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New 3D platform machine tool and its initial assembly pose error decoupling analysis Jin Zhenlin 12, Zhang Liping 2, Li Yanzhen 2 (1. Institute of Robotics, Beijing University of Aeronautics and Astronautics, Beijing 100083, China; 2. School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China) The parallel machine tool of the structure form is error-decoupled in its orthogonal pose, and the orthogonal pose is selected as the initial assembly pose of the machine tool, which improves the assembly processability of the machine tool.
Parallel machine tool, also known as virtual axis machine tool, is a mechatronics product combining robot technology and machine tool structure technology. Compared with traditional series machine tools, parallel machine tools have a major breakthrough in structure, with simple structure, high modularity and rigidity. Good, the inertial mass of the moving parts is small and the motion response is fast, and the disadvantages are small working space and complicated control algorithm. Most of the current parallel machine tools use the inverted Stewart platform for their prototypes. For the problems of such machine tools, such as severe motion coupling and poor assembly process, a new parallel machine tool structure is proposed. The parallel machine tool is 3 - 2 - 1 - SPS 3D. The platform mechanism is the original shape, and it has the characteristics of error decoupling in its orthogonal pose. Compared with the parallel machine tool structure prototyped by Stewit platform, it has better structure and assembly process.
1 New 3D platform machine structure layout characteristics and process analysis 1.1 Structure layout characteristics The parallel prototype of the machine tool prototype is a novel 3 - 2 - 1 SPS 3D platform mechanism, as shown, by the base 1, six The SPS kinematic chain branch 2 and the motion platform 3 are composed. The mechanism has the same kinematics model as the Stew-t platform, but its kinematic chain layout is different from that of the general Stewit platform. It is characterized in that each SPS kinematic chain forms a branch, and the linear moving pair in the branch is the driving pair. The six branches are divided into first, second, and third groups according to 3, 2, and 1, and the centers of the three sets of ball joints connected to the motion platform corresponding to the three sets of branches are respectively distributed in length, width, and height respectively of 2a. On the three mutually perpendicular surfaces of the base hexahedron of 2b, 2c, wherein the centers of the three ball joints of the first group are respectively located at three vertices of an equilateral triangle having a side length of 2d, and the two balls of the second group The centers of the hinges are respectively located at the two end points of the line segment of length 2d, and the center of the ball joint of the third group is located at the geometric center of the surface of the base cube.
The distribution of the six ball joints on the pedestal is similar to the six ball joints on the motion platform.
When the axes of the three sets of branches are perpendicular to the three mutually perpendicular surfaces of the base hexahedron, the mechanism is in an orthogonal pose.
Schematic diagram of the machine tool. The parallel machine tool consists of a base 1, a moving platform 3, six branches 2 consisting of a linear moving drive rod and a ball joint connected to the moving platform and the base, and an electric spindle mounted on the moving platform and cutting. The tool 4 is composed. The motion platform realizes the movement of any position and posture through the movement of the six branches of the linear movement drive rod, so that the tool mounted on the motion platform can complete the processing of any spatial surface.
The structure of the new 3D platform machine is shown. 2 Process analysis Whether the selection of the initial assembly pose of the parallel machine tool is reasonable, has a direct impact on the geometric accuracy and manufacturing cost of the machine tool. Parallel machine tools based on Stewart platform have many problems in their initial assembly posture, such as structure and assembly process. For example, in order to enlarge the working space, the six ball joints connected to the motion platform/base need to be tilted. Installation, which requires six inclined mounting surfaces and mounting holes on the motion platform/base. These six mounting surfaces and mounting holes are used in space projects: China Postdoctoral Science Foundation (230-21) ―101) Yanshan University Ph.D. Funded Project (B51) lt for the exam (introduction 5 Jin Zhenlin (1 fool-) male. Liaoning Fushun 1 teaching PhD 6 professional direction ft parallel robot technology frightsreserved. neither parallel nor vertical, give Design, assembly and inspection are very inconvenient.
According to the parallel parallel machine tool, the orthogonal pose is selected as the initial assembly pose, so that it has good structure and assembly processability. 145: In the initial assembly posture, each group of linearly moving drive rod axes and the corresponding ball joint mounting planes are mutually Vertical, this makes it easy to design assembly accuracy requirements and assembly accuracy requirements for overall assembly.
According to the layout characteristics, the mounting surfaces and mounting holes corresponding to the three sets of ball joints connected to the motion platform/base can be designed to be perpendicular to each other, for the design, processing and ball joint installation and inspection of the motion platform/base. Convenient.
