Fuminobu Kimura

Development of a 2-DOF softness feeling display for tactile tele-presentation of deformable surfaces

This paper presents a 2-DOF controlled softness display and its application to a tactile tele-presentation system. It has been reported that softness feelings can be displayed by reproducing contact area, or contact width, on a fingertip. Several softness displays based on the contact area control have been reported in past studies, but all of them had only one degree-of-freedom (DOF) for their contact area control. Resultantly, the reproduced contact area was symmetric, which could only produce uniform surface feelings. In some practical deformable surfaces, however, the contact conditions are not uniform over fingertip surfaces; for example, if there is a small lump beneath a soft deformable surface, resultant contact area can become asymmetric. To reproduce such asymmetric contact conditions, a softness display should have more controlled DOFs. This paper reports our trial to realize a multi-DOF controlled softness display. As a first step, this particular paper describes a 2-DOF controlled display. The display has two DC motors which independently control both sides of the contact area. Resultant asymmetric contact area can facilitate, e.g., discrimination of lump location in soft deformable surfaces. The display was integrated into a tactile tele-presentation system together with a contact width sensor, which measures asymmetric contact condition. Using the tele-presentation system, discriminations of lump location are demonstrated.

Development of a contact width sensor for tactile tele-presentation of softness

This paper presents a tele-presentation system for tactile softness. Tactile softness was estimated at a remote site, which was then reproduced at a master site, by focusing on change of contact width between a fingertip and an object. To realize the tele-presentation system, a new contact width sensor was developed based on an optical principle. The sensor was designed to have a soft structure to resemble human fingers. The prototype sensor was evaluated for five different samples. The result showed that the sensor could discriminate five samples from the contact width variation, although one pair of samples showed only a slight difference. The tele-presentation system that integrates the developed contact width sensor and a newly designed softness display was developed and evaluated. The evaluation result showed that a user can discriminate softness of a remote object using this system, although the perceived softness feelings did not perfectly match the real feelings of the remote objects, which would be due to insufficient optimization of the contact width sensor. This would be improved by improving the sensor to have a similar dimensions and stiffness as real human fingers, which will be addressed in our future work.

Rendering variable-sized lump sensations on a softness tactile display

This paper describes a new tactile rendering technique to produce lump sensations in virtual soft surfaces. Most softness displays reported so far reproduced only simple and uniform soft objects; nevertheless many real objects around us provide complicated softness. To reproduce various different softness sensations, we have previously developed a softness display utilizing a flexible sheet that wraps around a fingertip to stimulate fingertip cutaneous sensations. The device controls the softness sensations by changing tension of the flexible sheet, as well as the contact area between the sheet and a fingertip. During our pilot experiments, we found that users feel lump sensations from the softness display in particular conditions. Based on the findings, this paper proposes a technique to reproduce sensations of soft objects that contain lumps beneath their surfaces. The proposed technique can vary the size of the rendered virtual lumps through tension control; larger tension produces smaller size of lump sensation, and vice versa. Results of experiments using human subjects confirmed the validity of the proposed method.

Effect of delays in softness display using contact area control: rendering of surface viscoelasticity

This paper discusses effects of delays in a softness display, which increase viscosity in the displayed tactile feelings. Previous softness reproductions based on contact area control used a static contact model to calculate contact area and thus did not consider dynamic contact behavior, such as delay. To discuss the delay and the resultant viscous feelings, this paper proposes a new dynamic contact model that extends the previous static model. The proposed dynamic contact model has a nonlinear damper and is verified by experiments that measure contact area on a real object. For the contact area measurement experiments, the work proposes a new sheet-type sensor specialized for contact area detection. Using the proposed contact model, control delays of the softness display is evaluated in comparison with the real object to find out the frequency limitation for correct reproduction of surface feelings. Finally, the paper proposes to implement a partially linearized dynamic contact model to the softness display to render feelings of viscoelastic objects.

A Softness Feeling Display with an Active Tensioner Controlling Contact Pressure Distribution on a Fingertip

This paper describes a tactile display for softness feelings with a function of controlling contact area and pressure distribution. Contact area between a fingertip and a display is controlled by wrapping a flexible film around a finger. An active tensioner controls the tension of the flexible film to modify the contact pressure distribution. Controlling both area and pressure distribution realizes rendering of wider range of softness feelings. The effect was verified using photoelastic phenomenon. The experimental results show that the display can render the different contact conditions that arise from two differently-felt sponge samples with different thicknesses.

Multi-digit Softness: Development of a Tactile Display to Render Softness Feeling on Multiple Fingers

This paper describes a new tactile display that can present softness sensations to multiple phalanges on multiple fingers. Contact width control through sheet wrapping is adopted as a softness rendering method for each finger. Three separate mechanisms for contact width control for three fingers are integrated in one device. Passive mechanical linkages are employed to provide sensations to the whole fingers. The paper reports on the design of the developed device, as well as the result of psychophysical experiment that investigated the contributions of each phalange and finger in softness perception on this display.