ROS2与Ailibot2入门教程-校准-IMU校准

说明：

介绍如何在Ailibot2上校准imu
Ailibot2默认使用GY-85九轴陀螺仪
IMU校准的作用减少IMU高敏感度带来的误差
小车默认已经校准，除非数据明显差异，否则跳过次步骤

原理

小车提供的是自定义的imu的原始值，经过校准后减少误差，再进行imu_filter_madgwick包进行滤波处理，得到一个带四元数方向值的完整的ros2的imu数据值，并发布imu数据到话题/imu/data。

相关设备：

ailibot2差速系列：采购Ailibot2-D2,采购Ailibot2-D4
ailibot2全向系列：采购Ailibot2-M4，采购Ailibot2-O3，采购Ailibot2-O4

操作步骤

[小车] 启动底盘

ros2 launch ailibot2_bringup agent.launch.py

[Ailibot] 开始校准imu，最终生成的配置文件默认保存在包ailibot2_bringup/param/imu/文件夹里

$ ros2 run ailibot2_calib do_calib
......   
Orient IMU with X+ axis - Front side of the robot facing up. Press [ENTER] once done.
Calibrating! This may take a while....
 Done.
Orient IMU with X- axis - Rear side of the robot facing up. Press [ENTER] once done.
Calibrating! This may take a while....
 Done.
Orient IMU with Y+ axis - Left side of the robot facing up. Press [ENTER] once done.
Calibrating! This may take a while....
 Done.
Orient IMU with Y- axis - Right side of the robot facing up. Press [ENTER] once done.
Calibrating! This may take a while....
 Done.
Orient IMU with Z+ axis - Top side of the robot facing up. Press [ENTER] once done.
Calibrating! This may take a while....
 Done.
Orient IMU with Z- axis - Bottom side of the robot facing up. Press [ENTER] once done.
Calibrating! This may take a while....
 Done.
Computing calibration parameters... Success!
Saving calibration file... Success!

注：校准时需要根据终端上的提示来翻转小车；比如校准Y+方向的时候，将小车的左面朝上，z-方向就是底面朝上，等等，照此类推

[Ailibot] 查看文件日期，检查是否生成新的imu_calib.yaml配置文件

$ ll /home/ubuntu/ros2_ailibot2_ws/src/ailibot2/ailibot2_calib/param

确认校准的数据正确，将生成的imu_calib.yaml复制到/home/ubuntu/ros2_ailibot2_ws/src/ailibot2/ailibot2_bringup/param

$ cp /home/ubuntu/ros2_ailibot2_ws/src/ailibot2/ailibot2_calib/param/imu_calib.yaml /home/ubuntu/ros2_ailibot2_ws/src/ailibot2/ailibot2_bringup/param

[Remote PC] 启动机器人生成里程

$ ros2 launch ailibot2_bringup robot.launch.py

[Remote PC] 打开rviz查看imu数据

$ ros2 launch ailibot2_bringup rviz2_imu.launch.py

正常情况下，imu数据较为稳定，不会有大幅度偏移
效果如下：

请输入图片描述

查看imu数据

1.查看原始来自小车的imu数据

数据发布在话题/raw_imu

$ ros2 topic echo /raw_imu

---
linear_acceleration:
  x: 1.0346484375
  y: 0.15328125
  z: 9.8483203125
angular_velocity:
  x: -0.06799194713043478
  y: -0.015783844869565217
  z: -0.015783844869565217
magnetic_field:
  x: 2.392e-05
  y: 1.4259999999999999e-05
  z: -3.8731999999999994e-05
---

/raw_imu话题发布的频率

$ ros2 topic hz /raw_imu
average rate: 38.516
    min: 0.003s max: 0.048s std dev: 0.00812s window: 40
average rate: 38.716
    min: 0.002s max: 0.052s std dev: 0.00846s window: 79
average rate: 38.567
    min: 0.002s max: 0.052s std dev: 0.00872s window: 118

