Technical Field
[0001]
The present invention relates to a light source device,
a projector, and a projection system.
Background Art
[0002]
Discharge lamps such as high pressure mercury lamps emit
light by performing arc discharge in plasmarized gases.
Projectors that correspond to 3D and perform stereoscopic video
display by using such discharge lamps have been put into
practice. In one of the schemes for the projectors
corresponding to 3D, input signals are divided into right-eye
and left-eye signals, the right-eye and left-eye signals are
alternately transmitted in sequence, and right-eye and
left-eye videos are alternately projected. Observers wear
active shutter glasses in which two shutters are alternately
opened and closed and selectively see the left-eye videos with
the left eyes and the right-eye videos with the right eyes.
Thus, the observers recognize the videos seen by the observers
as stereoscopic videos. However, when the observers wear the
foregoing active shutter glasses, the videos coming to the eyes
of the observers are blocked by the shutter during a
substantially half period. For this reason, a problem arises
in that the videos are darkened.
[0003]
For this problem, projectors that adopt schemes of
performing light control on discharge lamps in synchronization
with active shutter glasses have been proposed (for example,
see PLT 1 below). Such projectors perform light control
operations of increasing luminance of the discharge lamps at
the time of opening of the shutters of the glasses and
decreasing the luminance of the discharge lamps at the time
of closing of the shutters of the glasses. In other words,
power supplied to the discharge lamps is increased at the time
of opening of the shutters, and power supplied to the discharge
lamps is decreased at the time of closing of the shutters. When
such light control is performed, the luminance at the time of
.opening of the shutter can be increased by an amount of
luminance decreased at the time of closing of the shutters
without changing average luminance of the discharge lamps.
Thus, the observers can view bright videos.
Citation List
Patent Literature
[0004]
PTL 1: JP-A-2012-32504
Summary of Invention
Technical Problem
[0005]
Incidentally, arc discharge is known to produce various
reactions inside discharge lamps and cause illumination drop
of the discharge lamps. In order to resolve the problems, it
is necessary to suppress the illumination drop of the discharge
lamps and increase life spans of the discharge lamps.
[0006]
In general, three main causes of blackening in which
electrode materials evaporated by arc discharge are attachedto
the inner walls of luminous tubes of discharge lamps,
devitrification in which the inner walls of the luminance tubes
are crystallized due to high heat to be clouded and
transmittance is lowered, and consumption of electrodes
occurring by arc. discharge are known as causes of the
illumination drop of the discharge lamps.
[0007]
In driving in which there is a power difference as in
a change in power supplied to the above-described discharge
lamps, loads applied to the electrodes of the discharge lamps
increase and the electrodes are easily consumed. As a result,
there are problems that the illumination of the discharge lamps
is dropped due to the consumption of the electrodes and the
life spans of the discharge lamps are shortened as a result.
[0008]
An aspect of the invention is devised in view of the
above-described problems of the related art and an object of
the invention is to provide a light source device capable of
suppressing consumption of an electrode of a discharge lamp
at the time of driving of the discharge lamp in which there
is a power difference and improving a life span of the discharge
lamp and a projector using the light source device. Further,
another object of the invention is to provide a projection
system using the projector.
Solution to Problem
[0009]
A light source device according to an aspect of the
invention includes: a discharge lamp that emits light; a
discharge lamp driving unit that supplies a driving current
for driving the discharge lamp to the discharge lamp; and a
control unit that controls the discharge lamp driving unit,
in which a driving current waveform of the driving current
alternately has first and second periods, an absolute value
of the driving current during the first period is relatively
smaller than an absolute value of the driving current during
the second period, and during the first period, an alternating
current of 750 Hz or more is supplied as the driving current
to the discharge lamp.
[0010]
Movement of arc luminescent spots is considered as one
of the reasons of consumption of electrodes in driving of the
discharge lamp in which there is a power difference. The
movement of the arc luminescent spots easily occurs when power
supplied to the discharge lamp transitions from a large state
to a small state. When the movement of the arc luminescent
spots occurs, the positions of melting electrodes or the amount
of melting electrodes are changed. As a result, the shapes
of the electrodes become unstable and the electrodes are easily
consumed.
[0011]
In this configuration, in contrast, a high-fre.quency
current of 750 Hz or more is used in the first period in which
the absolute value of the driving current is small, in other
words, the power is small. Therefore, when the power supplied
to . the discharge lamp decreases, the movement of the arc
luminescent spots is suppressed. As a result, the consumption
of the electrode is suppressed. Accordingly, the life span
of the discharge lamp can be improved.
[0012]
The absolute value of the driving current during the
first period may be 80% or less of the absolute value of the
driving current during the second period.
In this configuration, the light source device proper
for using the projector corresponding to 3D can be obtained.
[0013]
During the second period, an alternating current may be
supplied as the driving current to the discharge lamp.
In this configuration, consumption of the electrodes can
be further suppressed.
[0014]
During the two first periods temporally interposing the
one second period, an alternating current with mutually
opposite phases may be supplied as the driving current to the
discharge lamp.
In this configuration, since the consumption of both
electrodes is uniformized, it is possible to prevent one
electrode from being unevenly consumed and prevent a distance
between the electrodes from being spread.
[0015]
During the two second periods temporally interposing the
one first period, an alternating current with mutually opposite
phases may be supplied as the driving current to the discharge
lamp.
In this configuration, since the consumption of both
electrodes is uniformized, it is possible to prevent one
electrode from being unevenly consumed and prevent a distance
between the electrodes from being widened.
[0016]
A projector according .to an aspect of the invention
includes: the light source device according to the aspect of
the invention; a light modulation element that modulates light
emitted from a discharge lamp according to a video signal; and
a projection optical system that projects the light modulated
by the light modulation element to a projection surface.
[0017]
In this configuration, since the lifespan of the
discharge lamp can be improved, the projector with high
reliability can be obtained.
[0018]
A projection system according to an aspect of the
invention includes: the projector according to the aspect of
the invention; and active shutter glasses that include
right-eye and left-eye shutters, in which the projector
alternately switches and outputs right-eye and left-eye videos
at predetermined switching timings, and a period interposed
between the temporally adjacent switching timings starts in
the first period and ends in the second period.
[0019]
In this configuration, since the life span of. the
discharge lamp can be improved, the proj ection system with high
reliability can be obtained.
Brief Description of Drawings
[0020]
[Fig. 1] Fig. 1 is a schematic diagram illustrating the
configuration of a projector according to an embodiment.
[Fig. 2] Fig. 2 is a sectional view illustrating a
discharge lamp according to the embodiment.
[Fig. 3] Fig. 3 is a block diagram illustrating a
projection system according to the embodiment.
[Fig. 4] Fig. 4 is a circuit diagram illustrating a
discharge lamp lighting device according to the embodiment.
[Fig. 5] Fig. 5 is a block diagram illustrating a
configuration example of a control unit according to the
embodiment.
