A cable outer diameter real-time online detection method and system based on optical vision

Abstract

The present application relates to the technical field of optical diameter measurement, and particularly relates to a cable outer diameter real-time online detection method and system based on optical vision. The method comprises the following steps: determining the conductor eccentric direction and establishing a cross-section geometric relation equation group to obtain a preliminary cable outer diameter by extracting the total polarization intensity of the virtual bright band area in the back projection image and inversely solving the local sheath wall thickness distribution; simultaneously, separating the synchronous disturbance component and the asynchronous edge component by combining the spark tester driving voltage signal, extracting the refractive index fluctuation component caused by the ion wind by using the cosine value of the angle between the electrode arrangement direction and the gravity direction, and then correcting the preliminary outer diameter to obtain the real cable outer diameter. The present application effectively suppresses the total reflection virtual increase caused by the conductor eccentricity and the high-frequency disturbance caused by the ion wind of the spark tester, significantly improves the accuracy and stability of the cable outer diameter online detection, and guarantees the reliability of the outer diameter closed-loop control.

Description

Technical Field

[0001] This invention relates to the field of optical diameter measurement technology, and in particular to a method and system for real-time online detection of cable outer diameter based on optical vision. Background Technology

[0002] Optical vision inspection refers to the technology of obtaining the contour dimensions of a measured object using parallel backlight projection, imaging devices, and image edge analysis. The outer diameter of a cable is the diameter of the circular outline of the outer surface of the cable sheath. Current online cable outer diameter inspection methods mostly employ parallel backlight projection combined with linear scan cameras. The outer diameter value is obtained by edge localization and width conversion of the projected image. This type of non-contact measurement method is widely used in cable extrusion production lines, significantly improving inspection speed and automation compared to traditional mechanical measuring tools.

[0003] However, when the conductor inside the cable is eccentric and the sheath is made of semi-transparent material, a diffuse bright band formed by total internal reflection at the interface between the conductor and the sheath will appear outside the geometric shadow edge of the projected image, causing the edge positioning to shift. At the same time, the ion wind generated by the operation of the nearby spark testing machine causes fluctuations in the refractive index of the optical path, resulting in high-frequency jitter in the edge position signal. The above interference and the actual outer diameter fluctuation may overlap in the frequency domain, and conventional threshold segmentation and low-pass filtering are difficult to separate them accurately, resulting in the outer diameter measurement value containing false fluctuations, which affects the extrusion closed-loop control.

[0004] Therefore, there is an urgent need to study an optical vision method for outer diameter detection that can maintain high-precision measurement under the combined effects of internal structural artifacts and external ion wind disturbances, so as to improve the accuracy and stability of online detection of cable outer diameter. Summary of the Invention

[0005] To overcome the drawbacks of optical fictitious gain and ion wind disturbance, this invention provides a method and system for real-time online detection of cable outer diameter based on optical vision.

[0006] The technical implementation of this invention is a method for real-time online detection of cable outer diameter based on optical vision, comprising the following steps:

[0007] S1: Online real-time acquisition of the backlight projection image of the actual cable, and determination of the intensity distribution of the artificially increased brightness band based on the backlight projection image, and inverse solution of the intensity distribution of the artificially increased brightness band to form the local sheath wall thickness distribution;

[0008] S2: Determine the conductor eccentricity direction based on the local sheath wall thickness distribution, and obtain the conductor eccentricity and preliminary cable outer diameter based on the conductor eccentricity direction;

[0009] S3: Online real-time acquisition of the optical outer diameter detection projection edge position signal and the spark testing machine drive voltage signal, and determination of the synchronous disturbance component;

[0010] S4: Based on the synchronous disturbance component and the cosine value of the angle between the electrode arrangement direction of the spark tester and the gravity direction, the refractive index fluctuation component caused by the ion wind is obtained.

[0011] S5: Determine the true outer diameter of the cable based on the refractive index fluctuation component caused by ion wind, and output the true outer diameter of the cable to the outer diameter closed-loop control system online.

[0012] Preferably, the step of acquiring the backlight projection image of the actual cable online in real time and determining the intensity distribution of the artificially increased bright band based on the backlight projection image includes:

[0013] In a backlit projection image, a diffuse bright band region located outside the geometric shadow edge and with a brightness higher than the brightness threshold is defined as an artificially increased bright band region.

[0014] Extract the intensity of the s-polarization component and the p-polarization component in the artificially enhanced bright band region;

[0015] The sum of the two is used to obtain the total polarization intensity, which is then used as the intensity distribution of the artificially increased bright band.

[0016] Preferably, the step of inversely solving the intensity distribution of the artificially inflated bright band to form a local sheath wall thickness distribution includes:

[0017] The attenuation coefficient is obtained by dividing the product of the sheath refractive index and the reflectivity of the conductor surface by the sine of the critical angle of total internal reflection, and then by the preset normalized wall thickness constant. The attenuation coefficient is then multiplied by the illusory bright band intensity to obtain the rate of change of the illusory bright band intensity with the increase of the local sheath wall thickness.

[0018] If the absolute value of the rate of change decreases as the local sheath wall thickness increases, then it is confirmed that the intensity of the artificially increased bright band has a monotonically decreasing relationship with the local sheath wall thickness.

[0019] Based on the monotonically decreasing relationship, the intensity of the artificially increased bright band at each spatial location in the intensity distribution of the artificially increased bright band is solved point by point to obtain the local sheath wall thickness corresponding to each spatial location, thus forming a local sheath wall thickness distribution.

