Modified Denavit–Hartenberg (mdh)

Modified Denavit-Hartenberg parameters

Work in progress, use one the other libraries below (Inspiration)

Build kinematic chains using the modified Denavit-Hartenberg paramters

• d: offset along previous z to the common normal
• theta: angle about previous z, from old x to new x
• a: length of the common normal, assuming a revolute joint, this is the radius about previous z.
• alpha: angle about common normal, from old z axis to new z axis

Inspiration

You should probably use one of these, they inspired me to write a simpler module for my needs:

• pybotics
• pytransform3d, some matplotlib 3d examples
• robopy, has some good matplotlib 3d examples, but seems rather brittle and difficult to work with
• tinyik, uses open3d to visualize the mechanism

Example

import numpy as np
from mdh.kinematic_chain import KinematicChain
from mdh import UnReachable # exception

# make it print better
np.set_printoptions(suppress=True)

# modified DH parameters: alpha a theta d
# types: revolute=1, prismatic=2 (not implemented yet)
dh = [
    {'alpha': 0,  'a': 0, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': pi/2, 'a': 52, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': 0, 'a': 89, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': 0, 'a': 90, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': 0, 'a': 95, 'theta': 0, 'd': 0, 'type': 1}
]

kc = KinematicChain.from_parameters(dh)

# forward kinematics
angles = np.deg2rad([-45.00, 77.41, -98.15, -69.27, 0])
t = kc.forward(angles)
print(f">> {t}")

# inverse kinematics
pt = [110,0,-70]
deg = kc.inverse(pt)
rad = np.rad2deg(deg)
print(f">> {rad}")

MIT License

Copyright (c) 2019 Kevin J. Walchko

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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