Method and system for high-speed, 3-D imaging of an object at a vision station

• US 4,796,997 A
• Filed: 05/21/1987
• Issued: 01/10/1989
• Est. Priority Date: 05/27/1986
• Status: Expired due to Term

• Current Assignee: GSI Lumonics Corporation (Novanta Inc.)
• Original Assignee: Synthetic Vision Systems, Inc.
• Inventors: Smith, David N., Doss, Brian, Svetkoff, Donald J.
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US07/052,841
• Time in Patent Office: 600 Days
• Field of Search: 356/1, 356/375, 356/376
• US Class Current: 356/608
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures

Abstract

A method and system for high-speed, 3-D imaging of an object at a vision station including a flying spot laser scanner, a dynamically configurable spatial filter and a diffuser for spatial averaging, are used in conjunction with a variable transmission filter in an optical depth sensing system. The reflected laser signal received by the sensing system is first spatially filtered and averaged and then split into first and second beams which are imaged onto a pair of highly sensitive photodetectors which introduce capability for high-speed, 3-D sensing under low light level conditions. The first beam passes through a variable transmission filter which is used to encode position which, in turn, is proportional to the height of the object. The second or reference split beam is provided to compensate for changes in the reflectance of the object and the power of the laser scanner. A high-speed signal processing unit which incorporates special circuitry to greatly extend dynamic range computes the ratio of the transmitted signal to the sum of the reference signal and the transmitted signal to determine height information. The signal processing unit also contains noise rejection circuitry which is activated during "off" and "on" periods of laser diode TTL modulation and includes feedback control for pulse amplitude modulation of the laser diode source if necessary to increase dynamic range of the system.

Claims

1. A method for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the method comprising the steps of:

scanning a beam of controlled light at the surface of the object at a first predetermined angle to generate a corresponding reflected light signal;

receiving said reflected light signal at a second angle with a set of optical components;

spatially filtering the received signal;

spatially averaging the received light signal with the set of optical components to compensate for non-uniform intensity distributions in the received signal, said step of averaging including the step of creating a uniform spot of light;

optically splitting the received light signal into first and second split beams, the second split beam being a reference beam;

imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively, to produce corresponding first and second electrical signals proportional to the measurements;

normalizing the first and second electrical signals to lie within a predetermined range; and

computing a centroid value for the first split beam from the normalized signals.

3. The method as claimed in claim 1 or claim 2 wherein said step of normalizing includes the step of summing the first and second electrical signals to obtain a resultant signal wherein the resultant signal is normalized to lie within the predetermined range, and wherein the centroid is computed from the normalized sum.

4. The method as claimed in claim 1 or claim 2 wherein the first and second electrical signals have an analog representation and wherein said step of normalizing further includes the steps of generating a digital representation of the first and second electrical signals and utilizing the digital representation to scale the first and second electrical signals to lie within the predetermined range.

5. The method as claimed in claim 4 further comprising the steps of modulating the beam of controlled light to shift the frequency of the controlled light to a predetermined band of frequencies and demodulating the first and second electrical signals.

6. THe method as claimed in claim 5 wherein the step of demodulating includes the step of removing noise from the first and second electrical signals with a filter having a transmission band including the predetermined band of frequencies.

7. The method as claimed in claim 1 or claim 2 wherein said step of spatially filtering utilizes a programmable mask correlated with a height profile of the object at the vision station.

8. The method as claimed in claim 1 or claim 2 wherein said step of spatially averaging includes the step of converting the spot of light into a line of light.

9. The method as claimed in claim 8 wherein the step of spatially filtering the received light utilizes a spatial filter of the set of optical components.

10. The method as claimed in claim 1 or claim 2 wherein at least one of said photodetectors is a photodiode having a measuring area of less than 20 mm².

2. A method for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the method comprising the steps of:

scanning a beam of controlled light at the surface of the object at a first predetermined angle to generate a corresponding reflected light signal;

receiving said reflected light signal at a second angle with a set of optical components;

spatially filtering the received signal;

spatially averaging the received light signal with the set of optical components to compensate for non-uniform intensity distributions in the received signal, said step of averaging including the step of creating a uniform spot of light;

optically splitting the received light signal into first and second split beams;

transmitting a portion of the first split beam dependent on the second angle;

imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively, to produce corresponding first and second electrical signals proportional to the measurements;

normalizing the first and second electrical signals to lie within a predetermined range; and

computing a centroid value for the first split beam from the normalized signals.

