Effects of Contact Velocity and Transient Vibrations ... · Both tactile contact rendering devices...

IEEE TRANSACTIONS ON HAPTICS, GLEESON & PROVANCHER: EXPLORATION OF TACTILE CONTACT IN A HAPTIC DISPLAY 1

Exploration of Tactile Contact in a Haptic Display: Effects of Contact Velocity and

Transient Vibrations Brian T. Gleeson and William R. Provancher, Member, IEEE

Abstract— Experiments were conducted using a novel tactile contact rendering device to explore important factors of the tactile contact event. The effects of contact velocity and of event-based transient vibrations were explored. Our research was motivated by a need to better understand the perception of the tactile contact event and to develop a means of rendering stiff surfaces with a non-specialized haptic device. A passive tactile display, suitable for mounting on a Phantom robot, was developed and is capable of rendering the tactile sensation of contact on a fingertip over a range of velocities commonly experienced during everyday manipulation and tactile exploration. Experiments were conducted with this device to explore how tactile contact dynamics affect the perceived stiffness of a virtual surface. It was found that contact velocity does not have asignificant effect on perceived stiffness. These results can be explained by prior research that defines perceived hardness (akinto stiffness) in terms of rate hardness. However, in agreement with prior literature with stylus-based studies, the addition oftransient vibrations to the contact event can, in some cases, increase the perceived stiffness.

Index Terms— Tactile feedback, perception and psychophysics, haptic rendering, sensors —————————— ! ——————————

1 INTRODUCTIONaptic devices introduce a sense of touch to virtual environments and teleoperation applications. The majority of haptic devices render kinesthetic sensa-

tion (force feedback) but not tactile sensation. Typical devices employ a stylus or similar interface to mediate interaction between the user and the virtual environment. The experience is one in which the user experiences the virtual world through a tool, but may not make direct contact with the environment. The haptic device pre-sented in this paper simulates direct contact between the virtual environment and the user’s finger by rendering the tactile sensation of contact on the user’s fingerpad.

The addition of tactile feedback to a standard force feedback device has the potential to increase performance and the sense of presence during teleoperation or interac-tion with virtual environments, as shown by Hasser and Daniels [1]. Tactile sensation at the fingertip is important in detecting the making and breaking of contact, as shown in a study of fingertip afferents by Westling and Johansson [2]. The presence of tactile input has also been shown by Rao and Gordon to increase the accuracy of hand and arm movements [3].

We have developed a novel haptic device capable of rendering the tactile sensations of making and breaking contact with the fingerpad. Our device does so in a pas-sive manner, using optical measurements of finger posi-tion and a Phantom robot to achieve contact and separa-tion with the fingerpad. With this device, we have inves-tigated the tactile rendering of contact with a stiff surface

and factors which influence the perception of surface stiffness. The rendering of stiff surfaces is of interest as it presents a significant challenge in haptic rendering and is required for the realistic portrayal of virtual environ-ments. This paper begins to characterize the finger-interface contact event and explores the effect of two fac-tors on perceived stiffness: contact velocity and transient vibrations.

This paper presents two experiments on tactile contact rendering. Section 2 discusses related work, Section 3 de-scribes the test device and characterizes device perfor-mance. Experiments and results are presented in Sections 4 and 5, which detail the effects of contact velocity and transient vibrations, respectively. Section 6 contains con-cluding remarks.

2 BACKGROUNDBoth tactile contact rendering devices and stiff surface rendering have been researched independently. The ren-dering of stiff surfaces with tactile contact, however, has not been addressed and is the topic of the present study.

2.1 Tactile Contact Rendering In this paper, a haptic device was developed to render the tactile sensation of contact, that is the making and break-ing of contact between the finger and the interface, along with kinesthetic forces. Other researchers have built de-vices with similar goals encompassing a wide variety de-signs.

The device described in this paper is a thimble-based device. Our thimble-based device attaches a thimble me-chanism, capable of making and breaking contact with the finger, to a larger haptic device capable of rendering

xxxx-xxxx/0x/$xx.00 © 200x IEEE

———————————————— ! B.T. Gleeson and W.R. Provancher are in the Department of Mechanical

Engineering, University of Utah, Salt Lake City, UT, 84112. E-mail: [email protected], [email protected].

Manuscript received July 23 2009.

H

Gleeson, B.T., Horschel, S.K., and Provancher, W. R., “Exploration of Tactile Contact in a Haptic Display: Effects of Contact Velocity and Transient Vibrations,” Accepted to IEEE Transactions on Haptics, 2010.

2 IEEE TRANSACTIONS ON HAPTICS, GLEESON & PROVANCHER: EXPLORATION OF TACTILE CONTACT IN A HAPTIC DISPLAY

kinesthetic forces. In thimble-based devices, the position and orientation of the finger is known, either because the thimble is attached to a finger or because some type of non-contact tracking is employed. Hasser and Daniels used a solenoid actuator attached to a thimble in [1]. This device was used to render the making and breaking of contact, but problems arose from the mass of the device and no work on this design, beyond the initial descrip-tion, can be found in the literature. Yoshikawa and Nagu-ra developed a haptic thimble capable of rendering tactile contact in three dimensions in [4]. This device was capa-ble of rendering three dimensional environments but the measurement of finger location within the thimble was somewhat coarse. A similar device, but without finger position sensing, was developed by Kuchenbecker et al. [5]. Initial shape recognition experiments using tactile cues provided by this touch thimble showed promise but failed to demonstrate any improvement in subject per-formance. Hirota and Hirose used magnetic finger track-ing to develop a surface display that adjusts the orienta-tion of a contact plate to represent the orientation of a virtual object [6]. Another thimble-based device capable of rendering contact and surface orientation was devel-oped by Frisoli et al. [7]. Provancher et al. studied the rendering of contact location in [8] and [9]. These studies, which gave rise to the research presented in this paper, established the benefit of tactile contact rendering.

Aside from thimble-based contact displays, some mul-ti-finger “encounter-type” devices have been developed, as initially described by McNeely [10]. Yokokohji et. al. have developed a three-finger encounter-type device [11]. This grounded device arranges three small plates in space, simulating the shape of a virtual object via these three tangent planes. Although encounter-type devices are not typically attached to the user, an encounter-type hand exoskeleton was developed and presented by Na-kagawara et al. [12].

A variety of haptic interfaces capable of rendering the tactile sensation of contact have been developed, but the literature does not show any research attempting to better understand the important factors of the contact event. This paper attempts to fill that gap by presenting findings applicable to all tactile contact rendering devices.

2.2 Stiff Surface Rendering In order to better render realistic environments, research-ers have investigated the rendering of stiff surfaces. Jin-drich et al. observed subjects tapping on real surfaces while measuring force and fingerpad displacement and found large force transients in the first moments of im-pact [13]. A more general investigation into haptic per-formance metrics was conducted by Lawrence et al. with users grasping the handle on a custom haptic device [14]. Their study concluded that high rate-hardness, rather than force alone, influenced perceived hardness of a vir-tual surface, somewhat independently of the rendered time invariant stiffness. They define rate-hardness as the ratio of the initial rate of change of force versus initial velocity.

