JP2002156447A - Sweep oscillation device and fmcw distance measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sweep oscillation device and an FMCW distance measuring instrument which can measure a distance with high precision without being made large-sized. SOLUTION: The sweep oscillation device is equipped with a voltage- controlled oscillator, a frequency measuring means which supplies a stepped- waveform voltage to the voltage-controlled oscillator and measures the current output frequency from the voltage-controlled oscillator, and a control means which calculates an applied voltage for making a sweep speed constant from measured frequencies corresponding to respective stepped-waveform voltages obtained by the frequency measuring means and supplies the applied voltage to the voltage-controlled oscillator, and the FMCW distance measuring instrument is equipped with the sweep device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sweep for transmitting a frequency-modulated (FM) wave to a target object for distance measurement and for measuring a distance to the target object based on a reception signal of a reflected wave from the target object. The present invention relates to an oscillation device and an FMCW distance measurement device.

[0002]

2. Description of the Related Art FMCW widely applied to radars and the like.
In the distance measurement by the method, an FM-modulated transmission wave is transmitted toward a target object, a reflected wave from the target object is received, and a distance from the beat signal obtained by mixing the transmission wave to the target object is obtained. Seeking.

In the distance measurement by the FMCW method, various improvement measures have been proposed to improve the measurement accuracy. For example, in the FMCW distance measurement device shown in FIG. Voltage controlled oscillator 2
The bias voltage vs. frequency characteristic of the above is measured in advance, a triangular wave signal corrected by the inverse function of the measured bias voltage vs. frequency characteristic is generated, and the output of the voltage controlled oscillator 2 is controlled by the triangular wave signal. Is occurring. Then, this transmission signal is transmitted to the target object 7 through the directional coupler 4, the circulator 5, and the antenna 6,
The light is reflected by the target object 7 and the reflected wave is received by the antenna 6. The received reflected wave is input to the mixer 8 through the circulator 5, and the directional coupler 4
A beat signal is generated by being mixed with the transmission signal input through the antenna, and a distance from the antenna 6 to the target object 7 is calculated based on the beat signal. In such an FMCW distance measurement device, the frequency linearity of the voltage-controlled oscillator 2 is improved by the corrected triangular wave signal, and the transmission signal is transmitted stably, so that the measurement accuracy is improved.

However, in the above FMCW distance measuring device,
Although a correction table storing data for correcting non-linearity in the input voltage vs. oscillation frequency characteristic of the voltage controlled oscillator 2 is used, the correction table may be changed due to aging or temperature characteristics of each component constituting the voltage controlled oscillator 2. It was difficult to keep the sweep speed accurately and constant.

Further, as shown in FIG. 10, an FMCW distance measuring apparatus to which a coaxial cable 17 for reference is added is also known. That is, in this FMCW distance measuring device, an analog signal obtained by converting digital data from the microcomputer (MPU) 12 by a D / A converter or the like (not shown) is supplied to the control terminal of the voltage-controlled oscillator 14, The oscillation signal is input to the two high frequency processing units 15a and 15b. A transmission wave from the first high-frequency processing unit 15a is transmitted from the antenna 16 toward a target object (not shown),
Is transmitted to the coaxial cable 17 for distance reference. At the other end of the coaxial cable 17, the core wire and the outer wire are not connected (open) or connected (short circuit), and reflection due to impedance matching occurs.

Each of the two high-frequency processing units 15a and 15b has a built-in mixing circuit (not shown).
The high-frequency processing unit 15a mixes the transmission signal from the voltage-controlled oscillator 14 with the reflection signal from the antenna 16 and
, And the second high-frequency processing unit 15b outputs the beat signal from the voltage-controlled oscillator 14 and the coaxial cable 17
, And outputs a second beat signal. Here, since the frequency of the second beat signal has a value corresponding to the length of the coaxial cable 17, the frequency of the second beat signal is compared with the frequency of the first beat signal based on the frequency of the second beat signal. , The distance between the antenna 16 and the target object can be determined.

