Leg Mode Research Articles

AN EXPERIMENTAL INVESTIGATION ON NOVEL SEGMENTED OMNI WHEELED HYBRID MOBILE ROBOT TO ASSESS OBSTACLE CLIMBING CAPABILITY

Abstract This article introduces a novel quadrupedal hybrid mobile robot with a segmented omni wheel design capable of climbing obstacles of height greater than its wheel radius. The unique wheel design comprises of two parallel coaxial 240-degree segmented omni wheels per leg with independent offset angle control. The transformation from wheel to leg mode and vice versa can be seamlessly achieved by controlling the offset angle between the segmented omni wheels. A series of experiments are carried out to evaluate the robot's performance for obstacle climbing capability utilizing various wheel end effector designs, and a comparative analysis is presented. The results indicate that the obstacle climbing capability of segmented omni wheel design with zero offset angle is improved by 40.7% compared to standard wheel and the unique wheel design configuration facilitates seamless staircase climbing capability without any complex control scheme. In addition, statistical studies using Taguchi method and ANOVA are performed on the experimental findings. A linear regression model to predict power consumption has been developed and the significant factors influencing the robot's power consumption and stability are presented.

W-Leg Jumping Robot: Mechanical Design, Dynamical Analysis and Simulation of Jumping Dual Wheel-Leg Hybrid Robot

This study primarily focuses on design, mathematically model and simulate a novel two wheel-legged hybrid robot called W-Leg Jumping robot, which has a unique ability to overcome step-like obstacles efficiently. In general, in transformable wheel-leg robot studies, the leg and wheel structure perform their movements in an interdependent manner. However, in this study, it is aimed to design a robot in which the leg and wheel structure can move independently of each other and to develop a robot that can easily overcome obstacles on flat surfaces with the wheel mode and with the leg mode. The robot can fold its legs hidden within the wheels and deploy its two degree of freedom (DoF) legs when it detects step-like obstacles. This mechanism allows the robot to overcome an obstacle with a height of twice the radius of the robot's open/close mechanism of the legs, along with the two-dimensional kinematic and dynamic analyzes of the legs, are presented in detail within the scope of this study proportional-integral-derivative (PID) controller is designed to control the joint angles of the legs. The reference angle values to be followed according to the height of the obstacle are determined using artificial neural network (ANN). Additionally, motion simulations of the robot are conducted for four different obstacle heights (20, 30, 40, and 50 cm). As a result of the PID controller, when exceeding the highest obstacle of 50 cm, the average absolute joint angular tracking error is max. 1.8829°, average tracking error max. 0.265 s and max.

A Wheels-on-Knees Quadruped Assistive Robot to Carry Loads

This work introduces a high-performance, quadruped-assistive-robot expandable platform with wheel–leg mode transformation functions. The robot platform is designed for transporting goods in residential areas such as apartments, private houses, and office buildings. It is capable to move fast on flat ground on wheels or use legs to move in other places, especially for moving on and off residential staircases and wheelchair accessible ramps. To achieve higher load capacity and combine the knee joint with the drive wheel, we designed a compact torso–leg structure, driving the lower link through a ligament-like structure. Because the distance between the wheel and the torso is short, the mass centroid drops and the force arm caused by the load is reduced; the designed sample robot is capable to transport uniform mass loads up to 15 kg while keeping it affordable. The proposed ligament-like transmission structure also ensures the torso’s even gesture and load capability in its walking mode. Gait motion planning, finite element analysis, and task-oriented simulation have been conducted to prove its applicability and feasibility when given a heavy load to transport across flat and staired scenarios.

