4a77843845
Previously, the fillet started at a fixed value, tailored at 20° pressure angle, a fillet radius of 0.375 and a dedendum of 1.25. With PR #8184 those values became user-adjustable and thus the assumptions of the original code are not fullfilled any more. This resulted in significant artefacts, especially for higher pressure angles or smaller dedendums as commonly found in splines. This commit actually calculates the junction between fillet and involute so that the tangents of the both curves match. The mathematical approach is described in source code comments. The change in the fillet calculation also affects compatibility with files generated by earlier versions of FreeCAD. Those changes are way below 0.1% per tooth, however the earlier test required absolute equality down to the micron. This was relaxed and also changed to a relative, per tooth, tolerance. There is one particular case where the new algorithm performs slightly worse, though. That is when the fillet radius is too large to the dedendum, i.e. resulting in a single arc instead of two fillets, and effectively cannibalizes some of the clearance. This happens with internal gears having less than 25 teeth. At about 15 teeth it becomes visible that the fillet is not 100% tanget any more. However, as such a low number of teeth is highly unusual for internal gears and the effect, although noticeable, is minor, the overall benefits of the new algorithm outweighs the drawbacks. And now with the fillet radius being adjustable it is easy to fix, too. The technical reason is that the tangency is calculated correctly, but the fillet circle is displaced aferwards to avoid an overlap of the two fillets. For the new fillet position, the tangents do not align any more.
221 lines
11 KiB
Python
221 lines
11 KiB
Python
#***************************************************************************
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#* Copyright (c) 2021 Jonas Bähr <jonas.baehr@web.de> *
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#* *
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#* This program is free software; you can redistribute it and/or modify *
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#* it under the terms of the GNU Lesser General Public License (LGPL) *
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#* as published by the Free Software Foundation; either version 2 of *
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#* the License, or (at your option) any later version. *
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#* for detail see the LICENCE text file. *
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#* *
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#* This program is distributed in the hope that it will be useful, *
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#* but WITHOUT ANY WARRANTY; without even the implied warranty of *
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#* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
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#* GNU Library General Public License for more details. *
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#* *
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#* You should have received a copy of the GNU Library General Public *
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#* License along with this program; if not, write to the Free Software *
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#* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 *
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#* USA *
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#* *
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#***************************************************************************
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import unittest
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import pathlib
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import FreeCAD
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from Part import makeCircle, Precision
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import InvoluteGearFeature
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FIXTURE_PATH = pathlib.Path(__file__).parent / "Fixtures"
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class TestInvoluteGear(unittest.TestCase):
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def setUp(self):
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self.Doc = FreeCAD.newDocument("PartDesignTestInvoluteGear")
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def tearDown(self):
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FreeCAD.closeDocument(self.Doc.Name)
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def testDefaultGearProfile(self):
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InvoluteGearFeature.makeInvoluteGear('TestGear')
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gear = self.Doc.getObject('TestGear')
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self.assertSuccessfulRecompute(gear)
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self.assertClosedWire(gear.Shape)
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def testDefaultInternalGearProfile(self):
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gear = InvoluteGearFeature.makeInvoluteGear('InvoluteGear')
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gear.ExternalGear = False
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self.assertSuccessfulRecompute(gear)
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self.assertClosedWire(gear.Shape)
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def testLowPrecisionGearProfile(self):
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gear = InvoluteGearFeature.makeInvoluteGear('InvoluteGear')
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gear.HighPrecision = False
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self.assertSuccessfulRecompute(gear)
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self.assertClosedWire(gear.Shape)
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def testLowPrecisionInternalGearProfile(self):
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gear = InvoluteGearFeature.makeInvoluteGear('InvoluteGear')
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gear.ExternalGear = False
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gear.HighPrecision = False
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self.assertSuccessfulRecompute(gear)
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self.assertClosedWire(gear.Shape)
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def testCustomizedGearProfile(self):
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gear = InvoluteGearFeature.makeInvoluteGear('InvoluteGear')
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z = 12
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m = 1
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gear.NumberOfTeeth = z
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gear.Modules = f'{m} mm'
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gear.PressureAngle = '14.5 deg'
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self.assertSuccessfulRecompute(gear)
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self.assertClosedWire(gear.Shape)
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pitch_diameter = m * z
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default_addendum = 1
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default_dedendum = 1.25
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tip_diameter = pitch_diameter + 2 * default_addendum * m
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root_diameter = pitch_diameter - 2 * default_dedendum * m
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# the test purpose here is just to ensure the gear's parameters are used,
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# not super precise profile verification. Thus a lax delta is just file here.
