# Humanoid Robot : RoK-Arm9

# RoK-Arm9

RoK-Arm9 is a humanoid arm. Each arm of this robot consists of a 9-DOF. A configuration of this robot arm is mimicked by a human's configuration. Because the robot contains inner shoulder joints, it can perform complex motions. The total weight of the robot is about 30 kg, and its payload is 8 kg for each arm.

Control algorithm research of RoK-Arm9

RoK-Arm9 must be controlled by considering various constraints for stable operation. Owing to its high DOF, more constraints can be applied than those for other robot arms. Optimal control is a powerful tool. Differential dynamic programming (DDP) is one of the optimal controls focused on the nonlinear model.

DDP Overview

We task a backward pass from the target state to the initial state. We optimize the cost.

Once the backward reaches the initial state, we can know feed forward gain(k) and feedback gain(K).

Next we perform a forward pass which we use the model to calculate the next state.

Finally, we can know optimized state-trajectory and input-trajectory.