JPS6045378B2 - Distance measuring device using sound waves - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a distance measuring device using acoustic waves, and more particularly to an ultrasonic distance measuring device.

Background technology Ultrasonic distance measuring device for camera is disclosed in US Patent No. 35227
64, German Patent No. 864048, and 1. B.
M technology publication (1.B.M.Jechnica1Di
Sc10sure) Bulletin, Vol. 9, No. 7, 196, December, pages 744-745.

In each of the devices disclosed in these documents, ultrasonic energy is transmitted to an object to be photographed (measured object), and the ultrasonic energy is reflected by the object and returned to the camera. Then, the transmitting transducer and the receiving transducer are separated, the characteristics of the transmitting signal and the receiving signal are compared, and a control signal indicating the distance to the subject is generated. This control signal is used to drive the lens mounting member of the camera, and the camera is placed at a position corresponding to the distance between the lens mounting member and the subject, and the subject is brought into focus. What is disclosed in U.S. Pat. No. 3,522,764 is the time required for sound to propagate twice the maximum distance to the subject that can be adjusted by adjusting the position of the lens mounting member or more. 40KHz with a period of
It is designed to receive ultrasonic burst signals.

A reflected sound wave from the subject having the same frequency as the transmitted burst signal is received between the transmission periods of the burst signal,
The time between transmission and reception of the burst signal is related to the distance to the object and is used to determine the conduction rate of the first pulse generator. The second pulse generator is coupled to the lens attachment member and generates pulses of the same frequency as the first pulse generator, and its conductivity is determined by the position of the lens attachment member. The lens mounting member is then moved until the conductivity rates of these two pulse generators match. What is described in the German patent and the IBM technical bulletin is that the distance required for sound to propagate twice the maximum distance to the subject that can be obtained by moving the lens mounting member, or even longer, is The sound wave train is frequency modulated.

The sound waves from the subject are frequency modulated in the same way as the frequency of the transmitted energy, and the distance to the subject is determined by the instantaneous deviation between the frequency of the transmitted signal and the frequency of the received signal. Such prior art devices have the disadvantage of requiring two transducers and requiring a considerable amount of time to determine the distance to the object.

At room temperature, sound propagates 3407 TL per second, so it generally takes about 20 msec to reach the maximum distance required for focusing, 77 TL. Therefore, the operating cycle of the above device must be approximately 407 TLsec.
If it takes 10 cycles to find the distance to the object, then
It takes about 0.00 seconds for the camera to focus. This will consume 2 hours. Since such a time consumption is too long compared to human reflex movements, photographing requires two consecutive and separate steps: focusing and shutter operation. For the purpose of general distance measurement, a distance measurement device using ultrasonic pulses is disclosed in US Pat. No. 34549n.
Disclosed in the issue. The device is such that separate fixed frequency burst signals are transmitted by a transducer and the reflected sound waves are received by the same transducer after a time related to the distance to the target. It has been found that when using ultrasonic waves with a constant frequency, objects to be measured within the reception angle of the transducer or within the field of view of the camera are often not detected.

Experiments have shown that the reflected sound waves from various points on the object to be measured interfere with each other and disappear or attenuate before reaching the receiver, so the receiver does not respond and the object to be measured is not detected. Ta. This phenomenon is often observed when the object to be measured is relatively close to the transducer.
When taking a photo, the subject is 27T1. If the distance is within that range, the subject is considered to be in a close position.
Since many photographs are taken of subjects in relatively close positions, if the transponder fails to receive reflected sound waves from relatively close positions, the lens mounting member may be placed in an inappropriate position. . Sidelobes in the radiation pattern of ultrasound transmissions create another problem.

A target located off-axis relatively close to the transducer and in the attenuated sidelobes of the antenna pattern will produce reflected sound waves comparable in intensity to objects located on-axis at a considerable distance from the transducer. have surface or other characteristics that cause it to occur. In such a case, the lens mounting member of the camera is arranged according to the distance to the target, which is off-axis from the subject to be photographed. Although the transducer can increase its directivity by increasing its footprint, this method increases the dimensions of the range-measuring device coupled to the camera, and the transducer cannot be integrated into one, making it difficult to measure the distance. This increases the size and weight of the device. OBJECTS OF THE INVENTION The present invention has been made to eliminate the above-mentioned drawbacks and solve the problems of the conventional art, and an object of the present invention is to provide a new and improved ultrasonic distance measuring device.

More specifically, it is an object of the present invention to be suitable for use in a camera with an automatic focusing function, so that the reflected sound waves from objects to be measured at close distances disappear or are attenuated, so that the objects to be measured can be detected. It is an object of the present invention to provide a distance measuring device that does not cause such problems and that absorbs little reflected sound waves even from objects that are relatively far away. DISCLOSURE OF THE INVENTION AND EFFECTS The present invention provides an ultrasonic distance measuring device suitable for use in camera cameras, which allows the focus to be adjusted by moving the lens mounting portion according to the distance of the object to be photographed. .

A distance measuring device according to the present invention includes a transmitting device that transmits a burst signal having sonic energy toward an object to be measured;
A reflected sound wave that is at least a part of the burst signal reflected back from the object to be measured is detected, and a distance from the time interval from transmission of the burst signal to reception of the reflected sound wave to the object to be measured is detected. a signal processing device that generates a distance signal i related to the burst signal, and further, the burst signal has a portion in which the frequency changes from a high frequency to a low frequency in an initial portion thereof, and substantially in a final portion thereof. A control device is provided that controls the transmitting device so that the transmitting device has a constant frequency portion and the frequency of the constant frequency portion is equal to or lower than the lowest frequency of the frequency changing portion. shall be. According to experiments, the intensity of the reflected sound wave from a nearby object is determined by the frequency of the ultrasound burst signal.

