Kazunori Hase

Computational evolution of human bipedal walking by a neuro-musculo-skeletal model

The acquisition process of bipedal walking in humans was simulated using a neuro-musculo-skeletal model and genetic algorithms, based on the assumption that the shape of the body has been adapted for locomotion. The model was constructed as 10 two-dimensional rigid links with 26 muscles and 18 neural oscillators. Bipedal walking was generated as a mutual entrainment between neural oscillations and the pendulous movement of body dynamics. Evolutionary strategies incorporated, for example, as fitness in the genetic algorithms were assumed to decrease energy consumption, muscular fatigue, and load on the skeletal system. An initial population of 50 individuals was created, and an evolutionary simulation of 5000 steps was conducted. As a result, the shape of the body changed from that of a chimpanzee to that of a modern human, and the body size nearly reached the size of a modern human. These simulation results show that improving locomotive efficiency and reducing the load on the musculo-skeletal system are important factors affecting the evolution of the human body shape and bipedal walking. Such computer simulations help us to understand the process of evolution and adaptation for locomotion in humans.

Development of a Wearable Robot for Assisting Carpentry Workers

The work of fitting ceiling boards is one of the hardest in carpentry, as it requires large muscular power. Hence there is a need to develop assisting apparatus for such work. In order to use this apparatus anywhere a wearable robot is the most suitable. As the robot must be autonomous and lightweight, a design requiring low power is proposed. A semi-active control method has been developed using springs, which requires low energy but satisfies the requirements of compliance and assistive force. In this paper several aspects of design, control and experiments of the developed prototype is explained. The experimental results prove that the robot reduces the muscular fatigue of carpentry worker by providing suitable assistive force.

Robust control of CPG-based 3D neuromusculoskeletal walking model

This paper proposes a method for enhancing the robustness of the central pattern generator (CPG)-based three-dimensional (3D) neuromusculoskeletal walking controller. The CPG has been successfully applied to walking controllers and controllers for walking robots. However, the robustness of walking motion with the CPG-based controller is not sufficient, especially when subjected to external forces or environmental variations. To achieve a realistic and stable walking motion of the controller, we propose the use of an attracting controller in parallel with the CPG-based controller. The robustness of the proposed controller is confirmed through simulation results.

Stimulation Pattern-Free Control of FES Cycling: Simulation Study

The aim of this paper is to investigate control strategies for functional electrical simulation (FES) cycling, with particular focus on the generation of stimulation intensities for multiple muscles, without any predetermined stimulation pattern. The control system is developed by imitating the biological neuronal control system. Specifically, the control signal on the level of joint torque (quasi-joint torque) is generated from the feedback information of lower extremities. The quasi-joint torque is then distributed to each muscle and the muscle delay is compensated, and finally, the stimulation intensity is determined. Parameters of the control system are optimized by the genetic algorithm with cost function of energy consumption and cadence error. The proposed control system is evaluated by computer simulation. The controller generates efficient stimulation even during the muscle fatigue process and successfully continues cycling without any predetermined stimulation pattern. Moreover, the controller is robust to the parameter error in the muscle delay compensator and also to the disturbances. It is expected that the proposed method would improve the FES cycling performance and relieve patients by eliminating the experimental determination of the stimulation patterns.

Hybrid Control of Powered Orthosis and Functional Neuromuscular Stimulation for Restoring Gait

The restoration of motor functions of patients with spinal cord injury (SCI) is one of important subjects for study. For this purpose, methods of functional neuromuscular stimulation (FNS) have been investigated in medical science and practice during these three decades. However, we have not achieved complete restoration of motor functions in SCI patients. On the other hand, we have achieved useful devices in human-scaled transportation by using power assist technology. Thus, applying power assist technology to the problem of restoring motor functions is one of possible solutions and sounds practical. In this paper, we propose a new hybrid system to combine power assist technology and FNS for restoring motor functions of lower extremity in SCI patients. Both powered orthosis and FNS are used to generate and control the joints moments of lower extremity in the proposed hybrid system. The main role of powered orthosis Vs is to compensate the joints moments generated by FNS and to enhance the controllability of FNS with the actuators. The proposed hybrid control system has been experimentally evaluated in gait motions by measuring the angle trajectories and generated moments around the knee and hip joints in the cases when only actuators are used and both FNS and actuators of the orthosis are used. The results prove that the control method for the hybrid system is useful to restore motor functions of lower extremity in SCI patients.

