KR102009249B1 - Ball bar with geometric error measuring function - Google Patents

Abstract

Disclosed is a ball bar having a geometric error measuring function. The ball bar having a geometric error measuring function disclosed in the ball bar having a function of measuring the geometric error of the feed system, formed of one or more pipes are combined to be foldable bar can be adjusted in length; A first probe coupled to one end of the bar and in contact with the measurement object; A second probe coupled to the other end of the bar and in contact with a measurement object; A sensor mounted inside the bar to measure a relative distance between the first probe and the second pro part; A controller which receives the measurement signal of the sensor and calculates a geometric error of the transfer system; And a display unit displaying data measured by the sensor and data calculated by the controller, wherein the main axis of the measuring object feed system sequentially moves to four vertices of the tetrahedron. The geometric error of the transfer system is calculated from six data on the distance between the four vertices measured by.

Description

Ball bar with geometric error measuring function

The present invention relates to a ball bar having a geometric error measuring function, and more particularly, after forming a virtual tetrahedron and moving the main axis of the conveying body to four vertices of the formed tetrahedron, the distance between four vertices is viewed. It relates to a ballbar with a geometric error measurement function which measures directly and calculates geometric error of the conveying body from six data on the distance between the four vertices of the measured tetrahedron.

In general, the precision feed system refers to a mechanical device including two or more feed axes, and examples thereof include a multi-axis machine tool, a multi-axis joint robot, a CMM, and the like. Such a feed system generally comprises at least one linear axis and at least one axis of rotation. A representative example is a five-axis machine tool, which is usually composed of three linear axes and two rotary axes to perform machining of complex curved surfaces or shapes.

However, such a precision feed system is inevitably accompanied by geometric errors in the feed shaft due to machining errors and assembly errors of the parts. Therefore, in the field, the geometric error of the feed shaft is periodically measured and calibrated to ensure the accuracy of the produced product.

1 is a perspective view of a typical three axis machine tool. Three-axis machine tools have three feed axes. The geometry error of the feed shaft is explained using a three-axis machine tool as an example.

2 is a diagram illustrating a feed shaft error, and FIG. 3 is a diagram illustrating an error between feed shafts.

It demonstrates with reference to FIG. 2 and FIG.

R represents the standard coordinate system, X is a coordinate system fixed to the x direction feed axis by design, and X 'represents a coordinate system fixed to the actual x direction feed axis.

The geometric error about the feed axis is divided into the error between the feed axis and the squareness error. The feed shaft error refers to an error between the design position and the actual position of the feed shaft, and FIG. 2 shows the feed shaft error with respect to the x-direction feed shaft. Feed axis errors include three position errors and three angle errors.

On the other hand, the error between the feed axes means an error in the angle between the feed axes. For three-axis machine tools, there are three errors between the feed axes.

Therefore, in the case of a three-axis machine tool, the geometrical errors of the feed shaft are totaled 21, including 18 feed shaft errors and 3 errors between the feed shafts.

In the conventional production site, a laser interferometer was used to measure 21 geometric errors with respect to the feed system and then reassemble the feed system. However, this takes a very long time and it is practically impossible to calibrate all transfer systems, and it has been pointed out as a factor that reduces productivity.

On the other hand, measurement equipment such as a laser interferometer is very expensive, it is practically difficult to have a sufficient number of measurement equipment in the field with a large number of transfer systems.

Therefore, it is urgently needed to develop a more practical measuring device that can quickly measure the major geometrical errors of the feed system with only a low-cost measuring device reflecting the reality of such a production site. It is widely used in the inspection and will be a useful tool for the determination of the precision calibration target feed system.

Korean Patent Publication No. 10-1593330

The ball bar with a geometric error measuring function according to the present invention aims to measure the main geometric error of the feed system only with a ball bar.

In addition, the ball bar with a geometric error measurement function according to the present invention is to provide a consistent measurement results using a virtual standard tetrahedron.

In addition, the ball bar with a geometric error measurement function according to the present invention is to change the size of the virtual standard tetrahedron and the length of the ball bar to be able to be flexibly applied to a variety of sizes of conveying body.

