JPH05281355A - Vehicle-to-vehicle distance detecting device - Google Patents

Abstract

PURPOSE:To obtain a vehicle-to-vehicle distance detecting device which can reduce the occurrence of distance errors derived from the size variation of reflected pulsed optical signals. CONSTITUTION:A light receiving device 3 receives the reflected pulsed optical signals of pulsed optical signals emitted from a light emitting device 2 from an obstruction irradiated with the pulsed optical signals and obtains received pulse signals by performing photoelectric conversion on the received signals. A sample holder 8 sample-holds the signal level at one point in the received pulse signals based on a sample pulse signal controlled by a sample pulse generator 7 and a microcomputer 14 calculates the distance information to the obstruction by reading the number of pulsed optical signal sending times and the sample-held signal level and finding the falling point of the received pulse signals from signal levels at several points and numbers of sending times corresponding to the signals levels.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-vehicle distance detecting device, and in particular, it transmits a pulsed light signal, receives a reflected pulsed light signal from an illuminated obstacle, and measures the time required for the round trip. By detecting the distance to the obstacle.

[0002]

2. Description of the Related Art FIG. 7 shows, for example, Japanese Patent Application Laid-Open No. 2-228579.
FIG. 11 is a block diagram showing a circuit of a conventional inter-vehicle distance detecting device disclosed in Japanese Patent Publication No. In the figure, reference numeral 1 is a pulse generator for generating a transmission pulse signal, and 2 is a light transmitter for transmitting a pulsed light signal to the front, which is composed of a light emitting element such as a laser diode, its driving circuit and a lens system. Has been done. 3 receives the reflected pulse light signal from the irradiated front obstacle,
And a photodetector that photoelectrically converts and outputs the received pulse signal,
For example, it is composed of a light receiving element such as a photo diode and a lens system. Reference numeral 4 is a wide band amplifier having a bandwidth determined by the pulse width of the pulsed optical signal, 5 is a sampling processor composed of a sweeper 6, a sample pulse generator 7, a sample hold device 8 and a low frequency amplifier 9. The signal level of the received pulse signal, which is a high frequency signal, is sampled and held in order from the signal level at a point corresponding to a distance of 0 m and converted into a low frequency signal. Reference numeral 10 is a signal processor, which is a level determiner 1
1, a counter 12, a reference clock generator 13, and a microcomputer 14, and performs level determination for each signal level converted into a low frequency signal by the sampling processor 5 to obtain distance information such as a distance to an obstacle. To detect.

Next, the operation of the inter-vehicle distance detecting device will be described. The light transmitter 2 converts the transmission pulse signal into a pulse light signal and transmits the light forward. The light receiver 3 receives the reflected pulsed light signal having a propagation delay time T corresponding to the round-trip time to the obstacle in front of which the pulsed light signal is irradiated, and photoelectrically converts it to output a received pulse signal. The broadband amplifier 4 amplifies the received pulse signal. The sweeper 6 generates a sample timing signal and a sample start signal, and first generates and outputs a sample start signal when sample-holding the signal level at a point corresponding to the distance of 0 m of the received pulse signal. The delay time from the input of the transmission pulse signal to the generation and output of the sample timing signal is increased by a constant time T1 each time the transmission pulse signal is input, and corresponds to a distance of 0 m. An operation is performed such that a period corresponding to the maximum detection distance from time, for example, a range of about 667 ns when the maximum detection distance is 100 m, is periodically and repeatedly swept for each low frequency distance measurement cycle.

The sample pulse generator 7 inputs a sample timing signal and generates and outputs a sample pulse signal. The sample and hold device 8 samples and holds the signal level at one point of the received pulse signal amplified by the wide band amplifier 4 based on the delay time of the sample pulse signal and converts it into a low frequency signal. The low frequency amplifier 9 has a narrow band high gain and amplifies the signal level converted into the low frequency signal.
The level determiner 11 compares the signal level amplified by the low-frequency amplifier 9 with a predetermined level to determine whether the signal is a reflected pulsed light signal from an obstacle ahead and outputs a detection signal. The counter 12 counts the reference clock signal from the reference clock generator 13, and starts counting with a sample start signal and ends counting with a detection signal. The last microcomputer 14 uses the count value N of the counter 12 to obtain the propagation delay time T corresponding to the round trip time to the obstacle ahead by the equation 1, and calculates the distance R to the obstacle ahead by the equation 2. To do.

T = N × T1 (1) R = C × T / 2 (2) Here, the unit of the distance R is [m] and the unit of the propagation delay time T is [s]. C is the speed of light, and its unit is [m / s].

