JP2003090876A - Fw-cw distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a convenient FW-CW distance measuring device capable of measuring with high precision in a short time without limitation in measuring resolution and measuring range. SOLUTION: In this FW-CW distance measuring device for measuring the distance to a measuring object 9 by emitting FW-CW wave and receiving the reflected wave from the measuring object 9, the count number of sampling clock frequency fc counted during a differential frequency fb1 period that is the difference between emitted frequency and reflected frequency in a reference distance DREF is divided by the count number of sampling clock frequency fc counted during the differential frequency fb1 period in an optional measuring distance, and the resulting quatient is multiplied by the reference distance DREF to calculate a measuring distance D. This device comprises two or more memories 22-24 for storing the relation between the oscillating frequency control voltage of a voltage control oscillator 10 for emitting the FW-CW wave and the oscillated frequency, and a temperature sensor 6. Any one of the memories 22-24 is suitably selected on the basis of the measurement value of the temperature sensor 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FW-CW distance measuring device, and more particularly to an FW-CW distance measuring device used for measuring an inter-vehicle distance, detecting a target, and the like.

[0002]

2. Description of the Related Art Conventionally, an F signal obtained by performing FM modulation (frequency modulation) on a transmission signal of a CW radar (Continuous Wave Radar)
The distance measurement using the M-CW radar is performed, for example, as described in Japanese Patent Laid-Open No. 7-20233, by using a DSP LSI to calculate the residual frequency difference between the radiation frequency and the reflection frequency.
(Digital Signal Processor Large Scale Integratio
n) is programmed in FFT (Fast Fourier Tr
Ansform) Frequency analysis is the main method.

Further, as in the beat count type FM-CW distance measuring device described in Japanese Patent Laid-Open No. 5-297119, the oscillation of a VCO (voltage controlled oscillator) is controlled by a signal generator so that a radiation frequency and a reflection frequency can be obtained. It has been proposed to measure the distance by obtaining the residual frequency obtained by subtracting by the counter circuit.

[0004]

However, the above-mentioned Japanese Unexamined Patent Publication No.
In the distance measuring method by the FFT method as disclosed in Japanese Patent Laid-Open No. 20233, a personal computer (P
C) or a device for reading the program data of the DSP LSI, or the like, must be brought to the installation location of the distance measuring device, or the distance measuring device must be brought to a facility or the like equipped with these, which is not convenient.

Regarding the measuring range and measuring resolution,
In the case of the FFT method, there is a problem that the measurement resolution and the measurement range are limited by the number of data buses of the DSP LSI. On the other hand, even when the counter circuit is used, when the input residual frequency is data containing a decimal, the number of digits of the decimal part depends on the oscillation frequency of the VCO. In addition, the frequency count in the counter circuit is such that the frequency measurement up to the integer part when counting for 1 second, the frequency measurement up to 0.1 Hz when counting for 10 seconds, and so on. There is a problem that it takes time to measure the frequency in order to raise the frequency. As a countermeasure for this, a method of increasing the frequency by applying the residual frequency to a multiplier is considered, but the multiplication number of the multiplier becomes several tens to several thousands, which is not a fundamental solution from the viewpoint of manufacturing and maintenance.

Further, as temperature compensation of the VCO, ROM is used.
There is a method of raising and lowering the output frequency control voltage waveform based on the data by a multiplier. In this case, unless the relationship between the output frequency control voltage and the output frequency is a linear condition, the distance data derived from the residual frequency has an error. Also, VC
There was a problem that it also became a limiting condition when selecting O. .

Therefore, the present invention is based on the above conventional FW-CW.
This is a FW that has been made in view of the problems in the distance measuring device, is convenient, can measure in a short time without limiting the measurement resolution and the measurement range, and has high measurement accuracy.
-To provide a CW distance measuring device.

[0008]

In order to achieve the above object, the invention according to claim 1 radiates a FW-CW wave and receives a reflected wave from the object to be measured to determine the distance to the object to be measured. In the FW-CW distance measuring device for measurement, the count number of sampling clock frequencies counted in one cycle of the residual frequency, which is the difference between the radiation frequency and the reflection frequency at the reference distance, The measurement distance is calculated by multiplying the quotient obtained by dividing the quotient of the sampling clock frequencies counted therein by the reference distance.

According to the invention of claim 1, F
The measurement distance can be calculated in a short time because the counter circuit calculates the number of counts of the sampling clock frequency counted in one cycle of the residual frequency at an arbitrary measurement distance instead of using the FT method. In addition, if there is a handheld voltmeter, etc., in determining the malfunction of the FW-CW distance measuring device, it is necessary to bring a device for reading the program data of PC or DSP LSI to the installation place of the distance measuring device. Since there is no need to bring a distance measuring device to a facility equipped with these, convenience is improved.

