This paper presents a strategy meant to allow anthropomorphic robot hands to grasp objects of unknown shape in imitation of the human grasping reflex. A 10-month-old baby may bend his/her thumb and four fingers in an attempt to grasp an object when it comes in contact with the palm. After grasping it, if the object is attempted to be removed from the baby's hand, the baby holds the object more strongly. In addition, the palm of the hand often makes initial contact with the object very lightly. This reaction is called the grasping reflex. In the proposed grasping strategy, each joint of the thumb and the fingers of a robot hand is controlled independently using the contact force affecting its adjacent fingertip side-link to imitate the grasping reflex. By setting a suitable contact force, the robot can grasp an object by both the fingertips as well as an enveloping grasp involving the palm at a uniform grasping force. Experimental results regarding the grasping of three-dimensional objects of unknown shape by an anthropomorphic robot hand called the Gifu Hand III are shown.
In the industrial world, not only autonomous machinery as industrial robots but also man-machine cooperative systems as power-assist systems have attracted special interest recently. Kondo, et al. proposed the scheme of Man-Machine Collaborated Systems (MMCSs) and its application to some assembling work. In MMCSs, efficient mode switching from human-oriented task to machine-oriented task is important. However, its issue has not been fully addressed yet. This study discusses a mode switching control method for MMCSs. Especially, we treat the switching from a power-assist mode (PAM) to an automatic positioning mode (APM) for a simple robotic system. To obtain a smooth switching, this study utilizes a two-degree-of-freedom control system structure which consists of an on-line impedance control simulator and an LQI servo controller. Some smooth reference generation for APM is also introduced. No input saturation and stopping appear at the switching in this method. The effectiveness of the method is verified experimentally.
This paper proposes a new method for evaluating the synchronous inaccuracy of a translational axis and a rotational axis in five-axis controlled machining centers with a tilting rotary table. A circular trajectory whose shape is easy to evaluate the specific features is adopted for measuring the circular path described by the two axes. The influence of inaccurate synchronization on the circular path was simulated by changing the distance between the centers of the rotary table and the circular path, the radius of the circular path and the feed speed. Measurement conditions were determined based on the simulation results, and then ball bar measurements and machining experiments were conducted. From the simulation and experimental results, it is confirmed that the proposed method can be used for evaluating the inaccurate synchronization of a translational axis and a rotational axis. However, careful alignment of the center of the rotational axis and the machine coordinate origin is important for evaluating the synchronous accuracy. The ratio of the distance between both centers of the rotational axis and the circular path to the radius provides useful information for the evaluation.
In this paper we analyze a design and development process of a product or a knowledge-base using complexity and present a methodology to search a sequence using the active complexity, a measure of dynamically changing undefined information. We observe that the information content and parametric interaction of each design process evolve and each design process shows a distinct evolutionary pattern of design information. We analyze such an evolutionary aspect of the design process using complexity theory and optimize it for the minimum active complexity. The obtained optimum design process provides a development sequence with the minimum undefined attributes, which could be used as useful guidance in the product design and assembly planning. We illustrate our approach with examples
The environment in which Japanese industry has achieved great respect is changing tremendously due to the globalization of world economies, while Asian countries are undergoing economic and technical development as well as benefiting from the advances in information technology. For example, in the design of custom-made casting products, a designer who lacks knowledge of casting may not be able to produce a good design. In order to obtain a good design and manufacturing result, it is necessary to equip the designer and manufacturer with a support system related to casting design, or a so-called knowledge transfer and creation system. This paper proposes a new virtual reality based knowledge acquisition and job training system for casting design, which is composed of the explicit and tacit knowledge transfer systems using synchronized multimedia and the knowledge internalization system using portable virtual environment. In our proposed system, the education content is displayed in the immersive virtual environment, whereby a trainee may experience work in the virtual site operation. Provided that the trainee has gained explicit and tacit knowledge of casting through the multimedia-based knowledge transfer system, the immersive virtual environment catalyzes the internalization of knowledge and also enables the trainee to gain tacit knowledge before undergoing on-the-job training at a real-time operation site.
