Non-contact surface texture evaluation device

Abstract

An easy-to-use, compact, and relatively inexpensive non-contact surface property evaluation device is provided. The surface property evaluation device includes: a photodetector (240) for receiving and detecting scattered light from a target object; and a single optical aperture (250) or an array of optical apertures (250) arranged to face a light-receiving surface (242) of the photodetector (240). The relative positions of the optical apertures (250) and the photodetector (240) are fixed such that the gap between the optical apertures (250) and the light-receiving surface (242) of the photodetector (240) is constant. The surface properties of the target object are evaluated based on the intensity distribution of the light detected by the photodetector (240).

Description

Technical Field

[0001] This invention relates to a non-contact surface texture evaluation device, and more particularly to a non-contact surface roughness evaluation device. Background Technology

[0002] It is known that there exists a non-contact surface roughness measuring machine that measures the surface texture of an object by illuminating its surface with light and detecting the scattered light.

[0003] Patent documents

[0004] Patent Document 1: JP 2006-58224 A Summary of the Invention

[0005] Technical issues

[0006] Traditional non-contact surface roughness measuring machines use imaging sensors to receive scattered light at its maximum angle and evaluate the workpiece's surface roughness based on the imaging position (coordinates) of the scattered light at that maximum angle. In this process, even with the same scattering angle, the imaging position of the scattered light will vary depending on the distance (air gap) between the sensor and the workpiece. Therefore, the distance between the sensor and the workpiece must be precisely adjusted.

[0007] However, in the preparation stage before measurement, it is difficult to make strict positional adjustments between the sensor and the workpiece, which is costly and time-consuming. In addition, the accuracy of roughness measurement is affected by the setup precision (or skill), which is also a problem.

[0008] Furthermore, while it's necessary to ensure the imaging sensor receives scattered light at its maximum angle, it's also crucial to block unwanted light. Achieving this requires optimizing the size and shape of the aperture stop, necessitating the preparation and testing of several different aperture stop patterns. This is extremely labor-intensive.

[0009] It is necessary to form an image of the scattered light on the imaging sensor, which requires multiple high-performance lenses, such as objective lenses and imaging lenses. Procuring multiple high-performance lenses and assembling them with high precision is both time-consuming and expensive. Furthermore, due to the increased number of parts, traditional non-contact surface roughness measuring machines inevitably become bulky. Therefore, traditional non-contact surface roughness measuring machines are large and expensive.

[0010] The purpose of this invention is to provide an easy-to-use, compact, and relatively inexpensive non-contact surface texture evaluation device.

[0011] Solution to the problem

[0012] A non-contact surface texture evaluation device according to an embodiment of the present invention includes:

[0013] A photodetector that receives and detects scattered light from the object under test; and

[0014] Single or arrayed optical apertures are arranged to face the illuminated surface of the photodetector, wherein

[0015] The position of the optical aperture relative to the photodetector is fixed such that the gap between the optical aperture and the illuminated surface of the photodetector remains constant.

[0016] In one embodiment of the present invention, preferably, the optical aperture is a lens portion or a light-transmitting portion surrounded by a light-nontransmitting portion.

[0017] In one embodiment of the invention, preferably, a first substrate incorporating the photodetector and a second substrate incorporating the optical aperture are fixed to face each other with a gap, so as to keep the gap between the optical aperture and the irradiated surface of the photodetector constant.

[0018] In one embodiment of the invention, preferably, the first substrate incorporating the photodetector and the second substrate incorporating the optical aperture are attached to each other via a spacer member to maintain a constant gap between the optical aperture and the irradiated surface of the photodetector.

[0019] In one embodiment of the present invention, preferably, the non-contact surface texture evaluation device evaluates the surface texture of the object under test based on the intensity distribution of light detected by the photodetector.

[0020] In one embodiment of the invention, preferably, the non-contact surface texture evaluation device performs frequency decomposition to determine the amplitude of each frequency component of the intensity distribution of light detected by the photodetector, and evaluates the surface texture of the object under test based on the magnitude of the obtained amplitude.

