Dielectric Elastomer Actuator (DEA) is a promising technology for artificial muscle applications based on its large voltage-induced displacement and the ability to generate a large variety of motion. This paper presents a DEA based on a modified diaphragm configuration that improves electrically-induced displacement. Existing diaphragm DEAs are equal-biaxially pre-stretched before being constrained by rigid inner and outer rings. In this paper, we first apply equal-biaxial pre-stretch, and then relax its radial pre-stretch before securing it on the outer ring. By doing this, we allow the actuation space in a radial direction to be increased. Both analysis and experiment show significant improvement in actuation as compared to an equal-biaxially-secured one. Our analysis predicted a 53% more electrically-induced displacement as compared to that of equal-biaxially pre-stretched DEAs. Our experiments further showed that when actuated near electrical breakdown, a variable pre-stretched DEA can actuate more than 50% in its out-of-plane displacement with dead load. At large displacement, the output force of our modified DEA is also higher, thus increasing the stored mechanical energy. We hope to expand the applications of diaphragm DEAs with a variable pre-stretched diaphragm in robotic applications.

During interaction with objects using a tool, we experience force and tactile feedback. One form of tactile feedback is local fingerpad skin deformation. In this paper, we provide haptic feedback to users of a teleoperation system through a skin deformation tactile feedback device. The device is able to provide tangential and normal skin deformation in a coupled manner, and is designed so that users can grasp it with a precision grip using multiple fingerpads. By applying skin deformation feedback on multiple fingerpads, the device is able to provide multi-degree-of-freedom interaction force direction and magnitude information to the user. To evaluate the effectiveness of this approach for the performance of teleoperated manipulation tasks, we performed a study in which 20 participants used a teleoperation system to perform one of two manipulation tasks (peg transfer and tube connection) using force feedback, skin deformation feedback, and the combination of both feedback. Results showed that participants are able to use all feedback to improve task performance compared to the case without haptic feedback, although the degree of improvement depended on the nature of the task. The feedback also improved situation awareness, felt consistent with prior experience, and did not affect concentration on the task, as reported by participants.

Virtual and augmented reality systems that immerse users in a 3D environment could benefit from haptic (force and/or tactile) feedback to increase realism and task performance. A canonical task that cannot be achieved compellingly without haptic feedback is the grasp and lift of an object with mass. Traditional kinesthetic (force) feedback devices provide realistic physical interactions with virtual objects, but typically require large actuators, making them bulky and encumbering. In contrast, tactile feedback devices can use smaller actuators and may enable freer movement of a user in a virtual world. One form of tactile feedback, skin deformation feedback, has been previously shown to provide effective haptic feedback of force, stiffness, and friction. Here we compare human perception of mass via kinesthetic feedback and skin deformation feedback in a virtual environment. Participants grasp and lift two virtual blocks and attempt to equalize their masses by the method of adjustments. From the accuracy of this equalization, we determined that the Weber Fraction (the just noticeable difference in proportion to the original stimulus value) of virtual mass during a grasp and lift task was 0.11 for kinesthetic force feedback and 0.35 for skin deformation feedback. In addition, participants exhibited differences in exploratory procedures between the two types of feedback.

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.

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.

During robotic teleoperation, the dynamics of the master manipulators and the control of remote-side instruments impose challenges on the motor system of the human operator, and may impact performance and learning. In teleoperated robot-assisted minimally invasive surgery, there is a clear correlation between patient outcomes and the surgeon's case experience. However, the effect of the teleoperator on human motor skills and the relationship between these motor skills and patient outcomes are unknown. We used the da Vinci Research Kit, a custom research version of the da Vinci Surgical System, to compare teleoperated and open needle-driving movements of experienced da Vinci surgeons and novices. The experimental protocol consisted of structured but unconstrained needle driving trials repeated 80 times to allow for computational modeling of movement coordination and learning. Kinematic analysis showed that teleoperation increases trial time but reduces path length, that the trial times and path lengths of experienced surgeons are smaller than those of novices. In addition, there are significant differences in learning between experienced surgeons and novice users. Modeling of the movements and learning processes of experienced and novice surgeons may be used in the design of novel controllers that will expand robotic surgery capabilities and improve robot-assisted surgical skill acquisition.

