JPH0682155B2 - Ultrasonic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is an ultrasonic wave that recognizes the presence of an object that has entered a certain monitoring area by detecting that the object is stationary for a certain time or longer. The sensor is particularly effective when detecting whether or not a vehicle is parked in a parking space of a parking lot.

[Problems to be Solved by Prior Art and Invention]

In general, ultrasonic sensors detect whether a moving object has entered the surveillance area based on the presence or absence of a reflected wave and turn the sensor output ON / OFF, so the intruding object remains stationary within the surveillance area. In many cases, the robot malfunctioned when left alone or when there were pedestrians in the vicinity. In addition, ultrasonic waves are easily affected by wind and temperature, and are used outdoors only under limited conditions because of their low reliability.

On the other hand, regardless of whether it is a stationary object or a moving object, there is an infrared sensor as a sensor that detects when an object enters the monitoring area, but since it detects all objects that interrupt the transmitter and receiver, Since it is difficult to determine whether it is a moving object or a moving object, and it is easily affected by water droplets and dirt, it was also unsuitable for detecting a stationary object.

Furthermore, even if a stationary object is detected, for example, in a parking space of a parking lot, only the presence of a vehicle is detected, and the presence of pedestrians around the vehicle or people at rest are not detected. An ultrasonic sensor for detecting has not been invented in the past.

The present invention is to solve the above-mentioned conventional problems, and to detect the presence of a stationary object in the detection range regardless of whether it is indoors or outdoors,
It is another object of the present invention to provide an ultrasonic sensor capable of detecting only the existence of a specific type of object according to the property of a stationary object.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the present invention provides a transmitting means for intermittently transmitting a group of ultrasonic waves at a constant cycle, and a means for receiving ultrasonic waves.
Amplification means, level slicing circuit that extracts the detected signal element above a certain level after rectifying this amplified signal, predetermined by the distance between the transmitter and the receiver, and is turned on at direct wave detection timing. The wave gate signal, the reflected wave gate signal that turns on at the detection timing of only the reflected wave from the object within the distance assumed in advance, and the two gate signals for the above detection signal element are input to the AND gate, and the direct wave is input. A reflected wave / direct wave detection circuit consisting of a means for taking out separate digital signals from the reflected wave, a calculation means for measuring the time difference from the transmission wave to the reception of the reflected wave, and the previous measurement value as a reference value If the subsequent measurement value falls within the preset error tolerance of the previous measurement value, a means for cumulatively counting the number of times and a stationary object presence signal is output if the predetermined count is reached continuously. Then, while the measured value within the error tolerance value is being input, the above cumulative count is held on the reset side, and if the measurement value outside the error tolerance value is input, the above count is accumulated and continuously specified. Means for turning off the stationary object presence signal when the count reaches, and means for resetting the cumulative count and measuring again from the reference value if the measured value deviates from the error tolerance value before reaching each predetermined count. A configuration including a control circuit including and is adopted.

Further, a means of outputting a failure signal when the digital signal of the direct wave cannot be detected or when it deviates from a predetermined fixed period is adopted.

[Action]

The transmitting means transmits ultrasonic waves intermittently at a constant cycle, and the direct wave sneaking into the receiving / amplifying means is input in the same cycle with a slight delay, and an object exists in the monitoring area. If so, the reflected wave is input. Both these inputs are processed as one signal, but are separated into a direct wave digital signal and a reflected wave digital signal by a gate signal at the detection timing of the direct wave and the reflected wave in the AND gate.

If the reflected wave digital signal of the above digital signals is input to the control circuit, the time difference between the transmission time and the reception time of the reflected wave is calculated by digital processing or analog processing to calculate a value proportional to the distance to the object. If the measured value is within the given tolerance with the previous measured value as the reference value, the cumulative count is advanced, and if the predetermined value is reached, the stationary object presence signal is output as if the stationary object exists. On the contrary, when the measured value deviates from the error of the previous measured value, the cumulative count number is reset to zero and the measurement is restarted from the beginning. In any case, the current measurement value is treated as the reference value for the next measurement.

