize a lighting control device for a discharge lamp capable of such lighting control. Another object of the present invention is to provide an image forming apparatus including a discharge lamp whose lighting is controlled by such a lighting control device.

The present invention is directed to a case where the rotation speed of a color wheel included in an image forming apparatus depends on the environment in which the image forming apparatus is used. For example, when a projector is assumed as an example of the image forming apparatus, an application of projecting a video signal from the projector on a screen to be visually observed by a viewer is considered. In the case of using the color wheel for such an application, the number of turns (rotation speed) of the color wheel is determined for a predetermined time (for example, 1 second) based on a video signal input from the device to the image forming apparatus. The frequency of the video signal is determined by the country and the region, the required accuracy of the image, and the like. That is, it can be said that the rotation speed of the color wheel is expected to be a value different depending on the application environment of the image forming apparatus.

The present inventors have made studies to determine whether or not the illuminance maintaining function of light emitted from a discharge lamp is reduced in accordance with the application environment of an image forming apparatus by setting the rotation speed of a color wheel to a value that differs depending on the application environment. Further, based on the above-described studies, it has been studied to change the control content of the lighting device of the discharge lamp from the conventional one. As a result of earnest studies, the present inventors have found that the illuminance maintaining rate of the discharge lamp can be stabilized at a high level regardless of the application environment of the image forming apparatus by adopting the following configuration, and have completed the present invention.

The present invention provides a discharge lamp lighting device for an image forming apparatus, the image forming apparatus providing an alternating current to a discharge lamp and having a color wheel formed with a plurality of color regions, the discharge lamp having a pair of electrodes arranged in opposition to each other in a discharge vessel in which a predetermined gas is sealed, the discharge lamp lighting device including:

a pulse generating unit that receives a synchronization signal synchronized with a timing at which the color region of the object to be irradiated with the light from the discharge lamp is switched, and generates a pulse wave whose polarity is inverted in accordance with the synchronization signal; and

and a power supply unit to which a direct-current voltage is supplied, which converts the direct-current voltage into an alternating current corresponding to the frequency of the pulse wave, and which supplies the alternating current to the discharge lamp.

The pulse generating unit is configured to execute a control pattern including a first step of inverting a polarity of the pulse wave and a second step of maintaining the polarity of the pulse wave for a period of time during which the color wheel makes one rotation,

after the control pattern is repeatedly executed while the color wheel is rotated for a predetermined number of revolutions, the control pattern is repeatedly executed in a state where the polarity is reversed compared to the polarity of the pulse wave of the second step of the immediately preceding control pattern.

The pulse generating unit sets the predetermined number of turns to a first number of turns when the frequency of the synchronization signal is a frequency belonging to a first frequency band, and sets the predetermined number of turns to a second number of turns larger than the first number of turns when the frequency of the synchronization signal is a frequency belonging to a second frequency band higher than the first frequency band.

The time for which the color wheel rotates one turn depends on the rotational speed of the color wheel. The rotational speed of the color wheel is determined by the frequency of the synchronization signal. That is, when the frequency of the synchronization signal is high, the rotation speed becomes high, and conversely, when the frequency of the synchronization signal is low, the rotation speed becomes slow. That is, in the case of belonging to the second frequency band higher than the first frequency band, the rotation speed of the color wheel becomes faster and the time required for the color wheel to rotate one turn is shorter than in the case of belonging to the first frequency band in which the frequency of the synchronization signal is a value.

However, during the execution of the second step, the polarity of the pulse wave is fixed, and thus a voltage of the same polarity is continued from one electrode constituting the discharge lamp to the other electrode. This heats the electrode for a fixed time, and thus the effect of melting the fine protrusions, the irregularities, and the like can be obtained.

However, when the frequency of the synchronization signal is a value belonging to the second frequency band, the time required for the color wheel to rotate once is shorter than that in the case of the value belonging to the first frequency band, and therefore the time required for the polarity of the pulse wave to be fixed is inevitably shortened. As a result, the time for which the electrode is heated is shortened as compared with the case where the frequency of the synchronization signal is the first frequency band, and it is difficult to heat for a time sufficient to melt the fine protrusions, the irregularities, and the like.

Therefore, in the above configuration, when the frequency of the synchronization signal is a value belonging to the second frequency band, the number of times of repetition of the control pattern is set to be larger than that belonging to the first frequency band. More specifically, as follows. When the frequency of the synchronization signal is a value belonging to the first frequency band, the polarity of the pulse wave is inverted in the second step after the control pattern is repeatedly executed while the color wheel rotates by the first number of revolutions. On the other hand, when the frequency of the synchronization signal is a value belonging to a second frequency band higher than the first frequency band, the polarity of the pulse wave is reversed in the second step after the control pattern is repeatedly executed during a second number of revolutions of the color wheel which is greater than the first number of revolutions.

With this configuration, when the frequency of the synchronization signal is a value belonging to the first frequency band and a value belonging to the second frequency band, the difference in total time for intermittently applying the voltage in the same direction until the control pattern is repeated until the polarity of the pulse wave is inverted in the second step can be reduced. As a result, the minute projections and the irregularities formed on the electrodes can be melted to the same degree regardless of the frequency of the synchronization signal, and the illuminance maintenance ratio can be achieved to the same degree.

