Virtual Force Feedback
This project focused on using an vibrating device (AVD) to display haptic feedback. Simple vibrational cues have long been used in consumer electronics. Some examples are a cell phone’s vibrating alerts, or the “Force Touch” trackpads in MacBooks, However, these are merely binary cues for the user while some devices exhibit an ability to give much richer haptic feedback. A common example is the 6 DOF Phantom Omni which uses a grounded serial chain to transmit force feedback to the user via stylus. Such serial architecture is the most common for force-feedback devices, but the mechanical linkages required limit the workspace and do not make them suitable to situations like virtual reality where some mobility is desired.
Recent studies have shown that ungrounded AVDs can induce virtual force feedback sensations. While there is zero net force over time, they generate a perceived force for users that can be pretty effective. It was my goal with this project to give some measure of how effective they can be in guiding motion for a user. With that in mind, I set up a virtual 1-dimensional linear spring and ran a task oriented exeriment to determine whether or not user’s could locate the center of this virtual spring (ie. where the vibration waveform pattern is symmetric).
Four subjects were tested in this pilot experiment. Each one was seated at the table like the image below. Six trials were conducted for each subject.
Each trial started with a randomized calculation for spring center. Then, based on the position of the user’s arm/hand which was sensed using an HC-SR04 ultrasonic sensor and averaging filter, an asymmetric sine waveform was generated on the arduino and passed first through a low-pass filter (to handle noise) and then a high-pass filter (to handle dc biasing). Finally, the signal was amplified using a Pyle PCA1 stereo power amplifier and fed to the AVD (TactileLabs MM3C) which was held by the user in parallel to the virtual spring.
Below is a histogram of the positional error data in the experiment. It is clear that each subject was able to locate the center of the virtual spring in each trial. With a max error of about 4 cm in a 100 cm workspace, it is also clear that they were able to do so accurately. And given the crude nature of ultrasonic sensors, this was particularly encouraging.
 G. Robles-De-La-Torre and V. Hayward, “Force can overcome objects geometry in the perception of shape through active touch,” Nature, vol. 412, no. 6845, pp. 445-448, 2001.
 K. Drewing and M. Ernst, “Integration of force and position cues for shape perception through active touch,” Brain Research, vol. 1078, pp. 92-100, 2006.
 T. Amemiya and H. Gomi, “Distinct pseudo-attraction force sensation by a thumb-sized vibrator that oscillates asymmetrically,” in Proceedings of the 9th International Conference of EuroHaptics, 2014.
 H. Culbertson, J. M. Walker and A. M. Okamura, “Modeling and design of asymmetric vibrations to inducce ungrounded pulling sensation through asymmetric skin displacement,” Philadelphia, PA, 2016.
 H. W. Tappeiner, R. L. Klatzky, B. Unger and R. Hollis, “Good vibrations: Asymmetric vibrations for directional haptic cues,” in World Haptics 2009 - Third Joint EuroHaptics conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, Salt Lake City, UT, 2009 .