  Feedrate scheduling is a key step in computer numerical control (CNC)
machining, as it has a close relationship with machining time and surface
quality, and has now become a hot issue in industry and academia. To reduce
high chord errors and round-off errors, and generate continuous velocity,
acceleration, and jerk profile of parametric interpolation, a novel and
complete S-shape based feedrate scheduling algorithm is presented in this
paper. The algorithm consists of three modules: bidirectional scanning module,
velocity scheduling module and round-off error elimination module. The
bidirectional scanning module with the limitations of chord error, normal
acceleration/jerk and command feedrate aims to guarantee the continuity of the
feed rate at the junctions between successive NURBS sub-curves. After the NURBS
sub-curves have been classified into two cases, the velocity scheduling module
firstly calculates the actual maximum federate, and then generates the feed
rate profiles of all NURBS sub-curves according to our velocity scheduling
function. Later, the round-off error elimination module is proposed to make the
total interpolating time become an integer multiple of the interpolation
period, which leads to the elimination of round-off errors. Finally, benchmarks
are conducted to verify the applicability of the proposed method compared with
some other methods.
