Granted Patent B2

US 10,824,229 · App. 15/876,148 · Granted Nov 3, 2020

Abstract

Claims (42)

1. An eye-tracking method comprising:

identifying a first location of a cornea of an eye, the cornea having a corneal surface;

steering a beam of light in two dimensions through the effect of a microelectromechanical system (MEMS) operating at a resonant frequency, over a portion of the eye that comprises the cornea, wherein the MEMS is a 2-degree-of-freedom device having two axes, at least one of which is centered at a bias position that is based on the first location of the cornea and then operated in resonance around that bias position; and

detecting a first corneal glint reflected from the corneal surface with a non-imaging photodiode configuration.

2. The method of claim 1 wherein the steered beam of light strikes the corneal surface substantially at a glancing angle of 60°.

3. The method of claim 2 wherein the MEMS is a 2-degree-of-freedom device having a fast-axis and a slow-axis, the fast-axis operating at its resonant frequency and the slow-axis operating at 1/2 the resonant frequency.

4. The method of claim 3 wherein the fast-axis resonant frequency defines the horizontal scan rate of a system employing the method.

5. The method of claim 3 wherein the resonant frequency is substantially 3.3 kHz.

6. The method of claim 1 further comprising:

adjusting the detected response by a phase adjusted amount.

7. The method of claim 6 further comprising:

determining the phase adjusted amount.

8. The method of claim 1 wherein the beam of light is steered in a Lissajous pattern.

9. The method of claim 1 wherein the MEMS is a 2-degree-of-freedom device having a fast-axis and a slow-axis, the fast-axis being initially biased to an offset and then operating at its resonant frequency around that offset.

10. The method of claim 1 wherein the MEMS is a 2-degree-of-freedom device having a fast-axis and a slow-axis, the fast-axis being initially biased to a first offset and then operating at its resonant frequency around the first offset, the slow-axis being initially set to a second offset and then operating at 1/2 its resonant frequency around the second offset.

11. The method of claim 1 further comprising predicting a post-saccade position of the eye.

12. The method of claim 11 wherein the post-saccade position is predicted via operations comprising:

steering the beam of light to generate a plurality of scans in at least one of the two axes over at least a portion of the eye;

estimating a plurality of positions of the cornea, wherein each position of the plurality thereof is based on a corneal glint detected during a different scan of the plurality thereof, the plurality of corneal glints including the first corneal glint;

determining a velocity of the cornea during a saccade based on the plurality of positions; and

predicting a post-saccade position of the cornea based on the measured velocity.

13. The method of claim 1 further comprising:

estimating a first position of the cornea along a first dimension of the two dimensions based on the first corneal glint;

detecting a reflected signal at a non-imaging photodiode, wherein the reflected signal includes a portion of the beam of light reflected from the cornea;

providing a first output signal that is based on the intensity of the reflected signal;

generating a peak-hold signal based on the first output signal, wherein the peak-hold signal is characterized by an envelope having at least one inflection point; and

estimating a second position of the cornea along a second dimension of the two dimensions based on at the least one inflection point.

14. The method of claim 1 further comprising:

estimating a first position of the cornea along a first dimension of the two dimensions based on the first corneal glint;

establishing a second position along a second dimension of the two dimensions based on the first corneal glint;

detecting a reflected signal at a non-imaging photodiode, wherein the reflected signal includes a portion of the beam of light reflected from the cornea;

steering the beam of light to generate a first scan along the first dimension over at least a portion of the eye, wherein the first scan is generated at a positive position offset from the second position;

during the first scan, detecting a first peak magnitude of the reflected signal;

steering the beam of light to generate a second scan along the first dimension over at least a portion of the eye, wherein the second scan is generated at a negative position offset from the second position;

during the second scan, detecting a second peak magnitude of the reflected signal; and

incrementing the second position by (i) the positive offset position if the first peak magnitude is greater than the second peak magnitude, or (ii) the negative offset position if the second peak magnitude is greater than the first peak magnitude.

15. The method of claim 1 further comprising:

driving the MEMS in a first axis of the two axes with a first drive signal that is periodic;

detecting a second corneal glint reflected from the corneal surface, wherein the first and second corneal glints are detected during a first period of the first drive signal, and wherein the first corneal glint is characterized by a first peak at a first time and the second corneal glint is characterized by a second peak at a second time;

determining a phase offset based on a midpoint between the first time and second time; and

controlling the first drive signal based on the phase offset.

16. The method of claim 1 wherein the first location is identified based on a raster scan of the beam of light over the portion.

Assignments (9)