CN1346964A - Method and device for measuring position and attitude in space - Google Patents

Abstract

A method and device for measuring the full position and attitude in space. The method uses the special large-size ballbar of the present invention to measure the relative distance between three fixed points on a space-moving rigid body (that is, a moving coordinate system). Fix the distance between three fixed points in the coordinate system, and obtain the length values of 9 center distances of 3×3 between them; Read out the length values of the above nine center distances, list nine nonlinear equations according to the nine length parameters, and use the Zhan Chongxi method to analyze the nine nonlinear equations to obtain the above object to be measured. Spatial position and attitude. The measurement method is simple and easy to operate, does not need expensive instruments, is economical and practical, and can obtain the measured values of the three Euler angles with high precision. This measurement method has important application value for kinematics calibration of parallel machine tool/robot.

Description

A measuring method and device for space full position and attitude

Field

The present invention relates to a measurement method based on an optical measuring instrument and its device, to be precise, to a measurement method and device for space full position and attitude, and belongs to the technical field of spatial position and angle measurement.

Background technique

For a rigid body, its position in space can be described by position and orientation. The position is usually represented by Cartesian coordinates, that is, the three-dimensional coordinates of x, y, and z; and the attitude is usually represented by three Euler angles φ, θ, ψ, which are commonly referred to as the precession angle φ and the nutation angle. θ and rotation angle ψ. For the measurement methods and equipment of the above six spatial parameters, at present, three-coordinate measuring machines, theodolites, dual-frequency laser interferometers, and laser trackers are mainly used. However, the above-mentioned measuring devices or methods all have defects of one kind or another: either the price is relatively high, or they are only suitable for position measurement, and the measurement of the three Euler angles is often ineffective. However, in practical applications, such as cutting processing of parallel machine tools and position control of robots, how to realize the accurate measurement of the three Euler angles simply and conveniently has always been an important topic concerned by technicians in the machinery industry. In addition, the measurement range of the traditional ballbar is generally only a few millimeters, which is usually only used in the measurement of dynamic calibration of traditional machine tools, and cannot achieve the length measurement task of tens of millimeters or even a larger range.

Contents of the invention

The object of the present invention is to provide a measurement method for the full position and attitude of space that can solve the above problems. This measurement method is different from the previous measurement methods. It does not directly measure the above six parameters, but indirectly measures the spatial movement. The distance (length) of the three fixed points on the rigid body relative to the three fixed points in a certain fixed coordinate system is calculated to determine the position and attitude of the space-moving rigid body. The operation steps of this measurement method are simple and easy, no expensive instruments are needed, and it is economical and practical; more importantly, this method can obtain the measurement values of three Euler angles with high precision; Scientific calibration has important application value.

Another object of the present invention is to provide a measuring device for the above-mentioned method of measuring the overall position and attitude in space, so as to be able to measure the length of tens of millimeters or more, so that the above-mentioned measuring method can be implemented.

The measuring method for space full position and attitude of the present invention is realized like this: comprise the following steps: (1) at first a relatively fixed object, namely the reference object when measuring is set as fixed coordinate system, and in The fixed coordinate system, that is, three ball seat positions are set in a relatively fixed object;

(2) Then an object to be measured, that is, an object with relative motion, is set as the motion coordinate system, and three ball seat positions are also set in the motion coordinate system, that is, the object to be measured;

(3) According to the length of the nine center distances formed between the center positions of the three ball seats in the fixed coordinate system and the center positions of the three ball seats in the moving coordinate system, select a special measuring device with an appropriate length - Ballbar, and use the standard table to adjust the reference length of the ballbar to determine the measurement reference;

(4) When the above-mentioned object to be measured (moving coordinate system) moves to a certain position or posture that needs to be measured, use the special measuring device-ballbar to measure the above-mentioned fixed coordinate system (that is, relatively fixed object) and the center positions of the three set ball seats in the motion coordinate system (that is, the object to be measured) between the center positions of the three set ball seats in the motion coordinate system (that is, the object to be measured) The length value of 3 × 3 total 9 center distances ;

(5) Read the length values of the above-mentioned 9 center distances from the digital display on the ballbar or the computer connected to the ballbar, and list 9 nonlinear equations according to the 9 length parameters, Then, the Zhan Chongxi method is used to analyze the nine nonlinear equations to obtain the spatial position and posture of the object to be measured (moving coordinate system).

