U.S. patent application number 15/075396 was filed with the patent office on 2016-10-06 for lighting device, light apparatus, and signboard apparatus.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to Yohei HAYASHI, Shojirou KIDO.
Application Number | 20160295654 15/075396 |
Document ID | / |
Family ID | 57017916 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160295654 |
Kind Code |
A1 |
KIDO; Shojirou ; et
al. |
October 6, 2016 |
LIGHTING DEVICE, LIGHT APPARATUS, AND SIGNBOARD APPARATUS
Abstract
A lighting device includes: a drive circuit that supplies power
to a light source; a switch connected in series with the light
source; and a controller that controls pulse modulation for visible
light communication executed through switching ON and OFF of the
switch in a first interval, and stops the pulse modulation in a
second interval. The controller controls a peak value, which is a
high value of a pulsed current. supplied from the drive circuit to
the light source, to match an average current value in the first
interval with an average current value in the second interval.
Inventors: |
KIDO; Shojirou; (Osaka,
JP) ; HAYASHI; Yohei; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
57017916 |
Appl. No.: |
15/075396 |
Filed: |
March 21, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 45/44 20200101;
H05B 45/14 20200101; H04B 10/116 20130101; H05B 45/10 20200101 |
International
Class: |
H05B 33/08 20060101
H05B033/08; G09F 13/00 20060101 G09F013/00; G09F 15/00 20060101
G09F015/00; H05B 37/02 20060101 H05B037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2015 |
JP |
2015-077219 |
Claims
1. A lighting device comprising: a drive circuit that supplies
power to a light source; a switch connected in series with the
light source; and a controller that controls pulse modulation for
visible light communication executed through switching ON and OFF
of the switch in a first interval, and stops the pulse modulation
in a second interval, wherein the controller controls a peak value,
which is a high value of a pulsed current supplied from the drive
circuit to the light source, to match an average current value in
the first interval with an average current value in the second
interval.
2. The lighting device according to claim 1, wherein the controller
causes the drive circuit and the switch to cyclically repeat the
first interval and the second interval.
3. The lighting device according to claim 2, wherein the controller
causes the drive circuit to increase the peak value at a start of
the first interval and restore the peak value at a start of the
second interval.
4. The lighting device according to claim 1, wherein the controller
causes the peak value in the first interval to be a value obtained
by dividing the average current value in the second interval by a
duty cycle of a pulse modulation signal for the first interval.
5. The lighting device according to claim 1, wherein, in the second
interval, the controller causes the switch to switch ON and OFF at
a frequency different from a frequency of the pulse modulation in
the first interval and with a duty cycle identical to a duty cycle
of the pulse modulation.
6. The lighting device according to claim 5, wherein, in the second
interval, the controller causes the switch to switch ON and OFF to
generate a pulse train that is invalid in the visible light
communication.
7. The lighting device according to claim 1, wherein the controller
causes the first interval and the second interval to be cyclically
generated, and where the first interval is T1 seconds and the
second interval is T2 seconds, 1(T1+T2) is greater than or equal to
60 Hz.
8. The lighting device according to claim 1, wherein the pulse
modulation is an inverted pulse position modulation in which a
value of one symbol is represented by a position of an inverted
pulse in a plurality of slots, and the inverted pulse has a width
smaller than a slot width.
9. The lighting device according to claim 1, wherein the controller
outputs, to the drive circuit, a command value signal indicating a
magnitude of current that the drive circuit is required to supply
to the light source, and the drive circuit includes: a detector
that detects a current value of the current supplied to the light
source; and a suppresser that performs sampling and holding of the
current value detected at a time of transitioning from the second
interval to the first interval, and suppresses an overshoot in the
pulsed current to be supplied, to the light source, based on a
difference between the current value held in the sampling and
holding and a value indicated by the command value signal.
10. A light apparatus comprising the lighting device and the light
source according to claim 1.
11. A signboard apparatus comprising: a plurality of the light
apparatuses according to claim 10; and a control apparatus that
instructs visible light communication to each of the plurality of
the light apparatuses, wherein the plurality of the light
apparatuses are arranged as a collective signboard.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority of Japanese
Patent Application Number 2015-077219 filed on Apr. 3, 2015, the
entire content of which is hereby incorporated by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates to a lighting device, a light
apparatus, and a signboard device including plural light
apparatuses.
[0004] 2. Description of the Related Art
[0005] Japanese Unexamined Patent Application Publication No.
2006-120910 (Patent Literature (PTL) 1) discloses a semiconductor
light-emitting element power supply that can modulate and drive a
current-driven semiconductor light-emitting element, which (i)
includes a voltage source having a controllable voltage and an
average current detecting circuit that detects an average current
flowing in a semiconductor light-emitting element, and (ii)
controls an output voltage of the voltage source so that the
average current detected by the average current detecting circuit
becomes approximately constant. Accordingly, the average
light-emission amount of the semiconductor light-emitting element
is kept approximately constant whether the semiconductor
light-emitting element is modulated and driven (i.e., data transfer
is executed by visible light) or not.
SUMMARY
[0006] However, since PTL 1 keeps the average light-emission amount
of the semiconductor light-emitting element approximately constant
through feedback of the average current detected by the average
current detecting circuit, there are cases where a fluctuation in
the light-emission amount cannot be suppressed. For example, in the
case where a period in which data transfer is executed and a period
in which data transfer is not executed are alternately repeated,
there is the problem that, when the response time of the feedback
system is slow, the fluctuation in light-emission amount is not
fully suppressed and, visually, flickering may occur.
