Sony patents show that future PSVRs can be tracked through multiple MEMS (Micro Electro Mechanical System) projectors. This patent is undoubtedly an improvement in the tracking performance of PSVR, but Sony has not disclosed relevant plans for the time being. This article is related to MEMS in eye tracking, and hopes to help users understand the application of MEMS in the field of VR.
Eye Tracking refers to tracking eye movement by measuring the position of the eye's gaze point or the movement of the eyeball relative to the head. The eye tracker is a device that can track the position of the eyeball and the information of the eye movement. It is widely used in the research of visual systems, psychology and cognitive linguistics.
A more common non-invasive method is video/image capture. The camera captures the eye image and has some features that can be extracted. The image processing algorithm extracts these feature parameters to determine the eyeball position, which is used to determine the direction and target of the human eye. The calculation result is reflected by the processor CPU. On the VR/AR device you are using. According to 7invensun, eye diagram recording and corneal reflection are both methods of this type.
The following is an introduction from 7invensun
The eye diagram recording method mainly realizes eye tracking by recognizing the characteristics of the eyeball such as the pupil shape, the heterochromatic edge (iris, iris boundary), and the corneal reflection of the close-point pointing light source. According to the promotion of cloud video, the video technology mentioned in it that can understand people's "eyes consciousness" is based on this technology. However, iris recognition + pupil movement recognition can capture the eye movements but can not detect the gaze point of the human eye, this is the hardest injury!
Firstly, iris recognition and pupil recognition are based on a plane. To measure the fixation point, the head must be fixed, so that the relative positions of the eyes and the gaze point are the same. As one of the finest organs in the human body, the human eye only needs a small movement to move the fixation point, and the head movement caused by the human being just because of the breathing is enough to cause the measurement error to cause the positioning deviation. Then we will retreat 10,000 steps, even if the head is fixed, the identification of the iris is not so easy, the European human eye features are more obvious, the recognition is relatively easy, but it is not a home ordinary camera can judge the eyeball Characteristic, while the Asian pupils are mostly dark brown, the human eye features are weak, and the ordinary camera can hardly capture. Therefore, from the point of view of the eye tracking technology of the cloud vision chain, it is impossible to push the information you want through the eyes!
Corneal reflex method is widely recognized and applied in the field of eyeball tracking. It mainly captures human eye features through camera, establishes human eye two-dimensional or three-dimensional gaze point estimation model through algorithm, and judges human eye movement and gaze point through algorithm. The special structure of the eyeball will form one or more Purkinje images. The eyeball tracking based on this method generally locates the first Purkinje image. Through the calibration step, the human eye can be measured on the surface of the vertical plane realistic calibration point. The point of gaze.
Invasive means include embedding an eye movement measuring coil in the eye or using a microelectrode to trace the electrooculogram. The electrooculography detection method measures the potential change when the eyeball moves by the electrode, and the principle is that the eyeball can be considered as a dipole. The advantage is that the cost is low, but the popularity is poor.
MEMS can also achieve eye tracking. One of the MEMS eye tracking techniques described below comes from N. Sarkar and others at the University of Waterloo in Canada.
The eye and the cornea have different diameters, which is the basis of the design. The solution achieves improvements in size, price, power, bandwidth, and accuracy by using the simple design shown below. The design uses a beam of low-emission (1-10μW/cm2), infrared (850nm), divergent (~50mrad) beams. The beam is emitted from the laser source and directed toward the scanner. The scanner has a plane that functions like a mirror to reflect the incident beam. The beam is then directed by the scanner scanner to the cornea and then reflected from the corneal surface (the glancing angle from 60 to 90 degrees) to a photodiode. The function of the photodiode is to receive an optical signal and generate an electrical signal. The output electrical signal increases as the input light intensity increases. As the eye rotates, the scanner controls the beam to track the point on the cornea that allows the photodiode to receive the maximum signal.
It is worth noting that the surface of its photodiode can be used as a spatial filter, eliminating the need for a large area of ​​flat micromirrors. Accordingly, the design uses a Fresnel zone plate scanner. The support anchor can realize the deflection of the scanner scanner with two degrees of freedom (blue support and red support can be rotated), which can complete a large range of beam manipulation.
The following image shows another scanner scanner that also has two degrees of freedom. It works like the one above, and rotates the scanner by supporting the rotation of the anchor to manipulate the angle of the beam. The two central cylindrical lenses are vertically arranged to project a crosshair.
(Scanning electron micrograph of scanner scanner after color rendering)
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