Siemens SINUMERIK 840D sl Function Manual page 247

vector of zero length (all three components are zero) is ignored, i.e. the direction programmed
beforehand remains valid, no alarm is generated.
If only the start vector is programmed (A4, B4, C4) in a block, then the programmed surface
normal vector remains constant over the entire block. If only the end vector is programmed (A5,
B5, C5), then large-circle interpolation is used to interpolate between the end value of the
preceding block and the programmed end value. If both start and end vectors are programmed,
interpolation according to the large circle principle is also performed between the two
directions. The fact that the start vector may be reprogrammed in a block means that the
direction of the surface normal vector can change irregularly on a block transition. Irregular
transitions of the surface normal vector always occur in cases where there is no tangential
transition between the surfaces (planes) involved, i.e. if they form an edge.
Once a surface normal vector is programmed, it remains valid until a new vector is
programmed. In the basic position, the surface normal vector is set to equal the vector in the Z
direction. This basic setting direction is independent of the active plane (G17 - G19). If ORIWKS
is active, surface normal vectors refer to the active frame, i.e. when the frame is rotated, the
vectors rotate simultaneously. This applies both to programmed orientations and to those that
have been derived from the active plane. If ORIWKS is active, the surface normal vectors are
brought along during a frame change. An orientation modified as the result of frame rotations
is not returned to its original state on switchover from ORIWKS to ORIMKS.
It must be noted that the programmed surface normal vectors may not necessarily be the same
as those used internally. This is always the case if the programmed surface normal vector is not
vertical on the path tangent. A new surface normal vector is then formed, which lies within the
plane spanned by the path tangent and programmed surface normal vector, but which is
vertical on the path tangent vector. This orthogonality is required, because the path tangent
vector and the surface normal vectors (must) always be vertical to one another in a real surface.
However, since the two variables can be programmed independently of one another, they can
contain information that is mutually contradictory. Orthogonalization ensures that the
information contained in the path tangent vector has priority over the data in the surface normal
vector. An alarm is output if the angle between the path tangent vector and the programmed
surface normal vector undershoots the limit value, which is defined in the following machine
data:
MD21084 $MC_CUTCOM_PLANE_PATH_LIMIT (minimal angle between surface normal
vector and path tangent vector)
If a block is shortened (inside corner), then the interpolation range of the surface normal vector
is reduced accordingly, i.e. the end value of the surface normal vector is not reached as it would
be with other interpolation quantities such as, for example, the position of an additional
synchronized axis.
In addition to the usual methods of programming orientation, it is also possible to refer the tool
orientation to the surface normal vector and path tangent vector using the addresses LEAD
(lead or camber angle) and TILT (side angle). Interpretation of the angle specifications is thus
dependent on the setting in MD21094 $MC_ORIPATH_MODE (see Function Manual
"Transformations", Section "Multi-axis transformations"). The specification of the angle relative
to the surface normal is only an expanded option of orientation programming at the end of the
block. It does not imply that the lead and side angles reach their programmed values before the
path end point is reached.
The resulting tool orientation is determined from the path tangent, surface normal vector, lead
angle and side angle at the end of the block. This orientation is always implemented by the end
of the block, particularly in cases where the block is shortened (at an inside corner). If the
omitted path section is not a straight line in a plane, the lead and side angles generally deviate
Tools
Function Manual, 06/2019, A5E47435126B AA
W5: 3D tool radius compensation
3.1 Function
247