CN108871170B - Method for configuring pre-tightening force of trigger type measuring head and three-coordinate measuring machine - Google Patents

Method for configuring pre-tightening force of trigger type measuring head and three-coordinate measuring machine Download PDF

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CN108871170B
CN108871170B CN201810699957.8A CN201810699957A CN108871170B CN 108871170 B CN108871170 B CN 108871170B CN 201810699957 A CN201810699957 A CN 201810699957A CN 108871170 B CN108871170 B CN 108871170B
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force
trigger
pretightening
configuring
ball
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CN108871170A (en
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陈艳华
梁斌
刘伟强
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Shenzhen Lihe Precision Equipment Technology Co ltd
Shenzhen Research Institute Tsinghua University
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Shenzhen Lihe Precision Equipment Technology Co ltd
Shenzhen Research Institute Tsinghua University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/004—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points
    • G01B7/008—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points using coordinate measuring machines

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Abstract

The invention provides a method for configuring the pretightening force of a trigger type measuring head, which comprises the following steps: establishing a coordinate system in a plane of contact force action points of the support ball and the support column; setting space vector information of contact force of a support ball and a support column, space vector information of trigger force and space vector parameters of pretightening force of the spring; establishing a dynamic model of the system, and comparing the test data and the theoretical data of the trigger force according to a dynamic equation AF ═ B; and acquiring the corresponding relation between the pretightening force and the trigger force to determine the configuration parameters of the pretightening force. The invention starts from a dynamic model, and can conveniently research the characteristics of the trigger force under the condition of pretightening force change by means of a numerical simulation technology without repeatedly trial-and-error prototype testing; on the other hand, based on the test data of the measuring head, the characteristics of the reset force can be reversely deduced, and then the measuring head used for a period of time is evaluated in precision.

Description

Method for configuring pre-tightening force of trigger type measuring head and three-coordinate measuring machine
Technical Field
The invention relates to the technical field of testing, in particular to a configuration method of trigger type measuring head pretightening force and a three-coordinate measuring machine.
Background
This section is intended to provide a background or context to the embodiments of the invention that are recited in the claims. The description herein is not admitted to be prior art by inclusion in this section.
The sensors inside the probe have various forms, such as contact resistance, strain gauge, piezoelectric crystal, etc. The most common at present is the contact resistance, which is formed by the contact of the ball and the pillar. The ball and the column have slight deformation at the contact point under the action of the pretension force to form a contact surface. The larger this contact surface, the smaller the contact resistance. When the measuring head touches the measured piece, under the action of external force (trigger force), the pretightening force is gradually counteracted, so that the contact surface of the ball and the column is reduced, and the contact resistance is increased. When the contact resistance increases to a set threshold, a trigger signal is issued.
It can be seen from the working process of the measuring head that the external force (trigger force) is increased to a certain extent to send the trigger signal instead of sending the trigger signal at the moment when the measuring head contacts the measured piece. The application of external forces causes bending deformations of the stylus, which are systematic errors that increase the uncertainty of the measurement.
The nature of the preload (magnitude, direction and point of action) determines the nature of the trigger force (external force). In the design of the trigger type measuring head, the accuracy of the measuring head is directly determined by determining the pretightening force.
Disclosure of Invention
In view of the above, it is necessary to provide a method for configuring the preload of the touch trigger probe as a design basis for the touch trigger probe.
The invention also aims to design a high-precision measuring head by applying the method until a three-coordinate measuring machine for high-precision measurement is manufactured.
The technical scheme provided by the invention is as follows: a method for configuring the pre-tightening force of a trigger type measuring head is characterized in that a curved surface of a spring pre-tightening support column is contacted with a support ball below the support column in a tangent mode by a measuring head system, and the method comprises the following steps:
establishing a coordinate system in a plane of contact force action points of the support ball and the support column;
setting space vector information of contact force of a support ball and a support column, space vector information of trigger force and space vector parameters of pretightening force of the spring;
establishing a dynamic model of the system, and comparing the test data and the theoretical data of the trigger force according to a dynamic equation AF ═ B;
when the test data is not consistent with the theoretical data, adjusting the friction coefficient of the supporting ball and the supporting column;
and acquiring a corresponding relation between the pretightening force and the trigger force to determine configuration parameters of the pretightening force, wherein the configuration parameters comprise the pretightening force, the pretightening force direction and the pretightening force acting force, and the pretightening force is increased by controlling the increase of the compression amount of the spring.
