JP6003425B2 - Discharge lamp driving device and driving method, light source device, and projector - Google Patents

Description

  The present invention relates to a driving technique for a discharge lamp that is lit by discharge between electrodes.

  As a light source of an image display device such as a projector, a discharge lamp such as a high-pressure mercury lamp or a metal halide lamp is used. This discharge lamp is driven by, for example, a driving method for supplying a high-frequency alternating current. According to this driving method, discharge stability can be obtained, so-called blackening or devitrification of the discharge lamp body can be prevented, and a reduction in the life of the discharge lamp can be suppressed (for example, Patent Document 1). ).

JP 2007-115534 A

  By the way, the light emission of the discharge lamp in the AC drive changes the plasma density in the vicinity of the pair of electrodes in accordance with the positive / negative polarity switching of the AC current. This change in plasma density appears as the density of the internal gas density, which becomes a vibration and propagates from the vicinity of the pair of electrodes toward the inner wall. When this vibration is reflected by the inner wall and returns to the vicinity of the pair of electrodes again, the vibration may intensify by the resonance phenomenon. Due to this resonance phenomenon, there is a problem that the coil portion provided on the electrode is partially broken or the electrode is broken. The fundamental frequency at which the resonance phenomenon occurs is called the acoustic resonance frequency. The resonance phenomenon occurs not only at the acoustic resonance frequency but also at the frequency fc / 2n (n is a natural number) when the acoustic resonance frequency is fc. However, the amplitude of vibration decreases as n increases.

In order to prevent blackening, devitrification, and the like, when a high-frequency alternating current is supplied, there is a problem that it is more susceptible to a resonance phenomenon than a driving method that supplies a low-frequency alternating current.
An object of the present invention is to reduce damage to electrodes and the like when a high frequency alternating current is supplied.

  A driving apparatus according to an aspect of the present invention drives a discharge lamp having a first electrode and a second electrode in a cavity in which a discharge medium is sealed, and in the first period, An alternating current having a frequency higher than 1 kHz is supplied between the second electrode and the second electrode, and the alternating current in the first period is a first frequency having a first frequency higher than 1 kHz. It includes at least one alternating current and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency, and driving the discharge lamp by repeating the first period.

  In high-frequency driving, damage to electrodes and the like becomes a problem due to a resonance phenomenon. According to one aspect of the present invention, a first AC signal and a second AC signal having different frequencies are supplied to a discharge lamp in high-frequency driving. . As a result, while suppressing blackening and devitrification, even if a resonance phenomenon occurs in a certain waveform, the possibility of the resonance phenomenon occurring in another waveform having a different frequency can be reduced. It is possible to reduce damage and further change in light quantity.

  In one aspect of the driving device described above, it is preferable that the first alternating current and the second alternating current are direct current alternating current having a rectangular waveform. In this case, since a rectangular DC alternating current may be generated, the first AC current and the second AC current can be generated with a relatively simple bridge circuit or the like.

  In one aspect of the driving device described above, it is preferable that at least one of the first alternating current and the second alternating current has a supply time of a half cycle or less, and a waveform within the supply time is a direct current. According to one aspect of the present invention, since at least one of the first alternating current and the second alternating current has a supply time of half a cycle or less, even if a resonance phenomenon occurs due to one alternating current, the duration is shortened. It is possible to reduce damage to electrodes and the like due to acoustic resonance, and further to change in light quantity.

In one aspect of the driving device described above, after the first period is ended under a predetermined condition, the discharge lamp is driven by alternately repeating the second period and the third period, and in the second period, An alternating current having a frequency higher than 1 kHz is supplied between the first electrode and the second electrode between the first electrode and the second electrode, while an alternating current having a frequency of 1 kHz or less is supplied in the third period. An alternating current supplied between the first electrode and the second electrode and supplied in the second period is a third alternating current with a third frequency higher than 1 kHz, and a third alternating current higher than 1 kHz with the third frequency. It is preferable that at least a fourth alternating current having a different fourth frequency is included, and the alternating current supplied in the third period includes at least a fifth alternating current having a fifth frequency of 1 kHz or less.
According to one aspect of the invention, in the first period, high-frequency driving is intentionally executed instead of combination driving, so that change in the shape of the electrode at the start-up immediately after the start of operation is suppressed and blackening is prevented, Furthermore, damage to the electrodes and the like can be reduced. Furthermore, in the second period and the third period, high-frequency driving and low-frequency driving are performed alternately, so that the distance between the electrodes can be maintained while suppressing blackening and devitrification. Can be extended. Further, damage to the electrodes and the change in the amount of light can be reduced.

  Next, an aspect of the light source device according to the present invention includes the above-described driving device and a discharge lamp having a first electrode and a second electrode in a cavity in which a discharge medium is enclosed. According to this light source device, it is possible to reduce damage to the electrodes and the change in the amount of light while suppressing blackening and devitrification.

  Next, one aspect of the projector according to the present invention includes the light source device described above, a modulation device that modulates light emitted from the discharge lamp based on image information, and a projection that projects light modulated by the modulation device. Device. According to one embodiment of the present invention, damage to electrodes and the change in light amount can be reduced while suppressing blackening and devitrification, so that a stable image can be displayed for a long time.

