Image detector and method for detecting image

Abstract

To provide an image detector and a method for detecting an image which can reduce the focus return time when a focal position is displaced.SOLUTION: An image detector 1 includes: a focal point distance variable lens 8 in which a focal point distance is changed periodically by a periodic driving signal Cf; an illumination unit 5 for illuminating a measurement target object; an image detection unit 4 for detecting an image Im of the measurement target object through the focal point distance variable lens 8; a driving control unit 61 for outputting the driving signal Cf to the focal point distance variable lens 8; a light-emitting control unit 62 for outputting a light-emitting signal Ci in synchronization with the driving signal Cf to the illumination unit 5; a vibration sensor 65 for detecting vibration information Vd of the focal point distance variable lens 8; and a synchronization control unit 64 for adjusting the output timing of the light-emitting signal Ci on the basis of the vibration information Vd.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image detection device and an image detection method. [Background technology]

[0002] Image detection devices are used to detect images in a variety of fields. In image detection devices, an image sensor such as a camera is used to detect images, and an optical system including a lens and a focus adjustment mechanism is installed between the image sensor and the workpiece. An automatic focus adjustment mechanism is used as the focus adjustment mechanism. Image detection devices are also used for in-line inspection, where images of workpieces are taken during the production line. In-line inspection involves taking images of the workpieces held on the table of the processing device and judging defects in the detected images. Image detection devices for in-line inspection are inevitably affected by vibrations from surrounding manufacturing equipment. The effects of vibrations are more noticeable on the optical system that images the workpiece than on the workpiece held on the table, and vibrations can cause the optical system to lose focus on the workpiece. For this reason, an automatic focus adjustment mechanism has been developed that can efficiently restore the in-focus state even if the in-focus state is shifted due to vibration or the like (see Patent Document 1).

[0003] On the other hand, optical elements used in image detection devices include a high-speed variable focal length lens (VFL) called a variable acoustic gradient index lens (TAG lens) or a resonant liquid lens (see Patent Document 2). The TAG lens vibrates a piezoelectric element inside a container with a high-frequency drive signal of up to several hundred KHz, causing the internal fluid to resonate and form concentric standing waves with different refractive indices, allowing it to function as a high-speed VFL lens and capable of periodically changing the focal length at high speed according to the resonant frequency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-90982 A [Patent Document 2] JP 2019-49543 A Summary of the Invention [Problem to be solved by the invention]

[0005] The automatic focus adjustment mechanism described in Patent Document 1 and the like can prevent focus deviation caused by vibration during in-line inspection. However, when the optical system of the image detection device is a mechanical optical system that uses the movement of lens elements in the optical axis direction for focus adjustment, the lens elements need time to move before returning to the in-focus state, and during that time a blurred image in a defocused state is detected. Even in cases where the lens elements do not need to move in the optical axis direction for focus adjustment, such as in the TAG lens, a time lag occurs in the process of detecting the shift in the focus state or readjusting the focus state, and the detection of a blurred image in a defocused state during that time is unavoidable. If such a blurred image is detected, it may cause a degradation of image quality, for example, when detecting a multi-plane image or an extended depth of focus (EDOF) image.Therefore, there has been a demand for a method to reduce the focus recovery time when the focus position shifts, thereby making it possible to avoid the detection of a blurred image.

[0006] An object of the present invention is to provide an image detection device and an image detection method capable of reducing the time required for returning to focus when the focal position is shifted. [Means for solving the problem]

[0007] The image detection device of the present invention comprises a variable focal length lens whose focal length changes periodically in response to a periodic drive signal, an illumination unit which illuminates an object to be measured, an image detection unit which detects an image of the object to be measured through the variable focal length lens, a drive control unit which outputs the drive signal to the variable focal length lens, an emission control unit which outputs an emission signal synchronized with the drive signal to the illumination unit, a vibration sensor which detects vibration information of the variable focal length lens, and a synchronization control unit which adjusts the output timing of the emission signal based on the vibration information.

