Optical displacement measuring system using a triangulation including a processing of position signals in a time sharing manner

• US 5,814,808 A
• Filed: 08/27/1996
• Issued: 09/29/1998
• Est. Priority Date: 08/28/1995
• Status: Expired due to Fees

• Current Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Works Ltd (Panasonic Holdings Corporation)
• Inventors: Nishikawa, Takayuki, Takada, Yuji, Matsuda, Hiroshi
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US08/703,787
• Time in Patent Office: 763 Days
• Field of Search: 250/206.1, 250/206.2, 250/201.6, 250/201.4, 250/201.2, 250/559.31, 250/559.23, 250/214 AG, 250/214 R, 250/204, 250/222.1, 250/22.1, 356/3.01, 356/3.04, 356/3.06, 356/383, 356/384, 356/215, 356/356, 356/376, 356/381, 356/4.01, 356/4.06, 356/4.07, 396/106, 396/108, 396/96, 396/98, 396/120
• US Class Current: 250/206.1
• CPC Class Codes: G01C 3/085 with electronic parallax measurement
• CPC Class Codes: G01S 17/48 Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves

Abstract

An optical displacement measuring system using a triangulation comprises a light projecting unit for emitting to an object a light beam which is amplitude-modulated by a reference signal having a predetermined period, a light receiving unit for receiving light reflected back from the object and providing a pair of position signals, and a control signal generator for providing first and second control signals in synchronism with the reference signal. The position signals are processed by a switching unit in a time sharing manner according to the first control signal to obtain a first composite signal, in which the position signals occur alternately every integral number of the period of the reference signal. The first composite signal is amplified by a single amplifier at a desired amplification rate, and then sent to a distance determining unit, in which the polarity of the first composite signal is periodically reversed according to the second control signal to obtain a second composite signal, and a distance signal indicative of a distance between the light projecting unit and the object is determined from the second composite signal.

Claims

1. An optical displacement measuring system using a triangulation comprising:

a light projecting means for emitting a light beam, which is amplitude-modulated by a reference signal having a predetermined period, to an object;

a position signal generator for receiving light reflected by said object and providing a pair of first and second position signals;

a control signal generating means for providing first and second control signals in synchronism with said reference signal;

a first switching means for processing said first and second position signals in a time sharing manner according to said first control signal to obtain a first composite signal, in which said first and second position signals occur alternately and occur once every n periods of said reference signal, where n is a positive integer;

a single amplifying means for amplifying said first composite signal at a desired amplification rate; and

a distance determining means for periodically reversing the polarity of said first composite signal provided from said amplifying means according to said second control signal so as to obtain a second composite signal, and determining a distance between said light projecting means and said object from said second composite signal.

2. An optical displacement measuring system as set forth in claim 1, wherein said distance determining means comprises:

a single detecting means for processing said first composite signal according to said second control signal such that said first composite signal is polarity-reversed every half period of said reference signal to obtain said second composite signal;

a second switching means for dividing said second composite signal into a pair of third and fourth position signals according to said first control signal; and

a first operating means for determining said distance between said light projecting means and said object by using said third and fourth position signals.

3. An optical displacement measuring system as set forth in claim 2, wherein said first operating means outputs a light energy signal indicative of an amount of light energy received by said position signal generator, and wherein said distance determining means comprises:

a comparing means for comparing said light energy signal with a constant value to provide an analog output signal indicative of a difference therebetween; and

a feed-back control means for controlling at least one of the amplification rate of said amplifying means and a light output of said light projecting means in accordance with said output signal of said comparing means such that said light energy signal is maintained at the constant value.

4. An optical displacement measuring system as set forth in claim 3, wherein said feed-back control means provides a first feed-back control signal to said amplifying means to increase said amplification rate when said light energy signal is smaller than the constant value, and provides a second feed-back control signal to said light projecting means to reduce said light output when said light energy signal is larger than the constant value.

5. An optical displacement measuring system as set forth in claim 2, wherein said position signal generator comprises:

a light sensing means for receiving said light reflected by said object and providing a pair of preliminary position signals;

a second operating means for providing said second position signal which is one of said preliminary position signals and said first position signal indicative of a difference between said preliminary position signals to said first switching means.

6. An optical displacement measuring system as set forth in claim 5, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal;

an adding means for calculating a sum of outputs of said first and second low-pass filters to obtain a second operation signal, multiplying the output of said second low-pass filter by a correction constant to obtain a third operation signal, and adding said second operation signal to said third operation signal to obtain a fourth operation signal; and

a dividing means for dividing the output of said first low-pass filter by said fourth operation signal to obtain a fifth operation signal, from which said distance between said light projecting means and said object is determined.

7. An optical displacement measuring system as set forth in claim 2, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal;

an adding means for calculating a sum of outputs of said first and second low-pass filters to obtain a first operation signal;

a subtracting means for calculating a difference between the outputs of said first and second low-pass filters to obtain a second operation signal; and

a dividing means for dividing said second operation signal by said first operation signal to obtain a third operation signal, from which said distance between said light projecting means and said object is determined.

8. An optical displacement measuring system as set forth in claim 2, wherein said position signal generator comprises:

a light sensing means for receiving said light reflected by said object and providing a pair of preliminary position signals;

a second operating means for providing said first position signal indicative of a difference between said preliminary position signals, and said second position signal indicative of a sum of said preliminary position signals to said first switching means.

9. An optical displacement measuring system as set forth in claim 8, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal; and

a divider circuit for dividing an output of said first low-pass filter by an output of said second low-pass filter to obtain a third operation signal, from which said distance between said light projecting means and said object is determined.

