JP5584873B2 - Image measuring device - Google Patents

Description

  The present invention relates to an image measurement apparatus that measures a measurement object by imaging the measurement object.

  In an image measuring device equipped with an autofocus function, the image of the measuring object is sequentially acquired while moving the imaging device such as a camera or its optical system in the optical axis direction, and the position in the optical axis direction where the image with the highest contrast is acquired. Is the in-focus position with respect to the measurement object (Patent Document 1).

JP 2009-168607 A

  In such an image measuring apparatus, flicker may occur depending on the combination of the frame rate of the imaging apparatus and the emission frequency of the illumination that illuminates the imaging range, and the brightness of the acquired image may vary. In this case, since an image with a small amount of light has a small contrast between pixels, the contrast is small regardless of whether it is in the focus position, and conversely, an image with a large amount of light has a large contrast. For this reason, it is difficult to determine the in-focus position from the contrast, and there is a problem that the reliability of autofocus is lowered.

  In order to solve such a problem, the image measuring device generally includes an illumination device that does not flicker when combined with an imaging device. However, even in this case, there are many cases where it is difficult to eliminate the influence of disturbance light depending on the mode of the image measuring apparatus. Non-inverter fluorescent lamps (hereinafter referred to as room lamps) are examples of disturbing light that is difficult to eliminate and is problematic. The interior light repeatedly flickers at 100 Hz in an area where the power supply frequency is 50 Hz and 120 Hz in an area where the power supply frequency is 60 Hz, which adversely affects measurement results and autofocus results. In some cases, the lighting device itself may flicker.

  The present invention has been made in view of such a point, and an object thereof is to provide an image measuring apparatus capable of high-precision autofocus processing.

  An image measuring apparatus according to the present invention includes an imaging apparatus that images a workpiece, the exposure time is variable, an illumination apparatus that emits light at a predetermined emission frequency and irradiates the workpiece with illumination light, and an imaging apparatus that focuses on the imaging apparatus. A position control system that controls the position and outputs the in-focus position as position information in the in-focus axis direction, and the lighting frequency of the room light is the first frequency and the second frequency when the in-focus position is controlled by the position control system. And a control device that sets the exposure time of the imaging device to be an integral multiple of the lighting cycle of the room light based on which one of the lighting devices has an emission frequency of the first frequency and the second frequency. Set to a common multiple.

  In such a configuration, it is possible to perform highly accurate autofocus processing by eliminating the influence of disturbance light that repeatedly blinks at a constant period and acquiring an image with a constant brightness. It can also be used in common in regions with different power supply frequencies.

  In one embodiment of the present invention, the control device may detect the lighting frequency of room light with the lighting device turned off.

  In one embodiment of the present invention, the control device sets the exposure time of the imaging device to an integral multiple of the lighting cycle corresponding to the first frequency and the integer of the lighting cycle corresponding to the second frequency. In the case of setting to be doubled, each of the position control systems is controlled to perform imaging by the imaging device at a plurality of different in-focus positions, and the variation rate of the average brightness of the obtained image is calculated. The exposure time may be set to an integer multiple of the lighting cycle corresponding to the frequency with the lower average brightness fluctuation rate.

  In such a configuration, it is possible to automatically determine the frame rate of the imaging device and the light emission frequency of the lighting device without requiring complicated operations, and high-precision autofocus processing is easy in any region. Can be performed.

  In one embodiment of the present invention, the first frequency is 100 Hz and the second frequency is 120 Hz.

  Moreover, in one Embodiment of this invention, the light emission frequency of an illuminating device is 600 Hz.

  According to the present invention, it is possible to provide an image measuring apparatus capable of performing highly accurate autofocus processing.

1 is an overall view of an image measuring device according to a first embodiment of the present invention. It is a block diagram which shows the structure of the same apparatus. It is a block diagram showing the structure of a part of the apparatus. It is a figure which shows the method of the autofocus in the apparatus. It is a timing chart which shows the relationship between the lighting frequency of the room lamp and exposure time in the conventional image measuring apparatus. It is a figure which shows the relationship between the contrast in the conventional image measuring apparatus, and the Z coordinate of a camera. It is a timing chart which shows the relationship between the lighting frequency of the room lamp and exposure time in the conventional image measuring apparatus. It is a timing chart which shows the relationship between the lighting frequency of the room lamp and exposure time in the conventional image measuring apparatus. It is a timing chart which shows an example of the relationship between the lighting frequency of the interior lamp and exposure time in the image measuring device which concerns on embodiment of this invention. It is a flowchart which shows the determination method of the frame rate in the image measuring device which concerns on 1st Embodiment of this invention. It is a timing chart which shows the relationship between the light emission frequency in the conventional image measuring apparatus, and exposure time. It is a timing chart which shows the relationship between the light emission frequency and exposure time in the image measuring device which concerns on 1st Embodiment of this invention.

