An investigation on the neural networks based active vibration control of flexible redundant manipulators was conducted. The smart links of the manipulator were synthesized with the flexible links to which were attached piezoceramic actuators and strain gauge sensors. A nonlinear adaptive control strategy named neural networks based indirect adaptive control (NNIAC) was employed to improve the dynamic performance of the manipulator. The mathematical model of the 4-layered dynamic recurrent neural networks (DRNN) was introduced. The neuro-identifier and the neuro-controller featuring the DRNN topology were designed off line so as to enhance the initial robustness of the NNIAC. By adjusting the neuro-identifier and the neuro-controller alternatively, the manipulator was controlled on line for achieving the desired dynamic performance. Finally, a planar 3R redundant manipulator with one smart link was utilized as an illustrative example. The simulation results proved the validity of the control strategy.
A closed-form numerical algorithm (CFNA) is analyzed in detail. CFNA is widely used in mechanical dynamics for periodic solution of second-order original differential equations (SODE) with periodic time-variant coefficients. The principle of the algorithm is to discretize the motion period into many short time intervals, so the coefficient matrices of the equation set are regarded as constant in a time interval. Defects are found in the original algorithm in treating the modal coordinates at the two end-nodes and important modifications to the defects is made for the algorithm.The modified algorithm is finally used to solve the dynamic problem of a three-ring planetary gear transmission.
A model for conceptual design of mechanical devices is studied based on qualitative simulation. In this model, the desired functions are expressed by state-transit-diagrams(ST-diagrams)and design space is represented by qualitative-state-curves(QS-curves). The first design idea, called seeds idea, is proposed by the designer and then is abstracted into QS-curves. The qualitative simulation is implemented based on the QS-curves. By changing the motion of acting parts, the connection of parts and the motion of driving part, new design ideas are generated. With this model, a series of new design ideas derived from the seeds idea can be achieved.
A patented double-ring-plate gear reducer was designed and its dynamic performance was simulated. One unique characteristic of this novel drive is that the phase angle difference between two parallelogram mechanisms is a little less than 180 degree and four counterweights on two crankshafts are designed to balance inertia forces and inertia moments of the mechanisms. Its operating principle, advantages, and design issues were discussed. An elasto-dynamics model was presented to acquire its dynamic response by considering the elastic deformations of ring-plates, gears, bearings, etc. The simulation results reveal that compared with housing bearings, planetary bearings work in more severe conditions. The fluctuation of loads on gears and bearings indicates that the main reason for reducer vibration is elastic deformations of the system rather than inertia forces and inertia moments of the mechanisms.
