std_msgs/msg/Header
# Standard metadata for higher-level stamped data types.
# This is generally used to communicate timestamped data
# in a particular coordinate frame.
# Two-integer timestamp that is expressed as seconds and nanoseconds.
#stamp--时间戳，两个成员：秒和纳秒
builtin_interfaces/Time stamp
int32 sec
uint32 nanosec
# Transform frame with which this data is associated.
#
string frame_id作用：
sensor/msg/JointState
# This is a message that holds data to describe the state of a set of torque controlled joints.
#
# The state of each joint (revolute or prismatic) is defined by:
# * the position of the joint (rad or m),
# * the velocity of the joint (rad/s or m/s) and
# * the effort that is applied in the joint (Nm or N).
#
# Each joint is uniquely identified by its name
# The header specifies the time at which the joint states were recorded. All the joint states
# in one message have to be recorded at the same time.
#
# This message consists of a multiple arrays, one for each part of the joint state.
# The goal is to make each of the fields optional. When e.g. your joints have no
# effort associated with them, you can leave the effort array empty.
#
# All arrays in this message should have the same size, or be empty.
# This is the only way to uniquely associate the joint name with the correct
# states.
std_msgs/Header header
builtin_interfaces/Time stamp
int32 sec
uint32 nanosec
string frame_id
string[] name
float64[] position
float64[] velocity
float64[] effort- `string[] name`：机器人关节的名称，为一个字符串数组；
- `float64[] position`：机器人关节的位置，为一个双精度浮点数数组；
- `float64[] velocity`：机器人关节的速度，为一个双精度浮点数数组；
- `float64[] effort`：机器人关节的力/扭矩，为一个双精度浮点数数组。