[0006]

Since the conventional inter-vehicle distance detecting device is constructed as described above, the falling slope of the signal waveform of the received pulse signal changes every time the magnitude of the reflected pulse optical signal changes. Differently (the falling point of the signal waveform is stable), the point where the predetermined level and the signal waveform intersect is deviated. As a result, there is a problem that the distance error of the detected distance information increases.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an inter-vehicle distance detecting device capable of reducing a distance error due to a change in the magnitude of a reflected pulse light signal.

[0008]

An inter-vehicle distance detecting device according to the present invention receives a pulsed optical signal from a light transmitter for transmitting a pulsed optical signal and a reflected pulsed optical signal from an obstacle irradiated with the pulsed optical signal, Also, a photodetector that photoelectrically converts and outputs the received pulse signal, and a delay time from the sending of the pulsed light signal to the generation of the sample pulse signal at a constant cycle, and every time the pulsed light signal is sent. A sample pulse generator that controls to increase by a fixed time, a sample and hold device that samples and holds the signal level of one point of the received pulse signal by the sample pulse signal, and the number of times the pulsed optical signal is sent out and the sampled and held signal level is read And then
It is provided with a microcomputer which operates to calculate the distance information to the obstacle by obtaining the falling points of the received pulse signals from the signal levels of several points and the number of times of transmission corresponding thereto.

[0009]

In the inter-vehicle distance detecting device configured as described above, the received pulse signal is converted into the low frequency signal by the sample pulse swept in time, and the sampled and held signal level and the sample timing signal from the transmission pulse signal are converted. The microcomputer reads the number of times the transmission pulse signal is transmitted, which corresponds to the delay time until the occurrence of.
Then, based on the read signal levels of several points and the number of times of transmission corresponding thereto, the number of times of transmission corresponding to the falling point of the received pulse signal is calculated by software, and the distance information is detected from the number of times of transmission. That is, by sampling and holding the received pulse signal with the sample pulse swept in time, the microcomputer can read the number of times of sending the received pulse signal and the transmitted pulse signal converted into the low frequency signal. As a result, the information on the distance to the obstacle can be detected by finding the falling point of the received pulse signal by using an arbitrary number of signal levels and the number of times of transmission corresponding to the software.

[0010]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a circuit of an inter-vehicle distance detecting apparatus according to an embodiment of the present invention. In the figure, parts that are the same as or correspond to those of the conventional device are assigned the same reference numerals as in FIG. 7, and description thereof is omitted. In the figure, 1 is 10.24 kHz
A pulse generator for generating a transmission pulse signal of, a sweeper 6, a sample pulse generator 7, a sample hold device 8,
And the low-frequency amplifier 9 is a sampling processor, and the sweeper 6 generates a sample timing signal from the transmission pulse signal and outputs a sample timing signal every time the sweep pulse signal is input. Time width of T1
It is set to increase by (about 667 ps).
Reference numeral 14 is a microcomputer, which reads the number of times the pulsed optical signal is sent out and the sampled and held signal level, finds the falling point of the received pulse signal from the signal level at several points and the corresponding number of times sent to the obstacle. It operates to calculate the distance information of. 15 is an A / D converter, 1
Reference numeral 6 is a frequency divider that divides the transmission pulse signal by 1024 to generate a distance measurement cycle signal of 10 Hz.

Next, the operation of the inter-vehicle distance detecting device described above will be described. The light transmitter 2 converts the transmission pulse signal into a pulse light signal and transmits the light forward. The light receiver 3 receives the reflected pulsed light signal having a propagation delay time T corresponding to the round trip time to the obstacle ahead of which the pulsed light signal is emitted,
In addition, photoelectric conversion is performed and a reception pulse signal is output. The broadband amplifier 4 amplifies the received pulse signal output from the light receiver 3.

Next, the operation of the sampling processor 5 will be described. The sampling processor 5 is composed of a sweeper 6, a sample pulse generator 7, a sample hold device 8 and a low frequency amplifier 9. The sweeper 6 has a clear signal input
At L'level, the delay time from the input of the transmission pulse signal to the generation and output of the sample timing signal is cleared to zero. That is, it corresponds to a distance of 0 m. Also,'
At the time of H'level, each time the transmission pulse signal is input, the delay time is a time width T1 (about 667 ps) corresponding to a distance of 10 cm.
The sample timing signal is generated and output in increments. The sample pulse generator 7 inputs a sample timing signal, generates a sample pulse signal, and outputs it.
The sample and hold device 8 samples and holds the signal level at one point of the received pulse signal amplified by the wide band amplifier 4 based on the delay time of the sample pulse signal and converts it into a low frequency signal. The low frequency amplifier 9 has a narrow band high gain and amplifies the signal level converted into the low frequency signal.