In addition, it is preferable that the first number of turns and the second number of turns are set so that the total time for performing the second step by repeatedly executing the control pattern in the time required for the color wheel to rotate the first number of turns is substantially the same when the frequency of the synchronization signal is a frequency belonging to the first frequency band, and the total time for performing the second step by repeatedly executing the control pattern in the time required for the color wheel to rotate the second number of turns is set when the frequency of the synchronization signal is a frequency belonging to the second frequency band.

The substantial identity can be defined as follows, for example. When the frequency of the synchronization signal is a frequency belonging to the first frequency band, Ta is the total time for executing the second step by repeating the control pattern for the time required for the color wheel to rotate by the first number of revolutions. In addition, when the frequency of the synchronization signal is a frequency belonging to the second frequency band, the total time for executing the second step by repeatedly executing the control pattern for the time required for the color wheel to rotate the second number of revolutions is Tb. In this case, for example, the case where the following expression (1) is satisfied can be substantially the same.

0≤|Ta-Tb|/Ta≤1……(1)

Further, it is preferable that the following formula (2) is satisfied.

0≤|Ta-Tb|/Ta≤0.2……(2)

By setting the first and second numbers of turns for satisfying the above equations (1) and (2), the minute projections and the projections formed on the electrodes can be melted to the same extent regardless of whether the frequency of the synchronization signal is a value belonging to the first frequency band or a value belonging to the second frequency band.

The pulse generating unit may repeat the control pattern during the predetermined number of rotations of the color wheel in a state where a polarity of the pulse wave is reversed compared to that of the pulse wave in the second step of the immediately preceding control pattern after the control pattern is repeated during the predetermined number of rotations of the color wheel.

The pulse generating unit may set a value of the predetermined number of turns to be larger as the frequency of the synchronization signal is higher.

The pulse generating unit may repeatedly generate the same waveform as the pulse wave generated during one rotation of the color wheel immediately before, while the color wheel is rotating the predetermined number of rotations.

The second step may include controlling to change a peak value of the pulse wave in accordance with the synchronization signal while maintaining the polarity of the pulse wave. For example, different peak values can be set according to the color region of the color wheel through which the light emitted from the discharge lamp passes.

Further, an image forming apparatus according to the present invention includes:

the discharge lamp lighting device having the above feature;

a discharge lamp that is lit upon receiving a current supply from the discharge lamp lighting device;

a color wheel having a plurality of color regions and capable of rotating, passing light from the discharge lamp through one of the color regions, and outputting light of a color corresponding to the color region;

a color wheel driving unit configured to drive the color wheel to rotate; and

and a control processing unit for outputting the synchronization signal to the discharge lamp lighting device in accordance with a signal from the color wheel driving unit.

Effects of the invention

According to the discharge lamp lighting device of the present invention, lighting control is realized in which a stable illuminance can be maintained regardless of an application environment for a discharge lamp used as a light source for an image forming apparatus having a color wheel.

Drawings

Fig. 1 is a block diagram schematically showing an example of the configuration of an image forming apparatus of the type using a DMD.

Fig. 2 is a schematic diagram of a color wheel.

Fig. 3 is a circuit block diagram schematically showing the configuration of the discharge lamp lighting device.

Fig. 4 is a diagram schematically showing the waveform of the pulse wave P generated from the pulse generator.

Fig. 5 is a diagram comparing waveforms of the pulse waves P generated by the lighting control device of the present embodiment when the frequencies of the synchronization signals Sb are different.

Fig. 6 is a diagram for comparing waveforms of pulse waves P generated by a lighting control device that performs the same control regardless of the frequency of the synchronization signal Sb when the frequency of the synchronization signal Sb is made different.

Fig. 7 is a graph comparing the temporal change of the voltage between the lamps when the discharge lamps are lit by the respective lighting devices of the comparative example and the example.

Fig. 8A is a schematic cross-sectional view of a discharge lamp.

Fig. 8B is an enlarged cross-sectional view of the vicinity of the electrode tip of the discharge lamp.

Fig. 9A is an enlarged schematic cross-sectional view of the vicinity of the electrode tip in a state where a discharge arc is formed and a stable lighting state is maintained.

Fig. 9B is an enlarged schematic cross-sectional view of the vicinity of the electrode tip in a state where the minute projections are formed at a portion other than the electrode tip.

Fig. 10 is a diagram showing an example of a conventional lamp current waveform.

Description of the reference symbols

1 a lighting device; 3 a power supply unit; 4 a pulse generating section; 10 a discharge lamp; 11 a light emitting section; 12 a sealing part; 13 a metal foil; 14 an external lead; 20a, 20b electrodes; 21, a protrusion; 22 a discharge arc; 23 micro-protrusions; 29a, 29b electrode heads; 30a, 30b electrodes; 31 a step-down chopper; a 32DC/AC conversion section; 33 a starting part; 34 a power control unit; 35 a driver; 41 a pulse generating circuit; 42 repetition number setting unit; 43 a memory section; 44 a frequency detection unit; 60 an image forming device; 61 light source means; 62 a concave mirror; 63 a color wheel; 64 a light homogenizing rod; 65 an optical element; 66DMD elements; 67 an optical system; 68 a color wheel driving section; 69 a control processing unit; 70 image output equipment; 71 a device control section; 72 a light converging region; 75 filament.

