Tip-over Stability Research Articles

Application of Fuzzy Logic for Robotic Arm Joint Control of an Explosive Ordnance Disposal Unit

Precise luffing of payload in mobile cranes is a crucial part of material handling and safety in industrial operations. Explosive ordnance disposal uses a bomb disposal robot to safely disable explosive devices at a safe distance. This robot is a mobile jib crane type with a gripper as an end effector instead of the typical suspension cable with a hook. The common challenge of this crane type is the arm/jib movement sensitivity with respect to tip-over stability of the crane body. This is directly influenced by the payload and constrained by the degree of freedom. This paper presents a control strategy of the joint for luffing such that the back wheels remain in contact with the surface ground and avoid bucking at any given instance of weight change in the payload. Fuzzy logic was applied to control the motor torque and luffing angle of the arm in response to the load and gripper opening size to maintain the tip-over stability margin at the highest value possible. The response curves at different configurations of the two input signals were also analyzed based on the rules set to determine its precision with respect to the expected response curve.

Time and Energy Optimal Trajectory Planning of Wheeled Mobile Dual-Arm Robot Based on Tip-Over Stability Constraint

Trajectory planning and avoidance of tipping are the main keys to success in the mobile dual-arm manipulation, especially when the dual-arm or moving platform is running fast. The forces and moments between wheel-terrain and body-arm have been analyzed by kinematics and force analysis of a robot to define tip-over stability constraint. Then, an improved tip-over moment stability criterion for a wheeled mobile dual-arm robot is presented and defines tip-over stability constraint based on it. To improve the motion stability of the robot, this paper presents an optimal joint trajectory planning model based on time and energy. The quintic B-spline curve and an improved NSGA-II algorithm, which are time and energy, are applied to multi-objective optimization. The simulation results show that the motion stability of a robot is improved based on the tip-over stability constraint. This trajectory planning method based on the stability constraint can be applied to other mobile robots as well.

The Feasibility of Trajectory Controller by SS Equation of an Error Model in WMR

There has been an increasing amount of research on WMRs. The WMRs have lots of advantages: their mechanical system is usually simple; the whole movement mostly contains two dependent motors; and their motions in two-dimensional space are quite adaptable. At the same time, the WMRs have better power efficiency. WMRs have been studied from many points of view, such as modelling control, obstacle avoidance, localization, tip-over stability, and so on. This paper discusses the control algorithm. WMRs have nonholonomic constraints. That is, the mobile robot may not be able to reach a specific position and angle in a specific time; however, the robot can reach the target in a different motion or within a limited time. In this paper, an error model based on the WMR is introduced. The model explains the error between the actual position and the ideal or target position in the continuous motion of WMRs. The error model will be transformed into a state-space equation in order to demonstrate that the algorithm that controls the WMR`s movement is controllable. By splitting the inputs into and , the whole equation is transformed into a zero-input state-space system. Then, the errors can be minimized with the optimization of the feedback. The results show that by optimizing the time-varying feedback matrix, the error is asymptotically stable and close to zero. Therefore, by adding this control law to the controller, an approach to making mobile robots follow the planned trajectory is obtained.

Configuration selection for tip-over stability of a modular reconfigurable mobile manipulator under various application situations

AbstractA method is presented for configuration selection to obtain the best tip-over stability of a modular reconfigurable mobile manipulator (MRMM) under various application situations. The said MRMM consists of a modular reconfigurable robot (MRR) mounted on a mobile platform. The MRR in different configurations creates different wrenches onto the mobile platform, leading to different tip-over moments of the MRMM, even though the joint speeds or tip speeds remain the same. The underlying problem pertains to selecting one configuration of MRR for reconfiguration that would obtain the best tip-over stability under a given application. First, all the permissible configurations are identified through an enumeration method. Then, the feasible configurations are determined based on application-oriented workspace classifications. At last, two workspace indices, vertical reach and horizontal reach, are used to select an optimal configuration. The tip-over stability analysis and evaluation of MRMM are carried out for verification for three cases including vertical, horizontal, and general 3D space applications. The results demonstrate the effectiveness of the proposed method.

Static force and tipover stability analysis of an assistive device for paraplegics.

Stability plays a vital role in any robotic system. Its significance increases in systems related to health and medicine. For rehabilitation devices meant for Spinal Cord Injury (SCI) patients, stability is crucial and key element in ensuring patient safety and the usefulness of the devices. In this study, kinematics, force analysis, and the static tip-over stability of a device for rehabilitation of paraplegic patients is discussed. Kinematics modeling and static force analysis provide critical information about position and loading at different points on the device. Force-Angle Stability Criterion is used to find the static tip-over stability of the device while the patient is on board the device. The Criterion relies on the support boundary, tip-over mode axes, and the Center of Mass (COM) of the complete system. The Criterion is sensitive to the COM position and therefore is more suitable for the application. The linear actuator mounted on the device causes the end effector of the device to move. The patient, strapped with the end effector, in turn moves from sitting position to standing position. The study focuses on the analysis of stability based on changing COM during this motion. The results verify that although the system is well within the stability bounds, it is more stable as it moves from sitting position to standing position.

