From Motor Control to Motion Control: What Does It Take?

We are well into the era of Industry 4.0 with more and more technologies being adopted for industrial automation. Some newer technologies are enabling AI and machine learning, data analytics, industrial networking, cyber security and functional safety. However, the bulk of industrial automation that sits in the middle of all the other technologies still relies on robot and motion control.

From time to time, motion control is mentioned with motor control and there is some confusion about these two terms. What is the difference between these two concepts and how do we apply the right solution to either or both of them in industrial automation? Read on for a summary of the differences between motion control and motor control and how to make them work together.

What Is Motion Control?

Motion control is a sub-system of an industry automation system. It synchronizes and controls multiple motors to complete a sequence of movements. For example, a multi-axis robotic arm requires a number of motors to operate together seamlessly to make a specific move. Motion control is used mainly for trajectory planning, speed planning, interpolation algorithm and kinematics conversion. Motion control systems are often seen in printing, packaging and assembly applications.

As shown below, a motion control system typically consists of these major components:

• A motion controller that generates trajectory planning and then provides control commands to motor drivers
• Motor drivers that convert the control commands from the motion controller (usually a speed or torque signal) into a higher power voltage or current signal to drive the motors
• Motors that execute movement according to control commands
• Position sensors that provide the position/speed data of the motor rotor to the position/speed controller to achieve the precision position/speed control

Motor Control vs. Motion Control

Motor control, on the other hand, is a system or a technique that is more dedicated to controlling the spinning of the motor. A typical motor control system adjusts one or more of the parameters of the torque, speed and position of an individual motor to reach the target values. Depending on the type of the motor, the requirements and techniques to drive it can vary greatly. A motor controller usually has no planning ability—the advanced drivers have simple position and speed planning abilities. Therefore, a simple way to explain the difference between motor control and motion control is:

• Motor control is a part of the motion control system (usually a current loop, working in torque control mode)
• However, sometimes it can be confusing because the position loop/speed loop/torque loop of motor control can be implemented either in the motor controller or in the motion controller.

Now that we know the differences between the two systems, it becomes clear that the design requirements or resources for them are quite different as well.

Motor control is highly focused on making the motor spin properly, or rather, focused on communication. In order to do that, the motor controller needs to interface with a variety of sensors, process both analog and digital signals, as well as generate waveforms to drive the motor. These all happen in a very short loop of time that can range from 50us to 300us.

Motion control, however, often acts as a system supervisor that requires communication in between multiple motor controllers, other sources such as data via Ethernet (EtherCAT and TSN.), CAN, RS485 and commands from a human-machine interface (HMI) panel. As mentioned, a motion controller may also take part in some of the motor control tasks such as controlling the speed loop, the position loop or even the torque loop. Therefore, the real-time control loop of a motion controller can vary from 100us all the way to hundreds of milliseconds, depending on what actual tasks the motion controller is taking part in.

Designing a Motion Control System

A motion control system can be a fairly complex design that covers a lot of aspects such as motor control, industrial networking, HMI, encoder/decoder, security and safety. Thus, it requires multiple control units to coordinate with each other in the system.

This is where you need a full suite of devices for the motion control designers to choose from—and that’s where NXP and its wide portfolio of microcontrollers (MCU) and microprocessors (MPU) comes in.

For the motor controller, NXP’s Kinetis V MCUs, Kinetis E MCUs, LPC MCUs and digital signal controllers (DSCs) offer options from controlling a simple motor with an Arm^® Cortex^®-M0+ core, to running FOC algorithms on dual motors with a Cortex-M33 core or a highly efficient DSC core. With the popular flashless i.MX RT crossover MCUs, more motors can be controlled precisely at the same time. Not only do these MCUs have a wide range of processing capabilities to choose from, they are also integrated with the peripherals that are well-suited for motor control, such as high-speed and high-resolution ADCs, high-speed comparators, flexible motor control timers and PWMs and DSP accelerator. Safety features such as fault detection and auto-shutdown can work together seamlessly with the industrial safety compliances offered by these devices.

For the motion controller, NXP offers both the i.MX RT crossover MCUs and the MPU product lines, including the Layerscape and the i.MX series processors. Those devices support a rich integration of industrial communication interfaces such as Ethernet/IP, Profinet, EtherCAT and TSN. The multiple-core architecture generates enough horsepower for communication protocols, motion profile planning and real-time loops control. They are also equipped with advanced timers to support the multiple modes counting and flexible pulse train outputs.

To accelerate the time to market of the motion control system, a quick and easy way for proof-of-concept and prototyping is keen. Therefore, NXP has been developing reference design platforms that provide rich features in industrial motion control and meet industrial automation standards. We recently announced the i.MX RT industrial drive development platform, which is based on the i.MX RT crossover MCU and features multi-motor control, deterministic communications and a foundation for IEC 62443 security compliance. Available today, the quad motor control development platform implements a full set of NXP products including the i.MX RT crossover MCU and EdgeLock^® SE050 secure element. These devices work together to demonstrate the features needed for an industrial motor control system, such as power management, driving four motors, industrial communication interfaces, HMI touch panel interface and security integration.

In summary, we have covered the definition of motion control, the difference between motor control and motion control, as well as the trends in the industry for motion control system design requirements. Keep following NXP for more motor control solutions.