[0020] Preferably, the step of determining the conductor eccentricity direction based on the local sheath wall thickness distribution, and obtaining the conductor eccentricity and preliminary cable outer diameter based on the conductor eccentricity direction, includes:

[0021] Extract the circumferential minimum and circumferential maximum directions from the local sheath wall thickness distribution;

[0022] If the direction of the circumferential minimum is opposite to the direction of the circumferential maximum, the direction of the circumferential minimum is determined as the direction of conductor eccentricity;

[0023] The first projection width of the backlight projection image is obtained in the conductor eccentricity direction;

[0024] The second projection width of the backlight projection image is obtained in a direction perpendicular to the conductor eccentricity direction;

[0025] Based on the first projection width, the second projection width, the theoretical wall thickness, and the conductor radius, establish a set of equations relating the cross-section geometry.

[0026] Solve the set of equations relating the cross-section geometry to obtain the conductor eccentricity and the preliminary cable outer diameter.

[0027] Preferably, establishing the set of equations relating the cross-section geometry includes:

[0028] ;

[0029] in, This represents the theoretical wall thickness in the conductor's eccentric direction. The theoretical wall thickness is in the direction perpendicular to the conductor's eccentricity. It is half the initial cable outer diameter. Where is the conductor radius, For conductor eccentricity, The first projection width, The second projection width, This is the artificial offset at the edge in the direction of conductor eccentricity. This is an artificial offset at the edge in a direction perpendicular to the conductor's eccentricity.

[0030] and The intensity of the artificially increased bright band is obtained by inverse solving the theoretical wall thickness, and then converted according to the projection geometric relationship between the intensity of the artificially increased bright band and the edge offset.

[0031] Preferably, the step of obtaining the result based on the projected geometric relationship between the intensity of the artificially increased bright band and the edge offset includes:

[0032] Using the monotonically decreasing relation, the corresponding artificially increased bright band intensity is obtained by inverse solving the theoretical wall thickness in the conductor eccentric direction and the direction perpendicular to the conductor eccentric direction, respectively.

[0033] Based on the deviation path of the totally internally reflected light rays as they propagate within the sheath and exit from the outer surface relative to the geometric shadow edge, the deviation amount corresponding to the artificially increased brightness band intensity is calculated, and the deviation amount is determined as follows: and .

[0034] Preferably, the step of acquiring the optical outer diameter detection projection edge position signal and the spark testing machine drive voltage signal online in real time, and determining the synchronization disturbance component, includes:

[0035] The phase of the optical outer diameter detection projection edge position signal at the working frequency and harmonics of the spark testing machine is compared with the phase of the spark testing machine drive voltage signal at the same frequency.

[0036] Components with stable phase differences and less than the phase difference threshold are extracted as synchronization perturbation components.

[0037] Preferably, the step of obtaining the refractive index fluctuation component caused by the ion wind based on the synchronous disturbance component and the cosine of the angle between the electrode arrangement direction of the spark tester and the gravity direction includes:

[0038] Calculate the cosine of the angle between the electrode arrangement direction of the spark tester and the direction of gravity; multiply the preset reference coefficient by the cosine of the angle to obtain the linear coefficient;

[0039] Multiply the synchronization disturbance component by the linear coefficient to obtain the initial ion wind disturbance offset.

[0040] Dividing the initial ion wind disturbance offset by the object size corresponding to each pixel yields the dimensionless refractive index fluctuation component caused by the ion wind, which is a dimensionless quantity.

[0041] Preferably, the step of determining the true outer diameter of the cable based on the refractive index fluctuation component caused by the ion wind, and outputting the true outer diameter of the cable online to the outer diameter closed-loop control system, includes:

[0042] By utilizing the refractive index fluctuation component caused by ion wind and combining it with the projected geometric relationship corresponding to the outer diameter of the initial cable, the refractive index fluctuation component is multiplied by the equivalent optical path length corresponding to the outer diameter of the initial cable to obtain the residual offset of the outer diameter of the initial cable caused by ion wind disturbance.

[0043] The true outer diameter of the cable is obtained by subtracting the residual offset due to ion wind disturbance from the initial outer diameter of the cable.

[0044] Preferably, a real-time online detection system for cable outer diameter based on optical vision includes:

[0045] The module for extracting the wall thickness of the artificially enhanced bright band is used to acquire the backlight projection image, determine the intensity distribution of the artificially enhanced bright band, and inversely solve it into the local sheath wall thickness distribution.

[0046] The module for calculating the outer diameter in the eccentric direction is used to determine the conductor eccentricity direction based on the local sheath wall thickness distribution, and to establish a set of cross-sectional geometric relationship equations to solve for the conductor eccentricity and the preliminary cable outer diameter.

[0047] The ion wind disturbance component extraction module is used to obtain the projection edge position signal and the spark tester drive voltage signal, and combine the cosine value of the included angle to obtain the refractive index fluctuation component.

[0048] The cable true outer diameter output module is used to correct the preliminary cable outer diameter based on the refractive index fluctuation component to obtain the cable true outer diameter, and then output it online to the outer diameter closed-loop control system.

[0049] Beneficial Effects: This invention extracts the total polarization intensity of the artificially inflated bright band region in the backlight projection image online, solves the local sheath wall thickness distribution, determines the conductor eccentricity direction using the circumferential extreme value direction, and obtains the preliminary cable outer diameter by combining the cross-sectional geometric relationship equations. Simultaneously, it compares the phase of the optical outer diameter detection projection edge position signal with the spark tester drive voltage signal, separates the synchronous disturbance component and the asynchronous edge component, and extracts the refractive index fluctuation component caused by ion wind using the cosine of the angle between the electrode arrangement direction and the gravity direction. Based on this, the preliminary cable outer diameter is corrected to obtain the true cable outer diameter. This invention effectively suppresses the artificial inflated total internal reflection caused by conductor eccentricity and the high-frequency disturbance caused by the spark tester ion wind, significantly improving the accuracy and stability of online cable outer diameter detection and ensuring the reliability of closed-loop outer diameter control. Attached Figure Description

[0050] Figure 1 This is a flowchart of the real-time online detection method for cable outer diameter based on optical vision according to the present invention;

[0051] Figure 2 This is a structural diagram of the real-time online detection system for cable outer diameter based on optical vision according to the present invention. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0053] Example 1: A method for real-time online detection of cable outer diameter based on optical vision, such as... Figure 1 As shown, it includes the following steps:

[0054] S1-1: Acquire the backlight projection image of the actual cable online in real time, and determine the intensity distribution of the artificially increased brightness band based on the backlight projection image, including:

[0055] In a backlit projection image, a diffuse bright band region located outside the geometric shadow edge and with a brightness higher than the brightness threshold is defined as an artificially increased bright band region.

