JP2018018722A - Discharge lamp lighting device, and image forming apparatus with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device capable of maintaining stable illuminance regardless of a utilization environment with respect to a distance lamp to be utilized as a light source for an image forming apparatus comprising a color wheel.SOLUTION: A discharge lamp lighting device comprises a pulse generation part to which a synchronizing signal synchronized with timing of switching a target color region to be irradiated with a light from a discharge lamp is inputted and which generates a pulse wave of which the polarity is inverted based on the synchronizing signal. The pulse generation part executes a control pattern having a first step of inverting the polarity of the pulse wave and a second step of maintaining the polarity within a time in which a color wheel is rotated once, and executes the control pattern iteratively for a period in which the color wheel is rotated just for a predetermined rotation number. The predetermined rotation number is set to a first rotation number in a case where a frequency of the synchronizing signal is a frequency belonging to a first frequency band, and set to a second rotation number that is more than the first rotation number, in a case where the frequency is a frequency belonging to a second frequency band higher than the first frequency band.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a discharge lamp lighting device suitably used for a light source such as a projector. The present invention also relates to an image forming apparatus provided with the lighting device.

  There are roughly two types of data projector apparatuses using a discharge lamp as a light source. One is a liquid crystal system, which projects light emitted from a high-pressure discharge lamp onto a liquid crystal panel of RGB three colors. The other is a system using a DMD (Digital Mirror Device), which projects light emitted from a high-pressure discharge lamp onto the DMD through a color wheel.

As such a discharge lamp, a transparent glass discharge vessel in which, for example, 0.2 mg / mm ³ or more of mercury is sealed, and the pressure in the vessel at the time of lighting is 200 atmospheres or more is used. Yes. By increasing the mercury vapor pressure, light in the visible wavelength range can be obtained with high output.

  8A and 8B are schematic cross-sectional views of the discharge lamp. FIG. 8B is a schematic cross-sectional view in which the vicinity of the electrode tip in FIG. 8A is enlarged.

  As shown to FIG. 8A, the discharge lamp 10 has the substantially spherical light emission part 11 formed of the discharge container. In the light emitting portion 11, a pair of electrodes 20a and 20b are arranged to face each other at an extremely small interval of 2 mm or less.

  Further, sealing portions 12 are formed at both ends of the light emitting portion 11. A conductive metal foil 13 is hermetically embedded in the sealing portion 12, and shaft portions (30 a, 30 b) of the electrodes 20 a, 20 b are joined to one end of the metal foil 13. An external lead 14 is joined to the other end of the metal foil 13 and power is supplied from a power supply unit (not shown).

  In such a discharge lamp 10, during lighting, protrusions 21 are formed on the front-side surfaces of a pair of electrodes 20 a and 20 b disposed opposite to each other in the light emitting portion 11 of the arc tube, and a discharge arc 22 is formed between the protrusions 21. By being held, a stable lighting state is maintained (see FIGS. 8B and 9A).

  On the other hand, when the discharge lamp 10 is lit in the same state for a long time, a plurality of minute protrusions 23 may be formed due to a high temperature, or minute irregularities may be generated on the tip surface portion of the electrode (see FIG. 9B). ). These microprotrusions 23 and irregularities are formed by agglomeration of a compound formed by melting the material (for example, tungsten) constituting the electrodes 20a and 20b and combining with the gas sealed in the light emitting portion 11. This presence changes the shape of the surface portion of the electrode tip. Along with this, it is known that the starting point of the arc moves, the discharge position becomes unstable, and illuminance lowering and flickering occur.

  In order to solve such a problem, Patent Document 1 listed below supplies a current waveform of a pulse wave P1 having a predetermined frequency (fundamental frequency) to a discharge lamp and also a current of a pulse wave P2 having a frequency lower than the fundamental frequency. A discharge lamp lighting method is disclosed in which a waveform is intermittently or periodically inserted into a pulse wave of the fundamental frequency (see FIG. 10). More specifically, the fundamental frequency is set to one frequency selected from the range of 60 to 1000 Hz, and the low frequency is set to one frequency selected from the range of 5 to 200 Hz.

  By setting the pulse wave to a low frequency, the period in which one electrode is fixed to the anode and the other electrode to the cathode, that is, the period in which a high voltage is applied in one direction between the two electrodes is lengthened. As a result, the degree of heating of the electrode is increased, and heat can be transmitted not only to the tip of the electrode but also to a location away from the tip. Therefore, while a low-frequency pulse wave is applied, heat is also transmitted to a location away from the tip of the electrode, and the minute protrusions and irregularities generated at the location can be melted and evaporated. Thereby, it is possible to eliminate protrusions and irregularities other than the tip of the electrode that may adversely affect rather than the protrusion to be the arc starting point.

  Patent Document 2 below describes a lighting device that supports a method using DMD. This document describes that, in the case of a system using DMD, polarity inversion of a pulse wave is performed in synchronization with a timing at which a color region (segment) of a color wheel is switched. There is an aim to prevent flickering by performing polarity inversion of the pulse wave in synchronization with the segment switching timing.

Japanese Patent No. 4416125 Japanese Patent No. 5141703

  In order to stabilize the positions and shapes of the protrusions of the electrodes, the present inventors have studied using the techniques of Patent Documents 1 and 2 to control the discharge lamp lighting device corresponding to the projector having a color wheel. did. That is, the timing for reversing the polarity of the pulse wave corresponds to the rotation frequency of the color wheel, and a low-frequency pulse wave is inserted intermittently or periodically into the pulse wave of the basic frequency. Controlled. However, if the image is continuously displayed using the light from the discharge lamp while performing such control, the brightness of the displayed image may vary depending on the location and use. I understood.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to propose a lighting method that can maintain stable illuminance regardless of the use environment for 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 realize an image forming apparatus including a discharge lamp that is controlled to be lighted by such a lighting control device.

