A circular object rotation scanning structure and calibration method

Abstract

The present invention discloses a circular ring object rotating scanning structure, including a circular disk rotating platform, a circular ring object workpiece, and a laser displacement sensor. The circular ring object workpiece is placed on the circular disk rotating platform, the laser displacement sensor is fixed above the circular ring object workpiece, the circular disk rotating platform drives the circular ring object workpiece to rotate, and the laser displacement sensor is used to rotate and scan the circular ring object workpiece. The present invention discloses a calibration method for a circular ring object rotating scanning structure, which is a scanning and three-dimensional reconstruction method, and provides a high-precision calibration method. Compared with general practices, this method can use fewer laser sensors to achieve scanning and measurement of circular ring objects, can greatly reduce costs, and can ensure accuracy through calibration.

Description

Technical Field

[0001] The invention relates to a circular ring object rotation scanning structure.

[0002] The invention relates to a calibration method, in particular to a calibration method for a rotating scanning structure of a circular object. Background Art

[0003] Line scan sensors have many applications in industry. If the object to be measured is too large, it can be achieved by using multiple sensors or multiple scans and stitching of one sensor. However, there is a type of application that requires the use of lasers to scan larger circular objects.

[0004] The circular object rotates, and the laser displacement sensor remains stationary. After one rotation, the circular object passes under the laser displacement sensor. At this time, the data scanned by the laser displacement sensor needs to be combined with the rotation angle to perform 3D reconstruction. Otherwise, the 3D contour group obtained by the laser displacement sensor based on the time sequence will be quite different from the product itself. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a circular ring-shaped object rotating scanning structure, and also discloses a calibration method for the circular ring-shaped object rotating scanning structure.

[0006] The present invention provides the following technical solutions:

[0007] A circular ring object rotating scanning structure comprises a circular disk rotating platform, a circular ring object workpiece and a laser displacement sensor. The circular ring object workpiece is placed on the circular disk rotating platform, the laser displacement sensor is fixed above the circular ring object workpiece, the circular disk rotating platform drives the circular ring object workpiece to rotate, and the laser displacement sensor is used for rotationally scanning the circular ring object workpiece.

[0008] The workpiece of the circular object has three working surfaces, an upper plane, a lower plane and a conical surface located between the upper plane and the lower plane.

[0009] A calibration method for a circular object rotation scanning structure. The circular object workpiece is driven to rotate by a disc rotating platform, and the laser displacement sensor remains stationary. After one rotation, the circular object workpiece passes under the laser displacement sensor. The circular object workpiece has three working surfaces, an upper plane, a lower plane, and a conical surface between the upper plane and the lower plane. The function F is used to describe the working surface, that is, the point P{X, Y, Z} on the working surface satisfies,

[0010] F(X, Y, Z) = 0,

[0011] The distance from another point Q{QX, QY, QZ} in space to the working surface of the standard part is defined as D=D(F, QX, QY, QZ).

[0012] The standard part has 6 degrees of freedom in the device coordinate system O. Let the matrix of the standard part in the device coordinate system be T, then:

[0013] T=Trans(ΔX,ΔY,ΔZ)RotX(ax)RotY(ay)RotZ(αz),

[0014] The working surface of the standard part in the equipment coordinate system is described as TF, that is, the point P{X, Y, Z} on the working surface satisfies:

[0015] TF(X, Y, Z) = 0,

[0016] For the point P obtained by the laser displacement sensor L = {X, 0, Z}, point P obtained according to the motion model w {X W , Y W , Z W} should satisfy TF(X W , Y W , Z W )=0

[0017] Or satisfy the condition that the distance is 0, that is:

[0018] D=D(TF,X W , Y W , Z W )=0.

[0019] The above formula contains four kinematic parameters R, dx, dy, dz and six parameters ΔX, ΔY, ΔZ, ax, ay, az, which represent the six degrees of freedom of the standard part in the equipment. In addition, there are three independent variables, namely angle A and P. L The X coordinate and Z coordinate in the above formula are

[0020] Fun(α, β, θ) = 0,

[0021] Where α = {R, dx, dy, dz}, β = {ΔX, ΔY, ΔZ, ax, ay, az}, θ = {A, X, Z},

[0022] Further combining α and β into one variable, the above formula can be written as

[0023] Fun(ρ,θ)=0.

[0024] If ρ is more accurate, the left side of the above formula will be closer to 0. In order to obtain a more accurate ρ, we can solve a common optimization problem, that is,

[0025] Find a ρ such that sum((Fun(ρ,θ)) 2 ) is the smallest, that is:

[0026] The initial value of β is β0={0, 0, 0, 0, 0}, and the initial value of α is α0={R, 0, 0, 0}.

[0027] After collecting data from the device and setting the initial value, iterative calculations can be performed. After multiple iterations, a relatively accurate ρ can be obtained, from which the first four parameters are separated, which are α in the kinematic model. After obtaining the kinematic model parameters, for subsequent scans, the kinematic model is used to scan the points of the laser displacement sensor obtained, and the 3D data of the surface of the object being measured can be reconstructed.

