Measurement method and measurement device

Abstract

The present disclosure aims to provide a measurement method that can easily adjust the trade-off between measurement accuracy and measurement time while suppressing a decrease in measurement accuracy. [Solution] A measurement method according to one aspect of the present disclosure is a measurement method for obtaining characteristic information of an object using a sensor that measures the object along a line, and includes a scanning step of performing a line scan in a direction perpendicular to a plane passing through the line and the sensor, and a representative value determination step of determining a representative value of the characteristic information of a width region defined at regular intervals in the direction of the line scan from scan data corresponding to the line that belongs to that width region, wherein the line measurements of the object by the sensor are repeatedly performed at a fixed speed, and the number of scan data belonging to one width region is changed by changing the speed of the line scan.

Description

[Technical Field]

[0001] The present disclosure relates to a measurement method and a measurement apparatus. [Background technology]

[0002] As a method for efficiently acquiring characteristic information such as the shape and color of an object, a method using a line sensor camera is known (for example, Patent Publication No. 2019 / 112055).

[0003] A line sensor camera is a camera that can capture images of a line, and can capture an image of an object along a line. By scanning this line in a direction perpendicular to the line, it is possible to capture an image of the entire object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Re-tabled publication 2019 / 112055 Summary of the Invention [Problem to be solved by the invention]

[0005] When acquiring characteristic information of an object, there are two main cases: one where high measurement accuracy is required, and one where measurement in a short time is required.

[0006] For example, if high measurement accuracy is required, one method is to measure multiple times to improve the accuracy of each measurement point, but it is difficult to accurately measure the same position repeatedly, and errors due to positional deviations may occur.

[0007] On the other hand, when measurements are required to be taken in a short time, a method of thinning out the measurement points can be considered, but this tends to result in a reduction in measurement accuracy while reducing the degree to which the measurement time can be shortened.

[0008] It would be best to prepare measuring equipment suited to each condition, but in that case the cost of the measuring equipment may become too high.

[0009] The present disclosure has been made in light of the above-mentioned circumstances, and aims to provide a measurement method and a measurement device that can easily adjust the trade-off between measurement accuracy and measurement time while preventing a decrease in measurement accuracy. [Means for solving the problem]

[0010] A measurement method according to one aspect of the present disclosure is a measurement method for acquiring characteristic information of an object using a sensor that measures the object along a line, and includes a scanning step of performing a line scan in a direction perpendicular to a plane passing through the line and the sensor, and a representative value determination step of determining a representative value of the characteristic information of a width region defined at regular intervals in the direction of the line scan from scan data corresponding to the line that belongs to that width region, wherein the line measurements of the object by the sensor are repeatedly performed at a fixed speed, and the number of scan data belonging to one width region is changed by changing the speed of the line scan.

[0011] A measurement device according to another aspect of the present disclosure is a measurement device that acquires characteristic information of an object, and includes a sensor that measures the object along a line, a scanning mechanism that performs line scanning in a direction perpendicular to a plane passing through the line and the sensor, and a representative value determination mechanism that determines a representative value of the characteristic information of a width region defined at regular intervals in the direction of the line scanning from scan data corresponding to the line that belongs to that width region, wherein the line measurements of the object by the sensor are repeatedly performed at a fixed speed, and the number of scan data belonging to one of the width regions is changed by changing the speed of the line scanning. [Effects of the Invention]

[0012] The measurement method and measurement device of the present disclosure can easily adjust the trade-off between measurement accuracy and measurement time while preventing a decrease in measurement accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a flow diagram illustrating a measurement method according to one embodiment of the present disclosure. [Figure 2] FIG. 2 shows a measurement device used in the measurement method of FIG. 1, which is a measurement device according to one embodiment of the present disclosure. [Figure 3] FIG. 3 shows the trace of a line resulting from the scanning process performed by the measurement device of FIG. [Figure 4] FIG. 4 is an explanatory diagram for explaining the width region. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Description of the embodiments of the present disclosure] (1) A measurement method according to one aspect of the present disclosure is a measurement method for acquiring characteristic information of an object using a sensor that measures the object in lines, and includes a scanning step of performing a line scan in a direction perpendicular to a plane passing through the line and the sensor, and a representative value determination step of determining a representative value of the characteristic information of a width region determined at regular intervals in the direction of the line scan from scan data corresponding to the line that belongs to the width region, the width region being determined at regular intervals in the direction of the line scan. The line measurements of the object by the sensor are repeatedly performed at a fixed speed, and the number of scan data belonging to one width region is changed by changing the speed of the line scan.