Also, once the presence of a stationary object is recognized and the stationary object presence signal is output, the signals input to both reset and count inputs of the cumulative counter are switched through the switch circuit, so that the cumulative counter counts. Is the reverse of the description so far. That is, when the object is still still, the AND relation of the outputs of the upper and lower limit comparators is established, but since the comparison timing signal is input to the reset input of the cumulative counter through the switch circuit,
The content of the cumulative counter becomes zero. In this state, if the measured value exceeds the permissible error due to the temporary movement of the object or the presence of other moving objects in the surroundings, the output of the upper and lower limit comparator cannot be established. Instead, the comparison timing signal is input to the count input of the accumulator and the counter will proceed with its integration. in this way,
When the predetermined count is reached, the stationary object presence signal is turned off, but if the object is again recognized to be stationary before the predetermined count is reached, the cumulative counter is reset and returns to zero.

To summarize the operation of the above-mentioned accumulative counter, a stationary object presence signal is output when an object is recognized to be in a stationary state continuously until a predetermined count is reached, and the object moves at least once before that. If it is recognized that the accumulated counter is reset, the content becomes zero, and the standby state is again set for a predetermined number of continuous stationary measurements from the beginning. On the other hand, once it is recognized that a stationary object exists, the stationary object presence signal does not change even if the object moves for a very short time or is recognized as such due to noise from other objects, The cumulative counter reaches the predetermined count only when the object is continuously moving or when the existence thereof is not recognized continuously, and the stationary object existence signal is turned off accordingly.

On the other hand, the direct wave digital signal is reliably output as long as the circuit from the wave transmitting means to the AND gate is functioning normally, but by monitoring this signal, a failure of the device can be detected.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.
The figure shows the reflected / direct wave detection circuit of the ultrasonic sensor.
Is a wave-transmitting section that intermittently generates a group of ultrasonic waves at a constant period (for example, 1 ms is transmitted at 250 ms intervals), and 2 is a wave-transmitting device that sends this out to the outside. The ultrasonic wave sent from the wave transmitter 2 is input to the wave receiver 3, but in this case, when the direct wave directly wraps around from the wave transmitter 2 and the object 4 exists in the monitoring area. Both of the reflected waves that are input to the receiver 3 are input to the receiver 3 and form one input signal. Since this input signal has an extremely low level, it is amplified by the amplifier 5. The amplified signal is passed through the filter 6 and then detected by the detection circuit 7, and then passed through the level slicing circuit 8 for extracting a certain level or more, and the detection signal element of only the direct wave / reflected wave is taken out. In this way, noise components below the slice level are removed, and only the necessary signal components are output.

The filter 6 is not always necessary and may be omitted when the ultrasonic sensor is installed in a place where noise is small.

On the other hand, since there is a time lag between the direct wave and the reflected wave, it is possible to take out this point separately by the AND gates 9 and 10. That is, since the wave transmitter 2 and the wave receiver 3 are provided at a predetermined interval, the delay time from the wave transmission to the wave reception can be calculated based on the speed of sound, but it is possible to directly turn on at this timing. Make the wave gate signal 11. Also, the time required for the reflected wave to be received differs depending on the position of the object in the monitoring area, but it should be turned on at a timing that can cover the required reflection time at the shortest distance and the longest distance of a predetermined monitoring area (for example, 1 to 3 m). The reflected wave gate signal 12 is created at. If the direct wave gate signal 11 and the reflected wave gate signal 12 are input to the AND gates 9 and 10, respectively, and the detection signal elements are input in parallel to the AND gates 9 and 10, the direct wave reception signal and the reflection wave reception signal are obtained. It can be taken out separately. Reference numeral 13 is a transmission timing signal from the transmission unit 1.

FIG. 2 shows changes in the waveform from the transmission of the ultrasonic wave to the reception signal. The transmission timing 14, the transmission waveform 15, the reception waveform 16, the direct wave waveform 17, the reflected wave waveform 18, the detection output 19 respectively. , A level slice circuit determination level 20, a level slice circuit output 21, a direct wave gate signal 22, a reflected wave gate signal 23, a direct wave reception timing 24, and a reflected wave reception timing 25 are shown.

Of the above signals, the direct wave reception signal is output at a constant cycle regardless of the presence of reflected waves as long as the circuit is functioning normally.Therefore, by detecting this signal, it will function normally. However, on the contrary, if the signal is not detected for a certain reason, for example, if the signal is not output at a constant cycle, a failure signal is output to detect the abnormality of the circuit from the wave transmitting unit 1 to the AND gate 9. You can check.

