Self-reconfigurable Quadruped Robot: Design and Analysis

In this paper, in order to meet the requirements of stable foot support and balanced walking of quadruped hydraulic robot, a new control method is proposed. The "hard" contact between the feet of the quadruped hydraulic robot and the ground are changed into "semi flexible" contact to reduce the impact force produced by the contact and collision of the two and reduce the unbalance of the force. The designed "semi flexible" scheme was to coat the "semi flexible" modified polytetrafluoroethylene (PTFE) material on the surface of the bottom material of the robot's foot. The modification of PTFE was optimized by SRIM, and the optimization scheme was selected for experimental study to obtain the Al2O3/PTFE material for which the abrasive resistance met the requirement of robot motion. It was also used in robot force imbalance control experiment research optimization. The study clearly revealed that it can effectively reduce the power of the impact force caused by the contact and collision of the feet of the quadruped robot and the ground, reduce the swing and the unbalance of the motion force of the quadruped robot, and meet the requirements of the precise positioning and the force balance walking of the motion of quadruped hydraulic robot to a certain extent.

This paper deals with the concept of reconfigur-able and self reconfigurable robots. These robots are in-tended to be used as a main component of intelligent manufacturing systems. The paper presents basic concepts of this type of robots, kinematical methods used to build virtual models, numerical results and virtual models. Also, conclusions are at the end.

In this study, functional extension by connecting the different types of modular robots is discussed. The modular robots have to be connected each other in the structures, electric circuits and information systems automatically. Then the connector for the modular robots was designed here based on the tight lock coupler for railway vehicles. Two prototypes of the modular robot driven by two crawlers with the connector were also made. The robot composed of the two prototypes can move not only by four crawlers but also by four legs. Thus the robot with four crawlers can be the quadruped walking robot. This is an example of functional extension of the robot system by connecting the modular robots.

We discuss challenges a sprawling posture legged robot faces when moving in a complex environment. These kind of robots can be used for search and rescue applications when proper sensors are used and placed correctly. Finding an adequate position for placing sensors on legged robots with a segmented spine to maximize the information retrieval is not trivial. In this paper, we talk about equipping the salamanderlike robot Pleurobot with necessary sensors to understand its challenges. Our setup gathers visual and inertial information for 3D mapping and localization. To do so, we have come up with three different experimental terrains to analyze the sensing behavior. The results are examples to understanding the behavior of quadrupedal legged robots similar to Pleurobot in search and rescue scenarios.

Extraforaminal disc herniations represent up to 11% of all lumbar herniated discs. Numerous surgical approaches have been described. Percutaneous endoscopic discectomy (PED) is one of the minimally invasive techniques; after mastering this procedure it is a practical method that is used for treatment of foraminal or extraforaminal disc herniation. The outcome of PED for treatment of foraminal or extraforaminal disc herniation has been studied. A total of 66 patients with foraminal or extraforaminal lumbar disc herniation was treated by applying the PED technique between January 1998 and June 2005. The positions of the herniated disc levels were L2-3 (n=5, 8%), L3-4 (n=19, 28%) and L4-5 (n=42; 64%). The selected patients had no previous surgery, appropriate conservative therapies were done before the operations, and MRI was the main diagnostic method with the clinical findings. Evaluation of the patients with clinical examinations, visual analogue pain scale (VAS) and Oswestry scale was performed preoperatively, on postoperative day 7 and in the postoperative 6-12 months period. In two patients (n=1, L4-5 and n=1, L3-4) disc material could not be removed with PED, so discectomy was performed with microscopic visualization during the same session. Three patients (n=3, L4-5) were reoperated on three to six months after primary surgery due to recurring disc problems with microscope visualization. In two patients (n=2, L4-5) root nerves were partially damaged, and in two patients (n=2, L4-5) root nerves were impinged by the working channel. These 4 patients had dysesthesias from just after surgery to a mean of 45 days after surgery. One of recurrent cases was among these patients. Neurological examinations showed minimal muscle weakness of the quadriceps femoris and diminished sensation of the L4 dermatomal area in patients with partial nerve root damage. This patient improved and the neurologic examination became normal with disappearance of the dysesthesia. There was no sign of reflex sympathetic dystrophy (RDS). With these two patients VAS and Oswestry scales scores decreased significantly early in the postoperative follow-up. The postoperative 6-month average scores are favourable in comparison with the average score at postoperative day 7. The postoperative 12-month scores showed no significant differences to those of postoperative month 1. Percutaneous endoscopic discectomy is a minimally invasive method and offers many benefits to the patient, but extensive surgical practice is needed to become a capable surgeon. Consequently this technique can only be a treatment option on appropriate patients. This study reconfirmed that the removal of fragmented disc material is achieved and offers a pain-free status.

