JP2012151714A - Image measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable accurate and high-speed auto-focus processing.SOLUTION: An image measuring device comprises: an imaging apparatus having a variable frame rate for imaging a work; an illuminator which illuminates the work with light; a position control system which controls the focal position of the imaging apparatus to output the focal position as a positional information in the direction of a focal axis; and a controller which, in control of the focal position by the position control system, controls the frame rate of the imaging apparatus and adjusts the amount of light of the illuminator in accordance with the frame rate of the imaging apparatus.

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

  Such an image measuring apparatus can be easily realized by using only a camera and software, but has a problem that it takes time to perform autofocus processing. In order to solve such a problem, it is conceivable to move the camera or the optical system at high speed, but the pitch of image acquisition at the time of autofocus becomes coarse, and it is difficult to acquire an accurate in-focus position.

  The present invention has been made in view of these points, and an object of the present invention is to provide an image measuring apparatus capable of high-precision and high-speed autofocus processing.

  In order to solve such a problem, an image measurement apparatus according to the present invention controls an imaging device that images a workpiece, a variable frame rate, an illumination device that irradiates light on the workpiece, and an in-focus position of the imaging device. A position control system that outputs the in-focus position as position information in the in-focus axis direction, and controls the frame rate of the imaging device when controlling the in-focus position by the position control system, and illuminates according to the frame rate of the imaging device. And a control device for adjusting the amount of light of the device.

  In one embodiment of the present invention, the control device receives a part of the imaging range of the imaging device, controls the focusing position of the imaging device, increases the frame rate of the imaging device, and controls the light amount of the illumination device. It is possible to increase. According to such a configuration, it is possible to compensate for an increase in the frame rate of the imaging apparatus and a decrease in the exposure time associated therewith by an increase in the amount of light of the illumination apparatus, thereby realizing high-precision and high-speed autofocus.

  In the image measurement device according to another embodiment of the present invention, the control device may adjust the light amount of the illumination device according to the vertical synchronization signal output from the imaging device. With such a configuration, even when switching the frame rate of the imaging device, it is possible to always perform imaging with a constant light amount, and the operation screen does not become bright or dark for a moment, and excellent operability is achieved. It is possible to provide.

  Further, in the image measurement device according to another embodiment of the present invention, the control device, when controlling the in-focus position of the imaging device, a first frame rate calculated from the interval of the vertical synchronization signals output from the imaging device, You may make it adjust the light quantity of an illuminating device according to the 2nd frame rate currently used at the time of a normal measurement.

  In the image measurement device according to another embodiment of the present invention, the control device can also adjust the gain of the imaging device in accordance with the frame rate of the imaging device.

  According to the present invention, high-precision and high-speed autofocus processing is possible.

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 image measuring apparatus which concerns on the same system. It is a block diagram showing the structure of a part of image measuring device concerning the system. It is a figure which shows the method of the autofocus in the system. It is a timing chart which shows the method of autofocus in the system. It is a block diagram for demonstrating the lighting control method in the system. It is a block diagram for demonstrating the illumination control method in the image measuring device which concerns on 2nd Embodiment of this invention. It is a timing chart which shows the method of autofocus in the system. It is a timing chart which shows the method of the autofocus in the image measuring device which concerns on 3rd 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. 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 the frame rate to the camera 141 and a signal for designating the light amount of the illumination device 142 to the illumination control device 152. The camera 141 captures the workpiece 3 irradiated with 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. Various illuminations can be used as the illumination device 142, and for example, a PWM-controlled LED can also 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 the USB interface 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 the USB interface. 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.

  In such contrast-type autofocus, a more accurate in-focus position can be grasped by increasing the image output position. However, when the image output position is increased, the amount of data transmitted from the camera 141 to the PC 2 increases. In the present embodiment, since the camera 141 and the PC 2 are connected via a USB interface, the image data transfer speed is limited to about 400 Mbps, and the time required for autofocusing increases. For this reason, in the image measurement apparatus according to the present embodiment, during autofocus, only a part of the image in the imaging range is cut out and transmitted, thereby reducing the amount of data transmitted from the camera 141 to the PC 2 and the frame. I try to raise the rate.

  This autofocus process will be described with reference to FIG. FIG. 5 is a timing chart showing signals communicated between the camera 141 and the PC 2 during the autofocus of the image measuring apparatus according to the present embodiment. The upper part shows part of the signal transmitted from the PC 2 to the camera 141, and the lower part shows the signal transmitted from the camera 141 to the PC 2.

  In the live display state before the autofocus is started, the image data of the entire imaging range is transmitted from the camera 141 to the PC 2 as shown in the lower left of FIG. When an instruction to stop image output is transmitted from the PC 2 to the camera 141 at timing S1, the image output of the camera 141 is stopped, and an instruction to reset the latch counter is transmitted from the camera 141 to the position control system 151. When the latch counter is reset, the camera 141 is driven to the autofocus start position.