A number of haptic devices have been constructed to

render the high forces required for realistic stiff surface rendering. Constantinescu et al. used a powerful panto-graph-type device to investigate rendering methods for stable, stiff contact [15]. Researchers including Berkelman et al. have successfully used magnetically levitated haptic interfaces to deliver high forces [16]. These researchers have been able to render realistic stiff surfaces, but the high-force capabilities of these and other haptic devices come at the cost of workspace size and usable degrees of freedom.

Other researchers using stylus-based haptic interfaces with lower force capabilities have found that transient vibrations at the moment of contact play an important role in the perception of stiffness. This work has been termed ”event-based haptics” and investigates the use of brief open-loop force transients applied and the moment of contact. Hwang et al. applied a simple force step input at the moment of contact in [17] and found this to de-crease finger penetration (overshoot) into the virtual sur-face and improve realism. Kuchenbecker et al. have con-ducted a series of studies attempting to realistically repli-cate the contact vibration transients of real objects [18] [19]. They have found that the addition of realistic tran-sients improves simulation realism, perceived stiffness, and can allow a user to differentiate between different simulated materials. Reality-based modeling of contact vibrations has also been investigated by Okamura et al. [20]. In work by Kontarinis & Howe and Wellman & Howe, high frequency vibrations were delivered through a haptic interface augmented with a separate high-frequency voice-coil actuator [21, 22]. They found the ad-dition of high-frequency vibration content to aid in explo-ration and inspection tasks.

Some haptic devices have been developed to incorpo-rate transient contact forces into the mechanical design of a device. Vander Poorten and Yokokohji developed a me-thod of generating a strong force pulse by transferring energy from a fly-wheel to the stylus [23]. Springer and Ferrier constructed a hand exoskeleton in [24] that pro-duces contact transients through the physical collision of elements within the device. The above research has estab-lished the utility of contact transients in force-rendering haptic devices. In this paper we investigate the use of force transients, in the spirit of Huang et al. [17], in com-bination with contact velocity in rendering tactile contact.

3 TACTILE DISPLAY AND SYSTEM CONTROL A novel tactile interface was designed to realistically render contact with a virtual surface, including the tactile sensation of making and breaking contact with the sur-face. The device consists of a contact block attached to a thimble and to a SenseAble Phantom robot. A range sen-sor was built into the contact block to allow for non-contact measurement of the finger’s location, thus enabl-ing control of contact velocity using just the Phantom ac-tuators. This device was previously described by Gleeson & Provancher in [25].


The device can control the speed at which the contact block impacts the finger. With a rapidly moving contact block, energy is stored as momentum and then dissipated upon impact with the finger. While this transfer of mo-mentum does not change to total force output of the inter-face (our contact display is passive), it does alter the dy-namics of the contact event. Presumably, the finger would experience greater peak contact forces when impacting a faster moving contact block, but our device is not capable of directly measuring these forces.

3.1 Tactile Contact Display System

3.1.1 Mechanical Design All experiments were conducted using a modified Sens-Able Technologies Phantom Premium 1.0 (Fig. 1). The standard Phantom thimble and gimbals were removed and replaced with a custom built 1-axis gimbal and con-tact display. The contact display consists of a contact block with embedded range sensor (described below) and an open-bottom thimble used previously in [9]. The thim-ble was attached to a contact block with two 3 cm long cantilever spring-steel wires, 0.41 mm in diameter, with an approximate cantilever spring stiffness of 60 N/m (in-cluding both wires). The contact block is attached to the Phantom through a 1-DOF gimbal, allowing the contact block to rotate with the finger so that the surface of the block remains approximately parallel to the fingerpad.Thus, the user's finger is effectively coupled to the end of the Phantom through a 1-axis spring, whose motion axis is normal to the user's fingerpad. This allows the position of the contact block to be controlled by the Phantom without additional actuators.

The device was designed to allow for the making and breaking of contact between the finger and the contact block without any interference from the thimble. During experiments, an elastic band running between the thimble and the subject’s wrist was used to prevent the thimble from sliding off the end of the subject’s finger.

3.1.2 Sensor In order to control contact and separation between the finger and the contact block, a non-contact range sensor was required. Infrared range sensing was selected over other methods of range detection (e.g. capacitive sensing) because of its ability to produce a monotonic range-current relationship. We used a Vishay TCND5000 IR range sensor with an operating range of 1-14 mm and a peak operating distance at 2.5 mm. The sensor was em-bedded in a cylindrical epoxy contact block to a depth of about 4 mm using 20-3302LV transparent epoxy from Epoxies, Etc. Potting the sensor at this depth ensured a monotonic response across all possible finger positions. The outside of the contact block was wrapped in black electrical tape to block ambient light. The portion of the block with which the user made contact was a cylinder, approximately 10 mm in radius, with a flat, polished sur-face and slightly rounded edges.

A signal processing circuit was constructed as shown

schematically in Fig. 2. The IR emitter was driven with a 100 kHz square wave so that any DC signal (ambient light) could be filtered out. A transresistance stage pro-duced a voltage proportional to the current generated by the IR receiver. This signal was filtered through a high-pass filter, passed through a half-wave rectifier, and then filtered again through a low pass filter before amplifica-tion. A microcontroller (dsPIC30F4011) sampled the re-sultant voltage at 20 kHz and filtered the digital signal with a moving average (FIR) filter with 1 kHz time con-stant. The filtered value was transmitted to the control PC in real time at 5 kHz with 10 bit precision over the PC’s parallel port. The resulting system was not immune to the effects of outside light sources but was unaffected by

Fig. 1. A tactile contact display is used to accurately render the mak-ing and breaking of contact with the user's finger and to control contact velocity. The device consists of an IR range sensor em-bedded in an epoxy contact block mounted to a robot arm.

Fig. 2. Range sensor signal processing schematic. An infrared sig-nal is reflected off of the finger, detected, filtered and sampled. The distance between the sensor and the finger is communi-cated to the control computer via synchronized parallel com-munication.

Fig. 3. IR range sensor 2nd order calibration curve. In the range 0-2 mm, RMS error = 0.15 mm, max error = 0.4 mm. In the calibration equation shown, x is the sensor reading and y is the finger distance.


normal ambient light when used indoors.

3.1.3 Calibration The sensor was tested on subjects with different skin tones and finger shapes to ensure consistent operation across all potential subjects. A height gauge was placed against the top of the thimble to measure position while sensor readings were recorded over a range of finger dis-tances. Zero distance was set as the point at which the contact block could first be felt on the fingerpad.