[Fig. 6] Fig. 6 is a diagram illustrating the shapes of
projections at the front ends of electrodes of the discharge
lamp.
[Fig. 7] Fig. 7 is a timing chart illustrating various
operations of the projection system.
[Fig. 8] Fig. 8 is a diagram illustrating an example of
a driving current waveform.
[Fig. 9] Fig. 9 is a diagram illustrating movement of
arc luminescent spots at the front ends of the electrodes.
[Fig. 10] Fig. 10 is a diagram illustrating a photo in
which the movement of the arc luminescent spots is shown.
Description of Embodiments
[0021]
Hereinafter, a projection system according to an
embodiment of the invention will be described with reference
to Figs. 1 to 10.
The scope of the invention is not limited to the following
embodiment, but the embodiment may be modified in any manner
within the scope of the technical spirit of the invention. In
the following drawings, actual structures, scales or numbers
of the structures, and the like are different in some cases
to facilitate configurations.
[0022]
Fig. 3 is a block diagram illustrating a projection
system according to the embodiment.
As illustrated in Fig. 3, a projection system 400
according to the embodiment includes a projector 500 and active
shutter glasses 410. The projector 500 alternately projects
right-eye and left-eye videos to a screen 700 in a time division
manner.
[0023]
The active shutter glasses 410 include a right-eye
shutter 412 and a left-eye shutter 414. When an observer wears
the active shutter glasses 410, the right-eye shutter 412 is
closed so that a visual field of the right eye side is blocked.
When the observer wears the active shutter glasses 410, the
left-eye shutter 414 is closed so that a visual field of the
-1-0-
left eye side is blocked. The right-eye shutter 412 and the
left-eye shutter 414 are composed of, for example, liquid
crystal shutters.
[0024]
Hereinafter, an optical system of the projector 500 will
be described.
Fig. 1 is a schematic diagram illustrating the
configuration of the projector 500 according to the embodiment.
As illustrated in Fig. 1, the projector 500 according
to the embodiment includes a light source device 200, a
parallelizing lens 305, an illumination optical system 310,
a color separation optical system 320, three liquid crystal
light valves 330R, 330G, and 330B (light modulation elements) ,
a cross dichroic prism 340, and a projection optical system
350.
[0025]
Light emitted from the light source device 200 passes
through the parallelizing lens 305 and is incident on the
illumination optical system 310. The parallelizing lens 305
has a function of parallelizing the light from the light source
device 200.
[0026]
The illumination optical system 310 has a function of
performing adjustment so that the illumination of the light
emitted from the light source device 200 is uniformized in the
liquid crystal light valves 330R, 330G, and 330B. The
illumination optical system 310 has a function of arranging
a polarization direction of the light emitted from the light
source device 200 in one direction. The reason is that the
light emitted from the light source device 200 is effectively
used in the liquid crystal light valves 330R, 330G, and 330B.
[0027]
The light of which an illumination distribution and the
polarization direction are adjusted is incident on the color
separation optical system 320. The color separation optical
system 320 separates the incident light into three color pieces
of light, red light (R), green light (G), and blue light (B).
The three pieces of color light are modulated by the liquid
crystal light valves 330R, 330G, and 330B corresponding to the
respective colors. The liquid crystal light valves 330R, 330G,
and 330B include liquid crystal panels 560R, 560G, and 560B
to be described below and polarization plates (not
illustrated).
The.polarization plates are disposed on a light incident
side and a light exit side of' the liquid crystal panels 560R,
560G, and 560B.
[0028]
The three pieces of modulated light are synthesized by
the cross dichroic prism 340. The synthesized light is
incident on the projection optical system 350 . The projection
^ _
optical system 350 projects the incident light to the screen
700 (see Fig. 3). Thus, a video is displayed on the screen
700. Various known configurations can be adopted as the
configurations of the parallelizing lens 305, the illumination
optical system 310, the color separation optical system 320,
the cross dichroic prism 340, and the projection optical system
350.
[0029]
Fig. 2 is a sectional view illustrating the configuration
of the light source device 200. The light source device 200
includes a light source unit 210 and a discharge lamp lighting
device (discharge lamp driving device) 10. In Fig. 2, the
sectional view of the light source unit 210 is illustrated.
The light source unit 210 includes a main reflection mirror
112, a discharge lamp 90, and a sub-reflection mirror 50.
[0030]
The discharge lamp lighting device 10 supplies a driving
current (driving power) to the discharge lamp 90 to light the
discharge lamp 90. The main reflection mirror 112 reflects
light radiated from the discharge lamp 90 in an irradiation
direction D. The irradiation direction D is parallel to an
optical axis AX of the discharge lamp 90.
[0031]
The shape of the discharge lamp 90 is a rod shape extending
in the irradiation direction D. One end of the discharge lamp
90 is referred to as a first end 90el and the other end of the
discharge lamp 90 is referred to as,a second end 90e2. The
material of the discharge lamp 90 is, for example, a
transmissive material such as quartz glass. A middle portion
of the discharge lamp 90 is swollen in a spherical shape and
the inside of the spherical shape is referred to as a discharge
space 91. In the discharge space 91, a gas which is a discharge
medium containing a rare gas and a metal halogen compound is
sealed.
[0032]
In the discharge space 91, the front ends of a first
electrode 92 and a second electrode 93 are projected. The first
electrode 92 is disposed on the side of the first end 90el of
the discharge space 91. The second electrode 93 is disposed
on the side of the second end 90e2 of the discharge space 91.
The shapes of the first electrode 92 and the second electrode
93 'are rod shapes extending in the optical axis AX. In the
discharge space 91, the front ends of the first electrode 92
and the second electrode 93 are disposed to be separated by
a predetermined distance and to face each other. The material
of the first electrode 92 and the second electrode 93 are, for
example, metal such as tungsten.
[0033]
A first terminal 536 is provided at the first end 90el
of the discharge lamp 90. The first terminal 536 and the first
electrode 92 are electrically connected by a conductive member
534 passing through the inside of the discharge lamp 90.
Similarly, a second terminal 546 is provided at the second end
90e2 of the discharge lamp 90. The second terminal 546 and
the second electrode 93 are electrically connected by a
conductive member 544 passing through the inside of the
discharge lamp 90. The material of the first terminal 536 and
the second terminal 54 6 is, for example, metal such as tungsten.
As the material of the conductive members 534 and 544, for
example, molybdenum foil is used.
[0034]
The first terminal 536 and the second terminal 546 are
connected to the discharge lamp lighting device 10. The
discharge lamp lighting device 10 supplies a driving, current
to the first terminal 536 and the second terminal 546 to drive
the discharge lamp 90. As a result, arc discharge is generated
between the first electrode 92 and the second electrode 93.
Light (discharged light) generated by the arc discharge is
radiated in all directions from a discharge position, as
indicated by dotted arrows.
