Siemens SINUMERIK 840D sl Function Manual page 901

Example:
On a machine, the rotary axis of the table points in the positive Y direction. The table is
rotated by +45 degrees. PAROT defines a frame, which similarly describes a rotation of 45
degrees about the Y axis. The coordinate system is not rotated relative to the actual
environment (marked in the figure with "Position of the coordinate system after TCARR"), but
is rotated by -45 degrees relative to the defined coordinate system (position after PAROT). If
this coordinate system is defined with ROT Y-45, for example, and if the toolholder is then
selected with active TCOFR, an angle of +45 degrees will be determined for the rotary axis of
the toolholder.
Language command PAROT is not rejected if no orientational toolholder is active. However,
such a call then produces no frame changes.
Machining in direction of tool orientation
Particularly on machines with tools that can be oriented, traversing should take place in the
tool direction (typically, when drilling) without activating a frame (e.g., using TOFRAME or
TOROT), on which one of the axes points in the direction of the tool. This is also a problem if,
when carrying out oblique machining operations, a frame defining the oblique plane is active,
but the tool cannot be set exactly perpendicularly because an indexed toolholder (Hirth tooth
system) prevents free setting of the tool orientation. In these cases it is then necessary -
contrary to the actually requested motion perpendicular to the plane - to drill in tool direction,
as the drill would otherwise not be guided in the direction of its longitudinal axis, which
among other things would lead to breaking of the drill.
The end point of such a motion is programmed with MOVT= ....
The programmed value is effective incrementally in the tool direction as standard.
The positive direction is defined from the tool tip to the tool adapter. The content of MOVT is
thus generally negative for the infeed motion (when drilling), and positive for the retraction
motion. This corresponds to the situation with normal paraxial machining, e.g., with G91 Z
....
Instead of MOVT= ... it is also possible to write MOVT=IC( ...) if it is to be plainly visible
that MOVT is to function incrementally. There is no functional difference between the two
forms.
If the motion is programmed in the form MOVT=AC( ...), MOVT functions absolutely.
In this case a plane is defined, which runs through the current zero point, and whose surface
normal vector is parallel to the tool orientation. MOVT then gives the position relative to this
plane (see figure). The reference plane is only used to calculate the end position. Active
frames are not affected by this internal calculation.
Basic logic functions: Axes, coordinate systems, frames (K2)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.4 Frames
117