A flying ink droplet visual measurement method and system based on a scanning galvanometer

Abstract

The application belongs to the field of novel display, and particularly relates to a flying ink droplet visual measurement method and system based on a scanning galvanometer, comprising: setting a variable focus mirror at the end of the lens of a camera used for collecting ink droplet images, and setting a galvanometer for changing the direction of the light beam at a certain position of the light beam used for camera exposure; the galvanometer can rotate around a certain position under control, so that the reflected light beam can hit the flying ink droplet region corresponding to the jet hole in different directions at the certain position; the variable focus mirror is used for adjusting the camera lens focal length when collecting the flying ink droplet images corresponding to the jet holes at different distances from the reflection point of the galvanometer, so that the camera can clearly collect images; the overall visual observation range is aligned with the flying ink droplet region to be detected; by rotating the galvanometer and adjusting the variable focus mirror, the flying ink droplets sprayed by each jet hole in the detection region are sequentially collected; and the flying ink droplet visual measurement is completed through image processing. The application uses a small number of low-inertia moving parts to realize efficient detection of arrayed jet holes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new display, more particularly, to a flying ink droplet visual measurement method and system based on a scanning galvanometer. BACKGROUND

[0002] New display is one of the key development directions of China's strategic emerging industries, aiming to achieve the goals of ultra-high resolution, large size, light and thin flexibility, and low cost. Traditional vacuum evaporation technology has problems such as high energy consumption, serious material waste, and complex process. In contrast, inkjet printing technology configures functional raw materials into ink, and makes organic or inorganic electronic devices on rigid or flexible substrates through inkjet printing technology, which has the advantages of adaptability to large-area preparation, high material adaptability and utilization rate, low cost, and green manufacturing, and has become an important development direction of future new display industry.

[0003] In the inkjet printing process, due to the influence of process parameters such as the condition of the ejection orifice in the nozzle array, the properties of the ink, and the printing atmosphere environment, abnormal states such as ejection orifice blockage, ink droplet flight deflection, satellite ink droplet, tailing, and ink droplet volume and speed out-of-limit may occur, resulting in ink droplet volume or flight abnormalities, and eventually defects such as missing printing, connection, scattered dots, and uneven ink amount when landing on the substrate, thereby affecting the quality of the display screen. For inkjet printing of large-size substrates, multiple nozzles in the nozzle array are usually used to work simultaneously. Due to the large number of ejection orifices to be detected, it is necessary to efficiently detect the volume, speed, flight angle, and flight trajectory of the ejected ink droplets to ensure the printing effect.

[0004] At present, inkjet printing ink droplet measurement methods can be divided into offline and online two categories. Offline measurement mainly adopts weighing method, which collects a large number of ink droplets at a certain frequency and measures the total mass to calculate the average mass of a single ink droplet and the volume of the ink droplet according to the density. Although this method has high measurement accuracy, it is only suitable for deposited ink droplets, is easily affected by ink solvent evaporation, and cannot detect ink droplet flight speed and angle, so it is only suitable as a comparison and verification means for other measurement methods. Online measurement mainly includes induction method, laser interference method and visual method. The induction method judges whether the ejection is abnormal by measuring the self-induction voltage when the ejection orifice ejects, but it can only be qualitatively detected and is not suitable for accurate measurement of ink droplets. The laser interference method uses the principle of phase Doppler, uses multiple laser beams to interfere in the ink droplet measurement area, and calculates the volume, speed and angle of the ink droplet through interference signal analysis, but the high cost restricts its application to some extent. The visual method is a method of using a camera to shoot flying ink droplets in the inkjet process, and calculating the volume, speed and angle of the ink droplets through image processing technology. This method has low cost and can accurately measure flying ink droplets, but it can usually only detect a single ejection orifice at a time, and the detection interval time is long and the detection efficiency is low.

[0005] Therefore, for the case of multiple nozzles in the nozzle array being used at the same time and a large number of to-be-detected nozzle holes, designing a new detection system and scheme to realize efficient and accurate online measurement of the nozzle array has become a key technical requirement urgently needed to be solved in the field. SUMMARY

[0006] In view of the defects and improvement needs of the prior art, the present application provides a flying ink droplet visual measurement method and system based on a scanning galvanometer, which aims to improve the detection efficiency of arrayed flying ink droplets and realize efficient and accurate online measurement of the nozzle array.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present application, a flying ink droplet visual measurement method based on a scanning galvanometer is provided, comprising:

[0008] A variable focus mirror is arranged at the end of the lens of the camera used for collecting flying ink droplet images, and a scanning galvanometer for changing the direction of the light beam by reflection is arranged at a certain position of the light beam used for camera exposure; wherein the scanning galvanometer can be rotated around the certain position under control, so that the reflected light beam can hit the flying ink droplet region corresponding to the nozzle in different directions at the certain position in a direction perpendicular to the flight direction of the flying ink droplet; the variable focus mirror is used to adjust the focal length of the camera lens when collecting flying ink droplet images corresponding to nozzles with different distances from the reflection point of the scanning galvanometer to ensure clear image collection by the camera;

[0009] The position of the overall adjustment motion frame and / or the nozzle array is adjusted so that the visual observation range is aligned with the to-be-detected flying ink droplet region; by rotating the scanning galvanometer and adjusting the variable focus mirror, the flying ink droplets ejected by each to-be-detected nozzle in the to-be-detected flying ink droplet region are sequentially subjected to ink droplet image collection; through image processing, the flying ink droplet visual measurement is completed, wherein the visual observation range is determined according to the rotatable scanning range of the scanning galvanometer and the adjustable focal length range of the variable focus mirror.

[0010] Further, when performing visual measurement on arrayed flying ink droplets, the method further comprises, before S2:

[0011] Each arrayed flying ink droplet region corresponding to each nozzle is divided into a plurality of local scanning detection regions; wherein the shape and size of each local scanning detection region are determined by the following method: according to the rotatable angle range of the scanning galvanometer in a rotation plane, a sector region that can be scanned by the light beam reflected by the scanning galvanometer is determined, and according to the distance from the focal plane to the reflection point of the scanning galvanometer when the longest and shortest focal lengths of the variable focus mirror are used, the sector region is intercepted to obtain a fan ring region that can realize clear imaging, and the shape and size of the fan ring region are the shape and size of the local scanning detection region;

[0012] The specific implementation of S2 is:

[0013] The position of the visual observation motion frame and / or the nozzle array is adjusted as a whole so that the visual observation range is aligned with the current local scanning detection area to be detected; the flying ink drops ejected by each nozzle in the current local scanning detection area to be detected are sequentially imaged in the manner that the light source light beam is directed to the flying ink drop area of the nozzle to be detected by rotating the scanning galvanometer and the camera is clearly imaged by adjusting the variable focus lens; the step is repeated until the imaging of all local scanning detection areas is completed; wherein the visual observation range is determined according to the distance from the focus plane of the variable focus lens using the longest and shortest focal length to the reflection point of the scanning galvanometer and the scannable sector area of the scanning galvanometer.