Next, the operation of the signal processor 10 will be described. The signal processor 10 includes a microcomputer 14, A /
It is composed of a D converter 15 and a frequency divider 16. The A / D converter 15 A / D converts the signal level in synchronization with the sample timing signal. The frequency divider 16 sets the transmission pulse signal to 1
It is divided by 024 to generate a 10 Hz ranging cycle signal. The final microcomputer 14 will be described in detail later,
One distance measurement cycle is started in synchronization with the falling edge of one distance measurement cycle signal of 10 Hz, and the number of times the transmission pulse signal is transmitted and the signal level are read at every 10.24 kHz to detect and determine the obstacle. It operates to calculate the distance to.

Next, the operation of the microcomputer 14 will be described with reference to FIGS. First, the microcomputer 14 inputs the distance measurement cycle signal of 10 Hz output from the frequency divider 16 as shown in FIG. 2 and synchronizes one distance measurement cycle of 100 ms at the falling edge thereof. Then, about 50 ms in the first half of the distance measurement cycle signal is used as the distance measurement period of the maximum detection distance of 50 m, and the latter half is used as the data processing and transfer period.

FIG. 3 is a flowchart showing the details of this processing in the main routine. Step 3
In 1 (denoted as ST31 in the figure), the initial process of the inter-vehicle distance detection device and the interrupt process of the 10 Hz one-distance measurement cycle signal are permitted. In step 32, a synchronization flag, detected distance data R, and
The respective values of the detection flag, the second point extraction flag, and the transmission pulse signal transmission count N are set to zero. Step 33
Then, the clear signal is output to the sweeper 6 at the “L” level to initialize the delay time to zero. In step 34, the process waits until the synchronization flag is set by interrupt processing by the 10 Hz ranging cycle signal. In step 35, the sweeper 6
Then, the clear signal is output at the'H 'level to release the delay time from 0 and permit the interrupt processing at 10.24 kHz.

Further, in step 36, 10.24 kH
It waits until the distance up to the maximum detection distance of 50 m is measured by the interrupt processing of z. This is done by comparing the interrupt frequency 500 of 10.24 kHz and the transmission frequency N of the transmission pulse signal, which enters the distance measurement period of about 50 ms. to decide. Step 3
In 7, the interrupt processing of 10.24 kHz is prohibited. In step 38, if the detection flag is cleared by the 10.24 kHz interrupt processing, it is determined that no obstacle is detected, and the process proceeds to step 39 to set the detection distance data R to 0. If the detection flag is set, it is determined that an obstacle has been detected, and the process proceeds to step 40 to calculate the detected distance data R. Then, in step 41, the detected distance data R
Is output and the process proceeds to step 32 to process the next ranging cycle.

In FIG. 4, the vertical axis represents the signal level V (unit: [m
V]), and the horizontal axis represents the number of times N of transmission of the transmission pulse signal (unit is [bit]). As shown in the figure, signal levels V1 and V at three points on the signal waveform of the received pulse signal
2, V3 (the unit is [mV]) and the number of times of transmission N1, N2, N3 (the unit is [bit]) corresponding to them are extracted. Therefore, 10.24 kH in step 40 above.
In the interrupt processing of z, the number of times of transmission of the transmission pulse signal at the falling point of the reception pulse signal is obtained by the equation 3 using the above graph, and the detection distance data R is obtained by the equation 4.
Convert to.

[0018]

[Equation 1]

R = No × K (4)

Here, in the equation 3, Vav is an average value of signal levels at three points, the unit is [mV], and Nav is 3.
This is the average value of the number of times points are sent, and the unit is [bit]. Vo is a signal level at the falling point of the received pulse signal, which is the neutral potential of the low-frequency amplifier 9,
The unit is [mV]. Further, in Expression 4, K is a coefficient for converting the number of times of transmission into distance information, and its value is 10 [cm / bit].

Further, FIG. 5 shows the interrupt processing by the distance measurement cycle signal of 10 Hz.
Sets the synchronization flag to 1 in order to synchronize one distance measurement cycle with every interruption of one distance measurement cycle signal of 10 Hz, and in step 52, the neutral potential Vo of the low frequency amplifier 9 is read. When the sweeper 6 remains cleared to 0 by the 0 clear signal, there is no received pulse signal, that is, the low frequency amplifier 9
The neutral potential Vo of can be detected. After the interrupt processing is completed, the procedure returns to the main routine of normal processing.

FIG. 6 shows the 10.24 kHz interrupt processing. If the detection flag is cleared in step 61, it is determined that an obstacle has not been detected yet, and step 62 is executed to set the detection flag. If so, step 69 is executed assuming that an obstacle is detected. In step 62, the signal level V is A / D converted and read. In step 63, the signal level V is compared with a predetermined level, and if the signal level V is equal to or higher than the predetermined level, step 64 is performed, and if not, step 65 is performed. In step 64, the signal level V is recorded as V1 and the number of times N of transmission of the transmission pulse signal is recorded as N1 as the first point data on the signal waveform of the reception pulse signal.