[0007] Furthermore, assuming a collective signboard including
plural light sources having a transmission function for visible
light communication, there is the problem that the difference in
brightness between a light apparatus that is executing a data
transfer and a light apparatus that is not executing data transfer
is conspicuous and gives a sense of incongruity.
[0008] The present disclosure provides a lighting device, a light
apparatus, and a signboard apparatus which reduce the difference in
average illuminance between adjacent light sources having a
transmission function for visible light communication, and prevent
the sense of incongruity.
[0009] A lighting device according to an aspect of the present
disclosure includes: a drive circuit that supplies power to a light
source; a switch connected in series with the light source; and a
controller that controls pulse modulation for visible light
communication executed through switching ON and OFF of the switch
in a first interval, and stops the pulse modulation in a second
interval, wherein the controller controls a peak value, which is a
high value of a pulsed current supplied from the drive circuit to
the light source, to match an average current value in the first
interval with an average current value in the second interval.
[0010] Furthermore, a light apparatus according to an aspect of the
present disclosure includes the lighting device and the light
source.
[0011] Furthermore, a signboard apparatus according to an aspect of
the present disclosure includes: a plurality of the light
apparatuses; and a control apparatus that instructs visible light
communication to each of the plurality of the light apparatuses,
wherein the plurality of the light apparatuses are arranged as a
collective signboard.
[0012] A lighting device, a light apparatus, and a signboard
apparatus according to the present disclosure reduce the difference
in average illuminance between adjacent light sources having a
transmission function for visible light communication, and prevent
the sense of incongruity.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The figures depict one or more implementations in accordance
with the present teaching, by way of examples only, not by way of
limitations. In the figures, like reference numerals refer to the
same or similar elements.
[0014] FIG. 1 is a block diagram illustrating an example
configuration of a signboard apparatus according to Embodiment
1.
[0015] FIG. 2 is an external view of an example of a signboard
apparatus according to Embodiment 1.
[0016] FIG. 3 is a block diagram illustrating an example
configuration of a light apparatus according to Embodiment 1.
[0017] FIG. 4 illustrates time charts of example waveforms of
current flowing in a light source in each of a modulation. interval
and a pause interval according to Embodiment 1.
[0018] FIG. 5 is a flowchart illustrating an example process by a
controller according to Embodiment 1.
[0019] FIG. 6 is a time chart illustrating example waveforms of
current flowing in a light source according to Embodiment 2.
[0020] FIG. 7 illustrates time charts for example pulse modulation
according to Embodiment 3.
[0021] FIG. 8 is a time chart illustrating an example waveform of
current flowing in a light source in each of a modulation interval
and a pause interval according to Embodiment 4.
[0022] FIG. 9 is a block diagram illustrating an example
configuration of a light apparatus according to Embodiment 5.
[0023] FIG. 10 is a time chart illustrating example current
waveforms in each of a modulation interval and a pause interval in
a comparative example.
[0024] FIG. 11 is a block diagram illustrating an example
configuration of a suppresser according to Embodiment 5.
[0025] FIG. 12 is a time chart illustrating operation of the
suppresser according to Embodiment 5.
[0026] FIG. 13 is a time chart illustrating an example of exclusive
control of plural light apparatuses according to Embodiment 1.
[0027] FIG. 14 is a block diagram illustrating another example
configuration of a light apparatus.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0028] Hereinafter, exemplary embodiments of the present disclosure
shall be described in detail with reference to the drawings. It
should be noted that each of the subsequently-described exemplary
embodiments shows one specific example of the present disclosure.
The numerical values, shapes, materials, structural components, the
arrangement and connection of the structural components, etc. shown
in the following exemplary embodiments are mere examples, and are
not intended to limit the scope of the present disclosure.
Furthermore, among the structural components in the following
exemplary embodiments, components not recited in any one of the
independent claims which indicate the broadest concepts of the
present disclosure are described as arbitrary structural
components.
EMBODIMENT 1
[0029] A lighting device, a light apparatus, and a signboard
apparatus according to Embodiment 1 are described below.
[0030] [1.1 Structure of Signboard Apparatus]
[0031] FIG. 1 is a block diagram illustrating example configuration
of signboard apparatus 1 according to Embodiment 1. Furthermore, as
illustrated in FIG. 1, signboard apparatus 1 includes plural light
apparatuses 2, and control apparatus 4.
[0032] Each of light apparatuses 2 is a light panel apparatus
having a transmission function and a light-emitting face which are
for visible light communication (VLC). Light apparatuses 2 are
two-dimensionally arranged as a collective signboard.
[0033] Control apparatus 4 is, for example, a personal computer
(PC), and is connected to light apparatuses 2 via communication
lines. Control apparatus 4 controls the dimming and visible light
communication of signboard apparatus 1 by transmitting various
types of commands to signboard apparatus 1 via the communication
The various types of commands include, for example, a command
instructing a dimming level and a command instructing the execution
of visible light communication. It should be noted that
communication between control apparatus 4 and light apparatuses 2
may be implemented by wired communication or wireless
communication. Furthermore, control apparatus 4 performs exclusive
control of the visible light communication transmission function of
light apparatuses 2. In the exclusive control, control apparatus 4
causes each of light apparatuses 2 to execute the transmission
function exclusively of a light apparatus 2 that is adjacent in a
predetermined direction, and allows each of light apparatuses 2 to
execute the transmission function simultaneously with a light
apparatus 2 that is adjacent in a direction other than the
predetermined direction. The predetermined direction is any one of
the horizontal, vertical, and oblique directions, and it is
sufficient to arbitrarily specify a direction in which the greatest
number of adjacent light apparatuses 2 is present.
