Siemens SINUMERIK 828D Function Manual page 784

K2: Axis Types, Coordinate Systems, Frames
10.5 Frames
MD20184 $MC_TOCARR_BASE_FRAME_NUMBER
can also be used.
As with the note made in the description of the table offset, the second alternative here is not recommended for
use with new systems.
The rotation component of the part frame can be deleted with PAROTOF , independently of whether this frame is
found 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 orientational 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 oblique 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 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 Functions
784
Function Manual, 09/2011, 6FC5397-0BP40-2BA0