Understanding the 6 coordinate systems of industrial robots can help you operate them better. These coordinate systems are used to confirm the position and orientation of the robot, or to establish benchmarks on other workpieces. The coordinate system of a robot includes the base coordinate system, DH coordinate system, joint coordinate system, world coordinate system, workbench coordinate system, and tool coordinate system. These coordinate systems are used to confirm the position and posture of the robot or to establish benchmarks on other workpieces.
1. Base coordinate system
The base coordinate system consists of the robot base point and coordinate orientation, and serves as the foundation for other coordinate systems of the robot. This coordinate system is aligned with the Cartesian coordinate system in mathematics.
2. DH coordinate system
The DH coordinate system is a modeling method proposed by Denavit and Hartenberg in 1955, mainly used for robot kinematics. This method is to establish a coordinate system on each connecting rod and achieve the transformation of coordinates on two connecting rods through homogeneous coordinate transformation. In a multi link series system, multiple uses of homogeneous coordinate transformation can establish the relationship between the initial and final coordinate systems, and each axis always rotates around the Z-axis of the coordinate system when moving.
3. Joint coordinate system
The joint coordinate system is set in the robot joints, and the degree of joint rotation is based on the origin of the joint coordinate system. The origin of the joint coordinate system is related to the numerical value of the motor encoder, and the system will record the encoder value of a state as the origin. In this state, the values of joint coordinates are all 0. The robot uses an absolute value encoder motor, which is powered by a battery when the power is off. After restarting, the system will read the absolute encoder value of the motor from memory to ensure that the origin is not lost.
4. World coordinate system
The direction of the world coordinate system is consistent with the direction of the robot base coordinate system. The data of coordinate system XYZ is the sum of the linkage parameters of each axis, used to represent which point in space the robot is located at. The specific values are obtained by adding the corresponding linkage parameters. The three UVW data are represented by Euler angles, with rotation directions of Rx, Ry, and Rz. The world coordinate system is the position of a robot in space, which is aligned with the direction of the base coordinate system, but more broadly describes the position of the robot in the entire workspace. It's like GPS, no matter where the robot is in the factory, it can accurately know where it is.
5. Workbench coordinate system
The workbench coordinate system is a world coordinate system artificially set for a certain work platform. In the world coordinate system, the robot moves the XYZ axis with reference to the base coordinate axis. When the working plane of the robot is not parallel to the base coordinate system, in order to facilitate debugging, we will establish the worktable coordinate system with the two edges of the worktable as reference axes. After establishing the coordinates of the workbench, the robot's reference point will move from the base coordinate system to the origin of the workbench coordinate system, and the direction of the coordinate system will be consistent with the base coordinate.
Setting method: Select a corner of the workbench, keep the posture and record Po, Px, and Py points in sequence, then click OK to modify. The direction of the workbench coordinates refers to the robot base coordinates to ensure that the Z-axis direction is not reversed. After the robot reaches Po, it switches to the workbench coordinate system, and the values of XYZ are 0.
6. Tool coordinates
The tool coordinate is the coordinate system of the robot end effector, which determines how the tool interacts with the workpiece. When a specific tool or fixture is installed at the end of the robot, the tool coordinate system will be adjusted accordingly to ensure accurate use of the tool. Normally, the attitude transformation reference of the end TCP (tool center point) is at the flange center point position of the robot. The U axis rotates around the X axis, the V axis rotates around the Y axis, and the W axis rotates around the Z axis. When the fixture is installed at the end, the reference of the tool needs to be transformed from the flange coordinate system to the end of the fixture. Generally, the 6-point method is used for calibration calculation. When switching to the calibrated tool coordinate system, the reference point for robot posture calculation is no longer the flange coordinate system, but the calibrated position.
By understanding these six coordinate systems, operators can more accurately control robots, whether on complex assembly lines or in laboratories that require precise operations. The coordinate system is the cornerstone of robot operation; mastering it is mastering the dance steps of dancing with robots. With the continuous advancement of technology, the principles and applications of these coordinate systems will become more deeply integrated into every corner of industrial production, becoming the key to improving production efficiency and quality.