Design, characterisation, and application of multimodal haptic interaction systems for the torso in virtual environments

Resumen

The sense of touch is fundamental to interact with the surroundings in whichever daily situation since it provides diverse information of the environment and the objects, such as textures, weight, state (solid, viscous) or the temperature, that a human being cannot perceive through the rest of the senses. Currently, the simulation of a real situation in a virtual environment usually renders visual and auditory stimuli because they are simpler to create. However, the sense of touch remains underused, losing all that information that would contribute to develop the full sensation of being experiencing a real situation. During the last years, the inclusion of haptic devices in virtual reality systems have increased exponentially, but focusing on those areas of the body which allow an active interaction with the virtual scenario (e.g. the hands), forgetting those areas which can be passively stimulated (e.g. the torso or the legs). In this thesis, I designed and developed a haptic vest for the torso, which contains vibrotactile, thermal, and impact feedback. Vibrotactile actuators are eccentric rotating mass motors, which provide a broad range of vibrations intensity to create haptic patterns. In this case, the motors have been characterised to optimise their operation according to the experimental conditions of the haptic vest. The thermal actuators are Peltier cells, which allow the rendering of cold and hot stimuli with a single device. Lastly, I designed and developed a new actuator owing to the scarcity of systems for simulating impacts. The actuator is based on a mechanical system to render impacts readily perceptible. The last step was the design of the control systems for each actuator, and an overall control system to handle the entire haptic vest and communicate with virtual reality systems. It is also essential the textile design of the vest to place the actuators so that the definitive device is not heavy or bulky, and actuators remain always fully attached to the user’s skin for conveying the haptic information dependably. Both the distribution of actuators in the vest and the creation of haptic patterns which provide accurate information to users must be based on psychophysical variables of the perception over the torso, such as the vibrotactile and thermal spatial acuity afford to know the required distance between two actuators simultaneously operating so that users perceive two different stimuli. Distributing the actuators according to those distances confers more versatility to the creative procedure, and the ensuing haptic patterns can serve either to create a generalised stimulation or to develop haptic sequences to provide more specific information. Furthermore, the perceptual thresholds (absolute and differential) afford to know the limits to detect vibratory or thermal stimuli, in such a manner that created patterns are always perceptible, and they convey accurate information. It was necessary to validate the design and the development of the vest to ensure that the configuration is adequate, and the creation of vibrotactile, thermal, and impact patterns is reliable. The validation experiment consisted of creating stimuli all over the torso, which users had to identify and detail all their characteristics. As results were satisfactory, the haptic vest is ready for its integration into whichever virtual reality system. The next step was to conduct several tests to verify if the haptic vest is integrated appropriately into virtual reality systems and if it benefits the user’s experience. In the first experiment, the user had to interact with a virtual environment during a post-explosion scenario. Results determine that the haptic vest improves the subjective perception of the virtual environment (immersion and sense of presence) and, therefore, it provides benefits to end the entrusted tasks with more easiness and accuracy. Moreover, this experiment also denoted that the perception differs according to the previous expertise of users with similar systems. Professional users customarily assessed more critically than those users who had never employed virtual reality systems or haptic devices. The validation and the first experiment revealed corrective actions to enhance the operation of the haptic vest. The next experiment employed the optimised vest integrated into a stressful and distressing virtual environment, aiming to foster the user’s responses regarding the immersion and the sense of presence. Moreover, this experiment also employed objective measures (physiological constants or the observation of autonomous physical responses, among others) to reinforce the subjective results. Not only did the subjective perception improve regarding the previous experiment, but the objective measures firmly bolstered conclusions about the influence of the haptic vest for increasing the immersion and the sense of presence in the virtual environment, and optimising the performance to complete the entrusted tasks. Finally, the collaboration with the Perce Perceptual Robotics Laboratory (PERCRO) de la Scuola Superiore Sant’Anna - TeCIP Institute in Pisa afforded to move forward the development of full-body haptic devices, integrating a fingertip haptic device to interact actively with the same stressful virtual environment. The joint integration of both elements (i.e. the fingertip device and the haptic vest) gives more versatility to interact with a virtual scenario, optimising the user’s sensations during the experience and the performance to finish the tasks and fulfil the objectives. Results of this experiment support to set the foundation for creating full-body haptic devices so that users accomplish the perception of a virtual environment through whichever body part as if they were in a real situation.