JP4703830B2 - Obstacle detection sensor for automated guided vehicles - Google Patents

Description

[0001]
[Industrial application fields]
In the present invention, modulated light is applied to an object, a distance is measured from a phase change generated according to a round-trip distance to the object in a light reception signal of the reflected light, and whether or not the object is an obstacle is determined from this distance. In the obstacle detection sensor of an automatic guided vehicle, it aims at preventing malfunctioning by the object with a high reflectance in the position far from the measurable distance decided by a modulation frequency.
[0002]
[Prior art]
In order to prevent a collision accident, an automatic guided vehicle that travels on a traveling path in a factory while being guided by a predetermined guiding means is provided with an obstacle detection sensor.
[0003]
As this obstacle detection sensor, the projector 1 and the light receiver 2 facing in the same direction as shown in FIG. 3 are simultaneously rotated within a predetermined angular range by the rotation drive mechanism 3, and a predetermined rotation pitch Δθ as shown in FIG. Every time, the modulated light emitted from the projector 1 is reflected by the detection object 4 and returned to the light receiver 2 to obtain a distance L from the phase change φ to the object 4, and this distance L is within a predetermined detection area a. There is one that determines the presence or absence of an obstacle depending on whether or not there is an obstacle.
[0004]
The principle of this distance measurement will be described with reference to FIG. The projector 1 emits light with the high-frequency pulse f ₁ (ω ₁ t) generated by the oscillation circuit 5. High frequency pulse light having a phase change φ corresponding to the round trip distance 2L is incident on the light receiver 2 after being reflected by the object 4 and returned. The received light signal f ₁ (ω ₁ t + φ) is mixed with the local oscillation signal f ₂ (ω ₂ t) by the mixing circuit 6 to obtain a beat down signal f ₃ (ω ₃ t + φ). The frequency of this beat-down signal is the frequency difference f ₃ = f ₁ -f ₂ between f ₁ and f ₂ and holds the phase difference φ. This beat-down signal f ₃ (ω ₃ t + φ) is taken out by the low-pass filter 7, and the phase difference φ is measured by the phase measurement circuit 8 using the phase reference signal f ₄ (ω ₃ t). Since the distance L to the object is L = C · (φ / 2π) / 2f ₁ where the speed of light is C, the distance L is obtained by multiplying φ measured by the distance calculation circuit 9 by a predetermined coefficient. be able to.
[0005]
[Problems to be solved by the invention]
The distance measurement of the phase difference method can be performed under the condition that the distance 2L that the light wave reciprocates is smaller than one wavelength λ of the light wave, and the upper limit distance LM that cannot be measured at the modulation frequency f ₁ is obtained. Determined. That is, assuming that the speed of light is C (m / sec), L _M = C / 2f. For example, when the modulation frequency of light is 8 MHz, measurement is possible until the distance reaches 18.75 m. When the distance is 18.75 m, the measured distance becomes 0 m and measurement is impossible.
[0006]
In general, the detection of an obstacle of an automatic guided vehicle satisfies the required performance if it is about 3 m. However, the wall surface of the traveling path of the automatic guided vehicle may be made of a material having a high reflectance, as in the case where one surface is formed of a stainless steel plate. At this time, as shown in FIG. 6, the intensity of the reflected light ls from the stainless steel plate 10 which is 18.75 m away from the intensity of the reflected light lm from the person 11 wearing black clothes 0.5 m ahead is distinguished. Can not.
[0007]
As a countermeasure against this, a method is conceivable in which light is directed downward or upward so that the light is not optically returned. However, there is a possibility that the light will return after being reflected from the floor surface and the ceiling surface a plurality of times. If this angle is increased, the measurement distance varies depending on the height of the reflection position. Furthermore, there is a problem that a short detection object cannot be measured.
[0008]
Therefore, the present invention provides an obstacle detection device for an automatic guided vehicle that can be excluded from a measurement target even if there is strong reflection at a position far from the detection area, as reflection from an object outside the detection area. Objective.
[0009]
[Means for Solving the Problems]
The obstacle detection sensor of the automatic guided vehicle according to claim 1 of the present invention rotates the projector and the light receiver facing in the same direction by a predetermined step angle toward the surrounding space, and irradiates from the projector at each rotation step. An unattended person who measures the distance to the detection object by detecting the difference between the phase of the modulated light and the phase of the reflected light that is reflected by the detection object and returned to the light receiver. In the obstacle detection sensor of the transport vehicle, the measurement is performed once by changing the modulation frequency of the modulated light to a relatively large frequency and a relatively small frequency at each rotation step, and the distance measurement value of two adjacent steps is measured. with obtaining the difference between the, distinguish whether the distance measurement value, or due to light reflected from an object closer than measurable limit distance of the modulation frequency is relatively large modulated light from the reflection light from the distant object It sets the reference value of the order, when the difference of the distance measurement value is equal to or less than the reference value, treats the distance measurement as correct distance measurements, the difference of the distance measurement value exceeds the reference value The distance measurement value is excluded as an error .
