Motion Control Basics: The Engineering Behind Automation

Integral to the automation of manual operations, motion control entails the movement of machine components. “It’s the engineering behind automation,” says Matt Pelletier, product training engineer at Yaskawa America, Inc.

Motion control encompasses the systems or sub-systems involved in moving parts of machines in a controlled manner where precision and efficiency are critical. It is essential for modern robotics, computer numerical control (CNC) machines, and countless other applications.

“Motion control involves moving parts/objects in a precise and smooth manner,” explains Biren Patel, head of business development at maxon USA. “It’s similar to a conductor of an orchestra guiding each musician to play their instrument at the right time; motion controllers orchestrate the motors and actuators to perform precise automation in various applications.”

Motion control is about getting a part or tool from point A to point B. “What matters most to the machine designer is the process that occurs at those end points or along the path,” says Parker Hannifin - Motion Systems Group product manager Jim Wiley. “Understanding that machine process is critical to selecting the right motion control components. For example, in fields like digital pathology and dynamic metrology, the stability and settling time of the motion determines image quality throughput. Those application characteristics will dictate which actuator is the best for the application.”  

Motion Control Components

“Motion control consists of a motion controller,” explains Patel, “that is basically the brains of the operation. An actuator makes the movements and some sensors provide feedback. Those could be either an encoder, which provides pulse so the controller knows the actuator’s position, or possibly a torque/force sensor that lets you know that a certain amount of torque/force was applied.”

Motion systems typically involve multiple components. Analogous to human anatomy, a motion controller functions as the brain, processing motion algorithms, generating command signals, and requesting status updates to guide the trajectory and velocity of the machine.

A drive or amplifier and motor combine to make up the muscle, interpreting the controller’s low voltage command signals and supplying high power current/voltage to the motor, which then converts electrical energy into mechanical motion.

Like the central nervous system, a network of wires relays signals back and forth between system components. Sensors such as encoders, potentiometers, and tachometers act as the eyes of the system, allowing for adjustments to process changes. Finally, the mechanical stage acts as the skeletal structure, supporting the loads and actuators.

“Motion systems have five major components: the mechanism, the motor, the drive, the controller, and the HMI,” says Pelletier. “Motors are the heart of every motion control system.” They transform electrical energy into mechanical energy and come in various types, each suited for different applications and performance requirements.

Motion systems may use a variety of motor types, including servo motors, stepper motors, AC synchronous motors, AC asynchronous motors, and DC motors.

Servo Motors

Known for their precision and built-in feedback mechanisms, servo motors typically use encoders that collect data about the positioning and speed of the rotor and provide feedback. Servo motors are suitable for applications that require exact positioning and rapid response because they operate with high precision and consistency.

“Servo motors are the top of the food chain,” Pelletier explains. “They are the go-to solution that will almost always work and are the best choice when the highest output in the smallest package is needed, or when the machine is large, and the motor is larger than 1 HP. Stepper motors are much less expensive and can do the job well enough in a variety of applications. Steppers are a good choice for simple point-to-point motion of smaller mechanisms.”

Stepper Motors

Stepper motors offer positioning without the need for feedback sensors. Because they move in discrete steps, they are useful in open-loop applications where cost-effectiveness is a priority. Stepper motors can change direction quickly and excel in tasks requiring lower speeds and torque.

“Never size stepper motors based only on torque or power,” advises Pelletier. “Always consider inertia ratio and the required performance of the application, such as point-to-point settling time.”

AC Synchronous Motors

Rotor motion in AC synchronous motors is synchronized with the frequency of the supply current and the speed remains constant under various loads. These motors find application in robotics, instrumentation, and process control equipment where precision positioning is required.

However, the application will dictate the motor to be used, according to Patel. “For example, a medical robot may require a motor that is sterilizable. In the case of an autonomous vehicle, if it’s for an axis that’s exposed to see water or other fluids, then the motor may need to have an IP rating.”

Power supply limits also play a role in motor selection, according to Patel, and a highly efficient motor and gear may be necessary. “It’s also important to consider space constraints,” Patel explains. “Where must the motor fit within the system, and how much volume is allotted for it. How will heat be dissipated? If heat dissipation is inadequate, perhaps a motor with more power than necessary will be needed.”

AC Asynchronous Motors

Electromagnetic induction from the magnetic field of the stator winding generates an electric current in the AC asynchronous motor rotor, producing torque. Applications include compressors, pumps, conveyor systems, and lifting gear.

“The actuators in motion control systems are typically made up of motors with gears and encoder,” Patel explains. “Brushed, brushless DC, steppers, and other types of motors are used in motion control systems, but brushed types are the simplest to control as there is no commutation to be done externally. Brushless DC and steppers require electronics to do the commutation and to energize the appropriate phase.”

DC Motors

Brushed and brushless DC motors offer simplicity and reliability. Brushed DC motors offer reliable performance at a relatively low cost for more basic industrial equipment. Brushless DC motors provide longer life and reduced maintenance in speed and positional control applications such as fans, pumps, and compressors.

“The type of motors used depends on the application and how precisely the object needs to be controlled and how much error during motion is allowed,” says Patel. “In cases where batteries are used one will typically find brushed or brushless DC motors being used as these are more efficient than steppers.”

Fundamentals of Motion Control

Engineers and technicians working in automation must understand the fundamentals of motion control. A few key concepts include position control, velocity control, and torque control, which govern how motion control systems operate and interact with their environments. Motion systems may consist of just a single axis of motion, or include multiple, coordinated axes of motion.

There are two categories of motion control systems. Open-loop systems do not use feedback and rely on predetermined commands. Closed-loop systems use feedback mechanisms to continuously adjust and optimize.

