CN104708495B - A kind of two link-type ball bar of space based on spherical hinge - Google Patents

Abstract

The invention discloses a kind of two link-type ball bar of space based on spherical hinge.Bar long excursion very little when existing ball bar is measured, it is impossible to cover all regions in lathe impulse stroke.The accurate bead of the first of the present invention is fixed on the outer end of first connecting rod, and is fixed on the first accurate magnetic force bowl seat in 3 points of machinery positioning modes；Second accurate bead is fixed on the outer end of second connecting rod, and is fixed on the second accurate magnetic force bowl seat in 3 points of machinery positioning modes；The bulb of accurate spherical hinge and support ball-and-socket are separately fixed at the inner of second connecting rod and first connecting rod；First spherical capacitance electrode is located at the bulb bottom of accurate spherical hinge, and the second spherical capacitance electrode is located at the bottom for supporting ball-and-socket.The three-dimensional motion of ball bar realized by present invention spherical hinge, and detects angle between two connecting rod axis with sphere capacitance sensor, and according to angle value and two length of connecting rods, calculating main shaft does Circular test when space circular arc is moved, evaluates the dynamic accuracy of Digit Control Machine Tool.

Description

A Space Two-Link Ballbar Based on Ball Hinge

technical field

The invention belongs to the field of error detection of numerical control machine tools, and in particular relates to a space two-link ballbar based on a ball hinge.

Background technique

The machine tool is the main machine in the machinery manufacturing industry, and its precision directly affects the level of the manufacturing industry. With the popularization and application of numerical control equipment, the precision improvement methods and technologies of various numerical control machine tools have also become a hot spot for scientific research workers.

At present, the error detection methods of CNC machine tools mainly include direct measurement method, indirect measurement method and comprehensive error measurement method. The measurement method based on the ballbar is a typical comprehensive error measurement method, which has the advantages of fast detection, simple operation, and convenient portability. It is often used to evaluate and diagnose the dynamic accuracy of CNC machine tools.

The ballbar was originally proposed by James B.Bryan of the Lawrence Livermore National Laboratory (LLNL) in the United States. Later, some companies and scholars conducted in-depth research on it and developed several different types of ballbars. , such as: Professor John C.Ziegert, Department of Mechanical Engineering, University of Florida, USA, invented the laser ballbar, and Ma Xiqi, Northwestern Polytechnical University, proposed a double ball gauge measuring instrument. Some have also formed commercial products, such as: Renishaw's QC10 ballbar and so on. However, although the rod lengths of these current ballbars are scalable, the range of variation is very small. In order to meet the needs of different measurement space ranges, these ballbars are usually equipped with several rods of different lengths at the same time. In addition, the radius of the circular trajectory of the existing ballbar measurement space is basically unchanged (the amount of change is determined by the expansion and contraction of about 1 mm of the rod length), which cannot cover (or traverse) all the spatial areas within the working stroke range of the machine tool. Japanese scholars invented the two-link ballbar, in which the two connecting rods are connected by a common rotary joint and the angle between the two rods is measured by a rotary encoder, which effectively increases the measurement range of the ballbar. However, due to Due to structural limitations, the instrument can only move in one plane. If it is necessary to test the three planes of XY, YZ, and ZX on the machine tool, it is necessary to install and test the ballbar multiple times, so the measurement efficiency is low and it is difficult to guarantee High measurement accuracy.

Contents of the invention

The object of the present invention is to address the deficiencies of existing ballbars, and propose a space two-link ballbar based on ball hinges, which uses ball hinges to realize the three-dimensional movement of the ballbar within the spatial range, and uses spherical capacitive sensors to The principle detects the space angle between the axes of the two connecting rods, and according to the measured angle value and the length of the two connecting rods connected by the ball joint, calculates the circular trajectory of the main shaft when it is moving in a spatial arc through a simple geometric method, and obtains The geometric motion accuracy of the machine tool.

