Taking Stock of Modern Motion Control

Thanks to hype in the popular media, the term “automation” tends to conjure images of robots, artificial intelligence and the cloud in the minds of most people. The root of most manufacturing automation, however, remains old fashion motion-control technologies: a motor and a gear, ballscrew or some other sort of simple actuator. So, in this age of digitalization and the Internet of Things, it’s important to not overlook these root motion-control technologies.

To better gauge the state of today’s motion control tech, we spoke with Joe Scoccimaro, a product engineer at AutomationDirect; Matt Prellwitz, drive-technology product manager at Beckhoff Automation USA; and James Coleman, an applications engineer at Kollmorgen, a Regal Rexnord brand.

AW: How do today’s common motion control systems work and what are the key components involved?

Scoccimaro: A motion control system performs a defined physical movement using a drive and motor. Key components are a motion controller, drives, motors and cabling. The motors and drives could be stepper or servo, and the controller could be a dedicated motion controller, a PLC [programmable logic controller] capable of motion, or a motion controller integrated into a drive.

Among the many ways to design the architecture for a motion control system, one option is to use a motion-optimized PLC like AutomationDirect’s LS Electric XGB. This PLC combines automation control and data connectivity with multi-axis servo motion control over EtherCAT. Source: AutomationDirect

Coleman: The motion controller interfaces with the drive via I/O or digital communication and tells the drive what to do. The drive powers the motor and controls its torque, velocity or position, so that the system can produce the desired motion. The motion profile command can be generated in the motion controller or in the drive itself. Another common component tends to be some form of interface for a machine operator.

The motion controller receives input signals from such sources such as sensors, a vision system, a barcode reader, a higher-level computer program or a human operator. Based on the received signals, the motion controller’s program makes decisions about how to control the motion. Feedback sensors and encoders provide motion feedback to the drive or motion controller, so it can adjust the commanded motion as needed in real time.

Prellwitz: We do fieldbus-based drives in which we control every aspect of the motion control component through our software. A practice that has evolved over time is to integrate the motor and the drives together in a motor-drive combination. You still have a power connection going to the back of the motors and the fieldbus network going to the motor as well.

Joe Scoccimaro, product engineer, AutomationDirect.

AW: How do motion control systems integrate with other automation technologies commonly used in manufacturing?

Coleman: As only one part of a larger system, the motion control system must be able to work or communicate with other devices and systems. Where discrete inputs and outputs were traditionally used for handshaking between devices, it is now much more common for devices to communicate digitally on a machine network, a fieldbus.

Scoccimaro: Typically, the motion controller will have the capability to use communication protocols such as EtherCAT, EtherNet/IP, and Modbus TCP. This allows the controller to communicate with PLCs, HMIs (human-machine interfaces), pneumatics, I/O and other hosts.

Prellwitz: You can integrate predictive maintenance technology into the motor’s feedback. Fieldbus connectivity into the drive can give us diagnostics as the drive is being stressed and to receive information from the motor. The windings will tell us what the temperature is, and the encoder will tell us what the encoder temperature is. Because we manufacture our own motors, we can integrate an accelerometer through the encoder feedback, so there is no additional wiring for that.

Beckhoff’s AX8000 multi-axis servo system includes an axis module with SiC semiconductors, instead of conventional IGBTs. The result is 55% more output for the same size axis module. Source: Beckhoff Automation

AW: What are the primary challenges manufacturers may face when implementing motion control systems, and how can these challenges be overcome?

Coleman: A common challenge is the integration and tuning of multiple components. Each component needs to work with at least one other and could be required to interface with many others. Using components from one manufacturer that are specifically designed to work as a system can save a lot of time and effort. But when that is not possible, using components that have been proven to play well with others—using standardized protocols—can speed up the process. Working with suppliers that have the expertise needed to support the component interaction is also critical.

Programming is another challenge, especially for a new machine design. All too often, programming is pushed to the final step of the development process. Programming, however, should be a starting point before the mechanical system is built. Not everything can be fine-tuned at this point, but getting a head start on programming the motion control can be a time saver.

Matt Prellwitz, drive-technology product manager, Beckhoff Automation USA.

AW: What safety considerations or regulations do manufacturers need to be aware of when using motion control systems in their facilities?

Coleman: Motion control systems can be quite dangerous and even deadly. So, manufacturers should follow all applicable laws and regulations related to machine safety as required by governing authorities and corporate guidelines. This may include UL, CE, NEC, IEC and TUV.

Scoccimaro: All devices should be certified by a third-party testing firm, like TUV or UL. Some applications may require safe limited speed functionality, which allows people to perform tasks safely around potentially hazardous motion, as this capability controls operation of the motor at a slow speed and is monitored.

Prellwitz: Generally, the most important safety consideration is having a safe torque-off mode for the motor. In a catastrophic incident, you need to remove all torque from the motor. So, safe torque-off mode is used in probably 95% of our applications.

James Coleman, applications engineer, Kollmorgen.

AW: How does the selection of motors and drives affect the performance and precision of a motion control system?

Prellwitz: Many users specify motors by the kilowatt or horsepower rating, but that only gives you the speed and a torque of the motor. The motor’s mechanical information is also important. If you want precision, you need to know what the load inertia is and compare it to the motor’s inertia. For high-precision applications, you want the ratio of the motor’s inertia to the load’s inertia to be as close to one to one as possible to avoid complex tuning of the system.

Another a common practice is to specify motors that eliminate gearboxes. Besides reducing cost and inertia, eliminating gearboxes also allows a more solid and direct connection that avoids resonance in the mechanical setup. Gearboxes are also a source of wear, backlash and heat.

AW: What emerging technologies that may enhance motion control should users keep an eye on, and what do these technologies promise?

Scoccimaro: EtherCAT over Time-Sensitive Networks is a newer technology providing low-latency deterministic messaging, even over converged Ethernet networks that have many other types of devices on them. It allows controllers with EtherCAT masters to reliably operate drive nodes—which require rapid and responsive performance—even though there is other less-time-sensitive traffic on the network.

Prellwitz: At the end of the day, users should be looking at something that will offer them cost savings. Axis modules that use silicon-carbide semiconductors instead of IGPTs (insulated-gate bipolar transistors), for example, offer 55% more output for the same size axis module.