During tool-mediated interaction with everyday objects, we experience kinesthetic forces and tactile sensations in the form of vibration and skin deformation at the fingerpad. Fingerpad skin deformation is caused by forces applied tangentially and normally to the fingerpad skin, resulting in tangential and normal skin displacement. We designed a device to convey 3-degree-of-freedom (DoF) force information to the user via skin deformation, and conducted two experiments to determine the devices effectiveness for force-feedback substitution and augmentation. For sensory substitution, participants used 1-DoF and 3-DoF skin deformation feedback to locate a feature in a 3-DoF virtual environment. Participants showed improved precision and shorter completion time when using 3-DoF compared to 1-DoF skin deformation feedback. For sensory augmentation, participants traced a path in space from an initial to a target location, while under guidance from force and/or skin deformation feedback. When force feedback was augmented with skin deformation, participants reduced their path-following error over the cases when force or skin deformation feedback are used separately. We conclude that 3-DoF skin deformation feedback is effective in substituting or augmenting force feedback. Such substitution or augmentation could be used when force feedback is unattainable or attenuated due to device limitations or system instability.

An active needle is proposed for the development of magnetic resonance imaging (MRI)-guided percutaneous procedures. The needle uses a low-transition-temperature shape memory alloy (LT SMA) wire actuator to produce bending in the distal section of the needle. Actuation is achieved with internal optical heating using laser light transported via optical fibers and side coupled to the LT SMA. A prototype, with a size equivalent to a standard 16-gauge biopsy needle, exhibits significant bending, with a tip deflection of more than 14° in air and 5° in hard tissue. A single-ended optical sensor with a gold-coated tip is developed to measure the curvature independently of temperature. The experimental results in tissue phantoms show that human tissue causes fast heat dissipation from the wire actuator; however, the active needle can compensate for typical targeting errors during prostate biopsy.

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.

Teleoperated robots are used in a variety of applications. The immersive nature of the teleoperated experience is often limited by a lack of haptic information. However, in many applications there are difficulties conveying force information due to limitations in hardware fidelity and the inherent tradeoffs between stability and transparency. In situations where force feedback is limited, it is possible to use sensory substitution methods to convey this force information via other sensory modalities. We hypothesize that skin stretch feedback is a useful substitute for kinesthetic force feedback in force-sensitive teleoperated tasks. We created and tested a tactile device that emulates the natural skin deformation present during tool mediated manual interaction. With this device, experiment participants performed teleoperated palpation to determine the orientation of a stiff region in a surrounding artificial tissue using skin stretch, force, reduced gain force, graphic, or vibration feedback. Participants using skin stretch feedback were able to determine the orientation of the region as accurately as when using force feedback and significantly better than when using vibration feedback, but also exhibited higher interaction forces. Thus, skin stretch feedback may be useful in scenarios where force feedback is reduced or infeasible.

During robot-assisted minimally invasive surgery, teleoperation systems allow surgeons to perform operations at a distance via instruments inserted through small incisions in the body, thereby minimizing patient pain and recovery time. While the patient-side manipulator allows precise, dexterous gripping and manipulation by the surgical tools, current clinical systems provide the surgeon with limited haptic feedback about tool-environment interactions. This differs from direct grasp and manipulation of hand-held objects, during which we receive feedback that provides cues regarding object surface properties, slip, and load force. We use a custom research version of the da Vinci Surgical System to study the control of grip force during teleoperated manipulation of an elastic environment. We tested a placement task that involved stretching of a rubber band, with and without feedback of the patient-side load forces to the user. We hypothesized that there is greater coupling between the applied grip force and the patient-side load force when force feedback is provided, as is observed during direct manipulation of hand-held objects. With an experienced surgeon user, coupling between the applied grip force and the load force was greater with force feedback than without.

