Ryota Ishibashi

Inverse Dynamics of Human Passive Motion Based on Iterative Learning Control

Estimation of joint torque is an important objective in the analyses of human motion. In particular, many applications seek to discern torque during a desired human motion, which is equivalent to solving the inverse dynamics. The computed torque method is a conventional means of calculating inverse dynamics. The obtained torque, however, invariably includes errors resulting from inexact inertial and viscoelastic parameters. This paper presents a method for solving the inverse dynamics of a human arm passively during tracking. To achieve precise human motion tracking, iterative learning control is used for motion generation. Some experiments that target a human arm are executed to validate the proposed method.

Adaptive impedance control of a variable stiffness actuator

This paper proposes an optimal impedance control method for a variable stiffness actuator (VSA), in which a variable stiffness mechanism and an actuator are aligned in series. First, we introduce a circuit expression of the robotic system and provide a unified framework to determine an optimal index of robots driven by VSAs, irrespective of the presence or absence of the environment. Next, we design a torque controller for a one-degree-of-freedom (DOF) robot and find the optimal condition of the stiffness in the VSA for a given task. Then, we design a stiffness control law for the VSA exploiting the intrinsic indivisible property between motion and passive impedance. This stiffness control law adaptively tunes the passive stiffness to minimize the energy consumption without defining any explicit desired impedance, which is usually required in impedance controllers. The stability of the closed loop system is proved using Lyapunov’s analysis. Simulations and experimental results validate the effectiveness of the proposed method and the robustness in response to parameter changes. Graphical Abstract

Experimental Verification of a Mass Measurement Device under Zero Gravity with a Prismatic Variable Stiffness Mechanism

A new method to measure the mass of an object in microgravity is proposed in this paper. The proposed method uses a new system that consists of a prismatic variable stiffness mechanism and an actuator. The object to be measured is attached to the prismatic variable stiffness mechanism. The actuator vibrates the mechanism and the object. The stiffness is adjusted to satisfy the anti-resonance condition, and the mass is measured from the stiffness and the frequency. An advantage of the proposed measurement method is that the actuator vibration converges to zero as time tends to infinity. Moreover, the physical parameters, such as the inertia, and the damping parameters of the measurement system are not required to measure the mass value. Several experiments were executed to confirm the effectiveness of the proposed method.

A proposal of a SMA actuated wing mechanism using flexible structure for the capability of various flow speeds

This paper proposed a concept of flexible wing-mechanism for the underwater fishlike robots. The proposed system consists of a fishlike body and a pair of flexible wing. The flexible wing mechanism utilizes a Shape Memory Alloy (SMA) actuator to realize small and lightweight system with high output/weight ratio. The SMA actuator can be controlled to adjust the shape. In the flow of water, shape of the wings is controlled and then the fluid resistance will be changed. Then, we can control the posture of the robot. The wing mechanism is constructed mainly from flexible materials. Thus, range of the fluid resistance becomes different between the high speed flow and low speed flow. In the fast flow condition, flexible wing mechanism is compressed and the range of the shape control becomes low. Then, the mechanism can control the posture of the robot under the various flow speeds.

Study of human motion generation based on redundancy of musculoskeletal structure: Analysis of potential generated by internal force for two-link system

The human body has a musculoskeletal system with the muscles which exist around the bones and joints. Taking notice of the structural characteristics that a human possesses inherently, this paper analyzes feedforward position control for the musculoskeletal system. The feedforward positioning does not need any sensory feedback by use of internal force balancing at a desired posture. Targeting a non-pulley musculoskeletal system with two links and six muscles, this paper clarifies mathematical conditions of the feedforward positioning to converge at a desired posture. In the analysis, muscular length is approximated by Taylor expansion. Based on quasi-statical approach, the convergent conditions are clarified. The verification of the conditions is conducted through simulation.

A proposal of manipulability based model predictive control for the parallelogram linkage

Abstract This paper proposes a control method for a parallelogram linkage robot manipulator. Parallelogram linkage can generate motion control with high precision. However, this technique is geometrically constrained in the task space as a result of its mechanical properties. The proposed method uses a model predictive controller to account for the geometric constraints of the system. The key concept behind the controller developed here is to use manipulability for the cost function and geometric constraints in the model predictive controller. Thus, we can design a trajectory-tracking controller using a manipulator and accounting for the geometric constraints. In the simulation results, the effectiveness of the proposed method was verified using the singularity avoidance problem as an example of geometric constraints.

Mass estimation in microgravity with a variable stiffness mechanism

A new method to estimate the mass of an object in microgravity is proposed in this paper. The proposed method uses a new mechanism that consists of a variable stiffness mechanism and an actuator. A sample is attached at the tip of a blade spring in the variable stiffness mechanism, which controls an effective length of the blade spring to adjust the stiffness. An actuator swings the mechanism periodically and satisfies the anti-resonance condition. Then, the mass of an object is estimated with the period of the swing and the length of the blade spring in the anti-resonance mode. The controller requires no system parameters to adjust the stiffness. Simulations and experiments are executed to verify the effectiveness of the proposed method.

Proposal of a tactile feedback model with reaching motion based on nonlinear dynamics of the mechanoreceptors and finger-tip-consideration of a task space P-SD Servo controller

This paper, based on the skin-sensor dynamics model [20] and the anatomical insights, we develop a candidate of the tactile feedback controller for the arm reaching tasks. In the controller, the signal from the FA1(SA1) receptors as the velocity sensors is used for the tactile feedback like task-space P-SD Servo. The velocity of the fingertip seems to be affected by the skin and receptor dynamics. Then the sensor output of the task space velocity signal becomes sensitive in the low-load region. Especially, if the sensor is in the high-load region, the sensor output will be kept but the resolution become low and is able to avoid overload output. This paper focused on the finger-tip dynamics that consists of the tissue and the cutaneous mechanoreceptors called FA1(SA1), and investigate how they affect the control strategy of the tracing motion. In the experiments, we analyzed the nonlinear biomechanical properties of the cutaneous surface and showed that the subcutaneous mechanoreceptors affect human control skill learning. In these experiments, the validity of our hypothesis was investigated.

Modeling of the synchronization of cutaneous mechanoreceptors with Epidermal-dermal dynamics

This paper examined the effects of the nonlinear mechanical properties that originate in the subcutaneous geometric structure and the subcutaneous mechanoreceptors of the fingertip. We briefly analyzed nonlinear biomechanical properties of the cutaneous surface and showed that the subcutaneous mechanoreceptors affect tactile perception as nonlinear transducers. The validity of our hypothesis was assessed by experimentally investigating the vibrotactile sensation of a fingertip.