Illumination device calibration method and illumination system

Abstract

To provide a method for calibrating an illumination device by obtaining accurate correspondence between setting current and driving current.SOLUTION: An illumination device calibration method is a method for calibrating relation between setting current to be supplied to a driving unit of an illumination device and driving current that is supplied to a light source by the driving unit on the basis of the setting current. The illumination device calibration method includes a first step and a second step. In the first step, instability of output of the light source is measured while changing the setting current to be supplied to the illumination device and obtains reference setting current that is setting current when the instability becomes at its maximum. In the second step, correspondence between the setting current and the driving current is obtained on the basis of the reference setting current, known reference driving current corresponding to the reference setting current, and a known variation ratio showing a variation of the driving current with respect to a variation of the setting current.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates primarily to a method for calibrating a lighting device. [Background technology]

[0002] Patent Document 1 discloses a light-emitting element drive circuit that supplies a drive current to a light-emitting element. The light-emitting element drive circuit is provided with a current source circuit. A pulsed input signal consisting of a combination of 0s and 1s is input to the current source circuit. The ratio of 0s to 1s in this pulse signal is the mark ratio. The current source circuit supplies a current proportional to the mark ratio of the input signal to the amplifying element. As a result, the output current of the amplifying element is always proportional to the mark ratio of the input signal. Therefore, the peak value of the drive current is constant regardless of individual differences or temperature of the amplifying element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-226740 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a lighting device that receives a pulsed signal consisting of a combination of 0s and 1s as an input. In contrast, lighting devices that emit light according to the current value of an input set current are known. This type of lighting device generates a drive current according to the current value of the set current, and uses the drive current to make the light source emit light. In this type of lighting device, the correspondence between the set current and the drive current varies from device to device due to individual differences in components or aging. Therefore, calibration is required to determine the accurate correspondence between the set current and the drive current.

[0005] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a method for calibrating a lighting device by determining an accurate correspondence between a set current and a drive current.

[0006] The problem to be solved by the present invention is as described above. Next, the means for solving this problem and the effects thereof will be explained.

[0007] According to a first aspect of the present invention, there is provided a lighting device calibration method as follows. That is, the lighting device calibration method is a method for calibrating a relationship between a set current supplied to a driver of a lighting device and a drive current supplied to a light source by the driver based on the set current. The lighting device includes a first switching element and a second switching element. When the drive current is less than a threshold, the lighting device generates the pulsed drive current in a first combination using at least one of the first switching element and the second switching element. When the drive current is equal to or greater than a threshold, the lighting device generates the pulsed drive current in a second combination different from the first combination using at least one of the first switching element and the second switching element. The lighting device calibration method includes a first step and a second step. In the first step, the instability of the output of the light source is measured while changing the set current supplied to the lighting device, and a reference set current is determined, which is the set current when the instability is maximized. In the second step, the reference set current, a known reference drive current corresponding to the reference set current, and The ratio of the change in the set current to the change in the drive current Based on the known rate of change, The aforementioned Set current and The aforementioned The corresponding relationship of the drive current is obtained.

[0008] When switching between the first and second combinations of switching elements, the output of the light source becomes unstable, and the drive current (reference drive current) at that time is known. This makes it possible to determine the relationship between the reference set current and the reference drive current. Furthermore, because the rate of change of the drive current relative to the set current is known, this rate of change can be used to determine the accurate correspondence relationship between the set current and the drive current (a correspondence relationship that corrects for variations due to individual differences in parts or aging, etc.).

[0009] In the lighting device calibration method, it is preferable that the first switching element is provided between a power supply unit and the light source, and the second switching element is provided between an output terminal of the first switching element and a ground unit. When the drive current is less than a threshold, the pulsed drive current is generated using the first switching element but not the second switching element. When the drive current is equal to or greater than a threshold, the pulsed drive current is generated using both the first switching element and the second switching element.

[0010] This makes it possible to obtain an accurate correspondence relationship between the set current and the drive current in a commonly used two-stage lighting device.

[0011] In the lighting device calibration method, it is preferable that the first switching element includes a field effect transistor, and the second switching element includes a field effect transistor.

[0012] It is possible to correct variations in the correspondence relationship between the set current and the drive current due to component precision or individual differences in the field effect transistors.

[0013] In the illumination device calibration method, it is preferable that the first step detects the output of the light source by a photodetector, and the instability of the output of the light source is a variance value of the photodetection values ​​of the photodetector.

[0014] This allows the degree of instability to be accurately detected with a simple calculation.

