JPS59221684A - Ultrasonic distance measuring device - Google Patents

Abstract

PURPOSE:To select an optimum gain automatically and measure the distance to a body to be measured by increasing the gain of a variable gain amplifier gradually from a minimum valve. CONSTITUTION:The gain of the variable gain amplifier 12 is set to the minimum under the command of a CPU. An ultrasonic wave is reflected by the body to be measured and detected by a receiving sensor, an only an ultrasonic wave frequency component is passed through a band-pass filter 7 and amplified by the variable gain amplifier 12. At this time, when the output of the amplifier 12 does not attains to a threshold level set in a comparator 9, the comparator 9 sets an unmeasurable flag as a CPU signal x2, and the CPU clears a counter to increase the amplifier gain slightly with the command of an input x1 to a gain converting circuit 13, and outputs a measurement command gain. The series of operations is repeated by a trigger latch circuit 11 until a measurement end output is generated.

Description

[Detailed description of the invention] The present invention relates to an ultrasonic distance measuring device.

As shown in Fig. 1, the ultrasonic ratio II measuring device controls the logic circuit 2 based on commands from the CPUI to drive the transmitting circuit 3, and transmits pulsed ultrasonic waves from the transmitting sensor 4 toward the object to be measured. On the other hand, the receiving sensor 5 detects the ultrasonic waves reflected by the object to be measured, and the receiving circuit 6 sends a signal to the CPUI via the logic circuit 2, and the DCPUI detects the time between the time of transmission and the time of reception. The distance to the object to be measured is determined by measuring the distance. A timing chart for distance measurement based on this configuration is shown in FIG. Figure 2 (A) is the counter basic clock for time measurement, (B) is the CPU
(C) is the ultrasonic signal transmitted based on the measurement command, (D) is the received ultrasonic wave when the ultrasonic wave is reflected from the object to be measured, and (E) is this received ultrasonic signal. Latch signal from sound wave, (F) counter enable, (G)
is a Kara/tough rock from sending to receiving @.

Further, FIG. 3 shows the configuration of the receiving circuit 6 shown in FIG. 1,
When a reflected wave from the object to be measured is received, the output signal from the receiving sensor is passed through the bandpass filter 7 as shown in the third figure.
Only the frequency band of the ultrasound signal is extracted through
The signal is then amplified by an amplifier 8, compared with an appropriate threshold level by a comparator 9 to distinguish reflected waves from noise signals, and further passed through a waveform shaping circuit 10 to a trigger latch circuit 11 to generate an ultrasonic signal at the time of ultrasonic reception. A trigger is output and latched.

In the circuit configuration shown above, in the device that measures the distance to the object to be measured by emitting ultrasonic waves to the object and detecting the reflected waves from the object, the ultrasonic signal required for the receiving circuit 6 is and noise is input.

The output level of the receiving sensor 5 varies significantly depending on the distance from the ultrasonic sensor to the object to be measured, as shown in FIG. The vertical axis of the graph in Figure 4 is the output level of the receiving sensor, and the horizontal axis is the distance from the sensor to the object to be measured. However, in the case of ultrasonic waves with a wavelength of approximately r cm, the variation varies by several tens of times.

On the other hand, mechanical vibrations of the sensor and ultrasonic frequency components directly entering the receiving sensor from the transmitting sensor become noise and are taken into the receiving circuit 6. Since this noise has a level close to the ultrasonic signal to be obtained, a means for determining whether it is noise or not is required.

Conventionally, a signal or noise is determined by setting a threshold level VTH as shown in FIG. 5, and simply comparing the output of the amplifier 8 with the threshold level VTR using a comparator 9. !It was only done at 41 fixed. In such a case, when the amplifier gain of the amplifier 8 is increased as shown in FIG. 5(A) in order to measure a long-distance object, even the noise of the ultrasonic frequency component will be greatly amplified, resulting in the seventh problem. When the noise exceeds the threshold level, the output of the comparator 9 becomes an erroneous signal, and the trigger latch circuit 11 outputs a pulse as shown in FIG. 5 CB), resulting in erroneous measurement. In addition, in order to prevent the above-mentioned erroneous measurements, the amplifier 8
When the amplifier gain of the amplifier 8 becomes small as shown in Figure 5 (C) and the distance to the object to be measured increases, the output level of the receiving sensor decreases, and the output level of the amplifier 8 reaches the threshold level as shown in Figure 5 (CD). VrnwoM cannot be obtained and distance measurement becomes impossible.