[0034] Such an exclusive control is for reducing misrecognition of
optical signals from adjacent light apparatuses 2, and reducing
deterioration of reading speed, that is, information recognition
speed at the user-side.
[0035] In FIG. 1, each of light apparatuses 2 includes light source
10, drive circuit 30, and controller 40. It should be noted that
light apparatuses 2 in the figure are referred to as panel A1, A2,
. . . , C3 when distinguishing one from the other.
[0036] Light source 10 is a panel-shaped light-emitting body. Light
source 10 includes, for example, a tabular transparent resin board
and plural light-emitting diodes (LEDs). The LEDs introduce light
from the back or side of the transparent resin board so that light
is emitted from the entire front face (outer surface) of the
transparent resin board. A guide for a shop or other type of
advertisement, for example, is depicted on the front face of the
transparent resin board as a signboard. It should be noted that
light source 10 is not limited to a combination of the transparent
resin board and plural LEDs, and may be an organic
electroluminescent (EL) panel as long as it is a light-emitting
body capable of visible light communication.
[0037] Drive circuit 30 supplies power of a value corresponding to
the dimming level of light source 10, according to an instruction
(analog dimming signal) from controller 40, and executes pulse
modulation as a visible light communication transmission function,
according to an instruction (pulse modulation signal) from
controller 40. The pulse modulation may be, for example, the
4-value pulse position modulation (4PPM) defined in the "Visible
Light ID System" (CP-1222) standard of the Japan Electronics and
Information Technology Industries Association (JEITA). In 4PPM, for
example, one symbol time is 0.416 ms and one slot time is 0.104 ms.
Since one symbol is represented by two bits, the hit rate is 4.8
kbps. In order to increase lighting time percentage, the pulse
modulation according to this embodiment may be the I4PPM (inverted
4-value pulse position modulation) obtained by inverting the
4PPM.
[0038] Controller 40 is a microcomputer, and transmits an analog
dimming signal and a pulse modulation signal to drive circuit 30
according to a command from control apparatus 4. An analog dimming
signal is a signal for indicating the dimming level and the
magnitude of the constant current. A pulse modulation signal is a
signal for the above-described I4PPM. Pulse modulation is executed
in an interval instructed in a command from control apparatus 4. An
interval in which pulse modulation is executed is called a
modulation interval, and an interval in which pulse modulation is
not executed is called a pause interval. In the subsequent
description, the modulation interval is also called a first
interval, and the pause interval is also called a second
interval.
[0039] Furthermore, controller 40 causes drive circuit 30 to repeat
the modulation interval and the pause interval, according to a
command from control apparatus 4. At this time, controller 40
controls a peak value, which is the high value of the pulsed
current to be supplied from drive circuit 30 to light source 10, in
order to match the average current value in the modulation interval
with the average current value in the pause interval. Specifically,
controller 40 causes drive circuit 30 to increase the peak value at
the start of the modulation interval, and causes drive circuit 30
to restore the peak value at the start of the pause interval. For
example, controller 40 causes the peak value in the modulation
interval to be a value obtained by dividing the average current
value in the pause interval by the pulse modulation duty cycle.
Here, duty cycle refers to the duty cycle of a pulse modulation
signal, and is equivalent to (ON time/(ON time+OFF time)) of a
switch for switching ON and OFF the current to light source 10. In
the above-described I4PPM, the duty cycle is a constant value of
75%. In this case, the value obtained by dividing the average
current value in the pause interval by the duty cycle is 1.33 times
the average current value in the pause interval.
[0040] According to such control of the peak value of current in
the modulation interval, it is possible to reduce the difference in
average illuminance between the modulation interval and the pause
interval of light apparatuses 2, and prevent the sense of
incongruity. In addition, since controller 40 controls drive
circuit 30 at the starting point of each of the modulation interval
and the pause interval instead of using the feedback method in
which the current value is controlled by detecting the average
current value, it is possible to suppress fluctuations and
flickering caused by response delays.
[0041] It should be noted that when the pulse modulation is other
than I4PPM and the duty cycle is not constant, an average duty
cycle may be estimated in advance and an estimated value that is
assumed to be constant may be used.
[0042] [1.2 Structure of Signboard System]
[0043] Next, a structure of a signboard system according to this
embodiment will be described.
[0044] FIG. 2 is an external view of an example of a signboard
system according to Embodiment 1. As illustrated in FIG. 2, the
signboard system includes signboard apparatus 1 and plural portable
devices 5.
[0045] Although the light-emitting faces of respective light
apparatuses 2 are arranged in a matrix of 3 rows by 3 columns in
the example of FIG. 2, the arrangement is not limited to a matrix.
For example, the arrangement may be in a shape, size, and
positioning matching a floor layout. Furthermore, the sizes of the
respective light-emitting faces need not be the same.
[0046] Each of portable devices 5 is, for example, a smartphone or
tablet terminal device, and has a camera through which visible
light communication is received.
[0047] Furthermore, signboard apparatus 1 in FIG. 2 includes, on
the front face of the layout of light apparatuses 2 (light panel
apparatuses), invitation displays (e.g., 1a to 1e) having an icon
or a guidance message inviting the receiving of visible light
communication. Each of invitation displays 1a to 1e includes, for
example, icons or invitation messages such as "Visible light
communication ongoing; detailed attached information receivable by
smartphone.", "Please activate app and point camera toward desired
restaurant signboard.", "Hold smartphone upright and take a photo
of a restaurant signboard to view suggested menu.", "Hold
smartphone sideways and hold camera up to a restaurant signboard",
"Visible light communication-capable.", and so on. Accordingly, a
user of portable device 5 can obtain, as detailed restaurant
information, for example, a uniform resource locator (URL) of the
restaurant, an image of the restaurant interior, a recommended
menu, prices, available seating, waiting time, a discount coupon,
etc.
