Snakes actively utilize terrain irregularities and attain propulsion force by pushing their bodies against scaffolds. The objective of this study is to understand the mechanism underlying this locomotion on the basis of a synthetic approach. Our previous control scheme of a snake-like robot, in which the curvature derivative control method is combined with a reflexive mechanism using local pressures on the body wall, could not fully reproduce innate behavior of real snakes. In this study, we improve our previous control scheme. We show that the locomotion of a simulated robot with the improved control scheme is surprisingly in good agreement with the locomotion of a real snake. We also present a physical robot that we are currently developing.

Snakes actively utilize irregularities in terrains and attain propulsion force by pushing their bodies against scaffolds. The objective of this study is to understand the mechanism underlying such functionalities of snakes on the basis of a synthetic approach. We construct a model of a serpentine robot with viscoelastic properties, and we design an autonomous decentralized control scheme that employs local sensory feedback based on the muscle length and strain of the body, the latter of which is generated by the body softness. Simulation results show that the robot exhibits locomotion effectively by utilizing scaffolds such as high-friction areas and pegs, which is in fairly good agreement with biological findings.

The mechanism of multi-articular muscles that contributes to the emergence of macroscopic behavior of animals has not been clarified thus far. To address this issue, we focus on the slithering motion of snakes, which have numerous antagonistic muscle-tendon chains that span several tens of vertebrae. From theoretical analyses based on the continuum model, the acceleration of the body in the longitudinal direction is found to be proportional to the number of segments spanned by each muscle. On the basis of this theoretical result, we propose a decentralized control scheme for the efficient locomotion of a multi-articular snake-like robot. We conduct simulations using this control scheme, and the results show that the locomotion efficiency increases as the number of segments spanned by each muscle increases.

Autonomous decentralized control is a key concept in our understanding of the mechanism underlying locomotion of animals, wherein the phasic pattern of motion and the excitation pattern of muscle tonus are well reconciled. In our recent work, we proposed a decentralized control scheme in which phasic control and tonic control are well coordinated. In this study, we develop a real snake-like robot to validate our proposed control scheme. Experimental results show that the robot exhibits highly adaptive behavior in response to environmental changes. The results obtained are expected to shed new light on the design of autonomous decentralized control systems.

Despite its appealing concept, a systematic way of designing autonomous decentralized control system is still lacking. In order to alleviate this, we have so far proposed a design scheme for local sensory feedback control leading to adaptive behaviors from the entire system, based on a so-called discrepancy function that extracts the discrepancies between body (i.e., mechanical system), brain (i.e., control system) and environments. This paper intensively investigates the validity of this design scheme under the real world constraints by taking a two-dimensional serpentine robot exhibiting undulatory slithering locomotion as a practical example. The experimental results show that the robot exhibits adaptive behavior against environmental changes as well as the robustness against malfunctions of body segments due to the local sensory feedback control. The results obtained are expected to shed a new light on methodology for autonomous decentralized control system.

Decentralized control is a key concept to understand the mechanism of versatile and adaptive locomotion of animals under various environments. However, a systematic design of an autonomous decentralized control system has not been well established, because previous studies mainly focused on the control of phase relationship among body parts, i.e., phasic control, but not on the control of the spatio-temporal dynamics of muscle tonus, i.e., tonic control. In this paper, we propose a decentralized control scheme that enables to reconcile phasic control and tonic control, by taking serpentine locomotion as a practical example. Through modeling and simulations, we show that well-balanced coupling between the phasic and tonic control is crucial for the generation of adaptive and efficient locomotion.

Despite its appealing concept, a systematic way of designing autonomous decentralized control system is still lacking. In order to alleviate this, we have so far proposed a design scheme for local sensory feedback control based on so-called discrepancy function that extracts the discrepancies between body (i.e., mechanical system), brain (i.e., control system) and environments. This paper intensively investigates the validity of this design scheme by taking a two-dimensional serpentine robot exhibiting undulatory slithering locomotion as a practical example. Preliminary simulation results derived strongly indicate that our design methodology allows us to endow the robot with highly adaptability and fault tolerance. These results obtained are expected to shed a new light on design methodology for autonomous decentralized control system. Furthermore, together with a validity verification of the simulation results, this paper introduces a real two-dimensional serpentine robot that is currently under development.

