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@Dorebom(dorebom b)

IMUセンサのROS2ノードを作成

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今回は，ROS2でIMUセンサを使いたいと思い，WitMotionのBWT901CLをセンサノードにする．

はじめに

環境

今回の環境は以下の通り．

  • Ubuntu:20.04 on Docker
  • ROS2:Foxy
  • IMUセンサ:BWT901CL(WitMotion)
  • 既にROS2をインストールし，チュートリアルを動かしている

先人の知恵

この記事を記載している現在，公式からはPythonコードを提供していなかったので作る．ただし，既にPythonコードを書かれている方がいたので感謝しながら使わせてもらう．

参考にしたコードには2点の問題点があった．

  1. ROS2ノードがスリープしたときのUARTの同期が崩れる対策がされていない
  2. UART通信で受け取った2Byteバイナリデータを変換するときに，符号付きのオプションがなかったため，正しい値が読み込めない．

これら2点の問題に対策したコードを作った．

今回のコード

仕事の終わりのスキマ時間で作ったので，テキトーな点は目をつぶってほしい．

コードの解説

センサノードを作る目的のほかに，ROS2パッケージとノードとメッセージの3点を作る勉強も兼ねている．

ファイル構成

ros2_ws
 └ src
    └ bwt901cl_pkg
       ├ src
       │  ├ __init__.py
       │  └ bwt901cl.py
       ├ __init__.py
       ├ imu_bwt901cl.py
       ├ test
       ├ resource
       ├  └ bwt901cl_pkg
       ├ package.xml
       ├ setup.cfg
       └ setup.py

ここで，UART通信を行うPythonモジュールはbwt901cl.pyであり，ROS2のPublisherノードはimu_bwt901cl.pyである．

UART通信を行うPythonモジュール

bwt901cl.py
from serial import Serial
from time import sleep

class BWT901CL(Serial):
    def __init__(self, Port):
        self.myserial = super().__init__(Port, baudrate = 115200, timeout = 1)

        self.angular_velocity_x = 0.0
        self.angular_velocity_y = 0.0
        self.angular_velocity_z = 0.0
        self.angle_x = 0.0
        self.angle_y = 0.0
        self.angle_z = 0.0
        self.accel_x = 0.0
        self.accel_y = 0.0
        self.accel_z = 0.0
        self.Temp = 0.0
        self.magnetic_x = 0.0
        self.magnetic_y = 0.0
        self.magnetic_z = 0.0
        self.quaternion_x = 0.0
        self.quaternion_y = 0.0
        self.quaternion_z = 0.0
        self.quaternion_w = 1.0
        self.YY = 0
        self.MM = 0
        self.DD = 0
        self.hh = 0
        self.mm = 0
        self.ss = 0
        self.ms = 0
        self.D0 = 0
        self.D1 = 0
        self.D2 = 0
        self.D3 = 0

        while True:
            data = super(BWT901CL, self).read(size=1)
            if data == b'\x55':  # UARTのスタートBITを探索
                data = super(BWT901CL, self).read(size=10)
                print("success!")
                print(bytes(data))
                break
            print("trying", data)
        #print(super(BWT901CL, self).isOpen())
        self._readData()

    def _readData(self):
        try:
            for i in range(6):
                data = super(BWT901CL, self).read(size=11)

                if not len(data) == 11:
                    print('byte error:', len(data))
                    break
                if not data[0] == 0x55: # スタートBITに異常がある場合読み込み中止
                    print('UART sync error:', bytes(data))
                    break
               #Time
                if data[1] == 0x50:
                    self.YY = data[2]
                    self.MM = data[3]
                    self.DD = data[4]
                    self.hh = data[5]
                    self.mm = data[6]
                    self.ss = data[7]
                    self.ms = int.from_bytes(data[8:10], byteorder='little')

                #Acceleration
                elif data[1] == 0x51:
                    # signed=Trueオプションを忘れると，符号なしで認識されてバグることがある．
                    self.accel_x = int.from_bytes(data[2:4], byteorder='little', signed=True)/32768.0*16.0*9.8
                    self.accel_y = int.from_bytes(data[4:6], byteorder='little', signed=True)/32768.0*16.0*9.8
                    self.accel_z = int.from_bytes(data[6:8], byteorder='little', signed=True)/32768.0*16.0*9.8
                    self.Temp = int.from_bytes(data[8:10], byteorder='little', signed=True)/340.0+36.25

