JPH05223928A - Pulse radar - Google Patents

Abstract

PURPOSE:To improve distance measurement accuracy by a means for changing a threshold value and by calculating reception pulse rise time with a plurality of threshold values utilized. CONSTITUTION:Since threshold voltage input to a comparator COMP via a threshold changing means 5 is changed for every reception, the rise time of an output pulse of the COMP also changes for one pulse. In addition information on a reception level of a light receiver 2 is input to a microcomputer 3, and the threshold changing means 5 is controlled so that an appropriate threshold can be obtained according to the level. Thus a plurality of threshold values for each pulse input from the means 5 are set respectively at appropriate values according to their reception levels. Thus, based on output pulses from a flipflop 6 by a plurality of comparator outputs which have been detected sequentially at different thresholds for each of the reception, the rise time of the received pulse is determined by the microcomputer 3, and a distance to a target can be calculated based on the time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse radar, and more particularly to a pulse radar which detects a time interval between a transmission pulse and a reception pulse reflected by a target and calculates a distance to the target. Pulses of laser light, radio waves (microwave, millimeter wave, etc.), ultrasonic waves, etc. are used as these transmission / reception pulses.

[0002]

2. Description of the Related Art Generally, in the above-mentioned pulse radar, as shown in FIG. 5, a pulse (for example, a laser pulse) transmitted from a radar sensor is reflected by a target object and received again by the radar sensor. By detecting the time T up to the target with the radar sensor, the distance from the radar vehicle equipped with the radar sensor to the target (for example, the preceding vehicle) is calculated.

However, in this case, since the reception level of the reception pulse varies depending on the type and state of the target, an error occurs in detecting the rising time of the reception pulse, which causes an error in the distance accuracy. That is, conventionally, as shown in FIG. 6, the rising edge of the received pulse is detected with a constant threshold value. Therefore, when the received level of the received pulse is high, the time interval with the transmitted pulse is detected as T _1. On the other hand, when the reception level is small, the time interval with the transmission pulse is detected as T ₂ , which causes an error in detecting the rising time of the reception pulse (reception time of the reception pulse). ..

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the rising time of the received pulse (see FIG. 6 above) is irrespective of the received level of the received pulse.
By accurately detecting the point A), the measurement accuracy error (distance accuracy error) caused by the level fluctuation of the received pulse is reduced.

[0005]

According to the present invention, in order to solve such a problem, the distance to a target is calculated by detecting the time from the transmission of a transmission pulse to the reception of a reception pulse. And a means for changing a threshold value for detecting the rising edge of the received pulse, wherein the received pulse of the received pulse is changed based on a plurality of threshold values set by the threshold value changing means. There is provided a pulse radar characterized in that a rising time is calculated.

In changing the threshold value, the threshold value may be changed a plurality of times each time a received pulse is received (that is, every pulse) (that is, as shown in FIG. 3). A plurality of received waves are used to detect the rising time, and the rising times are detected on the assumption that the levels of the plurality of received waves are substantially constant during that time), or a plurality of threshold changing means are provided. It is also possible to set a plurality of threshold values for one reception wave at the same time and detect the rising time thereof.

[0007]

According to the above configuration, as shown in FIG. 4, the threshold value for the received pulse is changed to a plurality of values as shown in, for example, and the threshold value and the received pulse are Of a plurality of intersection points of the received pulse, and based on these intersection points, the rising point (rising time) A of the received pulse
Can be accurately obtained (as shown in the following embodiments, for example, a microcomputer is used for calculation).

The approximation of the waveform of the received wave based on the plurality of intersections can be performed by quadratic or linear approximation. For example, in the case of linear approximation, the threshold value is set to 2 It is also possible to set two values and perform linear approximation based on two intersections with the received pulse. The range in which the threshold value is changed may be increased or decreased according to the reception level of the reception pulse.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a pulse radar (for example, a laser radar) as one embodiment of the present invention, which is shown in FIG. 3 from the light emitter 1 at predetermined time intervals controlled by a microcomputer 3. Such a transmission wave (pulse of laser light) is transmitted, the transmission wave is reflected by the target, and
The received light is received by the photodetector 2 as a received wave as shown in, and the received pulse corresponding to the received wave is input to one side input terminal of the comparator COMP. In addition, the comparator CO
A predetermined threshold voltage is input to the other input terminal of MP via the threshold changing means 5, and thereby the rising time of the output pulse output from the comparator COMP is determined.