[0015] In the illumination device calibration method, the illumination device is preferably a surface light-emitting device.

[0016] This allows the surface light emitting device to be calibrated.

[0017] According to a second aspect of the present invention, there is provided a lighting system having the following configuration. That is, the lighting system comprises a control device, a drive unit, and a light source. The control device generates a set current. The drive unit generates a drive current based on the set current supplied from the control device. The light source emits light using the drive current supplied from the drive unit. The drive unit comprises a first switching element and a second switching element. When the drive current is less than a threshold, the drive unit generates the pulsed drive current using a first combination that uses at least one of the first switching element and the second switching element. When the drive current is equal to or greater than a threshold, the drive current is generated using a second combination that uses at least one of the first switching element and the second switching element, which is different from the first combination. The control device measures the instability of the output of the light source while changing the set current, and determines a reference set current that is the set current when the instability is maximized. The control device calculates the reference set current, a known reference drive current corresponding to the reference set current, and The ratio of the change in the set current to the change in the drive current The correspondence relationship between the set current and the drive current is determined based on a known change rate indicating the change rate.

[0018] When switching between the first and second combinations of switching elements, the output of the light source becomes unstable, and the drive current (reference drive current) at that time is known. This makes it possible to determine the relationship between the reference set current and the reference drive current. Furthermore, because the rate of change of the drive current relative to the set current is known, this rate of change can be used to determine the accurate correspondence relationship between the set current and the drive current (a correspondence relationship that corrects for variations due to individual differences in parts or aging, etc.). [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a block diagram of a lighting system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing the main circuit configuration of a drive unit. [Figure 3] 10 is a flowchart showing a process related to calibration of the lighting device. [Figure 4] 10 is a graph showing the relationship between the instability of the output of a light source and the drive current. [Figure 5] 10 is a graph showing the correspondence relationship between a set current and a drive current. [Figure 6] FIG. 10 is a diagram for explaining calculation of a set value from a target value using the correspondence relationship between a set current and a drive current. DETAILED DESCRIPTION OF THE INVENTION

[0020] Next, an embodiment of the present invention will be described with reference to the drawings. First, a lighting system 1 will be described with reference to FIG.

[0021] 1 includes a control device 10, a lighting device 20, and a photodetector 30. The lighting system 1 is capable of changing the output (total luminous flux) of the lighting device 20. Specifically, the control device 10 generates a set current according to a target output and supplies it to the lighting device 20. The lighting device 20 generates a drive current according to the set current and emits light using the drive current.

[0022] The lighting system 1 of this embodiment is applied to, for example, a surface light emitting device. Specifically, the lighting device 20 includes a plurality of light sources 22, which are arranged in a plane. Note that the lighting system 1 is not limited to surface light emitting devices and can be used in various light emitting devices. For example, the lighting system 1 can be applied to an imaging system that captures images of a subject in a dark place.

[0023] Furthermore, the lighting system 1 is capable of performing calibration. Even if the same set current is supplied to the lighting devices 20, the generated drive current may differ from device to device due to individual differences in the components or changes over time. Calibration is the process of determining an accurate correspondence relationship between the set current and the drive current. By using the correspondence relationship determined by performing calibration, it is possible to obtain a target drive current, and therefore a target output of the lighting device 20, regardless of individual differences in the components or changes over time.

[0024] Below, the components of the lighting system 1 will be described, followed by a description of calibration.

[0025] The control device 10 includes a calculation device such as a CPU and a storage device such as a flash memory. The calculation device of the control device 10 executes programs stored in the storage device to perform various controls related to the lighting system 1. For example, the control device 10 generates a set current and performs the above-mentioned calibration based on commands received from the outside.

[0026] The lighting device 20 includes a driving unit 21 and a light source 22. The driving unit 21 generates a driving current according to a supplied set current. As shown in Fig. 2, a current is supplied to the lighting device 20 from a power supply unit 40. The power supply unit 40 includes, for example, a DC power supply and a constant current circuit.

[0027] The driver 21 is an analog circuit and includes a known two-stage switching element. The driver 21 controls the drive current by switching to generate a pulsed drive current. Because this type of analog circuit is known, only a brief description will be given below. As shown in FIG. 2, the driver 21 includes a driver IC 21a, a first switching element 21b, and a second switching element 21c.

[0028] The driver IC 21a outputs control signals to the first switching element 21b and the second switching element 21c. The control signals are voltages applied to the gates of the FETs. The first switching element 21b is composed of two FETs (field effect transistors) arranged in parallel. The input terminal of the first switching element 21b is connected to the power supply unit 40. The second switching element 21c is composed of two FETs arranged in parallel. The second switching element 21c is arranged between the output terminal of the first switching element 21b and ground.

