Users are often seated in the real environment, while their virtual avatars either remain standing stationary or move in virtual reality (VR). This creates posture inconsistencies between the real and virtual embodiment representations. The relationship between posture consistency in locomotion techniques and sense of presence in VR is still unclear. This study investigates how visual and somatosensory integration affects the sense of standing (SoSt) and the sense of self-motion (SoSm) when the sitting posture is varied slightly, including highlighting the importance of sitting posture for locomotion design in VR. The degree and occurrence of SoSt and SoSm were assessed by subjective experiments, and it was found that higher sitting and lower sitting postures present higher SoSt and lower SoSm, respectively. Invocation of SoSt also influences postural perception. Perception of travel distance varied according to the posture condition when identical visual flow was presented. The findings suggest that visual and somatosensory integration related to posture enhances SoSt and SoSm, and a sitting posture with a higher seating position is recommended in seated VR locomotion design.

When a conventional robot arm, driven by magnetic motors and reduction gears, operates at high speed, it can produce an excessive force due to unexpected contact. Toward the development of a safe robot arm, the present study investigated a 2-degree-of-freedom robot arm driven by direct-drive electrostatic film motors. The motors operate synchronously, except when they are subjected to an excessive force. This loss of synchronicity is referred to as a “step-out” process, and in the present study it was used to produce a variable torque limiter. By setting appropriate limits, contact forces caused by unexpected collisions could be suppressed. The torque limiter was applied to a robot arm with a length of 50 cm. Experiments showed that the arm was impact-resistant; when it was struck by a hammer, the torque limiter was activated and suppressed the collision force, allowing the robot arm to successfully resume its motion. When the robot arm unexpectedly hit an obstacle while moving at 1.2 m/s, the collision force was maintained at 21 N by the torque limiter, which is sufficiently small for a high-speed collision. The experiments verified the effectiveness of the electrostatic film motor as a variable torque limiter to realize safe contact.

A psycho-physical experiment using constant method was conducted to investigate the characteristics of pseudo force sensation caused by pressurization to a palm. Kinesthetic force stimulus and tactile pressure stimulus were given to a subject at the same time, and their effect on force perception was investigated. Previous studies have reported two contradicting results regarding whether the strength of pseudo force sensation depends on the pressure or on the total amount of force. This paper further investigated this aspect using three types of indenters which differ in shape and width. The results suggested that the pseudo force sensation does not depend on total force. This, however, does not simply mean that the sensation depends on the pressure and the need for further investigations remains. The results found significant differences among subjects but also suggested that the narrower indenter with an integrated body is less susceptible to individual differences among subjects.

This paper investigates the performance of resonant electrostatic induction motors in multi-layer stacking, in which several sets of films are stacked to increase thrust force output and decrease required inductance. A mathematical analysis of this matter is performed, based on the previously deducted equations on resonant voltage and thrust force, which are used to model how these parameters are expected to scale with the number of layers. The analysis has revealed that thrust force should increase linearly with the number of layers, while coil size should decrease. A set of experiments is also performed in order to evaluate the model. The results have shown agreement with the predictions, suggesting this method can be used to achieve the expected gains.

In this paper, a novel proximity imaging method based on tomographic approach with a conductive sheet is proposed. Through defining capacitance density, physical proximity information is transformed into electric potential. A novel mathematical model is developed for solving the capacity density problem. Additionally, a reconstruction system is built to solve an inverse problem for estimating capacitance density on the surface using the voltage amplitude sets from electrodes on the border of the conductive sheet. Reasonable results are generated through reconstruction simulation. Then, a prototype was made for validating the proposed sensor design. As a result, the output of the prototype matched the proximity information of the object with an average position error of 15.4 % sheet length, in our 4-electrode prototype experiment.

This paper reports on a development of motion simulator for charge-induction electrostatic actuator. The simulator deals with planar 3-DOF motions, which are XY 2-DOF translations and rotation. To simplify the simulation process, the paper sets two assumptions on the electrostatic force generation within the actuator. One is that the induced charges on the slider will be kept fixed during a step motion of the slider. Second is regarding a skewed condition, where charge distribution on the slider is skewed against the stator electrodes. The paper assumed that, if we focus on a small element, the electrostatic force for the skewed condition can be calculated in the same manner as the normal condition. The simulated motion trajectories using those assumptions fairly matched with experimental observations. Also, how to simulate the friction between the stator and the slider is discussed using three simple friction models.

