Method for calibrating arc bending precision of bending machine

Abstract

The invention provides a method for calibrating the arc bending precision of a bending machine, and relates to the technical field of automatic control and calibration. The method specifically comprises the steps of generating a bent file; bending and image acquisition are conducted, specifically, the bending machine executes the bending control file, the bending piece is rotated after being bent, a camera is adopted to shoot a bending area, and a bending image is obtained; image processing and parameter extraction are carried out, and geometric parameters of tool bit boundaries and arcs are identified; a mapping relation between the theoretical bending angle and the actual bending radian is stored, and a calibration table is constructed; and based on the constructed calibration table, performing arc calibration through interpolation, and correcting subsequent bending file parameters. Accurate bending of a small-radius arc can be achieved, the equipment bending precision is high, repeated bending is avoided through one-time forming, and the quality stability of a bent part is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of automation control and calibration technology, in particular to a bending machine arc bending precision calibration method. BACKGROUND

[0002] The existing dental wire bending machine equipment relies on professional operation, the interface is complex, and the training period is long. Patent US11027323B2 provides a device and method for automatically calibrating a bending machine, which bends the wire through the bending machine, obtains the bending angle by taking a picture of the wire bending, and stores the bending angle for bending calibration. The invention patent is suitable for calibrating the fixed angle of the wire bending, and cannot realize the calibration of the wire arc bending. SUMMARY

[0003] The purpose of the present application is to provide a bending machine arc bending precision calibration method, which realizes the precision calibration of the wire arc bending.

[0004] To achieve the above purpose, the present application provides the following technical scheme: a bending machine arc bending precision calibration method, characterized in that the specific steps are:

[0005] S1, bending file generation, set up a bending file with a specific structure;

[0006] S2, bending and image acquisition, the bending machine executes the bending file, rotates the bent part after bending to make its front face face the camera, and uses the camera to shoot the bending area to obtain the bending image;

[0007] S3, image processing and parameter extraction, the bending image obtained in step S2 is processed to identify the cutter head boundary and the arc geometric parameter;

[0008] S4, store the mapping relationship between the theoretical bending angle and the actual bending radian, and construct a calibration table;

[0009] S5, based on the calibration table constructed in step S4, the arc is calibrated by interpolation, and the subsequent bending file parameters are corrected.

[0010] As a preferred, the bending control file of step S1 contains a plurality of arc segment wire lengths, specified bending angles, end segment lengths, and bending angles. The bending control file encodes the parameter sequence into machine-readable instructions through a bending machine control protocol.

[0011] As a preferred, step S3 for identifying the cutter head boundary and the arc geometric parameter specifically includes:

[0012] S31, the two side boundary lines of the right cutter head are obtained by Hough transform algorithm, and the pixel width of the two side boundary lines is calculated, specifically:

[0013] S311. Define the polar coordinate parameterized equation of a straight line. The formula is:

[0014] ρ=xcosθ+ysinθ;

[0015] Where ρ is the distance from the straight line to the origin, that is, the length of the normal line, and θ is the angle between the normal line and the x-axis, ranging from 0 ≤ θ < π;

[0016] S312, perform edge detection on the image using the Canny operator to obtain an edge point set: {(x i ,y i )};

[0017] S313. Discretize the parameter space into an accumulator array:

[0018] The range of ρ is: [-D, D]; D is the length of the image diagonal;

[0019] The range of θ is: [0, π);

[0020] S314, for each edge point (x i ,y i ), traverse θ and calculate the corresponding ρ. The formula is:

[0021] ρ=x i cosθ+y i sinθ;

[0022] Add 1 to the accumulator unit value corresponding to (ρ, θ);

[0023] S315. Select the straight line parameter corresponding to the peak value in the accumulator and convert it back to the Cartesian coordinate system. The formula is:

[0024] xcosθ * +ysinθ * =ρ * ;

[0025] S32. Identify arcs in the image using the Hough transform algorithm, select the outermost arc, and calculate the center, radius, and radian of the arc, specifically:

