Light wave distance measuring apparatus

1. A wave light distance measuring apparatus, comprising:

a light source portion for applying a distance measuring light amplitude-modulated with a reference electrical signal as a sine wave signal having a predetermined frequency to an object to be measured;

a light receiving portion for receiving the distance measuring light reflected by the object to be measured to convert the received distance measuring light into a received electrical signal;

A/D conversion means for A/D-converting the reference electrical signal and the received electrical signal based on a sampling signal;

phase difference detecting means for detecting phases of the reference electrical signal and the received electrical signal which are A/D-converted by the A/D conversion means to subtract the phase of the reference electrical signal from the phase of the received electrical signal, whereby detecting a phase difference between the reference electrical signal and the received electrical signal; and

distance detecting means for detecting a distance to the object to be measured based on the phase difference detected by the phase difference detecting means,

wherein the reference electrical signal has two kinds of frequencies which are different from each other and any one of which is alternatively selected,

the sampling signal is synchronized with the reference electrical signal having the two kinds of frequencies once every n times, and a frequency of the sampling signal is equal to an average value of the two kinds of frequencies of the reference electrical signals, and

the A/D conversion means carries out at least one A/D conversion per period of the reference electrical signal and the received electrical signal based on the sampling signal.

2. A light wave distance measuring apparatus according to claim 1 , wherein when one of the two kinds of frequencies of the reference electrical signal is assigned f 1 , the other is assigned f 2 , and the frequency of the sampling signal is assigned f s , a following relationship is met:

f 1 /f s =( n+ 1)/ n

f 2 /f s =( n− 1)/ n.

3. A light wave distance measuring apparatus according to claim 2 , wherein the distance measuring light is burst-emitted.

4. A light wave distance measuring apparatus according to claim 3 , wherein the phase difference detecting means removes a D.C. component contained in digital data of the reference electrical signal and the received electrical signal based on the received electrical signal during non-light emission of the distance measuring light converted into the digital data by the A/D conversion means.

5. A light wave distance measuring apparatus according to claim 4 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

6. A light wave distance measuring apparatus according to claim 3 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

7. A light wave distance measuring apparatus according to claim 2 , wherein the phase difference detecting means removes a D.C. component contained in digital data of the reference electrical signal and the received electrical signal based on the received electrical signal during non-light emission of the distance measuring light converted into the digital data by the A/D conversion means.

8. A light wave distance measuring apparatus according to claim 7 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

9. A light wave distance measuring apparatus according to claim 2 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

10. A light wave distance measuring apparatus according to claim 1 , wherein the distance measuring light is burst-emitted.

11. Alight wave distance measuring apparatus according to claim 10 , wherein the phase difference detecting means removes a D.C. component contained in digital data of the reference electrical signal and the received electrical signal based on the received electrical signal during non-light emission of the distance measuring light converted into the digital data by the A/D conversion means.

12. A light wave distance measuring apparatus according to claim 10 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

13. A light wave distance measuring apparatus according to claim 11 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

14. A light wave distance measuring apparatus according to claim 1 , wherein the phase difference detecting means removes a D.C. component contained in digital data of the reference electrical signal and the received electrical signal based on the received electrical signal during non-light emission of the distance measuring light converted into the digital data by the A/D conversion means.

15. A light wave distance measuring apparatus according to claim 14 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.

16. A light wave distance measuring apparatus according to claim 1 , wherein the sampling signal contains at least two kinds of signals which are identical in frequency to each other, but are different in phase from each other, and the phase difference detecting means restores the reference electrical signal and the received electrical signal by rearranging the individual digital data obtained through the A/D conversion in the A/D conversion means.