Optical ToF vs Ultrasonic ToF, which one is the better "range finder"?
Automated guided vehicles (AGVs) and autonomous mobile robots (AMRs) are indispensable "porters" in modern logistics and manufacturing. Although they look similar, they have subtle differences in the way they work. AGV is more like a soldier who follows orders and needs clear instructions to act; while AMR is more like an "independent thinking" robot that can autonomously plan routes, avoid obstacles, and even adjust its behavior according to changes in the environment.
Whether it is AGV or AMR, they all need a pair of "smart eyes" to perceive the surrounding environment and avoid collisions.
Among them, the time-of-flight (ToF) sensor plays an important role in the actual work of AGV and AMR with its precise ranging capability.
Light vs. sound: which one comes out on top?
ToF sensors can be divided into optical ToF and ultrasonic ToF. ToF sensors calculate the distance to the object by emitting a beam of light or ultrasonic wave to the object and then measuring the time it takes for the light or sound wave to return.
So, between optical ToF and ultrasonic ToF, which one is the real “range measurement expert”?
▌Optical ToF sensor: Currently, optical ToF sensors are often used in our mobile phone cameras to achieve autofocus. Optical ToF sensors can achieve smaller size and higher accuracy. But the disadvantage is that since it uses light to measure distance, it will be affected by environmental conditions and overall visibility. This means that it may not work properly in rainy, foggy days or when there is a strong light source in the field of view.
▌Ultrasonic ToF sensor: As the name implies, ultrasonic ToF emits ultrasonic waves to measure distance. It is like the "sonar" of a bat. Ultrasonic ToF is not affected by light, and even by most interference in various environments, including sound, dust or smoke. It can work in various environments and consumes less power. Ultrasonic ToF sensors are generally considered to be the best distance sensors for automotive, industrial, as well as drone and robot applications. However, due to their large size, they cannot be used in small consumer electronics.
The following figure shows the working principle of ultrasonic ToF. The sensor transmits an ultrasonic pulse (the green waveform in the figure), and the ultrasonic wave propagates at a certain speed. When the ultrasonic wave encounters an object, it is reflected and forms a reflected wave (the gray waveform in the figure). The sensor then receives the reflected ultrasonic wave. By calculating the time difference from transmitting the pulse to receiving the reflected wave (called "flight time"), the sensor can determine the distance of the ultrasonic wave from the sensor to the object.
How Ultrasonic ToF Works
It can be seen that there is no absolute advantage or disadvantage between optical ToF and ultrasonic ToF sensors, only more suitable application scenarios. But in general, ultrasonic ToF will play an important role in more scenarios.
Beyond obstacle avoidance, unlock more intelligent applications of ultrasonic ToF
Avnet's partner, TDK InvenSense, has developed the SmartSonic platform, a leader in ultrasonic ToF sensors. It uses micro-electromechanical systems (MEMS) technology to integrate the transmitter and receiver on a single chip, making it not only small but also extremely low power. They consume 100 times less power than infrared optical ToF sensors. This puts the technology firmly in applications where size, weight and power are critical.
The following figure shows the internal principle of this ultrasonic ToF sensor. The sensor mainly consists of two functional modules: the first is the piezoelectric micro-machined ultrasonic transducer (PMUT), which is used for both generating ultrasonic waves and detecting ultrasonic waveforms in a single sensor configuration.
Inside an ultrasonic ToF sensor
The system-on-chip (SoC) provides the intelligence to fully exploit the sensor’s capabilities. It generates the drive signals to transmit ultrasound waves, and detects and interprets received ultrasonic signals (i.e., reflections from objects in the field of view). The SoC integrates a digital signal processor (DSP) and a microcontroller (MCU), and runs firmware provided by TDK InvenSense to implement the required data processing.
The sensor communicates via two I 2 C interface addresses. One I 2 C address is used to load the firmware into the sensor's DSP and MCU at power-up, and the other I 2 C address is used to control and query the sensor via the integrated MCU during operation.
SmartSonic ultrasonic ToF sensor is not just "exclusive" for AGV and AMR. It is like a pair of omnipotent "eyes", playing an important role in production lines, vending machines, and even our home life. Whether it is monitoring moving objects on the production line, or detecting containers in vending machines and the liquid level when the containers are full or empty, SmartSonic can do it. In addition, it can also identify floors of different materials, detect the edges of objects, and even help us find parking spaces. It can be said that the application range of SmartSonic ultrasonic ToF sensors far exceeds our imagination, bringing more convenience and intelligence to our lives and work.
Looking ahead, ultrasonic ToF sensors will further improve ranging accuracy, especially in complex environments, such as dealing with multiple reflections and noise interference. Ultrasonic ToF sensors will become smaller and lighter, making them easier to integrate into a variety of devices, including mobile devices, robots, and smart home devices. Combined with artificial intelligence and advanced algorithms, ultrasonic ToF sensors will have stronger environmental adaptability and intelligent analysis capabilities, and will be able to process complex data in real time and make intelligent decisions. Overall, ultrasonic ToF technology has broad development prospects and will play a key role in multiple industries.
Both optical ToF and ultrasonic ToF have great potential.
Avnet will work closely with its partners to fully leverage the advantages of optical ToF and ultrasonic ToF to provide users with low-power, high-precision ranging solutions to meet the needs of smart homes, robots and other fields for precise perception.
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