Therefore, in view of the above-mentioned drawbacks, the present invention aims to provide a new ultrasonic distance measuring device in order to prevent erroneous measurements due to noise that makes distance measurement impossible.

The present invention achieves the above object by controlling a transmitting circuit according to a command from a CPU to emit an ultrasonic pulse from a transmitting sensor,
On the other hand, in an ultrasonic distance measuring device that measures the distance to the object by detecting the reflected wave from the object to be measured by a receiving sensor and receiving it by a receiving circuit, the receiving circuit uses a predetermined waveform from the output waveform of the receiving sensor to measure the distance to the object. A bandpass filter that extracts only the frequency component waveform of It has a comparator to remove, a trigger latch circuit to latch the output of this comparator, and a gain conversion circuit to convert the gain of the variable gain amplifier using a signal from the CPU, and the variable gain is changed by the gain conversion@path. The present invention is characterized in that the distance to the object to be measured is measured by gradually increasing the gain of the amplifier from the minimum value and automatically selecting the optimum gain.

The present invention will now be described in detail with reference to Figure J6 and subsequent figures.

In FIG. 6, the same parts as in FIG. 3 are given the same reference numerals. The receiving circuit 6 receives an ultrasonic reception signal from the receiving sensor, and first extracts only a predetermined ultrasonic frequency component using a bandpass filter 7. Next, the output of the bandpass filter 7 is input to the variable gain amplifier 12.

In the variable gain amplifier 12, the jig-in is changed by a signal from the gain conversion circuit 13. This variable gain amplifier 1
7 and 8 show specific circuits of the input conversion circuit 13 and the input conversion circuit 13.

Figure 7 (A) is a variable gain amplifier, operational amplifier 1.
4 as a coefficient circuit and changes the amplification degree by the ratio of resistors R8 and Rf. In this circuit, the feedback resistor R
An FBT 15 is connected in parallel with f, and the gate voltage of FB 715 controls the main channel to change the resistance value. Therefore, the feedback composite resistance is controlled by the gate voltage,
The amplification rate is changed.

FIG. 7(B) shows a gain conversion circuit 13 for applying a gate voltage to the circuit shown in FIG. 7(A).

The input to the gain conversion circuit 13 is a command from the CPU (see Figure 1).This command is sent to the digital-to-analog converter 1.
6, and it becomes an analog signal corresponding to the digital signal. This analog signal is input to the operational amplifier 17, where it is amplified by Rf/R8 similar to that described above. Next, an inverter 18 is arranged at the next stage of the operational amplifier 17. Therefore, in this circuit, C
The next analog voltage is output depending on the output of the PU.

FIG. 8(A) is a modification of FIG. 7(A) and shows an operational amplifier 14.
As the feedback resistor, t-2 series bodies of resistors R and switches G are connected in parallel, and a shorting switch G is further connected in parallel. This switch G, ,
The feedback resistance value can be changed by controlling the opening and closing of an appropriate combination of G, , G, and the amplification factor can be changed. in this case,
Although two switches G and two resistors R are provided, there is no particular problem with their number.

FIG. 8CB) shows a gain conversion circuit 13 that controls the switch of the circuit shown in FIG. A signal is created. At the next stage of the logic circuit 19 are respective switches Gt, G, ,
Buffer 20 a * 20 b e corresponding to G4
20c are arranged and stored and the switches Gt, G8.
G4 is controlled Returning to FIG. 6, the comparator 9, waveform shaping circuit 1O, and trigger latch circuit 1O are the same as described above, so their explanation will be omitted.

