JP2500224Y2 - Distance measuring device with spatial filter - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a distance measuring device using a spatial filter, which is improved to improve the measurement accuracy.

B. Outline of the device In a distance measuring device using a spatial filter, an error is likely to occur in the measurement accuracy when the reflected light from the road surface suddenly changes or is irregular.

Therefore, if two spatial filter operation units that use a weight function whose period is shifted by the relative phase difference ψ are provided and the phase difference Δθ in the phase space at the same sampling time is obtained, it is assumed that there is no error. If so, the relative phase should be ψ.

However, in reality, the phase difference Δθ does not match the relative phase difference ψ due to an error, so the error is estimated and the phase difference Δφ in the phase space at the time of the previous sampling and the current sampling is corrected according to the degree of the mismatch. Is.

As a result, the measurement error can be reduced even when the reflected light is not constant.

C. Conventional technology Conventionally, in automatic driving of unmanned guided vehicles, a method of laying an electromagnetic induction wire or optical reflection tape on the road to form a running guide, or attaching an encoder or tacho generator to the axle and measuring wheel There is a method of measuring the speed and moving distance of an unmanned vehicle from a pulse or analog voltage according to the rotation of the wheel.

However, these methods require the work of laying a reflective tape or the like on the road surface, and the work must be performed every time the traveling road is changed, which is complicated, and the unevenness of the road surface
Accurate measurement could not be performed due to slip due to external force and wheel wear.

For this reason, a distance measuring method using a spatial filter has been developed as a method of measuring a moving distance in a non-contact manner without requiring guidance from the outside.

The distance measuring method using this spatial filter is performed by the apparatus configuration shown in FIG. That is, as shown in the figure, the reflected light from the road surface 1 is detected by the one-dimensional line sensor (CCD) 3 through the optical system 2, sampled at a predetermined cycle, and converted into an electric signal. The optical system 2 and the line sensor 3 are attached to the bottom surface of the vehicle body (not shown). The line sensor 3 is formed by temporarily arranging optical conversion elements along the traveling direction, and sequentially outputs signals according to light and dark.

The output signal P from the line sensor 3 passes through the read circuit 4, is converted into CCD data of a digital signal by the A / D converter 6, and then is input to the spatial filter calculation unit 5. The spatial filter calculation unit 5 integrates this output signal within a predetermined range to extract an arbitrary frequency component from the reflected light composed of optically random frequencies, and from the temporal and temporal change, the fourth frequency component is extracted. The vector corresponding to the moving distance is obtained in the phase space shown in the figure. That is, CCD data D _i (i = 1, 2, ...) From the line sensor 3 consisting of N pixels.
N) is read together with the weighting function S _i (i = 1, 2, ... N), and products of equal subscripts are sequentially added N times to perform a product-sum operation to obtain a product-sum value b _n. Desired.
Here, the weight function S _i is the product of the sine wave function and the Hanning function, as shown in FIG. This sine wave function has n wave numbers in the length L of the line sensor, and its wavelength p (= L / n) is hereinafter referred to as a filter pitch.

Next, when the weighting function C _i (i = 1,2, ... N) is read, between the CCD data D _i (i = 1,2, ... N),
Product of equal subscript product-sum operation is performed by the added successively N times, Sekiwachi a _n is obtained. here,
The weighting function C _i is the product of the cosine wave function and the Hanning function, as shown in FIG.

Further, since the product sum values a _n and b _n are obtained for each sampling, the product sum value of the previous sampling is set to a _n−1 and b _n−1, and the product sum value of this sampling is a _n and b _n. I will decide.
By doing so, the vector A ₁ .A ₂ at each sampling time in the phase space in which the product sum values a _n-1 , b _n-1 , a _n , b _n are two-dimensional coordinates is shown in FIG. As shown. Therefore, the phase difference Δφ between the previous sampling and the current sampling is calculated by the phase difference calculating unit 7 as the following equation.

Here, the moving distance x ₀ and the phase difference Δφ are in a proportional relationship, and the proportional constant is the ratio of the filter pitch p (= L / n) to 2π, so that the moving distance x ₀ and the velocity V are It is requested as follows.

However, the phase difference during one sampling is within one rotation.

Therefore, thereafter, the phase difference Δφ is summed up by the accumulator 8 and (p / 2π) is accumulated by the multipliers 9 and 10 to obtain the moving distance x ₀ and the velocity V, respectively.

D. Problems to be Solved by the Invention As described above, the distance measuring device using the spatial filter is characterized by non-contact and highly accurate measurement.

However, in reality, there is a problem that the accuracy of detecting the moving distance is lowered in a place where the reflected light from the road surface suddenly changes or becomes irregular.

That is, in the distance measuring device using the spatial filter, there are an area outside the measurement range of the line sensor 3 and a new area within the measurement range due to the movement of the automatic guided vehicle, and these areas are included in these areas. The moving distance is detected on the assumption that the distributions of the spatial frequency components are equal, but the distributions are actually different.

