SPATIAL MODULATION OF LIGHT TO DETERMINE OBJECT POSITION

• US 20150276387A1
• Filed: 02/14/2014
• Published: 10/01/2015
• Est. Priority Date: 02/14/2014
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Kletter, Doron, Martini, Joerg, Bern, Marshall W., Johnson, Noble M., Kiesel, Peter, Cheng, Bowen, Recht, Michael I.
• Granted Patent: US 9,528,925 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01N 15/1429 Signal processing
• CPC Class Codes: G01N 15/1459 the analysis being performed on a sample stream
• CPC Class Codes: G01N 2015/0038 Investigating nanoparticles
• CPC Class Codes: G01N 2015/0053 in liquids, e.g. trouble
• CPC Class Codes: G01N 2015/1006 for cytology
• CPC Class Codes: G01N 2021/8592 Grain or other flowing solid samples

Abstract

Approaches for determining object position in a flow path are disclosed. A system includes a spatial filter having a length disposed along a longitudinal axis of the flow path and a width along a lateral axis of the flow path. The spatial filter has mask features configured to modulate light. Light emanating from objects moving along the flow path is detected. The detected light has a component along a detection axis that makes a non-zero angle with respect to the longitudinal and lateral axes. An electrical output signal that includes information about the trajectory depth of the object is generated in response to the detected light.

Claims

1. An assembly, comprising:

at least one spatial filter having a length along a longitudinal axis of a flow path and a width along a lateral axis of the flow path, the spatial filter having mask features disposed at least partially along the length of the spatial filter and extending at least partially across the width of the spatial filter, the mask features including at least first mask features having a first transmission characteristic and second mask features having a second transmission characteristic different from the first transmission characteristic;

at least one detector positioned to detect light with respect to a detection axis, the detection axis making a non-zero angle with respect to the longitudinal and lateral axes, the detected light emanating from at least one object and modulated according to the mask features as the object moves along the longitudinal axis, the detector configured to generate a time-varying electrical signal in response to the detected light, the time-varying electrical signal including information about a depth of the object in the flow path along the detection axis; and

an analyzer configured to determine the depth of the object based on the signal.

2. The assembly of claim 1, wherein:

the spatial filter is positioned between a light source that provides measurement light and the object; and

the spatial filter interacts with the measurement light to provide spatially modulated measurement light.

3. The assembly of claim 1, wherein:

the spatial filter is positioned between the object and the detector; and

the light emanating from the object interacts with the spatial filter to provide modulation of the sensed light.

4. The assembly of claim 1, wherein:

the light emanating from the object interacts with the spatial filter to provide cones of light that emerge from the mask, the angle of each cone related to the depth of the object; and

the time-varying signal includes at least one characteristic associated with the angle of the cone.

5. The assembly of claim 1, wherein:

the mask features include a first set of features alternating with a second set of features;

the first set of features comprises at least two transmissive regions having length L1, each transmissive region of length L1 separated from another transmissive region of length L1 by a less-transmissive region of length L2, where L1>

L2; and

the second set of features comprises at least two less-transmissive regions having length L1, each less-transmissive region of length L1 separated from another less transmissive region of length L1 by a transmissive region of length L2.

6. The assembly of claim 1, wherein:

the time-varying signal generated in response to the modulated light includes a first signal component of a first frequency superimposed with a second signal component of a second frequency, the first frequency being different from the second frequency.

7. The assembly of claim 6, wherein the second frequency is a multiple of the first frequency.

8. The assembly of claim 6, wherein the analyzer is configured to determine the depth of the object in the flow channel by comparing the amplitude of the first signal component to the amplitude of the second signal component.

9. The assembly of claim 1, wherein:

the time-varying signal generated in response to the modulated light includes a first signal component of a first frequency superimposed with a second signal component of a second frequency, the first frequency being different from the second frequency; and

the analyzer is configured to perform a Fourier transform of the time-varying signal and to compare an amplitude of the Fourier transform signal at the first frequency to an amplitude of the Fourier transform signal at the second frequency to determine the depth position of the object.