Feedback Sensors

Feedback devices collect and send data about the position and speed of the motor or actuator to the motion controller. Quadrature encoders provide position information relative to a starting point. Potentiometers give analog position feedback. Tachometers give velocity feedback, while absolute encoders and resolvers provide absolute position measurements.

Mechanical Components

Mechanical components such as bearings, gears, speed reducers, actuators, and linkages transform motor output shaft motion into the desired motion profile for a given application.

The purpose of plain, ball, and roller bearings is to support radial and axial loads while minimizing friction. Linear bearings support loads in the direction of motion, including vertical, horizontal, pitch, roll, or yaw moment loads, as well as combined loads.

Gearboxes increase torque while reducing the speed of the prime mover’s output shaft. Speed reducers multiply the amount of torque generated by an input shaft to increase the amount of usable work and achieve desired output speeds.

Linear actuators create motion in a straight line. Ball screws and lead screws are mechanical linear actuators that convert rotation to linear motion. There are also belt-driven, pneumatically driven, rack-and-pinion driven, and linear-motor driven actuators.

Factors to consider when choosing the right actuator include the amount of force required, the distance the actuator needs to move, and the required speed and accuracy. A mechanical linkage is an assembly of connected segments that manage force and movement.

Industry Standards in Motion Control

By ensuring interoperability, safety, and performance across different systems and manufacturers, industry standards help increase adoption of motion control technology. Standards cover various motion control aspects including terminology, communication interfaces, and performance test methods and procedures.

“The standards depend on the industry/market,” Patel explains. “Some common standards focused mainly around safety cross over many industries. For more established industries such as medical, standards are defined fairly well. However, for new technologies such are AGVs, AMRs, and e-mobility many standards have yet to be defined.” 

Adoption of open networking standards provides interoperable communications and facilitates seamless integration of motion control components from various vendors to increase design flexibility and reduce costs for end-users.

For example, the PLCopen motion control standard provides a way to have standard application libraries that are reusable across multiple hardware platforms. “When there is a standard programming language, engineers can focus more time on the application and less time on arbitrary nuances between manufacturers,” explains Pelletier.

With its high speed, determinism, and flexible topology, Ethernet for Control Automation Technology (EtherCAT) is also suitable for motion control applications. Such standardization efforts aim to simplify programming and improve portability of motion control applications.

“IEC 61131-3 and PLCopen are the most important programming standards,” says Pelletier. “PackML is another important standard, demanded by end users in the packaging industry, and EtherCAT is definitely the trending choice for deterministic motion and IO networks.”

Motion Control Applications

The versatility of motion control systems makes possible their use in automation applications across a wide range of industries. For example, in the field of photonics, precision motion control is crucial for applications such as laser materials processing, optical component manufacturing, and spectroscopy.

Motion control enables wafer handling, lithography, and inspection processes in semiconductor manufacturing. In fact, the demand for submicron accuracy and ultra-smooth motion in semiconductor fabrication has driven significant advancements in motion control technology.

In industrial automation, robotic systems, CNC machining, and assembly-line processes depend on motion control. Precision motion systems optimize production efficiency and enhance overall system performance in applications ranging from pick-and-place to high-speed packaging equipment.

Resources for Learning

For professionals looking to deepen their understanding of motion control, several resources are available. The Association for Advancing Automation (A3) offers comprehensive educational programs and certifications.

The A3 Motor & Motion College provides courses ranging from basic to advanced levels, covering various aspects of electric motors and components. These courses can be customized for in-house training, allowing companies to tailor the content to their specific needs.

A3 also offers the Certified Motion Control Professional (CMCP) program, which provides high-quality, core motion control training and industry certification. This program is designed to strengthen skills and enhance careers in the field of motion control.

For those just starting their journey in motion control, A3's Beginner's Guide offers a wealth of resources, including articles on specifying controllers, understanding motor types, and exploring the latest trends in the industry.

“Sizing, component selection, programming, and configuration all continue to be challenges,” advises Pelletier. “Software becomes easier to use, but also increases in scope to keep up with the hardware technology. It is important to partner with an organization that offers comprehensive training and with engineering support to guide you beyond the initial sale of components.”

Emerging Trends in Motion Control

The field of motion control is constantly evolving, with several key trends shaping its future. “Motion control is ever evolving,” Pelletier notes. “Devices are smarter than ever. We have encoder resolution over 68M pulses per revolution, which gives a ton of information to the servo amplifier. The servo amplifiers have faster processors and more memory to use that information to precisely control motion and suppress vibration.”

One significant trend is the integration of artificial intelligence (AI) and machine learning (ML) into motion control systems. These technologies are enhancing the predictive capabilities of motion control systems, enabling real-time optimization and complex task management.

The incorporation of wireless technology and the Industrial Internet of Things (IIoT) is another major trend in motion control. This integration allows for remote monitoring and control, improved system integration, and data-driven insights that drive operational efficiency.

Miniaturization and integration of components is also becoming increasingly prevalent in the motion control industry. This trend towards smaller, more compact systems is driving improvements in space efficiency, energy efficiency, and precision in motion control applications.

The advent of Industry 4.0 is set to revolutionize motion control systems further. This includes the development of smart factories; the use of digital twins for system simulation; and big data and advanced analytics for continuous improvement of motion control systems.

Conclusion

Motion control and motors form the foundation of modern automation, driving innovation across industries. As technology continues to advance, the importance of understanding motion control principles, staying updated on industry standards, and leveraging available resources for learning becomes increasingly crucial. With emerging trends like AI integration, IoT connectivity, and Industry 4.0 shaping the future of motion control, professionals in this field must continually adapt and expand their knowledge to stay at the forefront of this dynamic and essential technology.