Online Dynamic Tip-Over Analysis for a Wheeled Mobile Dual-Arm Robot with an Improved Tip-Over Moment Stability Criterion

Tip-over stability analysis is critical for the success of mobile manipulation of the dual arm, especially in the cases that the dual arm or the mobile platform moves rapidly. Due to strong dynamics coupling between the dual arm and mobile platform, online evaluation of dynamic stability of the mobile dual-arm robot still remains challenging. This paper presents an improved tip-over moment stability criterion dealing with the dual arm and mobile platform interaction and proposes an algorithm for calculating the tip-over stability margin of the arm end in the workspace to analyze the dynamic stability of the wheeled mobile dual-arm robot. The simulations on a four-wheeled mobile dual-arm robot validate the correctness and feasibility of the proposed method.

Simulation analysis on motion stability of smart wheelchair

Electric wheelchairs sometimes are used in complex terrain, such as slopes, stairs, ravines, etc. If there is no rapid and accurate judgment and decision-making for the current situation, the wheelchair may lose control and become unstable, which may will lead to serious consequences. The intelligent electric wheelchair studied in this paper can conduct stability analysis when moving on different terrains based on its own motion state. This paper uses ADAMS simulation software to build a wheelchair model according to the size of an existing wheelchair. The stability pyramid technique used in this paper has a good judgment on the tip-over stability of the object. This paper also has a more comprehensive judgment for slippage instability. In the simulation and experiment, the slippage and tip-over instability are verified. Theoretical analysis and actual simulation demonstrated that the developed smart wheelchair has high reliability for stability analysis in different environments.

Multi-terrain Quadrupedal-wheeled Robot Mechanism: Design, Modeling, and Analysis

For a robot to navigate in terrains of rough and uneven topographies, its drives and controllers must generate and control large mechanical power with great precision. This paper is aimed at developing an autonomous robot with active-suspensions in form of a hybrid quadrupedal-wheel drive mechanism. This involves a computational approach to optimizing the development cost without compromising the system’s performance. Using the Solidworks CAD tool, auxiliary components were designed and integrated with the bed structure to form an actively suspended robot drive mechanism. Also, using the S-Math Computing tool, the robot’s suspension system was optimized, employing a four-bar mechanism. To enhance the compatibility of this design with the intended controller, some mathematical equations and numerical validations were formulated and solved. These included the modeling of tip-over stability and skid steering, the trendline equations for computing the angular positions of the suspension servomotors, and the computation of R2– values for determining the accuracy of these trendline equations. Using finite element analysis (FEA), we simulated the structural integrity of key sub-components of the final structure. The results show that our mechanical design is appropriate for developing an actively suspended robot that can efficiently navigate in different terrestrial sites and topographies.

Multi-terrain Quadrupedal-wheeled Robot Mechanism: Design, Modeling, and Analysis

For a robot to navigate in terrains of rough and uneven topographies, its drives and controllers must generate and control large mechanical power with great precision. This paper is aimed at developing an autonomous robot with active-suspensions in form of a hybrid quadrupedal-wheel drive mechanism. This involves a computational approach to optimizing the development cost without compromising the system’s performance. Using the Solidworks CAD tool, auxiliary components were designed and integrated with the bed structure to form an actively suspended robot drive mechanism. Also, using the S-Math Computing tool, the robot’s suspension system was optimized, employing a four-bar mechanism. To enhance the compatibility of this design with the intended controller, some mathematical equations and numerical validations were formulated and solved. These included the modeling of tip-over stability and skid steering, the trendline equations for computing the angular positions of the suspension servomotors, and the computation of R2– values for determining the accuracy of these trendline equations. Using finite element analysis (FEA), we simulated the structural integrity of key sub-components of the final structure. The results show that our mechanical design is appropriate for developing an actively suspended robot that can efficiently navigate in different terrestrial sites and topographies.

Suspension Effect in Tip-over Stability and Steerability of Robots Moving on Sloping Terrains

This article describes a model for a skid steer robot that quantifies the reaction forces between the wheels and the ground, which includes the effect of the passive suspension when the robot moves on flat and inclined terrains. In addition to the internal parameters of the suspension, this model included external parameters related to other components of robot and the robot-terrain relationship. With this model, which was validated through simulation, it was studied the effect that suspension produces in tip-over stability and steerability of robot when it moves on different terrain inclinations, specifically when the parameters of suspension system and wheel-ground contact are varied.