Therefore, this difference in distribution appears as an error in the calculation of the phase difference, which leads to a decrease in the detection accuracy of the moving distance.

Therefore, the present inventors have already devised and applied for a moving distance measuring device with relatively high detection accuracy even when the reflected light from the road surface is not constant (Japanese Patent Application No. 63-145969).
No. 1-289980), but the accuracy improvement still has its limits.

The present invention has been made in view of the above prior art, and an object of the present invention is to provide a moving distance measuring device capable of detecting a moving distance with high accuracy even in a place where reflected light from a road surface suddenly changes or in an irregular place. It is what

F. Means and Actions for Solving the Problems In the present invention, as the spatial filter calculation unit, two spatial filter calculation units that use the load function whose period is deviated by the constant relative phase difference ψ are provided and the phase difference calculation unit is used. Two phase difference calculation units for calculating the phase differences Δφ ₁ and Δφ ₂ in the phase space based on the frequency signals extracted by the two spatial filter calculation units were provided.

Here, the phase differences Δφ ₁ and Δφ ₂ generally do not match because there is a change in the distribution of spatial frequency components, and the two signals extracted at the same sampling time by the two spatial filter operation units are two-dimensional. When the phase difference Δθ of the vector in the phase space that is the coordinate of is calculated, this phase difference Δθ generally does not match the relative phase difference ψ.

Therefore, a correction phase difference calculation unit is provided to correct either _{one of} the phase differences Δφ ₁ and Δφ ₂ according to the difference between the phase difference Δφ and the relative phase difference ψ.

As a result, even if the distribution of the spatial frequency component changes, it is possible to accurately calculate the moving distance and the velocity.

F. Embodiment Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. The same parts as those in the above-described embodiment are designated by the same reference numerals and suffixes and the description thereof will be omitted.

FIG. 1 shows a first embodiment of the present invention. As shown in the figure, the present embodiment is provided with two types of spatial filter operation units 5a, 5b, phase difference operation units 7a, 7b, and a relative phase operation unit 11, modified phase difference operation units 12a, 12b, etc. Is.

The spatial filter operation units 5a and 5b use weighting functions whose phases are relatively different by the phase difference ψ in the same cycle, and here, the relative phase difference ψ is set to π / 4. That is, as compared with the weighting function of the spatial filter calculating section 5a shown in FIG. 6A, the phase of the weighting function of the spatial filter calculating section 5b shown in FIG. 6B is shifted by π / 4. Then, the computed sum of product value by the spatial filter operation portion 5a respectively a _n.
b _n, and the sum of products calculated by the spatial filter calculation unit 5b is c _n .d _n . Sekiwachi a _n .b _n is the phase difference calculation unit 7a with the preceding value _{a n-1 .b n-1} , Sekiwachi c _n .d _n is the preceding value c _n-1 .b _n-1
Are input to the phase difference calculator 7b together with the phase difference Δφ ₁ . Calculate φ ₂ .

The phase difference Δφ ₁ . φ ₂ should match as shown in FIG. 2 if there is no change in the distribution of spatial frequency, but in general, there is a change in the distribution of spatial frequency, so there are many cases where they do not match.

On the other hand, the previous value of the sum of products a _n-1 .b _n-1 , c _n-1 .d _n-1 is input to the relative phase difference calculation unit 11, and the phase difference Δθ is calculated as in the following equation. .

The phase difference Δθ _n-1 calculated in this way should agree with π / 4 which is the relative phase difference ψ as shown in FIG. 2, unless the spatial frequency distribution changes. In practice, the spatial frequency distribution changes, so that it often does not match the relative phase difference ψ.

Therefore, π / which is the relative phase difference ψ of this phase difference Δθ _n-1
The phase difference Δφ ₁ . To correct φ ₂ ,
This phase difference Δθ _n-1 and the phase difference Δφ ₁ . φ ₂ is input to the modified phase difference calculation units 12a and 12b. Modified phase difference calculator 12
In a and 12b, the phase difference Δφ is corrected according to the following equation.

Here, which phase difference Δφ is to be used is determined by comparing with the comparator 13 and when the phase difference Δφ ₁ is positive,
If the phase difference Δφ ₁ is zero or negative, the lower Δ
Use φ. This is calculated on the basis of Δφ ₁ or Δφ ₂ between the previous values a _n-1 .b _n-1 and c _n-1 .d _n-1 in the phase space as shown in FIG. This is because. Note that Δφ ₁ and Δφ
_Since the signs of ₂ match, Δφ ₂ may be used in the comparator 13 instead of Δφ ₁ .

The phase difference Δφ thus corrected by the correction phase difference calculation units 12a and 12b is then subjected to the moving distance and speed through the accumulator 8 and a multiplier (not shown).

The moving distance measuring apparatus of the present embodiment having the above configuration is the seventh
It is implemented according to the flowchart of the figure.