  The inventors have noted that the rotation speed of the color wheel provided in the 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 an image forming apparatus, an application in which a video signal from the projector is projected on a screen and viewed by a viewer can be considered. When used for this purpose, the rotation speed (rotation speed) of the color wheel for a predetermined time (for example, 1 second) is determined based on a video signal input from the device to the image forming apparatus. The frequency of this video signal is determined by the country and region, the required image accuracy, and the like. That is, it can be said that the rotation speed of the color wheel is scheduled to be different depending on the use environment of the image forming apparatus.

  The inventors of the present invention have different values for the rotation speed of the color wheel depending on the usage environment of the image forming apparatus, and depending on the usage environment, the illuminance maintaining function of the light emitted from the discharge lamp is reduced. I considered it. And based on said consideration, it examined changing the control content of the lighting device of a discharge lamp from the conventional one. And after the earnest research of the present inventors, it was found that the illuminance maintenance rate of the discharge lamp can be stabilized at a high level regardless of the usage environment of the image forming apparatus by adopting the following configuration. It came to.

The present invention is for an image forming apparatus having a color wheel in which a plurality of color regions are formed for supplying an alternating current to a discharge lamp in which a pair of electrodes are arranged to face each other in a discharge vessel filled with a predetermined gas. A discharge lamp lighting device of
A synchronization signal that is synchronized with the timing at which the color region to be irradiated with light from the discharge lamp is switched, and a pulse generator that generates a pulse wave whose polarity is inverted based on the synchronization signal;
A power supply unit is provided that is supplied with a DC voltage, converts the current into an alternating current corresponding to the frequency of the pulse wave, and supplies the alternating current to the discharge lamp.

The pulse generator is
Executing a control pattern having a first step of reversing the polarity of the pulse wave and a second step of maintaining the polarity of the pulse wave within a period of one rotation of the color wheel;
After repeatedly executing the control pattern over a period in which the color wheel rotates by a predetermined number of rotations, the control is performed with the polarity reversed compared to the polarity of the pulse wave of the second step in the immediately preceding control pattern. In this configuration, the pattern is repeatedly executed.

  The pulse generator sets the predetermined rotation speed to a first rotation speed when the frequency of the synchronization signal is a frequency belonging to a first frequency band, and the frequency of the synchronization signal is higher than that of the first frequency band. When the frequency belongs to a high second frequency band, the predetermined rotation speed is set to a second rotation speed that is higher than the first rotation speed.

  The time for one rotation of the color wheel depends on the rotation speed of the color wheel. The rotation 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 is high. Conversely, when the frequency of the synchronization signal is low, the rotation speed is low. That is, when the frequency of the synchronization signal belongs to the second frequency band higher than the first frequency band, compared to the case where the frequency of the synchronization signal is a value belonging to the first frequency band, the rotation speed of the color wheel is high, and the color wheel The time required for one rotation is short.

  By the way, during the execution of the second step, since the polarity of the pulse wave is constant, a voltage having the same polarity is continuously applied from one electrode constituting the discharge lamp to the other electrode. As a result, the electrode is heated for a certain period of time, so that the effect of melting the minute protrusions and irregularities can be obtained.

  However, if the frequency of the synchronization signal is a value belonging to the second frequency band, the time required for one rotation of the color wheel is shorter than that of the value belonging to the first frequency band, so that the pulse is inevitably generated. The time during which the polarity of the wave is constant is shortened. As a result, as compared with the case where the frequency of the synchronization signal is in the first frequency band, the time during which the electrode is heated is shortened, and it is difficult to heat the electrode for a sufficient time to melt the minute protrusions and irregularities.

  Therefore, in the above configuration, when the frequency of the synchronization signal is a value belonging to the second frequency band, the number of repetitions of the control pattern is set larger than when the frequency belongs to the first frequency band. More specifically, it is as follows. When the frequency of the synchronizing signal is a value belonging to the first frequency band, the control pattern is repeatedly executed over a period in which the color wheel rotates by the first rotation speed, and then the polarity of the pulse wave is reversed in the second step. ing. On the other hand, when the frequency of the synchronization signal is a value belonging to the second frequency band higher than the first frequency band, the control is performed over a period in which the color wheel rotates by the second rotation speed higher than the first rotation speed. After repeatedly executing the pattern, the polarity of the pulse wave is reversed in the second step.

  By adopting such a configuration, the polarity of the pulse wave in the second step is inverted between the case where the frequency of the synchronization signal is a value belonging to the first frequency band and the case where it is a value belonging to the second frequency band. Thus, the difference in the total time during which the voltage is intermittently applied in the same direction within the time during which the control pattern is repeated can be reduced. As a result, regardless of the frequency of the synchronization signal, the minute protrusions and irregularities formed on the electrode can be melted to the same extent, and the same illuminance maintenance rate can be realized.

  In the case where the frequency of the synchronization signal is a frequency belonging to the first frequency band, the second control pattern is repeatedly executed over the time required for the color wheel to rotate by the first rotation speed. The control pattern is repeated over the time required for the color wheel to rotate by the second number of rotations when the step is executed and the frequency of the synchronization signal is a frequency belonging to the second frequency band. It is still more preferable that the first rotation speed and the second rotation speed are set such that the total time for executing the second step becomes substantially equal when executed.

