Through grasp experiments by human achieving an enveloping grasp for a small cylindrical object placed on a table, we found an interesting grasping motion, where human changes the finger posture from upright to curved ones after each finger makes contact with the object. During this motion, the object is automatically lifted up through either rolling or sliding motion between the finger tip and the object. A series of this motion is called as Detaching Assist Motion (DAM) . An advantage of DAM is that most of grasping motions can be done on the table instead of in the air. Therefore, we can avoid the worst scenario where the object falls down to the table. We first discuss the basic mechanism of DAM by human experiments. We then apply the DAM to a grasping motion by a multi-fingered robot hand. We show that the DAM can be explained by using Self-Posture Changing Motion. We also show some simulation and experimental results to confirm that a small object can be grasped easily by applying the DAM.
This paper presents a trajectory control scheme for flexible robot arms using an approximate position of the end effector as the controlled point. The scheme consists of five parts, namely, (i) selection of the approximate position to guarantee the stability of zero dynamics and the non-singularity of the inverse dynamics, (ii) computation of the corrected reference trajectory for the controlled point, (iii) transformation of the Cartesian coordinates of the con-trolled point and its reference trajectory to the equivalent joint angles assuming that the arm is rigid, (iv) derivation of the control input to make the equivalent joint angles to track their reference trajectories, (v) stabilization of the elastic vibration modes by the LQ method. Simulation results show that the accurate and stable tracking is achieved by the proposed scheme.
An isokinetic exercise is one of the training methods. Servomechanism using electric motor has been used for isoki netic exercise system. But, isokinetic exercises can be realized by using passive devices such as brakes or dampers. Since such passive systems are inherently safe, they are suitable for mechanical systems which are operated by hu man beings. In this study, we develop the brake using particle-type ER fluid. ER fluid is a fluid whose rheological characteristics can be controlled by electric field. ER brakes can response very quickly and have the characteristics like Coulomb friction. Then, we discuss the velocity control of ER brake system. Finally we confirmed the validity of the proposed method by control experiments.
A binocular motor control model based on the anatomic structure and physiological function of the brainstem is proposed. The simple control system of the model can realize vergence and conjugate eye movements, including smooth pursuit, optokinetic eye movements, and vestibular oculomotor reflex. The principles of vergence and conjugate eye movements are studied by analyzing the model from the viewpoint of system control engineering. Neural structures such as crossing image feedback pathways, which are not commonly found in system control engineering, are confirmed to play an important role in binocular motor control. The relationship of the neural pathway gains is obtained from the stability conditions of the model. As an application of the proposed model, an eye axis control system structured like the synthesized binocular motor model is implemented. In this eye axis control system, some characteristics existing in human eyes but not in conventional robot eyes are confirmed, including: (1) Both eyes can easily gaze at the same point simultaneously. (2) If one eye is closed or blocked by an obstacle, it will follow the movement of the other eye so that the obstructed eye can quickly find the target viewed by the other eye when the obstacle is removed.
This paper describes the vision system which recognizes 3-D objects in real-time by modeling shape of objects and matching the generated models. We develop following methods to practically solve the indispensable problems of integration, like the estimation of sensor accuracy and real-time processing: 1) We generate hierarchical mesh models in real-time by reduction of computation of signed-distance which is necessary to apply Marching Cubes Algorithm and selecting the optimal resolution of models to be generated using Octree. 2) We efficiently match multiple objects of different size by applying Spin-image matching with selecting the resolution of generated models and the coarse-to-fine algorithm.
This paper discusses forward and inverse kinematics problem of parallel wire mechanism where an end-effector of the mechanism is suspended by multiple wires. The mechanism allows not only three dimensional positioning but also three dimensional orientating of the end-effector, unlike typical wire suspension type mechanism such as overhead crane. To distinguish parallel wire mechanisms, the paper first defines constraint states of the end-effector, then parallel wire mechanisms are classified into three categories based on the definition. Each characteristic of the mechanism corresponding to the classification is discussed. Especially, incompletely restrained type parallel wire mechanism is mainly treated in the view point of inverse kinematics and forward kinematics problem. An inverse kinematics analysis and a forward kinematics calculation method for the incompletely restrained type parallel wire mechanism are presented.
This paper presents an effective method for designing a universal joint. To establish this method, we derived mathemati-cal conditions of design parameters to avoid the interference between its parts. Without any iterative computation, the method can determine such cutting sizes of the parts that minimize cut removal while satisfying required condition of attitudeís reachable range. Its efficacy is showed by the virtual experiments on a mechanical analysis software.