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. Author manuscript; available in PMC: 2011 Jul 15.
Published in final edited form as: J Neural Eng. 2007 May 4;4(3):234–245. doi: 10.1088/1741-2560/4/3/009

Figure 2.

Figure 2

Endpoint ellipses for the six models (A–C). Ellipses represent the endpoint inertia (A), stiffness (B), and viscosity (C) of the optimal joint (left in B and C), and endpoint (right in B and C) controllers. The stiffness matrix of the JD, and JU/JS model is diagonal resulting in highly eccentric endpoint stiffness ellipses (B), while the addition of symmetric terms to the viscosity matrix for the joint controller JU/JS results in a dramatically less eccentric endpoint viscosity ellipse (C). The addition of symmetric terms to kR and kB in the endpoint controllers ES and EU also result in dramatically less eccentric and smaller endpoint ellipses (B,C). All ellipses are of approximately the same orientation.