  Here, “substantially equal” can be defined as follows, for example. When the frequency of the synchronizing signal is a frequency belonging to the first frequency band, the total time for which the second step is executed can be obtained by repeatedly executing the control pattern over the time required for the color wheel to rotate by the first rotation speed. Ta. In addition, when the frequency of the synchronization signal is a frequency belonging to the second frequency band, the second step is executed by repeatedly executing the control pattern over the time required for the color wheel to rotate by the second rotational speed. Let time be Tb. At this time, the case where the following formula (1) is established can be made substantially equal.

  0 ≦ | Ta−Tb | / Ta ≦ 1 (1)

Furthermore, it is still more preferable that the following formula (2) holds.
0 ≦ | Ta−Tb | /Ta≦0.2 (2)

  Even if the frequency of the synchronizing signal is a value belonging to the first frequency band by setting the first rotation speed and the second rotation speed so that the above formula (1) and formula (2) are satisfied, Even if the value belongs to the frequency band, the minute protrusions and irregularities formed on the electrode can be melted to the same extent.

  The pulse generation unit repeatedly executes the control pattern over a period in which the color wheel rotates by the predetermined number of rotations, and then reverses the polarity compared to the pulse wave of the second step in the immediately preceding control pattern. In this state, the control pattern may be repeatedly executed over a period in which the color wheel rotates by the predetermined number of rotations.

  The pulse generator may be configured to set a larger value of the predetermined rotational speed as the frequency of the synchronization signal is higher.

  The pulse generator may repeatedly generate the same waveform as the pulse wave generated immediately before the color wheel rotates once over the period in which the color wheel rotates by the predetermined number of rotations. .

  The second step may include control for changing the peak value of the pulse wave based on 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 light emitted from the discharge lamp passes.

An image forming apparatus according to the present invention is
The discharge lamp lighting device having the above characteristics;
A discharge lamp that is lit by receiving a current supply from the discharge lamp lighting device;
A color wheel that has a plurality of color regions and is rotatable, and passes light from the discharge lamp to the one color region and outputs light of a color corresponding to the color region;
A color wheel drive unit for rotationally driving the color wheel;
And a control processing unit that outputs the synchronization signal to the discharge lamp lighting device based on a signal from the color wheel driving unit.

  According to the discharge lamp lighting device of the present invention, lighting control capable of maintaining stable illuminance regardless of the usage environment is realized for a discharge lamp used as a light source for an image forming apparatus having a color wheel.

1 is a block diagram schematically illustrating an example of a configuration of an image forming apparatus using a DMD. It is a schematic diagram of a color wheel. It is a circuit block diagram which shows typically the structure of a discharge lamp lighting device. It is drawing which showed typically the waveform of pulse wave P generated from a pulse generation part. It is drawing which compared the waveform of the pulse wave P produced | generated by the lighting control apparatus of this embodiment at the time of changing the frequency of the synchronizing signal Sb. FIG. 6 is a diagram comparing waveforms of a pulse wave 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 different. It is the graph which compared the time-dependent change of the voltage between lamp | ramp when each discharge lamp was lighted with each lighting device of a comparative example and an Example. It is a cross-sectional schematic diagram of a discharge lamp. It is the cross-sectional schematic diagram which expanded the electrode tip vicinity of the discharge lamp. It is the cross-sectional schematic diagram which expanded the electrode tip vicinity in the state in which the discharge arc was formed and the lighting state was maintained stably. It is the cross-sectional schematic diagram which expanded the electrode tip vicinity in the state in which the microprotrusion is formed in locations other than an electrode tip. It is a figure which shows an example of the conventional lamp current waveform.

  An embodiment of a discharge lamp lighting device of the present invention will be described with reference to the drawings. In each figure, the dimensional ratio in the drawing does not necessarily match the actual dimensional ratio.

[Lamp configuration]
First, an example of the configuration of a discharge lamp that is subject to lighting control by the lighting device of the present invention will be described with reference to FIGS. 8A and 8B. In addition, the discharge lamp used as the object controlled 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, and may be made of other materials. In the light emitting unit 11, a pair of electrodes 20a and 20b are disposed to face each other at an extremely small interval of, for example, 2 mm or less.

  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, a shrink seal. The shafts of the electrodes 20a and 20b are joined to one end of the metal foil 13, and the external lead 14 is joined to the other end of the metal foil 13, and power is supplied from the discharge lamp lighting device of the present invention described later. It is the composition which is done.

  For example, mercury, a rare gas, and a halogen gas are sealed in the light emitting portion 11 of the discharge lamp 10 in the present embodiment.

Mercury is used to obtain radiated light having a necessary visible light wavelength (for example, a wavelength of 360 to 780 nm). In terms of specific values, 0.20 mg / mm ³ or more is enclosed. Although the amount of sealing varies depending on the temperature condition, a high vapor pressure of 200 atm or more is realized as the pressure inside the light emitting unit during lighting. In addition, by enclosing more mercury, it is possible to make a high-pressure discharge lamp with a high mercury vapor pressure of 250 atm or higher and 300 atm or higher when the lamp is turned on. realizable.