[First Embodiment]
Next, the configuration of the image measuring apparatus according to the first embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall view of an image measuring apparatus according to this embodiment. The image measuring apparatus includes an image measuring machine 1 on which a camera 141 is mounted as an image pickup apparatus for picking up a workpiece 3, and a computer (hereinafter referred to as “PC”) 2 electrically connected to the image measuring machine 1. It has.

  The image measuring machine 1 is configured as follows. That is, the sample stage 12 is placed on the sample moving means 11 so as to coincide with the horizontal plane with the upper surface as a base surface, and the arm supports 13 a and 13 b erected from both ends of the sample moving means 11. The X-axis guide 13c is supported at the upper end. The sample stage 12 is driven in the Y-axis direction by the sample moving means 11. The imaging unit 14 is supported by the X-axis guide 13c so as to be driven in the X-axis direction. A camera 141 is attached to the lower end of the imaging unit 14.

  In the present embodiment, the form of imaging the workpiece 3 placed on the sample stage 12 is taken, but other formats may be used, for example, a form of imaging the workpiece placed on the floor from the lateral direction. But it ’s okay. As the camera 141, various cameras such as a CCD and a CMOS can be used.

  FIG. 2 is a block diagram of the image measuring apparatus according to this embodiment. In the present embodiment, the image measurement device includes a controller 15 in the image measuring machine 1, for example, and the controller 15 includes a position control system 151 and an illumination control device 152. Further, the imaging unit 14 includes an illumination device 142 that irradiates the work 3 with light. In the present embodiment, the illumination device 142 is a PWM (Pulse Width Modulation) controlled LED. The PC 2 controls the focal position of the camera 141 via the position control system 151. Further, the PC 2 transmits a signal for designating a frame rate to the camera 141, and transmits a PWM frequency command of the lighting device 142 to the lighting control device 152. The camera 141 captures an image of the work 3 irradiated with illumination light and room light from the illumination device 142 at a specified frame rate, and transmits image information to the PC 2. At this time, the position information of the camera 141 is transmitted from the position control system 151. In the present embodiment, PWM-controlled LED illumination is used as the illumination device 142, but various illumination can naturally be used.

  Next, the configuration of the imaging unit 14 in the image measurement device according to the present embodiment will be described. FIG. 3 is a block diagram illustrating a partial configuration of the image measurement apparatus according to the present embodiment. In this embodiment, the imaging unit 14 includes a camera 141, a linear encoder 143 that detects and outputs the Z coordinate of the camera 141, a camera drive mechanism 144 that drives the camera 141 in the Z-axis direction, and a camera drive mechanism 144. And a Z-axis motor 145 to be driven. The Z-axis motor 145 is controlled by the position control system 151 via the power unit 16 provided in the image measuring machine 1. The linear encoder 143 is attached so that the scale or the detection head moves in the Z-axis direction in conjunction with the camera 141. The position control system 151 includes a latch counter and a Z value latch buffer, acquires Z coordinate information of the camera 141 from the linear encoder 143 in accordance with the trigger signal, and holds the information in the Z value latch buffer. The camera 141 is connected to the PC 2 via a USB cable and the position control system 151 via a dedicated DIO (digital input / output).

  The position control system 151 outputs a Z-axis drive command to the power unit 16. The power unit 16 supplies driving power to the Z-axis motor 145, and the Z-axis motor 145 drives the camera 141 by the camera driving mechanism 144. The camera 141 captures an image at an arbitrary frame rate and transmits image information to the PC 2 via a USB cable. At this time, a vertical synchronization signal may be output from the camera 141 to the position control system 151 as a trigger signal. In this case, the position control system 151 receives the vertical synchronization signal, and acquires the Z coordinate of the camera 141 from the linear encoder 143 accordingly. The acquired Z coordinate is held in the Z value latch buffer, and the latch counter is updated. The held Z value is transmitted to the PC 2 in response to the read command. In the present embodiment, the camera 141 is driven in the Z-axis direction, but a similar operation can be performed by adjusting an optical system such as a lens provided in the camera 141. In this embodiment, the USB interface is used as the digital serial communication means, but other means such as Gig-E and FireWire can naturally be used.

