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#!/usr/bin/env python
#
# Copyright (C) 2007 Aaron Spike (aaron @ ekips.org)
# Copyright (C) 2007 Tavmjong Bah (tavmjong @ free.fr)
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#
"""
Generate gears in SVG
"""
from math import acos, cos, pi, radians, sin, sqrt
import inkex
from inkex import PathElement
def involute_intersect_angle(Rb, R):
Rb, R = float(Rb), float(R)
return (sqrt(R ** 2 - Rb ** 2) / Rb) - (acos(Rb / R))
def point_on_circle(radius, angle):
x = radius * cos(angle)
y = radius * sin(angle)
return x, y
def points_to_svgd(p):
f = p[0]
p = p[1:]
svgd = 'M{:.5f},{:.5f}'.format(f[0], f[1])
for x in p:
svgd += ' L{:.5f},{:.5f}'.format(x[0], x[1])
svgd += 'z'
return svgd
class Gears(inkex.GenerateExtension):
container_label = 'Rendered Gears'
def add_arguments(self, pars):
pars.add_argument("--teeth", type=int, default=24, help="Number of teeth")
pars.add_argument("--pitch", type=float, default=20.0, help="Circular Pitch")
pars.add_argument("--angle", type=float, default=20.0, help="Pressure Angle")
pars.add_argument("--centerdiameter", type=float, default=10.0, help="Diameter of hole")
pars.add_argument("--unit", default="px", help="unit for pitch and center diameter")
def generate(self):
teeth = self.options.teeth
pitch = self.svg.unittouu(str(self.options.pitch) + self.options.unit)
angle = self.options.angle # Angle of tangent to tooth at circular pitch wrt radial line.
centerdiameter = self.svg.unittouu(str(self.options.centerdiameter) + self.options.unit)
# print >>sys.stderr, "Teeth: %s\n" % teeth
two_pi = 2.0 * pi
# Pitch (circular pitch): Length of the arc from one tooth to the next)
# Pitch diameter: Diameter of pitch circle.
pitch_diameter = float(teeth) * pitch / pi
pitch_radius = pitch_diameter / 2.0
# Base Circle
base_diameter = pitch_diameter * cos(radians(angle))
base_radius = base_diameter / 2.0
# Diametrial pitch: Number of teeth per unit length.
pitch_diametrial = float(teeth) / pitch_diameter
# Addendum: Radial distance from pitch circle to outside circle.
addendum = 1.0 / pitch_diametrial
# Outer Circle
outer_radius = pitch_radius + addendum
outer_diameter = outer_radius * 2.0
# Tooth thickness: Tooth width along pitch circle.
tooth = (pi * pitch_diameter) / (2.0 * float(teeth))
# Undercut?
undercut = (2.0 / (sin(radians(angle)) ** 2))
needs_undercut = teeth < undercut
# Clearance: Radial distance between top of tooth on one gear to bottom of gap on another.
clearance = 0.0
# Dedendum: Radial distance from pitch circle to root diameter.
dedendum = addendum + clearance
# Root diameter: Diameter of bottom of tooth spaces.
root_radius = pitch_radius - dedendum
root_diameter = root_radius * 2.0
half_thick_angle = two_pi / (4.0 * float(teeth))
pitch_to_base_angle = involute_intersect_angle(base_radius, pitch_radius)
pitch_to_outer_angle = involute_intersect_angle(base_radius, outer_radius) - pitch_to_base_angle
centers = [(x * two_pi / float(teeth)) for x in range(teeth)]
points = []
for c in centers:
# Angles
pitch1 = c - half_thick_angle
base1 = pitch1 - pitch_to_base_angle
outer1 = pitch1 + pitch_to_outer_angle
pitch2 = c + half_thick_angle
base2 = pitch2 + pitch_to_base_angle
outer2 = pitch2 - pitch_to_outer_angle
# Points
b1 = point_on_circle(base_radius, base1)
p1 = point_on_circle(pitch_radius, pitch1)
o1 = point_on_circle(outer_radius, outer1)
b2 = point_on_circle(base_radius, base2)
p2 = point_on_circle(pitch_radius, pitch2)
o2 = point_on_circle(outer_radius, outer2)
if root_radius > base_radius:
pitch_to_root_angle = pitch_to_base_angle - involute_intersect_angle(base_radius, root_radius)
root1 = pitch1 - pitch_to_root_angle
root2 = pitch2 + pitch_to_root_angle
r1 = point_on_circle(root_radius, root1)
r2 = point_on_circle(root_radius, root2)
p_tmp = [r1, p1, o1, o2, p2, r2]
else:
r1 = point_on_circle(root_radius, base1)
r2 = point_on_circle(root_radius, base2)
p_tmp = [r1, b1, p1, o1, o2, p2, b2, r2]
points.extend(p_tmp)
path = points_to_svgd(points)
# Create SVG Path for gear
style = {'stroke': '#000000', 'fill': 'none', 'stroke-width': str(self.svg.unittouu('1px'))}
gear = PathElement()
gear.style = style
gear.path = path
yield gear
if centerdiameter > 0.0:
arc = PathElement.arc((0, 0), centerdiameter / 2)
arc.style = style
yield arc
if __name__ == '__main__':
Gears().run()
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