CN113183137B - A parameter calibration device and method for a six-degree-of-freedom parallel mechanism - Google Patents

Abstract

The invention relates to a parameter calibration device and method for a six-degree-of-freedom parallel mechanism, wherein the parameter calibration device includes a displacement sensor, a sensor base, a measured reference block, a bracket and a parameter calibration calculation module; the sensor base includes three mutually orthogonal planes, 1, 2 and 3 displacement sensors are respectively fixed on the three planes, and the measuring rod axis of the displacement sensor is perpendicular to the corresponding plane, and the sensor seat is fixed on the fixed platform of the six-degree-of-freedom parallel mechanism through the bracket; the measured reference The block includes three mutually orthogonal reference planes corresponding to the three planes one-to-one, and the contacts of the displacement sensor are all in contact with the corresponding reference planes, and the measured reference block is fixed on the top of the moving platform of the six-degree-of-freedom parallel mechanism; parameters The calibration calculation module calibrates and compensates the parameters of the 6-DOF parallel mechanism. The parameter calibration device of the six-degree-of-freedom parallel mechanism of the invention has the advantages of low cost, simple operation, time-saving and labor-saving, high calibration efficiency and the like.

Description

A parameter calibration device and method for a six-degree-of-freedom parallel mechanism

technical field

The invention relates to the technical field of mechanics, in particular to a parameter calibration device and method of a six-degree-of-freedom parallel mechanism.

Background technique

The 6-DOF parallel mechanism is widely used in the fields of fine adjustment of optical components and ultra-precision machining due to its advantages of high precision, high stiffness, and no accumulated error.

Due to the existence of machining and assembly errors, there is a certain deviation between the actual structural parameters of the six-degree-of-freedom parallel mechanism and the theoretical structural parameters, which makes a certain deviation between the kinematics model established according to the theoretical parameters and the actual structure. The use of high-precision machine tools can reduce the machining errors of structural parts, but the cost is high. Compensating the errors through parameter calibration is a low-cost and effective method.

During the calibration process of the six-degree-of-freedom parallel mechanism, its pose needs to be measured. At present, most of the three-coordinate measuring machines, measuring arms, laser trackers, laser interferometers and other equipment are used for position and orientation measurement. Although these equipments have the characteristics of high precision and wide adaptability, they are expensive, time-consuming and labor-intensive to operate, and have high operational requirements. The application is inconvenient, resulting in low calibration efficiency, especially for the parallel mechanism with large working space. Due to the limitation of space, some poses of the moving platform may not be able to be measured, and it is difficult to obtain satisfactory measurement data when the moving platform changes poses in a large working space. Therefore, it is necessary to consider other simple and efficient pose measurement methods to improve the calibration efficiency.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a simple and efficient 6-DOF parallel mechanism parameter calibration for the problems of high cost, time-consuming and labor-intensive operation, low calibration efficiency and low calibration accuracy of the existing 6-DOF parallel mechanism calibration method. The device and the method achieve the purpose of reducing costs, simplifying the calibration process and improving the calibration efficiency.

To achieve the above object, the present invention adopts the following technical solutions:

A six-degree-of-freedom parallel mechanism parameter calibration device, comprising a displacement sensor, a sensor base, a measured reference block, a bracket and a parameter calibration calculation module;

The sensor base includes three mutually orthogonal planes, and one, two and three displacement sensors are respectively fixed on the three planes, and the measuring rod axis of the displacement sensor is perpendicular to the corresponding plane, The sensor base is fixed on the fixed platform of the six-degree-of-freedom parallel mechanism through the bracket;

The measured reference block includes three mutually orthogonal reference planes corresponding to the three planes one-to-one, and the contacts of the displacement sensor are all in contact with the corresponding reference planes, and the measured reference block is fixed on the The top of the moving platform of the 6-DOF parallel mechanism;

The parameter calibration calculation module obtains the actual value of the expansion and contraction amount of each of the displacement sensors when the six-degree-of-freedom parallel mechanism is in different poses, and determines the optimal structural parameter error of the six-degree-of-freedom parallel mechanism according to the actual value of the expansion and contraction amount, The parameters of the six-degree-of-freedom parallel mechanism are calibrated and compensated according to the optimal structural parameter error.

