Yoshinori Fujihira

Experimental investigation of effect of fingertip stiffness on friction while grasping an object

In this study, we experimentally investigated the effect of robot fingertip stiffness on friction during grasping of an object. To make robots more human-friendly, robotic hands with soft surfaces have been developed. A soft fingertip, i.e., one with low stiffness, is considered desirable because it produces high friction. However, in our experiments, we were able to obtain high friction from a stiff fingertip under a certain condition. We initially investigated the maximum resistible force when solid objects with different angled surfaces were grasped by spherical fingertips of different stiffness. When the contact surface was flat, a stiffer fingertip produced larger frictional force. When the contact surface was highly convex, the maximum frictional force increased with decreasing fingertip stiffness. Secondly, we examined the relationships among the contact area, the load, and the maximum frictional force. We reformulated the relationship between the load and the maximum frictional force and, together with our experimental results, used it to determine the factor that increased the maximum frictional force.

Force Sensor Attachable to Thin Fiberscopes/Endoscopes Utilizing High Elasticity Fabric

An endoscope/fiberscope is a minimally invasive tool used for directly observing tissues in areas deep inside the human body where access is limited. However, this tool only yields visual information. If force feedback information were also available, endoscope/fiberscope operators would be able to detect indurated areas that are visually hard to recognize. Furthermore, obtaining such feedback information from tissues in areas where collecting visual information is a challenge would be highly useful. The major obstacle is that such force information is difficult to acquire. This paper presents a novel force sensing system that can be attached to a very thin fiberscope/endoscope. To ensure a small size, high resolution, easy sterilization, and low cost, the proposed force visualization–based system uses a highly elastic material—panty stocking fabric. The paper also presents the methodology for deriving the force value from the captured image. The system has a resolution of less than 0.01 N and sensitivity of greater than 600 pixels/N within the force range of 0–0.2 N.

Experimental investigation of effect of fingertip stiffness on resistible force in grasping

In this study, we experimentally investigated the effect of robot fingertip stiffness on the maximum resistible force. The maximum resistible force is defined as the maximum tangential force at which the fingertip can maintain contact when applying and increasing tangential/shearing force. We include in the definition of this term the effect of fingertip deformation. In contrast to our previous study [11], cylindrical fingertips with flat surfaces were used in this study so that the contact area would remain the same when there was no tangential/shearing force. This made it possible to see the effect of fingertip stiffness more clearly. We also investigated the effect of curvature of the contact surface, which was not investigated in depth in [11]. The main findings are as follows. 1) Harder fingertips produce larger resistible forces, irrespective of the shape of the contact surface (flat or curved). 2) For harder fingertips, the maximum resistible force depends largely on the shape of the contact surface, while for softer fingertips, the shape has little effect. 3) For softer fingertips, the magnitude of the resistible force changes little even when the normal force increases.

Three-axis force visualizing system for fiberscopes utilizing highly elastic fabric

This paper presents a novel force sensing system for fiberscopes. The key features of the system are its low cost, high resolution, small size, and ability to measure three-dimensional force. A previous study described a novel force sensing system that could be attached to a very thin fiberscope, based on a force visualization mechanism utilizing panty stocking fabric - a highly elastic material. However, this system measures force in only one direction. In this paper, the system is extended to measure forces in any of three directions. The system is targeted for application to neurosurgical examinations. It may also be useful for other medical and non-medical examinations that involve the use of fiberscopes.

New condition for tofu stable grasping with fluid fingertips

Tofu shows the following compression behavior. First, the behavior is non-linear; subsequently, the behavior becomes elastic/linear, followed by yielding and fracture. A linear behavior indicates that there is no fracture, but further increase of compression can cause yielding or fracture. The compression in the region of linear behavior then can be regarded as maximum. With this in mind, this paper presented a grasping condition of controlling the amount of compression so that the compression behavior can be linear. This condition is applied to the previously proposed fluid fingertip that utilizes a rubber bag filled with a viscoelastic fluid and having a rigid layer inside the fluid. In addition, this paper presents a methodology for checking whether the grasping condition is held, based on our previously developed phase change detection method of comparing the fitting accuracies of different approximation models. Additionally, this paper presents the reason behind the behavioral change of fluid pressure. Before phase change, the fluid fingertip behaves like a rigid fingertip, while after phase change, the contact pressure is transmitted to the fluid pressure and can be observed by the fluid pressure. The validity of the approach was shown through experiments.

