JPH04339285A - ultrasonic sensor - Google Patents

Abstract

PURPOSE:To prevent malfunction caused by multiple reflection without extending any pulse interval processing the maximum reflection wave as a first reflection wave when a plurality of reflection waves in a cycle of ultrasonic pulse emission exist. CONSTITUTION:A microcomputer 4 is driven to emit a transmission signal, a timer 4A is started. The microcomputer 4 is made a wave signal receiving state and, in the case where a wave receiving signal exists, the time from which a transmission signal is emitted is converted into a piece of distance information, which is stored into a memory 4B. The information of the size of the wave receiving signal is stored into another memory 4C, the address of the memories 4B, 4C is made the advance of +1 and a time-up interruption of the wave receiving signal and a timer 4A is waited. When the time-up of the timer 4A occurs, the contents (data) of the memory 4C of the number in which the wave receiving signal exists are compared to select the maximum data and, after the distance information of the memory 4B for the data is stored into a register 4D, the contents (data) of the register 4D are output 5. If the output is completed, a next transmission signal is emitted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor that measures the distance to an object by utilizing the propagation time of ultrasonic pulses, and particularly relates to a method for preventing malfunction.

0002

[Prior Art] An ultrasonic transducer periodically emits ultrasonic pulses, the ultrasonic pulse hits an object to be detected and is reflected, and the elapsed time from when this reflected wave returns to the ultrasonic transducer is measured. Ultrasonic sensors are conventionally used, which detect the distance to the object to be detected based on the measured data, output an analog voltage proportional to this distance, and output a switch output within a distance range set from the outside. Regardless of the ambient temperature, the drive voltage value of the ultrasonic transducer, the pulse width of the drive voltage, and the amplification factor of the ultrasonic receiving circuit are fixed constant, and the emission time interval of ultrasonic pulses is also fixed at a constant rate. Ta. Furthermore, even if there were multiple reflected waves within one cycle, the first reflected wave was processed.

0003

SUMMARY OF THE INVENTION Ultrasonic waves emitted from an ultrasonic transducer are absorbed by the air and attenuated while propagating through the air. The degree of attenuation changes depending on the temperature and humidity of the surrounding air, as shown in FIG. Therefore, as shown in FIG. 6, there is a large difference in the maximum detection distance of the ultrasonic sensor depending on whether the degree of attenuation is large or small, and when the degree of attenuation is small, objects outside the detection range may be detected. Furthermore, in an environment where the back surface of the ultrasonic sensor is a large wall and the area of the object to be detected is large, and the attenuation of ultrasonic waves is small, multiple reflections as shown in FIG. 7 occur. That is, ultrasonic transducer 1
The ultrasonic pulse from 1 becomes a transmitted wave A, hits the object to be detected 10 and is reflected to become a first reflected wave A, which hits the case surface or back wall of the ultrasonic transducer 1 and is reflected as a second reflected wave A. Become. This second reflected wave A hits the object to be detected 10 again and becomes a third reflected wave A, which enters the ultrasonic transducer 1 and causes a malfunction. When propagating through the air, it is attenuated, so the second reflected wave A becomes smaller than the first reflected wave A, and the third reflected wave A becomes smaller than the second reflected wave A, but the size of this third reflected wave A is The above-mentioned malfunction may occur depending on the situation. To explain this with reference to FIG. 8, a second reflected wave A is generated at the same time interval as the first reflected wave A of the transmitted wave A, and a third reflected wave A is further generated at the same time interval. In this case, the next transmitted wave B is emitted from the middle of the time interval between the second reflected wave A and the third reflected wave A, and the first reflected wave B, second reflected wave B,
The third reflected wave B is also located at the illustrated position. At this time, the transmitting wave B and the first
Normal operation occurs when time is measured with reflected wave B, but in the case shown, time is measured with third reflected wave A before first reflected wave B, which causes malfunction. There was a problem. To solve this problem, the next transmitted wave (corresponding to transmitted wave C in the figure) should not be emitted after the reflected wave due to multiple reflections (corresponds to third reflected wave B in the figure) disappears. This has the disadvantage that the time interval between transmissions (in the figure, the time interval N between transmission waves B and C is larger than the time interval M between transmission waves A and B) and the response speed becomes slower. There is.

[0004] Furthermore, if there is another ultrasonic device in the vicinity of this ultrasonic sensor, and the ultrasonic waves leaking from there become noise and enter the ultrasonic transducer of the ultrasonic sensor, the wave will be transmitted as shown in FIG. A malfunction occurred in which noise 1 was detected and processed instead of reflected wave 1 due to transmitted wave 1 (noise 3 instead of reflected wave 2 due to transmitted wave 2).

