STEP-NC AP238
Overview of Technical
Corrigendum
STEP Tools, Inc.
14 First Street, Troy, NY 12180
(518) 687-2848 / (518) 687-4420 fax
http://www.steptools.com
What is a Technical Corrigendum?
STEP Tools, Inc.
• A TC is a small set of change pages that correct
issues discovered after publication.
– Up to 2 TCs allowed, then must publish a new edition
• The AP238 TC draft has circulated since April
– Addresses issues discovered during past year of testing in
Ibusuki, Dallas, Sandviken, and Hartford rounds.
© Copyright 2008 — STEP Tools, Inc.
Slide 2
Corrigendum Contents
STEP Tools, Inc.
• Current issues addressed by TC
–
–
–
–
–
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Via points for better High-Speed Machining (HSM) support.
Cross section parameters for Feed Speed optimization.
Touch_probe as a real tool.
Datum and Datum_target reference to workpiece
Using workpieces for In-process geometry
Various grammar fixes and clarifications to the text.
• Potential items for TC
–
–
–
–
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Curve probing operation
Toolpath placement on Workplan
Simplify rawpiece/finshed piece
Enable/Disable?
others?
© Copyright 2008 — STEP Tools, Inc.
Slide 3
Via Points for HSM Size Reduction
STEP Tools, Inc.
• High Speed Machining toolpaths use many arcs.
– Requires several entities to represent arcs as trimmed curves,
(composite curve, composite curve segment, trimmed curve,
circle, axis placement, several directions and cartesian points)
– This is multiplied over several tool curves (basis, tool axis,
surface normal, speed profile)
• Describe using via points following approach
used by STEP kinematics model.
– Continue to use polylines with addition of cartesian point
subtype via_arc_point.
– Subtype for via_helix_point also added.
– Previous method can still be used for other types of curve.
© Copyright 2008 — STEP Tools, Inc.
Slide 4
Via Points for HSM Size Reduction
STEP Tools, Inc.
• Verified by Bordeaux HSM tests in March 2008.
• Measurements for Fishhead HSM Program
– Contains part geometry, tolerances and tool paths
– Old: 1.9 MB
– New: 1 MB
For comparison:
Mastercam 9 is 3.5 MB
G code is 0.574 MB
© Copyright 2008 — STEP Tools, Inc.
Slide 5
AIM EXPRESS Definitions
STEP Tools, Inc.
ENTITY via_arc_point
SUBTYPE OF (cartesian_point);
WHERE
WR1: SIZEOF(USEDIN(SELF, ‘POLYLINE.POINTS')) > 0;
WR2: (0 = SIZEOF (QUERY (pl <*
USEDIN(SELF, 'POLYLINE.POINTS') |
((pl.points[1] = SELF) OR
(pl.points[HiIndex(pl.points)] = SELF))
)));
END_ENTITY;
ENTITY via_helix_point
SUBTYPE OF (cartesian_point);
WHERE
WR1: SIZEOF(USEDIN(SELF, 'POLYLINE.POINTS')) > 0;
WR2: (0 = SIZEOF (QUERY (pl <*
USEDIN(SELF, 'POLYLINE.POINTS') |
((pl.points[1] = SELF) OR
(pl.points[HiIndex(pl.points)] = SELF))
)));
END_ENTITY;
© Copyright 2008 — STEP Tools, Inc.
Slide 6
Cross-Section Parameters
STEP Tools, Inc.
• Add a curve to toolpath that gives a
parameterized description of removal cross
section at each point.
– Tested initial set of parameters in March
– Addressed side milling
• Since March
– Parameters for plunge milling have been proposed
– Worked on harmonizing the parameters for milling and turning
and handling both side and plunge milling.
– Adjusted profile origins and parameter defs.
© Copyright 2008 — STEP Tools, Inc.
Slide 7
Cross Section Parameters
© Copyright 2008 — STEP Tools, Inc.
STEP Tools, Inc.
Slide 8
Cross-Section Parameters
STEP Tools, Inc.
• Current milling turning parameters handled by a
bounded curve.
– Same structure as tool position, axis, surface normal curves.