Currently available industrial robots are mainly of monolithic structure. Hence, the geometrical dimensions and the configuration of robotic arms are immutable. A modular design of serial manipulators allows to vary the structure of serial kinematic chains, for example, to adapt the system to a specific handling task. In this work we present the concept of a modular robot which has general kinematic structure by means of curved link elements. We show how to describe intuitively the assemblage of modular manipulators with curved links (referred to as Cuma-arms) by a parameter set. A Cuma-type arm and a dedicated path which can be followed by the end effector with 16 different postures is presented. For computation of the inverse kinematics of general serial 6R manipulators the algorithm of Husty and Pfurner is used and implemented on a real system.

Motion planning and control issue of quadruped robots is a challenging topic because it requires a lot of professional knowledge and tedious manual design based on traditional control methods. This paper proposes a novel method of training quadruped robots to generate locomotion gaits by combining the deep reinforcement learning. The control problem of quadruped robots is modeled as a Markov Decision Process, and a universal quadruped robot motion control reward mechanism is developed. A variety of gaits for the quadruped robot is generated by adding a gait reference frame. Two deep reinforcement learning algorithms are used for training and comparison. The desired gait locomotion control strategy is generated through training so that the robot can realize stable walking with the desired gait. Finally, the proposed method is tested and evaluated in a simulation environment using the A1 quadruped robot model.

Bionics has greatly improved the development of quadruped robot, in the paper we propose three bionic methods for the quadruped robot. These methods have been used for control method design, gait design and control architecture design. The quadruped robot control method has been divided into two parts, because the four-legged animals change their trot speed by adjustment of step length in swing phase and maintain their balance in support phase; control architecture is derived from the four-legged animals nerve system; gait of quadruped robot is based on event driven, and its trot gait is the same as German shepherd. Simulations and experiments are performed, which prove bionics design to be realizable for the quadruped robot.

Since the quadruped bionic robot can be widely applied to different terrains, the research on it has always been the focus of robotics-related field. This paper designs a quadruped bionic robot with 8 degrees of freedom. We analyze stability and movement speed of the robot in different gaits. The gait focuses on crawl in triangular gait and trot in diagonal gait. In the case of using 8 degrees of freedom (two per leg), through gait analysis, 3D modeling, physical testing and using larger sole to improve stability, the designed quadruped robot can achieve stable and fast movement.

This paper presents a central pattern generator (CPG) and vestibular reflex combined control strategy for a quadruped robot. An oscillator network and a knee-to-hip mapping function are presented to realize the rhythmic motion for the quadruped robot. A two-phase parameter tuning method is designed to adjust the parameters of oscillator network. First, based on the numerical simulation, the influences of the parameters on the output signals are analyzed, then the genetic algorithm (GA) is used to evolve the phase relationships of the oscillators to realize the basic animal-like walking pattern. Moreover, the animal’s vestibular reflex mechanism is mimicked to realize the adaptive walking of the quadruped robot on a slope terrain. Coupled with the sensory feedback information, the robot can walk up and down the slope smoothly. The presented bio-inspired control method is validated through simulations and experiments with AIBO. Under the control of the presented CPG and vestibular reflex combined control method, AIBO can cope with slipping, falling down and walk on a slope successfully, which demonstrates the effectiveness of the proposed walking control method.