The present invention provides a ball bar having a function of measuring a geometric error of a conveying system, the bar being formed of one or more pipes and coupled to be collapsible to adjust a length; A first probe coupled to one end of the bar and in contact with the measurement object; A second probe coupled to the other end of the bar and in contact with a measurement object; A sensor mounted on the bar to measure a relative distance between the first probe and the second pro unit; A controller which receives the measurement signal of the sensor and calculates a geometric error of the transfer system; And a display unit displaying data measured by the sensor and data calculated by the controller, wherein the main axis of the measuring object feed system sequentially moves to four vertices of the tetrahedron. It provides a ball bar with a geometric error measurement function, characterized in that to calculate the geometric error of the feed system from the six data on the distance between the four vertices measured by.

In addition, the geometric error of the present invention is characterized in that the scale error (scale error) defining the distance error in the direction of the feed axis, and the squareness error (squareness error) defining the angle error between the feed axis.

In addition, the control unit of the present invention, the vertex coordinates of the tetrahedral data storage unit is stored; A measurement coordinate calculation unit for calculating four vertex coordinates of the tetrahedron measured from the distance between the tetrahedral vertices measured by the sensor; And a geometric error calculator configured to calculate a geometric error of the feed system by applying a least square method to the relationship between the difference between the vertex coordinate of the tetrahedron and the measured vertex coordinate of the tetrahedron and the geometric error stored in the standard data storage unit. .

In addition, the relationship between the geometric error and the difference between the virtual tetrahedral vertex coordinates and the measured vertex coordinates of the tetrahedron of the present invention is characterized by the following equation (1).

[Equation 1]

here,

c _i : Feed axis error (i = X, Y, Z)

s _ij : Error between feed axes (i, j = X, Y, Z)

x _i : x coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)

y _i : y coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)

z _i : z coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)

x _{i, m} : x coordinate of the measured tetrahedral vertex (i = 1, 2, 3, 4)

y _{i, m} : y coordinate of the measured vertex vertex (i = 1, 2, 3, 4)

z _{i, m} : z coordinate of the measured tetrahedral vertex (i = 1, 2, 3, 4)

do.

In addition, the first probe and the second probe of the present invention is characterized in that the ball or three-point support socket.

In addition, the control unit of the present invention further includes a correction determination unit for determining whether or not the calculated geometric error meets a preset correction target of the transfer system.

The ball bar with the geometric error measuring function according to the present invention has the effect of measuring the main geometric error of the feed system with only the ball bar which is relatively inexpensive compared to the conventional error measuring equipment such as a laser interferometer.

In addition, the ball bar with a geometric error measurement function according to the present invention has the effect of providing a consistent measurement results even for repeated measurements using a virtual standard tetrahedron.

In addition, the ball bar with a geometric error measurement function according to the present invention has an effect that can be flexibly applied to the conveying body of various sizes.

In addition, the ball bar with a geometric error measurement function according to the present invention has an effect that can be applied to a three-dimensional coordinate measuring machine without additional tools.

In addition to the effects described above, the specific effects of the present invention will be described together with the following description of specifics for carrying out the invention.

1 is a perspective view of a typical three axis machine tool.
2 is a diagram illustrating a feed shaft error.
3 is a diagram illustrating an error between feed axes.
4 is a diagram illustrating the main geometric error.
5 is a view showing a ball bar with a geometric error measurement function according to the present invention.
6 is a view for explaining a method for sequentially moving the main axis of the conveying body to the vertex position of the tetrahedron according to the present invention.
7 is a view for explaining a method for measuring the distance between the vertices of the tetrahedron with the ballbar according to the present invention.
8 is a block diagram of a ball bar with a geometric error measurement function according to the present invention.

Hereinafter, various embodiments of the present disclosure will be described with reference to the accompanying drawings. However, this is not intended to limit the techniques described in this document to specific embodiments, but should be understood to cover various modifications, equivalents, and / or alternatives to the embodiments of this document. In connection with the description of the drawings, similar reference numerals may be used for similar components.

In addition, the expressions "first," "second," and the like used in this document may modify various components in any order and / or importance, and may distinguish one component from another. Used only and do not limit the components. For example, the 'first part' and the 'second part' may indicate different parts regardless of the order or importance. For example, without departing from the scope of rights described in this document, the first component may be called a second component, and similarly, the second component may be renamed to the first component.

Also, the terminology used herein is for the purpose of describing particular embodiments only and may not be intended to limit the scope of other embodiments. Singular expressions may include plural expressions unless the context clearly indicates otherwise. The terms used herein, including technical or scientific terms, may have the same meaning as commonly understood by one of ordinary skill in the art. Among the terms used in this document, terms defined in the general dictionary may be interpreted as having the same or similar meaning as the meaning in the context of the related art, and ideally or excessively formal meanings are not clearly defined in this document. Not interpreted as In some cases, even if terms are defined in the specification, they may not be interpreted to exclude embodiments of the present disclosure.