[0015] This measurement method determines a representative value for a width region from scan data belonging to that width region, thereby reducing noise and obtaining stable, highly accurate data. Furthermore, in this measurement method, increasing the line scan speed reduces the number of scan data belonging to the width region, thereby reducing measurement time. Conversely, increasing the line scan speed increases the number of scan data belonging to the width region, thereby improving measurement accuracy. This measurement method thus makes it easy to adjust the trade-off between measurement accuracy and measurement time.

[0016] (2) In the measurement method of (1) above, the scanning step may measure the scan position relative to the object, and add the scan position at which the scan data was acquired to part or all of the scan data. By adding the acquired scan position to the scan data in this way, a mechanism for controlling the scan data acquisition position, such as an external trigger, is not required, and scan data can be acquired continuously, thereby shortening the measurement time.

[0017] (3) In the measurement method (1) or (2), the fixed speed may be the maximum speed of the sensor. By setting the fixed speed to the maximum speed of the sensor in this way, the measurement time can be further reduced.

[0018] (4) In any of the measurement methods (1) to (3), the sensor may be an image sensor or a distance sensor. This measurement method can be suitably used to measure the brightness of an object using an image sensor or to measure the shape of an object using a distance sensor.

[0019] (5) In any of the measurement methods (1) to (4) above, the representative value may be an arithmetic mean value, a rank-weighted mean value, a median value, or a Gaussian distribution-weighted mean value. By determining the representative value using any of the above methods, the measurement accuracy can be further improved.

[0020] (6) In any of the measurement methods (1) to (4) above, the representative value may be the scan data of the line that has the smallest sum of the differential coefficients in the line direction of the corresponding scan data among the lines included in one width region. By using the scan data of the line that has the smallest sum of the differential coefficients as the representative value in this way, noise components can be reduced.

[0021] (7) A measurement device according to another aspect of the present disclosure is a measurement device for acquiring characteristic information of an object, and includes a sensor for measuring the object in a line, a scanning mechanism for performing a line scan in a direction perpendicular to a plane passing through the line and the sensor, and a representative value determination mechanism for determining a representative value of the characteristic information of a width region determined at regular intervals in the direction of the line scan from scan data corresponding to the line belonging to the width region, wherein the line measurements of the object by the sensor are repeatedly performed at a fixed speed, and the number of scan data belonging to one of the width regions is changed by changing the speed of the line scan.

[0022] This measurement device determines a representative value for a width region from scan data belonging to that width region, thereby reducing noise and obtaining stable, highly accurate data. Furthermore, with this measurement device, increasing the line scan speed reduces the number of scan data belonging to the width region, thereby reducing measurement time. Conversely, increasing the line scan speed increases the number of scan data belonging to the width region, thereby improving measurement accuracy. This measurement device thus makes it easy to adjust the trade-off between measurement accuracy and measurement time.

[0023] [Details of the embodiments of the present disclosure] A measurement method and a measurement device according to an embodiment of the present disclosure will be described below.

[0024] The measurement method according to one embodiment of the present disclosure shown in Fig. 1 can be performed by a measurement device 1 according to another embodiment of the present disclosure shown in Fig. 2. First, the measurement device 1 will be described.

[0025] [Measuring equipment] The measurement device 1 is a measurement device that acquires characteristic information of an object S. As shown in FIG. 2, the measurement device 1 includes a sensor 10, a scanning mechanism 20, a representative value determining mechanism 30, and an encoder 40.

[0026] <Sensor> The sensor 10 measures the object S along a line L. That is, the sensor 10 can acquire characteristic information on the line L on the object S.