[0021] In one embodiment of the present invention, preferably, the non-contact surface texture evaluation device evaluates the surface texture of the object under test based on the difference between the light intensity peak IP and the light intensity valley IB in the light image detected by the photodetector.

[0022] In one embodiment of the present invention, preferably, the non-contact surface texture evaluation device is configured to evaluate the surface texture of the object under test based on a normalized value obtained by dividing the difference between the light intensity peak IP and the light intensity valley IB in the light image detected by the photodetector by the overall average intensity.

[0023] In one embodiment of the present invention, preferably, the non-contact surface texture evaluation device further includes a parallel light illumination unit configured to illuminate the object to be tested with parallel light.

[0024] In one embodiment of the invention, preferably, the non-contact surface texture evaluation device is configured to evaluate the surface texture of the object under test based on the magnitude of an evaluation value obtained from a detection signal with a predetermined phase difference detected by the photodetector.

[0025] In one embodiment of the invention, preferably, the photodetector includes an array of light receiving elements arranged to correspond to the intensity distribution of light formed through the optical aperture and on the irradiated surface of the photodetector.

[0026] In one embodiment of the invention, preferably, the non-contact surface texture evaluation device is configured to evaluate the surface texture of the object under test based on the magnitude of an evaluation value related to the diameter of a Lissajous circle obtained from a phase signal from the light receiving element array. Attached Figure Description

[0027] Figure 1 This is a diagram illustrating the configuration of a surface texture measuring device according to a first exemplary embodiment of the present invention.

[0028] Figure 2 This is a diagram showing an example of a light receiving unit.

[0029] Figure 3 This is a diagram showing an example of a light receiving unit.

[0030] Figure 4 This is a diagram illustrating an example of an aperture functional unit including apertures arranged in a two-dimensional array.

[0031] Figure 5 This is a diagram showing an example of an image obtained by a light detector.

[0032] Figure 6 This is a diagram showing an example of light intensity distribution.

[0033] Figure 7 This is a diagram showing an example of light intensity distribution.

[0034] Figure 8 This is a graph illustrating an example of the relationship between roughness and evaluation index values.

[0035] Figure 9 This diagram schematically illustrates a situation where the distance between the object being measured and the sensor head is relatively narrow.

[0036] Figure 10This diagram schematically illustrates a situation where the distance between the object being measured and the sensor head is relatively wide.

[0037] Figure 11 This is a diagram showing an example configuration of the light illumination unit excluding the collimating lens.

[0038] Figure 12 This is a schematic diagram illustrating the scattered light when measuring the roughness of an object under test with a relatively wide distance between the object and the sensor head.

[0039] Figure 13 This is a graph showing the light intensity distribution of an image when measuring a mirror with a wide air gap.

[0040] Figure 14 This is a graph showing the light intensity distribution of an image when measuring a rough surface under a wide air gap.

[0041] Figure 15 This is a schematic diagram illustrating the scattered light when measuring the roughness of an object under test when the distance between the object and the sensor head is relatively narrow.

[0042] Figure 16 This is a graph showing the light intensity distribution of an image when measuring a mirror surface under narrow air gap conditions.

[0043] Figure 17 This is a graph showing the light intensity distribution of an image when measuring a rough surface in a narrow air gap.

[0044] Figure 18 This is a graph showing the Fourier transform results of the light intensity distribution on a mirrored surface and a rough surface.

[0045] Figure 19 This is a diagram illustrating an example of the irradiated surface of a photodetector according to a second exemplary embodiment.

[0046] Figure 20 This is a diagram showing an example of computing circuitry incorporated into a data processing unit. Detailed Implementation

[0047] Embodiments of the invention are illustrated and described with reference to the reference numerals assigned to elements in the accompanying drawings.

[0048] Note that each embodiment may be implemented independently, or two or more embodiments may be implemented in combination, and the variations added in each embodiment are applicable to other embodiments.

[0049] (First exemplary embodiment)

[0050] A first exemplary embodiment of the present invention will now be described.