Reflected sound waves of a certain frequency become very small due to interference, and reflected sound waves of other frequencies become large. However, according to the present invention, the reflection of any frequency component of the frequency change portion in the burst signal can be effectively received even from a close object, thereby achieving the above-mentioned object. In this case, the receiver may be configured to be able to receive all the frequency components of the frequency changing part and the constant frequency part, but the signal-to-noise ratio may deteriorate depending on the surrounding conditions for distant objects. Therefore, in a preferred embodiment, a variable Q filter whose Q changes with time is used to increase the predetermined time interval Q for the frequency component of the constant frequency portion.

A preferred form of a frequency-modulated burst signal is such that the first half changes in frequency with time (chirp in radar terminology), and the second half changes in frequency to the lowest frequency of the first half. have equal constant frequencies.

Since it has a frequency change part (Chirp), energy with many different frequency components is projected onto the subject, so even if other frequency components disappear, some frequency components may be transmitted from a relatively close subject. There is a high probability that it will be reflected back to the transducer. This is because the above-mentioned several frequency components cancel out the interference pattern. A preferred form of burst signal is U.S. Pat.
What is a frequency modulation ultrasonic distance measuring device that uses a single burst signal without a constant frequency part as shown in 378? They are different. In the present invention,
The frequency values and their time distributions are chosen appropriately to minimize the absorption effect at all distances and the disappearance of reflected sound waves when close to the object (measured object). In this case, the signal-to-noise ratio will not be adversely affected when the subject is located far away. During the distance measurement time at the beginning of the receiver, all reflected sound waves are from objects located relatively close to each other, and the frequency change part (Chi
rp) have many different frequencies.

The filter Q has a small value and the filter bandwidth is large enough to accommodate all frequencies of the frequency changing part (Chirp). A small value of Q will result in a lot of noise, but this noise will be canceled out by the strong signal from the nearby object. In the final part of the vacuole distance measurement time, reflected sound waves arrive from a subject located relatively far away, but the frequency of the higher frequency change portion (Chiri) does not arrive due to absorption. Also, during this period, the value of Lylter's Q increases and the bandwidth narrows, but the center frequency remains constant. This. Furthermore, the receiver is slightly sensitive to objects located far away. The signal-to-noise ratio (S/N ratio) is increased to prevent the received signal (signal corresponding to the anti-noni wave) from being cancelled. At the beginning of the receiver distance measurement time, the Q value of the filter is set to be smaller, so that it is less sensitive to reflected sound waves from objects close to the camera than it is to reflected sound waves from objects located far from the camera. It also reduces the filter response time (ie the filter response rises more quickly).

Therefore, the accuracy for a close object is better than for a far object. Furthermore, since errors in the position of the lens attachment member relative to a subject located at a close position can be detected with high sensitivity and accurate focusing can be performed, this is a great advantage for photography. During the receiver distance measurement time, the admittance of the variable Q filter increases and the receiver amplifies echo signals from distant objects more than echo signals from nearby objects.

Such techniques reduce the angular sensitivity of the transducer and provide discrimination against echo signals from nearby off-axis targets caused by sidelobes of the transducer's angular field pattern. The receiver according to the invention can further include a detection device for generating a distance signal when the output of the filter exceeds a predetermined level.

The time from when the keying pulse is generated to when such detection is performed indicates the distance to the object (object to be measured). The invention also resides in a camera with an ultrasonic distance measuring device as described above.

The camera according to the invention has a device that drives the lens mounting member of the camera in response to a distance signal and positions the lens mounting member at a position determined by the time delay between the keying pulse and the distance signal. Preferred Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 designates a camera equipped with a distance measuring device 11 according to the invention. The camera 10 includes a housing 12 as shown, and within the housing 12 is a lens mounting member 14 located on the opposite side of the film 13.
The lens mounting member 14 is supported by an optical axis 15, and the lens mounting member 14 is movable in the axial direction along the optical axis 15 between end positions separated by a certain period of time. When the lens mounting member 14 is at one end position, the object 16 is imaged on the film 13 when the object 16 is located close to the young camera 10, for example, at a distance of 25 cm from the camera. It's summery. When the lens mounting member 14 is at the other end position, the object 16 is 7.5n1. It is now in focus when the object is further away. The position of the lens attachment member 14 that can focus on the subject between the two end positions is indicated by a function of the distance to the subject. This function is a high-order nonlinear function and is called the lens-object function. The ultrasonic distance measuring device 11 generates the distance pulse 17 by a method described later.

This distance pulse 17 has a certain delay with respect to the keying pulse 18, and this delay time varies linearly with respect to the distance between the camera 10 and the subject 16. A focusing mechanism 19 is coupled to the camera 10 and moves the lens mounting member 14 to an axial position where the object 16 is in focus in response to the pulse 17. Focusing mechanism 1
Reference numeral 9 includes a logic circuit 20, which generates a pulse train in response to a distance signal 21 generated from a distance pulse generator 22, the number of which is determined by the number of pulses of the lens mounting member 14 when the subject 16 is in focus. Indicates axial position.

These pulses are applied to a counter 23 via a gate and are used to drive a motor 24. Electric motor 2
4 is mechanically connected to the lens mounting member 14 via a device 25. The device 25 is also connected to a feedback device such as an auxiliary pulse generator 26 which generates a predetermined number of pulses by rotating the electric motor 24 as controlled by the contents of the counter 23. Note that this one pulse indicates a unit displacement of the lens device. The logic circuit 20 determines when the lens mounting member 14 is moved to the position determined by the contents of the counter 23 in response to the output of the auxiliary pulse generator 26, thereby causing the object 16 to
is focused on. The ultrasonic distance measuring device of the present invention, designated by the reference numeral 11, is an ultrasonic transducer device 2.
7, this ultrasonic transducer device 27 includes 1
Acoustica published in 1960
, Gelde published in VOllOl pages 295 to 303. 6' cell principle written by K.
It includes a cell-type electrostatic transducer element similar to that shown in the article ``Oscillation Characteristics of Electroacoustic Transducers Using Apple''.