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delta = 0.01
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self.assertIntersection(gear.Shape, makeCircle(pitch_diameter/2), "Expecting intersection at pitch circle")
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self.assertNoIntersection(gear.Shape, makeCircle(tip_diameter/2 + delta), "Teeth extent beyond tip circle")
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self.assertNoIntersection(gear.Shape, makeCircle(root_diameter/2 - delta), "Teeth extend below root circle")
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def testCustomizedGearProfileForSplinedShaft(self):
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spline = InvoluteGearFeature.makeInvoluteGear('InvoluteSplinedShaft')
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z = 12
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m = 2
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add_coef = 0.5
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ded_coef = 0.9
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spline.NumberOfTeeth = z
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spline.Modules = f'{m} mm'
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spline.PressureAngle = '30 deg'
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spline.AddendumCoefficient = add_coef
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spline.DedendumCoefficient = ded_coef
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spline.RootFilletCoefficient = 0.4
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self.assertSuccessfulRecompute(spline)
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self.assertClosedWire(spline.Shape)
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pitch_diameter = m * z
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tip_diameter = pitch_diameter + 2 * add_coef * m
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root_diameter = pitch_diameter - 2 * ded_coef * m
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# the test purpose here is just to ensure the gear's parameters are used,
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# not super precise profile verification. Thus a lax delta is just file here.
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delta = 0.01
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self.assertIntersection(spline.Shape, makeCircle(pitch_diameter/2), "Expecting intersection at pitch circle")
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self.assertNoIntersection(spline.Shape, makeCircle(tip_diameter/2 + delta), "Teeth extent beyond tip circle")
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self.assertNoIntersection(spline.Shape, makeCircle(root_diameter/2 - delta), "Teeth extend below root circle")
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def testCustomizedGearProfileForSplinedHub(self):
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hub = InvoluteGearFeature.makeInvoluteGear('InvoluteSplinedHub')
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hub.ExternalGear = False
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z = 12
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m = 2
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add_coef = 0.5
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ded_coef = 0.9
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hub.NumberOfTeeth = z
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hub.Modules = f'{m} mm'
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hub.PressureAngle = '30 deg'
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hub.AddendumCoefficient = add_coef
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hub.DedendumCoefficient = ded_coef
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hub.RootFilletCoefficient = 0.4
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self.assertSuccessfulRecompute(hub)
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self.assertClosedWire(hub.Shape)
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pitch_diameter = m * z
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tip_diameter = pitch_diameter - 2 * add_coef * m
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root_diameter = pitch_diameter + 2 * ded_coef * m
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# the test purpose here is just to ensure the gear's parameters are used,
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# not super precise profile verification. Thus a lax delta is just file here.
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delta = 0.1 # FIXME it seems that the top land arc is in the wrong direction, thus a larger tolerance.