Detailed Description

An embodiment of a discharge lamp lighting device according to the present invention will be described with reference to the drawings. In the drawings, the dimensional ratio of the drawings does not necessarily coincide with the actual dimensional ratio.

[ Structure of the Lamp ]

First, an example of the structure of a discharge lamp to be subjected to lighting control by the lighting device of the present invention will be described with reference to fig. 8A and 8B. The discharge lamp to be subjected to the lighting control by the lighting device of the present invention is not limited to the configuration described below.

The discharge lamp 10 has a substantially spherical light-emitting portion 11 formed by a discharge vessel made of quartz glass. The material of the discharge vessel is not limited to quartz glass but may also consist of other materials. In the light emitting section 11, a pair of

electrodes

20a and 20b are arranged to face each other at a very small interval of, for example, 2mm or less.

Further, sealing portions 12 are formed at both ends of the light emitting portion 11. A conductive metal foil 13 made of molybdenum or the like is hermetically embedded in the sealing portion 12 by, for example, heat sealing. One end of the metal foil 13 is joined to the shaft portions of the

electrodes

20a and 20b, and the other end of the metal foil 13 is joined to the external lead wire 14, and electric power is supplied from a discharge lamp lighting device of the present invention described later.

The light emitting portion 11 of the discharge lamp 10 of the present embodiment is filled with, for example, mercury, an inert gas, and a halogen gas.

Mercury is used for obtaining the necessary visible light wavelength (for example, wavelength of 360 to 780nm), and is specifically enclosed at 0.20mg/mm³The above. The sealing amount varies depending on the temperature condition, and is used to realize a high vapor pressure such that the pressure inside the light emitting section at the time of lighting is 200 atm or more. Further, by enclosing a larger amount of mercury, a high-pressure discharge lamp having a high mercury vapor pressure such as 250 vapor pressure or more and 300 vapor pressure or more at the time of lighting can be produced, and a light source suitable for a projector can be realized as the mercury vapor pressure is higher.

As the inert gas, for example, about 13kPa argon gas is sealed. Its function is to improve lighting startability.

The halogen gas is enclosed in the form of a compound of iodine, bromine, chlorine, and mercury or other metals. The amount of halogen enclosed is from 10^-6μmol/mm³～10^-2μmol/mm³Is selected from the range of (1). The biggest reason for enclosing halogen is to increase the life of a discharge lamp using a so-called halogen cycle. In addition, when the discharge lamp 10 is designed to be small and have a high lighting vapor pressure, the function of preventing devitrification of the discharge vessel is also obtained by sealing halogen. Devitrification is a phenomenon in which crystallization proceeds from a metastable glassy state and changes to a polymer of crystal grains grown from many crystal nuclei.If this phenomenon occurs, light is scattered at the grain boundaries of the crystals, resulting in an opaque discharge vessel.

In the present invention, the gas sealed in the light emitting section 11 is not limited to the above-described gas if the same function can be achieved.

As an example of the discharge lamp 10, the maximum outer diameter of the light emitting part is 9.4mm, the inter-electrode distance is 1.0mm, and the inner volume of the discharge vessel is 55mm³The rated voltage is 70V, the rated power is 180W, and the power is supplied in an alternating current mode.

The discharge lamp 10 is supposed to be built in a projector which is being miniaturized, and the entire size is required to be extremely miniaturized, and a high light emission amount is also required. Therefore, the heat influence in the light emitting part is extremely severe, and the load on the tube wall of the lamp is 0.8 to 2.5W/mm²In particular 2.4W/mm². By mounting the discharge lamp 10 having a high mercury vapor pressure and a high wall load value to a demonstration device such as a projector or a head-up projector, it is possible to provide the demonstration device with radiant light having good color reproducibility.

[ shape of electrode tip ]

As shown in fig. 8B, the electrode 20a is composed of a head portion 29a and a shaft portion 30a, and the electrode 20B is composed of a head portion 29B and a shaft portion 30B. Further, a protrusion 21 is formed at the tip of each of the

electrodes

20a and 20 b. The protrusions 21 are formed by the coagulation of electrode materials melted at the electrode tips when the lamp is turned on. In the present embodiment, the electrode 20a and the electrode 20b are both made of tungsten, but the material is not limited to this.

When the

electrodes

20a and 20b are energized, they are heated and heated, and tungsten constituting these electrodes sublimates. The sublimated tungsten combines with the enclosed halogen gas in the region of the inner wall surface of the light emitting portion 11 at the relatively low temperature portion to form tungsten halide. Since tungsten halide has a relatively high vapor pressure, it moves again to the vicinity of the tips of the

electrodes

20a and 20b in a gaseous state. When the heating is performed again at this portion, the tungsten halide is separated into halogen and tungsten. Tungsten therein returns to the tips of the

electrodes

20a and 20b and condenses, and the halogen is recovered as a halogen gas in the light-emitting section 11. This phenomenon is referred to as halogen cycling. The condensed tungsten adheres to the vicinity of the tips of the

electrodes

20a and 20b to form the protrusions 21.

