With the improvement of automation in various industries, the importance of motion control is becoming increasingly prominent. In order to effectively drive the motor, control inputs that describe speed and position are essential. However, there are various technologies that can achieve this kind of sensing, each with different characteristics and application scenarios.

This article will compare different rotation sensing technologies and discuss the reasons for choosing them. Then, we will learn about some of the latest devices on the market.

Position sensing applications

In order to improve accuracy, increase yield, and reduce operating costs, many processes that previously required manual operation have been automated, which has led to the rapid growth of position sensing applications. In fact, as long as there is some form of motion, sensors need to provide position information to the controller.

Industry 4.0 has driven the industrial market to make significant progress in the field of automation. Robotics technology is becoming increasingly popular, achieving all-weather unmanned operation without fatigue or making mistakes - this requires each motion axis to be equipped with a sensor. The same goes for collaborative robots that work with humans in traditional factories.

Nowadays, many components are manufactured by machines - some use CNC machine tools, some use laser cutting machines, and some use 3D printers. These machines all have moving parts and require precise position control to meet quality objectives. After the parts are processed, they are usually transported through automated material handling or conveyor belts, which also require position sensing function.

Outside of factories, many places also require position control, such as large medical equipment that can move patients or scanners. In addition, robots can now perform surgeries, which also requires very precise control.

In the field of transportation, every application involves motion. Both traditional transportation vehicles such as trains, agricultural machinery, and construction machinery, as well as emerging applications such as autonomous mobile robots (AMRs) in warehousing and thousands of drones, require position sensing.

As all driving modes (internal combustion engine (ICE), pure electric drive (EV), and hybrid) of passenger cars are moving towards electrification, mechanical control solutions are being replaced by systems such as "wire controlled drive" and "wire controlled steering". In order for these systems to function properly, the position information of the accelerator pedal (accelerator) must be transmitted to the electronic control unit (ECU), or the position information of the steering wheel must be transmitted to the steering control system.

With the expansion of electronic control to almost all aspects of vehicle operation, position sensing technology is also widely used in suspension components (for leveling/driving control), powertrain, as well as power windows, sunroof, door locks, and other aspects.

Comparison of Position Sensing Technologies

Rotating position sensing mainly uses three technologies - optical, magnetic, and inductive, each with its own different working modes, advantages, disadvantages, and application scenarios.

Optical encoders are often considered the most accurate (although not always the case), and their working principle is to pass light through a perforated disk, using light pulses to detect motion as the disk rotates.

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Figure 1: The main methods of rotational position sensing include optical, magnetic, and inductive techniques

Usually, these types of devices are used for applications that require extremely high precision, such as precision robots and machine tools such as CNC lathes or laser cutting machines. Although they have high accuracy and are not sensitive to magnetic fields, they are susceptible to vibration and dirt on the disk, which may lead to their failure.

Magnetic encoders often have low accuracy and are mainly used in cost sensitive applications. They perform well in the presence of vibration and pollution, but external magnetic fields can have a significant impact on them, which limits their applicability.

Inductive encoders have better accuracy than magnetic encoders, can withstand higher levels of vibration and pollution, and are not sensitive to magnetic fields. Other advantages include good repeatability, insensitivity to temperature, fewer devices, small size, and no need for rare earth materials (i.e. magnets).

NCS32100 Dual Inductive Position Sensor

Ansemi's NCS32100 dual inductance position sensor achieves excellent non-contact position accuracy through two simple and innovative PCB plates, with accuracy better than+50 arcseconds or mechanical rotation of 0.0138 degrees. One PCB is fixed on the motor stator (stationary part), while the other single-layer PCB is fixed on the rotor or shaft. Two PCBs are placed parallel, separated by an air gap of 0.1mm to 2.5mm in the middle. NCS32100 is located on the stator PCB.

The thickness (double) conductive wire or coil is printed on two discs. The third conductive trace is called the excitation coil and is printed on the stator PCB. NCS32100 sends a 4MHz sine wave to the excitation coil, causing an electromagnetic field to be generated around the stator excitation coil. According to Faraday's law of mutual inductance, the thickness of the rotor's winding intersects with the electromagnetic field, coupling energy into the rotor coil and forming eddy currents.

