چكيده به لاتين
Today, the use of robots has expanded significantly, with their growing presence in fields such as military, exploration, and rescue operations. In addition to safeguarding human lives, robots have greatly aided in performing difficult tasks with high speed and precision. In most cases, using a robot for operations in the aforementioned fields requires mobility and the presence of a manipulator. These robots, called mobile manipulators, are an integrated system of an arm and a mobile base. Due to their mobility, these types of manipulators have a vast working space. Wheeled mobile bases offer high speed and low energy consumption on flat surfaces; however, they cannot be used on uneven terrain due to their limitations. On the other hand, legged mobile bases perform well on uneven surfaces but consume a lot of energy on smooth and flat terrains. Therefore, to combine the advantages of both types of mobile bases, the use of wheeled-legged mobile bases is recommended. These types of bases have adjustable height, allowing them to traverse uneven terrains effectively while maintaining low energy consumption and high movement speed on flat surfaces.
A critical issue that must be considered in wheeled-legged mobile bases is their dynamic stability, which becomes even more significant when manipulators are mounted on them. In many applications, the manipulators, due to their considerable weight, can destabilize the robot and severely disrupt its performance. One potential solution to this issue is the use of flexible arms, which reduce the robot’s weight. However, this introduces additional degrees of freedom that must be accounted for in the stability analysis.
In this research, the kinematics and dynamics of a rigid wheel-legged mobile manipulator have been modeled. A simulation has been conducted for a wheel-legged mobile manipulator with two rotary joints, and the results have been validated by comparing them with the results obtained from modeling the robot in ADAMS software. Next, an appropriate stability criterion has been chosen to evaluate the robot's stability, and the results have been compared with experimental data obtained from tests on a robot that has been constructed in the Robotics Laboratory at Iran University of Science and Technology. In the simulation, it was shown that when the front and rear legs are positioned at an angle of -160 degrees, and if the manipulator link with a mass of 0.675 kg and a length of 0.6 meters, which is at zero degrees, starts moving with an acceleration of 30 deg/s², the robot reaches the verge of instability, causing the rear wheels to lift off the ground. Afterward, a dynamic modeling algorithm for an N-link flexible manipulator with rotary-prismatic joints mounted on a wheel-legged base has been developed using the recursive Gibbs-Appell method, and the equations have been validated through simulation of a single-link flexible manipulator with rotary-prismatic joints and comparison of the results. Finally, given the importance of stability in this system, its stability has been evaluated using the selected stability criterion.
