An admittance-type robotic manipulator is a nonbackdrivable device whose motion is controlled to move in response to a user-applied force, typically with velocity proportional to force. This study characterizes the ability of ten human subjects to accurately and precisely control the velocity of such a device, using force applied by the index finger, as the user is provided visual feedback of device motion and a target velocity on a display. The admittance, the velocity, and the visualization scale factor are varied in a full factorial design, with parameter levels representative of microsurgery/micromanipulation tasks. The results indicate that: visual scaling has no effect, for the levels tested; low velocity at high admittance results in reduced precision and accuracy; high velocity at low admittance results in reduced accuracy; and an admittance-dependent velocity exists at which accuracy is maximized. The results suggest that gain scheduling will result in improved performance.

During multi-lateral collaborative teleoperation, where multiple human or autonomous agents share control of a teleoperation system, it is important to be able to convey individual user intent. One option for conveying the actions and intent of users or autonomous agents is to provide force guidance from one user to another. Under this paradigm, forces would be transmitted from one user to another in order to guide motions and actions. However, the use of force guidance to convey intent can mask environmental force feedback. In this paper we explore the possibility of using tactile feedback, in particular skin deformation feedback, skin deformation feedback to convey collaborative intent while preserving environmental force perception. An experiment was performed to test the ability of participants to use force guidance and skin deformation guidance to follow a path while interacting with a virtual environment. In addition, we tested the ability of participants to discriminate virtual environment stiffness when receiving either force guidance or skin deformation guidance. We found that skin deformation guidance resulted in a reduction of path-following accuracy, but increased the ability to discriminate environment stiffness when compared with force feedback guidance.

When a person interacts with an environment using a tool, he/she receives tactile information in the form of fingerpad skin deformation. Different interaction forces and torques on the tool cause different skin deformation patterns on the fingerpads. We designed a 6-degree-of-freedom tactile device that creates similar skin deformation patterns on the fingerpads. The device communicates force and torque information by translating and rotating skin deformation tactors relative to the fingerpads. An experiment was conducted to determine participants' ability to use skin deformation tactile cues to perform a peg-in-hole insertion task. Results show that participants can use the tactile cues to reduce interaction force and torque, and they use the tactile force cues to reduce interaction force more than they use the tactile torque cues to reduce interaction torque. Rendering force and torque cues simultaneously causes device saturation and degrades user performance. These results suggest that additional training may help participants use the skin deformation torque cues, and motivate a tactile device design that decouples force and torque skin deformation rendering to minimize device saturation. Fingerpad skin deformation is a promising form of tactile feedback to convey force and torque information in teleoperation systems such as robot-assisted surgery, where force feedback may be undesirable due to stability and safety concerns.

When we use a tool to explore or manipulate an object, friction between the surface of the tool and the fingerpads generates skin stretch cues that are related to the interaction forces between the tool and the object. In this study, we emulate these naturally occurring skin stretch cues in order to convey force direction and magnitude information to users during teleoperation. We hypothesize that skin stretch feedback is a useful substitute for kinesthetic force feedback in force-sensitive teleoperated tasks. In this study, ten participants performed teleoperated palpation to determine the orientation of a stiff region in a surrounding artificial tissue using five feedback conditions: skin stretch, force, reduced gain force, graphic, and vibration. When participants received skin stretch feedback, they localized the stiff region as well as with force feedback, with no increase in task completion time. Additionally, participants receiving skin-stretch feedback localized the stiff region statistically significantly more accurately than those using vibration feedback. Although participants using skin stretch exhibited higher interaction forces than when using force, vibration, and graphical feedback, skin stretch statistically significantly decreased interaction forces compared with reduced gain force feedback. Thus, skin-stretch feedback is a compelling substitute for force feedback and may be useful in scenarios where force feedback is reduced or infeasible.

The Planar Active Handrest (PAHR) is a large workspace assistive device that improves user precision manipulation. The PAHR is restricted in its use, because it does not rotate in the horizontal plane, which limits the workspace size and reduces user comfort. This paper evaluates an improved device, the Enhanced Planar Active Handrest (E-PAHR), which allows lateral/medial rotation of the upper arm. Under the E-PAHR design, the desired hand position can be obtained with redundant arm and device configurations. As such, we gave consideration to controller input choices and resultant device motions that are available. Three experiments evaluated the controller designs to select the most effective method to control our device. We conclude that a rotational DOF (degrees of freedom) allows the E-PAHR to better follow the kinematics of a user's planar arm movements while allowing skill level equal to the PAHR, with reduced user force input and lower perceived exertion.

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.

During tool-mediated interactions with objects, we experience force and fingerpad skin stretch resulting from shear forces caused by friction between the fingerpad skin and the stylus. When probing an object, for the same penetration distance, a stiffer object causes a larger load force and, thus, greater fingerpad skin stretch. We hypothesized that rendering additional artificial skin stretch together with force will increase perceived stiffness. We created a Skin Stretch Stylus that renders skin stretch through tactor displacement, attached it to a force-feedback device, and performed a study to characterize the effect of tactor displacement-induced skin stretch on stiffness perception. Results showed that adding artificial skin stretch causes additive augmentation of perceived stiffness across a range of surface stiffness, and the addition is a linear function of tactor displacement gain. However, intersubject variability in the estimated slope coefficient was large. We propose a model that explains the additive effect and suggests potential sources for the intersubject variability. We conclude that augmenting force feedback with skin stretch can increase users' perception of stiffness, but the effect is user-specific. Such augmentation may be useful in virtual environment and teleoperation scenarios when force feedback gains must be kept low to prevent feedback-induced instabilities, or when force feedback is limited due to actuator force limits.