[0008] In the present invention, an image of the object illuminated by the illumination unit is detected by the image detection unit through the variable focal length lens. The light emission control unit adjusts the synchronous phase of the light emission signal synchronized with the drive signal to adjust the focal length of the variable focal length lens, thereby making it possible to bring the detected image into focus at a predetermined focal length. When the focal length of the variable focal length lens fluctuates due to external vibrations or the like, the vibration information is detected by the vibration sensor, and the synchronization control unit adjusts the output timing of the light emission signal based on the vibration information, thereby compensating for the focal length fluctuation in the variable focal length lens and restoring the in-focus state. Compensation of the focal length based on the vibration information can be performed by, for example, arithmetic processing using a function or the like. For example, a displacement of the vibration can be detected based on the vibration information, a corresponding time difference can be calculated, and a process of shifting this time difference light emission signal can be performed. In the present invention, in order to recover the focus state, it is not necessary to repeat the feedback of the focus determination of the detected image Im as in the existing automatic focus adjustment mechanism, and it is also not necessary to perform a mechanical focus adjustment operation, so that the processing time until recovery of the focus can be significantly reduced. As a result, it is possible to avoid inconveniences caused by the detection of a blurred image when the focus state is shifted.

[0009] In the image detection device of the present invention, it is preferable that the vibration sensor is an acceleration sensor attached to a housing of the variable focal length lens, and the synchronization control unit is a pulse delay module that delays a pulse of the light emission signal. In the present invention, the synchronization control unit calculates the amount of displacement due to vibration from the acceleration detected by the acceleration sensor, and delays the light emission signal by a time difference corresponding to this amount of displacement, thereby moving the focal length of the variable focal length lens and restoring the in-focus state. In the present invention, the pulse delay module and acceleration sensor can be existing ones. Therefore, the device configuration can be simplified. Here, the pulse delay module is preferably capable of sending pulses of, for example, tens to hundreds of nanoseconds in order to obtain high speeds that can be synchronized with the resonance frequency of the TAG lens or VFL described above. The vibration sensor may detect the relative displacement between the workpiece and an optical system including a variable focal length lens, and detect vibrations from the change in the relative displacement over time.

[0010] The image detection method of the present invention uses an image detection device having a variable focal length lens whose focal length changes periodically in response to a periodic drive signal, an illumination unit which illuminates an object to be measured, an image detection unit which detects an image of the object to be measured through the variable focal length lens, a drive control unit which outputs the drive signal to the variable focal length lens, and an emission control unit which outputs an emission signal synchronized with the drive signal to the illumination unit, and detects an image of the object to be measured by adjusting the emission signal so that the image detected by the image detection unit is in focus, and detects vibration of the variable focal length lens to convert it into vibration information, and adjusts the output timing of the emission signal based on the obtained vibration information. According to the image detection method of the present invention, it is possible to obtain the effects as explained in the image detection apparatus of the present invention. Effect of the Invention

[0011] An object of the present invention is to provide an image detection device and an image detection method that can reduce the time required for returning to focus when the focus position is shifted. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing an image detection device according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a block diagram showing a control system according to the embodiment. [Diagram 3] 6 is a graph showing image detection in a single plane mode according to the embodiment. [Figure 4] 6 is a graph showing image detection in multiplane mode according to the embodiment. [Diagram 5] 5 is a graph showing a synchronous operation of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Image detection device 1] In FIG. 1, an image detection device 1 detects an image of the surface of a measurement object 9 while varying the focal length. For this purpose, the image detection device 1 is equipped with an objective lens 2 and a liquid lens unit 3 arranged on the same optical axis A that intersects the surface, an image detection unit 4 that detects an image of the object to be measured 9 obtained through the objective lens 2 and the liquid lens unit 3, an illumination unit 5 that illuminates the surface of the object to be measured 9, a lens control unit 6 that controls the operation of the liquid lens unit 3 and the illumination unit 5, and a control PC 7 for operating the lens control unit 6. In the image detection device 1, the objective lens 2 and the liquid lens unit 3 form a variable focal length lens 8.

[0014] The objective lens 2 is composed of a conventional convex lens. The liquid lens unit 3 is a high-speed variable focal length lens (VFL) that uses a type known as a variable acoustic gradient index lens (TAG lens) or a resonance liquid lens, and its refractive index changes periodically in response to a drive signal Cf input from the lens control unit 6. The drive signal Cf is an AC signal having a frequency that generates a standing wave in the liquid lens unit 3, and is, for example, a sine wave AC signal of 70 KHz. In the image detection device 1, the focal length Df of the variable focal length lens 8 to the focal position Pf is based on the focal length of the objective lens 2 and is modulated according to the refractive index of the liquid lens unit 3. As a result, the focal length Df of the variable focal length lens 8 fluctuates according to a sinusoidal focus fluctuation waveform Mf synchronized with the drive signal Cf.