  Next, an autofocus method of the image measuring apparatus according to the present embodiment will be described. FIG. 4 is a diagram for explaining an autofocus method of the image measuring apparatus according to the present embodiment, where the horizontal axis represents the Z coordinate of the camera 141 and the vertical axis represents contrast.

  In the autofocus of the image measuring apparatus according to the present embodiment, imaging is performed at a plurality of Z coordinates, the contrast is calculated from the image at each coordinate position, and the highest numerical value is shown among the calculated plurality of contrasts. The Z coordinate from which the image is acquired is determined as the in-focus position. In the example of FIG. 4, imaging is performed at seven Z coordinates (Z1 to Z7), and contrasts (P1 to P7) at the respective Z coordinates are calculated. In the example of FIG. 4, since the contrast P4 at Z4 is the highest, Z4 is determined as the in-focus position, and the Z coordinate of the camera 141 is adjusted to Z4.

  Next, problems in conventional contrast autofocus will be described. As described above, in such an image measurement apparatus, the workpiece 3 may be irradiated with disturbance light in addition to the light from the illumination device 142. In many cases, such an image measuring apparatus is used indoors, and disturbance light becomes light from an indoor lamp. The interior light repeatedly flickers at a constant cycle, and the acquired image may flicker depending on the relationship with the frame rate of the camera 141.

  The problem of this flicker will be described with reference to FIGS. Generally, the lighting frequency of fluorescent lamps other than the inverter type (hereinafter referred to as indoor lamp) depends on the power supply frequency, and is 100 Hz in an area where the power supply frequency is 50 Hz and 120 Hz in an area where the power supply frequency is 60 Hz. FIG. 5 shows the relationship between the lighting frequency of the room lamp and the frame rate when imaging is performed with the frame rate of the camera 141 set to 60 fps. The upper part shows the case where the power supply frequency is 60 Hz, and the lower part shows the case where the power supply frequency is 50 Hz.

  As shown in the upper part of FIG. 5, the camera 141 receives light for 1/60 s (about 16.7 msec) from the start of exposure, and transfers the image to the PC 2 when the light reception ends. When the image transfer to the PC 2 is completed, the exposure is started again, and thereafter the same operation is repeated. In FIG. 5, the image transfer time is set to be relatively long, but here, an example in which the frame period (reciprocal of the frame rate) and the exposure time are set to be approximately equal is shown. The fact that the phases of both are gradually shifted due to an error from the lighting frequency is emphasized.

  As described above, when the power supply frequency is 60 Hz, the lighting frequency of the room lamp is 120 Hz. Therefore, when the exposure time is set to 1/60 = 16.7 ms, the camera 141 receives the light quantity for two cycles of the indoor lamp between the start and end of light reception. Thereby, even if the lighting cycle of the room light and the frame cycle are shifted, the images received by the camera 141 all have the same brightness.

  On the other hand, when the power supply frequency is 50 Hz, that is, when the lighting frequency of the indoor lamp is 100 Hz, the indoor lamp repeats blinking at a cycle of 10 msec. Therefore, as shown in the lower part of FIG. 5, the exposure time of the camera 141 does not become an integral multiple of the lighting cycle of the room lamp. Therefore, the amount of light received each time an image is captured by the camera 141 varies, and the acquired image flickers.

  As described above, in contrast-type autofocus, the contrast is calculated from an image acquired by the camera 141. Therefore, when flickering occurs in the image from the camera 141, it is difficult to calculate the contrast correctly.

  FIG. 6 is a diagram for comparing the contrast that was originally obtained when flicker did not occur with the contrast that produced an error due to flicker, with the vertical axis representing the contrast and the horizontal axis representing the Z coordinate of the camera. Yes. The curve represented by the dotted line is the original contrast, and the curve represented by the solid line is the contrast causing the error. As shown in FIG. 6, flickering occurs in the acquired image, so that the contrast peak moves to a location different from the original position. As a result, the contrast P3 'becomes larger than the contrast P4', and Z3 is determined to be the in-focus position instead of Z4 which is the original in-focus position.

  FIG. 7 shows a diagram basically similar to FIG. 5 except that the frame rate of the camera is set to 60 fps in FIG. 5 but is set to 50 fps in FIG. ing. In this case, contrary to the case of FIG. 5, no flicker occurs between images acquired by the camera 141 when the lighting frequency of the room lamp is 100 Hz, but flickers when 120 Hz.

