Position Control

Give a motor or joint a target angle or position, and the controller drives it there and holds it.

Position control is the most common motor control mode: the upper level only supplies a target position — say, turn the joint to 30 degrees — and the driver's internal closed loop computes current from the gap between the encoder reading and the target, pulling the joint to that target and holding it there. Most servos and industrial robot arms default to this mode, since it's accurate and simple to use. Its downside is that it's 'stiff': at high gain, the joint pushes hard to reach its target regardless of whether it meets a person or an unexpected obstacle, without yielding — so tasks that require contact often switch to torque control, impedance control, or force control instead. In reinforcement-learning locomotion, the policy typically also outputs target joint angles, which a PD controller converts into torque, just with lower stiffness gains to leave the joints some compliance. Alongside position mode, the other common options are velocity mode and torque (current) mode.

ExampleROBOTIS's Dynamixel XM430 servo has 6 operating modes; setting Operating Mode to 3 selects position control mode, and once a target position is written, the servo's internal position PID drives it there and holds it.

Also called

Position Mode, Joint Position Control

Related

Velocity Control · Torque Control · Proportional-Derivative Control · Cascade Control · Stiffness and Damping Gains · MIT Mode

Sources

ROBOTIS e-Manual: XM430-W350（Operating Mode）
legged_gym: legged_robot.py（_compute_torques：P / V / T 三种控制类型） (Chinese)