10. An optical displacement measuring system as set forth in claim 1, where said position signal generator comprises:

a light sensing means for receiving said light reflected by said object and providing a pair of preliminary position signals which are current signals; and

a current/voltage converting means for converting said current signals to corresponding voltage signals.

11. An optical displacement measuring system as set forth in claim 1, wherein said first switching means provides said first composite signal, in which said first and second position signals occur alternately and occur once every one period of said reference signal.

12. An optical displacement measuring system as set forth in claim 11, wherein said distance determining means comprises:

a detecting means for processing said first composite signal according to said second control signal which is in out of phase relation to said first control signal by 90 degrees such that said first composite signal is polarity-reversed every one period of said reference signal to obtain said second composite signal, then extracting a third position signal from said second composite signal according to said first control signal, and integrating said second composite signal to obtain a fourth position signal; and

a first operating means for determining said distance between said light projecting means and said object by using said third and fourth position signals.

13. An optical displacement measuring system as set forth in claim 12, wherein said position signal generator comprises:

a light sensing means for receiving said light reflected by said object and providing a pair of preliminary position signals;

a second operating means for providing said first position signal indicative of a difference between said preliminary position signals, and said second position signal indicative of a sum of said preliminary position signals to said first switching means.

14. An optical displacement measuring system as set forth in claim 13, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal;

an adding means for calculating a sum of outputs of said first and second low-pass filters to obtain a third operation signal, multiplying the output of said second low-pass filter by a correction constant to obtain a fourth operation signal, and adding said third operation signal to said fourth operation signal to obtain a fifth operation signal; and

a dividing means for dividing the output of said first low-pass filter by said fifth operation signal to obtain a sixth operation signal, from which said distance between said light projecting means and said object is determined.

15. An optical displacement measuring system as set forth in claim 12, wherein said position signal generator comprises:

a light sensing means for receiving said light reflected by said object and providing a pair of preliminary position signals;

a second operating means for providing said first position signal which is one of said preliminary position signals and said second position signal indicative of a difference between said preliminary position signals to said first switching means.

16. An optical displacement measuring system as set forth in claim 15, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal;

an adding means for calculating a sum of outputs of said first and second low-pass filters to obtain a second operation signal, multiplying the output of said second low-pass filter by a correction constant to obtain a third operation signal, and adding said second operation signal to said third operation signal to obtain a fourth operation signal; and

a dividing means for dividing the output of said first low-pass filter by said fourth operation signal to obtain a fifth operation signal, from which said distance between said light projecting means and said object is determined.

17. An optical displacement measuring system as set forth in claim 11, wherein said control signal generating means further provides a third control signal in synchronism with said reference signal, which is in out of phase relation to said first control signal by 90 degrees.

18. An optical displacement measuring system as set forth in claim 17, wherein said distance determining means comprises:

a detecting means including a first circuit for processing said first composite signal according to said second control signal such that said first composite signal is polarity-reversed every half period of said reference signal to obtain a third position signal, and a second circuit for processing said first composite signal according to said third control signal such that said first composite signal is polarity-reversed every one period of said reference signal to obtain a fourth position signal; and

a first operating means for determining said distance between said light projecting means and said object by using said third and fourth position signals.

19. An optical displacement measuring system as set forth in claim 18, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal; and

a second low-pass filter for integrating said fourth position signal; and

a divider circuit for dividing an output of said second low-pass filter by an output of said first low-pass filter to obtain an operation signal, from which said distance between said light projecting means and said object is determined.

20. An optical displacement measuring system as set forth in claim 11, wherein said distance determining means comprises:

a detecting means including a first circuit for processing said first composite signal according to said second control signal which is in out of phase relation to said first control signal by 90 degrees such that said first composite signal is polarity-reversed every one period of said reference signal to obtain a third position signal, and a second circuit for processing said third position signal according to said first control signal such that said third position signal is polarity-reversed every one period of said reference signal to obtain a fourth position signal; and

a first operating means for determining said distance between said light projecting means and said object by using said third and fourth position signals.

21. An optical displacement measuring system as set forth in claim 20, wherein said first operating means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal; and

a divider circuit for dividing an output of said first low-pass filter by an output of said second low-pass filter to obtain an operation signal, from which said distance between said light projecting means and said object is determined.

22. An optical displacement measuring system as set forth in claim 11, wherein said distance determining means comprises:

a detecting means including a first circuit for processing said first composite signal according to said second control signal such that said first composite signal is polarity-reversed every half period of said reference signal to obtain a third position signal, and a second circuit for processing said third position signal according to said first control signal such that said third position signal is polarity-reversed every one period of said reference signal to obtain a fourth position signal; and

a first operating means for determining said distance between said light projecting means and said object by using said third and fourth position signals.

23. An optical displacement measuring system as set forth in claim 22, wherein said first operational means comprises:

a first low-pass filter for integrating said third position signal;

a second low-pass filter for integrating said fourth position signal; and

a divider circuit for dividing an output of said second low-pass filter by an output of said first low-pass filter to obtain an operation signal, from which said distance between said light projecting means and said object is determined.

24. An optical displacement measuring method comprising:

emitting a light beam, which is amplitude-modulated by a reference signal having a predetermined period, to an object;

receiving light reflected by said object and providing a pair of first and second position signals;

providing first and second control signals in synchronism with said reference signal;

processing said first and second position signals in a time sharing manner according to said first control signal to obtain a first composite signal, in which said first and second position signals occur alternately and occur once every n periods of said reference signal, where n is a positive integer;

amplifying said first composite signal at a desired amplification rate;

periodically reversing the polarity of said first composite signal provided from said amplifying means according to said second control signal so as to obtain a second composite signal; and

determining a distance between said light projecting means and said object from said second composite signal.