[ Structure of image Forming apparatus ]

Before the configuration of the lighting device, first, the configuration of an image forming apparatus to which the lighting device of the present invention is supposed to be applied is explained with reference to the drawings.

Fig. 1 is a block diagram schematically showing an example of the configuration of an image forming apparatus of the type using a DMD. Here, it is assumed that the image forming apparatus 60 is a single-plate type projector. The image forming apparatus 60 includes a light source device 61, a color wheel 63, an integrator rod 64, an optical element 65, a DMD element 66, an optical system 67, and the like.

The light source device 61 includes the discharge lamp 10 and the concave reflector 62. The discharge lamp 10 is an ac lighting type lamp, and is disposed so that an arc spot of the lamp substantially coincides with the first focal point of the concave reflecting mirror 62.

The reflected light from the concave mirror 62 is incident on the integrator rod 64 through the color wheel 63. Color wheel 63 is shown in fig. 2 as being divided into a plurality of color regions (here W, R, G, B, C, M) by filament 75. The color wheel 63 is driven by a color wheel driving unit 68 to perform driving control such as rotation and stop, and the light passing through a predetermined light converging region 72 is made incident on the integrator rod 64.

In the present embodiment, the color wheel 63 is described as being configured to divide each of the colors white (W), red (R), green (G), blue (B), cyan (C), and magenta (M) into the same angles, but the number of colors and the division method are not limited to this.

Image forming apparatus 60 includes a control processing unit 69 including a processor for performing calculations, a ROM for storing information such as programs necessary for the calculations, and a RAM for storing temporarily generated information. The control processing unit 69 performs processing for controlling the overall operation of the image forming apparatus 60. The color wheel driving unit 68 is connected to the control processing unit 69, and outputs a driving signal to the color wheel 63 based on a control signal from the control processing unit 69.

A rotary portion of the color wheel 63 is provided with a mark (not shown) for determining the position of the color region with respect to the color wheel 63. The color wheel driving unit 68 has a sensor (not shown) for reading the mark, and generates a rotational position detection signal Sc of the color wheel 63 by the sensor and outputs the signal Sc to the control processing unit 69. The control processing section 69 identifies on the basis of the rotational position detection signal Sc which color region the light that will pass through during operation is projected onto the screen.

The control processing unit 69 receives an image signal from a video output device 70 such as a DVD player or a computer, and outputs a rotation control signal Sd corresponding to the vertical synchronization signal Sz of the image signal to the color wheel driving unit 68. The color wheel driving unit 68 rotates the color wheel 63 at a fixed speed in accordance with the rotation control signal Sd from the control processing unit 69. The control processing unit 69 controls the operation of the device control unit 71 according to the rotational position of the color wheel 63, and causes the image display element to display an image for each color based on the image signal. That is, the color wheel driving unit 68 determines the rotation speed of the color wheel based on a signal input from the image output device 70.

The DMD element 66 is connected to a device control section 71 that performs a process for forming a necessary image on the DMD element 66. The device control unit 71 is also connected to the control processing unit 69.

The reflected light from the concave mirror 62 is transmitted through a light converging region 72 (see fig. 2) formed on the color wheel 63. The colors corresponding to the light converging region 72 are sequentially guided to the following integrator lens 64 by the rotation of the color wheel 63. That is, the respective colors of white (W), red (R), green (G), blue (B), cyan (C), and magenta (M) are projected in a time division manner, and thus only any one color is projected on the screen by the DMD element 66 at an instant, but human vision recognizes these colors or a mixed color thereof as an image.

White (W) is used to brighten the entire image, and by projecting white at fixed intervals, the effect of brightening the entire image can be obtained. For example, in the case where the color wheel 63 rotates at 180Hz (180 rotations per second), white (W), red (R), green (G), blue (B), cyan (C), and magenta (M) are projected 180 times during 1 second.

Color wheel 63 shown in fig. 2 is configured to have the same angle for each color region, but may define the area of each region in consideration of the color balance and brightness of the final image. The light converging region 72 formed in the color wheel 63 is, for example, a rectangular shape of 3.6 × 4.8 mm.

The lighting device 1 is connected to the control processing unit 69, and a synchronization signal Sb synchronized with the switching timing of the color region of the color wheel 63 is supplied from the control processing unit 69. The lighting device 1 inverts the polarity of the pulse wave based on the synchronization signal Sb.

[ Structure of Lighting device ]

Next, a specific configuration of the lighting device 1 is described with reference to the drawings. Fig. 3 is a circuit block diagram schematically showing the configuration of the lighting device 1. As shown in fig. 3, the lighting device 1 includes a power supply unit 3 and a pulse generation unit 4. The discharge lamp 10 is lighted by supplying the alternating current generated by the power supply unit 3 to the discharge lamp 10 based on the pulse wave P output from the pulse generation unit 4.

