CN105783816B - The three-coordinate measuring method in automatic identification radius compensation direction - Google Patents

Abstract

The invention discloses a three-coordinate measuring method for automatically identifying the radius compensation direction. Existing radius compensation methods require a lot of calculation. Concrete steps of the present invention: use the microarray mode on the measuring head to uniformly cover the capacitor plates with a small surface area, and the shape of a single plate is an equilateral triangle or a square; apply an excitation signal to the capacitor plate array on the measuring head, when When the probe is close to the metal object to be tested, the metal object to be tested and the capacitor plate with the facing area form a pair of flat capacitors to generate capacitance. At the same time, different sizes of the facing area will generate different sizes of capacitance. The size of the plate and the generated capacitance can calculate the position of the contact point, and then automatically identify the direction of radius compensation. When the accuracy requirement is not high, the present invention directly takes the capacitor plate with the largest output capacitance value as the contact point for radius compensation without calculation; when the accuracy requirement is high, the precise position of the contact point is deduced through calculation.

Description

Three-Coordinate Measurement Method for Automatically Identifying Radius Compensation Direction

technical field

The invention belongs to the technical field of three-coordinate measuring machines, and in particular relates to a radius compensation measuring method of a three-coordinate measuring machine covered with capacitor plates in a microarray mode, which can automatically identify the normal direction of radius compensation.

Background technique

Three-coordinate measuring machines are widely used in the geometric quality inspection of complex parts in the fields of machinery, electronics, automobiles and aerospace. The inspection content involved includes the size, shape and mutual positional relationship of parts. Because of its strong versatility, large measurement range, high precision, high efficiency, good performance, and the ability to connect with flexible manufacturing systems, it has been called the "measurement center" for complex parts. Its measurement principle is to convert the measurement of various geometric elements into the measurement of the coordinate positions of some point sets on these geometric elements. After the coordinate positions of these points are measured, the algorithm software calculates the required geometric element size, shape, relative position, etc. according to certain evaluation criteria.

The accuracy and efficiency (measuring speed) of the three-coordinate measuring machine mainly depend on the mechanical structure, control system, probe and software system. When the three-coordinate measuring machine uses a contact probe to perform measurement operations, because the spherical probe has a certain radius, the trajectory of the center of the probe and the actual contour of the object to be measured are inconsistent, and the radius needs to be determined on the basis of the measurement results. compensate. However, the contact point between the probe and the measured object is unknown to the algorithm software of the measuring machine. If the contact point cannot be obtained accurately, a radius compensation error will occur, which will affect the measurement accuracy.

The existing radius compensation methods can be roughly divided into two-dimensional compensation methods and three-dimensional compensation methods. The two-dimensional compensation method is widely used because of its simple processing and fast processing speed. The representative method of the two-dimensional compensation method is the three-point co-circle method. However, the two-dimensional compensation method will produce relatively large errors when measuring irregular surfaces. Therefore, on the basis of the two-dimensional compensation method, scholars at home and abroad have proposed a three-dimensional compensation method for the normal vector of the surface at the measurement point. The main representative method There are plane method, vector iterative method and direct measurement method and so on. However, whether it is a two-dimensional compensation method or a three-dimensional compensation method, a large amount of calculation is required to obtain the normal direction of the contact point between the probe of the three-dimensional coordinate measuring machine and the measured object.

In order to solve the above-mentioned defects, H.Aoyama et al. proposed a method for the metal measured object, taking four measurement points evenly on a certain longitude on the probe, when the probe is in contact with the metal measured object, the four Different potential differences will be measured at the measuring point, and the position of the contact point will be deduced according to four different potential difference values. The accuracy of this measurement method is 0.2°, but this measurement method requires the probe to be in contact with the object to be measured, and a large number of calculations are required to reverse the position of the contact point.

