The Research On Three-axis CNC Machining Feedrate Scheduling Based On The Feedrate Restricted Intervals Identification With Sliding Arc Tube

In high-speed and high-precision CNC machining,the time-optimized and smooth feedrate profile plays a significant role in improving the machining efficiency and quanlity under the constraint of specific tolerance.In order to alleviate the fluctuations in the feedrate with the conventional motion planning,a feedrate scheduling method for three-axis CNC machining based on the Feedrate Restricted Intervals(FRIs)identification with Sliding Arc Tube is proposed in this thesis.Because of the real-time requirement of Computer Numerical Control(CNC)in the machining process,FRIs identification on G01 blocks normally relies on limited local information.As the most effective and intuitive information to be the criterion for FRIs identification,discrete curvatures of CL points are difficult to be precisely estimated,which causes inaccurate FRIs identification.To address this problem,a Sliding Arc Tube(SAT)scheme is proposed in this thesis.With the proposed SAT,the FRIs can be precisely identified,and the improper acceleration and deceleration can be alleviated in this way.A statistic based determination method on G01 block feedrate scheduling parameters is proposed,which can easily determine the optimal machining parameters of a variety of parts.The optimal length and angle distribution models of G01 blocks are determined iteratively firstly.Then three G01 block feedrate scheduling parameters are calculated according to the distribution models.The three parameters are the values of the G01 block length upper limit,the lower limit and the smallest smoothing angle respecively,and they will be improtant criteria in the FRIs identification.A SAT based FRI identification method is proposed to solve the problem that FRIs would be unprecisely only with the discrete curvatures of CL points.SAT is a sliding arc-shape tube.Firstly,the continuous G01 block region are identified with the determined three parameters.Then FRIs in the continuous G01 block region are identified with the repeated processes of initialization,tube-shaping,tube-sliding and tube-blocked of SAT on the tool path.Finally,the feedreate profile is scheduled with 5-phase jerk-limited S-shape for each FRI.Simulation and real machining experiments are conducted and the results validate that,the three important parameters of G01 blocks can be calculated reasonably with the proposed statistic based determination method;the FRIs can be precisely and efficiently identified with the SAT,which alleviates the improper acceleration and deceleration of machine tool and improves the machining quality.