During manual interactions, we experience both kinesthetic forces and tactile sensations. Friction and normal force between the fingerpads and the tool/interaction surfaces cause shear and normal deformation of the skin. Capitalizing on this observation, we designed a 3-degree-of-freedom (DoF) tactile device that is grasped by a user and can render both tangential skin stretch and normal deformation on the skin of the user's fingerpads. Tactile feedback from the device is delivered in a manner consistent with natural tactile cues from manual interaction. An experiment assessed the accuracy with which users can locate the center of a contoured hole on a virtual surface. The task was completed under four conditions: the cases of skin deformation and force feedback, with both 3- and 1-DoF feedback in each case. With 3-DoF feedback, users located the hole faster and more accurately than with 1-DoF feedback, for both force and skin deformation feedback. These results indicated that users were able to interpret the additional DoF cues provided by our 3-DoF tactile device to improve task performance.

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.

Due to the limited control bandwidth of pneumatic artificial muscles, joint stiffness characteristics and their effects on safety and performance of human-friendly robots should be considered in the frequency domain. This paper introduces the concept of effective dynamic stiffness and validates its model with the Stanford Safety Robot. Experimental results show that the dynamic stiffness demonstrates limited effects on the impact acceleration given the same impact velocity and controller gain, whereas it significantly affects control performance of position tracking due to pressure-induced non-linearities. A stiffness optimization strategy for safety and performance is discussed as a design guideline of human-friendly robots.

From optimizing a car’s performance, encouraging safer driving to accurate insurance pricing, it is desirable to be able to identify a driver by his driving style. Using a car data supplied by MetroMile Inc., driving styles were analyzed and core features were extracted. Two learning models were investigated and evaluated:support vector machine (SVM) and multinomial logistic regression. High accuracies of around 90% were achieved for identifying a particular driver from a group of up to 6 drivers.

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.

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 side optical actuation method is presented for a slender MR-compatible biopsy needle. The needle includes an active region with a shape memory alloy (SMA) wire actuator, where the wire generates a contraction force when optically heated by laser light delivered though optical fibers, producing needle tip bending. A prototype, with multiple side heating regions, demonstrates twice as fast an initial response compared to fiber tip heating when 0.8 W of optical power is applied. A single-ended optical sensor with a gold reflector is also presented to measure the curvature independently of temperature as a function of optical transmission loss. Preliminary tests with the sensor prototype demonstrate approximately linear response and a repeatable signal, independent of the bending history.

A new generation of robots is being designed for human occupied workspaces where safety is of great concern. This research demonstrates the use of a capacitive skin sensor for collision detection. Tests demonstrate that the sensor reduces impact forces and can detect and characterize collision events, providing information that may be used in the future for force reduction behaviors. Various parameters that affect collision severity, including interface friction, interface stiffness, end tip velocity and joint stiffness irrespective of controller bandwidth are also explored using the sensor to provide information about the contact force at the site of impact. Joint stiffness is made independent of controller bandwidth limitations using passive torsional springs of various stiffnesses. Results indicate a positive correlation between peak impact force and joint stiffness, skin friction and interface stiffness, with implications for future skin and robot link designs and post-collision behaviors.

Joint stiffness plays an important role in both safety and control performance, particularly in human-friendly robots using artificial pneumatic muscles. Due to the limited control bandwidth of pneumatic muscles, stiffness characteristics and their effects on safety in the frequency domain should be taken into account. This paper introduces the concept of instantaneous stiffness and validates its model with the Stanford Safety Robot (S2 ρ . The potential effects of instantaneous stiffness on safety is explored through experimental comparison of peak impact accelerations under various impact conditions. Instantaneous stiffness demonstrates different effects on the impact acceleration depending on impact velocity and controller gain. Finally, the paper discusses the stiffness characteristics as a guideline for design and control to improve the robot safety while maintaining the control performance.