JP2005207840A - Object detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect an object or measure a distance up to the object in a short time, even when an undetected pulse is generated frequently. <P>SOLUTION: This object detector for detecting the measuring object by transmitting repeatingly signals for observation into a space, and by detecting the signals for the observation reflected by the measuring object, based on reception signals received from the space includes a reception rate determination part 22 for finding a reception rate of the signals for the observation, and controls processing based on the reception rate found in the reception rate determination part 22. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an object detection apparatus that detects an object using reflection of an observation signal.

  2. Description of the Related Art An object detection device that is mounted on a moving body such as an automobile, a train, or a ship and measures a distance to an obstacle or the like around the front, rear, or side of the moving body is widely used. The object detection device finds obstacles in the vicinity from the moving body, informs the driver of the distance, automatically avoids the moving body, automatically stops the moving body, and runs the moving body safely It is used to make it. Examples of the object detection device include a pulse radar that transmits a pulse and receives the pulse reflected by the object to measure the distance to the object. For example, a pulse width modulation circuit (PWM circuit) is used to output a pulse width modulation signal (PWM signal) having a pulse width proportional to the distance to the object, and the distance to the measurement object is obtained based on the output. An object detection device is known (Japanese Patent Laid-Open No. 2003-66136, Japanese Patent Laid-Open No. 2003-270332, etc.). It has a pulse width corresponding to the time difference between the time when the pulsed electromagnetic wave is transmitted, that is, the time when the transmission pulse is transmitted and the time when the pulse reflected from the received electromagnetic wave is detected, that is, the time when the received pulse is detected By generating a PWM signal and passing the pulse width of this PWM signal through a low-pass filter and converting it to a DC voltage, the distance from the voltage value to the object can be obtained.

JP 2000-241535 A

  However, in the object detection device using the PWM circuit, when the pulse cannot be detected from the received electromagnetic wave, the PWM signal having the pulse width that correctly reflects the distance to the measurement object cannot be generated correctly, and the object is detected. There is a problem that the object cannot be detected or the distance to the measurement object cannot be measured. For example, as shown in FIG. 13, the PWM signal is raised in response to a transmission trigger indicating the transmission time of a pulse electromagnetic wave, and the PWM signal is lowered in response to a reception trigger indicating the detection time of a pulse from the reception signal. Therefore, when the received pulse cannot be detected, the timing to fall the PWM signal cannot be obtained, and it depends on the distance from the original to the target object after the transmission pulse is transmitted until the next received pulse is received. A PWM signal having a pulse width larger than the pulse width to be output is output.

  In the object detection device, the voltage value proportional to the pulse width of the PWM signal is averaged, and the voltage proportional to the pulse width of the PWM signal is obtained to measure the distance from the device to the measurement object. The fact that the width is much larger than the value indicating the distance to the original object has caused a large error in distance measurement.

  An object of the present invention is to provide an object detection device that can detect a measurement object with high accuracy even in a situation where a missing reception pulse occurs in view of the above-described problems of the prior art.

  The present invention is an object detection apparatus for detecting a measurement object by repeatedly transmitting an observation signal to a space and detecting the observation signal reflected by the measurement object from a reception signal received from the space. And a reception rate determination unit for determining a reception rate of the observation signal, wherein the reception rate determined by the reception rate determination unit is used for processing.

  Specifically, a PWM signal generation unit that generates a PWM signal in which a time difference between the transmission time of the observation signal and the reception time of the observation signal is modulated to a pulse width; and the PWM signal is smoothed, and the measurement target A low-pass filter that outputs a distance signal indicating a distance to an object, and a processing unit that receives the distance signal and digitizes the distance signal and processes the distance signal, and the reception rate is a predetermined threshold value or less In addition, the input to the processing unit is limited, or the output from the processing unit is limited when the reception rate is a predetermined threshold value or less.

  For example, it includes a reception trigger generation unit that generates a reception trigger indicating a reception time of the observation signal and having a constant pulse amplitude and pulse width, and the reception rate determination unit smoothes the reception trigger with a low-pass filter By doing so, the reception rate can be obtained. And an observation signal receiving unit that extracts a detection signal on which the observation signal is superimposed from the reception signal, wherein the reception rate determination unit smoothes the detection signal with a low-pass filter, thereby reducing the reception rate. Can be requested. The reception rate determination unit corrects a signal obtained by smoothing the PWM signal with a low-pass filter by using a distance signal indicating a distance to the measurement object obtained based on the pulse width of the PWM signal. Thus, the reception rate can be obtained.

  Another aspect of the present invention is an object for detecting a measurement object by repeatedly transmitting an observation signal to space and detecting the observation signal reflected by the measurement object from a reception signal received from the space. The detection apparatus includes a reception rate change prediction unit that predicts a change in the reception rate of the observation signal, and uses the prediction result in the reception rate determination unit for processing.