  Next, one aspect of a method for driving a discharge lamp according to the present invention is a method for driving a discharge lamp having a first electrode and a second electrode disposed in a cavity in which a discharge medium is enclosed. In one period, an alternating current having a frequency higher than 1 kHz is supplied between the first electrode and the second electrode between the first electrode and the second electrode, and the alternating current in the first period is Including at least a first alternating current having a first frequency higher than 1 kHz and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency, and driving the discharge lamp by repeating the first period. It is characterized by. According to one embodiment of the present invention, it is possible to reduce damage to the electrodes and the change in the amount of light while suppressing blackening and devitrification.

It is a figure which shows the light source device which concerns on 1st Embodiment. It is principal part sectional drawing of the discharge lamp in the light source device. It is a figure which shows the electrical structure of a drive device. It is a graph which shows an example of the relationship between the frequency of an alternating current, and the standard deviation of the light quantity of a discharge lamp. It is a figure which shows the electric current waveform of a high frequency drive. It is a flowchart which shows the content of the high frequency drive process in the light source device. It is a figure for demonstrating the combination drive in the light source device which concerns on 2nd Embodiment. It is a figure which shows the measurement result of Examples 1-3. It is a figure which shows the measurement result of Comparative Examples 1-6. It is a figure which shows the projector using the light source device. It is a figure which shows the optical structure of the projector.

Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the drawings.
<First Embodiment>
The light source device according to the first embodiment of the present invention will be described.

FIG. 1 is a diagram illustrating an example of the structure of a light source device. As shown in this figure, the light source device 1 includes a light source unit 110 having a discharge lamp 500 and a driving device 200 for driving the discharge lamp 500. The discharge lamp 500 receives electric power from the driving device 200 and discharges it to emit light.
The light source unit 110 includes a discharge lamp 500, a main reflecting mirror 112 having a concave reflecting surface, and a collimating lens 114 that makes emitted light substantially parallel. The main reflecting mirror 112 and the discharge lamp 500 are bonded by an adhesive 116. Further, the main reflecting mirror 112 has a surface (inner surface) on the discharge lamp 500 side as a reflecting surface, and this reflecting surface forms a spheroidal surface in the illustrated configuration.

  The shape of the reflecting surface of the main reflecting mirror 112 is not limited to a spheroid, and may be a rotating paraboloid, for example. If the reflecting surface of the main reflecting mirror 112 is a paraboloid, the collimating lens 114 can be omitted if the light emitting part of the discharge lamp 500 is arranged at the so-called focal point of the paraboloid.

  The discharge lamp 500 includes a discharge lamp main body 510 and a sub-reflecting mirror 520 having a concave reflecting surface. The discharge lamp main body 510 and the sub-reflecting mirror 520 are disposed so that the sub-reflecting mirror 520 faces the main reflecting mirror 112 and the concave reflecting surface is disposed at a predetermined interval from the discharge lamp main body 510. As shown in FIG. Further, in the sub-reflecting mirror 520, the inner surface on the discharge lamp 500 side is a reflecting surface, and this reflecting surface forms a spherical surface in the illustrated configuration.

A central portion of the discharge lamp main body 510 is a hollow portion 512 that is sealed with a discharge medium sealed therein. The discharge lamp main body 510 is made of a light transmissive material such as quartz glass or light transmissive ceramics. The discharge medium is, for example, a discharge start gas or a gas that contributes to light emission. Among these, examples of the discharge start gas include noble gases such as neon, argon, and xenon. Examples of the gas that contributes to light emission include mercury, vaporized metal halide, and the like.
The discharge lamp main body 510 is provided with a pair of electrodes 610 and 710, a pair of conductive connection members 620 and 720, and a pair of electrode terminals 630 and 730. The electrodes 610 and 710 are attached to the cavity 512. Specifically, the tips of the electrodes 610 and 710 are attached to the cavity 512 of the discharge lamp main body 510 so as to be separated from each other by a predetermined distance and to face each other. Among these, the electrode (first electrode) 610 and the electrode terminal 630 are electrically connected to each other by the connection member 620. Similarly, the electrode (second electrode) 710 and the electrode terminal 730 are electrically connected to each other by a connection member 720. The electrode terminals 630 and 730 are each connected to the output terminal of the driving device 200.

  The driving device 200 supplies an AC current (AC power) described later to the electrode terminals 630 and 730. For this reason, in the electrode 610 connected to the electrode terminal 630 via the connection member 620 and the electrode 710 connected to the electrode terminal 730 via the connection member 720, the positive electrode having a relatively high potential, The polarity is alternately switched between the relatively lower negative electrode and the negative electrode.

When an alternating current is supplied to the electrode terminals 630 and 730, an arc discharge is generated between the tips of the electrodes 610 and 710 in the cavity 512, and the discharge medium emits light. Light generated by the arc discharge is radiated in all directions from the arc generation position (discharge position). Of the radiated light, the light radiated in the direction of the electrode 710 is mainly reflected by the sub-reflecting mirror 520. Reflected toward the reflecting mirror 112. For this reason, the light radiated | emitted in the direction of the electrode 710 can be utilized effectively.
In the present embodiment, the discharge lamp 500 includes the sub-reflecting mirror 520, but the discharge lamp 500 may be configured not to include the sub-reflecting mirror 520.