[0014] Further, the implementation of sequentially imaging the flying ink drops ejected by each nozzle in the current local scanning detection area to be detected is as follows:

[0015] According to the coordinates of the current detected nozzle and the coordinates of the next nozzle to be detected, the scanning galvanometer is rotated and the variable focus lens is adjusted to change the observation direction and the focus plane position, thereby realizing the imaging of the flying ink drops ejected by each nozzle in the current local scanning detection area;

[0016] wherein a reference observation point (α0, l0) is preset for the current local scanning detection area, α0 represents the initial deflection angle of the scanning galvanometer relative to the direction of the light source light beam before reflection, and l0 represents the initial distance from the focus plane of the variable focus lens to the reflection point of the scanning galvanometer;

[0017] When the image of the flying ink drops ejected by the next nozzle to be detected is collected, the deflection angle of the scanning galvanometer relative to the direction of the light source light beam before reflection is wherein A is the reflection point position of the scanning galvanometer, B is the position of the current detected nozzle, and C is the position of the next nozzle to be detected, A, B, and C are in the global coordinate system and correspond to coordinate data, respectively represent the lengths of vectors ;

[0018] the distance l from the focus plane of the variable focus lens to the reflection point of the scanning galvanometer i is taken as the focal length of the variable focus lens and is calculated based on the following manner:

[0019] Further, the image collection is performed in the manner that the flash exposure is used and each ejected ink drop is subjected to nanosecond-level double flashing in one exposure time period, so that the collected image has the projection images of the same ink drop at the front and rear two time points;

[0020] In the collected flight ink drop image of each nozzle, at least one group of ink drop projection images is contained, wherein each group of ink drop projection images includes two upper and lower projection images, the upper projection image of each group of ink drop projection images is a projection image of one ink drop at a previous moment corresponding to double flash or is a superimposed image of projection images of multiple ink drops at previous moments corresponding to double flash, and the lower projection image of each group of ink drop projection images is a projection image of one ink drop at a next moment corresponding to double flash or is a superimposed image of projection images of multiple ink drops at next moments corresponding to double flash.

[0021] Further, based on the flight ink drop image corresponding to each nozzle, the actual volume of the ink drop jetted by the nozzle is calculated, and the implementation is as follows:

[0022] Each projection image in the flight ink drop image is detected and a target frame is selected, and the image area in each target frame is denoised; the average gradient G of each denoised projection image is calculated as an evaluation index of the clarity of the projection image; the weighted coefficient corresponding to each projection image is determined based on the average gradient G of the projection image; the actual height of the ink drop corresponding to each projection image after edge detection is calculated according to the camera calibration value, the ink drop corresponding to each projection image is discretized into M slices with a thickness of △h in the height direction, and the actual volume V of the ink drop jetted by the nozzle is calculated based on the following expression:

[0023]

[0024] In the formula, λ i respectively represent the weighted coefficient of the i th projection image, i ∈ {1, 2, …, N}, d j represents the diameter of the j th circular slice layer cross section of the ink drop of the i th projection image, j ∈ {1, 2, …, M}.

[0025] Further, a deep learning target detection algorithm YOLO is used to frame and locate each projection image in the flight ink drop image;

[0026] Gaussian filtering based on the following expression is used to denoise the image area in each target frame: *Img=G 3×3 (x,y)*Img o ; In the formula, G(x,y) represents a Gaussian function at two-dimensional coordinates (x,y), σ is a standard deviation, Img o , and Img are the original gray projection image and the denoised projection image respectively, G 3×3 (x,y) is a 3×3 Gaussian smoothing convolution kernel generated with the origin as the center, and * represents convolution operation;

[0027] The average gradient G of each projection image is calculated by using Sobel operator based on the following expression:

[0028]

[0029]

[0030] G = Mean(G abs );

[0031] In the formula, G x , G y are the gradients of the projection image in the horizontal direction and the vertical direction respectively, G abs is the absolute value of the projection image gradient, and * represents convolution operation.

[0032] The weighted coefficient λ corresponding to each projection image is determined based on the following expression:

[0033]

[0034] In the formula, t i is the value of the average gradient G i of the i-th projection image after normalization to the interval [-10, 10], i∈{1, 2, …, N}, and N is the total number of projection images in the flying ink droplet image.

[0035] Further, when there are Q groups of ink droplet projection images in the flying ink droplet image corresponding to each nozzle through target detection, the flying speed of the jet ink droplet of the nozzle is calculated based on the flying ink droplet image corresponding to each nozzle in the following manner:

[0036] The interval time Δt between the two flash signals applied to the same ink droplet before and after the acquisition of the flying ink droplet image corresponding to the nozzle is determined;

[0037] The Q groups of ink droplet projection images are respectively denoised; the ink droplet contour lines are segmented from each denoised projection image, and the Q group of ink droplet contour line barycentric coordinates in the camera image coordinate system R Cam are determined according to the ink droplet contour lines:

[0038] (x 1,1 ,z 1,1 )(x 1,2 ,z 1,2 ),(x 2,1 ,z 2,1 )(x 2,2 ,z 2,2 ),…,(x Q,1 ,z Q,1 )(x Q,2 ,z Q,2 );

[0039] The weighted coefficient ρ corresponding to each group of ink drop projection images is determined based on the following expression:

[0040]

[0041] wherein λ i,1 , λ i,2 respectively represent the weighted coefficients of the upper and lower two projection images in the i-th group of ink drop projection images, i ∈ {1, 2, …, Q};

[0042] The flight speed S of the ink drop ejected from the nozzle is calculated based on the following expression:

[0043]

[0044] wherein ρ i represents the weight of the i-th group of ink drop projection images when it is used to calculate the flight speed of the ink drop ejected from the nozzle.

[0045] Further, the flight trajectory and flight angle of the ink drop ejected from the nozzle are calculated based on the flight ink drop image corresponding to the nozzle, in the following manner:

[0046] Each projection image is denoised, and the ink drop contour line is segmented from the denoised projection image, and the W group of ink drop contour line barycentric coordinates (x1, z1), (x2, z2), …, (x w , z w ) in the camera image coordinate system R Cam are determined according to the ink drop contour line, and a cubic polynomial model is used to fit the function f(x) = az 3 +bz 2 +cz+d as the flight trajectory of the ink drop in the camera observation direction, and the following expression is used to perform the flight angle γ measurement process of the flight ink drop in the camera observation direction: γ = tan -1 max(f′(a)).

[0047] The application further provides a flying ink drop visual detection system based on a scanning galvanometer, comprising a camera, a lens, a variable focus mirror, a scanning galvanometer and an illumination light source;

[0048] The camera is arranged on one side of the flying ink drop region; the variable focus mirror is arranged at the lens end of the camera; the scanning galvanometer is arranged at a certain position of the light source light beam for camera exposure, and is used to change the light beam direction by reflection.

[0049] The scanning galvanometer can be controlled to rotate around the certain position, so that the reflected light source light beam can hit the flying ink drop region corresponding to the nozzle in different directions at the certain position in a direction perpendicular to the direction of the flying ink drop; the variable focus mirror is used to adjust the focal length of the lens of the camera when collecting the flying ink drop image corresponding to the nozzle with a distance different from the reflection point of the scanning galvanometer, so as to ensure that the camera clearly collects the image.

[0050] The application also provides a scanning galvanometer-based array ink drop efficient visual measurement system for performing the scanning galvanometer-based flying ink drop visual measurement method as described above, comprising a control module, a data processing module, a mechanical auxiliary module, and the flying ink drop visual detection system as described above.

[0051] The flying ink drop visual detection system is used to collect the flying ink drop image.

[0052] The mechanical auxiliary module comprises a motion frame and a motion shaft, and is used to move and position the nozzle array and the flying ink drop visual detection system.

[0053] The data processing module is used to divide the arrayed flying ink drop region corresponding to each nozzle into a plurality of local scanning detection regions.