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.

We investigate the role of contact location information on the perception of local features during contour following in a virtual environment. An absolute identification experiment is conducted under force-alone and force-plus-contact-location conditions to investigate the effect of the contact location information. The results show that the participants identify the local features significantly better in terms of higher information transfer for the force-plus-contact-location condition, while no significant difference was found for measures of the efficacy of contour following between the two conditions. Further data analyses indicate that the improved identification of local features with contact location information is due to the improved identification of small surface features.

When interacting with everyday objects, we experience kinesthetic force feedback as well as various forms of cutaneous tactile feed-back. Skin stretch is part of the cutaneous tactile experience that is caused by friction between the skin and the grasped object. Interacting with stiffer objects causes larger force, and results in a larger amount of skin stretch. Therefore, we hypothesize that adding artificial fingerpad skin stretch to kinesthetic force feedback will increase users' perception of stiffness. A tactile display called the Skin Stretch Stylus was designed to augment kinesthetic force feedback with skin stretch feedback. The change in users' stiffness perception due to the addition of skin stretch feedback is quantified through a two-alternative forced-choice paradigm, method of constant stimuli experiment. In this experiment, subjects compared the stiffness of virtual springs with kinesthetic force feedback augmented with skin stretch feedback versus virtual springs with only kinesthetic force feedback. Results show that the addition of skin stretch causes a significant increase in the perception of stiffness, and this effect increases with higher amount of applied skin stretch. These results indicate that skin stretch feedback could be used to augment perceived stiffness in situations where it is not possible to increase force feedback gains. Such scenarios include teleoperation systems where force feedback gains must remain low to ensure stability, and haptic devices with limited actuator force.

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.

Skin stretch is a novel haptic feedback method that can provide a human operator with information about the magnitude and direction of an applied force. To evaluate the potential for skin stretch feedback to be used as a sensory substitute for kinesthetic (force) feedback in robotic teleoperation systems, a study was conducted to measure the ability of users to discriminate environment stiffness using varying levels of fingerpad skin stretch instead of force feedback. A new, high-fidelity skin stretch feedback device was developed that imposes tangential fingerpad skin stretch in proportion to the intended level of force feedback. In psychophysical experiments, users received skin stretch feedback with magnitude proportional to the users' penetration depth into a virtual wall. Users' stiffness discrimination capability using skin stretch was comparable to that of using force feedback. Furthermore, larger skin stretch cues were perceived by users as portraying greater stiffness without any advance training, which indicates that skin stretch feedback would be an intuitive sensory substitute for force feedback. Thus, skin stretch feedback is a promising method for conveying kinesthetic force information in applications such as robot-assisted surgery, where high levels of force feedback may not be desirable due to stability or safety concerns.

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.

Tangential skin displacement at the fingertip is an effective means of communicating direction or displaying static friction in haptic application. A tactile device capable of stretching the skin of the fingerpad can be mounted directly on the fingertip or embedded in haptic interfaces and hand-held devices. In both cases low weight and small dimensions are important requirements. We have developed a miniaturized tactile device capable of displaying tangential skin displacement in two directions. The actuation for the device is realized by SMA wires, in order to reduce bulk and weight, and the displacements are measured by optical sensors. The performance of the device has been verified experimentally.

We present a novel bio-inspired dynamic climbing robot, with a recursive name: ROCR is an Oscillating Climbing Robot. ROCR is a pendular two-link, serial chain robot that utilizes alternating hand-holds and an actuated tail to propel itself upward in a climbing style based on observation of human climbers and brachiating gibbons. ROCR's bio-inspired oscillating climbing strategy is simple and efficient. This robot is intended for autonomous surveillance and inspection on sheer vertical surfaces. Potential locomotion gait strategies were investigated in simulation using Working Model 2D. Strategy comparisons were drawn on a basis of climbing rate and energy efficiency. Simulation results show the feasibility and relative merits of these climbing gait strategies and compare them to the potential energy gained while climbing. A first generation ROCR design, having physical parameters based on simulation analysis, that utilizes actuated permanent magnet grippers and a geared-motor actuated tail was fabricated. Magnetic grippers are used for this initial prototype to facilitate investigating the robots climbing efficiency. Several climbing gaits which showed promise in simulation were implemented in the prototype. ROCR is a lightweight, flexible, self-contained robot with onboard microcontroller, tilt and acceleration sensing, power supply and wireless communication. We conclude with plans to evolve the simulation and design of the robot and plans for testing the prototype.

Shared control represents a middle ground between supervisory control and traditional bilateral control in which the remote system can exert control over some aspects of the task while the human operator maintains access to low-level forces and motions. Our telemanipulation system includes tactile, force and motion sensors that allow the slave to regulate grasp forces and impart rolling motions to a grasped object. We describe a set of experiments designed to determine whether shared control can improve the ability of an operator to handle objects delicately and to determine what combinations of force, visual and audio feedback provide the best level of performance and operator sense of presence. The results demonstrate the benefits of shared control and the need to choose carefully the types and methods of direct and indirect feedback.