Applied Mechanics and Materials Vols. 37-38

Abstract: In order to study forming shape distribution of laser molten pool in laser fabricating, a CCD-based image detection system was developed. The system mainly consists of a CCD-based detector, optical elements, an image acquisition card and its special software. Experiments on shape measurement of the laser molten pool were carried out. It was shown that 2D morphology and the dimension of laser molten pool could be measured in real time. The (X, Y) dimension of the laser molten pool in laser cladding was (2.6 mm, 2.5 mm) with an approximately ellipsoidal shape. Laser cladding parameters were optimized according to the measurement results. It was a non-destructive measurement method, which would be a new method for online measurement and feedback control in laser fabricating.

Abstract: In view of defects of static detection for screw, such as low efficiency, man made errors, this paper designed a dynamic detecting system, which employs two-frequency laser interferometer as the displacement benchmark and encoder as the angle benchmark. According to the lasting standards, the solution procedure of error evaluation algorithm is optimized by least square method to reduce computation. Experiment shows this system can dynamically detected screw, of which rank accuracy is more than two.

Abstract: This paper designed a type of freeform surface roughness measurement bench using parallel-mechanism. The virtual prototype of surface roughness measurement bench has been established. Basic structure parameters and work-space of bench have been calculated according to the program of surface roughness test. An example of bearing outer circle roughness measurement based on Stewart platform has been analysed. From the example of measurement bench it is observed that the designed bench based on Stewart platform can be used as a multi-DOF structure in the freeform surface roughness measurement.

Abstract: Based on the unique geometry and mechanical movement of beam pumping unit, this paper presented a simple swing equation and computed motorial parameter, meanwhile under the conditions of the static load and inertial load of the polished-rod of a conventional pumping unit, it also presented an equivalent dynamic model of the pumping unit system and the type-curves of net torque of the crankshaft with the characteristic of inertial counterbalance having been computed, the model can provide a theoretical base for study on the other transient working parameters of beam pumping unit. Being satisfied with motion accuracy and boundary constraints, the optimization model of beam pumping unit is established. The simulated annealing algorithm with penalty strategy is adopted to solve the optimal model, so that optimization process was simplified and the global optimal solution is ensured reliably.

Abstract: The cost of development for physical prototypes of parallel robots is high and the optimization cycle is long. The optimum method of high efficiency is explored. A virtual prototype model of 3RPS is established to analyze how the rotational angle of the robot is affected when the parameters of the robot vary. The results show that it is a good method and easy to be used in practice. The optimum parameters are obtainned for the workspace indicating that rotational angle is the best one.

Abstract: A new lower pressure water jet cutter has been invented, which adopts the technology of premixed abrasive jet and computer numerical control (CNC). A series of technical problems had been solved such as abrasive screen classification, abrasive tank filling, abrasive consistency regulation, valve group sequence control, etc, which are essential in the application of this technique. The structure, working principles, main technological parameters and practical application of the cutter are introduced in this paper. Experimental results show that the water jet cutter can cut steal, glass and other materials. It is characterized by its high efficiency, low specific power consumption and fine automation level. Therefore it is a new type of cold cutting machines.

Abstract: A method is described for performing the tensile strength of fragile material studies using electromagnetically launched expanding composite ring. The working principle is analyzed, where a fast-discharge capacitor system generates magnetic forces between the solenoid and driving ring, which accelerates radial velocities of the specimen rings. The dynamic measuring methods of instantaneous current and mechanical testing are established for analysis of electrical character and tensile strength of fragile specimen. The current pulse was tested experimentally which was provided by a capacitive discharge with the load solenoid connected in series with the power supply alone. It is shown that experimental results match the theoretical analysis well.

Abstract: Because welding system is given the look function by laser image sensing, the automation of welding system is well improved. But the two problems are image processing deviation under welding interference and adjusting deviation of machine set tracking. Targeting at these problems, the weld seam tracking (WST) system is designed. Some mathematics are brought forward, including the log grey transformation, Laplace edge detection, extracting center route of laser strip and detecting the characteristic points of weld seam image. The dynamic trend of WST is controlled by the current seam deviation calculated by seam characteristic points. The subsection control strategy and the decision algorithm of WST stability in abnormal circumstances are used. The WST experimental results show that tracking S shape weld seam is delivered effectively with high precision based on the proposed weld seam tracking, can meet welding technology requirement and provide experimental data for manufacturing WST system.

Abstract: Based on the group theory and the complex division method, the dimension classified method for planar multi-loop mechanism was analyzed. Firstly, the dimension classified inequation was derived from the singularity of constraint equation of the mechanism. Subsequently, by using the classified inequation, the complex division method of the structure-parameter-space was explored. By using the mechanism symmetry group, the simplification method of the division results was analyzed. Finally, by using an example, the classified methods were validated. The results show that all information about mechanism classification are included in the division results. Besides, this method is appropriate for complicated mechanism classification by computer.

Abstract: In order to verify the reliability of a calibration mechanism including a motion component used in the satellite, the dynamic analysis for this mechanism is conducted with modal coordinate reduction method. Firstly, FEM software ABAQUS is employed to calculate the eigenfrequency and mode shapes of this mechanism. Then, the transfer function at some key points can be acquired by coordinate transformation from its original format in modal coordinate. Finally, the power spectral density at the key points are obtained and compared with the results of random vibration experiments to prove the dynamics analytical validity.