FIG. 2 is an example of a cross-sectional view of a main part of the discharge lamp 500. In FIG. 2, the sub-reflecting mirror 520 in FIG. 1 is omitted.
As shown in FIG. 2, the electrode 610 includes a core rod 612, a coil portion 614, and a main body portion 616. The electrode 610 is formed by winding a wire rod of an electrode material around a core rod 612 to form a coil portion 614 and heating and melting the formed coil portion 614 in a stage before being enclosed in the discharge lamp main body 510. Is done. As a result, a body portion 616 having a large heat capacity is formed on the tip side of the electrode 610. The electrode 710 also includes a core rod 712, a coil portion 714, and a main body portion 716, and is formed in the same manner as the electrode 610.
In addition, as a constituent material of each electrode 610,710, high melting point metal materials, such as tungsten, etc. are mentioned, for example.

  In the state where the discharge lamp 500 has never been lit, the main body portions 616 and 716 are not formed with the protrusions 618 and 718, but the discharge lamp 500 is lit even once by the arc discharge AR as will be described later. Then, protrusions 618 and 718 are formed at the tip portions of the main body portions 616 and 716, respectively. The protrusions 618 and 718 are maintained while the discharge lamp 500 is turned on, and are also maintained after the lamp is turned off.

FIG. 3 is a diagram illustrating an example of an electrical configuration of the light source device 1, particularly the driving device 200. As shown in this figure, the driving device 200 includes a supply unit 30 that supplies an alternating current to the discharge lamp 500, a control unit 33 that controls the supply unit 30, and a voltmeter that measures the interelectrode voltage of the discharge lamp 500. 35.
Further, the supply unit 30 includes switches Sw <b> 1 to Sw <b> 4 that are bridge-connected to the constant current source 31. The constant current source 31 controls the current value returning from the positive electrode output terminal (+) to the negative electrode output terminal (−) to be constant at a value designated by the control unit 33.
The switches Sw1 to Sw4 are respectively controlled to be in an on (closed) state and an off (open) state by the control unit 33, and among these, the switches Sw1 and Sw4 are controlled to be in the same state, and the same The switches Sw2 and Sw3 are paired and controlled to be in the same state. However, the set of the switches Sw1 and Sw4 and the set of the switches Sw2 and Sw3 are not simultaneously turned on, but are controlled to be turned on exclusively.
The switch Sw1 is electrically inserted between the positive electrode output terminal (+) of the constant current source 31 and the electrode terminal 630 of the discharge lamp 500, and the switch Sw2 is the negative electrode output terminal of the electrode terminal 630 and the constant current source 31. It is electrically inserted between (-). The switch Sw3 is electrically inserted between the positive electrode output terminal (+) of the constant current source 31 and the electrode terminal 730 of the discharge lamp 500, and the switch Sw4 is the negative electrode output terminal of the electrode terminal 730 and the constant current source 31. It is electrically inserted between (-).
The voltmeter 35 measures the voltage between the positive electrode output terminal (+) and the negative electrode output terminal (−) of the constant current source 31 and supplies the measured value to the control unit 33.

In this driving device 200, when the set of switches Sw1 and Sw4 is controlled to be in the on state by the control unit 33, and when the set of switches Sw2 and Sw3 is controlled to be in the off state, a constant current is applied from the electrode terminal 630 to the electrode terminal. It flows toward 730. On the other hand, when the pair of switches Sw1 and Sw4 is controlled to be in an off state and the pair of switches Sw2 and Sw3 is controlled to be in an on state, a constant current flows from the electrode terminal 730 toward the electrode terminal 630. For this reason, when the control unit 33 alternately switches on and off states for the set of switches Sw1 and Sw4 and the set of switches Sw2 and Sw3, an alternating current flows between the electrodes 610 and 710, and the on and off states are switched. When the switching cycle is shortened, the frequency of the alternating current is increased.
In this description, regarding the current (or voltage) flowing between the electrodes 610 and 710, the case where the current flows from the electrode 610 toward the electrode 710 is a positive value (positive polarity), and conversely from the electrode 710 to the electrode 610 A negative value (negative polarity) is defined for the case of flowing toward. However, the voltage measured by the voltmeter 35 is the absolute value (positive value) of the voltage between the electrodes 610 and 710 regardless of the direction of the current flowing through the electrodes 610 and 710.

An alternating current supplied from the driving device 200 to the discharge lamp 500 will be described. In the present embodiment, in high frequency driving in which an alternating current of a predetermined frequency or higher is supplied to the discharge lamp 500, an alternating current is generated by switching a plurality of types of waveforms having a frequency of a predetermined frequency or higher and different periods.
According to the high frequency driving, the stability of the discharge can be obtained as described above, and the temperature change in the discharge lamp 500 including the electrodes 610 and 710 is small, so that the chemical reaction for suppressing and recovering the blackening is stable. Thus, blackening and accompanying devitrification can be prevented.