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

As the halogen gas, iodine, bromine, chlorine, etc. are enclosed in the form of a compound with mercury or other metals. The enclosed amount of halogen is selected from the range of 10 ⁻⁶ μmol / mm ³ to 10 ⁻² μmol / mm ³ . The biggest reason for enclosing the halogen is to extend the life of the 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 action of preventing devitrification of the discharge vessel can be obtained by enclosing the halogen. Devitrification means that crystallization proceeds from a metastable glass state and changes to an aggregate of crystal grains grown from many crystal nuclei. If such a phenomenon occurs, light is scattered at the grain boundaries of the crystal and the discharge vessel becomes opaque.

  In the present invention, as long as a similar function can be realized, the gas sealed in the light emitting unit 11 is not limited to the above gas.

As an example of the discharge lamp 10, the maximum outer diameter of the light emitting part is 9.4 mm, the distance between the electrodes is 1.0 mm, the inner volume of the discharge vessel is 55 mm ³ , the rated voltage is 70 V, and the rated power is 180 W. It can be set as a structure.

Further, it is assumed that the discharge lamp 10 is built in a projector that is becoming smaller in size, and is required to be extremely small as a whole size, and on the other hand, a high light emission amount is also required. For this reason, the thermal influence in the light emitting portion is extremely severe, and the lamp wall load of the lamp is 0.8 to 2.5 W / mm ² , specifically 2.4 W / mm ² . As described above, the discharge lamp 10 having a high mercury vapor pressure and a tube wall load value is mounted on a presentation device such as a projector or an overhead projector, thereby providing the presentation device with emitted light having good color rendering properties. be able to.

[Shape of electrode tip]
As shown in FIG. 8B, the electrode 20a includes a head portion 29a and a shaft portion 30a, and the electrode 20b includes a head portion 29b and a shaft portion 30b. Each of the electrode 20a and the electrode 20b has a protrusion 21 at the tip. The protrusion 21 is formed by agglomerating molten electrode material at the electrode tip when the lamp is turned on. In the present embodiment, the electrode 20a and the electrode 20b are described as both made of tungsten, but the material is not limited to this.

  When the electrode 20a and the electrode 20b are energized, the electrode 20a and the electrode 20b are heated to a high temperature, and tungsten constituting them is sublimated. The sublimated tungsten is combined with the enclosed halogen gas in the inner wall surface region of the light emitting portion 11 which is a relatively low temperature portion to form tungsten halide. Since the vapor pressure of tungsten halide is relatively high, it moves again in the vicinity of the tips of the electrodes 20a and 20b in the gas state. When heated again at this point, the tungsten halide is separated into halogen and tungsten. Among these, tungsten returns to the tips of the electrodes 20 a and 20 b and aggregates, and the halogen returns as the halogen gas in the light emitting unit 11. This is called a halogen cycle. The agglomerated tungsten adheres to the vicinity of the tips of the electrode 20a and the electrode 20b, whereby the protrusion 21 is formed.

[Configuration of Image Forming Apparatus]
Prior to the configuration of the lighting device, first, the configuration of an image forming apparatus assumed to be used in the lighting device of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram schematically showing an example of the configuration of an image forming apparatus using a DMD. Here, a single-plate projector is assumed as the image forming apparatus 60. The image forming apparatus 60 includes a light source device 61, a color wheel 63, a rod integrator 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 a concave reflecting mirror 62. The discharge lamp 10 is an AC lighting type lamp, and is arranged so that the arc luminescent spot of the lamp and the first focal point of the concave reflecting mirror 62 substantially coincide.

  Reflected light from the concave reflecting mirror 62 is incident on the rod integrator 64 via the color wheel 63. As shown in FIG. 2, the color wheel 63 is divided into a plurality of color regions (here, W, R, G, B, C, M) by spokes 75. The color wheel 63 is controlled to be rotated and stopped by the color wheel driving unit 68, and the light that has passed through the predetermined light converging region 72 is incident on the rod integrator 64.

  In the present embodiment, the color wheel 63 has white (W), red (R), green (G), blue (B), cyan (C), and magenta (M) at the same angle. Although described as a divided configuration, the number of colors and the division method are not limited to this form.

  The image forming apparatus 60 includes a control processing unit 69 including a processor that performs a calculation, a ROM that stores information such as a program necessary for the calculation, and a RAM that stores temporarily generated information. The control processing unit 69 performs processing for controlling the operation of the entire image forming apparatus 60. The aforementioned 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 the control signal from the control processing unit 69.

  The color wheel 63 is provided with a mark (not shown) on the rotating portion of the color wheel 63 in order to determine the position of the color region. The color wheel driving unit 68 includes a sensor (not shown) for reading the mark, and generates a rotational position detection signal Sc of the color wheel 63 and outputs it to the control processing unit 69. Based on this rotational position detection signal Sc, the control processing unit 69 recognizes which color region through which light has been projected on the screen during operation.

  The control processing unit 69 receives an image signal from a video output device 70 such as a DVD player or a personal 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 constant 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 in accordance with the rotational position of the color wheel 63, and displays an image for each color based on the image signal on the video display element. That is, the color wheel driving unit 68 determines the rotation speed of the color wheel based on the signal input from the video output device 70.

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

  Reflected light from the concave reflecting mirror 62 passes through a light condensing region 72 (see FIG. 2) formed on the color wheel 63. As the color wheel 63 rotates, the colors corresponding to the light condensing region 72 are sequentially guided to the rod integrator lens 64 at the subsequent stage. That is, each color of white (W), red (R), green (G), blue (B), cyan (C), and magenta (M) is projected in a time-division manner. Only colors are projected onto the screen via the DMD element 66, but these colors or a mixed color thereof are recognized as an image by human eyes.