Further, in step 65, the second point extraction flag is checked. If it is clear, the process proceeds to step 66, and if it is set, the process proceeds to step 67. In step 66, since the second point data on the signal waveform of the received pulse signal is recorded,
The signal level V is recorded as V2, and the number of times N of transmission of the transmission pulse signal is recorded as N2. Further, the second point extraction flag is set. In step 67, if the signal level V is V2 or higher, the process proceeds to step 69 so that the data at the third point on the signal waveform of the received pulse signal does not become the same as the data at the second point. If not, the process proceeds to step 68. In step 68, the signal level V for recording the third point data on the signal waveform of the received pulse signal
Is recorded as V3, and the number of transmission pulse signal transmissions N is N
Record as 3. Further, the detection flag is set.
In step 69, the number N of transmissions of the transmission pulse signal is incremented by one (increment), after which the interrupt process is terminated and the process returns to the main routine of the normal process.

As described above, according to this embodiment, the number of transmissions at the falling point of the signal waveform is calculated by using the signal levels at several points on the signal waveform of the reception pulse signal and the number of transmissions of the transmission pulse signal. Since the distance to the obstacle is detected from the number of times of transmission, the distance information is changed even if the falling slope of the signal waveform changes depending on the magnitude of the reflected pulse optical signal and the crossing point with the predetermined level changes. There is no effect on the error of. Therefore, there is an effect that an inter-vehicle distance detection device having a good detection distance characteristic can be obtained.

In the above embodiment, 10.24 kHz
Transmission pulse signal of 10Hz, distance measurement cycle signal of 10Hz,
The case where the distance measuring period is about 50 ms and the maximum detection distance is 50 m has been described, but the present invention is not limited to this.

Further, in the above embodiment, the case where the signal level of three points before and after the predetermined level and the number of times of transmission are used to obtain the falling point of the signal waveform of the received pulse signal has been described. Even if the falling point or the peak point is obtained by using the data of several points, the same effect as that of the above embodiment can be obtained.

Further, in the above embodiment, the case where the received pulse signal is detected in the minus direction with respect to the neutral of the low frequency amplifier 9 has been described, but the rising point of the signal waveform in the case of being detected in the plus direction is obtained. Even if it is a thing, the effect equivalent to the said Example is acquired.

[0028]

As described above, according to the present invention, a light transmitter for transmitting a pulsed light signal and a reflected pulsed light signal from an obstacle irradiated with the pulsed light signal are received and photoelectric conversion is performed. And output the received pulse signal, and the delay time from the sending of the pulsed light signal to the generation of the sample pulse signal at a fixed cycle and a fixed time each time the pulsed light signal is sent. A sample pulse generator that controls to increase, a sample and hold device that samples and holds the signal level of one point of the received pulse signal by the sample pulse signal, and the number of times the pulsed optical signal is sent out and the sampled and held signal level is read. A microcomputer that operates to calculate the distance information to the obstacle by obtaining the falling point of the received pulse signal from the signal level at several points and the number of times of transmission corresponding to it. Because a computer, even if the magnitude of the reflected pulsed light signal changes can prevent the influence of the error of the distance information, the effect of detection distance characteristic with good inter-vehicle distance detecting device is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit related to an inter-vehicle distance detecting device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing processing contents of one distance measurement cycle of the microcomputer according to the first embodiment.

FIG. 3 is a flowchart showing an operation of main routine processing of the microcomputer according to the first embodiment.

FIG. 4 is a graph relating to Example 1 and showing the relationship between the number of times a transmission pulse signal is transmitted and the signal level.

FIG. 5 illustrates a microcomputer 10 according to the first embodiment.
It is a flow chart which shows operation of Hz interruption processing.

FIG. 6 shows a microcomputer 1 according to the first embodiment.
It is a flowchart which shows operation | movement of a 0.24 kHz interruption process.

FIG. 7 is a block diagram showing a circuit relating to a conventional inter-vehicle distance detecting device.

[Explanation of symbols]

 2 Light transmitter 3 Light receiver 6 Sweeper 7 Sample pulse generator 8 Sample and hold device 14 Microcomputer

Claims (1)

[Claims] 1. A light transmitter for transmitting a pulsed light signal, and a light receiver for receiving a reflected pulsed light signal from an obstacle irradiated with the pulsed light signal and photoelectrically converting the received pulse signal to output a received pulse signal. And the delay time from transmitting the pulsed optical signal to the generation of the sample pulse signal at a constant cycle,
And a sample pulse generator that controls so as to increase by a constant time each time the pulsed light signal is transmitted, a sample hold device that samples and holds the signal level of one point of the received pulse signal by the sample pulse signal,
Distance information to the obstacle is obtained by reading the number of times the pulsed optical signal is sent out and the sampled and held signal level, and finding the falling point of the received pulse signal from the signal levels at the above-mentioned several points and the number of times of sending corresponding to it. And a microcomputer that operates to calculate the distance.