In this paper a novel 4 Degree-of-Freedom (DOF) parallel mechanism with the configuration of 4PUS-1RPU is first proposed, the mechanism is composed of four symmetrical driving chains and one central passive subchain. Based on the proposed 4-DOF parallel mechanism a 5-axis Hybrid Kinematics Machine (HKM) scheme is developed with an additional linear motion is combined, which can perform the 5-axis machining for freeform parts. The inverse kinematics of the 4-DOF parallel mechanism and the direct kinematics for the serial central sub-chain are then presented. The dexterity and the workspace analysis for the mechanism are also carried out. The dynamic characteristics of the PKM are investigated in detail. The simulation results show that the first four fundamental frequencies are the dominant factors that influence the dynamic characteristics of the developed PKM. The research provides the basis for the further parametric design with consideration of dynamic performances.
The acoustic radiation efficiency of a plate carrying concentrated masses has been studied. The variation of the radiation efficiency of a plate occurs due to attaching masses to the plate at frequency range below the coincidence frequency. The reason for the efficiency variation can be interpreted physically by using the conception of volume velocity cancellations. The volume velocities on the plate surface except in the regions near the four corners are canceled out when the plate is uniform, whereas the cancellation of the volume velocities is disturbed around the mass attached on the plate. Attaching a mass increases the radiation efficiency of a plate. In this paper, the approximate expression has been developed for the variation of the radiation efficiency of a plate due to attaching concentrated masses in the case where a large number of modes are excited. Experimental results show that the approximate expression is valid and useful.
This paper concerns kinematics and dimensional synthesis of a three universal-revolute-universal (3-URU) pure rotational parallel mechanism. The mechanism is composed of a base, a platform and three symmetric limbs consisting of U-R-U joints. This mechanism is a spatial non-overconstrained mechanism with three degrees of freedom. The joints in each limb are so arranged to perform pure rotational motion of the platform around a specific point. Equations for inverse displacement analysis and singularities were derived to investigate the relationship of the kinematic constants to the solution of the inverse kinematics and singularities. Based on the results, a dimensional synthesis procedure for the 3-URU parallel mechanism considering singularities and the workspace was proposed. A numerical example was also presented to illustrate the synthesis method.
In currently working seismic ACROSS (Accurately Controlled Routinely Operated Signal System) transmitters, an unbalanced rotor with large eccentric mass, which generates elastic waves, is supported by roller bearings. With such a type of bearings, bearing losses are so large that heat generation and cooling system become serious problems. To solve these problems, a trial test ACROSS transmitter using hydrostatic gas bearings are designed, made and carried out. The test results show that the hydrostatic gas bearings safely support a largely unbalanced rotor with eccentric mass. In this paper, a new type of hydrostatic journal gas bearings with asymmetric bearing area specially proposed for a largely unbalanced rotor are analyzed and tested. It is shown that hydrostatic asymmetric journal gas bearings have large load capacity for a largely unbalanced rotor and low gas flow rate compared to the conventional hydrostatic symmetric journal gas bearings.
This paper describes the theoretical and experimental investigations of static and dynamic characteristics of four types of high-speed gas film thrust bearings, such as stepped, pocketed, spiral and herring bone grooved bearings. The specially designed test rig is used to measure the air film thickness, friction torque, spring and damping coefficients of air film under the high speed operation conditions from 20000 rpm to 40000 rpm. It is verified that the maximum error in the measurements by the present test rig is less than 7 percent. On the other hand, the measured results are compared with the theoretical results for checking the applicability of numerical analysis method to bearing design. Good agreements are seen between the measured results and theoretical predictions, and applicability of theoretical prediction method is confirmed with experimental verifications.
In this paper, we consider a stability analysis for the impedance control of the robot in the human-robot cooperative task system. In the stability analysis, the effect of modeling conditions is investigated, such as the impedance characteristic of the robot, the time delay of a human operator and control of the robot, the compliance of the structure of the robot and environmental stiffness in interactive system. The proposed simulation of the stability analysis reveals that these conditions have significant effects on the stability of the system. To confirm the usefulness of stability analysis simulation, a verification experiment using a Mitsubishi PA-10 robot arm was performed. Experimental results show that the proposed stability analysis is effective in simulating the stability of the human-robot cooperative task system.