This paper proposes structures of multi-path filters robust to substrate noise and nonlinearity of elements under low supply voltage to achieve wide dynamic range. They are derived by combining two structures which have been known to suppress substrate noise and nonlinearity more than the balanced one. Dynamic ranges and substrate noises of three proposed structures, the balanced (two-path) one, and the single ended (one-path) one are examined and simulation results show that the proposed structures reduce substrate noise and nonlinearity more than the conventional structures.

This study is intended to deal with the interplay between control and mechanical systems, and to discuss the "brain-body interaction as it should be" particularly from the viewpoint of learning. To this end, we have employed a decentralized control of a two-dimensional serpentine robot consisting of several identical body segments as a practical example. The preliminary simulation results derived indicate that the convergence of decentralized learning of locomotion control can be significantly improved even with an extremely simple learning algorithm, i.e., a gradient method, by introducing biarticular muscles compared to the one only with monoarticular muscles. This strongly suggests the fact that a certain amount of computation should be off loaded from the brain into its body, which allows robots to emerge various interesting functionalities.

This paper proposes a low-power, small chip area design technique for flash analog-to-digital converters (A/D converters). The proposed technique reduces power consumption of flash A/D converters by 50 % reduction of the number of comparators. Because output signals of flash A/D converters are thermometer code, only a few comparators whose reference voltages are around the input signal are significant and the other comparators can be removed. A novel track and hold circuit (T/H circuit) which can exchange its two balanced output signals is introduced. Thanks to the T/H circuit, the required input range of the comparator is limited to half of that of conventional one. The proposed A/D converter using the proposed T/H circuit can realize the same accuracy with the conventional one. The proposed technique is applied to a 6-bit 528 Msamples/s A/D converter realization. Its power consumption is evaluated by HSPICE simulations. It is confirmed that the proposed technique can save 34% of power consumption compared with conventional one.

An operational transconductance amplifier (OTA) is one of the most important analog building blocks. This paper proposes a novel voltage-regulating circuit for an OTA realization. The voltage-regulating circuit allows one to implement a simple structure OTA using MOSFET's in the non-saturation region. The resultant OTA using the proposed voltage-regulating circuit operates under a single 1.5 V power supply voltage. Simulation results of the OTA show harmonic distortion less than 1% even when 0.7 V/sub p-p/ input voltage is applied. Its power consumption is 85.8 /spl mu/W and cutoff frequency is 7 MHz.

In this paper, we present the throughput performance of CDMA slotted ALOHA systems with modified channel load sensing protocol (MCLSP). In MCLSP, a hub station continuously senses channel load for a certain number of slots, and computes the probability with which each user station should transmit its packet, then broadcasts the computed value. As the access control is based on this probability, we can apply it to slotted system. We show that MCLSP can achieve significant improvement in throughput performance of CDMA slotted ALOHA systems even in large offered load. One of the issues in such a protocol is the access timing delay, which is the sum of process time and propagation time for the packet access control. We also show the effect of the access timing delay on the throughput performance.

Throughput analysis of direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA with fixed packet length is presented. As the levels of multi-user interference fluctuate during the packet transmission, we calculate the packet error probability and the throughput by considering not only the number of overlapped packets but also the amount of time overlap. On the assumption that packet generation is Poisson, the system can be thought as the queueing system M/D//spl infin/. With Gaussian approximation of multi-user interference, we obtain the throughput as the function of the number of chips in a bit, the packet length, and the offered load of the system. We also analyze the channel load sensing protocol (CLSP), and obtain the optimum threshold of CLSP.