Measurement method for geometric errors of numerical control turntable based on four-station laser tracer system

Patent metadata

Field	Value
Publication number	US-11543234-B2
Application number	US-202017005346-A
Country	US
Kind code	B2
Filing date	Aug 28, 2020
Priority date	Aug 30, 2019
Publication date	Jan 3, 2023
Grant date	Jan 3, 2023

Abstract

A method for measuring geometric errors of a numerical control turntable based on a four-station laser tracer system includes: establishing a self-calibration coordinate system and calibrating positions of tracking interferometers; respectively placing each of target lenses at three non-coplanar points that are above the numerical control turntable and keep certain distances from the numerical control turntable, controlling the numerical control turntable to rotate at a certain angular interval θj, and based on positions of the tracking interferometers being known after calibration, solving coordinates of each of measurement points in the self-calibration coordinate system using a non-linear least square method; establishing a turntable coordinate system; perform a conversion between the turntable coordinate system and the self-calibration coordinate system; separating six geometric errors of the numerical control turntable using spatial position errors of the three points at a same position and using the linear least squares method.

First claim

What is claimed is:

1. A measurement method for geometric errors of a numerical control turntable based on a four-station laser tracer system, comprising steps of:
S1: establishing a self-calibration coordinate system and calibrating positions of tracking interferometers;
S2: respectively placing each of target lenses at three non-coplanar points, each of the three non-coplanar points being located on or above the numerical control turntable, at least one of the three non-coplanar points located above the numerical control turntable keeping a certain distance from the numerical control turntable; controlling the numerical control turntable to rotate at a certain angular interval θ j ; and based on positions of the tracking interferometers being known after calibration, solving coordinates of each of measurement points in the self-calibration coordinate system using a non-linear least square method;
S3: after measurement, taking three initial position points as theoretical points on the numerical control turntable, and perform fitting using the non-linear least square method to obtain a fitting function of a center (x′ 0 , y′ 0 , z′ 0 ) and a radius R C of a spatial circle formed by the three initial position points;
S4: establishing a turntable coordinate system;
S5: perform a conversion between the turntable coordinate system and the self-calibration coordinate system;
S6: subtracting coordinates (x j , y j , z j ) of one of the theoretical points in the turntable coordinate system from actual coordinates (x′ j , y′ j , z′ j ) of one of the measurement points in the self-calibration coordinate system to obtain a spatial position error (Δx j , Δy j , Δz j ) of the one of the measurement points, and through establishing a model of six position-related geometric errors of the numerical control turntable, separating six geometric errors of the numerical control turntable using spatial position errors of the three initial position points at a same position and using the linear least squares method.

2. The measurement method for the geometric errors of the numerical control turntable based on the four-station laser tracer system according to claim 1 , wherein in the step S1, the self-calibration coordinate system are established based on four-station laser tracer interferometers LT ii (x pi L , y pi L , z pi L ), i=1, 2, 3, 4, in the turntable coordinate system; each of the target lenses P i (x j L , y j L , z j L ), j=1, 2, 3 . . . n in the turntable coordinate system is places at the three non-coplanar points located above the numerical control turntable that are away from the numerical control turntable at unequal heights; the numerical control turntable are rotated one revolution to form a cylindrical surface for measurement, light emitted by each of the four-station laser tracer interferometers is continuous during the measurement, a measured length between each of the target lenses and each of the four-station laser tracer interferometers read by the laser tracer interferometer and a formula of a distance between two points are used to form a non-linear equation set, and the non-linear equation set is solved to complete self-calibration of the laser tracer interferometer, and coordinates of a position of the laser tracer interferometer is determined.

3. The measurement method for the geometric errors of the numerical control turntable based on the four-station laser tracer system according to claim 2 , wherein the non-linear equation set formed by the measured length between the target lens and the laser tracer interferometer read by the laser tracer interferometer and the formula of the distance between two points is:

{

(

x
j
L

-

x

p
⁢

⁢
1

L

)

2

+

(

y
j
L

-

y

p
⁢

⁢
1

L

)

2

+

(

z
j
L

-

z

p
⁢

⁢
1

L

)

2

=

l
1

+

l

1
⁢
j

Assignees

• Univ Xi An Jiaotong

Inventors

• Zha Jun
• Chen Yaolong
• Han Lin

Classifications

• B23Q17/24 Primary

  using optics {or electromagnetic waves} · CPC title

• G01B21/042

  Calibration or calibration artifacts (G01B3/30, G01B9/02072 take precedence) · CPC title

• G01B5/0004

  Supports (G01B5/025 takes precedence) · CPC title

• B23Q2220/004

  Rotary tables · CPC title

• G01B11/002 Primary

  for measuring two or more coordinates · CPC title