4 is a diagram illustrating the main geometric error. FIG. 4A is a diagram illustrating a scale error, and FIG. 4B is a diagram illustrating a squareness error.

The scale error (c _i, i = X , Y , Z ) means a distance error of the feed axis in the feed axis direction. That is, C _x means the x direction scale error. Error between feed axes, that is, squareness error (s _{ij ,} i, j = X , Y , Z ) means the angular error between two feed axes. That is, s _yz means the angle error between the y-axis and the z-axis.

These scale errors and squareness errors are regarded as geometric errors that have a significant effect on the performance of the feed system.

Therefore, in the related art, after mounting a touch probe on a machine tool or a 3D coordinate measuring machine, a vertex of a standard tetrahedron is measured to calculate a scale error and a squareness error.

However, since the touch probe and the standard tetrahedron are very expensive, they are difficult to apply to all the feed systems.

Accordingly, the present invention has been developed a ball bar with a geometric error measurement function.

5 is a view showing a ball bar with a geometric error measurement function according to the present invention.

The ball bar according to the present invention includes a bar 100, a first probe 200, a second probe 210, a sensor (not shown), a control unit 300, and a display unit 400.

Bar 100 is formed of one or more pipes and is coupled to be foldable is adjustable in length.

The first probe 200 is coupled to one end of the bar 100 to contact the measurement object, and the second probe 210 is coupled to the other end of the bar 100 to contact the measurement object.

As the first probe 200 and the second probe 210, a ball or a three-point support socket is usually used. 5 illustrates a case in which balls are mounted at both ends of the bar 100.

The sensor is mounted inside the bar 100 to measure the relative distance between the first probe 200 and the second pro part. As the sensor, various kinds of sensors such as LVDT can be adopted.

The display unit 400 displays data measured by the sensor and data calculated by the controller 300. The display unit 400 may be mounted on the bar 100, but may be installed at a remote distance from the bar 100 to display and receive data wirelessly.

The controller 300 calculates a geometric error of the feed system from the data measured by the sensor.

A method for calculating the geometric error by the controller 300 according to the present invention will be described in detail.

6 is a view for explaining a method of sequentially moving the main axis of the conveying body to the vertex position of the tetrahedron, Figure 7 illustrates a method for measuring the distance between the vertices of the tetrahedron with the ballbar according to the present invention Drawing.

It demonstrates with reference to FIG. 6 and FIG.

The present invention uses a hypothetical tetrahedron instead of a standard tetrahedron.

Considering the processing volume of the measuring feed system, a virtual tetrahedron of appropriate size is formed.

In the case of using a conventional standard tetrahedron, the size is determined and it is not possible to flexibly cope with a transfer system of various sizes. However, by using a hypothetical tetrahedron, this problem was solved at once.

In addition, the conventional standard tetrahedron does not guarantee consistent measurement results over time due to wear due to repeated use, but the use of virtual tetrahedrons can provide consistent measurement results even for repeated use. will be.

Next, input the coordinates of the four vertices constituting the formed virtual tetrahedron into the measuring object transfer system.

A position indicator is mounted to indicate the position of the vertex at the main shaft end of the feed system. At this time, a tool ball or a three-point support socket is usually used as the position indicator.

The tool ball and the three-point support socket are coupled to the main shaft by magnetic force or by bolting. 6 shows a case where the tool ball is mounted on the main shaft.

The spindle with the tool ball is sequentially moved to the positions of the four input vertices. At this time, the center mount is mounted to contact the vertex while the main axis is moved to the vertex position to indicate the input vertex position. As a result, the center mount represents the position of the entered vertex.

In Figures 6 and 7, P represents the position of the tetrahedral vertex.

The center mount is mounted at each of the three vertices except the fourth vertex from which the main axis is moved.

As a result, the tool balls mounted at the three center mounts and the spindle ends indicate the positions of the four vertices of the input tetrahedron.

A ball bar is used to measure the distance between the three center mounts representing the positions of the four vertices and the tool balls mounted at the spindle ends. A total of six distances are measured. In Figure 7, L represents the measured distance between two vertices.

