Combined Modal-Joint Space Control of Continuum Manipulators

Combined Modal-Joint Space Control Architecture

We recently submitted a paper to Advanced  Robotics exploring a novel control architecture for continuum robotics.  Building on experience gained from our previous works, this architecture attempts to simultaneously address the two major issues faced when attempting to accurately position continuum robots: excessive steady-state error, and unwanted vibrations due to both external disturbances and rapid motion commands.  This new control architecture recognizes that these sources of error are driven by different sets of physics.  It then attempts to match the coordinate space of the control to these physics.  A trajectory tracking controller, formulated in either joint- or task-space, corrects for steady state errors.  This portion of the control ties in closely with the research we presented at both ICRA 2011 and ICRA 2012.  To control vibrations, we utilized a controller formulated in the modal-space of the device.  This space is composed of the normal modes of the device, as determined by a lumped parameter control model.  The modal positions and velocities are determined using a least squares estimator in conjunction with a Proportional-Integral (PI) Observer, also constructed in the mode-space.

Command tracking frequency response shows improvement when utilizing combined space control architecture

By utilizing this controller, significant improvements in control bandwidth, and settling time were achieved.  Control bandwidth was almost doubled, with a significant reduction in the effect of disturbances on the system.

Paper Submitted to Advanced Robotics on 8/22/2013

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