In the FMCW distance measuring device having the configuration shown in FIG. 10, the sweep speed accuracy due to temperature characteristic changes and aging of components of the voltage controlled oscillator 14 like the FMCW distance measuring device having the configuration shown in FIG. Although not affected by deterioration, etc., the coaxial cable 17 also has a temperature characteristic,
That correction is required. In addition, two high-frequency processing units are required, and two accompanying beat signal processing circuits and a beat signal comparison processing unit (neither of which is shown) are required. In addition, the size of the apparatus also increases.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a sweep oscillator and an FMCW capable of measuring distances with high accuracy without increasing the size of the device. An object of the present invention is to provide a distance measuring device.

[0009]

In order to achieve the above object, a sweep oscillator according to the present invention comprises a voltage-controlled oscillator that varies the oscillation frequency by a control voltage and outputs the same, A frequency measuring means for supplying to the oscillator and measuring an output frequency from the voltage-controlled oscillator at that time, and a sweep speed based on a measurement frequency corresponding to each voltage of the staircase waveform voltage obtained by the frequency measuring means. Control means for calculating an applied voltage for stabilizing the voltage, and supplying the applied voltage to the voltage-controlled oscillator at predetermined intervals.

According to another aspect of the present invention, there is provided an FMCW distance measuring apparatus, comprising: a sweep oscillating device; and a transmitting means for transmitting a transmission wave from a voltage-controlled oscillator of the sweep oscillator to a target object. Receiving means for receiving a reflected wave from the target object; and a beat signal for generating a beat signal by mixing a reflected wave received by the receiving means and a frequency of a transmission wave from the voltage-controlled oscillator. It is characterized by comprising a generating means, and a distance calculating means for calculating a distance to the target object based on the beat signal.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a sweep oscillator and an FMCW distance measuring device according to the present invention will be described in detail with reference to the drawings. For convenience of description, the following embodiment will be described as an FMCW distance measurement device including a sweep oscillator device.

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. As shown, this FM
The CW distance measurement device includes a microcomputer (MPU) 20 that executes overall control related to distance measurement.
The microcomputer 20 calculates a distance from the frequency component included in the beat signal to the target object, and (1) a transmission system evaluation phase, which will be described in detail below.
It includes a CPU 21 for executing the (2) control data calculation phase and the (3) distance measurement phase, and a counter 22 for measuring the oscillation frequency of the voltage controlled oscillator 37.

The FMCW distance measuring device converts a digital data, which will be described in detail later, from the microcomputer 20 into an analog voltage and outputs the analog voltage.
An A converter 35, a low-pass filter 36 that cuts off and outputs a high-frequency component superimposed on the analog voltage from the D / A converter 35, and an oscillation frequency based on a control voltage (analog voltage) from the low-pass filter 36. And a voltage-controlled oscillator 37 that outputs a transmission signal by controlling the value of

Further, the FMCW distance measuring device is configured to divide the transmission signal from the voltage controlled oscillator 37 and output the divided signal, and to convert most of the transmission signal from the voltage controlled oscillator 37. A directional coupler 39 that allows the signal to pass therethrough and branches the remainder to output to a mixer 41; a transmission signal that is branched by the directional coupler 39 is output to an antenna 42; And a circulator 40 that outputs a reflected wave reflected by a target object (not shown) and received by the antenna 42 to the mixer 41.

Next, the operation of the FMCW distance measuring device when measuring the distance will be described. Referring to FIG. 1, first, digital data from a CPU 21 executing a program stored in a memory (not shown) built in a microcomputer 20 or an external memory (not shown) is D / A. The analog control voltage is input to the converter 35 and output. This control voltage is output from the low-pass filter 36 with its high frequency cut off.
The control voltage from the low-pass filter 36 is input to the control terminal of the voltage-controlled oscillator 37.

The voltage-controlled oscillator 37 outputs a transmission signal having a frequency based on the value of the control voltage input to the control terminal. This transmission signal is input to the directional coupler 39 and then to the first end of the circulator 40,
A transmission signal is supplied to the antenna 42 from the end, and is radiated as a transmission wave to the target object. Then, the reflected wave from the target object is received by the antenna 42 and output to the mixer 41 from the third end of the circulator 40. Also, the mixer 41
, The transmission signal branched by the directional coupler 39 is input, mixed with the reflection signal, and the beat signal of the frequency difference is output to the MPU 20 or an external processing device, for example, a host computer which controls the entire device. You.

A part of the transmission signal from the voltage controlled oscillator 37 is input to a prescaler 38, and after being divided,
The frequency is measured by a counter 22 in the microcomputer 20.

