JPH0723908B2 - Ultrasonic rangefinder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic range finder, and more specifically, it transmits an ultrasonic wave, receives a reflected wave of the ultrasonic wave from the object, and detects an object based on a time difference between transmission and reception. The present invention relates to an ultrasonic range finder that calculates the distance to.

BACKGROUND ART Generally, in this type of ultrasonic rangefinder, when an ultrasonic wave transmitted from a rangefinder main body is reflected by an object, the reflected wave is detected to detect the distance to the object. The reflected waves from the object are usually reflected again by the body of the rangefinder to cause multiple reflections. In order to avoid such a malfunction due to multiple reflection, when the receivable period for receiving the reflected wave is set to a predetermined time width after the ultrasonic wave is sent from the wave sending means, and the level of the reflected wave is equal to or higher than the predetermined level. Conventionally, an ultrasonic range finder has been provided, which is regarded as a regular reflected wave from an object.

However, when the distance from the body of the rangefinder to the object is very short, the level of the reflected wave of the second or higher order in the multiple reflection becomes large, and the primary reflected wave is not received within the receivable period and the secondary reflected wave is not received. The above reflected waves may be received, resulting in malfunction. That is, it is assumed that the ultrasonic wave pulse is generated from the transmitting means at time t ₀ , then the receivable period is from time t ₁ to time t ₂ , and the primary reflected wave reaches the rangefinder main body at time t ₃ . To do. In this case, if t ₀ <t ₁ <t ₃ <t ₂ , the distance to the object can be measured, but if t ₀ <t ₃ <t ₁ <t ₂ , the primary reflection occurs during the receivable period. Since the wave is not received and the reflected wave of the second or higher order is received for the first time, and the level of the reflected wave exceeds the predetermined level, the measured distance becomes an integral multiple of the actual distance, and the actual distance becomes The problem of not being asked arises.

[Object of the Invention] The present invention has been made in view of the above points, and its main purpose is to set a measurement limit distance and not perform measurement at a distance shorter than the measurement limit distance. Thus, it is an object of the present invention to provide an ultrasonic range finder with improved reliability of measured values.

DISCLOSURE OF THE INVENTION In the present invention, a wave sending unit that intermittently sends out ultrasonic pulses, a wave receiving unit that receives a reflected wave of an ultrasonic wave sent from the wave sending unit, and a wave sending unit. A calculation means for calculating the distance to the object based on the time difference from the transmission of the ultrasonic pulse to the reception of the reflected wave by the receiving means; and a display means for displaying the distance calculated by the calculation means. In the ultrasonic range finder provided with, the receiving means is an amplification circuit for amplifying a received signal corresponding to the received ultrasonic wave,
The output level of the amplifier circuit is determined during a predetermined open period that starts after the specified time has elapsed after the ultrasonic wave pulse is transmitted from the wave transmission means, and amplification is performed when the output level of the amplifier circuit exceeds the predetermined level during the open period. After inputting the output of the circuit to the calculating means, the distance to the object is obtained from the time difference from the transmission of the ultrasonic wave to the reception of the ultrasonic wave, and if there is no input above the predetermined level from the amplification circuit during the open period, after the open period ends The determination circuit that generates an output notifying that measurement is impossible, and the minimum of the amplification circuit so that the reception signal corresponding to the primary reflected wave of the ultrasonic pulse is above the predetermined level and the secondary reflected wave is below the predetermined level Amplification is set and amplification is performed at a rate of change that keeps the output level of the amplification circuit for the primary reflected wave substantially constant regardless of the distance to the object during the open period of the judgment circuit. The amplification factor of the road discloses an ultrasonic distance meter and a gain control means for increasing gradually with time from the minimum gain.

According to the above configuration, the amplification factor of the amplification circuit becomes minimum at the start of the open period, and this amplification factor is determined if the received wave level is relatively high at the minimum distance of the measurement limit. It is set so that the determination circuit cannot pass through the reflected waves that pass through the circuit and have a low received level, such as secondary waves. Also, the longer the elapsed time from the transmission of the ultrasonic pulse, the farther the reflected wave is received, and the farther the ultrasonic pulse is reflected, the lower the received level becomes. In the above, the amplification factor is increased with the passage of time so that the input level to the determination circuit for the primary reflected wave is kept substantially constant regardless of the received wave level. Therefore, regardless of the distance to the object, the determination circuit discriminates between the first-order reflected wave and the second-order or higher reflected wave under the same determination condition during the open period, and the second-order or higher-order reflected wave is detected regardless of the distance to the object. It is possible to prevent input to the calculation means. In the end, it is possible to prevent erroneous measurement of values due to the reflected waves of the second or higher order. In addition, the opening period is started after a stipulated time has elapsed after transmitting the ultrasonic pulse, and the amplification factor is set so that the primary reflected wave is passed but the secondary and higher reflected waves are not passed during this opening period. By the setting, the output level of the amplification circuit for the primary reflected wave is kept substantially constant during the open period regardless of the distance to the object. Therefore, even if there is an object on the near side of the measurement range regulated by the open period and the reflectance of the object against ultrasonic waves is significantly higher than that of a general member, it is still outside the measurement range. It can be neglected and reliable distance measurements can only be made for objects that are within the measuring range. Moreover, in the determination circuit, if there is no input of the primary reflected wave during the open period, an output for notifying that measurement is impossible is generated after the end of the open period. Therefore, if the object is not within the measurement range, it is notified that measurement is impossible. It is possible.