Finally, the controller 300 calculates the geometric error of the feed system from the measured distances between the four vertices. Here, geometric error means scale error and squareness error of the feed axis.

The process of calculating the geometric error from the measured distance between the tetrahedral vertices will be described.

The controller 300 according to the present invention includes a standard data storage unit, a measurement coordinate calculator, and a geometric error calculator.

The standard data storage stores vertex coordinates for the virtual tetrahedron.

First, the measurement coordinate calculation unit calculates coordinates of the four vertices of the measured tetrahedron from the measured distance between the vertices of the tetrahedron.

The geometric error calculator calculates a difference between the imaginary vertex vertex coordinates and the measured vertex coordinates of the tetrahedron.

The geometric error calculator also defines the relationship between this coordinate value difference and the geometric error.

Equation 1 below is a formula that defines the relationship between the geometric error and the difference between the virtual vertex vertex coordinates and the measured vertex coordinates of the virtual tetrahedron.

[Equation 1]

here,

c _i : Scale error (i = X, Y, Z)

s _ij : Squareness error (i, j = X, Y, Z)

x _i : x coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)

y _i : y coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)

z _i : z coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)

x _{i, m} : x coordinate of the measured tetrahedral vertex (i = 1, 2, 3, 4)

y _{i, m} : y coordinate of the measured vertex vertex (i = 1, 2, 3, 4)

z _{i, m} : z coordinate of the measured tetrahedral vertex (i = 1, 2, 3, 4)

Finally, the geometric error calculator calculates the geometric error by applying the least square method to Equation 1.

8 is a block diagram of a ball bar with a geometric error measurement function according to the present invention. While the above has been shown and described with respect to preferred embodiments of the present invention, the present invention is not limited to the specific embodiments described above, it is usually in the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Baa 100
First probe 200
Second probe 210
Control unit 300
Display unit 400
Spindle 500
Position indicator 510
Center mount 520

Claims (6)

In the ballbar equipped with a function for measuring the geometric error of the feed system,
A bar formed from one or more pipes and coupled to be foldable to adjust a length;
A first probe coupled to one end of the bar and in contact with the measurement object;
A second probe coupled to the other end of the bar and in contact with a measurement object;
A sensor mounted on the bar to measure a relative distance between the first probe and the second pro unit;
A controller which receives the measurement signal of the sensor and calculates a geometric error of the transfer system; And
And a display unit displaying data measured by the sensor and data calculated by the controller.
In a state in which the main axis of the measuring object feed system is sequentially moved to the positions of the four vertices of the virtual tetrahedron, the controller calculates the geometric error of the feed system from six data on the distance between the four vertices measured by the sensor. Yields,
The geometric error is a scale error defining a distance error in the direction of the feed axis and a squareness error defining an angle error between the feed axes. Ballbar. delete The method of claim 1,
The control unit,
A standard data storage unit for storing vertex coordinates of the tetrahedron;
A measurement coordinate calculation unit for calculating four vertex coordinates of the tetrahedron measured from the distance between the tetrahedral vertices measured by the sensor;
A geometric error calculation unit calculating a geometric error of the feed system by applying a least-squares method to a relationship between a geometric error and a vertex coordinate of a tetrahedron stored in the standard data storage unit and a measured vertex coordinate of the tetrahedron; Ball bar with geometric error measurement function. The method of claim 3,
The relationship between the difference between the virtual tetrahedral vertex coordinates and the measured vertex coordinates of the tetrahedron and the geometric error is defined by Equation 1 below, ball bar with a geometric error measurement function.
[Equation 1]

here,
c _i : Feed axis error (i = X, Y, Z)
s _ij : Error between feed axes (i, j = X, Y, Z)
x _i : x coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)
y _i : y coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)
z _i : z coordinate of the vertex of the imaginary tetrahedron (i = 1, 2, 3, 4)
x _{i, m} : x coordinate of the measured tetrahedral vertex (i = 1, 2, 3, 4)
y _{i, m} : y coordinate of the measured vertex vertex (i = 1, 2, 3, 4)
z _{i, m} : z coordinate of the measured tetrahedral vertex (i = 1, 2, 3, 4) The method of claim 1
The first and second probes are ball or three-point support socket, characterized in that the ball bar with a geometric error measurement function. The method of claim 3,
The control unit further comprises a correction determination unit for determining whether the calculated geometric error meets a preset calibration target of the transfer system; Ball bar with a geometric error measurement function.

Images