[0027] Examples of the sensor 10 include an image sensor and a distance sensor. The image sensor can acquire, for example, the brightness of the object S, the intensity of RGB colors, and the intensity for each wavelength (IR or multispectral). The distance sensor can acquire the distance between the object S and the sensor 10 using, for example, a light-section method, and can measure the shape of the object S based on this distance information. The acquired brightness or distance becomes the characteristic information. This measurement method can be suitably used with the measurement device 1 to measure the brightness of the object S using an image sensor or to measure the shape of the object S using a distance sensor.

[0028] The sensor 10 acquires characteristic information (scan data) on the line L of the object S and transmits the acquired information to the representative value determination mechanism 30. At this time, it is advisable to add, for example, the x coordinate of one end point of the line L to the above information as position information in the line scanning direction (x direction in FIG. 2 ) described below. Based on the measured position information, the representative value determination mechanism 30 can accurately determine the representative value R. The above position information can be acquired, for example, by the encoder 40 described below.

[0029] The sensor 10 may acquire characteristic information while moving sequentially along the line L of the object S, and may serially send the acquired characteristic information to the representative value determination mechanism 30. In this case, for example, if characteristic information is acquired while moving from the front of the object S to the back in FIG. 2, the next acquisition may be performed while moving from the back to the front of the object S (i.e., while making a reciprocating motion), or the next acquisition may also be performed while moving from the front of the object S to the back. With this type of sensor 10, there is a minimum time during which characteristic information can be acquired from the next line L after moving sequentially along the line L of the object S, and the sensor 10 operates at maximum speed when operated within that minimum time.

[0030] The sensor 10 can also be configured to acquire characteristic information on a line L of the object S all at once. The information acquired all at once in this way is, for example, converted from parallel to serial and sent to the representative value determination mechanism 30. With this type of sensor 10, once characteristic information on a line L of the object S has been acquired and sent to the representative value determination mechanism 30, it becomes possible to acquire characteristic information from the next line L. When operating in the shortest time required for this, the sensor 10 operates at the maximum speed.

[0031] In the measurement device 1, the sensor 10 repeatedly measures the line L of the object S at a fixed speed. The fixed speed may be any speed equal to or less than the maximum speed, but may be the maximum speed of the sensor 10. By setting the fixed speed to the maximum speed of the sensor 10 in this way, the measurement time can be further reduced.

[0032] The characteristic information on the line L of the object S may be acquired continuously, but is generally acquired discretely because it is digitally processed. In other words, adjacent pieces of characteristic information on the line L of the object S are data separated by a certain distance. The certain distance is determined according to the size of the object S and the required measurement accuracy.

[0033] <Scanning mechanism> The scanning mechanism 20 performs a line scan in a direction perpendicular to a plane passing through the line L and the sensor 10 .

[0034] 2, the scanning mechanism 20 is composed of a stage that supports the object S. In the measuring device 1, by moving the stage in the direction of the arrow while keeping the sensor 10 fixed, the line L of the object S, which is the position where the sensor 10 acquires characteristic information, can be scanned from right to left of the object S. In this way, the measuring device 1 can acquire characteristic information of the entire object S.

[0035] In the measurement device 1, the number of scan data belonging to one width region W, which will be described later, is changed by changing the line scan speed. Details will be described later.

[0036] <Representative value determination mechanism> The representative value determination mechanism 30 determines a representative value R of the characteristic information of a width region W from scan data corresponding to lines L belonging to the width region W defined at regular intervals in the line scanning direction.

[0037] The representative value determining mechanism 30 can be realized by a microcontroller, a personal computer, or the like.

[0038] The detailed operation of the representative value determining mechanism 30 will be described later.

[0039] <Encoder> The encoder 40 measures the scan position relative to the object S. As the encoder 40, a rotary encoder or a linear encoder can be used.

[0040] In the measurement device 1 shown in Fig. 2, the encoder 40 is in contact with the stage constituting the scan mechanism 20 so as to capture the movement of the stage. Its position is aligned with the position of line L. The position where the encoder 40 is in contact with the stage does not necessarily have to be aligned with the position of line L, but if aligned, the position of the encoder 40 will match the position of line L, and therefore there is no need to perform correction or the like to extract the position of line L.