[0056] Extract the intensity of the s-polarization component and the p-polarization component in the artificially enhanced bright band region;

[0057] The sum of the two is used to obtain the total polarization intensity, which is then used as the intensity distribution of the artificially increased bright band.

[0058] It should be noted that in S1-1, the backlight projection image is acquired by a line scan camera after illuminating the actual cable with a parallel backlight source. The brightness threshold is automatically selected based on the grayscale histograms of the geometric shadow area and the artificially inflated bright band, taking the grayscale value corresponding to the intersection of their grayscale probability density curves. The outer edge of the geometric shadow refers to the area extending outward from the boundary of the cable projection dark area. Since the light from the total internal reflection at the interface between the conductor and the semi-transparent sheath propagates multiple times inside the sheath and then exits from this area, forming a diffuse bright band, it is necessary to identify the artificially inflated bright band area within this range.

[0059] The intensities of the s-polarization and p-polarization components are simultaneously separated and acquired using a polarization beam splitter. The vibration direction of the s-polarization component is perpendicular to the incident plane, while the vibration direction of the p-polarization component is parallel to the incident plane. Since the attenuation characteristics of s-polarization and p-polarization propagation within the sheath differ, using their combined intensity as a characterization of the artificially inflated bright band intensity provides greater physical consistency than using a single polarization component or polarization ratio. The resulting artificially inflated bright band intensity distribution is used to inversely determine the local sheath wall thickness, overcoming edge positioning offsets caused by optical artificial inflating in existing technologies.

[0060] S1-2: Inverse solution of the intensity distribution of the artificially enhanced bright band to form a local sheath wall thickness distribution, including:

[0061] The attenuation coefficient is obtained by dividing the product of the sheath refractive index and the reflectivity of the conductor surface by the sine of the critical angle of total internal reflection, and then by the preset normalized wall thickness constant. The attenuation coefficient is then multiplied by the illusory bright band intensity to obtain the rate of change of the illusory bright band intensity with the increase of the local sheath wall thickness.

[0062] If the absolute value of the rate of change decreases as the local sheath wall thickness increases, then it is confirmed that the intensity of the artificially increased bright band has a monotonically decreasing relationship with the local sheath wall thickness.

[0063] Based on the monotonically decreasing relationship, the intensity of the artificially increased bright band at each spatial location in the intensity distribution of the artificially increased bright band is solved point by point to obtain the local sheath wall thickness corresponding to each spatial location, thus forming a local sheath wall thickness distribution.

[0064] It should be noted that in backlit projection imaging, the refractive ability of the translucent sheath material to refract incident light is reflected by the sheath's refractive index. The higher the sheath's refractive index, the more pronounced the directional deflection of light as it propagates inside the sheath. The reflectivity of the conductor surface represents the proportion of incident light reflected by the conductor surface. The higher the conductor surface reflectivity, the stronger the energy of the totally internally reflected light rays reflected back into the sheath at the conductor-sheath interface. The critical angle for total internal reflection is determined by the ratio of the sheath's refractive index to the air's refractive index. When light is incident on the outer surface of the sheath at an angle greater than this critical angle, total internal reflection occurs, thus confining the light rays to continue propagating inside the sheath.

[0065] A preset normalized wall thickness constant is used as a length reference to unify the dimension of the attenuation coefficient to the reciprocal of the wall thickness, so as to ensure the consistency of the dimension when calculating the rate of change. Its specific value is set according to the nominal wall thickness of the cable sheath under test during system initialization, or it can be directly taken as 1 mm, and it does not participate in the actual wall thickness inversion accuracy control.

[0066] The attenuation coefficient calculated from the above parameters is used as the theoretical initial value to characterize the relative rate attenuation of intensity with wall thickness when the total internally reflected light propagates within the sheath. The larger the coefficient, the faster the intensity attenuates with increasing wall thickness. To further improve the inversion accuracy, the attenuation coefficient is verified and fine-tuned using standard cable samples with known wall thicknesses during system initialization or cable specification changes, and the reference strength required for the inversion is determined simultaneously.

[0067] Since the rate of change is negative, the larger the attenuation coefficient, the larger the absolute value of the rate of change, which is consistent with the physical meaning of the accelerated attenuation rate mentioned above. The rate of change of the intensity of the artificially increased bright band with the increase of the local sheath wall thickness is the product of the attenuation coefficient and the intensity of the artificially increased bright band. The above-mentioned change law of the absolute value of the rate of change is consistent with the characteristics of the exponential attenuation function, thus confirming that the intensity of the artificially increased bright band has a monotonically decreasing relationship with the local sheath wall thickness. That is, the thinner the wall thickness, the shorter the reflection path of the totally internalized light inside the sheath, and the higher the intensity of the artificially increased bright band emitted from the outer surface; the thicker the wall thickness, the longer the reflection path of the totally internalized light inside the sheath, the greater the energy attenuation, and the lower the intensity of the artificially increased bright band.