Next, the operation will be explained. First, the gain of the variable gain amplifier 12 is set to the minimum in the jig-in conversion circuit 13 according to a command from the CPU. Then, an ultrasonic wave is emitted as shown in Fig. 9 (C).This ultrasonic wave is reflected by the object to be measured and detected by the receiving sensor, and only the ultrasonic frequency component is passed through the bandpass filter 7, and the variable gain It is amplified by the amplifier 12.At this time, the amplifier output is amplified by the comparator 9.
Figure 9 (D
), the CPUK signal X from the comparator 9
, the unmeasurable flag as shown in Figure 9(E) is set, and C
PU″′c clears the counter and converts the gain conversion circuit 13.
After the amplifier gain is slightly increased by a manual command of Xl, a measurement command from the CPU is outputted again as shown in FIG. 9 (CF). This series of operations occurs when the amplifier output due to the received wave exceeds the threshold level and the trigger latch time w5
The process is repeated from 11 until an output indicating the end of measurement is output. In addition,
The explanation of the waveforms from Figure '9 CG) to (K) is shown in Figure 2 (
The explanations from C) to CG) will be omitted since they overlap.

As a result of the above, the amplifier gain of the receiving circuit can be set optimally, and amplification matching the signal level of the received wave can be performed.

As explained above, according to the present invention, it is possible to select the optimum amplifier gain for the received wave, and it is possible to avoid detecting noise by unnecessarily increasing the amplifier gain or inability to measure due to insufficient. This measurement can be prevented and the distance measurement range can be increased. With this method, it is possible to measure until the reception level due to reflected waves becomes almost equal to the noise level.

[Brief explanation of the drawing]

Figures 1 to 5 are examples of conventional ultrasonic distance measuring devices, with Figure 1 being an overall block diagram, Figure 2 being a time chart, Figure 3 being a block diagram of the receiving circuit, and Figure 4 being the output. Level-distance characteristic diagram; Fig. 5 shows the waveforms of the received wave and latch; Figs. 6 to 9 show examples of the ultrasonic distance measuring device according to the present invention; Fig. 6 is a block diagram of the receiving circuit. , FIG. 7(A) and FIG. 8(A) are circuit diagrams of two examples of a variable gain amplifier, FIG. 7(CB) and FIG. 8(B) are circuit diagrams of two examples of a gain conversion circuit, Figure 9 is a time chart. In the figure, l is the CPU. 3 is a transmitter circuit, 4 is a transmitter, 5 is a receiver sensor, 6 is a receiver circuit, 7 is a band pass filter, 9 is a comparator, 11 is a trigger latch circuit, 12 is a variable gain amplifier, 13 is a gain conversion circuit, 14 .17.18 is an operational amplifier, 15 is an FET. 19 is a logic circuit, and 20a, 20b, and 20c are buffers. Figure 1 Figure 2 (B) (G) Figure 3? Figure 4

Claims (5)

[Claims] (1) The multiplier circuit is controlled by the CPU command to emit an ultrasonic pulse from the transmitting sensor, while the reflected wave 'fI' from the measuring object is detected by the receiving sensor, received by the receiving circuit, and then In an ultrasonic distance measuring device that measures the distance to an object, the receiving circuit includes a bandpass filter that extracts only a predetermined frequency component waveform from the output waveform of the receiving sensor, and a variable channel that controls the output of this bandpass filter. a variable gain amplifier that amplifies the output of the variable gain amplifier, a comparator that compares the output of the variable gain amplifier with a threshold level and removes small signal components, a trigger latch circuit that latches the output of the comparator, and the CPU signal a gain conversion circuit that converts the gain of the variable gain amplifier and t
The distance to the object to be measured is measured by increasing the gain t of the variable gain amplifier gradually from the minimum value and automatically selecting the optimum gain by the gain conversion circuit. Sonic distance measuring device. (2) The ultrasonic distance measuring device according to claim 1, wherein an FET is connected in parallel with the feedback resistor of the operational amplifier as the variable gain amplifier. (3) The ultrasonic distance measuring device according to claim 1, wherein the variable gain amplifier includes a plurality of series bodies each consisting of a switch and a resistor in parallel with a feedback resistor of an operational amplifier. (4) The gain conversion circuit is a circuit that converts all the signals from the CPU into digital/analog, inputs this analog signal sound to an operational amplifier with a predetermined amplification factor, and then inverts the output of this operational amplifier. The ultrasonic distance measuring device according to scope 1. (5) The gain conversion circuit 1 discriminates the signal from the CPU in response to the opening/closing of a plurality of sets of a plurality of switches, and temporarily stores all of the discriminated data. Ultrasonic distance measuring device.