In the present paper, a newly developed ultrasonic brake is proposed. The ultrasonic brake can solve problems of conventional passive elements, such as time delay, instability, and large size, by using unique characteristics of ultrasonic motor, as fast response, silent motion, and non-magnetic feature. It can also be designed to be smaller than conventional elements due to its simple structure. The brake locks or releases the rotor by use of ultrasonic levitation phenomenon. First, we have designed the structure of the ultrasonic brake using an equation of ultrasonic levitation phenomenon, results from structural analysis and finite element (FE) analysis of piezoelectric material of the vibrator. Then we have manufactured the ultrasonic brake and have conducted a driving experiment. Finally, we have demonstrated that the maximum levitation force is around 40 N and the friction torque of the ultrasonic brake is up to 0.38 Nm. Moreover, we have confirmed that both response time and torque/inertia ratio of the ultrasonic brake are much more superior to the conventional ones.
A simple series hybrid power system composed of passive-type polymer electrolyte fuel cells (PEFCs) and electric double-layer capacitors was adapted to a lightweight electric vehicle. In order to numerically simulate the behavior of the hybrid system, a fuel cell equivalent circuit model was applied and the model parameters were determined using an electrochemical theory and experimental results. Including this PEFC equivalent circuit model, a simulation model of the power train system (PEFCs, capacitors, motor, power controller, inertia, etc) of a lightweight electric vehicle was composed. It has been confirmed that this simulation model can represent reasonably well the dynamic behavior and energy transmission of the system in the experiment on a fixed apparatus constructed as a model of the vehicle.
In this paper, design of control system and power combination mechanism of a power assist system of the walking chair was discussed based on kinetostatic characteristics of human arm. The walking chair is a welfare walking machine which is an alternative vehicle of the wheelchair, and expected to be driven by user's cranking operation with assisting actuator. To efficiently utilize user power as much as possible for long locomotion without giving much fatigue to the user while providing comfortable driving feeling to the user, the human arm characteristics were taken into consideration. Kinetostatic characteristics of the human arm were experimentally investigated for its modeling. This model was applied to the design of mechanism and control system of the power assist system of the walking chair, and design parameters were determined for achieving comfortable driving feeling and efficient utilization of user power.
To measure a 3D pose of the objects, we propose an artificial mark attached to objects. We propose three differently shaped marks, all of which have four point features. To measure the marks, the image processing system extracts the point features using edge extraction, erosion, and color extraction. Through measurement experiments, we compared error characteristic of these marks. The results showed that color extraction, which uses the simplest image processing method, was most robust when a mark was measured from various poses (mean of error: 10.4deg, mean of std. dev.: 7.06deg, worst std. dev.: 24.7deg) or was attached to the surface. Moreover, the mark enabled the shortest measurement time (0.478s/6marks). The usefulness of the mark with color extraction was verified through the success of an experiment in which a manipulator handled three marked objects.
The objective of sound field control is to make the acoustic characteristics of a listening room close to those of the desired system. Conventional methods apply feedforward controllers, such as digital filters, to achieve this objective. However, feedback controllers are also necessary in order to attenuate noise or to compensate the uncertainty of the acoustic characteristics of the listening room. Since acoustic characteristics are well modeled on the frequency domain, it is efficient to design controllers with respect to frequency responses, but it is difficult to design a multi input multi output (MIMO) control system on a wide frequency domain. In the present study, a partial model matching method on the frequency domain was adopted because this method requires only sampled data, rather than complex mathematical models of the plant, in order to design controllers for MIMO systems. The partial model matching method was applied to design two-degree-of-freedom controllers for acoustic equalization and noise reduction. Experiments demonstrated effectiveness of the proposed method.
In order to catch up with rapidly changing market environment, rapid and flexible redesign of production system is quite important. For effective and rapid redesign of production system, a redesign support system is eagerly needed. To this end, this paper proposes a redesign method of production system based on Quality Function Deployment (QFD). This method represents a designer's intention in the form of QFD, collects experts' knowledge as “Production Method (PM) modules,” and formulates redesign guidelines as seven redesign operations so as to support a designer to find out improvement ideas in a systematical manner. This paper also illustrates a redesign support tool of a production system we have developed based on this method, and demonstrates its feasibility with a practical example of a production system of a contact probe. A result from this example shows that comparable cost reduction to those of veteran designers can be achieved by a novice designer. From this result, we conclude our redesign method is effective and feasible for supporting redesign of a production system.