[0068] Specifically, from the rate of change relationship Points ,in As the reference strength, The attenuation coefficient is... To artificially inflate the intensity of the bright band, For local sheath wall thickness;

[0069] The reference strength is determined as follows: A direction with a known sheath wall thickness (e.g., a direction perpendicular to the conductor's eccentricity, where the wall thickness is obtained by combining cable specifications and geometric relationships) is selected, and the intensity of the artificially inflated bright band in this direction is measured as the reference strength. Alternatively, if the wall thickness is difficult to determine in advance, the reference strength is derived using the following online search method: An initial estimate of the reference strength is set, and this estimate is substituted into the monotonically decreasing relationship to solve for the wall thickness. The preliminary cable outer diameter is then obtained by combining this estimate with the cross-sectional geometric relationship equations in S2. The preliminary cable outer diameter is compared with the reference outer diameter obtained from offline measurement. The reference strength is adjusted according to the deviation, and the above process is repeated until the deviation between the preliminary cable outer diameter and the reference outer diameter is less than a preset outer diameter deviation threshold. The reference strength at this point is taken as I0 required for the inverse solution. The preset outer diameter deviation threshold is determined based on the allowable measurement error of the cable outer diameter, and the specific value is set by the operator based on a trade-off between actual accuracy and speed requirements.

[0070] The convergence of this search process is guaranteed by the following condition: the residual functions in the latter two projected width equations exhibit a unimodal characteristic near the theoretical estimate under the effective constraints of the former two wall thickness equations, and their global minimum corresponds to a unique combination of I0, R, and e. In practical applications, the search range of I0 is limited to a configurable percentage range (this range is set by the operator during system initialization based on the actual transmittance fluctuations of the sheath material: for material varieties with existing measurement data, a narrowed search range is set according to the historical transmittance fluctuation range; for new material varieties measured for the first time, the search range is appropriately expanded to ensure coverage of possible batch fluctuations), and a one-dimensional search is performed using the golden section method or parabolic interpolation method to ensure convergence to the global optimal solution within this interval within a finite number of steps. If the actual I0 exceeds this search range due to material batch differences, the algorithm will converge to the boundary value. At this time, the system outputs an alarm to prompt the operator to recalibrate and adjust the upper and lower limits of the search range accordingly. Therefore, the combination of theoretical calculation and calibration correction of the attenuation coefficient not only retains the formula characteristics of attenuation coefficient calculation based on optical parameters, but also solves the problem of missing reference intensity in actual inversion.

[0071] Taking the inverse function of this expression yields This is the quantitative relationship between the inverted local sheath wall thickness derived from the artificially inflated bright band intensity. At the reference strength... Once determined, the artificially increased brightness band intensity I(x,y) at each spatial location is substituted into the formula to obtain the corresponding local sheath wall thickness h(x,y).

[0072] Based on this monotonically decreasing relationship, the inverse solution is performed for each spatial location in the distribution of the artificially inflated bright band intensity. Substituting the artificially inflated bright band intensity at each spatial location into the inverse solution relationship yields the local sheath wall thickness corresponding to each spatial location. The local sheath wall thickness distribution reflects the circumferential variation of the sheath wall thickness within the same cross-section of the cable. The thinnest sheath wall corresponds to the conductor eccentricity direction, and the thickest sheath wall corresponds to the opposite direction of the conductor eccentricity direction. Therefore, the local sheath wall thickness distribution provides a direct geometric basis for subsequently determining the conductor eccentricity direction and correcting optical artificial inflators.

[0073] S2: Determine the conductor eccentricity direction based on the local sheath wall thickness distribution, and obtain the conductor eccentricity and preliminary cable outer diameter based on the conductor eccentricity direction, including:

[0074] Extract the circumferential minimum and circumferential maximum directions from the local sheath wall thickness distribution;

[0075] If the direction of the circumferential minimum is opposite to the direction of the circumferential maximum, determine that the direction of the circumferential minimum coincides with the direction of conductor eccentricity, and the direction of the circumferential maximum is opposite to the direction of conductor eccentricity, and determine the direction of the circumferential minimum as the direction of conductor eccentricity;

[0076] The first projection width of the backlight projection image is obtained in the conductor eccentricity direction;

[0077] The second projection width of the backlight projection image is obtained in a direction perpendicular to the conductor eccentricity direction;

[0078] Based on the first projection width, the second projection width, the theoretical wall thickness, and the conductor radius, establish a set of equations relating the cross-section geometry.

[0079] ;

[0080] in, This represents the theoretical wall thickness in the conductor's eccentric direction. The theoretical wall thickness is in the direction perpendicular to the conductor's eccentricity. It is half the initial cable outer diameter. Where is the conductor radius, For conductor eccentricity, The first projection width, The second projection width, This is the artificial offset at the edge in the direction of conductor eccentricity. This is an artificial offset at the edge in a direction perpendicular to the conductor's eccentricity.

[0081] and The intensity of the artificially increased bright band is obtained by inverse solving from the theoretical wall thickness, and then transformed according to the projection geometric relationship between the intensity of the artificially increased bright band and the edge offset.

[0082] Using the monotonically decreasing relation, the corresponding artificially increased bright band intensity is obtained by inverse solving the theoretical wall thickness in the conductor eccentric direction and the direction perpendicular to the conductor eccentric direction, respectively.

[0083] Based on the deviation path of the totally internally reflected light rays as they propagate within the sheath and exit from the outer surface relative to the geometric shadow edge, the deviation amount corresponding to the artificially increased brightness band intensity is calculated, and the deviation amount is determined as follows: and ;

[0084] Solve the set of equations relating the cross-section geometry to obtain the conductor eccentricity and the preliminary cable outer diameter.