2.经过校准后的imu数据

经过校准后的imu数据，增加协方差数据，并采用ros2标准的imu格式
发布在话题/imu/data_raw

$ ros2 topic echo /imu/data_raw
---
header:
  stamp:
    sec: 1696812611
    nanosec: 337837340
  frame_id: imu_link
orientation:
  x: 0.0
  y: 0.0
  z: 0.0
  w: 1.0
orientation_covariance:
- 0.0025
- 0.0
- 0.0
- 0.0
- 0.0025
- 0.0
- 0.0
- 0.0
- 0.0025
angular_velocity:
  x: -0.0013962631999999836
  y: 0.015261763846956516
  z: -0.0006070709565217415
angular_velocity_covariance:
- 1.0e-06
- 0.0
- 0.0
- 0.0
- 1.0e-06
- 0.0
- 0.0
- 0.0
- 1.0e-06
linear_acceleration:
  x: 0.643722012270846
  y: 0.04275854132881131
  z: 9.834792257029461
linear_acceleration_covariance:
- 0.0001
- 0.0
- 0.0
- 0.0
- 0.0001
- 0.0
- 0.0
- 0.0
- 0.0001
---

/imu/data_raw发布的频率

$ ros2 topic hz /imu/data_raw
average rate: 38.959
    min: 0.001s max: 0.070s std dev: 0.01033s window: 41
average rate: 38.522
    min: 0.001s max: 0.070s std dev: 0.00933s window: 80
average rate: 38.698
    min: 0.001s max: 0.070s std dev: 0.00869s window: 120

磁力计作为单独的话题，发布到/imu/mag

ros2 topic echo /imu/mag
---
header:
  stamp:
    sec: 1696812818
    nanosec: 501811546
  frame_id: imu_link
magnetic_field:
  x: 2.3736000000000004e-05
  y: 1.38e-05
  z: -3.900800000000001e-05
magnetic_field_covariance:
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
---

/imu/mag的发布频率

$ ros2 topic hz /imu/mag
average rate: 39.433
    min: 0.000s max: 0.293s std dev: 0.04919s window: 41
average rate: 38.778
    min: 0.000s max: 0.293s std dev: 0.03534s window: 80
average rate: 38.935
    min: 0.000s max: 0.293s std dev: 0.02892s window: 120
average rate: 38.807
    min: 0.000s max: 0.293s std dev: 0.02534s window: 159

3. 经过filter_madgwick进行滤波处理的imu数据

经过滤波处理的imu数据，增加四元数方向值
发布到话题/imu/data

$ ros2 topic echo /imu/data
---
header:
  stamp:
    sec: 1696813140
    nanosec: 65980297
  frame_id: imu_link
orientation:
  x: 0.02092601523280476
  y: -0.02469429004034984
  z: 0.5144051904860141
  w: 0.8569361667749394
orientation_covariance:
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
- 0.0
angular_velocity:
  x: -0.0013962631999999836
  y: 0.012833480020869559
  z: -0.003035354782608699
angular_velocity_covariance:
- 1.0e-06
- 0.0
- 0.0
- 0.0
- 1.0e-06
- 0.0
- 0.0
- 0.0
- 1.0e-06
linear_acceleration:
  x: 0.644725909157287
  y: 0.12006491677865708
  z: 9.795341470850872
linear_acceleration_covariance:
- 0.0001
- 0.0
- 0.0
- 0.0
- 0.0001
- 0.0
- 0.0
- 0.0
- 0.0001
---

/imu/data发布频率

$ ros2 topic hz  /imu/data
average rate: 36.923
    min: 0.013s max: 0.071s std dev: 0.00972s window: 39
average rate: 38.779
    min: 0.001s max: 0.091s std dev: 0.01634s window: 80
average rate: 38.446
    min: 0.001s max: 0.091s std dev: 0.01565s window: 119

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