The present invention also proposes a parameter calibration method based on the above-mentioned six-degree-of-freedom parallel mechanism parameter calibration device. The parameter calibration calculation module is used to execute the parameter calibration method, and the parameter calibration method includes the following steps:

S1: Preset the initial value of the structural parameters of the 6-DOF parallel mechanism, and add the corresponding structural parameter error to the structural parameters of the 6-DOF parallel mechanism;

S2: Preset the initial values of the structural parameters of the 6-DOF parallel mechanism parameter calibration device, and add the corresponding structural parameter error to the structural parameters of the 6-DOF parallel mechanism parameter calibration device;

S3: Preset the nominal pose of the moving platform of the 6-DOF parallel mechanism, and the number of the nominal poses is greater than or equal to the lower limit value;

S4: Calculate the nominal value of the expansion and contraction amount of each displacement sensor under each of the nominal poses;

S5: use the controller to drive the six-degree-of-freedom parallel mechanism, move the moving platform to each of the nominal poses, and record the actual value of the expansion and contraction of each of the displacement sensors under each of the nominal poses;

S6: making a difference between the actual value of the expansion and contraction amount of each of the displacement sensors under each of the nominal poses and the nominal value of the expansion and contraction amount to obtain the indication error of each of the displacement sensors under each of the nominal poses;

S7: Taking the minimum sum of squares of the indication errors of all the displacement sensors as the objective function, and taking the structural parameter errors of the 6-DOF parallel mechanism and the parameter calibration device of the 6-DOF parallel mechanism as the design variable, construct a mathematical model of the optimization problem ;

S8: Use advanced optimization software to search for the optimal solution of the mathematical model;

S9: Substitute the optimal solution obtained by the search into the mathematical model of the 6-DOF parallel mechanism to realize the parameter calibration and compensation of the 6-DOF parallel mechanism.

Compared with the prior art, the present invention has the following beneficial effects:

1) Low cost

The main components of the six-degree-of-freedom parallel mechanism parameter calibration device are: six high-precision displacement sensors, measured reference blocks and sensor bases. Compared with expensive instruments such as three-coordinate measuring machines and laser trackers, the cost is extremely low;

2) Simple operation

Before calibration, just fix the measured reference block on the 6-DOF parallel mechanism motion platform, fix the displacement sensor on the sensor base, and fix the sensor base on the 6-DOF parallel mechanism fixed platform through the bracket, then the parameters can be developed. Calibration; when calibrating, only the controller of the 6-DOF parallel mechanism needs to be operated, and there is no need to operate the parameter calibration device of the 6-DOF parallel mechanism. The entire calibration process is simple to operate, saving time and effort;

3) High calibration efficiency

As long as the position and posture of the end of the six-degree-of-freedom parallel mechanism changes, the measured value of the displacement sensor, that is, the actual value of the expansion and contraction amount can be obtained in an instant. At this time, there is no need to solve the posture and attitude, and the difference between the actual value of the expansion and contraction amount of the displacement sensor and the nominal value of the expansion and contraction amount can be obtained. , and into the advanced optimization software, the optimal structural parameter error of the 6-DOF parallel mechanism can be calculated in a short time, which greatly improves the efficiency of parameter calibration.

Description of drawings

1 is a schematic structural diagram of a parameter calibration device for a six-degree-of-freedom parallel mechanism in an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of FIG. 1 after the sensor seat and the bracket are hidden;

FIG. 3 is a schematic diagram of the relationship between the displacement sensor and the sensor base in FIG. 1;

4 is a schematic diagram of the relationship between the displacement sensor and the measured reference block in FIG. 1;

FIG. 5 is a schematic flowchart of a method for calibrating parameters of a six-degree-of-freedom parallel mechanism according to an embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments.

In one embodiment, as shown in Figures 1-4, the present invention discloses a parameter calibration device for a six-degree-of-freedom parallel mechanism. The device mainly includes: six displacement sensors, namely displacement sensor 1 to displacement sensor 6, a sensor seat 7. The measured reference block 8, the bracket 9 and the parameter calibration calculation module.