The main lobe and side lobe characteristics of the preferred form of this element are determined by the output pattern of the back plate (not shown) of the element. When a transducer of a certain size is used at a certain frequency, the fixed output of the transducer produces the narrowest beam. For example, a transducer of the type shown in the above article is driven at 50KHz and has an operating area of 3.5C77! In this case, the angle deviated by 6 motions from the central axis becomes the half-value angle. The first zero occurs at 13 motion and the first sidelobe occurs at 19. These angles are approximately inversely proportional to the transducer diameter and frequency, the first sidelobe has a relative power of -17.6 dB for transmit and receive conditions, and the overall relative power gain of the device is approximately -35 c1 B. be.

The improved pattern has slightly smaller angles but smaller sidelobes. The transducer device 27 is located in physical proximity to the lens mount 14 and its transmission pattern 28 is arranged in a field of view 30 from the lens mount 14.
It has a main lobe 29 that almost coincides with .

The main lobe of transmit pattern 28 is accompanied by side lobes 31, and the specific shapes of main lobe 29 and side lobes 31 are determined by the specific design of the transducer element. The distance measuring device 11 also drives the transducer device 27 according to the control voltage generator 35 and the keying pulse 18 applied to the control voltage generator 35, and from this transducer device 27 to the object (measured object) 16. a frequency modulator 32 that transmits a burst signal having ultrasonic energy towards the subject; and a receiver 33 for processing the generated reverberant signals.

Next, the operation of this embodiment will be explained.

For example, when a manual input is applied to the device of FIG. 1 by pressing a camera pushbutton (not shown), this manual input is converted by the tip detector 34 into a keying pulse, which is applied to a control voltage. is applied to generator 35. The output of control voltage generator 35 controls frequency modulator 32 to generate a frequency modulated burst signal from transducer device 27 . A control voltage generator 35 modulates the output voltage of the modulator 32 to vary the frequency between 50 KHz and 50 KHz during one half cycle of the transducer burst signal and approximately 50 KHz during the other half cycle of the transducer pulse. maintain the frequency at According to experimental results, it has been found that the amount of return from a nearby object (object to be measured) strongly depends on the frequency of the projected ultrasonic burst signal, and that no reflected sound waves may be generated at a certain frequency.

Since the projection signal has a frequency changing part (Chjrp), many frequencies are reliably projected onto the object. At least some frequencies are then passed back to the transducer without extinction. By keeping the half cycle of the burst signal constant at 50KHz, the absorption of ultrasonic energy is minimized. This makes it possible to reliably obtain reflections from distant objects in poor surrounding conditions. For example, the output of the reflected signal changes exponentially with respect to the distance from the subject, and is approximately inversely proportional to the fourth power of the distance to the subject. For example, when the distance to the object is changed from 25 cm to 5 m using a 550 KHz signal at 20° C., the reflected signal changes by about 60111B. Experiments have shown that the absorbance and change in absorbance with respect to temperature 2 and humidity increases with increasing frequency. Generally, the lower the frequency, the lower the absorption. The burst signal frequency at which the absorption is lowest at any temperature and humidity is 50 KHz. Under conditions of poor temperature and humidity, higher frequency components of the burst signal tend to be attenuated. Therefore,
Higher frequencies are effective when the camera is close to the subject. In other words, using a burst signal of a single frequency is effective in the case of a short distance where interference occurs. The (4)nse component of the burst signal has the least attenuation of all frequency components, and is suitable when the camera is far from the subject. When the object 16 is relatively close to the transducer device 27, the signal emitted from the transducer element and reflected back from the object 16 has a frequency change portion (chirp) with the exception of frequencies that are canceled due to interference. Contains almost all frequencies in the range.

Subject 16 is Tran. At a greater distance from the streak user device 27, the reflected signal will contain the least attenuated frequency component, ie, the lower frequency component of the frequency change portion (Chlrp). The burst signal has a frequency changing part (Chirp) of 65 to 50K and a frequency change part (Chirp) of 65 to 50K
Certain portions of KHz can be combined to form eight different signal aspects.

Half of these will contain step discontinuities in the transients of the two parts of the signal. In order to simplify the electronic circuit for generating the control voltage that drives the modulator, burst signals having discontinuous portions as described above are not preferred. The remaining four (continuous) burst signals are such that the frequency change portion (Chlrp) sequentially rises or falls to a constant frequency, and the frequency change portion is located before or after the constant frequency portion. It is. When the subject is close, interference, so-called speckle, becomes a problem; when the subject is far away, the signal-to-noise ratio becomes most important.

As is clear from the above, the frequency change part (Chl
It is desirable to first generate the rp), which allows operation at the leading edge of the burst signal and improves distance measurement accuracy, which improves focusing accuracy, which is particularly desirable when the subject is at a close distance. On the other hand, since lower frequencies have less absorption, such frequencies are preferably used in situations where the signal-to-noise ratio is important and the subject is located at a large distance. Therefore, first the frequency change part (Chj
rp) and drops to a lower constant frequency, the frequency of the burst signal is initially 65KHZ and 0.57T1. It is desirable that the pressure drop to 50K in seconds and then maintain the 50K ratio.

Referring again to FIG. 1, the keying pulse 18 is
The control voltage generator 35 is started to operate, and the transducer device 27 starts transmitting a frequency-modulated ultrasonic burst signal, which is also applied to the blanking gate 36 of the receiver 33 .