Further, by changing the count number of the sampling clock frequency counted in one cycle of the residual frequency which is the difference between the radiation frequency and the reflection frequency at the reference distance stored in the memory of the FW-CW distance measuring device, The measurement resolution and measurement range of the FW-CW distance measuring device can be freely changed. For example, the measurement resolution can be changed in units of mm, and the measurement range can be set to 1 to several hundred m.

According to a second aspect of the present invention, a plurality of memories storing the relationship between the oscillation frequency control voltage and the oscillation frequency of the voltage controlled oscillator that radiates the FW-CW wave for each ambient temperature range, and the ambient temperature. And a memory selector that selects one of the plurality of memories based on the measured value of the temperature sensor.

According to the second aspect of the present invention, since the temperature fluctuation of the voltage controlled oscillator can be compensated by switching the memory, it is possible to obtain a stable oscillation frequency corresponding to the change of the ambient temperature. In addition to improving the measurement accuracy, the maintainability is improved because the memory such as the ROM only needs to be replaced even if the oscillation of the voltage controlled oscillator occurs.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the FW-CW according to the present invention.
A specific example of the embodiment of the distance measuring device will be described with reference to the drawings.

FIG. 1 shows an embodiment of an FW-CW distance measuring device according to the present invention. This FW-CW distance measuring device is roughly classified into an RF oscillation unit 1 and a VCO controlling R.
It is composed of an OM unit 2, a control unit 3, and a frequency counting unit 4.

The RF oscillating unit 1 includes a VCO 10 for oscillating an FM-CW, a VCO isolator 11, a directional coupler 12 for extracting a part of a radiation signal as a local signal, and an RF AGC amplifier 13. An RF isolator 15, a circulator 17, and an antenna 19 are provided, and the measurement target is passed from the VCO 10 through the VCO isolator 11, the directional coupler 12, the RF AGC amplifier 13, the RF isolator 15, the circulator 17, and the antenna 19. The signal is emitted to the object 9.

Further, the RF oscillation unit 1 is an AG for LO.
C amplifier 14, LO isolator 16, and mixer 1
8, IF amplifier 110, and low-pass filter 111
And a reflected wave from the measurement object 9 is provided to the antenna 1
9, the circulator 17, and the mixer 18, and it receives.
Further, the local signal demultiplexed by the directional coupler 12 is
The residual signal input to the mixer 18 via the LO AGC amplifier 14 and the LO isolator 16 and output from the mixer 18 is an IF amplifier 110 and a low-pass filter 11.
It is output to the frequency counting unit 4 via 1.

The VCO control ROM unit 2 includes a memory selector 21, a high temperature VCO control ROM 22, a room temperature VCO control ROM 23, and a low temperature VCO control RO.
M24 and digital-analog converter (D / A) 25
And a ROM selected by the memory selector 21
The digital data 22 to 24 are converted into analog data by the D / A 25 to control the output frequency of the VCO 10.

The control unit 3 includes a CPU 31 and a RAM.
32 and ROM 33. The CPU 31 includes a temperature sensor 6, a reference data storage memory 5, a residual frequency count count circuit (counter) 46, a sampling clock count count circuit (counter) 47, a residual frequency count gate circuit 44, and a sampling clock count. The gate circuit 45 is managed and controlled, the measured distance is displayed on the display 7, and the measured distance data is transmitted to an external device via the external interface 8. Further, the RAM 32 temporarily stores the input / output data. The ROM 33 describes the operation contents of the system.

The frequency counting unit 4 includes a square wave shaping comparator 41, a sampling clock oscillator 42, and a sampling clock measuring 1 second timer 43.
A residual frequency count gate circuit 44, a sampling clock count gate circuit 45, a residual frequency count count circuit 46 (counter), and a sampling clock count count circuit 47 (counter).
Composed of and.

The method of generating the 1-second timer t1sec by the sampling clock measuring 1-second timer 43 is as follows.

This one second timer is an OCXO (Oven Con
trolled Crystal Oscillator) etc., but it is generated based on the output frequency of an oscillator with high accuracy but low output frequency. For example, when an OCXO having an oscillation frequency of 5 MHz is used as a reference frequency of a 1-second timer, a time of 1 second corresponds to 5 million cycles of OXCO, as shown in FIG. OCX
The rising edge of the first cycle of O is t1 sec.
If t1sec is lowered at the rising edge of the 5,000,000th cycle, the time from the rising edge of t1sec to the falling edge is 1 second. This method creates a 1 second timer.