Specifically, the sensor base 7 includes three mutually orthogonal planes, namely a plane 7-1, a plane 7-2 and a plane 7-3, and the plane 7-1 is fixed with the displacement sensor 1, the displacement sensor 2 and the displacement sensor 3, The displacement sensor 4 and the displacement sensor 5 are fixed on the plane 7-2, the displacement sensor 6 is fixed on the plane 7-3, and the measuring rod axes of the displacement sensor 1 to the displacement sensor 6 are perpendicular to the corresponding plane. The sensor base 7 is fixed on the fixed platform 10 of the 6-DOF parallel mechanism through the bracket 9, and neither the sensor base 7 nor the bracket 9 is in contact with the moving platform 11 of the 6-DOF parallel mechanism.

Preferably, the displacement sensor in this embodiment adopts a grating displacement sensor, which has the characteristics of large detection range, high detection accuracy and fast response speed. For example, the Czech ESSA grating displacement sensor SM30 series can be used.

Optionally, the sensor base 7 is a hollow cuboid or cube with an open bottom, and the inner hollow of the cuboid or cube is used to accommodate the measured reference block 8 .

The measured reference block 8 includes three mutually orthogonal reference planes corresponding to the planes 7-1, 7-2 and 7-3, respectively, which are the reference plane 8-1, the reference plane 8-2 and the reference plane. Plane 8-3, and the contacts of the displacement sensor are all in contact with the corresponding reference plane, that is, the contacts of the displacement sensor 1, the displacement sensor 2, and the displacement sensor 3 are in contact with the reference plane 8-1 of the measured reference block 8, and the displacement sensor 4. The contacts of the displacement sensor 5 are in contact with the reference plane 8-2 of the measured reference block 8, and the contacts of the displacement sensor 6 are in contact with the reference plane 8-3 of the measured reference block 8. The measured reference block 8 is fixed on the top of the moving platform 11 of the six-degree-of-freedom parallel mechanism.

Optionally, the measured reference block 8 is a cuboid or a cube, and the measured reference block 8 may be a solid structure or a hollow structure, which is not limited here.

Optionally, the material of the sensor base 7 and the measured reference block 8 is cast iron, and the material of the bracket 9 is 45 gauge steel, which has the advantages of high strength and not easy to deform.

The parameter calibration calculation module obtains the actual value of the expansion and contraction amount of each displacement sensor in the six-degree-of-freedom parallel mechanism in different poses, and determines the optimal structural parameter error of the six-degree-of-freedom parallel mechanism according to the actual value of the expansion and contraction amount. The parameters of the 6-DOF parallel mechanism are calibrated and compensated.

The device for calibrating parameters of a six-degree-of-freedom parallel mechanism proposed in this embodiment has the advantages of low cost, simple operation, time-saving and labor-saving, and high calibration efficiency.

In another embodiment, the present invention provides a method for calibrating parameters of a 6-DOF parallel mechanism. The method is implemented based on the device for calibrating parameters for a 6-DOF parallel mechanism described in the foregoing embodiments. The structure of the device for calibrating parameters for a 6-DOF parallel mechanism Refer to the foregoing embodiments, which will not be repeated here. The parameter calibration calculation module is used to execute the parameter calibration method of the six-degree-of-freedom parallel mechanism in this embodiment. Specifically, the parameter calibration method includes the following steps:

S1 (S100): Preset the initial values of the structural parameters of the 6-DOF parallel mechanism, and add corresponding structural parameter errors to the structural parameters of the 6-DOF parallel mechanism.