Efecto de la suspensión en la estabilidad al vuelco y direccionamiento de robots moviéndose sobre discontinuidades de terreno

En este artículo se estudia el efecto que produce el sistema de suspensión sobre la estabilidad al vuelco y la capacidad de direccionamiento en un robot móvil Skid Steer, cuando este se enfrenta a distintas discontinuidades del terreno: descenso (frontal y lateral) y ascenso sobre escalones, además del desplazamiento sobre zanjas. Específicamente, se estudió el instante cuando se generan cargas de impacto producto del movimiento del robot sobre la irregularidad del terreno. En cada caso se hizo un análisis correlacional del efecto sobre la estabilidad al vuelco y el direccionamiento (cuantificadas con métricas fundamentadas en las fuerzas de reacción de las ruedas con el suelo), al variar cuatro parámetros que definen el sistema de suspensión: constante de rigidez en los resortes, constante de amortiguamiento en los amortiguadores y las constantes de rigidez y amortiguamiento en las ruedas. Por último se estimó para cada caso, qué magnitudes deberían adquirir estos parámetros para garantizar una mejor estabilidad y direccionamiento del robot.

Tip-Over Stability Analysis of a Pelvic Support Walking Robot.

Discussed in this paper is the tip-over stability analysis of a pelvic support walking robot. To improve the activities of daily living (ADL) in hemiplegic patients, a pelvic support walking robot is proposed to help patients facilitating their rehabilitation. During the gait training with the robot, the abnormal man-machine interaction forces may lead to the tip-over of the robot, which is not beneficial to the rehabilitation process. A new method is proposed to predict the possibility of tipping over and evaluate the stability of the robot based on statics model, dynamics model, and zero-moment point (ZMP) theory. Through the interaction forces and moments analysis with static case, the safe point (ZMP) is studied, and the influence factors of force/moment are analyzed by dynamics case. An optimization algorithm based on the genetic algorithm (GA) is proposed to reduce the risk of tipping over. The simulation results show that the optimization algorithm can keep the robot from tipping over when the interaction forces exceed the safety threshold.

Design and Analysis of a Smart Rehabilitation Walker With Passive Pelvic Mechanism

AbstractIn response to the ever-increasing demand of community-based rehabilitation, a novel smart rehab walker iReGo is designed to facilitate the lower limb rehabilitation training based on motion intention recognition. The proposed walker provides a number of passive degrees-of-freedom (DoFs) to the pelvis that are used to smooth the hip rotations in such a way that the natural gait is not significantly affected, meanwhile, three actuated DoFs are actively controlled to assist patients with mobility disabilities. The walker first identifies the user’s motion intention from the interaction forces in both left and right sides of the pelvis and then uses the kinematic model to generate appropriate driving velocities to support the body weight and improve mobility. In this paper, workspace, dexterity, and the force field of the walker are analyzed based on the system Jacobian. Simulation and experiments with healthy subjects are carried out to verify the effectiveness and tip-over stability. These results demonstrate that the walker has sufficient workspace for pelvic motions, satisfactory dexterity, and near-linear force feedback within the prescribed workspace, and that the walker is easily controlled to ensure normal gait.

A Study on the Determination of the Tip-Over Stability of High Place Operation Car Using Multibody Dynamics Program and ZMP

A Study on the Determination of the Tip-Over Stability of High Place Operation Car Using Multibody Dynamics Program and ZMP

Derivation of motion equation for mobile manipulator with viscoelastic links and revolute–prismatic flexible joints via recursive Gibbs–Appell formulations

This paper investigates the dynamic equations of an N-flexible link manipulator with revolute–prismatic joints while considering the effects of manipulator locomotion by the mobile platform bound by non-holonomic kinematic constraints. Such constraints, in addition to creating dynamic interaction between manipulator and platform, cause serious motion limitations and introduction of more computational complexity. The manipulator’s flexible links are modeled by the assumed mode method, where the Timoshenko beam theory is used for the substitution of the assumed mode shapes. The internal and external damping effects are also studied for the model precision. Moreover, revolute–prismatic joints in each arm are exploited to develop the robot mobility. The new joint structure makes it possible to use mobile manipulators with long flexible links. However, in regard to the variations of links length caused by prismatic joints, time-varying dynamic equations are obtained, leading to comparatively complex and lengthy formulations. Therefore, the Gibbs–Appell formulation is utilized as an alternative to the Lagrange equations to facilitate the process of deriving the motion equations. In addition, the non-dimensional form of the Timoshenko beam theory mode shapes is recommended to circumvent the computation of time step mode shapes. It is also necessary to examine the system tip-over stability based on long and variable-length arms, lightweight base, and widespread environmental factors using the zero moment point methods. Finally, a numerical simulation for a mobile manipulator, with two flexible links and revolute–prismatic joints is carried out to demonstrate the performance of the presented model for such complex systems. Different amounts of link elasticity and the effects of internal and external damping coefficients are separately studied. The results are verified by recent fixed base flexible manipulators employing revolute–prismatic joints as well as the IUST Revolute–Prismatic joints experimental setup incorporating rigid links.