[0051] Figure 1This is a diagram illustrating the configuration of a surface texture measuring device according to a first exemplary embodiment of the present invention.

[0052] The surface texture measuring device 100 includes a stage 110, a light irradiation unit 220, a light receiving unit 230, and a data processing unit 300.

[0053] Note that the light irradiation unit 220 and the light receiving unit 230 can be integrated into a single unit and referred to as a non-contact surface texture sensor head (or non-contact surface texture probe) 200.

[0054] The stage 110 is a stage for mounting the object W to be measured.

[0055] The light illumination unit 220 illuminates the surface of the object W to be measured with light. The light illumination unit 220 includes a light source 221 and a collimating lens 222. The light source 221 can be a white LED. It can also be a laser light source, but coherent light is not necessary.

[0056] The light receiving unit 230 receives scattered light from the surface of the object to be measured W (the surface whose roughness is to be measured).

[0057] The optical receiving unit 230 includes a photodetector 240 and an aperture function unit 250.

[0058] Figure 2 An example of the optical receiving unit 230 is shown.

[0059] The photodetector 240 (image sensor in this specification) includes an imaging element 243 on the illuminated surface 242 of the first substrate 241. The imaging element 243 is a CCD, CMOS, or the like.

[0060] In this specification, the aperture functional unit 250 is a multi-slit structure. That is, multiple apertures (slits) 252 are arranged along a predetermined direction. The aperture functional unit 250 is formed by electroplating a light-insensitive material onto one surface of a glass substrate (second substrate) 251, leaving the apertures (slits) 252 exposed. (The glass can be inorganic or organic. The electroplating can be metallic, such as black chrome plating.)

[0061] The photodetector 240 and the aperture functional unit 250 are fixedly attached such that the distance (gap) between the slit (optical aperture) 252 and the illuminated surface 242 of the photodetector 240 remains constant. The distance (gap) between the slit (optical aperture) 252 and the illuminated surface 242 of the photodetector 240 is, for example, from tens of micrometers to several millimeters. On the illuminated surface side of the photodetector 240, a plurality of protrusions (bumps) 244 of a specified height are provided around the imaging element 243. These protrusions 244 define the gap (space), and the photodetector 240 and the aperture functional unit 250 are stacked and fixed together via these protrusions 244. These protrusions 244 serve as spacer members to maintain a constant gap.

[0062] Or, such as Figure 3 As shown, when the optical aperture (slit) 252 is formed on the surface of the glass substrate (second substrate) 251 away from the irradiated surface 242 of the photodetector 240, the glass substrate 251 and the photodetector 240 can be directly stacked. In this case, the thickness of the glass substrate (second substrate) 251 itself serves as a spacer member.

[0063] Alternatively, the gap can be adjusted by inserting transparent resin between the first substrate 241 and the second substrate 251. The gap between the photodetector 240 and the aperture functional unit 250 can be adjusted using protrusions (bumps), the thickness of the photodetector itself, and one or a combination of resins.

[0064] The method of forming a distance (gap) between the slit (optical aperture) 252 and the illuminated surface 242 of the photodetector 240 by inserting a spacer member between the first substrate 241 and the second substrate 251 is merely an example. The distance (gap) between the slit (optical aperture) 252 and the illuminated surface 242 of the photodetector 240 can be maintained by fixing the first substrate 241 and the second substrate 251 so that there is a gap between them, without inserting a spacer member between the first substrate 241 and the second substrate 251. For example, the first substrate 241 and the second substrate 251 can be fixedly arranged by forming a gap in the housing of the sensor head or the housing of the light receiving unit 230.

[0065] Note that, as aperture functional unit 250, a light-nontransmissive thin plate (e.g., a black resin plate) with a slit aperture can be used, for example. Alternatively, aperture functional unit 250 can be a lens array (microlens array) in which the optical aperture is a lens. The lens can be, for example, a spherical lens or a cylindrical lens. In addition to serving as an aperture stop for transmitting scattered light from the surface of the object W under test, the focusing function of the lens increases the light intensity, thereby producing a clearer image with enhanced contrast.