[0054] The control module is used to control the movement of the nozzle array according to the current local scanning detection region to be detected, and control the rotation of the scanning galvanometer in the flying ink drop visual detection system according to the coordinates of each nozzle in the current local scanning detection region to be detected, so that the light beam of the flying ink drop visual detection system is aligned with the flying ink drop ejected by the nozzle to be detected, and simultaneously control the variable focus mirror in the flying ink drop visual detection system, so that the ejected ink drop of the nozzle to be detected is located within the depth of field range, and clear imaging is realized.

[0055] The data processing module is also used to calculate the parameters of the ejected ink drop of each nozzle based on the flying ink drop image corresponding to the nozzle, and evaluate the ejection state.

[0056] Overall, the above technical solutions conceived by the application can achieve the following beneficial effects:

[0057] (1) The application introduces a scanning galvanometer and a variable focus mirror during visual observation, changes the direction of the light beam through the scanning galvanometer, and hits the ejected ink drop of different nozzles. Since the distances between the ejected ink drops of different nozzles and the scanning galvanometer are different, the focal length is adjusted through the variable focus mirror to collect a clear image. When detecting the flying ink drop region of a small range of array nozzles, the motion frame and / or nozzle position do not need to be adjusted as a whole, only the rotation angle of the scanning galvanometer and the focal length of the variable focus mirror need to be adjusted, so that clear imaging of the flying ink drops of multiple nozzles can be realized, and efficient visual measurement of the flying ink drops can be realized.

[0058] (2) The application introduces a scanning galvanometer and a variable focus lens when observing the arrayed flying ink drops, changes the direction of the light through the scanning galvanometer, and hits the ink drops sprayed from different nozzles. Since the distances between the ink drops sprayed from different nozzles and the scanning galvanometer are different, the focal length is adjusted through the variable focus lens to collect a clear image. Since the rotation amplitude of the scanning galvanometer is limited, the application proposes the concept of local scanning detection area for the detection of arrayed flying ink drops. According to the rotation amplitude of the scanning galvanometer and the focal length adjustment amplitude of the variable focus lens, the size and shape of the local scanning detection area are determined, so that the arrayed flying ink drop area corresponding to each nozzle is divided into multiple local scanning detection areas with the above size and shape. In a local scanning detection area, the deflection angle of the scanning galvanometer and the focal length of the variable focus lens are adjusted to realize fast switching of the observation target. When switching the local scanning detection area, the entire vision detection system or / and the nozzle array can be adjusted. Compared with the conventional flying ink drop detection scheme, the volume and motion inertia of components such as the scanning galvanometer and the variable focus lens are small, so that the vision detection system can quickly switch the detection target in a large range by quickly moving in a small range, which makes up for the long movement time when aligning the next nozzle after detecting the current nozzle, effectively improves the observation efficiency. In addition, the synchronous scanning detection method for the ink drop sprayed by the nozzle array designed by the application does not need to move during the scanning detection of the single local scanning detection area by the vision detection system, so that the ink drop spraying state is more stable, which is beneficial to improve the image acquisition quality and further increase the detection precision.

[0059] (3) The application proposes the concept of reference detection point for each local scanning detection area, and based on the reference detection point, the angle of the scanning galvanometer and the focal length of the variable focus lens are determined when detecting each nozzle in the local scanning detection area, which improves the execution efficiency of visual observation.

[0060] (4) The synchronous scanning detection method for the ink drop sprayed by the nozzle array designed by the application adopts the design of double flashes of the light source in the single exposure time of the camera, so that the projection images of the flying ink drops at the front and rear two times can be obtained in a single frame of picture, and the time interval of the two flashes can be adjusted. This image acquisition method of the vision system can calculate the flying speed and angle of the ink drop using a single frame of image, which significantly reduces the measurement time and saves the detection steps compared with the conventional detection scheme of comparing and calculating the flying speed and angle of the ink drop after collecting two frames of images at a certain time interval.

[0061] (5) regarding the calculation of the volume of the ink droplet, the present application firstly adopts the way of double flashing to collect the image of each ink droplet, and on this basis, through the way of weighted average, the volume calculation weight of the ink droplet corresponding to the clearer projection image is unsaturatedly increased, and the volume calculation weight of the ink droplet corresponding to the blurrier projection image is unsaturatedly reduced by adopting the negative direction one-sided saturated nonlinearity, so that the projection image information of all the ink droplets identified in the image is fully utilized, and the sampling rate and reliability of the volume measurement result are improved.

[0062] (6) further regarding the calculation of the flight speed of the ink droplet, the weight calculation method when calculating the volume of the ink droplet is quoted to determine the weight of each projection image, that is, the clarity of each image region is mapped to the weight for calculating the flight speed of the corresponding ink droplet by adopting the one-sided saturated activation function, so that the image region information of all the ink droplets identified in the image is fully utilized instead of only selecting the local image of the clear part to calculate the speed of the ink droplet, and the sampling rate and accuracy of the speed measurement are improved.

[0063] (7) further regarding the calculation of the flight angle of the ejected ink droplet, compared with only using the two centroid coordinates of the ink droplet at two time points before and after, the method of the present application utilizes the centroid coordinate data of all the ink droplets identified in the image, and at the same time, a nonlinear model is adopted to fit the flight trajectory of the ejected ink droplet, so that the fitting error is reduced, and the sampling rate and accuracy of the angle detection are improved. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 A flow chart of an array ink droplet efficient visual measurement method based on a scanning galvanometer is provided for the embodiment of the present application.

[0065] Figure 2 A local scanning detection region schematic diagram is provided for the embodiment of the present application.

[0066] Figure 3 A visual detection system control signal timing diagram is provided for the embodiment of the present application.

[0067] Figure 4 Another visual detection system control signal timing diagram is provided for the embodiment of the present application.

[0068] Figure 5 A flight ink droplet volume calculation schematic diagram is provided for the embodiment of the present application.

[0069] Figure 6 A schematic diagram of an array ink droplet efficient visual measurement system based on a scanning galvanometer is provided for the embodiment of the present application.

[0070] Figure 7 A three-dimensional structure schematic diagram of a scanning detection system of a printhead array ejecting ink droplets is provided for the embodiment of the present application.

[0071] Figure 8The overall method flowchart of the jet array jetting ink drop scanning detection provided by the embodiment of the application is shown.

[0072] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0073] 10 is a jet array, 20 is a coaxial flash light source, 21 is a camera, 22 is a lens, 23 is a variable focus mirror, 24 is a scanning galvanometer, 30 is a motion frame, 40 is a control module, and 50 is an ink collecting device. DETAILED DESCRIPTION

[0074] In order to make the objectives, technical solutions and advantages of the application clearer, the application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application. In addition, the technical features involved in the various embodiments of the application described below can be combined with each other as long as they do not conflict with each other.

[0075] Embodiment one

[0076] A flying ink drop visual measurement method based on a scanning galvanometer, as shown in FIG. 1, comprises the following steps: Figure 1

[0077] S1, a variable focus mirror is arranged at the end of the lens of the camera used for collecting flying ink drop images, and a scanning galvanometer for changing the direction of the light beam by reflection is arranged at a certain position of the light beam of the light source used for camera exposure; wherein the scanning galvanometer can be rotated around the above-mentioned position under control, so that the reflected light beam can hit the flying ink drop region corresponding to the nozzle in different directions located at the above-mentioned position in a direction perpendicular to the flying direction of the flying ink drop; the variable focus mirror is used to adjust the focal length of the camera lens when collecting the flying ink drop images of the nozzles with different distances from the reflection point of the scanning galvanometer to ensure clear camera imaging;

[0078] S2, the position of the visual observation motion frame and / or the jet array is adjusted as a whole so that the visual observation range is aligned with the flying ink drop region to be detected; the flying ink drop jetted by each nozzle to be detected in the flying ink drop region to be detected is sequentially collected in the form of adjusting the variable focus mirror to make the camera clearly image and rotating the scanning galvanometer to make the light source light beam hit the flying ink drop region of the nozzle to be detected; through image processing, the flying ink drop visual measurement is completed, wherein the visual observation range is determined according to the rotatable scanning range of the scanning galvanometer and the adjustable focal length range of the variable focus mirror.