[0035]" "
The main reflection mirror 112 is fixed to the first end
90el of the discharge lamp 90 by a fixing member 114. Of the
discharged light, light travelling toward the side opposite
to the irradiation direction D is reflected in the irradiation
direction D by the main reflection mirror 1.12. The shape of
the reflection surf ace (the surface on the side of the discharge
lamp 90) of the main reflection mirror 112 is not particularly
limited within the scope in which the discharged light can be
reflected in the irradiation direction D. For example, the
shape of the reflection surface may be spheroidal or
rotated-paraboloidal. For example, when the shape of the
reflection surface of the main reflection mirror 112 is
rotated-paraboloidal, the main reflection mirror 112 can
convert the discharged light into light substantially parallel
to the optical axis AX. Thus, the parallelizing lens 305 can
be omitted.
[0036]
The sub-reflection mirror 50 is fixed on the side of the
second end 90e2 of the discharge lamp 90 by a fixing member
522. The shape of the reflection surface (the surface on the
side of the discharge lamp 90) of the sub-reflection mirror
50 is a spherical shape surrounding the portion of the second
end 90e2 of the discharge space 91. Of the discharged light,
light travelling toward the side opposite to the side on which
the main reflection mirror 112 is disposed is reflected toward
the main reflection mirror 112 by the sub-reflection mirror
50. Thus, the use efficiency of the light radiated from the
discharge space 91 can be improved.
[0037]
The material of the fixing members 114 and 522 is not
particularly limited within the scope in which the material
is a heat-resistant material resisting heat generated from the
discharge lamp 90 and is, for example, an inorganic adhesive.
The method of fixing the disposition of the main reflection
mirror 112 and the sub-reflection mirror 50, and the discharge
lamp 90 is not limited to the method of fixing the main
reflection mirror 112 and the sub-reflection mirror 50 to the
discharge lamp 90, but any method can be adopted. For example,
the discharge lamp 90 and the main reflection mirror 112 may
be separately fixed to the casing (not illustrated) of the
projector. The same applies to the sub-reflection mirror 50.
[0038]
Hereinafter, the circuit configuration of the projector
500 will be described.
Fig. 3 is a diagram illustrating an example of the circuit
configuration of the proj ector 500 according to the embodiment.
The projector 500 includes an image signal conversion unit 510,
a direct-current power supply device 80, liquid crystal panels
560R, 560G, and 560B, an image processing device 570, and a
central processing unit (CPU) 580 in addition to the optical
system illustrated in Fig. 1.
[0039]
The image signal conversion unit 510 converts image
signals 502 (luminance-color difference signals, analog RGB
signals, or the like) input from the outside into a digital
RGB signal of a predetermined word length to generate image
signals 512R, 512G, and 512B and supplies the image signals
512R, 512G, and 512B to the image processing device 570. When
stereoscopic video signals in which right-eye and left-eye
videos are alternately switched are input as the image signals
502 at a predetermined switching timing, the image signal
conversion unit 510 supplies a synchronization signal 514 to
the CPU 580 based on the switching timing of the right-eye and
left-eye videos.
[0040]
The image processing device 57 0 performs image
processing on each of the three image signals 512R, 512G, and
512B. The image processing device 570 supplies driving
signals 572R, 572G, and 572B for driving the liquid crystal
panels 560R, 560G, and 560B to the liquid crystal panels 560R,
560G, and 560B.
[0041]-
The direct-current power supply device 80 converts an
alternating voltage supplied from an external
alternating-current power supply 600 into a constant
direct-current voltage. The direct-current power supply
device 80 supplies the direct-current voltage to the image
signal conversion unit 510 and the image processing device 570
on the secondary side of a transformer (included in the
direct-current power supply device 80 although not
illustrated) and to the discharge lamp lighting device 10 on
the primary side of the transformer.
[0042]
The discharge lamp lighting device 10 generates a high
voltage between the electrodes of the discharge lamp 90 at the
time of activation and produces dielectric breakdown to form
a discharge path. Thereafter, the discharge lamp lighting
device 10 supplies a driving current I so that the discharge
lamp 90 maintains the discharge.
[0043]
The liquid crystal panels 560R, 560G, and 560B are
included in the liquid crystal light valves 330R, 330G, and
330B described above, respectively. The liquid crystal panels
560R, 560G, and 560B modulate transmittance (luminance) of the
color light incident on the liquid crystal panels 560R, 560G,
and 560B via the above-described optical system based on the
driving signals 572R, 572G, and 572B, respectively.
[0044]
The CPU 580 controls various operations until the
projector 500 turns on and then turns off. For example, in
the example of Fig. 3, a turning-on command or a turning-off
command is output to the discharge lamp lighting device 10
through a communication signal 582. The CPU 580 receives
turning-on information of the discharge lamp 90 through the
: _t9
communication signal 584 from the discharge lamp lighting
device 10. Based on the synchronization signal 514, the CPU
580 outputs a control signal 586 for controlling the active
shutter glasses 410 in synchronization with the image signals
502 to the active shutter glasses 410 via a wired or wireless
communication unit. In the right-eye shutter 412 and the
left-eye shutter 414 of the active shutter glasses 410, opening
and closing operations are controlled based on the control
signal 586.
[0045]
Hereinafter, the configuration of the discharge lamp
lighting device 10 will be described.
Fig. 4 is a diagram illustrating an example of the circuit
configuration of the discharge lamp lighting device 10.
As illustrated in Fig. 4, the discharge lamp lighting
device 10 includes a power control circuit 20, a polarity
inversion circuit 30, a control unit 40, an operation detection
unit 60, and an igniter circuit 70.
[0046]
The power control circuit 20 generates a driving power
to be supplied to the discharge lamp 90. In the embodiment,
the power control circuit 20 is composed of a down-chopper
circuit that receives a voltage from the direct-current power
supply device 80 as an input, drops the input voltage,* and
outputs a direct current Id.
---2-0
[0047]
The power control circuit 20 is configured to include
a switch element 21, a diode 22, a coil 23, and a capacitor
24. The switch element 21 is composed of, for example, a
transistor. In the embodiment, one end of the switch element
21 is connected to a positive voltage side of the direct-current
power supply device 80 and the other end of the switch element
21 is connected to the cathode terminal of the diode 22 and
one end of the coil 23.
[0048]
One end of the capacitor 24 is connected to the other
end of the coil 23 and the other end of the capacitor 24 is
connected to the anode terminal of the diode 22 and a negative
voltage side of the direct-current power supply device 80. A
current control signal is input from the control unit 40 to
be described below to the control terminal of the switch element
21 so that ON/OFF of the switch element 21 is controlled. As
the current control signal, for example, a pulse width
modulation (PWM) control signal may be used.
[0049]
When the switch element 21 is turned ON, a current flows
in the coil 23 so that energy can be stored in the coil 23.
Thereafter, when the switch element 21 is turned OFF, the energy
stored in the coil 23 is radiated to a path passing the capacitor
24 and the diode 22. As a result, the direct current Id
2^
according to a ratio of a time m which the switch element 21
is turned ON is generated.
