What Is a ToF Camera?
A ToF (time-of-flight) camera is a camera that visualizes the distance to an object by measuring the time of flight of light.
Infrared light is mainly used to measure the distance to an object. The time it takes for the irradiated infrared light to return from the object is measured, and the distance is calculated from this time.
While a normal camera can only obtain two-dimensional information about an object, an image taken with a ToF camera includes depth information, making it possible to obtain three-dimensional information. The method of acquiring information through images, as with a camera, is called “3D-ToF,” while the method of simply knowing the distance is called “1D-ToF.”
Uses of ToF Cameras
ToF cameras have a wide range of applications in industry, medicine, and other fields as follows:
1. Person and Shape Recognition
ToF cameras are used for person and shape recognition. ToF cameras can be used to recognize the movement of a patient in a hospital and be useful when watching over the patient. They can also be installed in stores to track people’s movements and be used in counting the number of people.
Other uses of ToF cameras are in the automated operation of cars. ToF cameras can be used to detect pedestrians so that cars do not rear-end pedestrians.
2. Object Detection and Safety Monitoring
ToF cameras are used in factories and other production sites for object detection and safety monitoring. ToF cameras can be attached to industrial robots and transport equipment to detect intrusion of objects.
In addition, when ToF cameras are installed on presses, robots, and other sources of danger, it is possible to identify whether the approaching object is a transported object or a person. When used to observe crops, measuring their size and shape can be used to determine when to harvest them.
3. Application to Smartphones
ToF distance image sensors are increasingly being used in smartphones, which can accurately capture players’ physical movements and reflect them in games.
Also, when buying or selling something on an e-commerce site, it will be possible to measure and display the dimensions of the object instantly. In addition, ToF cameras are also used for facial recognition when logging in to smartphones.
By identifying the shape of the face with the ToF cameras, the face recognition function is realized. Unlike ordinary cameras, ToF cameras can prevent identity theft because it recognizes the owner’s face as a mere flat surface, even if a photo of the owner’s face is used.
Principle of ToF Cameras
ToF cameras consist of a lens, a detector that detects light, and a light source that synchronizes with the detector. The reference light emitted from the on-board light source is reflected by the object and the time it takes to reach the detector (time of flight) is measured.
The speed of light is about 300,000 km/s and is an invariant constant. Therefore, we know that the distance of the target grain is half the product of the two.
Types of ToF Cameras
There are two main types of time-of-flight measurement methods: direct TOF and indirect TOF.
1. Direct ToF Method
In the direct ToF method, a pulse light is irradiated as a reference light and the reflected light pulse is detected. This method measures the time of flight by directly measuring the time from irradiation to detection.
Simultaneously, with the irradiation of the reference light, a measurement pulse current with a known width and period is generated inside the measurement circuit. Time-of-flight can be measured from the difference between the time when the pulse current is generated by the detector and the time when the pulse current is generated by the measurement pulse current and the reflected light.
2. Indirect ToF Method
The indirect ToF method determines the distance from the phase shift with a reference light. The amplitude of the continuous wave emitted from the light source is modulated to generate a sine wave with a known frequency.
This is irradiated onto the object as a reference light, and the phase shift of the reflected light from the object is detected. The phase shift can be converted into a time difference using the frequency of the sine wave. This allows the calculation of the time of flight.
Specifically, the intensity of the reflected light is measured four times for one period of reference light. By discrete Fourier transforming this, the phase shift from the reference light can be obtained.
Other Information on ToF Cameras
Advantages of ToF Cameras
Advantages of the ToF method include its small size, low CPU load, and the ability to be used in dark locations. Each of these advantages is explained below.
1. Can Be Used in Dark Places
The advantage of ToF cameras is that they can be used in the dark because they use infrared light instead of visible light. Three-dimensional information on objects can be obtained even when there is no light source at all in the surroundings.
2. Small Size and Low CPU Load
ToF cameras have a simple device configuration, which allows them to be smaller than structured light systems. Another attractive feature is its low CPU load.
When considering incorporating a ToF sensor into production equipment used at a manufacturing site, a low CPU load reduces the risk of delays and makes it possible to construct a stable production system.
3. Low-cost Products Are Also Available
ToF cameras are not only expensive but also inexpensive, depending on the specifications. Since the price of ToF cameras varies greatly depending on the specifications, it is recommended that you consider the price of ToF cameras in relation to the specifications you need before purchasing.