  White (W) is for brightening the entire image, and the effect of brightening the entire image is obtained by projecting white at regular intervals. For example, when the color wheel 63 rotates at 180 Hz (180 rotations per second), white (W), red (R), green (G), blue (B), cyan (C), and magenta (M) are displayed per second. It will be projected 180 times.

  In the color wheel 63 shown in FIG. 2, all color regions are configured at the same angle, but each region area is defined in consideration of the color balance and brightness of the final image. It doesn't matter. The light condensing region 72 virtually formed on the color wheel 63 has a rectangular shape of, for example, 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.

[Configuration of lighting device]
Next, a specific configuration of the lighting device 1 will be 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 feeding unit 3 and a pulse generating unit 4. Based on the pulse wave P output from the pulse generator 4, the alternating current generated by the power feeder 3 is supplied to the discharge lamp 10, so that the discharge lamp 10 is lit.

(Power supply unit)
The power feeding unit 3 includes a step-down chopper unit 31, a DC / AC conversion unit 32, and a starter unit 33.

  The step-down chopper unit 31 steps down the supplied DC voltage Vdc to a desired low voltage and outputs it to the DC / AC conversion unit 32 at the subsequent stage. In FIG. 3, as a specific configuration example, the step-down chopper unit 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.

  Switching element Qx has one end connected to the + side power supply terminal to which DC voltage Vdc is supplied and the other end connected to one end of 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 the negative power supply terminal. The smoothing capacitor Cx has one end connected to the output side terminal of the reactor Lx and the other end (− side terminal) connected to the 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 realizes a current detection function. Further, the voltage dividing resistor Vx is connected between the negative side terminal and the positive side terminal of the smoothing capacitor Cx to realize a voltage detection function.

  The switching element Qx is driven by a gate signal Gx output from the power control unit 34. Based on the duty of the gate signal Gx, the step-down chopper unit 31 steps down the input DC voltage Vdc to a voltage corresponding to the duty and outputs it to the DC / AC conversion unit 32 at the subsequent stage.

  The DC / AC conversion unit 32 converts the input DC voltage into an AC voltage having a desired frequency, and outputs the AC voltage to the subsequent starter unit 33. In FIG. 3, as a specific configuration example, the DC / AC conversion unit 32 is configured by switching elements Q1 to Q4 connected in a bridge shape (full bridge circuit).

  The switching element Q1 is driven by a gate signal G1 output from the driver 35. Similarly, the switching element Q2 is driven by the gate signal G2, the switching element Q3 is driven by the gate signal G3, and the switching element Q4 is driven by the gate signal G4. The driver 35 outputs a gate signal to alternately repeat on / off for the pair of switching elements Q1 and Q4 and the pair of switching elements Q2 and Q3 arranged diagonally. Thereby, a rectangular wave AC 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 starter unit 33 is a circuit unit that boosts the AC voltage supplied from the DC / AC unit 32 and supplies the AC voltage to the discharge lamp 10 when the discharge lamp 10 is started. In FIG. 3, as a specific configuration example, the starter unit 33 is configured by 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, thereby A high voltage necessary for starting the discharge lamp 10 is generated on the secondary side, and this 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 shifted to a steady frequency (for example, 60 to 1000 Hz), and a steady lighting operation is performed. Note that the steady lighting operation includes control contents described later with reference to FIGS. 4 and 5.

  In the above circuit, the change in the frequency of the AC voltage supplied to the starter unit 33 is the on / off switching cycle of the set of the switching elements Q1 and Q4 and the set of the switching elements Q2 and Q3 in the DC / AC unit 32. It can be achieved by adjusting. Further, the change of the peak value of the AC voltage supplied to the starter unit 33 can be achieved by adjusting the operation duty of the switching element Qx in the step-down chopper unit 31.

  In other words, the switching element Qx of the step-down chopper unit 31 is turned on / off at a switching frequency corresponding to the duty of the gate signal Gx output from the power control unit 34, whereby the power supplied to the discharge lamp 10 changes. For example, when it is desired to increase the power supplied to the discharge lamp 10, the power control unit 34 performs control to increase the duty of the gate signal Gx so that a desired power value is obtained.

  The power control unit 34 appropriately changes the duty ratio of the gate signal Gx based on 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 sets the input power value as a target power value ( Feedback control for maintaining the control power value).

(Pulse generator)
The pulse generation unit 4 includes a pulse generation circuit 41, a repetition number setting unit 42, a memory unit 43, and a frequency detection unit 44, and outputs the generated pulse signal P to the driver 35 of the DC / AC unit 32. As described above, switching control for the switching elements Q1 to Q4 of the DC / AC unit 32 is performed based on the pulse signal.

  The pulse generation circuit 41 outputs a pulse wave based on the information regarding the control pattern held in the memory unit 43 and the number of repetitions set in the repetition number setting unit 42. The “control pattern” and “repetition number” will be described later.

  The frequency detection unit 44 receives the synchronization signal Sb supplied from the control processing unit 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.

  A mechanism in which the control processing unit 69 outputs the synchronization signal Sb in synchronization with the color region switching timing 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 personal 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. To do. The color wheel driving unit 68 rotates the color wheel 63 at a constant speed in accordance with the rotation control signal Sd from the control processing unit 69.