– Seven dimensions (ADmax, RDmax, Xmaxofs, Ymaxofs,
CSArea, XCGofs, YGCofs)
ENTITY trajectory
ABSTRACT
SUPERTYPE OF (ONEOF(cutter_location_trajectory,
cutter_contact_trajectory, axis_trajectory))
SUBTYPE OF (toolpath);
[ . . . ]
cross_section_area_flank_parameters:
OPTIONAL bounded_curve; -- ADDED BY TC
cross_section_area_plunge_parameters:
OPTIONAL bounded_curve; -- ADDED BY TC
END_ENTITY;
© Copyright 2008 — STEP Tools, Inc.
Slide 9
Parameters for Turning
STEP Tools, Inc.
• Cross-Section Origin for Turning Tools
– As documented, milling and turning parameters are measured
relative to the tool.
– Proposal to measure turning parameters relative to the
workpiece origin.
Y
Parameters
measured from
workpiece or tool?
X
© Copyright 2008 — STEP Tools, Inc.
Slide 10
Turning Parameters
STEP Tools, Inc.
• Origin on workpiece was driven by confusion
over a good origin point on the tool
– Origin on the tool is still preferred.
– Investigate ISO 14649-112 for existing discussion of tool origin
– Also see what ISO 13399 has to say about origin.
© Copyright 2008 — STEP Tools, Inc.
Slide 11
Parameters for Plunge Milling
STEP Tools, Inc.
• Plunge milling parameters have been proposed
– Use angular values rather than linear
• Issues
– Should they use linear parameters for consistency?
– Should these parameters be in a separate optional curve?
CSA
Feed (-Z)
Y
Feed (-Z)
Y
CG
ADmax
ACG offset
Coordinate
Origin (0, 0)
Amax offset
(step-over
X direction)
Rmax offset
Coordinate
Origin (0,
0)
RCG offset
X
RDmax
© Copyright 2008 — STEP Tools, Inc.
Slide 12
Touch Probe as a Real Tool
STEP Tools, Inc.
• ARM for touch probe changed so that probe is a
subtype of tool.
– Previously was a stand-alone stub.
– Simplifies use because software can handle probes in the
same way as other tools.
– Enables a connection between a probe and its shape geometry.
Previously, there was none.
– Change requires minor AIM mapping adjustments to
touch_probe and probing operations.
– Open to proposal for additional probe characteristics
neccesary to operate them effectively.
ENTITY touch_probe
SUBTYPE OF (machining_tool);
its_id: identifier;
END_ENTITY;
-- ADDED BY TC
See curve_probing.txt
© Copyright 2008 — STEP Tools, Inc.
Slide 13
Datum and Datum Target
STEP Tools, Inc.
• ARM for Datums and Datum Targets changed to
add Workpiece reference
– Datums and Datum Targets both link to a workpiece at the AIM
level, but there is no reference in the ARM model.
– Now more in line with features
ENTITY Datum
ABSTRACT SUPERTYPE;
its_workpiece: Workpiece;
END_ENTITY;
ENTITY Datum_target;
id : STRING;
its_workpiece: Workpiece;
END_ENTITY;
© Copyright 2008 — STEP Tools, Inc.
-- ADDED BY TC
-- ADDED BY TC
Slide 14
Workpieces for In-process Geometry
STEP Tools, Inc.
• Change in-process geometry from just shape_rep
reference to full workpiece reference
– No burden, any shape rep made by a CAD system is already
part of a workpiece/product.
– Allows in-process to have full range of product properties,
such as features and tolerances.
– Simplify by moving as-is, to-be, and removal links to supertype
» Was three separate sets of properties on Workplan,
Machining_workingstep, and Turning_workingstep.
» Move up to Executable so it can be used anywhere.
ENTITY executable
ABSTRACT SUPERTYPE OF (ONEOF( workingstep, nc_function,
program_structure));
its_id:
identifier;
as_is:
OPTIONAL Workpiece; -- ADDED BY TC
removal: OPTIONAL Workpiece; -- ADDED BY TC
to_be:
OPTIONAL Workpiece; -- ADDED BY TC
END_ENTITY;
© Copyright 2008 — STEP Tools, Inc.