  Specifically, a PWM signal generation unit that generates a PWM signal in which a time difference between the transmission time of the observation signal and the reception time of the observation signal is modulated to a pulse width; and the PWM signal is smoothed, and the measurement target A low-pass filter that outputs a distance signal indicating a distance to an object, and when the change in the reception rate tends to increase, the low-pass filter than when the change in the reception rate tends to decrease Set a large time constant for the filter. In addition, a processing unit that receives the distance signal and digitizes the distance signal and processes it, and when the change in the reception rate tends to be lower than the case where the change in the reception rate tends to increase. The input to the processing unit is limited, or when the change in the reception rate is in a downward trend, the output from the processing unit is limited as compared with the case in which the change in the reception rate is in an upward trend.

  For example, a reception trigger generation unit that generates a reception trigger indicating a reception time of the observation signal and having a constant pulse amplitude and pulse width, and the reception rate change prediction unit includes a plurality of low-pass signals having different response times A reception rate change can be predicted by including a filter, smoothing the reception trigger using the low-pass filter, and calculating the difference. An observation signal receiving unit that extracts a detection signal on which the observation signal is superimposed from the reception signal, and the reception rate change prediction unit includes a plurality of low-pass filters having different response times, By smoothing the detection signal using a band-pass filter and calculating the difference, a change in the reception rate can be predicted. The reception rate change prediction unit includes a plurality of low-pass filters having different response times, smoothes the PWM signal using the low-pass filters, and calculates a difference between them to change the reception rate. Can be predicted.

  According to any one of the present invention, even when pulses are not detected frequently, an object can be detected with high accuracy and in a short time, or the distance to the object can be measured.

<First Embodiment>
As shown in FIG. 1, the object detection apparatus 100 according to the first embodiment of the present invention includes a transmission trigger generation unit 10, an observation signal transmission unit 12, an observation signal reception unit 14, a reception trigger generation unit 16, and a distance. The signal generation unit 18, the digital signal processing unit 20, and the reception rate determination unit 22 are configured. The object detection device 100 is mounted on a moving body such as a vehicle, and is used for detecting an obstacle and measuring the distance between the vehicle and the obstacle.

  Hereinafter, the signal processing of the object detection apparatus 100 in the present embodiment will be described using the timing chart of FIG.

  As shown in FIG. 2A, the transmission trigger generation unit 10 generates a transmission trigger having a constant pulse amplitude and outputs the transmission trigger to the observation signal transmission unit 12 and the distance signal generation unit 18. In response to the transmission trigger from the transmission trigger generation unit 10, the observation signal transmission unit 12 outputs a pulse electromagnetic wave corresponding to the pulse width of the transmission trigger from the transmission antenna to the space as shown in FIG. This pulsed electromagnetic wave becomes an observation signal. For example, when the measurement range required for the object detection apparatus 100 is several meters to several tens of meters, the pulse period in the transmission trigger generation unit 10 is set to about 100 nsec to 1 μsec. Note that the observation signal is not limited to the pulse electromagnetic wave, and may be another signal such as a sound wave as long as the signal can be reflected by the measurement object.

  When a measurement object such as an obstacle exists in the direction in which the pulse electromagnetic wave is transmitted, the pulse electromagnetic wave hits the measurement object and is reflected.

  The receiving antenna receives electromagnetic waves that reach the object detection device 100 from space. The received signal is sent to the observation signal receiving unit 14 and output to the reception trigger generating unit 16 as a detected detection signal. The reception trigger generation unit 16 generates a reception trigger corresponding to the first rising time of the detection signal based on a predetermined detection condition.

  As shown in FIG. 2C, the electromagnetic wave received by the receiving antenna is superimposed with the pulse electromagnetic wave reflected by the object to be measured and the noise reaching from the external space of the object detection device. The observation signal receiving unit 14 receives the received signal from the receiving antenna and detects the received signal with an envelope. The reception trigger generation unit 16 compares the detected envelope with a reference voltage in a voltage comparator, and, as shown in FIG. 2 (d), a certain time from the time when the value of the envelope becomes higher than the reference voltage. Only a pulse is raised and a reception trigger having a constant voltage value and a constant pulse width is output. By this reception trigger, it is possible to detect an object to be measured in the transmission direction of the pulse electromagnetic wave. Here, the reception trigger is output to the distance signal generation unit 18 and the reception rate determination unit 22.

  The distance signal generation unit 18 receives a transmission trigger and a reception trigger from the transmission trigger generation unit 10 and the reception trigger generation unit 16, respectively, and outputs a distance voltage signal corresponding to the distance between the object detection device 100 and the measurement object. As shown in FIG. 1, the distance signal generator 18 can be configured to include a PWM signal generator 18a and a low-pass filter (LPF) 18b.

  The PWM signal generation unit 18a is a pulse width modulation circuit (Pulse Width Modulation: PWM circuit). In response to the transmission trigger from the transmission trigger generation unit 10 and the reception trigger from the reception trigger generation unit 16, the PWM signal generation unit 18a receives the transmission trigger and the reception trigger as shown in FIG. A constant voltage PWM signal having a pulse width corresponding to the time difference from the received time is generated.