  By the way, in the light emission of the discharge lamp 500 in the AC drive, the plasma density in the vicinity of the electrodes 610 and 710 changes in accordance with the positive / negative polarity switching of the AC current. This change in plasma density appears as the density of the internal gas density, which becomes a vibration and propagates from the center of the cavity 512 toward the inner wall. When this vibration is reflected by the inner wall of the cavity 512 and returns to the vicinity of the electrodes 610 and 710 again, the vibration may be strengthened by a resonance phenomenon. Such an alternating current frequency is referred to as an acoustic resonance frequency fc. The acoustic resonance frequency fc is determined by the shape of the discharge lamp 500 and the internal gas.

Due to the resonance phenomenon, the electrodes 610 and 710 vibrate, and there is a problem that the coil part 614 and the coil part 714 are partially damaged or the electrodes 610 and 710 are broken. Further, the amount of light changes due to the density of the plasma, The problem that light emission becomes unstable occurs.
Although depending on the shape of the discharge lamp 500, the acoustic resonance frequency fc is often several tens of kHz (for example, 60 kHz) in a small-sized one used in a projector. However, acoustic resonance also occurs when the frequency of the alternating current is fc / 2n (where n is a natural number).

FIG. 4 shows an example of the relationship between the alternating current frequency and the standard deviation of the light quantity of the discharge lamp 500. The peak of the light amount occurs due to a resonance phenomenon, and the light amount change gradually decreases as the frequency decreases. Then, the low frequency drive (less than 1 kHz), and eliminated the influence of resonance phenomena, damage to the coil portion and the electrode due to problems with such Ruoto sound resonance in high frequency driving, in view further to reduce the amount of light changes, the alternating current The frequency is preferably set to a frequency at which the resonance phenomenon does not occur.

  However, although the acoustic resonance frequency fc is determined by the shape of the discharge lamp 500 and the internal gas as described above, the acoustic resonance frequency fc changes due to manufacturing variations of the discharge lamp 500. For this reason, it is difficult to set the frequency of the alternating current so that the resonance phenomenon does not occur in all of the mass-produced discharge lamps 500.

  Therefore, in the present embodiment, in a high frequency drive that is easily affected by the resonance phenomenon, an alternating current is generated by switching a plurality of types of waveforms having a frequency equal to or higher than a predetermined frequency and having different periods. That is, in the period of high frequency driving, an alternating current is generated by switching a plurality of types of frequencies. As a result, even if a resonance phenomenon occurs at one of a plurality of types of frequencies selected by high-frequency driving, the possibility of the resonance phenomenon occurring at another frequency can be reduced, and the coil part or electrode is damaged by acoustic resonance. In addition, it is possible to reduce the change in the amount of light.

  A specific example of an alternating current waveform of high frequency driving is shown in FIG. Waveform example 1 is one cycle of cycle T1 (frequency f1) → one cycle of cycle T2 (frequency f2) → one cycle of cycle T3 (frequency f3) → one cycle of cycle T4 (frequency f4). This waveform is repeated as one unit.

  Next, the waveform example 2 includes a waveform of two cycles of cycle T1 (frequency f1) → a waveform of two cycles of cycle T2 (frequency f2) → a waveform of two cycles of cycle T3 (frequency f3) → a cycle T4 (frequency f4). The two-cycle waveform is set as one unit, and this is repeated.

  Next, waveform example 3 is a half-cycle waveform of cycle T1 (frequency f1) → a half-cycle waveform of cycle T2 (frequency f2) → a half-cycle waveform of cycle T3 (frequency f3) → cycle T4 (frequency f4). A half-cycle waveform of the cycle T5 (frequency f5) is set as one unit, and this is repeated. As described above, the resonance phenomenon occurs when the density of the internal gas density becomes vibration, is reflected by the inner wall of the cavity 512, and strengthens the vibration when reaching the vicinity of the electrodes 610 and 710. Therefore, the amplitude increases as the vibrations are repeatedly strengthened. In waveform example 3, since the frequency is switched every half cycle, even if the frequency of a certain waveform causes acoustic resonance, a waveform having a different frequency is selected in the next half cycle. By selecting waveforms with different frequencies, the possibility of intensifying vibrations can be reduced. Therefore, according to the waveform example 3, partial breakage of the coil portion and breakage of the electrode can be significantly suppressed.

In waveform example 3, switching is performed so that odd-numbered types (three or more) of waveforms are inverted every half cycle. In this case, the positive time and the negative time can be made equal in the odd-numbered unit period (first period) and the even-numbered unit period (first period). As a result, the temperature loads on the electrodes 610 and 710 can be made comparable, and the life of the discharge lamp 500 can be extended. Note that even-numbered (two or more) waveforms may be switched so as to be inverted every half cycle.
In waveform examples 1 to 3, the waveform is a rectangular alternating current. That is, alternating current is generated by switching direct current. Further, in the second period of high frequency driving, at least one of the first alternating current having the first frequency and the second alternating current having the second frequency may have a supply time of a half cycle or less. The waveform within this supply time is a direct current.

  Next, FIG. 6 is a flowchart of a high-frequency driving process executed by high-frequency driving. In this example, the waveform example 2 shown in FIG. 5 is generated. When driving is started, the control unit 33 selects a waveform of the first period T1 (frequency f1) (step S10), and then determines whether or not a predetermined period has elapsed (step S11). In this example, since the predetermined cycle is two cycles, the control unit 33 determines whether or not two waveforms of the frequency f1 have been generated. If the predetermined period has not elapsed, the control unit 33 returns the process to step S10 and repeats step S10 and step S11 until two periods have elapsed.

