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
  25 def involute_intersect_angle(Rb, R):
  26     Rb, R = float(Rb), float(R)
  27     return (sqrt(R**2 - Rb**2) / (Rb)) - (acos(Rb / R))
  28
  29 def point_on_circle(radius, angle):
  30     x = radius * cos(angle)
  31     y = radius * sin(angle)
  32     return (x, y)
  33
  34 def points_to_svgd(p):
  35     f = p[0]
  36     p = p[1:]
  37     svgd = 'M%.3f,%.3f' % f
  38     for x in p:
  39         svgd += 'L%.3f,%.3f' % x
  40     svgd += 'z'
  41     return svgd
  42
  43 class Gears(inkex.Effect):
  44     def __init__(self):
  45         inkex.Effect.__init__(self)
  46         self.OptionParser.add_option("-t", "--teeth",
  47                         action="store", type="int",
  48                         dest="teeth", default=24,
  49                         help="Number of teeth")
  50         self.OptionParser.add_option("-p", "--pitch",
  51                         action="store", type="float",
  52                         dest="pitch", default=20.0,
  53                         help="Circular Pitch (length of arc from one tooth to next)")
  54         self.OptionParser.add_option("-a", "--angle",
  55                         action="store", type="float",
  56                         dest="angle", default=20.0,
  57                         help="Pressure Angle (common values: 14.5, 20, 25 degrees)")
  58     def effect(self):
  59
  60         teeth = self.options.teeth
  61         pitch = self.options.pitch
  62         angle = self.options.angle  # Angle of tangent to tooth at circular pitch wrt radial line.
  63
  64         # print >>sys.stderr, "Teeth: %s\n"        % teeth
  65
  66         two_pi = 2.0 * pi
  67
  68         # Pitch (circular pitch): Length of the arc from one tooth to the next)
  69         # Pitch diameter: Diameter of pitch circle.
  70         pitch_diameter = float( teeth ) * pitch / pi
  71         pitch_radius   = pitch_diameter / 2.0
  72
  73         # Base Circle
  74         base_diameter = pitch_diameter * cos( radians( angle ) )
  75         base_radius   = base_diameter / 2.0
  76
  77         # Diametrial pitch: Number of teeth per unit length.
  78         pitch_diametrial = float( teeth )/ pitch_diameter
  79
  80         # Addendum: Radial distance from pitch circle to outside circle.
  81         addendum = 1.0 / pitch_diametrial
  82
  83         # Outer Circle
  84         outer_radius = pitch_radius + addendum
  85         outer_diameter = outer_radius * 2.0
  86
  87         # Tooth thickness: Tooth width along pitch circle.
  88         tooth  = ( pi * pitch_diameter ) / ( 2.0 * float( teeth ) )
  89
  90         # Undercut?
  91         undercut = (2.0 / ( sin( radians( angle ) ) ** 2))
  92         needs_undercut = teeth < undercut
  93
  94
  95         # Clearance: Radial distance between top of tooth on one gear to bottom of gap on another.
  96         clearance = 0.0
  97
  98         # Dedendum: Radial distance from pitch circle to root diameter.
  99         dedendum = addendum + clearance
 100
 101         # Root diameter: Diameter of bottom of tooth spaces.
 102         root_radius =  pitch_radius - dedendum
 103         root_diameter = root_radius * 2.0
 104
 105         half_thick_angle = two_pi / (4.0 * float( teeth ) )
 106         pitch_to_base_angle  = involute_intersect_angle( base_radius, pitch_radius )
 107         pitch_to_outer_angle = involute_intersect_angle( base_radius, outer_radius ) - pitch_to_base_angle
 108
 109         centers = [(x * two_pi / float( teeth) ) for x in range( teeth ) ]
 110
 111         points = []
 112
 113         for c in centers:
 114
 115             # Angles
 116             pitch1 = c - half_thick_angle
 117             base1  = pitch1 - pitch_to_base_angle
 118             outer1 = pitch1 + pitch_to_outer_angle
 119
 120             pitch2 = c + half_thick_angle
 121             base2  = pitch2 + pitch_to_base_angle
 122             outer2 = pitch2 - pitch_to_outer_angle
 123
 124             # Points
 125             b1 = point_on_circle( base_radius,  base1  )
 126             p1 = point_on_circle( pitch_radius, pitch1 )
 127             o1 = point_on_circle( outer_radius, outer1 )
 128
 129             b2 = point_on_circle( base_radius,  base2  )
 130             p2 = point_on_circle( pitch_radius, pitch2 )
 131             o2 = point_on_circle( outer_radius, outer2 )
 132
 133             if root_radius > base_radius:
 134                 pitch_to_root_angle = pitch_to_base_angle - involute_intersect_angle(base_radius, root_radius )
 135                 root1 = pitch1 - pitch_to_root_angle
 136                 root2 = pitch2 + pitch_to_root_angle
 137                 r1 = point_on_circle(root_radius, root1)
 138                 r2 = point_on_circle(root_radius, root2)
 139                 p_tmp = [r1,p1,o1,o2,p2,r2]
 140             else:
 141                 r1 = point_on_circle(root_radius, base1)
 142                 r2 = point_on_circle(root_radius, base2)
 143                 p_tmp = [r1,b1,p1,o1,o2,p2,b2,r2]
 144
 145             points.extend( p_tmp )
 146
 147         path = points_to_svgd( points )
 148
 149         # Embed gear in group to make animation easier:
 150         #  Translate group, Rotate path.
 151         t = 'translate(' + str( self.view_center[0] ) + ',' + str( self.view_center[1] ) + ')'
 152         g_attribs = {inkex.addNS('label','inkscape'):'Gear' + str( teeth ),
 153                      'transform':t }
 154         g = inkex.etree.SubElement(self.current_layer, 'g', g_attribs)
 155
 156         # Create SVG Path for gear
 157         style = { 'stroke': '#000000', 'fill': 'none' }
 158         gear_attribs = {'style':simplestyle.formatStyle(style), 'd':path}
 159         gear = inkex.etree.SubElement(g, inkex.addNS('path','svg'), gear_attribs )
 160
 161 if __name__ == '__main__':
 162     e = Gears()
 163     e.affect()
 164
 165
 166 # vim: expandtab shiftwidth=4 tabstop=8 softtabstop=4 fileencoding=utf-8 textwidth=99