The structural parameters of the six-degree-of-freedom parallel mechanism include the coordinates of the six hinge points on the fixed platform of the six-degree-of-freedom parallel mechanism in the fixed platform coordinate system, the coordinates of the six hinge points on the moving platform in the moving platform coordinate system, and the six support the length of the chain. Specifically, the number of structural parameters of the six-degree-of-freedom parallel mechanism is 42 in total, and the structural parameters are X _Bi , Y _Bi , Z _Bi , Li , X _Pi , Y _Pi , Z _Pi ( _i =1,2,3 ,4,5,6), where:

(1)[X _Bi Y _Bi Z _Bi ]=[ ⁿ X _Bi ⁿ Y _Bin Z _Bi ] ⁺ [ΔX _Bi ΔY _Bi ΔZ _Bi ] is the i-th hinge point on the fixed platform of the six-degree-of-freedom parallel mechanism on the fixed platform The coordinates in the coordinate system (hereinafter referred to as the fixed system), [ ⁿ X _B ⁿ Y _B ⁿ Z _Bi ] is the nominal value of the coordinates of the i-th hinge point of the fixed platform, and the upper left mark n is the abbreviation of "nominal" (nominal) (the same below), [ΔX _Bi ΔY _Bi ΔZ _Bi ] is the coordinate error of the i-th hinge point of the fixed platform;

(2)[X _Pi Y _Pi Z _Pi ]=[ ⁿ X _Pi ⁿ Y _Pi ⁿ Z _Pi ]+[ΔX _Pi ΔY _Pi ΔZ _Pi ] is the i-th hinge point on the moving platform of the six-degree-of-freedom parallel mechanism on the moving platform The coordinates in the coordinate system (hereinafter referred to as the dynamic system), [ ⁿ X _Pi ⁿ Y _Pi ⁿ Z _Pi ] is the nominal coordinate value of the i-th hinge point of the moving platform, [ΔX _Pi AY _Pi ΔZ _Pi ] is the i-th moving platform The coordinate error of the hinge point;

(3) l _i = ⁿ l _i +Δl _i is the length l _i of the i-th branch of the six-degree-of-freedom parallel mechanism, ⁿ l _i is the nominal value of the length of the i-th branch, and Δli is the _i -th branch Chain length error.

S2 (S200): Preset the initial value of the structural parameter of the 6-DOF parallel mechanism parameter calibration device, and add the corresponding structural parameter error to the structural parameter of the 6-DOF parallel mechanism parameter calibration device.

Optionally, S2 presets the initial values of the structural parameters of the six-degree-of-freedom parallel mechanism parameter calibration device, including the following steps:

S21: Construct the measured reference block coordinate system.

Firstly, the parameter calibration device of the six-degree-of-freedom parallel mechanism is modeled. The intersection of the three planes of the measured reference block 8 is abstracted as the origin of the measured reference block coordinate system (hereinafter referred to as the reference block system), and the reference plane 8-1 is abstracted as the XOY plane of the reference block system, abbreviated as "I plane", the reference plane The intersection line of 8-1 and the reference plane 8-2 is abstracted as the X axis, and the plane passing through the X axis and perpendicular to the reference plane 8-1 is defined as the XOZ plane, abbreviated as "II plane", the plane passing through the origin and perpendicular to the X axis. The plane is defined as the YOZ plane, abbreviated as "III plane". So far, the coordinate system of the measured reference block is completed. Displacement sensor 1 to displacement sensor 6 are abstracted as space straight lines S1 to S6, in which the intersections of straight lines S1, S2 and S3 with plane I are defined as M1, M2, M3, and the intersections of straight lines S4 and S5 with plane II are defined as M4, M5, the intersection of the straight line S6 and the III plane is defined as M6.

S22: Preset the pose of the measured reference block coordinate system under the six-degree-of-freedom parallel mechanism dynamic system.

The pose of the preset reference block system under the six-degree-of-freedom parallel mechanism is:

where:

为基准块系原点在动系中的坐标，

为基准块系坐标原点在动系中的坐标名义值，

为基准块系坐标原点在动系中的坐标误差；

is the coordinate of the origin of the reference block system in the dynamic system,

is the nominal value of the coordinate origin of the reference block system in the dynamic system,

is the coordinate error of the coordinate origin of the reference block system in the dynamic system;

为基准块系在动系中的姿态角，

为基准块系在动系中的姿态角名义值，

为基准块系在动系中的姿态角误差。

is the attitude angle of the reference block in the dynamic system,

is the nominal value of the attitude angle of the reference block in the dynamic system,

is the attitude angle error of the reference block in the dynamic system.

The formula (1) can be written in the form of homogeneous coordinate transformation as:

In the formula, c represents cos and s represents sin.

