Light source drive unit, light irradiation device, surface inspection system, and control method for light source drive unit

Abstract

The present invention provides a light irradiation device that can emit light (turn on) repeatedly in a shorter time, and a light source drive unit used therein. [Solution] A light source drive unit that lights up a light irradiation unit by supplying a pulse drive current exceeding the maximum rated current specified for continuous lighting, having a special mode in which the restriction that the duty cycle of the lighting time in one blinking cycle must be less than or equal to a predetermined upper limit is removed, wherein in this special mode, the on / off control is performed such that one cycle consists of blinking the LED light irradiation unit multiple times by supplying the pulse drive current, and the ratio of the lighting time in at least one blinking cycle is set to a value exceeding the upper limit, while the ratio of the total lighting time in one cycle is set to be less than or equal to the upper limit, and the total lighting time in one cycle is set to be less than or equal to a predetermined upper limit of the pulse width of the pulse drive current.

Description

[Technical Field]

[0001] The present invention relates to a light irradiation device for irradiating a workpiece with light for surface inspection, and a light source driving unit used therein. [Background technology]

[0002] In recent years, in the field of light irradiation devices used for surface inspection of products (workpieces), in order to shorten the inspection cycle time by reducing the imaging time of the workpiece, a strobe emission method has been developed, as shown in Patent Document 1, which involves passing a large current exceeding the rated current to the LED light source for a short period of time to emit high-intensity pulsed light.

[0003] On the other hand, such light irradiation devices are subject to a duty cycle, which involves a period of time between each activation and the next activation. This is because exceeding this duty cycle could lead to LED degradation or failure due to overheating. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6410076 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the aforementioned duty cycle limits can become a bottleneck, preventing further reduction of the inspection cycle time.

[0006] For example, if, in order to improve inspection accuracy, the same workpiece is illuminated with light two (or more) times in the shortest possible time, and the inspection is performed based on the image captured for each illumination, the aforementioned problems are particularly likely to occur.

[0007] In view of these problems, the present invention was made for the first time through the diligent efforts of the inventors, and aims to provide a light irradiation device and a light source drive unit used therein that can emit light (turn on) repeatedly in a shorter time without causing unexpected deterioration. [Means for solving the problem]

[0008] In other words, the light source drive unit according to the present invention lights up a light irradiation unit by supplying a pulse drive current that exceeds the maximum rated current specified for continuous lighting, and has a special mode in which the restriction that the duty cycle of the lighting time in one blinking cycle must be less than or equal to a predetermined upper limit is removed, and in this special mode, the on / off control is performed in which the supply of the pulse drive current causes the light irradiation unit to blink multiple times, which constitutes one cycle, and the ratio of the lighting time in at least one blinking cycle is set to a value exceeding the upper limit, while the ratio of the total lighting time in the cycle is set to be less than or equal to the upper limit, and the total lighting time in the cycle is set to be less than or equal to a predetermined upper limit of the pulse width of the pulse drive current.

[0009] With this configuration, strobe flashes can be performed at a faster frequency than the upper limit of the duty cycle, significantly reducing the inspection cycle time.

[0010] Furthermore, the ratio of the total illumination time in one cycle consisting of multiple flashing cycles is set to be less than or equal to the aforementioned upper limit, and the total illumination time in one cycle is set to be less than or equal to the predetermined upper limit of the pulse width of the pulse drive current, thereby preventing unexpected deterioration or failure of the light irradiation unit.

[0011] The effects described above are particularly noticeable when inspecting the same workpiece by irradiating it with strobe light multiple times.

[0012] To further improve the accuracy of the inspection or increase the variety of inspections, it is preferable that the duration of at least one of the multiple flashing periods within one cycle differs from the duration of any of the other flashing periods, or that the pulse drive current for at least one flashing period differs from the pulse drive current for any of the other flashing periods.

[0013] If the flashing is repeated twice in the aforementioned cycle, it offers high versatility in actual inspections and minimizes the load on the light irradiation unit, thereby more reliably preventing unexpected deterioration or failure.

[0014] A more specific embodiment is a light irradiation device comprising the light source driving unit described above and a light irradiation unit that is lit by being supplied with current from the light source driving unit.

[0015] An example of an application in which the effects of the present invention are more pronounced is a surface inspection system comprising the above-described light irradiation device, imaging device, and image processing device, wherein the light irradiation device irradiates a single workpiece with all pulsed light emitted from the light irradiation unit in one cycle, the imaging device captures an image of the workpiece each time it is irradiated with pulsed light in one cycle, and the image processing device calculates information for inspection of the workpiece based on each image of the workpiece captured each time it is irradiated with pulsed light.

[0016] The present invention also includes a control method for a light source drive unit that lights up a light irradiation unit by supplying a pulse drive current that exceeds the maximum rated current specified for continuous lighting.

