Siemens SINUMERIK 840D sl Function Manual page 772

K2: Axis Types, Coordinate Systems, Frames
10.5 Frames
The rotation component of the part frame can be deleted with PAROTOF, irrespective of whether
this frame is in a basic or a system frame.
The translation component is deleted when a toolholder which does not produce an offset is
activated or a possibly active orientable toolholder is deselected with TCARR=0.
PAROT or TOROT take into account the overall orientation change in cases where the table or
the tool are oriented with two rotary axes. With mixed kinematics, only the corresponding
component caused by a rotary axis is considered. It is thus possible, for example, when using
TOROT, to rotate a workpiece such that an inclined plane lies parallel to the XY plane fixed in
space, whereby rotation of the tool must be taken into account in machining where any holes
to be drilled, for example, are not perpendicular to this plane.
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
around 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 orientable 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 inclined machining operations, a frame defining the inclined 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 motion actually requested perpendicular to the plane - to drill in the tool direction,
as the drill would otherwise not be guided in the direction of its longitudinal axis (tool breaks).
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.
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Function Manual, 01/2015, 6FC5397-0BP40-5BA2
Basic Functions