Next, the operation of the FW-CW distance measuring device having the above configuration will be described mainly with reference to FIGS. 1 and 3.

After the power of the FW-CW distance measuring device is turned on, the ambient temperature is measured by the temperature sensor 6 in step S1, and the VCO is selected by the memory selector 21 from the measured temperature information of the temperature sensor 6 in step S2. After selecting one of the oscillation control ROMs 22 to 24 for high temperature, room temperature, or low temperature, the start address of the VCO oscillation control ROMs 22 to 24 is changed.

Here, in the temperature characteristic of the output frequency of the VCO 10 versus the output frequency control voltage, as shown in FIG. 4, the waveform moves up and down due to the temperature change. When the temperature changes at a certain output frequency control voltage value, it is necessary to move the drift of the output frequency substantially linearly. for that reason,
Depending on the temperature sensed by the temperature sensor 6, the VCO control ROMs 22 to 24 corresponding to the temperature are selected.
Stabilize the oscillation of 10. Optional VCO control ROM2
The correction of the temperature in 2 to 24 is performed by the VCO control ROM 2
The oscillation of the VCO 10 is stabilized by shifting and oscillating the start addresses 2 to 24.

After the above changing work, in step S3, the VCO 10 is operated to oscillate the RF signal. The counting of the residual frequency fb between the incident wave and the reflected wave from the measurement object 9 in step S4 is performed from the time when the residual signal is detected. After determining whether or not one cycle has elapsed in step S5, if one cycle has elapsed, in step S6, the counting of the residual frequency fb is terminated,
In step S7, the count of the residual frequency fb is read.

Next, the sampling pulse count number Fbc representing the residual frequency fb and the sampling clock frequency f
Measure c. In step S8, the counting of the sampling clock frequency fc is started. In step S9, it is determined whether or not 1 second has elapsed. If 1 second has elapsed, in step S10, the sampling clock frequency fc is counted. Stop, step S1
At 1, the count of the sampling clock frequency fc is read.

Here, if the measured sampling clock frequency fc is different from the sampling clock frequency fcREF at the time of product shipment recorded in the reference distance data storage memory 5, the reference recorded in the reference distance data storage memory 5 is used. The data value of the distance data FbcREF is changed to the value at the sampling clock frequency fc and is re-recorded in the reference distance data storage memory 5 as the reference distance data FbcREF.

Next, in step S12, the reference distance DREF and the residual frequency fb are read.
Is calculated as follows.

As shown in FIG. 5, the sampling pulse count number Fbc indicates how many cycles tc of the sampling clock frequency fc occur during the cycle tb of the residual frequency fb. That is, the sampling pulse count number Fbc
Is as in Equation 1.

[0030]

[Formula 1] Further, as shown in FIG. 5, since the sampling clock frequency fc at the time of measurement is obtained by how many times it is counted in 1 second, it is a quotient obtained by dividing the sampling clock frequency fc by the sampling pulse count number Fbc from the formula 1. The residual frequency fb is obtained.

Then, the residual frequency f at the measurement distance D
The sampling pulse count number Fbc indicating b is obtained as follows.

First, the residual frequency fb (Hz) at the measurement distance D (m) is given by the equation (2).

[0033]

[Formula 2] Here, C is the speed of light, and C = 3 × 10 ⁸ (m / se
c) and fw are modulation frequency bands (Hz), and τ is a modulation cycle (sec). Then, from Equation 1 and Equation 2, the measurement distance D
The relational expression between the sampling pulse count number Fbc and the sampling pulse count number is as shown in Expression 3.

[0034]

[Formula 3] Note that int () is an expression that returns an integer value in parentheses.

From Equation 3, the sampling pulse count number Fbc and the sampling clock frequency fc are in a proportional relationship, and when the sampling clock frequency fcREF and the sampling clock frequency fc are different from each other, the reference distance data FbcREF is set to the sampling clock. Frequency fc
The reason for changing to the value at the time is to prevent the measurement error due to the difference in the reference distance DREF depending on the value of the sampling clock frequency fc.

Further, the sampling pulse count number Fbc
Since the measurement distance D is inversely proportional to the measurement distance D, the reference distance D
In order to calculate the measurement distance D by the multiple of REF, it is necessary to obtain the quotient obtained by dividing the reference distance data FbcREF by the measured sampling pulse count number Fbc. However, this quotient only shows how many times the measured distance D is the reference distance DREF. The product of this quotient and the reference distance DREF is obtained as the measurement distance D. Therefore, the relationship between the measurement distance D and the reference distance DREF is as shown in Expression 4.

