Abstract
In the RoboCup Middle Size League two teams of mobile robots play soccer against each other. During the game, agility, i.e. the ability to quickly change the direction of platform movements, is important to react or anticipate fast on the intention of opponents to efficiently perform maneuvers like ball shielding and interception. Therefore, high accelerations are desired which ideally would ask all wheels to contribute to traction in the target direction. However none of the current omnidirectional wheel-based robots in the league offers such a feature. Each pair of wheels can rotate independently about its suspension axis . The new configuration brings new challenges in control: the platform becomes kinematically nonholonomic due to the kinematic constraints around the pivot axes, but it is shown that in the context of the driving task the controller can keep the wheel configurations such that they can generate a force and torque in the directions needed by the task. Hereby, the restriction to minimize the position-error in its three degrees of freedom with respect to a predefined trajectory is relaxed by taking only the degrees of freedom relevant for the task into consideration. A cascaded control strategy is proposed that combines kinematic and dynamic control and also addresses the control-allocation problem. Compared to a full kinematic approach as typically applied on steerable wheeled systems, 2.3 times higher translational and 1.8 times higher angular velocity are demonstrated. For the translational acceleration and angular acceleration, improvement factors of 2.7 and 3.2 are achieved, respectively. The platform made a successful debut during the RoboCup Portuguese Open 2019, showing the robustness of the proposed approach.
Highlights
The RoboCup-initiative, a platform to promote robotics and research in artificial intelligence [1], has set its ultimate goal of beating the human world champion team in 2050 with a team of autonomous robots
On the route to this objective, various competitions are set up. Among those competitions is the RoboCup Middle Size League (MSL), in which teams of five fully autonomous, wheeled robots having a maximum size of 50 × 50 × 80 [cm] play soccer with a regularly sized FIFA soccer ball on a field of 22 × 14 [m] [2]
Compared to steerable wheels which consist of an actuation and a steering motor, the latter motor is placed parallel to the actuation motor such that both actuators are able to contribute to the platform movement
Summary
The RoboCup-initiative, a platform to promote robotics and research in artificial intelligence [1], has set its ultimate goal of beating the human world champion team in 2050 with a team of autonomous robots. In the near future, such rollers will be contaminated with sand and grass if these robots will be playing on an outdoor soccer pitch These drawbacks form the main motivation for the development of an eight-wheeled platform consisting of four pairs of hub-drive motors. Examples are seen in various domains such as mobile manipulation [5], logistics [6,7], (domestic) services [8,9,10], industry [11,12] and automotive [13,14] The former Philips RoboCup team had a steerable wheeled platform [3] already in the early days of RoboCup, which in correspondence with the other systems in practice showed limited speed and acceleration [15].
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