Motion control (MC) is a branch of automation that uses devices commonly known as servo mechanisms, such as hydraulic pumps, linear actuators, or motors , to control the position or speed of a machine.
The application of motion control in robotics and CNC machine tools is more complex than its application in specialized machines, as the latter have simpler motion patterns and are often referred to as general motion control (GMC). Motion control is widely used in the packaging, printing, textile, and assembly industries.
Development of motion control
Traditional mechanical transmission systems (in the past)
Mechanical linear shaft system
PLC control
Hybrid mechanical systems (currently)
Mechanical linear shaft system
Distributed intelligent servo drive
PLC control
Key parameters of the controlled object in a control system:
• Torque: Output torque, response, torque disturbance
• Speed: Constant speed, adjustable speed, acceleration/deceleration
• Location: resolution, positioning accuracy, trajectory
Typical motion control system
Types of motors used for motion control
DC motor
• AC motor
• Stepper motor
• Linear motor
The characteristics of various motors will be described below:
1. DC motor
DC motors are excitation methods divided into permanent magnet and excitation methods. Their most significant characteristic is that n∝U, meaning the rotational speed is directly proportional to the voltage. The problems with DC motors are:
2. AC motor
Alternating current (AC) generates a rotating magnetic field within the motor, causing the rotor to rotate. The motor's speed is determined by the frequency of the AC current, and it is generally used in applications requiring constant speed operation.
Operating principle of AC motor
AC motor examples
AC motors are further divided into synchronous motors and induction (asynchronous) motors. Synchronous motors, according to their excitation method, are further divided into excitation type and permanent magnet type.
AC synchronous motor structural diagram
Rotor of an AC asynchronous motor
3. Stepper motor
• An electric motor that converts electrical pulses into angular displacement
• The torque is generated based on the magnetic reluctance effect between the stator and rotor.
Structural diagram
Operating principle diagram
Operating characteristics:
• Angular displacement corresponding to the number of input pulses
• It has a certain holding torque when at rest
4. Linear motor:
Features of linear motors:
Advantages: Direct thrust generation, high-speed operation, contactless operation, simple structure
Disadvantages: Relatively low efficiency and power factor, high cost.
Having introduced the principles and characteristics of motors in motion control systems, let's now discuss how to select a motor. The important factors to consider are as follows:
• Power and torque required by the load
• Mechanical characteristics of the load
• Other requirements, such as the range and accuracy of speed variation, torque variation and response.
• Work mode, such as continuous or intermittent
• Noise requirements
• Shape, installation method, dimensions, etc.
• Usage Environment
Mechanical characteristics of common electric motors
Main applications of electric motors:
Speed control: AC motors, DC motors, brushless DC motors
Positioning: Stepper motor, permanent magnet synchronous servo motor, linear motor