[0079] ​The embodiment introduces a scanning galvanometer and a variable focus lens during visual observation. The scanning galvanometer changes the direction of light to the jet ink droplets of different nozzles. Since the jet ink droplets of different nozzles have different distances from the scanning galvanometer, the variable focus lens adjusts the focal length to collect clear images. Due to the small volume and motion inertia of the scanning galvanometer and the variable focus lens, when detecting the flight ink droplet area of a small range array nozzle, the overall motion frame and / or the position of the nozzle do not need to be adjusted. Only the rotation angle of the scanning galvanometer and the focal length of the variable focus lens need to be adjusted to achieve clear image acquisition of multiple nozzle flight ink droplets and efficient visual measurement of flight ink droplets.

[0080] Based on the embodiment method, as a preferred example, the embodiment also proposes an array ink droplet efficient visual measurement method based on a scanning galvanometer for array flight ink droplet detection task scenarios, which includes:

[0081] (1) A variable focus lens is arranged at the end of the lens of the camera used to collect flight ink droplet images, and a scanning galvanometer is arranged at a position of the light beam of the light source used for camera exposure to change the direction of the light beam by reflection; wherein the scanning galvanometer can be rotated around the position under control, so that the reflected light beam can hit the flight ink droplet area corresponding to the nozzle in different directions located at the position in a direction perpendicular to the flight direction of the flight ink droplet; the variable focus lens is used to adjust the focal length of the camera lens when collecting flight ink droplet images corresponding to nozzles with different distances from the reflection point of the scanning galvanometer to ensure clear image acquisition of the camera;

[0082] (2) Each array flight ink droplet area corresponding to a nozzle is divided into multiple local scanning detection areas; wherein the shape and size of each local scanning detection area are determined by the following method: according to the rotatable angle amplitude of the scanning galvanometer in a rotation plane, a fan-shaped area that can be scanned by the reflected light beam of the scanning galvanometer is determined, and according to the distance from the focal plane to the reflection point of the scanning galvanometer when the variable focus lens uses the longest and shortest focal length, a part of the fan-shaped area is intercepted to obtain a fan ring-shaped area that can realize clear imaging, and the shape and size of the fan ring-shaped area are the shape and size of the local scanning detection area;

[0083] As shown in Figure 2 , the above-mentioned local scanning detection area is fan ring-shaped, and the determination method of the size is as follows: the fan-shaped area swept by the rotation of the scanning galvanometer is determined, and the distances l1 and l2 from the focal plane to the reflection point of the scanning galvanometer when the variable focus lens uses the longest and shortest focal length are determined, and the part of the fan-shaped area intercepted by l1 and l2 constitutes the local scanning detection area, so that the size of the local scanning detection area is obtained, and the area is Wherein, δ represents the rotatable angle amplitude;

[0084] (3) adjust the position of the visual observation motion frame and / or the nozzle array as a whole so that the visual observation range is aligned with the current local scanning detection area to be detected; sequentially collect the flying ink droplet images of each nozzle in the current local scanning detection area to be detected by rotating the scanning galvanometer so that the light source light beam hits the flying ink droplet area of the nozzle to be detected and adjusting the variable focus lens so that the camera can clearly image, and repeat the step until the image collection of all local scanning detection areas is completed; wherein the visual observation range is determined according to the distance from the focus plane when the variable focus lens uses the longest and shortest focal length to the reflection point of the scanning galvanometer in the scannable sector of the scanning galvanometer.

[0085] Due to the scanning detection range limitation of the visual detection system, the outer contour line of the entire detection area of each nozzle can be formed according to the coordinate points of all the nozzles to be detected, and the area contained in the contour line is divided into multiple visual detection system local scanning detection areas which are sequentially spliced. The adjacent local scanning detection areas can have a small amount of overlapping part to ensure that all the nozzles to be detected are included, but during detection, the nozzles are required not to be repeatedly detected.

[0086] The visual observation direction and the focal length of the embodiment can be adjusted synchronously, and because the scanning galvanometer has a high and adjustable rotation speed and the variable focus lens has a short control response time, the ink droplet synchronous scanning detection method of the nozzle array designed in the embodiment can effectively shorten the detection interval and improve the detection efficiency.

[0087] As a preferred implementation, the implementation of sequentially collecting the flying ink droplet images of each nozzle in the current local scanning detection area to be detected is as follows:

[0088] According to the coordinate of the current detected nozzle and the coordinate of the next nozzle to be detected, the included angle between the scanning galvanometer and the optical axis and the focal length of the variable focus lens are adjusted, so that the observation direction and the focal plane position of the visual detection system are changed, and the image collection of the flying ink droplets of each nozzle in the current local scanning detection area is realized; that is, according to the coordinate of the current detected nozzle and the coordinate of the next nozzle to be detected, the included angle between the scanning galvanometer and the optical axis and the focal length of the variable focus lens are determined, based on the determined included angle and focal length, the deflection angle of the scanning galvanometer is first adjusted so that the optical axis of the visual detection system is aligned with the flying ink droplet of the next nozzle to be detected, and the focal length of the variable focus lens is adjusted so that the flying ink droplet of the next nozzle to be detected is still located within the front and rear depth of field of the focal plane of the visual detection system, and does not appear out of focus due to the change of the observation direction of the visual detection system.

[0089] The way to determine the included angle between the scanning galvanometer and the optical axis and the focal length of the variable focus lens is as follows:

[0090] preset a reference observation point (a0, l0) of a vision detection system for a current local scanning detection area, a0 represents an initial deflection angle of the scanning galvanometer, and l0 represents an initial distance from a focal plane of the variable focus lens to a reflection point of the scanning galvanometer; when an image of a flying ink drop sprayed by a next to-be-detected nozzle is collected, the angle between the scanning galvanometer and the optical axis is wherein A is a reflection point position of the scanning galvanometer, B is a position of a current detected nozzle, and C is a position of a next to-be-detected nozzle, A, B, and C have corresponding coordinate data in a global coordinate system, respectively represent the lengths of vectors respectively; the distance l from the focal plane of the variable focus lens to the reflection point of the scanning galvanometer is i as the focal length of the variable focus lens, is calculated based on the following manner: In other embodiments, a threshold value δ is introduced due to the influence of nozzle arrangement spacing in the printhead array, and if there is a calculation result that the deflection angle of the scanning galvanometer or the focal length changes less than the threshold value, the calculation result is set to zero.

[0091] Regarding the adjustment of the scanning galvanometer and the variable focus lens to clearly collect ink drops sprayed by a next nozzle, in actual application and operation, it can be first determined that the next to-be-detected nozzle is located on which side of a line connecting a current detected nozzle and a reflection point of the scanning galvanometer, and the coordinates of the current detected nozzle B in the global coordinate system are (x1, y1), the coordinates of the next to-be-detected nozzle C are (x i i i ), and the coordinates of the reflection point A of the scanning galvanometer are (x r i r ), the outer product of vectors is calculated. If the outer product of vectors is greater than zero , then point C is on the left of the vector , and the scanning galvanometer needs to be counterclockwise rotated; if the outer product of vectors is less than zero , then point C is on the right of the vector , and the scanning galvanometer needs to be clockwise rotated; if the outer product of vectors is equal to zero , then point C is on the vector , and the scanning galvanometer does not need to be rotated.

