Introduction
Recently, many PLC developers have been asking questions about motion control cards and motion controllers. Many people are unclear about the differences and connections between them. Today, I would like to share with you the differences between PLCs, motion control cards, and motion controllers, as well as how to select the right one.
Background
With the advancement of industrial technology, industrial robots are being applied more widely. PLCs are no longer merely simple programmable logic controllers. Various manufacturers have introduced their own motion control-type PLCs to achieve certain motion control functions. At the same time, motion control cards and motion controllers are also developing rapidly.
For an electrical engineer, if our project involves motion-related control, we must first select the appropriate motor. If high precision is required, we generally choose a servo motor; otherwise, we can use a stepper motor for motion control. However, whether it is a stepper motor or a servo motor, it is typically paired with its corresponding driver. The subsequent question is: How can we control stepper (servo) motors using stepper (servo) drivers?
Solutions
Generally, we have the following options:
1. Use a PLC for control. Most PLCs on the market support motion control, with most capable of expanding up to 32 axes. Depending on the driver type, control methods can include pulse control, bus control, or analog control.
2. Use a motion control card for control. A motion control card is a specialized controller designed for motion control, capable of controlling up to 256 axes. Motion control cards require PC programming.
3. Use a motion controller for control. The key difference between a motion controller and a motion control card is that a motion controller can operate independently of a PC. After programming, the code can be downloaded directly to the controller to control the drive.
Selection
So, how should we make the selection? Let's first look at their differences and connections.
First, it is important to clarify that whether it is a PLC, motion controller, or motion control card, they are all essentially controllers responsible for controlling motion axes in an automation system, while also supporting input/output signal control. The main differences are as follows:
1. PLCs excel at logic I/O control, making it easy to implement complex logic control. For motion control, low-end PLCs typically use high-speed output points for pulse control, while mid-to-high-end PLCs generally use bus-based control, with common buses including Profinet, EtherCAT, and CC-Link.
2. Motion control cards are installed in the PC's host via a PCI slot, or connected to the PC host via Ethernet; development is performed using high-level programming languages such as C++, C#, VB, VB.NET, and LabVIEW; during programming, the control card API interface functions provided by the motion control card manufacturer are used to access control card resources; motion control cards are categorized into pulse-type and bus-type, with bus-type cards generally being slightly more expensive than pulse-type cards.
3. PLCs have advantages such as reliable operation and simple programming, but their motion control functions are relatively basic. In PLC applications, the main interface is PLC + HMI, which limits the visualization capabilities. Therefore, upper-level applications based on PLCs are becoming increasingly widespread;
4. Motion control cards can leverage the powerful functions of PCs, such as CAD functionality, machine vision functionality, and advanced software programming; they utilize FPGA+DSP/ARM+DSP chip functionality to achieve high-precision motion control (multi-axis linear and arc interpolation, motion tracking, PWM control, etc.).
5. The algorithms of motion controllers and motion control cards are almost identical. The main difference between them is that motion control cards rely on PC programming, while motion controllers can directly write and download programs, enabling offline operation.
6. With the widespread application of machine vision, motion control and machine vision have been well integrated. Compared to using motion control cards in vision projects, this approach can significantly reduce hardware costs.
In summary, PLCs are more focused on logic control and less on motion control, while motion control cards and motion controllers are more focused on motion control and less on logic control. Additionally, motion control cards and motion controllers have relatively higher technical barriers for developers. Therefore, users should select the appropriate solution based on their specific requirements.