                #Angular velocity
                elif data[1] == 0x52:
                    self.angular_velocity_x = int.from_bytes(data[2:4], byteorder='little', signed=True)/32768*2000.0
                    self.angular_velocity_y = int.from_bytes(data[4:6], byteorder='little', signed=True)/32768*2000.0
                    self.angular_velocity_z = int.from_bytes(data[6:8], byteorder='little', signed=True)/32768*2000.0
                    self.Temp = int.from_bytes(data[8:10], byteorder='little')/340.0+36.25

                #Angle
                elif data[1] == 0x53:
                    self.angle_x = int.from_bytes(data[2:4], byteorder='little', signed=True)/32768*180
                    self.angle_y = int.from_bytes(data[4:6], byteorder='little', signed=True)/32768*180
                    self.angle_z = int.from_bytes(data[6:8], byteorder='little', signed=True)/32768*180

                #Magnetic
                elif data[1] == 0x54:
                    self.magnetic_x = int.from_bytes(data[2:4], byteorder='little', signed=True)
                    self.magnetic_y = int.from_bytes(data[4:6], byteorder='little', signed=True)
                    self.magnetic_z = int.from_bytes(data[6:8], byteorder='little', signed=True)

                #Quatrernion
                elif data[1] == 0x59:
                    self.quaternion_x = int.from_bytes(data[2:4], byteorder='little', signed=True)/32768
                    self.quaternion_y = int.from_bytes(data[4:6], byteorder='little', signed=True)/32768
                    self.quaternion_z = int.from_bytes(data[6:8], byteorder='little', signed=True)/32768
                    self.quaternion_w = int.from_bytes(data[8:10], byteorder='little', signed=True)/32768

                #Data output port status
                elif data[1] == 0x55:
                    self.D0 = int.from_bytes(data[2:4], byteorder='little',signed=True)
                    self.D1 = int.from_bytes(data[4:6], byteorder='little',signed=True)
                    self.D2 = int.from_bytes(data[6:8], byteorder='little',signed=True)
                    self.D3 = int.from_bytes(data[8:10], byteorder='little',signed=True)

        except KeyboardInterrupt:
            super(BWT901CL, self).close()

    def getAngle(self):
        self._readData()
        return (self.angle_x, self.angle_y, self.angle_z)

    def getAnglurVelocity(self):
        self._readData()
        return (self.angular_velocity_x, self.angular_velocity_y, self.angular_velocity_z)

    def getAccel(self):
        self._readData()
        return (self.accel_x, self.accel_y, self.accel_z)

    def getTemperature(self):
        return self.Temp

    def getData(self):
        super(BWT901CL, self).reset_input_buffer()
        is_not_sync = True
        while is_not_sync:
            data = super(BWT901CL, self).read(size=1)
            if data == b'\x55': # UARTの同期エラーをリカバリ
                data = super(BWT901CL, self).read(size=10)
                is_not_sync = False
                break

        self._readData()
        return  (self.angle_x, self.angle_y, self.angle_z), \
                (self.angular_velocity_x, self.angular_velocity_y, self.angular_velocity_z), \
                (self.accel_x, self.accel_y, self.accel_z), \
                self.Temp, \
                (self.magnetic_x, self.magnetic_y, self.magnetic_z), \
                (self.quaternion_x, self.quaternion_y, self.quaternion_z, self.quaternion_w), \
                (self.MM, self.DD, self.hh, self.mm, self.ss, self.ms)

if __name__ == "__main__":

    jy_sensor =  BWT901CL("/dev/ttyUSB0")
    #sleep(1)
    #jy_sensor.wake_up()
    while True:
        #print('Angle: ', jy_sensor.getAngle())
        #print('Anglular velocity: ', jy_sensor.getAnglurVelocity())
        sleep(0.5)
        jy_sensor.getData()