Now, when trying to detect an absolute stationary object, theoretically the reflected wave received signal is output in a cycle that exactly matches the transmission cycle, so compare the timing of both. Is enough. However, ultrasonic waves do not have a constant time until reflected waves are received due to the influence of wind and changes in the outside temperature, and even stationary objects do not maintain a completely stationary state and are affected by external influences. It always causes fluctuations. Therefore, it is necessary to consider some tolerance. Furthermore, for example, the magnitude of the fluctuation is different between a parked car and a stationary person.

In view of this point, the present inventor uses the following control circuit in order to detect a certain fluctuation within an allowable range and identify a stationary object.

First, FIG. 3 shows a block diagram in the case of performing control using a digital circuit. The transmission timing signal 14 and the reflected wave reception timing signal 25 output when an object enters the monitoring area of the ultrasonic sensor are used. The operation is started.
In the figure, reference numeral 26 is a time interval counter which measures the time from transmission to reception by counting a separately supplied reference clock. Next, the A block is a circuit that compares the current count value of the counter 26 with the previous count value to determine whether or not the new count value is within the preset error tolerance. Is a latch circuit, 28 and 29 are adders for calculating upper and lower limits of a predetermined error, that is, an allowable error value, and 30 and 31 are comparators for comparing the count value and the upper and lower limit of the allowable error value, respectively. , 32 are AND gates that output a stillness determination output signal when the count value is within the error tolerance of the reference value.

Incidentally, 33 is a control timing generation circuit, which resets the counter 26 in synchronization with each measurement timing and
The timing signal of the latch is sent to 27, and the timing signal for accumulating a stillness determination output signal described later is output.

Next, the block B is a circuit for accumulating the stillness determination output signal for each time and outputting a still object presence signal, 34 is an exclusive OR gate, 35 is a stillness determination output signal cumulative counter, and 36 is a cumulative counter 35. It is a changeover switch for counting or resetting, and is interlocked with the changeover switch of 37. 38 is an output flip-flop.

The operation of the control circuit will be described. When the time difference in the above measurement is N counts in the time interval counter 26, this measured value N is first stored in the latch circuit 27 of the A block as a reference value for the next measurement. Remembered. Next, the preset allowable error Δ is added / subtracted by the adders 28 and 29 to obtain N + Δ and N−Δ
Are input to the comparators 30 and 31, respectively. Then, when the second time difference signal is calculated by the time interval counter 26 and N _{1 is} counted, the count value is input to the comparators 30 and 31.
When the comparators 30 and 31 determine that they are within the preliminarily calculated allowable error, the AND gate 32 is turned on. Further, the time interval count 26 is reset by the signal from the control timing generating circuit 33, the latch circuit 27 is also controlled by the latch timing signal, the previously stored N is cleared, and N ₁ is stored in the latch circuit. Substituting, and using this as a reference value, subsequent measurements are continuously executed one after another.

Next, the output control of the stationary object presence signal in the B block will be described. The output signal from the AND gate 32 which is the final stage of the A block is input to the exclusive OR gate 34, which is input to the changeover switch 36. The output terminal of the stationary object presence signal is input to the other input of the exclusive OR gate 34. Further, the comparison timing signal is input to the changeover switch 36 from the control timing generation circuit 33, and the cumulative counter 35 is output only when the changeover switch 36 is in the state shown by the solid line in FIG. 3 from the exclusive OR gate 34 at this timing. I am trying to accumulate. Thus, the accumulating counter 35 integrates the count only when the AND gate 32 outputs the signal of logic 1 at the timing of comparison, and when the predetermined number n is reached, the output flip-flop 38 is set. , A stationary object presence signal is output.

However, when the cumulative counter 35 is within n-1 times and the count value of the next time interval counter 26 does not fall within the error tolerance of the immediately preceding count value, the AND gate 32 outputs a logic 0, The comparison timing signal is input to the changeover switch 36, but in this case, the changeover switch 36 is connected to the reset side, so that the cumulative counter 35 is reset to zero.