(Power supply part)

The power supply unit 3 includes a step-down chopper 31, a DC/AC converter 32, and a starter 33.

The step-down chopper 31 steps down the supplied direct-current voltage Vdc to a desired low voltage, and outputs the stepped-down voltage to the subsequent DC/AC converter 32. Fig. 3 shows a specific configuration example in which the step-down chopper 31 includes a switching element Qx, a reactor Lx, a diode Dx, a smoothing capacitor Cx, a resistor Rx, and a voltage dividing resistor Vx.

One end of the switching element Qx is connected to a + side power supply terminal to which the dc voltage Vdc is supplied, and the other end is connected to one end of the reactor Lx. The diode Dx has a cathode terminal connected to a connection point between the switching element Qx and the reactor Lx, and an anode terminal connected to a negative power supply terminal. One end of the smoothing capacitor Cx is connected to an output side terminal of the reactor Lx, and the other end (-side terminal) is connected to an output side terminal of the resistor Rx. The resistor Rx is connected between the negative terminal of the smoothing capacitor Cx and the anode terminal of the diode Dx, and performs a function of detecting a current. The voltage-dividing resistor Vx is connected between the negative-side terminal and the positive-side terminal of the smoothing capacitor Cx, and realizes a function of detecting voltage.

The switching element Qx is driven in accordance with the gate signal Gx output from the power control unit 34. In accordance with the duty ratio of the gate signal Gx, the step-down chopper 31 steps down the input DC voltage Vcd to a voltage corresponding to the duty ratio, and outputs the voltage to the subsequent DC/AC converter 32.

The DC/AC conversion unit 32 converts the input DC voltage into an AC voltage of a desired frequency, and outputs the AC voltage to the following starting unit 33. Fig. 3 shows a specific example of the configuration (full-bridge circuit) in which the DC/AC converter 32 is constituted by switching elements Q1 to Q4 connected in a bridge shape.

The switching element Q1 is driven in accordance with a gate signal G1 output from the driver 35. Similarly, the switching element Q2 is driven by a gate signal G2, the switching element Q3 is driven by a gate signal G3, and the switching element Q4 is driven by a gate signal G4. The driver 35 outputs a gate signal for alternately repeating on/off to the group of diagonally arranged switching elements Q1 and Q4 and the group of switching elements Q2 and Q3. Thereby, a rectangular wave-shaped alternating-current voltage is generated between the connection point of the switching elements Q1 and Q2 and the connection point of the switching elements Q3 and Q4.

The starting unit 33 is a circuit unit for boosting the AC voltage supplied from the DC/AC unit 32 and supplying the boosted AC voltage to the discharge lamp 10 when the discharge lamp 10 is started. Fig. 3 shows a specific example of the configuration in which the starting unit 33 is composed of a coil Lh and a capacitor Ch. When the discharge lamp 10 is started, an AC voltage having a high switching frequency (for example, several hundred kHz) near the resonance frequency of the LC series circuit including the coil Lh and the capacitor Ch is applied from the DC/AC unit 32, whereby a high voltage necessary for starting the discharge lamp 10 is generated on the secondary side of the starting unit 33, and the voltage is supplied to the discharge lamp 10. After the discharge lamp 10 is lit, the frequency of the AC voltage supplied from the DC/AC unit 32 is set to a constant frequency (for example, 60 to 1000Hz), and a constant lighting operation is performed. The constant lighting operation includes control contents described later with reference to fig. 4 and 5.

In the above circuit, the frequency of the AC voltage supplied to the starter 33 is changed by adjusting the on/off switching cycle of the group of switching elements Q1 and Q4 and the group of switching elements Q2 and Q3 in the DC/AC unit 32. Further, the operating duty ratio of the switching element Qx in the step-down chopper 31 is adjusted, thereby changing the peak value of the ac voltage supplied to the starter 33.

That is, the switching element Qx of the step-down chopper 31 is turned on/off at a switching frequency corresponding to the duty ratio of the gate signal Gx output from the power control unit 34, and thereby the power supplied to the discharge lamp 10 changes. For example, when the power supplied to the discharge lamp 10 is to be increased, the power control unit 34 performs control to increase the duty ratio of the gate signal Gx so that a desired power value is achieved.

The power control unit 34 performs feedback control as follows: the duty ratio of the gate signal Gx is appropriately changed according to the value of the current flowing through the resistor Rx of the power supply unit 3 and the voltage value indicated by the voltage-dividing resistor Vx, and the input power is maintained at a target power value (control power value).

(pulse generating section)

The pulse generating unit 4 includes a pulse generating circuit 41, a repetition number setting unit 42, a memory unit 43, and a frequency detecting unit 44, and outputs the generated pulse signal P to the driver 35 of the DC/AC unit 32. As described above, the switching of the switching elements Q1 to Q4 of the DC/AC unit 32 is controlled in accordance with the pulse signal.

The pulse generating circuit 41 outputs a pulse wave based on the information about the control mode stored in the memory unit 43 and the number of repetitions set in the number of repetitions setting unit 42. The "control mode" and the "number of repetitions" will be described later.

