Towards Elucidating Control Mechanism underlying Legged Locomotion 

Intelligence through Embodiment

The concept of embodiment [1], in which intelligence emerges through the interaction between brain, body, and environment, is the key to understand extraordinary locomotive ability of animals on the earth and to build robots that can adaptively locomote in the real world.

[1] R. Pfeifer, C. Scheier, Understanding intelligence, (MIT Press, Cambridge, MA, 1999).

Embodied-synthesis

A synthetic approach grounded in embodiment, whereby we aim to understand the mechanisms underlying animal locomotion by building a physical robot that can move in the real world [2,3]. This approach has two advantages:

1. we can test such a robot in environments similar to those encountered by animals without the need to model the environments, thus allowing for sound evaluation of their performance, e.g., in terms of efficiency.
2. we can design a minimal robot by simplifying its musculoskeletal and neural systems, allowing for extraction of sufficient conditions to explain the underlying mechanism of interest.

[2] B. Webb, Nature 417, 359 (2002).

[3] A. J. Ijspeert, Science 346, 196–203 (2014).

Neuro-robotics: Neuroscience for Robotics, Robotics for Neuroscience

•  Understanding of human motor performance (adaptation to environments and plasticity of neural and biomechanical systems) from the viewpoint of both “Engineering” and “Neuroscience”.
• Motor control, Learning mechanism, Sensory perception
• Robotics technology for neuroscience analysis
• Neuro-rehabilitation that enables to maximize motor learning effects.

Robotics

Quadruped robot, oscillex

Versatile gait patterns that depend on the locomotion speed, environmental conditions, and animal species are observed in quadrupeds. Locomotor patterns are generated via the interlimb coordination, which is partially controlled by an intraspinal neural network called the “central pattern generator” (CPG). However, there is currently no clear understanding of the adaptive interlimb coordination mechanism. We hypothesize that the interlimb coordination should rely more on the physical interaction between leg movements through the body rather than the interlimb neural connection. To understand the coordination mechanism, we developed a simple-structured quadruped robot [4, 5, 6] and proposed an unconventional CPG model that consists of four decoupled oscillators with only local force feedback in each leg. Experimental results show that our CPG model allows the robot to exhibit steady gait patterns [4], adaptability to changes in body properties [4], and adaptive gait transition from walking, to trotting [5], to galloping [6]. Our robot mimics locomotor patterns of real quadrupeds following which it can capture the basic mechanism underlying the adaptive interlimb coordination.

[4] D. Owaki et al., J. of Roy Soc Interface, vol. 10, doi: 10.1098/rsif.2012.0669 (2012).

[5] D. Owaki et al., Proc. of IROS2012, pp. 1950-1955 (2012).

[6] D. Owaki and A. Ishiguro, Scientific Reports, 7:277, doi: 10.1038/s41598-017-00348-9, (2017).

Hexapod robot, Mushibot2

Insects exhibit adaptive and versatile locomotion despite their minimal neural computing. Such locomotor patterns are generated via coordination between leg movements, i.e., an interlimb coordination, which is largely controlled in a distributed manner by neural circuits located in thoracic ganglia. However, the mechanism responsible for the interlimb coordination still remains elusive. Understanding this mechanism will help us to elucidate the fundamental control principle of animals’ agile locomotion and to realize robots with legs that are truly adaptive and could not be developed solely by conventional control theories. This study aims at providing a “minimal” model of the interlimb coordination mechanism underlying hexapedal locomotion, in the hope that a single control principle could satisfactorily reproduce various aspects of insect locomotion. To this end, we introduce a novel concept we named “Tegotae,” a Japanese concept describing the extent to which a perceived reaction matches an expectation. By using the Tegotae-based approach, we show that a surprisingly systematic design of local sensory feedback mechanisms essential for the interlimb coordination can be realized. We also use a hexapod robot we developed to show that our mathematical model of the interlimb coordination mechanism satisfactorily reproduces various insects’ gait patterns.

[7] D. Owaki et al., Front. Neurorobot., vol.11:29, doi: 10.3389/fnbot.2017.00029 (2017)

Biped robot, oscilloid

Despite the appealing concept of “central pattern generator” (CPG)-based control for bipedal walking, there is currently no systematic methodology for designing a CPG controller. To tackle this problem, we employ a unique approach: We attempt to design local controllers in the CPG model for bipedal walking based on the viewpoint of “TEGOTAE”, which is a Japanese concept describing how well a perceived reaction matches an expectation. To this end, we introduce a TEGOTAE function that quantitatively measures TEGOTAE. Using this function, we can design decentralized controllers in a systematic manner. We designed a two-dimensional bipedal walking model using TEGOTAE functions and constructed simulations using the model to verify the validity of the proposed design scheme. We found that our model can stably walk on flat terrain.

[8] D. Owaki et al., Living Machines 2016, pp. 472-479 (2016). 

[9] D. Owaki et al., Frontirts in Neurorobotics, https://doi.org/10.3389/fnbot.2021.629595, (2021). 

Rehabilitation

Sensory Modality Transforming Prosthetics: Auditory Foot

Rehabilitation aims for long-term improvements in motor dysfunction through short-term trainings during daily interventions. “Kinesthesia”, i.e. a sense of movement of a body part, plays a crucial role in long-term motor learning as well as in short-term motor control, suggesting that utilizing this kinesthetic feedback is essential for the rehabilitation. Thus, rehabilitation for patients with sensory impairments including kinesthesia should be difficult to improve impaired motor functions.