[0048] As in the case of invitation displays 1a to 1c, plural
invitation displays may be placed at approximately equal intervals,
between light-emitting faces.
[0049] [1.3 Structure of Light Apparatus]
[0050] Next, the structure of light apparatus 2 as a light panel
apparatus will be described.
[0051] FIG. 3 is a block diagram illustrating a more detailed
example configuration of light apparatus 2 according to Embodiment
1. As illustrated in the figure, light apparatus 2 includes light
source 10 and lighting device 3.
[0052] Light source 10 is, as already described, a panel-shaped
light-emitting body,
[0053] Lighting device 3 includes switch 20, resistor 21, drive
circuit 30, controller 40, and power supply 50.
[0054] Switch 20 switches ON and OFF the current to be supplied to
light source 10 from drive circuit 30. The ON and OFF switching
pulse-modulates the visible light from light source 10. This pulse
modulation is, for example, the above-described I4PPM.
[0055] Resistor 21 is connected in parallel with switch 20, and
connected in series with light source 10. Resistor 21 can pass
current to light source 10 when switch 20 is OFF. In the
aforementioned pulse modulation, light source 10 is switched,
rapidly between the two states of "dark light-emission" and "bright
light-emission", in accordance with the switching ON and OFF of
switch 20. The level of the "dark light-emission" can be determined
according to the resistance of resistor 21. When visible light is
to be 100% modulated when "dark light-emission" is replaced with
"no light-emission"), resistor 21 need not be included, and thus is
illustrated in phantom as optional. It should be noted that an LED
may be included in place of resistor 21.
[0056] Drive circuit 30 includes first receiver 31, current
controller 32, constant current circuit 33, second receiver 34, and
modulator 35.
[0057] First receiver 31 receives the analog dimming signal from
controller 40, and instructs the dimming level to current
controller 32.
[0058] Current controller 32 instructs, to constant current circuit
33, the magnitude of the constant current that constant current
circuit 33 is required to supply to light source 10, according to
the dimming level instructed by first receiver 31.
[0059] Constant current circuit 33 supplies light source 10 with
constant current of the magnitude instructed by current controller
32.
[0060] Second receiver 34 receives the pulse modulation signal for
visible light communication from controller 40, converts the level
of the pulse modulation signal, and outputs the result to modulator
35.
[0061] Modulator 35 outputs to switch 20 a switch driving signal
which causes switch 20 to switch ON and OFF, according to the pulse
modulation signal from second receiver 34.
[0062] Controller 40, as already described, generates and outputs,
to drive circuit 30, an analog dimming signal and a pulse
modulation signal, according to a command from control apparatus
4.
[0063] Power supply 50 is an alternating current-to-direct current
(AC-DC) converter and includes a power factor correction (PFC)
circuit and a harmonic reduction circuit.
[0064] Next, the current supplied to light source 10 in the
modulation interval (first interval) and the pause interval (second
interval) will be described.
[0065] FIG. 4 illustrates time charts for examples of current
waveforms of light source 10 in the modulation interval and the
pause interval according to Embodiment 1. In FIG. 4, (a) is a time
chart for the case where the average current; value in the
modulation interval is matched with the current value in the pause
interval. In FIG. 4, (b) is a time chart for the case where the
average current value in the modulation interval is not matched
with the current value in the pause interval.
[0066] As in (a) and (b) in FIG. 4, pulse modulation for visible
light communication is not executed in the pause interval. In the
pause interval, constant current is supplied from constant current
circuit 33 to light source 10. The magnitude of the constant
current can be changed by controller 40, first receiver 31, and
current controller 32, according to a command instructing the
dimming level from control apparatus 4.
[0067] As in (a) and (b) in FIG. 4, pulse modulation is executed in
the modulation interval. The pulse modulation is executed through
the switching ON and OFF of switch 20 according to the pulse
modulation signal from controller 40.
[0068] In (a) in FIG. 4, the peak current value is increased in
order to match the average current value in the modulation interval
with the current value in the pause interval, This is implemented
by controller 40 outputting an analog dimming signal at the start
of the pulse modulation interval to change the dimming level to a
value obtained by dividing the dimming level in the pause interval
by the duty in the modulation interval. By doing so, the average
brightness in the pause interval and the modulation interval are
made the same even when the cycles of the pause interval and the
modulation interval are long or when the modulation is deep (100%
modulation, etc.), and thus visual flickering can be
suppressed.
[0069] On the other hand, in (b) in FIG. 4, the peak current value
in the modulation interval is the same as the average current value
in the pause interval. As such, there are instances where the
difference in brightness between the pause interval and the
modulation interval is conspicuous in the form of visual
flickering. In order to reduce flickering, it is sufficient to
raise the frequency of the repetition of the pause interval and the
modulation interval. For example, when the frequency is greater
than or equal to 60 Hz, visual flickering can be suppressed. It
should be noted that the frequency may be deliberately lowered (for
example, less than or equal to 30 Hz). Accordingly, by causing
visual flickering to occur, the panel that is executing visible
light communication within signboard apparatus 1 can be
specified.
[0070] [2.1 Operation of Light Apparatus]
[0071] The operation of signboard apparatus 1 configured in the
manner described above will be described.
[0072] FIG. 5 is a flowchart illustrating an example process of
controller 40 according to Embodiment 1.
