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ssik

PyPI Python License: BSD-3-Clause

Analytical inverse kinematics for 6R and 7R revolute robot arms. Each arm becomes a single self-contained Python module that returns every IK branch with FK closure well below typical robot repeatability — and tightenable to machine precision when needed.

pip install ssik

Two-minute quickstart

from ssik.prebuilt import franka_panda_ik
import numpy as np

T_target = np.eye(4)
T_target[:3, 3] = [0.5, 0.1, 0.3]
sols = franka_panda_ik.solve(T_target)        # every analytical IK branch

13 prebuilt arms ship with the wheel: UR5, Puma 560, JACO 2, iiwa14, Gen3, Franka Panda, Rizon 4, Kassow KR810, UFactory xArm7, UFactory xArm6, Unitree Z1, AgileX PiPER, Flexiv Rizon 10. For other arms, run ssik build <your.urdf> once and import the emitted module.

Where to go next

  • Just want to use it? → Quickstart
  • Adapting to your robot? → Setting up your robot — calibration, custom tools, link conventions
  • Need the API surface? → API reference — Manipulator, Solution, Diagnostic, TolerancePolicy, postprocess helpers
  • Want to understand the dispatch? → Architecture — solver tier catalog + algorithmic lineage
  • Checking arm coverage? → Arm coverage — per-arm fixtures, speeds, FK floors

Why ssik exists

Numerical-IK libraries take a seed, run damped least-squares to a single converged configuration, and stop. ssik returns every analytical branch at near-machine precision. Branch enumeration matters for motion planning (try every branch, pick the one with best clearance), for dexterity analysis (the manipulability ellipsoid is per-branch), and for trajectory continuation across kinematic singularities.

ssik covers the kinematic classes that the subproblem-decomposition libraries (EAIK, IK-Geo) refuse: non-Pieper 6R (Kinova JACO 2's 55° twists, UFactory xArm6's joint-6 y-offset, AgileX PiPER's tilted wrist axes), non-SRS 7R (Flexiv Rizon 4, Kassow KR810), approximate-SRS (Kinova Gen3, 12 mm offset). See the README comparison table for measured numbers.

License

BSD-3-Clause. Clean-room reimplementations of algorithms from BSD-3-licensed IK-Geo and the academic publications of Raghavan–Roth (1990), Manocha–Canny (1994), Singh–Kreutz (1989), and Husty–Pfurner (2007). Algorithmic lineage documented in module docstrings.