Many years ago, when I first entered the industry, I was asked about the difference between servo drives and frequency converters, which is similar to the question about the difference between PLCs and motion controllers. If you're discussing this just to pass an exam, then disregard what I said. But if it's about understanding the interesting aspects of these two products, then it's a worthwhile activity.
Both PLCs (Programmable Logic Controllers) and motion controllers are named according to their application. However, PLCs entered the market earlier, while motion controllers were named using the abbreviation MC for Motion Control, which sounded more sophisticated. In an era when hardware was expensive, PLCs were generally non-real-time systems, while motion controllers required real-time systems to ensure the effectiveness and dynamic performance of motion control. Therefore, PLCs typically had higher hardware costs and were more expensive. Under the ingrained belief that "expensive is better," motion controllers appeared more high-end than PLCs.
However, with the development of control chips for real-time control products, motion controllers are relatively easy to integrate with PLCs and other functionalities. Furthermore, as software platforms like CODESYS integrate the functions of CNC, MC, and PLC, the hardware designs of these control products are converging, with differences primarily residing in the software. This makes distinguishing between PLCs with motion control and motion controllers increasingly difficult, and more of a theoretical discussion. The actual user experience is already very similar; the main difference lies in the development level of the ecosystem. PLCs, generally promoted by industry leaders, are relatively closed systems. Motion controllers, on the other hand, often have more sophisticated, niche designs and require greater compatibility with other products.
The future of the PLC and motion control market will undoubtedly see a shift similar to the PC market, namely a separation of software and hardware. PLC and motion control functions will simply be different software package options, focusing on differentiated services and attracting a diverse range of companies, large and small. Meanwhile, the primary function of hardware platforms will be to provide cost-effective and reliable products, often monopolized by a few large enterprises. Therefore, discussions about the differences between PLCs and motion controllers will, like discussions about branded versus custom PCs, disappear as consumers become more sophisticated. In the future, we might see products like "Master Lu" evaluating your PLC and motion controller; let's set aside subjective perceptions and just play around with these benchmarking software programs.
Cao Haixiao | KEBA China
Motion controllers can be classified into simple and high-performance types. PLC architecture is suitable for simple applications, such as bus-type or pulse-type applications with low precision requirements and a limited number of axes; while high-performance motion controllers mainly meet the application requirements of multi-axis, high precision, high real-time response, and complex motion trajectories.
Future motion controllers will not only meet higher performance requirements for motion control, but will also be able to process image and visual signals, enabling advanced data analysis-based applications such as predictive maintenance and adaptive control. Furthermore, functions designed for digital twin applications can be implemented in high-performance, high-capacity motion controllers, satisfying the control, management, and optimization needs from single-machine setups to entire process control. Regarding motion controllers and motion control PLCs, the main difference lies in their target application scenarios. Generally, motion controllers from various manufacturers are positioned at a higher level than motion control PLCs. Motion controllers are designed from the outset for servo axis control, with key performance indicators including the number of controlled axes, scan time, bus type, and specific servo series. Motion control PLCs, on the other hand, prioritize PLC-related parameters, including I/O and communication expansion capabilities, before considering whether to use pulse or bus signals for axis control, resulting in a wider range of servo types. Functionally, current motion control PLCs are indeed not far behind motion controllers in terms of servo control capabilities. However, due to differences in their initial design goals, there are significant differences in the selection of control chips and bus scan times. This leads to differences in performance and price positioning. Therefore, when configuring a solution, users generally make selections based on machine performance requirements and acceptable price, taking several factors into consideration. On the other hand, not every user pursues the ultimate cost-effectiveness; often, "good enough" is sufficient. Factors such as brand influence, service, and the machine's industry positioning are also considered. These factors all contribute to differences in selection and configuration.
Of course, when comparing these two, we generally limit ourselves to the same brand. This is because only brands within the same brand differentiate their product lines during the design phase, targeting different users or applications. Comparing different brands is less meaningful, because while both may be able to implement the same functionality, the underlying soft power varies greatly and is subjective.
Qiao Zeng | Schneider Electric
With the rapid development of microprocessors, Industrial Ethernet, and the Internet of Things (IoT), there is no longer a significant performance difference at the application level between traditional motion controllers and PAC automation controllers with motion control capabilities. While dedicated motion controllers still have a place in some scenarios requiring extremely high synchronization performance, PACs or PCs with high-speed gigabit networks and high-performance processors are sufficient for most users' needs in a wide range of industrial servo applications. Furthermore, user demands for motion control extend beyond motion control performance itself. Easy-to-use integrated development environments, predictive servo maintenance, built-in machine learning, enhanced network security, and IoT-oriented design are all future directions for controller development. For example, Rockwell Automation's CompactLogix 5480 controller is a highly scalable edge computing platform for high-performance servo applications, helping users effectively improve equipment performance and production efficiency.