[0041] For example, assuming the state in FIG. 2 is the initial state, the position where the line L passes on the object S in the initial state can be set as the reference position (e.g., x=0). When the stage moves from this position in the direction of the arrow in FIG. 2, the movement distance x1 is measured with high precision by the encoder 40. Since the object S moves integrally with the stage, in this case, it can be determined that the line L passes through the position x=-x1. In this way, the scan position for the object S can be measured using the encoder 40.

[0042] [Measurement method] The measurement method is a measurement method for acquiring characteristic information of an object S using a sensor 10 that measures the object S along a line L. As shown in Fig. 1, the measurement method includes a scanning step S1 and a representative value determination step S2.

[0043] <Scanning process> In the scanning step S1, a line scan is performed in a direction perpendicular to a plane passing through the line L and the sensor 10. The scanning step S1 can be performed using the scanning mechanism 20 of the measurement device 1.

[0044] As described in the description of the measuring device 1, the sensor 10 repeatedly measures the line L of the object S at a fixed speed, which is preferably the maximum speed.

[0045] Furthermore, it is preferable that the above measurement be free-running and not use a trigger or the like that controls the start of each line L of the target object S. If scan data acquisition is started at the appropriate time when performing line scanning, it is possible to ensure that the acquired scan data is data from the desired position. The trigger indicates this start timing. On the other hand, in order to be able to start acquiring scan data with a trigger, it is necessary that acquisition of the previous scan data has finished. For this reason, it is necessary to wait until a time when it is possible to guarantee that acquisition of the previous scan data has finished before generating the trigger, and this waiting time results in a loss of measurement time.

[0046] As a method that does not use a trigger, it is preferable to measure the scan position relative to the object S in the scanning step S1 and add the scan position at which the scan data was acquired to the scan data. As described above, the scan position can be measured by using the encoder 40. If the scan position is acquired at the same time as the scan data is acquired, it becomes clear which position the acquired scan data is associated with, so a mechanism for controlling the scan data acquisition position, such as an external trigger, is not required. Furthermore, since the scan position can be acquired independently of the scan data acquisition, scan data can be acquired continuously. By adding the acquired scan position to the scan data in this way, the measurement time can be shortened.

[0047] The scan positions may be added to all of the scan data, or to a portion of the scan data. When the scan positions are added to a portion of the scan data, the scan positions of the scan data to which no scan positions have been added can be determined by interpolation from the scan data to which scan positions have been added. From the viewpoint of interpolation accuracy, it is preferable that scan positions be added to at least two, and preferably three or more, of the scan data included in one line L.

[0048] The line scanning speed can be changed. When a short measurement time is required for the object S, the line scanning speed is set high. On the other hand, when a high measurement accuracy is required for the object S, the line scanning speed is set low. Note that the line scanning speed can be changed within the measurement of one object S, but it is preferable that it is constant within the measurement of one object S, and different line scanning speeds are set between different objects S. In other words, in this measurement method, measurements can be performed by changing the line scanning speed for each object S while using the same measurement device 1.

[0049] The upper limit of the line scanning speed is the speed at which at least one line L is included in each width region W described below. On the other hand, the lower limit of the line scanning speed is, in principle, not limited as long as imaging and data acquisition are completed, but is generally determined so that measurement is completed within a desired time.

[0050] The trajectory of the line L after scanning in the scanning step S1 is shown in FIG.

[0051] <Representative value determination process> In the representative value determination step S2, a representative value R of a width region W is determined from scan data corresponding to lines L belonging to the width region W defined at regular intervals in the line scanning direction.

[0052] This will be explained in detail using Figure 4. In Figure 4, for the sake of convenience, the object S and the line L are shown separated into upper and lower parts.

[0053] As shown in Figure 4, width regions W are defined at regular intervals in the line scanning direction. The width region W is defined within the range where at least the line L exists. One representative value R is then determined for each width region W. The width of the width region W is determined appropriately based on the size and shape of the target object S, the required measurement accuracy, etc. In Figure 4, it is divided into four width regions W.

