In this article, a novel guidance law derivation and new synchronization strategy are proposed for a virtual structure-based formation flight. These are designed using both aerodynamic and dynamics...

Formation control of aerial robots using virtual structure and new fuzzy-based self-tuning synchronization

Development of an 8DOF quadruped robot and implementation of Inverse Kinematics using Denavit-Hartenberg convention.

In the present work, we show the development of an active exoskeletal device to aid the spine. This device is targeted at able-bodied people, who for various reasons may need help with lifting weights from the ground or more simply in daily movements. The characteristics of the device must respond to the characteristics of ergonomics, lightness, functionality, resistance, durability, and, last but not least, inexpensiveness, so as to be able to meet the needs of a large public. In order to equip the exoskeletal device with the listed characteristics, it was decided to create it using a combination of materials: polylactic acid for the back and the terminal shell, steel for the pins and spacers, and aluminum for the structure. This way, all the basic requirements for the success of the device have been met. Moreover, as for actuators, McKibben-type pneumatic muscles have been used, as they have particular characteristics of compliance and high power-to-weight ratio and are well suited to bioengineering systems. 

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Development of an Active Exoskeleton for Assisting Back Movements in Lifting Weights

An MPC-based two-dimensional push recovery of a quadruped robot in trotting gait using its reduced virtual model

As an important branch of mobile robots, quadruped robots have high flexibility, high adaptability, and high dynamics, which provide excellent maneuverability and environmental adaptability. In the past ten years, researchers have done a lot of research on the ability of the quadruped robot to cope with the complex environment and published many results in order to make the working environment of the quadruped robot closer to reality. This paper collected these research results and divided these literatures into three categories according to different situations: crossing challenging terrain, walking on slope, and coping with interference, respectively, introducing representative methods. The purpose of this review is to summarize and analyze the previous research results and provide guidance for future research on quadruped robots in complex situations.

https://www.mdpi.com/2079-9292/8/12/1414/pdf

Survey of Quadruped Robots Coping Strategies in Complex Situations

In this paper, dynamics and gait planning of a quadruped robot is discussed. To this end, using Lagrangian method the equations of motion are first derived. Then, an approach is proposed to eliminate the terms corresponding to the constraints caused by the feet on the ground. The obtained dynamics model is validated using Matlab SimMechanics. Finally, gait planning of the robot is developed such that the robot can walk with a given speed over a flat terrain while the robot center of mass remains inside the support polygon. Obtained results reveal stable walking of a quadruped robot based on the proposed approach.

Dynamics and stable gait planning of a quadruped robot

Legged robots may become unstable when subjected to unexpected disturbances such as external pushes and environmental irregularities mostly while moving on natural terrains. To enhance the mobility performance, legged robots should be able to keep or restore their balanced configuration when a sudden disturbance is exerted. The aim of this article is to design a controller for a quadruped robot to restore its balanced configuration despite exerting external pushes. This is achieved based on developing a full-dynamics model of the robot moving over even and uneven terrains. The proposed controller is based on a PD module which calculates the required accelerations for restoring the robot equilibrium. However, these accelerations may make the robot unstable and also cause the slippage of stance feet. Therefore, an optimization algorithm is used to compute the maximum admissible accelerations. The constraints of the optimization problem are the conditions which guarantee the robot stability and the stance feet slippage avoidance. The optimization algorithm is transformed into a linear constrained least-squares problem to be solved in real-time. The main contributions of this article are the development of a push recovery algorithm for quadruped robots and also the introduction of an appropriate condition which guarantees the stability of the robot even on uneven terrains. This stability condition is developed based on a full-dynamics model of the robot. The proposed algorithm is applied on an 18-DOF quadruped robot when the robot is standing over both even and uneven terrains. The obtained results show that the robot can successfully restore its balanced configuration by precise adjustment of the position and orientation of its main body while a massive external disturbance is exerted.

Push recovery of a quadruped robot on challenging terrains

Quadruped animals have high agility and grace skills in the motion over natural environment. An important feature of such animals is their abilities in the selection of appropriate gait in the response to the terrain irregularities and also the smooth transition between them in order to increase the stability or conserve the energy. In this paper, a Cartesian CPG-based controller for the gait generation and the transition between them will be developed. The proposed approach uses nonlinear coupled oscillators for generating rhythmic signals. These patterns can be modulated by a programmed excitation signal and proportionally changing the frequency, amplitude and the coupling parameters among oscillators. According to these variations, the step length, duration of swing and stance phases of all legs, relative phase between the legs and the sequence of leg lifting can be adjusted smoothly especially by the duration of gait transition. Then, trajectories of swing legs along the z- and x-axeis will be computed through the data obtained form the CPG controller. The reference ZMP path will be desgined on the basis of the footprints of legs. Then, the COG trajectories will be calculated with a preview servo controller. Finally, some simulations are conducted to verify the effectiveness of the proposed approach both in the gait generation and smooth gait transition for a quadruped robot.

CPG-based gait transition of a quadruped robot

Model-based Control of a quadruped robot based on designed stable gaits is the focus of this paper. To this end, first explicit dynamics equations are obtained. Next, stable gait planning of the robot is investigated such that the robot can walk with a given speed over the terrain. Finally, the Sliding Mode Control (SMC) approach is applied, and a new chattering elimination method is proposed by adding a PD term to the control input. Obtained simulation results show that the performance of the SMC in terms of the tracking errors will be improved even in the presence of significant disturbances. Therefore, using the proposed approach compared to the conventional SMC will be more practically reliable.

PD regulated sliding mode control of a quadruped robot

Maintaining the balance or stability of legged robots in natural terrains is a challenging problem. Besides the inherent unstable characteristics of legged robots, the sources of instability are the irregularities of the ground surface and also the external pushes. In this paper, a push recovery framework for restoring the robot balance against external unknown disturbances will be demonstrated. It is assumed that the magnitude of exerted pushes is not large enough to use a reactive stepping strategy. In the comparison with previous methods, which a simplified model such as point mass model is used as the model of the robot for studying the push recovery problem, the whole body dynamic model will be utilized in present work. This enhances the capability of the robot to exploit all of the DOFs to recover its balance. To do so, an explicit dynamic model of a quadruped robot will be derived. The balance controller is based on the computation of the appropriate acceleration of the main body. It is calculated to return the robot to its desired position after the perturbation. This acceleration should be chosen under the stability and friction conditions. To calculate main body acceleration, an optimization problem is defined so that the stability, friction condition considered as its constraints. The simulation results show the effectiveness of the proposed algorithm. The robot can restore its balance against the large disturbance solely through the adjustment of the position and orientation of main body.

Mahdi Khorram

Papers

Dynamics and stable gait planning of a quadruped robot

Push recovery of a quadruped robot on challenging terrains

CPG-based gait transition of a quadruped robot

PD regulated sliding mode control of a quadruped robot

Balance recovery of a quadruped robot