[0050]
The polarity inversion circuit 30 inverts the polarity
of the direct current Id input from the power control circuit
20 at a predetermined timing. Thus, the polarity inversion
circuit 30 generates and outputs a driving current I which is
a direct current continuing for a controlled time or a driving
current I which is an alternating current with any frequency.
In the embodiment, the polarity inversion circuit 30 is
composed of an inverter bridge circuit (full-bridge circuit) .
[0051]
The polarity inversion circuit 30 includes, for example,
a first switch element 31, a second switch element 32, a third
switch element 33, and a fourth switch element 34 composed of
transistors or the like. The polarity inversion circuit 30
has a configuration in which the first switch element 31 and
the second switch element 32 that are connected to each other
in series and the third switch element 33 and the fourth switch
element 34 that are connected to each other in series are
connected to each other in parallel. A polarity inversion
control signal is input from the control unit 4 0 to each of
the control terminals of the first switch element 31, the second
switch element 32, the third switch element 33, and the fourth
switch element 34. Based on the polarity inversion control
signal, ON/OFF operations of the first switch element 31, the
second switch element 32, the third switch element 33, and the
fourth switch element 34 are controlled.
[0052]
In the polarity inversion circuit 30, an operation of
alternately turning ON/OFF the first switch element 31 and the
second switch element 32, and the third switch element 33 and
the fourth switch element 34 is repeated. Thus, the polarity
of the direct current Id output from the power control circuit
20 is alternately inverted. The driving current I which is
a direct current with the same polarity state continuing for
a controlled time or the driving current I which is an
alternating current with a controlled frequency is generated
and output from a common connection point of the first switch
element 31 and the second switch element 32 and a common
connection point of the third switch element 33 and the fourth
switch element 34.
[0053]
That is, the polarity inversion circuit 30 performs
control such that the second switch element 32 and the third
switch element 33 are turned OFF when the first switch element
31 and the fourth switch element 34 are turned ON, and the second
switch element 32 and the third switch element 33 are turned
ON when the first switch element 31 and the fourth switch
element 34 are turned OFF. Accordingly, when the first switch
element 31 and the fourth switch element 34 are turned ON, the
driving current I flowing in an order of the first switch
element 31, the discharge lamp 90, and the fourth switch element
34 is generated from the one end of the capacitor 24. When
the second switch element 32 and the third switch element 33
are turned ON, the driving current I flowing in an order of
the third switch element 33, the discharge lamp 90, and the
second switch element 32 is generated from the one end of the
capacitor 24.
[0054]
In the embodiment, a combined portion of the power
control circuit 20 and the polarity inversion circuit 30
corresponds to a discharge lamp driving unit 230. That is,
the discharge lamp driving unit 230 supplies the driving
current I for driving the discharge lamp 90 to the discharge
lamp 90.
[0055]
The control unit 40 controls the discharge lamp driving
unit230. In the example of Fig. 4, the control unit 4 0 controls
a hold time in which the same polarity of the driving current
I continues, a current value and a frequency of the driving
current I, and the like by controlling the power control circuit
20 and the polarity inversion circuit 30. The control unit
40 performs polarity inversion control on the polarity
inversion circuit 30 such that the hold time in which the same
polarity of the driving current I continues, the frequency of
the driving current I, and the like are controlled in accordance
with a polarity inversion timing of the driving current I. The
control unit 40 performs current control on the power control
circuit 20 such that the current value of the direct current
Id to be output is controlled.
[0056]
The configuration of the control unit 40 is not
particularly limited. In the embodiment, the control unit 40
is configured to include a system controller 41, a power control
circuit controller 42, and a polarity inversion circuit
controller 43. A part or all of the control unit 40 may be
composed of a semiconductor integrated circuit.
[0057]
The system controller 41 controls the power control
circuit 20 and the polarity inversion circuit 30 by controlling
the power control circuit controller 42 and the polarity
inversion circuit controller 43. The system controller 41 may
control the power control circuit controller 42 and the
polarity inversion circuit controller 43 based on the driving
current f and a driving voltage Via detected by the. operation
detection unit 60.
[0058]
In the embodiment, the system controller 41 is configured
to include a storage unit 44. The storage unit 44 may be
provided independently from the system controller 41.
[0059]
The system controller 41 may control the power control
circuit 20 and the polarity inversion circuit 30 based on
information stored in the storage unit 44. For example, the
storage unit 44 may store information regarding driving
parameters of the hold time in which the same polarity of the
driving current I continues, the current value and the
frequency of the driving current I, a waveform, and a modulation
pattern.
[0060]
The power control circuit controller 42 controls the
power control circuit 20 by outputting a current control signal
to the power control circuit 20 based on a control signal from
the system controller 41.
[0061]
The polarity inversion circuit controller 43 controls
the polarity inversion circuit 30 by outputting a polarity
inversion control signal to the polarity inversion circuit 30
based on a control signal from the system controller 41.
[0062]
The control unit 40 is realized using a dedicated circuit
and can perform various kinds of control on the control
described above or a process to be described below. In contrast,
the control unit 40 can also perform various kinds of control
on the processes, for example, by causing the CPU 580 to execute
a control program stored in the storage unit 44 and function
as a computer.
[0063]
Fig. 5 is a diagram illustrating another configuration
example of the control unit 40. As illustrated in Fig. 5, the
control unit 40 may be configured to function as a current
control unit 40-1 that controls the power control circuit 20
and function as a polarity inversion control unit 40-2 that
controls the polarity inversion circuit 30 in accordance with
the control program.
[0064]
In the example illustrated in Fig. 4, the control unit
40 is composed of a part of the discharge lamp lighting device
10. In contrast, some of the functions of the control unit
40 may be configured to be performed by the CPU 580.
[0065]
The operation detection unit 60 includes, for example,
a voltage detection unit that detects the driving voltage Via
of the discharge lamp 90 and outputs driving voltage
information to the control unit 40 and a current detection unit
that detects the driving current I and outputs driving current
information to the .control unit 40. In the embodiment, the
operation detection unit 60 is configured to include a first
resistor 61, a second resistor 62, and a third resistor 63.
nn
[0066]
.In the embodiment, the voltage detection unit detects
the driving voltage Via by a voltage divided into the first
resistor 61 and the second resistor 62 connected in series to
each other in parallel to the discharge lamp 90. In the
embodiment, the current detection unit detects the driving
current I by a voltage generated in the third resistor 63
connected in series to the discharge lamp 90.
[0067]
The igniter circuit 70 operates only at the time of start
of the turning-ON of the discharge lamp 90. The igniter circuit
70 supplies a high voltage (a voltage higher than at the time
of normal turning-on of the discharge lamp 90) necessary to
produce dielectric breakdown and form a discharge path between
the electrodes (the first electrode 92 and the second electrode
93) of the discharge lamp 90 at the time of start of the
turning-on of the discharge lamp 90 between the electrodes (the
first electrode 92 and the second electrode 93) of the discharge
lamp 90 . In the embodiment, the igniter circuit 7 0 is connected
in parallel to the discharge lamp 90.