On the other hand, when the cumulative counter 35 reaches the predetermined number n and the output flip-flop 38 is set, and the output is ON, this output is fed back to the exclusive OR gate 34.
, Which causes the exclusive OR gate to act as an inverter. That is, when the object is still and the AND gate 32 outputs the signal of logic 1, the output of the exclusive OR gate 34 becomes logic 0, and the changeover switch 36 is connected to the reset side of the accumulation counter. Therefore, the cumulative counter 35 maintains the reset state.

On the other hand, when the stationary object actually moves out of the monitoring area, there is no signal to detect in the A block, so the output from the AND gate 32 becomes a logic 0, and the exclusive OR gate 34 outputs a signal of logic 1. Since it outputs, the accumulating counter 35 starts integration for detecting the absence of a stationary object by the comparison timing signal from the control timing generating circuit 33, and when it reaches n times, the output flip-flop 38
It resets to, and turns off the stationary object presence signal that had been output until then. Also in this case the cumulative counter 35
If the object is again found to be stationary before the (N-1) count is reached, the accumulator counter 35 is reset. Therefore, once it is determined that there is a stationary object, the cumulative counter 35 is reset to the reset state even if a slight fluctuation of the object occurs or the object actually moves for a short time, and This can be ignored.

FIG. 4 shows a timing chart when a digital circuit is used.

Note that the exclusive OR gate 34 may have another configuration such as a combination of an AND gate and a NAND gate.
In short, the signal from the output flip-flop 38 is once logic 1
In this case, a circuit that functions as an inverter for the other input signal is sufficient.

Next, FIG. 5 shows a block diagram in the case where the time interval counter 26 and the A block of the digital circuit are controlled by using an analog circuit. 39 is a latter stage according to the transmission timing and the reflected wave reception timing. , 40 is a constant current power supply, 41 is a charge switch that turns on only during the time from transmission to reception of reflected waves, 42 is a capacitor charged with constant current, 43 is a discharge switch, and 44 is high. A buffer amplifier circuit with input impedance, 45 is a sample hold circuit that holds and outputs the amplified voltage for a certain period of time, and 46 and 47 set the upper and lower limit voltages of the setting error for the output from the sample hold circuit 45. , A comparator for determining whether the next voltage value is within that range,
Reference numeral 48 is an AND gate which is turned on when it is within the above setting error, and outputs an ON signal to the B block in the above digital circuit.

The operation of the analog circuit will be described. First, when an object enters the monitoring area of the ultrasonic sensor and a reflected wave reception signal is output, the transmission timing and the reflected wave reception timing are input to the timing generation circuit 39. The timing signal from this circuit turns on the charging switch 41 composed of a switching element or the like for the time interval between transmission and reception of reflected waves,
The capacitor 42 is charged. Since charging is done with a constant current, the voltage across capacitor 42 rises linearly in perfect proportion to time. The voltage V amplified by the buffer amplifier 44 is input to and stored in the sample hold circuit 45, and output to the comparators 46 and 47. The upper and lower limits of the error Δ% preset by the comparators 46 and 47 are the comparison voltage (10
Input as 0 × Δ) V / 100 and (100−Δ) V / 100. That is, for example, if the setting error is 5%, the input of the upper limit comparator is 1.05, and the input of the lower limit comparator is R ₂ / (R ₁ + R ₂ ) = 0.95 due to the resistance. Specified in. Here, in the above embodiment, the permissible error is given as a percentage with respect to each measured value, but it is also easy to give a comparative value as an absolute value instead. Then, according to the output from the timing generation circuit by the second timing signal, the capacitor that was discharged by the discharge switch 43 in advance and was in the standby state is charged again for the time interval between the transmission of the reflected wave and the reception of the reflected wave. The voltage V _a is the buffer amplifier
When it is output from 44, it is input to the comparators 46 and 47, and if it is within the allowable error value, the AND gate 48 is turned on, and the cumulative count is integrated by the same processing as the block B in the digital circuit. Further, after this, the sample hold circuit 45 in place of the initial voltage V V _a is held in preparation for the next measurement, the capacitor 42 is discharged by the discharge switch 43, control of the sampling and hold and discharge Is performed by a signal from the timing generation circuit 39. After that, as in the case of the digital circuit, the stationary object presence signal is first output when the cumulative counter counts n times. The configuration (not shown) in which the count is reset and returned to the initial state even when the setting error deviates within n-1 times is the same as that described in the digital circuit.

