Lope Ben Porquis

Representation of softness sensation using vibrotactile stimuli under amplitude control

An experimental study was done to examine the relationship between vibrotactile amplitude displacement and softness sensation. Merkel Disk behavior relative to softness sensation was studied under psychophysical experimentation of human participants. Restrictions are carefully applied on contact area spreading so that vibration will be the only factor that would induce a sensation. A vibrotactile device was excited at constant frequency and its amplitude is adjusted at different levels to alter the amount of skin displacement. Volunteers participated in a two-alternative force choice experiment were ask to compare the perceived softness difference between voice coil and silicone rubber. Statistical analysis on the responses of participants showed a decline of spring constant. It was interesting to note, that even though contact area was significantly restrained participants were still able to discriminate softness sensation form vibrotactile stimulation. Such observation possibly shows that illusion of contact area spread rate can be reproduced by vibrotactile stimulation.

Tactile-based torque illusion controlled by strain distributions on multi-finger contact

Humans experience torque when using a tool such as a stick or a stylus when exploring or manipulating an object. Forces that exert on the tool affects the pressure distribution on contact areas of the digits involved. In this paper we proposed a tactile rendering method that can elicit torque illusion by controlling the strain distribution beneath the contact areas. We assume that controlling the strain distribution on multiple fingers can affect strain energy density to a relative extent. Also, we expect that Merkel Disk response increases with the strain energy density. We control the strain distribution beneath the contact areas using a unique vacuum driven tactile interface. Six participants are requested to perform a psychophysical experiment and evaluate the torque sensation on the tactile interface. The device can move in a rotating frame with one degree of freedom. Experimental results suggest that participants felt an increasing torque sensation during strain redistribution. Point of subjective equality increases as much as 56% from lowest to highest stimuli level. This data shows an early confirmation on a method that can induce torque illusion.

Presenting virtual stiffness by modulating the perceived force profile with suction pressure

This paper reports a study on modulating the perceived stiffness by controlling the perceived force evoked from suction pressure stimuli. It demonstrates an early attempt of using suction pressure stimuli for augmenting the perceived stiffness of a spring. The purpose of this work is twofold; 1) to validate a requirement needed for the device in force enhancement applications, 2) to tentatively explore the effect of suction pressure stimuli on stiffness perception. In this study, we used physical springs for the stiffness stimuli, and a tool (tactile interface) was used for stiffness exploration. Human subjects were requested to explore and estimate the stiffness of a spring sample. Suction pressure stimuli were applied on the contact areas between the finger the tool during stiffness exploration. The amount of suction stimuli adjusts correspondingly with the measured force, but it is regulated by a psychophysical function. We introduced the gain to scale the measured force, thereby adjusting the profile of the pressure stimuli. We found that the perceived stiffness of the spring appears to increase with higher gain. The result seems to suggest that stiffness augmentation is feasible by modulating the stiffness perception using multipoint suction pressure stimuli.

Enhancement of human force perception by multi-point tactile stimulation

Perception of minute force through tactile feedback from a tool is an important aspect for humans to maintain dexterity during manipulation of embedded objects invisible to the naked eye, such as repairing tissues in minimally invasive surgery. Different pressure levels at finger contacts could be responsible factors concerning the perception of forces on a tool. In this paper, an experimental study was done to verify if pressure stimulation to the thumb and index fingers on a precision grip position could alter the perception of force. We requested participants to perform a psychophysical experiment by holding a grounded pen-type interface having a single degree of freedom which induces pressure sensation using air suction. Perceived force was observed to increase when pressure was applied increasingly. Experimental results suggested that vacuum pressure can be used as a complementary tactile stimulus for inducing force sensation. This study had confirmed that negative pressure stimulus can be used to augment force perception.

Haptic cue of forces on tools: Investigation of multi-point cutaneous activity on skin using suction pressure stimuli

This paper presents an initial data that could show a possible contribution of mechanoreceptor activity to the perception of forces applied on grasped objects. Here, we obtained detailed psychophysical characteristics of perceived force-magnitude in multiple degrees of freedom (MDOF) using multi-point suction pressure stimuli. To obtain such data, we developed a multi-point stimulation method that can represent MDOF perceived force on a tool. We characterized the perceived force response of human subjects to suction pressure stimuli through psychophysical experiments. Moreover, we analyzed the strain energy density (SED) on the finger pads considering the force applied through finite element simulation. The results of the psychophysical experiments showed that multi-point stimulation method is effective for evoking MDOF perceived force on a tool. Interestingly, we found that the results of the finite element analysis agree with those of the psychophysical data. Therefore, we have verified that it is possible to use multi-point suction pressure stimulation for representing perceived force on objects held in a hand. In addition, a preliminary insight into the role of SED for perceiving force on tools is provided.

Pseudo-Haptic Interface Using Multipoint Suction Pressures and Vibrotactile Stimuli

Dexterity for fine manipulation requires information from multiple skin contacts to detect the external forces applied on a tool. In this study, we developed a haptic interface to represent the external forces or stiffness of objects so that the pressure distributions at the contact pads can be controlled by using suction stimuli. The original interface had the drawback of being unable to represent high-frequency force sensations such as friction and collision because of air stimuli have large-scale characteristics. Thus, we integrated vibrotactile stimuli into the interface to represent high-frequency force sensations.

A Multi-DOF Haptic Representation Using Suction Pressure Stimuli on Finger Pads

Humans can perceive external forces applied on a grasping tool based on skin pressure distribution at multiple contact areas during grasp. The authors have tried to represent external forces and torques by controlling the skin pressure distributions using suction stimuli and confirmed the potential but in a heuristic manner. In this paper, we investigate an improved method of skin stimulation based on a combination of psychophysical experiments and mechanical simulation. We focus on a simplification method of the complex strain energy density (SED) distribution at the contact areas with four quadrant values (SED index). The relationship between suction pressure and SED index was achieved by connecting the experiment and the mechanical simulation. We confirmed that a suitable SED index could represent the magnitudes of forces in multiple directions with a linear function. Experimental results also showed that the proposed method could represent arbitrary directions between pairs of the orthogonal axes.

Multi-contact vacuum-driven tactile display for representing force vectors applied on grasped objects

In this paper we demonstrate an idea of multi---point tactile stimulation for representing force illusions on hand-held objects using vacuum pressure stimuli. The device used for the demonstration is pen-based and it is held by the fingers and thumb in a precision grip. There are two types of these devices; a three degree of freedom and a five degree of freedom tactile interfaces. These degrees of freedom are essentially illusions observed from the tactile stimuli. The initial prototype is capable of displaying force-like sensations in the three basic coordinate axes and moment-like sensations along two axes.

Can multiple tactile pressure stimulation in gripping position induce virtual force directions

Perception of minute force direction through tactile sensations during tool manipulation is an important factor for humans in skill acquisition. Different pressure levels on finger contacts could be responsible factors pertaining to the perception of force direction. In this paper, an experimental study was done to verify if pressure stimulation pattern applied to the thumb and fingers on a gripping position could produce a sense of force direction. Six participants performed a force direction discrimination experiment by holding a grounded pen type interface which induces pressure sensation using air suction technique. Experimental results showed that participants felt three distinct force directions from applied pressure stimulation patterns. It was verified in this experiment that the feasibility of applying different pressure levels at skin contact locations on a pen grip position can produce a sensation of force directions.