The frequency detector 44 receives the synchronization signal Sb supplied from the control processor 69, detects the frequency of the synchronization signal Sb, and outputs the information to the repetition number setting unit 42. The repetition number setting unit 42 sets the number of repetitions of the control pattern based on the information stored in the memory unit 43 and the frequency of the synchronization signal Sb.

The configuration in which the control processing unit 69 outputs the synchronization signal Sb in synchronization with the switching timing of the color region of the color wheel 63 will be described with reference to fig. 1 again.

As described above, the control processing unit 69 receives the image signal from the video output device 70 such as a DVD player or a computer, and outputs the rotation control signal Sd corresponding to the vertical synchronization signal Sz of the image signal to the color wheel driving unit 68. The color wheel driving unit 68 rotates the color wheel 63 at a fixed speed in accordance with the rotation control signal Sd from the control processing unit 69.

The control processing unit 69 also generates a synchronization signal Sb for synchronizing with the timing (filament timing) at which the light from the discharge lamp 10 passes through the boundary of the color region in the color wheel 63, based on the rotational position detection signal Sc, and outputs the synchronization signal Sb to the lighting device 1. More specifically, the synchronization signal Sb is supplied to the pulse generation circuit 41 and the frequency detection unit 44 (see fig. 3). The pulse generating circuit 41 inverts the polarity of the pulse wave P in accordance with the timing of the synchronization signal Sb, and inverts the polarity of the lamp current by the DC/AC conversion unit 32.

Fig. 1 shows a configuration in which the lighting device 1 outputs the lighting detection signal Sa to the control processing unit 69. This signal is a signal for making the control processing section 69 recognize that the lighting device 1 is operating correctly, but is not necessarily a signal.

(pulse waveform)

Next, the waveform of the pulse signal P output from the pulse generating unit 4 will be described with reference to the drawings.

Fig. 4 is a diagram schematically showing the waveform of the pulse wave P generated from the pulse generating unit when the synchronization signal Sb has a predetermined frequency (here, 96Hz as an example). In the example of fig. 4, the time during which the color wheel 63 makes one rotation is denoted by T1, and the step S1 of reversing the polarity of the pulse wave P and the step S2 of maintaining the polarity of the pulse wave P are performed during the time T1. Specifically, first, at the slave time t_a0To time t_a1Performs step S1 of inverting the polarity of the pulse wave P, and then at the time t_a1To time t_a2Step S2 of maintaining the polarity of the pulse wave P is executed.

In the present embodiment, as described with reference to fig. 2, the color wheel 63 is divided into 6 color regions. That is, the time T1 required for the color wheel 63 to rotate one turn is divided into 6 sector periods (sg1 to sg6), and the peak value of the pulse wave P changes as necessary according to the switching timing of each sector period. Here, since the areas of the color regions formed by the color wheel 63 are set to be the same as described above, the sector periods (sg1 to sg6) are indicated at the same time, but the configuration is not limited to this. That is, the length of each sector period (sg1 to sg6) varies according to the ratio of the areas of the color regions formed by color wheel 63.

In the configuration of the present embodiment, it is assumed that a preferable ratio of the peak value is set for each color passing through the light converging region 72. For example, the pulse wave P has different wave height values among the sector sg4, the sector sg5, and the sector sg6, and is set to a wave height value suitable for a color corresponding to each sector. Such information on the ratio of the peak value of each color may be stored in, for example, the memory section 43.

When the synchronization signal Sb is input, the frequency detector 44 detects that the frequency of the synchronization signal Sb is 96 Hz. When recognizing that the frequency of the synchronization signal Sb belongs to a predetermined first wavelength band (for example, a wavelength band of 90Hz to 125 Hz), the repetition number setting unit 42 sets the repetition number to 2 times. At this time, the output from the pulse generating circuit 41 such as at the slave time t_a0To time t_a2During time T1 between and from time T_a2To time t_a4During the time T1 between the pulses, that is, during the period in which the color wheel 63 rotates two turns, the pulse wave P is generated by repeating the same waveform twice. At this time, at the slave time t_a1To time t_a2And from time t_a3To time t_a4While maintaining the same polarity, a voltage is applied from one electrode to the other electrode, whereby the tips of the electrodes are heated.

Then, the pulse generating circuit 41 generates the same pulse wave P in a state where the polarity is inverted. That is, the pulse wave generated in step S1 and the pulse wave generated in step S2 are reversed in polarity, respectively, compared to the pulse wave generated during two rotations of the immediately preceding color wheel 63. I.e. at the slave time t_a5To time t_a6And from time t_a7To time t_a8And from time t_a1To time t_a2And from time t_a3To time t_a4The same polarity is maintained for the state reversed therebetween. Thereby, the tip of the electrode on the opposite side to the former is heated.