  At timing S2, a command for designating an image output range is transmitted from the PC 2 to the camera 141. As a result, the range of the image transmitted from the camera 141 to the PC 2 is limited, for example, as shown in the lower center of FIG. At this time, it is also possible to issue an instruction to output a vertical synchronizing signal at the same time. Subsequently, at timing S3, an instruction to start image output is issued from the PC 2 to the camera 141, and image data and a time stamp are output from the camera 141 to the PC 2. If a command for outputting a vertical synchronization signal is issued at timing S2, a vertical synchronization signal is transmitted from the camera 141 to the position control system 151, and the Z coordinate and time stamp when the camera 141 obtains an image are displayed. Retained. In addition, when the vertical synchronization signal is not used, the position of the camera 141 and the position of the camera 141 are controlled by different methods such as calculating the imaging timing of the camera 141 from the frame rate of the camera 141 and acquiring the Z coordinate of the camera 141 at the calculated timing. It is also possible to synchronize with the system 151.

  At timing S4 when the autofocus is finished, an instruction to stop image output is issued from the PC 2 to the camera 141. Subsequently, at timing S5, a signal for canceling the setting of the camera 141 during autofocus (designation of the image output range and output of the vertical synchronization signal) is transmitted. In addition, a Z movement stop command, a latch end command, and a latch number read command are transmitted from the PC 2 to the position control system 151. The position control system 151 stops the movement of the camera 141, stops the operation of the latch counter and the Z value latch buffer, and transmits the number of latches to the PC2. Subsequently, a latch data read command is output from the PC 2 to the position control system 151, and data (Z coordinate and time stamp) in the Z value latch buffer is transmitted from the position control system 151 to the PC 2. The PC 2 associates the image information with the Z coordinate from the time stamp, and grasps the relationship between the contrast calculated from the image information and the Z value. Thereafter, the Z value at which an image with the highest contrast is obtained is determined as the focus position, and the Z coordinate of the camera 141 is moved to the calculated focus position.

  Finally, when an instruction to resume live display image output is issued at timing S6, the autofocus operation ends, and transmission of image data in the entire normal imaging range is resumed. At this time, the image transmitted from the camera 141 to the PC 2 has the same size as that before the start of autofocus, as shown in the lower right of FIG.

  In such a method, the size of the image transmitted from the camera 141 to the PC 2 is reduced, and the frame rate of the camera 141 can be greatly increased regardless of the transfer rate of the USB interface. However, in such a method, the exposure time for each frame is reduced, and the amount of light of the acquired image is reduced. As a result, the contrast is lowered and the accuracy of the autofocus is also lowered.

  In order to solve such a problem, in this embodiment, the light amount of the illumination device 142 is increased during autofocus. This illumination control will be described with reference to FIG. FIG. 6 is a block diagram for explaining an illumination control method in the image measuring apparatus according to the present embodiment.

  A lighting control device 152 and a camera 141 are connected in parallel to the PC 2, and a lighting device 142 is connected to the lighting control device 152. When autofocusing is started, an image output stop command is transmitted at timing S1 in FIG. 5 as described above, and a signal output start command is issued at timing S3. In the present embodiment, the lighting control device from the PC 2 to the lighting control device from the timing S1 to S3, that is, until the image output from the camera 141 to the PC 2 is stopped and the image output is resumed at the designated frame rate. A brightness command is transmitted to 152.

  Thus, by increasing the light amount of the illumination device 142 according to the increase in the frame rate of the camera 141, it is possible to compensate for the decrease in the light amount accompanying the decrease in the exposure time and to prevent the decrease in contrast. Therefore, it is possible to significantly increase the number of frames of image information acquired per unit time while maintaining the accuracy of contrast, and high-precision and high-speed autofocus is possible. Further, such a configuration can be realized simply and inexpensively by using only an existing PC and an image measuring machine and using only software. Note that it is also possible to calculate an average value such as brightness and contrast of the acquired image by the PC 2 and to control the illumination control device 152 according to this.

[Second Embodiment]
Next, an image measuring apparatus according to the second embodiment of the present invention will be described. In the image measurement device according to the present embodiment, the light amount of the illumination device 142 is controlled from the vertical synchronization signal output from the camera 141.

