ams and OSRAM lead HOD technology innovation to improve driving safety
Today, cars are transforming from traditional means of transportation into large-scale smart devices. On the road to automobile intelligence, the two key technologies of sensors and light sources are inseparable. Sensors are the core of all information sources, and light is the most simple, direct, efficient and uninterrupted way to collect sensory information. As a leader in smart sensors and transmitters, ams-OSRAM is leading the in-depth integration of light and sensing technologies, painting a picture for future smart cars that “pays more attention to the full life cycle user experience and has more emotional warmth”. A whole new picture.
ams-OSRAM's products cover key optical applications around the vehicle, including headlights, signal lights, interior functional lighting and other fields. In high-tech fields such as lidar transmitters, rain sensors and cabin sensing, ams-OSRAM also occupies a leading position in the industry. These innovative optical and sensing technologies lay a solid foundation for the development of future smart cars.
On the road to the development of smart cars, safety is always a crucial consideration. In its continuous innovation of optical and sensing technologies, ams Osram also pays close attention to the advancement of driving safety technology. Among them, HOD (Hands Off Detection) technology is a prominent example. As more and more cars introduce autonomous driving technology, autonomous vehicles above L2+ are required to add HOD detection functions. HOD technology can detect whether the driver puts his hands on the steering wheel through sensors. If the driver's hands leave the steering wheel for more than a certain period of time, the system will issue a warning to remind the driver to pay attention. HOD technology can effectively improve the driver's emergency avoidance ability during autonomous driving, thereby increasing driving safety. These sensors often require extremely high sensitivity and reliability, which is where ams Osram excels.
Capacitive Sensing: Reinventing HOD Technology
The automotive industry's demand for HOD technology mainly comes from the following aspects: first, the requirements for autonomous driving, such as lane keeping assist driving; second, the requirements of standards and regulations, such as the R79 standard of the Economic Commission for Europe (ECE), when the vehicle speed When exceeding 60 km/h, the vehicle must have the HOD function; the third is public safety requirements, such as preventing passengers from snatching the steering wheel; the fourth is that HOD technology can remind the driver to pay attention to road conditions and avoid accidents caused by distracted driving.
In fact, HOD (hands-off detection) technology is not a new technology. There are currently a variety of HOD technology solutions on the market:
• One solution is based on torque sensing measurement, but this solution has a big disadvantage, it must turn the steering wheel to identify. Moreover, the gesture of the hand cannot be recognized, and it is easy for humans to deceive the solution, such as hanging a heavy object. This kind of scheme has been gradually withdrawn from the market.
• The other is image sensing and analysis based on optical systems. It uses a multi-chip solution consisting of a series of light fillers + drivers + cameras, which can perform high-precision hand detection, but this solution also increases the cost. In addition, due to the dead zone of the viewing angle, it is impossible to completely observe whether the driver's hands are really on the steering wheel, so there is also a certain risk.
• The more popular solution now is to use capacitive sensing measurement. This method uses a conductive metal wire or conductive metal mesh wrapped inside the steering wheel as an electrode, and uses the capacitance change formed between the electrode and the hand holding the steering wheel to make a judgment. The advantage is that high-precision hand detection can be performed without turning the steering wheel. Moreover, it is a single-chip design and the cost is relatively low. This is also the solution recommended by ams and OSRAM.
The more commonly used capacitive sensing solutions are usually time-based solutions. The scheme is based on the charging time (T) of a capacitor (C) through a resistor (R), where the product of R and C gives the corresponding time measurement of the capacitance value. Although this method is simple, when it comes to complex environments, such as wet steering wheels or hand contact, or when wearing thick gloves to hold the steering wheel, parasitic resistance appears in the loop, causing the resistance R that should be constant in the measurement loop to occur. changes, causing errors in measured capacitance values. This may lead to inaccurate capacitance measurement, which may cause some misjudgment problems in steering wheel hands-off detection. Many customers have discovered problems with this solution.
Image source: ams-osram
In view of these pain points and problems, ams-OSRAM has developed a new impedance measurement solution, also known as the I&Q orthogonal method. This method uses two orthogonal demodulation components to measure the resistance R and capacitance C respectively. Through this orthogonal demodulation method, the impedance including the resistance component and the capacitance component can be separated and measured separately. Further, a vector value representing the impedance is obtained through the vector calculation method.
