JPH0126032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field of the Invention The present invention relates to an ultrasonic distance measuring device, particularly a device that can be used, for example, as a coordinate input device of an electronic computer, which uses ultrasonic waves to accurately measure distances. The present invention relates to an ultrasonic distance measuring device that enables distance measurement.

(B) Technical background and problems FIG. 1 shows an example of a received ultrasonic waveform.

A method is known in which the distance between an ultrasonic transmitter and a receiver is measured by multiplying the time it takes to transmit an ultrasonic wave and receive it by the propagation speed of the ultrasonic wave.
The ultrasonic transmitter is equipped with an ultrasonic transducer and emits ultrasonic waves, but the received waveform of the ultrasonic waves is as shown in FIG. 1, for example, and the S/N ratio in the rising portion is generally poor. Therefore, it is difficult to identify and detect the first wavelength. For example, when the frequency of ultrasonic waves is 100 KHz and the speed of sound is 340 m, a detection error of one wavelength will result in a difference of 3.4 mm in the measured value. In particular, when the transmitter and receiver are brought closer together, the signal component becomes larger, but so is the noise. Conversely, when the transmitter and receiver are moved farther apart, both the signal and noise components become smaller. Therefore, it is not easy to stably detect the arrival of ultrasonic waves on the receiver side without being affected by the distance to be measured.

(C) Purpose and structure of the invention The present invention aims to solve the above problems, and for example,
Peaks A, B, C, ... of the received waveform shown in the figure
To be able to stably detect any one of the following regardless of the distance between a transmitter and a receiver, and to be able to measure the distance based on the accurate time from emission to reception of ultrasonic waves. It is an object. Therefore, the ultrasonic distance measuring device of the present invention includes an ultrasonic transmitter and an ultrasonic receiver, and measures distance based on the time it takes to receive emitted ultrasonic waves. An approximate distance measuring section that approximately measures the distance between the ultrasonic transmitter and the ultrasonic receiver, and an adjustment corresponding to the distance at an address position corresponding to the distance that is the output information of the approximate distance measuring section. A level adjustment section that has a memory for storing information, obtains adjustment information from the memory, and adjusts a slice level applied to the received waveform or the transmission power or reception gain of the ultrasonic wave, and adjusts the adjustment state by the level adjustment section. The feature is that the distance is measured based on the received signal detected under the

This will be explained below with reference to the drawings.

(D) Embodiments of the invention Before describing embodiments of the invention, the principle of the invention will be briefly explained. FIG. 2 shows an example of a received waveform related to the present invention, and FIGS. 3 and 4 show relationship diagrams between distance and reception level.

The reception waveform of the ultrasound emitted from the ultrasound transducer has a poor S/N ratio at the rising edge.
As explained in Figure 1, depending on the distance between the ultrasonic transmitter and receiver, Figure 2 A and 2.
As shown in Figure 2, the overall reception level changes. If the distance between the transmitter and receiver is short, the reception level will be high as shown in FIG. 2A, but if the distance is long, the reception level will be relatively small as shown in FIG. 2B.
For example, when waveform B of the received wave shown in FIG. 2 is taken as the arrival point of the ultrasonic wave, the voltage of the received waveform at point B is generally not constant. Therefore, in order to detect point B, it is necessary to consider the relationship with the voltage in the previous received wave A. For this reason, in the present invention, attention is paid to the potential difference between the voltage and the voltage, and adjustment is made so that the slice level is always maintained during this potential difference.

That is, for example, as shown in FIG. 3, when the potential of and changes depending on the distance, the slice level C is also made to change depending on the distance.
Alternatively, for example, as shown in FIG. 4, the transmission power is varied depending on the distance so that the voltages received by the receiver are always constant, giving a fixed slice level C. By doing this,
The received waveform B can be detected stably regardless of the distance.

FIG. 5 shows the configuration of an embodiment of the present invention, and FIG.
FIG. 4 is a diagram illustrating processing operations of the illustrated embodiment.

In the figure, 1 is an ultrasonic transmitter, 2 is an ultrasonic receiver,
3 is a driver, 4 is an ultrasonic transducer, 5 is an ultrasonic detector, 6 is a counter, 7 is an address converter, 8 is a read-only memory (ROM), and 9 is a digital/
In the analog conversion circuit, 10 is an operational amplifier, 11 is an input/output port, and 12 is a processor (CPU).

When measuring the distance between the ultrasonic transmitter 1 and the ultrasonic receiver 2, the ultrasonic transmitter 1 first
Accordingly, the ultrasonic transducer 4 is driven to oscillate ultrasonic waves. At this time, a firing signal indicating the timing of firing is output to the counter 6 of the ultrasonic receiver 2. The ultrasonic detector 5 converts received ultrasonic waves into electrical signals.

The counter 6 measures the time since the ultrasonic wave is emitted, and is also used to measure approximate distance. Note that the approximate distance here does not have to have an absolute unit of distance, but also includes a relative time interval that is proportional to the distance. When the counter 6 receives the emission signal from the ultrasonic transmitter 1, it outputs a predetermined clock signal.
Count operation is started by CLK. The count value of the counter 6 is input to the address conversion section 7. The address converter 7 converts the count value corresponding to the approximate distance into an address corresponding to the distance on the ROM 8, but it is not necessarily necessary to provide it when the count value can be directly used as the address of the ROM 8. do not have.