[0092] It should be noted that when moving from one local scanning detection area to the next local scanning detection area, the initial detection position of the local scanning detection area can be directly at the reference detection point, and the position of the nozzle array or the entire vision detection system in space is adjusted so that the ink droplet ejected from a nozzle located in the next local scanning detection area is captured in the vision observation field of view to obtain a clear image, and the subsequent nozzle detection adjusts the vision detection system according to the above formula; the initial detection position of the local scanning detection area can also be at other positions other than the reference detection point, and by determining the first nozzle to be detected, the angle between the scanning galvanometer and the optical axis in the vision detection system and the focal length of the variable focus lens are adjusted to clearly capture the image of the flying ink droplet of the first nozzle, and the updated reference observation point (a0, l0) is adjusted, and the subsequent nozzle detection adjusts the vision detection system according to the above formula.

[0093] As an example, the nozzle closest to the center of each local scanning detection area is taken as the starting observation nozzle of the local scanning detection area, and when the local area needs to be detected, the position of the motion frame and / or the nozzle array is adjusted first so that the ink droplet ejected from the starting observation nozzle is located at the reference observation point of the vision detection system, so that the corresponding a0, l0 of the local scanning detection area can be determined.

[0094] The vision detection system can use a coaxial illumination stroboscopic exposure vision system to realize rapid scanning detection of multiple nozzles in the nozzle array, and the number L of nozzles scanned each time can be selected according to actual needs. In actual application of the method, the vision detection system can include a camera, a lens, a coaxial illumination stroboscope, a scanning galvanometer, and a variable focus lens module to capture flying ink droplets ejected from each nozzle in the nozzle array. As a preferred embodiment, the above-mentioned vision detection system uses a stroboscopic exposure and nanosecond double flashing of each ink droplet in an exposure time period to perform image acquisition, so that the captured image has the projection images of the same ink droplet at the front and rear two time points.

[0095] That is, for the camera of the vision detection system, as shown in Figure 3 , its exposure signal S2 is set to lag behind the ejection signal S1 of its corresponding observation nozzle in the synchronous trigger controller of the control module, and the camera exposure lag time t1 is independently adjustable; correspondingly, for the flash signal S3 of the stroboscopic light source, its two nanosecond-level flash pulse widths T 2_1 and T 2_2The sum of the interval time T2 of the two nanosecond-level flash pulses is set to be included in the above-mentioned exposure signal width T1, that is, the two flash pulse widths plus the pulse interval is less than the camera exposure signal width, and the flash pulse width, the flash pulse interval and the flash lag time are also independently adjustable in the synchronous trigger controller. The two flash signals constitute a set of double flashes, which are reflected in the same frame image, and have the same ink droplet projection image at the front and back two time points.

[0096] The method designed the ink droplet synchronous scanning detection method of the nozzle array, adopts the design of two flash lights of the light source in the single exposure time of the camera, can obtain the projection images of the flying ink droplets at the front and back two time points in the single frame picture, and the interval time of the two flash lights is adjustable. The image acquisition mode of the visual system can calculate the flying speed and angle of the ink droplets using the single frame image. Compared with the detection scheme of comparing and calculating the flying speed and angle of the flying ink droplets after collecting the front and back two frame images, the measurement time is significantly reduced and the detection steps are saved.

[0097] As a preferred embodiment, the flying ink droplet image of each nozzle collected by the above-mentioned visual detection system contains at least one set of ink droplet projection images, wherein each set of ink droplet projection images includes upper and lower projection images, the upper projection image of each set of ink droplet projection images is a projection image of an ink droplet at a previous time point corresponding to double flash or is a superimposed image of projection images of multiple ink droplets at respective previous time points corresponding to double flash, and the lower projection image of each set of ink droplet projection images is a projection image of an ink droplet at a subsequent time point corresponding to double flash or is a superimposed image of projection images of multiple ink droplets at respective subsequent time points corresponding to double flash.

[0098] That is, in a relatively long exposure time period, the nozzles are triggered to spray the nanosecond-level double flash of the light source multiple times at a certain frequency, so that the camera collects superimposed ink droplet images, which can improve the image contrast. The upper projection image in the flying ink droplet image is a superposition of the projection images collected by the flash at the previous time points corresponding to the double flash of each sprayed ink droplet, and the lower projection image in the flying ink droplet image is a superposition of the projection images collected by the flash at the subsequent time points corresponding to the double flash of each sprayed ink droplet.

[0099] Specifically, as shown in Figure 4 The camera exposure signal S2 lags behind the spraying signal S1 of the nozzle 10, the lag time t2 of the signal S2 is independently adjustable, the period of the light source flash signal S3 is set to be the same as or an integer multiple of the spraying signal S1, the exposure time T2 of the camera is prolonged, and multiple sets of nanosecond-level double flash T 3_1 and T 3_2 are included in S2, that is, the first pulse width T 3_1, pulse interval time T3 and second pulse width T 3_2 The sum of the pulse width T2 and the lag time t3 of S2 is also independently adjustable.

[0100] As a preferred embodiment, the actual volume of the ink droplet ejected by the nozzle is calculated based on the corresponding flying ink droplet image of the nozzle, and the implementation is as follows:

[0101] Select the position of each projection image frame in the flying ink droplet image, and denoise the image area in each target frame respectively; calculate the average gradient G of each projection image after denoising as the definition evaluation index of the projection image; determine the weighting coefficient corresponding to the projection image based on the average gradient G of each projection image; calculate the actual height of the ink droplet corresponding to each projection image after edge detection according to the camera calibration value, and as shown in Figure 5 , the height direction of each projection image corresponding to the ink droplet is dispersed into M slices with thickness △h, and the actual volume V of the ink droplet ejected by the nozzle is calculated based on the following expression:

[0102]

[0103] In the formula, λ i respectively represent the weighting coefficient of the i-th projection image, i∈{1,2,…,N}, d j represents the diameter of the j-th circular slice layer cross section of the i-th projection image, j∈{1,2,…,M}.

[0104] On the basis of collecting the image of each ink droplet in the form of double flash, the method proposes to increase the volume calculation weight of the clearer projection image corresponding to the ink droplet by using the weighted average method, and to reduce the volume calculation weight of the blur projection image corresponding to the ink droplet by using the negative direction one-sided saturation nonlinearity, so as to fully utilize the projection image information of all ink droplets identified in the image, and to improve the sampling rate and reliability of the volume measurement result.

[0105] As a preferred embodiment, the target frame position of each projection image in the flying ink droplet image is selected based on the deep learning target detection algorithm YOLO;

[0106] Gaussian filtering based on the following expression is used to denoise the image area in each target frame:

[0107]

[0108] Img=G 3×3 (x,y)*Img o ;

[0109] In the formula, G(x,y) represents the Gaussian function at two-dimensional coordinates (x,y), σ is the standard deviation, and Imgo Img and G are the original grayscale projection image and the denoised projection image, respectively. 3×3 (x,y) is a 3×3 Gaussian smooth convolution kernel generated with the origin as the center, and * indicates the convolution operation;

[0110] The average gradient G for each projected image is calculated using the Sobel operator based on the following expression:

[0111]

[0112]

[0113] G = Mean(G abs );

[0114] In the formula, G x G y G represents the gradient of the projected image in the horizontal and vertical directions, respectively. abs The absolute value of the gradient of the projected image; * indicates convolution operation.