[0066] The aperture 252 of the aperture functional unit 250 can be arranged in a two-dimensional array.

[0067] Figure 4 This is a diagram illustrating an example of an aperture functional unit 250 including apertures 252 arranged in a two-dimensional array.

[0068] If the aperture 252 is arranged in a two-dimensional array, the roughness of the surface of the object under test can be evaluated in two directions simultaneously.

[0069] The shape of the aperture is not limited to rectangle; it can also be circular or elliptical.

[0070] Furthermore, the aperture can be configured to clearly distinguish the boundary between the light-transmitting portion and the light-nontransmitting portion, or to allow the light-transmitting portion to gradually and continuously (or stepwise) change into the light-nontransmitting portion.

[0071] When the light irradiation unit 220 irradiates the object W under test, the reflected light enters the light receiving unit 230 and is received. Specifically, in the reflected light, the light that has passed through the aperture 252 of the aperture functional unit 250 reaches the irradiated surface 242 of the photodetector 240 and is received by the imaging element 243. The photodetector 240 transmits the detection signal to the data processing unit 300 for analysis.

[0072] If the surface of the object W to be measured is almost mirror-like, then the first reflected light is strongly specularly reflected light (specular reflection), and the light that has passed through aperture 252 is imaged as clear, bright lines corresponding to the multiple slits of aperture functional unit 250, such as... Figure 5 As shown in A. If the surface of the object W to be measured is a rough surface, the light scattered from the surface of the object W to be measured will be diffused and imaged as a slightly distorted or blurred image, such as... Figure 5 As shown in B in the diagram. For ease of explanation, Figure 5 The black and white colors in the image are reversed. Furthermore, Figure 5 B in the image is an example of an image acquired by the photodetector 240 (imaging element 243) when the light source 221 emits incoherent light (e.g., light from an LED), and is an example of a slightly blurred image. For example, if coherent light, such as laser light, is emitted from the light source 221, a slightly distorted image called speckle is obtained.

[0073] The data processing unit 300 evaluates the surface roughness of the object under test based on the captured light and dark pattern image.

[0074] By scanning Figure 5 The patterns shown in A and B are plotted, and the light intensity is obtained. Figure 6 and Figure 7 The light intensity distribution is shown. Clear, bright line patterns (such as...) Figure 5The light intensity distribution of A) in the image is likely to appear as a series of rectangles, with high maximum peaks and almost zero minimum valleys, such as... Figure 6 As shown. In images of objects with rough surfaces and significant light scattering (e.g., ...). Figure 5 In case B), the peak light intensity IP is correspondingly smaller. Therefore, surface texture (surface roughness) can be evaluated based on the magnitude of the peak light intensity IP.

[0075] The data processing unit 300 calculates the peak light intensity IP and the valley light intensity IB, and determines the difference between them ΔI = (IP - IB).

[0076] Surface roughness can be evaluated based on the difference between light and dark areas ΔI.

[0077] Here, the light intensity peak IP can be the peak value (maximum brightness value or pixel value) within the entire captured image (or a preset area range).

[0078] Alternatively, the light intensity peak IP can be determined by extracting individual bright lines from the captured image data, calculating the peak value of each bright line, and then calculating the average value IP of these peak values.

[0079] Similarly, the light intensity valley value IB can be determined by extracting the valley values ​​between bright lines from the captured image data, calculating the valley value for each valley, and then calculating the average of these valley values ​​IB.

[0080] Alternatively, normalized contrast can be used, which is obtained by dividing the contrast ΔI by the average value of the entire image data (or a preset area range).

[0081] Although the intensity of light incident on the light receiving unit may vary depending on the intensity of the light source, the lifespan of the light source, and the reflectivity of the workpiece, information related only to roughness can be extracted by using brightness difference or normalized brightness difference, without being affected by the light source or reflectivity.

[0082] The normalized denominator is not limited to the average light intensity of the entire imaging data (or a preset area range). For example, the sum of the extracted peak IP and valley IB values ​​can be used as the denominator.