S23: Preset the pose of the measured reference block under the fixed platform coordinate system of the six-degree-of-freedom parallel mechanism when the moving platform coordinate system is at the zero position, and obtain the XOY plane and XOZ of the measured reference block when the moving platform coordinate system is at the zero position Expressions for faces and YOZ faces.

In this step, when the preset dynamic system is at the zero position, the pose of the reference block system under the fixed system of the six-degree-of-freedom parallel mechanism is expressed as the RPY angle:

where:

为基准块系原点在定系中的坐标，

为基准块系坐标原点在定系中的坐标名义值，

为基准块系坐标原点在定系中的坐标误差；

is the coordinate of the origin of the reference block system in the fixed system,

is the nominal value of the coordinate origin of the reference block system in the fixed system,

is the coordinate error of the coordinate origin of the reference block system in the fixed system;

为基准块系在定系中的姿态角，

为基准块系在定系中的姿态角名义值，

为基准块系在定系中的姿态角误差。

is the attitude angle of the reference block in the fixed system,

is the nominal value of the attitude angle of the reference block in the fixed system,

is the attitude angle error of the reference block in the fixed system.

The equation (3) can be written in the form of homogeneous coordinate transformation as:

In the formula, c represents cos and s represents sin.

According to formula (4), the expression of the I plane of the measured reference block when the moving system is at zero position can be obtained:

为I面上一点，即基准块系的坐标原点，

及

为I面内的向量。In the formula,

is a point on the I surface, that is, the coordinate origin of the reference block system,

and

is a vector in the I plane.

And the expression of the II side of the measured reference block when the dynamic system is in the zero position:

为II面上一点，

及

为II面内的向量。In the formula,

For a point on the II side,

and

is a vector in the II plane.

And the expression of the III surface of the measured reference block when the dynamic system is at the zero position:

为III面上一点，

及

为III面内的向量。In the formula,

is a point on face III,

and

is a vector in plane III.

S24: Preset the expression of the straight line where each displacement sensor is located.

The linear expression where the preset displacement sensor 1 to the displacement sensor 6 is located:

L _k =[x _k y _k z _k dx _k dy _k dz _k ],k=1,2,3,4,5,6 (8)

where:

[x _k y _k z _k ]=[ ⁿ x _k ⁿ y _k ⁿ z _k ]+[Δx _k Δy _k Δz _k ] represents the coordinates of a point on a straight line, and [ ⁿ x _k ⁿ y _k ⁿ z _k ] is a point on the straight line The nominal coordinate value of , [Δx _k Δy _k Δz _k ] is the coordinate error of a point on the straight line;

[dx _k dy _k dz _k ]=[ ⁿ dx _k ⁿ dy _k ⁿ dz _k ]+[Δdx _k Δdy _k Δdz _k ] represents the vector of the straight line, [ ⁿ dx _k ⁿ dy _k ⁿ dz _k ] is the nominal vector of the straight line value, [Δdx _k Δdy _k Δdz _k ] is the vector error of the straight line.

Through the above S21 to S24, the structural parameters of the six-degree-of-freedom parallel mechanism parameter calibration device are preset, and the structural parameters are 48 in total.

S3 (S300): Preset the nominal pose of the moving platform of the six-degree-of-freedom parallel mechanism, and the number of nominal poses is greater than or equal to the lower limit value.

The nominal poses of the moving platform of the preset six-degree-of-freedom parallel mechanism are:

为第j个名义位姿下动系的坐标原点在定系中的坐标，

为第j个名义位姿下动系在定系中的姿态角，且j≥m，m为名义位姿的数量的下限值，可选地，m＝15。In the formula,

is the coordinate of the coordinate origin of the moving system under the jth nominal pose in the fixed system,

is the attitude angle of the moving system in the fixed system under the jth nominal pose, and j≥m, m is the lower limit of the number of nominal poses, optionally, m=15.

S4 (S400): Calculate the nominal value of the expansion and contraction amount of each displacement sensor under each nominal pose.

