Our lab has developed a haptic feedback device to provide ungrounded tactile feedback through the motion of actuated sliding plate contactors. Interaction with a virtual environment is provided to a user through a device equipped with tactile feedback and six degree-of-freedom spatial position sensing. Our tactile feedback device is composed of three sliding plate skin stretch displays positioned around the handle, providing feedback to a user's palm. Our dual-handed tactile feedback system allows independent motion of hands, while providing feedback that creates a kinesthetic experience. We demonstrate fundamental physical interactions such as mass, spring, and damper interactions, which are the building blocks used in every virtual model. Various virtual environments are used to demonstrate physical interactions with objects.

The Active Handrest is a large workspace assistive robotic device that has been shown to significantly improve the user performance of various movement tasks. This device has the potential to assist highly accurate motions without the need for a robotically enabled or comanipulated tool while allowing the user to retain complete control over a grasped tool. This paper evaluates the Active Handrest's effect on the kinematics of user movements together with various virtual fixture control strategies to further improve the human performance while using the Active Handrest. The most effective fixture strategy for tracing straight lines is first determined. Then, this fixture strategy is directly implemented on the Active Handrest's motions. Finally, the performance of different fixture strategies is assessed through speed-accuracy tradeoff and movement kinematics. It is concluded that fixtures implemented on the Active Handrest are as effective as those implemented on a grasped tool, which enables users of the Active Handrest high accuracy with ordinary tools such as a scalpel or paint brush. The performance is further improved when fixtures are implemented on both the Active Handrest and the grasped tool.

This paper presents the design and development of a novel device for providing tactile feedback in five degrees of freedom (5-DOF). Four translational and four rotational motions of the hand can be communicated to a user using two independently controlled 2-DOF skin stretch feedback devices placed back-to-back. An additional two rotational motions of the hand can be communicated through spiral motions of the two skin stretch feedback devices. The user's index finger and thumb grasp the device at the location of the moving contactor (tactor) of each of the 2-DOF skin stretch displays, respectively. Experiments show user responses to have high directional accuracy (> 98%) for each of the five degrees of freedom communicated by the device. A second experiment also shows a proof of concept for using the back-to-back skin stretch display to guide users' hand motions to match a specified target angle in a one degree-of-freedom wrist rotation task. Findings from this preliminary study will be used in future studies to investigate users' ability to track paths in multiple degrees of freedom or to direct the hand motions of a user, which could be relevant to tasks such as upper limb rehabilitation, swing training, or other motion training.

This paper presents a two degree-of-freedom (2-DOF) force feedback joystick with a 2-DOF skin stretch feedback device integrated into the top of its handle (where the user rests his/her thumb). An experiment is conducted to better understand how users interpret directional information from force and skin stretch cues. Results show that users exhibit significantly greater accuracy when responding to force cues, but have significantly greater precision when responding to skin stretch cues. Precision is further improved when these cue types are combined. Integrating skin stretch and low-magnitude force cues in this manner shows promise for applications where force information is beneficial, but cannot be presented due to the risk of creating feedback instabilities. Hence skin stretch feedback could be used to supplement lower, non-destabilizing levels of force feedback, or to augment underpowered force feedback systems. Skin stretch may also be used as a lower cost, more compact substitute to force feedback.

A novel, low inertia, two degree-of-freedom (2-DOF) contact location display (CLD) device has been designed, prototyped, and tested. This device positions a small spherical contactor beneath the user's fingerpad at the point of contact between the finger and a virtual surface. Kinesthetic forces are provided by a custom haptic device attached to the CLD. The contactor is remotely driven by push-pull wires to reduce the effective inertia of the device at the user's fingertip; however, this design results in significant mechanical backlash. This backlash is characterized and partially compensated for in software. An experiment was used to evaluate several methods of rendering tactile feedback, each using a different method of prepositioning the contactor. The results show no statistical performance differences between rendering conditions. However, a post-experiment survey shows that participants perceived contact location + kinesthetic feedback as more realistic than pure kinesthetic feedback.

The effect of contact location information on the perception of virtual edges was investigated by comparing human edge sharpness discrimination under the force-alone and force-plus-contact-location conditions. The virtual object consisted of the 2D profile of an edge with two adjoining surfaces. Edge sharpness JNDs for both conditions increased from about 2 to 7 mm as the edge radii increased from 2.5 to 20.0 mm, and no significant difference was found between the two conditions. A follow-up experiment with the contact-location alone condition resulted in higher (worse) edge sharpness discrimination thresholds, especially at higher edge radius values. Our results suggest that contact location cues alone are capable of conveying edge sharpness information, but that force cues dominate edge sharpness perception when both types of cues are available.