Illumination control device

Abstract

To provide an illumination control device capable of suppressing a bounce feeling that makes an image seem darker than normal for an instant when the brightness is gradually changed such as in a fade-out.SOLUTION: When ECU 3 fades out an LED lighting module 4 to a target duty ratio (brightness), the ECU 3 starts fading with a duty ratio change amount from the fade start to the slow stop start duty ratio, and then changes the duty ratio change amount to the slow stop period to fade out to the target duty ratio (brightness). The slow stop period is shorter than the period based on the change amount before the slow stop.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a lighting control device for LED lighting or the like provided in a vehicle. [Background technology]

[0002] For example, LED (light emitting diode) lighting is sometimes used as interior lighting or illumination in the cabin of a vehicle.

[0003] This type of LED lighting is known to be controlled by a PWM (Pulse Width Modulation) signal, and the brightness can be increased or decreased by fading in or out by changing the duty ratio of the PWM signal (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-32470 A Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have confirmed a phenomenon in which, when fading out (gradually dimming the brightness to the target brightness) in illumination using the above-mentioned LED lighting, when switching to steady state at the target brightness, the change in brightness feels momentarily unstable (feeling like flickering). This phenomenon is felt as if the brightness is momentarily darker than steady state when switching to steady state, and since it feels like it is returning (bouncing) after becoming darker than steady state, hereafter this phenomenon will be referred to as bouncing sensation.

[0006] When this bouncing sensation occurred, the inventors measured the change in LED illuminance using an illuminance sensor and observed the waveform of the PWM signal, but both were normal. Therefore, at present, this bouncing sensation is believed to be a human sensory phenomenon such as an optical illusion.

[0007] However, when this occurs, the smoothness of the fade-out is lost, giving the impression that the lighting quality has deteriorated.

[0008] In view of the above problems, the present invention has an objective of providing a lighting control device that can suppress the sense of bouncing that makes the light feel darker than steady when the brightness is gradually changed, such as in a fade-out. [Means for solving the problem]

[0009] The invention made to solve the above problems is a lighting control device that includes a control unit that controls the brightness of LED lighting installed in a vehicle, and when gradually changing the brightness of the LED lighting to a target brightness, the control unit starts the change with a first amount of change, and then changes to a second amount of change that is smaller than the first amount of change, to change the brightness to the target brightness, and a period during which the brightness changes by the second amount of change is shorter than the period during which the brightness changes by the first amount of change. Effect of the Invention

[0010] According to the present invention, when the brightness approaches the target brightness, the amount of change is reduced, thereby making it possible to suppress the sense of bouncing. [Brief description of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a system including a lighting control device according to an embodiment of the present invention. [Diagram 2] 13 is a graph summarizing the experimental results regarding the feeling of bouncing. [Diagram 3] 2 is a flowchart of an example of a fade-out operation of the ECU shown in FIG. 1. [Figure 4] 13 is a graph showing changes in the duty ratio over time when the slow stop is disabled and enabled. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a diagram showing the configuration of a system including a lighting control device according to an embodiment of the present invention.

[0013] 1, the system 1 includes an ECU 2, an ECU 3, and an LED lighting module 4. The system 1 is mounted on, for example, a vehicle. The ECU 2 and the ECU 3, and the ECU 3 and the LED lighting module 4 are connected to each other by signal lines such as wire harnesses.

[0014] The ECU 2 is a well-known electronic control unit and includes a CPU (Central Processing Unit), a communication circuit, an output circuit, etc. The ECU 2 outputs a turn-on instruction signal, etc. to the ECU 3 as a master.

[0015] The ECU3 is an electronic control unit similar to the ECU2, and includes a CPU, a communication circuit, an output circuit, etc. The ECU2 receives a lighting instruction signal, etc. from the master ECU2, and outputs a PWM signal, etc. to the LED lighting module 4 based on the lighting instruction signal. The ECU3 performs lighting control, such as turning the LED lighting module 4 ON / OFF and its brightness. In other words, the ECU3 functions as a control unit that controls the brightness of the LED lighting provided in the vehicle.

[0016] The LED lighting module 4 is installed, for example, as illumination in a vehicle interior. The LED lighting module 4 includes an LED, which is a light-emitting element, and a drive circuit that adjusts brightness by changing the current supplied to the LED using a PWM signal or the like from the ECU 3.