Further, the middle part of the system comprises a vertical measuring needle, the measuring needle is perpendicular to the axis of the supporting column, and the Z axis of the coordinate system is along the axis direction of the measuring needle.
Furthermore, the system comprises 3 groups of ball column structures which are uniformly distributed in the circumferential direction, each group is provided with 1 supporting column which contacts 2 adjacent supporting balls, and the intersection point of the plane of the 3 groups of contact force action points and the axis of the measuring needle is set as the origin of a coordinate system.
Further, the space vector information of the contact force comprises the magnitude and the direction of the force; the contact force of the three groups of support balls and the support columns is controlled by
Figure GDA0002700637330000021
Which are shown in their respective directions α, β.
Further, the space vector information of the trigger force comprises the magnitude and direction of the force; trigger force is provided by
Figure GDA0002700637330000022
Is shown in the direction of
Figure GDA0002700637330000023
And (4) determining.
Further, the space vector information of the pretightening force comprises an action point, the magnitude and the direction of the force. The pre-tightening force of the spring is
Figure GDA0002700637330000024
In the direction of
Figure GDA0002700637330000025
And determining the action point by (r, h).
Further, 3 groups of ball column structures are set on the same plane, the contact force direction angles of the support ball and the column body are equal (alpha is equal to beta), a test value of the trigger force is measured when a ring gauge is arranged in a horizontal plane, and a theoretical value under the same condition is calculated.
Further, the kinetic equation of the system is AF ═ B, where:
Figure GDA0002700637330000031
Figure GDA0002700637330000032
Figure GDA0002700637330000033
further, when the theoretical value is matched with the experimental value, the corresponding relation of the pre-tightening force, the pre-tightening force direction angle and the pre-tightening force action point to the trigger force is obtained based on a theoretical equation.
Further, under the condition that the direction of the pre-tightening force is coincident with the Z axis, the corresponding relation between the pre-tightening force and the trigger force is obtained.
Further, the relation between the direction angle of the pretightening force in the vertical plane or the horizontal plane and the magnitude of the trigger force is obtained, and the threshold value of the direction angle of the pretightening force in the vertical plane and the horizontal plane is determined.
Further, the relation between the distance of the pretightening force deviating from the origin in the vertical plane or the horizontal plane and the size of the trigger force is obtained, and the action point of the pretightening force is determined.
The invention also provides a three-coordinate measuring machine, which comprises a triggering measuring head with a ball column structure, wherein the configuration method of the pre-tightening force of the triggering measuring head of the measuring head sets the action point and the pre-tightening force of the spring, and comprises the following steps:
the method for configuring the pre-tightening force of the trigger type measuring head is characterized in that the measuring head system contacts a curved surface of a spring pre-tightening support column with a support ball below the support column in a tangent mode, and comprises the following steps:
establishing a coordinate system in a plane of contact force action points of the support ball and the support column;
setting space vector information of contact force of a support ball and a support column, space vector information of trigger force and space vector parameters of pretightening force of the spring;
establishing a dynamic model of the system, and comparing the test data and the theoretical data of the trigger force according to a dynamic equation AF ═ B;
and acquiring the corresponding relation between the pretightening force and the trigger force to determine the configuration parameters of the pretightening force.
Further, the middle part of the system comprises a vertical measuring needle, the measuring needle is perpendicular to the axis of the supporting column, and the Z axis of the coordinate system is along the axis direction of the measuring needle.
Furthermore, the system comprises 3 groups of ball column structures which are uniformly distributed in the circumferential direction, each group is provided with 1 supporting column which contacts 2 adjacent supporting balls, and the intersection point of the plane of the 3 groups of contact force action points and the axis of the measuring needle is set as the origin of a coordinate system.