That is, in the example shown in fig. 4, the pulse generating unit 4 is configured to execute a control pattern including a first step S1 of inverting the polarity of the pulse wave P and a second step S2 of maintaining the polarity of the pulse wave P during a time T1 when the color wheel 63 rotates one revolution, and to repeat the control pattern for two revolutions of the color wheel 63. In the next pattern, in a state where the polarity is reversed from the pattern immediately before, a control pattern including a first step S1 of reversing the polarity of the pulse wave P and a second step S2 of maintaining the polarity of the pulse wave P is executed for a time T1 when the color wheel 63 rotates one turn, and the control pattern is repeated for two turns of the color wheel 63. Thereafter, the same control is performed, and the pulse wave P is continuously output.

Fig. 5 is a diagram comparing waveforms of the pulse wave P when the frequencies of the synchronization signals Sb are different. In fig. 5, (a) corresponds to the case of 96Hz as in fig. 4, (b) corresponds to the case of 40Hz, and (c) corresponds to the case of 180 Hz. In fig. 5, for easy understanding of the drawing, a waveform portion of the pulse wave P in the period in which the positive polarity is maintained is diagonally upward to the right, and a waveform portion of the pulse wave P in the period in which the negative polarity is maintained is diagonally downward to the right.

When recognizing that the frequency of the synchronization signal Sb belongs to a predetermined second wavelength band (for example, a wavelength band of 125Hz to 155 Hz), the repetition number setting unit 42 sets the repetition number to 3 times. This corresponds to the case where the synchronization signal Sb is 140 Hz.

When recognizing that the light belongs to a predetermined third wavelength band (for example, a wavelength band of 155Hz to 180 Hz), the repetition number setting unit 42 sets the repetition number to 4 times. This corresponds to the case where the synchronization signal Sb is 180 Hz.

As shown in fig. 5, by increasing the number of repetitions in accordance with the frequency of the synchronization signal Sb, the total value of the periods in which the same polarity is intermittently maintained can be set to be approximately the same regardless of the value of the synchronization signal Sb. This point will be further described with reference to fig. 6.

Fig. 6 is a diagram for comparing waveforms of the pulse wave P when the number of repetitions of the control pattern is a fixed value regardless of the frequency of the synchronization signal Sb when the frequency of the synchronization signal Sb is made different.

As is clear from fig. 6, as the frequency of the synchronization signal Sb increases, the total value of the periods in which the same polarity is intermittently maintained decreases. More specifically, as compared with the case where the frequency of the synchronization signal Sb is 96Hz and the case where the frequency of the synchronization signal Sb is 180Hz, the total value of the periods in which the pulse wave P intermittently exhibits positive polarity greatly differs. That is, when the frequency of the synchronization signal Sb is 180Hz, the polarity of the pulse wave P in step S2 is inverted during a period of time sufficient for heating to melt the fine protrusions 23 and the concavities and convexities formed on one electrode. As a result, when the frequency of the synchronization signal Sb increases to some extent, the minute projections 23 and the irregularities formed on the electrodes cannot be sufficiently melted, and the position of the arc changes with the lapse of the lighting time, and the illuminance maintenance ratio decreases.

As described above, the frequency of the synchronization signal Sb is determined according to the vertical synchronization signal Sz of the image output apparatus 70. That is, according to the lighting device 1 of the present embodiment, regardless of the type of the video output apparatus 70 to which the discharge lamp 10 is connected, the minute protrusions 23 and the unevenness formed on the electrodes can be melted, and an effect of stabilizing the illuminance maintenance rate can be achieved.

Fig. 7 is a graph showing temporal changes in the lamp voltage V of the discharge lamp 10 in the control of the lighting device of the present embodiment (example) and the lighting control by the pulse wave shown in fig. 5 (comparative example). In addition, the following lamps were used for the measurement.

(Lamp size)

Rated power: 330W

Rated voltage: 85V

Internal volume of light-emitting part: 250mm³

Inter-electrode distance: 1.5mm

An enclosure: 0.29mg/mm of mercury³Argon 13kPa, halogen 10^-6～10^-2μmol/mm³

Frequency of the synchronization signal: 180Hz

The lamp voltage was measured by continuously lighting the lamp for 180 hours using each lighting device of examples and comparative examples. As is apparent from fig. 7, the lighting control using the lighting device of the embodiment can be suppressed to a lower lamp voltage than the lighting control using the lighting device of the comparative example.

As the lighting time is longer, the projections 21 of the electrodes melt and move, and the inter-electrode distance becomes longer. Since the lamp voltage is proportional to the inter-electrode distance, this means that the inter-electrode distance of a lamp in which the voltage value changes to increase significantly compared to the initial voltage value is increased, that is, the protrusion 21 does not move at a predetermined position.

That is, as is apparent from fig. 7, when the frequency of the synchronization signal Sb is high, the number of times of repetition of the control pattern is increased, so that the time during which the pulse waves P exhibit the same polarity is intermittently increased, and the movement of the projection 21 can be suppressed. In contrast, when the number of repetitions of the control pattern is fixed regardless of the frequency of the synchronization signal Sb as in the control method of the comparative example, the time during which the pulse wave P exhibits the same polarity is shortened when the frequency of the synchronization signal Sb is high, which means that the time during which the minute projections and the irregularities are sufficiently melted cannot be heated.