Within the typical range of operation (less than 10 mm of finger separation) all fingers produced calibration curves with similar slopes but with different constant offsets. Near contact (0-2 mm) the sensor calibration had RMS error of 0.15 mm and a maximum error of 0.4 mm. Fig. 3 shows a typical calibration curve. It was observed that the sensor produced usable measurements after con-tact as the sensor depressed the fingerpad. These mea-surements were, however, less reliable than the pre-contact measurements and were not used in the experi-ment.

To account for the finger-specific constant offset, offset data were collected on each subject’s finger at the point of contact and at the resting separation distance between the finger and contact block. Using these data, the calibration curve for each individual was adjusted accordingly. Al-though this calibration procedure required only a few seconds, this may be inconvenient in some applications. Potentially, the addition of a simple contact sensor (e.g. a circuit for electrically detecting contact between the block and the finger) could eliminate the need for this calibra-tion procedure.

3.2 Software, Control and Virtual Environment The Phantom robot was controlled at a servo rate of 1 kHz by a PC running RTAI Linux 3.1 and using custom software written in C and C++. A simple haptic virtual environment was implemented consisting of a stiff, hori-zontal plane (stiffness = 450 N/m) and soft virtual fix-tures (stiffness = 30 N/m) to constrain the finger to a ver-tical line. There was no graphical representation of the environment.

Two software interfaces were also written to interact with the robot control software: a graphical interface for the experimenter and a text-based interface for interaction with test subjects. The graphical interface displayed data, facilitated data logging, and allowed the experimenter to alter various control constants. The text-based interface was used by subjects during perceptual testing. It dis-played both text and sound cues directing the subject through the experiment and logged the subject’s res-ponses. Both interfaces are written in C++ and the graph-ical interface utilized the QT application development framework.

PD controllers were written and empirically tuned for various states of motion: maintaining block-finger separa-tion in free space, surface rendering, and impact render-ing. Particular attention was paid to the transitions be-tween the different control states. These transitions were designed to prevent sudden changes in force, instability,

or any other artifact noticeable to the user, as described below. To prevent damage to the test hardware, output forces in all of our experiments conducted were capped at approximately 3.5 N.

When the user’s finger moved through free space, a separation of approximately 5 mm is stably maintained between the contact block and the user’s fingerpad. The virtual surface is a standard penalty-based surface (vir-tual spring) with stiffness 450 N/m. Two types of contact control were developed: a traditional penalty-based con-tact (CPen) and an experimental velocity-controlled contact (CVel). These two control modes are shown schematically in Fig 4. Rendered positions and forces are shown qualita-tively in Fig. 5. The curves representing the forces felt by the finger in Fig. 5 were unmeasured; these plots represent our best estimate of contact forces. All other curves in Fig. 5 (positions/rendered forces) represent da-ta collected in real contact events. The scales of these posi-tions/forces change depending on the taping behavior of the user, but for reference, the peak rendered forces range from 0.25 – 3.5 N and the penetration distances into the virtual surfaces range from 0.5 – 5 mm.

In the case of the penalty-based contact, the contact is achieved by simply stopping the contact block when it penetrates the virtual surface. When the block reaches the virtual surface, a PD controller on position holds the con-tact block at the height of the virtual surface. The instan-taneous onset of this position controller results in a pre-contact spike in rendered forces, as shown in Fig. 5. We believe that this pre-contact force spike had an important

Fig. 4. Schematic representation of control modes. In the penalty-based control mode (CPen), the contact block stops at the virtual surface and the finger comes down into contact with the block. Hence, the contact velocity is equal to the finger velocity. In the velocity controlled control mode (CVel), the contact block is moved up into the finger, producing contact velocities that differ from the finger velocity.


effect on perceived stiffness, as we discus in Section 5. After the block has been brought to a stop, it is impacted by the finger. Thus, the contact velocity with the block is equal to the finger's velocity. For penalty-based contact, the surface is rendered the same before and after contact; no controller transitions occur. The controller for the pe-nalty-based surface is show in Eq. 1, where x and v are the position and velocity, respectively, of the finger. The vir-tual surface is defined as x=0. Control gains are k = 500 N/m, and b = 10 N/m"s-1.

)1(0#$%$& xforvbxkF The velocity-controlled contact achieves contact over a

range of speeds. When rendering velocity-controlled con-tact, the control software computes a linear trajectory be-tween the starting position of the contact block and the predicted future position of the finger such that contact is made at the correct position and velocity. A modified proportional controller controls the position of the contact block along this desired trajectory. The controller is mod-ified so that no downward (away from the finger) forces are rendered, even when the contact block over-shoots the desired trajectory. Disallowing downward forces re-sulted in increased system stability and the subjective feel of the contact event is improved. The velocity-controlled contact is rendered by the controller show in Eq. 2, where e is the error between position of the contact block and the desired trajectory. The control gain k = 500 N/m. For e<0, i.e. when the block overshoots the desired trajectory, no forces are rendered.

)2(0'$& eforekF The transition between the finger-following controller

(free-space movement) and the contact controller is ma-naged by a predictive model of future finger location. Finger location and velocity are monitored and potential surface contacts are predicted. When contact is predicted, the contact block is accelerated up towards the finger. The velocity-controlled contact is rendered so as to bring the contact block into contact with the finger at the moment the finger reaches the virtual surface. However, the sys-tem in unable to respond to sudden changes in finger velocity and variations in actual contact height can occur. Typical errors are less than 1 cm. As no graphical repre-sentation of contact is presented, small deviations in vir-tual surface height were not a concern.

At contact, the controller transitions to render a penal-ty-based surface. This transition was designed to avoid discontinuities in rendered force. At the moment of con-tact, the height of the virtual surface is adjusted upward so that the force rendered by the penalty-based surface controller will be equal to the current rendered force. Then, when control switches to the penalty-based surface, there is no sudden change in rendered force. When the contact block impacts the finger with sufficient speed, the finger is brought to a stop and pushed slightly upwards. The upward motion of the finger, and accompanying de-crease in the force rendered by the penalty-based surface controller, is shown in Fig. 5. All controller transitions were evaluated in pilot testing and were not perceivable.

3.3 System Performance The haptic device described above performed sufficiently well for our experiments. After calibration, the range sen-sor was characterized for noise and drift. Random sensor noise was acceptably low; RMS noise was less than 0.02 mm. Sensor drift was measured to be less than 0.025 mm / 10 minutes (typical experiment duration). It was observed that sensor noise and drift produced occa-sional spurious contact velocity measurements, e.g. speeds less than 0. Such readings were not a concern, however, due to the analysis methods employed (see Sec-tion 4.2).

