Manivannan P. V.

Trajectory planning of robot’s center of gravity (CoG) is the main concern when a legged robot is walking. The trajectory of the robot should be framed such that the center of pressure (CoP) of the robot should lie within supporting polygon at all time. This paper deals with the study of support polygon and graphical analysis to find the location of CoG, where the robot has high chances to go to instability. The quadrilateral supporting phases are utilized to avoid these instability locations. Further, the analysis is done to find the timely sequence of lift and touchdown of legs (lift and touch are called as events of legs). Based on the sequence of events and the support polygon analysis, trajectory of the robot is defined, which can produce smooth, steady, and stable robot motion. Though the robot gains static stability by trajectory planning, its dynamic stability should also be verified. This is done using zero moment point (ZMP) method. The analysis done in this paper is for the unswaying robot, walking on flat terrain.

The developed Bio-inspired Robot can transform its posture from erect to sprawl and vice versa. This paper deals with the inverse dynamics of various reconfigurable postures and a few inspired by nature. The corresponding joint torques are compared, in order to study the change in torque requirements for these postures. Initially, a reductionist model of robot walk was developed and joint torques were calculated analytically and compared with torque output obtained using "Solidworks" for verifying the model. Subsequently, inverse kinematics was carried out by assuming certain parameters such as velocity, stroke length, and robot dimensions. The angular velocity profiles obtained from inverse kinematics analysis were used to run inverse dynamics; thereby obtaining the joint torques. Using the same process for various configurations, we compared different postures and their torque requirements. These results can further be used to minimize torque and energy requirements, enabling the robot to reconfigures itself to the most energy efficient configuration suited to terrain changes. The potential fields of application of this robot include: search and rescue, surveillance and other military operations.

This paper deals with the conceptual design of a bio-inspired reconfigurable robot, capable of transforming its gait from an erect to the sprawling configuration, depending on the terrain to move with maximum stability. Taking inspiration from biological systems, various studies were carried out on numerous link and joint arrangements in order to arrive at this leg design that can facilitate gait transformation. Based on gait analysis and assuming robots kinematic parameters such as velocity, stroke length, body length & width, support polygon was built. The trajectory planning of foot in swing phase was carried out, to minimize the impact force on touchdown. Angular velocity profile of each joint was obtained by inverse kinematics. These angular velocity profiles were fed into a dynamic simulator to carry out multi-body dynamics of the complete robot, for estimating the required torque and force on each joint. Using obtained torque and force values, the dimensions of leg components were refined using finite element analysis. Torque requirement for sprawl and upright motion are compared to finalize the actuators. The potential fields of application of this robot include: search and rescue, surveillance and other military operations.