  At this time, as shown in FIG. 2, a PWM signal can be generated by raising a pulse having a constant pulse amplitude at the time when the transmission trigger is received and lowering the pulse at the time when the reception trigger is received. . Conversely, the PWM signal may be generated by falling the pulse at the time when the transmission trigger is received and raising the pulse at the time when the reception trigger is received.

  The pulse width of the PWM signal corresponds to the time from when the pulse electromagnetic wave, which is an observation signal, is transmitted from the transmitting antenna, reflected by the measurement object, and received by the receiving antenna. Therefore, the distance from the object detection device 100 to the measurement object can be obtained based on the pulse width of the PWM signal.

  As explained in the prior art, when the pulse electromagnetic wave cannot be detected from the received signal due to weak reflection on the object, the PWM signal has a pulse width that continues until the pulse electromagnetic wave is detected from the received signal next time. It will have. That is, the pulse width of the PWM signal is larger than the distance from the object detection apparatus 100 to the measurement object, which causes a large error in the distance measurement result. In this embodiment, the reception rate determination unit 22 obtains the reception rate of the pulse electromagnetic wave, and controls the process according to the reception rate to reduce the measurement error. The operation of the reception rate determination unit 22 will be described later.

  The LPF 18b is used to output a distance signal having a signal intensity corresponding to the pulse width of the PWM signal. The LPF 18b can be configured by, for example, an L-type low-pass filter (LPF) composed of a combination of a resistor and a capacitor. The LPF 18b receives the PWM signal, averages the PWM signal for the response time determined by the time constant of the filter, and outputs the averaged signal to the digital signal processing unit 20. The response time of the filter is determined by the combination of the resistance value and the capacitance value of the capacitor.

  When the low-pass filter is an RC type, the time constant is defined by RC. This is the time until the output becomes 1 / e times (e is the base of natural logarithm) when a voltage is applied to the filter. The response time of the low-pass filter is determined according to the time constant, and means the time required for the difference between the input signal and the output signal to become sufficiently small when a voltage is applied to the filter. For example, it is defined by the time until the output signal converges to 99% of the input signal and the time 10 times the time constant τ.

  The resolution of the distance is determined by the detection accuracy of the output voltage of the low-pass filter. Considering that observation is performed up to about 10 times the distance to be measured in order to avoid the influence of unnecessary waves, the final detection accuracy may be set to about 0.1% to 1% with respect to the dynamic range. preferable. When detection is performed with an accuracy of 1%, if the observation range is 50 m, the resolution is 50 m ÷ 100 = 50 cm (5 cm when 0.1% is set). In general, if the detection accuracy is increased, the resolution of the distance is also increased. However, it is not preferable to increase the resolution excessively in consideration of the noise level of the signal. When the low-pass filter output is observed using an 8-bit analog / digital converter, the resolution is 50 m ÷ 256 = about 20 cm. Normally, when designing a low-pass filter for the purpose of direct current, the time constant is set so that no fluctuations exceeding the detection limit remain in the output. This is because, in general, if a variation that exceeds the detection limit remains, the distance cannot be uniquely determined.

  For example, if the response time of the LPF 18b is set to be shorter than the observation signal transmission cycle, the PWM signal output from the PWM signal generation unit 18a cannot be sufficiently smoothed, and the LPF 18b within the observation signal transmission cycle cannot be smoothed. Output value fluctuates unnecessarily. Therefore, the response time of the LPF 18b is preferably set longer than the observation signal transmission cycle. As a result, it is possible to avoid the output value of the LPF 18b from fluctuating unnecessarily.

  Moreover, it is preferable to set the response time of the LPF 18b to be shorter than the sampling period in the digital signal processing unit 20. If the response time is set to be longer than the sampling period, the recovery from the missing state is delayed when a loss occurs, and the loss is affected at the next sampling time. As a result, the error of distance measurement becomes large.

  On the other hand, when missing observation signals are detected with high frequency, the response time of the LPF 18b is preferably set shorter than the time when observation signals are detected with low frequency. As a result, it is possible to reduce the error in the case where the lack of pulse detection continues for a long time.

  In this way, by averaging the intensity of the PWM signal having a pulse width indicating the distance between the apparatus and the measurement object using the LPF 18b, when the reflection from the measurement object is small or the noise from the external environment is large In some cases, the influence on the distance measurement when the observation signal cannot be detected from the received signal can be reduced.

  The digital signal processing unit 20 includes an analog / digital converter (A / D converter) 20a, a gate circuit 20b, and an error reduction processing unit 20c. The A / D converter 20a receives the distance signal from the distance signal generator 18, samples the analog distance signal, converts it to a digital signal, and outputs the digital signal to the gate circuit 20b. The gate circuit 20b receives the determination signal from the reception rate determination unit 22, and controls whether or not to output the distance signal input from the A / D converter 20a to the error reduction processing unit 20c according to the determination signal.