Development and Analysis of a Closed-Chain Wheel-Leg Mobile Platform

Current research concerning legged platforms and wheeled platforms primarily focuses on terrain adaptive capability and speed capability, respectively. Compared with wheeled platforms, legged platforms with a closed-chain mechanism still present deficiencies regarding speed ability. To integrate the advantages of these two types of platforms, a wheel-leg mobile platform with two modes based on a closed-chain mechanism is proposed. First, a closed-chain mechanism that generates a high-knee trajectory in legged mode is designed and analyzed based on kinematic analysis. To improve the platform’s obstacle-surmounting performance, the dimensional parameters of the closed-chain mechanism are optimized and the design requirements for the platform’s frame are analyzed. In addition, the particular structure of the leg group is designed to realize transformation between legged mode and wheeled mode. The mobility of the constructed platform is calculated through an obstacle-surmounting probability analysis. The performances of the two motion modes are analyzed and compared by conducting dynamic simulations. Finally, experiments are carried out to verify both the theoretical analyses and the prototype performance. This study proposes a new approach to designing wheel-leg platforms with prominent speed ability and mobility based on a closed-chain mechanism.

FUHAR: A transformable wheel-legged hybrid mobile robot

This paper introduces a mobile robot with a new type of transformable wheel legs that can be used for flat and rough terrain. It integrates the stability and maneuverability of a wheeled robot and the legged robot’s obstacle climbing capacity using a transformable mechanism with wheel legs. With a transformation structure based on a four-bar mechanism, these two modes can be easily changed. This paper analyzes the movements for the proposed robot in wheeled and legged mode. Dynamic modeling and design of a control system were obtained. Then, the obstacle climbing strategies under legged modes were carried out. Finally, on the basis of the simulation, a prototype of the proposed robot was designed and produced. The results from the experiments validate the efficiency of the designed hybrid mobile robot.

Frozen Leg Operation of a Three-Phase Dual Active Bridge Converter

Three-phase dual active bridge (DAB) topology is a potential alternative for high-power applications when a compact and efficient converter with a bidirectional power transfer capability is desired. In a constructed prototype, high-power SiC modules with dedicated drivers are utilized to achieve high-efficiency and compact size. Each module has two interconnected switches with anti-parallel diodes resembling a converter leg. It is observed that the driver halts the module operation as a result of protective actions such as overcurrent, gate undervoltage, or gate overvoltage. In this frozen leg mode, the module operates as a leg with two diodes until an external hardware signal resets the driver. The converter continues operation but with a reduced performance. Analysis, simulation, and verification of a three-phase DAB converter under a frozen leg operation are considered in this paper. The converter with a frozen leg has two different behaviors at light loads and heavy loads. Consequently, two different analysis methods are developed to solve converter operation in different load conditions. Results show that the power transfer capability is reduced, but this fault mode is nondestructive.

Unlocking the value from origin and destination revenue management

“O&D RM provides incremental revenue benefits compared to Leg RM” – the statement has been proven through many simulation studies and many airlines have implemented and reported the benefits from O&D RM. The key value driver of this benefit is the network optimization model that uses O&D forecasts and market representative fares to do effective trade-offs. There are a multitude of factors that are at play in ensuring the proposed benefits from O&D RM are materialized. Some of the key challenges that airlines face today are the complexity of forecast management, maintaining accurate fares for optimization, and using advanced availability processors to achieve this goal. The other major challenge is the big organizational change from Leg mode to O&D mode among the managers and RM analysts. Additionally, distribution aspects such as seamless availability, married segments, and journey controls also play an important role in effectively reaping the benefits of O&D RM. In this study, we leverage APOS (Airline Planning and Operations Simulator) of Sabre and analyze how each of these factors impacts the O&D RM value across different load factors and flow traffic levels.