[0115] The weighting coefficient λ for each projected image is determined based on the following expression:

[0116]

[0117] In the formula, t i The average gradient G of the i-th projected image i The value after normalization to the interval [-10, 10], i∈{1,2,…,N}, where N is the total number of projected images in the flying ink droplet image.

[0118] As a preferred embodiment, when Q sets of droplet projection images are detected within the image of each nozzle's flying droplet, the flight velocity of the ejected droplets from that nozzle is calculated based on the image of each nozzle's flying droplet as follows:

[0119] Determine the time interval Δt between applying two consecutive flash signals to each of the same ink droplets when acquiring the image of the flying ink droplets corresponding to the nozzle;

[0120] The Q groups of ink droplet projection images were processed using Gaussian Laplace transform to suppress noise; the ink droplet contour lines were segmented from each of the denoised projection images, and the coordinates in the camera image system R were determined based on the corresponding ink droplet contour lines. Cam The centroid coordinates (x) of the Q group of ink droplet profiles 1,1 ,z 1,1 (x) 1,2 ,z 1,2 ),(x 2,1 ,z 2,1 (x) 2,2 ,z2,2 ),…,(x Q,1 ,z Q,1 )(x Q,2 ,z Q,2 ), and the weighted coefficient p corresponding to each group of ink drop projection images is determined based on the following expression:

[0121]

[0122] wherein λ i,1 and λ i,2 respectively represent the weighted coefficients of the upper and lower projection images in the i-th group of ink drop projection images, i∈{1,2,…,Q};

[0123] The flight speed S of the ejected ink drop of the nozzle is calculated based on the following expression:

[0124]

[0125] wherein p i represents the weight of the i-th group of ink drop projection images when it is used to calculate the flight speed of the ejected ink drop of the nozzle.

[0126] The method is directed to the case that there is at least one group of ink drop projection images in the flight ink drop image, and proposes to use the way of determining the weight of each projection image according to the sharpness when calculating the volume of the ink drop as described above, to represent the contribution of each projection image to the calculation of the flight speed by the weight, and to calculate the average flight speed to represent the flight speed of the ink drop of the corresponding nozzle.

[0127] It should be noted that when there is only one group of ink drop projection images in the flight ink drop image corresponding to each nozzle after target detection, the way of calculating the flight speed of the ejected ink drop of the nozzle based on the flight ink drop image is:

[0128] The interval time Δt of applying the front and rear two flash signals to the same ink drop when collecting the flight ink drop image corresponding to each nozzle is determined;

[0129] The upper and lower projection images of the flight ink drop image corresponding to each nozzle are processed by Gaussian Laplace transform respectively to suppress noise; the edge of each of the two projection images is detected, and the two centroid coordinates (x1, z1) and (x2, z2) of each ink drop contour line in the camera image coordinate system R Cam are determined according to the ink drop contour lines corresponding to the upper and lower projection images after edge detection; the instantaneous speed of the ejected ink drop in the observation direction of the camera is calculated based on the following expression:

[0130] As a preferred embodiment, the way of calculating the flight trajectory and flight angle of the ejected ink drop of the nozzle based on the flight ink drop image corresponding to each nozzle is:

[0131] Gauss Laplace transform is used to suppress noise for each projection image; the ink drop profile line is segmented from each denoised projection image, and the W group ink drop profile line centroid coordinates (x1, z1), (x2, z2), …, (x Cam ,z w ) in the camera image coordinate system R w is determined according to the ink drop profile line, and a cubic polynomial model is used to fit the function f(x) = az 3 +bz 2 +cz+d as the flight trajectory of the ink drop in the camera observation direction, and the following expression is used to perform the flight angle γ measurement of the flying ink drop in the camera observation direction:

[0132] γ = tan -1 max(f′(x))

[0133] It should be noted that when there is only one group of ink drop projection images in the flying ink drop image corresponding to a nozzle through target detection, the flight angle of the jet ink drop of the nozzle is calculated based on the ink drop profile line centroid coordinates (x1, z1) and (x2, z2) of the two projection images before and after the group of ink drop projection images, and the flight angle γ of the flying ink drop in the camera observation direction is calculated using the following expression:

[0134] Embodiment two

[0135] A flying ink drop visual detection system based on a scanning galvanometer, comprising a camera, a lens, a variable focus mirror, a scanning galvanometer, and an illumination light source; wherein the camera is arranged on one side of the flying ink drop region; the variable focus mirror is arranged at the end of the lens of the camera; the scanning galvanometer is arranged at a certain position of the light beam for camera exposure, and is used to change the direction of the light beam by reflection;

[0136] The scanning galvanometer can be controlled to rotate around the certain position, so that the reflected light source light beam can hit the flying ink drop region corresponding to the nozzle in different directions located at the certain position in a direction perpendicular to the direction of the flying ink drop;

[0137] Embodiment three

[0138] As an application of embodiment two, this embodiment proposes an array ink drop high-efficiency visual measurement system based on a scanning galvanometer, which is used to execute a flying ink drop visual measurement method based on a scanning galvanometer as described in embodiment one, such as Figure 6As shown, it comprises a control module, a data processing module, a mechanical auxiliary module, and a flying ink droplet visual detection system as described in Embodiment Two.

[0139] The flying ink droplet visual detection system is used to collect flying ink droplet images; the mechanical auxiliary module comprises a moving frame and a moving shaft, which are used to move and position the printhead array and the flying ink droplet visual detection system; the data processing module is used to divide the arrayed flying ink droplet region corresponding to each printhead into multiple local scanning detection regions; the control module is used to control the movement of the printhead array according to the current local scanning detection region to be detected, control the rotation of the scanning galvanometer in the flying ink droplet visual detection system according to the coordinates of each nozzle in the current local scanning detection region to be detected, so that the light beam of the flying ink droplet visual detection system is aligned with the flying ink droplet ejected by the nozzle to be detected, and at the same time control the variable focus lens in the flying ink droplet visual detection system, so that the ejected ink droplet of the nozzle to be detected is located within its depth of field range, to realize clear imaging; the data processing module is also used to calculate the parameters of the ejected ink droplet of each nozzle based on the flying ink droplet image corresponding to each nozzle, and evaluate the ejection state.

[0140] The flying ink droplet visual detection system adopts coaxial flash exposure to realize image collection and detection of the ink droplets ejected by the printhead array. The visual detection system comprises a camera 21, a lens 22, a variable focus lens 23, a coaxial flash light source 20, and a scanning galvanometer 24.

[0141] The printhead is provided with the following features: the printhead array is composed of multiple printheads 10 of the same specification spliced in the same direction, and the printhead array is installed on a moving component with Y1, Z1 degrees of freedom, i.e. the first horizontal longitudinal degree of freedom and the first vertical degree of freedom; the multiple nozzles of the printhead are all located on the lower surface E of the printhead, and the nozzles of each printhead in the printhead array are all located on the same horizontal plane F, i.e. E=F after the printhead is spliced.

[0142] For the mechanical auxiliary module, as shown in Figure 6 and Figure 7 It comprises a moving frame 30 on which the detection module is arranged, and a support arm and a moving shaft on which the printhead array is hung.