  Further, the control processing unit 69 generates a synchronization signal Sb for synchronizing the light from the discharge lamp 10 with the timing (spoke time) 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 output 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 generation circuit 41 inverts the polarity of the pulse wave P based on the timing of the synchronization signal Sb, and inverts the polarity of the lamp current via the DC / AC converter 32.

  In FIG. 1, the lighting detection signal Sa is output from the lighting device 1 to the control processing unit 69. This is a signal for causing the control processing unit 69 to recognize that the lighting device 1 is functioning correctly, but is not necessarily an essential signal.

(Pulse waveform)
Hereinafter, the waveform of the pulse signal P output from the pulse generator 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 generator 41 when the synchronization signal Sb has a predetermined frequency (here, 96 Hz as an example). In the example of FIG. 4, the time for which the color wheel 63 makes one rotation is represented by T1, and during this time T1, the step S1 for inverting the polarity of the pulse wave P and the step S2 for maintaining the polarity of the pulse wave P are performed. Is running. Specifically, first, Step S1 in which the polarity of the pulse wave P is inverted is executed between the time t _a0 and the time t _a1 , and then the polarity of the pulse wave P is changed between the time t _a1 and the time t _a2. The maintained step S2 is executed.

  In the present embodiment, as described with reference to FIG. 2, it is assumed that the color wheel 63 is divided into six color regions. That is, the time T1 required for one rotation of the color wheel 63 is divided into six segment periods (sg1 to sg6), and the peak value of the pulse wave P changes as necessary based on the switching timing of each segment period. . Here, as described above, since the areas of the color regions constituted by the color wheel 63 are set to be equal, the segment periods (sg1 to sg6) are represented by the same time. The configuration is not limited to that described above. That is, the length of each segment period (sg1 to sg6) changes according to the ratio of the area of each color region formed by the color wheel 63.

  In the configuration of the present embodiment, it is assumed that a preferable ratio of peak values is set for each color passing through the light condensing region 72. For example, the reason why the peak value of the pulse wave P is different between the segment sg4, the segment sg5, and the segment sg6 is that the peak value corresponding to the color corresponding to each segment is set. Information regarding the ratio of the crest value for each color may be stored in the memory unit 43, for example.

When the synchronization signal Sb is input, the frequency detection unit 44 detects that the frequency of the synchronization signal Sb is 96 Hz. When the repetition setting unit 42 recognizes that the frequency of the synchronization signal Sb belongs to a predetermined first wavelength band (for example, a wavelength band of 90 Hz or more and 125 Hz or less), the repetition setting unit 42 sets the number of repetitions to two. At this time, from the pulse generation circuit 41, during the time T1 between the time t _a0 and the time t _a2 and during the time T1 between the time t _a2 and the time t _a4 , that is, while the color wheel 63 rotates twice. In addition, a pulse wave P that outputs the same waveform twice is output. At this time, the same polarity is maintained from time t _a1 to time t _a2 and from time t _a3 to time t _a4 , and a voltage is applied from one electrode to the other, The tip of the electrode is heated.

Next, the pulse generation circuit 41 generates the same pulse wave P with the polarity reversed. That is, the polarity of the pulse wave generated in step S1 and the pulse wave generated in step S2 are reversed compared to the pulse wave generated immediately before the color wheel 63 makes two revolutions. . In other words, the state is inverted between time t _a5 and time t _a6 , between time t _a7 and time t _a8 , between time t _a1 and time t _a2 , and between time t _a3 and time t _a4. The same polarity is maintained. Thereby, the tip of the electrode opposite to the previous one is heated.

  That is, in the example shown in FIG. 4, the pulse generation unit 4 performs the first step S <b> 1 for inverting the polarity of the pulse wave P and the polarity of the pulse wave P within the time T <b> 1 when the color wheel 63 rotates once. The control pattern having two steps S <b> 2 is executed, and this control pattern is repeated over the time that the color wheel 63 rotates twice. In the next turn, the first step S1 for reversing the polarity of the pulse wave P within the time T1 in which the color wheel 63 makes one rotation while the polarity is reversed from that of the immediately preceding turn, The control pattern having the second step S2 for maintaining the polarity is executed, and this control pattern is repeated over the time for which the color wheel 63 rotates twice. Hereinafter, the pulse wave P is continuously output by performing the same control.

  FIG. 5 compares the waveforms of the pulse waves P when the frequency of the synchronization signal Sb is varied. 5, (a) corresponds to the case of 96 Hz as in FIG. 4, (b) corresponds to the case of 140 Hz, and (c) corresponds to the case of 180 Hz. In FIG. 5, in order to make the drawing easy to understand, the waveform portion in the period in which the pulse wave P is maintained in the positive polarity is hatched to the right and the waveform portion in the period in which the pulse wave P is maintained in the negative polarity is lowered to the right. Has been hatched.

  When the repetition setting unit 42 recognizes that the frequency of the synchronization signal Sb belongs to a predetermined second wavelength band (for example, a wavelength band of 125 Hz or more and 155 Hz or less), the repetition setting unit 42 sets the number of repetitions to three. This corresponds to the case where the synchronization signal Sb is 140 Hz.

  In addition, when the repetition setting unit 42 recognizes that it belongs to a predetermined third wavelength band (for example, a wavelength band of 155 Hz or more and 180 Hz or less), it sets the number of repetitions to four. This corresponds to the case where the synchronization signal Sb is 180 Hz.

  As shown in FIG. 5, by increasing the number of repetitions according to the frequency of the synchronization signal Sb, the total value of the period in which the same polarity is intermittently maintained is made substantially the same regardless of the value of the synchronization signal Sb. It can be seen that it can be set. This point will be further described with reference to FIG.