The output voltage level of the blanking gate 36 is
is added to the output of about 0.4 TrL, and the transducer burst signal is output. After a predetermined period of time, preferably about 407 T1. seconds, the output of the receiver 33 is enabled, designated as the receiver distance measurement time. The output of receiver 33 is held in the active region for a period of seconds. At an altitude of 0 and a temperature of 20'C, the sound emitted by the transducer during such a given period of time is about 7.3 Tn. It bounces back at a target located far away. By providing the output of the receiver 33 with a delay of 04 TL seconds, the transducer element of the transducer device 27 is activated after the burst signal generation has finished.
Allow sufficient time to stabilize. Then, the closest distance to the subject to which the distance measuring device can adapt the delay time is determined, which in the above example is 25a. As shown in FIG. 1, the output of blanking gate 36 is also applied to preamplifier 37, so that preamplifier 37 operates with the delay described above. The echo signal generated by the transducer device 27 receiving reflected sound waves from the object 16 is applied via a signal line 38 to a preamplifier 37 whose output is processed by a filter network 39. .

Filter network 39 includes a variable Q filter 40 and an amplifier 41 whose gain can be arbitrarily varied, as will be described in detail later with reference to FIG. Variable gain amplifier 41
When the threshold level is reached, the level detector 42 generates a distance pulse 17. The variable Q filter 40 is the Q control circuit 4
The Q control circuit 43 operates to increase the Q of the filter 40 during the receiver distance measurement time in response to the keying pulse.

The center frequency of filter 40 is equal to the lowest frequency of the burst signal, here 50 KHz. In this embodiment, the control circuit 43 controls the filter 4 during the receiver distance measurement time.
Change the Q value of 0 from 5 to 70. Q filter 40
The admittance of is a number of frequencies, and its change with respect to frequency is shown in FIG. 2 with Q as a parameter.

When the Q of filter 40 is small, the bandwidth of filter 40 is relatively wide, as shown by curve 44 in FIG.
It is wide enough to pass all frequencies in the frequency changing part (Chirp). During the initial part of the receiver distance measurement time, objects close to the transceiver provide reflected sound waves to the transducer device 27, during which time
The value of Q of filter 40 is relatively small. During the final portion of the receiver ranging period, the Q value of filter 40 is relatively large and the bandwidth of filter 40 is relatively narrow, allowing a high signal-to-noise ratio to be obtained.

The 50 KHz component of the burst signal best reaches the object farthest from the transducer and is the strongest of the reflected sound waves.

As mentioned above, at the end of the receiver distance measurement interval, the bandwidth of the filter 40 is relatively narrow, making it suitable for distance measurements of objects far from the camera. As shown in FIG. 2, the admittance of the filter 40 when the value of Q is small is much smaller than that when the value of Q is large. Therefore, the impedance of filter 40 will be greater at the beginning of the receiver ranging time than at the end. If the subject is close,
Although the emitted sound wave is large and the reverberation signal applied to the amplifier 37 is also large, the output of the preamplifier 37 is attenuated because the impedance of the filter 40 changes as described above. That is, the output of the filter 40 has a level that is independent of the position of the subject. In general, the filter network 3
The gain of amplifier 41, which forms part of circuit 9, is program controlled by a gain control circuit 46 connected to this amplifier.

Control circuit 46 generates a control signal upon application of keying pulse 18 to increase the gain of amplifier 41 during the distance measurement time. Operating in this manner, reflected sound waves provided by a subject at a relatively long distance from the transducer device 27 are transmitted to the transducer device 27.
7 is amplified to a greater extent than the reflected sound waves given by the object located close to the object. In this way, the filter network 39
The advantage of changing the gain of the side lobe 3 shown in Figure 1 is
Target 16 within range of the presence of 1 and one of the side lobes
This will be explained in relation to A.

Since the target 16A is located outside the field of view of the camera's objective lens, the distance measuring device detects the object 16 within the field of view as target 1.
6A is highly desirable. filter 40
by changing the admittance of the amplifier 42, or if the operation of the filter 40 alone is insufficient.
The above distinction is made as described below by also changing the gain of . Since the object 16 is located further from the transducer device 27 than the target 16A, the reflected sound waves from the target 16A reach the transducer device 27 earlier than the reflected sound waves from the object 16.

Not only is the reflected sound wave from the object 16A relatively weak due to the influence of the strength of the side lobe, but also the level of the signal reaching the detector 42 is below the threshold of this detector due to the operation of the filter 40 and amplifier 41. By the time the reflected sound waves from the object 16 reach the transducer device 27, the admittance of the filter 40 has increased from the value it had when receiving the reflected sound waves from the target 16A.
(meaning that the impedance to the echo-signal is reduced). Furthermore, the gain of amplifier 41 is also increased from its previous value. Therefore, the output of the amplifier 41 exceeds the threshold of the detector 42 and the distance. A pulse 17 is generated. Varying the value of Q of filter 40 changes the admittance of filter 40, thereby reducing the angular sensitivity of transducer device 27, which has the desirable result of discriminating off-axis targets 16A. Besides, another favorable result is obtained.

This favorable result is achieved because filter 40 has a shorter rise time when its Q value is small than when it is large. When the subject gets relatively close to the camera, the echo signal rises relatively quickly. The shorter the rise time, the faster the detection of the tip of the echo signal.
When the subject is in a close position, by making the rise more rapid, the accuracy of distance pulse generation is further improved. This corresponds to the requirements of the camera. The reason for this is that focusing is more susceptible to errors when the subject is closer to the camera than when the subject is farther away. A preferred configuration example of the ultrasonic distance measuring device is shown in FIG. 3 with reference numeral 11A.

The distance measuring device 11A includes an ultrasonic transducer element 2
7A, a modulator 50 that drives the transducer element 27A in response to the application of the keying pulse 18 to transmit a burst signal of frequency-modulated ultrasonic energy toward the object under test; Equipped with vessel 33A,
The receiver 33A has a filter 51, and receives the reflected sound wave given from the object to be measured (not shown) within a predetermined time interval following the burst signal (that is, within the distance measurement time of this ultrasonic distance measuring device). The receiver 33 processes the echo signal generated from the transducer element 27A.
A generates the distance signal 17 with a delay of time τ with respect to the keying pulse 18. The time τ has a linear relationship with the distance from the object to be measured (that is, the time τ is twice the time required for sound to propagate between the transducer and the object to be measured). Referring again to FIG. 3, modulator 50 includes a gate signal generator 52, a voltage generator 53, a voltage controlled oscillator 54, an amplifier 55, a transformer 56, and a decoupling diode 57.