For rehabilitation of sensory impairments, we proposed a novel biofeedback prosthesis [10] that transforms weak or deficient kinesthetic feedback into an alternative sensory modality. The aim of this study was to verify the short- and long-term effects of this prosthesis in patients with sensory impairments. We applied our prosthesis, called Auditory Foot, which transforms multipoint cutaneous plantar sensations into auditory feedback signals, for walking rehabilitation in a stroke patient with hemiplegia [11].

[10] D. Owaki et al., in Proc. of MHS2015, pp. 229-230, 2015.

[11] D. Owaki et al, Neural Plasticity, doi: 10.1155/2016/6809879, 2016.

Ankle Foot Orthosis Using Spring-cam Mechanism

In a stroke, motor paralysis, e.g., gait disorder, occurs as a main symptom due to damage in the brain, leading to major disability and health care costs worldwide. Stroke patients require rehabilitation to return to functional capacity and their work. The ability to walk safely represents a fundamental locomotor function in daily life; hence, gait restoration directly improves Quality of Life (QoL). However, 40% of stroke patients cannot return to their society with a self-satisfying walking ability.

We developed an unconventional, lightweight, and motor-less device, which easily attaches to a conventional ankle foot orthosis (AFO) and compensate ankle push-off power during walking by using spring-cam mechanism. Clinical experiments for 11 stroke patients with hemiplegia showed that the device effectively compensated the maximum ankle power generation in late-stance phase, resulting in a significant higher change in knee flexion in paretic swing phase as a side effect. Insufficient knee flexion in the swing phase during walking is one of crucial problems should be overcome in walking rehabilitation for stroke patients.

Insufficient knee flexion leads to lower toe clearance in the swing phase, then, resulting in stumbling on the ground and finally falling down. To overcome the insufficient knee flexion, patients exhibit frontal-plane compensatory movement, i.e., circumduction or hip hiking on the paretic side, which increases the mechanical energetic cost, resulting in more inefficient gaits. Furthermore, circumduction/hip hiking walking make gait appearance a bit strange. This inefficiency and abnormal gait appearance results in a decrease patient’s motivation for rehabilitation.

[12] Y. Sekiguchi et al., Gait & Posture, doi: 10.1016/j.gaitpost.2020.06.029, 2020. 

[13] 大脇大ほか，Proceedings of the 2017 JSME Conference on Robotics and Mechatronics, 2P1-P11, Fukushima, Japan (2017). 

Insects

How Insects Activate Muscles to Adapt to Limbs Removed

Adaptability explains why insects spread so widely and why they are the most abundant animal group on earth. Insects exhibit resilient and flexible locomotion, even with drastic changes in their body structure such as losing a limb. We now understands more about adaptive locomotion in insects and the mechanisms underpinning it. This knowledge not only reveals intriguing information about the biology of insects, but it can also help to design more robust and resilient multi-legged robots that are able to adapt to similar physical damage.

The insect nervous system is comprised of approximately 10^5 to 10^6 neurons. Understanding the process behind this requires researchers to consider the role of the intrinsic neural circuits that influence the adaptions of insects under unfavorable circumstances and the sensory feedback mechanisms reflected in their body characteristics and physical interactions with the environment.

We simultaneously recorded the leg movements and muscle activation of crickets, both before and after middle leg amputation. Their findings showed that the walking manner of crickets shifted from a tetrapod/tripod gait to a four-legged trot after the middle leg had been removed. Electromyogram (EMG) analysis of the muscles at the base of the middle leg revealed that the muscles were active in opposite phases when walking. Activation timing of the middle leg muscles synchronized in phase when both legs had been removed, whereas the activation timing showed anti-phase synchronization for crickets with all of their legs.

The findings demonstrated two things. First, an intrinsic contralateral connection exists within the mesothoracic ganglion, which generates in-phase synchronization of muscle activation. Second, mechanoreceptive informational feedback from the campaniform seensilla of the legs overrides the centrally generated patterns, resulting in the anti-phase leg movements of a normal gait.

[14] D. Owaki et al., Scientific Reports, 11:327, DOI: 10.1038/s41598-020-79319-6, (2017).

 

“Motion Hacking”

Collaborative Researches with Prof. Dr. Volker Durr and Josef Schmitz at Bielefeld University 

Insect cyborgs may sound like science fiction, but it’s a relatively new phenomenon based on using electrical stimuli to control the movement of insects. These hybrid insect computer robots, as they are scientifically called, herald the future of small, high mobile and efficient devices.

Despite significant progress being made, however, further advances are complicated by the vast differences between different insects’ nervous and muscle systems.

In a recent study published in the journal eLife, an international research group has studied the relationship between electrical stimulation in stick insects’ leg muscles and the resultant torque (the twisting force that makes the leg move).

We focused on three leg muscles that play essential roles in insect movement: one for propulsion, one for joint stiffness, and one for transitioning between standing and swinging the leg. The experiments involved the researchers keeping the body of the stick insects fixed, and electrically stimulating one out of the three leg muscles to produce walking-like movements.

“Based on our measurements, we could generate a model that predicted the created torque when different patterns of electrical stimulation were applied to a leg muscle,” points out Owaki. “We also identified a nearly linear relationship between the duration of the electrical stimulation and the torque generated, meaning we could predict how much twisting force we would generate by just looking at the length of the applied electrical pulse.”

Using only a few measurements, we could apply this to each individual insect. As a result of these findings, scientists will be able to refine the motor control of tuned biohybrid robots, making their movements more precise.

While the team knows their insights could lead to adaptable and highly mobile devices with various applications, they still cite some key challenges that need to be addressed.

“First, model testing needs to be implemented in free-walking insects, and the electrical stimuli must be refined to mimic natural neuromuscular signals more closely,”

[15] D. Owaki et al., eLife, 10.7554/elife.85275, (2023).