Hiroyuki Nabae

A Novel Electromagnetic Actuator Based on Displacement Amplification Mechanism

This paper introduces a new type of linear actuator using the electromagnetic attractive force, which enables a submillimeter stroke. In general, actuation by the electromagnetic attractive force causes a tradeoff problem between the thrust force and the stroke because the thrust force depends on the gap between the electromagnet and the armature; an increase in the gap (stroke) drastically degrades the thrust force. To realize a submillimeter stroke while retaining a high thrust force, a structure that adopts a displacement amplification mechanism is proposed, which is often used to expand the stroke of a piezoelectric actuator. First, the electromagnetic attractive force is theoretically examined with and without displacement amplification. We verify that displacement amplification could create a higher thrust force and energy efficiency over a certain displacement. On the basis of this examination, a prototype actuator is designed, and the driving principle is illustrated. Further, an analytical model of the proposed actuator is developed for control and performance estimation. Several fundamental experiments with a developed actuator are performed in order to reveal the potential of the proposed actuator. The performance evaluations show that the maximum stroke is approximately 450 μm and a bandwidth greater than 300 Hz can be realized, and more a time constant is approximately 2 ms for a stroke of 450 μm. In addition, the experimental results were compared with the simulation results calculated from the analytical model to verify whether the prototype drives predictably according to the proposed concept under a dynamic situation. These results demonstrate that the proposed actuator enables good actuation performance, and it implies that there are tremendous advantages from the viewpoints of manufacturing, assembly, control, etc.

A novel manipulation method of human body ownership using an fMRI-compatible master-slave system

Bodily self-consciousness has become an important topic in cognitive neuroscience aiming to understand how the brain creates a unified sensation of the self in a body. Specifically, full body illusion (FBI) in which changes in bodily self-consciousness are experimentally introduced by using visual-tactile stimulation has led to improve understanding of these mechanisms. This paper introduces a novel approach to the classic FBI paradigm using a robotic master-slave system which allows us to examine interactions between action and the sense of body ownership in behavioral and MRI experiments. In the proposed approach, the use of the robotic master-slave system enables unique stimulation in which experimental participants can administer tactile cues on their own back using active self-touch. This active self-touch has never been employed in FBI experiments and it allows to test the role of sensorimotor integration and agency (the feeling of control over our actions) in FBI paradigms. The objective of this study is to propose a robotic-haptic platform allowing a new FBI paradigm including the active self-touch in MRI environments. This paper, first, describes the design concept and the performance of the prototype device in the fMRI environment (for 3T and 7T MRI scanners). In addition, the prototype device is applied to a classic FBI experiment, and we verify that the use of the prototype device succeeded in inducing the FBI. These results indicate that the proposed approach has a potential to drive advances in our understanding of human body ownership and agency by allowing novel manipulation and paradigms.

Effect of Force Feedback on Rubber Hand Illusion

Our previous study has proposed a novel approach with a robotic/haptic technology to tactile rubber hand illusion (TRHI) paradigm in order to open new discussions about the manipulation of human body-parts ownership. The results demonstrated that the use of master-slave system can cause the TRHI, enabling a unique condition-active self-touch. As an advanced approach, this study examines the effect of force feedback on the TRHI under the active self-touch. We hypothesize that appropriate force feedback plays an important role to determine our body-parts ownership, people would not experience the TRHI if the force feedback from a fake hand largely differs from the contact force on a real hand. This paper, in particular, discusses how the force feedback affects the TRHI under the active self-touch by variously changing force rendering on the master device.

A Novel Rubber Hand Illusion Paradigm Allowing Active Self-Touch With Variable Force Feedback Controlled by a Haptic Device

This paper introduces an approach for manipulating bodily self-consciousness, in particular, senses of body ownership and illusory self-touch by using a robotic/haptic technology. This study especially focuses on the rubber hand illusion (RHI). In the classic RHI paradigm, an invisible participants hand and a visible fake rubber hand are manually stimulated by an experimenter. However, our approach, which is termed active self-touch, allows the participants to administrate the tactile stimulation with variable force feedback by using a robotic master-slave system. Three RHI experiments with active self-touch were performed to demonstrate the utility of the proposed approach for assessment of bodily self-consciousness. The embodiment of a fake hand was assessed with the classic RHI paradigm, and the RHI paradigm with somatic sensation was applied to examine the effect of variable force feedback on the sense of illusory self-touch. These experiments verified that active self-touch allows participants to experience the classic RHI. In addition, the results implied that the sense of illusory self-touch can be induced, even if force feedback is absent in the dynamic self-touch condition, and that illusory sensation is easily modulated by variable force feedback during quasi-static self-touch rather than during dynamic self-touch. These findings suggest that our proposed approach has the potential to reveal relationships between action/haptic perception and the sense of body ownership.

Manipulation of Particles in Liquid Using the Standing Waves Generated by Oscillation

This paper introduces a novel technique of trapping or gathering particles sinking under a liquid using the standing wave generated by oscillating the container. In this study, a prototype oscillation system based on a respective control is developed to generate various standing wave fields in water. First, the gathering positions of particles are attempted to be predicted by analyzing the wavelength of standing wave, considering the oscillation frequency of container as a key parameter. Based on the analysis, the oscillation system was driven in several wavelengths (modes) and the distribution of particles was compared with the predicted positions by using an image processing. Through this experiment, we present how the oscillation of container produces the transitions of particles in the water and examine the mechanism.Copyright

Application of a Repetitively-Controlled Viscoelastometer to Large Deformation

In dynamic viscoelastic measurement, accurate control of strain (or displacement) is one of the most important functions because the strain becomes dominant in viscoelasticity as it increases. However, it is difficult to achieve the accurate strain with commonly-used control methods when the specimen should be deformed largely. This is because the oscillation profile is distorted by the nonlinear viscoelastic response from the specimen and it produces the phase lag and gain loss in the control. In order to solve these problems, a viscoelastometer using a repetitive control was proposed in our previous work, and the applicability has been discussed in linear viscoelastic measurement. In this paper, we examine the applicability of proposed method to nonlinear viscoelastic measurement.Copyright