Due to the dynamic complexity of robot-human sys-tem, precise control of contact velocity in the velocity-controlled contact mode was difficult. Measured contact velocities were found to vary from commanded velocities, with the degree of variance depending on the user. This variance is one of the expected challenges of human-in-the-loop control, as the mechanical impedance of a hu-man finger has been shown to be different between indi-viduals and to change with posture and muscle contrac-tion ([26] and [13]). This control difficulty did not hinder our experiments. While it was necessary to render a range of contact velocities in our experiments, it was not neces-sary to command exact velocities. Actual impact velocities were recorded and used to sort stimuli in post-processing.

Fig. 5. Qualitative plots of forces and positions in penalty-based con-tact (CPen) (top) and velocity-controlled contact (CVel) (bottom). For CPen, the contact block stops when it reaches the virtual sur-face and is held in place by a virtual spring force. At contact, the finger experiences a small impact force. For CVel, the contact block moves below the virtual surface and then is driven up to impact the finger as the finger touches the virtual surface. At contact, the finger experiences a large impact force from the moving contact block. The height of the virtual surface is ad-justed at the moment of contact to prevent a force discontinuity.


4 EXPERIMENT 1: EFFECT OF CONTACT VELOCITYWith a haptic interface capable of rendering tactile contact with variable contact velocity, we sought to explore how contact velocity affects the perceived stiffness of a virtual surface. We hypothesized that higher contact velocity would result in higher perceived stiffness.

4.1 Experiment Design An experiment to evaluate the role of contact velocity

on perceived stiffness was completed by 10 volunteer subjects, 9 male, 1 female, all right hand dominant, rang-ing in age from 22 to 37 years. In the experiment, users brought their right index finger into contact with a virtual surface. A Phantom was used to render kinesthetic resis-tance and a novel contact display allowed the user to make and break contact with a contact element, simulat-ing the making and breaking of contact with the virtual surface. All virtual surfaces were rendered with identical stiffness (450 N/m), but the dynamics of the contact event were varied.

All experiments presented in this paper follow the same forced-choice, paired comparison design. Before testing, each subject was asked to read a set of test in-structions and procedures. The experimenter repeated key points of the procedures. Subjects were asked to an-swer which of the two paired stimuli felt subjectively stif-fer. All subjects were from an engineering background and were familiar with the technical meaning of stiffness. Particular emphasis was given to the assertion that there were no correct answers and only the subject’s percep-tions were important. The subject put the device on the right index finger and calibrated the sensor with the aid of the experimenter. The device and the subject’s hand were covered in a cloth and the subject wore headphones playing white noise, preventing influence from visual or auditory cues. The subjects were instructed to tap on the virtual surfaces with smooth motions, keeping the finger relatively straight and the palm of the hand flat on a foam armrest. The subject was allowed unlimited time to tap on virtual surfaces until comfortable with the device. When ready, the experimenter began the experiment.

The experiment consisted of 60 pairs of velocity-controlled (CVel) stimuli, presented in random order. The two stimuli were rendered with different contact veloci-ties, but were otherwise identical. The subject was cued to tap each surface by a tone played through the head-phones and by text instructions on the monitor. The sub-ject was allowed to tap each surface once. When the sub-ject’s finger was raised back up to a pre-defined location, the next tone was sounded and the next stimulus ren-dered. After both surfaces were presented, a second tone sounded and the text, “Enter a 1 if the first stimulus felt stiffer. Enter a 2 if the second stimulus felt stiffer.” was displayed and the subject’s answer was recorded. At the end of the experiment, the subject’s age, gender, and do-minant hand were recorded. All experiments discussed in this paper required approximately 15 minutes to com-plete. See Fig. 6 for a photograph of the experimental se-tup. All experiments were conducted with the approval of the University of Utah Institutional Review Board.

4.2 Analysis Method Subject responses were analyzed for correlation between contact velocity and perceived stiffness. In all analyses, the contact velocity was the relative velocity between the contact block and the finger, i.e. the velocity of the finger in the contact block’s frame of reference. For each stimu-lus pair, the slower of the two stimuli was considered the ‘reference’ stimulus and the faster stimulus was consi-dered the ‘variable’ stimulus. For each individual subject, stimuli were sorted by the absolute difference between the two contact velocities and placed into four equally sized bins. By placing data into large bins, the effects of sensor noise are minimized; sensor noise was rarely large enough to cause a stimulus to move from one bin to another and therefore had little or no effect on our results. Because each subject had a different range and distribu-

TABLE 1EXPERIMENT 1: RENDERED CONTACT VELOCITIES

The range of contact velocities and the velocity differences between the two stimuli in experiment 1. *Due to sensor noise, some contact velocities were measured as slightly less than zero. These readings simply represent very slow contacts **Some stimulus pairs had identical contact velocities, to within the accuracy of the sensor.

Fig. 7. Experiment 1 results. Error bars represent 95% confidence intervals. There is no statistically significant relationship between contact velocity and perceived stiffness. Note that this plot is qualita-tive in nature; subjects each had a different range of velocities in each of the bins.

Fig. 6. Experiment setup. The cloth cover is pulled back for clarity to show robotic arm and test device.


tion of contact velocities, the range of velocities differenc-es in each bin varied between subjects. For reference, the average bin centers were 0.5, 1.6, 3.4 and 6.3 cm/sec for bins 1 through 4, respectively. The range of rendered ab-solute velocities and velocity differences are reported in Table 1. Each bin was scored by the percentage of variable stimuli (faster contacts) chosen as stiffer than the refer-ence stimulus (slower contacts). A simple test for correla-tion was performed on each subject’s data by fitting a line through the bin scores. The slope of the fit line would indicate the presence of a correlation. These slopes were computed for all subjects and the set was tested for statis-tical significance using a t-test for a single group mean.

4.3 Results There was no statistically significant correlation between contact velocity and perceived stiffness. The test for corre-lation resulted in an average slope of 2.18 ±4.17 with units [proportion of faster contacts chosen] per [difference in contact velocities in m/sec]. This test for correlation also failed a t-test for statistical significance (t (9) = 1.18, p=0.27). Data were aggregated from all subjects and plot-ted in Fig. 7 to illustrate the relationship between contact velocity and perceived stiffness. This plot of pooled data is only intended to illustrate the general trend in the data and was not used for analysis. The range of contact ve-locity differences rendered during the experiment is shown in Table 1. The range of velocity differences is large enough to fully characterize the effect of contact velocity on perceived stiffness for normal interactions.

4.4 Experiment 1 Discussion The results from this experiment indicate that contact velocity has no significant effect on perceived stiffness. This runs contrary to our initial hypothesis. The plot shown in Fig. 7 suggest a slight correlation, but this corre-lation is not statistically significant and is so small as to be inconsequential.

From a device design perspective, it is disappointing that the range of renderable surface stiffness cannot be extended by controlling contact velocity. However, the subjects’ insensitivity to contact velocity provides a de-gree-of-freedom to device developers. Precise finger posi-tion is difficult to measure in a tactile contact rendering device, requiring accurate non-contact range finding. Many contact rendering devices do not directly measure finger position in any way (e.g.[7], [5]), while others have only coarse measurement (e.g.[4]). Given the above re-sults, future work with contact rendering devices need not be concerned with precise control of contact velocity.