[0083] For example, by representing the normalized difference in brightness as a relationship between the roughness evaluation index (IR) and the workpiece surface roughness (here, for example, the arithmetic mean roughness Ra), a model can be established as follows: Figure 8 The evaluation index (IR) shown tends to decrease as roughness (Ra) increases. Conversely, roughness (e.g., Ra) can be estimated from the evaluation index (IR) value. It is desirable to measure several sample workpieces with known roughness in advance using the method of the present invention, prepare them into a roughness evaluation table, and use the table as a reference for evaluating roughness.

[0084] The effects of this embodiment will be described.

[0085] According to this embodiment, even if the distance between the object to be measured W and the sensor head 200 changes, the roughness evaluation value IR will not change.

[0086] Figure 9 and Figure 10 Examples are shown where the distance (air gap) between the object under test W and the sensor head 200 varies.

[0087] Figure 9 This is a schematic diagram illustrating the scattered light when measuring the roughness of the object W under test when the distance (air gap) between the object W under test and the sensor head 200 is relatively narrow.

[0088] Figure 10 This is a schematic diagram illustrating the scattered light when measuring the roughness of the object W under test with a relatively wide distance (air gap) between the object W and the sensor head 200.

[0089] exist Figure 9 In this context, it is assumed that scattered light from incident points A1 and A2 on the workpiece, as the outermost rays, passes through the aperture (slit) 252 and reaches the photodetector 240. On the other hand, in... Figure 10 In the case of incident points A1 and A2 on the workpiece, scattered light is blocked by the aperture functional unit 250 and cannot reach the photodetector 240. However, instead, scattered light from incident points B1 and B2 at the same angle, different from A1 and A2, passes through the aperture (slit) 252 and reaches the photodetector 240 as the outermost ray. Here, in this embodiment, the gap between the aperture functional unit 250 and the photodetector 240 in the light receiving unit 230 is fixed and constant. Therefore, there is no difference in the amount of light passing through the aperture functional unit 250 to image on the imaging element, and there is no difference in the evaluation index value (IR) obtained with respect to brightness difference or normalized brightness difference. Therefore, the estimated surface roughness of the object under test is equivalent. This means that the accuracy of the workpiece setup does not affect the surface roughness evaluation value, which leads to high robustness.

[0090] Note that in this embodiment, because the light irradiation unit emits parallel light, therefore... Figure 9 and Figure 10 Between the cases shown, there is no difference in the light spread detected by the photodetector 240. Taking these factors into consideration, the light illumination unit is preferably a parallel light illumination unit that emits parallel light using a collimating lens or the like.

[0091] Although the above embodiments describe an example where the light illumination unit includes a collimating lens and emits parallel light, the effect of this embodiment can be maintained even without a collimating lens. Figure 11 In this configuration, the light irradiation unit 220 does not include a collimating lens and irradiates the workpiece with light at the same emission angle as the light source 221. Alternatively, a lens that converges or diverges light can be placed between the light source 221 and the workpiece W. In either case, if the light is reflected by a mirror (regularly), light that does not pass through the exact center will enter the light receiving unit 230 at an angle (rather than perpendicularly).

[0092] Figure 12 and Figure 15 Examples are shown where the distance (air gap) between the object under test W and the sensor head 200 varies.

[0093] Figure 12 This is a schematic diagram illustrating the scattered light when measuring the roughness of the object W under test with a relatively wide distance (air gap) between the object W and the sensor head 200.

[0094] Figure 15 This is a schematic diagram illustrating the scattered light when measuring the roughness of the object W under test when the distance (air gap) between the object W under test and the sensor head 200 is relatively narrow.

[0095] Figure 13 It shows in Figure 12 The light intensity distribution of the image when measuring the mirror surface under a wide air gap is shown.

[0096] Figure 14 It shows in Figure 12 The image shown depicts the light intensity distribution when measuring a rough surface under a wide air gap.