Liang Qi | Rockwell Automation
Motion controllers were originally developed to address the shortcomings of PLCs in motion control. However, with technological advancements, more and more controllers can simultaneously perform PLC functions (i.e., logic control) and motion control, blurring the lines between PLCs and dedicated motion controllers. Beckhoff controllers have consistently adhered to this technological philosophy—on a PC-based control platform, logic control, motion control, and other HMI and vision applications are all seamlessly integrated into the overall control platform.
Cai Minke | Beckhoff Automation
A motion control PLC is essentially a combination of a motion controller and a PLC, theoretically capable of replacing both a standalone PLC and a standalone motion controller. Because both physically share the same CPU and memory, instruction and data transmission between them are not limited by any hardware network, making the PLC's intervention in the motion process more flexible. The PLC can even send the target position to the motion controller every cycle, such as 1ms; or intervene logically or trigger PLC outputs at any stage of the target action's execution. Motion control PLCs, combined with EtherCAT networks and servo drives, can perform complex control of large systems with over 200 axes. Early motion control PLCs were geared towards large, high-end applications; however, with improvements in CPU and memory performance and price reductions, current motion control PLCs can cover small to medium-sized applications with up to 10 axes.
However, for applications with a small number of axes and simple movements, traditional motion controllers, due to their integrated multi-channel pulse and encoder interfaces, combined with servo drives using analog or high-speed pulse interfaces, make the entire system very economical, even with the addition of a PLC. Furthermore, if the motion controller integrates specialized process algorithms that are directly output to the integrated DO or AO points, its response speed may far exceed that of any PLC.
Therefore, in general, motion control PLCs and traditional motion controllers each have their own suitable application scenarios.
Chen Lijun | Beckhoff Automation
Motion controllers are a product of their time: traditional PLCs couldn't handle motion tasks, so motion controllers were developed using DSPs/CPLDs/FPGAs to assist PLCs in controlling the entire machine. Today, the hardware capabilities of main processors and real-time communication technologies have solved problems requiring "low-granularity" timing, such as electronic gear and cam synchronization, and interpolation algorithms. Combined with RTOS scheduling and the rich and flexible development tools supported by it (such as C/C++), motion control has become more economical and flexible. Furthermore, PLCopen's Part IV cooperative motion control allows for complete PLC-based implementation, making programming more standardized and regulated. Therefore, PC/PLC-based motion control has naturally become the trend.
However, for some highly demanding applications, such as many applications in the electronic semiconductor industry (e.g., core equipment like lithography machines), general motion control is still insufficient. This is not only a matter of motion control, but also involves measurement systems and intelligent algorithms, which are generally handled by highly specialized professionals – essentially making the motion controller a dedicated processor in the past. Therefore, motion control in areas like lithography and wafer fabrication is handled by extremely high-caliber specialized companies, and automation players in the general motion control field rarely get involved.
Therefore, motion control needs to be viewed holistically, including software capabilities (algorithm efficiency), measurement system accuracy and signal processing capabilities, hardware and software architecture, clocking mechanisms, and other aspects.
Song Huazhen | B&R Industrial Automation
The main difference between PLCs and motion controllers previously lay in their application scenarios. PLCs primarily focus on logic control, with axis control as a secondary function, and are categorized into large, medium, and small types based on their application emphasis. Small PLCs are mainly used for stand-alone machine control, while medium and large PLCs are primarily used for production line control. Motion controllers (such as Yaskawa Electric's MP3300) are mainly used to control moving axes, such as positioning, synchronization, and cam control. They also possess some logic processing capabilities, but if the equipment's operating process and logic are complex, a dedicated PLC is still required.
Liu Xiaonan | Yaskawa Electric
Generally speaking, the advantage of dual-CPU control with PLC and motion controller lies mainly in the decentralized control of automation applications, where each component performs its own function. PLC is mainly used for logic and network control, while motion controller is more specialized in motion control.
If the requirements for motion control applications are not high, users can indeed consider using a PLC with motion control capabilities as a unified system control platform for automated equipment from an overall cost perspective. However, in general, the motion control function of a PLC still has certain limitations. In some automation applications with relatively high requirements for motion control performance, a separate motion controller is still quite necessary.
Mitsubishi Electric Automation (China)
