JP2685922B2 - Long-distance ranging sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention receives light reflected by a detected object of a light beam projected on a detection area, and determines the distance to the detected object. The present invention relates to a long distance measuring sensor.

[Prior Art] Conventionally, a long-distance measuring sensor of this type, which receives reflected light of a light beam projected on a detection area by a detected object and determines a distance to the detected object, As shown in FIG. 2, a reference oscillator 1 that generates a reference signal Vs of a predetermined type f _{0 and} the reference signal Vs that is driven by a drive circuit 2.
The light emitting element 3 for projecting the light beam whose brightness is modulated by the detection area to the detection area, the light receiving element 4 for receiving the reflected light of the light beam by the object X to be detected, and the output of the light receiving element 4 are amplified to generate a necessary signal. to create an amplifying filter section 5 for taking out, the reference signal frequency f ₀ to (N-1) / N times the signal of the frequency f ₁
A PLL circuit 6, a mixing circuit 8 that mixes the output of the amplification filter unit 5 and the output of the PLL circuit 6, and a filter unit 10 that extracts a frequency of 1 / N times the reference signal frequency f _{0 from} the output of the mixing circuit 8.
A frequency converter consisting of the reference signal frequency f ₀ of 1 / N times the frequency f divider circuit 7 to form a _second signal 'based on the reference signal Vs, the filter unit 8 outputs a frequency converter (frequency divider 7 ') is composed of a phase difference detection unit 11 for detecting the phase difference φ of the output, and a distance judgment unit 12 for judging the distance to the detected object X based on the output of the phase difference detection unit 11 and projecting light beams intensity modulated by the signal from the light-emitting element 3 in the detection area, receives light reflected by the detected object X by the light receiving element 4, the reference signal (emission signal) Vs and the light receiving signal V _R
The phase difference φ of 1 is detected to determine the distance 1 to the detected object X.

Now, as shown in FIG. 4, in the case where the detected object X exists at a position separated from the distance measuring sensor Y by l (m),
The reference signal Vs is received signal V _R expressed as follows.

Vs = I _S sin2πf ₀ t VR = I _R sin2πf ₀ (t−2l / c) where I _S and I _R are the reference signal Vs and the amplitude of the received light signal V _R , f ₀ is the frequency of the reference signal Vs, and c is The speed of light (m / s).

Therefore, the phase difference φ between the two signals V _S and V _R is φ = f ₀ (2l / c).

Here, it is possible to determine the distance 1 to the object X to be detected by measuring the phase difference φ, but it is difficult to measure the phase difference φ in this state. Therefore, the brightness modulation frequency of the light beam (of the reference signal Frequency slightly different from frequency f ₀ )
By mixing f ₁ with the received light signal V _R , it is converted into a low frequency signal and the phase difference φ is detected. Further, in an actual circuit, in order to cancel the phase change of the circuit system, the optical path is switched by using the optical system including the mirror 14 driven by the optical path switching means 13, and the light beam projected in the first optical path. Is directly incident on the light receiving element 4, and the reflected light from the object X to be detected is incident on the light receiving element 4 in the second optical path, and is obtained in the light projecting signal Vs ′ and the first optical path. Received light signal
A phase difference phi ₁ between V _R1, the light projection signal Vs' and the detected object X based on the phase difference phi ₂ between the light-receiving signal V _R2 obtained by the second optical path
The distance l up to is determined.

Here, a frequency f ₁ slightly different from the reference signal frequency f ₀
The PLL circuit 6 is used to generate the signal of
A signal of (N-1) / N times ₀ is generated. On the other hand, in the frequency dividing circuit 7'that constitutes the frequency conversion unit, the reference frequency f ₀
It forms a phase difference detection signal having a frequency f ₂ that is 1 / N times the frequency f ₂ .

[Problems to be Solved by the Invention] However, in the above-described conventional example, the frequency f ₂ of the phase difference detection signal output from the frequency conversion unit including the frequency dividing circuit 7'is very stable. Whereas, PLL
Since the frequency f ₁ of the output of the circuit 6 slightly changes at the low frequency of the VCO control voltage due to the influence of the loop filter,
The output of the mixing circuit 8 is also the frequency f _{2 which} is 1 / N times the reference signal frequency f _0.
Will fluctuate at a lower frequency. Therefore,
As shown in FIG. 3, the output of the phase difference detection unit 11 is a state (Δφ ₁ , Δφ ₂ , where the differences of the cycles T ₀ , T _{1 to} T ₃ between the output of the mixing circuit 8 and the output of the frequency conversion unit are integrated). Δφ ₃ ……) and PLL
Phase difference detector even if the frequency f _{1 of the} output of the circuit 6 changes slightly
There is a problem that a large phase difference signal (distance signal) is output from 11 and the distance measurement error increases.

The present invention has been made in view of the above points, and an object of the present invention is to provide a long-distance ranging sensor that can obtain high ranging accuracy even if there is a frequency change in the output of a PLL circuit. is there.

