CN105234743A - Deflection error compensation method for five-axis machining center tool - Google Patents

Abstract

The invention discloses a deflection error compensation method for a five-axis machining center tool. The deflection error compensation method includes the steps that the milling force is computed according to a built five-axis machining milling force model; the theoretical tool location point and a tool-axis vector serve as the benchmark of mirror image reversible deflection compensation; the tool deflection error, caused by the milling force, of the current tool position is worked out according to the tool deflection; mirror image reversible deflection compensation is conducted on the current tool location point and the tool-axis vector, and a new tool location point and a new tool-axis vector are worked out according to the tool deflection error; a new tool deflection error is computed according to the compensated tool location point data, and whether the new error exists or not is judged; if the requirement is met, operation is stopped, and the tool location point information is stored; and the compensated tool location point data information corresponding to the tool path positions from 1 to N is collated, accordingly the compensated tool location locus is obtained, and a compensated numerical control program is generated through post-processing software.

Description

A kind of Five-axis NC Machining Center cutter distortion error compensating method

Technical field

The present invention relates to Computerized Numerical Control processing technology field, particularly relate to a kind of Five-axis NC Machining Center cutter distortion error compensating method.

Background technology

In the process of reality, Milling Process system is generally made up of a few parts such as lathe, cutter, fixture, workpiece, wherein the rigidity of lathe and fixture is commonly considered as enough, workpiece (non-thin-wall part) deflection is also smaller, and the rigidity of cutter is relatively fragile, in milling system, the distortion of cutter is a unavoidable problem, when especially using " elongate rod " tool sharpening, the distortion of cutter be can not ignore, it easily occurs bending and deformation under the effect of cutting force, is the principal element causing finished surface geometric error.5-shaft linkage numerical control technology has unique advantage in the processing of complicated surface, namely can cutter be made by the pose adjusting cutter to keep optimum cutting state and avoid cutter interference, thus improve the processing and manufacturing precision of part.Therefore analyze cutter distortion in five-axis robot process, research error compensating method tool is of great significance.

(1) RaoVS and RaoPVM is by cutter distortion quantitative analysis in process, proposes a kind of cutter distortion error compensating method caused by cutting force.(see RaoVS, RaoPVM (2006) Tooldeflectioncompensationinperipheralmillingofcurvedgeo metries.IntJMachToolsManuf46 (15): 2036-2043).

(2) BeraTC, DesaiKA and RaoPVM analyzes cutter distortion and the combined influence of thin-wall part distortion to mismachining tolerance in milling process, by changing the cutter path in process, and then its error to be compensated, and by laboratory proofing the feasibility of the method.(see BeraTC, DesaiKA, RaoPVM (2011) Errorcompensationinflexibleendmillingoftubulargeometries .JournalofMaterialsProcessingTechnology211 (1): 24-34).

(3) ZhuS, DingG, QinS, LeiJ, ZhuangL and YanK utilize the geometric error of ball bar to five-axis machine tool to identify, establish the mismachining tolerance compensation model caused by machine tool error.(see ZhuS, DingG, QinS, LeiJ, ZhuangL, YanK (2012) Integratedgeometricerrormodeling, identificationandcompensationofCNCmachinetools.IntJMachT oolsManuf52 (1): 24-29).

The cutter distortion error compensating method proposed in document (1) (2) is main or for three axis machining, inapplicable for the cutter distortion error compensation of five-axis robot.

The error compensation model set up in document (3), considers the geometric error in machine tool motion process, but does not relate to the cutter distortion error in five-axis machine tool process.