[0017] Here, a lighting control method executed by the system 1 having the above-mentioned configuration will be described. First, the above-mentioned bouncing sensation will be described with reference to FIG. 2. FIG. 2 is a graph summarizing the results of an experiment on the presence or absence of a bouncing sensation due to differences in the target duty ratio of the PWM signal when the rate of change (slope) of the fade-out is constant. Note that the fade-out in this embodiment does not include a target duty ratio of 0%. The bouncing sensation is a phenomenon in which the brightness feels darker than normal for an instant when switching to normal at the target brightness as described above, because the brightness cannot become any darker when it is 0% (off).

[0018] In the experiment, the results of which are summarized in Figure 2, a similar configuration to that of Figure 1 was constructed indoors, and data from three subjects was collected as samples. The experiment consisted of changing the fade time for each arbitrary target duty ratio, and having the subjects visually confirm at what gradient the sense of bouncing was visible. The fade time was changed in 0.3 second increments from 0.3 to 2.1 seconds. In cases where opinions differed on the same gradient, the less favorable data was used. For example, if even one of the three subjects felt a sense of bouncing, it was determined that there was a sense of bouncing.

[0019] In the graph of FIG. 2, the vertical axis shows the slope (amount of change) when the LED lighting module 4 is faded out, and the horizontal axis shows the target duty ratio at the time of fade-out. The circles in the graph indicate that no sense of bounding was felt, and the crosses indicate that a sense of bounding was felt. The dashed line is a curve obtained by regression analysis of the crosses, and the dashed line is a curve obtained by regression analysis of the circles. R 2 is the coefficient of determination. The dashed lines show the relationship between the slope and the target duty ratio when the fade time is set to 0.3 seconds, 0.6 seconds, 0.9 seconds, 1.2 seconds, 1.5 seconds, 1.8 seconds, and 2.1 seconds.

[0020] Here, the area surrounded by the 0.3 second fade time line, the two-dot chain line, and the horizontal axis is the area where no bouncing feeling is felt (OK), and the area surrounded by the 0.3 second fade time line, the one-dot chain line, and the vertical axis is the area where a bouncing feeling is felt (NG).

[0021] In other words, if the slope is in the NG region just before fading out and reaching a steady state (a state where the brightness is constant) at the target duty ratio, the sense of bounding is easily felt. On the other hand, if the slope is in the OK region just before reaching the steady state, the sense of bounding is less felt. In other words, it became clear that the sense of bounding can be made less noticeable depending on the target duty ratio and fade time, and that a smaller slope tends to make the sense of bounding less noticeable.

[0022] Therefore, in this embodiment, the slope (the rate of change of the fade-out) is changed to be smaller just before the target duty ratio. A specific operation example will be described with reference to the flowchart of Fig. 3. The value indicating just before, that is, when to change the slope, can be set in advance by the number of pulses of the PWM signal. Fig. 3 is a flowchart of the fade-out (gradual change of brightness) operation executed by the ECU 3.

[0023] First, when fade-out starts, the ECU 3 obtains the current duty ratio, the target duty ratio (target brightness), and the fade time (change time) as a turn-on instruction signal from the ECU 2 (step S1).

[0024] Next, the ECU 3 determines whether an operation for decreasing the slope immediately before the target duty ratio (hereinafter, referred to as slow stop as necessary) is enabled or disabled (step S2). This enable or disable is set in the ECU 3 in advance, and the determination is made by referring to the setting information.

[0025] If the slow stop is disabled as a result of the determination in step S2, the ECU 3 performs linear fading by interpolating from the current duty ratio acquired in step S1 to the target duty ratio (step S3). At this time, the ECU 3 performs the interpolation so that the target duty ratio is reached in the fade time acquired in step S1.

[0026] On the other hand, if the result of the determination in step S2 is that the slow stop is enabled, the ECU 3 determines whether the duty change amount automatic switching function is enabled or disabled (step S4). In this step S4, it is determined whether to execute step S5 described later. Step S5 dynamically switches the duty change amount according to the target duty ratio. For example, when multiple lights are faded simultaneously, if the duty change amounts are different, a lack of uniformity may be felt. Therefore, the execution of step S5 is set to be enabled or disabled in advance, and a determination is made based on the setting. Note that the setting of the duty change amount automatic switching function to be enabled or disabled may be arbitrarily changed.

[0027] If the result of the determination in step S4 is that the duty change amount automatic switching function is disabled, the process proceeds to step S6 described below without executing step S5. In other words, a slow stop is always performed. On the other hand, if the result of the determination in step S4 is that the duty change amount automatic switching function is enabled, it is determined whether the target duty ratio is less than 40% (step S5).

