Rotational skin stretch feedback: A new approach to wearable haptic display

We live in an increasingly technologically mobile environment where personal devices fit easily in our pockets and information is literally at our fingertips. However, while the information is at our fingertips, we obtain almost none of it with our fingertips, i.e., via tactile or haptic feedback from the devices. In contrast, haptic cues are an essential means by which humans and all other animals receive information about the world around them.;The work in this thesis is motivated by the idea that new modes of haptic interaction are needed to expand the range of activities and applications for wearable electronic devices. In applications ranging from motion training and physical rehabilitation to teleoperation of a remote system, haptic feedback can provide valuable information about forces and motions, particularly when vision and audition are otherwise occupied.;Today, by far the most widely used haptic technology for portable devices is vibration, as commonly found in cell phones. Vibration is easy to implement, but is best suited for transient event cues and is less effective when used continuously. It can lead to desensitization and many users find the stimulus annoying after a prolonged period of time. In addition, sensitivity to vibrations can be reduced when people are in motion. An under appreciated component of haptic sensation, particularly for applications involving portable devices, is skin stretch. Skin stretch is a known part of the normal physiological apparatus for proprioception, contributing to our sense of motion and location of our limbs. The motions and velocities necessary to impart skin stretch can be low, allowing for the design of compact, low-power, wearable devices. With this motivation, the work in this thesis has focused on skin stretch for the display of proprioceptive information associated, for example, with the motions of a person's limbs. Two skin stretch devices are described. The first is a highly adjustable benchtop device for controlled testing; the second is a compact, wearable device to test skin stretch feedback in applications similar to those that might ultimately be encountered in motion training or proprioceptive feedback for amputees.;The major sections of this thesis are focused on understanding and quantifying the ability of humans to use and interpret rotational skin stretch. A series of psychophysical tests were completed to quantify the resolution of the devices. Our ability to interpret the feedback depends heavily on the setting and task. In an isolated environment, users are able to discriminate between different rotational displacements of stretch within 2-5 degrees, depending on the reference stimulus. In a more realistic setting where users are able to use the feedback to actively orient a virtual object, they are capable of positioning the object within +/- 6 degrees on average. However, when users sit passively and are asked simply report the position of an autonomously moving object which they do not control, performance degrades. There is also a region of stretch near zero degrees, in which subjects have difficulty in interpreting the feedback accurately, which we call a "region of uncertainty". The size of this region depends on the details of the skin stretch end effector that is in contact with the skin. A three-dimensional analysis of skin motions, using visual tracking of markers on the skin, provides additional insight into the region of uncertainty and the factors that contribute to it.;A final set of experiments considers skin stretch in applications related to rehabilitation, or to the control of a prosthetic or teleoperated device, where skin stretch feedback substitutes for normal proprioception. Skin stretch feedback is compared to vibration feedback and to a baseline case of no haptic feedback. The results suggest that subjects can use skin stretch feedback to improve their control of a virtual device. A particular benefit of skin stretch feedback in comparison to vibration is that it provides subjects with a sense of velocity as well as postion.