Summary of the invention

The invention provides a kind of Five-axis NC Machining Center cutter distortion error compensating method, the present invention passes through cutter distortion quantitative analysis in five-axis robot process, consider the impact of cutter distortion on processing profile, a kind of cutter distortion error compensating method being applied to five-axis robot is proposed, for high-accuracy processed complex curved surface part provides theoretical, described below:

A kind of Five-axis NC Machining Center cutter distortion error compensating method, described error compensating method comprises the following steps:

Set up tool coordinate system, Conversion Relations between workpiece coordinate system and lathe coordinate system three, obtain the kinematic parameter of lathe in five-axis robot process;

Under tool coordinate system, obtain the deflection of cutter; Read the theoretical cutter location data file automatically generated by CAM software;

Milling Force size is calculated according to the five-axis robot Milling Force Model set up; Using the benchmark that theoretical cutter location and generating tool axis vector compensate as mirror image reversible deformation;

The cutter distortion error obtaining current tool position and caused by Milling Force is calculated according to cutter distortion gauge;

Mirror image reversible deformation compensation is carried out to current cutter location and generating tool axis vector, obtains new cutter location and generating tool axis vector according to cutter distortion error calculation;

Calculate new cutter distortion error according to the cutter location data after compensating, judge whether new error is set up; If met the demands, then stop computing, preserve cutter location information;

Arrange cutter path position from the compensation cutter location data message corresponding to 1 to N, so the Path after being compensated, the nc program after being compensated by postpositive disposal Software Create.

The beneficial effect of technical scheme provided by the invention is: the present invention is based on cantilever beam theory, sets up the cutter distortion model in five-axis robot process.Before truly processing, the margin of error obtaining and cause workpiece machining surface is calculated by the cutter stress deformation model set up, the Path file that CAM software generates automatically is modified, the Path of theory is realized error compensation along the same margin of error of part to be processed surface offset, finally be used in actual process according to amended Path file, thus improve the accuracy of manufacture of five-axis robot, the validity of the method is verified finally by cutting experiment.

Accompanying drawing explanation

Fig. 1 is Five-axis NC Machining Center movement relation figure;

Fig. 2 is cutter distortion schematic diagram;

Fig. 3 is error compensating method schematic diagram;

Fig. 4 is generating tool axis vector compensate for reference reference map;

Fig. 5 is cutter location compensate for reference reference map;

Fig. 6 is processing parts figure;

Fig. 7 error profiles versus schemes;

Fig. 8 is a kind of flow chart of Five-axis NC Machining Center cutter distortion error compensating method.

Detailed description of the invention

For making the object, technical solutions and advantages of the present invention clearly, below embodiment of the present invention is described further in detail.

Below in conjunction with accompanying drawing, for B yaw C turntable five-axis linkage machine tools ball-end milling, describe the concrete enforcement of the embodiment of the present invention in detail.

101: set up tool coordinate system, Conversion Relations between workpiece coordinate system and lathe coordinate system three, obtain the kinematic parameter of lathe in five-axis robot process;

The embodiment of the present invention, for C turntable B yaw structure five-axle number control machine tool, is analyzed kinematic relation between each coordinate, is set up the transformational relation of tool coordinate system, workpiece coordinate system and lathe coordinate system.

The movement locus of cutter in five-axis machine tool process, sets up coordinate system as shown in Figure 1 for convenience of description.During lathe original state, workpiece coordinate system [O _w, X _w, Y _w, Z _w] and lathe coordinate system [O _m, X _m, Y _m, Z _m] direction is consistent, workpiece coordinate system initial point overlaps with lathe coordinate system initial point; Tool coordinate [O _c, X _c, Y _c, Z _c] initial point is positioned at point of a knife point place, its coordinate system direction is consistent with lathe coordinate system; [O _m1, X _m1, Y _m1, Z _m1] be rotating coordinate system, cutter is around axle Y _m1the anglec of rotation be θ _b(being just counterclockwise), its coordinate system direction is consistent with lathe coordinate system; [O _m2, X _m2, Y _m2, Z _m2] be revolution coordinate system, workpiece is around axle Z _m2angle of revolution be θ _c(being just counterclockwise), its coordinate system direction is consistent with lathe coordinate system.Under lathe original state, O _co _m1between distance be L, O _wo _m2between distance be H, the original state of lathe translation shaft is wherein represent lathe X respectively, Y, the initial position of Z axis.Under in tool coordinate system, any point can be switched to workpiece coordinate system, transformation matrix of coordinates T is:

T＝T ₅T ₄T ₃T ₂T ₁(1)