10068]
Hereinafter, a relation between the polarity of the
driving current I and a temperature will be described.
Figs . 6 (A) to 6 (D) are diagrams illustrating the relation
between the polarity of the driving current I supplied to the
-2-8-
discharge lamp 90 and the temperature of the electrodes . Figs .
6(A) and 6(B) illustrate operation states of the first
electrode 92 and the second electrode 93. In the drawings,
the front ends of the first electrode 92 and the second
electrode 93 are illustrated. Protrusions 552p and 562p are
formed at the front ends of the first electrode 92 and the second
electrode 93. Discharge occurring between the first electrode
92 and the second electrode 93 occurs mainly between the
protrusions 552p and 562p. When there are the protrusions 552p
and 562p as in the embodiment, movement of discharge positions
(positions of arc luminescent spots) in the first electrode
92 and the second electrode 93 can be suppressed further than
when there are no protrusions.
[0069]
Fig. 6 (A) illustrates a first polarity state Psl in which
the first electrode 92 operates as an anode and the second
electrode 93 operates as a cathode. In the first polarity state
Psl, electrons move from the second electrode 93 (the cathode)
to the first electrode 92 (the anode) through the discharge.
The electrons are radiated from the cathode (the second
electrode 93). The electrons radiated from the cathode (the
second electrode 93) collide against the front end of the anode
(the first electrode 92).
Heat is generated due to this collision and the
temperature of the front end (the protrusion 552p) of the anode
(the first electrode 92) increases.
[0070]
Fig. 6(B) illustrates a second polarity state Ps2 in
which the first electrode 92 operates as a cathode and the
second electrode 93 operates as an anode. In the second
polarity state Ps2, in contrast- to the first polarity state
Psl, electrons move from the first electrode 92 to the second
electrode 93. As a result, the temperature of the front end
(the protrusion 562p) of the second electrode 93 increases.
Thus, the temperature of the anode which the electrons
collide against is easily higher than the temperature of the
cathode radiating the electrons.
[0071]
Fig. 6(C) is a timing chart illustrating an example of
the driving current I supplied to the discharge lamp 90. The
horizontal axis represents a time T and the vertical axis
represents a current value of the driving current I. The
driving current I indicates a current that flows in the
discharge lamp 90. A positive value indicates the first
polarity state Psl and a negative value indicates the second
polarity state Ps2.
[0072]'
In the example illustrated in Fig. 6(C), a square-wave
alternating current is used as the driving current I. In the
example illustrated in Fig. 6(C) , the first polarity state Psl
-3-0-
and the second polarity state Ps2 are alternately repeated.
Here, a first polarity section Tp indicates a time in which
the first polarity state Psl continues and a second polarity
section Tn indicates a time in which the second polarity state
Ps2 continues. In the example illustrated in Fig. 6(C), an
average current value in the first polarity section Tp is Iml
and an average current value in the second polarity section
Tn is -Im2 . The frequency of the driving current I proper for
the driving of the discharge lamp 90 can be decided
experimentally in accordance with the characteristics of the
discharge lamp 90 (for example, a value is adopted in the range
of 30 Hz to 1 kHz) . Other values Iml, -Im2, Tp, and Tn can
similarly be decided experimentally.
[0073]
Fig. 6(D) is a timing chart illustrating a temperature
change of the first electrode 92. The horizontal axis
represents a time T and the vertical axis represents a
temperature H. In the first polarity state Psl, the
temperature H of the first electrode 92 increases. In the
second polarity state Ps2, the temperature H of the first
electrode 92 decreases. Since the first polarity state Psl
and the second polarity state Ps2 are repeated, the temperature
H is changed periodically between a minimum value Hmin and a
maximum value Hmax. Although not illustrated, the temperature
of the second electrode 93 is changed at an opposite phase to
_3_]_ :
the temperature H of the first electrode 92. That is, the
temperature of the second electrode 93 decreases in the first
polarity state Psl and the temperature of the second electrode
93 increases in the second polarity state Ps2.
[0074]
•
Hereinafter, a specific example of control of the driving
current I in the projection system 400 will be described.
Fig. 7 is a timing chart illustrating various operations i
of the projection system. ]
i
As illustrated in Fig. 7, content of the driving signals
572R, 572G, and 572B, open and closed states of the right-eye
shutter 412, open and closed states of the left-eye shutter
414, periods, and a temporal change in a switching timing are
shown. The horizontal axis of Fig. 7 represents a time.
[0075]
In the. example illustrated in Fig. 7, the driving signals
572R, 572G, and 572B are driving signals corresponding to a
i
right-eye video from time tl to time t3, a left-eye video from )
time t3 to time t5, and a right-eye video from time t5 to time
7. Accordingly, in the example illustrated in Fig. 7, the
projector 500 switches and alternately outputs the right-eye
i
and left-eye videos using time tl, time t3, time t5, and time
t7 as switching timings.
[0076] J
A period interposed between temporally adjacent
_3_2 :
i
i
switching timings starts at a first period PI and ends at a
second period P2. In the example illustrated in Fig. 7, for
example, a period interposed between time tl and time t3 which
are switching timings starts in the first period PI between
time tl and time t2 and ends in the second period P2 between
time t2 to time t3. The same also applies to a period interposed
between time t3 and time t5 which are switching timings and
a period interposed between time t5 and time t7 which are
switching timings.
[0077]
In the example illustrated in Fig. 7, the length of the
first period PI and the length of the second period P2 are the
same. However, the length of the first period PI and the length
of the second period P2 can be appropriately set as necessary.
A third period may be present between the first period Pi and
the second period P2. During the third period, control
different from the control of the driving current I during the
first period Pi and the second period P2 may be performed, as
will be described below.
[0078]
In a case illustrated in Fig. 7, video signals are written
to the liquid crystal light valves 330R, 330G, and 330B once
during each of the first period PI and the second period P2.
That is, a total of two-time video signals are written to the
liquid crystal light valves 330R, 330G, and 330B during a
33
one-time period of one-eye videos. At this time, when the
length of the period (one field) of the one-eye videos is 1/120
s, video signals are written to the liquid crystal light valves
330R, 330G, and 330B at a one-time ratio during l/240s. In
other words, the driving frequency of the liquid crystal light
valves 330R, 330G, and 330B is 240 Hz.