[0015] The image detection unit 4 is composed of an existing CCD (Charge Coupled Device) image sensor or a camera of another type, and can output the incident image Lg to the control PC 7 as a detected image Im in a predetermined signal format. The illumination unit 5 is composed of light-emitting elements such as LEDs (Light Emitting Diodes), and by irradiating the illumination light Li onto the object to be measured 9, the reflected light Lr reflected from the surface of the object to be measured 9 forms an image Lg through the objective lens 2 and the liquid lens unit 3, and is detected as a detection image Im by the image detection unit 4. The illumination unit 5 emits light for a predetermined short time when an emission signal Ci is input from the outside, thereby performing pulsed illumination. Therefore, the detected image Im detected by the image detection unit 4 is an image of the measurement object 9 at the time of pulsed illumination.

[0016] The lens control unit 6 controls the driving of the liquid lens unit 3, the light emission of the illumination unit 5, and the image detection of the image detection unit 4. For this purpose, the lens control unit 6 outputs a drive signal Cf to the liquid lens unit 3, outputs a light emission signal Ci to the illumination unit 5, and outputs an image detection signal Cc to the image detection unit 4. On the other hand, the lens control unit 6 receives back the effective power or drive current applied to the liquid lens unit 3 as the vibration state Vf of the liquid lens unit 3.

[0017] In Figure 2, the lens control unit 6 has a drive control unit 61 that outputs a drive signal Cf to the liquid lens unit 3, an emission control unit 62 that outputs an emission signal Ci to the illumination unit 5, and an image detection control unit 63 that outputs an image detection signal Cc to the image detection unit 4. The drive control unit 61 outputs a drive signal Cf to the liquid lens unit 3 to generate a resonant state of the liquid lens unit 3, and also inspects the vibration state Vf of the liquid lens unit 3 to control the drive signal Cf so that the liquid lens unit 3 is in the desired resonant state. The image detection control unit 63 outputs an image detection signal Cc to the image detection unit 4 to control image detection. The light emission control unit 62 outputs a light emission signal Ci to the illumination unit 5 to control the illumination state of the measurement object 9, thereby making it possible to select the image format of the detection image Im detected by the image detection unit 4.

[0018] In the light emission control unit 62, the light emission signal Ci from the light emission control unit 62 is output as a pulse at an arbitrary phase in the focus fluctuation waveform Mf of the focal length Df, so that the measurement object 9 is pulse-illuminated by the illumination unit 5, and an image at the arbitrary phase is detected by the image detection unit 4. As a result, the image detection unit 4 obtains a detection image Im focused on the focal position Pf at the time of light emission. For example, in the focus fluctuation waveform Mf of the focal length Df, if an image is detected at one point in one period, the in-focus plane will be a single-plane mode image, and if images are detected at multiple points, the in-focus plane will be a multi-plane mode image. Furthermore, by combining these image formats, frame-by-frame mode, combined mode, etc. can be selected.

[0019] In FIG. 3, in the single plane mode, an image detection loop LPs including only a single plane image detection operation Cms is repeatedly executed. As described above, in the image detection device 1, the focus fluctuation waveform Mf of the focal length Df of the focal length variable lens 8 fluctuates sinusoidally in synchronization with the drive signal Cf. Therefore, when the drive signal Cf input from the lens control unit 6 to the liquid lens unit 3 is at a maximum value, the focus fluctuation waveform Mf also becomes a maximum value, and the focal length Df of the liquid lens unit 3 and the objective lens 2 becomes the focal length Dt that is closest to the objective lens 2, and similarly, when the drive signal Cf and the focus fluctuation waveform Mf are at a minimum value, the focal length Df becomes the farthest focal length Db. In the image detection loop LPs in single plane mode, during one cycle of the drive signal Cf, an emission signal Ci is sent from the lens control unit 6 to the illumination unit 5 at a phase θ1 position corresponding to the specified focal length D1, and the image detection unit 4 obtains a single plane detection image focused at the focal length D1.

[0020] In FIG. 4, in the multi-plane mode, the lens control unit 6 is caused to repeatedly execute an image detection loop LPm including only a multi-plane image detection operation Cmm. In the image detection loop LPm in multi-plane mode, when the number of focal points np = 2, two focal lengths D1, D2 are specified in one period of the drive signal Cf, and an emission signal Ci is sent from the lens control unit 6 at the corresponding phase positions θ1, θ2, respectively, and a multi-plane detection image Imm focused at the focal lengths D1, D2 is obtained.