The gate signal generator 52 generates a gate signal from its output shaft c when the keying pulse 18 is applied to its input terminal b. The gate signal generator 52 uses a one-shot multivibrator having an automatic delay reset function, that is, an RC delay function, in combination with a shot-mitt trigger circuit. As shown in FIG. 4c, the gating signal 58 is approximately 4 TL, which corresponds to the time required for the sound to propagate a distance of approximately 77 TL from the transducer to the target and back.
0T1. It has a duration of sec. This distance corresponds to the afocal position of the lens mounting member 14. Measured object 7T
r1. If the distance is above, the focal length of the lens mounting member 14 is limited to infinity. In response to the gate signal 58, the voltage generator 53 generates a voltage pulse 59 having a time variation as shown in FIG. 4d.

An example of the configuration of the voltage generator 53 is shown in FIG. In FIG. 5, a pulse generator 98 consisting of, for example, a one-shot multivibrator having an automatic delay reset function and triggered by the gate signal generator 52 has a pulse generator of 1.0 Tn. S input pulses (corresponding to the length of the burst signal applied to each circuit section 100 and 102 of the parallel circuit). Pulse generator 98
supplies an appropriate voltage from nodes 103 and 105 to output 108 via a pair of diodes 104 and 106, respectively, and the higher voltage at node 103 or 105 is transmitted from output 108. During the application of the input pulse, capacitor 110 provides a gradually decreasing voltage to node 105, resistor 112 provides a constant low voltage to node 103, and output 108 initially provides a gradually decreasing voltage to node 105. When it receives a decreasing voltage and matches the voltage at node 103, it generates a shaped voltage pulse 59.
Specifically, the voltage generated by the voltage generator 53 increases from zero to 6V at the start point of the gate pulse generation, and then decreases approximately linearly until the voltage reaches 0.5 m. sec later, it becomes about 4V, and then it is maintained at about 4V for 0.5msec, and then decreases to zero. The above voltage values and voltage fluctuation modes are only examples of those that can be used in practice, and those skilled in the art will appreciate that the voltage values and voltage fluctuation modes can be set over a wide range by making various changes to the modulator. should be obvious. A voltage controlled oscillator 54 generates a waveform-shaped voltage pulse 5.
9 (see FIG. 4) generates a matched frequency modulated burst signal.

The frequency of this burst signal changes almost linearly from approximately 50K to approximately 50K while the output voltage (pulse 59) of the voltage generator 53 decreases from 6V to 4V, and the output voltage decreases from approximately 4V to approximately 50K.
(2) While it is maintained at approximately 50K, it remains almost constant. After the amplification operation of the amplifier 55, the frequency modulated burst signal is applied to the primary winding 60 of the transformer 56. transformer 5
The secondary winding 61 of 6 is connected to the transducer element 27A via a decoupling diode 57. Secondary winding 6
The output voltage of 1 is made as large as possible for transducer element 27A, for example approximately 300V peak, and a diode-capacitor combination circuit 62 provides a bias voltage of, for example, 150V dc to transducer element 27A after a few cycles. In this manner, the output voltage of secondary winding 61 drives transducer element 27A, which emits a strongly directional frequency modulated burst signal as shown by arrow 63 in FIG. The above drive or bias voltage values applied to transducer element 27A are based on the use of a 6 μm Mylar film in transducer element 27A.

If the thickness of the mylar thin film takes on different values, the voltage value is set accordingly, and the output of the transducer element 27A and the sensitivity to the reverberation signal simultaneously reach a maximum value. Furthermore, although the Q value of the output circuit partially depends on the capacitance of the transducer element 27A, the frequency fluctuation part (Chirp) of the burst signal is transmitted with a constant amplitude and is not significantly affected by the capacitance of the transducer element 27A. In order to achieve this, the value of Q of the output circuit must be relatively small. By making the value of Q relatively small, the energy output from the device decays quickly at the end of application of the drive voltage, allowing transducer element 27A to absorb reflected sound waves from relatively closely located objects under test. Receive a static state quickly. Decoupling diode 57
transducer element 27 while receiving reflected sound waves.
It operates so that no signal is transmitted from A to the transformer secondary winding 61.

While transmitting, the voltage drop across the diode is 0.7V.
is very small compared to the 300 V peak drive voltage, so decoupling diode 57 has no effect on transmission. However, during reception, the reverberant signal generated by transducer element 27A is 2μ■ to 20TrL
(2), and these diodes operate as open circuits for reflected signals. In Figure 3,
The reflected sound waves from the object under test are indicated by reference numeral 64, and the echo signals generated by transducer element 27A are processed by receiver 33A.

The receiver 33A includes a preamplifier 65 and the aforementioned filter 5.
1 and the Q of the filter 51 at the receiver distance measurement time.
and a detection device 67 for converting the echo signal into a distance pulse 17. During the receiver distance measurement period, the DC voltage applied to transducer element 27A is maintained at approximately 150V DC. Preamplifier 65
The input impedance of is matched to the impedance of transducer element 27A (approximately 12KΩ). The output impedance of preamplifier 65 is selected to correspond to the highest Q value of filter 51 (here approximately 70). The gain of preamplifier 65 is approximately 48C1B. The filter 51 is an LC filter, and includes a secondary winding 61 of a transformer 56 that provides the inductance of this filter, and capacitors 68 and 69 between which the output terminal of a preamplifier 65 is connected. There is.