[0026] S321. Define the general parametric equation of an arc. The formula is:

[0027] (xa) 2 +(yb) 2 =r 2 ;

[0028] Where (a, b) is the coordinate of the center of the circle, r is the radius, and the parameter space of the arc is: (a, b, r);

[0029] S322, edge detection is performed on the image by a canny operator to obtain an edge point set {(x i , y i )};

[0030] S323, discretize the parameter space (a, b, r) into an accumulator array, specifically:

[0031] a∈[a min , a max ], with a step size of Δa;

[0032] b∈[b min , b max ], with a step size of Δb;

[0033] r∈[r min , r max ], with a step size of Δr;

[0034] S323, for each edge point (x i , y i ) and radius r, solve the center (a, b) that satisfies the condition, the formula is:

[0035] a=x i -rcosθ;

[0036] b=y i -rsinθ;

[0037] S324, select the peak value in the accumulator, which corresponds to the circular arc parameters (a * , b * , r * );

[0038] S33, according to the pixel width and actual width ratio of the tool head, convert the pixel distance of the calculated radius into spatial distance, the formula is:

[0039]

[0040] Wherein, L1 is the pixel width of the tool head, L2 is the actual width, D1 is the pixel distance of the calculated radius, and D2 is the spatial distance.

[0041] As preferred, the step S5 described by interpolation for circular arc calibration, specifically cubic spline interpolation calibration, specifically:

[0042] S51, a set of data points {(x i , y i )} is given, wherein x i is strictly increasing;

[0043] S52, for each inner point x i, calculate the slope of five adjacent points, the formula is:

[0044]

[0045]

[0046]

[0047]

[0048] The slope S is calculated by weighted averaging of adjacent slopes. i , the formula is:

[0049]

[0050] S53, in [x i , x i+1 ] interval, construct a cubic polynomial, the formula is:

[0051] P i (x) = a i +b i (xx i )+c i (xx i ) 2 +d i (xx i ) 3 ;

[0052] Among them, the interpolation condition: P i (x i )=y i , P i (x i+1 )=y i+1 ;

[0053] Slope continuity: P' i (x i )=S i , P' i (x i+1 )=S i+1 ;

[0054] Specifically: a i =y i ;

[0055] b i =S i ;

[0056]

[0057]

[0058] Among them, h i =x i+1 -x i ,

[0059] Preferably, the bending control file is a series of files, and the arc segments thereof specify bending angles ranging from 5° to 50°, which are increased by 1°.

[0060] Compared with the existing technology, the present invention has the following advantages: the bending machine arc precision calibration method provided by the present invention is applicable to bending machines that are simple to operate, have a low learning curve, are easy to use, and are more easily adapted to the current fast-paced and high-efficiency work requirements. The present invention can achieve precise bending of small-radius arcs, with high bending accuracy, and avoids repeated bending in one step, thereby improving the quality stability of the bent parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a flow chart of the present invention.

[0062] Figure 2 This is the overall structure diagram of the bending machine.

[0063] Figure 3 It is a cross-sectional view of an arc taken by a bending machine.

[0064] Figure 4 It is a schematic diagram of bending image parameter extraction.

[0065] The reference numerals in the figures are: wire reel 1; wire feeding mechanism 2; clamping mechanism 3; wire bending mechanism 4; camera 5; backlight source 6; steel wire 7. DETAILED DESCRIPTION

[0066] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0067] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," "the other end," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0068] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "connected," etc., should be understood in a broad sense. For example, "connected" may refer to a fixed connection, a detachable connection, or an integral connection; it may refer to a mechanical connection or an electrical connection; it may refer to a direct connection or an indirect connection through an intermediate medium; it may refer to internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0069] Reference Figure 1 The arc precision calibration method of the dental wire bending machine provided by the present invention comprises the following specific steps:

[0070] S1, bending file generation, setting the bending file of a specific structure;

[0071] S2, bending and image acquisition, the bending machine executes the bending file, the bending part is rotated according to the angle symbol after bending, and the bending area is photographed by a camera to obtain the bending image;

[0072] S3, image processing and parameter extraction, performing image processing on the bending image obtained in step S2 to identify the tool head boundary and arc geometric parameters;

[0073] S4, storing the mapping relationship between the theoretical bending angle and the actual bending arc, and constructing a calibration table;

[0074] S5, based on the calibration table constructed in step S4, arc calibration is performed by interpolation to correct subsequent bending file parameters.