  FIG. 6 compares the waveforms of the pulse waves P when the frequency of the synchronization signal Sb is varied and the number of control pattern repetitions is constant regardless of the frequency of the synchronization signal Sb.

  According to FIG. 6, it can be seen that the total value of the period in which the same polarity is intermittently maintained becomes shorter as the frequency of the synchronization signal Sb increases. More specifically, comparing the case where the frequency of the synchronization signal Sb is 96 Hz and the case where the frequency is 180 Hz, it can be seen that the total value of the periods in which the pulse wave P intermittently shows positive polarity is greatly different. That is, when the frequency of the synchronization signal Sb is 180 Hz, the pulse wave P in step S2 is heated until it is heated for a sufficient time to melt the microprojections 23 and the unevenness formed on one electrode. The polarity will be reversed. As a result, when the frequency of the synchronization signal Sb is increased to some extent, the minute protrusions 23 and irregularities formed on the electrodes are not sufficiently melted, and the arc position fluctuates as the lighting time elapses, so that the illuminance maintenance rate is increased. It will decline.

  As described above, the frequency of the synchronization signal Sb is determined depending on the vertical synchronization signal Sz of the video output device 70. That is, according to the lighting device 1 of the present embodiment, the minute projections 23 and the unevenness formed on the electrodes are melted and the illuminance regardless of the video output device 70 to which the discharge lamp 10 is connected. The effect of stabilizing the maintenance rate is realized.

  FIG. 7 is a graph showing a change with time of the lamp voltage V of the discharge lamp 10 in the control by the lighting device of the present embodiment (example) and the lighting control by the pulse wave shown in FIG. 5 (comparative example). is there. In all cases, measurement is performed using the following lamps.

(Lamp specifications)
・ Rated power: 330W
・ Rated voltage: 85V
-Internal volume of light emitting part: 250 mm ³
・ Distance between electrodes: 1.5mm
Enclosed matter: mercury 0.29 mg / mm ³ , argon gas 13 kPa, halogen 10 ⁻⁶ to 10 ⁻² μmol / mm ³
・ Synchronous signal frequency: 180 Hz

  The lamps were continuously lit for 180 hours, and the lamp voltage was measured by the lighting devices of the examples and comparative examples. As can be seen from FIG. 7, when the lighting control is performed by the lighting device of the example, the lamp voltage is suppressed lower than when the lighting control is performed by the lighting device of the comparative example.

  The longer the lighting time, the longer the distance between the electrodes because the protrusions 21 of the electrodes melt and move. Since the lamp voltage is proportional to the distance between the electrodes, the lamp that fluctuates so that the voltage value greatly increases compared to the initial voltage value has an increased distance between the electrodes, that is, the protrusion 21 is not in a predetermined position. It means that it has moved.

  That is, according to FIG. 7, when the frequency of the synchronization signal Sb is high, the number of times of repetition of the control pattern is increased, and the time during which the pulse wave P exhibits the same polarity is intermittently lengthened. It can be seen that the movement can be suppressed. On the other hand, when the number of repetitions of the control pattern is constant regardless of the frequency of the synchronization signal Sb as in the control method of the comparative example, the pulse wave P has the same polarity when the frequency of the synchronization signal Sb is high. It is suggested that a sufficient time to melt the minute protrusions and irregularities cannot be heated.

  When the distance between the electrodes is increased, the length of the arc is increased or the shape of the arc is deformed. As a result, the light emitted from the discharge lamp 10 cannot be collected to the maximum extent to the subsequent optical system (for example, the rod integrator 64), and the illuminance decreases. According to the lighting control device of the present embodiment, it is possible to maintain a high illuminance maintenance rate regardless of the frequency of the synchronization signal Sb.

[Another embodiment]
Hereinafter, another embodiment will be described.

  <1> While the control pattern is being repeatedly executed, the pulse wave P generated within the repetition period may have the waveform itself that is not completely the same as long as the change in polarity of steps S1 and S2 is the same. I do not care. If the number of repetitions of step S2 showing the same polarity is set according to the frequency of the synchronization signal Sb, the same effect as the discharge lamp lighting device 1 of the above embodiment can be obtained. That is, during the repeated execution of the control pattern, the peak values of step S1 and step S2 may indicate different values from the immediately preceding step S1 or step S2.

  <2> In the above description, the number of wavelength bands of the frequency of the synchronization signal Sb for which the number of control pattern repetitions is determined is three. However, the number of types is not limited to three.

  <3> In the above description, a case has been described in which step S1 for performing polarity reversal and step S2 for maintaining the polarity are executed in each control pattern. However, this is not intended to exclude from the present invention the case where only the step S1 is executed or the control mode in which the step S2 is executed is performed during one rotation of the color wheel 63. . That is, there is a time zone in which the control pattern in which the step S1 for performing polarity inversion and the step S2 in which the polarity is maintained is executed is repeatedly executed, and the number of repetitions of the control pattern is the frequency of the synchronization signal Sb Is within the scope of the present invention.

  For example, when the elapsed time from the start of lighting becomes longer, step S <b> 1 may be inserted for a time of about 1 to 2 rotations of the color wheel 63. This is for the following purpose, for example.

