JPH081441B2 - 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. Summary of the invention In a distance measuring device using a spatial filter, if dust or scratches are present on the photodetector for detecting the reflected light from the road surface or its optical system, the DC component will be added to the sine wave signal and the cosine wave signal. However, since the vector is rotated away from the origin in the phase space as the vehicle travels, in the present invention, since the direct-current component is removed by the high-pass filter, the vector is set to the origin in the phase space. The measurement error can be reduced without rotating away.

C. Conventional technology Conventionally, when automatically driving an automated guided vehicle, a method of laying an electromagnetic induction wire or an optical reflection tape on the road to form a travel guide, or attaching an encoder or tacho generator to the axle or measuring wheel is used. 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 transmitted through the optical system 2 to the line sensor (CC
D) 3 is detected, 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. The vector corresponding to the moving distance is obtained in the phase space shown in the figure. That is, as shown in the flowchart in FIG. 9, first, the CCD data D _i (i = 1,2, ... n) from the line sensor 3 consisting of n pixels is converted into the sin weighting function S _i (i = 1,2, n). N), the products of the same subscript are sequentially added n times to perform the product-sum operation to obtain the product-sum value S _b . Here, the sin weighting function S _i is the product of the sine function and the Hanning function, as shown in FIG. This sine 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 cos weighting function C _i (i = 1,2, ... n) is read, the products of the same subscripts with the CCD data D _i (i = 1,2, ... n) are sequentially n. The product-sum operation is performed by being added twice, and the product-sum value S _a is obtained. Here, the cos weighting function C _i is a product of a cosine function and a Hanning function, as shown in FIG.

Further, since the product sum values S _a and S _b are obtained for each sampling, the product sum values of the previous sampling are set to S _a1 and S _b1, and the product sum values S _a2 and S _{b2 of} this sampling are set. . Then, the vectors t ₁ and t ₂ at each sampling in the phase space in which the sum of products values are S _a1 , S _b1 , S _a2 , and S _b2 are two-dimensional coordinates are shown in FIG. Be done. Therefore, 1
The rotation angle Δφ between the samplings is calculated by the phase difference calculation unit 7 by the following equation.

Here, the moving distance x ₀ and the rotation angle Δφ are in a proportional relationship, and the proportional constant is a filter pitch p (= L / n) and 2
Since it is a ratio with π, the moving distance X ₀ and the speed V are obtained as follows.

D. Problem to be Solved by the Invention According to the above-mentioned conventional technique, if the product sum values S _a and S _b obtained by the spatial filter operation unit 5 have amplitude around zero as shown in FIG. Vector t ₁ in phase space,
t ₂ should rotate about the apex as shown in FIG.

However, in reality, the line sensor 3 or its optical system 2
Since dust or dust adheres to the surface or the light intensity distribution of the illumination is non-uniform, the signal P from the line sensor 3 has a stationary portion that does not move as shown in FIG.
When the frequency component coincides with the frequency component extracted by the spatial filter, the DC component as shown in FIG. 13 (b) is superimposed on the product sum values S _a and S _b obtained by the spatial filter calculation unit 5. For this reason, as shown in FIG. 13 (b), the vector is rotated outside the origin in the phase space, the rotation angle Δφ is not proportional to the movement distance X ₀ , and an error occurs in the calculation result. It was

The present invention has been made in view of the above-mentioned prior art, and an object of the present invention is to provide a distance measuring device using a spatial filter capable of obtaining a moving distance with high accuracy even if there is an optical obstacle. is there.

E. Means and Actions for Solving the Problems In the present invention, since the high-pass filter for removing the DC component of the two signals extracted by the spatial filter operation unit is provided, the light detection for detecting the reflected light from the road surface is detected. Even if dust or scratches exist on the element or its optical system and the DC component is superimposed on the sine wave signal and cosine wave signal, the DC component is removed by the high-pass filter and the vector rotates away from the origin in the phase space. It is possible to reduce the measurement error without doing so.

F. Examples Hereinafter, the present invention will be described in detail based on Examples shown in the drawings.

FIG. 1 shows a first embodiment of the present invention. As shown in the figure, this embodiment has high-pass filters 8a and 8b added, and the other configuration is the same as the conventional configuration shown in FIG. That is, the reflected light from the road surface 1 enters the line sensor 3 provided on the bottom surface of the vehicle body via the optical system 2.
The CCD provided as the line sensor 3 is formed by arranging a large number of photoelectric conversion elements in a one-dimensional array along the traveling direction, and a signal P corresponding to light and shade is read from each photoelectric conversion element by the reading circuit 4. , Digital signal C at A / D converter 6
After being converted into CD data, it is input to the spatial filter calculation unit 5. The spatial filter calculation unit 5 extracts an arbitrary frequency component and obtains the sum of products S _a S _b as described above. This sum of products value S _a S _b is passed through the high-pass filters 8a and 8b, and then input to the phase difference calculation unit 7, where each rotation Δφ is obtained by the above-mentioned equation (1), and further the above-mentioned (2) (3 The moving distance X ₀ and the velocity V can be obtained by the equation). Here, the high-pass filters 8a and 8b have a function of removing the DC component and passing only the AC component. Therefore, as shown in FIG. 2A, the sum of products S _a S _b including the DC component is included.
When is passed through the high-pass filters 8a and 8b, the DC component is removed from it, and only the AC component that oscillates around the zero point remains. Therefore, the high pass filters 8a, 8b
If it is used as a vector in the phase space without passing through to, it will rotate away from the origin as shown in Fig. 2 (b). As shown in Fig. 3, the vector rotates around the origin.

