What is motion control ? As an industrial control engineer, I often talk about motion control. So, in the field of industrial control and automation, what exactly does motion control refer to?
Motion control is mainly divided into two directions: one is motion control, which is usually used in the mechanical field; the other is process control, which is usually used in the chemical industry. Motion control refers to a type of system that originated from early servo systems, based on the control of electric motors, to control changes in physical quantities such as angular displacement, torque, and speed of an object.
Motor control and motion control
The definition above mentions motor control, but motor control and motion control are different.
In terms of focus, motor control (referring to servo motors) primarily focuses on controlling one or more parameters of a single motor, such as torque, speed, and position, to achieve given values. Motion control, on the other hand, focuses on coordinating multiple motors to complete specified motions (synthetic trajectories, synthetic velocities), emphasizing trajectory planning, velocity planning, and kinematic transformations; for example, in CNC machine tools, the XYZ axis motors need to be coordinated to complete interpolation movements.
Motor control is often used as a component of motion control systems (usually a current loop, operating in torque mode), focusing more on the control of the motor. It generally includes three control loops: position control, speed control, and torque control. It generally does not have planning capabilities (some drivers have simple position and speed planning capabilities).
Motion control is often applied to products and includes mechanical, software, and electrical modules, such as robots, drones, and motion platforms. It involves real-time control and management of the position and speed of mechanical moving parts, enabling them to move according to the expected trajectory and specified motion parameters.
There is some overlap between the two: the position loop/speed loop/torque loop can be implemented in the motor driver or in the motion controller, so the two are easily confused.
Basic architectural components
The basic architecture of a motion control system includes:
1. Motion controller: Used to generate trajectory points (desired output) and close the position feedback loop. Many controllers can also internally close a velocity loop.
Motion controllers are mainly divided into three categories: PC-based, dedicated controllers, and PLCs. PC-based motion controllers are widely used in industries such as electronics and EMS; dedicated controllers are represented by industries such as wind power, photovoltaics, robotics, and molding machinery; while PLCs are favored in industries such as rubber, automotive, and metallurgy.
2. Drive or amplifier: Used to convert control signals (usually speed or torque signals) from the motion controller into higher-power current or voltage signals. More advanced intelligent drives can close their own position and speed loops to achieve more precise control.
3. Actuators: such as hydraulic pumps, cylinders, linear actuators or motors, used to output motion.
4. Feedback sensors: such as photoelectric encoders, rotary transformers, or Hall effect devices, are used to provide feedback on the actuator's position to the position controller to achieve the closure of the position control loop. Numerous mechanical components are used to convert the actuator's motion into the desired motion; these include gearboxes, shafts, ball screws, toothed belts, couplings, and linear and rotary bearings.