[0143] The flying ink droplet visual detection system (camera 21, lens 22, stroboscopic light source 20, variable focus mirror 23, scanning galvanometer 24) is installed on the moving frame 30 and can move with the moving frame 30; the moving frame 30 has two mutually perpendicular degrees of freedom X2 and Y2, and the degree of freedom X2 is the same as the degree of freedom X1, and the degree of freedom Y2 is the same as the degree of freedom Y1; the ink collecting device 50 is used to collect the ink droplets sprayed from the nozzle of the nozzle array 10, and the size of the ink collecting device 50 should be larger than the spraying range corresponding to the nozzle to be detected; specifically, the optical axes of the camera 21, the lens 22, the variable focus mirror 23 and the scanning galvanometer 24 are the same height and collinear, and are several millimeters higher than the upper end surface of the ink collecting device 50; when performing scanning detection, the nozzle array 10 is located above the ink collecting device 50 through each moving part, and the optical axis of the visual detection system is located below the nozzle and close to the lower surface of the nozzle, so as to collect the ink droplets in a stable flying state.

[0144] As shown in Figure 6 , the control module 40 is connected with the nozzle 10, the light source 20, the camera 21, the variable focus mirror 23, the scanning galvanometer 24 and the moving frame 30 in the nozzle array, and includes a motion controller, a synchronous trigger controller and a nozzle controller, wherein the nozzle controller is used to control the opening and closing of the nozzle, thereby controlling the spraying of the nozzle and outputting a spraying trigger signal to the synchronous trigger controller; the synchronous trigger controller receives the spraying trigger signal and triggers the visual detection system to work after a delay, thereby performing real-time detection on the flying ink droplets including volume, speed and angle, and switching to the next nozzle observation position after the image acquisition is completed; wherein the motion controller is used to control the position of the moving part in each degree of freedom.

[0145] This embodiment only uses one set of visual detection system to scan and acquire images of the ink droplets sprayed by multiple nozzles in the nozzle array, and obtains the volume, speed and angle of the ink droplets. The camera 21 can complete the conversion between pixel coordinates and world coordinates for the images collected by different targets, and the camera 21 needs to be calibrated, for example, a high-precision calibration ball is placed at the working distance of the camera 21, then the camera 21 is controlled to acquire images, and the conversion relationship between pixel coordinates and world coordinates is obtained according to the pixel coordinates in the image and the size of the calibration ball, thereby completing the calibration of the camera 21.

[0146] Based on the detection system, the synchronous scanning detection of the ink droplets sprayed by the nozzle array can be performed according to the following process, as shown in Figure 8 .

[0147] (a) First positioning: using the control module, the starting nozzle of the region to be detected in the printhead array sprays ink droplets, moves the printhead array 10 in the freedom Y1 direction and moves the motion frame 30 in the freedom Y2, X2 direction, moves the ink droplets sprayed by the starting nozzle of the region to be detected to the reference observation point of the vision detection system, and makes the camera observe the ink droplets sprayed thereby;

[0148] (b) Using the vision detection system, performing real-time vision detection including volume, speed, angle, trajectory on the ink droplets sprayed by the current nozzle;

[0149] (c) Using the control module, according to the nozzle coordinate array of the current region to be detected, driving the galvanometer and variable focus lens, switching to the next nozzle observation position to keep the camera aligned with the next nozzle;

[0150] (d) Using the control module, the next nozzle to be observed in the current detection region sprays ink droplets;

[0151] (e) Repeat steps (b), (c) and (d) to sequentially traverse the remaining nozzles in the current local scanning detection region until the detection of the ink droplets sprayed by all nozzles in the current local scanning detection region is completed.

[0152] (f) Using the control module, according to the nozzle coordinate array of the next region to be detected, the starting nozzle of the next region to be detected sprays ink droplets, moves the printhead array 10 in the freedom Y1 direction and moves the motion frame 30 in the freedom Y2, X2 direction, so that the camera observes the ink droplets sprayed thereby;

[0153] (g) Repeat steps (b), (c), (d), (e) and (f) to sequentially traverse all regions to be detected until the detection of the ink droplets sprayed by all nozzles in all detection regions is completed.

[0154] The method designs an array ink droplet high-efficiency vision measurement system based on a scanning galvanometer, which can execute the above detection process and effectively improve the detection efficiency while ensuring the detection accuracy.

[0155] The related technical solution is the same as that of Embodiment One, which will not be repeated here.

[0156] In general, the array droplet high-efficiency visual measurement method based on a scanning galvanometer and the system for executing the method can realize rapid scanning detection of a to-be-detected nozzle in a nozzle array, effectively improve the detection efficiency compared with a long detection interval and a small detection range of an existing detection scheme, and effectively realize high-precision measurement of multiple parameters such as a flying droplet volume, a speed, a flight trajectory, and a jet angle.

[0157] Those skilled in the art will easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A scanning galvanometer-based flying-ink visual measurement method, characterized in that, Comprise: S1, set a variable focus mirror at the end of the lens of the camera used to collect the image of the flying ink droplet, and set a scanning galvanometer for changing the direction of the light beam by reflection at a certain position of the light beam used for the exposure of the camera; wherein the scanning galvanometer can be rotated around the certain position under control, so that the reflected light beam can hit the flying ink droplet region corresponding to the nozzle in different directions located at the certain position in a direction perpendicular to the direction of the flying ink droplet; the variable focus mirror is used to adjust the focal length of the camera lens when collecting the image of the flying ink droplet corresponding to the nozzle with different distances from the reflection point of the scanning galvanometer to ensure that the camera clearly collects the image; S2, adjust the position of the visual observation motion frame and / or the nozzle array as a whole so that the visual observation range is aligned with the flying ink droplet region to be detected; in the manner of rotating the scanning galvanometer so that the light source light beam hits the flying ink droplet region of the nozzle to be detected and adjusting the variable focus mirror so that the camera clearly images, the flying ink droplets sprayed by each nozzle to be detected in the flying ink droplet region to be detected are sequentially collected for ink droplet image collection; through image processing, the visual measurement of the flying ink droplet is completed, wherein the visual observation range is determined according to the rotatable scanning range of the scanning galvanometer and the adjustable focal length range of the variable focus mirror.

2. The flying ink drop visual measurement method of claim 1, wherein, When used for visual measurement of arrayed flying ink droplets, before performing S2, the method further comprises: Divide the arrayed flying ink droplet region corresponding to each nozzle into a plurality of local scanning detection regions; wherein the shape and size of each local scanning detection region are determined in the following manner: according to the rotatable angle range of the scanning galvanometer in a rotation plane, a sector region that can be scanned by the light beam reflected by the scanning galvanometer is determined, and according to the distance from the focal plane to the reflection point of the scanning galvanometer when the longest and shortest focal lengths are used by the variable focus mirror, the sector region is intercepted to obtain a fan ring region that can realize clear imaging, and the shape and size of the fan ring region are the shape and size of the local scanning detection region; Then the specific implementation of S2 is: Adjust the position of the visual observation motion frame and / or the nozzle array as a whole so that the visual observation range is aligned with the current local scanning detection region to be detected; in the manner of rotating the scanning galvanometer so that the light source light beam hits the flying ink droplet region of the nozzle to be detected and adjusting the variable focus mirror so that the camera clearly images, the flying ink droplets sprayed by each nozzle in the current local scanning detection region to be detected are sequentially collected for ink droplet image collection, and this step is repeated until the image collection of all local scanning detection regions is completed; wherein the visual observation range is determined according to the scannable sector region of the scanning galvanometer and the distance from the focal plane to the reflection point of the scanning galvanometer when the longest and shortest focal lengths are used by the variable focus mirror.