When the waveform of the frequency f1 is generated for two periods, the determination result in step S11 is “YES”, and the control unit 33 selects the waveform of the second period T2 (frequency f2) (step S12). Then, it is determined whether or not a predetermined period has elapsed (step S13). When the waveform of the frequency f2 is generated for two cycles, the determination result in step S23 is “YES”, and the control unit 33 selects the third cycle T3 (frequency f3) (step S14), and then the predetermined cycle is set. It is determined whether or not it has elapsed (step S15). When the waveform of the frequency f3 is generated for two cycles, the determination result in step S25 is “YES”, and the control unit 33 selects the waveform of the fourth cycle T4 (frequency f4) (step S16), and thereafter It is determined whether or not the period has elapsed (step S1 7 ). Waveform 2 cycles of the frequency f4, the generated, the decision result in the step S1 7 is "YES", the control unit 33 returns the process to step S10. As a result, the waveform of frequency f1 → the waveform of frequency f2 → the waveform of frequency f3 → the waveform of frequency f4 is repeatedly selected.

In this example, the predetermined cycle is two cycles. However, when the waveform example 1 shown in FIG. 5 is generated, the predetermined cycle is one cycle, and when the waveform example 3 shown in FIG. 5 is generated, the predetermined cycle. Is a half cycle. Furthermore, the predetermined period may not be the same for a plurality of types of frequencies, and is arbitrary. For example, the frequency f1 may be 1 period, the frequency f2 may be 1.5 periods, the frequency f3 may be 2 periods, and the frequency f4 may be 2.5 periods. In addition, the order of selecting a plurality of types of frequencies may not be constant for each unit period, may be random, or may be a predetermined order. For example, in the first-th unit period, the frequency f1 → the frequency f2 → frequency f3 → frequency f4, the second th unit period may be a frequency f2 → frequency f3 → frequency f4 → frequency f1. Further, from the viewpoint of preventing the same frequency from continuing, it is preferable to set the frequency selected at the end of a certain unit period to be different from the frequency selected at the beginning of the next unit period.

Second Embodiment
In the first embodiment described above, an alternating current is generated by switching a plurality of types of waveforms having different periods in high-frequency driving, thereby preventing blackening and accompanying devitrification and the like. Reduced breakage and broken electrodes. However, in high-frequency driving, because the arc discharge generated between the electrodes 610 and 710 causes the electrodes 610 and 710 to melt at a high temperature, the distance between the electrodes gradually increases. When the distance between the electrodes increases, not only the light use efficiency decreases, but also the impedance changes between the electrodes, resulting in an increase in reactive power, resulting in a decrease in efficiency.
On the other hand, according to the low frequency driving, when the discharge lamp is lit, a protrusion is formed at the tip of the electrodes 610 and 710, and the protrusion grows by repeated melting and solidification, so that the distance between the electrodes is narrow. The state can be maintained.
However, in the driving method of supplying a low-frequency current to the discharge lamp 500, the temperature change in the discharge lamp 500 is large, so that the chemical reaction for suppressing blackening becomes unstable, and blackening, devitrification, etc. occur. There is a problem that the life of the discharge amount is reduced.

Therefore, in the second embodiment, as shown in FIG. 7, after a predetermined condition (for example, elapse of a predetermined time) is satisfied and the first period ends, the second period in which high-frequency driving is performed and low-frequency driving are performed. The combination drive which switches alternately in combination with the third period to be performed is adopted.
By the way, when the discharge lamp is used as a light source for a projector or the like, the power is turned on (turned on) and turned off (shut off) many times.
The electrode temperature of the discharge lamp 500 is approximately room temperature when a sufficient time has elapsed from the previous use state, and the pressure of the cavity 512 is low. On the other hand, in the rated state of the discharge lamp 500, the temperature of the electrodes 610 and 710 of the discharge lamp 500 is extremely high (1000 ° C. or higher), and the pressure of the cavity 512 is also high (50 atm or higher). For this reason, in order to quickly shift the discharge lamp 500 from the time the power is turned on to the steady state, it is necessary to supply the discharge lamp 500 with a current that is close to the steady state or equivalent to the steady state after the power is turned on. is there. However, since a large heat load is applied to the electrodes 610 and 710 after the power is turned on, the protrusions 618 and 718 formed at the tips are deformed or blackening due to electrode sublimation occurs.

  For this reason, in the present embodiment, as shown in FIG. 7, in the first period immediately after power-on, high-frequency driving is intentionally executed instead of combination driving. In this case, the high-frequency driving is performed by switching a plurality of types of waveforms having different periods as in the first embodiment. Thereby, the shape change of the electrodes 610 and 710 at the time of start-up is suppressed, blackening is prevented, and damage to the coil portion and the electrodes can be reduced. The control unit 33 ends the first period when a predetermined condition is satisfied. For example, the time from power-on may have reached a predetermined time.