Slide 15
Proposal: Curve Probing
STEP Tools, Inc.
See curve_probing.txt
• Motivation
– New devices are becoming available that can measure curves
– STEP-NC data contains many bounded curves (tool paths) that
can be measured
– Applications like the Impeller can be evaluated using bounded
curves on the surface
ENTITY curve_probing
SUBTYPE OF (touch_probing);
curve_to_be_measured
: bounded_curve;
start_position
: OPTIONAL axis2_placement_3d;
start_direction
: OPTIONAL direction;
distance
: OPTIONAL length_measure;
curve_axis
: OPTIONAL bounded_curve;
as_measured_curve
: OPTIONAL bounded_curve;
as_measured_normal
: OPTIONAL bounded_curve;
its_technology:
: OPTIONAL technology;
path_maximum_deviation : OPTIONAL bounded_curve;
-- its_probe??
END_ENTITY
© Copyright 2008 — STEP Tools, Inc.
Slide 16
Proposal: Toolpath Xform on Workplan
STEP Tools, Inc.
• Motivation
– Transform is already possible on individual workingstep
– Adding transform to workplan allows more significant reuse.
– Transform moves toolpaths from all workingsteps or nested
workplans at once.
– Could result in a stack of transforms for nested workplans.
– Result: ADD
ENTITY workplan
SUBTYPE OF (program_structure);
its_elements: LIST[0:?] OF executable;
[ . . .]
toolpath_orientation: OPTIONAL axis2_placement_3d; -ADD?
END_ENTITY;
© Copyright 2008 — STEP Tools, Inc.
Slide 17
Proposal: Simplify Raw/Finished Part
STEP Tools, Inc.
• Motivation
– Now that as-is and to-be descriptions are workpieces, what is
the difference between
» The as-is workpiece of the main workplan and a rawpiece
» The to-be workpiece of the main workplan and a finished
part?
– Can we simplify the rawpiece/finished piece relationship by
removing it as a workpiece attribute and using the workplan
instead?
– Current understanding on next slide.
© Copyright 2008 — STEP Tools, Inc.
Slide 18
Current Scoping
STEP Tools, Inc.
• Every executable may have an as-is, to-be, delta
and fixture model.
• When an executable is selected the as-is model,
to-be model, delta model and fixture model are
determined using the following scoping rules:
– The models defined for this executable
– The model defined for the workplan containing this executable,
or the workplan containing that workplan, and so on until the
main workplan is found
– If no model is found then do not show a model for the as-is, tobe, delta or fixture.
• Project may have a list of workpieces. These are
the pieces produced by the project.
• A workpiece may have a rawpiece. The rawpiece
defines the original starting state (stock) for this
workpiece at the beginning of the main workplan.
© Copyright 2008 — STEP Tools, Inc.
Slide 19
Proposed Scoping
STEP Tools, Inc.
• Main workplan
– as-is workpiece describes the state of the material at the start
of the workplan (what we have been calling stock)
– to-be workpiece describes the state of the material at the end
of the workplan (what we have called “workpiece”, finished
part, or often just “part”)
• Any nested workplans or workingsteps
– as-is/to-be can be specified to give additional detail/granularity,
and give intermediate forms.
• Project list of workpieces
– Workpieces that the project makes (the final deliverables)
– May be more than just the to-be of the main workplan because
sub workplans may produce finished parts included here.
• Workpiece “rawpiece” attribute
– Initial state of this workpiece before any machining.
© Copyright 2008 — STEP Tools, Inc.
Slide 20
Proposal: Enable/Disable Executable
STEP Tools, Inc.
• Add an attribute to store the enabled/disabled
state of an executable.
– Current state is not saved, so everything is enabled whenever
you read a file.
– Making it part of the model would allow us to put disabled
alternates into the file.
– Separate issue with Locking executables to disallow any
change.
ENTITY executable
ABSTRACT SUPERTYPE OF (ONEOF( workingstep, nc_function,
program_structure));
[ . . . ]
enabled:
END_ENTITY;
OPTIONAL BOOLEAN;
© Copyright 2008 — STEP Tools, Inc.
-- ADDED BY TC
Slide 21