Incidentally, the distance (R [m]) to the target object by the FMCW method can be calculated from the following equations (1) to (4). R = １ ／ · td · c (1) ΔF / T = fb / td (2) where, td: round trip time [sec] of a transmission wave to / from the target object ΔF: sweep frequency width [Hz] T: sweep time [sec] fb: frequency of beat signal c: speed of light [m] Also, if Vf: sweep speed (= ΔF / T), equations (3) and (4) are established. R = c · fb · T / 2ΔF = c · fb / 2Vf (3) fb = 2ΔF · R / (c · T) = 2Vf · R / c (4)

Therefore, the distance R from the sweep speed (Vf) and the frequency (fb) of the beat signal to the target distance can be obtained. However, the sweep speed needs to be constant for accurate distance measurement. In the present invention, the sweep speed is stabilized by executing the following (1) transmission system evaluation phase, (2) control data calculation phase, and (3) distance measurement phase.

Next, the operation corresponding to the present invention will be described in detail. FIG. 2 is a block diagram showing a procedure for controlling the output frequency of the voltage-controlled oscillator 37. Each element is denoted by a reference numeral in parentheses. The basic operation is composed of the following three phases. (1) Transmission system evaluation phase (2) Control data calculation phase (3) Distance measurement phase

(1) Transmission System Evaluation Phase This transmission system evaluation phase
Evaluates the characteristics of the voltage-controlled oscillator 37.
In this transmission system evaluation phase, the relationship between the digital data value from the microcomputer 20 input to the D / A converter 35 and the frequency of the oscillation signal of the voltage controlled oscillator 37 is evaluated, and the digital data value versus frequency characteristic is evaluated. Get.

Here, digital data from the microcomputer 20 will be described. The value of the digital data corresponds to the value of the control voltage that determines the oscillation frequency of the voltage controlled oscillator 37, and is used by the CPU 21 to control the oscillation frequency of the voltage controlled oscillator 37. In the CPU 21, the D / A converter 35 and the low-pass filter 3 provided between the CPU 21 and the voltage-controlled oscillator 37 in order to control the voltage-controlled oscillator 37 accurately.
6 and the linearity of the oscillation frequency of the voltage-controlled oscillator 37 due to the non-linearity of the voltage-controlled oscillator 37, the temperature characteristics, and the effects of aging. The microcomputer 20 outputs digital data for implementing this correction.

FIG. 3 is a flowchart showing a processing procedure in the transmission system evaluation phase. Referring to FIGS. 3, 2, and 1, the operation of the transmission system evaluation phase is started in response to the input of the timing signal to the terminal T. First, the microcomputer 20 starts the evaluation start voltage of the voltage-controlled oscillator 37. Is output to the D / A converter 35, where it is converted into an analog control voltage (step S11).

The control voltage from the D / A converter 35 is input to a low-pass filter 36, which removes high-frequency components and supplies it to a voltage-controlled oscillator 37. At this time, a timer (not shown) built in the microcomputer 20 is started at the same time, and the counter 2 cleared to 0 is started.
The counting operation of 2 is started. Further, the transmission signal from the voltage controlled oscillator 37 is divided by the prescaler 38,
The frequency of the divided transmission signal is counted and measured by the counter 22 in the microcomputer 20 for a predetermined time generated by the timer (step S12).

Next, the elapse of a predetermined time is determined, and the completion of frequency measurement of the divided transmission signal is determined (step S1).
3). If the frequency measurement has not been completed (S13: No),
The determination of the elapse of the fixed time is repeated, and when the measurement is completed (S13: Yes), the counter operation of the counter 22 is ended, the count value read from the counter 22, the value of the fixed time by the timer, and the prescaler 38.
Is converted into the oscillation frequency of the voltage controlled oscillator 37, and this data is stored in a memory (not shown) in the microcomputer 20 (step S14).

Next, the increment Δx is added to the digital data x to obtain digital data X (step S15). Further, it is determined whether the value of the digital data X has reached the digital data value corresponding to the voltage at which the evaluation of the voltage-controlled oscillator 37 has been completed (step S16). If it has not reached (S16: No), the process returns to step S12, and if it has reached (S16: Yes), the transmission system evaluation phase ends.

