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How the capabilities of Motion Controllers enable greater flexibility compared to PLCs

POSTED 10/10/2023  | By: Greg Dieck, Product Manager - Motion

What sets pure play motion controllers apart from other controller types, such as PLCs

PLCs are designed to control large quantities of I/O and are used for synchronizing automation flow. PLCs are also quite adept at interfacing with vision systems, RFID systems as well as SCADA/MES applications, and IIOT requirements. While PLC’s can typically handle motion, if motion becomes the main focus of the application instead of simply a portion of it, we start to look at motion controllers.

Motion controllers are usually designed with more advanced motion features such as multi-axis synchronization, advanced tuning capabilities, high bandwidth servo loop closures, and a huge toolkit for shaping trajectories and motion profiles according to the exact requirements of a given application. Typically, a motion controller is more capable of interfacing with a broad range of motors, feedback devices, communication protocols, and user software interfaces. Motion controllers are used more for OEM’s that produce a product with motion inside and are used in applications where GCODE/CAD/CAM interface is necessary.

A wide variety of applications can be solved by utilizing either a motion controller or a PLC. As time goes on and key players in the automation market develop products to align with customer demands, the gray area between PLC and motion controllers only grows larger. The key distinguishing factor between most PLCs and motion controller applications is the amount of I/O the user will be interfacing with.  

Benefits of using a designated motion controller versus a PLC

The benefits of a PLC are typically the familiarity of the programming environment and ease of use when connecting to other peripheral equipment, such as safety or IO. This makes it relatively simple to commission a PLC, given the understanding of ladder logic or other PLC programming languages. If the customer has engineers who are exclusively ladder programmers, PLC’s hold a large benefit in a given application due to the comfort level of the programmer.

A key benefit to using a PLC is typically the user interface software – most PLC commissioning software utilizes a live highlighted diagram of what is currently executing in the program – a helpful diagnosis tool during development. Most motion controllers do not have this live view functionality, so other methods such as watch windows and tracking variables are utilized. However, PLC motion control is typically more limited in the pre-built function blocks, and managing any custom needs can get tricky. PLC’s are typically more rigid in their input, motor, and feedback capabilities – while motion controllers allow for a wide variety of application requirements.

Motion controllers are typically programmed in text-based programming languages that appear similar to basic, or C. Most motion controller manufacturers have developed their own language objects and time must be taken to read the software reference manual or utilize sample code to learn the language syntax. Once understood, however – motion controller programming is powerful and significantly more flexible than a given PLC. In most cases, motion controllers are dedicated to motion control and have features geared specifically for motion that PLCs do not have.

Some motion controllers allow for advanced users to create their own servo and kinematic algorithms, while you can solve kinematics in PLC code, it will execute at the PLC cycle time, which is typically much slower than we can execute in the motion controller with dedicated tasks.

When to integrate a motion controller in place of, or alongside, a PLC

When motion control is the critical or even central part of their process, such as with shape cutting or many lasers applications. As well as when flexible architectures are necessary to interface with – such as an application where a wide variety of motors, drives, feedback devices, and peripherals are involved – motion controllers are the first choice.

Other cases when using motion controls in place of a PLC is ideal is when multi-axis synchronization is necessary – above something simple like conveyor tracking or part feeder indexing. For example, in applications in life sciences for medical devices, machining systems such as EDM, waterjet, CNC – where we require motion to be fully controlled throughout the trajectory – we lean towards motion controllers. Motion controllers are also typically more cost effective for the same quantity of axis control as PLC’s.

There are also many cases where users inject a motion controller into a system with a PLC – or multiple PLC’s. In applications where a PLC is being utilized to control a sequence of events, multiple machine synchronization for processes, or overhead communications between a SCADA/MES system, users often will utilize a motion controller for the actual machine functionality and motion. Then, send key information such as part counts, machine status, etc. to the PLC for overall factory communications.  The PLC also commonly feeds the motion controller recipe calls, start/stop commands, and high-level handshaking commands as well.

What is a cutting-edge motion controller capable of?

 A modern motion controller typically possesses the ability to set up a motor quickly, allowing for a wide variety of motor types, feedback types, and axis configurations. Most modern motion controllers also have powerful tuning engines built into their software, allowing for a given system to be analyzed, tuned, and characterized effectively. There is a vast adoption of the EtherCAT fieldbus, so most modern motion controllers strive to optimize their EtherCAT integrations and troubleshooting toolkits. As the industry shifts towards data collection for adaptive and predictive maintenance, the ability to utilize TCP communications while maintaining secure connections has also become more important. Features like high-speed position capture or compare, compensation tables, the ability to do multiple move modes such as PVT and Spline.

With ongoing advancements in sensor technology, machine learning algorithms, and user interface design, these controllers continue to push the boundaries of what is possible in the realm of human-computer interaction.

Summary
We’ve explored the distinctions, benefits, and capabilities of pure play motion controllers in the context of today's automation landscape. We've highlighted how motion controllers excel in advanced motion features, multi-axis synchronization, and tuning flexibility, making them the preferred choice when motion control is central to a process.

While PLCs offer familiarity with programming and user interface software, motion controllers offer unparalleled flexibility and customization. We've discussed when it's ideal to integrate a motion controller alongside a PLC, emphasizing scenarios that demand multi-axis synchronization and precise control throughout a trajectory.

Finally, we've touched upon the cutting-edge capabilities of modern motion controllers, including their adaptability to various motor types, EtherCAT integration, and support for data-driven predictive maintenance. As the automation industry continues to evolve, these controllers will play a pivotal role in pushing the boundaries of human-computer interaction, embracing advancements in sensor technology, machine learning algorithms, and user interface design.