[0029] The driver IC 21a switches between the first switching element 21b and the second switching element 21c, whereby a pulsed driving current having a constant current value and a current value corresponding to the set current is generated and supplied to the light source 22.

[0030] When the drive current output from the drive unit 21 is less than a threshold, the driver IC 21a generates a pulsed drive current using a first combination that uses the first switching element 21b but not the second switching element 21c. When the drive current output from the drive unit 21 is equal to or greater than the threshold, the driver IC 21a generates a pulsed drive current using a second combination that uses both the first switching element 21b and the second switching element 21c. This makes it possible to stabilize the drive current both when the drive current is low and when it is high.

[0031] The drive unit 21 may use a combination different from that of this embodiment as long as it uses at least two combinations of switching elements. For example, the first combination may be the same as that of this embodiment, and the second combination may use the second switching element 21c without using the first switching element 21b. The type or number of stages of the switching elements may also be different from that of this embodiment. For example, a thyristor or an IGBT may be used as the switching element in addition to an FET. The switch configuration is not limited to two stages, and may be three or more stages.

[0032] The light source 22 is a semiconductor laser. The light source 22 emits light with an output corresponding to the magnitude of the supplied drive current. The illumination device 20 is a vertical cavity surface emitting laser (VCSEL) array element equipped with a plurality of semiconductor laser light sources. The illumination device 20 is provided, for example, in a laser processing machine that processes a workpiece using a processing laser, and is used as a light source for an observation optical system that photographs a processed portion of the workpiece during laser processing to monitor the properties of the processed portion. The light source 22 is not limited to a semiconductor laser, and may be, for example, an LED (light emitting diode).

[0033] The light detection device 30 includes a camera 31 and an image processing device 32 .

[0034] The camera 31 detects an image of an object illuminated by the light source 22. When performing calibration, the light source 22 detects an image of a white test plate (a test member for calibration). When the illumination system 1 is applied to an imaging system, the image of the test plate may be detected using an imaging device included in the imaging system. Alternatively, an optical sensor such as a photodiode may be used instead of the camera 31.

[0035] The image processing device 32 performs image processing on the image input from the camera 31, calculates a light detection value indicating the brightness (illuminance) of the test plate, and transmits it to the control device 10. Note that at least a part of the processing performed by the image processing device 32 may be performed by the control device 10.

[0036] Next, the calibration performed by the control device 10 will be described with reference to FIGS.

[0037] 3 is performed by the control device 10 in response to an appropriate operation by the operator. Alternatively, at least one of the processes in steps S101 to S108 may be performed manually by the operator.

[0038] First, the control device 10 supplies a set current to the lighting device 20 (S101). Next, the control device 10 instructs the photodetector 30 to photograph the test plate and analyze the image, and acquires photodetection values ​​from the photodetector 30 (S102). Next, the control device 10 calculates a variance value of the photodetection values ​​(S103). Note that if there are not enough photodetection values ​​collected to calculate the variance value, step S103 may be omitted.

[0039] Here, the relationship between the instability of the light detection value and the drive current will be described with reference to Fig. 4. The instability is the degree of variation in the output of the light source 22, and the greater the fluctuation in the output of the light source 22 when the drive current is constant, the higher the instability. In this embodiment, the variance value is used as the instability, but a value calculated by a method other than the variance value may also be used as the instability.

[0040] As described above, the driver 21 uses different switching methods depending on whether the drive current is equal to or greater than a threshold value or less. Therefore, when the drive current is close to the threshold value, the switching method changes, causing the control of the light source 22 to become unstable, resulting in the light source 22 flickering. As a result, the instability of the light source 22 increases significantly. Specifically, the instability reaches its maximum when the drive current matches the threshold value. In other words, when the instability reaches its maximum, the drive current matches the threshold value. Hereinafter, the drive current at this time will be referred to as the reference drive current.

[0041] After calculating the variance value, the control device 10 determines whether or not the maximum of the variance value has been identified (S104). If the maximum of the variance value cannot be identified, the control device 10 changes the set current (S105) and performs the processes of steps S101 to S104 again. There are various ways to change the set current, but for example, it is changed as follows. That is, the initial value of the set current is set to a value that generates a drive current significantly larger than the reference drive current. Then, the set current is gradually reduced. Alternatively, the initial value of the set current may be set to a value that generates a drive current significantly smaller than the reference drive current, and the set current may be gradually increased.