  The reception rate determination unit 22 includes a low-pass filter (LPF) 22a and a threshold determination processing unit 22b. The reception rate determination unit 22 is used to receive the reception trigger from the reception trigger generation unit 16 and obtain the reception rate of the pulse electromagnetic wave based on the input frequency of the reception trigger. Here, the reception rate refers to the ratio of the frequency at which a pulsed electromagnetic wave is detected from a received signal to the frequency of transmission of a pulsed electromagnetic wave that is an observation signal within a predetermined period. Since the pulse electromagnetic wave is transmitted at a constant period, the reception rate can be obtained based on the number of reception triggers output from the reception trigger generation unit 16 within a predetermined reference time.

  Specifically, as shown in FIG. 3, the LPF 22a receives the reception trigger and smoothes the reception trigger with a predetermined time constant. The output of the LPF 22a increases as the reception trigger input frequency per unit time increases. The output of the LPF 22a corresponds to the reception rate. The LPF 22a can use a filter having a simple configuration such as an RC type. For example, when the LPF 22a is an RC type, the time constant is defined by RC, and there is an advantage that the reference time can be easily set and changed by changing the resistance value or the capacitance value.

  The threshold determination processing unit 22b determines whether or not the output of the LPF 22a is larger than a predetermined threshold. If the output of the LPF 22a is equal to or greater than the threshold, a “permitted” determination signal is output, and if the output of the LPF 22a is smaller than the threshold, a “prohibited” determination signal is output. The threshold determination processing unit 22b can be configured by, for example, a differential amplifier circuit. In this case, by comparing the constant reference voltage with the output of the LPF 22a using the threshold voltage, for example, “permitted” can be an H level output and “prohibited” can be an L level output.

  When the determination signal is “permitted”, that is, when the output of the LPF 22a is equal to or greater than the threshold value, the gate circuit 20b outputs a distance signal to the error reduction processing unit 20c because the reception rate of the pulse electromagnetic wave is high. On the other hand, when the determination signal is “prohibited”, that is, when the output of the LPF 22a is smaller than the threshold value, the reception rate of the pulse electromagnetic wave is low, so that the distance signal is not output to the error reduction processing unit 20c.

As described above, by performing the gate processing on the distance signal according to the reception rate of the pulse electromagnetic wave, it is possible to perform adaptive real-time signal processing according to the reception state in a system in which the reception state changes from moment to moment. In particular, in the system for measuring the distance to the object to be measured according to the pulse width of the PWM signal as in the present embodiment, a signal including an error due to the lack of reception of the pulse electromagnetic wave is processed after the gate circuit 20b. There is an advantage that can be prevented. At this time, in accordance with the period _{T 1} of the sampling in the A / D converter 20a, it is preferable that the response time of LPF22a sets the time constant of LPF22a to correspond to the period _{T 1.} For example, if the period _{T 1} of the sampling of the A / D converter 20a was 50 [mu] s, it is preferably a value close to the response time 50 [mu] s of LPF 22a.

  The error reduction processing unit 20c performs processing for reducing errors included in the distance signal. For example, in the object detection apparatus 100 mounted on an automobile, it is preferable to select and output a minimum value from a plurality of sampling values sampled within a predetermined time. Thereby, even when the reflection of the pulse electromagnetic wave is weak or the noise from the external environment is large, the distance to the obstacle in the vicinity of the automobile can be obtained with relatively high accuracy.

In the present embodiment, the gate circuit 20b is provided between the A / D converter 20a and the error reduction processing unit 20c. However, like the object detection device 102 shown in FIG. It may be provided on the output side. In response to the determination signal from the reception rate determination unit 22, a signal including an error due to lack of reception of the pulse electromagnetic wave is output by performing gate processing on the final output from the error reduction processing unit 20 c. Can be prevented. At this time, in accordance with the period _{T 2} of the sampling in the error reduction processing unit 20c, it is preferable that the response time of LPF22a sets the time constant of LPF22a to correspond to the period _{T 2.} For example, if the period _{T 2} of the sampling of the error reduction processing unit 20c was 1ms, it is preferably a value close to the response time of 1ms LPF 22a.

  The reception rate determination unit 22 may be provided with two types of filters, and gate circuits may be provided for the outputs of the A / D converter 20a and the error reduction processing unit 20c. As described above, by providing a plurality of gate circuits, it is possible to further reduce errors due to lack of reception of pulsed electromagnetic waves.

<Second Embodiment>
In the first embodiment, the reception rate is determined using the reception trigger from the reception trigger generation unit 16. Since the binarized detection signal in the observation signal receiving unit 14 is a reception trigger, the reception rate can be obtained using a detection signal having properties similar to the reception trigger.