[0073] First, light apparatus 2 pauses visible light communication
in an initial state immediately after power supply is introduced
(S0). Specifically, modulator 35 stops modulation at the initial
state. In this state, when controller 40 receives a command
instructing the execution of visible light communication from
control apparatus 4 (YES in S1), controller 40 starts or resumes
visible light communication, that is, transitions from the pause
interval to the modulation interval (S2). In addition, when time
T1, which is the length of the modulation interval, elapses (YES in
S3), controller 40 stops the visible light communication, that is,
transitions from the modulation interval to the pause interval
(S4). With this, light apparatus 2 executes visible light
communication only in the period of time T1 from when the command
is received, as the modulation interval, and does not execute
visible light communication in a period other than the modulation
interval, as the pause interval.
[0074] Next, the transition from the pause interval to the
modulation interval in step S2 will be described in detail. In step
S2, controller 40 determines a target current value corresponding
to the present dimming level, or in other words, determines the
current value presently being supplied from drive circuit 30 to
light source 10 in the pause interval. Controller 40 divides the
determined target current value by the duty cycle of the pulse
modulation (S22). In the case of I4PPM, the quotient value becomes
1.33 times the target current value. In addition, controller 40
reflects the quotient value in the analog dimming signal, and
outputs this signal to drive circuit 30 (S23). With this, the
current to be supplied from drive circuit 30 to light source 10
becomes a value obtained by dividing the average current value in
the pause interval by the duty cycle of the pulse modulation signal
in the modulation interval. In the case of I4PPM, the current to be
supplied becomes 1.33 times the average current value in the pause
interval. In addition, controller 40 starts or resumes the pulse
modulation for the visible light communication (S24).
[0075] Next, the transition from the modulation interval to the
pause interval in step S4 will be described in detail. In step S4,
controller 40 stops the pulse modulation for the visible light
communication (S41). In addition, controller 40 determines a target
current value corresponding to the dimming level in the immediately
preceding pause interval. This determining may use a value which is
the stored target current value in step S21 or may use a value
obtained by multiplying the present (i.e., in the modulation
interval) target current value by the aforementioned duty cycle. In
addition, controller 40 reflects the target current value
determined in step S42 in the analog dimming signal, and outputs
this signal. to drive circuit 30 (S43). With this, the value of the
current to be supplied from drive circuit 30 to light source 10
returns to a value that is the same as that in the immediately
preceding pause interval.
[0076] In this manner, controller 40 controls the peak, which is
the high value of the pulsed current to be supplied from drive
circuit 30 to light source 10, in order to match the average
current value in the modulation interval with the average current
value in the pause interval. By doing so, it is possible to reduce
the difference in average illuminance between the first interval
and the second interval in light apparatus 2, and prevent the sense
of incongruity. In addition, since controller 40 controls drive
circuit 30 at the starting point of each of the modulation interval
and the pause interval instead of using the feedback method in
which the current value is controlled by detecting the average
current value, is possible to suppress fluctuations and flickering
caused by response delays.
[0077] It should be rioted that although the modulation factor of
the pulse modulation is 100%, that is, the light-ON state and the
light-OFF state are used in I4PPM, the modulation factor may be
other than 100%. Furthermore, instead of I4PPM, InPPM (where n is
an integer greater than or equal to 2) may be used, or a different
pulse modulation may be used.
[0078] Furthermore, light apparatus 2 is not limited to the
internally illuminated type, and may be of the externally
illuminated type.
EMBODIMENT 2
[0079] A signboard apparatus and a signboard system according to
Embodiment 2 are described below. The structure of signboard
apparatus 1 according to this embodiment is the same as according
to Embodiment 1. In this embodiment, the times of the modulation
interval (first interval) and the pause interval (second interval)
are particularly defined.
[0080] FIG. 6 is a time chart illustrating example waveforms of
current flowing in a light source according to Embodiment 2. The
figure illustrates waveforms of a load current, a pulse modulation
signal, and an analog dimming signal are illustrated in the
figure.
[0081] The load current is the current flowing in the load, that
is, light source 10. As described according to Embodiment 1, the
peak current value in the modulation interval is set so that the
average current value in the modulation interval matches the
average current value in the pause interval.
[0082] A pulse modulation signal and an analog dimming signal are
outputted from controller 40 to drive circuit 30.
[0083] In the figure, the modulation interval is set to be T1
seconds and the pause interval is set to be T2 seconds. In this
embodiment, 1/(T1+T2) is greater than or equal to 60 Hz. By doing
so, visual flickering caused by the difference in brightness
between the modulation interval and the pause interval can be
reduced and made inconspicuous.
EMBODIMENT 3
[0084] A signboard apparatus and a signboard system according to
Embodiment 3 are described below. The structure of signboard
apparatus 1 according to this embodiment is substantially the same
as according to Embodiment 1 but different in that the width of the
inverted pulse in I4PPM is smaller than the slot width.
Hereinafter, description will be carried out focusing on the points
of difference.
[0085] FIG. 7 illustrates time charts for an example pulse
modulation according to Embodiment 3. Here, (a) in FIG. 7
corresponds to Embodiment 1, and (b) in FIG. 7 corresponds to
Embodiment 3.
[0086] In (a) in FIG. 7, the pulse modulation signal is an inverted
4-pulse position modulation (I4PPM) signal, and one symbol period
is divided into four slot periods. One slot period w is 1/4 of one
symbol period. The width of the inverted pulse is equal to one slot
period w.
[0087] In contrast, in (b) in FIG. 7, the pulse modulation signal
is also an I4PPM signal, but inverted, pulse width v is smaller
than one slot period w. Specifically, the inverted pulse width v is
approximately 1/2 to 1/3 of one slot period w. For example, when
one slot period w is 0.104 ms, it is sufficient that the inverted
pulse width v be 0.05 ms. Controller 40 makes inverted pulse width
v smaller than one slot period w by adjusting the position of at
least one of the front edge (falling edge) and the back edge
(rising edge) of an inverted pulse in the pulse modulation
signal.