[0085] It should be noted that the essence of the local sheath thickness distribution is the asymmetric change in sheath thickness along the circumference caused by conductor eccentricity. Under total internal reflection conditions, the intensity of the artificially inflated bright band has a monotonically decreasing relationship with the local sheath thickness. At the thinnest point of the sheath, the total internal reflection light travels the shortest reflection path within the sheath, resulting in the least energy attenuation and the strongest artificially inflated bright band; at the thickest point, the reflection path is the longest, resulting in the greatest energy attenuation and the weakest artificially inflated bright band. Therefore, the direction of the circumferential minimum physically corresponds to the direction of the thinnest sheath, which is the direction of conductor eccentricity; the direction of the circumferential maximum corresponds to the direction of the thickest sheath, which is the opposite direction of conductor eccentricity. The opposite directions of the two extrema are a necessary result of the eccentric geometry, thus determining the conductor eccentricity direction. The first and second projected widths are obtained along the eccentricity direction and the vertical direction, respectively, because the projected width along the eccentricity direction includes the maximum edge artificial offset, and the projected width along the vertical direction includes the reference edge artificial offset.

[0086] In the system of equations relating cross-section geometry, and The absolute physical width (dimension: length) obtained directly by the linear scan camera is a known quantity in the system of equations; The conductor radius is provided by the cable specification parameters and is also a known quantity. , For the theoretical wall thickness, based on geometric relationships and The wall thickness value obtained from the inverse solution of S1 is used as a reference for iterative verification. Since the wall thickness value from the inverse solution of S1 and the projected width directly measured by the camera come from different information extraction paths, they may be inconsistent. Therefore, when solving the equations, the wall thickness value given by S1 is not directly substituted as a known quantity, but rather treated as a quantity to be verified: during the iteration process, according to... and The current estimate is determined by geometric relations. , The theoretical wall thickness is calculated and its consistency with the wall thickness obtained from the inverse solution of S1 is verified. When the iteration converges, the theoretical wall thickness is consistent with the inverse solution value of S1, thus verifying the wall thickness inverse solution result of S1, and R and e are also determined.

[0087] The first two wall thickness equations carry geometric constraints—by - As can be seen from e, the difference in wall thickness determines the magnitude of the eccentricity e; the latter two projection width equations and It carries the absolute physical scale— and These are millimeter-level widths measured directly by the camera, providing anchor points for the absolute length of the equations. Therefore, the four equations constitute a system based on absolute measurements. , Anchored to absolute scale, by geometric constraints and A complete solution system for determining the relationship between eccentricity and radius.

[0088] and It serves as a bridge connecting the two levels mentioned above; the specific calculation method will be explained in subsequent paragraphs. Because... and Depends on and ( , ),and and And depend on and ,therefore , In fact, it is also and The function of . The latter two projection width equations express this dependency as: , —The left side shows known measurements, and the right side shows measurements including unknown parameters. and The theoretical expression for .

[0089] In actual solution, set and The initial estimated value of R is set according to the nominal outer diameter specification of the cable, and the initial estimated value of e is set to 0 or according to historical production data; since the subsequent iteration steps will gradually correct R and e, the initial estimated value only needs to be within a reasonable order of magnitude range. The iterative calculation is carried out according to the following steps: (1) According to geometric relationship , Theoretical wall thickness obtained and Then by and Through exponential decay relationship (2) Calculate the corresponding bright band intensities I1 and I2; (3) Calculate the corresponding edge offset from I by Δ=f(I). and The dimension is length, but the actual calculation is in millimeters; (3) , Substitute the last two projection width equations to calculate the theoretical width. , (4) Theory , With actual measurement , Compare and calculate the residuals; when the residuals converge, the theoretical wall thickness determined by the geometric relationship is consistent with the wall thickness of the inverse solution of S1, that is, the wall thickness inverse solution result of S1 is verified; (5) Adjust according to the residuals and The estimated value is obtained by repeating steps (1)-(4) until the change in the sum of squared residuals is less than the preset residual convergence threshold. and These are the target parameters to be solved. The preset residual convergence threshold is set based on the measurement noise level of the edge position signal, and the specific value is set by the operator according to the actual accuracy and speed requirements.

[0090] Therefore, the latter two projection width equations are used as the objective equations for least-squares fitting and solved iteratively. The four equations jointly constrain the values ​​of R and e: the first two wall thickness equations constrain the geometric consistency of R and e, while the latter two projection width equations use absolute measurements W1 and W2 to anchor the absolute dimensions of R and e, ensuring that the final solved R and e simultaneously satisfy both geometric relationships and optical measurement results. After solving, the conductor eccentricity e and the preliminary cable outer diameter 2R are obtained (where R is half of the preliminary cable outer diameter). Here, "preliminary" means that the outer diameter has been calculated by subtracting... , The optical spurious offset has been corrected, but the refractive index fluctuation offset caused by ion wind in subsequent steps has not yet been deducted.

[0091] and The intensity of the artificially increased bright band is derived from the theoretical wall thickness and then converted using the projected geometric relationship between the intensity of the artificial bright band and the edge offset. A greater artificial bright band intensity indicates stronger energy of the totally internalized light rays propagating within the sheath and exiting from the outer surface, and a greater outward deviation of the exiting light rays relative to the geometric shadow edge. Based on the deviation path of the totally internalized light rays after multiple reflections within the sheath and exiting from the outer surface relative to the geometric shadow edge, the intensity of the artificial bright band is converted into the corresponding edge offset, resulting in... and The wall thickness is thinnest in the eccentric direction, and the intensity of the artificially inflated bright band is greatest. Maximum; the vertical wall thickness is the baseline wall thickness, and the artificially increased bright band intensity is relatively small. The values ​​are relatively small. Substituting these two offsets into the projection width equation can correct the projection width deviation caused by optical artificial augmentation.