[0042] The local maximum of the variance value is identified, for example, as follows. That is, by gradually decreasing or increasing the set current, the variance value increases until it reaches or exceeds a predetermined threshold, and then decreases. The point where the variance value is largest is identified as the local maximum of the variance value. Note that if the switching elements are configured in three stages, there will be two variance values. In that case, for example, the variance value of the one with the smaller drive current can be identified, and the same processing as in the case of a two-stage configuration can be performed.

[0043] When the control device 10 identifies the maximum of the variance value, it stores the set current at the time when the variance value becomes maximum as a reference set current (S106). Here, the relationship between the set current and the drive current will be described with reference to FIG. 5. As described above, even when the set current is the same, the generated drive current may differ due to individual differences or aging of the drive unit 21. Therefore, in order to generate a target drive current, it is necessary to determine the correspondence relationship between the set current and the drive current, taking into account individual differences or aging of the drive unit 21.

[0044] Furthermore, the reference drive current, i.e., the drive current corresponding to the switching threshold of the lighting device 20, is known, and the rate of change (slope) between the set current and the drive current is also known. These can be obtained by conducting experiments in advance using the lighting device 20 and are stored in advance in the control device 10. There are various methods for the experiment, but for example, the reference drive current can be obtained by measuring the drive current when a reference set current is supplied. Furthermore, the rate of change can be obtained by measuring each drive current when multiple set currents are supplied and finding the ratio of the amount of change in the set current to the amount of change in the drive current.

[0045] The reference drive current and the rate of change are approximately the same regardless of individual differences, so by conducting an experiment on a single lighting device 20, it is possible to omit experiments on lighting devices 20 with the same specifications. The reference drive current and the rate of change are not easily affected by changes over time, so there is no need to conduct further experiments after the lighting system 1 is put into operation. Note that if the seller of the lighting device 20 or other source publishes data on the reference drive current (threshold value) and the rate of change, that data may be used.

[0046] The control device 10 reads out the reference drive current and the rate of change (slope) between the set current and the drive current, which were calculated and stored using the method described above (S107). Next, the control device 10 creates a correspondence relationship between the set current and the drive current (S108). Note that if a correspondence relationship has already been created, the control device 10 updates the correspondence relationship. It is known that the set current and the drive current are proportional to each other. Therefore, the control device 10 can calculate this correspondence relationship based on the reference set current calculated in step S106 and the reference drive current and rate of change read out in step S107.

[0047] By performing the above processing, it is possible to obtain a target drive current, and therefore a target output of the lighting device 20, regardless of individual differences or aging of the driving unit 21. This calibration is performed before the lighting system 1 is put into operation (for example, at the time of shipping or installation). Thereafter, calibration is performed again when the operating time of the lighting system 1 exceeds a predetermined time.

[0048] Finally, referring to FIG. 6, a method for utilizing the correspondence relationship between the set current and the drive current will be briefly described. The control device 10 stores in advance the correspondence relationship between the output of the lighting device 20 and the drive current. The correspondence relationship between the output of the lighting device 20 and the drive current is hardly affected by individual differences or aging. The control device 10 then specifies the required drive current according to the target output of the lighting device 20. Next, the control device 10 specifies the set value (FIG. 6) of the set current for obtaining the target value of the drive current (FIG. 6) based on the correspondence relationship between the set current and the drive current. The control device 10 then generates the set current of the specified set value and supplies it to the drive unit 21.

[0049] As described above, in this embodiment, the lighting device calibration method is performed as follows. The lighting device 20 includes a first switching element and a second switching element 21c. When the drive current is less than a threshold, the lighting device 20 generates a pulsed drive current using a first combination that uses at least one of the first switching element 21b and the second switching element 21c. When the drive current is equal to or greater than the threshold, the lighting device 20 generates a pulsed drive current using a second combination that uses at least one of the first switching element 21b and the second switching element 21c, which is different from the first combination. The lighting device calibration method includes a first step and a second step. In the first step, the instability of the output of the light source is measured while changing the set current supplied to the lighting device 20, and a reference set current is determined, which is the set current at which the instability is maximized. In the second step, a correspondence relationship between the set current and the drive current is determined based on the reference set current, a known reference drive current corresponding to the reference set current, and a known rate of change that indicates a change in the drive current relative to a change in the set current.

[0050] When switching between the first and second combinations of switching elements, the output of the light source becomes unstable, and the drive current (reference drive current) at that time is known. This makes it possible to determine the relationship between the reference set current and the reference drive current. Furthermore, because the rate of change of the drive current relative to the set current is known, this rate of change can be used to determine the accurate correspondence relationship between the set current and the drive current (a correspondence relationship that corrects for variations due to individual differences in parts or aging, etc.).