A Wheel-legged Robot with Active Waist Joint: Design, Analysis, and Experimental Results

This paper presents a wheel-legged robot that features an active waist joint. The proposed wheel-legged robot is composed of a front module, a rear module, and an active waist joint. The proposed robot can perform rectilinear motion and turning motion in both wheeled and legged modes. The active waist joint module is added to make the robot pass through the curved narrow channel. Several experiments have been done to evaluate the performance of the proposed wheel-legged robot. The maximum velocities of the proposed robot in wheeled and legged modes are 17.2 and 10.4 m/min respectively. And the average corresponding deflection rates of the proposed robot in wheeled and legged modes are 3.1 and 3.7 % respectively. The mobility efficiencies of the robot in wheeled and legged modes are up to 96.3 and 94.3 % respectively. Compared with the proposed robot in legged mode, the performance in the turning motion with the active waist joint is better when the proposed robot is in wheeled mode. Two approaches of climbing obstacles are proposed for the proposed robot in legged mode. The wheel-legged robot can climb an obstacle with maximum height of 10 cm.

Quattroped: A Leg--Wheel Transformable Robot

This paper reports on the design, integration, and performance evaluation of a novel four-leg/four-wheel transformable mobile robot, Quattroped. In contrast to most hybrid platforms that have separate mechanisms and actuators for wheels and legs, this robot is implemented with a unique transformation mechanism that directly switches the morphology of the driving mechanism between the wheels (i.e., a full circle) and 2 degrees of freedom leg (i.e., combining two half circles as a leg), so that the same system of actuation power can be efficiently utilized in both wheeled and legged modes. The design process, mechatronics, software infrastructure, behavioral development, and leg-wheel dynamic characteristics are described. The performance of the robot is evaluated in various scenarios, including driving and turning in wheeled mode, driving, step and bar crossing, irregular terrain passing, and stair climbing in legged mode. Taking advantage of the leg-wheel combination on a single platform, the comparison of the wheeled and legged locomotion is also discussed.

RT-Mover: a rough terrain mobile robot with a simple leg–wheel hybrid mechanism

There is a strong demand in many fields for practical robots, such as a porter robot and a personal mobility robot, that can move over rough terrain while carrying a load horizontally. We have developed a robot, called RT-Mover, which shows adequate mobility performance on targeted types of rough terrain. It has four drivable wheels and two leg-like axles but only five active shafts. A strength of this robot is that it realizes both a leg mode and a wheel mode in a simple mechanism. In this paper, the mechanical design concept is discussed. With an emphasis on minimizing the number of drive shafts, a mechanism is designed for a four-wheeled mobile body that is widely used in practical locomotive machinery. Also, strategies for moving on rough terrain are proposed. The kinematics, stability, and control of RT-Mover are also described in detail. Some typical cases of rough terrain for wheel mode and leg mode are selected, and the robot’s ability of locomotion is assessed through simulations and experiments. In each case, the robot is able to move over rough terrain while maintaining the horizontal orientation of its platform.

A Space Vector PWM Technique for Symmetrical Six-Phase Voltage Source Inverters

Six-phase a.c. motor drives are usually supplied from two-level six-phase voltage source inverters (VSIs), which are controlled using appropriate PWM techniques. Most of the existing work applies to the asymmetrical six-phase VSI, supplying an asymmetrical a.c. machine (two three-phase windings shifted in space by 30° degrees) with two isolated neutral points. However, it has been shown recently that a symmetrical six-phase induction machine (equidistant spacing of all six-phases, with 60° spatial displacement between any two consecutive phases) offers the same quality of performance as the asymmetrical machine, provided that good quality current control and an adequate PWM technique are utilised for the symmetrical six-phase VSI (Fig. 1) control. Since this requires sinusoidal VSI output voltages (neglecting the PWM ripple), a space vector PWM technique (SVPWM) is described in this paper, such that sinusoidal or at least near-sinusoidal output voltages are generated across the whole range of the available output voltage fundamental for the six-phase load with a single neutral point. Operation of the SVPWM scheme is investigated by extensive experimentation and time-domain waveforms and spectra are given for inverter leg, phase-to-neutral, line-to-line and common mode voltages, as well as for the load current, for a variety of operating conditions. Total voltage harmonic distortion (THD) is also calculated using experimental results and is used as a figure of merit in evaluation of the quality of performance of the SVPWM schemes.