$T_1=\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& 1& -L\\ 0& 0& 0& 1\end{array}\right],T_3=\left[\begin{array}{cccc}1& 0& 0& x_s^M\\ 0& 1& 0& y_s^M\\ 0& 0& 1& z_s^M-H+L\\ 0& 0& 0& 1\end{array}\right],T_5=\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& 1& H\\ 0& 0& 0& 1\end{array}\right]$

$T_2=\left[\begin{array}{cccc}{\mathrm{cos\θ}}_B& 0& {\mathrm{sin\θ}}_B& 0\\ 0& 1& 0& 0\\ -{\mathrm{sin\θ}}_B& 0& {\mathrm{cos\θ}}_B& 0\\ 0& 0& 0& 1\end{array}\right],T_4=\left[\begin{array}{cccc}{\mathrm{cos\θ}}_C& {\mathrm{sin\θ}}_C& 0& 0\\ -{\mathrm{sin\θ}}_C& {\mathrm{cos\θ}}_C& 0& 0\\ 0& 0& 1& 0\\ 0& 0& 0& 1\end{array}\right]$

In formula (1), T ₁, T ₃and T ₅for translation matrix, T ₂with T ₄for spin matrix.

Under tool coordinate system, the position vector of any point q can be expressed as the direction vector that q point and tool coordinate initial point form directed line segment can be expressed as under workpiece coordinate system, the position vector of corresponding q point can be expressed as the direction vector that q point and workpiece coordinate initial point form directed line segment can be expressed as therefore, under tool coordinate system, any point relative to the transformational relation of workpiece coordinate system is:

${\[x_q^W,y_q^W,z_q^W,1\]}^T=T{\[x_q^C,y_q^C,z_q^C,1\]}^T---\left(2\right)$

${\[i_q^W,j_q^W,k_q^W,0\]}^T=T_4{T}_2{\[i_q^C,j_q^C,k_q^C,0\]}^T---\left(3\right)$

Formula (2), (3) are launched to obtain:

$\{\begin{array}{c}{x}_q^W=x_q^C{\mathrm{cos\θ}}_B{\mathrm{cos\θ}}_C+y_q^C{\mathrm{sin\θ}}_C+z_q^C{\mathrm{sin\θ}}_B{\mathrm{cos\θ}}_C+x_s^M{\mathrm{cos\θ}}_C+y_s^M{\mathrm{sin\θ}}_C-L{\mathrm{sin\θ}}_B{\mathrm{cos\θ}}_C\\ y_q^W=-x_q^C{\mathrm{sin\θ}}_C{\mathrm{cos\θ}}_B+y_q^C{\mathrm{cos\θ}}_C-z_q^C{\mathrm{sin\θ}}_B{\mathrm{sin\θ}}_C-x_s^M{\mathrm{sin\θ}}_C+y_s^M{\mathrm{cos\θ}}_C+L{\mathrm{sin\θ}}_B{\mathrm{sin\θ}}_C\\ z_q^W=-x_q^C{\mathrm{sin\θ}}_B+z_q^C{\mathrm{cos\θ}}_B-L{\mathrm{cos\θ}}_B+L+z_s^M\\ i_q^W=i_q^C{\mathrm{cos\θ}}_B{\mathrm{cos\θ}}_C+j_q^C{\mathrm{sin\θ}}_C+k_q^C{\mathrm{sin\θ}}_B{\mathrm{cos\θ}}_C\\ j_q^W=-i_q^C{\mathrm{sin\θ}}_C{\mathrm{cos\θ}}_B+j_q^C{\mathrm{cos\θ}}_C-k_q^C{\mathrm{sin\θ}}_B{\mathrm{sin\θ}}_C\\ k_q^W=-i_q^C{\mathrm{sin\θ}}_C+k_q^C{\mathrm{cos\θ}}_B\end{array}---\left(4\right)$

When five-shaft numerical control is programmed, by the cutter path of CAD/CAM Software Create, be generally calculate according to the cad model of workpiece to obtain point of a knife point relative to the position vector of workpiece and direction vector.Therefore, the position vector of point of a knife point under tool coordinate system and direction vector can be expressed as with bring formula (4) into can obtain:

$\left\{\begin{array}{c}{x}_q^W=x_s^M{\mathrm{cos\θ}}_C+y_s^M{\mathrm{sin\θ}}_C-L{\mathrm{sin\θ}}_B{\mathrm{cos\θ}}_C\\ y_q^W=-x_s^M{\mathrm{sin\θ}}_C+y_s^M{\mathrm{cos\θ}}_C+L{\mathrm{sin\θ}}_B{\mathrm{sin\θ}}_C\\ z_q^W=-L{\mathrm{cos\θ}}_B+L+z_s^M\\ i_q^W={\mathrm{sin\θ}}_B{\mathrm{cos\θ}}_C\\ j_q^W=-{\mathrm{sin\θ}}_B{\mathrm{sin\θ}}_C\\ k_q^W={\mathrm{cos\θ}}_B\end{array}\right.---\left(5\right)$

Can be calculated in five-axis robot process by (5) formula, the kinematic parameter of lathe.

$\left\{\begin{array}{c}{\mathrm{\θ}}_B=arccos\left(k_q^W\right)\\ {\mathrm{\θ}}_C=arctan(-j_q^W/i_q^W)\\ x_s^M=x_q^W{\mathrm{cos\θ}}_C-y_q^W{\mathrm{sin\θ}}_C+L{\mathrm{sin\θ}}_B\\ y_s^M=x_q^W{\mathrm{sin\θ}}_C+y_q^W{\mathrm{cos\θ}}_C\\ z_s^M=z_q^W+L{\mathrm{cos\θ}}_B-L\end{array}\right.---\left(6\right)$

102: under tool coordinate system, obtain cutter at X _c, Y _cdeflection δ x on direction ^c, δ y ^c;

Cutter distortion amount is calculated, as shown in Figure 2 according to cantilever beam theory.Under tool coordinate system, owing to acting on axial Z _ccutting force make cutter produce stretch or compression, at X _c, Y _cthe cutting force in direction makes it produce flexural deformation, and it is generally acknowledged that cutter is at Z _cthe rigidity in direction is comparatively large, very little to the error effect of milling profile, is generally ignored, therefore mainly considers X _c, Y _cthe bending deformation quantity that direction cutter produces.Under tool coordinate system, at X _c, Y _cdeflection δ x on direction ^c, δ y ^ccan be expressed as:

$\left\{\begin{array}{c}{\mathrm{\δx}}^C=\frac{F_X^C{Z_0}^2\left(3\right(D-0.5a_p/{\mathrm{cos\θ}}_B)-Z_0)}{6EI}\\ {\mathrm{\δy}}^C=\frac{F_Y^C{Z_0}^2\left(3\right(D-0.5a_p/{\mathrm{cos\θ}}_B)-Z_0)}{6EI}\end{array}\right.---\left(7\right)$

In formula, be illustrated respectively in X _c, Y _ccomponent on direction; D is knife bar cantilevered length; a _pfor cutting depth; E is the elastic modelling quantity of cutter material; I is the moment of inertia of cutter; Z ₀for deflection measurement location.

Five-axis robot cutter distortion error compensation is mainly divided into the content of two aspects: cutter location compensates and generating tool axis vector compensates.As shown in Figure 3.

103: read the theoretical cutter location data file automatically generated by CAM software, i-th cutter location coordinate is generating tool axis vector is i ∈ (1, N), N are cutter location number;

104: loop initialization starts, i=1; Milling Force size is calculated according to the five-axis robot Milling Force Model set up;

105: the benchmark that theoretical cutter location and generating tool axis vector are compensated as mirror image reversible deformation;

106: calculate the cutter distortion error E obtaining current tool position and caused by Milling Force according to cutter distortion gauge ₁;

107: mirror image reversible deformation compensation is carried out, according to cutter distortion error E to current cutter location and generating tool axis vector ₁calculate and obtain new cutter location and generating tool axis vector;

108: calculate new cutter distortion error E according to the cutter location data after compensating ₂, judge new error E ₂whether < ε (tolerance) sets up;

If met the demands, then stop computing, preserve cutter location information, perform step 109; Otherwise, forward step 106 to, until meet the demands;

109: arrange cutter path position from the compensation cutter location data message corresponding to 1 to N, so the Path after being compensated, the nc program after being compensated by postpositive disposal Software Create.