Optionally, S4 calculating the nominal value of the expansion and contraction amount of each displacement sensor under each nominal pose includes the following steps:

S41: Calculate the zero position coordinates in the fixed system of the contact points of each displacement sensor and the corresponding coordinate plane in the reference block system when the dynamic system is at the zero position. Combining equations (5), (6), (7), and (8), the contact coordinates can be obtained, which can be written as:

是动系处于零位时位移传感器k与基准块系中对应坐标平面的触点在定系中的坐标，即为零位坐标。In the formula,

It is the coordinate of the contact point of the displacement sensor k and the corresponding coordinate plane in the reference block system in the fixed system when the dynamic system is at the zero position, that is, the zero position coordinate.

S42: Calculate the pose coordinates in the fixed system of the contact points of each displacement sensor and the corresponding coordinate plane in the reference block system when the dynamic system is in the nominal pose.

According to S1 to S3, the expressions of homogeneous coordinate transformation of different nominal poses and the plane expressions of coordinate plane I, plane II and plane III under different nominal poses can be derived. By combining the linear expression of the displacement sensor with the plane expressions of the coordinate plane I, plane II, and plane III under different nominal poses, the coordinates of the contact points of each displacement sensor and the corresponding coordinate plane in the reference block system can be obtained. ,Referred to as:

是动系处于各位姿下的位移传感器k与基准块系中对应坐标平面的触点在定系中的坐标，即为位姿坐标。In the formula,

It is the coordinate of the contact point in the fixed system between the displacement sensor k of the dynamic system in each pose and the corresponding coordinate plane in the reference block system, that is, the pose coordinate.

S43: Calculate the straight-line distance between the two contacts of each displacement sensor in each nominal posture according to the zero position coordinates and the posture coordinates, and obtain the nominal value of the expansion and contraction amount of each displacement sensor in each nominal posture.

The straight-line distance between the two contacts of each displacement sensor when the dynamic system is at the zero position and when the dynamic system is in the nominal pose can be calculated from equations (10) and (11):

When the contact point when the dynamic system is in the nominal pose moves to the positive reference axis relative to the contact point when the dynamic system is in the zero position, the nominal value of the expansion and contraction amount of the displacement sensor is specified to be positive, that is,

h _k = |h _k | (13)

When the contact point when the dynamic system is in the nominal pose moves in the negative direction of the reference axis relative to the contact point when the dynamic system is in the zero position, the nominal value of the expansion and contraction of the specified displacement sensor is negative, that is,

h _k =-|h _k | (14)

The reference axis is a coordinate axis parallel to the normal line of the coordinate plane corresponding to the displacement sensor in the reference block system.

From this, the nominal value of the expansion and contraction of each displacement sensor under each nominal pose is calculated, which is recorded as:

ⁿ H _j = [ ⁿ h _j1 ⁿ h _j2 ⁿ h _j3 ⁿ h _j4 ⁿ h _j5 ⁿ h _j6 ] (15)

In the formula, ⁿ h _j1 , ⁿ h _j2 , ⁿ h _j3 , ⁿ h _j4 , ⁿ h _j5 , ⁿ h _j6 are the nominal values of the expansion and contraction of the six displacement sensors, respectively.

S5 (S500): Use the controller to drive the six-degree-of-freedom parallel mechanism to move the moving platform to each nominal pose, and record the actual value of the expansion and contraction of each displacement sensor under each nominal pose.

The controller is used to drive the six-degree-of-freedom parallel mechanism, so that the moving platform moves to the nominal pose in sequence, and the displacement sensor is used to measure the actual value of the expansion and contraction under different nominal poses. The measurement results of each nominal pose are recorded as:

^a H _j = [ ^a h _j1 ^a h _j2 ^a h _j3 ^a h _j4 ^a h _j5 ^a h _j6 ] (16)

In the formula, ^a h _j1 , ^a h _j2 , ^a h _j3 , ^a h _j4 , ^a h _j5 , and ^a h _j6 are the nominal values of the expansion and contraction of the six displacement sensors, and the upper left mark a is "actual" (actual) abbreviation of.