The slice level corresponding to the distance or the gain on the receiving side is stored in the ROM 8 in advance. The slice level stored here corresponds to the slice level C shown in FIG. 3, which has been determined in advance through experiments and the like. Hereinafter, an example in which slice levels are stored will be referred to as a first type, and an example in which reception gain information is stored will be referred to as a second type.

According to the address information supplied from the address converter 7, the ROM 8 is accessed and the slice level or the gain on the receiving side corresponding to the distance is read out. The digital/analog conversion circuit 9 is
The value read from the ROM 8 is converted into an analog quantity and supplied to the operational amplifier 10. operational amplifier 1
0, for example, part B of the received waveform shown in FIG. 2 is detected from the received signal. Note that by sampling the received signal as a digital quantity in advance, it is also possible to detect the B part of the received waveform by digital processing.

When the detection signal of the B portion of the received signal is notified to the processor 12 via the input/output port 11, the processor 12 reads the value of the counter 6 at that time via the input/output port 11. Since this read count value corresponds to the accurate time from the emission of the ultrasonic wave until it reaches the ultrasonic receiver 2, the accurate distance can be calculated based on this value. In addition, if necessary, temperature correction may be performed in consideration of changes in sound speed due to temperature changes, and the actual arrival of ultrasonic waves may be
Instead, it is also possible to calculate a more accurate distance by determining the amount of offset for waveform A in advance at a fixed distance through experiments, etc., and then performing offset correction. .

If the processing operation of the above embodiment is expressed in the form of a flowchart, it will be as shown in FIG. That is,
A counter is operated by emitting a transmission signal, and an approximate distance is obtained by the counter. The address is converted based on this approximate distance and the ROM is accessed.
Next, the value read from the ROM is converted into an analog quantity. Here, in the case of the first type, the received signal is sliced using the converted analog quantity to detect a specific waveform. In the case of the second type, a specific waveform is detected by changing the gain of the received signal using the analog amount and applying a fixed slice. Using this time, the processor calculates an accurate distance.

FIG. 7 shows the configuration of another embodiment of the present invention, and FIG. 8 shows an explanatory diagram of the processing operation of the embodiment shown in FIG. The symbols in the figure correspond to those in FIG.

In the embodiment shown in FIG. 5, the ROM 8 stores information regarding the slice level or gain on the receiving side corresponding to the distance, whereas in the embodiment shown in FIG. Store transmission power adjustment information. and,
After the value read from the ROM 8 is converted into an analog quantity by the digital/analog conversion circuit 9, the converted quantity is sent to the ultrasound transmitter 1 to adjust the transmission power of the ultrasound. That is, when the distance between the transmitter and the receiver is long, the transmission power is increased, and when the distance is short, the transmission power is decreased. As a result, the reception level at the receiver becomes constant regardless of the distance, as shown in FIG. 4, for example. By doing so, a specific received waveform can be detected by applying a fixed slice level Vref corresponding to C in FIG. 4 to the received signal using the operational amplifier 10.

FIG. 8 shows the processing operation of this third type of embodiment in the form of a flowchart. That is, a counter is operated by emitting a transmission signal, and an approximate distance is obtained by the counter. Convert this address and access the ROM. The read value is converted into an analog quantity, and the voltage for emitting ultrasonic waves is changed according to this analog quantity. The received waveform of this adjusted ultrasonic wave is
By applying fixed slices, you can find specific waveforms. The processor can calculate the exact distance by multiplying the time from emission to detection by the speed of sound.

In the above embodiment, a so-called virtual approximate distance is obtained using the counter 6, but the actual approximate distance may be measured using, for example, a fixed slice level.

(E) Effects of the Invention As explained above, according to the present invention, it becomes possible to stably detect a specific received ultrasonic waveform, and thus it becomes possible to measure distance with high accuracy. for example,
It can be widely applied to coordinate information input devices such as cursor pointing devices of information processing devices.

[Brief explanation of drawings]

Fig. 1 is an example of a received ultrasonic waveform, Fig. 2 is an example of a received waveform related to the present invention, Figs. 3 and 4 are relationship diagrams between distance and reception level, and Fig. 5 is an example of a received waveform related to the present invention. 6 is an explanatory diagram of the processing operation of the illustrated embodiment in FIG. 5, FIG. 7 is an explanatory diagram of the processing operation of the embodiment illustrated in FIG. 7, and FIG. 8 is an illustration of the processing operation of the embodiment illustrated in FIG. shows. In the figure, 1 is an ultrasonic transmitter, 2 is an ultrasonic receiver,
5 represents an ultrasonic detector, and 6 represents a counter.

Claims (1)

[Claims] 1. An ultrasonic distance measuring device that includes an ultrasonic transmitter and an ultrasonic receiver and measures distance based on the time it takes to receive emitted ultrasonic waves, the ultrasonic transmitter as described above. and an approximate distance measuring unit that approximately measures the distance between the ultrasonic receiver and the ultrasonic receiver; and a memory that stores adjustment information corresponding to the distance at an address position corresponding to the distance that is the output information of the approximate distance measuring unit. and a level adjustment unit that obtains adjustment information from the memory and adjusts the slice level applied to the received waveform or the transmission power or reception gain of the ultrasonic wave, and detects under the adjusted state by the level adjustment unit. An ultrasonic distance measuring device that measures distance based on a received signal.