At the same time, the thick and thin coils of the stator are connected to up to eight NCS32100 receiver inputs. When the rotor rotates, the eddy currents in the rotor will interfere with the stator receiving coil. NCS32100 measures the rotor position by processing these interferences through proprietary algorithms of its internal DSP (Digital Signal Processor).

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Figure 2: Dual inductance technology provides high performance through a simple solution

Using a 40mm PCB sensor, the NCS32100 can achieve position accuracy of ± 50 arcseconds at a speed of 6000 RPM, with a speed of up to 45000 RPM at the expense of some precision. By using larger PCB sensors or precisely aligning the rotor with the stator, higher accuracy can be achieved within+/-10 arcseconds.

This simple solution only requires a small number of electronic devices, ensuring small size and low cost. In addition, it is completely insensitive to temperature fluctuations, pollution, and external magnetic fields.

Integrated solution of dual inductance technology

Ansemy's NCS32100 supports the design of high-precision rotary position sensors for industrial applications and environments. It is an absolute position device that can determine its position without movement. NCS32100 can also calculate speed at speeds up to 45000 RPM.

At speeds up to 6000 RPM, the NCS32100 provides complete accuracy of ± 50 arcseconds, comparable to the performance of many optical encoders. Does the device also integrate Arm? Cortex? M0+MCU, providing high configurability and internal temperature sensors.

The built-in calibration routine of NCS32100 allows sensors to self calibrate through a single command, which only takes two seconds. It does not require a reference encoder, as long as the rotor speed is between 100 and 1000 RPM, the program can run at any time. All calibration coefficients are stored in non-volatile memory (NVM).

A typical optical solution requires a total of three PCBs - optical discs, stator PCBs, and LED driver PCBs, with approximately 100 devices required to achieve all functions.

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Figure 3: The dual inductance technology is comparable in accuracy to optical technology, but has lower complexity and cost compared to the latter

In contrast, the NC32100 based solution only requires two PCBs: the rotor is a single-layer PCB without any components, while the stator PCB only contains 12 components.

In automotive applications, although cost and reliability are important, safety is even more crucial, especially in applications such as steering or braking. Ansemy's automotive grade absolute position sensor NCV77320 complies with the ISO26262 standard and is specifically designed for these critical application scenarios. The position accuracy of NCV77320 is 194.3 arcseconds or 0.0539 degrees of mechanical rotation (depending on PCB geometry), mainly because it only has 3 receiver inputs, while NCS32100 has 8 receiver inputs, and NCV77320 does not support thick and thin coil PCB configurations. NCV77320 and NCS32100 can both operate as rotary encoders or linear encoders.

The applications of NCV77320 include brake pedal sensors, accelerator pedal sensors, motor position sensors, brake system sensors, vehicle level sensors, transmission gear sensors, throttle position sensors, and exhaust gas recirculation valve sensors.

Like NCS32100, NCV77320 is insensitive to pollution, temperature changes, and magnetic field interference, and can be used in automotive environments with an ambient temperature range of -40oC to+150oC.

NCV77320 can operate at speeds up to 10800 RPM and communicate with the matching MCU through SENT, SPI, or analog interfaces.

summary

With the increasing popularity of automation, there is a growing demand for position sensing of rotating motors. There are currently multiple technologies available to achieve this function, including optical, magnetic, and inductive technologies. Optical technology has high precision, but it is expensive and easily affected by pollution. Magnetic technology has low cost, but is susceptible to magnetic field interference.

Inductance technology is increasingly favored, and with the emergence of dual inductance sensors, it is now possible to create sensors that have both optical level accuracy and cost-effectiveness.

About The Author

This is reported by Top Components, a leading supplier of electronic components in the semiconductor industry. They are committed to providing customers around the world with the most necessary, outdated, licensed, and hard-to-find parts.

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Name: John Chen

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