[0079]
The right-eye shutter 412 enters an open state during
at least some of the periods in that the driving signals 572R,
572G, and 572B corresponding to the right-eye videos are input
to the liquid crystal panels 560R, 560G, and 560B. In the
example illustrated in Fig. 7, the right-eye shutter 412 is
in the closed state from time tl to time t2, that is, during
the first period PI and is in the open state from time t2 to
time t3, that is, during the second period P2. During a period
in which the driving signals 572R, 572G, and 572B corresponding
to the left-eye videos are input to the liquid crystal panels
560R, 560G, and 560B, the right-eye shutter 412 starts to close
from the switching time (time t3) and ends the close during
the first period PI (from time t3 to time t4), and is in the
closed state during the second period P2 (from time t4 to time
t5) . The change in the open and closed states of the right-eye
shutter 412 from time t5 to time t7 is the same as the change
in the open and closed states from time tl to time t'5.
[0080]
In regard to the left-eye shutter 414, the switching
timings are deviated by one switching timing and the same open
and close operations as the right-eye shutter 412 are performed
That is, during a period (for example, a period from time tl
to a time t3) in which the right-eye videos are output, the
left-eye shutter 414 performs the same opening and closing
operations as the right-eye shutter 412 during a period (for
example, a period from time t3 to time t5) in which the left-eye
videos flow. Further, during a period (for example, a period
from time t3 to time t5) in which the left-eye videos are output,
the left-eye shutter 414 performs the same opening and closing
operations as the right-eye shutter 412 during a period (for
example, a period from time t5 to time t7) in which the right-eye
videos flow.
In the example illustrated in Fig. 7, in the first period
PI, there is a period in which both of the right-eye shutter
412 and the left-eye shutter 414 are closed.
[0081]
Fig. 8 is a timing chart illustrating an example of a
driving current waveform.
The vertical axis represents a power ratio of the driving
current supplied to the discharge lamp 90. The power ratio
is a relative value of the driving power when the driving power
of a rated normal mode (at the time of 2D display) is set to
1. When the distance between the electrodes is constant, the
driving voltage is considered to be constant. At this time,
since the driving current and the driving power have a
proportional relation, the waveform in Fig. 8 can be regarded
as a waveform indicating the relative value of the driving
current when the driving current of the rated normal mode (the
time of 2D display) is 1. In Fig. 8, the power ratio in the
first polarity state Psl is shown as a positive value and the
power ratio in the second polarity state Ps2 is shown as a
negative value.
The horizontal axis represents a time, and a timing at
which the right-eye shutter 412 or the left-eye shutter 414
is opened, that is, a boundary (for example, time t2, time t4,
or time t6 in Fig. 7) in which the first period PI transitions
to the second•period P2, is shown as 0 s.
[0082]
In the embodiment, as illustrated in Fig. 8, the driving
current supplied to the discharge lamp 90 is a square-wave
alternating current. In other words, the driving current
supplied to the discharge lamp 90 during the first period PI
and the second period P2 is a square-wave alternating current.
The alternating current during the first period PI is
a high-frequency alternating current. For example, the
frequency of the alternating current during the first period
PI is equal to or more than 750 Hz and equal to or less than
10 kHz. A specific example of the frequency is, for example,
-3-6-
960 Hz in Fig. 8.
[0083]
The frequency of the alternating current during the
second period P2 is not particularly limited, but can be set
to be proper for specification or use of the discharge lamp.
The frequency of the alternating current during the second
period P2 may differ for each second period P2, as illustrated
in Fig. 8. For example, in Fig. 8, the frequency of the
alternating current during the second period P2 is set to 320
I
Hz during a period P2a, 160 Hz during a period P2b, and 960
Hz during a period P2c. I
[0084]
A power ratio (driving current ratio) during the first
period PI is set to be smaller than a power ratio (driving
current ratio) during the second period P2. In other words,
the absolute value of the driving current during the first
period PI is set to be relatively smaller than the absolute
value of the driving current during the second period P2 . The
power ratio (driving current ratio) during the first period
]
PI is equal to or smaller than, for example, 80% of the power
ratio (driving current ratio) during the second period P2. j
[0085]
The power ratio (driving current ratio) of the first
period PI to the second period P2 can be set according to the
lengths of the first period PI and the second period P2 . That
3_7
i
is, an average power ratio of a combined period of the first
period PI and the second period P2 can be set to be equal to
an average power ratio of the rated normal mode. Hereinafter,
the detailed description will be made.
[0086]
First, a case of the driving current waveform illustrated
in Fig. 8 will be described as a first example.
In an example of the driving current waveform illustrated
in Fig. 8, a combined length of the first period PI and the
second period P2, that is, the length of a period in which
one-eye video, is set to 1/120 s. This is because the length
of one frame of a video is set to 1/60 s, and each of a field
of a right-eye video and a field of a left-eye video forming
one frame is set to a length of half of one frame. For example,
one frame in Fig. 7 is a period from time tl to time t5. The
field of the right-eye video is a period from time tl to time
t3 and the field of the left-eye video is a period from time
t3 to time t5.
[0087]
In Fig. 8, a length ratio of the first period PI to the
second period P2 is set to 1:~3. That is, the length of the
first period PI is 1/480 s and the length of the second period
P2 is 1/160 s. In this case, during a one-time one-eye video
period, a one-eye video signal is written to the liquid crystal
light valves 330R, 330G, and 330B a total of four times. The
-38-
first writing is performed during the first period PI and the
second to fourth writings are performed during the second
period P2. In this case, writing of the video signal to the
liquid crystal light valves 330R, 330G, and 330B is performed
once for 1/480 s. In other words, the driving frequency of
the liquid crystal light valves 330R, 330G, and 330B is 480
Hz.
[0088]
In the foregoing case, for example, when the power ratio
of the second period P2 is set to be higher than the power ratio
of the rated normal mode by 15%, the power ratio of the first
period PI is set to about 48% of the power ratio of the second
period P2, so that the average power ratio of the combined
period of the first period PI and the second period P2 can be
equalized to the average power ratio of the rated normal mode.
Specifically, for example, as illustrated in Fig. 8, when the
power ratio is a positive value, the power ratio of the first
period PI is set to 0. 55 and the power ratio of the second period
P2 is set to 1.15. When the power ratio is a negative value,
the power ratio of the first period PI is set to -0.55 and the
power ratio of the second period P2 is set to -1.15. Thus,
the average power ratio of the combined period of the first
period PI and the second period P2 can be set to 1 (the average
power ratio of the rated normal mode).
[0089]
Next, a case in which the length of the first period PI
is set to be equal to the length of the second period P2, as
illustrated in Fig. 7, will.be described as a second example.
When the length of a one-eye video period is set to 1/120
s as in Fig. 8, the length of the first period Pi is the same
as the length of the second period P2, and thus each of the
lengths of the first period PI and the second period P2 is 1/240
s. In this case, for example, when the power ratio of the second
period P2 is higher than the power ratio of the rated normal
mode by 15%, the power ratio of the first period PI is set to
about 74% of the power ratio of the second period P2, so that
i
i the average power ratio of the combined period of the first
j period PI and the second period P2 can be equalized to the
average power ratio of the rated normal mode.