Further, the space vector information of the contact force comprises the magnitude and the direction of the force, the space vector information of the trigger force comprises the magnitude and the direction of the force, and the space vector information of the pretightening force comprises an action point, the magnitude and the direction of the force.
Further, 3 groups of ball column structures are set on the same plane, the contact force direction angles of the support ball and the column body are equal, the test value of the trigger force is measured when a ring gauge in the horizontal plane is measured, and the theoretical value under the same condition is calculated.
Further, when the theoretical value is matched with the experimental value, the corresponding relation among the pre-tightening force, the pre-tightening force direction angle, the pre-tightening force acting point and the trigger force is obtained based on a theoretical equation.
Further, under the condition that the direction of the pre-tightening force is coincident with the Z axis, the corresponding relation between the pre-tightening force and the trigger force is obtained.
Further, the relation between the direction angle of the pretightening force in the vertical plane or the horizontal plane and the magnitude of the trigger force is obtained, and the threshold value of the direction angle of the pretightening force in the vertical plane and the horizontal plane is determined.
Further, the relation between the distance of the pretightening force deviating from the origin in the vertical plane or the horizontal plane and the size of the trigger force is obtained, and the action point of the pretightening force is determined.
Compared with the prior art, the method for configuring the pre-tightening force of the trigger type measuring head comprises the following steps: establishing a coordinate system in a plane of contact force action points of the support ball and the support column; setting space vector information of contact force of a support ball and a support column, space vector information of trigger force and space vector parameters of pretightening force of the spring; establishing a dynamic model of the system, and comparing the test data and the theoretical data of the trigger force according to a dynamic equation AF ═ B; and acquiring the corresponding relation between the pretightening force and the trigger force to determine the configuration parameters of the pretightening force. The invention starts from a dynamic model, and can conveniently research the characteristics of the trigger force under the condition of pretightening force change by means of a numerical simulation technology without repeatedly trial-and-error prototype testing; on the other hand, based on the test data of the measuring head, the characteristics of the reset force can be reversely deduced, and then the measuring head used for a period of time is evaluated in precision.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1A is a schematic structural diagram of a trigger probe system according to the present invention.
FIG. 1B is a schematic view of a portion of the structure shown in FIG. 1A.
Fig. 1C is a current circuit diagram of the ball stud structure shown in fig. 1A.
FIG. 2A is a kinetic model of the system shown in FIG. 1A. Wherein
Figure GDA0002700637330000061
Is in a plane parallel to XOZ.
FIG. 2B is a kinetic model of the system shown in FIGS. 1B and 1C.
Fig. 3 is a graph of distribution of experimental data and theoretical data of the trigger force in the next horizontal plane of the kinetic model of fig. 2A.
Fig. 4 is a rule of influence of the pre-tightening force on the trigger force shown in fig. 2A.
Fig. 5 is a rule of the influence of the pretightening force direction shown in fig. 2A on the trigger force.
Fig. 6 is a diagram illustrating the influence of the pre-tightening force acting point on the trigger force shown in fig. 2A.
Description of reference numerals:
measuring head system 10
End measuring ball 18
Measuring probe 17
Ball seat 16
Support ball 15
Support column 13
Probe support 12
Spring 11
Conducting wire 14
The following detailed description further illustrates embodiments of the invention in conjunction with the above-described figures.
Detailed Description
So that the manner in which the above recited objects, features and advantages of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. In addition, the features of the embodiments of the present application may be combined with each other without conflict.
In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the invention, and the described embodiments are merely a subset of embodiments of the invention, rather than a complete embodiment. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the embodiments of the present invention.
As used herein, a "gauge ring" is a standard device, a circle whose diameter is measured. The "probe" and "probe system" herein refer to a structure comprising a ball end, a stylus, a support ball, a support post, and a spring.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present invention belong. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the invention.
