JPH0511048A - Ultrasonic-wave distance sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect distances highly accurately in a broad detecting range with a single ultrasonic-wave piezoelectric transducer by changing the strength of the transmitted ultrasonic-wave pulse when an output voltage exceeds a threshold voltage. CONSTITUTION:An analog voltage which is proportional to a distance is outputted based on the measurement of the elapsed time from the periodic transmissions of ultrasonic-wave pulses from an ultrasonic-wave piezo-electric transducer 1 to the returning of the reflected waves from a body to be detected to the transducer 1. At this time, when the body to be detected approaches the transducer 1 within a detecting range, the output voltage is decreased in proportion to the distance. When the voltage becomes lower than the threshold value of the voltage corresponding to the detecting distance, a signal A from a gate-signal output port 11 is changed to B. Thus, bidirectional switches 92 and 102 are turned ON, and the strength of the transmitted ultrasonic wave pulse is made weak through resistors 72 and 82. The effect of the reverberation of the ultrasonic wave pulse can be made small. Therefore, the detecting range can be changed by changing the strength of the transmitted ultrasonic-wave signal with one transducer 1, and detection can be performed in the broad range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the elapsed time until an ultrasonic wave pulse is periodically emitted by an ultrasonic wave oscillator and the ultrasonic wave pulse hits an object to be detected and is reflected back to the ultrasonic wave oscillator. The present invention relates to an ultrasonic distance sensor that outputs an analog voltage that is proportional to the distance, and particularly to improvement of its detection range and detection accuracy.

[0002]

2. Description of the Related Art An ultrasonic distance sensor, as shown in the block diagram of FIG. 4, includes an ultrasonic transducer 1, a transmitting circuit 2, a receiving circuit 3 and a microcomputer (hereinafter abbreviated as microcomputer).
4 and an output circuit 5. The transmission circuit 2 excites the ultrasonic oscillator 1 in response to a command from the microcomputer 4, and the ultrasonic oscillator 1 emits ultrasonic pulses. Further, the receiving circuit 3 amplifies a signal obtained by converting the ultrasonic reflected wave from the object to be detected by the ultrasonic transducer 1 and inputs the amplified signal to the microcomputer 4. Then, the microcomputer 4 measures the elapsed time until the ultrasonic reflected wave from the detected object is received by the ultrasonic transducer 1 and input to the microcomputer 4 through the receiving circuit 3, and the detected time is detected based on this measured time. The distance to the object is detected, and the voltage corresponding to this distance is output from the output circuit 5.

[0003]

Such an ultrasonic distance sensor generally has an undetectable range due to the reverberation of the transmitted signal, as shown in the detection characteristic diagram of FIG.
This range is about 20% of the maximum detection distance. Therefore, if the maximum detection distance is made large, that is, if the detection object that is present at a long distance is tried to be detected, the minimum detection distance becomes small, and the detection object that exists near cannot be detected. Conversely, if the minimum detection distance is made small, That is, if an attempt is made to detect an object to be detected that is present in the vicinity, the maximum detection distance will be reduced, and there will be a problem that an object to be detected present in the distance cannot be detected. So over a wide range,
That is, when detecting an object to be detected that is present at a distant place and an object to be detected that is present in the vicinity, an ultrasonic distance sensor having a large maximum detection distance and an ultrasonic distance sensor having a small minimum detection distance are prepared, and these Switch as needed or use one ultrasonic distance sensor with ultrasonic transducers with different detection distance ranges.
It is conceivable to use these ultrasonic transducers by switching them in a circuit according to the detection distance. However, this method requires at least two ultrasonic distance sensors or two
It is obviously expensive as it requires two ultrasonic transducers. Further, in the conventional ultrasonic distance sensor, the detection accuracy is constant over the entire detection range, and it has not been possible to measure the accuracy with high accuracy only in a specific detection distance range, particularly in a portion with a short detection distance.

An object of the present invention is to provide an ultrasonic distance sensor which can detect with high accuracy over a wide detection range with a single ultrasonic transducer and in a specific range.

[0005]

According to the present invention, in order to achieve the above object, an ultrasonic wave oscillator periodically emits ultrasonic wave pulses, and the ultrasonic wave pulse hits an object to be detected and is reflected. An ultrasonic distance sensor that measures an elapsed time until returning to the above and outputs an analog voltage proportional to a distance is provided with a means for changing the intensity of an ultrasonic pulse emitted when the output voltage exceeds a certain threshold value. Further, in such means, the means for changing the intensity of the ultrasonic pulse to be emitted is performed by changing the voltage value applied to the ultrasonic transducer or the applied voltage pulse width. Further, in any one of the above means, there is provided means for increasing a clock frequency for distance detection in a certain specific distance detection range.

[0006]

In the ultrasonic distance sensor according to the present invention,
When the output voltage exceeds a certain threshold value, the intensity of the ultrasonic pulse to be emitted can be reduced by, for example, weakening the voltage value applied to the ultrasonic transducer or shortening the applied voltage pulse width. The effect of pulse reverberation is reduced. Furthermore, since a means for increasing the clock frequency for distance detection in a certain specific distance detection range is provided, if the clock frequency is increased by limiting the range in a short distance detection range, for example, the output voltage / distance becomes large and detection is increased. The accuracy can be increased.

