share/extensions/gears.py

   1 #! /usr/bin/env python
   2 '''
   3 Copyright (C) 2007 Aaron Spike  (aaron @ ekips.org)
   4 Copyright (C) 2007 Tavmjong Bah (tavmjong @ free.fr)
   5
   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.
  10
  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.
  15
  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 '''
  20
  21 import inkex
  22 import simplestyle, sys
  23 from math import *
  24 import string
  25
  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))
  29
  30 def point_on_circle(radius, angle):
  31     x = radius * cos(angle)
  32     y = radius * sin(angle)
  33     return (x, y)
  34
  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
  43
  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):
  68
  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)
  73
  74         # print >>sys.stderr, "Teeth: %s\n"        % teeth
  75
  76         two_pi = 2.0 * pi
  77
  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
  82
  83         # Base Circle
  84         base_diameter = pitch_diameter * cos( radians( angle ) )
  85         base_radius   = base_diameter / 2.0
  86
  87         # Diametrial pitch: Number of teeth per unit length.
  88         pitch_diametrial = float( teeth )/ pitch_diameter
  89
  90         # Addendum: Radial distance from pitch circle to outside circle.
  91         addendum = 1.0 / pitch_diametrial
  92
  93         # Outer Circle
  94         outer_radius = pitch_radius + addendum
  95         outer_diameter = outer_radius * 2.0
  96
  97         # Tooth thickness: Tooth width along pitch circle.
  98         tooth  = ( pi * pitch_diameter ) / ( 2.0 * float( teeth ) )
  99
 100         # Undercut?
 101         undercut = (2.0 / ( sin( radians( angle ) ) ** 2))
 102         needs_undercut = teeth < undercut
 103
 104
 105         # Clearance: Radial distance between top of tooth on one gear to bottom of gap on another.
 106         clearance = 0.0
 107
 108         # Dedendum: Radial distance from pitch circle to root diameter.
 109         dedendum = addendum + clearance
 110
 111         # Root diameter: Diameter of bottom of tooth spaces.
 112         root_radius =  pitch_radius - dedendum
 113         root_diameter = root_radius * 2.0
 114
 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
 118
 119         centers = [(x * two_pi / float( teeth) ) for x in range( teeth ) ]
 120
 121         points = []
 122
 123         for c in centers:
 124
 125             # Angles
 126             pitch1 = c - half_thick_angle
 127             base1  = pitch1 - pitch_to_base_angle
 128             outer1 = pitch1 + pitch_to_outer_angle
 129
 130             pitch2 = c + half_thick_angle
 131             base2  = pitch2 + pitch_to_base_angle
 132             outer2 = pitch2 - pitch_to_outer_angle
 133
 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 )
 138
 139             b2 = point_on_circle( base_radius,  base2  )
 140             p2 = point_on_circle( pitch_radius, pitch2 )
 141             o2 = point_on_circle( outer_radius, outer2 )
 142
 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]
 154
 155             points.extend( p_tmp )
 156
 157         path = points_to_svgd( points )
 158
 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)
 165
 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 )
 179
 180 if __name__ == '__main__':
 181     e = Gears()
 182     e.affect()
 183
 184
 185 # vim: expandtab shiftwidth=4 tabstop=8 softtabstop=4 fileencoding=utf-8 textwidth=99