FIG. 4 is a diagram showing a control voltage input to the control terminal of the voltage controlled oscillator 37 in the above flowchart. As shown in the figure, the control voltage increases stepwise, and the oscillation frequency is measured during a period in which the voltage is constant (“frequency measurement range” in the figure). This measurement is performed by the microcomputer 20 through the prescaler 38. Then, for example, a relationship between the digital data x and the oscillation frequency (f) as shown in FIG. 5 is obtained.

(2) Control Data Calculation Phase In this control data calculation phase, the following step (3) distance measurement is performed based on the data measured in the above (1) transmission system evaluation phase and the oscillation frequency of the voltage controlled oscillator 37. The microcomputer 20 calculates a control voltage value (digital data value) for controlling the oscillation frequency of the voltage-controlled oscillator 37 used in the phase.

Here, the relationship between the oscillation frequency of the voltage controlled oscillator 37 and time as shown in FIG. 6 is used. That is, the interval between the timing T0, which is the start of the sweep, and the timing Tn, at which the sweep ends, is divided into n portions, and the divided portions are set as timings T1, T2,... The oscillation frequency of the voltage controlled oscillator 37 at the timing T0 is defined as F0, and the oscillation frequencies for the timings T1, T2,.
F2 ... Fn. Further, the voltage-controlled oscillator 37 based on the increment time ΔT within the timing Tm from the timing T0.
Is constant, and this change is referred to as a frequency increase ΔF.

When the relationship shown in FIG. 6 is associated with the data shown in FIG. 5, the oscillation frequencies F0 and F0 are obtained as shown in FIG.
1, F2... Fn are obtained, and the digital data values corresponding to the digital data values X0, X1, X
2 ... Xn. These digital data values X0, X1, X
2... Xn are digital data (oscillation control data) from the microcomputer 20 for controlling the oscillation frequency of the voltage-controlled oscillator 37, which is used in the subsequent (3) distance measurement phase.

(3) Distance Measurement Phase In this distance measurement phase, first, the control data X0 calculated in the above (2) control data calculation phase is transmitted from the microcomputer 20 to the D / A converter 35 at the sweep start timing T0. Is output. Thereafter, digital data values X1, X2... Xn corresponding to the respective timings T1, T2... Tn are sequentially output from the microcomputer 20 to the D / A converter 35. Then D
The high-frequency component of the control voltage from the / A converter 35 is removed by the low-pass filter 36, and this control voltage is input to the control terminal of the voltage-controlled oscillator 37. As a result, the oscillation signal from the voltage-controlled oscillator 37 exhibits a sweep characteristic with excellent linearity, and the transmission wave is transmitted from the antenna 42 toward the target object.

By keeping the sweep speed constant as described above, the frequency of the beat signal does not fluctuate, and high-precision distance measurement becomes possible.

In the above description, (1) the transmission system evaluation phase may be started at regular intervals, or (3) after the distance measurement is executed a predetermined number of times in the distance measurement phase, (1) the transmission system evaluation phase The process may automatically shift to the evaluation phase. These can be easily achieved by inputting corresponding timing signals to the terminals T or by directly jumping to the head of the transmission system evaluation phase. Further, by providing a signal from an external device connected to the FMCW distance measuring device to the terminal T, (1) the transmission system evaluation phase may be started. By doing so, a signal can be given to the terminal T before the distance is truly measured, so that the linearity can be calibrated when necessary.

Further, instead of the directional coupler 39 and the circulator 40, a hybrid circuit having an equivalent function may be used.

Further, (2) the example in which discrete data is linearly interpolated in the control data calculation phase has been described.
Interpolation may be performed using a polynomial curve. In this case, since the sweep speed can be kept more constant, the distance measurement accuracy is further improved. In the interpolation using the polynomial curve, the amount of discrete data is reduced, so that the number of frequency points to be measured is reduced, and (1) the operation time of the transmission system evaluation phase can be shortened. That is,
The (1) transmission system evaluation phase and the (2) control data calculation phase are time zones in which distance measurement cannot be performed. If high-speed distance measurement is required such that the response time of distance measurement becomes a problem. It is preferable to apply interpolation using a multi-order curve in which the amount of discrete data is reduced.

Next, a second embodiment will be described.

FIG. 8 is a block diagram showing the configuration of the second embodiment. As shown, the second embodiment is different from the voltage-controlled oscillator 37 of the first embodiment shown in FIG.
Is provided between the output terminal and the counter 22. The down converter 50 includes an oscillator and a mixer. Other configurations are the same as those of the first embodiment.

