(Common to Power Mate i–D and –H)
4. INTERPOLATION FUNCTIONS
Before G12.1 is specified, a local coordinate system (or workpiece
coordinate system) where the center of the rotary axis is the origin of the
coordinate system must be set. In the G12.1 mode, the coordinate system
must not be changed (G92 relative coordinate reset etc.).
Tool length offset must be specified in the polar coordinate interpolation
cancel mode before G12.1 is specified. It cannot be
specified in the polar coordinate interpolation mode. Furthermore, no
offset values can be changed in the polar coordinate interpolation mode.
Polar coordinate interpolation converts the tool movement for a figure
programmed in a Cartesian coordinate system to the tool movement in the
rotation axis (C–axis) and the linear axis (X–axis). When the tool moves
closer to the center of the workpiece, the C–axis component of the
feedrate becomes larger and may exceed the maximum cutting feedrate
for the C–axis (set in parameter (No.1422)), causing an alarm (see the
figure below). To prevent the C–axis component from exceeding the
maximum cutting feedrate for the C–axis, reduce the feedrate specified
with address F or create a program so that the tool does not move close
to the center of the workpiece.
L :Distance (in mm) between the tool center and workpiece center when the tool center is the nearest to the
R :Maximum cutting feedrate (deg/min) of the C axis
Then, a speed specifiable with address F in polar coordinate interpolation can be given by the formula below.
Specify a speed allowed by the formula. The formula provides a theoretical value; in practice, a value slightly
smaller than a theoretical value may need to be used due to a calculation error.
Consider lines L1, L2, and L3. ∆X is the distance the tool moves per time unit at
the feedrate specified with address F in the Cartesian coordinate system. As the
tool moves from L1 to L2 to L3, the angle at which the tool moves per time unit
corresponding to ∆X in the Cartesian coordinate system increases fromθ1 to θ 2
In other words, the C–axis component of the feedrate becomes larger as the tool
moves closer to the center of the workpiece. The C component of the feedrate
may exceed the maximum cutting feedrate for the C–axis because the tool
movement in the Cartesian coordinate system has been converted to the tool
movement for the C–axis and the X–axis.
F < L × R ×
Coordinate system for
the polar coordinate
Tool length offset
Cutting feedrate for the