Tatsuya Masuda

Hierarchical sensitivity analysis of priority used in analytic hierarchy process

The analytic hierarchy process (AHP) initialed by Saaty (1980) has recently been attracting attention as a useful support method for multi-objective decision making. This paper presents some useful theorems for the sensitivity analysis of priority that is playing an important role in the AHP. These theorems are derived from the principle of hierarchical composition which is expressed in the form of a reachability matrix. Using the theorems, we can easily calculate the degrees of effects caused by local or global changes in the priorities of some criteria, and also we can examine the possibility of rank reversal among alternatives. Furthermore, by applying these theorems to a dwelling selection problem, this paper verifies their effectiveness.

Gait transition by tuning muscle tones using pneumatic actuators in quadruped locomotion

The development of an oscillator controller for a quadruped robot with antagonistic pairs of pneumatic actuators is reported. Periodic motions of the legs switch between the swinging and supporting stages based on the phase of the oscillators. The oscillators receive touch sensor signals at the end of the legs as feedback when the leg touches the ground and compose a steady limit cycle of the total periodic dynamics of quadruped locomotion. And also muscle tone is adaptively controlled according to the dynamic state of the main body. This system can generate gait transition from one to another by changing locomotion speed and muscle tone. The effectiveness and performance of the proposed controller were evaluated with numerical simulations and experiments with the hardware.

Facilitating multi-modal locomotion in a quadruped robot utilizing passive oscillation of the spine structure

An important topic in robotics is the design of a robot body using passive mechanical properties, such as viscoelasticity, to obtain energy-efficient locomotion at low computational costs. To achieve this aim, this study examines adopting a spinal structure with variable viscoelasticity and multiple joints. In order to investigate the effect of this spinal structure, a physical model of the spinal structure and a quadruped robot incorporating this design were developed, and the relationship between the gait pattern of the legs of the robot and viscoelasticity as a source of passive oscillation of the spinal structure was observed. The experimental results indicate that there are several interactions between the gait pattern and the viscoelasticity that can achieve one of various types of successful locomotion. These results suggest that the proposed spinal structure is a suitable body design for facilitating multi-modal locomotion at low computational costs.

Oscillator-Controlled Bipedal Walk with Pneumatic Actuators

The development of an oscillator controller for a bipedal robot with antagonistic pairs of pneumatic actuators is reported. Periodic motions of the legs switch between the swinging and supporting stages based on the phase of the oscillators. The oscillators receive touch sensor signals at the end of the legs as feedback when the leg touches the ground and compose a steady limit cycle of the total periodic dynamics of bipedal locomotion. The effectiveness and performance of the proposed controller were evaluated with numerical simulations and experiments with the hardware.

Feasibility Study on Stability of Gait Patterns with Changeable Body Stiffness Using Pneumatic Actuators in a Quadruped Robot

An oscillator-type gait controller for a quadruped robot with antagonistic pairs of pneumatic actuators is proposed. By using the controller, a feasibility study on the stability of gait patterns with changeable body stiffness is reported. The periodic motions of the legs are generated and controlled by an oscillator network with state resetting. This type of controller has robustness in its gaits against variation in walking conditions or changes of environment. However, it sometimes loses robustness under conditions of actuation delay, decrease of actuator accuracy, etc. We investigated whether an oscillator-type controller with phase resetting is also effective under such conditions. The stability of locomotion also strongly depends on the mechanical properties of the body mechanism, especially the joint stiffness. In this report, the muscle tone of the robot on the pitching motion at the trunk is changeable by using the changeable elasticity of the pneumatic actuators. The stability of quadruped locomotion in walk and trot patterns with changeable body stiffness was evaluated with numerical simulations and hardware experiments.

Mechanical Design of a Trunk with Redundant and Viscoelastic Joints for Rhythmic Quadruped Locomotion

Passive mechanisms, such as free joints and viscoelastic components, enable natural oscillation of the robot body, which allows rhythmic locomotion with low energy and computational costs. In particular, joint viscoelasticity can be a powerful candidate for changing natural oscillation and so influence the operation performance of locomotion. The present study considers the passive mechanism of a trunk, and investigates the contributions of a trunk mechanism with redundant joints and tunable viscoelasticity to quadruped locomotion. A physical quadruped robot with a trunk mechanism is developed, and the walking performance of this robot for various gait patterns and joint viscoelasticities is investigated. A simulation model is also constructed based on the physical robot, and the contribution of the viscoelasticity to trunk oscillation and the appropriate joint viscoelasticity and number of trunk joints are discussed. Experimental results obtained using the physical robot indicate that the proposed trunk mechanism contributes to successful locomotion as compared to a robot with a rigid trunk and that the velocity is influenced by not only the gait pattern, but also the joint viscoelasticity (i.e., there are appropriate couplings of the joint viscoelasticity and gait pattern). The simulation results indicate that the trunk mechanism requires joint viscoelasticity in order to achieve oscillation and that a greater number of joints having a smaller joint viscoelasticity enables higher velocity. These results suggest that, in addition to the leg mechanism and the controller design, the design of the trunk mechanism is also important.

Stochastic tabu search for rectangle packing

The rectangle packing problem is a combinatorial optimization problem, and is hard to solve it exactly in practical applications. In this paper, a tabu search heuristic is applied to the rectangle packing problem. First, each solution of the problem is represented by a pair of permutations of rectangles, and then the proposed method is described in detail, where the first admissible move strategy and a concept of stochastic tabu restrictions are employed. The experimental results are given to demonstrate the effectiveness of the proposed method.

A study on adaptive gait transition of quadruped locomotion

The development of an oscillator controller for a quadruped robot with antagonistic pairs of pneumatic actuators is reported. Periodic motions of the legs switch between the swinging and supporting stages based on the phase of the oscillators. The oscillators receive touch sensor signals at the end of the legs as feedback when the leg touches the ground and compose a steady limit cycle of the total periodic dynamics of quadruped locomotion. And also muscle tone is adaptively controlled according to the dynamic state of the main body. This system can generate gait transition from one to another by changing locomotion speed and muscle tone. The effectiveness and performance of the proposed controller were evaluated with numerical simulations and experiments with the hardware.

Passive trunk mechanism for controlling walking behavior of semi-passive walker

Although passive and semi-passive walkers provide energy-efficient locomotion, walking behavior such as a walking cycle cannot be controlled because it depends on a fixed mechanical property such as the center of mass or the foot shape. In this paper, referring to the upper body of a human, we propose a trunk mechanism that has redundant and viscoelastic joints and changes their viscoelasticity with relatively low energy consumption. By using physical and simulation models, we observe the relationship between the viscoelasticity of the trunk joints and the walking cycle. Results of the physical experiment and the simulation show that there are correlations between the joint viscoelasticity and the walking cycle, and thus, the proposed trunk mechanism is considered a suitable mechanism that controls the walking behavior of a semi-passive walker.

An adaptive locomotion of a quadruped robot on irregular terrain using simple biomimetic oscillator and reflex controllers without visual information

This paper describes the development of an oscillator and reflex-based controller for a quadruped robot that does not use visual information about the physical properties of its environment. The periodic motions of the legs switch between the swing and stance phases based on the oscillator phases. The oscillator phase is reset by the touch sensor signal at the end of each leg when the leg touches the ground. This global feedback loop composes a steady limit cycle of the total periodic dynamics of quadruped locomotion. Reflex actions are also generated against perturbations of the steady locomotion or against sudden disturbances on posture, such as becoming stuck in a hole. This system has the capability to adapt to unknown walking properties on irregular terrain. The proposed controllers effectiveness and performance were evaluated with numerical simulations and hardware experiments.