  As shown in FIG. 3, when the AC / DC unit 32 is a full-bridge inverter circuit, a power source for driving the high-side switches Q1 and Q4 is required. As this power source, for example, a bootstrap circuit can be used, and when the high-side switches Q1 and Q4 are OFF, a bootstrap capacitor (not shown) is charged. However, if the charging amount of this capacitor is insufficient, the switches Q1 and Q4 cannot be driven ON because the power supply voltage is insufficient. For this reason, for the purpose of charging the capacitor, the pulse wave P constituted by step S1 may be generated exceptionally for a time of about one to two rotations of the color wheel 63.

  As another object, in the projector using the DMD as described above, control is performed to invert the polarity in synchronization with the color region switching timing of the color wheel 63 so that the projected image is not adversely affected. In this polarity reversal, the capacitor is charged. Here, for the same reason as described above, when the elapsed time from the start of lighting becomes long and the amount of charge to the capacitor becomes insufficient, the color wheel 63 is exceptionally rotated from one rotation to the other for the purpose of charging the capacitor. The pulse wave P configured by step S1 may be generated for a time of about two rotations.

  <4> In the above embodiment, a case has been described in which the control pattern executed within the time for which the color wheel 63 makes one revolution is the control content in which step S2 is executed after step S1 is executed. However, the execution order of step S1 and step S2 may be reversed. Further, the control pattern may be such that after step S1 is executed, step S2 is executed, and then step S1 is executed again.

DESCRIPTION OF SYMBOLS 1: Lighting device 3: Power supply part 4: Pulse generation part 10: Discharge lamp 11: Light emission part 12: Sealing part 13: Metal foil 14: External lead 20a, 20b: Electrode 21: Protrusion 22: Discharge arc 23: Minute protrusion 29a, 29b: Electrode heads 30a, 30b: Electrode shaft part 31: Step-down chopper part 32: DC / AC conversion part 33: Starter part 34: Power control part 35: Driver 41: Pulse generation circuit 42: Repeat number setting Unit 43: memory unit 44: frequency detection unit 60: image forming device 61: light source device 62: concave reflecting mirror 63: color wheel 64: rod integrator 65: optical element 66: DMD element 67: optical system 68: color wheel driving unit 69: Control processing unit 70: Video output device 71: Device control unit 2: light condensing area 75: spoke

Claims (7)

Discharge lamp lighting for an image forming apparatus having a color wheel in which a plurality of color regions are formed to supply an alternating current to a discharge lamp having a pair of electrodes opposed to each other in a discharge vessel filled with a predetermined gas A device,
A synchronization signal that is synchronized with the timing at which the color region to be irradiated with light from the discharge lamp is switched, and a pulse generator that generates a pulse wave whose polarity is inverted based on the synchronization signal;
A DC voltage is supplied, and includes a power feeding unit that converts the alternating current according to the frequency of the pulse wave to supply the alternating current to the discharge lamp,
The pulse generator is
Executing a control pattern having a first step of reversing the polarity of the pulse wave and a second step of maintaining the polarity of the pulse wave within a period of one rotation of the color wheel;
After repeatedly executing the control pattern over a period in which the color wheel rotates by a predetermined number of rotations, the control is performed with the polarity reversed compared to the polarity of the pulse wave of the second step in the immediately preceding control pattern. It is a configuration that repeatedly executes a pattern,
The pulse generator sets the predetermined rotation speed to a first rotation speed when the frequency of the synchronization signal is a frequency belonging to a first frequency band, and the frequency of the synchronization signal is higher than that of the first frequency band. The discharge lamp lighting device characterized by setting the predetermined rotational speed to a second rotational speed higher than the first rotational speed when the frequency belongs to a high second frequency band.   The pulse generation unit repeatedly executes the control pattern over a period in which the color wheel rotates by the predetermined number of rotations, and then reverses the polarity compared to the pulse wave of the second step in the immediately preceding control pattern. 2. The discharge lamp lighting device according to claim 1, wherein the control pattern is repeatedly executed over a period in which the color wheel rotates by the predetermined number of revolutions in a state where the color wheel rotates.   3. The discharge lamp lighting device according to claim 1, wherein the pulse generator sets a larger value of the predetermined rotation speed as the frequency of the synchronization signal is higher.   The pulse generator repeatedly generates the same waveform as the pulse wave generated immediately before the color wheel makes one rotation over a period in which the color wheel rotates by the predetermined number of rotations. The discharge lamp lighting device according to any one of claims 1 to 3.   5. The control according to claim 1, wherein the second step includes control of changing a peak value of the pulse wave based on the synchronization signal while maintaining a polarity of the pulse wave. Discharge lamp lighting device.   In the case where the frequency of the synchronization signal is a frequency belonging to the first frequency band, the second step is performed by repeatedly executing the control pattern over a time required for the color wheel to rotate by the first rotation speed. When the total time to be executed and the frequency of the synchronization signal is a frequency belonging to the second frequency band, the control pattern is repeatedly executed over the time required for the color wheel to rotate by the second rotation speed. The first rotation speed and the second rotation speed are set so that the total time during which the second step is executed is substantially equal. The discharge lamp lighting device according to claim 1. The discharge lamp lighting device according to any one of claims 1 to 6,
A discharge lamp that is lit by receiving a current supply from the discharge lamp lighting device;
A color wheel that has a plurality of color regions and is rotatable, and passes light from the discharge lamp to the one color region and outputs light of a color corresponding to the color region;
A color wheel drive unit for rotationally driving the color wheel;
An image forming apparatus comprising: a control processing unit that outputs the synchronization signal to the discharge lamp lighting device based on a signal from the color wheel driving unit.

Images