Design and Evaluation of a 3-DoF Haptic Device for Directional Shear Cues on the Forearm.

Wearable haptic devices on the forearm can relay information from virtual agents, robots, and other humans while leaving the hands free. We introduce and test a new wearable haptic device that uses soft actuators to provide normal and shear force to the skin of the forearm. A rigid housing and gear motor are used to control the direction of the shear force. A 6-axis force/torque sensor, distance sensor, and pressure sensors are integrated to quantify how the soft tactor interacts with the skin. When worn by participants, the device delivered consistent shear forces of up to 0.64 N and normal forces of up to 0.56 N over distances as large as 14.3 mm. To understand cue saliency, we conducted a user study asking participants to identify linear shear directional cues in a 4-direction task and an 8-direction task with different cue speeds, travel distances, and contact patterns. Participants identified cues with longer travel distances best, with an 85.1% accuracy in the 4-direction task, and a 43.5% accuracy in the 8-direction task. Participants had a directional bias, with a preferential response in the axis towards and away from the wrist bone.

Mechanofluidic Instability-Driven Wearable Textile Vibrotactor.

Vibration is a widely used mode of haptic communication, as vibrotactile cues provide salient haptic notifications to users and are easily integrated into wearable or handheld devices. Fluidic textile-based devices offer an appealing platform for the incorporation of vibrotactile haptic feedback, as they can be integrated into clothing and other conforming and compliant wearables. Fluidically driven vibrotactile feedback has primarily relied on valves to regulate actuating frequencies in wearable devices. The mechanical bandwidth of such valves limits the range of frequencies that can be achieved, particularly in attempting to reach the higher frequencies realized with electromechanical vibration actuators ( 100 Hz). In this paper, we introduce a soft vibrotactile wearable device constructed entirely of textiles and capable of rendering vibration frequencies between 183 and 233 Hz with amplitudes ranging from 23 to 114 g. We describe our methods of design and fabrication and the mechanism of vibration, which is realized by controlling inlet pressure and harnessing a mechanofluidic instability. Our design allows for controllable vibrotactile feedback that is comparable in frequency and greater in amplitude relative to state-of-the-art electromechanical actuators while offering the compliance and conformity of fully soft wearable devices.

Effect of Tactile Masking on Multi-Sensory Haptic Perception.

Multi-sensory wearable haptic devices are able to encode a variety of information using multiple haptic cues. However, simultaneous cues can be misperceived due to tactile masking effects. In this paper, we investigate the effect of masking on the perception of skin stretch and squeeze. We performed three experiments measuring the just-noticeable difference (JND) and the absolute threshold of skin stretch and squeeze alone and in the presence of simultaneous haptic cues. Additionally, we investigate the relative perceptual amplitudes of these haptic cues. Results indicate that the JND for a skin stretch cue increases with a masking squeeze cue, while the JND for a squeeze cue does not change with a masking stretch cue. Also, masking has a significant effect on the absolute threshold of both skin stretch and squeeze. These results suggest that the effect of masking diminishes as haptic cues become larger in amplitude. The results from the subjective equality experiment suggest a potential nonlinear relationship between perceptual magnitudes. Further testing should be carried out to investigate this relationship. Future multi-sensory devices can use these perceptual experiment findings to ensure the delivery of salient cues to users.