Hiromitsu Hikita

Kinematics and dynamics of a 6 degree-of-freedom fully parallel manipulator with elastic joints

Abstract This paper deals with the kinematics and dynamics analysis of a 6 degree-of-freedom RTS fully parallel manipulator with elastic joints. The elastic joints are used to realize highly precise operation. Rotary input is applied to drive six groups of four-bar linkages in this system. Two displacement equations and velocity analysis of the active links and elastic joints are firstly addressed. The angular-velocity of the elastic joints in the motional state are described. In order to investigate the effect of the elastic moment in the dynamic analysis, the elastic bending and the torsional deformation of the elastic joints are presented by only using the vector operation. The standard dynamics formulation including the equivalent torque of the elastic moment with the generalized input is established by virtue of the principle of virtual work and the Lagrange’s method. A study through simulation is provided for a trajectory given in the task-space. Because of employing the kinematic influence coefficients, the dynamic modeling does become simply and the dynamics can readily be formulated in the simulation.

A motion rule for human-friendly robots based on electrodermal activity investigations and its application to mobile robot

This paper investigates impressions on the robot motion based on EDA experiments, deduces a motion rule for human-friendly robots from the investigations, and applies it to a mobile robot experimental apparatus. In our previous work, it was suggested that actuation noise come from the robots tended to raise the sympathetic nerve system (SNS) response of the heart rate variability. In another experiment it is observed that blocking out either the sound or the sight attenuated the electrodermal activity (EDA), which reflects the SNS, to the robot motion. In the present work, the experiment was designed not so as to avoid the influence of the habituation differently from the previous experiments, which was the significant factor contributing to reducing the EDA responses. As a result of statistical analysis, it was concluded that the present work supported the result of the previous work. Based on these investigations, we deduced the motion rule for human-friendly robots from this investigation, that robots must reduce their motion speed in the immediate vicinity of humans. We constructed the experimental setup that a mobile robot approached human with its speed decreased in conformity with the rule. To estimate the distance from the human, the skin color detection and depth-from-focus techniques were applied to a monocular color video camera system with pan/tilt/zoom operation. The experimental result showed that a proper choice of commands could perform the robot motion to reduce its speed in the immediate vicinity of the human.

A repetitive control system of a model following type

A repetitive control system of the model-following type is proposed. The model that the system output should track is introduced. The dynamic system that represents the tracking error behavior can be considered to be driven by periodic disturbances, and the repetitive control can be applied to this dynamic system. Highly accurate tracking is attained, since the dynamic behavior can be adjusted and the disturbance signals driving the error dynamics can be extremely small. It is shown that a state observer is effective in the case in which there are inaccessible state variables, although the observer can not estimate the exact states of a system as t approaches infinity . The results are applied to repetitive motion control by a DC servomotor.<<ETX>>

Artificial cross talk reduction of associative memory

A cross talk reduction method of an associative memory based on the outer product algorithm is presented. Because of crosstalk among superposed memories, memory capacity is limited and is much too low. To increase memory capacity, extensions to a higher-order correlation memory have been proposed. An associative memory architecture for realizing crosstalk reduction by using cross products as small as possible is presented. Higher-order cross product terms are obtained by using the Krawtchouk polynomial.<<ETX>>

Servo-type output tracking control via variable structure technique

A design method of a servo-type output tracking system by variable structure control (VSC) is proposed for a class of nonlinear systems. This VSC system requires neither model following structure nor high order differential of a reference signal for output tracking. The VSC system is completely decoupled into a set of VSC subsystems with single-input and single-output. Two types of dynamic compensators which are composed of a set of dynamic subcompensators and a set of switching hyperplanes are introduced in this VSC system. One of the dynamic compensators is a feedforward one which improves the transient response of the output. The other being in the closed loop path contains the internal model of a reference signal generator in order to realize output tracking with no steady state error. The VSC system is stabilized by suitably designing the dynamic compensators and the switching hyperplane. The projection of the trajectory into a subspace in the state space stays in the hyperplane during sliding mode caused by VSC. The subspace is chosen so that the internal model and the feedforward compensation do not become invalid when the VSC is applied. How to design the dynamic compensators and the hyperplane are studied for a servomechanism and a repetitive control system. It is possible to achieve good performance in the transient response and the steady state of the output of the servomechanism. The repetitive control system effectively reduces the tracking error if the same pattern is periodically repeated in the reference signal. The robustness against parameter uncertainties and unknown disturbances is still valid for the VSC systems. The simulation results indicate that the proposed control strategy is extremely useful.<<ETX>>

