1. Base coordinate system

The base coordinate system is based on the robot mounting base

A rectangular coordinate system used to describe the motion of the robot body.

Any robot cannot be separated from the basic coordinate system, which is also the basic coordinate system necessary for the robot TCP to move in the three-dimensional space (facing the robot front and rear: X axis, left and right: Y axis, up and down: Z axis). The coordinate system follows the right-handed rule

2. Geodetic coordinate system

Geodetic coordinate system: Geodetic coordinate system is a rectangular coordinate system with the earth as the reference. 90% of the geodetic coordinate system is coincident with the base coordinate system, which will be used in multiple robots and robots with external axes. However, the geodetic coordinate system does not coincide with the base coordinate system in the following two cases:

(1) Robot flip.

As shown in Figure 3 below, the base coordinate of the inverted robot is opposite to the direction of the Z axis of the geodetic coordinate. The robot can reverse, but the earth cannot reverse.

Fig. 3 6-axis robot geodetic coordinate system

(2) Robot with external axis. As shown in Figure 4, the geodetic coordinate system is fixed, while the base coordinate system can move with the overall movement of the robot.

Figure 4 Geodetic coordinate system

3. Tool coordinate system

What is the tool coordinate system

Tool coordinate system: the coordinate system fixed on the tool (flange, tool installed on the flange)

Features: The relative center of the manipulator flange remains unchanged.

Tool coordinate system origin (TCP): the center point of manipulator motion.

Robot TCP refers to the tool working point installed by the robot.

Why to establish a tool coordinate system

The manipulator has a default tool coordinate system Tool 0: the position is in the center of the flange. However, in the actual movement of the manipulator, tools such as suction cups, welding guns and cylinders are often installed in the center of the flange. At this time, if the motion center of the manipulator is still in the center of the flange, it will cause great inconvenience. Therefore, it is necessary to teach the required tool coordinate system according to the actual situation.

Tool coordinate system: it takes the tool center point as the zero point, and the robot’s trajectory refers to the tool center point. It is no longer the robot wrist center point Tool0 (as shown in Figure 5), but the new tool center point (as shown in Figure 6).

For example, when welding, the tool we use is the welding gun, so we can transplant the tool coordinates to the vertices of the welding gun. The suction cup is used to suck the workpiece, so we can transplant the tool coordinates to the surface of the suction cup (as shown in Figure 7 below).

The tool coordinate system can be determined by the N (N ＞=4) point method: the robot TCP contacts a fixed point through N different postures, and obtains multiple sets of solutions. Through calculation, the corresponding positions of the current TCP (Tool Central Point) and the tool installation flange center point (tool0) are obtained. The direction of the coordinate system is consistent with tool0.

Fig. 8 Calibration of tool coordinate system

4. Workpiece coordinate system

Workpiece coordinate system: Workpiece coordinate system is a rectangular coordinate system based on the workpiece, which can be used to describe the coordinate system of TCP motion.

Fig. 9 Workpiece coordinate system

Making full use of the workpiece coordinate system can make our programming achieve twice the result with half the effort.

For example, when the robot processes workpiece 1, the trajectory programming has been completed, and there is another workpiece 2, the trajectory does not need to be programmed repeatedly, as long as the workpiece coordinate system 1 is changed to the workpiece coordinate system 2.

Fig. 10 Different workpiece coordinate systems

The workpiece coordinate system is used to determine the position and orientation of the workpiece, which is composed of the workpiece origin and coordinate orientation. The workpiece coordinate system can be determined by the three-point method: the line between point X1 and point X2 forms the X axis, the vertical line drawn through point Y1 to the X axis is the Y axis, and the direction of the Z axis is determined by the right-handed rule.

Fig. 11 Method for determining workpiece coordinate system

5. Joint coordinate system

Joint coordinate system is the coordinate system set in the robot joint. It is the absolute angle of each axis relative to its origin position.

Fig. 12 Robot joint coordinate system

6. User coordinate system

The user coordinate system is a rectangular coordinate system customized by the user for each workspace. It is used for teaching and executing the position register, and executing the position compensation instructions. When there is no definition, the geodetic coordinate system will replace the coordinate system.