The center positions of the above-mentioned three ball seats respectively set in the fixed coordinate system and the moving coordinate system can be the respective vertices of two groups of isosceles right triangles of different lengths; In order to reduce the computational workload and avoid redundant nonlinear equations.

The ball diameter of the concave spherical surface in the above ball seat position is 3/4 inch, and its asphericity should be ≤0.5μm.

The measuring device for space full position and attitude of the present invention is realized like this: comprise: the grating scale that is made of grating, leaf spring, extension spring, damper, zero datum plane and shell by grating and its outside, it is characterized in that : The two ends of the grating scale are respectively connected with a fixed shaft and a movable shaft through precise fit. The axes of the fixed shaft and the movable shaft should be strictly coincident and on the same axis, and one end surface of the movable shaft is processed to match the standard ball The inner concave spherical arc surface with the same radius as the spherical surface, and then the standard ball is bonded with the adhesive; the other end of the fixed shaft is embedded in the groove of a cylindrical joint, and is locked by the locking screw on the side of the joint. For fastening and positioning, the other end of the cylindrical joint is threaded with an extension rod.

The spherical diameter of the concave spherical surface on one end surface of the above-mentioned movable shaft is 3/4 inch, and its asphericity should not be greater than 0.5 μm.

The misalignment of the axes of both the fixed shaft and the movable shaft should be less than 10 microns.

The bonding agent used for the bonding of the concave spherical surface on one end surface of the movable shaft and the standard ball is AB glue.

In addition to the above characteristics, the measurement method of the present invention has the following advantages: the method is easy to realize full digital measurement, has the advantages of high measurement accuracy, convenient use, and little influence by environmental factors; at the same time, compared with other measurement methods, the The price of the measuring device to be configured is relatively low, and has high use value and performance-price ratio. The measurement method of the present invention is mainly used in the calibration of the motion accuracy of parallel machine tools, and can realize the measurement of the position and attitude of the motion platform of the parallel machine tool with a certain accuracy; it can also realize the plane position and attitude of various new machine tool tools based on the plane parallel mechanism model It can also be used to measure the spatial position and attitude of the parallel manipulator, and then realize its motion accuracy calibration. If this method can be further improved in future research and application, it is expected to become the main means of precision calibration of parallel machine tools. Therefore, the method of the present invention has high commercial value and good market prospect.

Furthermore, the present invention also provides technical support means for the implementation of the measuring method, that is, it provides a special measuring device using the principle of grating length measurement - a ballbar, which greatly expands the range of the ballbar, which can usually only measure a few millimeters. , can measure the length of tens of millimeters or even tens of millimeters, and its maximum measuring range can reach 50 millimeters. Coupled with a series of extension rods, the device can theoretically measure the length of a larger length range, and can realize High measurement accuracy.

Description of drawings

Fig. 1 is a schematic diagram of the measurement principle of the measurement method of the present invention.

Fig. 2 is a schematic diagram of the measurement method of the present invention.

Fig. 3 is a structural schematic diagram of the measuring device of the present invention.

