Servo motors, as core power components in the field of industrial automation, are widely used in data centers, robotics, medical equipment, and many other fields due to their precise position, speed, and torque control capabilities. Their positioning methods, absolute positioning and relative positioning, each have unique characteristics and applicable scenarios.
Absolute positioning: a precise starting point
Absolute positioning relies on the motor controller accurately determining the motor's current position and then precisely moving it to a designated location using control signals. This process primarily depends on two key technologies: encoders and absolute displacement sensors.
Encoders, as key devices for motor position detection, convert the motor's rotational position into digital or analog pulse signals using devices such as photoelectric gratings, magnetic gratings, or Hall effect sensors, providing precise position information to the motor controller. The accuracy of this method is highly dependent on the type and resolution of the encoder, enabling very precise position detection. Therefore, encoders play a crucial role in applications requiring extremely high positioning accuracy, such as assembly robots on automated production lines.
Absolute displacement sensors offer a more direct method of position detection. They directly measure the displacement on the motor shaft and transmit the value to the motor controller. The advantage of this method is that it can read the motor's position information even when the motor is not rotating, which is highly advantageous in certain specialized applications. However, absolute displacement sensors are typically more expensive and may have limitations in high-speed motion applications.
The advantage of absolute positioning is that it can accurately determine the position of the motor without finding a reference point or repeated initialization. This is especially important in applications that require synchronous control of multiple servo motors, because the position information of each motor is accurate and consistent. However, absolute positioning also has some limitations, such as the potentially complex and time-consuming initialization process, and limitations imposed by the accuracy of encoders or sensors.
Relative positioning: Flexible and convenient displacement control
Relative positioning, on the other hand, involves adjusting the position based on the current location. It uses control signals to move a servo motor to a new position relative to the current location; this process can be achieved by specifying the movement distance or angle.
The advantage of relative positioning lies in its simplicity and flexibility. No complex initialization process is required; only corresponding displacement adjustments based on control signals are needed. This makes relative positioning widely used in applications that do not require absolute precision, such as the driving control of line-following robots. The line-following robot can adjust its position using relative positioning based on feedback signals from sensors ahead to maintain its position on a preset path.
Furthermore, relative positioning is also suitable for applications requiring periodic repetitive movements, such as reciprocating robotic arms on industrial assembly lines. Through relative positioning, the robotic arm can precisely complete back-and-forth movements to assemble workpieces.
However, relative positioning also has some limitations. Due to the lack of absolute position information, relative positioning can accumulate errors, requiring periodic position calibration. Furthermore, relative positioning is not suitable for applications requiring high-precision absolute position control, such as precise positioning and grasping in robot operations.
In summary, absolute positioning and relative positioning each have their advantages and applicable scenarios. When choosing a positioning method, a trade-off must be made based on the specific application requirements. For applications requiring high-precision absolute position control, such as assembly robots and synchronous control, absolute positioning is a better choice. However, for applications that do not require absolute precision and position confirmation, such as line-following robots and reciprocating motion, relative positioning is more suitable. In practical applications, absolute and relative positioning can also be combined to achieve more complex motion control requirements.