Referring to fig. 1A, a Coordinate Measuring Machine (CMM) is a new type of high-efficiency precision Measuring instrument in the 60 th of the 20 th century. On one hand, the automatic machine tool, the numerical control high-efficiency machining and the original more parts with complex shapes need to be matched with a quick and effective detection device; another aspect is that the development of electronics, computer technology, digital control technology and precision machining technology provides a technical basis for the production of CMMs. In 1960, the first CMM in the world was successfully developed by Ferranti corporation in the united kingdom, and by the end of the 60's of the 20 th century, more than thirty countries had been producing CMMs, although CMMs in this time were still in prime stage. After the 80's of the 20 th century, new products were continuously introduced by companies such as Zeiss, Leitz, DEA, LK, Mitutoy, Sip, Ferranti, Moore, etc., so that the development speed of CMMs was accelerated. Modern CMM not only can accomplish various complex measurements under the control of computer, but also can realize the control of processing by exchanging information with the numerical control machine tool, and can also realize reverse engineering according to the measured data. At present, CMM has been widely used in various departments of machine manufacturing industry, automobile industry, electronic industry, aerospace industry, national defense industry, etc., and has become an indispensable general-purpose geometric measurement instrument for modern industrial inspection and quality control.
The CMM uses a stylus to pick up a signal, and the performance of the stylus directly affects the measurement accuracy and efficiency, and the function of the measuring machine cannot be performed without an advanced stylus. The measuring head of the coordinate measuring machine has two working modes of a trigger type and a simulation type, the trigger type measuring head is mainly used for contact judgment, when the measuring end contacts a measured body, the measuring head sends out a pulse signal, and at the moment, a scale system of the coordinate measuring machine records the current coordinate value. The working mode has high efficiency in measuring regular geometric characteristics (circular arc, straight line and the like); the analog measuring head can continuously output the displacement information of the measuring end and is suitable for measuring irregular geometric characteristics such as free curved surfaces.
The coordinate measuring machine measures the measurement process using the trigger probe (shown in fig. 1A) as follows: three axes of the coordinate measuring machine rapidly approach the measured piece under the instruction of the controller, then decelerate, touch the measured piece at a lower speed and continue to move forwards. And as the measuring head continues to move forwards, the stress at the tail end of the measuring head is continuously increased. When the stress reaches the preset value of the sensor in the measuring head, the measuring head sends out a trigger signal, and at the moment, the controller starts to acquire the grating values of the three axes, namely the coordinates of the touch point. When the controller receives the trigger signal, the controller also sends out deceleration and rollback instructions. Thereafter, the coordinate measuring machine is three-axis retracted away from the workpiece under test. It can be seen that at the moment when the measuring head contacts the measured piece, the measuring head does not send out the trigger signal, but only needs the external force (trigger force) to be increased to a certain extent. The application of external forces causes bending deformations of the stylus, which are systematic errors that increase the uncertainty of the measurement. The nature of the preload (magnitude, direction and point of action) determines the nature of the trigger force (external force). In the design of the trigger type measuring head, the accuracy of the measuring head is directly determined by determining the pretightening force.
The structure of the trigger probe system 10 of the present invention will be described in detail with reference to fig. 1A, 1B, and 1C.
Fig. 1A shows the structure of a trigger probe system 10 according to an embodiment, and it can be seen that the system 10 includes, in order from the bottom:
the end measuring ball 18 is of a spherical structure and is in contact with an object to be measured to generate displacement;
the measuring pin 17 is vertically arranged, and the lower end of the measuring pin 17 is connected with the end measuring ball 18;
a ball seat 16, disc-shaped, horizontally disposed, for supporting the system 10;
a support ball 15 having a hemispherical shape, the spherical surface of which is disposed above the top surface of the ball seat 16 and the plane of which is in contact with the top surface of the ball seat 16;
a support column 13, cylindrical with a curved surface in tangential contact with said support ball 15;
the probe support 12 is used for supporting the supporting column 13;
and the spring 11 is sleeved on the measuring probe bracket 12 and used for pre-tightening the supporting column 13 and the supporting ball 15.
FIG. 1B shows: the system 10 is equipped with three group's ball post structures, and the hoop evenly distributed is in 16 tops of ball seats, every group includes 1 support column 13 and 2 support balls 15, 2 there is certain clearance between the support ball 15, support column 13 is tangent (under the natural state) with 2 support balls 15 are all. Fig. 1C also shows that the bottom surface of the support ball 15 is mounted with a wire 14.