When the inter-electrode distance is increased, the length of the arc is extended, and the shape of the arc is deformed. As a result, the light emitted from the discharge lamp 10 cannot be condensed to the maximum extent by the following optical system (for example, the integrator rod 64), resulting in a decrease in illuminance. According to the lighting control device of the present embodiment, a high illuminance maintenance rate can be continued regardless of the frequency of the synchronization signal Sb.

[ other embodiments ]

Next, another embodiment will be explained.

<1> in the process of repeatedly executing the control mode, if the polarity of the pulse wave P generated during the repetition period is changed in the same manner in step S1 and step S2, the waveforms themselves may not be completely the same. If the number of repetitions of step S2 for displaying the same polarity is set according to the frequency of the synchronization signal Sb, the same effects as those of the discharge lamp lighting device 1 of the above embodiment can be obtained. That is, while the control mode is repeatedly executed, the respective wave height values of step S1 and step S2 may be made to show different values from those of step S1 and step S2 immediately before.

In the above description, the frequency bands of the synchronization signal Sb for determining the number of repetitions of the control pattern are three, but the number of types is not limited to three.

<3> in the above description, the case where the step S1 of reversing the polarity and the step S2 of maintaining the polarity are executed in each control mode has been described. However, the gist thereof is not to exclude the case where the control mode is performed in which only step S1 is performed and step S2 is performed during one rotation of the color wheel 63 in a certain period of time from the present invention. That is, it is within the scope of the present invention that there is a time period for repeatedly executing the control pattern of the step S1 of reversing the polarity and the step S2 of maintaining the polarity, and the number of times of repetition of the control pattern is determined according to the frequency of the synchronization signal Sb.

For example, if the elapsed time from the start of lighting is long, step S1 may be inserted for a time period of approximately one to two rotations of color wheel 63. This is based on the object described below, for example.

As shown in fig. 3, when the AC/DC unit 32 is a full-bridge inverter circuit, a power supply for driving the switches Q1 and Q4 on the high-level side is required. For this power supply, for example, a bootstrap circuit can be used to charge a bootstrap capacitor, not shown, when the high-side switches Q1 and Q4 are turned off. However, when the amount of charge of the charger is insufficient, the switches Q1 and Q4 cannot be driven to be on due to the shortage of the power supply voltage. Therefore, for the purpose of charging the capacitor, the pulse wave P formed in step S1 may be generated during a period of time from one rotation to two rotations of the color wheel 63.

As another object, in the projector using the DMD system as described above, control is performed to reverse the polarity in synchronization with the timing of switching the color region of the color wheel 63, and the above-described charging of the capacitor is performed at the time of the polarity inversion so that the projected image is not adversely affected. Here, for the same reason as described above, when the elapsed time from the start of lighting is long and the amount of charge in the capacitor is insufficient, the pulse wave P formed in step S1 may be generated for a period of time of approximately one to two revolutions of the color wheel 63, for the purpose of charging the capacitor.

<4> in the above-described embodiment, it was explained that the control pattern executed during the time when the color wheel 63 makes one rotation is such as the control content of executing step S2 after executing step S1. However, the execution order of step S1 and step S2 may be reversed. In addition, it may be the control mode that executes step S2 after executing step S1, and then executes step S1 again.

Claims

1. A discharge lamp lighting device for an image forming apparatus that supplies an alternating current to a discharge lamp having a color wheel in which a plurality of color regions are formed, the discharge lamp having a pair of electrodes arranged in opposition to each other in a discharge vessel in which a predetermined gas is sealed, the discharge lamp lighting device comprising:

a power supply unit to which a DC voltage is supplied, which converts the DC voltage into an AC current corresponding to the frequency of the pulse wave, and which supplies the AC current to the discharge lamp,

repeatedly executing the control pattern during the rotation of the color wheel for a predetermined number of turns in a state where a polarity is reversed compared to a polarity of the pulse wave of the second step of the immediately preceding control pattern after the control pattern is repeatedly executed during the rotation of the color wheel for the predetermined number of turns,

2. The discharge lamp lighting device according to claim 1,

the pulse generating unit sets a value of the predetermined number of turns to be larger as the frequency of the synchronization signal is higher.

3. The discharge lamp lighting device according to claim 1,

the pulse generating unit repeatedly generates the same waveform as the pulse wave generated immediately before the color wheel makes one rotation while the color wheel makes the predetermined number of rotations.

4. The discharge lamp lighting device according to claim 1,

the second step includes a control of varying a wave height value of the pulse wave based on the synchronization signal while maintaining the polarity of the pulse wave.

5. The discharge lamp lighting device according to claim 1,

setting the first and second turns such that the following two overall times are substantially the same: an overall time for performing the second step by repeatedly executing the control pattern in a time required for the color wheel to rotate the first number of revolutions in a case where the frequency of the synchronization signal is a frequency belonging to the first frequency band, and an overall time for performing the second step by repeatedly executing the control pattern in a time required for the color wheel to rotate the second number of revolutions in a case where the frequency of the synchronization signal is a frequency belonging to the second frequency band.

6. An image forming apparatus is characterized by comprising:

the discharge lamp lighting device according to any one of claims 1 to 5;

a color wheel driving unit configured to drive the color wheel to rotate; and