[Means for Solving the Problems] A long-distance measuring sensor according to the present invention includes a reference oscillating unit for generating a reference signal of a predetermined frequency, and a light emission for projecting a light beam whose brightness is modulated by the reference signal onto a detection area. An element, a light-receiving element for receiving the reflected light of the light beam from the object to be detected, an amplification filter section for amplifying the output of the light-receiving element to take out a necessary signal, and a reference signal frequency multiplied by (N-1) / N A PLL circuit that creates a signal of a frequency; a first mixing circuit that mixes the output of the amplification filter unit and the output of the PLL circuit; and a frequency that extracts 1 / N times the reference signal frequency from the output of the first mixing circuit. 1 filter section, a frequency conversion section that forms a phase difference detection signal having a frequency of 1 / N of the reference signal frequency based on the reference signal, and a phase difference between the first filter section output and the frequency conversion section output. The phase difference detector that detects In a more becomes long range distance measuring sensor and distance determination unit the distance to the detection object based on the phase difference detection unit outputs,
The frequency conversion unit is formed by a second mixing circuit that mixes the reference signal and the output of the PLL circuit and a second filter unit that passes a signal having a frequency 1 / N times the reference signal frequency.

[Operation] The present invention is configured as described above, and in the same long-distance measuring sensor as the conventional example, the second mixing circuit for mixing the reference signal and the output of the PLL circuit, and 1 / of the reference signal frequency. N
The frequency conversion unit is formed by the second filter unit that passes the signal of double frequency, and the phase difference detection signal is formed based on the output of the PLL circuit. Even if there is, it is possible to prevent the phase difference detection unit from performing integration, and it is possible to realize a long-distance measuring sensor having high distance measuring accuracy.

[Embodiment] FIG. 1 shows an embodiment of the present invention. In a long distance measuring sensor similar to the conventional example, a reference signal Vs and a PLL circuit 6 are used.
A second mixing circuit 7 for mixing the output and the reference signal frequency
A second filter unit 9 that allows a signal having a frequency f _{2 that} is 1 / N times f ₀ to form a frequency conversion unit, and other configurations and operations are the same as those in the above-described embodiment.

Hereinafter, the operation of the embodiment will be described. Now, the optical path is switched by the mirror 14 driven by the optical path switching means 13, and the optical path is the first optical path (the light beam from the light emitting element 3 is reflected by the mirror 14 and is received by the light receiving element 4). When it is switched to the (light receiving optical path), the phase difference signal output from the phase difference detection unit 11 is stored in the phase difference storage unit as phase difference data. On the other hand, when the optical path is switched to the second optical path (the optical path where the light receiving element receives the reflected light of the light beam projected from the light emitting element 3 by the object X to be detected) The output phase difference signal is compared with the phase difference data stored in the phase difference storage section, and the phase difference signal obtained by canceling the phase change caused by the circuit system is sent to the distance determination section 12 as a distance signal. The distance determination unit 12 determines the distance 1 to the detected object X based on the distance signal output from the phase difference detection unit 11. In this case, the frequency of the output of the frequency conversion unit including the second mixing circuit 7 and the filter unit 9 is always the same as the frequency of the output of the first filter unit 10, and the PLL circuit 6 as in the conventional example is used.
Since the frequency variation of the output is not integrated by the phase difference detecting unit 11, the error of the distance signal output from the phase difference detecting unit 11 is the oscillation frequency variation of the PLL circuit 6 except the internal noise of the circuit. This is the only cause, and high distance measurement accuracy can be obtained.

EFFECTS OF THE INVENTION The present invention is configured as described above, and in the same long-distance range sensor as the conventional example, the second mixing circuit for mixing the reference signal and the output of the PLL circuit and the reference signal frequency 1 / N
The frequency conversion unit is formed by the second filter unit that passes the signal of double frequency, and the phase difference detection signal is formed based on the output of the PLL circuit. Even if there is, it is possible to prevent integration in the phase difference detection unit, and there is an effect that a long-distance measuring sensor having high distance measuring accuracy can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional example, and FIGS. 3 and 4 are operation explanatory diagrams of the same. 1 is a reference oscillating unit, 2 is a drive circuit, 3 is a light emitting element, 4 is a light receiving element, 5 is an amplification filter section, 6 is a PLL circuit, 7 and 8 are mixing circuits, 9 and 10 are filter sections, and 11 is phase detection. The part, 12 is a distance determination part.

Claims (1)

(57) [Claims] 1. A reference oscillating section for generating a reference signal of a predetermined frequency, a light emitting element for projecting a light beam whose brightness is modulated by the reference signal onto a detection area, and a reflected light of the light beam reflected by an object to be detected. Light-receiving element that receives light, amplification filter section that amplifies the output of the light-receiving element to extract the required signal, PLL circuit that creates a signal with a frequency that is (N-1) / N times the reference signal frequency, and amplification filter section output And a PLL circuit output, a first mixing circuit, a first filter unit for extracting a frequency 1 / N times the reference signal frequency of the first mixing circuit output, and a reference signal frequency based on the reference signal A frequency conversion unit that forms a phase difference detection signal having a frequency of 1 / N times
A long distance including a phase difference detection unit that detects the phase difference between the output of the first filter unit and the output of the frequency conversion unit, and a distance determination unit that determines the distance to the detected object based on the output of the phase difference detection unit. In the distance measuring sensor, a second mixing circuit that mixes the reference signal with the output of the PLL circuit and the reference signal frequency
A long-range distance measuring sensor, characterized in that the frequency conversion section is formed by a second filter section that passes a signal having a frequency of 1 / N times.