Contents of the invention

The purpose of the present invention is to improve the measuring head of the three-coordinate measuring machine in view of the deficiency that the radius compensation direction of the measuring head of the existing three-coordinate measuring machine cannot be accurately obtained, so that when the measuring head is close to the metal object to be measured, the contact between the measuring head and the metal can be known. The position of the contact point of the measured object, and then perform error compensation on the measurement result. Specifically, microarrays are used to evenly cover the capacitive plates on the measuring head, and the shape of a single plate is an equilateral triangle or square. Apply an excitation signal to the capacitive plate array on the probe (refer to the excitation method of the capacitive sensor), when the probe is close to the metal measured object, the metal measured object and the capacitive plate with a facing area will form a pair Plate capacitors generate capacitance, and different sizes of facing areas will generate different sizes of capacitance. The location of the contact point can be calculated according to the plate that generates the capacitance and the size of the capacitance.

Concrete steps of the present invention are as follows:

Step 1. Spread capacitor plates evenly in an array on the measuring head of the three-coordinate measuring machine, and record the position of each capacitor plate on the measuring head. The capacitor plate is in the shape of a square or an equilateral triangle.

Step 2, calculating the capacitance value of the capacitance element. Each capacitive plate on the measuring head and the metal object to be measured form a capacitive element; the capacitive plate on the measuring head is marked as G, and the value of the area S is less than 100μm ² . Project the capacitive plate G onto the surface of the overcapacitive plate G and parallel to the cut plane of the projection of the capacitive plate G on the metal object to be measured to form a projected capacitive plate G′; the area of the projected capacitive plate G′ is Scosθ, where θ is the angle between the capacitive plate G and the projected capacitive plate G′. According to the capacitance value calculation formula can be obtained: Wherein, d represents the gap between the projected capacitor plate G′ and the projection of the capacitor plate G on the metal object to be measured, and ε represents the dielectric constant.

Step 3, judging the position of the contact point between the measuring head and the metal object to be measured. When the capacitor plate used is a regular triangle, when the measuring head is in contact with the metal object to be measured, the position of the contact point on the measuring head will have three situations: falling on the apex of the regular triangle capacitor plate, falling on the regular triangle On the triangular edge of the capacitor plate, it falls in the regular triangle capacitor plate. According to the calculation formula of the capacitance value, the three positions are distinguished by the capacitance output value of the capacitor plate: if the capacitance output value of the capacitor plate has six values that are the same and are all the maximum value, then the contact point falls on the equilateral triangle capacitor plate on the vertex; if the capacitor output value of the capacitor plate has two values that are the same and both are the maximum value, then the contact point falls on the triangle edge of the regular triangle capacitor plate; if the capacitor output value of the capacitor plate has only one maximum value , then the contact point falls within the regular triangle capacitor plate. When the capacitor plate is a square, the position of the contact point on the measuring head will also have three situations: falling on the apex of the square capacitor plate, falling on the edge of the square capacitor plate, and falling in the square capacitor plate. According to the calculation formula of the capacitance value, the three positions are distinguished by the capacitance output value of the capacitor plate: if the capacitance output value of the capacitor plate has four values that are the same and are all maximum values, then the contact point falls on the square capacitor plate. on the vertex; if the capacitance output value of the capacitor plate has two values that are the same and both are the maximum value, then the contact point falls on the side of the square capacitor plate; if the capacitance output value of the capacitor plate has only one maximum value, then the contact point The points fall within the square capacitor plates. In this way, after the capacitor plate has a capacitance value output, the position of the contact point can be judged according to the position of the capacitor plate that generates capacitance and the size of the generated capacitance. For the case where the capacitance output value of the capacitor plate has only one maximum value, it can be directly determined. The position of the contact point, and then automatically identify the direction of radius compensation.

When judging the position of the contact point, it is not necessary to analyze each capacitor plate with a capacitance output value. It is only necessary to select several capacitor plates with larger capacitance output values for analysis according to the shape and accuracy requirements of the capacitor plate. That's it.

The beneficial effects of the present invention are:

1. When the accuracy requirement is not high, the present invention directly takes the capacitor plate with the largest output capacitance value as the contact point for radius compensation without calculation.

2. When the accuracy requirement is high, the present invention can deduce the precise position of the contact point through some calculations, so as to meet the high precision requirement.

3. The present invention only needs to cover the measuring head of the three-coordinate measuring machine with extremely small capacitive plates in the form of a microarray, without affecting the structure of the existing three-coordinate measuring machine, with strong realizability and simple structure .

