The SSV3 version of the APT4 + Sculptured Surfaces System has a new
facility for checking for possible interference of ball-ended, corner
radius and flat-ended cutters with a parametric surface during regional
milling and taking appropriate action to avoid gouging. In addition an
APT3 type GOUGCK facility similar to that provided in the Arelem has
been added to regional milling. Note that these facilities are
currently only available when using the regional milling commands SCON
and SMIL and not with the isoparametric milling command GOLOFT.
Also the full APT seven segment cutter has been implemented in regional
milling and additional tool axis control provided with SCON/AXIS.
The interference checking process is a two stage algorithm that is
performed each time a new cutter position is computed. The first step is
to identify all patches of the surface where there is a possibilty of
penetration occuring, this is a non-iterative process; the second step
is to check for actual interference with each of these candidate
patches, perforce this is an iterative procedure. Every effort has been
made to speed up the iteration, for example by taking the results of the
iterative process at the previous cutter location as start values for
the current position.
Interference checking in regional milling is selected or cancelled by
using the command:
CHKSRF/ › PS,ON ! › ,surface_name,ON !
OFF 1 OFF
PS check for interference with current part surface.
surface_name check for interference with a named surface.
ON switches interference checking on.
OFF cancels interference checking.
Note that only CHKSRF/PS,... is currently implemented. The additional
couplets have been provided for possible future extension to check for
interference with adjacent surfaces.
o CHKSRF/PS,ON will initiate interference checking.
All subsequent cutter locations within regional milling will be tested
and should penetration occur the maximum will be located and
documented on the verification listing as follows:
TE = x , y , z TA = i , j , k
WORST PENETRATION = penmax AT PATCH = pnum U = u V = v
TE and TA are the tool end coordinates and tool axis vector;
penmax is the worst penetration detected;
pnum , u and v are the ppatch number, u and v parameters of the
point on the surface at which the worst penetration occured;
If an avoidance strategy has been specified (see section 15.2),
appropriate action will be taken to avoid the penetration and a
further check made to ensure no new penetration has occured.
If the interference is successfully avoided the message 'INTERFERENCE
AVOIDED' will be output, if not warning no: 3555 'UNABLE TO AVOID
INTERFERENCE WITH CURRENT PARAMETERS' will be output to the
Optionally, details of the avoidance action taken or attempted may
also be printed on the verification listing (see section 15.3).
INTERFERENCE AVOIDED BY LIFTING OFF BY dist PARALLEL TO TA
INTERFERENCE AVOIDED BY PITCHING THROUGH n DEGREES AND LIFTING OFF BY
dist NORMAL TO PS
UNABLE TO FIND TOOL AXIS ORIENTATION WITHIN SELECTED RANGE
WHERE TOOL CAN BE POSITION IN NON_INTERFERING CONTACT WITH SURFACE
R = x , y , z NPAT = pnum U = u V = u ( details of surface point)
TOOL RADIUS GT RADIUS OF CURVATURE AT
...... details of surface point .....
as can be seen the message output have been designed to give as much
useful information as possible.
Occasionally, when the curvature of the surface around the point of
penetration is almost the same as the curvature of the corresponding
point on the tool, the iterative procedure will not converge within
the limits set. In this case the following message will be printed on
the verification listing,
PENETRATION DETECTED WITHOUT CONVERGENCE
PENMAX = penmax
After all the candidate patches have been examined, the worst
penetration will be selected, from all those detected including those
where convergence did not occur. In most cases this will result in
the avoidance procedures being able to successfully avoid the
interference, however if penetration still occurs then warning number
3555 will be output, preceded by a message indicating what action was
attempted if the optional avoidance action logging has been requested.
o CHKSRF/PS,OFF will cancel interference checking.
***** Note that invoking interference checking will significantly *****
***** increase the processing time. *****
The strategy(ies) to be employed to avoid interference if penetration of
the tool into the part surface is detected may be selected by the
› (AXIS )!
AVCTRL/( ON )
( OFF )
CUTANG indicates that automatic variation of the tool axis
should be used as the primary method to avoid
interference. This will be applied as either a
'roll' or 'pitch' dependent on the location of the
point of maximum penetration with respect to the
tool contact point.
A 'pitch' angle will be in the plane defined by the
programmed tool axis and the local forward motion
direction, positive being in the direction of
A 'roll' angle will be in the orthogonal plane
through the tool axis, positive being in the
direction of the vector = TA x FWD
CONST,g defines a fixed 'technological' angle which will be
added to the computed angular variation of the tool
axis in order to clear the surface.
