Yoshihisa Honda

Analytical model of a magnetorheological damper and its application to the vibration control

Magnetorheological (MR) fluid and its damper have received a great deal of attention in the recent years. It is very useful for this MR controllable damper in the vibration control system, especially as a semi-active control device. To develop the control algorithms that take maximum advantage of the unique features of the MR damper a model must be developed that can adequately characterize the damper intrinsic behavior In this paper following a review of three mechanical models for MR damper the effect of these models on the vibration control is analyzed in a one-degree-of-freedom system. Numerical simulations are performed when the MR damper is used as the passive type damper on-off type damper and quasi-skyhook type damper. The results show that the models are less affecting the vibration control performance, and the MR damper appears the best control performance in the quasi-skyhook type.

Loads on Lower Limb Joints and Optimal Action of Muscles for Shock Reduction.

In this paper, a new method was proposed to theoretically analyze the forces on the toe, ankle and knee joint using a musculoskeletal model of lower limb. It was shown that the maximum force on the knee joint when a human jump down vertically from a height of 0.3 meter could come up to 11.2 times of his weight without an active movement of shock absorbing. Moreover, the optimal movement of lower limb muscle during a vertical landing on a hard surface was proposed to be solved by converting the multi dimentional and monlinear optimal control problem to a parameter optimazation problem. Detail investigations were performed in three cases when minimize the forces on the toe, on the ankle and on the knee joint, respectively. By using this optimal movement, it is possible to reduce the forces on the toe and knee joint by half. It was made clear from the optimization result that it is more appropiate to use the forces on the toe as an object function. Furthermore, it was found that the force on the toe and the activation level of lower limb muscle predicted by parameter optimization agreed well with the experimental results.

Shock-Absorbing Mechanism of Human Leg.

The shock-absorbing mechanism to minimize the vertical acceleration when jumping down onto a hard surface was investigated. The dynamic model of a human leg was built with a link joint. The muscle model consisted of a contractile element, a elastic element and a viscous element. The equivalent linear spring constant and equivalent linear damping coefficient decreased upon lowering of the hip by varying the bending angles of the ankle and knee. The numerical results showed that shock could be absorbed passively by deep bending, and to a greater degree actively in the same bending position.

Stability of a Rotating Disk Restrained at a Fixed Point in Space. Undamped System.

The stability of a rotating elastic disk with a stationary restraint, such as a computer memory disk with a magnetic head, is theoretically analyzed in the case where there is no damping. A graphical stability criterion for an undamped system is presented, and exact expressions of stability boundaries in a mass-stiffness plane are derived. It is clarified that a static instability region exists just above each critical speed of the disk and that a dynamic instability region exists in the vicinity of each speed where a curve with negative modal parameters intersects a curve with positive modal parameters in Campbells diagram. For the restraint of a single degree of freedom, the minimum critical mass and the minimum critical stiffness are introduced so that a stable system may be designed, and the effects of the rotation speed on these values are discussed.

Passive and Active Shock Absorption of Legs When Skiing.

Skiers control their stability by pumping their bodies up and down. The dynamic model of a skier traversing an undulant snowy surface was formulated in order to investigate the mechanism of a pumping strategy to minimize the vertical acceleration. A mechanical model of legs was built with a link joint. The muscle was modeled by a contractile element, a series of elastic elements and a damping element. By numerical calculations, the strategies to avoid the separation of the feet from the snowy surface were investigated. The stiffness of the leg is softened by bending the knee ; consequently, the shock can be absorbed passively by deep bending. Up-pumping first increases the pressure against the snowy surface and then decreases it, and down-pumping induces the opposite effect. The shock is also reduced actively by pumping.

Cantilever-Type Dynamic Vibration Absorbers Considering the Effects of Force and Moment

Cantilever-type dynamic vibration absorbers apply not only a force but also a moment to a main vibratory system. The vibration response of the main system with this type of absorber is analyzed using receptance matrices. By analogy with a conventional absorber of one degree of freedom, a method of optimal tuning of the natural frequency and damping of the absorber is derived. An index, the equivalent mass ratio which shows the effectiveness of the absorber, is defined. Numerical calculation and experimentation are carried out, and their results suggest that the cantilever-type absorber can be more effective than the conventional absorber.