How the above results relate to previous work is un-certain, because our work focuses on pre-contact control of the device while other researchers have looked at post-contact information. Still, certain interesting comparisons can be drawn. Jindrich et al. proposed a viscoelastic mod-el of the fingerpad and looked at contact forces [13]. They show that in contact with a real surface of constant stiff-ness, higher contact velocities produce higher contact forces. The relationship between contact force and contact

velocity is qualitatively the same in our system, with con-tact forces increasing with contact velocity. With this si-milarity between our system and a real surface of con-stant stiffness, it is not surprising that users perceived our virtual surface to have a constant stiffness, independent of contact velocity.

Lawrence et al. proposed rate-hardness (!F/v) as the best metric for judging surface hardness, which is akin to stiffness. Their work focused on post-contact control of a device and investigated non-tactile interaction with a vir-tual surface, using a manipulandum. That is, it did not involve the making and breaking of contact [14]. Howev-er, our results seem to agree with Lawrence et al. Our device produces high impact forces (large !F), but these forces come from stored momentum (mv). Dissipation of the haptic system’s momentum at contact is quite com-plex, so it is difficult to state what the exact affect on rate-hardness would be. However, a major component of the momentum will be absorbed as the contact block impacts the finger, resulting in fingerpad deformation. As re-ported by Jinderich et al., the viscoelastic nature of skin will result in a higher !F with increased contact velocity, but these forces scale with velocity. This suggests that the rate-hardness of our system could be invariant. If so, our results would then appear to agree with the conclusion of Lawrence et al., which would explain why we did not observe an effect on perceived stiffness. This suggests that the concept of rate-hardness applies to tactile contact in addition to non-tactile, manipulandum-based interfaces, as previously investigated [14].

In summary, we built a device that allowed for con-trol of contact velocity; however, when this degree of freedom was explored, we found that impact velocity alone does not affect perceived stiffness. This suggests the question: if contact velocity isn’t an important factor, then what factors do influence the perceived stiffness in tactile contact? This question is the topic of our second experi-ment.

5 EXPERIMENT 2: EFFECT OF TRANSIENT VIBRATION

The first experiment established that contact velocity has little or no effect on perceived surface stiffness. A search for factors that do have a strong influence on perceived stiffness led to a second experiment: a test for the effect of transient vibrations at contact. It was observed in subse-quent pilot tests, presented below, that the penalty-based (CPen) contact event felt stiffer and contained strong high frequency contact transients while the velocity-based (CVel) contact event did not, suggesting a link between contact transients and perceived stiffness. Additionally, other researchers have shown transient vibration to play an important role in the perceived stiffness and realism of virtual surfaces rendered with stylus- and joystick-based interfaces.

5.1 Pilot Test A pilot test was conducted to explore factors influencing the perceived stiffness of tactile contact. This experiment


compared penalty-based contact (CPen) to velocity-controlled contact (CVel). Each comparison pair consisted of one CPen stimulus and one CVel stimulus of varying im-pact velocity. During the experiment, 60 stimulus pairs were presented, in random order, each with a different contact velocity. The same ten subjects from Experiment 1 participated in this experiment.

Contact velocities from near 0 to approximately 30 cm/sec were rendered for both CPen and CVel stimuli. Subjects perceived the CPen stimuli as stiffer in approx-imately 78% of comparisons. To gain insight into which factors contributed to this large difference in perceived stiffness, we analyzed the two stimulus types in hopes of finding relevant differences.

Observations of the two stimuli and a review of the li-terature (e.g. [18], [20], [21], [22]) suggested a difference in transient vibrations as a potential cause of the perceptual difference. While the role of transient vibrations in the tactile contact event has not previously been evaluated, results from stylus-based experiments suggest that these vibrations are important. Transient vibrations were measured for the two stimuli (see discussion in Section 5.2). The CVel stimulus was found to lack the high-frequency content associated with real surface contact (Fig. 10). Reflecting upon the two stimuli used in this pilot experiment, this difference in frequency content is not surprising. The CVel stimuli were rendered with a velocity controller tuned to maintain constant velocity and smooth motion as the contact block approached the finger. Any vibrations (oscillatory changes in velocity) were actively controlled out of the system. While the CPen stimulus was also designed to minimize oscillation, we believe that the pre-contact force spike in the CPen controller (Fig. 5) ex-cited the high-frequency dynamics of our device, result-ing in the vibrations shown in Figs. 8, 9 and 10. To better understand the importance of transient vibrations in tac-tile contact, the following experiments were conducted.

5.2 Transient Design Recent research by Kuchenbecker et al. [27] into transient vibrations has focused on high fidelity reproduction of contact transients using a stylus-based interface. In this experiment, we did not focus on reproducing a particular transient profile, but instead implemented a transient with broad-band frequency content. This was done for two reasons. First, the mechanics of our device make pre-cise acceleration matching impractical. Second, a simple contact transient was sufficient for our experimental goals, as we sought only to address the general impor-tance of contact transients in a tactile contact event, not to reproduce any particular surface.

Our contact transient was similar to the transient im-plemented by Hwang et al. in [17]. The transient con-sisted of a step force input, 10 ms in duration and with magnitude proportional to the incoming speed of the fin-ger. The relationship between force magnitude and in-coming finger speed was tuned empirically through pilot testing to maximize perceived stiffness and realism. The median step force applied during the experiments was

approximately 3 N. Initial pilot tests were conducted with the force input normal to the virtual surface but produced poor results and negative user feedback. The transient was then tested as a horizontal force (parallel to the vir-tual surface and user’s finger), with much better results. The device is stiffest in this direction, parallel to the long axis of the cantilever springs, thus better able to transmit high frequency vibration when the forces were applied horizontally. While the step force was applied in the hori-zontal direction, similar vibrations were induced in both the horizontal and vertical directions (see Fig. 9).

Two new stimulus types were created by adding con-tact transients to the existing contact events: penalty-based contact with contact transient (CPen+T) and velocity-controlled contact with contact transient (CVel+T). In both cases, the force step is triggered when the range sensor first indicates contact between the contact element and finger.

Vibration transients were characterized by measuring the accelerations present at the contact block. An accele-rometer (Freescale MMA7260QT) was mounted to the contact block with a small piece of modeling clay. The signal was filtered with a 1-pole low-pass filter with cor-ner frequency 1.6 kHz, buffered with an LM6144 op-amp and sampled at 2 kHz with a National Instruments PCI 6014 DAQ card. Accelerations were recorded for 30 con-tact events of each stimulus type. A baseline, ‘real’, sur-face was also characterized by placing the contact block on a hard wood surface and tapping on the stationary contact block. This provided acceleration data typical of a finger contacting a real, rigid surface. Because the contact block was grounded in this case, the measured accelera-tions were of smaller amplitude than those measured from the virtual surface. This is a reasonable approach, as we are only concerned with the distribution of energy over the frequency range and not the magnitude of the acceleration.