Identification of danger state for grasping delicate tofu with fingertips containing viscoelastic fluid

In this study, we experimentally investigated the process leading to fracture in tofu grasping by deformable fingertips filled with a fluid. In our previous papers [1, 2], we developed deformable fingertips using a rubber bag filled with a viscoelastic fluid, and presented a strategy for delicate tofu grasping without any advance knowledge about fracture. However, the predication point was close to fracture, and the prediction was then still a gamble. In order to realize fracture prediction at an earlier stage, we examined the process leading to fracture when pushing tofu by the deformable fingertips. The stiffness of the fingertips can be controlled with the pressure of the fluid inside the fingertips. The pushing force and fluid pressure were examined for different levels of stiffness of the fingertips. The main findings and contributions are as follows. 1) The convergence of the ratio of the contact force to fluid pressure gives an indication of dent occurrence. This convergence could be seen when fingertip rubber bag was not filled (low stiffness). 2) It was easier for a dent to occur when the fingertip rubber bag was not filled than when it was filled (high stiffness). 3) Changes in the rate of increase of the fluid pressure as the tofu was pushed were repeatedly observed. We defined this as a phase change and present a method for detecting such changes. The phase change points were detected by comparing the fitting accuracies of different approximation models. 4) The last and second to the last phase changes before fracture were detected by detecting the first phase change (after the convergence of the rate of the contact force to fluid pressure if the fingertip bag was not completely filled). The detected points can be regarded as alert points indicating a fracture risk that is not close to the fracture point.

Application and performance evaluation of a lifting device with alternating rotation hoist

There exist vertical long ropes that need periodical inspection for infrastructure maintenance. Development of lifting devices along with the ropes is demanded for steady observation at human-unreachable positions. The lifting device based on alternating rotation hoist has been proposed for carrying inspection devices to the target level. This research realizes an automatic movement of the lifting device by computer control for the improvement of speed and accuracy. Furthermore, a new frame which is equipped with the inspection device is developed for saving weight and keeping balance. Through experiments, performances of the new frame and control system are evaluated from the aspects of speed, accuracy, weight and balance. The results show that the newly developed frame has advantages in weight and speed. The inclination of frame and ascender is measured. The error values are calculated to analyze the accuracy. And the developed control system can control frame effectively.

Evaluation of whole circumference image acquisition system for a long cylindrical structures inspection robot

In an inspection of aging infrastructures has become a problem. Vertical long cylindrical structures is one of inspection targets. Therefore, we have been developing an inspection robot system for these structures. In order to inspect a surface condition of these structures, whole circumference images need to be acquired. In this peper, we implemented a whole circumference image acquisition system for an inspection of these structures in the inspection robot. This system is based on proposed multi-view imaging theory using two cameras and three mirrors. We also evaluated whole the circumference images which is obtained by the developed system using a monochrome pattern.

Exercise classification using CNN with image frames produced from time-series motion data

Exercise support systems for the elderly have been developed and some were equipped with a motion sensor to evaluate their exercise motion. Normally, it provides three-dimensional time-series data of over 20 joints. In this study, we propose to apply Convolutional Neural Network (CNN) methodology to the motion evaluation. The method converts the motion data of one exercise interval into one gray scale image. From simulation results, the CNN was possible to classify the images into specified motions.

Bent Sheet Grasping Stability for Sheet Manipulation

In this study, we focused on sheet manipulation with robotic hands. This manipulation involves grasping the sides of the sheet and utilizing the convex area resulting from bending the sheet. This sheet manipulation requires the development of a model of a bent sheet grasped with fingertips. We investigated the relationship between the grasping force and bending of the sheet and developed a bent sheet model. We also performed experiments on the sheet grasping stability with a focus on the resistible force, which is defined as the maximum external force at which a fingertip can maintain contact when applying an external force. The main findings and contributions are as follows. 1) After the sheet buckles, the grasping force only increases slightly even if the fingertip pressure is increased. 2) The range of the applicable grasping forces depends on the stiffness of the fingertips. Stiffer fingertips cannot provide a small grasping force but can resist large external forces. Softer fingertips can provide a small grasping force but cannot resist large external forces. 3) A grasping strategy for sheet manipulation is presented that is based on controlling the stiffness of the fingertips.