[0017] The control method of this light source driving unit has a special mode in which the limitation of setting the duty ratio of the lighting time in one flashing cycle to be not more than a predetermined upper limit value is removed. In this special mode, on / off control is performed, where supplying the pulse drive current to flash the light irradiation unit a plurality of times is defined as one cycle. At the same time, the ratio of the lighting time in at least one flashing cycle is set to a value exceeding the upper limit value, while the ratio of the total lighting time in one cycle is set to be not more than the upper limit value, and the total lighting time in one cycle is set to be not more than the upper limit value of the pulse width of the predetermined pulse drive current.

Effect of the Invention

[0018] According to the present invention, stroboscopic light emission can be performed at a high cycle exceeding the conventional upper limit value of the duty ratio, so that the inspection tact time can be significantly shortened.

[0019] In addition, the upper limit value of the duty ratio of the total lighting time in one cycle is ensured, and the total lighting time in one cycle is set to be not more than the upper limit value of the pulse width of the predetermined pulse drive current. Therefore, unexpected deterioration or failure of the light irradiation unit can be avoided.

Brief Description of the Drawings

[0020] [Figure 1] A diagram schematically showing the configuration of a surface inspection system 100 according to an embodiment of the present invention. [Figure 2] A diagram for explaining the operation mode of the light source driving unit in the normal mode of the embodiment. [Figure 3] A diagram for explaining the operation mode of the light source driving unit in the special mode of the embodiment. [Figure 4] A diagram for explaining the stroboscopic light emission mode in the special mode of another embodiment.

Mode for Carrying Out the Invention

[0021] Hereinafter, a surface inspection system 100 according to an embodiment of the present invention will be described based on the drawings.

[0022] The surface inspection system 100 of this embodiment is used to inspect the surface of an object W (hereinafter referred to as "workpiece") such as industrial products or agricultural products. As shown in Figure 1, it comprises a light irradiation device 1 that irradiates the surface of the workpiece W with inspection light, an imaging device 2 that images the workpiece W being irradiated with inspection light, and an image processing device 3 that analyzes the workpiece image captured by the imaging device 2.

[0023] The following describes each part.

[0024] The light irradiation device 1 comprises a light irradiation unit 11 and a light source driving unit 12 that supplies a driving current to the light irradiation unit 11 to cause it to emit light.

[0025] The light irradiation unit 11 described here is a ring-shaped unit comprising a housing that is annular in plan view and a plurality of light sources (specifically LEDs) 11a arranged on a conical concave surface formed in the housing, which irradiates the workpiece W with inspection light from all sides. However, the light irradiation unit 11 is not limited to this.

[0026] The light source drive unit 12 is equipped with a current supply circuit (not shown). When this current supply circuit receives a trigger signal generated internally or input from an external source, it supplies a pulse drive current to the light irradiation unit 11, causing the light irradiation device 1 to emit pulsed inspection light corresponding to the waveform of the drive current. This drive current is set to a value exceeding the maximum rated current specified for continuous operation of the light source 11a. This is known as overdrive.

[0027] Furthermore, when the light source 11a is made to emit light using overdrive, the upper limit of the overdrive current and the upper limit of the pulse width LT must be specified. max and the upper limit of the duty cycle in one blinking cycle DT max This is defined for each type of light source 11a.

[0028] The imaging device 2 images the workpiece W being irradiated with the inspection light through the observation hole 11b provided in the light irradiation unit 11, and transmits the image data to the image processing device 3. The imaging is performed in synchronization with a trigger signal output from the light irradiation device 1. Alternatively, the imaging device 2 may output a trigger signal indicating the imaging timing, and the emission of inspection light from the light irradiation device 1 may be synchronized to this trigger signal.

[0029] The image processing device 3 receives the image data, analyzes the image data, and calculates and outputs information required for inspection, such as the presence or absence of scratches on the surface of the workpiece W, the readability of characters on the surface of the workpiece W, and the shape of the surface of the workpiece W.

[0030] However, the light source drive unit 12 in this embodiment is configured to be switchable between two operating modes: normal mode and special mode.

[0031] In normal mode, as mentioned above, the upper limit of the overdrive current and the upper limit of the pulse width LT are set. max and the upper limit of the duty cycle in one blinking cycle DT max It is required to set the drive current so that it does not exceed any of the above limits. This setting is done by the operator via panel operation or communication from an external device. If the set value exceeds any of the aforementioned upper limits, that setting will be invalid.

[0032] For example, as shown in Figure 2, the upper limit of the duty cycle DT during one blinking cycle. max Since this is predetermined, if the pulse width of the pulse drive current for a certain trigger signal, i.e., the lighting period, is set to a1, then the time A1 until the next trigger signal is a1 / DT max It must be set to the above level.

[0033] Next, I will explain the special modes.

[0034] In this special mode, the duty cycle of the light source 11a during one blinking cycle is conditionally set to the aforementioned upper limit DT.max It becomes possible to set it beyond. That is, the software setting that makes the duty ratio the upper limit value DT max or less is released.

[0035] Specifically, in this special mode, on / off control is performed with one cycle being to supply the pulse drive current and blink the light irradiation unit 11 a plurality of times (here, twice), and the ratio of the lighting time in at least one blink cycle is the upper limit value DT of the duty ratio max is set to a value exceeding it, while the ratio of the total lighting time in one cycle is set to the upper limit value DT of the duty ratio max or less, and the total lighting time in one cycle is set to the upper limit value LT of the pulse width of the pulse drive current max or less.