ROS2のPublisherノード

ノードの構成

以下に示すノード1つだけを作った．

  1. imu_bwt901cl

メッセージの構成

公式の共通メッセージのGithubを参考に，センサのメッセージを4つ作った．

  1. /sensor/bwt901cl/Imu(Imu)
  2. /sensor/bwt901cl/MagneticField(MagneticField)
  3. /sensor/bwt901cl/Temperature(Temperature)
  4. /sensor/bwt901cl/Angle(Vector3)

書いたコード

imu_bwt901cl.py

import rclpy
from rclpy.node import Node
from sensor_msgs.msg import Imu, Temperature, MagneticField
from geometry_msgs.msg import Vector3
import subprocess

from .src.bwt901cl import BWT901CL

class Imu901cl(Node):
    def __init__(self, time_interval=1.0):
        super().__init__('imu_bwt901cl')
        self.pub_imu = self.create_publisher(Imu, '/sensor/bwt901cl/Imu', 10)
        self.pub_mag = self.create_publisher(MagneticField, '/sensor/bwt901cl/MagneticField', 10)
        self.pub_tmp = self.create_publisher(Temperature, '/sensor/bwt901cl/Temperature', 10)
        self.pub_ang = self.create_publisher(Vector3, '/sensor/bwt901cl/Angle', 10)
        self.tmr = self.create_timer(time_interval, self.timer_callback)
        subprocess.call("sudo chmod 777 /dev/ttyUSB0", shell=True)
        self.imu_sensor =  BWT901CL("/dev/ttyUSB0")

    def timer_callback(self):
        msg_imu = Imu()
        msg_mag = MagneticField()
        msg_tmp = Temperature()
        msg_ang = Vector3()

        angle, angular_velocity, accel, temp, magnetic, quaternion, time = self.imu_sensor.getData()

        msg_tmp.temperature = temp
        self.pub_tmp.publish(msg_tmp)

        msg_mag.magnetic_field.x = float(magnetic[0])
        msg_mag.magnetic_field.y = float(magnetic[1])
        msg_mag.magnetic_field.z = float(magnetic[2])
        self.pub_mag.publish(msg_mag)

        msg_imu.orientation.x = quaternion[0]
        msg_imu.orientation.y = quaternion[1]
        msg_imu.orientation.z = quaternion[2]
        msg_imu.orientation.w = quaternion[3]
        msg_imu.angular_velocity.x = angular_velocity[0]
        msg_imu.angular_velocity.y = angular_velocity[1]
        msg_imu.angular_velocity.z = angular_velocity[2]
        msg_imu.linear_acceleration.x = accel[0]
        msg_imu.linear_acceleration.y = accel[1]
        msg_imu.linear_acceleration.z = accel[2]
        self.pub_imu.publish(msg_imu)

        msg_ang.x = angle[0]
        msg_ang.y = angle[1]
        msg_ang.z = angle[2]
        self.pub_ang.publish(msg_ang)

        #print("Time:", time)
        #print("th:", angle)
        #print("d_th: ", angular_velocity)
        #print("d_x: ", accel)
        #print("mag: ", magnetic)
        #print("tmp: ", temp)
        #print(quaternion)

def main(args=None):    
    print('Hi from bwt901cl_pkg.')

    rclpy.init(args=args)
    node_imu_bwt901cl = Imu901cl(time_interval=0.1)
    rclpy.spin(node_imu_bwt901cl)

    node_imu_bwt901cl.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

自分で作成したPythonモジュールを登録

py_modules=[]を使って，作成したモジュールbwt901cl.pyを登録し忘れると，colcon build時にinstallフォルダにモジュールがコピーされず，正常に動作しない点に注意する．

setup.py
from setuptools import setup

package_name = 'bwt901cl_pkg'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='dorebom',
    maintainer_email='dorebom.b@gmail.com',
    description='Package for using sensor module BWT901CL',
    license='MIT License',
    tests_require=['pytest'],
    entry_points={
        'console_scripts': [
            'imu_bwt901cl = bwt901cl_pkg.imu_bwt901cl:main'
        ],
    },
    py_modules=["bwt901cl_pkg.src.bwt901cl"]
)

今後の課題

現在のコードは読み込みが一定周期ではない．また時間があるときに改善を行うつもりである．

参考にしたページ

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