Takashi Nakakuki

A mechanism design of waist power assist suit for a caregiver by using torsion springs

We currently develop a motor-driven power assist suit for a caregiver that helps his/her waist strain in heaving a load Since the total weight is about 15 kg of which dominant elements are the actuators, any lightweight solution is required toward a practical use in a hospital or at home. Especially, a torque requirement to assist waist muscular power in typical personal care tasks is over 100 Nm, and a weight of high-torque motor tends to be large for a wearable robot suit. Then, we consider a mechanism design with torsion springs as an additional torque supplier to reduce torque requirement for motors. As a first step, in this paper, we design a prototype with torsion springs to investigate which location and how many springs are appropriate. The performance is evaluated with surface EMG in which the activities of some muscles including erector spinae muscles that are used in a lifting motion are observed.

Molecular governor that regulates DNA reactions for molecular robotics

In this study, we propose a controller design for molecular robotics, realized by DNA reactions. The control objective is to regulate the concentration of a target DNA strand to a desired level using practical DNA circuits. A DNA comparator-based controller with DNA amplifiers is proposed, and it is shown to successfully achieve the control objective. The property of the system is evaluated in terms of retroactivity. To our knowledge, this study is the first to realize a regulator in a practical DNA reaction system.

A study on stability analysis of biochemical reaction system with negative feedback regulation

In this paper, stability of a biochemical reaction system with negative feedback regulation is considered. It is well known that such a system induces a Hopf bifurcation depending on an input level or kinetic parameters. Although the eigenvalue analysis is a powerful method for evaluating the bifurcation and the stability, applying the method to a high-dimensional system with many nonlinear rate equations would be a troublesome task in model-based analysis since many hand-calculations of partial differentiation are needed to obtain a Jacobian matrix. Then, a simple and straightforward method based on Nyquist criterion is proposed. The method is a kind of describing function method, and the vector locus for the Nyquist criterion is drawn computationally by performing frequency response test for equivalent transfer function of the open loop system.

A study on a waist power assist suit for a caregiver to prevent lower back pain

We currently develop a waist power assist suit for a caregiver that physically supports his/her lifting and twist motions to prevent lower back pain. In our earlier studies, a DC motor-driven mechanism has been proposed where two motors that are attached at both sides of lower back generate the assistive torque for a lifting motion by driving them in the same direction, and for a twist motion by driving them in different directions. In this paper, we address to reduce the suit weight, refine the design, and to improve how to put on the suit. Regarding a signal processing for motion recognition, we also have studied a surface EMG-based signal processing with support vector machine. Although the recognition rate with the sensing system is promising off-line, the algorithm is quite complicated for implementation to a microcomputer. In this paper, we propose a simple signal processing for motion recognition based on surface EMG.

DNA integral controller learning from biological system

Realization of a feedback controller on artificial molecular circuits is one of the important tasks in the field of molecular robotics. In particular, a regulator that keeps the operation of a biological actuator constant is needed in a variety of practical applications. Importantly, such a regulator must be designed using biochemical reaction networks to function normally in a reaction field. In this paper, we propose an integral controller for a molecular robot. Our controller is inspired by an integral control system existing in an intracellular signal transduction pathway, and is realized on DNA strand displacement reactions.

Development of drinking support device for spinal cord injuries to enhance quality of life

Spinal cord injury causes a paralysis of any part of the body depending on which part of spinal cord is destroyed. It is well known that a severity of the paralysis is determined by both a location and a degree of injury in the vertebral bones. For example, in a case of injury at the C4 vertebral bone a patient is paralyzed from the neck down, and needs a caregiver to help almost all activities of daily life. Recently, a quality of life is considered to be important, and various welfare devices have been proposed to realize a better life of a patient. Regarding a C4 patient, drinking water by oneself whenever he/she wants to do is strongly desired in the daily life. In this paper, we develop a drinking support device for a C4 patient. The device is evaluated in a rehabilitation hospital, and it is shown that all requirements on structure, degree of freedom, safety, conform, daily maintenance, etc. are satisfied with an acceptable level.