[0036] For example, as shown in FIG. 3, if the blinking operation is performed twice in one cycle (period) S1, and each blink cycle is P1 and P2 respectively, and the lighting time in each blink cycle is b1 and b2 respectively, then the ratio b1 / P1 of the lighting time to the blink cycle P1 can be set to exceed the upper limit value DT max It can be set beyond.

[0037] On the other hand, when looking at one cycle (period) S1 including the subsequent blink cycle P2, the ratio (b1 + b2) / S1 of the total lighting time to one cycle S1 must be set to the upper limit value DT max or less. Also, a setting exceeding this is invalid. [[ID=Twenty-six]]

[0038] Furthermore, the total lighting time (b1 + b2) in one cycle S1 must be set to the upper limit value LT of the pulse width of the pulse drive current max or less. A setting exceeding this is also invalid.

[0039] Furthermore, in this embodiment, the illumination time b2 in the second flashing cycle P2 is made longer than the illumination time b1 in the first flashing cycle P1. As a result, the image processing device 3 calculates inspection information for a single workpiece W based on two image data with different brightness levels.

[0040] According to the embodiment described above, the upper limit value of the duty cycle DT max Because strobe flashes can occur at a faster cycle than [a certain speed], the inspection cycle time can be significantly reduced.

[0041] Furthermore, the ratio of the total illumination time in one cycle, which is the sum of multiple flashing cycles, is the upper limit value DT of the duty cycle. max The following settings are used, and the total lighting time in one cycle is set to the upper limit value LT of the pulse width of the pulse drive current. max The following settings prevent unexpected deterioration or failure of the light irradiation unit 11.

[0042] However, the present invention is not limited to the embodiments described above.

[0043] For example, in other embodiments, the pulse drive current for at least one of the lights in each of the multiple flashing cycles may be different from the pulse drive current for any of the other lights. For example, as shown in Figure 4(a), the pulse drive current in the second flashing cycle may be greater than the pulse drive current in the first flashing cycle. This makes it possible to obtain two image data with different brightness levels. Another way to change the pulse drive current is to change the number of light-emitting light sources 11a, as shown in Figure 4(b).

[0044] Furthermore, although the light source 11a was an LED in the above embodiment, it is not limited to this. In other embodiments, the light source 11a may be a laser diode.

[0045] Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. [Explanation of Symbols]

[0046] 100... Surface inspection system 1...Light irradiation device 11 ···Light irradiation unit 11a···LED 11b... Observation hole 12 ···Drive Unit 2. Imaging device 3. Image processing device W ···Work

Claims

1. A light source drive unit that lights up a light irradiation unit by supplying a pulse drive current that exceeds the maximum rated current specified for continuous lighting, It has a special mode in which the restriction that limits the duty cycle of the lighting time in one flashing cycle to a predetermined upper limit is removed. In this special mode, the on / off control is performed such that supplying the pulse drive current causes the light irradiation unit to blink multiple times, which constitutes one cycle. A light source drive unit characterized in that the ratio of illumination time in at least one flashing cycle is set to a value exceeding the upper limit, while the ratio of total illumination time in one cycle is set to be less than or equal to the upper limit, and the total illumination time in one cycle is set to be less than or equal to a predetermined upper limit of the pulse width of the pulse drive current.

2. The light source driving unit according to claim 1, wherein the duration of at least one of the illuminations in the multiple flashing cycles within one cycle is different from the duration of any of the other illuminations.

3. The light source drive unit according to claim 1, wherein the pulse drive current for at least one of the multiple flashing cycles within one cycle is different from the pulse drive current for any of the other flashing cycles.

4. The light source driving unit according to claim 1, 2, or 3, wherein the blinking is repeated twice in the aforementioned cycle.

5. A light irradiation device comprising a light source drive unit according to claim 1 and a light irradiation unit that is lit by being supplied with current from the light source drive unit.

6. The light irradiation device, imaging device, and image processing device according to claim 5 are provided, The light irradiation device irradiates a single workpiece with all the pulsed light emitted from the light irradiation unit during the cycle. The imaging device, in the cycle, images the workpiece each time it is irradiated with pulsed light. The image processing device is characterized by calculating information for inspection of the workpiece based on the image of the workpiece captured each time pulse light is irradiated.

7. A control method for a light source drive unit that lights up a light irradiation unit by supplying a pulse drive current that exceeds the maximum rated current specified for continuous lighting, It has a special mode in which the restriction that limits the duty cycle of the lighting time in one flashing cycle to a predetermined upper limit is removed. In this special mode, the on / off control is performed such that supplying the pulse drive current causes the light irradiation unit to blink multiple times, which constitutes one cycle. A control method for a light source drive unit, characterized in that the ratio of lighting time in at least one blinking cycle is set to a value exceeding the upper limit, while the ratio of total lighting time in one cycle is set to be less than or equal to the upper limit, and the total lighting time in one cycle is set to be less than or equal to a predetermined upper limit of the pulse width of the pulse drive current.

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