[0092] The conversion relationship between the artificially increased brightness band intensity and the edge offset is determined as follows: Based on the lateral deviation distance of the total internal reflection ray exiting the outer surface of the sheath relative to the geometric shadow edge, a mapping relationship between the artificially increased brightness band intensity and the offset is established. Specifically, if the artificially increased brightness band intensity at a certain spatial location is... The corresponding edge offset Calculate using the following formula: Δ = f(I), where f is a nonlinear mapping function determined by the geometric ray tracing of the total internal reflection ray, for example, using the form Where k is obtained through standard part calibration. During system initialization, standard cables with known wall thickness and eccentricity are used for calibration to establish an experimental mapping curve between the artificially increased bright band intensity and the edge offset. During actual measurement, the edge offset is obtained by looking up a table or by linear interpolation.

[0093] S3: Online real-time acquisition of the optical outer diameter detection projection edge position signal and the spark testing machine drive voltage signal, and determination of the synchronization disturbance component, including:

[0094] The phase of the optical outer diameter detection projection edge position signal at the working frequency and harmonics of the spark testing machine is compared with the phase of the spark testing machine drive voltage signal at the same frequency.

[0095] Components with stable phase differences and less than the phase difference threshold are extracted as synchronous disturbance components, while components with unstable phase differences or greater than or equal to the phase difference threshold are extracted as asynchronous edge components.

[0096] It should be noted that the optical outer diameter detection projection edge position signal is obtained by sampling the edge position in the backlit projection image using a linear scan camera, while the spark tester drive voltage signal is synchronously acquired by the voltage transformer of the spark tester control system. The operating frequency of the spark tester and the phase at its harmonics represent the phase angle of that frequency component in the edge position signal. This is compared with the phase at the same frequency of the spark tester drive voltage signal to identify the synchronous disturbance component caused by the electric field of the spark tester in the edge jitter, thereby distinguishing the synchronous disturbance component from the asynchronous edge component.

[0097] The quantification method for phase difference stability involves calculating the phase difference over multiple consecutive time windows. If the range of phase difference variation is less than a phase difference variation threshold, the phase difference is considered stable. The phase difference variation threshold is determined by adding two standard deviations to the average range of phase difference variation during normal operation of the spark tester. Alternatively, it can be determined by adding three standard deviations to the average phase difference during normal operation of the spark tester. Components with stable phase differences less than the phase difference threshold are extracted as synchronous disturbance components, representing ion wind disturbances synchronized with the electric field of the spark tester. Components with unstable phase differences or greater than or equal to the phase difference threshold are extracted as asynchronous edge components, representing the true edge geometric location and random noise.

[0098] This step separates the interference in the edge signal that is phase-locked with the EDM voltage, solving the problem of high-frequency jitter at the edge position caused by ion wind disturbance. Asynchronous edge components do not directly participate in the ion wind correction calculation. After obtaining the time series of the preliminary cable outer diameter, a moving average filter is applied to this time series to retain the low-frequency changes of the true outer diameter and suppress high-frequency noise in the asynchronous edge components. The filter window length is determined based on the sampling frequency of the edge position signal and the operating frequency of the EDM machine, ensuring that the filter window covers at least one EDM cycle. The preliminary cable outer diameter after filtering serves as the basis for subsequent ion wind correction, preventing high-frequency components in the asynchronous edge components from affecting the closed-loop control of the outer diameter. This processing method retains the true outer diameter change information and suppresses high-frequency noise without increasing computational complexity.

[0099] S4: Based on the synchronous disturbance component and the cosine of the angle between the electrode arrangement direction of the spark tester and the gravity direction, the refractive index fluctuation component caused by the ion wind is obtained, including:

[0100] Calculate the cosine of the angle between the electrode arrangement direction of the spark tester and the direction of gravity; multiply the preset reference coefficient by the cosine of the angle to obtain the linear coefficient;

[0101] The initial ion wind disturbance offset is obtained by multiplying the synchronization disturbance component by a linear coefficient, and the dimension of the initial ion wind disturbance offset is length.

[0102] Dividing the initial ion wind disturbance offset by the object size corresponding to each pixel yields the dimensionless refractive index fluctuation component caused by the ion wind.

[0103] It should be noted that, under the influence of gravity, the ion wind generated by the spark testing machine is deflected upwards, causing different degrees of disturbance in the upper and lower halves of the optical outer diameter detection projection edge position signal in the vertical direction. The cosine of the angle between the electrode arrangement direction of the spark testing machine and the direction of gravity controls the intensity of the upward deflection of the ion wind; the smaller the angle, the larger the cosine value, and the more obvious the vertical asymmetry. Therefore, the linear coefficient = preset reference coefficient × cosθ reflects the actual conversion ratio between the amplitude of the synchronous disturbance component and the outer diameter measurement deviation, converting the synchronous disturbance component into the edge position deviation amplitude caused by the ion wind under the current electrode direction.

[0104] The preset reference coefficient is calibrated using a standard cable with a known outer diameter in the spark tester. It is obtained by measuring the correspondence between the amplitude of the synchronous disturbance component and the outer diameter measurement deviation, and is a dimensionless constant.

[0105] Dividing the initial ion wind disturbance offset (dimension: length) by the object size corresponding to each pixel yields the dimensionless refractive index fluctuation component caused by the ion wind. Since the refractive index itself is a dimensionless ratio, this operation converts the length-dimension offset into a dimensionless quantity characterizing the relative change in refractive index. The object size corresponding to each pixel is in the length dimension, determined by the pixel spacing and imaging magnification of the linear array camera. This component characterizes the relative change in refractive index caused by the ion wind; its absolute value reflects the relative amplitude of the ion wind disturbance, used to subsequently eliminate ion wind disturbances from the initial cable outer diameter and improve the stability of the edge position signal.