Description of drawings

Fig. 1 adopts the schematic diagram that the mode of array is covered with capacitance plate on the measuring head of the present invention;

Fig. 2 is a schematic diagram of the measuring head approaching the metal object to be measured in the present invention.

Fig. 3 is the local enlargement figure that is covered with square capacitive pole plate on the measurement head of the present invention;

Fig. 4 is the schematic diagram that capacitance plate and metal measured object form capacitance element among the present invention;

Fig. 5 is a schematic diagram showing the position classification of contact points in six adjacent equilateral triangular capacitive plates on the measuring head.

Fig. 6 is a schematic diagram showing the position classification of contact points in four adjacent square capacitor plates on the measuring head.

Detailed ways

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

The three-coordinate measurement method of automatically identifying the direction of radius compensation, the specific steps are as follows:

Step 1. As shown in Figure 1, the measuring head of the CMM is evenly covered with capacitor plates in an array, and the position of each capacitor plate on the measuring head is recorded separately. Figure 1 only shows the spherical surface In practice, the area of the capacitor plate is extremely small. As shown in Figure 2, the measuring head is close to the metal measured object. As shown in Figure 3, zooming in on a part of the spherical surface of the measuring head covered with capacitor plates, it can be seen that the number of capacitor plates is very large and the area is very small, which can be approximated as a point. The shape of the capacitive plate in Fig. 3 is a square, and an equilateral triangle as shown in Figs. 1 and 2 can also be used.

Step 2, as shown in FIG. 4 , the capacitance value of the capacitive element is calculated. Each capacitive plate on the measuring head and the metal object to be measured form a capacitive element; the capacitive plate on the measuring head is marked as G, and the value of the area S is less than 100μm ² . Project the capacitive plate G onto the overcapacitive plate G and the projection of the capacitive plate G on the metal object to be tested (it has been explained above that the surface of the capacitive plate is very small and can be approximated as a point, so the The projection on the object can also be approximated as a point) on the plane parallel to the cut plane to form the projected capacitor plate G′; the area of the projected capacitor plate G’ is Scos θ, where θ is the capacitor plate G and the projected capacitor plate Angle of plate G'. According to the capacitance value calculation formula can be obtained: Wherein, d represents the gap between the projected capacitor plate G′ and the projection of the capacitor plate G on the metal object to be measured, and ε represents the dielectric constant.

When the capacitor plate is on the hemisphere facing the metal test object, the distance between the capacitor plate and the metal test object closer to the contact point will be smaller, and the angle between the metal test object and the metal test object will be smaller. The smaller, so the capacitance output value of the capacitor plate closer to the contact point is larger.

Step 3, judging the position of the contact point between the measuring head and the metal object to be measured. If the capacitor plate used is a regular triangle, when the measuring head is in contact with the metal object to be measured, as shown in Figure 5, the position of the contact point on the measuring head will have three situations: 1. Falling on the regular triangle capacitor plate 2. It falls on the triangular edge of the equilateral triangle capacitor plate, namely contact point B; 3. Falls in the equilateral triangle capacitor plate, namely contact point C. According to the calculation formula of the capacitance value, the three positions are distinguished by the capacitance output value of the capacitor plate: if the capacitance output value of the capacitor plate has six values that are the same and are all the maximum value, then the contact point falls on the equilateral triangle capacitor plate on the vertex; if the capacitor output value of the capacitor plate has two values that are the same and both are the maximum value, then the contact point falls on the triangle edge of the regular triangle capacitor plate; if the capacitor output value of the capacitor plate has only one maximum value , then the contact point falls within the regular triangle capacitor plate. It can be analogized for capacitor plates of other shapes. For example, if the capacitor plate is a square, as shown in Figure 6, the position of the contact point on the measuring head will also have three situations: 1. Fall on the apex of the square capacitor plate, that is, contact point D; fall on the square On the edge of the capacitor plate, that is, the contact point E; falls in the square capacitor plate, that is, the contact point F. According to the calculation formula of the capacitance value, the three positions are distinguished by the capacitance output value of the capacitor plate: if the capacitance output value of the capacitor plate has four values that are the same and are all maximum values, then the contact point falls on the square capacitor plate. on the vertex; if the capacitance output value of the capacitor plate has two values that are the same and both are the maximum value, then the contact point falls on the side of the square capacitor plate; if the capacitance output value of the capacitor plate has only one maximum value, then the contact point The points fall within the square capacitor plates. In this way, after the capacitor plate has a capacitance value output, the position of the contact point can be judged according to the position of the capacitor plate that generates capacitance and the size of the generated capacitance. For the case where the capacitance output value of the capacitor plate has only one maximum value, it can be directly determined. The position of the contact point, and then automatically identify the direction of radius compensation.