[0097] Figure 16 It shows in Figure 15 The light intensity distribution of the image when measuring the mirror surface under narrow air gap is shown.

[0098] Figure 17 It shows in Figure 15 The image shown depicts the light intensity distribution when measuring a rough surface under a narrow air gap.

[0099] When the light from the illumination unit (light source 221) is divergent, the period of the image of the slit 252 of the aperture functional unit 250 varies depending on the difference in the air gap between the sensor head 210 and the workpiece W. That is, as the air gap narrows, the period of the bright and dark image widens. However, if the period of the bright and dark image changes due to the difference in the air gap between the sensor head 210 and the workpiece W, the trend of the maximum and minimum values ​​of the light intensity distribution caused by the workpiece surface texture (e.g., roughness) remains unchanged. Therefore, by using the difference in brightness or normalized difference in brightness, information related only to roughness can be extracted.

[0100] (First variation)

[0101] A variation of data processing for evaluating the surface roughness of an object under test based on captured images of light and dark patterns.

[0102] In order to evaluate surface roughness from light intensity distribution, data processing unit 300 converts the spatial light intensity distribution to the frequency domain, decomposes it into frequency components, and calculates the amplitude of each frequency component.

[0103] This can be done using what is called the Fourier transform.

[0104] Figure 18 It is a graph showing the Fourier transform results of comparing the light intensity distribution (or captured images) of mirrored and rough surfaces.

[0105] Images obtained from a mirror are clear and project the shape of the aperture, while images obtained from a rough surface are distorted and blurry.

[0106] When a Fourier transform is applied to each image and the amplitudes of frequencies considered to be the most abundant are compared, differences in magnitude emerge. (The fundamental frequency considered to be the most abundant can, for example, be related to the pitch of the aperture (slit) 252.) In other words, the peak amplitudes differ when a Fourier transform is applied to each image.

[0107] The amplitude peak obtained by applying Fourier transform to the light intensity distribution (or captured image) from a mirror surface (a surface with low roughness) is large, while the amplitude peak obtained by applying Fourier transform to the light intensity distribution (or captured image) from a rough surface (a surface with high roughness) is small.

[0108] exist Figure 18 The comparison of the amplitudes of the frequency components after the bottom row Fourier transform shows a comparison of the fundamental frequency peaks. (Note that the leftmost peak is the DC component.)

[0109] Therefore, the amplitude peak (or peak-based value) obtained by applying a Fourier transform to the light intensity distribution (or captured image) can be used as an evaluation value for surface roughness.

[0110] Both the surface roughness assessment based on the brightness difference ΔI (the difference between the peak light intensity IP and the valley light intensity IB) described in the first exemplary embodiment and the Fourier transform method are common in evaluating the surface roughness of the object under test based on the magnitude of the light intensity when the photodetector 240 detects light that has passed through the aperture functional unit 250. However, depending on the surface texture of the object under test, fringe distortion may become significant, and simply attempting to obtain the difference between the peak light intensity IP and the valley light intensity IB, ΔI = (IP - IB), has limitations in terms of resolution and accuracy. In this regard, by performing a Fourier transform of frequency decomposition, extracting the amplitude at the desired (target) frequency, and using it as the roughness assessment value, resolution and accuracy can be improved.

[0111] Note that information from the peaks of frequency components above the fundamental frequency peak (or peak-based values) can be used to evaluate surface roughness instead of the fundamental frequency peak itself. Alternatively, in addition to using the fundamental frequency peak itself, surface roughness can also be evaluated by using information from the peaks of frequency components above the fundamental frequency peak (or peak-based values).

[0112] (Second exemplary embodiment)

[0113] A second exemplary embodiment of the present invention will now be described.

[0114] In a second exemplary embodiment, an array of light receiving elements 260 is provided, which is arranged on the irradiated surface 242 of the photodetector 240 to correspond to the light intensity distribution formed on the irradiated surface 242.

[0115] In a second exemplary embodiment, it is assumed that the light irradiation unit 220 emits parallel light.