  FIG. 8 also shows a diagram basically similar to FIGS. 5 and 7, but in FIG. 8, the frame rate of the camera is set to 20 fps. In this case, when the lighting frequency of the indoor light is 100 Hz and 120 Hz, the exposure time 50 ms is an integral multiple of the lighting cycle of the indoor light, and thus flicker does not occur. However, when imaging is performed at such a frame rate, the imaging speed is greatly reduced, so that it takes a long time for autofocusing.

  In order to solve such a problem, in the present invention, the exposure time of the camera 141 is adjusted in accordance with the lighting frequency of the room light. This adjustment method is shown in FIG. FIG. 9 is basically the same as FIG. 5 except that the exposure time of the camera is set to 1/60 s when the power supply frequency is 60 Hz and 1/50 s when the power frequency is 50 Hz. Is different. Thus, by flexibly adjusting the exposure time according to the power supply frequency, it is possible to acquire an image that does not cause flickering due to ambient light. In FIG. 9, the exposure time of the camera 141 is twice the time of one cycle of the lighting frequency of the room light, but it is not always required to be twice, and it may be an integral multiple. . Practically, it is conceivable to increase the speed of the autofocus operation by shortening the exposure time, that is, by setting the frame rate large. Specifically, it is conceivable to set the camera exposure time to 1/120 s when the power supply frequency is 60 Hz, and to set the camera exposure time to 1/100 s when the power supply frequency is 50 Hz. In addition, when ambient light other than room light is irradiated to the work 3, by setting the exposure time longer, that is, by setting the frame rate small, noise is suppressed and the reliability of the autofocus operation is improved. It is possible to make it. In the present embodiment, the exposure time of the camera 141 only needs to be set to an integral multiple of the lighting cycle of the room lamp, and is not related to the frame rate. By setting in this way, even if the exposure start timing during the frame period is indefinite, since a constant amount of light is always exposed, flicker does not occur.

  Next, a method for automatically detecting the lighting frequency of the room lamp using software will be described.

  FIG. 10 shows a flow of processing for detecting the lighting cycle of the indoor lamp. FIG. 10 shows a frame rate adjustment method for setting the frame rate of the camera to 120 fps when the power supply frequency is 60 Hz and the camera frame rate to 100 fps when the power supply frequency is 50 Hz. It is a flowchart when performing using. When the adjustment of the frame rate is started, the PC 2 first turns off the illumination device 142 in order to confirm the influence of disturbance light (S1). Next, the frame rate of the camera 141 is set to 100 fps (S2). Next, imaging by the camera 141 is performed, an image of the work 3 is acquired, and a variation rate of the average brightness is calculated (S3). In step S3, three or more images of the workpiece 3 are preferably acquired. Next, the frame rate of the camera 141 is changed to 120 fps (S4), and the image of the work 3 is acquired and the variation rate of the average brightness is calculated (S5). Finally, the fluctuation rate of the average brightness when the frame rate of the camera 141 is set to 100 fps is compared with the fluctuation rate of the average brightness when the frame rate of the camera 141 is set to 120 fps, and the frame rate of the camera 141 is changed. The frame rate with the smaller rate is set (S6). The frame rate of the camera 141 may be set to 60 fps and then changed to 50 fps. In step S6, if both of the compared average brightness fluctuation rates are equal to or greater than a predetermined threshold, the frame rate may be set to 60 fps. Further, when both the calculated average brightness fluctuation rates are low, the frame rate may be set manually. It is also possible to perform the method as described above at the time of starting the image measuring apparatus or dedicated software.

  Next, operation | movement of the illuminating device 142 of the image measuring device which concerns on this embodiment is demonstrated. In the present embodiment, a PWM-controlled LED is used as the lighting device 142, and the PWM frequency is set to an integral multiple of 600 Hz, which is the least common multiple of 120 and 100. The reason will be described below.

  FIG. 11 is a timing chart showing the relationship between the light emission time of the illumination device 142 and the exposure time of the camera 141 when the PWM frequency is set to 480 Hz. The upper row shows the case where the frame rate of the camera 141 is 60 fps, and the lower row shows the case where the frame rate of the camera is 50 fps.

  As shown in the upper part of FIG. 11, when the PWM frequency is 480 Hz and the frame rate of the camera 141 is 60 fps, the PWM frequency is 8 times the frame rate of the camera 141. Therefore, the light from the illumination device 142 is received by the camera 141 for 8 pulses, and the light amounts of the captured images are all equal. On the other hand, as shown in the lower part of FIG. 11, when the frame rate of the camera 141 is 50 fps, the PWM frequency is 9.6 times the frame rate of the camera. Accordingly, since the PWM frequency of the illuminating device 142 is not an integral multiple of the frame rate, an error occurs between the frame rate of the camera 141 and the irradiation cycle of the illuminating device 142 as shown in the lower part of FIG. Flickering occurs between the images that are displayed. In such a case, as in the case described with reference to FIGS. 5 and 6, an error occurs between the acquired contrast and the original contrast, and the accuracy of autofocus is impaired.