[0005] In view of the above-mentioned problems, an object of the present invention is to prevent malfunctions due to multiple reflections without increasing the time interval between wave transmissions (without slowing down the response speed), and to prevent ultrasonic noise from invading the ultrasonic transducer. The object of the present invention is to provide an ultrasonic sensor that does not malfunction even when the sensor is in use.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention periodically emits ultrasonic pulses from an ultrasonic transducer, and the ultrasonic pulses hit an object to be detected and are reflected.
Measuring the elapsed time until the reflected wave returns to the ultrasonic transducer, detecting the distance to the object to be detected using the measured data, and outputting an analog voltage proportional to this distance;
In an ultrasonic sensor that outputs a switch output within a distance range set from the outside, when multiple reflected waves exist within one cycle of ultrasonic pulse emission, the magnitude of each reflected wave is compared and the largest reflected wave is selected. It is characterized in that the wave is processed as the first reflected wave within its period. To do this, the data obtained by converting the distance between emitting a transmission signal from an ultrasonic transducer and receiving it as a reception signal is stored in a memory, and when the timer times up, the data stored in the memory is compared. Extract and output the largest data. In addition, when external ultrasonic noise exists within one cycle of ultrasonic pulse emission, compare the sizes of the respective waveforms and consider only the largest waveform (t2 in Figure 10) as the regular reflected wave. The distance is measured as the first reflected wave, and the largest waveform within the next cycle is regarded as the normal emitting part, and the distance is measured as the second reflected wave. It is output only when the first distance measurement data match, and when there is a reflected wave of the same size as the first reflected wave within the next cycle (t8 in Figure 11).
= t11) When distance measurement is performed as a second reflected wave, and the first distance measurement data and the second distance measurement data match (T8 = T11 in FIG. 11)
Output only.

[0007]

[Operation] When multiple reflected waves exist within one cycle of ultrasonic pulse emission, distance measurement data and information on the size of the received waves are stored in memory for the number of received signals, and within one cycle. Since the maximum received wave is selected from the memory and distance information for that received wave is output, a malfunction such as outputting distance information for the closest received wave within one cycle does not occur. In addition, if there is ultrasonic noise from the outside within one period of ultrasonic pulse emission, the maximum reflected wave within one period is selected from the memory, the maximum reflected wave within the next period is selected, and both distance measurement distance data are obtained. Since it outputs only when the two match, malfunctions such as detecting ultrasonic noise will not occur.

[0008]

[Embodiment] Fig. 1 is a circuit block diagram of an ultrasonic sensor which is an embodiment of the present invention, and includes an ultrasonic transducer 1, a transmitting circuit 2,
It is equipped with a receiving circuit 3, a microcomputer 4, and an output circuit 5, and the microcomputer 4 has ROM, RAM, timer 4A,
Memory 4B, 4C, register 4D, 4E, 4
Equipped with F, 4G and counters to control each part. The transmitting circuit 2 is connected to oscillate an ultrasonic frequency according to a command from the microcomputer 4 and to emit the ultrasonic frequency. Also, the receiving circuit 3
The ultrasonic wave emitted from the object to be detected 10 is transmitted to the ultrasonic transducer 1
The microcomputer 4 is connected to amplify the received and converted electrical signal and input it to the microcomputer 4.

The operation of such an ultrasonic sensor to prevent malfunctions due to multiple reflections depending on the atmospheric temperature will be explained based on the flowchart shown in FIG. The S number in the figure indicates the number of each step in the flowchart. First, drive the microcomputer 4 to emit a transmission signal (S
1) Start timer 4A of microcomputer 4 (
S2). Next, the microcomputer 4 is set to receive the received signal, and if there is a received signal (S3), convert the time since the transmitting signal was emitted into distance information and store it in the memory 4B (S4)
. Next, information on the size of this received signal is stored in memory 4C (S5), and the addresses in memories 4B and 4C are advanced by +1 (S6), and the process returns to (S3) to generate the received signal and the time-up interrupt of timer 4A. wait. Here timer 4
When the time-up of A occurs (S7), the contents (data) of the memory 4C of the number of received signals are compared, the largest data is selected, and the distance information of the memory 4B for that data is stored in the register 4D. (S8) Output the contents (data) of rear register 4D (S9
). When the output is completed, the process returns to (S1) and a transmission signal is emitted.

The operation for preventing malfunctions caused by ultrasonic waves leaking from other ultrasonic devices in the vicinity of this ultrasonic sensor and entering the ultrasonic transducer as noise is based on the flowchart shown in FIG. I will explain. First, drive the microcomputer 4 to emit a transmission signal (S11),
Start timer 4A (S12). Next, the microcomputer 4 is placed in a receiving signal receiving state, and if there is a receiving signal, the time from when the transmitting signal is emitted is converted into distance information and stored in the memory 4B (S14). Next, the magnitude of the received signal is converted and stored in the memory 4C (S15), and the addresses of the memories 4B and 4C are incremented by +1 (S16), and then the process returns to (S13) to wait for the received signal and time-up interrupt. When a time-up interrupt from timer 4A occurs (S17), the contents of register 4D are placed in register 4F, and the contents of register 4E are placed in register 4G (S18). The sizes of the data stored in the memory 4C are compared, the largest data is placed in the register 4E, and the distance information of the memory 4B corresponding to that memory 4C is placed in the register 4D (S19). Next, compare the contents of register 4E and register 4G (S20), if they are not the same, return to (S11), and if they are the same, register 4D
(S21) If they are not the same, the process returns to (S11), and if they are the same, the contents of the register 4D are output.