S6 (S600): Make the difference between the actual value of the telescopic amount of each displacement sensor under each nominal pose and the nominal value of the telescopic amount to obtain the indication error of each displacement sensor under each nominal pose. The indication error of the displacement sensor is recorded as:

ΔH _j =[Δh _j1 Δh _j2 Δh _j3 Δh _j4 Δh _j5 Δh _j6 ] (17)

In the formula, Δh _j1 , Δh _j2 , Δh _j3 , Δh _j4 , Δh _j5 , Δh _j6 are the difference between the nominal value of the expansion and contraction of the six displacement sensors and the actual value of the expansion and contraction.

S7 (S700): Taking the minimum sum of squares of the indication errors of all displacement sensors as the objective function, and taking the structural parameter error of the 6-DOF parallel mechanism and the parameter calibration device of the 6-DOF parallel mechanism as the design variable, the mathematics of the optimization problem is constructed. Model.

In this step, a mathematical model of the optimization problem is constructed. Taking the minimum sum of squares of the indication errors of all displacement sensors as the objective function, namely

where m is the number of nominal poses.

Taking the 6-DOF parallel mechanism and the structural parameter error of the 6-DOF parallel mechanism parameter calibration device as the design variable, that is,

The constraint condition of the variable is the value range of the variable under the existing processing and assembly capabilities, and the error at the end point of the value range is ±0.1 (mm).

S8 (S800): Use advanced optimization software to search for the optimal solution of the mathematical model. The advanced optimization software in the present invention can be implemented by the software in the prior art, for example, OASIS software. The OASIS software realizes the search for the optimal solution of the mathematical model based on the advanced optimization algorithm, and the optimal solution of the mathematical model is obtained, that is, the optimal solution is obtained. Structural parameter error.

S9 (S900): Substitute the optimal solution obtained by the search into the mathematical model in the control software of the 6-DOF parallel mechanism to realize parameter calibration and compensation of the 6-DOF parallel mechanism.

The six-degree-of-freedom parallel mechanism parameter calibration device or method proposed by the above embodiments of the present invention has the following beneficial effects:

1) Low cost

The main components of the six-degree-of-freedom parallel mechanism parameter calibration device are: six high-precision displacement sensors, measured reference blocks and sensor bases. Compared with expensive instruments such as three-coordinate measuring machines and laser trackers, the cost is extremely low;

2) Simple operation

Before calibration, just fix the measured reference block on the 6-DOF parallel mechanism motion platform, fix the displacement sensor on the sensor base, and fix the sensor base on the 6-DOF parallel mechanism fixed platform through the bracket, then the parameters can be developed. Calibration; when calibrating, only the controller of the 6-DOF parallel mechanism needs to be operated, and there is no need to operate the parameter calibration device of the 6-DOF parallel mechanism. The entire calibration process is simple to operate, saving time and effort;

3) High calibration efficiency

As long as the position and posture of the end of the six-degree-of-freedom parallel mechanism changes, the measured value of the displacement sensor, that is, the actual value of the expansion and contraction amount can be obtained in an instant. At this time, there is no need to solve the posture and attitude, and the difference between the actual value of the expansion and contraction amount of the displacement sensor and the nominal value of the expansion and contraction amount can be obtained. , and into the advanced optimization software, the optimal structural parameter error of the 6-DOF parallel mechanism can be calculated in a short time, which greatly improves the efficiency of parameter calibration.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (5)