[0088] By doing so, difference D2 between the peak current value
and the average current value in (b) in FIG. 7 becomes smaller than
difference D1 between the peak current value and the average
current value in (a) in FIG. 7. Stated differently, the duty cycle
of the pulse modulation signal in (b) in FIG. 7 is bigger, and thus
the peak current value can be made smaller. Specifically, in the
transition from the pause interval to the modulation interval, the
fluctuation in the current supplied from drive circuit 30 to light
source 10 can be made smaller (i.e, difference D2<difference
D1), and the flickering caused by the current fluctuation and the
sense of incongruity caused by the difference in brightness with
the surroundings can be reduced. The flickering described here
includes flickering caused by overshoot occurring mainly in the
pulse waveform at the time of transitioning from the pause interval
to the modulation interval.
EMBODIMENT 4
[0089] Next, a signboard apparatus and a signboard system according
to Embodiment 4 are described below. The structure of signboard
apparatus 1 according to this embodiment is substantially the same
as according to Embodiment 1. but is different in that control to
make the peak current value bigger in the modulation interval
(first interval) is not performed, and in that switch 20 is
controlled to switch ON and OFF at a frequency different from the
frequency of the pulse modulation in the modulation interval and
with a duty cycle identical to the duty cycle of the pulse
modulation, in the pause interval (second interval). Hereinafter,
description is carried out focusing on the points of
difference.
[0090] FIG. 8 is a time chart illustrating an example waveform of
current flowing in a light source in each of a modulation interval
and a pause interval according to Embodiment 4.
[0091] First, since control for making the peak current value
larger in the modulation interval is not performed, the analog
dimming signal to be outputted from controller 40 to drive circuit
30 is the same signal for the modulation interval and the pause
interval. As a result, as illustrated in FIG. 8, the peak current
values in the modulation interval and the pause interval have the
same magnitude.
[0092] Furthermore, since controller 40 controls the switching ON
and OFF of switch 20 even in the pause interval, the load current
becomes a pulse train even in the pause interval. This pulse train
is controlled so as to have a frequency different from the
frequency of the pulse modulation in the modulation interval and
have a duty cycle identical to the duty cycle of the pulse
modulation. As a result, the average current values of the
modulation interval and the pause interval, have the same
magnitude.
[0093] Accordingly, it is possible to reduce the difference in
average illuminance between the modulation interval and the pause
interval and suppress the visual sense of incongruity, without
controlling the peak current value in the modulation interval.
[0094] Furthermore, in the pause interval, controller 40 causes
switch 20 to switch ON and OFF to cause the generation of a pulse
train that is to be judged as invalid in visible light
communication. By doing so, it becomes possible to avoid
erroneously receiving, as visible light communication data, the
pulse train in the pause interval.
EMBODIMENT 5
[0095] Next, a signboard. apparatus and a signboard system
according to Embodiment 5 are described below.
[0096] FIG. 9 is a block diagram illustrating an example
configuration of signboard apparatus 2 according to Embodiment 5.
Compared to FIG. 3, signboard apparatus 1 in the figure is
different in that current detector 33a and suppresser 36 are added.
Hereinafter, description is carried out focusing on the points of
difference.
[0097] Current detector 33a and suppresser 36 are provided in order
to suppress an overshoot which tends to occur with the load current
at the time of transitioning from the pause interval to the
modulation interval.
[0098] FIG. 10 is a time chart illustrating example current
waveforms in each of a modulation interval and a pause interval in
a comparative example. The figure illustrates waveforms of a load
current, a pulse modulation signal, and an analog dimming signal.
An overshoot, though dependent on the circuit structure, can more
or less occur at the rising edge of each of the signals. In
particular, since the fluctuation is big at the rising edge at the
time of transitioning from the pause interval to the modulation
interval, a big overshoot tends to occur. In FIG. 10, the overshoot
at the rising edge at the time of transitioning from the pause
interval to the modulation interval is illustrated schematically
with emphasis.
[0099] Current detector 33a detects the current value of current
supplied o light source 10.
[0100] Suppresser 36 performs sampling and holding of the current
value detected at the time of switching from the pause interval to
the modulation interval, and suppresses the overshoot in the pulsed
current supplied to light source 10 based on the difference between
the held value and a value indicated in a command value signal.
Here, the command value signal is a signal which corresponds to the
above-described analog dimming signal and indicates the magnitude
of the current that drive circuit 30 is required to supply to light
source 10.
[0101] Next, a detailed example configuration of suppresser 36 will
be described.
[0102] FIG. 11 is a block diagram illustrating an example
configuration of suppresser 36 according to Embodiment 5. As
illustrated in the figure, suppresser 36 includes amplifier circuit
361, sample-and-hold circuit 362, and error amplifier circuit 363.
In FIG. 11 and FIG. 9, a, b, and c are assigned to a detected
current value, a switch driving signal, a command value signal, and
a post-suppression command value signal, respectively.
[0103] Amplifier circuit 361 amplifies the detected current value
detected by current detector 33a.
[0104] Sample-and-hold circuit 362 samples the amplified detected
current value from amplifier circuit 361, at the rise of the switch
driving signal (i.e., at the timing when switch 20 switches from ON
to OFF), and holds the sampled value.
[0105] Error amplifier circuit 363 amplifies the error between the
command value signal from controller 40 and the value held by
sample-and-hold circuit 362, and outputs the amplified error as a
post-suppression command value to constant current circuit 33.