[0054] As shown in FIG. 4, each width region W has lines L that belong to that width region W. The number of lines L that belong to each width region W is one or more, but preferably multiple, and more preferably five or more. By having multiple lines L that belong to each width region W, noise can be reduced by the averaging process described below. Examples of the noise include time-axis noise such as electrical dark noise and thermal noise, and spatial noise such as laser speckle noise (the effect of interference due to minute differences in surface texture).

[0055] For ease of understanding, the following description will be given taking as an example a case where there are multiple lines L belonging to the width region W. Note that if there is only one line L belonging to the width region W, the representative value R will be the line L belonging to the width region W itself even if the following processing is performed.

[0056] The calculation of the representative value R is performed for points on multiple lines L belonging to the width region W where the y coordinate is equal, and the y coordinate value is taken as the value of the representative value R. Therefore, the representative value R exists on the line L measured by the sensor 10. Also, since it is the representative value R of the width region W, its position should be the median of the x coordinate of the width region W (see Figure 4). Note that Figure 4 is a diagram showing the measurement position of the line L and the definition position of the representative value R, and is not the measurement value or the representative value itself.

[0057] There are multiple points with the same y coordinate on multiple lines L belonging to the width region W, and each point has a measurement value, so a representative value R at the same y coordinate is determined from these multiple measurement values.

[0058] The representative value R may be an arithmetic mean value, a rank-weighted mean value, a median value, or a Gaussian distribution-weighted mean value. By determining the representative value R by any of the above methods, the measurement accuracy can be further improved.

[0059] The arithmetic mean value is a simple average value calculated by dividing the sum of each measurement value by the number of lines L. It is effective when it is determined that there is relatively little difference in the measurement values ​​within the width region W, and when the representative value R is used as the arithmetic mean value, it is easy to cancel out randomly occurring positive and negative noise in each measurement value.

[0060] Rank-weighted average is a method of calculating the average by weighting each measurement value by its rank. If a particular measurement value is judged to be reliable, the accuracy of the representative value R can be improved by weighting that measurement value more heavily. It can also improve robustness when sufficient processing time is available. One method of weighting by rank is to sort the measurement values ​​in order of magnitude and then take the average of the values ​​near the middle. In the case of eight data sets, this is equivalent to sorting the data in order of magnitude, and assigning a weight of 0 to the four data sets (the two smallest and two largest) and a weight of 1 to the remaining four data sets (near the middle).

[0061] The intermediate value is calculated by arranging multiple measurements in order of magnitude and using the middle value. With this method, if there is a sudden abnormal value due to, for example, a disturbance, that data is easily eliminated. In this way, when there is a lot of noise in the measurement values, this method provides a more reliable value than other methods.

[0062] The Gaussian distribution weighted average is a method of calculating the average by weighting each measurement value using a Gaussian distribution. This method offers an excellent balance between robustness and processing time. It is also easy to perform spatial weighting, and it is recommended to maximize the weight at the center of the region, for example.

[0063] As the representative value, it is also possible to use the scan data of the line among the lines included in one width region, for which the sum of the differential coefficients in the line direction of the corresponding scan data is the smallest. Generally, when noise components are superimposed on the scan data of a line, the scan data changes significantly in the area where the noise components are superimposed. In other words, the rate of change (differential coefficient) becomes large. Conversely, it can be said that the noise components of the scan data of the line for which the sum of the differential coefficients in the line direction is the smallest are small. Therefore, by using the scan data of the line for which the sum of the differential coefficients is the smallest as the representative value, it is possible to reduce the noise components.

[0064] Here, the "sum of differential coefficients in the line direction" is, for example, the sum of scan data {y1, y2, . . . y} extracted at equal intervals (Δx) in the line direction. i , y n}, (y i -y i-1 ) / Δx (i=2 to n). If the (approximate) function of the scan data y with respect to the position x is known, it may be calculated by integral calculation.