[0075] Reference Figure 2 、 Figure 3 The specific process of the dental wire bending machine to prepare the bent parts through arc calibration is as follows:

[0076] Construct a bending file, which includes a file header and data. The file header records the parameter information of the bending file, including the wire diameter and the simulation information of the bending part. The data part records the bending data of the entire bending part. Each line of data includes the line number, wire length, bending angle and turning angle, as shown in Table 1 below:

[0077] WireDiameter:0.8

[0078] ;IsSimulated:true

[0079] Table 1

[0080] Index Length Folding angle Corner N001 A1.2000 B0.000 C0.000 N002 A1.2000 B5.000 C0.000 N003 A1.2000 B5.000 C0.000 N004 A1.2000 B5.000 C0.000 N005 A1.2000 B5.000 C0.000

[0081] In this embodiment, the wire length of the arc segments of the bending file with a specified angle is 1.2 mm, the angle is the specified angle, and the turning angle is 0°. The end length of the bending file with a specified angle is 10 mm, the angle is -90°, and the turning angle is 0°.

[0082] The bending file is fed into the bending machine, which reads the bending file, turns on the backlight source 6, and starts bending. The bending machine is driven to move according to several sections of bending data in the file: first, the wire feeding mechanism 2 pushes the steel wire 7 forward to the wire length, the clamping mechanism 3 clamps the steel wire 7, and then drives the wire bending mechanism 4 to push the steel wire 7 to bend the specified angle according to the specified bending angle. The above process is repeated until all bending data are executed. The steel wire 7 is transported to the bending position through the wire reel 1, the wire feeding mechanism 2, and the clamping mechanism 3, and the bending file is executed by the wire bending mechanism 4 for bending. After bending, the bent part is rotated according to the sign of the angle so that its front side faces the camera, the light source 6 fills the light and takes a picture through the camera 5 to obtain the bending image, and the image obtained by taking the picture is stored and processed. The algorithm is used to identify the boundary of the tool head and the geometric parameters of the arc. Specifically including:

[0083] The cutter head part in the lower right corner of the image is captured, and the straight lines in the screenshot are identified using the Hough transform algorithm. The boundary lines on both sides of the cutter head are found based on the number and position of the identified straight lines, and the pixel widths of the boundary lines on both sides are calculated.

[0084] S311. Define the polar coordinate parameterized equation of a straight line. The formula is:

[0085] ρ=xcosθ+ysinθ;

[0086] Where ρ is the distance from the straight line to the origin, that is, the length of the normal line, and θ is the angle between the normal line and the x-axis, ranging from 0 ≤ θ < π;

[0087] S312, perform edge detection on the image using the Canny operator to obtain an edge point set: {(x i ,y i )};

[0088] S313. Discretize the parameter space into an accumulator array:

[0089] The range of ρ is: [-D, D]; D is the length of the image diagonal;

[0090] The range of θ is: [0, π), discretized by step size;

[0091] S314, for each edge point (x i ,y i ), traverse θ and calculate the corresponding ρ. The formula is:

[0092] ρ=x i cosθ+y i sinθ;

[0093] Add 1 to the accumulator unit value corresponding to (ρ, θ);

[0094] S315. Select the straight line parameter corresponding to the peak value in the accumulator and convert it back to the Cartesian coordinate system. The formula is:

[0095] xcosθ * +ysinθ * =ρ * ;

[0096] S32. Identify arcs in the image using the Hough transform algorithm, select the outermost arc, and calculate the center, radius, and radian of the arc, specifically:

[0097] S321. Define the general parametric equation of an arc. The formula is:

[0098] (xa) 2 +(yb) 2 =r 2 ;

[0099] Where (a, b) is the coordinate of the center of the circle, r is the radius, and the parameter space of the arc is: (a, b, r);

[0100] S322, perform edge detection on the image using the Canny operator to obtain the edge point set: {(x i ,y i )};

[0101] S323. Discretize the parameter space (a, b, r) into an accumulator array, specifically:

[0102] a∈[a min , a max ], the step size is Δa;

[0103] b∈[b min , b max ], the step size is Δb;

[0104] r∈[r min , r max ], the step size is Δr;

[0105] S323, for each edge point (x i ,y i ) and radius r, solve the center (a, b) that meets the conditions, the formula is:

[0106] a=x i -rcosθ;

[0107] b=y i -rsinθ;

[0108] S324, selecting the peak value in the accumulator, corresponding to the arc parameters (a * , b * , r * );

[0109] All the arcs in the image are calculated by the above algorithm, and the center and radius of each arc are calculated. Through filtering the radius size and the position of the arc, the outer arc of the steel wire is obtained.

[0110] S33, referring to Figure 4 , according to the pixel width and actual width ratio of the tool head, the pixel distance of the calculated radius is converted into spatial distance, the formula is:

[0111]

[0112] Wherein, L1 is the pixel width of the tool head, L2 is the actual width, D1 is the pixel distance of the calculated radius, and D2 is the spatial distance. The geometric parameters of the arc are extracted.

[0113] The actual radian and radius obtained by inputting the bending file into the folding angle, taking a photo after bending by the bending machine and image processing are stored one by one in the arc calibration data table. Each folding angle in the range of 5° to 50° is bent and recorded respectively, and the calibration table is constructed.

[0114] The folding angle of the arc segment of the bending part is obtained, and the arc folding angle is calibrated, the method comprising:

[0115] The folding angle is obtained by cubic spline interpolation in the arc calibration table to obtain the calibrated arc folding angle;

[0116] According to the arc folding angle in the file, the arc radius is calculated, and the calibrated arc folding angle is obtained by cubic spline interpolation in the arc calibration table.

[0117] Cubic spline interpolation is used for arc calibration, specifically:

[0118] S51, a set of data points {(x i , y i )} is given, wherein x i is strictly increasing;

[0119] S52, for each inner point x i , the slope of the adjacent five points is calculated, and the formula is:

[0120]

[0121]

[0122]

[0123]

[0124] The slope S is calculated by weighted averaging of adjacent slopes. i , the formula is:

[0125]

[0126] S53, in [x i , x i+1 ] interval, construct a cubic polynomial, the formula is:

[0127] P i (x) = a i +b i (xx i )+c i (xx i ) 2 +d i (xx i ) 3 ;

[0128] Among them, the interpolation condition: P i (x i )=y i , P i (x i+1 )=y i+1 ;

[0129] Slope continuity: P' i (x i )=S i , P' i (x i+1 )=S i+1 ;

[0130] Specifically: a i =y i ;

[0131] b i =S i ;

[0132]

[0133]

[0134] Among them, h i =x i+1 -x i ,

[0135] In this embodiment, the bending machine folds a standard arc that meets the size requirements through bending calibration.

[0136] Anything not described in detail in the present invention is well known to those skilled in the art.

[0137] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified and replaced with equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for calibrating the arc bending accuracy of a bending machine, characterized in that: The specific steps are: S1, bending file generation, setting the bending file of a specific structure; S2, bending and image acquisition, the bending machine executes the bending file, rotates the bent part after bending so that its front side faces the camera, and uses the camera to photograph the bending area to obtain the bending image; S3, image processing and parameter extraction, performing image processing on the bending image obtained in step S2 to identify the tool head boundary and arc geometric parameters; S4, storing the mapping relationship between the theoretical bending angle and the actual bending arc, and constructing a calibration table; S5, based on the calibration table constructed in step S4, performing arc calibration by interpolation, and correcting subsequent bending file parameters.