The technical scheme adopted in the present invention is:

The present invention is mainly composed of a first connecting rod, a second connecting rod, a precision ball hinge, a first precision magnetic bowl, a second precision magnetic bowl, a spherical capacitive sensor, a first precision ball and a second precision ball; The above-mentioned first precision ball is fixed on the outer end of the first connecting rod, and is fixed on the first precision magnetic cup base by three-point mechanical positioning; the second precision ball is fixed on the second connecting rod The outer end is fixed on the second precision magnetic bowl seat by three-point mechanical positioning; the ball head of the precision ball hinge is fixed on the inner end of the second connecting rod, and the supporting ball socket of the precision ball hinge is fixed on the first The inner end of the connecting rod; the spherical capacitance sensor includes a first spherical capacitive electrode and a second spherical capacitive electrode; the first spherical capacitive electrode is arranged at the bottom of the ball joint of the precision ball hinge, and the second Two spherical capacitive electrodes are arranged on the bottom of the supporting ball socket.

The radius of the ball head of the precision ball hinge and the inner radius of the supporting ball socket are both R ₂ , and the centers of the ball head and the supporting ball socket coincide, which is recorded as point C. The distance from the center of the first precision ball to C is denoted as L ₁ , and the distance from the center of the second precision ball to C is denoted as L ₂ . The center distance between the first precision ball and the second precision ball is equivalent to a connecting rod, so the equivalent rod length L can be expressed as:

L ² ＝L ₁ ² +L ₂ ² -2L ₁ L ₂ cos(π-θ)

Wherein, θ is the angle between the axis of the first connecting rod and the axis of the second connecting rod detected by the spherical capacitive sensor. When θ=0, the corresponding equivalent rod length L obtains the maximum value L _max =L ₁ +L ₂ ; when θ=θ _max , the corresponding equivalent rod length L obtains the minimum value L _min ; θ _max =90° -arcsin(h/R ₂ )-arcsin(r/R ₂ ) is the limit swing angle of the precision ball hinge, where r is the radius of the outer circle of the second connecting rod, and h is the supporting ball with a transverse split structure Nest end cap height. Therefore, the variation range of the equivalent rod length is L _max -L _min .

The corresponding central angles between the center of the spherical cap and the edge of the first spherical capacitive electrode and the second spherical capacitive electrode are equal, and both are 10-60°.

The first spherical capacitive electrode and the second spherical capacitive electrode constitute two detection plates of the spherical capacitive sensor.

The beneficial effects of the present invention are:

1. Because the ball hinge has the advantages of compact structure and flexible movement, it is used for the connection of two connecting rods, and it is easy to realize the movement of the instrument in the entire space and the continuity of the measurement range (full coverage).

2. The present invention uses the principle of a spherical capacitive sensor to detect the angle between the axes of the two connecting rods, which can ensure high measurement accuracy.

3. The present invention realizes the measurement function of the ballbar through two connecting rods and a ball hinge, and has simple structure and simple algorithm.

Description of drawings

Fig. 1 is the general structural diagram of the present invention;

Fig. 2 is the schematic diagram of the assembly of the first connecting rod and the second connecting rod in the present invention;

Fig. 3 is the arrangement schematic diagram of two spherical capacitive electrodes among the present invention;

4 is a schematic diagram of the position of the first spherical capacitive electrode on the ball head of the precision ball hinge in the present invention;

Fig. 5 is a schematic diagram of the position of the second spherical capacitive electrode in the supporting ball socket of the precision ball hinge in the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figures 1 and 2, a space two-link ballbar based on a ball hinge is mainly composed of a first link 1-1, a second link 2-1, a precision ball hinge 3, a first precision magnetic Bowl 4, the second precision magnetic bowl 5, spherical capacitive sensor, the first precision ball 1-2 and the second precision ball 2-2; the spherical capacitive sensor includes the first spherical capacitive electrode D1 and the second Spherical capacitive electrode D ₂ . The first precision ball 1-2 is fixed on the outer end of the first connecting rod 1-1, and the second precision ball 2-2 is fixed on the outer end of the second connecting rod 2-1; the ball head 3 of the precision ball hinge 3 -1 is fixed at the inner end of the second connecting rod 2-1, and the supporting ball socket 3-2 of the precision ball hinge 3 is fixed at the inner end of the first connecting rod 1-1. The radii of the first precision ball 1-2 and the second precision ball 2-2 are both R ₁ , and their centers are respectively marked as point A and point B; the ball head radius of the precision ball hinge 3 and the inner diameter of the supporting ball socket The radius is R ₂ , and the center of the ball head and the supporting ball socket coincides, which is recorded as point C. The length of AC is denoted as L ₁ , and the length of BC is denoted as L ₂ .