Here, the threshold voltage input to the comparator COMP through the threshold changing means 5 changes every time a received wave is received (that is, every pulse) as shown in FIG. Therefore, the rising time of the output pulse output from the comparator COMP also changes for each pulse. Further, the light receiving device 2 is provided to the microcomputer 3 via the reception level detecting means 4.
Since the information on the reception level of the reception wave received at is input, the microcomputer 3 operates the threshold changing means 5 so that the range for changing the threshold voltage is an appropriate range according to the reception level. Can be controlled so that the comparator CO can be controlled by the threshold changing means 5.
The threshold value (a plurality of threshold values) for each pulse input to the MP is set to an appropriate voltage value according to the reception level.

Next, the transmission pulse corresponding to the transmission wave transmitted from the light emitter 1 and the output pulse of the comparator COMP based on the reception wave generated by the transmission wave reflected by the target are respectively output from the flip-flop 6. By being input as the set and reset inputs, a pulse corresponding to the time difference between the transmission wave being transmitted from the output side of the flip-flop 6 and the rising of the output pulse of the comparator COMP is received by the reception wave. It is output every time it is done. The pulse width of the output pulse from the flip-flop is adjusted by the multiplier 7
It is input to the microcomputer 3 after being multiplied by the time width that can be counted by. In this way, each time the received wave is received, the microcomputer 3 detects the output pulse from the flip-flop generated by the plurality of comparator outputs detected at different thresholds. The rising time A of the received pulse is determined as described in FIG. 4, and the distance to the target is calculated based on this.

In the embodiment shown in FIG. 1, the threshold value is changed every time a received wave is received (that is, a plurality of received waves are used, as shown in FIG. 3). Then, the threshold value is changed at a predetermined time interval), but instead, for example, as shown in FIG.
A plurality of sets of the comparators, threshold changing means, flip-flops, multipliers, etc. are provided according to the number of thresholds, and the thresholds input from the threshold changing means to the corresponding comparators are set to mutually different values. Thus, the rising time of the output pulse of each comparator with respect to each threshold value is simultaneously detected by one received wave, and the output of each corresponding flip-flop is input to the microcomputer side through the multiplier. You may do it. Further, the number of the thresholds can be set as appropriate. For example, when the rising time A is obtained by linear approximation as described above, two values may be set as the thresholds. Good.

[0013]

According to the present invention, the rise time can be accurately determined even if the reception level of the received wave fluctuates, so that the accuracy of the distance data to the target can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a pulse radar as one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a pulse radar as another embodiment of the present invention.

FIG. 3 is a timing diagram showing a situation in which the threshold value for a received wave is changed in the device shown in FIG.

FIG. 4 is a diagram showing that a rising time A is obtained by changing a threshold value for a received wave.

FIG. 5 is a diagram illustrating a general operation of a pulse radar.

FIG. 6 is a diagram illustrating a situation in which the rising time of a received pulse varies depending on the reception level of the received pulse.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light emitting device 2 ... Light receiving device 3 ... Microcomputer 4 ... Reception level detecting means 5, 51, 52 ... Threshold changing means 6, 61, 62 ... Flip-flop 7, 71, 72 ... Multiplier COMP, COMP1, COMP2 ... Comparator

Claims (4)

[Claims] 1. A pulse radar in which the distance to a target is calculated by detecting the time from the transmission of a transmission pulse to the reception of a reception pulse, for detecting the rising edge of the reception pulse. Pulse radar, wherein the rising time of the received pulse is calculated based on a plurality of threshold values set by the threshold value changing means. 2. The pulse radar according to claim 1, wherein the threshold value is changed every time a received pulse is received. 3. A plurality of threshold value changing means are provided, 1
The pulse radar according to claim 1, wherein a plurality of threshold values are set at the same time for one received pulse and the rising time is calculated. 4. The pulse radar according to claim 1, further comprising reception level detection means for the reception pulse, wherein a range in which the threshold value is changed is variable according to the detected reception level. ..