The following will describe a method for configuring the pre-tightening force of the spring 11 in the structure shown in fig. 1A, 1B, and 1C with reference to fig. 2A and 2B, including the following steps:
step 1, as shown in fig. 2A, establishing a coordinate system in a plane of a contact force action point of a support ball 15 and a cylinder;
wherein:
the Z-axis of the coordinate system is along the direction of the axis of the stylus 17 (set positive upward);
the intersection point of the planes of the 3 groups of contact force action points and the axis of the measuring needle 17 is set as an origin O of a coordinate system, the origin O is used as a starting point, the middle point of a line segment pointing to the 2 groups of contact force action points is set as an X axis or a Y axis, and X, Y, Z are mutually vertical.
Step 2, setting space vector information of contact force of a support ball 15 and a support column 13, space vector information of trigger force and space vector parameters of pretightening force of the spring 11;
wherein:
the space vector information of the contact force comprises the magnitude and the direction of the force; the contact force of the three groups of supporting balls 15 and the supporting columns 13 is controlled by
Figure GDA0002700637330000091
Which are shown in their respective directions α, β.
The space vector information of the trigger force comprises the magnitude and the direction of the force; trigger force is provided by
Figure GDA0002700637330000092
Is shown in the direction of
Figure GDA0002700637330000093
And (4) determining.
The space vector information of the pretightening force comprises an action point, the magnitude and the direction of the force. The spring 11 has a pre-tightening force of
Figure GDA0002700637330000094
In the direction of
Figure GDA0002700637330000095
And determining the action point by (r, h).
Step 3, establishing a dynamic model of the system 10, and comparing the test data and the theoretical data of the trigger force according to a dynamic equation AF ═ B;
wherein:
Figure GDA0002700637330000101
Figure GDA0002700637330000102
Figure GDA0002700637330000103
setting 3 groups of ball column structures on the same plane, wherein the contact force direction angles of the support ball 15 and the column body are equal (alpha is beta), measuring a test value of the trigger force when a ring gauge is arranged in a horizontal plane, and calculating a theoretical value under the same condition.
Step 3, comparing the theoretical value with the experimental value;
when the theoretical value is matched with the experimental value, determining the equation coefficient (mu)1、μ2、μ3) (ii) a Here μ1、μ2、μ3The friction coefficients between the three sets of support balls 15 and support columns 13 are taken as (mu) regardless of the friction force when the ball columns are not worn and are well lubricated1、μ2、μ3) (0,0, 0); in the case where abrasion occurs between the ball cylinders after the stylus 10 is used for a certain period of time, (mu)1、μ2、μ3)≠(0,0,0)。
When the theoretical value is not consistent with the experimental value, the equation coefficient (mu) is adjusted1、μ2、μ3) The theoretical value is matched with the experimental value, so that the abrasion degree of the ball column is obtained, and the accuracy of the measuring head 10 used for a period of time is evaluated;
obtaining a law graph of influence of the pre-tightening force magnitude, the pre-tightening force direction angle and the pre-tightening force action point on the trigger force based on a theoretical equation;
and 4, step 4: and acquiring an influence rule of the pretightening force on the trigger force, and designing and determining parameters of the pretightening force.
Wherein:
and acquiring the corresponding relation between the pretightening force and the trigger force under the condition that the direction of the pretightening force is coincident with the Z axis.
And acquiring the relationship between the direction angle of the pretightening force in the vertical plane or the horizontal plane and the magnitude of the trigger force, and determining the threshold value of the direction angle of the pretightening force in the vertical plane and the horizontal plane.
And acquiring the relation between the deviation distance of the pretightening force from the original point in the vertical plane or the horizontal plane and the magnitude of the trigger force, and determining the action point of the pretightening force.
The design analysis of the pre-load force of the spring 11 in an embodiment will be described with reference to fig. 2A, 2B to 6.