That is, the product sum value a _n .
b _n , c _n .d _n are calculated, and then Δθ _n- 1..n is calculated by the phase difference calculation units 7a and 7b and the relative phase difference calculation unit 11 based on the above-described formula.
Δθ ₁ . Δφ ₂ is calculated.

Then, by the comparator 13, Δφ ₁ . When Δφ ₂ is compared with zero, the phase difference Δφ is calculated by distinguishing between the case where it is larger and the case where it is smaller, and the moving distance is calculated by accumulating. The moving speed may be calculated without accumulating.

As described above, in the present embodiment, the difference in phase difference Δθ 1 and the relative phase difference ψ obtained by the relative phase difference calculation unit 11 causes the phase difference Δφ ₁ . Since Δφ ₂ is corrected, it is possible to calculate the moving distance and the velocity with relatively high accuracy even when the spatial frequency component of the incident light changes abruptly and at irregular places.

For example, as shown in the measurement result of FIG. 8, the phase difference calculation unit is used at a place where the spatial frequency component of the incident light suddenly changes.
The calculated Δθ does not match the [pi / 4 by 11, Therefore, [Delta] [phi ₁ that is computed phase difference calculation unit 7a, at 7b. Δφ ₂ greatly varies and does not match the moving distance measured by the encoder, but Δφ corrected by the correction phase difference calculation unit 11
Is in good agreement with the measurement result by the encoder.

The measurement results in FIG. 8 are obtained by measuring the surface of the belt conveyor with the moving distance measuring apparatus according to the present embodiment while rotating the belt conveyor.

C. Effect of the Invention As described above in detail based on the embodiments, the present invention is provided with the high-pass filter that removes the DC components of the two signals extracted by the spatial filter calculation unit, so Even if dust or scratches are present on the photodetection element that detects the reflected light or its optical system and the DC component is superimposed on the sine wave signal and the cosine wave signal, the DC component is removed by the high-pass filter, and in the phase space Since the vector does not rotate away from the origin, measurement error can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing the construction of a spatial filter distance measuring device according to an embodiment of the present invention, FIG. 2 is a graph showing the rotation of a vector in a phase space, and FIG. 3 is a conventional diagram using a spatial filter. FIG. 4 is a block diagram showing a distance measuring device, FIG. 4 is a graph showing rotation of a vector in a phase space, FIG. 5 is a graph of a weighting function used for spatial filter calculation, and FIG.
FIG. 7 is a graph showing a load function having a phase difference .psi. Used in the present invention, FIG. 7 is a flow chart according to an embodiment of the present invention, and FIG. 8 is a graph showing measurement results. In the drawings, 1 is a road surface, 2 is an optical system, 3 is a line sensor, 4 is a readout circuit, 5, 5a and 5b are spatial filter arithmetic units, 6 is an A / D converter, 7,
7a and 7b are phase difference calculators, 8 is an accumulator, 9 and 10 are multipliers, 11
Is a relative phase difference calculator, 12a and 12b are modified phase difference calculators, 13
Is a comparator.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-1-266606 (JP, A) JP-A-2-278312 (JP, A) JP-A 58-3483 (JP, A) JP-A 62- 112069 (JP, A) JP 61-36161 (JP, B2) JP 4-67613 (JP, B2) JP 61-43641 (JP, B2) JP 6-50728 (JP, Y2)

Claims (1)

(57) [Scope of utility model registration request] 1. A photoelectric conversion element for converting incident light into an electric signal, a readout circuit for sampling the photoelectric conversion element at a predetermined cycle and sequentially outputting the electric signal, and an electric signal sequentially output for each sampling from the readout circuit. The sine wave and the cosine wave are separately multiplied as a weighting function and integrated within a predetermined range, and a spatial filter operation unit for extracting an arbitrary frequency component and two signals extracted by the spatial filter operation unit A phase difference calculation unit that calculates the phase difference Δφ between the previous time and the current sampling time centered on the origin on the phase plane of the vector that is two-dimensional coordinates, and the position calculated by the phase difference calculation unit. In a distance measuring device using a spatial filter having a distance calculating section for calculating a moving distance proportional to a phase difference, the spatial filter calculating section has a constant relative phase difference ψ without a cycle. The phase difference [Delta] [phi ₁ of each phase space on the basis of the signal of the frequency extracted by two spaces filter calculation unit as the phase difference calculation unit provided with two spatial filter operation unit that uses the weighting function was, [Delta] [phi ₂
And two phase difference calculation units for calculating the phase difference Δθ of a vector in a phase space having two-dimensional coordinates of two signals extracted at the same sampling time by the two spatial filter calculation units. A relative phase calculation unit is provided, and when the phase difference Δθ obtained by the relative phase calculation unit does not match the relative phase difference ψ, the phase difference Δθ
A spatial filter characterized in that a correction phase difference calculation unit for correcting either the phase difference Δφ ₁ or Δφ ₂ is provided, and the moving distance is calculated by the phase difference Δφ corrected by the correction phase difference calculation unit. Distance measuring device by.