[0028] Compared with the prior art, the invention has the following beneficial effects: the invention proposes a scanning and three-dimensional reconstruction method and provides a high-precision calibration method. Compared with the general practice, the method can realize the scanning and measurement of circular objects with fewer laser sensors, which can greatly reduce the cost, and the accuracy can be guaranteed through calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the scanning structure layout of a circular object.

[0030] Figure 2 This is a data graph obtained by rotating and scanning using a laser displacement sensor.

[0031] Figure 3 The present invention is calibrated Figure 2 3D data graph after reconstructing the data.

[0032] Figure 4 This is a schematic diagram of the structure of a standard circular object workpiece.

[0033] In the figure: 1. Laser displacement sensor, 2. Disc rotating platform, 3. Circular object workpiece. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0035] See also Figure 1A structure for rotating and scanning an annular object includes a disk rotating platform 2, an annular object workpiece 3, and a laser displacement sensor 1. The annular object workpiece 3 is placed on the disk rotating platform 2, and the laser displacement sensor 1 is fixed above the annular object workpiece 3. The disk rotating platform 2 drives the annular object workpiece 3 to rotate, and the laser displacement sensor 1 is used for rotating and scanning the annular object workpiece 3. The disk rotating platform 2 is a platform on which the workpiece can be placed, and the platform can rotate.

[0036] In order to perform a perfect 3D reconstruction of the annular object workpiece 3, it is first necessary to perform kinematic modeling on the scanning mechanism. According to the kinematic model, the kinematic parameters of the scanning mechanism are determined.

[0037] For this scanning system, the device coordinate system O is established on the rotating axis, where the X-axis is the direction indicated by the rotating axis 0 degrees, the upward direction is the Z-axis, and the Y-axis is determined according to the right-hand rule. Assuming that the laser displacement sensor is installed in the direction of the X-axis, the X-axis direction of the laser displacement sensor is consistent with the X-axis direction of the system. The zero point position of the X-axis of the laser displacement sensor is at a distance of R from the rotating axis. At this time, errors caused by the installation of the laser will cause the laser to rotate with three degrees of freedom. Therefore, for point P obtained by the laser displacement sensor L = {X, 0, Z}, its coordinate point P in the device coordinate system O w = Pw = MP L ,

[0038] This formula is the kinematic model of the scanning mechanism.

[0039] M=RotZ(A)Trans(R,0,0)RotX(dx)RotY(dy)RotZ(dz),

[0040]

[0041]

[0042]

[0043]

[0044] Where A is the angle of rotation, R is the distance from the X-axis zero point of the laser displacement sensor to the rotation axis, and dx, dy, and dz are the errors of the laser displacement sensor. Here, A is a variable of the kinematic model, and R and dx, dy, and dz are all parameters of the kinematic model. Once the mechanism is installed, the value remains basically unchanged. However, due to factors such as installation errors, these values ​​are not completely consistent with the design values. This requires obtaining these values ​​through kinematic calibration methods.

[0045] The circular object workpiece (standard part) is as follows Figure 4 As shown, the standard part has three working surfaces, an upper plane and a lower plane, and a conical surface is between the upper plane and the lower plane.

[0046] Determine whether it is necessary to leave a hole in the middle of the standard part depending on the situation of the rotating platform. When designing, it is necessary to ensure that the laser displacement sensor can scan the upper and lower working surfaces at the same time. Use function F to describe the working surface, that is, the point P{X, Y, Z} on the working surface satisfies,

[0047] F(X, Y, Z) = 0,

[0048] The distance from another point Q{QX, QY, QZ} in space to the working surface of the standard part is defined as D=D(F, QX, QY, QZ).

[0049] The standard part has 6 degrees of freedom in the device coordinate system O. Let the matrix of the standard part in the device coordinate system be T, then:

[0050] T=Trans(ΔX, ΔY, ΔZ)RotX(ax)RotY(ay)RotZ(az),

[0051] The working surface of the standard part in the equipment coordinate system is described as TF, that is, the point P{X, Y, Z} on the working surface satisfies:

[0052] TF(X, Y, Z) = 0,

[0053] For the point P obtained by the laser displacement sensor L = {X, 0, Z}, point P obtained according to the motion model w {X W , Y W , Z W}Should satisfy TF(X W , Y W , Z W )=0

[0054] Or satisfy the condition that the distance is 0, that is:

[0055] D=D(TF,X W , Y W , Z W )=0

[0056] In fact, due to installation errors and uncertainties in the placement of standard parts, the above formula may not be equal to zero.

[0057] The above formula contains four kinematic parameters R, dx, dy, dz and six parameters ΔX, ΔY, ΔZ, ax, ay, az, which represent the six degrees of freedom of the standard part in the equipment. In addition, there are three independent variables, namely angle A and P.L The X coordinate and Z coordinate in the above formula are

[0058] Fun(α, β, θ) = 0,

[0059] Where α = {R, dx, dy, dz}, β = {ΔX, ΔY, ΔZ, ax, ay, az}, θ = {A, X, Z},

[0060] Further combining α and β into one variable, the above formula can be written as

[0061] Fun(ρ,θ)=0,

[0062] If ρ is more accurate, the left side of the above equation will be closer to 0. In order to obtain a more accurate ρ, we can solve a common optimization problem.