  The object detection device 104 in the second embodiment has the same configuration as the object detection device 100 in the first embodiment as shown in FIG. The difference is that a detection signal is input from the receiver 14.

  As shown in FIG. 2C, the detection signal in the observation signal receiving unit 14 is a signal on which a pulse electromagnetic wave reflected by the measurement object is superimposed. As shown in FIG. 6, the LPF 22a of the reception rate determination unit 22 receives the detection signal from the observation signal reception unit 14 and smoothes the detection signal with a predetermined time constant. The output of the LPF 22a corresponds to the average power of the pulse electromagnetic wave, but since the reception trigger is a binarization of the detection output, the average reception power can be substituted for the reception rate. As in the first embodiment, the LPF 22a can use a filter with a simple configuration such as an RC type. For example, when the LPF 22a is an RC type, the time constant is defined by RC, and there is an advantage that the reference time can be easily set and changed by changing the resistance value or the capacitance value. At this time, the response time of the LPF 22a is preferably set in accordance with the sampling period of the gate circuit 20b of the digital signal processing unit 20. The threshold determination processing unit 22b determines whether the output of the LPF 22a is larger than a predetermined threshold and outputs a determination signal according to the determination result. The gate circuit 20b of the digital signal processing unit 20 performs gate processing on the output from the A / D converter 20a using this determination signal.

  As described above, by determining the reception rate using the detection signal output from the observation signal receiving unit 14, it is possible to prevent a distance signal including an error due to lack of reception of a pulsed electromagnetic wave from being processed. be able to. The same effect can be obtained even if the gate circuit 20b is provided on the output side of the error reduction processing unit 20c.

<Third Embodiment>
In addition to the detection signal, there is a PWM signal as a signal similar in nature to the reception trigger. Therefore, the pulse electromagnetic wave reception rate can be obtained using the PWM signal.

  As shown in FIG. 7, the object detection apparatus 106 in the third embodiment has the same configuration as that in the first and second embodiments, but the distance from the distance signal generation unit 18 to the reception rate determination unit 22. A difference is that a signal is input and a distance bias correction unit 22c is provided.

The PWM signal output from the PWM signal generation unit 18a of the distance signal generation unit 18 has a constant pulse amplitude as in the case of the reception trigger as shown in FIG. 2 (e), but depending on the distance to the measurement object. The pulse width is modulated. The LPF 22a of the reception rate determination unit 22 receives the PWM signal and smoothes the PWM signal with a predetermined time constant. However, as shown in FIG. 8, simply smoothing the PWM signal changes the output value of the LPF 22a according to the distance to the measurement object, and the reception rate cannot be estimated. Therefore, a distance bias correction unit 22c is provided in the reception rate determination unit 22, and the output of the LPF 22a is corrected by feeding back the distance output output from the digital signal processing unit 20. If the output of the LPF 22a when the measurement object is at the distance x is d _x , and the output of the LPF 22a when there is no measurement object is d ₀ , the output L (t) of the LPF 22a using Equation (1). The reception rate P can be calculated by correcting. Here, the output d _x of the LPF 22a when the measurement object is at the distance x can be obtained from the distance output output from the digital signal processing unit 20.

  As shown in FIG. 9, the reception rate P corrected by the distance bias correction unit 22 c becomes a value irrelevant to the distance to the measurement object. The threshold determination processing unit 22b determines whether the output of the distance bias correction unit 22c is larger than a predetermined threshold and outputs a determination signal according to the determination result. The gate circuit 20b of the digital signal processing unit 20 performs gate processing on the output from the A / D converter 20a using this determination signal.

  As described above, by determining the reception rate using the PWM signal output from the distance signal generation unit 18, it is possible to prevent the distance signal including an error associated with the lack of reception of the pulse electromagnetic wave from being processed. Can do. The same effect can be obtained even if the gate circuit 20b is provided on the output side of the error reduction processing unit 20c.

<Fourth embodiment>
In the object detection devices in the first to third embodiments, gate processing for output is performed according to the current reception rate. In the following embodiments, gate processing is performed by predicting a future change in reception rate based on a change in reception rate from the past to the present.

  As shown in FIG. 10, the object detection apparatus 108 according to the fourth embodiment has the same configuration as that of the first to third embodiments, but a reception rate change prediction unit instead of the reception rate determination unit 22. 24 is different.

  The reception rate change prediction unit 24 includes low-pass filters (LPF) 24a and 24b and a reception rate change determination processing unit 24c. The reception rate change prediction unit 24 is used to receive a reception trigger from the reception trigger generation unit 16 and predict a change in the reception rate of the pulse electromagnetic wave.

The LPFs 24a and 24b receive the reception trigger from the reception trigger generation unit 16 and smooth the reception trigger with different time constants τ ₁ and τ ₂ , respectively. Here, it is assumed that time constant τ ₁ <time constant τ ₂ . When the reception rate of the pulse electromagnetic wave decreases, the output of the LPF 24a having a small time constant decreases rapidly, but the output of the LPF 24b having a large time constant decreases more slowly than the output of the LPF 24a. Conversely, when the reception rate increases from a low pulse electromagnetic wave reception rate, the output of the LPF 22a with a small time constant increases rapidly, but the output of the LPF 24b with a large time constant increases more slowly than the output of the LPF 24a. .