As shown in Figures 3, 4 and 5, the bottom of the ball head of the precision ball hinge 3 is provided with a first spherical capacitive electrode D1, and the bottom of the supporting ball socket is provided with a _second spherical capacitive electrode D2; the first spherical capacitive electrode D2 The corresponding central angles between the center of the spherical cap and the edge of the electrode D1 and the _second spherical capacitive electrode D2 are both α=60°. The first spherical capacitive electrode D1 and the second spherical capacitive electrode D2 form _two detection pole plates of the spherical capacitive sensor, which are used to detect the distance between the axes of the first connecting rod 1-1 and the second connecting rod 2-1. angle. The first precision magnetic bowl seat 4 can be fixed on the machine tool workbench through the T-shaped slot, and the second precision magnetic bowl seat 5 is installed on the machine tool spindle. The first precision ball 1-2 and the second precision ball 2-2 are respectively fixed on the first precision magnetic bowl seat 4 and the second precision magnetic bowl seat 5 in a three-point mechanical positioning manner.

During the working process, the ball head 3-1 of the precision ball hinge 3 rotates relative to the supporting ball socket 3-2, and the effective overlapping area between the first spherical capacitive electrode D1 and the _second spherical capacitive electrode D2 changes, The output capacitance value of the spherical capacitive sensor changes, and the angle θ between the axes of the two connecting rods can be calculated according to the output capacitance value.

For two spherical capacitive electrodes with the same area, that is, when the corresponding central angles between the center of the spherical cap and the edge of the two spherical capacitive electrodes are both α, the effective overlapping area S of the two spherical capacitive electrodes is the same as that of the two spherical capacitive electrodes. The relationship between the angle θ between the connecting rod axes can be expressed as:

In the formula,

η=tan ^-1 [(cosα-cosαcosθ)/(cosαsinθ)],

Since the corresponding central angle between the center of the spherical cap and the edge is known as α, according to the formula (1), the effective overlapping area S of the two spherical capacitive electrodes and the angle θ between the axes of the two connecting rods have a value of The corresponding mathematical relationship, for the convenience of expression, can be recorded as:

S=g(θ) (2)

According to the capacitance value calculation formula Among them, d represents the gap between the two plates, and ε represents the dielectric constant. A layer of epoxy resin is distributed on the surface of the ball head and the supporting ball socket as the dielectric, and ε and d remain unchanged. According to the formula (2), the expression of the capacitance value Therefore, there is a one-to-one mathematical relationship between the angle θ between the axes of the two connecting rods and the capacitance value C detected by the spherical capacitance sensor. For the convenience of expression, it can be recorded as:

θ=f(C) (3)

The first spherical capacitive electrode is loaded with a voltage V _INPUT , while the second spherical capacitive electrode is loaded with a voltage of 0 . The two spherical capacitive electrodes are connected to the signal processing circuit of the capacitive sensor by a cable, and the computer is equipped with a data acquisition card and data processing software to analyze and process the signal from the capacitor to obtain the first connecting rod 1-1 and the second connecting rod The angle between the 2-1 axes.

The distance AB between the center of the first precision ball 1-2 and the second precision ball 2-2 is equivalent to a connecting rod, so the equivalent rod length L can be expressed as:

L ² ＝L ₁ ² +L ₂ ² -2L ₁ L ₂ cos(π-θ) (4)

When θ=0, the corresponding equivalent rod length L obtains the maximum value L _max =L ₁ +L ₂ ; when θ=θ _max , the corresponding equivalent rod length L obtains the minimum value L _min , where θ _max = 90°-arcsin(h/R ₂ )-arcsin(r/R ₂ ) is the limit swing angle of the precision ball hinge 3, r is the radius of the outer circular surface of the second connecting rod 2-1, and h is the transverse split formula The height of the supporting ball-and-socket end cap of the structure. Therefore, the variation range of the equivalent rod length is L _max -L _min .