1. A parameter calibration method based on a six-degree-of-freedom parallel mechanism parameter calibration device, the six-degree-of-freedom parallel mechanism parameter calibration device comprising a displacement sensor, a sensor base (7), a measured reference block (8), a bracket (9) ) and parameter calibration calculation module; The sensor seat (7) includes three mutually orthogonal planes, one, two and three displacement sensors are respectively fixed on the three planes, and the axis of the measuring rod of the displacement sensor corresponds to the corresponding one. The plane is vertical, and the sensor seat (7) is fixed on the fixed platform (10) of the six-degree-of-freedom parallel mechanism through the bracket (9); The measured reference block (8) includes three mutually orthogonal reference planes corresponding to the three planes one-to-one, and the contacts of the displacement sensor are all in contact with the corresponding reference planes, and the measured reference planes The block (8) is fixed on the top of the moving platform (11) of the six-degree-of-freedom parallel mechanism; The parameter calibration calculation module obtains the actual value of the expansion and contraction amount of each of the displacement sensors when the six-degree-of-freedom parallel mechanism is in different poses, and determines the optimal structural parameter error of the six-degree-of-freedom parallel mechanism according to the actual value of the expansion and contraction amount, The parameters of the six-degree-of-freedom parallel mechanism are calibrated and compensated according to the optimal structural parameter error; it is characterized in that the parameter calibration calculation module is used to execute the parameter calibration method, and the parameter calibration method includes the following steps: S1: Preset the initial value of the structural parameters of the 6-DOF parallel mechanism, and add the corresponding structural parameter error to the structural parameters of the 6-DOF parallel mechanism; S2: Preset the initial values of the structural parameters of the 6-DOF parallel mechanism parameter calibration device, and add the corresponding structural parameter error to the structural parameters of the 6-DOF parallel mechanism parameter calibration device; S3: Preset the nominal pose of the moving platform of the 6-DOF parallel mechanism, and the number of the nominal poses is greater than or equal to the lower limit value; S4: Calculate the nominal value of the expansion and contraction amount of each displacement sensor under each of the nominal poses; S5: use the controller to drive the six-degree-of-freedom parallel mechanism, move the moving platform to each of the nominal poses, and record the actual value of the expansion and contraction of each of the displacement sensors under each of the nominal poses; S6: making a difference between the actual value of the expansion and contraction amount of each of the displacement sensors under each of the nominal poses and the nominal value of the expansion and contraction amount to obtain the indication error of each of the displacement sensors under each of the nominal poses; S7: Taking the minimum sum of the squares of the indication errors of all the displacement sensors as the objective function, and taking the structural parameter errors of the 6-DOF parallel mechanism and the parameter calibration device of the 6-DOF parallel mechanism as the design variable, construct a mathematical model of the optimization problem :

where m is the number of nominal poses, j and k are variable symbols; S8: using optimization software to search for the optimal solution of the mathematical model; S9: Substitute the optimal solution obtained by the search into the mathematical model of the 6-DOF parallel mechanism to realize the parameter calibration and compensation of the 6-DOF parallel mechanism. 2. parameter calibration method according to claim 1, is characterized in that, The structural parameters of the six-degree-of-freedom parallel mechanism include the coordinates of the six hinge points on the fixed platform of the six-degree-of-freedom parallel mechanism in the fixed platform coordinate system, the coordinates of the six hinge points on the moving platform in the moving platform coordinate system, and the six support the length of the chain. 3. The parameter calibration method according to claim 1 or 2, wherein step S2 comprises the following steps: Construct the measured reference block coordinate system; Preset the pose of the measured reference block coordinate system in the six-degree-of-freedom parallel mechanism moving platform coordinate system; When the coordinate system of the moving platform is at the zero position, the pose of the measured reference block in the fixed platform coordinate system of the six-degree-of-freedom parallel mechanism is preset, and the XOY plane, XOZ plane and The expression of the YOZ face; The expression of the straight line where each of the displacement sensors is located is preset. 4. parameter calibration method according to claim 1 and 2 is characterized in that, S4 comprises the following steps: S41: Calculate the zero position coordinates of the contact points of each of the displacement sensors and the corresponding coordinate planes in the coordinate system of the measured reference block in the coordinate system of the fixed platform when the coordinate system of the moving platform is at the zero position; S42: Calculate the pose coordinates in the fixed platform coordinate system of each of the displacement sensors and the contact points of the corresponding coordinate planes in the measured reference block coordinate system when the moving platform coordinate system is in the nominal pose; S43: Calculate the straight-line distance between the two contacts of each of the displacement sensors in each of the nominal poses according to the zero position coordinates and the pose coordinates, and obtain the The nominal value of the expansion and contraction of the displacement sensor. 5. parameter calibration method according to claim 4, is characterized in that, When the contact point when the coordinate system of the moving platform is in the nominal pose moves to the positive direction of the reference axis relative to the contact point when the coordinate system of the moving platform is at the zero position, the nominal value of the expansion and contraction of the displacement sensor is positive. When the shaft moves in the negative direction, the nominal value of the expansion and contraction of the displacement sensor is negative.

Images