3. The flying ink drop visual measurement method of claim 2, wherein, The implementation of sequentially collecting the flying ink droplets sprayed by each nozzle in the current local scanning detection region for ink droplet image collection is: According to the coordinates of the current detected nozzle and the coordinates of the next to be detected nozzle, the scanning galvanometer is rotated and the variable focus lens is adjusted, so as to change the observation direction and the focal plane position, and realize the image acquisition of the flying ink drops jetted by each nozzle in the current local scanning detection area; wherein a reference observation point is preset for a current local scanning detection area , represents an initial deflection angle of the scanning galvanometer relative to the direction of the light beam of the light source before reflection, represents an initial distance from the focal plane of the variable focus mirror to the reflection point of the scanning galvanometer. When the image of the flying ink drop ejected by the next nozzle to be detected is collected, the deflection angle of the scanning galvanometer relative to the direction of the light beam of the light source before reflection , wherein A is the reflection point position of the scanning galvanometer, B is the position of the nozzle currently detected, and C is the position of the next nozzle to be detected, A, B, and C are located in a global coordinate system and correspond to coordinate data, respectively represent the lengths of the vectors . The distance of the focal plane of the variable focus mirror to the reflection point of the scanning galvanometer As the focal length of the variable focus mirror, the following method is used for calculation: .

4. The flying ink drop visual measurement method according to any one of claims 1 to 3, characterized in that, The image acquisition is performed in the way of adopting stroboscopic exposure and nanosecond double flashes of each jetted ink drop in one exposure time period, so that the acquired image has the projection images of the same ink drop at the front and rear two time points; In each flying ink drop image of each nozzle acquired, at least one group of ink drop projection images are contained, wherein each group of ink drop projection images includes upper and lower projection images, the upper projection image of each group of ink drop projection images is the projection image of one ink drop at the previous time point corresponding to the double flashes or the superimposed image of the projection images of multiple ink drops at the previous time points corresponding to the double flashes respectively, and the lower projection image of each group of ink drop projection images is the projection image of one ink drop at the next time point corresponding to the double flashes or the superimposed image of the projection images of multiple ink drops at the next time points corresponding to the double flashes respectively.

5. The flying ink drop visual measurement method of claim 4, wherein, Based on the flying ink drop image corresponding to each nozzle, the actual volume of the jetted ink drop of the nozzle is calculated, and the implementation is as follows: Each projection image in the flying ink droplet image is detected and located by bounding box, and the image region within each target bounding box is denoised; the average gradient of each denoised projection image is calculated. This serves as an evaluation metric for the sharpness of the projected image; based on the average gradient of each projected image... The weighting coefficients corresponding to the projected image are determined; based on the camera calibration values, the actual height of the ink droplet corresponding to each projected image after edge detection is calculated, and the ink droplet corresponding to each projected image is discretized into a thickness of Δ along the height direction. h Using M slices, calculate the actual volume of the ejected ink droplets from the nozzle based on the following expression. V : ； wherein respectively represent the weighting coefficients of the i th projection image, , represent the diameter of the ink drop i th projection image, j th circle slice layer cross section, .

6. The flying ink drop visual measurement method of claim 5, wherein, The deep learning target detection algorithm YOLO is adopted to frame the position of each projection image in the flying ink drop image; The image region in each target frame is denoised respectively by using Gaussian filtering based on the following expression: ; ; wherein, represents a Gaussian function under two-dimensional coordinates , is a standard deviation, , are an original gray projection image and a denoised projection image respectively, is a Gaussian smoothing convolution kernel generated with the origin as the center, and represents a convolution operation. The average gradient of each projection image is calculated using Sobel operator based on the following expression : ； ； ； ； wherein , are the gradients of the projected image in horizontal and vertical direction, respectively, is the absolute value of the projected image gradient, denotes a convolution operation; And based on the following expression, determine the corresponding weighting factor of each projection image : ； wherein is the average gradient of the i th projection image normalized to the interval [-10, 10], N is the total number of projection images in the flying drop image.​ 7. The flying ink drop visual measurement method of claim 5, wherein, When there are Q groups of ink drop projection images in the flying ink drop image corresponding to each nozzle through target detection, based on the flying ink drop image corresponding to each nozzle, the flying speed of the jetted ink drop of the nozzle is calculated in the following way: determining an interval time of applying the two flash signals before and after to each same ink drop when collecting the flying ink drop image corresponding to the nozzle ; The Q group ink drop projection images are respectively denoised; the ink drop contour lines are segmented from the denoised projection images, and the Q group ink drop contour line centroids in the camera image coordinate system are determined according to the ink drop contour lines ​ ； The weighted coefficients corresponding to each group of ink drop projection images are determined based on the following expression : ； In the formula, respectively represent the first i weighting coefficients of the upper and lower two projection images in the group of ink drop projection images, ; The flight speed of the jet ink drop of the nozzle is calculated based on the following expression S : ； In the formula, represents the i weight of the group of ink drop projection images when it is used to calculate the jetting ink drop flight speed of the jet.

8. The flying ink drop visual measurement method of claim 5, wherein, Based on the flying ink drop image corresponding to each nozzle, the flying trajectory and flying angle of the jetted ink drop of the nozzle are calculated in the following way: The projection images are respectively de-noised; the ink drop contour lines are segmented from the de-noised projection images, and the W group ink drop contour line barycentric coordinates in the camera image coordinate system are determined according to the ink drop contour lines , a cubic polynomial model is used to fit the function as the flight trajectory of the ink drop in the camera observation direction, and the following expression is used to measure the flight angle of the flying ink drop in the camera observation direction Measurement process: .

9. A scanning galvanometer-based flying ink droplet vision detection system, characterized in that, It comprises a camera, a lens, a variable focus lens, a scanning galvanometer and an illumination light source; The camera is arranged on one side of the flying ink drop area; the variable focus lens is arranged at the lens end of the camera; the scanning galvanometer is arranged at a certain position of the light source light beam for camera exposure, and is used to change the light beam direction by reflection; The scanning galvanometer can be rotated around the certain position under control, so that the reflected light source light beam can hit the flying ink drop area corresponding to the nozzle in different directions at the certain position; the variable focus lens is used to adjust the lens focal length of the camera when the flying ink drop image corresponding to the nozzle with different distances from the reflection point of the scanning galvanometer is to be acquired, so as to ensure that the camera can clearly acquire the image.

10. A scanning galvanometer based array drop ejection vision measurement system, characterized in that, A flying ink drop visual measurement method based on a scanning galvanometer is used to execute any one of claims 1 to 8, comprising a control module, a data processing module, a mechanical auxiliary module, and a flying ink drop visual detection system according to claim 9; The flying ink drop visual detection system is used to acquire the flying ink drop image; The mechanical auxiliary module comprises a motion frame and a motion shaft, and is used to move and position the nozzle array and the flying ink drop visual detection system; The data processing module is used to divide the arrayed flying ink drop area corresponding to each nozzle into multiple local scanning detection areas; The control module is configured to control movement of the array of nozzles according to a current local scanning detection area to be detected, control rotation of a scanning galvanometer in the flying ink droplet visual detection system according to coordinates of each nozzle in the current local scanning detection area to be detected, so that a light beam of the flying ink droplet visual detection system is aimed at a flying ink droplet sprayed by the nozzle to be detected, and control a variable focus lens in the flying ink droplet visual detection system at the same time, so that the sprayed ink droplet of the nozzle to be detected is located within a depth of field range of the nozzle to be detected, and clear imaging is achieved. The data processing module is further configured to calculate parameters of the sprayed ink droplet of each nozzle based on a corresponding flying ink droplet image of the nozzle, and evaluate a spraying state.

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