[0028] This target duty ratio is obtained in step S1. If the target duty ratio exceeds 40%, the ECU 3 proceeds to step S3. That is, the ECU 3 interpolates from the current duty ratio obtained in step S1 to the target duty ratio and fades it linearly (fades it at a constant rate).

[0029] On the other hand, if the target duty ratio is 40% or less, the ECU 3 acquires the gradient of the duty ratio change during the slow stop and the number of pulses (step S6). As described above, the gradient is the fade-out change rate, that is, the amount of duty change, and the number of pulses is the number of pulses of the PWM signal. The gradient and the number of pulses are preset in the ECU 3, but may be changeable to allow tuning of the bounce feeling.

[0030] In this embodiment, the threshold value (target duty ratio) determined in step S5 is 40%, because the result shown in Fig. 2 indicates that the bounce feeling is difficult to feel when the duty ratio exceeds 40%. However, the target duty ratio determined in step S5 is not limited to 40% and may be changed as appropriate.

[0031] In the above-mentioned steps S5 and S6, when the target duty ratio (brightness) is greater than a predetermined threshold, the ECU 3 (control unit) changes the duty ratio (brightness) to the target duty ratio (brightness) by a constant amount of change. The control using this threshold can be switched between execution and non-execution.

[0032] Next, the ECU 3 calculates each parameter of the fade (step S7). The parameters calculated in step S7 include the slow stop period, the start duty ratio of the slow stop, the change amount (% / cycle) of the duty ratio during the slow stop period, the number of pulses from the start of the fade to the start duty ratio of the slow stop, and the change amount (% / cycle) of the duty ratio from the start of the fade to the start duty ratio of the slow stop.

[0033] Here is an example of how to calculate the above parameters. First, let us assume that the current duty ratio obtained by the lighting instruction signal is 90%, the target duty ratio is 40%, and the fade time is 900 ms. Let us also assume that one period of the PWM signal is 10 ms, the slope of the duty ratio change during slow stop is 10% / s, and the number of pulses during the slow stop period is 3.

[0034] Under the above conditions, the slow stop period is calculated as the number of pulses x one cycle time, which is 3 x 10 ms = 30 ms. The slow stop start duty ratio is calculated as the slope of the duty ratio change x the slow stop period + the target duty ratio, which is 10% / s x 30 ms + 40% = 40.3%.

[0035] The change in duty ratio during the slow stop period is calculated as (slow stop start duty ratio - target duty ratio) ÷ number of pulses, so (40.3% - 40%) ÷ 3 = 0.1%. In other words, when the duty ratio becomes 40.3%, the duty ratio is decreased by 0.1%.

[0036] The number of pulses from the start of fade to the starting duty ratio of slow stop is calculated as (fade time - slow stop period) ÷ 1 cycle, so it is (900ms - 30ms) ÷ 10ms = 87. The change in duty ratio from the start of fade to the starting duty ratio of slow stop is calculated as (current duty ratio - starting duty ratio of slow stop) ÷ the number of pulses from the start of fade to the starting duty ratio of slow stop, so it is (90% - 40.3%) ÷ 87 = 0.571% / cycle. In other words, the duty ratio decreases by 0.571% as the duty ratio goes from 90% to 40.3%.

[0037] In this calculation example, the duty ratio is decreased by 0.571% as a first change amount from 90% to 40.3%, and then the duty ratio is decreased by 0.1% as a second change amount from 40.3% to 40. As is clear from this calculation example, the period of fading with the second change amount is shorter than the period of fading with the first change amount.

[0038] Returning to the explanation of Fig. 3, when the calculation of each of the above parameters is completed, the ECU 3 executes fade-out by slow stop (step S8). That is, the ECU 3 fades out linearly by changing the duty ratio from the current duty ratio to the start duty ratio of the slow stop by the amount of change in the duty ratio from the start of fade to the start duty ratio of the slow stop every cycle. Then, when the start duty ratio of the slow stop is reached, the ECU 3 fades out linearly by changing the duty ratio of the slow stop period every cycle.

[0039] When the target duty ratio is reached, fade-out is completed and the flow chart ends.

[0040] By executing the above-mentioned flowchart, it is possible to perform the operation as shown in Fig. 4. Fig. 4 is a graph showing the change in duty ratio with respect to time (t) when the slow stop is disabled and enabled.

[0041] The dashed and dotted line in FIG. 4 shows the case where the slow stop is disabled. In this case, the fade-out is linear to the target duty ratio, as in the conventional fade-out. On the other hand, the solid line shows the case where the slow stop is enabled. In this case, the fade-out is linear to the slow stop start duty ratio, and the slope is reduced from the slow stop start duty ratio to the target duty ratio and fade-out is linear. Here, regardless of whether the slow stop is enabled or disabled, the above-mentioned parameters are calculated so that the target duty ratio is reached within the fade time specified by the master ECU2.