Next, combined driving is executed in the second period and the third period after the first period to achieve both maintenance of the distance between the electrodes and prevention of blackening. At this time, in combination driving, high frequency driving is performed first. Thereby, even if the protrusions 618 and 718 are deformed at the time of start-up, the deformed portion is melted by the high-frequency driving in the combination driving and smoothed by the surface tension, that is, the shape is reset, so that the combination driving is normal. Can continue to. Note that, also in the high-frequency driving in the second period, an alternating current is generated by switching a plurality of types of waveforms having different periods as in the first embodiment.
More specifically, the alternating current in the first period includes at least a first alternating current having a first frequency higher than 1 kHz and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency. The alternating current supplied in the second period includes at least a third alternating current having a third frequency higher than 1 kHz and a fourth alternating current having a fourth frequency higher than 1 kHz and different from the third frequency. Furthermore, the alternating current supplied in the third period includes at least a fifth alternating current having a fifth frequency of 1 kHz or less.

In combination driving in the second period, first, an upper limit value Vmax and a lower limit value Vmin are set in advance for the voltage between the electrodes 610 and 710. As described above, since the driving device 200 supplies a constant current to the electrodes 610 and 710, the voltage between the electrodes 610 and 710 increases as the distance between the electrodes increases. Therefore, the interelectrode voltage indicates the distance between the electrodes 610 and 710.
Secondly, for example, the voltage between the electrodes is measured while supplying a high frequency current, and when the measured voltage reaches the upper limit value Vmax, the high frequency driving is switched to the low frequency driving. Note that when switching to low frequency driving, as shown in FIG. 7, the voltage between the electrodes decreases, and the distance between the electrodes gradually decreases. On the other hand, blackening is unavoidable.
Third, when the measured voltage reaches the lower limit value Vmin, the low frequency driving is switched to the high frequency driving. When switching to high frequency driving, as shown in the figure, the interelectrode voltage gradually increases and the interelectrode distance gradually increases. On the other hand, blackening generated by low frequency driving is caused by the above chemical reaction. May recover.
That is, a first voltage value that is a voltage between electrodes when a predetermined current value during the second period of high frequency driving is applied is measured, and a predetermined current value during the third period of low frequency driving is measured. The second voltage value, which is the voltage between the electrodes when the voltage is applied, is measured, and the transition from the second period to the third period occurs when the first voltage value exceeds a predetermined upper limit value Vmax (first threshold value). When the second voltage value exceeds a predetermined lower limit value Vmin (second threshold value), the transition is made from the third period to the second period.

According to this combination driving, the distance between the electrodes is maintained in a range from a distance corresponding to the lower limit value Vmin of the interelectrode voltage to a distance corresponding to the upper limit value Vmax, and blackening does not occur during high frequency driving. In addition, blackening that occurs when a low-frequency current is supplied may be recovered. For this reason, it is possible to achieve both maintenance of the distance between the electrodes and prevention of blackening. The predetermined frequency that becomes the boundary between the high frequency driving and the low frequency driving may be determined from the viewpoint of keeping the distance between the electrodes within a predetermined range and suppressing blackening, and in this example, 1 kHz is adopted. Further, the frequency of the low frequency drive is preferably 10 Hz or more and 1 kHz or less, and the frequency of the high frequency drive is preferably more than 1 kHz and less than 10 GHz.
In the first high-frequency driving in the second period, the inter-electrode distance is widened by the high-frequency driving in the first period, so that the inter-electrode voltage reaches or exceeds the upper limit when the second period starts. There may be. In this case, the combination driving described above immediately switches to the low frequency driving in the third period, but the control unit 33 ignores the voltage from the voltmeter 35 in the first high frequency driving in the second period. Forcible high frequency driving may be used. At this time, the time length of the high frequency driving is set to 5 minutes, for example.
Further, the low frequency driving in the third period may be performed immediately after the first period. Furthermore, the switching between the high-frequency driving and the low-frequency driving may not be based on the interelectrode voltage, and the control unit 33 may determine that a predetermined switching condition has been satisfied. For example, the high-frequency driving time and the low-frequency driving time may each be determined, and the high-frequency driving and the low-frequency driving may be switched when the times are reached.

Next, examples of the present invention will be described in comparison with comparative examples.
Here, the embodiment is the light source device 1 shown in FIGS. 1 and 3, and the discharge lamp 500 shown in FIG. 2 is used. The driving conditions of this embodiment are as follows.

<Example 1>
Material of the discharge lamp body: Quartz glass Inclusion in the discharge lamp body: Argon, mercury, methyl bromide
Pressure at lighting in the discharge lamp body: 200 atm
Electrode constituent material: Tungsten Electrode distance: 1.1 mm
Rated power: 200W
AC current value (average): 2.9 A
Low frequency current frequency: 135 Hz (rectangular wave, 50% duty ratio)
The frequency of the high-frequency current: 5 kHz → 4.54 kHz → 4.16 kHz → 3.86 kHz → 3.55 kHz → 3.33 kHz every 4 cycles, and so on.

<Example 2>
The frequency of the high-frequency current: 5 kHz → 4.54 kHz → 4.16 kHz → 3.86 kHz → 3.55 kHz → 3.33 kHz for each cycle, and this is repeated thereafter.
Other conditions are the same as in Example 1.