  FIG. 7 is a block diagram for explaining an illumination control method in the image measuring apparatus according to the present embodiment. The image measurement apparatus according to the present embodiment is basically the same as the image measurement apparatus according to the first embodiment, but in this embodiment, the controller 15 further includes a frame rate detector 153 and a standard frame rate holding unit 154. However, it is different in that it is connected to the camera 141 and the illumination control device 152. In the present embodiment, a vertical synchronization signal is output from the camera 141 to the frame rate detector 153. The frame rate detector 153 calculates the frame rate of the camera 141 from the vertical synchronization signal and outputs it to the illumination control device 152. The illumination controller 152 receives a difference between the calculated frame rate and the standard frame rate output from the standard frame rate holding unit 154. At this time, the illuminance determined by the color or reflectance of the workpiece surface output from the PC 2 may be input to the illumination control device 152 as a reference value, and the illuminance may be adjusted according to the frame rate.

  FIG. 8 is a timing chart showing the light amount of the illumination device 142 of the image measuring apparatus according to the present embodiment, the gain of the camera 141, and the signal output from the camera 141. In the upper part of the figure, the light quantity of the illumination device 142 is shown, the gain of the camera 141 is shown in the middle part, and the signal output from the camera 141 is shown in the lower part. At the time of normal measurement, the light amount of the illumination device 142 is a constant value. However, when autofocus is started at the timing S11, the illumination control device 152 causes the light amount of the illumination device 142 according to the vertical synchronization signal output from the camera 141. Increase. When the autofocus is completed at timing S12, the illumination control device 152 returns the light amount of the illumination device 142 to the light amount at the time of normal measurement in response to the stop of the output of the vertical synchronization signal from the camera 141. In the present embodiment, the vertical synchronization signal is output from the camera 141 only during autofocusing, but the vertical synchronization signal may always be output.

  In the first embodiment, since the frame rate of the camera 141 and the light amount of the illumination device 142 are separately controlled by the PC 2, a timing for instructing the camera 141 and a timing for instructing the illumination device 142 due to a delay in calculation processing by the PC 2 and the like. There is a risk of lagging behind. For this reason, when switching between normal measurement and autofocus, an undesired phenomenon may occur in measurement operations, such as an image displayed on the PC 2 being dark for a moment or conversely becoming too bright for a moment. However, in this embodiment, since the frame rate of the camera 141 and the light amount of the illumination device 142 are directly synchronized by the vertical synchronization signal, imaging is always performed with an appropriate light amount when switching between normal measurement and autofocus. It is possible to prevent such a problem that the brightness varies on the screen of the PC 2.

  Many cameras having a vertical synchronizing signal output function are distributed, and the frame rate detector 153 and the standard frame rate holding unit 154 can be easily manufactured. Furthermore, when using the existing controller 15 on which a microcomputer or the like is mounted, this additional circuit can be mounted by firmware. Therefore, such a configuration is realized at a very low cost.

[Third Embodiment]
Next, an image measuring device according to a third embodiment of the present invention will be described. The image measurement apparatus according to the present embodiment is substantially the same as the image measurement apparatus according to the second embodiment, but differs in that the gain of the camera 141 is operated under a certain condition described later.

  FIG. 9 is a timing chart illustrating the light amount of the illumination device 142, the gain of the camera 141, and the signal output from the camera 141 during autofocus of the image measurement device according to the present embodiment. FIG. 9 is basically the same as FIG. 8, but differs in that the light amount of the illumination device 142 is the maximum output during autofocus and the gain of the camera 141 is increased.

  In the image measurement device according to the present embodiment, the light amount of the illumination device 142 is increased during autofocusing. In such a case, the necessary light amount may exceed the maximum output of the illumination device 142. In this embodiment, the shortage of the light amount of the illumination device 142 is compensated by increasing the gain of the camera 141. According to such a configuration, even when the amount of light of the illumination device 142 is insufficient, it is possible to realize high-precision and high-speed autofocus with excellent operability.

  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 ... illumination device, 143 ... linear encoder, 144 ... camera drive mechanism, 145 ... Z-axis motor, 151 ... position control system, 152 ... illumination control device, 153 ... frame rate detector, 154: Standard frame rate holding unit.

Claims (5)

An imaging device with a variable frame rate for imaging a workpiece;
An illumination device for irradiating the workpiece with 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;
A control device that controls a frame rate of the imaging device when controlling the in-focus position by the position control system, and adjusts a light amount of the illumination device according to the frame rate of the imaging device. Image measuring device. The control device, when controlling the in-focus position of the imaging device,
Receiving a part of the imaging range of the imaging device;
Increasing the frame rate of the imaging device;
The image measurement device according to claim 1, wherein the light amount of the illumination device is increased. The image measurement device according to claim 1, wherein the control device adjusts a light amount of the illumination device according to a vertical synchronization signal output from the imaging device. The control device uses a first frame rate calculated from an interval of vertical synchronization signals output from the imaging device when controlling a focusing position of the imaging device, and a second frame rate used during normal measurement. The image measuring device according to claim 3, wherein the light amount of the illumination device is adjusted accordingly. The image measuring device according to claim 1, wherein the control device adjusts a gain of the imaging device in accordance with a frame rate of the imaging device.

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