11. A method for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the method comprising the steps of:

scanning a beam of controlled, modulated light at the surface of the object at a first predetermined angle to generate a corresponding reflected light signal;

receiving said reflected light signal at a second angle with a set of optical components;

spatially filtering the received light signal with the set of optical components;

spatially averaging the received light signal with the set of optical components to compensate for non-uniform intensity distributions in the received signal, said step of averaging including the step of creating a uniform spot of light;

optically splitting the received light signal into first and second split beams, the second split beam being a reference beam;

imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively, to produce corresponding first and second electrical signals proportional to the measurements;

normalizing the first and second electrical signals wherein the step of normalizing includes the step of scaling the first and second electrical signals to lie within a predetermined range;

demodulating the scaled first and second electrical signals; and

computing a centroid value for the first split beam from the demodulated signals.

12. An imaging system for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the system comprising:

a source for scanning a beam of controlled light at the surface of the object at a first predetermined angle to generate a corresponding reflected light signal;

a set of optical components for receiving the reflected light signal ta second angle, for spatially filtering the received signal, for spatially averaging the received light signal to compensate for non-uniform intensity distributions in the received signal, and for optically splitting the received light signal into first and second split beams, the second split beam being a reference beam said set of optical components including means for creating a uniform spot of light;

first and second photodetector means for measuring the amount of radiant energy in the first split beam and the reference beam, respectively, and producing first and second electrical signals proportional to the measurements, respectively;

means for imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively; and

signal processing means for normalizing the first and second electrical signals to lie within a predetermined range and for computing a centroid value for the first split beam from the normalized signals.

14. The system as claimed in claim 12 or claim 13 wherein the signal processing means includes a summing circuit for summing the first and second electrical signals to obtain a resultant signal wherein the resultant signal is normalized to lie within the predetermined range and wherein the centroid is computed from the normalized sum.

15. The system as claimed in claim 12 or claim 13 wherein the first and second electrical signals have an analog representation and wherein the signal processing means includes generating means for generating a digital representation of the first and second electrical signals.

16. The system as claimed in claim 15 wherein said signal processing means includes scaler means coupled to the generating means and utilizing the digital representation to scale the first and second electrical signals to lie within the predetermined range.

17. The system as claimed in claim 16 wherein said scaler means includes a set of programmable amplifiers for selectively amplifying the first and second electrical signals in response to the digital representation.

18. The system as claimed in claim 17 further comprising modulating means for modulating the beam of controlled light to shift the frequency of the controlled light to a predetermined band of frequencies and wherein said signal processing means includes a demodulator for demodulating the first and second digital signals.

19. The system as claimed in claim 18 wherein said demodulator includes a filter having a transmission band including the predetermined band of frequencies for removing noise from the first and second electrical signals.

20. The system as claimed in claim 12 or claim 13 wherein said set of optical components includes means for spatially filtering the received light signal including a programmable mask correlated with a height profile of the object at the vision station.

21. The system as claimed in claim 12 or claim 13 wherein said set of optical components includes a spot-to-line converter for converting the spot of light into a line of light.

22. The system as claimed in claim 21 wherein said means for spatially filtering includes a spatial filter for spatially filtering the received light.

23. The system as claimed in claim 12 or claim 13 wherein areas of the first and second photodiodes, respectively.

24. The system as claimed in claim 12 or claim 13 wherein each of said first and second photodetector means includes a single photodiode having a measuring area of less than 20 mm² for converting the radiant energy into an electrical current.

25. The system as claimed in claim 24 wherein each of said photodiodes has a measuring area of less than 10 mm².

26. The system as claimed in claim 12 or claim 13 wherein said set of optical components includes splitting means for optically splitting the received light signal into the first and second split beams.

