State estimation and path following on curved and flat vertical surfaces with Omniclimber robots:

Kinematics and control.
People involved:
  • Mahmoud Tavakoli
  • Lucio Sgrigna
  • Carlos Viegas
  • Anibal T de Almeida
Omnidirectional wheels used on Omniclimber inspection robot and in other robots enable a holonomic drive and a good maneuverability. On the other hand, they have a poor wheel traction and suffer from vertical and horizontal vibration, decreasing the trajectory following accuracy of the robot. In this study, we address this problem by integrating an orientation estimation and correction algorithm in the Omniclimber control by integration of an accelerometer. Moreover, since the Omniclimber chassis adapts to curved structures, the kinematics of the robot change when moving on a curved surface. We integrated an additional algorithm which corrects the robot’s kinematics based on the curvature diameter and the current robot orientation. By integrating these two algorithms we could make remarkable improvements on the path following accuracy of the Omniclimber on flat and curved structures.

OmniClimber-VI, showing dimensions and reference axis.

Kinematics model of the 3 wheeled omnidirectional platform with representation of relevant axis and velocities. Notation: x, y – static world axis; β – Yaw angle [rad]; l – distance between the wheels and center of the robot [m]; v1, v2, v3 – wheels linear velocity [m/s]; ω1, ω2, ω3 – wheels angular velocity [rad/s]; V, V n – robot front and lateral velocity [m/s]; ω – robot angular velocity [rad/s]; α – Bending angle of the arms [rad]; R – radius of the structure [m]; h – height of the CG of the robot (roughly equal to the radius of the omnidirectional wheel) [m]; d – half length of the robot arm [m];

Geometric relations used to determine the distance l between the point of contact (POC) with the surface and the center of the robot. Notation: x, y, z – static world axis; β – Yaw angle [rad]; R – radius of the structure [m]; h – height of the CG of the robot (roughly equal to the radius of the omnidirectional wheel) [m]; d – half of the robot arm length [m]; l – distance between the wheel POC and center of the robot [m];

3D simulation for new kinematic model validation.

Snapshots from the Omniclimber experiments on a pole of 220mm diameter, without and with the new controller. Rotating around the pole while keeping the robots orientation constant.

Closed loop control diagram.

Snapshots from the Omniclimber experiments on a pole of 220mm diameter, without and with the new controller. Moving vertically parallel to the pole axis.

For more information please read this article:
State estimation and path following on curved and flat vertical surfaces with Omniclimber robots: Kinematics and control.

M. Tavakoli, L. Sgrigna, C. Viegas and A. T. de Almeida, “State estimation and path following on curved and flat vertical surfaces with Omniclimber robots: Kinematics and control,” 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Hamburg, 2015, pp. 3326-3331. doi: 10.1109/IROS.2015.7353840