Hisayoshi Muramatsu
Assistant Professor
Machinery Dynamics Lab.
Mechanical Engineering Program
Hiroshima UniversityHPYouTube

We aim to develope robotics and mechatronics technologies to understand, create, and design new machinery movements fromthe perspectives of control, machinery, and humans. In particular, we have conducted control engineering research focusing on
periodic/aperiodic, quasi-periodic, and quasi-aperiodic, developed a mobile quad-arm robot: ARMS, and conducted research on
analysis and control of human-robot interaction.

Overview

Periodic/Aperiodic Separation Control[1]

We research definition, analysis, separation, andcontrol technologies for periodic/aperiodic, quasiperiodic, and quasi-aperiodic of a signal. We havedefined periodic/aperiodic, quasi-periodic, quasiaperiodic, and periodic/aperiodic separation functions
and proved the closure property, linearity, andorthogonality for them. They have been applied toquasi-periodically precise and quasi-aperiodically safe
motion control, anomaly chatter detection for milling,
and anomaly leaking package detection.
Periodic/Aperiodic
motion control

Chatter detection

Controller

Periodic/Aperiodic signal

PlantController

Quasi-aperiodic signal

State

Periodic/Aperiodic Separation Filter

Quasi-periodic signal

Quasi-periodic state
Quasi-aperiodic state

Diagnosis

Diagnosis

Leaking package detection

Periodic-pass characteristic

Aperiodic-pass characteristic

Movie

Movie

Mobile Quad-Arm Robot[2]

We develop a mobile quad-arm robot: ARMS for unifying
wheel-legged tripedal mobility, wheeled mobility, and quad-arm
manipulation. The four arms have different mechanics and aredesigned to be general-purpose arms to enable the wheel-legged
hybrid mobilities and manipulation. The front arm has an active
wheel, which is used for wheel-legged tripedal walking and wheel
driving with passive wheels attached to the torso. The rear arms areseries elastic arms, which are used for wheel-legged tripedal walking,object grasping, and manipulation. The upper arm is used formanipulation only; its position and orientation are determined bycoordinating all arms. ARMS was experimentally validated on thebasis of the following four tasks: wheel-legged walking, wheel
driving, wheel driving with grasping, and carrying a bag.

Wheel-legged walkingWheel driving

Wheel driving with grasping

Movie
Carrying a bag
Teleoperation device

Stability Analysis for Involuntary Human-Robot Interaction[3]

In human-robot interaction, there is a risk that a
feedback loop causes unstable force interaction, in
which force escalation exposes a human to danger.
Previous studies have analyzed the stability ofvoluntary interaction but have neglected involuntary
behavior in the interaction. In contrast to the previousstudies, this study considered the involuntary
behavior: a human's force reproduction bias fordiscrete-event human-robot force interaction. Wederived an asymptotic stability condition based on amathematical bias model and found that the bias
asymptotically stabilizes a human's implicit
equilibrium point far from the implicit equilibrium
point and destabilizes the point near the point. The
bias model, convergence of the interaction toward theimplicit equilibrium point, and divergence around thepoint were consistently verified via behavioral
experiments under three kinds of interactions using
three different body parts: a hand finger, wrist, andfoot. Our results imply that humans implicitly securea stable and close relationship between themselves
and robots with their involuntary behavior.

Interaction experiment

Force reproduction experiment

Stability analysis

Prediction of convergence

The interaction force signiﬁcantly
converged toward each participantʼs
implicit equilibrium point.

Subjectively marginally stable discrete-event interaction

Ref.

[1] H. Muramatsu, “Separation and Estimation of Periodic/Aperiodic State,” Automatica, vol. 140, p. 110263, Jun. 2022.
[2] H. Muramatsu, K. Kitagawa, J. Watanabe, and R. Hisashiki, “A Mobile Quad-Arm Robot ARMS: Wheel-Legged Tripedal Mobility and Quad-Arm Manipulation,”
arXiv, arXiv:2305.01406, May 2023.
[3] H. Muramatsu, Y. Itaguchi, and S, Katsura, “Involuntary Stabilization in Discrete-Event Physical Human-Robot Interaction,” IEEE Transactions on Systems,
Man, and Cybernetics: Systems, vol. 53, no. 1, pp. 576‒587, Jan. 2023.

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