[0051] In the lighting device calibration method of this embodiment, the first switching element 21b is provided between the power supply unit 40 and the light source 22. The second switching element 21c is provided between the output terminal of the first switching element 21b and ground. When the drive current is less than a threshold, a pulsed drive current is generated using the first switching element 21b but not the second switching element 21c. When the drive current is equal to or greater than the threshold, a pulsed drive current is generated using both the first switching element 21b and the second switching element 21c.

[0052] This makes it possible to obtain an accurate correspondence relationship between the set current and the drive current in the lighting device 20 having a commonly used two-stage switching element.

[0053] In the lighting device calibration method of the present embodiment, the first switching element 21b includes a field effect transistor, and the second switching element 21c includes a field effect transistor.

[0054] It is possible to correct variations in the correspondence relationship between the set current and the drive current due to component precision or individual differences in the field effect transistors.

[0055] In the illumination device calibration method of this embodiment, in the first step, the output of the light source 22 is detected by the photodetector 30. The instability of the output of the light source 22 is the variance of the photodetection values ​​of the photodetector 30.

[0056] This allows the degree of instability to be accurately detected with a simple calculation.

[0057] In the illumination device calibration method of this embodiment, the illumination device 20 is a surface light-emitting device.

[0058] This allows the surface light emitting device to be calibrated. [Explanation of symbols]

[0059] 1. Lighting system 10 Control device 20 Lighting equipment 21 Drive unit 21a driver IC 21b First switching element 21c second switching element 22 Light source 30 Photodetector 31 Camera 32 Image processing device

Claims

1. 1. A lighting device calibration method for calibrating a relationship between a set current supplied to a driver of a lighting device and a drive current supplied to a light source by the driver based on the set current, comprising: The lighting device includes: a first switching element and a second switching element, When the drive current is less than a threshold, a pulsed drive current is generated using a first combination that uses at least one of the first switching element and the second switching element; When the drive current is equal to or greater than a threshold, a pulsed drive current is generated using a second combination that is different from the first combination and that uses at least one of the first switching element and the second switching element; a first step of measuring the instability of the output of the light source while changing the set current supplied to the lighting device, and determining a reference set current which is the set current when the instability is maximized; a second step of determining a correspondence relationship between the set current and the drive current based on the reference set current, a known reference drive current corresponding to the reference set current, and a known change rate indicating a ratio between a change amount of the set current and a change amount of the drive current; 10. A lighting device calibration method comprising:

2. 2. The lighting device calibration method according to claim 1, the first switching element is provided between a power supply unit and the light source, the second switching element is provided between an output terminal of the first switching element and a ground terminal, The lighting device includes: When the driving current is less than a threshold value, the driving current is generated in a pulse form using the first switching element and without using the second switching element; a first switching element that switches the driving current to a predetermined value and a second switching element that switches the driving current to a predetermined value; a second switching element that switches the driving current to a predetermined value and a second switching element that switches the driving current to a predetermined value;

3. 3. The lighting device calibration method according to claim 1, further comprising: the first switching element includes a field effect transistor; The method for calibrating a lighting device, wherein the second switching element includes a field effect transistor.

4. 4. The lighting device calibration method according to claim 1, further comprising: In the first step, an output of the light source is detected by a light detection device; 10. A method for calibrating an illumination device, wherein the instability of the output of the light source is a variance value of the light detection values ​​of the light detection device.

5. 5. The lighting device calibration method according to claim 1, further comprising: The illumination device calibration method is characterized in that the illumination device is a surface light-emitting device.

6. a control device that generates a set current; a drive unit that generates a drive current based on the set current supplied from the control device; a light source that emits light in response to the drive current supplied from the drive unit; Equipped with the drive unit includes a first switching element and a second switching element, When the drive current is less than a threshold, a pulsed drive current is generated using a first combination that uses at least one of the first switching element and the second switching element; When the drive current is equal to or greater than a threshold, a pulsed drive current is generated using a second combination that is different from the first combination and that uses at least one of the first switching element and the second switching element; the control device measures the instability of the output of the light source while changing the set current, and determines a reference set current which is the set current when the instability is maximized; The control device determines the correspondence between the set current and the drive current based on the reference set current, a known reference drive current corresponding to the reference set current, and a known change rate indicating the ratio between the amount of change in the set current and the amount of change in the drive current.

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