As described above, in this embodiment, since the dust and dust adhere to the line sensor 3 or the optical system 2 thereof and the light intensity of the illumination is non-uniform, the product sum value S _a S _b obtained by the spatial filter calculation unit 5 is obtained.
High-pass filters 8a, 8
Since it is passed through b, the DC component is removed and each rotation Δφ
And the moving distance X ₀ and the speed V are accurately proportional,
Measurement errors can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the time constant T of the high pass filters 9a and 9b is changed at any time based on Δφ obtained in the previous sampling. That is, the high pass filters 8a, 8
When the cutoff frequency f _s (1 / sec) of b is 1/10 of the spatial filter extraction frequency f (1 / sec), the following relationship holds.

f _s = 1 / 10f (4) f = v / mp (5) where v is the speed of the object, m is the scale factor, and p is the filter pitch. Therefore, the time constant is expressed as a time expression.

T = 1 / 2πf _s = 10 / 2πf = 10mp / 2πv (6) Further, the velocity v is expressed by the following equation, and when this is substituted into the equation (6), it becomes as follows.

v = (mp / 2π) Δφ (7) T = 10 / Δφ (8) As shown in the formula (8), the rotation angle Δφ and the time constant T are in a proportional relationship, and therefore, depending on the rotation angle Δφ The time constant T can be changed at any time. Therefore, by making the time constant T variable in this way, the DC component can be reliably removed even if the spatial filter extraction frequency changes.

The rest of the configuration is similar to that of the above-described embodiment,
Has the same effect.

5 and 6 show a third embodiment of the present invention. In this embodiment, the moving distance and the velocity are calculated for each fixed rotation angle Δφ _ref . That is, when S _a (t) and S _b (t) output from the spatial filter calculation unit 5 pass through the high-pass filters 10a and 10b, S _aH (t) and S a
_bH (t) is calculated, and the result and the previous value _SaH (t-
Δφ is calculated from 1) and S _bH (t-1). Here, the number in parentheses indicates the number of times of sampling.
If this Δφ absolute value is equal to or less than a certain value Δφ _ref , Δφ = 0 is set and the calculation of speed and movement distance is not performed.
Then, the previous values S _aL (t−1), S _bL (t−1). S
_aH (t-1) and _SbH (t-1) are not rewritten and are held as they are. When the speed and the moving distance are calculated based on these previous values and Δφ is obtained, and if the constant value Δφ _ref is exceeded, the speed and the moving distance are calculated by this value. Then, S _aL (t), S _bL (t). S
_aH (t), S _bH (t) are the previous values S _aL (t-1), S _bL (t
-1). Rewrite as S _aH (t-1) and S _bH (t-1), and calculate Δφ with reference to this in the future.

As described above, in the present embodiment, since the moving distance and the velocity are calculated for each constant rotation angle Δφ _ref , it can be said that the sampling is performed in the distance dimension. The time constant T of the high-pass filter does not need to be variable because Δφ is constant.

G. Effects of the Invention As described above in detail with reference to the embodiments, the present invention is provided with the high-pass filter for removing the DC components of the two signals extracted by the spatial filter operation unit, so Even if dust or scratches are present in the photodetector or its optical system that detects reflected light, and the DC component is superimposed on the sine wave signal and 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 of a spatial filter distance measuring device according to a first embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are graphs showing the output waveform of a spatial filter arithmetic unit and its change in phase space, respectively. FIGS. 3 (a) and 3 (b) are graphs showing the output waveform of the spatial filter arithmetic unit that has passed through the high-pass filter and its change in the phase space, and FIG. 4 is the spatial filter distance measurement according to the second embodiment of the present invention. Device configuration diagram, FIG. 5 is a configuration diagram of a spatial filter distance measuring device according to a third embodiment of the present invention, and FIGS. 6 (a) and 6 (b) are movement distances according to the third embodiment of the present invention. , A flowchart showing a process of calculating a velocity, FIG. 7 is a block diagram of a spatial filter distance measuring device according to a conventional technique, FIG. 8 is an explanatory diagram showing a phase space, and FIG. 9 is a process of calculating a moving distance and a velocity. Fig. 10 is a flow chart showing Graph showing the filter weighting function, 11
Fig. 12 is a graph showing the output waveform of the spatial filter, Fig. 12 is a graph showing the signal P from the line sensor, and Fig. 13 (a).
(B) is a graph of the output waveform of the spatial filter computing unit on which the DC component is superimposed and the change in the phase space thereof. In the drawings, 1 is a road surface, 2 is an optical system, 3 is a line sensor, 4 is a readout circuit, 5 is a spatial filter calculation unit, 6 is an A / D converter, 7 is a phase difference calculation unit, 8a, 8b, 9a, 9b.10a and 10b are high-pass filters.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-273064 (JP, A) JP-A-57-127854 (JP, A) JP-A-3-152468 (JP, A)

Claims (1)

[Claims] 1. A photoelectric conversion element, which is arranged in a large number along a traveling direction of a vehicle body, detects light reflected on a traveling road surface and converts the light into an electric signal, and the photoelectric conversion element samples at a predetermined cycle and sequentially outputs the signals. A read circuit, a spatial filter calculation unit for extracting an arbitrary frequency component by multiplying an electric signal sequentially output from the read circuit by a sine wave and a cosine wave, and integrating the product within a predetermined range, and the spatial filter calculation unit. In a distance measuring device using a spatial filter having a calculation unit that calculates a moving distance of the vehicle body from a rotation angle of a vector having two signals extracted by the two-dimensional coordinates as a two-dimensional coordinate with respect to an origin on a phase plane. A distance measuring device using a spatial filter, wherein a high-pass filter that removes DC components of the two signals extracted by the spatial filter calculating unit is provided.