[0007]

1 is a block diagram of an ultrasonic distance sensor according to an embodiment of the present invention. An ultrasonic transducer 1, a transmitting circuit 2, a receiving circuit 3, a microcomputer 4, an output circuit 5, a resistor for determining a clock oscillation frequency. Devices 71 and 72 and bidirectional switches 91 and 92
Clock oscillation circuit 6 including a built-in resistor 6, resistors 81, 82 for determining the amplification factor of a received signal, bidirectional switches 101, 10
2, gate signal output port 11 and indicators 12, 13
Etc. Here, the transmission circuit 2 is connected so as to oscillate an ultrasonic frequency according to a command from the microcomputer 4 and send it to the ultrasonic transducer 1 to emit an ultrasonic pulse. The receiving circuit 3 is connected so as to amplify the electric signal received by the ultrasonic transducer 1 and input it to the microcomputer 4. The microcomputer 4 includes an A / D conversion unit and the like in addition to the ROM and the RAM, and controls each unit.

The detection characteristics of this ultrasonic distance sensor will be described below with reference to FIG. In FIG. 2, when the detected object is in the detection range Q and approaches the ultrasonic distance sensor (ultrasonic transducer), the output voltage decreases in proportion to the distance and the output voltage Vb2 corresponding to the detection distance b. When the value becomes equal to or lower than the (threshold value), switching is performed so as to weaken the intensity of the ultrasonic signal. As a result, the output voltage is switched to the value within the detection range P. When the object to be detected enters the detection range P, the accuracy of the detection distance increases, and it becomes possible to control a minute amount. Next, when the detected object is in the detection range P and moves away from the ultrasonic distance sensor (ultrasonic transducer), the intensity of the ultrasonic signal is increased when Vb1 (threshold value) equal to or larger than the detection distance b is reached. Switch to make it stronger. As a result, the output voltage is switched to the detection range Q.

The operation for obtaining the above-mentioned detection characteristic will be described with reference to the block diagram of FIG. 1, the detection characteristic diagram of FIG. 2 and the flowchart of FIG. The S number in FIG. 3 is the number of each step in the flowchart. If the microcomputer 4 starts, (S
The number of times n of checking the output voltage value at the time of switching is set in 1), and the gate signal output port 11 of FIG.
Output signal A to output bidirectional switches 91 and 101.
Is turned on and the detection range P is set by the resistors 71 and 81. Next, in (S3), an ultrasonic pulse is emitted from the ultrasonic transducer 1, the reflected wave is received, distance measurement is performed, and it is checked in (S4) whether the output voltage is Vb1 or less with respect to the data. . If the result of the check is NO (if there is no detected object within the detection range P or if there is a detected object at a distance greater than the detection distance b) (S6), (S6)
Check 7 times in n). The result of (S7) is YES
If so, the display 12 of the detection range P is turned off in (S8), and the signal from the gate signal output port 11 is switched to B in (S9) to turn on the bidirectional switches 92 and 102 to turn on the resistors 72 and 82. And switch to the detection range Q,
In (S10), reset (n-1) to n (S11)
Proceed to. If the result of the check in (S4) is YES (when the detected object is within the detection range P), the display 12 of the detection range P is turned on in (S5) and the process returns to (S3) to repeat the distance measurement. .

If there is no object to be detected in the detection range P or there is an object to be detected which is farther than the detection distance b in FIG. 2, and the range is switched to the detection range Q in (S9) (S10).
Then, (n-1) is reset to n, the process proceeds to (S11), distance measurement is performed, and it is checked whether the output voltage is Vb2 or more in (S12) for the data. When the result of (S12) is YES (that is, the detected object is in the detection range Q
(In case of), the display 13 of the detection range Q is turned on and the process returns to (S11) and repeats the distance measurement. Also (S12)
If the result is NO (that is, if the detection distance is less than or equal to b, (n-1) times are checked in (S14) (S15).
If the result of (n-1) = 0 is YES (S16)
Then, the indicator 13 in the detection range Q is turned off (S17), the signal B is switched from the gate signal output port 11 to the signal A, the bidirectional switches 91 and 101 are turned on by the signal A, and the resistors 71 and 81 are detected. Switch to range P. (S18)
Then, n-1 is reset to n and the process returns to (S3).

[0011]

According to the present invention, since the detection range can be changed by changing the intensity of the ultrasonic signal emitted by only one ultrasonic vibrator, for example, the tank liquid level that is automatically controlled can be changed. It is also suitable when used as a sensor that is required to be able to detect over a wide range, such as when detecting the liquid level. In that case, coarse and fast control is used in long-distance detection, and short-distance detection is used. Fine adjustment is possible.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic distance sensor that is an embodiment of the present invention.

FIG. 2 is a detection characteristic diagram of the ultrasonic distance sensor shown in FIG.

FIG. 3 is an operation flowchart of the ultrasonic distance sensor shown in FIG.

FIG. 4 is a block diagram of a conventional ultrasonic distance sensor.

FIG. 5 is an operation flowchart of a conventional ultrasonic distance sensor.

[Explanation of symbols]

1 Ultrasonic transducer 2 Transmitter circuit 3 Receiver circuit 4 Microcomputer 5 output circuits

Claims (3)

[Claims] 1. An ultrasonic transducer periodically emits ultrasonic pulses, the elapsed time until the ultrasonic pulse hits an object to be detected and is reflected back to the ultrasonic transducer is measured and is proportional to the distance. An ultrasonic distance sensor for outputting an analog voltage, comprising means for changing the intensity of an ultrasonic pulse emitted when the output voltage exceeds a certain threshold value. 2. The device according to claim 1, wherein the means for changing the intensity of the ultrasonic pulse to be emitted is performed by changing the voltage value applied to the ultrasonic transducer or changing the applied voltage pulse width. Ultrasonic distance sensor. 3. The ultrasonic distance sensor according to claim 1 or 2, further comprising means for increasing a clock frequency for distance detection in a certain specific distance detection range.