[0010]
Embodiment
In the obstacle detection sensor having the configuration shown in FIGS. 3 to 5, the present invention changes the frequency of the modulated light emitted from the projector 1 to, for example, 8 MHz and 7.5 MHz every time the projector 1 and the receiver 2 are rotated one step. Switch to and measure the distance.
[0011]
Specifically, the obstacle detection sensor of the present invention is configured using a one-chip microcomputer incorporating an A / D converter, for example, as shown in FIG.
[0012]
In FIG. 1, 4 is a detection object, and 12 is a projector / receiver. The light projector / receiver 12 emits high-frequency pulsed light through a light projecting mirror 14 and a light receiving mirror 15 that are simultaneously rotated in the same direction by a pulse motor 13 that is a rotation drive mechanism, and the light projecting mirror 14. The light emitting element 16 and the light receiving element 17 that receives the high frequency pulse light reflected by the detection object 4 through the light receiving mirror 15 are configured.
[0013]
An oscillation circuit 18 generates a high frequency pulse signal f ₁ to be supplied to the light projecting element 16, a high frequency pulse signal f ₂ for mixing, and a phase reference signal f 3. These signals f ₁ , f ₂ , and f ₃ are switched in frequency, for example, when measuring at 8 MHz and when measuring at 7.5 MHz. An amplifier 19 with an AGC circuit amplifies the light reception signal f ₁ (ω ₁ t + φ) output from the light receiving element 17. A mixing circuit 20 for performing heterodyne detection mixes the received light signal f ₁ (ω ₁ t + φ) amplified by the amplifier 17 with a high-frequency pulse signal f ₂ (ω ₂ t) for mixing to generate a beat down signal f ₃ ( ω ₃ t + φ). This beat-down signal has a phase change φ generated in the light receiving signal f ₃ according to the reciprocating distance 2L from the light projecting element 16 to the light receiving element 17 via the detection object 4.
[0014]
A level conversion circuit 21 compares the phase change φ generated in the beat-down signal f ₃ (ω ₃ t + φ) with the phase reference signal f ₃ (ω ₃ t), and a voltage signal V ₁ corresponding to the phase delay. Is output. Reference numeral 22 denotes a one-chip microcomputer incorporating an A / D converter, which receives the analog voltage V1 input from the level conversion circuit 21 as a distance measurement value and converts it into a digital value by the A / D converter, and whether there is an obstacle. Is output through the output circuit 23. The microcomputer 22 also controls the oscillation circuit 18 and the motor drive IC 24.
[0015]
The operation of the obstacle detection sensor A of FIG. 1 will be described based on the flowchart of FIG. Initialization is performed first. This initializes the internal data and returns the rotational position of the projector / receiver 12 to the initial position by the pulse motor 13. Next, while performing distance measurement for each rotation step of Δθ (for example, 1.6 °) as shown in FIG. 4, distance measurement is performed for a measurement range of, for example, 160 °, and all measured values are stored. This measurement is performed by changing the modulation frequency of the modulated light at f1 to, for example, 8 MHz and 7.5 MHz every rotation step. In conjunction with this switching, the local oscillation frequency f ₂ and the phase reference signal f ₃ are also switched at the same time.
[0016]
When these measurements are completed, the process for eliminating the measurement value due to the reflected light from outside the measurable range described in FIG. 6 is performed.
[0017]
This process is a process of comparing measured values of adjacent measurement points, determining that the difference is less than a reference value (for example, 0.5 m), and determining that the distance measurement value is correct, and replacing the error value when the reference value is exceeded. Repeat from one end of the measurement area to the other. This is because when the distance to an object within the measurable range is measured, the correct distance is measured even if the modulation frequency f1 is changed, whereas when the modulation frequency f1 is changed when measuring outside the measurement range. This is based on the fact that the measured value varies greatly.
[0018]
This will be further described. In the measurement that can be performed within the measurable range, the measurement frequency is changed at each step of the rotation with the modulation frequency f ₁ being changed. However, since the measurement target position moves along the outer shape of the detection object, even if two adjacent points are compared, there is little change in the distance. On the other hand, when measurement is performed with reflected light from an object located far from the measurable range, the measurement value varies greatly. For example, when the measurement is performed at 8 MHz and 7.5 MHz, the measurement distance is 0 m at 18.5 m at 8 MHz and 0 m at 20 MHz at 7.5 MHz. Therefore, as shown in FIG. Is 18.5 m ≦ L <20 m, the difference is 18.5 m, and a distance of 20 m or more causes a difference of 1.5 m. By utilizing this relationship, it is possible to extract only measured values in the measurable range as correct data.