Detailed ways

Please refer to Fig. 1 and Fig. 2 simultaneously, introduce the present invention to be used for the operation step of the measurement method of space full position and attitude and its working principle: at first a motion coordinate system oxyz is set up on the space motion rigid body 20, afterwards in a relatively fixed A fixed coordinate system OXYZ is established on the object 30, that is, the reference object during measurement, and the position of the space-moving rigid body 20 relative to the fixed object 30 is determined by the coordinates of the origin o of the moving coordinate system oxyz in the fixed coordinate system OXYZ. Indicates that the posture of the moving rigid body is expressed by the three Euler angles of the moving coordinate system oxyz relative to the fixed coordinate system OXYZ. Next, set three ball seats 21 on the motion rigid body 20 (ie, the motion coordinate system oxyz), which are respectively A ₀₁ , A ₀₂ , and A ₀₃ (only one ball seat is drawn in Fig. 2 ), and The center positions of the three ball seats A ₀₁ , A ₀₂ , A ₀₃ have sufficient accuracy relative to the positioning of the motion coordinate system oxyz, and at the same time, there are three sets on the relatively fixed object 30 (that is, the fixed coordinate system). Ball seats 31, which are respectively B ₀₁ , B ₀₂ , and B ₀₃ (only one of the ball seats is shown in FIG. 2 ), and the centers of the three ball seats B ₀₁ , B ₀₂ , and B ₀₃ are opposite to each other. The positioning in the fixed coordinate system is also quite accurate; then according to the center positions of the three ball seats B ₀₁ , B ₀₂ , B ₀₃ in the above fixed coordinate system OXYZ and the three ball seats A ₀₁ , A in the moving coordinate system oxyz ₀₂ , A ₀₃ The lengths of the 9 center distances formed between the center positions of A 03, select the special measuring device of the present invention-ballbar 40 with an appropriate length, and use the standard table to adjust the reference length of the ballbar , to determine the measurement benchmark; then measure the distance from the center of the three ball seats A ₀₁ , A ₀₂ , A ₀₃ on the above-mentioned moving rigid body (moving coordinate system) to the static fixed rigid body by the special measuring device of the present invention-the ballbar 40 The length distances between the centers of the three ball seats B ₀₁ , B ₀₂ , and B ₀₃ can be used to obtain 9 length values in total (Fig. 2 shows a schematic diagram of the measurement method). Then list 9 nonlinear equations according to the 9 length parameters, and finally analyze the 9 nonlinear equations by using the Zhan Chongxi method to obtain the spatial position and attitude of the above-mentioned object to be measured (moving coordinate system).

It should be noted that the center positions of the three ball seats respectively set in the fixed coordinate system and the moving coordinate system can be the respective vertices of two groups of isosceles right triangles with different lengths, and at the same time, the two groups of right triangles should be as far as possible. in a docked position to reduce computational effort and avoid redundant nonlinear equations.

In addition, to measure the position and attitude of a rigid body in space motion, theoretically, it is only necessary to measure 6 values of the above-mentioned 9 lengths. The reason why the present invention adopts redundant measurement is that the main purpose is to eliminate some measured values with large deviations by checking the compatibility between the nine parameters, so as to improve the overall measurement accuracy, and can pass redundant The measurement data gives an estimate of the level of error precision for that measurement.

Referring to the measuring device-ballbar for the full position and attitude of the present invention shown in FIG. The grating scale that shell 8 forms, and movable shaft 6, fixed shaft 7, standard ball 9, cylindrical joint 10 and extension rod 12 are formed. The two ends of the grating scale are respectively connected with a fixed shaft 7 and a movable shaft 6 through precise fit. The axes of the fixed shaft 7 and the movable shaft 6 should be strictly coincident and on the same axis, and the misalignment should be less than 10 microns , to ensure the measurement accuracy. One end surface of the movable shaft 6 of the grating scale is processed into a concave spherical arc surface with the same spherical radius as the standard ball 9, and then the standard ball 9 is bonded with an adhesive. The adhesive used here is AB glue. . The other end of the fixed shaft 7 is embedded in the groove of a cylindrical joint 10, and is fastened and positioned by the locking screw 11 on the side of the joint. pole 12. The spherical diameter of the concave spherical surface on one end surface of the movable shaft 6 is 3/4 inch, and its asphericity should not be greater than 0.5 μm.

The measuring device of the present invention is refitted from a grating ruler, and the most critical thing is to ensure that the connection and positioning of the standard ball 9 and the movable shaft 6 in the grating ruler are as accurate as possible, while ensuring that the standard ball cannot be larger. deformation. For this reason, in the process of manufacturing the ballbar, one end face of the movable shaft 6 of the grating ruler must be milled into a concave spherical arc surface with the same radius as the spherical surface of the standard ball 9, and it is scraped with a standard spherical surface. , to improve the accuracy of its insphericity, and then use AB glue to bond the standard ball on the concave spherical surface. The mechanical strength of the structural parts connected by this kind of AB glue is very high. Even if the parts are cut on the machine tool, the standard ball will not fall off, so that the spherical surface of the standard ball will not be greatly deformed, thus The overall accuracy of the ballbar is guaranteed. The used standard ball of the present invention is the standard ball of 3/4 inches, and its asphericity should be no more than 0.5 micron, and the precision of the maximum full scale (50mm) of this ballbar will be controlled within 2 microns.