[0063] Find a ρ such that sum((Fun(ρ,θ)) 2 ) is the smallest. That is:

[0064]

[0065] A common solution to this optimization problem is the Gauss-Newton method and its improved algorithms. These algorithms often require a set of initial values, which can be obtained using the designed installation position. For example, the initial value of β is β0 = {0, 0, 0, 0, 0}.

[0066] The initial value of α is α0 = {R, 0, 0, 0}. After the device collects data and sets the initial value, iterative calculations can be performed. After multiple iterations, a relatively accurate ρ can be obtained, from which the first four parameters are separated, which are α in the kinematic model. After obtaining the kinematic model parameters, the subsequent scans can reconstruct the 3D data of the surface of the object being measured by the rotational scan by using the points of the laser displacement sensor obtained by the scan.

[0067] Figure 2 It is the data obtained by rotating and scanning using a laser displacement sensor. Figure 3 After calibration Figure 2 The 3D data reconstructed from the data is

[0068] Figure 2 and Figure 3 For comparison, Figure 2 Only a long strip of outline can be obtained, and multiple scans are required to obtain the basic outline. Figure 3 The 3D profile obtained from the data obtained by the laser displacement sensor can be reconstructed through the calibration method of the present invention. The reconstructed data is consistent with the product itself and can meet the requirements for measurement accuracy.

[0069] The calibration of the present invention uses standard parts with a simple structure and extremely low requirements on the placement accuracy of the standard parts used for calibration. The calibration method of the rotation center of the offset disk rotating platform is achieved by rotating the offset disk four times, which can greatly reduce the cost of scanning annular objects and only use one sensor with only one degree of freedom of movement.

[0070] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A calibration method for a circular object rotation scanning structure, characterized in that: It includes a disc rotating platform, a circular object workpiece and a laser displacement sensor. The circular object workpiece is placed on the disc rotating platform, the laser displacement sensor is fixed above the circular object workpiece, the disc rotating platform drives the circular object workpiece to rotate, and the laser displacement sensor is used to rotate and scan the circular object workpiece; the circular object workpiece has three working surfaces, an upper plane, a lower plane and a conical surface between the upper plane and the lower plane; the circular object workpiece is driven to rotate by the disc rotating platform, and the laser displacement sensor remains stationary. As long as the circular object workpiece passes under the laser displacement sensor after one rotation, the circular object workpiece has three working surfaces, an upper plane, a lower plane and a conical surface between the upper plane and the lower plane. The function F is used to describe the working surface, that is, the point P{X, Y, Z} on the working surface satisfies, F(X, Y, Z) = 0, The distance from another point Q{QX, QY, QZ} in space to the working surface of the standard part is defined as D=D(F,QX,QY,QZ), The standard part has 6 degrees of freedom in the device coordinate system O. Let the matrix of the standard part in the device coordinate system be T, then: T=Trans(ΔX, ΔY, ΔZ)RotX(ax)RotY(ay)RotZ(az), The working surface of the standard part in the equipment coordinate system is described as TF, that is, the point P{X, Y, Z} on the working surface satisfies: TF(X, Y, Z) = 0, For the point P obtained by the laser displacement sensor L = {X, 0, Z}, point P obtained according to the motion model w {X W , Y W , Z W }Should satisfy TF(X W , Y W ,Z W )=0 Or the distance is 0, that is: D=D(TF,X W ,Y W ,Z W )=0; The above formula contains four kinematic parameters R, dx, dy, dz and six parameters ΔX, ΔY, ΔZ, ax, ay, az, which represent the six degrees of freedom of the standard part in the equipment. In addition, there are three independent variables, namely angle A and P. L The X coordinate and Z coordinate in the above formula are Fun(α, β, θ) = 0, Where α = {R, dx, dy, dx}, β = {ΔX, ΔY, ΔZ, ax, ay, az}, θ = {A, X, Z}, Further combining α and β into one variable, the above formula can be written as Fun(ρ,θ)=0; If ρ is more accurate, the left side of the above formula will be closer to 0. In order to obtain a more accurate ρ, we can solve a common optimization problem, that is, Find a ρ such that sum((Fun(ρθ)) 2 ) is the smallest, that is: , The initial value of β is β 0 ={0, 0, 0, 0, 0}, and the initial value of α is α 0 ={R, 0, 0, 0}.

2. A calibration method for a circular object rotation scanning structure according to claim 1, characterized in that: After collecting data from the device and setting the initial value, iterative calculations can be performed. After multiple iterations, a relatively accurate ρ can be obtained, from which the first four parameters are separated, which are α in the kinematic model. After obtaining the kinematic model parameters, for subsequent scans, the kinematic model is used to scan the points of the laser displacement sensor obtained, and the 3D data of the surface of the object being measured can be reconstructed.

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