[0021] Returning to FIG. 2, a control PC 7 is connected to operate image detection conditions such as the settings of the lens control unit 6. The control PC 7 has a lens operation unit 71 that performs operations on the lens control unit 6 such as setting image detection conditions, an image processing unit 72 that imports and processes the detected image Im from the image detection unit 4, and an operation interface 73 that accepts user operations on the image detection device 1. The control PC 7 is configured by an existing personal computer, and achieves the desired functions by executing predetermined control software.

[0022] In this embodiment, the lens control unit 6 is provided with a synchronization control unit 64 based on the present invention, and the liquid lens unit 3 is provided with a vibration sensor 65 . The vibration sensor 65 is configured by, for example, an existing acceleration sensor, and is capable of detecting acceleration as the vibration information Vd. The vibration sensor 65 is attached to the container of the liquid lens unit 3. The vibration sensor 65 may be attached to any portion of the optical system from the variable focal length lens 8 to the image detection unit 4.

[0023] The synchronization control unit 64 calculates the amount of displacement due to vibration from the vibration information Vd obtained by the vibration sensor 65, and adjusts the output timing of the light emission signal Ci output from the light emission control unit 62 so as to eliminate this displacement at the focal length Df of the focal length variable lens 8. Specifically, the vibration spectrum is analyzed by performing an FFT (Fast Fourier Transform) on the vibration information Vd from the vibration sensor 65, and the main vibration frequency and phase are detected. By adding the optical magnification and the vibration amplitude and vibration phase of the variable focal length lens 8 to the obtained vibration frequency and phase, the delay time with respect to the output timing of the light emission signal Ci can be calculated. Once the delay time is obtained, the light emission signal Ci is delayed by that amount to move the focal length Df of the variable focal length lens 8 and restore the in-focus state. The calculation of the amount of displacement from the vibration information Vd and the calculation of the adjustment amount of the output timing of the light emission signal Ci according to the amount of displacement can be set as functions, and the calculation can be made to be able to refer to a data table of values ​​that have been appropriately adjusted in advance through testing.

[0024] 5, if vibration information Vd is detected at point P11 on the focus fluctuation waveform Mf and the calculated displacement amount is dD1, the focal length Df of the variable focal length lens 8 has shifted from the focal position D11 at point P11 on the focus fluctuation waveform Mf to a focal position D12. Therefore, by delaying the output timing of the light emission signal Ci by a time difference dT1 corresponding to the displacement amount dD1, the point P11 on the focus fluctuation waveform Mf can be displaced to point P12, and the focal length Df of the variable focal length lens 8 can be restored to the focal position D12.

[0025] A similar process can be carried out when the displacement is in the opposite direction. If vibration information Vd is detected at point P21 on the focus fluctuation waveform Mf and the calculated displacement amount is dD2, the focal length Df of the variable focal length lens 8 has shifted from the focal position D21 at point P21 on the focus fluctuation waveform Mf to focal position D22. However, it is not possible to delay to point P22A, which is the closest point to focal position D22. Therefore, by selecting point P22 corresponding to the displacement amount dD2 after one period of the focus fluctuation waveform Mf and delaying the output timing of the light emission signal Ci by the time difference dT2 up to that point, point P21 on the focus fluctuation waveform Mf is displaced to point P22, and the focal length Df of the variable focal length lens 8 can be restored to the focal position D22.

[0026] In the present embodiment described above, the following effects can be obtained. In this embodiment, an image of a measurement object 9 illuminated by an illumination unit 5 is detected by an image detection unit 4 through a variable focal length lens 8 (objective lens 2 and liquid lens unit 3). An emission control unit 62 (see FIG. 2) adjusts the synchronous phase of an emission signal Ci synchronized with a drive signal Cf to adjust a focal length Df of the variable focal length lens 8, thereby enabling a detected image Im to be in focus at a predetermined focal length Df. When the focal length Df of the variable focal length lens 8 fluctuates due to external vibrations or the like, vibration information Vd is detected by the vibration sensor 65 (see Figure 2), and the synchronization control unit 64 adjusts the output timing of the light emission signal Ci based on the vibration information, thereby compensating for the fluctuation in the focal length Df of the variable focal length lens 8 and restoring the in-focus state. Therefore, when recovering the focus state, it is not necessary to repeat the feedback of the focus determination of the detected image Im as in the existing automatic focus adjustment mechanism, and since there is no need for mechanical focus adjustment, the processing time until recovery of the focus can be significantly reduced. As a result, it is possible to avoid inconveniences caused by detection of a blurred image when the focus state is shifted.

