## 1 Introduction
The global curve-fitting method applied to five-axis linear-segment toolpath can ensure toolpath smoothness, but the fitting error is hard to control and evaluate [22; 23]. Moreover, the global curve-fitting method usually synchronizes two trajectories by sharing the same curve parameter (parameter synchronization). The parameter synchronization method [22; 23] plans the tool-tip trajectory according to translational motion constraints and then makes the tool orientation follow the tool-tip in the curve parameter space. However, if the tool orientation is merely parameter synchronized with tool-tip position, the rotary motion may be discontinuous at certain locations. After path smoothing and synchronization, the geometric information of toolpath is transferred to the feedrate, acceleration (the change rate of feedrate) and jerk (the change rate of acceleration) trajectories in CNC system [24]. The toolpath with high-order continuity can raise the feedrate at the sharp corner, decline the fluctuation of feedrate and acceleration, thus improve the machining quality. Many feedrate scheduling methods have been proposed in the literature, including the jerk-limited method [25; 26; 27], the optimization method [28], the linear programming method [29; 30; 31], and the time-synchronization method [32]. [PERSON] et al. [25] present a complete S-shape feedrate scheduling approach (CSFA) with limited jerk, acceleration and feedrate for the three-axis parametric toolpath. [PERSON] et al. [28] propose a Velocity Profile Optimization (VPOp) algorithm which has been implemented for various toolpath format. [PERSON] et al. [29] reduce the velocity planning problem to an equivalent linear programming problem with polynomial computational complexity O(N3.5) to find the optimal solution. [PERSON] et al. [32] advise a real-time feed scheduling method for five-axis machining by simultaneously planning linear and angular trajectories (SLATP) considering axial kinematic constraints. For path smoothing, the global curve-fitting method has difficulty in controlling fitting error and the local corner-smoothing method has large curvature extreme which decreases nominal velocity in feedrate scheduling. For path synchronization, the parameter synchronization method cannot guarantee smooth rotary motion. With the aim of resolving these problems, a double B-spline curve-fitting and synchronization-integrated feedrate scheduling method for five-axis linear-segment toolpath is presented in this paper. Two cubic B-spline curves are used for fitting the tool-tip position and tool orientation respectively. The data points are initially fitted by a B-spline curve and then the curve segments exceeding the fitting tolerance are locally refined to get the final curve. After curve-fitting, synchronization and feedrate scheduling is required to guarantee smooth motion and machining efficiency. Feedrate scheduling of the tool-tip position is conducted first to address the axial kinematic constraints. Then the feedrate of the tool orientation is deformed to share the same motion time with the tool-tip position so that the tool-tip position and tool orientation arrive at specific locations simultaneously. The rest of the paper is organized as follows. The fitted curves for tool-tip position and tool orientation under fitting tolerance are generated in Section 2. The synchronization and feedrate scheduling of the tool-tip position and tool orientation are implemented in Section 3. Simulations and experiments are carried out in Section 4 to demonstrate the feasibility and effectiveness of the proposed method. Conclusions are drawn in Section 5.