Industrial robots are currently the most widely used and mature type of robot on the market. Their widespread application is due to the various control methods they offer. Based on different tasks, they can be mainly divided into four control methods: point-to-point control, continuous trajectory control, force (torque) control, and intelligent control. The key features of these control methods will be explained in detail below.
01. Point-to-Point (PTP) Control Method
This control method only controls the position w of the industrial robot's end effector at certain specified discrete points in the workspace . During control, it only requires the industrial robot to move quickly and accurately between adjacent points, without specifying the trajectory for reaching the target point.
Positioning accuracy and the time required for movement are the two main technical indicators of this control method. This control method is easy to implement and does not require high positioning accuracy; therefore, it is often used in operations such as loading and unloading, material handling, spot welding, and inserting components onto circuit boards—where only the accurate orientation of the end effector at the target point is required. This method is relatively simple, but achieving a positioning accuracy of 2–3 μm is quite difficult.
02. Continuous Trajectory Control (CP)
This control method continuously controls the position and posture of the end effector of the industrial robot in the work space, requiring it to move strictly according to a predetermined trajectory and speed within a certain precision range, with controllable speed, smooth trajectory, and stable movement to complete the task.
Industrial robots perform continuous and synchronous joint movements, allowing their end effectors to form continuous trajectories. The main technical indicators of this control method are the trajectory tracking accuracy and stability of the end effector's pose. This control method is commonly used in robots performing arc welding, painting, deburring, and inspection operations.
03. Force ( Torque ) Control Method
When performing tasks such as assembly and object handling, in addition to accurate positioning, the applied force or torque must be appropriate. This necessitates the use of a torque servo system. The principle of this control method is essentially the same as that of position servo control, except that the input and feedback signals are force (torque) signals instead of position signals. Therefore, a force (torque) sensor is required in this system. Sometimes, proximity and sliding sensors are also used for adaptive control.
04. Intelligent Control Method
Intelligent control of robots involves acquiring knowledge of the surrounding environment through sensors and making corresponding decisions based on their internal knowledge base. Employing intelligent control technology enables robots to possess strong environmental adaptability and self-learning capabilities.
The development of intelligent control technology relies on the rapid advancements in artificial intelligence in recent years, including artificial neural networks, gene algorithms, genetic algorithms, and expert systems. Perhaps this control method is what truly brings " artificial intelligence " to industrial robots , but it is also the most difficult to control well, heavily dependent on the precision of components in addition to algorithms.
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