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PD: Refactor InvoluteGear's Bezier Approximation

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The goal of this refactor is to get rid of gear-specific knowledge from
the implementation and argument list. This is to remove the duplicate
definition of addenddum and dedendum that was hidden there.
This commit is contained in:
Jonas Bähr
2023-01-08 14:32:26 +01:00
committed by Uwe
parent 3933825840
commit 647a2356b7
1 changed files with 20 additions and 19 deletions
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39
src/Mod/PartDesign/fcgear/involute.py
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@@ -70,13 +70,13 @@ def CreateExternalGear(w, m, Z, phi, split=True):
if split:
# approximate in 2 sections, split 25% along the involute
fm = fs + (fe - fs) / 4 # fraction of length at junction (25% along profile)
dedInv = BezCoeffs(m, Z, phi, 3, fs, fm)
addInv = BezCoeffs(m, Z, phi, 3, fm, fe)
dedInv = BezCoeffs(Rb, Ra, 3, fs, fm)
addInv = BezCoeffs(Rb, Ra, 3, fm, fe)
# join the 2 sets of coeffs (skip duplicate mid point)
inv = dedInv + addInv[1:]
else:
inv = BezCoeffs(m, Z, phi, 4, fs, fe)
inv = BezCoeffs(Rb, Ra, 4, fs, fe)
# create the back profile of tooth (mirror image)
invR = []
@@ -168,13 +168,13 @@ def CreateInternalGear(w, m, Z, phi, split=True):
if split:
# approximate in 2 sections, split 25% along the involute
fm = fs + (fe - fs) / 4 # fraction of length at junction (25% along profile)
addInv = BezCoeffs(m, Z, phi, 3, fs, fm)
dedInv = BezCoeffs(m, Z, phi, 3, fm, fe)
addInv = BezCoeffs(Rb, Rf, 3, fs, fm)
dedInv = BezCoeffs(Rb, Rf, 3, fm, fe)
# join the 2 sets of coeffs (skip duplicate mid point)
invR = addInv + dedInv[1:]
else:
invR = BezCoeffs(m, Z, phi, 4, fs, fe)
invR = BezCoeffs(Rb, Rf, 4, fs, fe)
# create the back profile of tooth (mirror image)
inv = []
@@ -318,19 +318,20 @@ def bezCoeff(i, p, polyCoeffs):
return sum(binom(i, j) * polyCoeffs[j] / binom(p, j) for j in range(i+1))
# Parameters:
# module - sets the size of teeth (see gear design texts)
# numTeeth - number of teeth on the gear
# pressure angle - angle in degrees, usually 14.5 or 20
# order - the order of the Bezier curve to be fitted [3, 4, 5, ..]
# fstart - fraction of distance along tooth profile to start
# fstop - fraction of distance along profile to stop
def BezCoeffs(module, numTeeth, pressureAngle, order, fstart, fstop):
Rpitch = module * numTeeth / 2 # pitch circle radius
phi = pressureAngle # pressure angle
Rb = Rpitch * cos(phi * pi / 180) # base circle radius
Ra = Rpitch + module # addendum radius (outer radius)
ta = sqrt(Ra * Ra - Rb * Rb) / Rb # involute angle at addendum
def BezCoeffs(baseRadius, limitRadius, order, fstart, fstop):
"""Approximates an involute using a Bezier-curve
Parameters:
baseRadius - the radius of base circle of the involute.
This is where the involute starts, too.
limitRadius - the radius of an outer circle, where the involute ends.
order - the order of the Bezier curve to be fitted e.g. 3, 4, 5, ...
fstart - fraction of distance along the involute to start the approximation.
fstop - fraction of distance along the involute to stop the approximation.
"""
Rb = baseRadius
Ra = limitRadius
ta = sqrt(Ra * Ra - Rb * Rb) / Rb # involute angle at the limit radius
te = sqrt(fstop) * ta # involute angle, theta, at end of approx
ts = sqrt(fstart) * ta # involute angle, theta, at start of approx
p = order # order of Bezier approximation