Servo motors do not necessarily need to be used in conjunction with PLCs (Programmable Logic Controllers). The relationship between them is common and closely coordinated, but not the only or mandatory combination. Whether to use PLC depends on specific application requirements and the architecture of the control system.
Here is a clearer explanation:
The core components of the servo system are:
Servo motor: an actuator responsible for precise position, speed, or torque output.
Servo drive: This is an essential supporting equipment. The driver receives instructions from the "upper controller" (such as target position, speed, torque) and converts them into the precise current and voltage required by the motor. At the same time, the driver receives feedback signals from the motor encoder to achieve closed-loop control. Without a driver, the servo motor cannot function.
Upper controller: This is the "brain" that sends instructions to the servo drive. PLC is a very common choice for upper level controllers, but it is not the only option.
PLC as the upper controller:
Common scenarios: In the field of industrial automation, especially in complex equipment such as assembly lines, robotic arms, packaging machines, CNC machine tools (as auxiliary axis control), PLC is widely used as the core controller.
Function:
Perform overall logical control of the device (start, stop, safety interlock, sequence control, etc.).
Calculate the target position, speed, or torque that the servo motor needs to achieve based on the process flow or operator instructions.
Send motion commands to servo drives through pulse/direction signals (commonly used for stepper and simple servos) or communication buses (such as EtherCAT, CANopen, PROFINET, Modbus TCP/IP, etc., more advanced and flexible).
Receive feedback signals from drivers or encoders and monitor the motion status.
Advantages: High reliability, strong anti-interference ability, programming (ladder diagrams, structured text, etc.) friendly to electrical engineers, skilled in handling complex logic and sequential control, easy to integrate various sensors and other actuators (cylinders, frequency converters, etc.).
Alternative solutions for PLC (other upper level controllers):
Specialized motion controller/multi axis controller:
Focusing on high-precision, high-speed, and complex multi axis synchronous motion control (such as electronic cam and electronic gear).
The performance is usually superior to the motion control function of general PLCs.
They can work independently or collaborate with PLCs through communication buses (PLC processes logic, motion controller processes motion).
Single chip microcontroller/microcontroller:
Suitable for relatively simple, cost sensitive, and few axis applications (such as small instruments and simple automation devices).
Developers need to have strong embedded programming skills (such as C/C++).
The development cycle may be longer, and reliability design requires more consideration.
PC Based Controller:
Use industrial PC or embedded PC, paired with real-time operating system and motion control card (or directly control the driver through real-time Ethernet bus).
Provides extremely high computing power and flexibility, suitable for very complex algorithms, machine vision integration, big data processing, etc.
The cost, development complexity, and maintenance requirements are relatively high.
CNC system:
The core control system of CNC machine tools is essentially a highly specialized motion controller optimized for metal cutting and other processes. It directly controls the servo axis (spindle, feed axis) to complete the machining trajectory.
Robot controller:
Industrial robots have their own dedicated controllers, which integrate powerful multi axis servo control algorithms such as inverse kinematics and trajectory planning, directly driving the servo motors of each joint of the robot. PLC is usually used to send advanced commands such as startup and program selection to robot controllers, rather than directly controlling the servo of each joint.
Independent human-machine interface/operation panel:
For some very simple single axis servo applications (such as setting a fixed position), the driver may come with basic control functions or perform parameter settings and jog control through a matching small operation panel (HMI), without the need for additional PLC or complex controllers.
A servo motor must be paired with a servo driver to function.
The driver requires an 'upper controller' to send motion commands to it.
PLC is an extremely common, important, and practical choice in this "upper level controller" role, especially in industrial automation scenarios that require the combination of complex logic and motion control.
However, PLC is not the only option. Specialized motion controllers, microcontrollers, PC based systems, CNC systems, robot controllers, and even simple operation panels can serve as upper level controllers for servo drives based on the complexity, performance requirements, cost budget, and development resources of the application.
Therefore, servo motors are often used in conjunction with PLCs, but not necessarily. The key is to understand that servo systems require a structure of drivers and upper level command sources, and PLC is only one mainstream form of upper level command sources.