JP2658534B2 - Temperature Compensation Method of Detection Sensitivity in Ultrasonic Sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for compensating temperature of detection sensitivity when an ultrasonic sensor is used in an environment where the fluctuation range of the ambient temperature is large.

[Prior art]

A pulse is periodically emitted from the ultrasonic vibrator, and the ultrasonic pulse is reflected upon the object to be detected, and the elapsed time until the reflected wave returns to the ultrasonic vibrator is measured. Based on the measured data, The ultrasonic sensor that detects the distance to the object to be detected, outputs an analog voltage proportional to this distance, and outputs a switch output within an externally set distance range, regardless of the conventionally used 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 were fixed.

[Problems to be solved by the invention]

Ultrasonic waves emitted from the ultrasonic transducer are absorbed by air and attenuated when propagating in the air. The degree of attenuation varies depending on the temperature and humidity of the surrounding air as shown in FIG. As a result, there is a large difference in the maximum detection distance between the case where the attenuation is large and the case where the attenuation is small, as shown in FIG. That is, when the ultrasonic sensor is used in a place where there is an object such as a wall or a column outside the range of use, in the winter, when the attenuation of the ultrasonic wave is small, even if there is no object to be detected, a distant object other than the rated detection distance is used. The malfunction of detection as shown in the figure occurred. In an environment where the back surface of the ultrasonic sensor has a large wall shape and the area of the object to be detected is large and the attenuation of the ultrasonic wave is small, a malfunction due to multiple reflection as shown in FIG. 9 may occur. . Further, even when the ambient temperature is low and the emission time interval of the ultrasonic waves is extended, there is a problem that the first reflected wave and the second reflected wave cause malfunctions as shown in FIGS. An object of the present invention is to provide an ultrasonic sensor capable of preventing malfunction of the ultrasonic sensor and performing stable detection in a normal state in view of the above-described problems.

[Means for Solving the Problems]

In the present invention, in order to achieve the above object, an ultrasonic pulse is periodically emitted from the ultrasonic transducer, and the ultrasonic pulse is reflected upon the object to be detected, and a process until the reflected wave returns to the ultrasonic transducer. An ultrasonic sensor that measures the time, 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 externally. The temperature of the detection sensitivity was compensated by controlling the voltage value of the driving voltage applied to the sensor according to the ambient temperature of the ultrasonic sensor. Further, the pulse width of the drive voltage applied to the ultrasonic transducer was controlled in accordance with the ambient temperature of the ultrasonic sensor, and the temperature of the detection sensitivity was compensated.

[Operation]

By controlling the voltage value of the drive voltage applied to the ultrasonic vibrator in accordance with the ambient temperature of the ultrasonic sensor and adjusting the detection sensitivity, the detected object other than the rated detection distance in an environment where the ultrasonic attenuation is small A malfunction such as detecting an error is eliminated. By controlling the pulse width of the drive voltage applied to the ultrasonic vibrator in accordance with the ambient temperature of the ultrasonic sensor and adjusting the detection sensitivity, the detected object other than the rated detection distance in an environment where the ultrasonic attenuation is small A malfunction such as detecting an error is eliminated.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a circuit block diagram showing a method for compensating the temperature of the detection sensitivity of an ultrasonic sensor according to a first embodiment of the present invention. The ultrasonic sensor is a microcomputer including an ultrasonic transducer 1, a transmission circuit 2, a reception circuit 3, a ROM, a RAM, an A / D converter 4a, a gate signal output port 4b, etc. 4), a temperature sensing element 5 connected to the A / D converter, an output circuit 6, a step-up transformer 7 connected to the ultrasonic transducer 1, a drive transistor 8, and a gate signal output port 4b. It comprises a plurality of bidirectional switches 9 provided between the step-up transformers 7 and the like. The transmission circuit 2 oscillates an ultrasonic frequency according to a command from the microcomputer 4, turns on and off the drive transistor 8, generates a drive voltage with the boosting transformer 7, and transmits the drive voltage to the ultrasonic vibrator 1. The ultrasonic transducer 1 converts the electric signal into an ultrasonic pulse and emits it into the air. The emitted ultrasonic pulse hits the object to be detected and is reflected to become a reflected wave. The reflected wave again enters the ultrasonic vibrator 1, is converted into an electric signal, is amplified and shaped by the receiving circuit 3, and is input to the microcomputer 4. Connected. Hereinafter, this operation will be described with reference to the flowchart shown in FIG. The S number shown in the figure indicates each step of the flowchart. The voltage of the temperature sensing element 5 that has detected the ambient temperature in step S1 is converted into a digital value by the A / D converter 4a. The gator output port 4b is selected by comparing and comparing this digital value with a calibration table stored in RAM (memory) (any of a, b, c, and d shown in FIG. 1).
Select any of the primary side intermediate taps of the step-up transformer 7 and select the voltage VP
Is applied (S2). An ultrasonic pulse is emitted from the ultrasonic vibrator 1 by a signal from the transmission circuit 2 (S3), and a reflected wave from the detected object is received by the ultrasonic vibrator 1 and converted into an electronic signal here. The signal is amplified and shaped by the receiving circuit 3 and sent to the microcomputer 4 to measure the reflection time and convert the distance (S
4), and sends the measurement data to the output circuit 6 for output (S
5), and return to step S1. FIG. 3 is a circuit block diagram showing a temperature compensation method of the detection sensitivity of an ultrasonic sensor according to a second embodiment of the present invention. The difference between this embodiment and the first embodiment is that the ultrasonic transducer is used. In the point that the pulse width of the drive voltage applied to is controlled in accordance with the ambient temperature of the ultrasonic sensor to compensate for the temperature of the detection sensitivity, the primary side intermediate tap of the step-up transformer 7 in FIG. A plurality of bidirectional switches 9 and a gate signal output port 4b are not required. The operation of the ultrasonic sensor 1 thus configured will be described with reference to the flowchart shown in FIG. That is, the voltage of the temperature sensing element 5 is A / D
The conversion unit 4a converts the digital value into a digital value (S11), compares the digital value with a calibration table stored in a RAM (memory), compares the digital value with a calibration table, and applies a voltage to the ultrasonic transducer 1 (pulse width). Time) (S12). Next, an ultrasonic pulse is emitted from the ultrasonic transducer 1 by a signal from the transmission circuit 2 (S1).
3) The reflected wave from the detected object is received by the ultrasonic vibrator 1 and converted into an electric signal, then amplified and shaped by the receiving circuit 3 and sent to the microcomputer 4 to measure the reflection time. Distance conversion is performed (S14). The measurement data is output to an output circuit 6
(S15), and returns to (S11). FIG. 5 is a circuit block diagram showing a method for compensating the temperature of the detection sensitivity of the ultrasonic sensor according to the third embodiment of the present invention. In this embodiment, the amplification factor of the receiving circuit is controlled in accordance with the ambient temperature, and the detection is performed. A signal from the gate signal output port 4b is applied to the bidirectional switch 9 to compensate the temperature of the sensitivity, the ultrasonic oscillator and the operational amplifier 10 for amplification are conducted, and the signal is input to the receiving circuit 3. doing. The operation of this ultrasonic sensor will be described with reference to the flowchart shown in FIG. That is, the voltage of the temperature sensing element 5 is
The data is converted into a digital value by the A / D converter 4a (S1).
In step 2), the digital value is compared with a calibration table stored in a RAM (memory) to select the gate output port 4b, and the input resistance (R1, R2, R3, R) of the operational amplifier 10 for amplification is selected.
4) is selected and the amplification factor is set, and the reflected wave received by the ultrasonic transducer 1 is amplified in the preceding stage. The amplification factor of this operational amplifier 10 for amplification is The amplification factor is determined by selecting the bidirectional switch 9. Next, an ultrasonic pulse is emitted from the ultrasonic vibrator 1 with a signal from the receiving circuit 2 (S3), and a reflected wave from the detected object is received by the ultrasonic vibrator 1 and converted into an electric signal. The signal is converted, input to the receiving circuit 3 via the operational amplifier 10 for amplification, amplified, shaped, sent to the microcomputer 4, and the reflection time is measured to convert the distance (S4).
After sending the measurement date to the output circuit 6 (S5), the process returns to (S1). In the above description of the operation, the calibration table stored in the RAM is a memory that stores conversion data for performing a process of lowering the sensitivity as the temperature decreases as shown in Table 1 below.