This paper presents a design method and experiments for whole-body locomotion by a modular robot. There are two types of locomotion for modular robots: a repeating self-reconfiguration and whole-body motion such as walking or crawling. For whole-body locomotion, designing a control method is more difficult than for ordinary robots because a modular robotic system can form various configurations, each of which has many degrees of freedom. This study proposes a unified framework for automatically designing an efficient locomotion controller suitable for any module configuration. The method utilizes neural oscillators (central pattern generators, CPGs), each of which works as a distributed joint controller of each module, and a genetic algorithm to optimize the CPG network. We verified the method by software simulations and hardware experiments, in which our modular robotic system, named M-TRAN II, performed stable and effective locomotion in various configurations.

Modular robotic systems have been investigated to change the appearance and functions by controlling robotic modules. These reconfigurable modular systems are developed for the interactions between the external environment including humans. Capabilities of compliant interactions are as helpful as those of self-reconfiguration for the modular systems in adapting to the environments. This paper presents a novel concept of a modular robot that has the abilities of compliant actuation and self-reconfiguration to form compliant structures. The authors develop the initial prototype of the modular robots, named Module-W (M-W). Empirical results with the prototype suggest that M-W has the potential to form compliant structures.

A reconfigurable robot is a robot that can change shape. Programming reconfigurable robots is complicated by the need to adapt the behavior of each of the individual module to the overall physical shape of the robot. In this position paper, we investigate a simple approach to allow the programmer to abstract over the concrete shape of a robot using the notion of a label as a simple means of addressing various parts of the structure of a robot. Labels provide the programming language designer with a means of stratifying two main components of a spatial programming language for modular robots, namely specifying the physical structure of a robot and specifying its behavior. Based on previous experience with the ATRON robot, we find that labels are a useful concept for programming modular robots.

In unpredictable scenarios, quadruped robots with behavior-controllable capabilities can often improve their adaptability through interaction with users. In this paper, we propose a behavior-controllable motion control method, integrating user commands with adversarial motion priors, enabling the quadruped robot to achieve behavior-controllable capabilities. Firstly, a motion trajectory library is constructed to provide motion prior knowledge. To obtain stable trajectory data for various motions, optimal control methods are used to generate dynamic trajectories with whole-body dynamic constraints. These trajectory data are then standardized and assigned different weights, resulting in the construction of a motion trajectory library for the quadruped robot. Secondly, an adversarial motion prior network structure combined with user commands is proposed. Reward functions tailored to different motion behaviors are designed to achieve behavior control. This network structure acts as a single-motion prior discriminator, which, compared to a multi-motion prior discriminator, avoids complex architectures. Furthermore, the incorporation of user commands effectively addresses the issue where the single-motion prior discriminator struggles to clearly select actions as the dataset expands. Finally, simulations and comparative experiments are conducted to evaluate the effectiveness of the proposed method.

With the development of society and science, quadruped robot has been researched and used in security patrols, logistics sorting, logistics distribution, and working in harsh environment for the low cost and its strong flexibility. The gait planning is the most direct manifestation of the movement ability and performance of the quadruped robot, which requires the robot's gait to have high coordination and stability. The Central Pattern Generator (CPG) can generate simple harmonic rhythmic motion of specific joints like humans or other organisms, but the traditional CPG control method has some defects, such as the inability to change the trajectory characteristics, the high coupling of trajectory parameters, and the inability to complete the spanning phase planning, etc. In this paper, an independent foot trajectory planning method is proposed. The foot trajectory is independently designed and planned in the task space, which can meet more customized requirements, and its parameters are decoupled which means the adjustment is more flexible. The locomotion control of the manufactured robot is carried out by the traditional CPG and the control method that integrates the CPG and the independent foot trajectory planning respectively, and it is demonstrated that the new method has the characteristic that allows more complex control of quadruped robot.