[0042] Also, according to Fig. 4, it is clear that the slope of the slow stop period is smaller than the slope when the slow stop is disabled. And the slow stop period is shorter than the period before it. This is because the fade time before switching to the slow stop is lengthened to approach the slope when the slow stop is disabled.

[0043] According to this embodiment, when fading out the LED lighting module 4 to a target duty ratio (brightness), the ECU 3 starts fading with a duty ratio change amount from the fade start to the slow stop start duty ratio, and then changes the duty ratio change amount to the slow stop period to fade out to the target duty ratio (brightness). The slow stop period is shorter than the period based on the change amount before the slow stop.

[0044] By operating as described above, the ECU 3 reduces the amount of change in the duty ratio when the target duty ratio (brightness) is approached, thereby suppressing the feeling of bouncing. This is because, as shown in Figure 2, the smaller the gradient (amount of change), the less the feeling of bouncing is felt until the duty ratio becomes smaller, so by reducing the gradient near the target duty ratio, the feeling of bouncing is reduced.

[0045] Furthermore, when the target duty ratio is, for example, 40% or more, the ECU 3 changes the duty ratio to the target duty ratio by a fixed amount of change. By doing so, when the target duty ratio is a value that causes almost no sense of bounding, a smooth fade-out can be achieved by performing a linear fade-out as in the conventional method.

[0046] In addition, the ECU 3 can switch between enabling and disabling the fade curve automatic switching function. In this way, when multiple lights are to be faded simultaneously, the function can be disabled to provide a sense of unity in the changes in the lights.

[0047] Furthermore, the ECU 3 outputs a PWM signal to the LED lighting module 4, and changes the duty ratio of the PWM signal to change the brightness of the LED lighting module 4. In this way, by changing the duty ratio of the PWM signal, it is possible to easily fade out the light, and also to easily execute a slow stop operation.

[0048] Furthermore, the ECU 3 acquires the current duty ratio, the target duty ratio, and the fade time, and calculates the amount of change in the duty ratio from the start of fade to the start duty ratio of the slow stop and the amount of change in the duty ratio during the slow stop period so that the target duty ratio is reached within the fade time. In this way, the amount of change in the duty ratio from the start of fade to the start duty ratio of the slow stop and the amount of change in the duty ratio during the slow stop period can be calculated to execute the fade-out operation.

[0049] In the above embodiment, the fade-out (gradual darkening) is described, but the fade-in (gradual brightening) can also be applied. In that case, the threshold value of 40% or the like described in step S5 is preferably set to a not-too-high value such as 50%. This is because the sensitivity of the human eye is higher in dark places, and it is considered that the smaller the target duty ratio when brightening, the easier it is to feel the sense of bounding.

[0050] Furthermore, the present invention is not limited to the above-described embodiment. In other words, a person skilled in the art can implement the present invention by modifying it in various ways in accordance with conventionally known knowledge without departing from the gist of the present invention. As long as the lighting control device of the present invention is still provided even after such modification, it is of course included in the scope of the present invention. [Explanation of symbols]

[0051] 1 System 2 ECU 3 ECU (control unit, lighting control device) 4 LED lighting module (LED lighting)

Claims

1. A control unit is provided for controlling the brightness of LED lighting provided in the vehicle, the control unit, when gradually changing the brightness of the LED illumination to a target brightness, starts the change with a first change amount, and then changes the change to a second change amount that is smaller than the first change amount, thereby changing the brightness to the target brightness; A period during which the brightness changes by the second amount of change is shorter than a period during which the brightness changes by the first amount of change. A lighting control device comprising:

2. The lighting control device according to claim 1 , wherein the control unit changes the brightness to the target brightness by a constant amount when the target brightness is greater than a predetermined threshold value.

3. The lighting control device according to claim 2 , wherein the control using the threshold value can be switched on and off.

4. 4. The lighting control device according to claim 1, wherein the control unit outputs a PWM signal to the LED lighting and changes the brightness by changing a duty ratio of the PWM signal.

5. 5. The lighting control device according to claim 4, wherein the control unit acquires a current duty ratio, a duty ratio corresponding to the target brightness, and a change time to the target brightness, and calculates a duty ratio which becomes the first amount of change and a duty ratio which becomes the second amount of change so that the target brightness is reached within the change time to the target brightness.

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