27. The system as claimed in claim 12 or claim 13 wherein said source is a laser scanner.

28. The system as claimed in claim 27 wherein said laser scanner is a flying spot laser scanner.

13. An imaging system for high-speed 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the system comprising:

a source for scanning a beam of controlled light at the surface of the object at a first predetermined angle to generate a corresponding light signal;

a set of optical components for receiving the reflected light signal at a second angle, for spatially filtering the received signal, for spatially averaging the received light signal to compensate for non-uniform intensity distributions in the received signal, and for optically splitting the received light signal into first and second split beams, the set of optical components including transmitting means for transmitting a portion of the first split beam dependent on the second angle, said set of optical components including means for creating a uniform spot of light;

first and second photodetector means for measuring the amount of radiant energy in the transmitted portion of the first split beam and the second split beam, respectively, and producing first and second electrical signals proportional to the measurements, respectively;

means for imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively; and

signal processing means for normalizing the first and second electrical signals to lie within a predetermined range and for computing a centroid value for the first split beam from the normalized signals.

29. An imaging system for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the system comprising:

a source for scanning a beam of controlled modulated light at the surface of the object at a first predetermined angle to generate a corresponding reflected light signal;

a set of optical components for receiving the reflected light signal at a second angle, the set of optical components including means for spatially filtering the received light signal, averaging means for averaging the received light signal to compensate for non-uniform intensity distributions in the received signal said averaging means including means for creating a uniform spot of light, and splitting means for optically splitting the received light signal into first and second split beams, the second split beam being a reference beam;

first and second photodetector means for measuring the amount of radiant energy in the first split beam and the reference beam, respectively, and producing first and second electrical signals proportional to the measurements, respectively;

means for imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively; and

signal processing means for normalizing the first and second electrical signals, said signal processing means including scaler means for scaling the first and second electrical signals to lie within a predetermined range and a demodulator for demodulating the first and second electrical signals to reduce noise in the signals, said signal processing means computing a centroid value for the first split beam from the demodulated signals.

30. A method for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the method comprising the steps of:

(a) scanning a beam of controlled light at the surface of the object at a first predetermined angle to generate a corresponding reflected light signal;

(b) receiving said reflected light signal at a second angle with a set of optical components;

(c) spatially filtering the received light signal with the set of optical components;

(d) spatially averaging the received light signal with the set of optical components to compensate for non-uniform intensity distributions in the received signal, said step of averaging including the step of creating a uniform spot of light;

(e) optically splitting the received light signal into first and second split beams, the second split beam being a reference beam;

(f) imaging the first and second split beams to first and second predetermined measuring areas of first and second photodetector means, respectively, to produce a corresponding pair of electrical signals proportional to the measurements;

generating a feedback signal dependent on the pair of electrical signals;

utilizing the feedback signal to control the modulation of a source of controlled light;

utilizing a beam of the controlled light in steps (a) through (f);

normalizing the second pair of electrical signals wherein the step of normalizing includes the step of scaling the second pair of electrical signals to lie within a predetermined range;

demodulating the scaled second pair of electrical signals; and

computing a centroid value for the first split beam of the second pair of electrical signals from the demodulated signals.

31. An imaging system for the high-speed, 3-D imaging of an object at a vision station to develop dimensional information associated with the object, the system comprising:

a source including first and second sources for sequentially scanning first and second beams of controlled modulated light respectively, at the surface of the object at a first predetermined angle to generated corresponding reflected light signals;

a set of optical components for receiving the reflected light signals at a second angle, the set of optical components including means for spatially filtering the received light signal;

means for spatially averaging the received light signal to compensate for non-uniform intensity distributions in the received signal, said means for averaging including means for creating a uniform spot of light and splitting means for optically splitting each of the received light signals into first and second pairs of split beams, the second split beam being a reference beam;

first and second photodetector means for measuring the amount of radiant energy in the first split beams and the reference beams, respectively, and producing first and second pairs of signals proportional to the measurements, respectively, the first pair electrical signals corresponding to the first pair of split beams and the second pair of electrical signals corresponding to the second pair of split beams;

means for imaging the first and second split beams to first and second predetermined measuring areas of the first and second photodetector means, respectively, to produce corresponding first and second electrical signals proportional to the measurements;

feedback means for generating a feedback signal dependent on the first pair of electrical signals, the feedback means controlling the modulation of the second source to improve noise suppression and extension of the dynamic range of the system; and

signal processing means for normalizing the second pair of electrical signals, said signal processing means including scaler means for scaling the second pair of electrical signals to lie within a predetermined range and a demodulator for demodulating the second pair of electrical signals to reduce noise in the signals, said signal processing means computing a centroid value for the first split beam of the second pair of split beams from the demodulated signal.