RANGE,bmin,bmax defines the algebraic limits within which the tool
axis can be varied from the programmed (i.e. ideal)
NORMPS specifies lift off normal to the part surface.
AXIS specifies lift off parallel to the tool axis.
›This is the default lift off and will be applied
if no secondary action is specified and tilting is
unsucessful in avoiding penetration!
LIMIT,distance specifies a limit to the permitted lift off.
›Default = MAXDP!
ON either reinstates an avoidance strategy temporarily
disabled or invokes the default lift off AXIS.
OFF disables the avoidance strategy but interference
data will still be logged on the listing.
Details of the avoidance action taken or attempted can be optionally
printed or inhibited by the command,
This is an extension to the existing PRINT command and may be used as an
additional couplet in a manner similar to SSPRT and SSTEST.
AVPRT/ON details of avoidance action will be listed on the
verification listing, following the notification of
AVPRT/OFF inhibits the printing of the avoidance action details
but the messages indicating if interference has been
avoided or not will still be printed.
PARTNO/'SIMPLE EXAMPLE DEMONSTRATING INTERFERENCE CHECKING'
CUTTER/10,2 $$ CORNER RADIUS CUTTER
CHKSRF/PS,ON $$ INVOKE INTERFERENCE CHECKING
AVCTRL/CUTANG,CONST,2,RANGE,-90,90,AXIS $$ SPECIFY AVOIDANCE ACTION
$$ 1) TILT TOOL
$$ WITH 2 DEG. CLEARANCE
$$ WITHIN + 90 DEG OF TA
$$ ( TA = VECTOR/0,0,1 )
$$ 2) UNLIMITED LIFT OFF
$$ PARALLEL TO TOOL AXIS
PRINT/AVPRT,ON $$ DOCUMENT AVOIDANCE ACTION
SCON/DS,DC1,PARAM,0,1,AT,VP $$ GUIDE CURVE
SCON/PS,TO,INTSS1,PLUS,0 $$ PART SURFACE
The full APT 7 segment cutter has been implemented in regional milling
and has the following effects. The diagrams below show the tool end
point TE that is calculated given the various combinations of
SCON/PS,... and SCON/DS,... and tool axis vector TA.
For the TLOFPS, TLAT condition,
For the TLOFPS,TLON condition,
Tool control point is TEB the
effective tool end of a
spherical cutter with radius
equal to the corner radius of
the actual cutter.
For the TLONPS,TLON and TLONPS,TLAT conditions,
Additional tool axis control has been provided in regional milling,
still programmed using the SCON/AXIS command.
SCON/AXIS,ATANGL, DS,a,CUTANG, ›, LEAD ! ,b
PS › LAG !
DS indicates that the tool axis is controlled with
respect to the guide surface.
PS indicates that the tool axis is controlled with
respect to the part surface.
ATANGL,...,a indicates the 'roll' angle a (in degrees) that is
to be maintained between the tool axis and the
controlling surface normal.
In the case of PS control this will be in the
plane perpendicular to the motion direction FWD,
(where FWD is projected onto the part surface
tangent plane). A positive angle will be CCLW
Note: If ZIGZAG motion is operative the 'roll'
will always be applied in the same sense as on
the first pass, i.e. a will change from being
CCLW to CLW about the motion direction on
In the case of DS control this will be in the
plane defined by the tool axis and the guide
surface step-over direction or guide curve
Values of a with absolute values greater than 90
will have the effect of 'inverting' the surface
CUTANG,b indicates the 'pitch' angle b (in degrees) that
is to be maintained between the tool axis and the
controlling surface normal in the direction of
motion. Positive will be in the direction of
LEAD tilt tool axis in the motion direction for a
LAG tilt the tool axis backwards for a positive b.
An APT3 type GOUGCK facility has been added to regional milling. This
causes a check to be made on each cut vector computed to ensure that
gouging with the point of contact does not occur because either there is
a very rapid change in the surface curvature and thus the computed
stepout although OK for curvature at initial point is too large, or
where the point of contact on the tool changes significantly caused by a
change of sign of the cross product of the surface normal and the tool
axis. The effect will be to generate addition cut vectors.
GOUGCK/ON will invoke gouge checking in both the Arelem and
GOUGCK/OFF will cancel all gouge checking.