A typical stimulus event is show in Fig. 8. Large acce-leration is seen as the contact block is brought to a stop. In many cases, these high accelerations saturated the sensor, seen in Fig. 8 where the signal floors at -1.5 g. This loss of information is acceptable as it occurs before the contact element reaches the finger. Contact with the finger is marked by a sharp change in acceleration. Figure 8 also shows high-frequency vibrations which diminish after contact. Previous work has suggested that such damped, high frequency vibration increases the perceived stiffness of a surface [20].

Figure 9 shows representative acceleration profiles, in both recorded directions, for all stimulus types as well as the real surface. All contact events show similar pre-contact and contact acceleration, but differ post-contact. The velocity-controlled contact event shows very little post contact vibration compared to the traditional penal-ty-based stimulus. The addition of the contact transient to both of these stimulus types greatly increases the ampli-tude of post-contact vibration.


Power spectra were computed for each stimulus type using data aggregated from all 30 contact events. Hori-zontal and vertical accelerations produced similar spectra. Spectra for vertical accelerations are shown in Fig. 10. The real surface was found to have significant high frequency content in the 100-300 Hz range. Looking at the two sti-muli types, the velocity-controlled contact event had much less energy in this frequency range than the penal-ty-based stimuli. This supports the conclusion that the presence of high frequency contact transients was impor-tant in making the penalty-based stimulus feel stiffer.

The stimuli enhanced with contact transients were also analyzed. The step input was found to add significant high frequency content to the contact event, as can be seen in Fig. 10 by comparing the CPen spectrum to the CPen+T spectrum, and the CVel spectrum to the CVel+T spec-trum. The increase in high frequency vibrations is par-ticularly marked in the case of the velocity-controlled stimulus. Both CPen+T and CVel+T contact events exhibit the same resonant peaks, although the CPen+T stimulus has a more uniform distribution of energy in the 100-300 Hz range.

The step input contact transient was judged to be ade-quate for our experiment; it successfully introduced high frequency vibration into the contact event in the same range of frequencies present in a contact with a real stiff surface. Pilot testing produced positive feedback from users regarding the improved realism of transient-enhanced stimuli.

5.3 Experiment 2a: Transient Vibrations Added to All Stimulus Types The effect of high frequency transient vibrations on per-ceived surface stiffness was explored using both penalty-based contact and velocity-controlled stimuli. This expe-riment used penalty-based contact (CPen) as a reference stimulus and compared it against three different stimuli: velocity-controlled contact (CVel), penalty-based contact with added contact transient (CPen+T) and velocity-controlled contact with added contact transient (CVel+T). Based on previous work and pilot testing, it was hypothe-sized that the addition of contact transients would in-crease the perceived stiffness of both the CPen and CVel stimuli. Our previous experiment showed contact velocity to be of little importance in perceived surface stiffness, but in order to eliminate the possibility of confounding variables, the stimuli in this experiment were tuned so that they all produce similar contact velocities. In this way, the effects of contact velocity could be more clearly understood. The experiment was conducted on 10 sub-jects, 9 male, 1 female, aged between 22 and 38 years. All were right-hand dominant. Each subject was presented with each of the three stimulus pairs 25 times, in random order. The experimental procedure was the same as was described in Section 4.1.

5.3.1 Results The application of transient vibrations to the contact event increased the mean perceived stiffness for both sti-mulus types, but these increases were not statistically

Fig. 8. Acceleration profile of typical penalty-based contact event, showing large accelerations as the contact block is brought to a stop and at the moment of contact. After contact, damped, tran-sient vibrations are observed. Saturation of the sensor can be seen, but as this occurs before the contact event, it is not a con-cern.

Fig. 9. Typical acceleration profiles, in the vertical and horizontal direc-tions, for all stimulus types and a “real” (wood desk) reference surface.

Fig. 10. Vibration power spectra for all stimulus types and a “real” (wood desk) reference surface. The addition of transient vibrations atcontact increased the high frequency content of the contact event, allowing the stimuli to better simulate a real surface. Spectra areshown here for vibrations in the vertical direction only. Horizontal vibra-tion energy spectra are qualitatively similar.


significant. All stimulus types were successfully rendered over similar velocity ranges. Table 2 shows the rendered contact velocities for each stimulus type. In light of the results of Experiment 1, the differences in contact velocity were not a concern. Results are shown in Fig. 11(a).

On average, the addition of the transient vibrations to the contact event increased perceived surface stiffness for both CPen and CVel stimuli, with increased response per-centages of 7% and 10%, respectively. Statistical testing, however, does not show these increases to be statistically significant. T-tests for dependent means on the individual stimuli show that CVel and CVel+T stimuli were both per-ceived to be different than the reference stimulus (CPen) (t(9) > 3.2, p < 0.01), but the difference between CPen and CPen+T stimuli was not statistically significant. The small effect of transient vibrations on the perception of CPen stimuli was expected, due to the significant vibrations already present in the CPen event. This is discussed fur-ther in Section 5.5. The large perceived difference be-tween both velocity-controlled stimuli and the reference stimulus created a floor effect, i.e. both CVel and CVel+T stimuli felt much less stiff than the reference, so the dif-ference in subject response to the two velocity-controlled stimuli was small. To analyze the effect of transient vibra-tions on velocity-controlled stimuli, Tukey’s Honest Sig-nificant Difference test was used. The difference between the CVel and CVel+T stimuli was not statistically significant.

The above results suggested that the addition of vibra-tion transients to the contact event increases the perceived stiffness of the virtual surface. However, the lack of statis-tical significance indicated a need for further testing.

5.4 Experiment 2b: Isolated Effect of Transient Vibrations on Velocity-Controlled Stimuli

In the previous experiment, results for velocity-controlled stimuli (CVel) and transient enhanced velocity-controlled stimuli (CVel+T) did not show a statically significant differ-ence. Because both stimuli were so frequently perceived as less stiff than the reference stimuli, the data from these two stimuli suffered from a floor effect. To clearly estab-lish the relationship between these two stimuli, an addi-tional experiment was performed directly comparing CVel to CVel+T. Subjects were asked to judge which of the two stimuli felt stiffer in series 25 randomized trials. The 10 subjects used in Experiment 2a participated again here.

5.4.1 Results The addition of transient vibration to the velocity-controlled contact was found to increase the perceived stiffness of the surface by a statistically significant amount. Both stimulus types were successfully rendered over the same range of velocities (Table 2), meaning that the difference observed between the two stimuli resulted only from the addition of the contact transient and was not affected by contact velocity. Results for this experi-ment are shown in Fig. 11(b). A t-test for dependent means was performed and found the increase in per-ceived stiffness (average increase = 14%) to be statistically significant (t (9) = 2.44, p = 0.04). From these data, we are able to draw concrete conclusions regarding the impor-

tance of transient vibrations in the contact event.