Study on Roller-Walker – Multi-mode Steering Control and Self-Contained Locomotion –

We have proposed a new leg-wheel hybrid mobile robot named ""Roller-Walker"". Roller-Walker is a vehicle with a special foot mechanism, which changes to a sole in walking mode and a passive wheel in skating mode. On rugged terrain the vehicle walks in leg mode, and on level or comparatively smooth terrain the vehicle makes wheeled locomotion by roller-skating using the passive wheels. The characteristics of Roller-Walker are: 1) it has a hybrid function but it is light-weight, 2) it has the potential capability to exhibit high terrain adaptability in skating mode if the control method for roller-wolfing is fully investigated in the future. In this paper, the 4 leg trajectory of straight Roller-Walk is optimized in order to achieve maximum constant velocity. Also steering roller-walk control method is proposed. It is obtained by the expansion of the straight roller-walk trajectory theory adding an offset to the swinging motion. This steering method resembles that of a car. The control system was modified into an untethered system, and control experiments were performed. The realization of the steering motion was verified by them.

ローラーウォーカーに関する研究 基本的運動の生成と自立推進実験

We have proposed a new leg-wheel hybrid mobile robot named“Roller-Walker”. Roller-Walker is a vehicle with a special foot mechanism, which changes to a sole in walking mode and a passive wheel in skating mode. On rugged terrain the vehicle walks in leg mode, and on level or comparatively smooth terrain the vehicle makes wheeled locomotion by roller-skating using the passive wheels. The characteristics of Roller-Walker are: 1) it has a hybrid function but is light-weight, 2) it has the potential capability to exhibit high terrain adaptability in skating mode if the control method for roller-walking is fully investigated in the future. In this paper, the 4leg trajectory of straight roller-walk is optimized in order to achieve maximum constant velocity. Also steering roller-walk control method is proposed. It is obtained by the expansion of the straight roller-walk trajectory theory adding an offset to the swinging motion. This steering method resembles that of a car. The control system was modified into an untethered system, and control experiments were performed. The realization of the steering motion was verified by them.

ローラーウォーカーに関する研究 システムの構成と基本的動作実験

We have proposed a new leg-wheel hybrid mobile robot named “Roller-Walker”. Roller-Walker is a vehicle with a special foot mechanism on each leg which changes to a sole in walking mode and a passive wheel in skating mode. On rugged terrain the vehicle walks in leg mode, and on level or comparatively smooth terrain the vehicle makes wheeled locomotion by roller-skating using the passive wheels. The characteristics of Roller-Walker are: 1) it has a hybrid function but is lightweight, 2) it has the potential capability to exhibit high terrain adaptability in skating mode if the control method for roller-walking is fully investigated in the future. In this paper, the 2 leg trajectory for straight roller-walking is optimized in order to achieve the maximum constant velocity. Also a changeable ankle mechanism was integrated into the Roller-Walker system. Experiments were performed to demonstrate the validity of the concept of Roller-Walker and the results of straight roller-walk experiments are compared with those derived through simulation.

Roller-Walker: A New Leg-Wheel Hybrid Mobile Robot.

A new leg-wheel hybrid vehicle called is proposed. The Roller-Walker is a vehicle with a special foot mechanism which changes between feet soles for the walking mode and passive wheels for the wheel. On rugged terrain, the vehicle walks in the leg mode, and on level or comparatively smooth terrain, the vehicle moves by wtheeled locomotion using the passive wheel in a manner resembling roller-skating. The characteristics of the Roller-Walker are that (1) it has a hybrid function but can have lightweight design and, (2) it will have the capability for high terrain adaptability in the wheeled mode if the method of controling the Roller-Walking is fully investigated in the future. We perform basic simulation experiments of the Roller-Walk and clarify its fundamental behavior and demonstrate basic relations in the terrain adaptive trajectory control method.