A tactile sensor with high spatio-temporal resolution will greatly contribute to improving the performance of object recognition and human interaction in robots. In addition, being able to switch between higher spatial and higher temporal resolution will allow for more versatile sensing. To realize such a sensor, this paper introduces a method of increasing the sensing electrodes and adaptively selecting the grounding conditions in a tomography based tactile sensor. Several types of grounding conditions are proposed and evaluated using spatio-temporal metrics. As a result, the grounding method based on the location of contact had a good balance of temporal resolution (1 ms) and spatial resolution (only 1.55 times larger than using all electrodes as grounding conditions). When reconstructing dynamic contact data, the proposed method was able to obtain a much higher detailed waveform compared to the conventional method. By using the proposed method as default and switching to other grounding methods depending on the purpose of sensing, a versatile tactile sensor with high spatio-temporal resolution can be made.

In recent years, human augmentation has attracted much attention. One type of human augmentation, motion augmentation makes perceived motion larger than in reality, and it can be used for a variety of applications such as rehabilitation of motor functions of stroke patients and a more realistic experience in virtual reality (VR) such as redirected walking (RDW). However, as augmented motion becomes larger than the real motion, a variety of senses that accompany will be more inconsistent with those perceived from somatic sensations, which will cause a severe sense of discomfort. To address the problem, we focus on kinesthetic illusions that are psychological phenomena where a person feels as if his or her own body is moving. Kinesthetic illusions are expected to fill the gap between the intended augmented motion and perceived physical motion. However, it has not been explored if and how large kinesthetic illusions are produced while a user is moving their limbs voluntarily in VR. To expand the knowledge on kinesthetic illusions, we have conducted two user studies on the impact of tendon vibration and visual stimuli on kinesthetic illusions. First experiment confirmed that the perceived elbow angle becomes larger than the actual angle when presented with tendon vibration. Second experiment revealed that the increase of the perceived elbow angle was about 20 degrees when both tendon vibration and visual stimuli were presented whereas it was about 10 degrees when only visual stimuli were presented. Through these experiments, it has been confirmed that combining tendon vibration and visual stimulation enhances kinesthetic illusions.

In virtual reality (VR) systems, a user avatar is typically manipulated based on actual body motion in order to present natural immersive sensations resulted from proprioceptors. It is useful to be able to feel a large body motion in a virtual environment while it is actually smaller in the real environment. As a method to achieve this, we have been working on kinesthetic illusions induced by tendon vibration. In this article, we report on a user study focusing on the effects of a combination of visual stimulus and tendon vibration. In the user study, we measured subjects' perceived elbow angles while they observed the corresponding virtual arm bending to 90 degrees, with different rotation amplification ratios between 1.0 and 1.5, with and without tendon vibration on the wrist joint. The results show that the perceived angle is increased by up to 8 degrees when tendon vibration is applied, roughly in proportion to the rotation amplification ratio. Our study suggests that the vision-induced kinesthetic illusion is further increased by tendon vibration, and that our technique can be applied to VR applications to make users feel larger body motion than that in the real environment.

This research aims at constructing an intrinsic tactile interface for ubiquitous haptic AR. In order to avoid obstruction of natural object manipulation with the fingertip, we focused on electrotactile interface. We proposed a time division multiplexing technique with compensating processes allowing detection and augmentation of touch feeling through shared electrodes. In this paper, we investigated the performance as a sensor and display by a pressing task. First, we obtained an optimized parameter for the multiplexing. Next, the stimulus effect on the sensor performance was tested. Finally, we confirmed that the proposed interface has a potential to modulate user's cutaneous feeling.

The fine concavo-convex shape of the object surface is a critical component that determines its texture. A previous electrotactile display could not tactually present fine concavo-convex objects but only a line pattern on the plane. In this study, the authors proposed a physiology-based tactile mapping method by formulating nerve activities that stem from a mechanical stimulus. The proposed electrical stimulus allows a human to perceive a concavo-convex shape. A stimulus frequency coded the skin displacement given by a concavo-convex shape and represented the adaptation of receptors with exponential approximation. As an example of tactually presenting a concavo-convex shape, roughness was introduced by using a Brownian surface, which enables a user to touch a surface of varying degrees of roughness with a developed tactile display mounted on a computer mouse. The results of subjective experiments showed a statistical difference among the perceived roughness of displayed rough surfaces. This study concluded that the proposed tactile mapping method was effective to present a touch sensation for concavo-convex shapes corresponding to a stimulus frequency below 100 Hz.