The working principle of the measuring head system 10 is as follows:
the main structure of the ball/post support is shown in fig. 1A. The V-shaped supporting grooves formed by the three groups of balls are distributed at an angle of 120 degrees in the same plane, and the three supporting columns 13 are placed in the V-shaped grooves. The three sets of balls are connected by wires 14 as shown in fig. 1B, and when the balls and posts are in good contact, a path is formed through which current can flow between the balls and posts as shown in fig. 1C. The supporting structure has a good self-centering function, can ensure repeated positioning precision, and further reduces measurement errors.
When the measuring end ball 18 does not touch the measured part, the three groups of supporting balls 15 and the supporting columns 13 are in good contact under the action of the pretightening force of the return spring 11, so that a conductive path is formed. When the ball 18 touches the object, the stylus 17 is touched and is deflected. The deflection of the stylus 17 causes the support post 13 and the support ball 15 to separate, which in turn causes the circuit to open and a trigger signal to be emitted (the corresponding touch force is referred to as the trigger force).
After the return spring 11 has been determined, i.e. after the pretension of the measuring head has been determined, the trigger force is different in different directions (fluctuations in the trigger force). This is because the moment arm at which the trigger force starts to open the ball/post is different in different directions. The fluctuation of the trigger force causes the trigger probe to exhibit significant anisotropy, which is the largest source of error for the trigger probe, causing the stylus 17 to deform differently when measured in different directions. The anisotropy of the trigger probe can be corrected for certain errors at a later stage, but the effect is limited. The best approach is to predict and control the fluctuation of the trigger force during the design of the stylus.
Fig. 2A and 2B show a kinetic model of the probe system 10.
Figure GDA0002700637330000121
The vector of the ball-column contact force on the left side of the first group, the direction angle in the vertical plane being alpha1；
Figure GDA0002700637330000122
The vector of the contact force of the ball column on the right side of the first group, the direction angle in the vertical plane is beta1；
Figure GDA0002700637330000123
The vector of the ball column contact force on the left side of the second group, the direction angle in the vertical plane being alpha2；
Figure GDA0002700637330000124
The vector of the contact force of the ball column on the right side of the second group, the direction angle in the vertical plane is beta2；
Figure GDA0002700637330000125
The vector of the contact force of the ball column on the left side of the third group, the direction angle in the vertical plane is alpha3；
Figure GDA0002700637330000126
Is the vector of the contact force of the ball column on the right side of the third group, and the direction angle in the vertical plane is beta3；
Figure GDA0002700637330000127
As a vector of the trigger force, projected in the XY plane as a vector
Figure GDA0002700637330000128
Angle of direction in the vertical plane (i.e. direction angle in the vertical plane)
Figure GDA0002700637330000129
And
Figure GDA00027006373300001210
angle therebetween) is
Figure GDA00027006373300001211
The direction angle in the horizontal plane with the X-axis (i.e. angle of orientation)
Figure GDA00027006373300001212
The included angle between the X axis and the X axis) is theta;
Figure GDA00027006373300001213
the vector of the pretightening force of the spring 11 has a direction angle phi in the vertical plane and a direction angle phi with the X axis in the horizontal plane
Figure GDA00027006373300001214
The height from the origin O in the vertical plane is h (i.e., the vertical distance from the point of action to the XY plane), and the distance from the origin O in the horizontal plane is r (i.e., the vertical distance from the point of action to the Z axis).
And L is the vertical distance from the measuring end ball to the origin.
m is the perpendicular distance of the origin (point of intersection) of each set of contact forces from the Z-axis.
μ1Is the coefficient of friction between the first set of ball posts.
μ2Is the coefficient of friction between the second set of balls.
μ3The coefficient of friction between the third set of balls.
The kinetic equation for the system 10 is established: AF ═ B (1)
Figure GDA0002700637330000131
Figure GDA0002700637330000132
Figure GDA0002700637330000141
Giving initial coefficient values mu1、μ2、μ3；
In the process of acquiring the pretightening force, the support of the balls and the columns is set as an ideal condition, namely three groups of balls are coplanar, and the direction angles of the support force are equal (alpha-beta). Although errors are caused in the manufacturing and assembling process, so that the ball and the column deviate from the ideal condition, because the trigger force is in any spatial direction, random errors in the manufacturing and assembling process do not substantially influence the fluctuation of the trigger force, and the random errors can be verified through numerical simulation; in addition, the method provided by the invention is still applicable under the condition of considering the manufacturing and assembling errors of the ball column.