Influence of auditory and visual modalities on skin potential response to robot motions

This paper addresses the issue of investigating the relationship between skin potential response (SPR) and robot motion from the aspect of auditory and visual modalities. The motion of the robotic devices primarily gave stimulus to the human through the auditory and visual modalities. Our previous work indicated that actuation noise caused from the robots tended to raise the sympathetic nerve system response of the heart rate variability. However, it was difficult to evaluate instantaneous response corresponding to a specific stimulus using the HRV. The SPR is possible to reflect the instantaneous response to the stimulus. In the experiment, we controlled the conditions of the visual and/or auditory modalities by blocking out the sound and sight from the robot, a manipulator with 5 D.O.F. We also changed the position of the robot around subjects for stimuli variety. As the result, it is shown that the SPR magnitudes, under the condition of blocking out not only the sound but also the sight from the robot, tended to be significantly lower than without blocking.

Kinematics and Force Analysis of a 6 D.O.F. Parallel Mechanism with Elastic Joints

This paper concerns a novel type of small 6 D.O.F. RTS fully parallel mechanism with elastic joints. The elastic joints are used to realize highly precise operation for the mechanism. Rotary input is applied to drive six groups of four-bar linkages in this system. Two displacement equations of the mechanism are derived and the inverse kinematics analysis is presented. We further investigate about the bending and torsional deformation of elastic joints from a kinematic point of view. The formula of elastic moment and torque is also described by the linear model within the elastic deformation range. Finally, an equivalent force-balance-equation of the 6 D.O.F. parallel mechanism is obtained. The equation includes all the elastic moment and torque, the input torque, the load of the upper platform and the force of inertia of six links, etc.

Further cross talk reduction of associative memory and exact data retrieval

The analytical formulation of crosstalk due to superposition, which is an essential concept of associative memory based on the outer product algorithm, is presented in terms of Hamming distance between the memorized keys and the input key. The formulated result of crosstalk becomes similar to the Krawtchouk polynomial. Some properties of crosstalk, such as symmetricity, linear independency and cancellation characteristics, are derived by using the Krawtchouk polynomial. These properties are highly useful for reducing crosstalk and make it possible to propose a new architecture of associative memory with a smaller number of high-order correlation cross products rather than the conventional one. The architecture proposed completely removes crosstalk due to the memorized keys having an odd number Hamming distance from the input key. A relatively large part of the remaining crosstalk due to the memorized keys having an even number Hamming distance from the input key is removed by utilizing the coding technique, which constructs a simple error-correcting Hamming code introducing little redundancy.<<ETX>>

Exact data retrieval of associative memory based on cross talk formulation

Based on mathematical formulation of cross talk, a new associative memory architecture that completely eliminates cross talk due to the memorizing keys having odd number Hamming distance from the input key has been presented (Y. Kumagai et al., 1992). An architecture by utilizing further advanced properties of the formulated cross talk which are theoretically guaranteed to be able to reduce the remaining cross talk is proposed. Compared to the conventional architecture that needs monotonic increment of the degree of high-order correlation and the architecture proposed earlier, it is shown that the architecture proposed here with somewhat more high-order cross products than the previously proposed one substantially improves exact data retrieval ability.<<ETX>>

Construction of high-order correlation associative memory with novel retrieval cost performance

Crosstalk due to superposition, which is an essential concept of associative memory based on the outer product algorithm, is explicitly formulated in terms of Hamming distance between the memorized keys and input key. Some noticeable properties of crosstalk, such as symmetricity, linear independency, and cancellation characteristics, are derived by using the Krawtchouk polynomial. These properties are highly useful for reducing crosstalk and make it possible to propose a new architecture of associative memory with fewer high-order correlation cross products than the conventional architecture. The architecture proposed completely removes crosstalk due to the memorized keys having odd number Hamming distance from the input key. In order to remove relatively large parts of the residual crosstalk due to even number Hamming distance from the input key, a coding technique which constructs a simple error correcting Hamming code including relatively little redundancy is introduced.<<ETX>>