[0106] Accordingly, the detected current value is sampled the
timing when switch 20 switches from ON to OFF and this detected
current value is held, and thus, at the timing when switch 20
switches from OFF to ON, instead of feeding back the drastically
changing detected current value itself (i.e., the detected current
value having the overshoot), the held value is fed back to error
amplifier circuit 363. As a result, it is possible to suppress the
overshoot occurring at the timing when switch 20 switches from OFF
to ON.
[0107] FIG. 12 is a time chart illustrating operation of suppresser
36 according to Embodiment 5. The figure illustrates switch driving
signal a, detected current value b, output value A (i.e., the held
value) of sample-and-hold circuit 362, and a pulse modulation
signal in modulation interval T1 and pause interval T2. An
overshoot tends to occur at the rise of detected current value a,
but because output value A of sample-and-hold circuit 362 is the
value obtained in the sampling and holding at the fall, as
indicated by the broken line frames, the drastic change of detected
current value a is suppressed. The drastic change of the command
value outputted from error amplifier circuit 363 is also
suppressed, and the drastic change of the load current flowing in
light source 10 is suppressed.
[0108] As described above, signboard apparatus 1 according to this
embodiment is capable of suppressing an overshoot of the load
current flowing in light, source 10 from the pause interval to the
modulation interval, and suppressing the visual flickering caused
by the overshoot.
Modifications
[0109] It should be noted that, in each of the foregoing
embodiments, control apparatus 4 may perform exclusive control to
cause each of light apparatuses 2 to execute the transmission
function exclusively of an adjacent light apparatus 2.
[0110] FIG. 13 is a time chart rating the exclusive control
performed on light apparatuses 2. The arrangement of light
apparatuses 2 in FIG. 1 and FIG. 2 (denoted here as panels A1 to
A3, B1 to B3, and C1 to C3) is illustrated on the left side of FIG.
13. Time charts depicting the modulation intervals (the "ID
transmission" intervals in the figure) for each panel are
illustrated on the right side of FIG. 13.
[0111] Controller 4 classifies panels into groups and stores the
classification. In the figure, group G1 is composed of panels A1,
B3, and C2. Group G2 is composed of panels A2, B1, and C3. Group G3
is composed of panels A3, B2, and C1. Specifically, the grouping
into groups G1 to G3 is carried out so that each of the panels
executes the transmission function exclusively of a vertically or
horizontally adjacent panel.
[0112] At time t1, control apparatus 4 transmits a command
instructing the start of modulation, to panels A1, B3, and C2
belonging to group G1. Accordingly, panels A1, B3, and C2
transition from the pause interval to the modulation interval, in
this modulation interval, the other panels that are vertically or
horizontally adjacent to each of panels A1, B3, and C2 are in the
pause interval. Subsequently, each of panels A1, B3, and C2
transition from the modulation interval to the pause interval after
a fixed time elapses. The fixed time is a time less than or equal
to t2-t1.
[0113] In addition, at time t2, control apparatus 4 transmits a
command instructing the start of modulation, to panels A2, B1, and
C3 belonging to group G2. Accordingly, panels A2, B1, and C3
transition from the pause interval to the modulation interval. In
this modulation interval, the other panels that are vertically or
horizontally adjacent to each of panels A2, B1, and C3 are in the
pause interval. Subsequently, each of panels A2, B1, and C3
transition from the modulation interval to the pause interval after
the fixed time elapses.
[0114] In addition, at time t3, control apparatus 4 transmits a
command instructing the start of modulation, to panels A3, B2, and
C1 belonging to group G3. Accordingly, panels A3, B2, and C1
transition from the pause interval to the modulation interval. In
this modulation interval, the other panels that are vertically or
horizontally adjacent to each of panels A3, B2, and C1 are in the
pause interval. Subsequently, each of panels A3, B2, and C1
transition from the modulation interval to the pause interval after
the fixed time elapses.
[0115] From time t4 onward, control apparatus 4 repeats the command
transmission in times t1 to t3 in the same manner.
[0116] In this manner, control apparatus 4 can easily implement
exclusive control by merely storing groups corresponding to the
exclusive control, and transmitting a command instructing the start
of a modulation interval, to each of the groups. Accordingly,
during the receiving of visible light communication, it is possible
to reduce misrecognition, and reduce deterioration of the reading
speed, that is, information recognition speed. at the portable
device-side.
[0117] It should be noted that the transition from the modulation
interval to the pause interval may be triggered by a command from
control apparatus 4 instead of the elapse of a fixed time.
Furthermore, the length of the modulation interval for the
respective groups need not be the same, and may be different for
each of the groups.
[0118] It should be noted that light apparatus 2 in FIG. 3 may
include a constant voltage circuit in place of constant current
circuit 33. An example configuration of light apparatus 2 in this
case will be described.
[0119] FIG. 14 is a block diagram illustrating another example
configuration of light apparatus 2. Compared to FIG. 3, light
apparatus 2 in FIG. 14 is different in terms of including voltage
controller 32a, constant voltage circuit 33b, and light source 10a,
in place of current controller 32, constant current circuit 33, and
light source 10. Hereinafter, description is carried out focusing
on the points of difference.
[0120] Voltage controller 32a instructs, to constant voltage
circuit 33b, the magnitude of the constant voltage that constant
voltage circuit 33b should supply to light source 10a, according to
the dimming level instructed by first receiver 31.
[0121] Constant voltage circuit 33b supplies the constant voltage
to light source 10a. However, this constant voltage is controlled
to be a voltage of the magnitude instructed by voltage controller
32a.
