Currently, the most widely used robots on the market are industrial robots, which are also the most mature and sophisticated. Industrial robots have a wide range of applications because they employ various control methods, thus offering broad application prospects.
Industrial robots can employ various control methods depending on the task. Currently, industrial robots are mainly divided into four control modes: point control mode, continuous trajectory control mode, force (torque) control mode, and intelligent control mode.
1. Point-to-Point (PTP) Control Method
This control method only controls the pose of the industrial robot's end effector at certain specific discrete points in the workspace. In this control, the industrial robot is only required to move quickly and accurately between adjacent points, without any adjustment to the trajectory of the target point.
Positioning accuracy and motion time are the two main technical indicators of this control method. This control method is characterized by its simplicity of implementation but low positioning accuracy. Therefore, it is commonly used for loading, unloading, handling, spot welding, and component insertion on circuit boards, requiring only the accurate position and orientation of the end effector at the target point. While relatively simple, this method struggles to achieve a positioning accuracy of 2-3 μm.
2. Continuous trajectory control (CP) mode
This control method continuously controls the position and orientation of the end effector of an industrial robot within the workspace, requiring it to move strictly according to a predetermined trajectory and speed within a certain precision range. The speed must be controllable, the trajectory smooth, and the movement stable to complete the mission. The joints of the industrial robot move continuously and synchronously, forming a continuous trajectory for the end effector. The main technical indicators of this control method are the trajectory tracking accuracy and stability of the end effector. This control method is commonly used in welding, painting, deburring, and inspection robots.
3. Force (torque) control method
When assembling and fixing objects, in addition to precise positioning, the applied force or torque must be appropriate. In this case, (torque) servo mode must be used. The principle of this control method is basically the same as that of position servo control, except that the input and feedback are not position signals, but force (torque) signals. Therefore, the system must have a powerful (torque) sensor. Sometimes, adaptive control is achieved by utilizing the sensor's approximation and sliding functions.
4. Intelligent control method
Intelligent control of robots involves acquiring knowledge of their surroundings through sensors and making corresponding decisions based on their internal knowledge base. Intelligent control technology endows robots with strong environmental adaptability and self-learning capabilities. The development of intelligent control technology relies on the rapid advancements in artificial neural networks, genetic algorithms, and expert systems in recent years. Perhaps this control mode truly gives industrial robots a "human-made" feel, but it is also the most difficult to control well. Besides algorithms, it also heavily depends on the precision of components.
