Novel Finger-like Soft Pneumatic Actuators for Affective Movement
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The ability to communicate emotion through movement is an important element to enable engaging social human-robot interaction. It has been shown that humans are capable of conveying emotion through hand and arm movements alone. Thus, simple robotics structures might be capable of emotion conveyance. In this thesis, the design and implementation of a finger-like robotic structure capable of performing movements that convey emotion is investigated. First, the requirements for such a mechanism are derived directly from human affective movement dynamics, coupled with application-specific constraints. Comparative analysis is performed on various actuation options based on these requirements. Studies suggest that fast dynamic motion is required for the conveyance of many emotions. Therefore, the analysis focused on determining actuation options that can produce controllable finger-like motion with fast dynamics. A class of pneumatic actuators called soft pneumatic artificial muscles (SPAMs) were determined to fit the requirements for finger-like affective motion better than the other available actuator options. SPAMs are a type of pneumatic actuator that provides customizable motion trajectories in three dimensional space without the need for rigid links or a transmission mechanism. The motion of these actuators can be designed to be similar to the motion of the human finger. Their motion also achieves high velocities and accelerations. In addition, SPAMs provide high power to weight ratios and are compliant, making them suitable for interaction with human users. In this thesis, a novel design for producing SPAMs, named wrapped SPAMs (WSPAMs) is introduced. Unlike previous SPAM designs, the production process of WSPAM is highly repeatable, while the motion trajectory can be easily tailored at the design stage. A model is presented for predicting the steady state angular displacement of the WSPAM actuator based on its geometrical parameters and the elasticity of the materials used in its production. The model is validated by experimental analysis. Two sets of experiments are designed and presented. The first set enables the estimation of the model parameters. In the second set of experiments, the estimated parameters are used to model WSPAMs through the possible range of design parameters. Six WSPAMs with design parameters within the physical limitations are constructed. Comparison of their performance against the modeled results is presented, and shows that the model is capable of estimating the performance of WSPAM within the physical limitations of its design. Finally, a pneumatic circuit and a closed-loop controller for the finger-like movement of these soft pneumatic actuators is developed. An innovative approach, which uses a gyroscopic sensor, is used to add feedback on the position of these actuators and make closed-loop control possible. Additionally, a simple and low-cost solution is designed to significantly improve the noisy behavior of the existing pneumatic driving mechanisms. The proposed controller design is validated on physical SPAM prototypes. Experimental results demonstrate the performance of the pneumatic and control system for the actuator, and its ability to track human movement trajectories with affective content.