(Example) Hereinafter, the Example of this invention is described based on drawing. First
As shown in the figure, the ultrasonic range finder basically receives a wave transmitting means 1 for intermittently transmitting an ultrasonic pulse, and a reflected wave from the object of the ultrasonic pulse transmitted by the wave transmitting means 1. Calculation means 3 for calculating the distance to the object based on the time difference between the wave receiving means 2 and the time when the ultrasonic wave pulse is transmitted from the wave transmitting means 1 until the reflected wave is received by the wave receiving means 2. The display means 4 displays the distance calculated by the means 3.

The transmitting means 1 is a first for setting a transmitting interval of ultrasonic pulses.
Of the integrator circuit 11 and the first monostable multivibrator (hereinafter abbreviated as monostable multi) 12 and a pulse corresponding to the pulse width of the ultrasonic pulse using the rising edge of the output of the first monostable multi 12 as a trigger signal. Generating a second monostable multi 13, an oscillation circuit 14 that outputs a high frequency having a frequency equal to the frequency of the ultrasonic pulse during the period when the pulse is output from the second monostable multi 13, and an oscillation circuit 14 The driver circuit 15 that amplifies the output level of 1 to a level that can drive the ultrasonic transducer, and the transducer 5 that is the ultrasonic transducer. As a result, when the power is turned on, the first integrator circuit 11 starts to integrate the power supply voltage with a predetermined time constant, and the output level of the first integrator circuit 11 exceeds the input threshold value of the first monostable multi-circuit 12. Then, a pulse having a predetermined time width is transmitted from the first monostable multi 12. The first integrator circuit 11 continues the integration while the pulse is output from the monostable multi 12, and when the pulse from the monostable multi 12 falls,
It is designed to be reset by the fall. After the reset, the integration is restarted, so that this operation is continued and pulses are generated at a predetermined cycle. That is, the first integrating circuit 11 and the first monostable multi-circuit 12
And constitute an unstable multi. The generation period of this pulse is the transmission interval of the ultrasonic pulse, and the rising edge of this pulse is input as the trigger signal of the second monostable multi 13, and the second monostable multi
A pulse with a short time width is output from 13. The oscillation circuit 14 is adapted to obtain an oscillation output only during the period when the output pulse of the second monostable multi 13 is being sent out. Therefore, the output of the first monostable multi 12 is output as the output of the oscillation circuit 14. A high frequency pulse having a time interval corresponding to the pulse and a time width corresponding to the output pulse of the second monostable multi 13 is obtained. By raising the level of this high frequency pulse to the vibration level of the ultrasonic transducer via the driver circuit 15 and applying it to the transducer 5, the ultrasonic pulse corresponding to the high frequency pulse is transmitted from the transducer 5. .