[0065] In this measurement method, changing the line scan speed changes the number of lines L contained in one width region W. Specifically, increasing the line scan speed reduces the number of lines L contained in one width region W (and therefore shortens the measurement time), whereas decreasing the line scan speed increases the number of lines L contained in one width region W. As the number of lines L contained in one width region W increases or decreases, the number of scan data (measurement values) belonging to one width region W also increases or decreases, and the number of measurement values ​​to be averaged in the representative value R described above also increases or decreases. As the number of measurement values ​​to be averaged in the representative value R increases, the measurement accuracy increases, and as the number of measurement values ​​to be averaged in the representative value R decreases, the measurement time is shortened. This measurement method is characterized by the fact that the trade-off between measurement accuracy and measurement time can be achieved with a single variable: the line scan speed.

[0066] Furthermore, this measurement method obtains multiple measurement values ​​in a single scan to be averaged using a representative value R. Therefore, compared to obtaining measurement values ​​by performing multiple measurements, measurement errors caused by, for example, the starting point not matching between trials can be eliminated, preventing a decrease in measurement accuracy. Furthermore, there is no need for the time required for initial setup, etc., when performing multiple measurements, so there is little loss of measurement time.

[0067] <Advantages> The measurement method and the measurement device 1 determine the representative value R of a width region W from scan data belonging to that width region W, thereby reducing noise and obtaining stable, highly accurate data. Furthermore, with the measurement method and the measurement device 1, increasing the line scan speed reduces the number of scan data belonging to the width region W, thereby reducing the measurement time. Conversely, increasing the line scan speed increases the number of scan data belonging to the width region W, thereby improving the measurement accuracy. In this way, the measurement method and the measurement device 1 make it easy to adjust the trade-off between measurement accuracy and measurement time.

[0068] [Other embodiments] The present disclosure is not limited to the above-described embodiments, and can be implemented in various forms including the above-described embodiments, as well as forms with various modifications and improvements.

[0069] In the above embodiment, the scanning mechanism of the measurement device is described as being configured with a stage that supports the object, but the scanning mechanism is not limited to this. For example, the scanning mechanism may be a mechanism that moves a sensor. [Industrial Applicability]

[0070] The measurement method and measurement device of the present disclosure can easily adjust the trade-off between measurement accuracy and measurement time while preventing a decrease in measurement accuracy. [Explanation of symbols]

[0071] 1. Measuring equipment 10 sensors 20 Scanning mechanism 30 Representative value determination mechanism 40 Encoder S Object L line W width area R typical value

Claims

1. A measurement method for acquiring characteristic information of an object using a sensor that measures the object with a line, comprising: a scanning step of performing a line scan in a direction perpendicular to a plane passing through the line and the sensor; a representative value determination step of determining a representative value of the characteristic information of a width region from scan data corresponding to the line belonging to the width region determined at regular intervals in the line scanning direction; Equipped with The line of measurements of the object by the sensor is repeated at a fixed rate; A measurement method in which the number of scan data belonging to one of the width regions is changed by changing the speed of the line scan.

2. 2. The measuring method according to claim 1, wherein the scanning step measures a scan position relative to the object, and adds the scan position at which the scan data was acquired to part or all of the scan data.

3. 3. The measurement method according to claim 1, wherein the fixed speed is a maximum speed of the sensor.

4. 3. The measuring method according to claim 1, wherein the sensor is an image sensor or a distance sensor.

5. 3. The measurement method according to claim 1, wherein the representative value is an arithmetic mean value, a rank-weighted mean value, a median value, or a Gaussian distribution-weighted mean value.

6. 3. The measurement method according to claim 1, wherein the representative value is the scan data of a line among the lines included in one width region, the scan data of which has the smallest sum of the differential coefficients in the line direction of the corresponding scan data.

7. A measurement device that acquires characteristic information of an object, a sensor for measuring the object with a line; a scanning mechanism that performs a line scan in a direction perpendicular to a plane that passes through the line and the sensor; a representative value determination mechanism for determining a representative value of the characteristic information of a width region from scan data corresponding to the line belonging to the width region determined at regular intervals in the line scanning direction; Equipped with The line of measurements of the object by the sensor is repeated at a fixed rate; A measurement device that changes the number of scan data belonging to one of the width regions by changing the speed of the line scan.

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