  On the other hand, in the image measuring device according to the present embodiment, the light emission frequency of the illumination device 142 is set to a multiple of 600 Hz. In this manner, FIG. 12 shows a state when the light emission frequency of the illumination device 142 is set to a multiple of 600 Hz. FIG. 12 is basically the same as FIG. 11 except that the light emission frequency of the illumination device 142 is set to 600 Hz. As can be seen from the upper part of FIG. 12, when the frame rate of the camera 141 is 60 fps, the amount of light irradiated onto the work 3 by the illumination device 142 during one exposure time of the camera 141 is 10 of the illumination device 142. It is the amount of light for the pulse. Further, when the frame rate of the camera 142 is 50 fps, the light amount of 12 pulses of the lighting device 142 is received. Therefore, even when the frame rate of the camera 141 is set to 50 fps or 60 fps, light can always be received with a constant light amount.

  According to such a configuration, it is possible to acquire an appropriate image without flicker even when the frame rate of the camera 141 changes. In addition, when lighting is turned on with a switching type power circuit, a ripple due to switching is generated in principle. This ripple can also cause flickering and flicker in the input image, but this configuration can solve this problem.

  In this embodiment, since the camera frame rate is selected from 100 fps and 120 fps, the light emission frequency of the illumination device 142 is set to 600 Hz. However, it may be a common multiple of a plurality of frame rates to be selected. For example, when the frame rate of the camera is selected from 50 fps and 60 fps, it can be set to 300 Hz which is the least common multiple. When the frame rate of the camera 141 is set to a value other than 50 fps and 60 fps, the light emission frequency of the lighting device 142 can be automatically adjusted to an integer multiple of the frame rate of the camera 141. Furthermore, the illumination device 142 may receive a vertical synchronization signal from the camera 141, for example, and cause the illumination device 142 to emit light for a certain pulse within the exposure time.

  Furthermore, for example, when controlling a very small current or voltage in a switching type power circuit, the efficiency can be improved by thinning the switching, or a current or voltage smaller than the actual capability of the switching control element can be obtained. There is a way to make it appear to be in control. In this case as well, if the thinning cycle is made constant and the frequency is set to a common multiple of the frame rate, flicker will not occur in the input image.

  DESCRIPTION OF SYMBOLS 1 ... Image measuring machine, 2 ... Computer (PC), 3 ... Workpiece, 11 ... Sample moving means, 12 ... Sample stand, 13a, b ... Arm support, 13c ... X-axis guide, 14 ... Imaging unit, 15 ... Controller , 16 ... power unit, 141 ... camera, 142 ... lighting device, 143 ... linear encoder, 144 ... camera drive mechanism, 145 ... Z-axis motor, 151 ... position control system, 152 ... lighting control device.

Claims (5)

An imaging device for imaging a workpiece and having a variable exposure time;
An illumination device that emits light at a predetermined emission frequency and irradiates the workpiece with illumination light;
A position control system that controls a focusing position of the imaging device and outputs the focusing position as position information in a focusing axis direction;
The exposure time of the imaging device is an integral multiple of the lighting cycle of the room light based on whether the lighting frequency of the room light is the first frequency or the second frequency when controlling the in-focus position by the position control system. And a control device for setting so that
The light emission frequency of the said illuminating device is set to the common multiple of the said 1st frequency and a 2nd frequency. The image measuring device characterized by the above-mentioned. The controller is
The image measurement device according to claim 1, wherein a lighting frequency of the room light is detected in a state where the lighting device is turned off. The controller is
When the exposure time of the imaging device is set to an integral multiple of the lighting cycle corresponding to the first frequency, and when set to be an integral multiple of the lighting cycle corresponding to the second frequency, respectively Control the position control system to perform imaging by the imaging device at a plurality of different in-focus positions,
Calculate the average brightness fluctuation rate of the obtained image,
The image measurement apparatus according to claim 2, wherein an exposure time of the imaging device is set to an integral multiple of a lighting cycle corresponding to a frequency having a lower variation rate of the average brightness.   The image measuring apparatus according to claim 3, wherein the first frequency is 100 Hz and the second frequency is 120 Hz.   The image measurement device according to claim 4, wherein the light emitting frequency of the illumination device is 600 Hz.

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