Further, the operation of an embodiment different from that shown in FIG. 3 will be explained based on the flowchart shown in FIG. (S31) to (S36) are (S11) to (S36) in FIG.
The explanation is omitted as it is the same as S16), but if there was no reception in the previous cycle (S38), the sizes of the data stored in the memory 4C are compared, the largest data is selected, and its contents are stored in the register 4E. and enter the distance information of memory 4B corresponding to that memory 4C into register 4D (S
39). If a wave was received in the previous cycle (S38) If the same memory 4C as the register 4E is not searched (S40), the process returns to (S31); if there is a wave (S40), the process returns to (S4)
Proceed to step 1) to find if there is a memory 4B that is the same as register 4D. If not (S41), return to (S31),
If yes (S41), output the contents of register 4D and return to (S1).

0012

Effects of the Invention According to the present invention as described above, the back surface of the ultrasonic sensor is a large wall and the area of the object to be detected is large. Eliminates malfunctions due to reflexes,
Moreover, stable detection operation is possible without extending the time interval between wave transmissions (without reducing response speed), and if there are other ultrasonic devices near the ultrasonic sensor, the ultrasonic waves leaking from them may become noise. Even if the ultrasonic noise enters the ultrasonic transducer of the ultrasonic sensor, the above-described means eliminates malfunctions due to the influence of ultrasonic noise and enables stable detection operation.

[Brief explanation of drawings]

[Fig. 1] Circuit block diagram of an ultrasonic sensor that is an embodiment of the present invention.

[Figure 2] Operation flowchart of an ultrasonic sensor that prevents malfunctions due to multiple reflections

[Figure 3] Operation flowchart of an ultrasonic sensor that prevents malfunctions due to ultrasonic noise intrusion

[Fig. 4] Operation flowchart of an ultrasonic sensor that operates in an embodiment different from that shown in Fig. 3.

[Figure 5] Curve diagram showing changes in the degree of attenuation due to air absorption of ultrasonic waves depending on temperature and humidity

[Figure 6] Curve diagram showing the relationship between ultrasonic detection distance and relative sensitivity

[Figure 7] Diagram showing multiple reflections occurring between the ultrasonic transducer and the detected object

[Figure 8] Diagram showing malfunction of ultrasonic sensor due to multiple reflections

[Figure 9] Diagram showing malfunction due to ultrasonic noise

[Figure 10]
Diagram showing measures against ultrasonic noise

[Figure 11] Diagram showing countermeasures against ultrasonic noise

[Explanation of symbols]

1 Ultrasonic transducer 2 Transmission circuit 3 Receiving circuit 4 Microcomputer 5 Output circuit 10 Object to be detected

Claims (4)

[Claims] Claim 1: Periodically emitting ultrasonic pulses from an ultrasonic transducer, measuring the elapsed time from when this ultrasonic pulse hits an object to be detected and is reflected to when this reflected wave returns to the ultrasonic transducer. In an ultrasonic sensor that detects the distance to the object to be detected based on the measured data, outputs an analog voltage proportional to this distance, and outputs a switch output within a distance range set from the outside, one cycle of ultrasonic pulse emission An ultrasonic sensor characterized in that when a plurality of reflected waves are present in the period, the magnitudes of the respective reflected waves are compared and the largest reflected wave is treated as the first reflected wave within the period. 2. The device according to claim 1, wherein data obtained by converting the time from emitting a transmission signal from the ultrasonic transducer to receiving it as a reception signal is stored in the memory of the microcomputer, and a timer is used to set the time. An ultrasonic sensor characterized in that when the data is uploaded, the data stored in the memory is compared, and the largest data is extracted and output. 3. In the device according to claim 1, the size of each waveform is compared and only the largest waveform is regarded as a regular reflected wave, distance is measured as a first reflection plate, and the next period is The largest waveform among them is regarded as the regular reflected wave, and the distance is measured as the second reflected wave, and it is output only when the first distance measurement data and the second distance measurement data match. An ultrasonic sensor featuring: 4. In the device according to claim 3, if there is a reflected wave of the same magnitude as the first reflected wave within the next cycle, the distance is measured as the second reflected wave and the distance is measured as the first reflected wave. An ultrasonic sensor characterized by outputting only when measurement data and second distance data match.