The wave receiving means 2 includes a wave transmitter / receiver 5, an amplifier circuit 21 for amplifying an ultrasonic wave received by the wave transmitter / receiver 5, and a detection circuit 22 for extracting only an envelope component excluding a high frequency component from the output of the amplifier circuit 21. And a determination circuit 23 that outputs a detection signal when the output level of the detection circuit 22 is equal to or higher than a predetermined level and obtained within a predetermined open period, and the first monostable multi-wave 12 of the wave transmission means 1. Based on the output of the gate setting circuit 24 that sets the open period of the determination circuit 23, and based on the output of the gate setting circuit 24, the integration is started from the time when the determination circuit 23 is opened, and the output of the amplifier circuit 12 is amplified. A second integration circuit 25 as an amplification factor control means for controlling the rate, and a non-measurable display circuit 26 that indicates that the object is not within the measurement distance range when the detection signal is not output from the determination circuit 23 and indicates that measurement is impossible. Composed. The gate setting circuit 24 is a circuit for generating a pulse of a predetermined time width that rises after a predetermined time delay from the rising of the output of the first monostable multi 12 based on the output of the first monostable multi 12. The determination circuit 23 is opened while the pulse is output from 24. That is, the period during which the pulse is output from the gate setting circuit 24 is the receivable period, and the distance can be measured only when the reflected wave is received during this period. Since the delay time from the rise of the first monostable multi 12 to the rise of the output pulse of the gate setting circuit 24 and the time width of the open period of the judgment circuit 23 vary depending on the measurement distance range, they may be different depending on the measurement distance range. The gate setting circuit 24 is provided with a changeover switch SW so that the measurement can be performed. The second integration circuit 25 starts integration from the rising edge of the output pulse of the gate setting circuit 24. The amplification rate of the amplification circuit 21 is variable, the amplification rate is small when the output level of the second integration circuit 25 is small, and the amplification rate gradually increases as the output level of the second integration circuit 25 increases. Is done. In other words, the amplification factor increases as time elapses after the determination circuit 23 is opened, which means, for example, that the bias of the amplification circuit 21 is changed to the second integration circuit 25.
It is realized by using a so-called voltage control type operational amplifier in which the amplification factor is variable according to the control voltage and the amplification factor changes according to the control voltage. The minimum amplification factor of the amplifier circuit 21 is such that the received signal corresponding to the primary reflected wave exceeds the threshold level set in the determination circuit 23 and the received signal corresponding to the secondary or higher-order reflected waves exceeds the threshold level. It is set to the extent that it does not exist. The measurement impossible display circuit 26 has a display such as a light emitting diode, and when the detection signal is not output from the determination circuit 23 despite the pulse output from the gate setting circuit 24, the open period of the determination circuit 23 ends. After that, it is displayed that measurement is impossible.

The output of the determination circuit 23 and the output of the second monostable multi 13 are input to the arithmetic circuit 31 as the arithmetic means 3, and the detection signal output from the determination circuit 23 from the rising of the output of the second monostable multi 13. The time difference until the rise of the object is measured, and the distance to the object is calculated based on the time difference. That is, when the outside air temperature is Th degree Celsius, the sound velocity Vs is represented by (331 + 0.6Th), and the time from the transmission of the ultrasonic pulse by the wave transmission means 1 to the reception by the wave reception means 2 is Tm. Then, the distance Ds to the object is expressed by the following equation.

Ds = Vs × (Tm / 2) = (331 + 0.6Th) × (Tm / 2) The arithmetic circuit 31 calculates the above equation to obtain the distance to the object. To correct the outside temperature,
It suffices to appropriately provide temperature measuring means for measuring the outside air temperature, and perform the calculation of the above formula based on the measurement result of the temperature measuring means.

The output of the arithmetic circuit 31 is input to the display circuit 41 which is the display means 4, and the calculation result of the arithmetic circuit 31 is displayed.

The circuit part of the ultrasonic distance meter constructed as described above is housed in a housing 52 having a scope 51 as shown in FIG. On the outer peripheral surface of the housing 52, a transducer 5 having a horn for enhancing directivity, a power switch 6, a knob 7 of a changeover switch SW connected to a gate setting circuit 24, a display connected to a distance display circuit 41 The container 42 and the like are exposed. The orientation of the scope 51 is attached so as to match the orientation of the wave transmitter / receiver 5, and ultrasonic waves are transmitted toward the object viewed by the scope 51. In other words, when measuring the distance to the object, if the scope 51 is aimed at the object, it is possible to know the approximate distance to the object, and it is possible to accurately emit ultrasonic waves toward the object. It is like this. With this configuration, as shown in FIG. 3, when the shelf 54 is arranged in front of the wall 53 and the distance to the shelf 54 is not measured, ultrasonic waves are emitted toward the wall 53, Even though the distance to the shelf 54 is measured, the inconvenience of measuring the distance to the wall 53 is eliminated, and the ultrasonic waves can be reflected correctly at the target object to be measured, and the distance can be measured accurately. It comes to be. Also the scope
Since the distance to the object can be roughly known by 51, the measurement distance range can be set appropriately by adjusting the knob 7 of the changeover switch SW.
As shown in FIGS. 5 (c), (d) and (e), the time from the transmission of the ultrasonic pulse to the start of the receivable period and the time width of the receivable period can be adjusted. By this adjustment, unnecessary reflected waves can be removed, and only the reflected waves from the target object can be taken out. In this way, it is possible to accurately measure the distance by removing the unnecessary reflected wave by accurately reflecting the ultrasonic wave on the target object and extracting only the desired reflected wave. is there.

