News from the University of Surrey

Stiff-flop module

The STIFF-FLOP consortium successfully demonstrated the integration of the large-scale system using two flexible modules and validated its performance in real-time for an ex-vivo tissue ablation case study. The two optimised STIFF-FLOP modules are integrated with position and force sensors.

The Aurora magnetic position sensor is used to calculate the bending angle of the modules which in turn are used for the closed loop control of the robot system, as well as for the 3D visuali-zation of the flexible manipulator. The functionality of the integrated system was demonstrated to one of the reviewers at Kings College London, in September 2014 and described in reports to the Project Officer.

UoS led the work on developing the controller for the 2-segment STIFF-FLOP arm, and contributed strongly to the creation of segments and the phantom organ shown in the figure. The integrated platform was shown to be capable of navigating around a phantom organ of the colon as well as performing ablation of tissue.

Stiffness control in soft robots is challenging because the kinematics and force mapping cannot be decoupled at the tip. In order to sense the stiffness of soft robots, such as the STIFF-FLOP manipulator, an accurate force sensor mounted at the tip is utilized. Moreover, the pressures of the chambers of each segment can be controlled accurately, and they can have direct effects on the stiffness and the tip force of the manipulator. Preliminary investigations were conducted by the team at the University of Surrey to exploit these features to control the stiffness/force at the tip of the STIFF-FLOP manipulator, in order to resist external disturbances. An adaptable stiffness matrix concept, similar to what is used in the control of rigid robots, is utilized here to get a stiffness matrix that relates the force at the tip to the pressures of the chambers.  



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The integrated Stiff-Flop system at UoS



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