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feat(pid_longitudinal_controller): update readme
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Signed-off-by: Berkay Karaman <brkay54@gmail.com>
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brkay54 committed Feb 6, 2024
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41 changes: 17 additions & 24 deletions control/pid_longitudinal_controller/README.md
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Expand Up @@ -55,18 +55,27 @@ For reliable stopping, the target acceleration calculated by the FeedForward sys

Based on the slope information, a compensation term is added to the target acceleration.

There are two sources of the slope information, which can be switched by a parameter.
There are two sources of the slope information, both sources are used in controller with respect to state of the node.

- Pitch of the estimated ego-pose (default)
- Pitch of the estimated ego-pose
- Only used when `slope_source` is "raw_pitch"
- Calculates the current slope from the pitch angle of the estimated ego-pose
- Pros: Easily available
- Cons: Cannot extract accurate slope information due to the influence of vehicle vibration.
- Cons: Can not be used in combination with delay compensation.
- Z coordinate on the trajectory
- Calculates the road slope from the difference of z-coordinates between the front and rear wheel positions in the target trajectory
- Pros: More accurate than pitch information, if the z-coordinates of the route are properly maintained
- Pros: Can be used in combination with delay compensation (not yet implemented)
- Only used when `slope_source` is "trajectory_pitch"
- Calculates the road slope from the difference of z-coordinates between the front and rear wheel positions in the target trajectory.
- Pros: More accurate than pitch information, if the z-coordinates of the route are properly maintained.
- Pros: Can be used in combination with delay compensation.
- Cons: z-coordinates of high-precision map is needed.
- Cons: Does not support free space planning (for now)
- Cons: Does not support free space planning (for now).
- Adaptive pitch information
- Only used when `slope_source` is "trajectory_adaptive"
- It switches the slope sources with respect to velocity of the ego vehicle
- The trajectory_pitch is used when the vehicle's velocity is higher than `adaptive_trajectory_velocity_th` otherwise pitch of the estimated ego-pose is used for slope value.
- Pros: Can be used in combination with delay compensation for high speeds
- Cons: There might be a loss of comfort when slope source is switched

**Notation:** This function works correctly only in a vehicle system that does not have acceleration feedback in the low-level control system.

Expand Down Expand Up @@ -108,23 +117,6 @@ Depending on the actuating principle of the vehicle, the mechanism that physical

In this controller, the predicted ego-velocity and the target velocity after the delay time are calculated and used for the feedback to address the time delay problem.

### Slope compensation

Based on the slope information, a compensation term is added to the target acceleration.

There are two sources of the slope information, which can be switched by a parameter.

- Pitch of the estimated ego-pose (default)
- Calculates the current slope from the pitch angle of the estimated ego-pose
- Pros: Easily available
- Cons: Cannot extract accurate slope information due to the influence of vehicle vibration.
- Z coordinate on the trajectory
- Calculates the road slope from the difference of z-coordinates between the front and rear wheel positions in the target trajectory
- Pros: More accurate than pitch information, if the z-coordinates of the route are properly maintained
- Pros: Can be used in combination with delay compensation (not yet implemented)
- Cons: z-coordinates of high-precision map is needed.
- Cons: Does not support free space planning (for now)

## Assumptions / Known limits

1. Smoothed target velocity and its acceleration shall be set in the trajectory
Expand Down Expand Up @@ -178,7 +170,8 @@ AutonomouStuff Lexus RX 450h for under 40 km/h driving.
| min_acc | double | min value of output acceleration [m/s^2] | -5.0 |
| max_jerk | double | max value of jerk of output acceleration [m/s^3] | 2.0 |
| min_jerk | double | min value of jerk of output acceleration [m/s^3] | -5.0 |
| use_trajectory_for_pitch_calculation | bool | If true, the slope is estimated from trajectory z-level. Otherwise the pitch angle of the ego pose is used. | false |
| slope_source | string | It defines the slope source for the vehicle. Available options: "raw_pitch", "trajectory_pitch" or "trajectory_adaptive" | "raw_pitch" |
| adaptive_trajectory_velocity_th | double | Threshold velocity value for state transition of slope sources. Only usable when `slope_source` is "trajectory_adaptive". [m/s] | 1.0 |
| lpf_pitch_gain | double | gain of low-pass filter for pitch estimation | 0.95 |
| max_pitch_rad | double | max value of estimated pitch [rad] | 0.1 |
| min_pitch_rad | double | min value of estimated pitch [rad] | -0.1 |
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