Operability of joystick-type steering device considering human arm impedance characteristics

In this paper, we present some results from the study on the impedance characteristics of a human arm during the execution of vehicle steering control tasks by using a joystick-type steering device. We propose a new model of human-machine interaction where the damping coefficient of the interface device can be tuned to match the impedance characteristics of the human arm. To verify the proposed model, we developed a special experimental setup. We used a robot and force/torque sensors to simulate the joystick operation. We explored human-machine interactions when the operator uses only one hand to control the vehicle. The reaction forces of the joystick were simulated by a virtual impedance field tuned to match human arm impedance. In the tests, we simulate situations when the movement of the joystick in the forward-backward direction sets the speed of the vehicle while the lateral rotation of the same control stick changes the turning radius of the vehicle. The robot allowed us to simulate various impedance characteristics. With the tests, we investigated the operability of the simulated vehicle by tuning the viscosity coefficient of the joystick in order to match it with the stationary human arm impedance and time-varying human arm impedance. The test results allowed us to propose a new method to improve the operability of a joystick-type steering device, based on the online adaptive matching of the impedance characteristics of the human arm. The usefulness of the proposed method is confirmed through experiments.

Computer simulation study of human locomotion with a three-dimensional entire-body neuro-musculo-skeletal model: (IV. Simulation of running motion and its transition process)

In the present study, the computer simulation technique to autonomously generate running motion from walking was developed using a three-dimensional entire-body neuro-musculo-skeletal model. When maximizing locomotive speed was employed as the evaluative criterion, the initial walking pattern could not transition to a valid running motion. When minimizing the period of foot-ground contact was added to this evaluative criterion, the simulation model autonomously produced appropriate three-dimensional running. Changes in the neuronal system showed the fatigue coefficient of the neural oscillators to reduce as locomotion patterns transitioned from walking to running. Then, when the running speed increased, the amplitude of the non-specific stimulus from the higher center increased. These two changes indicate mean that the improvement in responsiveness of the neuronal system is important for the transition process from walking to running, and that the comprehensive activation level of the neuronal system is essential in the process of increasing running speed.

Trajectory planning of a robot for lower limb rehabilitation

We introduce a method for lower-limb physical rehabilitation by means of a robot that applies preliminary defined forces to a patients foot while moving it on a preliminary defined trajectory. We developed a special musculoskeletal model that takes into consideration the generated muscle forces of 27 musculotendon actuators and joint stiffness of the leg and allows the calculation of the motion trajectory of the robot and the forces that the robot needs to apply to the foot in each moment of the therapeutic exercise. Robotic treatment programs are customized for the individual patient by using a genetic algorithm (GA) that refers to the musculoskeletal model and calculates the parameters of the spline curves of the motion trajectory of the robot and forces acting on the foot.

Motion analysis of optimal rowing form by using biomechanical model

Rowing motion analysis was carried out by using kinematic measurement and a three dimensional biomechanical model. We developed a measurement device for the rowing external force, which is interfaced with a Concept II rowing ergometer. This device acquired the chain force and the stretcher reaction force. We simultaneously obtained kinematic data from three dimensional landmark measurement and electromyograms (EMG). We also developed a three dimensional biomechanical model, which was used to calculate muscle force, consumption energy and rowing energy from these data. Rowing energy and rowing efficiency, and the ratio between the rowing energy and the consumption energy, were calculated for three different rowing styles. From these results, we estimated the optimal rowing motion.

Design of lower limb prosthesis with contact pressure adjustment by MR fluid

This paper reports on the development of a new lower limb prosthesis that can change its volume and hardness based on the users requirements. The size and viscosity of several Magneto-Rheological fluid filled bags, fixed on the inner side of the socket is changed, in order to vary the socket properties. TSB (total surface bearing) sockets have been most selling ones during these two decades. From the users point of view, it is excellent in this type of sockets that the weight of user is supported with the entire socket surface. However, it is impossible to cope with the volume change of the users stump. Experimental results show that the performance of the developed MR socket is better than the conventional TSB sockets because the MR socket is controllable in the size and viscosity.