2 Error decoupling analysis of the initial assembly pose As shown, the coordinate system fixed to the motion platform is established: P:O'-xy/, the origin is at the geometric center of the basic hexahedron, and the three axes are respectively three with the cube. The mutually perpendicular sides are parallel. In the coordinate system, the spatial position of the ball joint point Bi connected to the motion platform is represented by a vector; the coordinate system QO-xyz fixed to the base is established, and the ideal position and posture in the initial assembly posture, coordinates The origin of the system 0 and the three coordinate axes respectively coincide with the origin of the coordinate system P and the three coordinate axes. In the coordinate system Q, the spatial position of the ball joint point B/ connected to the motion platform is represented by a vector, and the spatial position of the ball joint point Ai connected to the base is represented by a vector, 2. (=1, 2,...,6), and set in the initial position of the initial assembly pose, the length of the six SPS kinematic chain branches (the distance between the two ball joints in the branch) is /. It is characterized by the machine layout: In the initial assembly pose, let the motion platform point "the position error vector for the O point is As = (AxAyAz) T, and the attitude error vector of the motion platform point O to the O point is Ar = (Aa Qiu and Ay are respectively the swivel angles. Pitch angle and deflection angle error, corresponding to the length of the six SPS kinematic chain branches (distance of the two ball hinge points in the branch) error vector is A / = Li Bing. Parallel machine prototype prototype design and performance analysis. Harbin: Harbin Institute of Technology, 1999 Jin Zhenlin, Gao Feng. 3―2―1 Structure 6 Degrees of Freedom Orthogonal Parallel Machine Tool. China Jin Jinlin, Peak. Flexibility Index of New Parallel Machine Tool and Its Distribution in Work Space. China Mechanical Engineering, 2002 Huang Zhen, Kong Lingfu Fang Yuefa. Theory and Control of Mechanism of Parallel Robots. Beijing: Mechanical Industry Press, 1997. Mobility Analysis of Two-DOF Multi-ring Hybrid Drive Mechanism Li Yonggang, Meng Caifang, Zhang Ce, Li Hui (Mechanical Engineering of Tianjin University , Tianjin 300072) The method of mobility analysis, that is, the speed input and output matrix of the mechanism is first introduced, and the conditions for the singular configuration of the mechanism are introduced, combined with the mobility requirements of the mechanism and the mobility of the single-ring multi-rod mechanism. The necessary and sufficient conditions, the mobility of each loop of the whole organization is analyzed, and finally the comprehensive analysis shows the mobility condition of the hybrid drive mechanism. The crank press has a wide range of applications in the field of metal forming processing. The processing technology has different requirements on the speed variation characteristics of the part deformation process. Therefore, the stamping speed characteristic of the crank press becomes one of the important factors that limit its application. The traditional crank press is mostly a single degree of freedom mechanism. Constant-speed motor drive, the output characteristics of the mechanism are determined by the length of the rod, so when the output requirements change, its output characteristics are difficult to change, which makes the same mechanism unable to meet the requirements of various stamping processes for the stamping speed. The motor is driven, and the controllability of the servo motor speed can be utilized to pass the rod length without changing the mechanism.
The idea of ​​hybrid drive mechanisms proposed in recent years, 12-12, is a good way to solve this problem. That is, a two-degree-of-freedom hybrid driving one-stage mechanism is used as a driving mechanism of the press, and one of the motive members is driven by a constant speed motor for uniform motion, and the other motive member is controlled by the servo motor to make it Compensating for motion so that the mechanism accurately achieves a given motion. In this way, without changing the length of the mechanism rod, as long as the motion law of the servo motor is controlled by programming, the same mechanism can meet various output requirements. On this basis, a new type of two-degree-of-freedom hybrid-driven 111-stage mechanism was studied. As we all know, institutional research, first of all, inevitably to conduct institutional mobility analysis. For the mobility of multi-rod mechanism, there are many researches at home and abroad, such as the in-depth analysis of the mobility of the planar single-loop multi-rod mechanism based on the assemblability of the planar link mechanism and the extreme value of the transmission angle. 5~8; the existence condition of the crank of the plane five-bar mechanism and the type of discriminating mechanism 110; with any combination of the motion of the two motives, the mechanism is operated to the most difficult position as a mechanical model, and the two-degree-of-freedom five-bar mechanism The derivation of sufficient conditional mobility 1111; |12丨 gives a calculation method for the mobility condition of a two-degree-of-freedom mechanism.
However, these are the mobility conditions of the single-loop multi-rod mechanism studied, and the mobility conditions of the multi-degree-of-freedom multi-ring mechanism are not analyzed. The hybrid drive mechanism is mostly a multi-degree-of-freedom multi-ring mechanism, such as a two-degree-of-freedom multi-ring hybrid drive mechanism (). In view of this important significance, the mobility of the two-degree-of-freedom hybrid drive-stage one-stage mechanism shown is deep. Analysis, and combined with examples to verify the correctness of the analysis.
1 The singularity analysis of the mechanism is known by 3, when the coefficient matrix of the velocity matrix AX+劢=0 derived from the position constraint equation of the mechanism: F(3,x)=0 is zero, ie det(A) When =0 or det(B) = 0, the mechanism will have singularity. And divided into three types: *: 2002 - 12 - 05; revised date: 2003 - 04 - 07 Fund Project: National Ministry of Education, Doctoral Fund Project (2000005630)