1. Point-to-Point (PTP) Control Method
Point-to-point control systems are actually a type of position servo system. Their basic structure and composition are basically the same, but their focuses are different, and their control complexity also varies.
A point-to-point control system generally includes a final mechanical actuator, a mechanical transmission mechanism, a power component, a controller, a position measuring device, etc. The mechanical actuator is the action component that ultimately completes the functional requirements, such as the manipulator of a welding robot or the worktable of a CNC machining tool. In a broader sense, the actuator also includes motion support components such as guide rails, which also play a key role in positioning accuracy.
This control method only controls the pose of the industrial robot's end effector at certain specified discrete points in the workspace. During control, only the robot's ability to move quickly and accurately between adjacent points is required; the trajectory to reach the target point is not specified. Positioning accuracy and the time required for movement are the two main technical indicators of this control method. This 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 component placement on circuit boards—where only accurate end effector pose at the target point is required. While this method is relatively simple, achieving a positioning accuracy of 2–3 μm is quite difficult.
2. Continuous trajectory control (CP) mode
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, and with controllable speed, smooth trajectory, and stable movement to complete the task.
Trajectory accuracy and motion stability are the two most important indicators.
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.
3. Force (torque) control method
When robots perform tasks involving forces from their environment, such as grinding or assembly, simple position control can result in excessive forces due to positional errors, potentially damaging parts or the robot itself. In such restrictive environments, robots often require force control in conjunction with positional control, necessitating the use of a torque servo system.
The principle of this control method is basically the same as that of position servo control, except that the input and feedback signals are not position signals, but force (torque) signals, so a force (torque) sensor must be present in this system. Sometimes, proximity, sliding, and other sensing functions are also used for adaptive control.
4. 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 gives robots 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 truly brings "artificial intelligence" to the industrial robot market; however, it is also the most difficult to control well, heavily dependent on the precision of components in addition to algorithms.