A tap 70 is located close to the ground point of the secondary winding 61 from which the output of the filter 51 is applied to a high impedance output amplifier 71 through a resistor 72 having a value of approximately 1 KΩ. Resistor 72 is in parallel with the LC circuit of filter 51 and forms part of a preprogrammed Q control circuit 66. The Q control circuit 66 changes the Q value of the filter 51, and further includes a current generator 73 and a dynamic variable resistance device 74 connected in series between the resistor 72 and the input terminal 71A. The resistance device 74 is a fixed resistor 75 (approximately 1M) connected in parallel with the diode 76.
Ω). Diode 76 is adapted to be conductive while current generator 73 supplies current.
In order to maximize the signal-to-noise ratio of the reflected sound wave from the object to be measured located at the farthest distance from the camera (that is, about 7 TTL apart), the center frequency of the filter 51 and the response output are halved. The deviation Δf from the constant frequency pulse width has a relationship of 0.2/(constant frequency pulse width). Pleasant fruit! In the embodiment, the output half-width of the filter 51 must be about 08 KHz near the end of the receiver distance measurement time when the reflected sound waves from the object to be measured at a long distance are subjected to signal processing. During the first part of the receiver distance measurement time, when the reflected sound waves from the object to be measured located close to the camera are being processed, the bandwidth of the filter 51 is changed to the frequency change part (Chir).
p) has a frequency width that passes all frequencies of p).
Therefore, filter 51 initially has an output half width of about 30 KHz, and a center frequency of about 50 KHz. To provide the required change in bandwidth, the Q value of the filter 51 is approximately 5 at the beginning of the distance measurement time, and the Q value is changed to approximately 5 at the end of the distance measurement time. This is achieved by setting the value to approximately 70. For a typical d°C circuit (capacitance about 300 pF), the resistance in parallel with the circuit must vary from about 1KΩ to about 1MΩ. The resistance parallel to the LC circuit of filter 51 is the effective resistance of resistor 72 in series with the parallel circuit of resistor 75 and diode 76.

The dynamic resistance of diode 76 to a small AC signal supplied from preamplifier 65 is approximately inversely proportional to the DC current flowing through this diode and is independent of the diode characteristics. When the DC current is relatively large, the dynamic resistance of diode 76 is much smaller than the resistance of resistors 72 and 76. This is because the effective resistance of filter 51 is determined substantially only by resistor 72. Therefore, when the current flowing through the diode 76 is large, the filter 5
The value of Q of 1 depends on the value of resistor 72. The value of the resistor 72 is selected taking into account the inductance and capacitance values of the filter 51, and
A Q is obtained that sets a bandwidth such that all frequencies of rp) pass through the filter 51. When the current flowing through diode 76 is relatively small, the dynamic resistance of diode 76 has a magnitude of the same order of magnitude as the value of the resistance of resistor 15, and the effective resistance of filter 51 is essentially determined by resistor 75. . Therefore, when a small current is flowing through the diode 76, the Q value of the filter 51 is equal to that of the resistor 7.
5, and the value of resistor 75 is selected to provide a bandwidth that matches as closely as possible the fixed frequency of the burst signal. The filter 5 temporally changes the current supplied from the current generator 73 to the diode 76.
This is to appropriately change the effective value of the resistance parallel to the first circuit.

For this purpose, in response to the gate pulse 58, the current generator 73 generates a direct current which has a large value during a relatively short period at the beginning of the distance measurement time and then decreases monotonically, as shown in the curve 77 of FIG. 4e. occurs. Curve 77 is created with relatively simple components to provide greater repeatability and stability than a monotonically increasing curve. Preferably, current generator 73 includes a plurality of RC circuits, each having a separate time constant, so as to provide a gradually decreasing current. Curve 77 has three parts: a transient part 77A for about 4 msec where the current quickly drops to a nearly constant level, an initial part 77B for about 67 TLsec where the current is almost constant, and It consists of a final portion 77C that decreases almost linearly. Transitional part. During a period of 77 A, the value of the effective resistance in parallel with the LC circuit increases, but the value of Q of filter 51, determined primarily by the value of resistor 72, changes slightly as shown in Figure 4f. Only. During the first part 77B, the filter 51
The value of Q is maintained approximately constant. Therefore, the object to be measured is approximately 1.5 rn. Within the range of , the bandwidth and admittance of the filter 51 are approximately constant. The object to be measured is 1.57 TL from the transducer element. If the distance is more than
As shown in FIG. 2, as the Q value of the filter 51 increases, the bandwidth gradually decreases and the admittance of the filter 51 decreases. A change in the admittance of the filter is a change in the effective gain of the receiver, and according to the principles described above, the object under test is approximately 1
．． When the distance is within the range of 5 m, the effective gain is relatively small and takes a substantially constant value, and when the object to be measured exceeds the above range, the effective gain increases. And 427TL. Approximately 9rrL, which corresponds to approximately 115 to 116 of the distance measurement time of S.
During s, the bandwidth remains relatively wide and approximately constant, and during the remainder of the distance measurement time, the bandwidth becomes progressively narrower.

In other words, the bandwidth, Q, etc. are constant during the first part of the distance measurement time when the reflected sound wave is received from the object to be measured at a close position (up to 1.5 m from the camera), and the bandwidth and Q are constant during the frequency change part. Enables reliable reception of all frequencies and speeds up filter activation. and,
During the remainder of the distance measurement time, the bandwidth is narrower and the signal-to-noise ratio is larger. The output of the filter 51 is applied to the input end 71A of the amplifier 71, and the input impedance of the amplifier 71 is high to prevent the filter from being heavily loaded and to prevent the Q from becoming low. Although the back-to-back diode and tap 70 of the Q-controller 76 are located close to ground, the transmission of pulses is limited, but the amplifier 71 is still in overdrive.
However, it is designed to quickly return to its original state and can handle the echo signal through the filter approximately 03 TrLsec following the transmitted pulse. The output impedance of this amplifier is low and the gain is 65 dB. The output of amplifier 71 is applied to detection circuitry 67.

