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, simplestyle, sys
  22 from math import *
  23
  24 def involute_intersect_angle(Rb, R):
  25     Rb, R = float(Rb), float(R)
  26     return (sqrt(R**2 - Rb**2) / (Rb)) - (acos(Rb / R))
  27
  28 def point_on_circle(radius, angle):
  29     x = radius * cos(angle)
  30     y = radius * sin(angle)
  31     return (x, y)
  32
  33 def points_to_svgd(p):
  34     f = p[0]
  35     p = p[1:]
  36     svgd = 'M%.3f,%.3f' % f
  37     for x in p:
  38         svgd += 'L%.3f,%.3f' % x
  39     svgd += 'z'
  40     return svgd
  41
  42 class Gears(inkex.Effect):
  43     def __init__(self):
  44         inkex.Effect.__init__(self)
  45         self.OptionParser.add_option("-t", "--teeth",
  46                         action="store", type="int",
  47                         dest="teeth", default=24,
  48                         help="Number of teeth")
  49         self.OptionParser.add_option("-p", "--pitch",
  50                         action="store", type="float",
  51                         dest="pitch", default=20.0,
  52                         help="Circular Pitch (length of arc from one tooth to next)")
  53         self.OptionParser.add_option("-a", "--angle",
  54                         action="store", type="float",
  55                         dest="angle", default=20.0,
  56                         help="Pressure Angle (common values: 14.5, 20, 25 degrees)")
  57     def effect(self):
  58
  59         teeth = self.options.teeth
  60         pitch = self.options.pitch
  61         angle = self.options.angle  # Angle of tangent to tooth at circular pitch wrt radial line.
  62
  63         # print >>sys.stderr, "Teeth: %s\n"        % teeth
  64
  65         two_pi = 2.0 * pi
  66
  67         # Pitch (circular pitch): Length of the arc from one tooth to the next)
  68         # Pitch diameter: Diameter of pitch circle.
  69         pitch_diameter = float( teeth ) * pitch / pi
  70         pitch_radius   = pitch_diameter / 2.0
  71
  72         # Base Circle
  73         base_diameter = pitch_diameter * cos( radians( angle ) )
  74         base_radius   = base_diameter / 2.0
  75
  76         # Diametrial pitch: Number of teeth per unit length.
  77         pitch_diametrial = float( teeth )/ pitch_diameter
  78
  79         # Addendum: Radial distance from pitch circle to outside circle.
  80         addendum = 1.0 / pitch_diametrial
  81
  82         # Outer Circle
  83         outer_radius = pitch_radius + addendum
  84         outer_diameter = outer_radius * 2.0
  85
  86         # Tooth thickness: Tooth width along pitch circle.
  87         tooth  = ( pi * pitch_diameter ) / ( 2.0 * float( teeth ) )
  88
  89         # Undercut?
  90         undercut = (2.0 / ( sin( radians( angle ) ) ** 2))
  91         needs_undercut = teeth < undercut
  92
  93
  94         # Clearance: Radial distance between top of tooth on one gear to bottom of gap on another.
  95         clearance = 0.0
  96
  97         # Dedendum: Radial distance from pitch circle to root diameter.
  98         dedendum = addendum + clearance
  99
 100         # Root diameter: Diameter of bottom of tooth spaces.
 101         root_radius =  pitch_radius - dedendum
 102         root_diameter = root_radius * 2.0
 103
 104         half_thick_angle = two_pi / (4.0 * float( teeth ) )
 105         pitch_to_base_angle  = involute_intersect_angle( base_radius, pitch_radius )
 106         pitch_to_outer_angle = involute_intersect_angle( base_radius, outer_radius ) - pitch_to_base_angle
 107
 108         centers = [(x * two_pi / float( teeth) ) for x in range( teeth ) ]
 109
 110         points = []
 111
 112         for c in centers:
 113
 114              # Angles
 115              pitch1 = c - half_thick_angle
 116              base1  = pitch1 - pitch_to_base_angle
 117              outer1 = pitch1 + pitch_to_outer_angle
 118
 119              pitch2 = c + half_thick_angle
 120              base2  = pitch2 + pitch_to_base_angle
 121              outer2 = pitch2 - pitch_to_outer_angle
 122
 123              # Points
 124              b1 = point_on_circle( base_radius,  base1  )
 125              p1 = point_on_circle( pitch_radius, pitch1 )
 126              o1 = point_on_circle( outer_radius, outer1 )
 127
 128              b2 = point_on_circle( base_radius,  base2  )
 129              p2 = point_on_circle( pitch_radius, pitch2 )
 130              o2 = point_on_circle( outer_radius, outer2 )
 131
 132              if root_radius > base_radius:
 133                  pitch_to_root_angle = pitch_to_base_angle - involute_intersect_angle(base_radius, root_radius )
 134                  root1 = pitch1 - pitch_to_root_angle
 135                  root2 = pitch2 + pitch_to_root_angle
 136                  r1 = point_on_circle(root_radius, root1)
 137                  r2 = point_on_circle(root_radius, root2)
 138                  p_tmp = [r1,p1,o1,o2,p2,r2]
 139              else:
 140                  r1 = point_on_circle(root_radius, base1)
 141                  r2 = point_on_circle(root_radius, base2)
 142                  p_tmp = [r1,b1,p1,o1,o2,p2,b2,r2]
 143
 144              points.extend( p_tmp )
 145
 146         path = points_to_svgd( points )
 147
 148         # Create SVG Path for gear
 149         gear = self.document.createElement( 'svg:path' )
 150         style = { 'stroke': '#000000', 'fill': 'none' }
 151         gear.setAttribute( 'style', simplestyle.formatStyle(style) )
 152         gear.setAttribute( 'd', path )
 153
 154         # Embed gear in group to make animation easier:
 155         #  Translate group, Rotate path.
 156         g=self.document.createElement('g')
 157
 158         g.setAttribute( 'inkscape:label', 'Gear' + str( teeth ) )
 159         t = 'translate(' + str( self.view_center[0] ) + ',' + str( self.view_center[1] ) + ')'
 160         g.setAttribute( 'transform', t )
 161         self.current_layer.appendChild( g )
 162         g.appendChild( gear )
 163
 164 e = Gears()
 165 e.affect()
 166