  The reception rate change determination processing unit 24c receives outputs from the LPFs 24a and 24b, determines whether the reception rate is increasing or decreasing, and the LPF 18b of the distance signal generation unit 18 and the digital signal processing unit 20 Control of the A / D converter 20a and the error reduction processing unit 20c is performed. In the reception rate change determination processing unit 24c, if (output of the LPF 22a having a small time constant) − (output of the LPF 22b having a large time constant)> 0, the reception rate tends to increase, and (the LPF 22a having a small time constant) (Output) − (output of LPF 22b having a large time constant) <0, it is determined that the reception rate tends to decrease. Each part is controlled in accordance with the determination result.

  Here, it is considered how to set the ratio of the response times of the two LPFs 24a and 24b. Assuming that the response time of the LPF 24a with a small time constant is time T from time t-T to time t, the output value L (t, t-T) of the LPF 24a when the input to the LPF 24a, 24b is s (τ). Is expressed by Equation (2).

  On the other hand, if the response time of the LPF 24b having a large time constant is k times that of the LPF 24a, that is, the time kT from the time t-kT to the time t, the output value L (t, t-kT) of the LPF 24b is expressed by Equation (3). It is represented by

  The difference between the output value of the LPF 24a and the output value of the LPF 24b is expressed by Equation (4).

  Here, when k is 2, Equation (4) is converted to Equation (5). Equation (5) is equivalent to obtaining and comparing the average value of the signal s (τ) at just the interval of time T. Therefore, it can be said that it is preferable to set the time constant of the LPF 24b to about twice the time constant of the LPF 24a.

  For example, when the LPF 18b of the distance signal generator 18 is controlled, when the reception rate tends to increase, the time constant of the LPF 18b is increased, and the PWM signal is averaged over a long period of time to obtain a stable output. it can. On the other hand, when the reception rate tends to decrease, smoothing the PWM signal for a long time causes accumulation of errors, so control is performed so as to reduce the time constant of the LPF 18b.

  Further, when controlling the digital signal processing unit 20, when the reception rate tends to increase, the sampling period of the A / D converter 20a or the error reduction processing unit 20c is reduced to increase the data processed per unit time. Can do. On the other hand, when the reception rate tends to decrease, the sampling period can be increased so that the error included in the distance signal does not affect the processing as much as possible. Also, by increasing the sampling period, it is possible to perform advanced signal processing that requires a longer processing time.

  At this time, a change in the reception rate can also be obtained by counting the reception trigger and directly measuring the reception rate of the pulse electromagnetic wave. However, since the reception trigger is output at a high cycle of about several hundreds ns to several μs, the circuit that counts the reception trigger and predicts the change in the reception rate becomes very complicated and expensive, and the processing burden on the circuit Also gets higher. It is also possible to predict the future reception rate by providing a differentiator after the low-pass filter and measuring the change in the reception rate. However, considering that the signal input to the low-pass filter is pulsed, it is not preferable to use a differentiator sensitive to noise. Therefore, it is more preferable to predict the change in the reception rate using the difference between the outputs from the plurality of low-pass filters as in the present embodiment.

  As described above, according to the present embodiment, it is possible to control the processing for the distance signal in accordance with the change in the reception rate of the pulse electromagnetic wave. Accordingly, adaptive signal processing can be performed by predicting a change in the reception state in a system in which the reception state changes from moment to moment.

<Fifth embodiment>
In the fourth embodiment, the change in the reception rate is determined using the reception trigger from the reception trigger generation unit 16. Although it is preferable to use a reception trigger to accurately determine the change in the reception rate, the processing can also be performed by capturing an approximate change in the reception rate. In this embodiment, a change in the reception rate is determined using a detection signal having properties similar to the reception trigger.

  As shown in FIG. 11, the object detection device 110 in the fifth embodiment has the same configuration as the object detection device 108 in the fourth embodiment, but for the observation of the reception rate change prediction unit 24. The difference is that a detection signal is input from the signal receiving unit 14.

The LPFs 24a and 24b of the reception rate change prediction unit 24 receive the detection signal from the observation signal reception unit 14 and smooth the detection signal with different time constants τ ₁ and τ ₂ , respectively. Assuming that time constant τ ₁ <time constant τ ₂ , when the reception rate of the pulse electromagnetic wave decreases, the output of LPF 24 a having a small time constant rapidly decreases, but the output of LPF 24 b having a large time constant is smaller than the output of LPF 24 a. Also slowly decreases. Conversely, when the reception rate increases from a low pulse electromagnetic wave reception rate, the output of the LPF 22a with a small time constant increases rapidly, but the output of the LPF 24b with a large time constant increases more slowly than the output of the LPF 24a. . Accordingly, in the reception rate change determination processing unit 24c, when (output of LPF 22a having a small time constant) − (output of LPF 22b having a large time constant)> 0, the reception rate tends to increase, and (LPF 22a having a small time constant). Output) − (output of LPF 22b having a large time constant) <0, it can be determined that the reception rate tends to decrease. At this time, as in the fourth embodiment, it is preferable to set the time constant of the LPF 24b to about twice the time constant of the LPF 24a.