[0116] Figure 19 This is a diagram illustrating an example of the illuminated surface 242 of the photodetector 240 in a second exemplary embodiment.

[0117] exist Figure 19 In this arrangement, on the illuminated surface 242 of the photodetector 240, light-receiving elements 261 are arranged according to the period (pitch) of the aperture (slit) 252 of the aperture functional unit 250. The illuminated surface 242 of the photodetector 240 is a so-called array of light-receiving elements 260. Here, the light-receiving elements 261 are arranged to detect light with a 90-degree phase difference relative to one period (one pitch) λ of the slit 252 of the aperture functional unit 250. (The phase difference pitch of the light-receiving elements can be 120 degrees or 45 degrees, as long as any value related to the diameter of the Lissajous circle can ultimately be calculated.)

[0118] Optical receiving element 261 is connected to output pads 262 to 265 in each phase group to extract the optical received signal for each phase. Here, there are first output pad 262, second output pad 263, third output pad 264 and fourth output pad 265, which correspond to 0°, 90°, 180° and 270° respectively.

[0119] The phase signal from the first output pad 262 is denoted as phase A, and the phase signal from the third output pad 264 is denoted as inverted phase A. Therefore, phase A and inverted phase A are in opposite phase. The phase signal from the second output pad 263 is denoted as phase B, and the phase signal from the fourth output pad 265 is denoted as inverted phase B. Therefore, phase B and inverted phase B are in opposite phase.

[0120] Figure 20 This is a diagram showing an example of a computing circuit incorporated into the data processing unit 300.

[0121] Since the positional relationship (phase) of the light signals received by the light receiving element 261 is always the same in response to the bright and dark areas formed by the slit 252 on the irradiated surface 242, a fixed processing step can be applied to each light received signal. For example, the same coefficient can be multiplied each time, or the same addition or subtraction can be performed.

[0122] Since the calculation is fixed, there is no need for complex image processing when it is incorporated into the calculation circuit, allowing the roughness evaluation index value to be obtained directly.

[0123] Here, after each phase signal is amplified by an operational amplifier (amplifier), an analog computing circuit is used to calculate the difference (differential signal) VA between phase A (Ia) and inverted A (Ia'), and the difference (differential signal) VB between phase B (Ib) and inverted B (Ib').

[0124] Simultaneously, the sum Vdc of all signals (Ia, Ia', Ib, and Ib') is calculated. Furthermore, the evaluation value calculation circuit 350 calculates the following evaluation value P.

[0125] P=2·((Va / 2) 2 +(Vb / 2) 2 ) (1 / 2) / Vdc

[0126] This molecule corresponds to the diameter of the so-called Lissajous circle, and the evaluation value P corresponds to the normalized brightness difference. As the surface roughness of the workpiece increases, the contrast of the stripes decreases, resulting in a smaller diameter of the Lissajous circle. When defined as an evaluation value P normalized by summation, this is used as an evaluation value related to surface texture (e.g., roughness). Therefore, an easy-to-use, compact, and relatively inexpensive non-contact surface texture evaluation device can be provided.

[0127] (Second variation)

[0128] The second exemplary embodiment describes an example in which a light-receiving element array 260 is arranged on the illuminated surface 242 of a photodetector 240. However, when calculating the diameter of a Lissajous circle, the photodetector is not limited to a light-receiving element array.

[0129] For example, if the light detector is an image sensor, and specific pixel regions are assigned to, for example, phase A, phase B, inverted A, and inverted B, then the light detection value (light intensity) for each phase can be obtained from the respective pixel regions. Based on these values, a value corresponding to the diameter of the Lissajous circle can be calculated.

[0130] Note that in the case of an image sensor, the detected values ​​are digital, so post-processing involves digital calculations. However, if an array of light-receiving elements is used, post-processing can be performed analogically, making it suitable for chip integration of analog computing circuitry and high-speed processing.

[0131] Note that the present invention is not limited to the above embodiments, and appropriate modifications can be made without departing from the spirit of the invention.

[0132] There are no particular restrictions on the width and spacing of the apertures in the aperture functional unit.