[0122] Light source 10a includes plural light-emitting circuits 10b
which are connected in parallel. Each of light-emitting circuits
10b includes plural LEDs and a resistance element. The LEDs and the
resistance element are connected in series. The resistance element
is provided for controlling the current flowing in. light-emitting
circuit 10b.
[0123] Drive circuit 30, whether in a configuration including
constant current circuit 33 as in FIG. 3 or a configuration
including constant voltage circuit 33b as in FIG. 14, supplies
power of a magnitude that is in accordance with the dimming level
to light source 10 or light source 10a, respectively.
[0124] It should be noted that light apparatus 2 in FIG. 14 may
include current detector 33a and suppresser 36 in FIG. 9. In this
case, it is sufficient that the output signal of voltage controller
32a, that is, the signal instructing the magnitude of the constant
voltage be converted to a signal instructing the magnitude of the
constant current.
[0125] As described above, lighting device 3 according to one or
more of the exemplary embodiments includes: drive circuit 30 that
supplies power to a light source (10 or 10a); switch 20 connected
in series with the light source (10 or 10a); and controller 40 that
controls pulse modulation for visible light communication executed
through switching ON and OFF of switch 20 in a first interval, and
stops the pulse modulation in a second interval, wherein controller
40 controls a peak value, which is a high value of a pulsed current
supplied from drive circuit 30 to the light source (10 or 10a), to
match an average current value in the first interval with an
average current value in the second interval.
[0126] Accordingly, it is possible to reduce the difference in
average illuminance between the first interval and the second
interval in light apparatus 2, and prevent the sense of
incongruity.
[0127] Here, controller 40 may cause drive circuit 30 and switch 20
to cyclically repeat of the first interval and the second
interval.
[0128] Accordingly, it is possible to reduce visual flickering
occurring due to the difference in average illuminance between the
first interval and the second interval in light apparatus 2, and
prevent the sense of incongruity.
[0129] Here, controller 40 may cause drive circuit 30 to increase
the peak value at a start of the first interval and restore the
peak value at a start of the second interval.
[0130] Accordingly, since controller 40 controls drive circuit 30
at the starting point of each of the first interval and the second
interval instead of using the feedback method in which the current
value is controlled by detecting the average current; value, it is
possible to suppress fluctuations and flickering caused by response
delays.
[0131] Here, controller 40 may cause the peak value in the first
interval to be a value obtained by dividing the average current
value in the second interval by a duty cycle of a pulse modulation
signal for the first interval.
[0132] Accordingly, since the duty cycle of the pulse modulation
signal can be handled as a constant value, current can be
controlled with high. precision at the starting point of each of
the first interval and the second interval.
[0133] Here, in the second interval, controller 40 may cause switch
20 to switch ON and OFF at a frequency different from a frequency
of the pulse modulation in the first interval and with a duty cycle
identical to a duty cycle of the pulse modulation.
[0134] Accordingly, it is possible to reduce the difference between
in average illuminance between the first interval and the second
interval and prevent the sense of incongruity, without having to
control the peak current value in the first interval.
[0135] Here, in the second interval, controller 40 may cause switch
20 to switch ON and OFF to generate a pulse train that is invalid
in the visible light communication.
[0136] Accordingly, it becomes possible to avoid erroneously
receiving, as visible light communication data, the pulse train in
the second interval.
[0137] Here, controller 40 may cause the first interval and the
second interval to be cyclically generated, and where the first
interval is T1 seconds and the second interval is T2 seconds,
1/(T1+T2) may be greater than or equal to 60 Hz.
[0138] Accordingly, it is possible to reduce visual flickering
caused by the difference in brightness between the first interval
and the second interval.
[0139] Here, the pulse modulation may be an inverted pulse position
modulation in which a value of one symbol is represented by a
position of an inverted pulse in slots, and the inverted pulse may
have a width smaller than a slot width.
[0140] Accordingly, since the duty cycle of the pulse modulation
signal is made bigger, the illuminance in the first interval can be
raised.
[0141] Here, controller 40 outputs, to drive circuit 30, a command
value signal indicating a magnitude of current that drive circuit
30 is required to supply to light source 10, and drive circuit 30
includes: current detector 33 that detects a current value of the
current supplied to light source 10; and suppresser 36 that
performs sampling and holding of the current value detected at a
time of transitioning from the second interval to the first
interval, and suppresses an overshoot in the pulsed current to be
supplied to light source 10, based on a difference between the
current value held in the sampling and holding and a value
indicated by the command value signal.
[0142] Accordingly, it is possible to suppress visual flickering
caused by an overshoot.
[0143] Furthermore, light apparatus 2 according to one or more of
the exemplary embodiments includes lighting device 2 and light
source 10 (10a)
[0144] Furthermore, signboard apparatus 1 according to one or more
of the exemplary embodiments includes: light apparatuses 2; and
control apparatus 4 that instructs visible light communication to
each of light apparatuses 2, wherein light apparatuses 2 are
arranged as a collective signboard.
[0145] Although the signboard apparatus according to the present
disclosure has been described based on exemplary embodiments, the
present disclosure is not limited, to these embodiments. Forms
obtained by various modifications to the exemplary embodiments that
can be conceived by a person of skill in the art as well as other
forms realized by combining part of the structural components in
the exemplary embodiments and modifications, which are within the
scope of the essence of the present disclosure are included in the
present disclosure.
[0146] While the foregoing has described what are considered to be
the best mode and/or other examples, it is understood that various
modifications may be made therein and that the subject matter
disclosed herein may be implemented in various forms and examples,
and that they may be applied in numerous applications, only some of
which have been described herein. It is intended by the following
claims to claim any and all modifications and variations that fall
within the true scope of the present teachings.
* * * * *