(Operation) The operation will be described below with reference to FIG. Incidentally, in FIG. 4, S _{1 to} S ₄ represent signals of the portions indicated by the corresponding symbols in FIG. First, when power supply is started, the output level of the first integrating circuit 11 gradually increases and exceeds the threshold level of the input level of the first monostable multi 12, and the monostable multi 12
Is triggered and a pulse with a relatively long time width is output. The first integrator circuit 11 is reset by the trailing edge of this pulse, and the output level increases again, so that pulses are sent out at a predetermined cycle. The second monostable multi 13 uses the rising edge of the output of the first monostable multi 12 as a trigger signal and outputs a pulse having a relatively short time width. In other words, the second monostable multi 13 outputs a pulse with a short time width at the repetition period of the pulse output from the first monostable multi 12. A high frequency pulse is output from the oscillation circuit 14 during the period in which this pulse is output. That is, as shown in FIG. 4 (a), high frequency pulses are obtained intermittently at a constant cycle. This high frequency pulse is applied to the wave transmitter / receiver 5 via the driver circuit 15, converted into an ultrasonic pulse, and emitted. As described above, the ultrasonic pulse generated intermittently can be obtained.

The ultrasonic wave output from the wave transmission means 1 and reflected by the object in this manner is received by the wave transmitter / receiver 5, amplified by the amplification circuit 21, detected by the detection circuit 22, and then input to the determination circuit 23. As shown in FIG. 4 (b), a pulse for setting the open period of the determination circuit 23 is input to the determination circuit 23 from the gate setting circuit 24, and the output level of the detection circuit 22 is equal to or higher than a predetermined level. If the level is reached during the receivable period in which the pulse is output from the gate setting circuit 24, the detection signal is output at that time. The pulse output from the gate setting circuit 24 is delayed by a predetermined time T ₁ after the output of the first monostable multi-circuit 12 rises and rises. The delay time T ₁ and pulse width
T ₂ is set in multiple stages by the changeover switch SW. As a result, the distance range to the object can be limited. At the same time that the pulse output from the gate setting circuit 24 rises, the output level of the second integrating circuit 25 for integrating this pulse increases as shown in FIG. Gate setting circuit
The pulse output from 24 rises gradually as time elapses. However, when the distance to the object is shorter than the measurement distance limit set by the gate setting circuit 24, multiple reflection occurs, but in general, one reflection causes a rapid decrease in the level of ultrasonic waves, and thus a high-order of higher than the second order. The level of the secondary reflected wave is much smaller than that of the primary reflected wave, and the amplification factor of the amplifier circuit 21 is small in the first half of the receivable period. The output is below the threshold level of the determination circuit 23, and the detection signal is not output. Since the amplification factor of the amplifier circuit 21 in the first half of the receivable period is set to such an extent that the primary reflected wave can exceed the level set by the determination circuit 23, the determination circuit 23 can detect the primary reflected wave. However, the higher-order reflected waves of the second order and higher are not detected,
As a result, it is possible to prevent the second or higher-order reflected waves from being confirmed as the first-order reflected waves from the object and displaying an incorrect value. Also, if a signal of a threshold level or higher is not input to the measuring circuit 23 within the receivable period, it is determined that the object is outside the measurement distance limit, and the measurement impossible display circuit 26 displays the measurement impossible display. You can recognize that you are not inside.

