Using pot-magnets to enable stable and scalable electromagnetic tactile displays

We present the design, fabrication, characterization and psychophysical testing of a scalable haptic display based on electromagnetic (EM) actuators. The display consists of a 4x4 array of taxels, each of which can be in a raised or a lowered position, thus generating different static configurations. One of the most challenging aspects when designing densely-packed arrays of EM actuators is obtaining large actuation forces while simultaneously generating only weak interactions between neighboring taxels. In this work we introduce a lightweight and effective magnetic shielding architecture. The moving part of each taxel is a cylindrical permanent magnet embedded in a ferromagnetic pot, forming a pot-magnet. An array of planar microcoils attracts or repels each pot-magnet. This configuration reduces the interaction between neighboring magnets by more than one order of magnitude, while the coil/magnet interaction is only reduced by 10%. For 4 mm diameter pins on an 8 mm pitch, we obtained displacements of 0.55 mm and forces of 40 mN using 1.7 W. We measured the accuracy of human perception under two actuation configurations which differed in the force vs. displacement curve. We obtained 91% of correct answers in pulling configuration and 100% in pushing configuration

The effects of realistic tactile haptic feedback on user surface texture perception

Haptic interaction plays an important role in virtual reality and human-computer interaction paradigms. However, most haptic devices only create kinesthetic feedback or simple unrealistic tactile feedback. This study presents theory and practice for creating realistic tactile feedback. The approach is based upon skin sensing capabilities, tactile perception principles, and tactile stimulation techniques. The approach uses a vibration sensor, controller, and actuator to create a tactile haptic device. The device is portable, small, light, and cost-effective. This study uses the device to create realistic tactile sensations from actual surface features, and measures the effects of tactile haptic feedback on user surface texture perception. Verification test results show that the device can create realistic tactile feedback that matches actual surface features well. User test results show that users can match actuator vibrations for 40-grit and 180-grit surface textures to actual 40-grit and 180-grit surface textures 99.3 % of the time

The effects of realistic tactile haptic feedback on user surface texture perception

Haptic interaction plays an important role in virtual reality and human-computer interaction paradigms. However, most haptic devices only create kinesthetic feedback or simple unrealistic tactile feedback. This study presents theory and practice for creating realistic tactile feedback. The approach is based upon skin sensing capabilities, tactile perception principles, and tactile stimulation techniques. The approach uses a vibration sensor, controller, and actuator to create a tactile haptic device. The device is portable, small, light, and cost-effective. This study uses the device to create realistic tactile sensations from actual surface features, and measures the effects of tactile haptic feedback on user surface texture perception. Verification test results show that the device can create realistic tactile feedback that matches actual surface features well. User test results show that users can match actuator vibrations for 40-grit and 180-grit surface textures to actual 40-grit and 180-grit surface textures 99.3 % of the time

Optimization of the force and power consumption of a microfabricated magnetic actuator

The force (F) and the power consumption (P ) of a magnetic actuator are modeled, measured and optimized in the context of developing micro-actuators for large arrays, such as in portable tactile displays for the visually impaired. We present a novel analytical approach complemented with finite element simulation (FEM) and experiment validation, showing that the optimization process can be performed considering a single figure of merit. The magnetic actuator is a disc-shaped permanent magnet displaced by planar microcoil. Numerous design parameters are evaluated, including the width and separation of the coil traces, the trace thickness, number of turns and the maximum and minimum radius of the coil. We obtained experimental values ranging from 2 to 12 mN/ sqrt(W) using up to 2-layer coils of both microfabricated and commercial printed circuit board (PCB) technologies. This performance can be further improved by a factor of two by adopting a 6-layer technology. The method can be applied to a wide range of electromagnetic actuators

Multimodal interaction: developing an interaction concept for a touchscreen incorporating tactile feedback