Detection circuitry 67 includes a conventional ramp circuit 80, an RC integrator 81, and a detector 82. The circuit 80 is driven by a blanking pulse generator 83, which generates a blanking pulse 85 as shown in FIG. 4h in response to the gate pulse 58. Pulse 85 is about 1.5rrL. Continuing during SeC, while this pulse is being output, clamp circuit 80 holds the input of detector 82 at ground potential. Following generation of the blanking pulse, the reverberant signal passed through filter 51 and amplified by amplifier 71 is rectified and correlated.

The integrator 81 receives several cycles of the echo signal within a certain time interval (for example 0.2 msec) and generates a voltage across its capacitor that reaches the threshold level of the amplifier 84 and generates a distance measuring pulse. It's becoming like that.
The correlation analysis technique used here does not improve the signal-to-noise ratio of the input signal, but rather provides a filter to discriminate signal spikes originating from the logic circuitry coupled to the mechanism that moves the camera lens stage. It is something to be prepared for. As mentioned above, the variable Q filter increases the gain between the transmit and receive times. However, the gain of amplifier 71 can also be varied between transmit and receive times using devices such as ramp signal generator 96. The ramp signal generator 96 applies a gain control signal that continuously increases to the amplifier 71 during a predetermined transmission-reception time of about 42 TLSeC in response to the gate pulse of the gate signal generator 52, and adjusts the gain of the amplifier as time progresses. Increase by 7 virtually continuously. With only slight modifications to the circuit described above, it is possible to operate it in a variety of different ways.

As described in the preferred embodiment, a single burst signal, a single transmitted pulse having a duration of 1 TrLsec, is used. In such a configuration in which the amplifier gain is not controlled by a ramp signal, from 25G to approximately 5Tr1,
It is possible to detect an object at a distance of , and the time required to measure this distance is approximately 35 Tr1, SeC or less. When the gain of the amplifier is controlled by a ramp signal, the upper limit of the detection distance is approximately 9rrL. This embodiment is suitable for snapshot-type cameras. The reason is that focusing and exposure can be completed with just one manual operation. In another embodiment, the varying portion of the burst signal is formed digitally in steps as shown in FIG. 6, in this case 42TI. In response to the SeC gate pulse 58, a stepped frequency pulse 120 is generated by a clock signal generator 122 and a program controlled frequency divider 124.

As shown in FIG.
It decreases in a series of small steps during 0K pressure.
Another mode of operation is to use several different pulses, each pulse corresponding to one of several different distances.

For example, if the short width pulse is 10C! A second, longer duration pulse has been used when the object is at a distance of 17 TL from the RL. The Q of the filter must be adjusted according to the pulse width. However, the maximum value of Q is different for different pulses. Since the signal-to-noise ratio is proportional to the parallel root of the pulse width, the measurement distance can be increased by varying the pulse width.
The device uses pulses with a width of 0.5 msec to
．． If the distance is to be measured, the pulse width should be set to a maximum of 5 m. Information on objects to be measured at a distance of 6.5 m can also be obtained in seconds. However, the Q value of the filter is 1. It is desirable to set it to . The present invention
It can be used in continuous pulse generators suitable for use in motion picture cameras whose focus is continuously adjusted during operation.

Perfect reverberation can be obtained by improving the signal-to-noise ratio. Varying the Q of the filter as in the preferred embodiment has many advantages for use in camera distance measuring devices. First, in many cases, the configuration of the present invention shown in FIG. 1 does not require a separate lamp gain control circuit. Second, it does not require a matched filter to receive the fluctuating portion, which simplifies the circuit.
The frequency variation part (Chirp) is used to reduce the sensitivity to interference when the object is close, and does not require a very large signal-to-noise ratio even when the object is far away.

Thirdly, when the object for which improvement in absolute accuracy is most desirable is located in a close position, the Q of the filter is reduced to shorten the rise time to ensure high accuracy. Finally, electronic drift of the output frequency with respect to the filter frequency, or frequency fluctuations caused by moving targets (Doppler effect), only affect when the subject is far away, and are not a problem for photographic cameras. No. The greater the drift or frequency variation, the closer distance measurements will be affected. In a device with a constant value of Q, the effect of the gradually increasing docrito at all distances is comparable to the total disappearance of the reflected sound waves. The above-mentioned frequency values, pulse widths, etc. are just examples, and these parameters are appropriately selected depending on the purpose of use of the distance measuring device to which the present invention is applied.

For example, a frequency of 50 KHz was chosen to allow reliable measurements of the greatest distances even in the presence of acoustic and thermal noise. In addition, the dimensions of the transducer, permissible angles, etc. are also taken into consideration when selecting the frequency. The technique of changing the effective resistance of the filter described above is also just one example.

Instead of keeping the resistor in parallel with the LC circuit, it can be connected in series. In this case, it is necessary to change the value of the resistor. Also, instead of using current controlled diodes, field effect transistors operating in depletion mode can be used,
In this case, it is desirable to use transistors connected in parallel. The distance measuring devices 11 and 11A can be used not only for cameras but also for a wide range of general purposes.

For example, these devices may be applied to devices that assist the blind, devices that assist in maintaining proper spacing between vehicles, and anything else that requires distance information. From the above description of the preferred embodiment, the improvements and advantages of the device will become apparent.

