Muneharu Saigo

Real-time 3D walking pattern generation for a biped robot with telescopic legs

Meltran V, a new biped robot with telescopic legs, is introduced. For 3D walking control of the robot we analyze the dynamics of a three-dimensional inverted pendulum in which motion is constrained to move along an arbitrarily defined plane. From this analysis we obtain simple linear dynamics, the three-dimensional linear inverted pendulum mode (3D-LIPM). Using a real-time control method based on 3D-LIPM, the Meltran V robot successfully demonstrated 3D dynamic walking without the use of any prepared trajectories.

Balancing a humanoid robot using backdrive concerned torque control and direct angular momentum feedback

A balance control method for a humanoid robot is presented. It consists of a contact torque controller which is designed to have a good backdrivability and a feedback control of the total angular momentum and the center of gravity of a robot. A simulation result of a balance control using a 26 DOF humanoid robot model is shown.

An Approach to Vibration Control of Multiple-Pendulum System by Wave Absorption

In this paper, a new wave-absorbing strategy has been studied to suppress the vibration of a multiple-pendulum system by controlling the lateral movement of the support. The wave-absorbing condition is derived from the difference between the equation of motion of the boundary pendulum and that of an inner pendulum. An on-line real-time simulation method using the numerical solution is proposed to control the movement that satisfies the wave-absorbing condition. According to this method, vibration of a multiple-pendulum system with arbitrary degrees of freedom can be controlled by measuring only the deflection angle of the uppermost pendulum adjacent to the support if the dimensions of the uppermost pendulum and the total mass of the system are known. Both the numerical simulations and the experiments have confirmed the effectiveness of this method. The basic idea of this control method can easily be applied to any discrete vibrating system whose equations of motion have no traveling-wave solution.

Vibration control of a smart structure embedded with metal-core piezoelectric fibers

This paper addresses the active vibration control of a new smart board designed by mounting piezoelectric fibers with a metal core on the surface of the CFRP composite. These complex fibers function as sensors and actuators in the CFRP board. A finite-element model of a cantilever and a reduced order model for controller design were established. The piezoelectric fibers are uneven in the actuator outputs. Therefore, a linear fractional transformation (LFT) is formulated considering the unevenness of the actuator outputs as the perturbation. Next, the controller is designed by using μ synthesis, considering the perturbation and robust stability. The control performance of the proposed method is verified by experiment and demonstrates that piezoelectric fibers can be effectively used in vibration control.

Torsional vibration suppression by wave-absorption control with imaginary system

We discuss vibration suppression in a lumped torsional system using wave-absorption control with online computation of an imaginary wave-propagation system similar to the real-controlled system. The basic concept of control was presented elsewhere for a multiple pendulum system to suppress free vibrations. We studied the suppression of forced vibration by a wave-absorption control for a lumped torsional system. Results confirmed that the proposed method works well on forced vibrations as on free vibrations. Initialization, setting amplitudes and velocities to zero, of the imaginary system for forced vibration control influences controlled amplitudes more than that for free vibration because vibration energy invariably comes in the system. Using numerical simulation, we studied initializations. Theoretical analysis on wave propagation in a lumped system has shown that smaller mass and larger spring stiffness of an imaginary system absorb vibration energy better, giving the optimum design for the imaginary system. Experiments are conducted for one-, two-, and three-degrees-of-freedom systems.

Vibration Control of a Traveling Suspended System Using Wave Absorbing Control

This paper describes vibration control of a suspended system using a wave absorbing method. Here, we treat a system that accepts a traveling command. This system is called a traveling system. In the previous paper we treated a system that performs only the vibration control, where the support of the suspended system moves only for vibration control and eventually settles at the original position. This system is called a nontraveling system. In a traveling system, the support moves both for traveling and for vibration control. We present a new control strategy for these two different aims by applying the vibration control method developed in the previous paper A traveling multiple-pendulum system and a traveling wire-and-load system are treated. The wire-and-load system has a small rigid pendulum between the support and the wire. The vibration control is performed by monitoring this small rigid pendulum. The wire-and-load system is extended to a model crane system that has a motor system to roll up and down the suspended mass like a real crane. The same program with different parameter values controls these three systems. Both numerical simulation and experiment have been conducted, and the developed control method has been shown to be quite effective.

Damage detection and gain-scheduled control of CFRP smart board mounting the metal core assisted piezoelectric fiber

This paper reports damage detection and vibration control of a new smart board designed by mounting piezoelectric fibers with metal cores on the surface of a CFRP composite. Damage to the board is identified on the assumption that the piezoelectric fibers used as sensors and actuators are broken simultaneously at the damaged location. When such damage-induced breakage occurs, the piezoelectric fibers expand and contract between the root and the damaged position on the cantilever beam. Damaged positions are detected by focusing attention on this property. Furthermore, this deterioration of sensors and actuators caused by breaks in the piezoelectric fibers is a consideration in the design of the gain-scheduled controller. First, the length of the piezoelectric fibers is measured to derive a finite-element method (FEM) model of the cantilever beam. If the fiber length is shortened due to a break, there is a decrease not only in actuator performance but also in the sensor output. Thus, peak gain of the FEM model is calculated for the length of every piezoelectric fiber. Damage detection is based on the computed relation between peak gain and the damage position. Furthermore, a reduced-order model that considers only the first mode is derived for the controller design and transformed into a linear fractional transformation (LFT) representation for the gain-scheduled controller design. The position of the damage is the contributing parameter in the variation. Next, the gain-scheduled controller is designed using LFT representation. Finally, the simulation and experimental results of the damage detection and the gain-scheduled control are presented. These results show that our gain-scheduled controller can improve control performance when damage cause a break in the piezoelectric fiber.

Active Wave Control of String Near Fixed Boundary

We studied a wave control of a string near a fixed end. The equation of motion of a string is approximated as a lumped-parameter spring-and-mass system using the finite difference method. Finite difference equations (FDEs) for interior node points have the same set of coefficients, whereas the FDEs for boundary node points have a different set of coefficients. By using the control, the latter equation is modified to be as the same equation as the former one. The propagating wave is absorbed through a control actuator as if no boundary existed, and virtually, an infinite system is thus realized. Control is at the string position of the finite difference mesh spacing inside the fixed boundary that is free from supporting loads. We confirmed the effectiveness of the controller by numerical simulation for the traveling string and also did that by numerical simulation and by an experiment for the nontraveling string.

Robust vibration control of the metal-core-assisted piezoelectric fiber embedded in CFRP composite

This paper addresses the active vibration control of a new smart board designed by mounting piezoelectric fibers with a metal core on the surface of the CFRP composite. These complex fibers function as sensors and actuators in the CFRP board. A finite element model of a cantilever and a reduced order model for controller design were established. The piezoelectric fibers are uneven in the actuator outputs.Therefore, the linear fractional transformation (LFT) is formulated considering the unevenness of the actuator outputs as the perturbation. Next, the controller is designed by using mu synthesis, considering the perturbation and robust stability. The control performance of the proposed method is verified by experiment and demonstrates that piezoelectric fibers can be effectively used in vibration control.

Active modal control of a truss structure considering displacement constraint

For the purpose of reducing the cost, a control system for a truss structure with a simplified controller equipped with amplifying function alone is proposed. In order to realize a sensor in consideration of system stability, the sensor is provided with multiplication-addition capability and a distributed modal filter capable of isolating multiple vibration modes. Then, a control system is built up to amplify the sensor output through a power amplifier, by using a moment actuator which can exert actuation comparable to that of the velocity feedback for damping the system. Finally, the control system is incorporated to the truss structure and the vibration control effect through direct feedback is studied.