Application Note Download from onsemi

Reliable intelligent power and sensing solutions

With capabilities similar to self-driving cars, autonomous mobile robots are complex, intelligent designs made up of sub-systems that allow the robot to move, see and operate safely with minimal human interaction.

onsemi minimises this complexity with reliable intelligent power and sensing solutions that provide the essential building blocks of your design. Its sub-system solutions, ranging from rugged, high-resolution imaging systems to high-power motor control to highly efficient and compact battery charging solutions, are all built using decades of experience serving the automotive industry.

onsemi developed a new Industrial Rotary Position Sensor to combine high accuracy, high speed, and robustness – taking inductive position sensing to a new level and making it suitable for industrial applications such as autonomous mobile robots.

Inductive position sensors are an alternative method to optical and magnetic encoders for measuring rotational position. Various types of inductive position sensors have been used for automotive applications but have typically been limited to accuracies that are not acceptable for industrial applications. Several improvements have been made by onsemi to the inductive sensor design that allows it to get to better accuracies while still maintaining the benefits of inductive encoding such as low sensitivity to contaminants and vibration.

The primary use is for rotary position (and velocity) sensing, where the technology can deliver 20-bit resolution. A wide variety of sensor sizes are possible to address many different applications.

At rotational speeds of around 6,000 RPM, +/-50 arcsec accuracy can be achieved with a 38mm sensor. The NCS32100 can operate all the way up to 100,000 RPM if the sensor is designed for it – albeit with reduced accuracy at higher speeds.

Inductive sensors are insensitive to almost all forms of contamination or interference, including liquids, dirt and dust, magnetic fields, EMI, and strong vibrations. With its low sensitivity to mechanical vibration, the NCS32100 can discriminate between rotor-to-stator translation and rotor-to-stator rotation. For example, it can distinguish between rotational movement (which is measured) and vibration in the x, y, or z axis (which can be rejected if desired).

The NCS32100 offers a level of integration that makes it a simple and easy-to-use solution. It contains an Arm Cortex-M0+ processor with Flash memory to store configuration settings. It comes with an integrated and fast self-calibration routine (to minimise production time) which allows it to compensate for PCB asymmetries. This calibration only requires that the rotor turns and completes in two seconds. It has an easy-to-use programming interface used with various sensors and PCBs with different designs, shapes, sizes, and form factors for maximum design flexibility.

This solution has an absolute position output meaning that the device always knows its position even if the power if off, removing the need to derive this information from a raw analog signal. The NCS32100 can reduce the number of other components needed and the design time and risk. A solution based on NCS32100 could be done with 12 components, while a comparable 38mm optical encoder requires over 100 components. Comparing these two solutions, a sensor based on the NCS32100 provides an order-of-magnitude reduction in the BOM.

Flexible mechanical specifications allow for achieving +/- 50 arcsec accuracy in real-world conditions. For example, a rotor-to-stator air gap of 0.1mm to 0.5mm is perfectly acceptable with the NCS32100 reference design, as is a rotor-to-stator tilt that does not exceed 0.5°. The sensor can achieve different airgaps other than the 0.1 to 0.5mm offered by the reference design, and 1mm is a common typical airgap. In addition, no reference encoder is required for self-calibration; simply ensure that the rotor moves between 100 RPM and 1,000 RPM.

High levels of configurability enable use with a wide range of PCB sensor designs, allowing end users to configure and differentiate their solutions.

The front end of the NCS32100 features a programmable gain amplifier (PGA) and an integrated analog-to-digital converter (ADC). The integrated Arm Cortex-M0+ microcontroller includes non-volatile Flash memory (NVM) and a configurable interface for communication with the host processor.

A range of optional features is available to enhance the NCS32100 further, including latency extrapolation, low pass filtering (LPF), open coil detection, and auto-zeroing. Additionally, reference design and evaluation boards are available for designers to enable rapid evaluation and fast time-to-market.

To continue reading and learn more, you can download a detailed application note which summaries the sensor improvements that are utilised by the NCS32100 by completing the brief form.