1 #! /usr/bin/env python
2 '''
3 Copyright (C) 2007 Aaron Spike (aaron @ ekips.org)
4 Copyright (C) 2007 Tavmjong Bah (tavmjong @ free.fr)
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2 of the License, or
9 (at your option) any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; if not, write to the Free Software
18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
19 '''
21 import inkex
22 import simplestyle, sys
23 from math import *
24 import string
26 def involute_intersect_angle(Rb, R):
27 Rb, R = float(Rb), float(R)
28 return (sqrt(R**2 - Rb**2) / (Rb)) - (acos(Rb / R))
30 def point_on_circle(radius, angle):
31 x = radius * cos(angle)
32 y = radius * sin(angle)
33 return (x, y)
35 def points_to_svgd(p):
36 f = p[0]
37 p = p[1:]
38 svgd = 'M%.3f,%.3f' % f
39 for x in p:
40 svgd += 'L%.3f,%.3f' % x
41 svgd += 'z'
42 return svgd
44 class Gears(inkex.Effect):
45 def __init__(self):
46 inkex.Effect.__init__(self)
47 self.OptionParser.add_option("-t", "--teeth",
48 action="store", type="int",
49 dest="teeth", default=24,
50 help="Number of teeth")
51 self.OptionParser.add_option("-p", "--pitch",
52 action="store", type="float",
53 dest="pitch", default=20.0,
54 help="Circular Pitch (length of arc from one tooth to next)")
55 self.OptionParser.add_option("-a", "--angle",
56 action="store", type="float",
57 dest="angle", default=20.0,
58 help="Pressure Angle (common values: 14.5, 20, 25 degrees)")
59 self.OptionParser.add_option("-c", "--centerdiameter",
60 action="store", type="float",
61 dest="centerdiameter", default=10.0,
62 help="Diameter of central hole - 0.0 for no hole")
63 self.OptionParser.add_option("-u", "--unit",
64 action="store", type="string",
65 dest="unit", default="px",
66 help="unit of measure for circular pitch and center diameter")
67 def effect(self):
69 teeth = self.options.teeth
70 pitch = inkex.unittouu( str(self.options.pitch) + self.options.unit)
71 angle = self.options.angle # Angle of tangent to tooth at circular pitch wrt radial line.
72 centerdiameter = inkex.unittouu( str(self.options.centerdiameter) + self.options.unit)
74 # print >>sys.stderr, "Teeth: %s\n" % teeth
76 two_pi = 2.0 * pi
78 # Pitch (circular pitch): Length of the arc from one tooth to the next)
79 # Pitch diameter: Diameter of pitch circle.
80 pitch_diameter = float( teeth ) * pitch / pi
81 pitch_radius = pitch_diameter / 2.0
83 # Base Circle
84 base_diameter = pitch_diameter * cos( radians( angle ) )
85 base_radius = base_diameter / 2.0
87 # Diametrial pitch: Number of teeth per unit length.
88 pitch_diametrial = float( teeth )/ pitch_diameter
90 # Addendum: Radial distance from pitch circle to outside circle.
91 addendum = 1.0 / pitch_diametrial
93 # Outer Circle
94 outer_radius = pitch_radius + addendum
95 outer_diameter = outer_radius * 2.0
97 # Tooth thickness: Tooth width along pitch circle.
98 tooth = ( pi * pitch_diameter ) / ( 2.0 * float( teeth ) )
100 # Undercut?
101 undercut = (2.0 / ( sin( radians( angle ) ) ** 2))
102 needs_undercut = teeth < undercut
105 # Clearance: Radial distance between top of tooth on one gear to bottom of gap on another.
106 clearance = 0.0
108 # Dedendum: Radial distance from pitch circle to root diameter.
109 dedendum = addendum + clearance
111 # Root diameter: Diameter of bottom of tooth spaces.
112 root_radius = pitch_radius - dedendum
113 root_diameter = root_radius * 2.0
115 half_thick_angle = two_pi / (4.0 * float( teeth ) )
116 pitch_to_base_angle = involute_intersect_angle( base_radius, pitch_radius )
117 pitch_to_outer_angle = involute_intersect_angle( base_radius, outer_radius ) - pitch_to_base_angle
119 centers = [(x * two_pi / float( teeth) ) for x in range( teeth ) ]
121 points = []
123 for c in centers:
125 # Angles
126 pitch1 = c - half_thick_angle
127 base1 = pitch1 - pitch_to_base_angle
128 outer1 = pitch1 + pitch_to_outer_angle
130 pitch2 = c + half_thick_angle
131 base2 = pitch2 + pitch_to_base_angle
132 outer2 = pitch2 - pitch_to_outer_angle
134 # Points
135 b1 = point_on_circle( base_radius, base1 )
136 p1 = point_on_circle( pitch_radius, pitch1 )
137 o1 = point_on_circle( outer_radius, outer1 )
139 b2 = point_on_circle( base_radius, base2 )
140 p2 = point_on_circle( pitch_radius, pitch2 )
141 o2 = point_on_circle( outer_radius, outer2 )
143 if root_radius > base_radius:
144 pitch_to_root_angle = pitch_to_base_angle - involute_intersect_angle(base_radius, root_radius )
145 root1 = pitch1 - pitch_to_root_angle
146 root2 = pitch2 + pitch_to_root_angle
147 r1 = point_on_circle(root_radius, root1)
148 r2 = point_on_circle(root_radius, root2)
149 p_tmp = [r1,p1,o1,o2,p2,r2]
150 else:
151 r1 = point_on_circle(root_radius, base1)
152 r2 = point_on_circle(root_radius, base2)
153 p_tmp = [r1,b1,p1,o1,o2,p2,b2,r2]
155 points.extend( p_tmp )
157 path = points_to_svgd( points )
159 # Embed gear in group to make animation easier:
160 # Translate group, Rotate path.
161 t = 'translate(' + str( self.view_center[0] ) + ',' + str( self.view_center[1] ) + ')'
162 g_attribs = {inkex.addNS('label','inkscape'):'Gear' + str( teeth ),
163 'transform':t }
164 g = inkex.etree.SubElement(self.current_layer, 'g', g_attribs)
166 # Create SVG Path for gear
167 style = { 'stroke': '#000000', 'fill': 'none' }
168 gear_attribs = {'style':simplestyle.formatStyle(style), 'd':path}
169 gear = inkex.etree.SubElement(g, inkex.addNS('path','svg'), gear_attribs )
170 if(centerdiameter > 0.0):
171 center_attribs = {'style':simplestyle.formatStyle(style),
172 inkex.addNS('cx','sodipodi') :'0.0',
173 inkex.addNS('cy','sodipodi') :'0.0',
174 inkex.addNS('rx','sodipodi') :str(centerdiameter/2),
175 inkex.addNS('ry','sodipodi') :str(centerdiameter/2),
176 inkex.addNS('type','sodipodi') :'arc'
177 }
178 center = inkex.etree.SubElement(g, inkex.addNS('path','svg'), center_attribs )
180 if __name__ == '__main__':
181 e = Gears()
182 e.affect()
185 # vim: expandtab shiftwidth=4 tabstop=8 softtabstop=4 fileencoding=utf-8 textwidth=99