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self.assertIntersection(hub.Shape, makeCircle(pitch_diameter/2), "Expecting intersection at pitch circle")
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self.assertNoIntersection(hub.Shape, makeCircle(tip_diameter/2 - delta), "Teeth extent below tip circle")
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self.assertNoIntersection(hub.Shape, makeCircle(root_diameter/2 + delta), "Teeth extend beyond root circle")
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def testUsagePadGearProfile(self):
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profile = InvoluteGearFeature.makeInvoluteGear('GearProfile')
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body = self.Doc.addObject('PartDesign::Body','GearBody')
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body.addObject(profile)
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pad = body.newObject("PartDesign::Pad","GearPad")
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pad.Profile = profile
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pad.Length = '5 mm' # that our gear's "Face Width"
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self.assertSuccessfulRecompute()
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self.assertSolid(pad.Shape)
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def testUsagePocketInternalGearProfile(self):
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profile = InvoluteGearFeature.makeInvoluteGear('GearProfile')
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profile.ExternalGear = False
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# boolean cuts with lots of B-splines are quite slow, so let's make it less complex
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profile.HighPrecision = False
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profile.NumberOfTeeth = 8
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body = self.Doc.addObject('PartDesign::Body','GearBody')
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body.addObject(profile)
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cylinder = body.newObject('PartDesign::AdditiveCylinder','GearCylinder')
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default_dedendum = 1.25
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rim_width = 3 * FreeCAD.Units.MilliMetre
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cylinder.Height = '5 mm' # that our gear's "Face Width"
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cylinder.Radius = profile.NumberOfTeeth * profile.Modules / 2 + default_dedendum * profile.Modules + rim_width
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pocket = body.newObject('PartDesign::Pocket','GearPocket')
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pocket.Profile = profile
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pocket.Reversed = True # need to "pocket upwards" into the cylinder
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pocket.Type = 'ThroughAll'
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self.assertSuccessfulRecompute()
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self.assertSolid(pocket.Shape)
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def testRecomputeExternalGearFromV020(self):
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FreeCAD.closeDocument(self.Doc.Name) # this was created in setUp(self)
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self.Doc = FreeCAD.openDocument(str(FIXTURE_PATH / "InvoluteGear_v0-20.FCStd"))
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created_with = f"created with {self.Doc.getProgramVersion()}"
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gear = self.Doc.InvoluteGear # from fixture
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fixture_length = 187.752 # from fixture, rounded to micrometer
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self.assertClosedWire(gear.Shape) # no recompute yet, i.e. check original
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self.assertAlmostEqual(fixture_length, gear.Shape.Length, places=3,
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msg=f"Total wire length does not match fixture for gear {created_with}")
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gear.enforceRecompute()
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self.assertSuccessfulRecompute(gear, msg=f"Cannot recompute gear {created_with}")
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relative_tolerance_per_tooth = 1e-3 # wild guess: changes of <0.1%/tooth are ok
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length_delta = fixture_length * relative_tolerance_per_tooth * gear.NumberOfTeeth
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self.assertAlmostEqual(fixture_length, gear.Shape.Length, delta=length_delta,
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msg=f"Total wire length changed after recomputing gear {created_with}")
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def testRecomputeInternalGearFromV020(self):
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FreeCAD.closeDocument(self.Doc.Name) # this was created in setUp(self)
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self.Doc = FreeCAD.openDocument(str(FIXTURE_PATH / "InternalInvoluteGear_v0-20.FCStd"))
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created_with = f"created with {self.Doc.getProgramVersion()}"
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gear = self.Doc.InvoluteGear # from fixture
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fixture_length = 165.408 # from fixture, rounded to micrometer
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self.assertClosedWire(gear.Shape) # no recompute yet, i.e. check original
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self.assertAlmostEqual(fixture_length, gear.Shape.Length, places=3,
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msg=f"Total wire length does not match fixture for gear {created_with}")
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gear.enforceRecompute()
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self.assertSuccessfulRecompute(gear, msg=f"Cannot recompute gear {created_with}")
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relative_tolerance_per_tooth = 1e-3 # wild guess: changes of <0.1%/tooth are ok
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length_delta = fixture_length * relative_tolerance_per_tooth * gear.NumberOfTeeth
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self.assertAlmostEqual(fixture_length, gear.Shape.Length, delta=length_delta,
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msg=f"Total wire length changed after recomputing gear {created_with}")
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def assertSuccessfulRecompute(self, *objs, msg=None):
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if (len(objs) == 0):
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self.Doc.recompute()
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objs = self.Doc.Objects
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else:
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self.Doc.recompute(objs)
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failed_objects = [o.Name for o in objs if 'Invalid' in o.State]
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if (len(failed_objects) > 0):
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self.fail(msg or f"Recompute failed for {failed_objects}")
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def assertClosedWire(self, shape, msg=None):
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self.assertEqual(shape.ShapeType, 'Wire', msg=msg)
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self.assertTrue(shape.isClosed(), msg=msg)
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def assertIntersection(self, shape1, shape2, msg=None):
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self.failUnless(self._check_intersection(shape1, shape2), msg or "Given shapes do not intersect.")
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def assertNoIntersection(self, shape1, shape2, msg=None):
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self.failIf(self._check_intersection(shape1, shape2), msg or "Given shapes intersect.")
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def _check_intersection(self, shape1, shape2):
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distance, _, _ = shape1.distToShape(shape2)
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return distance < Precision.intersection()
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def assertSolid(self, shape, msg=None):
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self.assertEqual(shape.ShapeType, 'Solid', msg=msg)
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