[0019]
When the measurement is performed with the modulation frequency changed to 8 MHz and 7.5 MHz, when the distance reaches 300 m, both measured values become 0 m, and both measured values are theoretically the same between 300 m and 318.5 m. It becomes. However, at a distance of 300 m or more, the attenuation of light is significant, and this reflected light is not detected, so there is no problem.
[0020]
When the process of eliminating the measurement value due to reflected light from outside the measurement range as an error ends, the presence or absence of an obstacle is determined based on whether or not the measured distance is in the detection area a.
[0021]
In the above embodiment, the frequency of the modulated light is changed for each rotation step, and the measurement is performed once for each rotation step. This is to shorten the measurement time. If the measurement is performed twice with the modulation frequency f ₁ being changed at the same measurement target position, the number of measurements is doubled and a long time is required for the measurement, and the automatic guided vehicle is moved at high speed. Become an obstacle for.
[0022]
Further, in the present invention, in order to exclude the measurement value due to the reflected light from outside the measurable range, a process of comparing the measurement values of the adjacent measurement points is performed. In order to eliminate it, it is necessary to perform it originally, and this processing does not affect the processing time.
[0023]
【The invention's effect】
The invention according to claim 1 of the present invention is an obstacle detection device that measures a distance by detecting a phase change of modulated light reflected and returned by a sensing object, and is located farther than a measurable distance limited by a modulation frequency. Can be eliminated as an error value by changing the modulation frequency at each rotation step and comparing it with the distance measurement value of the adjacent measurement points. In particular, in the present invention, it is only necessary to perform measurement once per rotation step, and comparison with adjacent measurement points is a process that is originally necessary as a process for removing noise and does not increase the processing time. For this reason, it is possible to keep the measurement time short and to drive the automatic guided vehicle at high speed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a flowchart for explaining the operation of the apparatus in FIG. 1. FIG. 3 is a diagram showing a projector and a receiver that measure distance by phase detection. 4 is a diagram illustrating a detection area in which the presence / absence of an obstacle is determined from measured values. FIG. 5 is a block diagram illustrating the principle of distance measurement by phase detection. FIG. 6 is a result of reflection from an object far away from a measurable range. Diagram explaining the cause of malfunction [Explanation of symbols]
1 Emitter 2 Receiver 4 Sensing Object 12 Emitter / Receiver 13 Pulse Motor (Rotation Drive Mechanism)
14 Emitting mirror 15 Receiving mirror 16 Emitting element 17 Receiving element 18 The oscillation circuit generates a high-frequency pulse signal f ₁ to be supplied to the projecting element 16, a high-frequency pulse signal f ₂ for mixing, and a phase reference signal f ₃ To do. These signals f ₁ , f ₂ , and f ₃ are switched in frequency, for example, when measuring at 8 MHz and when measuring at 7.5 MHz.
19 amplifier 20 mixing circuit 21 level conversion circuit 22 one-chip microcomputer 23 output circuit 24 motor drive IC
a Detection area

Claims (1)

Rotate the projector and receiver facing the same direction by a predetermined step angle toward the surrounding space, and at each rotation step, the phase of the modulated light emitted from the projector and this light is reflected by the detection object and returned to the receiver. In the obstacle detection sensor of the automatic guided vehicle that detects the difference in the phase of the reflected light and measures the distance to the detection object, and determines the presence or absence of the obstacle by these distances,
At each rotation step, the modulation frequency of the modulated light is changed to a relatively large frequency and a relatively small frequency, and measurement is performed once to obtain a difference between distance measurement values of two adjacent steps , and the distance measurement. A reference value for distinguishing whether the value is due to reflected light from an object closer to the measurable upper limit distance of the modulated light having a relatively high modulation frequency or reflected light from a far object is set, and when the difference of the distance measurement value is equal to or less than the reference value, eliminating treats the distance measurement as correct distance measurements, when the difference of the distance measurement value exceeds the reference value, the distance measurement as an error An obstacle detection sensor for an automatic guided vehicle.

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