Method and device for enhancing accuracy in ultrasonic range measurement

• US 7,724,355 B1
• Filed: 06/26/2008
• Issued: 05/25/2010
• Est. Priority Date: 11/29/2005
• Status: Expired due to Fees

• Current Assignee: Navisense
• Original Assignee: Navisense
• Inventors: McIntosh, Jason, Boillot, Marc Andre
• Primary Examiner(s): Tarcza, Thomas H
• Assistant Examiner(s): Brainard, Timothy A
• Application Number:
  US12/146,445
• Time in Patent Office: 698 Days
• Field of Search: 367/100
• US Class Current: 356/5.01
• CPC Class Codes: G01S 15/104 wherein the transmitted pulses use a frequency- or phase-modulated carrier wave
• CPC Class Codes: G01S 15/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S15/46
• CPC Class Codes: G01S 15/50 Systems of measurement, based on relative movement of the target
• CPC Class Codes: G01S 15/66 Sonar tracking systems
• CPC Class Codes: G01S 15/88 Sonar systems specially adapted for specific applications seismic or acoustic prospecting or detecting G01V1/00
• CPC Class Codes: G06F 3/043 using propagating acoustic waves

Abstract

A device (100) and method (300) for enhancing range detection accuracy in ultrasonic touchless sensing applications can include transmitting (302) an ultrasonic signal intended to reflect off a finger and produce an echo, receiving (304) the echo, saving (306) most recent echoes to a history (400), selectively discarding (308) echoes less recently saved in the history to produce a sparse history, identifying (310) a relative phase of the echo with respect to a previously received echo in the sparse history, tracking (312) a location and a movement of the finger from an arrival time of the echo and the relative phase, and providing (314) touchless control to a user interface control in accordance with the location and the movement of the finger.

Claims

1. A method for short range detection using ultrasonic sensing, comprising:

shaping a pulse signal to produce a pulse shaped signal;

transmitting the pulse shaped signal, the pulse shaped signal reflecting off a finger to produce a reflected signal;

receiving the reflected signal;

identifying a relative phase of the reflected signal with respect to a previously received reflected signal;

tracking a location and a movement of the finger from an arrival time of the reflected signal and the relative phase;

saving most recent echoes to a history, and selectively discarding echoes less recently saved in the history based on a similarity measure between echoes in the history; and

providing touchless control to a user interface control in accordance with the location and the movement of the finger,

wherein the shaping uses a combination of amplitude modulation, frequency modulation, and phase modulation.

2. The method of claim 1, further comprising converting the location and the movement to a coordinate or control action to associate with the user interface control.

3. The method for claim 1, wherein the step of identifying further comprises:

identifying an arrival time from a correlation between a first reflected signal and a second reflected signal;

identifying a phase delay from the correlation for establishing a relative displacement of the finger; and

controlling the user interface control in accordance with the arrival time and the relative displacement.

4. The method of claim 1, wherein the step of discarding echoes comprises selectively pruning the history based on one among an L2 norm based, spectral distortion based, log-likelihood based, or mean-squared error based metric.

5. The method of claim 1, comprising

creating a sparse history of echoes based on a difference rate between echoes;

and

updating an index table to the echoes in the history according to the sparse history,

wherein the sparse history weights echoes more heavily in the near-time than in the far-time.

6. The method of claim 5, comprising

scanning through the history to identify an index for the echoes where an echo difference (ePR(i)−

ePR(i−

n)) is significantly greater than a noise difference (n(i)−

n(i−

n)),

where the index is large and that the echo difference for current and past ambient conditions are below a predetermined minimum threshold.

7. A method for enhancing range detection accuracy suitable for use in ultrasonic touchless sensing applications, comprising

transmitting an ultrasonic signal intended to reflect off a finger and produce an echo;

receiving the echo and saving most recent echoes to a history;

selectively discarding echoes less recently saved in the history to produce a sparse history;

identifying a relative phase of the echo with respect to a previously received echo in the sparse history;

comparing the echoes in the history for similarity and selectively pruning echoes in the history with high similarity;

replacing the pruned echoes with echoes having low similarity;

tracking a location and a movement of the finger from an arrival time of the echo and the relative phase; and

providing touchless control to a user interface control in accordance with the location and the movement of the finger.

8. The method of claim 7, comprising

generating an index table for the echoes in the history such that the history then identifies echoes with time indexes and corresponding distance measures.

9. The method of claim 7, comprising

comparing a present echo to the echoes in the history to calculate an updated set of differences;

and

removing echoes in the history that do not contribute a noticeable difference based on the updated set of differences for pruning the echoes in the history.

10. The method of claim 9, comprising subtracting off an echo if a current ambient components is distorting the echo.

11. The method of claim 7, where the history table indirectly stores information associated with previous ambient components.

12. The method of claim 7, comprising subtracting from an echo return that includes a primary response (PR) component, a direct path (DP) component, an ambient component (A), and a noise (N) component a Primary Response (PR) component of a previous echo saved in the history.

13. The method of claim 12, comprising adaptively removing echo components received from a non-moving object in proximity of the finger to increase a signal to noise ratio of the echo for tracking the finger when the finger is moving.