[Effects of the Invention] As described above, the present invention has a wave transmitting means for intermittently transmitting an ultrasonic wave, a wave receiving means for receiving a reflected wave of an ultrasonic wave transmitted from the wave transmitting means, and a wave transmitting means. Calculation means for calculating the distance to the object based on the time difference from the transmission of the ultrasonic pulse from the wave means to the reception of the reflected wave by the reception means, and a display for displaying the distance calculated by the calculation means In the ultrasonic range finder provided with means, the wave receiving means starts after a specified time has elapsed after the ultrasonic wave pulse was sent from the wave sending means and the amplifying circuit that amplifies the received signal corresponding to the received ultrasonic wave. The output level of the amplifier circuit is determined during the predetermined open period, and when the output level of the amplifier circuit becomes equal to or higher than the predetermined level during the open period, the output of the amplifier circuit is input to the calculation means to transmit the ultrasonic wave to receive the ultrasonic wave. Due to the time difference between Corresponding to the primary reflected wave of the ultrasonic pulse and the determination circuit that generates the output that notifies the measurement failure after the end of the open period unless there is an input above the predetermined level from the amplifier circuit during the open period The minimum amplification factor of the amplifier circuit is set so that the received signal becomes equal to or higher than the predetermined level and the secondary reflected wave becomes equal to or lower than the predetermined level, and the output level of the amplifier circuit for the primary reflected wave is set in the open period of the determination circuit. An amplification rate control means for gradually increasing the amplification rate of the amplification circuit from the above-mentioned minimum amplification rate over time at a rate of change that keeps it substantially constant irrespective of the distance to the object. Then, the amplification factor of the amplification circuit becomes the minimum, and if the minimum amplification factor is the primary reflected wave with a relatively high received wave level at the minimum distance of the measurement limit, it will pass through the judgment circuit and be received. Because in the second or of the reflected wave low level is set so as not to be passed through the decision circuit, only the primary reflected wave is inputted to the computing unit through the decision circuit distance determined. In addition, as the elapsed time from the transmission of the ultrasonic pulse is longer, the reflected wave in the far distance is received, and the received level becomes smaller as the ultrasonic pulse is reflected in the far distance. By increasing the amplification factor with the passage of time during the open circuit period, the primary reflected wave can be input to the determination circuit at a substantially constant level regardless of the received wave level. Therefore, regardless of the distance to the object, the determination circuit uses the same determination condition 1 during the open period.
It is possible to discriminate between the secondary reflected wave and the secondary or higher reflected waves and prevent the secondary or higher reflected waves from being input to the calculation means regardless of the distance to the object. This has the advantage that erroneous values can be prevented from being measured and the reliability of the measured values is improved.

In addition, the opening period is started after a stipulated time has elapsed after transmitting the ultrasonic pulse, and the amplification factor is set so that the primary reflected wave is passed but the secondary and higher reflected waves are not passed during this opening period. Since it is set, the output level of the amplification circuit for the primary reflected wave is kept almost constant during the open period regardless of the distance to the object, and as a result, it is closer than the measurement range regulated by the open period. Even if there is an object on the side and the reflectance of the object for ultrasonic waves is considerably higher than that of a general member, it can be ignored as outside the measurement range, and the object existing within the measurement range Only the distance can be reliably measured.

Moreover, in the determination circuit, if there is no input of the primary reflected wave during the open period, an output for notifying that measurement is impossible is generated after the end of the open period. Therefore, if the object is not within the measurement range, it is notified that measurement is impossible. If there is an object at a distance closer than the measurement range, it is clarified that the cause of the distance measurement not being performed is not a fault by notifying that the object is outside the measurement range. Therefore, there is an advantage that the user does not feel uneasy.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an external perspective view of the same as above, FIG. 3 is an operation explanatory view showing an example of use of the same as above, and FIGS. 4 and 5 are same as above. FIG. 1 is a transmitting means, 2 is a receiving means, 3 is a calculating means, 4 is a distance displaying means, 21 is an amplifying circuit, 23 is a judging circuit, 24 is a gate setting circuit, 25 is an integrating circuit, and 26 is an unmeasurable display circuit. , 31 are arithmetic circuits, and 41 is a display circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01S 15/18 9382-5J

Claims (1)

[Claims] 1. A wave transmitting means for intermittently transmitting an ultrasonic wave, a wave receiving means for receiving a reflected wave of an ultrasonic wave transmitted by the wave transmitting means from an object, and an ultrasonic pulse from the wave transmitting means. Ultrasonic distance provided with calculation means for calculating the distance to the object based on the time difference from the reception of the reflected wave to the reception means by the receiving means, and display means for displaying the distance calculated by the calculation means In the meter, the receiving means is an amplification circuit for amplifying the received signal corresponding to the received ultrasonic wave, and an amplification circuit for a predetermined open period that starts after a specified time has passed after the ultrasonic pulse is sent from the transmitting means. The output level of the circuit is judged, and when the output level of the amplification circuit becomes equal to or higher than a predetermined level during the open period, the output of the amplification circuit is input to the calculation means and the distance to the object is determined by the time difference between the transmission and reception of ultrasonic waves. Ask and open A judging circuit for generating an output for informing the unmeasurable after the end of the opening period there is no input above the predetermined level from the amplifying circuit between one of the ultrasonic pulses
The minimum amplification factor of the amplifier circuit is set so that the received signal corresponding to the secondary reflected wave becomes equal to or higher than the predetermined level and the secondary reflected wave becomes equal to or lower than the predetermined level, and the primary reflected wave is amplified in the open period of the determination circuit. An amplification factor control means for gradually increasing the amplification factor of the amplification circuit from the minimum amplification factor with the lapse of time so that the output level of the circuit is kept substantially constant regardless of the distance to the object. An ultrasonic rangefinder.