5.5 Experiment 2 Discussion This experiment has shown transient vibrations to be im-portant in the rendering of tactile contact. Experiment 2a implies an increase in perceived stiffness for both CPen and CVel stimuli when transients are added to the contact event. Experiment 2b shows a clear, statistically signifi-cant effect of transient vibrations on the CVel contact event. Because all stimuli were rendered at similar contact veloc-ities and because varying contact velocity was previously shown to have little effect on perceived stiffness, it can be concluded that the effects seen in this experiment are the result of transient vibrations alone.

The addition of transient vibrations to the contact event was found effective in increasing the perceived stiffness of a virtual surface. It should also be noted, anecdotally, that subjects had a positive response to the vibration-enhanced stimuli and reported that these stimu-li felt more realistic. These results are important because they suggest a simple means of increasing the perfor-mance and realism of any tactile contact rendering haptic

Fig. 11. Experiment 2 results: (a-left) effect of contact transient vibra-tions on perceived surface stiffness with penalty-based contact as the reference stimulus, and (b-right) velocity-controlled contact as the reference stimulus. Error bars indicate 95% confidence intervals. The dotted lines illustrate the response level expected from indistin-guishable stimuli (random responses: 50%). In general, transient vibrations were found to increase the perceived surface stiffness.

TABLE 2EXPERIMENT 2: RENDERED CONTACT VELOCITIES

Median and standard deviation of contact velocities rendered during experi-ment 2 for penalty-based contacts (CPen), penalty-based contacts with transient vibrations (CPen+T), velocity-controlled contacts (CVel), and velocity-controlled contact with transient vibrations (CVel+T). The distribution of rendered veloci-ties was approximately normal. The rendered velocities showed no significant differences between Experiments 2a and 2b


device, as also previously observed in stylus-based inter-faces [18] [20]. The method developed here of using a simple force pulse parallel to the virtual surface should be simple to implement on a range of tactile contact interfac-es; it does not complicate of the control of contact dynam-ics as it does not apply any force in the direction of con-tact. It should be noted, however, that this method would only be effective when used on a device with high stiff-ness in the direction of the applied transient.

The results of this experiment are in accord with pre-vious research on non-tactile contact rendering ([17] [27] [18] [20] [19]). This suggests that other event-based me-thods used successfully in non-tactile contact rendering, such as acceleration matching ([27]) and adjusting tran-sient forces according to the user’s muscle state ([19]), might also be applicable in tactile contact applications. While this experiment used only a simple broad-spectrum vibration transient, our approach could be modified using the methods presented in [20] to better simulate contact with specific materials. The adaptation and implementa-tion of such techniques could be the subject of future re-search.

An important observation is that the addition of tran-sient vibrations increased the perceived stiffness of the CVel contact event more than the CPen contact event. This result was expected, and supports the use of energy spec-tra to evaluate transient vibrations (see Fig. 10). The addi-tion of transient vibrations to the CVel contact event re-sulted in a large change of the stimulus’ energy spectrum and correspondingly large change in perceived stiffness. The addition of transients to the CPen contact event pro-duced a smaller change in the associated energy spectrum and a smaller change in perceived stiffness. Put another way, the addition of transient vibrations to the CPen con-tact event did not make a big difference because the CPen contact event already had significant high frequency vi-brations coming from the pre-contact force spike. There-fore, superimposed contact transients may be unneces-sary in a tactile contact device if sufficient vibrations are already present, as was the case with our CPen stimuli.

Other researchers have observed transient vibrations to improve the stiffness or realism of penalty-based con-tact (e.g. [18], [20]). This prior work, however, all utilized manipulandum-based devices (joystick or stylus). We expect that these manipulandum-based devices had more mechanical damping than our device and therefore pro-duced less innate vibration during un-augmented penal-ty-based contact. Our lightly-damped device, with signif-icant innate high frequency vibration, had less to gain from the addition of event-based contact transients.

Also noteworthy is that the addition of transient vibra-tions increased the perceived stiffness of the CVel contact event, but that these contact events were still perceived as less stiff than the un-augmented CPen contact event. This suggests that the addition of vibration transients to the contact event did not fully replace all vibrations that were cancelled out by the velocity controller. This is supported by the data in Fig. 10, which shows the energy spectrum of the CVel+T contact event to have distinct gaps where little energy is present. It could also be that other aspects

of contact dynamics, not explored in this research, were affecting the perceived stiffness.

6 CONCLUSIONIn this paper we have explored how different aspects of contact dynamics affect the perceived stiffness of a virtual surface using a novel device capable of render-ing tactile contact. Previous research has characterized the important aspects of non-tactile contact rendering. We have begun a similar exploration in the field of tactile contact rendering. Two aspects of the tactile contact event were investigated: contact velocity and the addition of transient vibrations to the contact event. Contact velocity was not found to have a signif-icant impact of the perception of surface stiffness, but transient vibrations were observed to enhance the per-ceived stiffness of velocity controlled contact events. Our insensitivity to contact velocity in judging per-ceived surface stiffness could be explained by prior research by Lawrence et al. that defines perceived hardness (akin to stiffness) in terms of rate-hardness [14]. Future work will continue this exploration, ex-amining other aspects of contact dynamics that influ-ence perception of tactile contact. Additionally, the agreement between our findings and previous non-tactile contact rendering research suggests the possibil-ity of adapting a range of event-based haptic tech-niques to tactile rendering applications.

ACKNOWLEDGMENTThis work was supported, in part, by the National Science Foundation under awards DGE-0654414 and IIS-0904456.

REFERENCES

[1] C. J. Hasser and M. W. Daniels, "Tactile feedback with adaptive controller for a force-reflecting haptic display.," in Proc. 15th Southern Biomedical Engineering Conf., 1996, pp. 526-529.

[2] G. Westling and R. S. Johansson, "Responses in glabrous skin mechanoreceptors during precision grip in humans," Experimental Brain Research, vol. 66, pp. 128-140, 1987.

[3] A. Rao and A. Gordon, "Contribution of tactile information to accuracy in pointing movements," Experimental Brain Research, vol. 138, pp. 438-445, 2001.

[4] T. Yoshikawa and A. Nagura, "A Touch/Force Display Sys-tem for Haptic Interface," Presence: Teleoperators & Vir-tual Environments, vol. 10, pp. 225-235, 2001.

[5] K. J. Kuchenbecker, D. Ferguson, M. Kutzer, M. Moses, and A. M. Okamura, "The Touch Thimble: Providing Fin-gertip Contact Feedback During Point-Force Haptic Inte-raction," in Proc. Symposium on Haptic Interfaces for Vir-tual Environment and Teleoperator Systems, 2008, pp. 239-246.


