| Traditional coordinate measuring machines (CMMs) with Cartesian coordinate system, columniation coordinate system and other coordinate systems are widely used. However with the development of modern manufacturing industry, these systems cannot meet some special measurement purposes. Combined robot technology with coordinate measuring techniques, non-orthogonal CMM with high flexibility have leading the development and application of CMM to a new field. Non-orthogonal CMM has become one of the developing trends of CMM.A new type non-orthogonal and noncontact CMM with serial-link mechanism is designed and developed to implement the noncontact and high accurate measurement of free-form surface of rotation. Many aspects about the new non-orthogonal CMM, such as the system structure design, method of 3D measurement, kinematics, measuring machine calibration, error analysis and compensation, control system and software et al, are sufficiently discussed in the dissertation. It can accelerate the course of engineering application by solving several key practical problems.The main work and innovation in this dissertation are as follows:1) A new model non-orthogonal and noncontact CMM using serial-link mechanism is proposed in this dissertation. A RRP robot manipulator is applied as the measuring framework, and the measuring system consists two optical noncontact sensors, a laser displacement sensor and a CCD camera. Then geometrical dimensions and surface imperfections of the free-form surface of rotation could be obtained. In order to improve the resolution of revolute joint displacements within a limited space, specific structures are designed to measure the arc length. Via simple conversion, angular displacement could be gain.2) The kinematics of RRP robot is analyzed, and corresponding analytical equations of the pose (position and orientation) of the end-effector and inverse kinematics are derived. Based on this, the error of measuring machine is discussed, and the expression of error extremum is presented that can be used to direct the design, manufacture and assemble.3) A new model of identification kinematic parameter of robot manipulator based onreference configuration is presented. Each joint variable divides into two parts in this model, one is the nominal joint variable of reference configuration relative to base frame, and the other is joint displacement relative to reference configuration. With the input of the pose of end-effector and joint displacements relative to reference configuration, the constant kinematic parameters and joint variables of reference configuration relative to base frame can be identified.4) Measurement of the pose of end-effector is different in robot calibration. Rely on the characteristic of the measuring system, the position and orientation of end-effector is measured separately. A specific artifact is designed to measure the position. And a new resolution method is put forward for the measurement the pose of end-effector of robot manipulator.5) The errors of laser sensor, joint transform and kinematic parameter of the measuring machine are calibrated. In order to identify the kinematic parameters, self-calibration method and identification model based on reference configuration are used. Depended on the data of the pose of end-effector and joint encode readings, the parameters can be identified. In the calibration of joint transform error, laser autocollimator and polyhedron are employed to decide the relationship between joint encoder outputs and actual joint displacements accurately, and to reduce the effect of the manufacturing and assembling error of grating holder to measuring precision. The results of experimentation indicate that the precision of the measuring machine is greatly improved.6) The method combined point-scanning and surface-scanning is applied to measure the surface imperfection of inner and outer spherical surface. This method not only have high accurate, but also improve the measurement efficiency. And a tri-region extension method based on spherical coordinate system is proposed in this dissertation to identify the surface imperfection in the whole surface scanning of laser sensor.7) Evaluate method and principle of deciding reference plane of spherical surface imperfection is given. And a new opinion on how to define the reference plane is advanced that complement the define specified in GB/T15757-2002 eqv ISO 8785:1998. All of this is valuable to surface imperfection evaluation.8) The development of control system with master slave control mode and software of the measuring machine is accomplished. AH of this realizes the functions and measuring factor evaluate of the machine.With a great deal of research and experimentation, this measuring machine achieves high measurement precision. The measuring precision of the radius of sphere and column is ±5u.m.
|
PDF Full Text Request