Note that the present invention is limited only to the scope of the claims.
Various changes and modifications can be made within the scope and spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the entire configuration example in which an embodiment of the ultrasonic distance measuring device according to the present invention is coupled to a camera, and FIG.
The figure is a characteristic diagram showing the ideal response of the variable Q filter, Figure 3 is a circuit diagram showing a preferred embodiment of the distance measuring device according to the present invention, and Figure 4 is a waveform showing ideal waveforms of each part of the device in Figure 3. 5 is a circuit diagram showing a voltage generator used in the device of FIG. 3, and FIG. 6 is a block diagram showing an alternative embodiment of the transducer drive shown in the distance measuring device of FIG. 7 are waveform diagrams showing the ultrasonic burst signal generated from the embodiment of FIG. 6. 10... Camera, 11... Distance measuring device, 12... Housing, 13... Film,
14... Lens mounting member, 15... Optical axis, 16... Subject, 17... Distance pulse, 18... Keying pulse, 19...
...Focusing mechanism, 20...Logic circuit, 21...
... Distance signal, 22 ... Distance pulse generator, 23 ... Counter, 24 ... Electric motor, 2
6...Auxiliary pulse generator, 27...Ultrasonic transducer, 27A...Transducer element, 28...Transmission pattern, 29...
Main lobe, 30... Field of view, 31... Side lobe, 32... Frequency modulator, 33, 3
3A...Receiver, 34...Tip detector, 35...Control voltage generator, 36...
Blanking gate, 37... Preamplifier, 3
9... Filter circuit network, 40... Variable Q filter, 41... Variable gain amplifier, 42... Lebel detector, 43, 46... Q control circuit, 50・・・
...Modulator, 51...Filter, 52...
・Gate signal generator, 53... Voltage generator, 54...
... Voltage controlled oscillator, 55... Amplifier, 56...
...Transformer, 57... Decoupling diode, 58
......gate signal, 59...voltage pulse,
60...Primary winding, 61...Secondary winding, 62
...Diode and capacitor combination circuit, 64...
・Reflected sound wave, 65... Preamplifier, 66...
...Q control circuit, 67...Detection device, 68,6
9... Capacitor, 70... Tap,
71... High impedance output amplifier, 72...
...Resistor, 73...Current generator, 74.
...Dynamic variable resistance device, 75...Fixed resistor, 76...Q control device, 80...
Clamp circuit, 82...Detector, 83...
・Blanking pulse generator, 84...Amplifier, 85...Blanking pulse, 96...
Ramp signal generator, 98...Pulse generator, 1
03,105... Connection point, 104,106...
...Diode, 108...Output shaft, 11
0...Capacitor, 112...Resistor, 12
0... Pulse, 122... Clock signal generator, 124... Program controlled frequency divider.

Claims (1)

[Claims] 1. A transmitting device that transmits a burst signal having sound wave energy toward an object to be measured, and a reflected sound wave that is at least a part of the burst signal that is reflected back from the object to be measured. and a signal processing device that detects the burst signal and generates a distance signal related to the distance to the object from the time interval from transmission of the burst signal to reception of the reflected sound wave. The signal has a portion in which the frequency changes from a high frequency to a low frequency at the beginning thereof, and a portion whose frequency is substantially constant at the end portion, and the frequency of the constant frequency portion is higher than that of the frequency changing portion. A distance measuring device using acoustic waves, characterized in that a control device is provided for controlling the transmitting device so that the frequency is equal to or lower than the lowest frequency. 2. A distance measuring device using acoustic waves according to claim 1, wherein the constant frequency portion occupies at least 1/4 of the length of the burst signal. 3. In claim 1, the frequency of the portion where the frequency of the burst signal changes is approximately 65 kHz to 5 kHz.
A distance measuring device using sound waves, characterized in that the frequency is reduced to 0 KHz. 4. A distance measuring device using a sound wave according to claim 1, wherein the frequency changing portion changes discontinuously. 5. In claim 1, the signal processing device that detects the reflected sound wave and generates the distance signal compares the bandwidth of the filter and the filter within a predetermined time interval following the start of transmission of the burst signal. What is claimed is: 1. A distance measuring device using sound waves, comprising a device for changing the target between a large value and a relatively small value. 6. According to claim 5, the device for varying the bandwidth makes the bandwidth relatively wide during the first part of the predetermined time interval and during the remainder of the predetermined time interval. A distance measuring device using sound waves, characterized in that the bandwidth is narrowed. 7. In claim 5, the device for changing the bandwidth maintains the bandwidth relatively wide for about the first one-fifth of the predetermined time interval, and to ensure that all frequencies of the burst signal can be reliably received, and gradually change the bandwidth to a relatively narrow value as time progresses in the predetermined time interval to measure an object at a long distance. A distance measuring device using sound waves, characterized in that the signal-to-noise ratio is improved. 8. In claim 5, the center frequency of the bandwidth of the filter is approximately equal to the frequency of the constant frequency portion of the burst signal, and at the beginning of the predetermined time interval, the bandwidth of the filter is approximately equal to the frequency of the constant frequency portion of the burst signal. is wide enough to encompass the frequency of the frequency change portion;
At subsequent times in the predetermined time interval, the bandwidth is reduced to reduce the bandwidth of the filter relative to the faster reflected sound waves arriving from a nearby object to be measured. A distance measuring device using sound waves, characterized in that the bandwidth is wider than the bandwidth of the sound wave. 9 In claim 5, the Q of the filter is
is adjustable, and the signal processing device includes a Q control circuit programmed to increase the Q of the filter for a predetermined time interval following the start of the transmission, and an amplifier for amplifying the output of the filter; and a gain control circuit programmed to increase the gain of the amplifier during the predetermined time interval. 10. According to claim 5, the device for changing the bandwidth of the filter comprises a diode connected to the filter and forming part of its resistance, and a dynamic resistance of the diode for the predetermined time interval. What is claimed is: 1. A distance measuring device using sound waves, characterized by comprising a device for changing the distance. 11. Distance measurement by acoustic waves according to claim 10, characterized in that the device for varying the dynamic resistance of the diode comprises a current generator programmed to supply a time-varying direct current to the diode. Device. 12. In claim 5, for a predetermined period of time related to the minimum value of a predetermined measurement range for this distance measuring device from the start of transmission of the burst signal,
A distance measuring device using sound waves, characterized in that a device for disabling the reception processing device is provided. 13. According to claim 5, the distance measuring device is characterized in that the operating time of the reception processing device is limited to a certain predetermined time corresponding to a maximum value of a predetermined measurement range for the distance measuring device. Distance measuring device.