The error can be set and the detection time can be arbitrarily set according to the object to be detected. For example, when treating an object that has a fluctuation of 1 cm with respect to the sensor direction as a stationary object, the human body will not be detected if an error corresponding to that range is set (a person intentionally tries to stand still. Inevitably there will be more movement, so it will be removed from the detection target). Therefore, since only the parked car can be detected in the parking lot or the like, the presence or absence of the parking space can be detected without error. The cumulative count n
The larger is the more accurate detection is possible, but it takes longer until a stationary object is recognized. Therefore, it is necessary to determine an appropriate value for the size of n according to the installation location of the ultrasonic sensor and the nature of the detection target. Further, the value of n for outputting the stationary object presence signal and the value when this signal is turned off do not have to match and can be set as different values.

〔The invention's effect〕

The ultrasonic sensor of the present invention detects a time difference from transmission to reception and compares this with the next time difference, and the stationary object detection signal is not detected until a predetermined number of measurements that continuously enter a setting error are counted. Is output, and in other cases, the calculation is performed from the beginning, so not only can the stationary state of the object be reliably detected, but also the slightly moving object can be treated as a stationary object by adjusting the error setting value. Furthermore, the object can be identified by setting an appropriate error according to the character of the object.

Also, by setting a certain width and setting the error, it can be detected as a stationary object even if the object fluctuates due to wind, etc., so it can be used without malfunction even outdoors where the conventional ultrasonic sensor was unsuitable. We were able to.

Furthermore, since a predetermined count can be set arbitrarily, increasing the number of times enables fine detection.

Furthermore, since only the direct wave is separately extracted and detected, it is said that some failure occurred between the wave transmitter and the AND gate when this signal is not output or when the cycle is not constant. It was possible to provide an ultrasonic sensor capable of confirming and reducing the labor even in daily maintenance, which can solve the problems that could not be solved in the past at once. Especially in parking lots that use a large number of sensors, in order to prevent malfunctions,
It is also effective for facilitating diagnosis of failures.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a reflected wave / direct wave detection circuit of an ultrasonic sensor of the present invention, FIG. 2 is a graph showing changes in the waveform of ultrasonic waves, and FIG. 3 is an embodiment of digital control. FIG. 4, a timing chart of FIG. 4, and FIG. 5 are block diagrams showing an example of analog control. In the figure, 2 ... Wave transmitter, 3 ... Wave receiver, 8 ... Level slice circuit, 9.10 ... AND gate, 11 ... Direct wave gate signal,
12 ... Reflected wave gate signal.

Claims (2)

[Claims] 1. A transmitting means for continuously transmitting a group of ultrasonic waves at a constant cycle, a means for receiving and amplifying ultrasonic waves, and a detection signal element having a certain level or more after detecting the amplified signal. The level slice circuit 8 to be taken out and the distance between the wave transmitter 2 and the wave receiver 3 are set in advance and at a direct wave detection timing.
The direct wave gate signal 11 that turns on, the reflected wave gate signal 12 that turns on at the timing of detecting only the reflected wave from the object within the distance assumed in advance, and the above detection signal element in parallel to the two AND gates 9 and 10. And the direct wave gate signal to one AND gate 9 and the reflected wave gate signal to the other AND gate 10 to output separate digital signals of the direct wave and the reflected wave. A reflected wave / direct wave detection circuit consisting of, a calculation means for measuring the time difference from the transmission wave to the reception of the reflected wave, and the previous measurement value as a reference value, and the subsequent measurement value is preset to the previous measurement value. Means for cumulatively counting the number of times when the error is within the allowable error value, and output of a stationary object presence signal when the predetermined count is continuously reached, and thereafter while the measured value within the allowable error value is being input. Is the above While holding the product count on the reset side, if a measurement value that is out of the error tolerance is input, the count is accumulated again, and when the predetermined count is reached continuously, the stationary object presence signal is turned off, and And a control circuit including means for resetting the cumulative count and measuring again from the reference value when the measured value deviates from the error allowable value or is within the allowable value until reaching the respective predetermined counts. An ultrasonic sensor characterized in that. 2. The ultrasonic sensor according to claim 1, wherein a failure signal is output when the digital signal of the direct wave is not received or deviates from a predetermined fixed period.