A novel 5-DOF PMT (Parallel Machine Tool) is proposed, which has five driving limbs and a passive limb. It can perform three translational DOFs (degrees of freedom) and two rotational DOFs. The passive limb can act as not only a constraint chain, but also a measuring chain. Multi-axis simultaneous control must be performed and the mapping transformation of motion from the virtual to actual axis is the core of the control algorithms. The control algorithms, such as coarse interpolation of the tool path, the mapping transformation from the CL (cutter location) data to the length of driving axis, velocity control of the driving axis and pose measuring method of the tool, are analyzed in detail. The CNC system software based on the algorithms has been developed and applied to the novel 5-DOF PMT in our laboratory. The machining experiments are made and the better machining performance is achieved. Index Terms -PMT 5-DOF path control pose measuring
To improve control performance of parallel manipulator, servo control is optimized according to 2-DOF control with Internal Model Control. Position loop of the controller is redesigned based on the original current loop and speed loop. The hybrid force/position control strategy on the basis of cross-coupling is proposed. With mechatronic cosimulation system, it is proved that the force/position hybrid control on the basis of 2-DOF Internal Model Control has better stability and position precision compared with the traditional PID control. The control precision and stability of the parallel manipulator are improved effectively in actual experiment. Two types of compliance operation including peg in hole and surface tracking are realized in 6PUS-UPU parallel manipulator and both have good applicable effect.
AbstractˉIn high-speed machining process, in order to improve the machining accuracy, the velocity should be optimized flexibly in advance. The s-curve acceleration and deceleration control mode was more used in velocity control than others. Based on the essential principle of the s-curve acceleration and deceleration control mode, the pre-interpolation acceleration and deceleration control was adopted to work out the relevant motional parameters of different program blocks. Using the look-ahead method, the adaptive acceleration and deceleration was introduced to evaluate the data far in advance and adjust the feed rate. The adaptive velocity control method is simulated and the result shows that the velocity curve is smoother and the machining time is shorter than traditional method. The velocity control of NC machining is solved effectively and the machining accuracy and productivity will be improved greatly. Index Terms -Computerized Numerical Control system; Scurve acceleration/deceleration; adaptive control( )°°°°°°°°® − − = J J J J t J J JT JT J J JT JT J t A
This article presents a derivation of the stiffness matrix of a general redundantly actuated parallel mechanism based on the overall Jacobian. The Jacobian of the constraints and actuations is derived using reciprocal screw theory. Based on the mapping relationship between constraint, actuated and external forces combined with the principle of virtual work, a compatibility equation for the deformation of all of the limbs is achieved, and the stiffness model of the general redundantly actuated parallel mechanism is derived. The 5-UPS/PRPU redundantly actuated parallel machine tool is used to illustrate this method. The parallel machine tool comprehensively reveals the effect of the elastic deformation of activepassive joints and some basic transmission parts. The stiffness model is further validated by experimental data. Moreover, the global stiffness matrix of the general redundantly actuated parallel mechanism can be separated into two parts via matrix decomposition. The first part is the stiffness matrix of the corresponding non-redundant parallel mechanism, and the second part is the stiffness matrix of the redundantly actuated limbs (actuators). The redundantly actuated 5-UPS/PRPU parallel machine tool is also investigated for further analysis. The different stiffness characteristics of the machine tool and its corresponding non-redundant 5-UPS/PRPU parallel machine tool are compared. Actuation redundancy is found to improve the stiffness performance of the machine tool efficiently.
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