  As described above, the LPF 18b of the distance signal generation unit 18, the A / D converter 20a and the error reduction processing unit of the digital signal processing unit 20 are determined by using the detection signal instead of the reception trigger to determine the change in the reception rate. 20c can be controlled.

<Sixth Embodiment>
In the present embodiment, a change in the reception rate of the pulse electromagnetic wave is determined using a PWM signal that is a signal that is very similar in nature to the reception trigger.

  As shown in FIG. 12, the object detection apparatus 112 in the sixth embodiment has the same configuration as the object detection apparatuses 106 and 108 in the fourth and fifth embodiments, but the reception rate change prediction unit 24. However, the difference is that the PWM signal is input from the distance signal generator 18.

The LPFs 24a and 24b of the reception rate change prediction unit 24 receive the detection signal from the observation signal reception unit 14 and smooth the detection signal with different time constants τ ₁ and τ ₂ , respectively. The PWM signal has the same pulse amplitude as the reception trigger, but the pulse width is modulated according to the distance to the object to be measured, so distance information is also superimposed on the output values of the LPFs 24a and 24b. It will be a thing. At this time, if the response time of the LPFs 24a and 24b is sufficiently long with respect to the relative speed between the measurement object and the object detection device, the distance between the measurement object and the object detection device hardly changes within the response time. For example, if the relative speed between the measurement object and the object detection device is 100 km and it takes 360 μs for the measurement object to move by 1 cm, the time constant of the LPFs 24a and 24b is generally less than a few ms. Since it is set, the moving distance of the measurement object within the response time is several centimeters. Therefore, by calculating and comparing the difference between the outputs of the two LPFs 24a and 24b, it is possible to cancel the DC component of the outputs of the LPFs 24a and 24b and extract only the information on the change in the reception rate.

  Accordingly, in the reception rate change determination processing unit 24c, when (output of LPF 22a having a small time constant) − (output of LPF 22b having a large time constant)> 0, the reception rate tends to increase, and (LPF 22a having a small time constant). Output) − (output of LPF 22b having a large time constant) <0, it can be determined that the reception rate is decreasing. At this time, like the fourth and fifth embodiments, it is preferable to set the time constant of the LPF 24b to about twice the time constant of the LPF 24a.

  As described above, the LPF 18b of the distance signal generation unit 18, the A / D converter 20a and the error reduction processing unit of the digital signal processing unit 20 are determined by using the detection signal instead of the reception trigger to determine the change in the reception rate. 20c can be controlled.

It is a block diagram which shows the structure of the object detection apparatus in 1st Embodiment. It is a figure which shows the timing chart for demonstrating the signal processing in the object detection apparatus in 1st Embodiment. It is a figure which shows the relationship between the input condition of the reception trigger in the reception rate determination part in 1st Embodiment, and the output value of LPF. It is a block diagram which shows the structure of the modification of the object detection apparatus in 1st Embodiment. It is a block diagram which shows the structure of the object detection apparatus in 2nd Embodiment. It is a figure which shows the relationship between the input condition of the detection signal in the receiving rate determination part in 2nd Embodiment, and the output value of LPF. It is a block diagram which shows the structure of the object detection apparatus in 3rd Embodiment. It is a figure which shows the relationship between the input condition of the PWM signal in the receiving rate determination part in case there is no feedback circuit, and the output value of LPF. It is a figure which shows the relationship between the input condition of the PWM signal in the receiving rate determination part in 3rd Embodiment, and the output value of LPF. It is a block diagram which shows the structure of the object detection apparatus in 4th Embodiment. It is a block diagram which shows the structure of the object detection apparatus in 5th Embodiment. It is a block diagram which shows the structure of the object detection apparatus in 6th Embodiment. It is a figure which shows the timing chart for demonstrating the signal processing in the conventional object detection apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Transmission trigger generation part, 12 Observation signal transmission part, 14 Observation signal reception part, 16 Reception trigger generation part, 18 Distance signal generation part, 18a PWM signal generation part, 18b Low-pass filter (LPF), 20 Digital signal Processing unit, 20a Analog / digital converter (A / D converter), 20b Gate circuit, 20c Error reduction processing unit, 22 Reception rate judgment unit, 22a Low-pass filter (LPF), 22b Threshold judgment processing unit, 22c Distance Bias correction unit, 24 reception rate change prediction unit, 24a, 24b low-pass filter (LPF), 24c reception rate change determination processing unit, 100, 102, 104, 106, 108, 110, 112 object detection device.