Figure 3 shows the comparison of the test trigger force with the theoretical trigger force when measuring a gauging ring in the horizontal plane. It can be seen that there are three minimum values (0.04N) and three maximum values (0.1N) for the trigger force at this time, and the fluctuation of the trigger force (i.e. the difference between the maximum and minimum values) reaches 0.06N, which is 1.5 times the minimum trigger force, so that the fluctuation is relatively significant. As can be seen from fig. 3, the trigger force obtained based on the theoretical equation is well matched with the experimental data, so that the kinetic equation based on the set coefficient can be used to analyze the fluctuation condition of the trigger force.
During the design of the pretension (restoring force), its magnitude is first determined. At the moment, the direction of the pre-tightening force is considered to coincide with the Z axis,
Figure GDA0002700637330000142
fig. 4 shows the magnitude of the pretension and the fluctuation of the trigger force. It can be seen that, as the pre-tightening force increases, the maximum value and the minimum value of the trigger force both increase linearly, and the fluctuation of the trigger force also increases linearly, that is, as the pre-tightening force increases, the fluctuation amount of the trigger force becomes larger, and the measurement error also increases. However, the greater pretension increases the reliability of the reset, so that in use, the pretension cannot be too small. On the other hand, depending on the application, for example, when measuring a workpiece that is not easily deformed, a larger pre-tightening force and a thicker stylus 17 may be used; when a workpiece which is easy to deform is measured, a measuring head with small pretightening force is adopted. Several different pretensioning probes can be designed for this purpose.
Fig. 5 shows the effect of the direction of application of the pretensioning force on the trigger force fluctuation, wherein the color bar changes from black to white corresponding to a trigger force fluctuation of from 0.05N to 0.075N. As can be seen from the figure, the directional angle ψ of the pretension in the vertical plane has a large influence on the fluctuation of the trigger force, meaning that the more the direction of the pretension deviates from the stylus axis (Z) axis, the larger the fluctuation of the trigger force. When this deviation direction angle is not more than 2 °, the fluctuation of the trigger force does not change significantly. To ensure accuracy, the deviation of this orientation angle should not be greater than 5 °. Direction angle of pretightening force in horizontal plane
Figure GDA0002700637330000151
The influence on the fluctuation of the trigger force is small, and the fluctuation of the trigger force increases from 0 ° to 360 ° in accordance with the configuration of the stylus, and there are three maximum values and minimum values.
Fig. 6 shows the effect of the application point of the pretension on the trigger force, wherein a color bar going from black to white corresponds to a fluctuation of the trigger force from 0.05N to 0.16N. It has been found from fig. 5 that the directional angle ψ of the pretension in the vertical plane has a large influence on the fluctuation of the trigger force, while the directional angle in the horizontal plane
Figure GDA0002700637330000152
The influence on the trigger force fluctuation is small. Thus, we now choose the pretightening force direction angle psi as 1,
Figure GDA0002700637330000153
it should be noted that, as shown in fig. 1A, the pre-tightening force is provided by the spring 11, and when the height h of the pre-tightening force in the vertical plane increases, the compression amount of the spring 11 increases, so that the pre-tightening force increases.
It can be seen from fig. 6 that the influence of the deviation distance r of the pretension in the horizontal plane on the fluctuation of the trigger force is significant, and when the pretension is 1.2N, so that the fluctuation of the trigger force is not greater than 0.05N, the deviation distance r of the pretension in the horizontal plane from the center should not be greater than 0.5x10-3mm. And the point of application of the pretension is close to, preferably in the XOY plane.
