MECHANICAL and AEROSPACE ENGINEERING Active Reconfiguration for Performance Enhancement in Articulated Wheeled Vehicles Aliakbar Alamdari PhD Candidate The State University of New York at Buffalo Venkat N. Krovi Associate Professor Primary: Mechanical and Aerospace Engineering Adjunct: Electrical Engineering Adjunct: Gynecology-Obstetrics Adjunct: Pathology & Anatomical Sciences The State University of New York at Buffalo

 Introduction to Articulated Wheeled Vehicles (AWVs)  Kinematic Model Development  Articulation and Platform Motion Effects on the Wheel-Terrain Interaction  Kinetostatic Formulation in Wheel-Terrain Interaction  Articulation and Slippage Effects on the Platform Motion  Manipulability and Maneuverability of AWVs  Redundancy Resolution and Posture Control  Articulated Suspension Stability Criteria  Simulation Results  Conclusion 2 Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION

1.The terrain-contact wheels are attached to the chassis via an articulated multi- body chain. 2.Wheel-relocation with respect to chassis during locomotion. 3.Provide significant re-configurability and redundancy. 4.Intermediate articulation plays as suspension system. 5.AWV can change the location of center of mass by adjusting linkages. 6.AWV can avoid roll-over when passing uneven terrain. 7.Improve stability and obstacle surmounting and enhance robustness. 3 Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION Articulated Wheeled Vehicles Challenges 1.Wheel velocities governed by a set of no-slip constraints could be violated which can result vibration. 2.Minimization of wheel-slipping and skidding by proper coordination of the rolling/steering of the wheels. 3.Reconfiguration to enhance the traction condition and stability. 4.Determination of the best pose for internal configuration.

4 Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION Developing a twist-based kinematic modeling for Articulated Wheeled Vehicle Parameters vector for each leg-wheel

5 Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION The velocity of the contact frame respect to fixed frame expressed in {C} frame Twist vectors expressed in local frames by Adjoint Transformation Forming velocity level kinematic equations

6 Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION Contact point velocity vector Remove columns of matrices associated with contact tilt and sway slippage Contact Kinematics

7 Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION Determining the platform motion in terms of wheels slippage and joints rate Partitioned to sensed and not sensed quantities Navigation Kinematics

forward kinematic singularity 8 Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction & Manipulability REDUNDANCY RESOLUTION Determination of the best pose for internal configuration of the redundant leg-wheel vehicle to maximize manipulability. Homogenous transformation between the various frames of references Contact twists expressed in contact frame Legs can assume a variety of configurations without altering the pose of the chassis Twist vectors expressed in local frames Applying the non-holonomic constraints Forming velocity level kinematic equations Investigating the singularities of AWV pose Inverse kinematic singularity det(G) = 0 The platform cannot resist forces or moments in some directions The moving platform gains 1 or more degree-of-freedom

9 Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction Redundancy Resolution Purpose: Enable the robot to change the arrangement of its legs while moving around on uneven terrain. Two control tasks: Path following & Posture regulation for controlling the platforms Pitch, Roll and Yaw Closed loop control Kinematic redundancy & Actuation redundancy needs to be resolved Task space variables Controlled variables Sensor Fusion Interaction & Manipulability

10 The overall vehicle tip over measure A balanced vehicle configuration is defined as one has the low tip over measure. Thus, we define the objective function as Introduction Dynamics Sensor Fusion Control sys. Introduction Kinematic Model Interaction Redundancy Resolution Sensor Fusion Interaction & Manipulability

11 Results of redundancy resolution and balancing in different scenarios 1- Sloped terrain 2- One side of the vehicle moves on sloped terrain and the other side moves on flat surface Introduction Dynamics Simulation Conclusion

Bumpy terrain In the motion control we tried to force the longitudinal, lateral and detachment slippage equal to zero. Introduction Dynamics Simulation Conclusion

 A systematic and general approach to the kinematic modeling, analysis and control of articulated leg-wheel mechanisms while navigating over rough- terrains was presented.  Compact form of contact kinematics and Navigation Kinematics was established.  Best pose for internal configuration of the redundant leg-wheel vehicle was determined.  Motion control for redundancy resolution and balancing was formulated Introduction Dynamics Simulation Conclusion

MECHANICAL and AEROSPACE ENGINEERING