Nadia Vanessa Garcia-Hernandez

Feeling through Tactile Displays: A Study on the Effect of the Array Density and Size on the Discrimination of Tactile Patterns

Tactile arrays are devices that can provide spatially distributed cutaneous signals delivering crucial information during virtual haptic exploration or remote manipulation procedures. Two of the key specifications of a tactile array are the tactor spacing and array size that are believed to directly affect the device performance. In most of the systems developed so far, these two parameters have been chosen by trial and error or by trying to match the tactor density to the spatial resolution in the human fingertip. The objective of this work is to study the effect of tactor spacing and array size on the tactile arrays performance by measuring human tactile discrimination ability. Psychophysical experiments were performed to obtain the differential threshold for discrimination of a ridge angle and the shape recognition performance while exploring edge-based patterns. The patterns were explored through different passive (nonactuated) tactile arrays of vertically moving pins and also directly with the finger. Results indicate that a tactile array of 1.8 mm tactor spacing and 1 cm2 array size transmits the pattern information with a good level of accuracy. This work shows that tactile devices with low complexity (small number of tactors) are still effective in conveying tactile cues. Moreover, this work provides performance measures that determinate the capabilities of tactile pin arrays to convey accurately tactile information.

How Tactor Size and Density of Normal Indentation Tactile Displays Affects Grating Discrimination Tasks

Tactile fingertip devices of vertically moving tactors have two important design parameters that significantly affect physical feedback and human tactile perception: tactor size and tactor density. However, there are a limited number of research studies that have evaluated the effect of these parameters on human tactile perception. This paper investigated the influence and interaction of these two parameters on a discrimination task. The task consisted of discriminating the spatial-period of sinusoidal gratings through the use of passive-guided touch. In two complementary experiments 40 participants performed the discrimination task under two different tactile conditions: (I) using direct bare fingertip sensing (baseline condition), and (II) using tactile displays with different tactor spacings and diameters. In both experiments differences between and within subjects were considered for Condition II, and for all test conditions the spatial-period Weber fraction for each participant was measured. Results from both experiments were consistent in indicating that tactile performance improves as tactor spacing is decreased and tactor diameter is increased. However, tactor spacings below 1.1 mm might not result in any significant further improvement. The findings of this study might help designers to choose design parameters for tactile displays based upon the cost-benefit of tactor density versus perceptual performance.

Active and efficient motor skill learning method used in a haptic teleoperated system

This paper presents a new haptic training method for motor skill acquisition working in a teleoperated system. The method promotes a visuo-motor learning process base on the active attention and participation of the apprentice during training. Using a robot end-effector, the master describes a desired path which is followed by the apprentice using a haptic device. The master aids the apprentice by restricting his motion within upper and lower boundaries parallel to the path being created in real time. The boundaries are located at a given distance established by the master base on the apprentice learning improvement. Using this method, the master does not disturb or control the position and velocity of the apprentice directly which avoids apprentice dependence on the master. A training handdrawing scheme was designed and implemented to evaluate the visuo-haptic method; experimental results show faster and better apprentices motor performance than using only visual information. These results suggest a possible implementation of the method in complex motors tasks such as calligraphy or surgery, to name a few.

Haptic Teleoperated Robotic System for an Effective Obstacle Avoidance

A novel haptic teleoperated scheme for an efficient obstacle avoidance under human guidance is introduced. A remote robot immersed in an environment with obstacles is guided by a user using the end-effector of a haptic device. The system provides force feedback to the user when he approaches a potential field surrounding an obstacle. The user assigns the potential fields to the obstacles based on subjective judgments, i.e. a loose fitting potential field whether the obstacle is fragile or tough, to avoid a close approach to it. Obstacle avoidance experiments under visual and force feedback were performance and the results confirm the effectiveness of this scheme.

Humanoid Robot Teleoperation with Vibrotactile Based Balancing Feedback

One of the main challenges while teleoperating a humanoid robot consists in maintaining the slave’s balance while satisfying the operator’s intention. The main goal of this work is to settle whether feeding back the robot’s balance state to the operator by the mean of a vibrotactile belt can lead to an enhanced quality teleoperation. This study examines if an adequate cutaneous guidance can enable the operator to understand when the robot is approaching a loss-of-balance configuration, and use this information to adjust his teleoperation strategy. To achieve this objective, three different feedback patterns were compared during an initial experimental study. The evaluation focused on the subjects capacity to recognize the boundaries of a virtual workspace under each feedback mode and to adapt accordingly their teleoperated motions. The best suited feedback mode was selected and used during a second experiment which compared the performances obtained with and without tactile feedback during the teleoperation of the humanoid robot COMAN. Results clearly reveal that the cutaneous feedback of the slave’s balance state leads towards an enhanced quality teleoperation combining an increased safety as well as an unrestrained use of the entire stable workspace.

Orientation discrimination of patterned surfaces through an actuated and non-actuated tactile display

This paper investigates the tactile orientation discrimination of virtual, small-scale, patterned surfaces through a tactile display. The tactile display is an array of 4×4 vertically moving pins which can simulate the shape of small scale features. Its small size and low mass allow users to explore virtual surfaces freely and intuitively. The evaluation method consisted of measuring the orientation discrimination threshold for virtual surfaces with sinusoidal profiles. The threshold was compared with the threshold obtained using a non-actuated tactile display of equal spatial resolution and with the threshold obtained using the bare finger to explore real surfaces. This comparison was done to evaluate the quality of the rendered virtual surfaces, the performance of the device as a control system and the efficiency of the tactile rendering algorithm. This study also measured the speed and normal force during the tactile exploration that allowed investigation of the exploration strategies used when touching through normal indentation displays and through the bare finger. Furthermore they are the necessary interaction parameters for assessing the bandwidth and force output of the device.

Human Tactile Ability to Discriminate Variations in Small Ridge Patterns thorugh a Portable-Wearable Tactile Display

This work presents a quantitative evaluation of subjects’ tactile ability to discriminate small virtual ridge patterns through a portable–wearable tactile device. The virtual patterns have been recreated by controlling the vertically moving pins of the device. Psychophysical experiments were performed to measure subjects’ thresholds for spatial variation discrimination of ridge patterns. Moreover, for comparison reasons, further psychophysical experiments were performed with real ridge patterns using a non-actuated version of the tactile device and touching directly with the bear finger. During experiments, the exploration velocity was monitored. The present results help to understand, compare and characterize the tactile display when rendering small ridge patterns. The output of the presented study can also assist in the development of new tactile systems.

Effectiveness of a tactile display for providing orientation information of 3d-patterned surfaces

This paper studies the effectiveness of a tactile display in providing information about the orientation of 3d-patterned surfaces. In particular, it investigates the perception of the orientation of sinusoidal gratings rendered through the display in a passive guided touch modality. The results of this study have revealed that participants could successfully perceive variations in the orientation of the rendered sinusoidal gratings. Moreover, they indicate a small difference in the perception of orientation between touching virtual gratings and touching real gratings.