The pre-tightening force parameter optimally configured by the method can be used for setting the action point, the pre-tightening force and the direction of the spring 11 of the contact type measuring head in the three-coordinate measuring machine, and the high-precision measurement of the three-coordinate measuring machine is met. The invention starts from a dynamic model, and can conveniently research the characteristics of the trigger force under the condition of pretightening force change by means of a numerical simulation technology without repeatedly trial-and-error prototype testing; on the other hand, based on the test data of the measuring head, the characteristics of the reset force can be reversely deduced, and then the measuring head used for a period of time is evaluated in precision.
Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the embodiments of the present invention.

Claims (10)

1. A method for configuring the pre-tightening force of a trigger type measuring head is characterized in that a measuring head system adopts a curved surface of a spring pre-tightening support column to contact with a support ball below the support column in a tangent mode, and the method comprises the following steps: the method comprises the following steps:
establishing a coordinate system in a plane of contact force action points of the support ball and the support column;
setting space vector information of contact force of a support ball and a support column, space vector information of trigger force and space vector parameters of pretightening force of the spring;
establishing a dynamic model of the system, and comparing the test data and the theoretical data of the trigger force according to a dynamic equation AF ═ B;
when the test data is not consistent with the theoretical data, adjusting the friction coefficient of the supporting ball and the supporting column;
and acquiring a corresponding relation between the pretightening force and the trigger force to determine configuration parameters of the pretightening force, wherein the configuration parameters comprise the pretightening force magnitude, the pretightening force direction and a pretightening force action point, and the pretightening force is increased by controlling the increase of the compression amount of the spring.
2. The method for configuring the trigger-type gauge head pretensioning force according to claim 1, wherein: the middle part of the system comprises a vertical measuring needle, the measuring needle is vertical to the axis of the supporting column, and the Z axis of the coordinate system is along the axis direction of the measuring needle.
3. The method for configuring the trigger-type gauge head pretensioning force according to claim 2, wherein: the system comprises 3 groups of ball column structures which are uniformly distributed in the circumferential direction, wherein each group is provided with 1 supporting column which contacts 2 adjacent supporting balls, and the intersection point of the plane of 3 groups of contact force action points and the axis of the measuring needle is set as the origin of a coordinate system.
4. The method for configuring the trigger-type gauge head pretensioning force according to claim 1, wherein: the space vector information of the contact force comprises the magnitude and the direction of the force, the space vector information of the trigger force comprises the magnitude and the direction of the force, and the space vector information of the pretightening force comprises an action point, the magnitude and the direction of the force.
5. The method for configuring the trigger-type gauge head pretensioning force according to claim 3, wherein: setting 3 groups of ball column structures on the same plane, wherein the contact force direction angles of the support balls and the column bodies are equal, measuring a test value of the trigger force when measuring a ring gauge in a horizontal plane, and calculating a theoretical value under the same condition.
6. The method for configuring the trigger-type gauge head pretensioning force according to claim 5, wherein: and when the theoretical value is consistent with the experimental value, acquiring the corresponding relation among the pre-tightening force, the pre-tightening force direction angle, the pre-tightening force action point and the trigger force based on a kinetic equation.
7. The method for configuring the trigger-type gauge head pretensioning force according to claim 6, wherein: and acquiring the corresponding relation between the pretightening force and the trigger force under the condition that the direction of the pretightening force is coincident with the Z axis.
8. The method for configuring the trigger-type gauge head pretensioning force according to claim 6, wherein: and acquiring the relationship between the direction angle of the pretightening force in the vertical plane or the horizontal plane and the magnitude of the trigger force, and determining the threshold value of the direction angle of the pretightening force in the vertical plane and the horizontal plane.
9. The method for configuring the trigger-type gauge head pretensioning force according to claim 6, wherein: and acquiring the relation between the deviation distance of the pretightening force from the original point in the vertical plane or the horizontal plane and the magnitude of the trigger force, and determining the action point of the pretightening force.
10. The utility model provides a three-coordinate measuring machine, includes the formula gauge head that triggers of sphero-cylindrical structure, its characterized in that: the gauge head adopts the method for configuring the pre-tightening force of the trigger gauge head according to any one of claims 1 to 9 to set the action point and the pre-tightening force of the spring.
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