Tactile Feedback at the Finger Tips for Improved Direct Interaction in Immersive Environments

Abstract

We present a new tactile feedback system for finger-based interactions in immersive virtual reality applications. The system consists of tracked thimbles for the fingers with shape memory alloy wires wrapped around each thimble. These wires touch the inside of the finger tips and provide an impression when they are shortened. We complement the impression on the finger tips by a subsequent vibration of the wire to generate a perceivable tactile stimulus over a longer period of time. The shortening and relaxation process of the wires as well as the vibration is controlled through a micro-controller receiving commands from the virtual reality application.We use the tactile feedback for communicating finger contacts with virtual objects in an application prototype for usability and reachability studies of car interiors. Our experiments with the system and an initial pilot study revealed that this type of feedback helps users to perform direct manipulation tasks with more reliability. Our users also preferred the system with tactile feedback over a system without the feedback. INTRODUCTIONThe automotive industry performs numerous analyses concerning safety, ergonomics, design, assembly and in many other areas during the development process of new car models. Today hardware models are commonly used for these analyses. The construction of these mock-ups is time-consuming and cost-intensive, their variability is limited. Some of the necessary analyses have the potential to be performed within virtual environments. Virtual models can be directly derived from CAD data and they are therefore available in very early phases of the development process. Variants and modifications can be accomplished easily and tools can be used that are not available in reality, e.g. arbitrary cuts and pseudo-colored visualizations of air flows inside the car.The use of virtual environments for ergonomic studies in a car interior is particularly challenging since the realistic interaction with various parts of the interior needs to be supported. We have developed the Immersive Interactive Data Model (I²D) [MF05], which allows users to directly interact with assemblies of the car such as doors, steering wheel, sun visors, etc. Two things are essential for this type of application in a CAVE-like environment: the real hand has to be exactly registered to the virtual hand to allow reachability studies and the users have to be able to recognize collisions of their fingers with virtual objects for reliable grasps and manipulations. However pure visual feedback is often not sufficient and haptic feedback systems are difficult to use in CAVE-like environments.We developed a tactile feedback system for the finger tips supporting users during direct interaction in immersive environments. The system consists of tracked thimbles for the fingers with thin shape memory alloy wires wound around each thimble (figure 1). The wires can be shortened by slightly heating them up by an electrical current. This effect is used to create an impression on the ...

A narrative review on haptic devices: relating the physiology and psychophysical properties of the hand to devices for rehabilitation in central nervous system disorders

“… Ultrasound, which may also target the FA-II afferents generating light touch [81]; and  Shape memory alloys that change shape when an electric current is passed through the alloy thus constricting the finger and generating pressure [49] [82] [83].…”

Design and qualitative evaluation of tactile devices for stroke rehabilitation

“…A commonly encountered problem with SMA wires is that they take a significant period of time to return to Martensite (through cooling); hence, both of these reported designs use external forces, applied by springs or permanent magnets, to combat this. The concept investigated in this research is based upon a design by Scheibe et al [24], where thimbles worn on the fingertips contain ø80µm SMA wires 'wrapped' around the finger. Upon the application of an electric current, the SMA wires shorten by 1.5-2.5mm, applying pressure to the fingertip.…”

“…However, through preliminary evaluation, it was reported that the device was large, restricted movement, and provided a weak sensation. Instead, it was found that direct contact of the SMA wires with the finger created a more noticeable sensation, hence we adopted and developed the design reported by Scheibe et al [24]. The first iteration (Fig.…”

“…With the previous devices, a constant PWM signal was used to drive the SMA wires; this means that to keep the temperature within comfortable limits during the stimulation period, the application of pressure is gradual (hence feeling like touching a 'spongy' object). This control scheme is depicted graphically by the dashed line in Fig 6. Instead of using the 'two-state' duty-cycle scheme reported by Scheibe et al [24] (which would require manual calibration for different size devices, and introduce considerable variability in the level of applied stimulation), PID resistance-control was implemented on the MSP430 microcontroller [22] [26]. This operates on the principle that as the phase of the SMA changes between Austenite and Martensite, its electrical resistance also changes.…”

Studying One and Two-Finger Perception of Tactile Directional Cues

“…The fingertips are among the most sensitive parts of the human body [9]. When haptically exploring the world with our hands, we usually make use of multiple fingers and multiple fingertips.…”