Trajectory: Joint Position

Note

The Streaming Mode ID for this mode is 1.

Note

We highly recommend using the Position+Velocity mode, due to its superior tracking performance.

This mode may, in presence of high joint acceleration, tend to overshoot the desired positions. In order to mitigate, we suggest:

  • increasing the streaming frequency (> 250 Hz)

  • if feasible, use the position and velocity streaming mode

Streaming Message Format
../../../_images/streaming_message_joint_pos.drawio.svg

In Pos mode, the robot is controlled by commanding the desired position for each joint.

In order to use this mode, a trajectory generation algorithm is required that generates a feasible trajectory satisfying each joint’s dynamic limits. Please see below for suggested limits in streaming mode:

Joint Limits
1Joint Position: ±270 deg
2Joint Velocity:
3    Drive 193: ±1.25 [rad / s]
4    Drive 148: ±2.00 [rad / s]
5    Drive 116: ±4.00 [rad / s]
6    Drive  86: ±5.00 [rad / s]
7Joint Acceleration: ± 4.0 [rad / s2]
8Joint Jerk: ± 100.0 [rad / s3]

The controller will receive the streaming messages and pre-process them using a Kalman filter, in order to obtain smooth and accurate estimates of the derivatives.

In some cases - for example due to rounding errors or packet loss - larger jumps can occur, specifically in the derivatives. Therefore, to guarantee best possible robustness, the commanded joint properties are post processed and the controller is aiming to best possibly follow the commanded joint trajectory. However, this postprocessing assumes the trajectory is valid, i.e. it respects the feasibility limits for joint position, velocity and acceleration.