The second embodiment is particularly effective when the oscillation frequency of the voltage controlled oscillator 37 is relatively high. That is, when the oscillation frequency of the voltage controlled oscillator 37 is high and exceeds the maximum operating frequency of the prescaler 38, frequency division cannot be performed, and the oscillation frequency of the voltage controlled oscillator 37 is reduced to a low frequency by using the down converter 50. After the conversion, it is output to the prescaler 38. Then, the counter 22 measures the output signal of the prescaler 38. Other operations are the same as those of the first embodiment.

In the second embodiment, the oscillating section of the down converter 50 generally uses, for example, a dielectric oscillator which is a combination of a dielectric resonator and a transistor. In particular, when high-precision distance measurement is required, it is necessary to use a crystal-controlled oscillator that can obtain a stable oscillation frequency.

In each of the above embodiments, the voltage-controlled oscillator 37 is a microwave oscillation diode or a voltage-controlled oscillator for a microwave band, so that the transmission wave can be a microwave. The microwave can detect a target object even in a high-temperature environment where an optical system cannot be applied, or in an environment where obstacles such as water vapor and mist are floating. Therefore, by incorporating a microwave oscillation diode or a voltage-controlled oscillator for the microwave band into the sweep oscillator, accurate distance measurement can be performed in a wider range of applications.

[0041]

As is apparent from the above description, according to the present invention, the sweep speed in the voltage-controlled oscillator can be kept constant, and high-accuracy distance measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a sweep oscillator and an FMCW distance meter measuring device according to the present invention.

FIG. 2 is a functional block diagram for explaining the operation of the first embodiment.

FIG. 3 is a flowchart illustrating a processing procedure of a transmission system evaluation phase in the first embodiment.

FIG. 4 is a diagram showing control signals of a voltage controlled oscillator used in the first embodiment.

FIG. 5 is a diagram illustrating an example of data measured in a transmission system evaluation phase according to the first embodiment.

FIG. 6 is a diagram for explaining the relationship between oscillation frequency and time used in the distance measurement phase in the first embodiment.

FIG. 7 is a diagram for explaining the relationship between oscillation frequency and time obtained by linearly interpolating between discrete data in the first embodiment.

FIG. 8 is a block diagram illustrating a configuration of a second embodiment.

FIG. 9 is a block diagram showing a configuration of a conventional FMCW distance measuring device.

FIG. 10 is a block diagram showing a configuration of another FMCW distance measuring device in a conventional example.

[Explanation of symbols]

 Reference Signs List 20 microcomputer 21 CPU 22 counter 35 D / A converter 36 low-pass filter 37 voltage-controlled oscillator 38 prescaler 39 directional coupler 40 circulator 41 mixer 42 antenna 50 downconverter T input terminal

Claims (5)

[Claims] 1. A voltage-controlled oscillator that varies and outputs an oscillation frequency by a control voltage, and supplies a staircase waveform voltage to the voltage-controlled oscillator, and measures an output frequency from the voltage-controlled oscillator at that time. Frequency measuring means to perform, from the measurement frequency corresponding to each voltage of the staircase waveform voltage obtained by the frequency measuring means, calculate an applied voltage for stabilizing the sweep speed, the applied voltage at a predetermined interval And a control means for supplying the voltage-controlled oscillator to the sweep oscillator. 2. An FMCW distance measuring device for measuring a distance to a target object by an FMCW method, wherein a transmission wave is transmitted from the sweep oscillation device according to claim 1 and the voltage controlled oscillator of the sweep oscillator toward the target object. Transmitting means, receiving means for receiving a reflected wave from the target object, generating a beat signal by mixing the reflected wave received by the receiving means and the frequency of the transmitted wave from the voltage-controlled oscillator. FMC comprising: a beat signal generating unit that calculates a distance to a target object based on the beat signal;
W distance measuring device. 3. The FMCW distance measuring apparatus according to claim 2, further comprising a terminal for externally supplying a start signal for activating a frequency measuring means of the sweep oscillator. 4. The FMCW distance measuring apparatus according to claim 2, wherein the transmission wave is a microwave. 5. The FMCW distance measuring apparatus according to claim 2, wherein the transmitting means and the receiving means are constituted by a single antenna.