class Follower:
def init(self):
self.bridge = cv_bridge.CvBridge()
self.image_sub = rospy.Subscriber("/usb_cam/image_raw", Image, self.image_callback)
self.cmd_vel_pub = rospy.Publisher("/cmd_vel", Twist, queue_size=1)
self.twist = Twist()
清晰的描述问题