[0037]

[Formula 4] From the above, in step S13, the reference distance data F
Divide bcREF by the measured sampling pulse count Fbc and multiply the quotient by the reference distance DREF to obtain the measured distance D.
Becomes Then, in step S14, the count of the residual frequency fb is erased, and in step S15, V
The oscillation of CO10 is stopped.

Here, the sampling pulse count number F
Until calculating bc, it is calculated by the counter circuit,
The quotient obtained by dividing the reference distance data FbcREF by the sampling pulse count number Fbc can be easily obtained by using a desk calculator or a CPU capable of performing four arithmetic operations of floating point. You can check the measurement error.

After the measurement distance is calculated, the measurement distance is displayed on the display 7 in step S17, and the measurement distance data is externally output in step S19 only when the measurement distance data is requested from the external interface in step S18. Send via interface 8.

After transmitting the measured distance data according to the request from the external interface 8 or when there is no request from the external interface 8 in step S18, the operation returns to the ambient temperature measuring operation in step S1 and the same operation is performed until the power is turned off. Repeat the operation.

Next, the measurement resolution of the FW-CW distance measuring device will be described. The measurement resolution AD is as follows from Equation 4.

[0042]

[Formula 5] By substituting the equation 3 into the equation 5, the equation 6 is obtained.

[0043]

[Formula 6] From the equation 6, it can be seen that the measurement resolution AD is proportional to the square of the measurement distance D, and therefore the measurement distance at a certain resolution has an upper limit. The measurement resolution in the present invention is 1 mm.
Therefore, the upper limit of the measurement distance at the measurement resolution of 1 mm is expressed by Expression 7.

[0044]

[Formula 7] Therefore, the upper limit of the measurement distance can be changed by changing the values of the modulation period τ, the modulation frequency band fw, and the sampling clock frequency fc. Further, the measurement resolution can be easily changed by changing the values of the modulation period τ, the modulation frequency band fw, and the sampling clock frequency fc.

[0045]

As described above, according to the present invention,
FW-CW, which is convenient and can measure in a short time without limiting the measurement resolution and measurement range and has high measurement accuracy.
A distance measuring device can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of an FW-CW distance measuring device according to the present invention.

2 is an operation explanatory diagram of a sampling clock measuring 1 second timer of the FW-CW distance measuring device of FIG. 1;

FIG. 3 is a flowchart showing an operation of the FW-CW distance measuring device of FIG.

FIG. 4 is a temperature characteristic diagram of VCO output frequency vs. output frequency control voltage of the FW-CW distance measuring device of FIG.

5 is a timing chart of residual frequency count of the FW-CW distance measuring device of FIG.

[Explanation of symbols]

1 RF oscillation unit 2 VCO control ROM unit 3 control unit 4 Frequency counting unit 5 Reference data storage memory 6 Temperature sensor 7 Display 8 External interface 9 Object to be measured 10 VCO 11 VCO Isolator 12-way coupler 13 RF AGC amplifier 14 LO AGC amplifier 15 RF Isolator 16 LO Isolator 17 Circulator 18 mixer 19 antennas 21 memory selector 22 High temperature VCO control ROM 23 Room temperature VCO control ROM 24 Low temperature VCO control ROM 25 D / A 31 CPU 32 RAM 33 ROM 41 Square wave shaping comparator 42 Sampling clock oscillator 43 1 second timer for sampling clock measurement 44 Residual frequency counting gate circuit 45 Sampling clock counting gate circuit 46 Counting circuit for residual frequency count 47 Counting circuit for sampling clock count 110 IF amplifier 111 Low-pass filter

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5H180 AA01 CC12 CC14 LL01 LL02                       LL04 LL06                 5J070 AB17 AC02 AD01 AE01 AF03                       AH31 AK22 BA01

Claims (2)

[Claims] 1. An F for radiating an FW-CW wave and receiving a reflected wave from a measurement target to measure a distance to the measurement target.
In the W-CW distance measuring device, the count number of sampling clock frequencies counted in one cycle of the residual frequency, which is the difference between the radiation frequency and the reflection frequency at the reference distance, is calculated in one cycle of the residual frequency at any measurement distance. An FW-CW distance measuring device, characterized in that a quotient obtained by dividing a counted sampling clock frequency by a count is multiplied by the reference distance to calculate a measured distance. 2. A plurality of memories that store the relationship between the oscillation frequency control voltage and the oscillation frequency of the voltage controlled oscillator that radiates the FW-CW wave for each ambient temperature range, and a temperature sensor that measures the ambient temperature. The FW-CW distance measuring device according to claim 1, further comprising: a memory selector that selects one of the plurality of memories based on a measurement value of the temperature sensor.