Design Concept for Haptic and Thermal Sensorial modalities in Virtual Reality Interactions Evaluation

Virtual Reality (VR) is one of the most innovative and captivating technologies under development in the 21st century. Its potential is largely attached to the many possibilities it offers in varied industries. Virtual reality (VR) is a simulated experience that can be similar to or completely different from the real world. The aim of VR is to create a sensory experience for the user sometimes including sight, touch, hearing, smell, or even taste. The VR industry as a whole is growing at a fast pace, with the market size of consumer virtual reality hardware and software projected to increase from 6.2 billion U.S. dollars in 2019 to more than 16 billion U.S. dollars by 2022.

One of the essential aspects in this context is the degree of realism in the touch of materials that the user can experience in a VR environment. Until recently, most of the VR technology was limited to audible and visual experiences. However, with the development of various controllers, people can now interact with the VR contents using the same gestures they use in everyday life. In addition, equipment such as a VR glove can be used to experience the sense of touch using vibrations while interacting with the VR contents. However, there is a limit to universal use due to the costliness of a VR glove and inconvenience in wearing them owing to the size of the gloves. Additionally, the level of immersion is still limited to immature and constraining technologies. This project documents a design proposal for a VR system that uses haptic and thermal sensorial modalities to simulate simulating texture and temperature of a surface in a simulated environment. The basic idea is to use material analysis through texture maps and shaders along with heat monograms to provide prime properties of substance before projecting them to the VR system.

Current Academic Work

            There is a moderate profusion of research relating to sensorial modalities for human computer interaction systems.

Spagnoletti et al. (2018) have presented a paper on rendering of pressure and textures using wearable haptics in which they exhibited a novel wearable haptic system for immersive virtual reality experiences. It conveys the sensation of touching objects made of different materials, rendering pressure and texture stimuli through a moving platform and a vibrotactile motor. The device is composed of two platforms: one placed on the nail side of the finger and one in contact with the finger pad, connected by three cables. One small servomotor controls the length of the cables, moving the platform towards or away from the fingertip. One voice coil actuator, embedded in the platform, provides vibrotactile stimuli to the use in immersive VR environments.

            Lécuyer, Burkhardt, & Etienne, (2004) presented a new interaction technique to simulate textures in desktop applications without a haptic interface. They proposed technique consisted in modifying the motion of the cursor on the computer screen – i.e. the Control/Display ratio. Assuming that the image displayed on the screen corresponds to a top view of the texture, an acceleration (or deceleration) of the cursor indicates a negative (or positive) slope of the texture. Experimental evaluations showed that participants could successfully identify macroscopic textures such as bumps and holes, by simply using the variations of the motion of the cursor. Furthermore, the participants were able to draw the different profiles of bumps and holes which were simulated, correctly. These results suggested that their technique enabled the participants to successfully conjure a mental image of the topography of the macroscopic textures. Applications for this technique are: the feeling of images (pictures, drawings) or GUI components (windows’ edges, buttons), the improvement of navigation, or the visualization of scientific data.

            Most of the current research work on human thermal perception and psychophysical mechanisms, involved during haptic exploration, focus on hot/warm and cold thresholds. Other projects such as developed at CM, Inc, have defined a system called DTSS (Displaced Temperature Sensing System). This system has a collection of eight thermodes (each thermode is composed of a radiator, a Peltier effect semiconductor and a temperature sensor). Caldwell et al. proposed an anthropomorphic teleoperation system that integrates temperature sensors on a robot gripper and a temperature feedback supplier on an operator master glove Benali-Khoudjal et al. (2003) proposed a Thermal feedback model for virtual reality. Their goal was to to model the thermal transfer between the skin and any explored surface in order to reproduce the different thermal sensations when exploring virtual objects in virtual environments. Their model was based on an electric analogy and took into account various phenomena, including convection of the air, convection of the blood and conduction of the skin, as well as other important parameters like the applied pressure by the finger, the speed of the blood circulation, the surface state of the skin and the material.