The touchscreen, as an alternative user interface for applications that normally require mice and keyboards, has become more and more commonplace, showing up on mobile devices, on vending machines, on ATMs and in the control panels of machines in industry, where conventional input devices cannot provide intuitive, rapid and accurate user interaction with the content of the display. The exponential growth in processing power on the PC, together with advances in understanding human communication channels, has had a significant effect on the design of usable, human-factored interfaces on touchscreens, and on the number and complexity of applications available on touchscreens. Although computer-driven touchscreen interfaces provide programmable and dynamic displays, the absence of the expected tactile cues on the hard and static surfaces of conventional touchscreens is challenging interface design and touchscreen usability, in particular for distracting, low-visibility environments. Current technology allows the human tactile modality to be used in touchscreens. While the visual channel converts graphics and text unidirectionally from the computer to the end user, tactile communication features a bidirectional information flow to and from the user as the user perceives and acts on the environment and the system responds to changing contextual information. Tactile sensations such as detents and pulses provide users with cues that make selecting and controlling a more intuitive process. Tactile features can compensate for deficiencies in some of the human senses, especially in tasks which carry a heavy visual or auditory burden. In this study, an interaction concept for tactile touchscreens is developed with a view to employing the key characteristics of the human sense of touch effectively and efficiently, especially in distracting environments where vision is impaired and hearing is overloaded. As a first step toward improving the usability of touchscreens through the integration of tactile effects, different mechanical solutions for producing motion in tactile touchscreens are investigated, to provide a basis for selecting suitable vibration directions when designing tactile displays. Building on these results, design know-how regarding tactile feedback patterns is further developed to enable dynamic simulation of UI controls, in order to give users a sense of perceiving real controls on a highly natural touch interface. To study the value of adding tactile properties to touchscreens, haptically enhanced UI controls are then further investigated with the aim of mapping haptic signals to different usage scenarios to perform primary and secondary tasks with touchscreens. The findings of the study are intended for consideration and discussion as a guide to further development of tactile stimuli, haptically enhanced user interfaces and touchscreen applications

The Hand-Held Force Magnifier: Surgical Tools to Augment the Sense of Touch

Modern surgeons routinely perform procedures with noisy, sub-threshold, or obscured visual and haptic feedback,either due to the necessary approach, or because the systems on which they are operating are exceeding delicate. For example, in cataract extraction, ophthalmic surgeons must peel away thin membranes in order to access and replace the lens of the eye. Elsewhere, dissection is now commonly performed with energy-delivering tools – rather than sharp blades – and damage to deep structures is possible if tissue contact is not well controlled. Surgeons compensate for their lack of tactile sensibility by relying solely on visual feedback, observing tissue deformation and other visual cues through surgical microscopes or cameras. Using visual information alone can make a procedure more difficult, because cognitive mediation is required to convert visual feedback into motor action. We call this the “haptic problem” in surgery because the human sensorimotor loop is deprived of critical tactile afferent information, increasing the chance for intraoperative injury and requiring extensive training before clinicians reach independent proficiency. Tools that enhance the surgeon’s direct perception of tool-tissue forces can therefore potentially reduce the risk of iatrogenic complications and improve patient outcomes. Towards this end, we have developed and characterized a new robotic surgical tool, the Hand-Held Force Magnifier (HHFM), which amplifies forces at the tool tip so they may be readily perceived by the user, a paradigm we call “in-situ” force feedback. In this dissertation, we describe the development of successive generations of HHFM prototypes, and the evaluation of a proposed human-in-the-loop control framework using the methods of psychophysics. Using these techniques, we have verified that our tool can reduce sensory perception thresholds, augmenting the user’s abilities beyond what is normally possible. Further, we have created models of human motor control in surgically relevant tasks such as membrane puncture, which have shown to be sensitive to push-pull direction and handedness effects. Force augmentation has also demonstrated improvements to force control in isometric force generation tasks. Finally, in support of future psychophysics work, we have developed an inexpensive, high-bandwidth, single axis haptic renderer using a commercial audio speaker