Modelling soft tissue-mechatronic tool interactions during indentation

Models that predict soft tissue indentation forces have many important applications including estimation of interaction forces, palpation simulation, disease diagnosis and robotic assistance. These models play an essential role in developing mechatronic systems required in many medical applications, such as rehabilitation, clinical palpation and manipulation of organs, since the proper characterising of soft tissue properties mainly depends on the accurate estimation of indentation forces. A new indentation model for estimating circular indenter 'force-displacement' characteristics is presented in this paper. The proposed model is motivated by a 'force-displacement' soil-tool model and is computationally efficient. The main feature of the proposed model is that it can be used to predict the force variations for a variety of tools without the need for retuning the model parameters for each tool. A six-degree of freedom robot manipulator with force and position sensors is used to validate the indentation model. Measured force versus tool displacement data for lamb liver and kidney, for a variety of tool diameters, are presented and compared with the forces predicted by the model, showing very good agreement (root mean square error, RMSE < 8%).