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Existing Technology

Wearable haptics is recently attracting great attention in the fields of robotics, haptics, and mechanical engineering. Being able to provide effective haptic stimuli through lightweight, inexpensive, and unobtrusive devices can significantly enlarge the applications of haptic systems to new and exciting fields, such as gaming, rehabilitation, and remote maintenance. Recently, we have also seen a few start-up companies taking up this challenge and start developing wearable haptic devices for the fingertips. For example, Tactai (USA) has presented a fingertip wearable haptic device able to render pressure, texture, and the sensation of making and breaking contact with virtual objects. It can apply up to 6 N to the fingertip, and it weighs 29 g for 75×55×30 mm dimensions. In Europe, GoTouchVR (France) developed a 1-DoF wearable device equipped with a mobile platform capable of applying pressure and making/breaking contact with the fingertip. It can exert up to 1.5 N on the skin, it weighs 40 g for 50×12×30 mm dimensions, it is wireless, and the battery guarantees up to 2 hours of playtime. These companies have also already been showing demonstrations of their wearable haptics systems featuring immersive environments displayed through commercial virtual reality headsets For example, at CES 2017, both TACTAI and GoTouchVR showed their devices in a virtual reality application, using an Oculus Rift to render the scene and a Leap Motion controller for fingertip tracking. Also in the literature we can find several examples of wearable devices for the fingertips The challenge is to be able to provide effective stimuli while guaranteeing a high wearability, ergonomy, and low power consumption and cost.

From the technological point of view, the goal of surface haptics is to design and develop new devices in order to display tactile feedback to the users by modulating the interaction forces between the finger and the touch surface. In general, the current actuation technologies can be grouped based on the direction in which the finger is stimulated by the interaction forces, when the stimulation is in the normal direction, an actuator placed in the periphery of the surface creates a mechanical vibration that propagates inside the material and reaches the finger. This type of stimulation, denoted by normal vibration, is directly detectable by our tactile system if it occurs at a frequency below 1 kHz. In fact, vibration actuators are already embedded in mobile phones today for this purpose and used to alert the user about incoming calls and to provide confirmation for button press events. Although it is highly difficult to generate complex tactile effects using these simple actuators, they have been used by manufacturers due to their low-cost and low energy requirements. Using multiple actuators allows for more sophisticated stimulation techniques in the normal direction that lead to unique tactile effects. For example, imposing multiple vibrations on the surface with adequate amplitude or phase modulation provides a vibration sensation midway between the actual stimulated points, which can either be static or moving. This so-called tactile phantom sensation has been already studied intensively and used for many applications.

Other techniques are also possible mostly to localize vibrations to a small region on the surface by obtaining constructive and destructive waves where needed. The theory behind this principle has been investigated under the names of inverse filtering and modal composition. Instead of displaying continuous vibrations, short vibration pulses can be used to generate tactile effects in the normal direction, which is more challenging due to the resonating nature of the touch surface. The mechanical excitation of the surface produces echoes, which have to be cancelled out in order to obtain a short burst of normal displacement at a specific location. For that purpose, multiple actuators are placed on the surface, and their control signals are synchronized in order to create constructive and destructive interference. The references for these signals can be deduced from the time reversal theory.

It is also possible to modulate the contact force in the tangential plane to display tactile effects if there is a relative displacement between the finger and the tactile surface. For example, due to the viscoelastic properties of finger pulp, the lateral movement of the tactile surface can induce tangential forces inside the finger pulp and thus lateral vibrations. By modulating this lateral movement as a function of the finger displacement, it is even possible to render virtual textures on a tactile surface. Indeed, by means of a phenomenon called causality inversion, the forces produced by the lateral movement of the tactile surface can be matched to those produced by a real textured surface when a finger slides on it. Alternatively, researchers have devised ways to dynamically create friction modulation between the tactile surface and the finger sliding on its surface. This can be, for example, achieved by using actuators that generate ultrasonic waves on the tactile surface           

  The human being is homoeothermic. This allows him to make thermal exchanges by conduction, convection and evaporation. The temperature plays a major role in tactile exploration and in the perception of surrounding objects.

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