Motion control originated from early servo control. Simply put, motion control is the real-time control and management of the position, speed, and other parameters of moving mechanical parts, ensuring they move according to a predetermined trajectory and specified motion parameters. Early motion control technology developed alongside CNC technology, robotics, and factory automation. Early motion controllers were essentially independent, dedicated controllers, often requiring no additional processor or operating system. They could independently perform motion control functions, other functions required by technological processes, and human-machine interaction. These controllers can function as independent motion controllers. These controllers are primarily designed for specialized CNC machinery and other automated equipment, often with functions pre-designed according to the application industry's process requirements. Users only need to write application processing code files according to the protocol requirements and transmit them to the controller via RS232 or DNC, and the controller can then complete the relevant actions. These controllers often cannot be used across industries without adhering to their specific process requirements; their openness depends solely on the controller's processing code protocol, and users cannot reconfigure their motion control systems according to application requirements.
Motion control
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 and/or speed of machines. The application of motion control in robotics and CNC machine tools is more complex than in specialized machines, where the motion is simpler; this is often referred to as general-purpose motion control (GMC). Motion control is widely used in the packaging, printing, textile, and assembly industries.
Basic architecture of motion control system
A motion controller is used to generate trajectory points (desired output) and close a position feedback loop. Many controllers can also internally close a velocity loop.
A driver or amplifier is used to convert control signals (typically speed or torque signals) from a motion controller into higher-power current or voltage signals. More advanced intelligent drives can close their own position and speed loops for more precise control.
An actuator, such as a hydraulic pump, cylinder, linear actuator, or motor, is used to output motion.
A feedback sensor, such as a photoelectric encoder, a rotary transformer, or a Hall effect device, is used to feed back the position of the actuator to the position controller in order to achieve the closure of the position control loop.
Numerous mechanical components are used to convert the motion of an actuator into the desired motion; these include gearboxes, shafts, ball screws, toothed belts, couplings, and linear and rotary bearings.
In terms of motion control, the control trajectories required for several movements
(1) Point-to-point motion: The use of a single axis, through the instruction set of the motion control card, controls the single axis to move from point A to point B, so it is also called point-to-point motion.
(2) Interpolation: Interpolation can generally be divided into linear interpolation and circular interpolation. Linear interpolation can usually be composed of two or more axes, while circular interpolation is composed of two axes, forming a multi-dimensional or two-dimensional motion trajectory. Interpolation is usually used for motion control of continuous trajectories, such as carving or shoe molds. The analysis of interpolation determines the control accuracy of the trajectory motion.
(3) Spiral motion: It is composed of two-dimensional circular motion and linear motion of vertical axis, and is mostly used in machine tool applications.
(4) Simultaneous movement or simultaneous stop of multiple axes: control two or more motion axes to move simultaneously or stop simultaneously.
(5) Synchronous motion control: Through the absolute synchronization of the motion control card, the motion of multiple axes can be accurately controlled according to a certain time sequence. It is also possible to make the axes move according to their mutual relationship by setting conditions. Usually, this type of control can only be achieved by using a serial motion controller. Since the serial controller and the motor driver have a specific communication protocol, they can achieve absolute motion control based on the operating clock.