The figure below shows the system architecture and working principle of ams-OSRAM using the I&Q orthogonal method for capacitance detection. The entire system consists of sensors, transmitters, receivers and output interfaces. By sending a sine wave current to the load, the load is composed of the impedance of the steering wheel system and the impedance change caused by holding the steering wheel. Generally speaking, the size of the resistance in the load determines the amplitude of the voltage signal on the load, and the capacitance The component will determine the change in phase of the signal on the load. After the voltage signal on the load is collected, amplified and filtered, it is input to the in-phase and quadrature demodulators. The in-phase demodulator measures the in-phase component (I) of the signal, while the quadrature-phase detector measures the 90-degree phase difference component (Q) of the signal. The I component corresponding to the resistive component and the Q component corresponding to the capacitive component are obtained and processed through a filter to remove noise and perform offset compensation. The final result of the automatic measurement is the change in resistance and capacitance in the impedance of the load.
Image source: ams-osram
In actual vehicle application detection solutions, an electrode is embedded in it. When the hand touches the steering wheel, the capacitance and resistance values between the human body and the electrode change, thus changing the amplitude or phase of the oscillation signal. This signal is generally between 45-125KHz. The advantage of this method is that it can more accurately distinguish between resistance and capacitance, thus accurately measuring impedance. It is not affected by wet hands, gloves, etc., nor can it be cheated by placing objects near the sensor, and can well identify parasitic resistance. Therefore, it can accurately detect whether a person's hands have left the steering wheel in a complex vehicle environment, thus improving the reliability of the system and user experience.
AS8579 chip: high precision, multi-function, small size, new choice for HOD technology
The AS8579 chip launched by ams Osram is an advanced product specially designed for HOD (hands-off detection) market applications. It has 10 independent measurement channels and can perform accurate capacitance collection. This chip supports 4 different frequency measurements for accurate impedance detection, and also adds an active shielding function to avoid the impact of stray parasitic capacitance on measured values. AS8579 not only fully meets the ISO26262 safety standard, but also has a complete safety mechanism, reaches the ASIL B safety level, and complies with the automotive AEC-Q100 Grade1 standard.
The outstanding features of the AS8579 are its high sensitivity and 14bit resolution, with a measurement range from 20 to 2000pF. It can also compensate for temperature changes through DC offset adjustment, effectively overcoming temperature effects and ensuring measurement stability.
Image source: ams-osram
AS8579 comes in a small SSOP24 package, making the system design more compact. At the same time, for the application of steering wheel hands-off detection, many steering wheels now have added heating functions. The AS8579 chip can directly reuse the steering wheel heating wire as a sensor, which can save customers' costs.
Image source: ams-osram
In addition to steering wheel hands-off detection in the field of autonomous driving, the AS8579 chip can also be used to detect passengers in the car, such as seat occupancy detection. Can also be used for other capacitive interior controls and switches such as air conditioners, radios, navigation, etc. Since the AS8579 chip has 10 sensing lines and can detect up to 10 different areas, it can also be used in some steering wheel button or proximity sensing applications. For example, in the steering wheel, it can be detected whether the steering wheel is held by the left or right hand.
More application cases for automotive capacitors
• The application of in-vehicle capacitors is not limited to hand-off detection on the steering wheel. Capacitive technology also has broad application prospects in many scenarios such as fuel level sensing, seat occupancy sensing, trunk opening, and in-car control switches.
• Capacitive touch button: Capacitive touch button is one of the typical application scenarios of automotive capacitive technology. On the smart skin in the car, capacitive touch buttons can be made translucent, with LED indicators hidden behind them to complete functions such as switch control, volume adjustment, and air conditioning adjustment.
• Seat detection: Capacitive sensing can also be used for seat detection. Combined with the heated blanket of the seat, it can effectively detect the status of people or items occupying seats, which can prevent problems such as problems left by children.
• Door handle switch: Capacitive sensing can also be used to detect door handle switches. The new generation product of ams and Osram can increase the distance from the hand to 10 centimeters. When a person approaches to 10 centimeters, the key will be awakened, which can reach Very good power saving.
• Trunk opening: ams' vehicle-mounted capacitive products have multiple sensing points, so in addition to detecting the approaching state of the human body, it can also detect left and right sliding or spiral movements, which is a good way to apply capacitive sensing Operation of trunk switch.
By integrating the key innovation of HOD technology into its broad product portfolio, ams-OSRAM is demonstrating its commitment to a future of safe, reliable and highly interactive smart cars. HOD solutions based on capacitive sensing technology not only demonstrate their technical leadership in the field of smart cars, but also provide consumers with a richer and deeper driving experience.
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