From cantilever beam Deformation Theory, cutter is a camber line in the distortion of axis direction.Therefore, if it is unreasonable that error compensation reference data is selected, the situation occurring " cross and cut " or " owing to cut " in compensation process will be caused, especially in Flank machining process, compensation effect can be subject to serious impact, thus causes the mismachining tolerance after having compensated than larger before not compensating.For this reason, the error compensation reference data selecting rational generating tool axis vector and cutter location is needed.

As shown in Figure 4, in theoretical Path, the position vector of any point P and direction vector are with in Digit Control Machine Tool process, due to the effect of Milling Force, cutter stress deformation forms new cutter location and cutter vector with as shown in Figure 4, when changing generating tool axis vector, vector be parallel to vector therefore, the error compensation reference data of generating tool axis vector may be defined as by point arrives point forms the direction vector of directed line segment can represent and become:

$\left[\begin{array}{c}{i}_r^W\\ j_r^W\\ k_r^W\end{array}\right]=\left[\begin{array}{c}{x}_i^W-x_d^W\\ y_i^W-y_d^W\\ z_i^W-z_d^W\end{array}\right]---\left(8\right)$

Wherein

$\left[\begin{array}{c}{x}_d^W\\ y_d^W\\ z_d^W\\ 1\end{array}\right]=T\left[\begin{array}{c}{x}_i^C+{\mathrm{\&delta;x}}_i^C\\ y_i^C+{\mathrm{\&delta;y}}_i^C\\ z_i^C\\ 1\end{array}\right]$

As shown in Figure 5, the error compensation reference data of cutter location can be expressed as:

$\left[\begin{array}{c}{x}_r^W\\ y_r^W\\ z_r^W\end{array}\right]=\left[\begin{array}{c}{x}_d^W-U_x^W\\ y_d^W-U_y^W\\ z_d^W-z_i^W\end{array}\right]---\left(9\right)$

Wherein

$\left[\begin{array}{c}{U}_x^W\\ U_y^W\\ U_z^W\\ 1\end{array}\right]=T\left[\begin{array}{c}\left({\mathrm{\&delta;x}}_{\min }^C+{\mathrm{\&delta;x}}_{\max }^C\right)/2\\ \left({\mathrm{\&delta;y}}_{\min }^C+{\mathrm{\&delta;y}}_{\max }^C\right)/2\\ z_i^C\\ 1\end{array}\right]$

In formula, minimum and maximum cutter stress deformation amount under expression tool coordinate system respectively.

Experimental verification

For verifying the feasibility of this programme, the part shown in Fig. 6 being used respectively and does not compensate cutter path and compensate cutter path processing profile 1 and profile 2, measuring the part error after machining.The global error of profile 2 decreases drastically relative to profile 1, demonstrates the feasibility of this compensation method, as shown in Figure 7.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number, just to describing, does not represent the quality of embodiment.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. a Five-axis NC Machining Center cutter distortion error compensating method, is characterized in that, described error compensating method comprises the following steps:

Set up tool coordinate system, Conversion Relations between workpiece coordinate system and lathe coordinate system three, obtain the kinematic parameter of lathe in five-axis robot process;

Under tool coordinate system, obtain the deflection of cutter; Read the theoretical cutter location data file automatically generated by CAM software;

Milling Force size is calculated according to the five-axis robot Milling Force Model set up; Using the benchmark that theoretical cutter location and generating tool axis vector compensate as mirror image reversible deformation;

The cutter distortion error obtaining current tool position and caused by Milling Force is calculated according to cutter distortion gauge;

Mirror image reversible deformation compensation is carried out to current cutter location and generating tool axis vector, obtains new cutter location and generating tool axis vector according to cutter distortion error calculation;

Calculate new cutter distortion error according to the cutter location data after compensating, judge whether new error is set up; If met the demands, then stop computing, preserve cutter location information.

2. a kind of Five-axis NC Machining Center cutter distortion error compensating method according to claim 1, it is characterized in that, described error compensating method also comprises:

Arrange cutter path position from 1 to N, corresponding compensation cutter location data message, and then the Path after being compensated, the nc program after being compensated by postpositive disposal Software Create, N is cutter location number.