#! /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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
'''
import inkex
import simplestyle, sys
from math import *
import string
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' % f
for x in p:
svgd += ' L%.5f,%.5f' % x
svgd += 'z'
return svgd
class Gears(inkex.Effect):
def __init__(self):
inkex.Effect.__init__(self)
self.OptionParser.add_option("-t", "--teeth",
action="store", type="int",
dest="teeth", default=24,
help="Number of teeth")
self.OptionParser.add_option("-p", "--pitch",
action="store", type="float",
dest="pitch", default=20.0,
help="Circular Pitch (length of arc from one tooth to next)")
self.OptionParser.add_option("-a", "--angle",
action="store", type="float",
dest="angle", default=20.0,
help="Pressure Angle (common values: 14.5, 20, 25 degrees)")
self.OptionParser.add_option("-c", "--centerdiameter",
action="store", type="float",
dest="centerdiameter", default=10.0,
help="Diameter of central hole - 0.0 for no hole")
self.OptionParser.add_option("-u", "--unit",
action="store", type="string",
dest="unit", default="px",
help="unit of measure for circular pitch and center diameter")
def effect(self):
teeth = self.options.teeth
pitch = self.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.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 )
# Embed gear in group to make animation easier:
# Translate group, Rotate path.
t = 'translate(' + str( self.view_center[0] ) + ',' + str( self.view_center[1] ) + ')'
g_attribs = {inkex.addNS('label','inkscape'):'Gear' + str( teeth ),
'transform':t }
g = inkex.etree.SubElement(self.current_layer, 'g', g_attribs)
# Create SVG Path for gear
style = { 'stroke': '#000000', 'fill': 'none', 'stroke-width': str(self.unittouu('1px')) }
gear_attribs = {'style':simplestyle.formatStyle(style), 'd':path}
gear = inkex.etree.SubElement(g, inkex.addNS('path','svg'), gear_attribs )
if(centerdiameter > 0.0):
center_attribs = {'style':simplestyle.formatStyle(style),
inkex.addNS('cx','sodipodi') :'0.0',
inkex.addNS('cy','sodipodi') :'0.0',
inkex.addNS('rx','sodipodi') :str(centerdiameter/2),
inkex.addNS('ry','sodipodi') :str(centerdiameter/2),
inkex.addNS('type','sodipodi') :'arc'
}
center = inkex.etree.SubElement(g, inkex.addNS('path','svg'), center_attribs )
if __name__ == '__main__':
e = Gears()
e.affect()
# vim: expandtab shiftwidth=4 tabstop=8 softtabstop=4 fileencoding=utf-8 textwidth=99
