Collision Avoidance Sensors Information
Collision avoidance sensors (CAS), or collision sensors, detect an object in the path of a moving vehicle so the human operator, or the vehicle’s automated system, can take action to avoid a collision. The most common automobile application is a reverse sensor that alerts drivers to obstacles in their path when backing up. Collision avoidance sensors are also common in automated guided vehicles in factories and warehouses.
Collision sensors are usually mounted on the front and rear of the vehicle. Once an object is detected, the sensor triggers an audio or visual alarm, or may activate the vehicle’s brakes.
All sensors except the GPS based devices operate on basic radar or sonar principles. This is also known as echo ranging. A high frequency light, radio frequency, or audio frequency directional pulse is sent out by the ranger in the collision avoidance sensors. If an object is in the way of the pulse, it reflects part of the pulse energy back at the ranger where it is detected. In the case of the laser, the beam is always on and the detector in the CAS detects any of the laser light reflected back. The difference in time from when the detection pulse was sent out to the arrival of the reflected wave is then multiplied by the speed of the wave to calculate the range.
Ultrasound: These are sound waves with frequencies above 20 KHz. Ultrasound sensors are the most common type and are ideal for low speeds and short ranges. This technology is commonly used in back-up reversing systems. Wind, the Doppler effect and external noises make this a poor choice for high-speed road use.
Millimeter wavelength radar: Millimeter wavelength radar sensors can sense objects within 200 meters. This is the best overall system since it almost light speed and high energy enough to avoid most radio frequency interference. Most modern self- or assisted-driving cars employ millimeter wavelength radar.
Laser: Laser detection is common in controlled systems where reflectors are set up in the machine’s path. It can give inaccurate readings from objects that have poor to no reflectivity. Laser detection provides extremely high speed and eliminates radio frequency issues, but cannot reflect light from cloth-like objects.
LED sensors: These use infrared emitting LEDs, or light emitting diodes, at around 880 nm wavelength for detection. Like ultrasound sensors, they are used for short range detection of less than 10 feet. LED sensors are economical but they do have a drawback in areas with high temperature sources. These are mainly used in industrial applications but some reverse auto sensors use them.
GPS RF detection: These use a centralized system where each vehicle has a radio transceiver that is connected to a GPS based tracking system. When two vehicles are too close to each other, warnings are sent to both vehicles. These GPS based systems are scalable and can cover a large fleet of vehicles moving at high speeds, but they are relatively expensive.
(left to right) Laser, ultrasound, and LED collision sensor types.