Lázaro: Robot Móvil dotado de Brazo para Contacto con el Suelo

This paper aims to describe Lázaro, which is a small mobile robot that has an arm designed especially to provide an additional contact point with the ground that can be used to improve the tipover stability and to overcome obstacles. Specifically, the description of the mechanical structure and electronic components for perception, communication and control is discussed. Subsequently, the operating characteristics of the robot are reviewed in terms of kinematics, control architecture, operating modes and interface. Finally, a description of some performance tests is presented.

Tip-Over Stability Analysis for a Wheeled Mobile Manipulator

A method is presented for tip-over stability analysis of a wheeled mobile manipulator. A wheeled mobile manipulator may tip over resulting from its operation. In this study, first a Newton–Euler formulation is applied to formulate the manipulator’s reaction forces and moments exerted onto the mobile platform. Tip-over criterion is derived to judge the system stability. Three load and motion analyses are carried on. The first static load deals with links and payload to show the effect of the horizontal position of the system’s center of gravity (CG). The second and third are the inertial forces resulting from joint speeds and accelerations, respectively. Case study is path planning with tip-over criterion result which can make the system stable along the path. The simulation results demonstrate the effectiveness of the proposed method.

Caster-leg aided maneuver for negotiating surface discontinuities with a wheeled skid-steer mobile robot

Crossing surface discontinuities, such as ditches or curbs in urban environments, is a relevant navigation issue for ground mobile robots. This paper proposes a maneuver for negotiating surface discontinuities for a hybrid locomotion system consisting on a skid-steer wheeled vehicle with a single caster-leg mechanism. This maneuver is appropriate for gaps, steps, and ramps, both upwards and downwards. Furthermore, an analysis of tipover stability and steerability through the different states of the maneuver is performed, resulting in sensor-based stability margins that can be computed online. Experimental results have been obtained by means of realistic Simulink/ADAMS simulations and actual tests with the Lazaro mobile robot. The results confirm the effectiveness of the proposed maneuver as well as the applicability of stability margins.

Adding low-cost passive toe joints to the feet structure of SURENA III humanoid robot

SUMMARYAdding active toe joints to a humanoid robot structure has lots of difficulties such as mounting a small motor and an encoder on the robot feet. Conversely, adding passive toe joints is simple, since it only consists of a spring and a damper. Due to lots of benefits of implementing passive toe joints, mentioned in the literature, the goal of this study is to add passive toe joints to the SURENA III humanoid robot which was designed and fabricated at the Center of Advanced Systems and Technologies (CAST), University of Tehran. To this end, a simple passive toe joint is designed and fabricated, at first. Then, stiffness and damping coefficients are calculated using a vision-based measurement. Afterwards, a gait planning routine for humanoid robots equipped with passive toe joints is implemented. The tip-over stability of the gait is studied, considering the vibration of the passive toe joints in swing phases. The multi-body dynamics of the robot equipped with passive toe joints are presented using the Lagrange approach. Furthermore, system identification routine is adopted to model the dynamic behaviors of the power transmission system. By adding the calculated actuating torques for these two models, the whole dynamic model of the robot is computed. Finally, the performance of the proposed approach is evaluated by several simulations and experimental results. Results show that using passive toe joints reduces energy consumption of ankle and knee joints by 15.3% and 9.0%, respectively. Moreover, with relatively large values of stiffness coefficients, the required torque and power of the knee and hip joints during heel-off motion reduces as the ankle joint torque and power increases.

Optimization of a Mobile Platform for a Wheeled Manipulator

A method for optimizing a mobile platform to form a wheeled manipulator is presented. For a given manipulator, this mobile platform is optimized to have maximum tip-over stability against the reaction forces and moments caused by the movement of the manipulator. This optimization is formulated as a max–min problem, i.e., to maximize a stable region ratio (SRR) over the manipulator's workspace while minimizing a tip-over moment (TOM). For a practical solution, this max–min problem is converted to two subproblems. The first one is the worst-case analysis to determine the maximum positive value of TOM through searching over the manipulator's workspace. A positive value of TOM indicates tip-over instability. The three parameters used for this search are pertaining to the mobile platform itself, i.e., the number of support wheels, the size, and mass of the mobile platform. The second subproblem is to optimize the placement of the manipulator and accessory on the mobile platform against the identified worst case so that the entire manipulator's workspace is stable. The effectiveness of the proposed method is demonstrated by applying it to optimize a mobile drilling and riveting robot.