[0027] In this embodiment, the synchronization control unit 64 calculates the displacement amounts dD1, dD2 (see Figure 5) due to vibration from the acceleration detected by the vibration sensor 65, and delays the light emission signal by the time differences dT1, dT2 corresponding to these displacement amounts dD1, dD2, thereby moving the focal length Df of the focal length variable lens 8 (objective lens 2 and liquid lens unit 3) and restoring the in-focus state. In this embodiment, a low-pass filter is used as the pulse delay module in the synchronization control unit 64, and an existing acceleration sensor is used as the vibration sensor, which allows the device configuration to be simplified and the cost to be reduced.

[0028] The present invention is not limited to the above-described embodiment, and modifications within the scope of the present invention are included in the present invention. In the above embodiment, an acceleration sensor is used as the vibration sensor 65. However, the vibration sensor 65 is not limited to an acceleration sensor, and other types of sensors capable of measuring the state of vibration propagated from the outside to the variable focal length lens 8 or image detection unit 4, which is the optical system of the image detection device 1, may be used. Furthermore, the vibration sensor 65 may detect the relative displacement between the optical system including the variable focal length lens 8 (the objective lens 2 and the liquid lens unit 3) and the measurement object 9, and detect vibration information Vd from the change over time.

[0029] In the embodiment, the synchronization control unit 64 calculates the time differences dT1 and dT2 corresponding to the displacement amounts dD1 and dD2 detected from the vibration information Vd, and performs processing to shift the light emission signal Ci by the time difference. However, other methods may be used, such as obtaining the period and amplitude from the vibration information Vd and reading out the adjustment amount of the light emission signal Ci under the corresponding conditions from a data table. [Industrial Applicability]

[0030] The present invention can be used in an image detection device and an image detection method. [Explanation of symbols]

[0031] 1...image detection device, 2...objective lens, 3...liquid lens unit, 4...image detection unit, 5...illumination unit, 6...lens control unit, 7...control PC, 8...variable focal length lens, 9...measurement object, 61...drive control unit, 62...light emission control unit, 63...image detection control unit, 64...synchronization control unit, 65...vibration sensor, 71...lens operation unit, 72...image processing unit, 73...operation interface, A...optical axis, Cc...image detection signal, Cf...drive signal, Ci...light emission signal, Cmm...multiplane image Detection operation, Cms...single-plane image detection operation, D1, D2, Db, Df, Dt...focal length, D11, D12, D21, D22...focal position, Im...detected image, Imm...multi-plane detected image, LPm...image detection loop, LPs...image detection loop, Lg...image, Li...illumination light, Lr...reflected light, Mf...focus fluctuation waveform, Pf...focus position, Vd...vibration information, Vf...vibration state, dD1, dD2...displacement amount, dT1, dT2...time difference, np...number of foci, θ1...phase.

Claims

1. a variable focal length lens whose focal length changes periodically in response to a periodic drive signal; An illumination unit that illuminates the measurement object; an image detection unit that detects an image of the measurement object through the variable focal length lens; a drive control unit that outputs the drive signal to the variable focal length lens; a light emission control unit that outputs a light emission signal synchronized with the drive signal to the illumination unit; a vibration sensor for detecting vibration information of the variable focal length lens; and a synchronization control unit that adjusts the output timing of the light emission signal based on the vibration information.

2. 2. The image detection device according to claim 1, the vibration sensor is an acceleration sensor attached to a housing of the variable focal length lens, The synchronization control unit is a pulse delay module that delays a pulse of the light emission signal.

3. a variable focal length lens whose focal length changes periodically in response to a periodic drive signal; An illumination unit that illuminates the measurement object; an image detection unit that detects an image of the measurement object through the variable focal length lens; a drive control unit that outputs the drive signal to the variable focal length lens; a light emission control unit that outputs a light emission signal synchronized with the drive signal to the illumination unit, Detecting an image of the measurement object by adjusting the light emission signal so that the image detected by the image detection unit is in focus; An image detection method in which vibration of the variable focal length lens is detected to obtain vibration information, and output timing of the light emission signal is adjusted based on the obtained vibration information.

Images