[0106] S5: Determine the true outer diameter of the cable based on the refractive index fluctuation component caused by ion wind, and output the true outer diameter of the cable online to the outer diameter closed-loop control system, including:

[0107] By utilizing the refractive index fluctuation component caused by ion wind and combining it with the projected geometric relationship corresponding to the outer diameter of the initial cable, the refractive index fluctuation component is multiplied by the equivalent optical path length corresponding to the outer diameter of the initial cable to obtain the residual offset of the outer diameter of the initial cable caused by ion wind disturbance. The dimension of the residual offset of ion wind disturbance is length.

[0108] The true outer diameter of the cable is obtained by subtracting the residual offset due to ion wind disturbance from the initial outer diameter of the cable.

[0109] It should be noted that the refractive index fluctuation component caused by ion wind causes a shift in the position of the optical outer diameter detection projection edge, and the shift direction is consistent with the direction of refractive index change in the optical path. The projection geometry refers to the object-space dimension corresponding to each pixel. Multiplying the refractive index fluctuation component (dimensionless) by the equivalent optical path length corresponding to the initial cable outer diameter yields the residual offset of ion wind disturbance on the initial cable outer diameter, with the dimension of length. The equivalent optical path length refers to the actual geometric path length of the parallel backlight emanating from the backlight source, passing through the air gaps on both sides of the cable, and reaching the imaging target surface, determined by the mechanical dimensions of the system's optical layout. Subtracting the residual offset of ion wind disturbance from the initial cable outer diameter eliminates the spurious fluctuations in outer diameter caused by ion wind disturbance, yielding the true outer diameter of the cable. The outer diameter closed-loop control system receives the true outer diameter of the cable and adjusts the extruder's extrusion rate or traction speed according to the true outer diameter to maintain the stability of the cable outer diameter.

[0110] It should be noted that the residual offset of the ion wind disturbance is a disturbance component extracted synchronously in real time. This component is subtracted from the initial cable outer diameter to achieve real-time cancellation of the same-frequency disturbance. To further eliminate residual high-frequency components, an adaptive notch filter is used on the subtracted outer diameter signal to form a deep notch at the operating frequency of the spark testing machine and its integer multiples of harmonics, accurately suppressing this specific frequency and its harmonics, while protecting other frequency components of the true outer diameter signal from being affected.

[0111] Example 2: Based on Example 1, a real-time online detection system for cable outer diameter based on optical vision, such as... Figure 2 As shown, it includes:

[0112] The module for extracting the wall thickness of the artificially enhanced bright band is used to acquire the backlight projection image, determine the intensity distribution of the artificially enhanced bright band, and inversely solve it into the local sheath wall thickness distribution.

[0113] The module for calculating the outer diameter in the eccentric direction is used to determine the conductor eccentricity direction based on the local sheath wall thickness distribution, and to establish a set of cross-sectional geometric relationship equations to solve for the conductor eccentricity and the preliminary cable outer diameter.

[0114] The ion wind disturbance component extraction module is used to obtain the projection edge position signal and the spark tester drive voltage signal, and combine the cosine value of the included angle to obtain the refractive index fluctuation component.

[0115] The cable true outer diameter output module is used to correct the preliminary cable outer diameter based on the refractive index fluctuation component to obtain the cable true outer diameter, and then output it online to the outer diameter closed-loop control system.

[0116] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for real-time online detection of cable outer diameter based on optical vision, characterized in that, Includes the following steps: S1: Online real-time acquisition of the backlight projection image of the actual cable, and determination of the intensity distribution of the artificially increased brightness band based on the backlight projection image, and inverse solution of the intensity distribution of the artificially increased brightness band to form the local sheath wall thickness distribution; S2: Determine the conductor eccentricity direction based on the local sheath wall thickness distribution, and obtain the conductor eccentricity and preliminary cable outer diameter based on the conductor eccentricity direction; S3: Online real-time acquisition of the optical outer diameter detection projection edge position signal and the spark testing machine drive voltage signal, and determination of the synchronous disturbance component; S4: Based on the synchronous disturbance component and the cosine value of the angle between the electrode arrangement direction of the spark tester and the gravity direction, the refractive index fluctuation component caused by the ion wind is obtained. S5: Determine the true outer diameter of the cable based on the refractive index fluctuation component caused by ion wind, and output the true outer diameter of the cable to the outer diameter closed-loop control system online.

2. The method for real-time online detection of cable outer diameter based on optical vision according to claim 1, characterized in that, The process of acquiring the backlight projection image of the actual cable in real time online and determining the intensity distribution of the artificially inflated bright band based on the backlight projection image includes: In a backlit projection image, a diffuse bright band region located outside the geometric shadow edge and with a brightness higher than the brightness threshold is defined as an artificially increased bright band region. Extract the intensity of the s-polarization component and the p-polarization component in the artificially enhanced bright band region; The sum of the two is used to obtain the total polarization intensity, which is then used as the intensity distribution of the artificially increased bright band.

3. The method for real-time online detection of cable outer diameter based on optical vision according to claim 1, characterized in that, The process of inversely solving the intensity distribution of the artificially inflated bright band to form a local sheath wall thickness distribution includes: The attenuation coefficient is obtained by dividing the product of the sheath refractive index and the reflectivity of the conductor surface by the sine of the critical angle of total internal reflection, and then by the preset normalized wall thickness constant. The attenuation coefficient is then multiplied by the illusory bright band intensity to obtain the rate of change of the illusory bright band intensity with the increase of the local sheath wall thickness. If the absolute value of the rate of change decreases as the local sheath wall thickness increases, then it is confirmed that the intensity of the artificially increased bright band has a monotonically decreasing relationship with the local sheath wall thickness. Based on the monotonically decreasing relationship, the intensity of the artificially increased bright band at each spatial location in the intensity distribution of the artificially increased bright band is solved point by point to obtain the local sheath wall thickness corresponding to each spatial location, thus forming a local sheath wall thickness distribution.