<Example 3>
The frequency of the high-frequency current: 5 kHz → 4.54 kHz → 4.16 kHz → 3.86 kHz → 3.55 kHz → 3.33 kHz every half cycle, and so on.
Other conditions are the same as in Example 1.

<Comparative Example 1>
High-frequency current frequency: 5 kHz (square wave, 50% duty ratio)
Other conditions are the same as in Example 1.

<Comparative example 2>
High frequency current frequency: 4.16 kHz (square wave, duty ratio 50%)
Other conditions are the same as in Example 1.

<Comparative Example 3>
High frequency current frequency: 3.86 kHz (rectangular wave, duty ratio 50%)
Other conditions are the same as in Example 1.

<Comparative example 4>
Frequency of high frequency current: 3.33 kHz (rectangular wave, duty ratio 50%)
Other conditions are the same as in Example 1.

<Comparative Example 5>
Only high frequency drive without low frequency drive Frequency of high frequency current: 5 kHz (rectangular wave, duty ratio 50%)
Other conditions are the same as in Example 1.

<Comparative Example 6>
Low frequency drive is eliminated and only high frequency drive is used.
Every cycle, 5 kHz → 4.54 kHz → 4.16 kHz → 3.86 kHz → 3.55 kHz → 3.33 kHz, and so on.

<Evaluation>
About Examples 1-3 and Comparative Examples 1-6, the lighting test was done about each five samples, and the electrode state was investigated when 200 hours passed. The evaluation results of Examples 1 to 3 are shown in FIG. 8, and the evaluation results of Comparative Examples 1 to 6 are shown in FIG. In addition, the maintenance between electrodes evaluated about the voltage between electrodes, and the voltage between electrodes 70V-80V was evaluated as "good", 80V-100V was evaluated as "normal", and 100V or more was evaluated as "bad". As for blackening, “good” indicates no blackening at any location, “normal” indicates blackening at the base of the electrode, and “bad” indicates blackening in the entire tube. "
As shown in FIGS. 8 and 9, in Comparative Examples 1 to 4, the coil is removed and the electrode is broken. In Comparative Example 5, the coil is removed, the electrode is broken, and the gap is not maintained. Further, in Comparative Example 6, although the coil is removed and the electrode is not broken, the gap between the electrodes cannot be maintained.
On the other hand, in Example 1, although some samples can be coiled, there is no electrode breakage and the gap can be maintained. In Example 2 and Example 3, it is possible to remove the coil in all the samples, and the distance between the electrodes can be maintained without electrode breakage. From these things, the lifetime of a discharge lamp is extended, suppressing the partial breakage of a coil part and the bending of an electrode by switching several types of waveforms from which a period mutually differs in a 1st period, and producing | generating an alternating current. be able to.
As is clear from the first embodiment, by switching the waveform every four cycles, damage to the coil part and the electrode can be reduced, and as is clear from the third embodiment, the waveform is switched every half cycle. Furthermore, damage to the coil part and the electrode can be reduced. Therefore, it is preferable that the time for selecting one of the plurality of types of waveforms in the first period is not less than half cycle and not more than 4 cycles of the selected one type of waveform.

<Projector>
Next, an example of a projector to which the light source device 1 described above is applied will be described.
FIG. 10 is a diagram illustrating an example of an external configuration of the projector. As shown in this figure, the projector 2100 is a stationary type, and a projection lens 2114 for projecting an image is provided in front of the projector 2100. A switch 38 is provided.

FIG. 11 is a plan view showing an example of the optical configuration of the projector 2100.
As shown in this figure, the projector 2100 is a so-called three-plate type using transmissive liquid crystal light valves 100R, 100G, and 100B.
Inside the projector 2100, the above-described light source device 1 is provided, an alternating current is supplied from the driving device 200 to the discharge lamp 500, white light is emitted from the discharge lamp 500, and an optical element such as a main reflector. It is injected in the direction of 3 o'clock in the figure by the member. The emitted white light is separated into three primary colors of R (red), G (green), and B (blue) by three mirrors 2106 and dichroic mirrors 2108 and 2109 arranged inside, and corresponds to each primary color. Are incident on the liquid crystal light valves 100R, 100G, and 100B, respectively. More specifically, the dichroic mirror 2108 transmits light in the R wavelength region out of white light incident from the 9 o'clock direction in the drawing, and reflects the remaining light in the G and B wavelength regions in the 6 o'clock direction. The dichroic mirror 2109 transmits light in the B wavelength region out of light in the G and B wavelength regions incident from the 12 o'clock direction, and reflects light in other G wavelength regions in the 3 o'clock direction. Since B has a longer optical path than R and G, B is guided through a relay lens system 2121 including an incident lens 2122, a relay lens 2123, and an exit lens 2124 in order to prevent loss.

