NXP MCX microcontrollers enhance motor control capabilities for mobile robots

Excellent performance, smooth motion and reliable operation of mobile robots require efficient and precise control. The increasing autonomy and complexity of robots have put a great demand on advanced control and other tasks. NXP's new generation MCX microcontroller portfolio features advanced peripherals to help developers optimize motor control in mobile robotic systems.

The MCX A and N series feature a versatile, highly configurable enhanced Flex Pulse Width Modulator (eFlexPWM) module that enables precise motor control and offers a broad feature set to meet the various needs of mobile robotics applications. In addition to advanced control of drive motors, the eFlexPWM module can also be used to build switch-mode

A key feature of the eFlexPWM module is the support of aligned, edge-aligned, and asymmetric pulse width modulation (PWM).

Center-aligned PWM maintains phase alignment and minimizes ripple in brushless DC (BLDC) motors, which are commonly used in mobile robotics for their high efficiency and torque density. By using center-aligned PWM, developers can achieve smoother motor operation, reduce electromagnetic interference (EMI), and extend the life of the motor windings.

Center-Aligned PWM

Edge-aligned PWM simplifies duty cycle calculations and makes it easier to control H-bridge circuits. It is widely used in mobile robotics for bidirectional motor control, precise positioning, and speed regulation. The FlexPWM module simplifies the generation of necessary control signals for H-bridge circuits, reduces software complexity, and improves firmware response speed.

Edge-aligned PWM signal

The FlexPWM module also offers phase-shifted PWM, a valuable feature for mobile robotics applications involving multiple phases. By phase-shifting the PWM signals, developers can optimize multiple motors simultaneously, ensuring smooth, coordinated motion for systems with multiple degrees of freedom, such as arms or multi-wheeled platforms.

The FlexPWM module also has powerful fault protection and automatic fault clearing mechanisms to ensure system safety and reliability. Once a fault occurs, the module will immediately cut off the PWM output to prevent damage to sensitive components such as motor windings. After the fault is eliminated, the module can automatically clear the fault state and resume normal operation, minimizing downtime and enhancing the robustness of the entire system.

For more information on MCX N Series features and peripherals, click to read the white paper >>

Quadrature Decoder (Q)

Mobile robots require accurate position and velocity feedback to form an effective closed loop. MCX microcontrollers feature a Quadrature Decoder (QDC) module, a dedicated peripheral that simplifies the process of decoding quadrature signals and provides reliable position and velocity measurements.

QEI

The quadrature encoder generates two orthogonal signals, phase A and phase B, which are 90 degrees out of phase. The QDC module determines the position and rotation direction of the motor shaft by analyzing the order and frequency of the signals. The module's advanced features, such as interference filtering and edge detection, ensure the integrity and reliability of the decoded position and velocity data, even in the presence of noise or signal interference.

The QDC module provides flexibility in counter initialization, allowing developers to adjust the position of the counter based on specific events or situations. For example, the counter can be initialized based on the pulses generated by the encoder every revolution. This feature also simplifies the implementation of homing routines and absolute positioning. In addition, the QDC module also supports initialization based on external or switch-triggered homing signals, allowing precise control and calibration of mobile robotic systems.

The QDC module provides multiple speed measurement methods to meet different application needs. Developers can calculate motor speed by monitoring position changes within a fixed time interval, balancing resolution and response time. In addition, the module can measure the accumulated time between consecutive orthogonal edges, providing high-resolution speed measurement for applications that require fast response and fine control.

AND/ INVERT (AOI) Module

The AOI modules in the MCX A Series complement the FlexPWM and QDC modules in optimizing motor control. The AOI modules enable developers to create combinatorial Boolean logic that generates event outputs based on specific input conditions. In the MCX N Series microcontrollers, two AOI modules and a configurable trigger form the event generator (EVTG) module.

The AOI module provides an efficient solution for motor control, offloading event detection and trigger generation tasks from the main flow, thereby reducing firmware overhead and improving system responsiveness. By configuring the AOI module to monitor various input signals such as position, speed or fault status, developers can create custom triggers to initiate specific motor control actions without constant software intervention.

For example, the AOI module can be programmed to generate a trigger signal when a certain combination of conditions is met, such as when the motor position reaches a predetermined threshold and the speed is within a certain range. This trigger signal can then be used to automatically adjust the PWM duty cycle, change the motor commutation sequence, or perform any other desired motor control operation.

Developers can use the AOI module's programmable logic to implement complex control strategies, respond quickly to real-time events, and improve overall performance and efficiency. The AOI module is very flexible and supports the creation of custom trigger conditions based on the specific requirements of each application, enabling developers to optimize motor control based on the unique characteristics of their robot platform.

FRDM-MC-LVPMSM Expansion Board

The FRDM-MC-LVPMSM expansion board from NXP facilitates the development and prototyping of motor control applications. The FRDM board combines hardware and software resources to accelerate the design process. It is designed in a shield expansion board form factor and can be seamlessly integrated with NXP's Freedom development board platform.

The FRDM-MC-LVPMSM expansion board, combined with NXP's permanent magnet motor control reference software, provides a complete motor control reference design. The software suite includes a range of pre-configured motor controls, libraries and example projects that enable developers to quickly implement and optimize motor control systems for their specific mobile robotics applications.

This expansion board uses a low-voltage three-phase permanent magnet synchronous motor (PMSM), which is widely used in the field of mobile robots due to its high efficiency, high torque density and precise control capabilities. In addition, the board also includes basic components such as circuits and encoders, providing a complete platform for motor control development.

Developers can significantly reduce the time and effort required to design and verify mobile robot motor control systems using the FRDM-MC-LVPMSM expansion board and associated reference software. The board is compatible with the FRDM-MCX development platform for seamless integration, allowing developers to select the appropriate microcontroller based on their specific application requirements.

Xpresso Developer Experience

NXP provides a low-cost FRDM development platform for rapid prototyping using MCX. The FRDM development board has standard and headers for easy connection to the MCU's input/output, and has a built-in MCU-Link debugger with a -C cable.

NXP's GitHub also provides access to application examples, which can be accessed using the Application Code Center portal (H).

MCUXpresso IDE and MCUXpresso for VS Code have built-in ACH browsing capabilities that allow developers to easily search available demos and examples and filter by device, application technology or peripheral/function before directly loading a project for use.

The Expansion Board Hub (EBH) is an extension of the K Builder website where developers can find a range of add-on boards from NXP and its partners to extend the functionality of their selected evaluation board. The hub offers intuitive filtering to quickly find boards and available supporting software. Developers can pair their boards with different types of expansion boards to evaluate specific use cases or applications and for rapid prototyping.

NXP Motor Control Solutions for Mobile Robots

NXP's MCX microcontroller portfolio represents a significant advancement in motor control technology, offering a complete set of peripherals specifically designed to optimize motor control in mobile robotics applications.

The FlexPWM module provides high flexibility and reliability to support precise motor control, while the Quadrature Decoder (QDC) module provides the precise position and velocity feedback required for closed-loop control systems. The AOI/EVTG module adds a layer of programmable logic that enables developers to create custom hardware triggers and offload event detection functions from the host processor.

Review editor: Liu Qing