2. The arc bending accuracy calibration method of a bending machine according to claim 1, characterized in that: The bending control file in step S1 includes several arc segment wire lengths, specified bending angles, end segment lengths, and bending angles. The bending control file encodes the parameter sequence into machine-readable instructions through the bending machine control protocol.

3. The arc bending accuracy calibration method of a bending machine according to claim 1, characterized in that: Step S3 of identifying the tool head boundary and arc geometric parameters specifically includes: S31. Obtain and identify the boundary lines on both sides of the right blade head through the Hough transform algorithm, and calculate the pixel width of the boundary lines on both sides, specifically: S311. Define the polar coordinate parameterized equation of a straight line. The formula is: ρ=xcosθ+ysinθ; Where ρ is the distance from the straight line to the origin, that is, the length of the normal line, and θ is the angle between the normal line and the x-axis, ranging from 0 ≤ θ < π; S312, perform edge detection on the image using the Canny operator to obtain an edge point set: {(x i ,y i )}; S313. Discretize the parameter space into an accumulator array: The range of ρ is: [-D, D]; D is the length of the image diagonal; The range of θ is: [0, π); S314, for each edge point (x i ,y i ), traverse θ and calculate the corresponding ρ. The formula is: p=x i cosθ+y i sinθ; Add 1 to the accumulator unit value corresponding to (ρ, θ); S315. Select the straight line parameter corresponding to the peak value in the accumulator and convert it back to the Cartesian coordinate system. The formula is: xcosθ * +ysinθ * =ρ * ; S32. Identify arcs in the image using the Hough transform algorithm, select the outermost arc, and calculate the center, radius, and radian of the arc, specifically: S321. Define the general parametric equation of an arc. The formula is: (x-a) 2 +(y-b) 2 =r 2 ; Where (a, b) is the coordinate of the center of the circle, r is the radius, and the parameter space of the arc is: (a, b, r); S322, perform edge detection on the image using the Canny operator to obtain the edge point set: {(x i ,y i )}; S323. Discretize the parameter space (a, b, r) into an accumulator array, specifically: a∈[a min , a max ], the step size is Δa; b∈[b min , b max ], the step size is Δb; r∈[r min , r max ], the step size is Δr; S323, for each edge point (x i ,y i ) and radius r, solve the center (a, b) that meets the conditions, the formula is: a=x i -rcosθ; b=y i -rsinθ; S324, select the peak value in the accumulator, corresponding to the arc parameter (a * , b * , r * ); S33. According to the ratio of the pixel width of the tool head to the actual width, the calculated pixel distance of the radius is converted into a spatial distance. The formula is: Among them, L1 is the pixel width of the tool head, L2 is the actual width, D1 is the pixel distance of the calculated radius, and D2 is the spatial distance.

4. The arc bending accuracy calibration method of a bending machine according to claim 1, characterized in that: The arc calibration is performed by interpolation in step S5, specifically cubic spline interpolation calibration, specifically as follows: S51, given a set of data points {(x i ,y i )}, where x i Strictly increasing; S52. For each interior point x i , calculate the slope of five adjacent points, the formula is: The slope S is calculated by weighted averaging of adjacent slopes. i , the formula is: S53, in [x i , x i+1 ] interval, construct a cubic polynomial, the formula is: P i (x)=a i +b i (x-x i )+c i (x-x i ) 2 +d i (x-x i ) 3 ; Among them, the interpolation condition: P i (x i )=y i , P i (x i+1 )=y i+1 ; Slope continuity: P' i (x i )=S i , P' i (x i+1 )=S i+1 ; Specifically: a i =y i ; b i =S i ; Among them, h i =x i+1 -x i , 5. The arc bending accuracy calibration method of a bending machine according to claim 1, characterized in that: The bending control file described in step S1 is a series of files, and the arc segments thereof specify bending angles ranging from 5° to 50°, increasing in increments of 1°.

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