【The invention's effect】

According to the present invention, the following effects are obtained because the detection sensitivity of the ultrasonic sensor is adjusted according to the ambient temperature. 1) In a low-temperature environment in which the attenuation of ultrasonic waves is reduced, a malfunction of detecting an object other than the rated detection distance (see FIG. 8) which has occurred when there is no detected object is eliminated, and the detection operation is stabilized. 2) Malfunction due to multiple reflections occurring at a time when the attenuation of the ultrasonic wave is reduced under the conditions of use where the back surface of the mounting portion of the ultrasonic sensor is a large wall and the area of the object to be detected is large (FIG. 9) And the detection operation becomes stable.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a method for temperature compensation of detection sensitivity of an ultrasonic sensor according to a first embodiment of the present invention.

FIG. 2 is an operation flowchart of the ultrasonic sensor.

FIG. 3 is a circuit block diagram showing a temperature compensation method for detecting sensitivity of an ultrasonic sensor according to a second embodiment of the present invention.

FIG. 4 is an operation flowchart of the ultrasonic sensor.

FIG. 5 is a circuit block diagram showing a method for temperature compensation of detection sensitivity of an ultrasonic sensor according to a third embodiment of the present invention.

FIG. 6 is a curve diagram showing changes due to temperature and humidity at the time of attenuation due to absorption of ultrasonic air.

FIG. 7 is a curve diagram showing a relationship between a detection distance of ultrasonic waves and a relative sensitivity.

FIG. 8 is a diagram showing a malfunction caused by a first reflected wave because the ultrasonic sensor has excessive sensitivity.

FIG. 9 is a diagram showing a malfunction caused by a second reflected wave because the ultrasonic sensor has excessive sensitivity.

[Explanation of symbols]

 1: Ultrasonic transducer.

Claims (2)

(57) [Claims] An ultrasonic pulse is periodically emitted from an ultrasonic transducer, and the ultrasonic pulse is reflected on an object to be detected, and the elapsed time until the reflected wave returns to the ultrasonic transducer is measured. The ultrasonic sensor detects the distance to the object to be detected according to the measurement data, outputs an analog voltage proportional to the distance, and outputs a switch output within a distance range set from the outside. A temperature compensation method for a detection sensitivity in an ultrasonic sensor, wherein a temperature value of a detection sensitivity is compensated by controlling a voltage value of a driving voltage according to an ambient temperature of the ultrasonic sensor. 2. The method according to claim 1, wherein a pulse width of a driving voltage applied to the ultrasonic transducer is controlled in accordance with an ambient temperature of the ultrasonic sensor to perform temperature compensation of detection sensitivity. Temperature compensation method of detection sensitivity in ultrasonic sensor.