The projector 2100 is supplied with video signals corresponding to the respective colors of R, G, and B from upper circuits not shown, and the liquid crystal light valves 100R, 100G, and 100B are respectively supplied to the R, G, and B, respectively. Driven by the corresponding video signal. As a result, light incident on the liquid crystal light valves 100R, 100G, and 100B is emitted with its transmittance modulated for each pixel. That is, the liquid crystal light valves 100R, 100G, and 100B function as a modulation device that modulates the light emitted from the discharge lamp 500 based on the video signal (image information).
The lights modulated by the liquid crystal light valves 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, R and B light is refracted by 90 degrees, while G light travels straight. Therefore, after the modulated lights of the respective colors are combined, a color image is projected onto the screen 2120 by the projection lens 2114. These optical systems function as a projection device that projects light modulated by the liquid crystal light valves 100R, 100G, and 100B, respectively.

  Since light corresponding to each of R, G, and B is incident on the liquid crystal light valves 100R, 100G, and 100B by the dichroic mirror 2108, a color filter is not provided as in the direct view type. Further, the transmission images of the liquid crystal light valves 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmission image of the liquid crystal light valve 100G is projected as it is, so that the horizontal scanning by the liquid crystal light valves 100R and 100B is performed. The direction is opposite to the horizontal scanning direction by the liquid crystal light valve 100G, and a horizontally reversed image is created.

  Further, as a modulation device, a DLP (Digital Light Processing) type projector may be configured by using a DMD (Digital Mirror Device) which is an assembly element of micromirrors instead of the liquid crystal light valves 100R, 100G and 100B. DMD is a panel in which a large number of fine micromirrors are formed. Each of these micromirrors is mounted so that it can be tilted by about ± 10 degrees. For example, one mirror reflects incident light from the discharge lamp 500 in the direction of the projection lens when tilted at +10 degrees corresponding to one pixel, and does not reflect in the direction of the projection lens when tilted at −10 degrees. To act on. Accordingly, the DMD that has received the digital signal of the display image changes the inclination angle of each mirror to turn on / off the light emitted from the light source lamp. Since the tone can be controlled, it can be configured as a projector capable of obtaining a clear image without color unevenness. Further, the DLP projector may have a color wheel and a single DMD.

  DESCRIPTION OF SYMBOLS 1 ... Light source device, 30 ... Supply part, 31 ... Constant current source, 33 ... Control part, 35 ... Voltmeter, Vmax ... Upper limit value, Vmin ... Lower limit value, 200 ... Drive apparatus, 500 ... Discharge lamp, 610, 710 ... Electrode, 100R, 100G, 100B ... Liquid crystal light valve, 2100 ... Projector.

Claims (7)

A driving device for driving a discharge lamp having a first electrode and a second electrode,
A supply unit for supplying an alternating current between the first electrode and the second electrode;
The supply unit
In the first period, a first alternating current having a first frequency higher than 1 kHz and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency are between the first electrode and the second electrode. To supply
Driving the discharge lamp by repeating the first period ;
The first AC current and the second AC current are DC alternating currents having a rectangular waveform,
At least one of the first alternating current and the second alternating current is a direct current supplied between the first electrode and the second electrode with a half cycle length. . A driving device for driving a discharge lamp having a first electrode and a second electrode,
A supply unit for supplying an alternating current between the first electrode and the second electrode;
The supply unit
In the first period, a first alternating current having a first frequency higher than 1 kHz and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency are between the first electrode and the second electrode. To supply
Driving the discharge lamp by repeating the first period when starting up the discharge lamp;
When the predetermined condition is satisfied, the first period is ended, and after the first period, the second period and the third period are alternately repeated to drive the discharge lamp,
In the second period, a third alternating current having a third frequency higher than 1 kHz and a fourth alternating current having a fourth frequency higher than 1 kHz and different from the third frequency are obtained by the first electrode and the second electrode. Supply in between
In the third period, a fifth alternating current having a fifth frequency of 1 kHz or less is supplied between the first electrode and the second electrode. The drive device according to claim 1 ,
The supply device repeats the first period while the discharge lamp is turned on. A drive device according to any one of claims 1 to 3 ,
The discharge lamp;
A light source device comprising: A light source device according to claim 4 ;
A modulation device that modulates light emitted from the light source device based on image information;
A projection device for projecting light modulated by the modulation device;
A projector characterized by comprising: A method of driving a discharge lamp having a first electrode and a second electrode,
In the first period, a first alternating current having a first frequency higher than 1 kHz and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency are between the first electrode and the second electrode. Supplying to, and
Repeating the first period;
Equipped with a,
The first AC current and the second AC current are DC alternating currents having a rectangular waveform,
At least one of the first alternating current and the second alternating current is a direct current supplied between the first electrode and the second electrode with a half cycle length. Driving method. A method of driving a discharge lamp having a first electrode and a second electrode,
In the first period, a first alternating current having a first frequency higher than 1 kHz and a second alternating current having a second frequency higher than 1 kHz and different from the first frequency are between the first electrode and the second electrode. Supplying to,
Repeating the first period when starting up the discharge lamp;
Ending the first period when a predetermined condition is satisfied, and driving the discharge lamp by alternately repeating a second period and a third period after the first period;
In the second period, a third alternating current having a third frequency higher than 1 kHz and a fourth alternating current having a fourth frequency higher than 1 kHz and different from the third frequency are obtained by the first electrode and the second electrode. Supplying in between,
Supplying a fifth alternating current having a fifth frequency of 1 kHz or less between the first electrode and the second electrode in the third period;
A method for driving a discharge lamp, comprising:

Images