In the past, most motor-control system designs have been based on the use of microcontrollers, which have the advantage of being both affordable and flexible. While many applications will still benefit from the simplicity of an MCU, many more designs require greater performance and more integrated functionality.
To meet this demand while preserving the great usability of an MCU, NXP Semiconductors has introduced the i.MX RT Crossover series, based on an Arm® Cortex®-M7 core. These crossover devices bridge the gap between high-performance application processors and flexible MCUs, and are intended for industrial and consumer markets, including next- generation motor-control systems.
The i.MX RT may be used in systems controlling up to four AC motors. System configurations for which the i.MX RT is suitable include:
• two sensorless motors controlled by a Field-Oriented Commutation (FOC) scheme, in addition to a camera and an LCD preview
• four high-speed, sensorless FOC Electronic Speed Controllers (ESCs) for drones
• control of servo motor actuators (permanent magnet synchronous motor and stepper motor) in four-axis Computer Numerical Control (CNC) milling equipment or 3D printers
• other systems controlling up to four advanced AC motors
Higher performance and more integrated capabilities
The i.MX RT processor offers far more capabilities than motor control alone, however, including high-speed communications and peripheral interfaces, image processing and sensor interfaces. This provides for a high level of integration in sophisticated automation systems that include one or more motors.
An automated parking garage, for example, reads a licence plate number and determines whether to allow a vehicle to enter. If the licence plate scan shows the car belongs to an authorised vehicle, the chip automatically operates the motors to open and close a garage door, gate or other secure barrier. This calls for interfaces and image-processing capabilities, as well as the ability to control one or more motors.
The i.MX RT’s integrated multimedia features, supporting displays, touch sensing and audio, can help to equip this and other types of industrial equipment with advanced Human Machine Interface (HMI) capabilities.
The combined features and capabilities of i.MX RT processors also enable developers to implement systems that achieve higher performance while reducing complexity and Bill-of-Materials (BoM) expenses. In particular, the i.MX RT provides a means to gain increased performance without needing to use a more expensive applications processor, or to tackle the complex task of implementing a design in the Linux® environment.
3D printers: precision and simplicity
The scope for simplifying system designs is easily seen in the case of 3D printers. A typical 3D printer requires four MCUs: three for the motors which control the x-, y- and z-axis print heads, plus an additional MCU for the extruder.
The i.MX RT replaces these four chips with a single device which includes four FlexPWM interfaces to address the printer’s four motors. This dramatic reduction in component count not only simplifies the design, it also reduces BoM costs, while enabling the adoption of better control algorithms.
The i.MX RT’s multi-motor control peripherals also make it easier to synchronise the motors, and thus to achieve greater precision in the printer output. The device uses an advanced micro-stepping motor- control algorithm running on its high-performance CPU and peripherals to improve system performance even more.
Other integrated features which directly apply to next-generation 3D printer designs include support for advanced graphics, multimedia and the HMI for easy programming. These features make it possible to use only one i.MX RT chip to implement a 3D printer system design.
Lighter drones for longer flying times
In drones, the i.MX RT can run four high-speed, sensorless FOC ESCs for motor control.
Combining the flight controller and ESC in a single chip makes for a simpler circuit, and a lighter and cheaper hardware design, without sacrificing processing performance.
The software development kit provided with the i.MX RT also enables easy interfacing to radio chips or modules, to provide for wireless remote control via a Wi-Fi®, Bluetooth®, Bluetooth Low Energy, ZigBee® or ThreadTM radio. In addition, i.MX RT solutions give low dynamic power consumption thanks to features such as a fully integrated power management IC including a DC-DC converter and efficient power gating. These features help to prolong battery run-time in drones and many other types of portable device.
i.MX RT motor-control features
• Arm® Cortex®-M7 core operating at up to 600MHz
• 32kbyte L1 instruction cache and 32kbyte L1 data cache
• Up to 512kbyte on-chip RAM
• Four FlexPWM interfaces which are easily configured to work in synchronous mode
• Multiple output hardware triggers at each PWM cycle
• Two 12-bit ADCs with 16 input channels
• Four QuadTimers
• Four 32-bit periodic interrupt timers
• Two 32-bit general-purpose timers
• Four quadrature encoders/ decoders
• Four analogue comparators with 6-bit DAC