For the convenience of analysis, when inverting the position of the contact point, it is not necessary to analyze each capacitor plate with capacitance output value, only need to take several capacitor output values according to the shape and accuracy requirements of the capacitor plate Larger capacitive plates can be analyzed. If higher accuracy is required, the capacitance values output by the capacitor plates around the capacitor plate with the largest output capacitance value can be used to accurately deduce the specific position of the contact point. Reducing the area of the capacitive plates and increasing the number of capacitive plates can also be used to improve measurement accuracy.

Claims (2)

1. the three-coordinate measuring method in automatic identification radius compensation direction, it is characterised in that：This method is as follows：

Step 1: capacitor plate is uniformly covered with array way in the measurement head of three coordinate measuring machine, and record is each respectively Position of the capacitor plate in measurement head；Capacitor plate shape is square or equilateral triangle；

Step 2: the capacitance of capacity cell calculates：Each capacitor plate has been respectively formed one with metal measured object in measurement head A capacity cell；Capacitor plate in measurement head is denoted as G, the value of area S is less than 100 μm²；Capacitor plate G is projected to It crosses capacitor plate G and on the faces that section is parallel at the projection on metal measured object capacitor plate G, is formed and project capacitance pole Plate G '；The area for projecting capacitor plate G ' is Scos θ, wherein θ is the angle of capacitor plate G and projection capacitor plate G '；According to Capacitance calculation formula can obtain：Wherein, d indicates that projection capacitor plate G ' and capacitor plate G is tested in metal The gap of section at projection on object, ε indicate dielectric constant；

Step 3: judging the contacting points position of measurement head and metal measured object：When the capacitor plate used is equilateral triangle, when When measurement head is contacted with metal measured object, position of the contact point in measurement head will be there are three types of situation：It falls in equilateral triangle On the vertex of capacitor plate, falls on three arms of angle of equilateral triangle capacitor plate, fall in equilateral triangle capacitor plate；According to electricity The calculation formula of capacitance differentiates these three positions by the capacitance output valve of capacitor plate：If the capacitance output valve of capacitor plate There are six being worth identical and being all maximum value, then contact point is fallen on the vertex of equilateral triangle capacitor plate；If the electricity of capacitor plate Hold output valve there are two being worth identical and being all maximum value, then contact point is fallen on three arms of angle of equilateral triangle capacitor plate；If electric There are one maximum values, then contact point to fall in equilateral triangle capacitor plate for the capacitance output valve of appearance pole plate；Capacitor plate is just When rectangular, position of the contact point in measurement head also will be there are three types of situation：It falls on the vertex of square capacitor plate, falls On the side of square capacitor plate, fall in square capacitor plate；According to the calculation formula of capacitance, pass through capacitor plate Capacitance output valve differentiates these three positions：If the capacitance output valve of capacitor plate connects there are four being worth identical and being all maximum value Contact is fallen on the vertex of square capacitor plate；If there are two be worth identical and be all maximum for the capacitance output valve of capacitor plate Value, then contact point is fallen on the side of square capacitor plate；If only there are one maximum values for the capacitance output valve of capacitor plate, connect Contact is fallen in square capacitor plate；In this way after capacitor plate has capacitance output, according to the capacitor plate for generating capacitance Position and generate capacitance size can butt contact position judged there was only one for the capacitance output valve of capacitor plate The case where a maximum value, can directly determine the position of contact point, and then automatic identification radius compensation direction.

2. the three-coordinate measuring method in automatic identification radius compensation according to claim 1 direction, it is characterised in that：Docking When contact position is judged, without analyzing each capacitor plate for having capacitance output valve, it is only necessary to according to capacitance The shape of pole plate and required precision, the capacitor plate for taking several capacitance output valves larger are analyzed.