Claims (13)

An object detection device for detecting a measurement object by repeatedly transmitting an observation signal to space and detecting the observation signal reflected by the measurement object from a reception signal received from space,
A reception rate determination unit for obtaining a reception rate of the observation signal;
An object detection apparatus characterized in that the reception rate obtained by the reception rate determination unit is used for processing. The object detection apparatus according to claim 1,
A PWM signal generation unit that generates a PWM signal in which a time difference between a transmission time of the observation signal and a reception time of the observation signal is modulated to a pulse width;
A low-pass filter that smoothes the PWM signal and outputs a distance signal indicating the distance to the measurement object;
A processing unit that receives the distance signal and digitizes and processes the distance signal;
An object detection apparatus that restricts input to the processing unit when the reception rate is equal to or lower than a predetermined threshold. The object detection apparatus according to claim 1,
A PWM signal generation unit that generates a PWM signal in which a time difference between a transmission time of the observation signal and a reception time of the observation signal is modulated to a pulse width;
A low-pass filter that smoothes the PWM signal and outputs a distance signal indicating the distance to the measurement object;
A processing unit that receives the distance signal and digitizes and processes the distance signal;
An object detection apparatus that limits output from the processing unit when the reception rate is equal to or less than a predetermined threshold. In the object detection device according to any one of claims 1 to 3,
A reception trigger generator for generating a reception trigger indicating a reception time of the observation signal and having a constant pulse amplitude and pulse width;
The object detection apparatus according to claim 1, wherein the reception rate determination unit obtains the reception rate by smoothing the reception trigger with a low-pass filter. In the object detection device according to any one of claims 1 to 3,
An observation signal receiving unit that extracts a detection signal on which the observation signal is superimposed from the reception signal;
The reception rate determination unit obtains the reception rate by smoothing the detection signal with a low-pass filter. In the object detection device according to claim 2 or 3,
The reception rate determination unit obtains the reception rate by correcting a signal obtained by smoothing the PWM signal with a low-pass filter based on the distance signal. An object detection device for detecting a measurement object by repeatedly transmitting an observation signal to space and detecting the observation signal reflected by the measurement object from a reception signal received from space,
A reception rate change prediction unit for predicting a change in the reception rate of the observation signal;
An object detection apparatus characterized in that a prediction result in the reception rate determination unit is subjected to processing. The object detection apparatus according to claim 7,
A PWM signal generation unit that generates a PWM signal in which a time difference between a transmission time of the observation signal and a reception time of the observation signal is modulated to a pulse width;
A low-pass filter that smoothes the PWM signal and outputs a distance signal indicating the distance to the measurement object,
The object detection apparatus according to claim 1, wherein when the change in the reception rate tends to increase, the time constant of the low-pass filter is set larger than when the change in the reception rate tends to decrease. The object detection apparatus according to claim 7,
A PWM signal generation unit that generates a PWM signal in which a time difference between a transmission time of the observation signal and a reception time of the observation signal is modulated to a pulse width;
A low-pass filter that smoothes the PWM signal and outputs a distance signal indicating the distance to the measurement object;
A processing unit that receives the distance signal and digitizes and processes the distance signal;
An object detection apparatus that restricts input to the processing unit when the change in the reception rate tends to be lower than when the change in the reception rate tends to increase. The object detection apparatus according to claim 7,
A PWM signal generation unit that generates a PWM signal in which a time difference between a transmission time of the observation signal and a reception time of the observation signal is modulated to a pulse width;
A low-pass filter that smoothes the PWM signal and outputs a distance signal indicating the distance to the measurement object;
A processing unit that receives the distance signal and digitizes and processes the distance signal;
An object detection apparatus that limits the output from the processing unit when the change in the reception rate tends to be lower than when the change in the reception rate tends to increase. In the object detection device according to any one of claims 7 to 10,
A reception trigger generator for generating a reception trigger indicating a reception time of the observation signal and having a constant pulse amplitude and pulse width;
The reception rate change prediction unit includes a plurality of low-pass filters having different response times, smoothes the reception trigger using the low-pass filters, and predicts a change in reception rate by calculating a difference between the reception triggers. An object detection apparatus characterized by: In the object detection device according to any one of claims 7 to 10,
An observation signal receiving unit that extracts a detection signal on which the observation signal is superimposed from the reception signal;
The reception rate change prediction unit includes a plurality of low-pass filters having different response times, smoothes the detection signal using the low-pass filter, and predicts a change in reception rate by calculating the difference between the smoothed detection signals. An object detection apparatus characterized by: In the object detection device according to any one of claims 8 to 10,
The reception rate change prediction unit includes a plurality of low-pass filters having different response times, smoothes the PWM signal using the low-pass filters, and predicts a change in reception rate by calculating a difference between them. An object detection apparatus characterized by:

Images