[6] K. Hirota and M. Hirose, "Implementation of Partial Sur-face Display," Presence: Teleoperators & Virtual Environ-ments, vol. 7, pp. 638-649, 1998.

[7] A. Frisoli, M. Solazzi, F. Salsedo, and M. Bergamasco, "A Fingertip Haptic Display for Improving Curvature Discrimi-nation," PRESENCE: Teleoperators and Virtual Environ-ments, vol. 17, pp. 550-561, 2008.

[8] K. J. Kuchenbecker, W. R. Provancher, G. Niemeyer, and M. R. Cutkosky, "Haptic display of contact location," in Proc. 12th Intl. Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2004, pp. 40-47.

[9] W. R. Provancher, M. R. Cutkosky, K. J. Kuchenbecker, and G. Niemeyer, "Contact Location Display for Haptic Perception of Curvature and Object Motion," The Intl. Journal of Robotics Research, vol. 24, pp. 691-702, 2005.

[10] W. A. McNeely, "Robotic graphics: a new approach to force feedback for virtual reality," in Proc. IEEE Virtual Re-ality Annual International Symposium, 1993, pp. 336-341.

[11] Y. Yokokohji, N. Muramori, Y. Sato, and T. Yoshikawa, "De-signing an encountered-type haptic display for multiple fin-gertip contacts based on the observation of human grasp-ing behavior," in Proc. 12th Intl. Symposium on Haptic In-terfaces for Virtual Environment and Teleoperator Sys-tems, 2004, pp. 66-73.

[12] S. Nakagawara, S. Nakagawara, H. Kajimoto, N. Kawa-kami, S. A. T. S. Tachi, and I. A. K. I. Kawabuchi, "An En-counter-Type Multi-Fingered Master Hand Using Circuit-ous Joints," in Proc. Intl. Conference on Robotics and Au-tomation, 2005, pp. 2667-2672.

[13] D. L. Jindrich, Y. Zhou, T. Becker, and J. T. Dennerlein, "Non-linear viscoelastic models predict fingertip pulp force-displacement characteristics during voluntary tapping," Journal of Biomechanics, vol. 36, pp. 497-503, 2003.

[14] D. A. Lawrence, L. Y. Pao, A. M. Dougherty, M. A. Salada, and Y. Pavlou, "Rate-hardness: a new performance metric for haptic interfaces," IEEE Transactions on Robotics and Automation, vol. 16, pp. 357-371, 2000.

[15] D. Constantinescu, S. E. Salcudean, and E. A. Croft, "Hap-tic rendering of rigid contacts using impulsive and penalty forces," IEEE Transactions on Robotics and Automation, vol. 21, pp. 309-323, 2005.

[16] P. J. Berkelman, R. L. Hollis, and S. E. Salcudean, "Inte-racting with virtual environments using a magnetic levita-tion haptic interface," in Proc. Intl. Conference on Intelli-gent Robots and Systems, 1995, pp. 117-122 vol.1.

[17] J. D. Hwang, M. D. Williams, and G. Niemeyer, "Toward event-based haptics: rendering contact using open-loop force pulses," in 12th Intl. Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2004, pp. 24-31.

[18] K. J. Kuchenbecker, J. Fiene, and G. Niemeyer, "Improving contact realism through event-based haptic feedback," Transactions on Visualization and Computer Graphics, vol. 12, pp. 219-230, 2006.

[19] J. Fiene, K. J. Kuchenbecker, and G. Niemeyer, "Event-based haptic tapping with grip force compensation," in Proc. IEEE Haptic Symposium, 2006, p. 87.

[20] A. M. Okamura, M. R. Cutkosky, and J. T. Dennerlein,

"Reality-based models for vibration feedback in virtual en-vironments," IEEE/ASME Transactions on Mechatronics, vol. 6, pp. 245-252, 2001.

[21] D. A. Kontarinis and R. D. Howe, "Tactile display of vibra-tory information in teleoperation and virtual environments " Presence: Teleoperators and Virtual Environments, vol.4, pp. 387-402, 1995.

[22] P. Wellman and R. D. Howe, "Towards realistic vibrotactile display in virtual environments," in Proc. ASME Dynamic Systems and Control Division, 1995, pp. 713-718.

[23] P. Emmanuel Vander and Y. Yasuyoshi, "Rendering a Rigid Virtual World through an Impulsive Haptic Interface," in In-telligent Robots and Systems, 2006 IEEE/RSJ Internation-al Conference on, 2006, pp. 1547-1552.

[24] S. L. Springer and N. J. Ferrier, "Design and Control of a Force-Reflecting Haptic Interface for Teleoperational Grasping," Journal of Mechanical Design, vol. 124, pp. 277-283, 2002.

[25] B. T. Gleeson and W. R. Provancher, "Toward Developing a Velocity Controlled Tactile Impact Display," in Sympo-sium on Haptic interfaces for Virtual Environment and Te-leoperator Systems, 2008, pp. 373-374.

[26] A. Z. Hajian and R. D. Howe, "Identification of the mechan-ical impedance at the human finger tip," Transactions of the ASME. Journal of Biomechanical Engineering, vol.119, pp. 109-14, 1997.

[27] K. J. Kuchenbecker, J. Fiene, and G. Niemeyer, "Event-based haptics and acceleration matching: portraying and assessing the realism of contact," in First Joint Eurohap-tics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2005, pp. 381-387.

Brian T. Gleeson earned a B.S. in Engineering Physics at the University of Colorado in 2003. He is currently pursuing a Ph.D. in Mechanical Engi-neering at the University of Utah. Before he began his studies in Utah, Brian was employed at the Center for Astrophysics and Space Astronomy, Zhejiang Sci-Tech University, and Design Net En-gineering. His primary research interests currently involve the use of tangential skin displacement for

the communication of direction, for which he earned a Best Paper Award at the 2009 World Haptics Conference.

William R. Provancher has earned a B.S. in Mechanical Engineering and an M.S. in Materials Science and Engineering, both from the Universi-ty of Michigan. His Ph.D. from the Department of Mechanical Engineering at Stanford University was in the area of haptics, tactile sensing and feedback. His postdoctoral research involved investigating and designing bioinspired climbing robots, focusing on creating foot designs for

climbing vertical surfaces with compliantly supported microspines. He is currently an Assistant Professor in the Department of Mechani-cal Engineering at the University of Utah. He teaches courses in the areas of mechanical design, mechatronics, and haptics. His active areas of research include haptics, tactile sensing and feedback, and the design of novel climbing robots. Dr. Provancher received a Best Paper Award at the 2009 World Haptics Conference for his work on tactile feedback for the communication of direction. Details of his research and related publications are linked of off Dr. Provancher’s homepage: http://www.mech.utah.edu/wil/.

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