[0133] Even if the width or spacing of the aperture is very narrow, causing light to diffract or overlap with adjacent fringes, the surface roughness assessment of the present invention can still be performed.

[0134] Although the presence or absence of light diffraction or overlap may lead to differences in properties, in both cases, by measuring several sample workpieces with known roughness in advance, preparing them into a roughness evaluation table, and using this table as a reference for evaluating roughness, the surface roughness of the object under test can be evaluated by subsequent numerical settings (calibration).

[0135] Reference Symbol List

[0136] 110 Platform

[0137] 200 sensor heads

[0138] 220 light irradiation units

[0139] 221 Light Source

[0140] 222 Collimating Lens

[0141] 230 optical receiving unit

[0142] 240 photodetectors

[0143] 250 aperture functional unit

[0144] 241 First substrate

[0145] 242 Irradiated surface

[0146] 243 Imaging elements

[0147] 251 Glass substrate

[0148] 252 aperture

[0149] 300 Data Processing Units

Claims

1. A non-contact surface texture evaluation device, comprising: A photodetector configured to receive and detect scattered light from the object under test; as well as Single or arrayed optical apertures are arranged to face the illuminated surface of the photodetector, wherein The position of the optical aperture relative to the photodetector is fixed such that the gap between the optical aperture and the illuminated surface of the photodetector remains constant.

2. The non-contact surface texture evaluation device according to claim 1, wherein... The optical aperture is either a lens portion or a light-transmitting portion surrounded by a light-nontransmitting portion.

3. The non-contact surface texture evaluation device according to claim 1, wherein... A first substrate incorporating the photodetector and a second substrate incorporating the optical aperture are fixed facing each other with a gap to keep the gap between the optical aperture and the irradiated surface of the photodetector constant.

4. The non-contact surface texture evaluation device according to claim 3, wherein... The first substrate incorporating the photodetector and the second substrate incorporating the optical aperture are attached to each other via spacer members to maintain a constant gap between the optical aperture and the irradiated surface of the photodetector.

5. The non-contact surface texture evaluation device according to claim 1, wherein the non-contact surface texture evaluation device is configured to evaluate the surface texture of the object under test based on the intensity distribution of light detected by the photodetector.

6. The non-contact surface texture evaluation apparatus of claim 1, wherein the non-contact surface texture evaluation apparatus is configured to perform frequency decomposition to determine the amplitude of each frequency component of the intensity distribution of light detected by the photodetector, and to evaluate the surface texture of the object under test based on the magnitude of the obtained amplitude.

7. The non-contact surface texture evaluation device according to claim 1, wherein the non-contact surface texture evaluation device is configured to evaluate the surface texture of the object under test based on the difference between the light intensity peak IP and the light intensity valley IB in the light image detected by the photodetector.

8. The non-contact surface texture evaluation device according to claim 1, wherein the non-contact surface texture evaluation device is configured to evaluate the surface texture of the object under test based on a normalized value obtained by dividing the difference between the light intensity peak IP and the light intensity valley IB in the light image detected by the photodetector by the overall average intensity.

9. The non-contact surface texture evaluation device according to claim 1, further comprising: A parallel light illumination unit is configured to illuminate the object under test with parallel light.

10. The non-contact surface texture evaluation apparatus of claim 9, wherein the non-contact surface texture evaluation apparatus is configured to evaluate the surface texture of the object under test based on the magnitude of an evaluation value obtained from a detection signal of a predetermined phase difference detected by the photodetector.

11. The non-contact surface texture evaluation apparatus according to claim 9 or 10, wherein the photodetector includes an array of light receiving elements arranged to correspond to the intensity distribution of light formed through the optical aperture and on the irradiated surface of the photodetector.

12. The non-contact surface texture evaluation apparatus of claim 11, wherein the non-contact surface texture evaluation apparatus is configured to evaluate the surface texture of the object under test based on the magnitude of an evaluation value related to the diameter of a Lissajous circle obtained from a phase signal from the array of light receiving elements.

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