10. The assembly of claim 9, wherein the analyzer is configured to determine the depth of the object in the flow channel based on a difference between the amplitude of the Fourier transform signal at the first frequency and the amplitude of the Fourier transform signal at the second signal component.

11. The assembly of claim 1, wherein:

the signal generated in response to the sensed light has a modulation envelope, the modulation envelop defined by a lower envelope function and an upper envelope function; and

the analyzer is configured to determine the depth of the object based on one or more characteristics of the modulation envelope.

12. The assembly of claim 11, wherein the depth is determined based on an amount of modulation of the lower envelope function.

13. The assembly of claim 1, wherein:

an edge between the first and second mask features for at least some of the mask features extends at an angle that is not perpendicular and not parallel to the longitudinal axis of the mask; and

the spatial filter includes at least one reference feature that is substantially parallel to the lateral axis.

14. The assembly of claim 13, wherein the time-varying signal also includes information about a position of the object along at least one of the lateral and longitudinal axes.

15. The assembly of claim 1, wherein:

the mask features include a first set of features alternating with a second set of features;

the first set of features comprises at least two transmissive regions having length L1, each transmissive region of length L1 separated from another transmissive region of length L1 by a less-transmissive region of length L2, where L1>

L2; and

the second set of features comprises at least two less-transmissive regions having length L1, each less-transmissive region of length L1 separated from another less transmissive region of length L1 by a transmissive region of length L2, wherein each mask feature has at least one edge that is not parallel and not perpendicular to the longitudinal axis of the mask.

16. The assembly of claim 1, wherein the mask features have a changing frequency across the lateral axis of the spatial filter.

17. The assembly of claim 1, wherein the analyzer is further configured to determine position of the object along the lateral and longitudinal axes based on the signal.

18. The assembly of claim 1, wherein:

the spatial filter includes;

a first group of mask features; and

second group of mask features;

the detector is configured to generate a time varying electrical signal, the time varying electrical signal having a first portion generated in response to detected light modulated according to the first group of mask features and having a second portion generated in response to detected light modulated according to the second group of mask features.

19. The assembly of claim 18, wherein at least one edge between a first mask feature and a second mask feature of the first group of mask features is not parallel or perpendicular to the longitudinal axis.

20. The assembly of claim 19, wherein the first group of mask features includes one or more triangular mask features.

21. An assembly, comprising:

a first spatial filter arranged along an x-y plane of a flow path characterized in three dimensional space by x, y, and z axes, the first mask having a first group of mask features;

a second spatial filter arranged along an x-z plane of the flow path, the second mask having a second group of mask features;

a first detector positioned to detect light emanating from at least one object and modulated according to the first group of mask features as the object moves along the flow path, the first detector configured to generate a first time-varying electrical signal in response to the detected light modulated according to the first group of mask features;

a second detector positioned to detect light emanating from at least one object and modulated according to the second group of mask features as the object moves along the flow path, the second detector configured to generate a second time-varying electrical signal in response to the detected light modulated according to the second group of mask features; and

an analyzer configured to determine a position of the object along the x, y, and z axes based on the first and second time-varying signals.

22. The assembly of claim 21, wherein at least one edge between a first mask feature and a second mask feature of the first group of mask features is not parallel or perpendicular to a flow direction of the flow path.

23. A method, comprising:

detecting light emanating from objects moving along a flow path, the emanating light modulated by at least one spatial filter having a length along a longitudinal axis of a flow path and a width along a lateral axis of the flow path, the spatial filter having mask features configured to modulate light, the detected light having a component along a detection axis that makes a non-zero angle with respect to the longitudinal and lateral axes;

generating an electrical output signal in response to the detected light; and

determining a depth of the object in the flow path along the detection axis based on the output signal.

24. The method of claim 23, wherein determining the depth of the object comprises performing a time domain analysis.

25. The method of claim 23, wherein determining the depth of the object comprises performing a frequency domain analysis.