The center A of the first precision ball 1-2 coincides with the origin O(0,0,0) of the table coordinate system, and P(x,y,z) is the center B of the second precision ball 2-2. Nominal coordinates, when the machine tool moves to the target position, set the actual position of the machine tool as P'(x',y',z'). Then the spatial error of the machine tool can be expressed as:

In the formula, Δx, Δy, Δz are the displacement errors between points P and P'.

When there are errors Δx, Δy, Δz, the following formula holds:

L ² =x' ² +y' ² +z' ² =(x+Δx) ² +(y+Δy) ² +(z+Δz) ² (6)

When the ballbar is working, the machine tool runs around the center seat on the workbench according to a preset circular trajectory with a radius of R, so the ideal distance of AB is R, ignoring the higher-order error items above the second order, then R ² = x ² +y ² +z ² . According to formulas (4) and (6), we can get:

Formula (7) expresses the relationship between the positioning error at point P and the rotation angle of the precision ball hinge in the ballbar, so this formula can be used for error diagnosis of machine tools.

The measurement function of the ballbar is realized by two connecting rods and a ball hinge, which is easy to realize the movement of the instrument in the entire spatial range and the continuity of the measurement range (full coverage). In addition, using the principle of the spherical capacitance sensor to detect the angle between the axes of the two connecting rods can ensure high measurement accuracy. The overall device structure is simple and the algorithm is simple.

Claims (3)

1. a kind of two link-type ball bar of space based on spherical hinge, mainly by first connecting rod, second connecting rod, accurate spherical hinge, First accurate magnetic force bowl seat, the second accurate magnetic force bowl seat, sphere capacitance sensor, the first accurate bead and the second accurate little set of balls Into, it is characterised in that：

The accurate bead of described first is fixed on the outer end of first connecting rod, and is fixed on the first essence in the way of 3 points of machinery positionings On close magnetic force bowl seat；The accurate bead of described second is fixed on the outer end of second connecting rod, and solid in the way of 3 points of machinery positionings It is scheduled on the second accurate magnetic force bowl seat；The bulb of the accurate spherical hinge is fixed on the inner of second connecting rod, accurate spherical hinge Ball-and-socket is supported to be fixed on the inner of first connecting rod；Described sphere capacitance sensor includes the first spherical capacitance electrode and second Spherical capacitance electrode；The first described spherical capacitance electrode is arranged on the bulb bottom of accurate spherical hinge, and second is spherical Capacitance electrode is arranged on the bottom for supporting ball-and-socket；

The inside radius of the Probe-radius of the accurate spherical hinge and support ball-and-socket is R₂, the centre of sphere coincidence of bulb and support ball-and-socket, It is designated as point C；The centre of sphere of the first accurate bead is designated as L to the distance of C₁, the centre of sphere of the second accurate bead is designated as L to the distance of C₂；Will The centre of sphere distance of the first accurate bead and the second accurate bead is equivalent to a connecting rod, and therefore the long L of equivalent bar is expressed as：

L²=L₁ ²+L₂ ²-2L₁L₂cos(π-θ)

Wherein, θ is the angle between the first connecting rod and second connecting rod axis that the detection of sphere capacitance sensor is obtained；When θ=0, The long L of corresponding equivalent bar obtains maximum L_max=L₁+L₂；As θ=θ_maxWhen, the long L of corresponding equivalent bar obtains minima L_min； θ_max=90 ° of-arcsin (h/R₂)-arcsin(r/R₂) be accurate spherical hinge limit pivot angle, wherein, r is outer for second connecting rod Disc radius, h are the support ball-and-socket end cap height using horizontal split type structure；Therefore, the excursion of equivalent bar length is L_max-L_min.

2. a kind of two link-type ball bar of space based on spherical hinge according to claim 1, it is characterised in that：Described One spherical capacitance electrode, the spherical crown center of the second spherical capacitance electrode are equal with corresponding central angle between edge, are 10 ～60 °.

3. a kind of two link-type ball bar of space based on spherical hinge according to claim 1, it is characterised in that：Described First spherical capacitance electrode and the second spherical capacitance electrode constitute two Detection electrodes of sphere capacitance sensor.