4. The method for real-time online detection of cable outer diameter based on optical vision according to claim 1, characterized in that, The process of determining the conductor eccentricity direction based on the local sheath wall thickness distribution, and obtaining the conductor eccentricity and preliminary cable outer diameter based on the conductor eccentricity direction, includes: Extract the circumferential minimum and circumferential maximum directions from the local sheath wall thickness distribution; If the direction of the circumferential minimum is opposite to the direction of the circumferential maximum, the direction of the circumferential minimum is determined as the direction of conductor eccentricity; The first projection width of the backlight projection image is obtained in the conductor eccentricity direction; The second projection width of the backlight projection image is obtained in a direction perpendicular to the conductor eccentricity direction; Based on the first projection width, the second projection width, the theoretical wall thickness, and the conductor radius, establish a set of equations relating the cross-section geometry. Solve the set of equations relating the cross-section geometry to obtain the conductor eccentricity and the preliminary cable outer diameter.

5. The method for real-time online detection of cable outer diameter based on optical vision according to claim 4, characterized in that, The establishment of the set of equations relating the cross-section geometric relationships includes: ； in, This represents the theoretical wall thickness in the conductor's eccentric direction. The theoretical wall thickness is in the direction perpendicular to the conductor's eccentricity. It is half the initial cable outer diameter. Where is the conductor radius, For conductor eccentricity, The first projection width, The second projection width, This is the artificial offset at the edge in the direction of conductor eccentricity. This is an artificial offset at the edge in a direction perpendicular to the conductor's eccentricity. and The intensity of the artificially increased bright band is obtained by inverse solving the theoretical wall thickness, and then converted according to the projection geometric relationship between the intensity of the artificially increased bright band and the edge offset.

6. The method for real-time online detection of cable outer diameter based on optical vision according to claim 5, characterized in that, The process of transforming the intensity of the artificially inflated bright band with the edge offset based on the projected geometric relationship includes: Using the monotonically decreasing relation, the corresponding artificially increased bright band intensity is obtained by inverse solving the theoretical wall thickness in the conductor eccentric direction and the direction perpendicular to the conductor eccentric direction, respectively. Based on the deviation path of the totally internally reflected light rays as they propagate within the sheath and exit from the outer surface relative to the geometric shadow edge, the deviation amount corresponding to the artificially increased brightness band intensity is calculated, and the deviation amount is determined as follows: and .

7. The method for real-time online detection of cable outer diameter based on optical vision according to claim 1, characterized in that, The online real-time acquisition of the optical outer diameter detection projection edge position signal and the spark testing machine drive voltage signal, and the determination of the synchronization disturbance component, includes: The phase of the optical outer diameter detection projection edge position signal at the working frequency and harmonics of the spark testing machine is compared with the phase of the spark testing machine drive voltage signal at the same frequency. Components with stable phase differences and less than the phase difference threshold are extracted as synchronization perturbation components.

8. The method for real-time online detection of cable outer diameter based on optical vision according to claim 1, characterized in that, The refractive index fluctuation component caused by ion wind is obtained based on the synchronous disturbance component and the cosine of the angle between the electrode arrangement direction of the spark tester and the gravity direction, including: Calculate the cosine of the angle between the electrode arrangement direction of the spark tester and the direction of gravity; multiply the preset reference coefficient by the cosine of the angle to obtain the linear coefficient; Multiply the synchronization disturbance component by the linear coefficient to obtain the initial ion wind disturbance offset. Dividing the initial ion wind disturbance offset by the object size corresponding to each pixel yields the dimensionless refractive index fluctuation component caused by the ion wind.

9. The method for real-time online detection of cable outer diameter based on optical vision according to claim 1, characterized in that, The process of determining the true outer diameter of the cable based on the refractive index fluctuation component caused by ion wind, and outputting the true outer diameter of the cable online to the outer diameter closed-loop control system includes: By utilizing the refractive index fluctuation component caused by ion wind and combining it with the projected geometric relationship corresponding to the outer diameter of the initial cable, the refractive index fluctuation component is multiplied by the equivalent optical path length corresponding to the outer diameter of the initial cable to obtain the residual offset of the outer diameter of the initial cable caused by ion wind disturbance. The true outer diameter of the cable is obtained by subtracting the residual offset due to ion wind disturbance from the initial outer diameter of the cable.

10. A real-time online detection system for cable outer diameter based on optical vision, used to implement the real-time online detection method for cable outer diameter based on optical vision as described in any one of claims 1-9, characterized in that, include: The module for extracting the wall thickness of the artificially enhanced bright band is used to acquire the backlight projection image, determine the intensity distribution of the artificially enhanced bright band, and inversely solve it into the local sheath wall thickness distribution. The module for calculating the outer diameter in the eccentric direction is used to determine the conductor eccentricity direction based on the local sheath wall thickness distribution, and to establish a set of cross-sectional geometric relationship equations to solve for the conductor eccentricity and the preliminary cable outer diameter. The ion wind disturbance component extraction module is used to obtain the projection edge position signal and the spark tester drive voltage signal, and combine the cosine value of the included angle to obtain the refractive index fluctuation component. The cable true outer diameter output module is used to correct the preliminary cable outer diameter based on the refractive index fluctuation component to obtain the cable true outer diameter, and then output it online to the outer diameter closed-loop control system.

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