For a serial linkage mechanism, the kinematic relationship between the end effector and the joint angles is nonlinear. The kinematics highly affects the dynamics of the mechanism near singular configurations where the relationship is singular. In this paper, we examine dynamic characteristics of singular configurations for a two-link robot arm, and show that the singular configurations are advantageous in reducing the joint torques necessary to achieve the task of pulling a heavy object.
It is important in project time management to estimate adequately the workload (e.g. personhours) of each activity taking into account project uncertainties such as over-/underestimations of the activity durations, workers, sudden sickness absence and so forth. In this paper, we propose a new method of the workload estimation aiming at enhancing a so-called schedule stability. It is expected that the schedule stability can be enhanced by considering the minimization of the delay cost associated with the deviations between planned and actual activity starting times. The proposed method successively changes the amount of resources allocated to the activities as well as the activity durations in order to minimize the expected delay cost. In the computational experiments,the proposed method is compared with two conventional estimation methods by using benchmark problem instances of project scheduling. The experimental results reveal that the proposed method is effective from stability point of view.
This paper presents a unied stability analysis method for thermoacoustic systems based on the Nyquist stability criterion for MIMO systems. The method consists of two procedures: (i) conventional frequency response function (transfer matrix) is transformed into the one for causal system whose input and output signals are incoming and outgoing traveling-wave pressure components; (ii) the transformed response is used to analyze the closed-loop stability by the Nyquist stability criterion for MIMO systems. It is shown that the stability analysis for both standing- and traveling-wave thermoacoustic engines can be carried out by a unied procedure. The analysis results are consistent with the actual situations of oscillation indicating reasonable stability and/or instability margins for various geometrical changes as well as the temperature ratios in engines.