[0090]
Specifically, for example, when the power ratio is a
positive value, the power ratio of the first period PI is set
to 0.85 and the power ratio of the second period P2 is set to
1.15. When the power ratio is a negative value, the power ratio
of the first period PI is set to -0.85 and the power ratio of
i
the second period P2 is set to -1.15. Thus, the average power
ratio of the combined period of the first.period PI and the
second period P2 can be set to 1 (the average power ratio of
the rated normal mode) . In this case, the driving frequency
of the liquid crystal light valves 330R, 330G, and 330B is 240
4_0
Hz.
[0091]
As exemplified above, the power ratio of the second
period P2 in which one of the right-eye shutter 412 and the
left-eye shutter 414 is opened is set to be larger than 1 (the
average power ratio of the rated normal mode) , the power ratio
of the first period PI in which both of the right-eye shutter
412 and the left-eye shutter 414 are closed is set to be less
than 1 (the average power ratio of the rated normal mode), the
average luminance of the discharge lamp 90, that is, the average
power supplied to the discharge lamp 90, is equalized as that
of the rated normal mode, and thus deterioration in the
luminance of the videos entering the eyes of an observer can
be reduced.
[0092]
In the embodiment, since the frequency of the alternating
current during the first period PI in which the power supplied
to the discharge lamp 90 is small is a high frequency, the
consumption of the first electrode 92 and the second electrode
93 can be suppressed, and thus the life span of the discharge
lamp 90 can be improved. Hereinafter, the detailed
description will be described.
[0093]
Figs. 9(A), 9(B), and 9(C) are diagrams illustrating
aspects of arc discharge in the first electrode 92 and the
second electrode 93. In Fig. 9(A), the first polarity state
Psl is illustrated. That is, the first electrode 92 is an anode
and the second electrode 93 is a cathode. In Figs. 9(B) and
9(C), the second polarity state Ps2 is illustrated. That is,
the first electrode 92 is a cathode and the second electrode
93 is an anode.
[0094]
Fig. 9 (A) illustrates the aspect of discharge during the
second period P2. An arc AR1 is generated between the first
electrode 92 and the second electrode 93. Arc luminescent
spots 910 are formed on protrusions 900a and 900b formed on
the surfaces of the first electrode 92 and the second electrode
93. Since the power supplied to the discharge lamp 90 is large
during the second period P2, the arc luminescent spots 910 are
largely formed. Thus, the protrusion 900a formed on the
surface of the first electrode 92 which is the anode is melted
and the surface of the protrusion 900a is flattened.
[0095]
Next, Fig. 9(B) is a diagram illustrating the second
polarity state Ps2 realized when the second period P2 is
switched to the first period PI and the polarity is inverted.
As illustrated in Fig. 9(B) , an arc AR2a is generated between
the first electrode 92 and the second electrode 93. Since the
power supplied to the discharge lamp 90 decreases during the
first period PI, arc luminescent spots 920 formed on the
protrusions 900a and 900b decrease.
[0096]
Next, Fig. 9 (C) is a diagram illustrating a case in which
the period is switched to the first period Pi and a
predetermined time has passed. As illustrated in Fig. 9(C),
the positions of the arc luminescent spots 920 of the cathode
side (the side of the first electrode 92) move to the lower
side. This is because the arc luminescent spots 920 during
the first period PI are smaller than the arc luminescent spots
910 during the second period P2 and easily move on the surface
of the protrusion 900a flattened during the second period P2.
The movement of the arc luminescent spots occurs only on the
cathode side from which the electrons are radiated.
[0097]
When the positions of the arc luminescent spots 920 move,
the distance between the arc luminescent spots increases.
That is, the distance between the arc luminescent spots is the
distance between the electrodes. In Fig. 9(B), both of the
position of the arc luminescent spot 920 on the side of the
first electrode 92 and the position of the arc luminescent spot
on the side of the second electrode 93 are located in the middle
of the protrusions 900a and 900b in the vertical direction.
Therefore, the arc AR2a is generated substantially
horizontally, and a distance Wl between the arc luminescent
spots is the same as the substantially horizontal distance
-4-3-
between the protrusions 900a and 900b.
[0098]
In contrast, since the arc luminescent spot 920 on the
cathode side (the side of the first electrode 92) moves downward
in Fig. 9 (C) , an arc AR2b is generated in a state inclined from
the horizontal state, and thus a distance W2 between the arc
luminescent spots is greater than the distance Wl between the
arc luminescent spots.
[0099]
Accordingly, when the arc luminescent spots on the
electrodes move, the distance between the electrodes increases,
and thus the luminance of the discharge lamp deteriorates.
When the positions of the arc luminescent spots move,
the positions of the melting electrodes or the amount of melting
electrodes are changed. As a result, the shapes of the
electrodes become unstable and the electrodes are easily
consumed.
[0100]
Figs. 10(A) and 10(B) illustrate photos in which the
actual movement of the arc luminescent spots is shown. Both
of Figs. 10(A) and 10(B) illustrate the case of the second
polarity state Ps2.
Fig. 10(A) illustrates a moment (0 s) at which the first
period PI is entered. As illustrated in Fig. 10(A), it can
be confirmed that an arc luminescent spot 920A is formed in
the vertical direction in the middle of a protrusion 900aA
formed on a first electrode 92A immediately after the first
period PI is entered.
[0101]
On the other hand, Fig. 10(B) is a diagram illustrating
a state after the first period PI is entered and 1/240 s has
passed. As illustrated in Fig. 10 (B) , it can be confirmed that
the arc luminescent spot 920A moves downward on the protrusion
900aA.
[0102]
On the other hand, in the embodiment, since the
high-frequency alternating current is supplied during the
first period PI, the polarity of each electrode is switched
rapidly and a time in which each electrode serves as the cathode
becomes considerably short. A movement speed of the arc
luminescent spot is about 50 mm/s when acceleration is
neglected. Therefore, when the time in which each electrode
serves as the cathode is considerably short, a distance by which
the arc luminescent point moves is extremely short while the
electrode serves as the cathode and the movement of the arc
luminescent spot is consequently suppressed. Accordingly,
since the movement of the arc luminescent spots is suppressed,
the consumption of the electrodes is suppressed, and thus the
life span of the discharge lamp can be improved.
[0103]
In the embodiment, the following configurations can be
adopted.
[0104],
During the second period P2, the current supplied to the
discharge lamp 90 may be a direct current.
[0105]
In Fig. 8, all of the first periods PI and the second
periods P2 start from the second polarity state Ps2. In other
words, the alternating currents during all of the first periods
PI and the second periods P2 have the same phase.
In contrast, two first periods Pi temporally interposing
one second period P2 may have mutually reverse phases. That
is, when one first period PI starts from the second polarity
state Ps2, a subsequent first period PI may start from the first
polarity state Psl.
[0106]
'Further, two second periods P2 temporally interposing
one first period PI may have mutually reverse phases. That
is, when one second period P2 starts from the second polarity
state Ps2, a subsequent second period P2 may start from the
first polarity state Psl.