The measuring device and measuring method of the present invention have been used to carry out the experiment of measuring and calibrating a certain parallel machine tool, and the result of the test is a rather ideal effect: the precision of the machine tool has been greatly improved, even if the machine tool reaches And meet the standard requirements of the relevant national regulations, laying the foundation for its future commercialization.

Claims (7)

1, a kind of measuring method that is used for space full position and attitude, it is characterized in that: comprise the following steps: (1) at first a relatively fixed object, namely the reference object when measuring is set as fixed coordinate system, and Set three ball seat positions in the fixed coordinate system, that is, relatively fixed objects; (2) Then an object to be measured, that is, an object with relative motion, is set as the motion coordinate system, and three ball seat positions are also set in the motion coordinate system, that is, the object to be measured; (3) According to the length of the nine center distances formed between the center positions of the three ball seats in the fixed coordinate system and the center positions of the three ball seats in the moving coordinate system, select a special measuring device with an appropriate length - Ballbar, and use the standard table to adjust the reference length of the ballbar to determine the measurement reference; (4) When the above-mentioned object to be measured moves to a certain position or attitude that needs to be measured, use the special-purpose measuring device-ballbar to measure the three points in the above-mentioned fixed coordinate system (that is, relatively fixed objects) respectively. The length values of 3 x 3 total center distances between the center positions of a set ball seat and the center positions of three set ball seats in the motion coordinate system (that is, the object to be measured); (5) Read the length values of the above-mentioned 9 center distances from the digital display on the ballbar or the computer connected to the ballbar, and list 9 nonlinear equations according to the 9 length parameters, Then, the Zhan Chongxi method is used to analyze the nine nonlinear equations to obtain the spatial position and posture of the object to be measured (moving coordinate system). 2. The method for measuring the full position and attitude in space according to claim 1, characterized in that: the center positions of the three ball seats respectively set in the fixed coordinate system and the moving coordinate system can be different in two groups. The respective vertices of the isosceles right triangles of the length; and try to make the two groups of right triangles be in the butt joint position. 3. The method for measuring the full position and attitude in space according to claim 1, characterized in that: the diameter of the concave spherical surface in the position of the ball seat is 3/4 inch, and its out-of-sphericity should be ≤ 0.5 μm . 4. A measuring device for all positions and attitudes in space, comprising: a grating scale composed of a grating, a leaf spring, a tension spring, a damper, a zero reference plane and a housing on the outside thereof, characterized in that: the grating The two ends of the ruler are respectively connected with a fixed shaft and a movable shaft through precision fit. The axes of the fixed shaft and the movable shaft should be strictly coincident and on the same axis. One end surface of the movable shaft is processed to the spherical radius of the standard ball. The same concave spherical arc surface is bonded with a standard ball by adhesive; the other end of the fixed shaft is embedded in the groove of a cylindrical joint, and is fastened by the locking screw on the side of the joint Positioning, the other end of the cylindrical joint is threaded with an extension rod. 5. The measuring device for space full position and attitude according to claim 4, characterized in that: the spherical diameter of the concave spherical arc surface on one end surface of the above-mentioned movable shaft is 3/4 inch, and its out-of-sphericity should not Greater than 0.5 μm. 6. The measuring device for all spatial positions and attitudes according to claim 4, characterized in that: the misalignment of the axes of the fixed shaft and the movable shaft should be less than 10 microns. 7. The measuring device for all positions and attitudes in space according to claim 4, characterized in that: the bonding method used for the bonding of the concave spherical arc surface and the standard ball on one end surface of the movable shaft of the grating scale is The agent is AB glue.

Images