Accordingly, since the consumption of the .first
electrode 92 and the consumption of the second electrode 93
can be substantially uniformized, expansion of the distance
between the electrodes due to biased consumption of the
electrode can be suppressed.
[0107]
Hereinafter, embodiments will be described.
First, embodiment 1 will be described.
An experiment of movement of arc luminescent spots at
the time of changing of the frequency of the driving current
during the first period and the frequency of the driving current
during the second period was performed.
[0108]
A high-pressure mercury lamp of which rated power is 230
W was used as a discharge lamp.
A square-wave alternating current was used as the driving
current during both of the first and second periods. When the
frequency of the first period was changed into 240 Hz, 480 Hz,
and 960 Hz, the frequency of the second period was changed into
160 Hz, 320 Hz, and 640 Hz, respectively.
[0109]
The frequency of the second period was set to be constant
in each experiment. In other words, unlike the driving current
waveforms exemplified in Fig. 8, driving current waveforms of
which the frequency is the same during the periods P2a, P2b,
and P2c were used. The same applies to the first period.
The absolute value of the power ratio during the first
period was set to 0.55 and the absolute value of the power ratio
during the second period was set to 1.15. That is, the power
4 „ 7
ratio (driving current ratio) of the first period was set to
about 48% of the power ratio (driving current ratio) of the
second period.
Like the driving current waveform exemplified in Fig.
8, the length of the first period was set to 1/480 s and the
length of the second period was set to 1/160 s.
[0110]
As illustrated in Figs. 10(A) and 10(B), the movement
of the arc luminescent spots was observed using photos obtained
by photographing the electrodes. The electrodes were each
photographed after the discharge lamp was turned on and a
predetermined time passed, in other words, after an operation
of the discharge lamp was stabilized and 1/960 s passed after
a moment at which the second period was switched to the first
period and a moment at which the period was switched to the
first period. How the arc luminescent spots move was evaluated
from the positions of the arc luminescent spots in the two
photographed photos. The result is shown in Table 1.
[0111]
4-8-
In Table 1, a mark x indicates a case in which the arc
luminescent spots moved and a mark O indicates a case in which
the arc luminescent spots did not move.
From Table 1, it can be understood that the movement of
the arc luminescent spots occurs in any of the cases in which
the frequency of the second period is 160 Hz, 320 Hz, and 640
Hz when the frequency of the first period is 240 Hz and 480
Hz. In contrast, it can be understood that no movement of the
arc luminescent spots occurs in any of the cases in which the
frequency of the second period is 160 Hz, 320 Hz, and 640 Hz
when the frequency of the first period is 960 Hz.
Accordingly, by setting the frequency of the first period
to a high frequency, it was confirmed that the movement of the
arc, luminescent spots is suppressed irrespective of the
frequency of the second period.
[0113]
Next, embodiment 2 will be described.
Measurement of a movement distance of the arc luminescent
spots at the time of the changing of the frequency of the first
period without changing the driving current waveform pattern
of the second period was performed. The driving current
waveform pattern during the second period was set so that the
frequency was changed during each period (for example, the
periods P2a, P2b, and P2c) as exemplified in Fig. 8.
Specifically, the frequency of the second period was set to
be changed periodically in the order of 160 Hz, 320 Hz, and
960 Hz during each period. The driving current waveform
pattern during the first period was set so that the frequency
was the same during any period, as in embodiment 1.
The used discharge lamp, the power ratios of the first
period to the second period, and the lengths of the first and
second periods were set to be the same as those of embodiment
1.
[0114]
The measurement of the movement distance of the arc
luminescent spots was each performed when the frequency of the
first period was changed to 200 Hz, 240 Hz, 400.Hz, 480 Hz,
800 Hz, and 960 Hz. The measurement of the movement distance
of the arc luminescent spots was performed through image
measurement using photos obtained by photographing the
electrodes. The photographing of the electrodes is the same
as that of embodiment 1. The result is shown in Table 2.
[0115]
•5-0-
As shown in Table 2, it can be understood that the movement
distance of the arc luminescent spots decreases as the
frequency of the first period increases. Further, it can be
confirmed that the movement distance of the arc luminescent
spots is 0 mm when the frequency of the first period is 800
Hz or more and the movement of the arc luminescent spots is
suppressed. From the viewpoint of the tendency that the
movement distance of the arc luminescent spots decreases from
200 Hz to 480 Hz, the movement of the arc luminescent spots
is considered to be sufficiently suppressed when the frequency
of the first period is about 750 Hz or more.
As described above, by setting the frequency of the first
period to 750 Hz or more, it was confirmed that the movement
of the arc luminescent spots is suppressed and the consumption
of the electrodes of the discharge lamp can be suppressed.
Reference Signs List
[0117]
10 discharge lamp lighting device (discharge lamp
driving device)
40 control unit
90 discharge lamp
200 light source device
230 discharge lamp driving unit
330R, 330G, 330B liquid crystal light valves (light
modulation elements)
350 projection optical system
410 active shutter glasses
500 projector
PI first period
P2 second period
•52

CLAIMS
[Claim 1]
A light source device comprising:
a discharge lamp that emits light;
a discharge lamp driving unit that supplies a driving
current for driving the discharge lamp to the discharge lamp;
and
a control unit that controls the discharge lamp driving
unit,
wherein a driving current waveform of the driving current
alternately has first and second periods,
wherein an absolute value of the driving current during
the first period is relatively smaller than an absolute value
of the driving current during the second period, and
wherein during the first period, an alternating current
of 750 Hz or more is supplied as the driving current to the
discharge lamp.
[Claim 2]
The light source device according to claim 1,
wherein the absolute value of the driving current during
the first period is 80% or less of the absolute value of the
driving current during the second period.
[Claim 3]
The light source device according to claim 1 or 2,
wherein during the second period, an alternating current
is supplied as the driving current to the discharge lamp.
[Claim 4]
The light source device according to any one of claims
1 to 3,
wherein during the two first periods temporally
interposing the one second period, an alternating current with
mutually opposite phases is supplied as the driving current
to the discharge lamp.
[Claim 5]
The light source device according to any one of claims
1 to 4,
wherein during the two second periods temporally
interposing the one first period, an alternating current with
mutually opposite phases is supplied as the driving current
to the discharge lamp.
[Claim 6]
A projector comprising:
the light source device according to any one of claims
1 to 5;
a light modulation element that modulates light emitted
from the discharge lamp according to a video signal; and
a projection optical system that projects the light
modulated by the light modulation element to a projection
surface.
[Claim 7]
A projection system comprising:
the projector according to claim 6; and
active shutter glasses that include right-eye and
left-eye shutters,
wherein the projector alternately switches and outputs
right-eye and left-eye videos at predetermined switching
timings, and
wherein a period interposed between the temporally
adjacent switching timings starts in the first period and ends
in the second period.