JPS5839312B2 - Vehicle speed measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle speed measuring method that uses Doppler radar to measure the presence of a vehicle and its speed, and an object of the present invention is to accurately measure the speed of a vehicle.

A Doppler radar for vehicle detection can extract a vehicle presence signal as an output by monitoring the amplitude of the Doppler signal.

On the other hand, by measuring the frequency or period of the Doppler signal, the speed of the vehicle can also be extracted as an output.

However, in order to increase the resolution of vehicle identification for vehicle detection, it is necessary to limit the sensing area of the radar to as small as possible, which inevitably limits the sensing area to the road surface near the antenna.

As a result, the vector connecting the vehicle traveling direction vector and the antenna vehicle is the observed speed when it is assumed that the angle rapidly increases as the vehicle approaches, and the vehicle is originally traveling straight toward the sensor, and the actual observation speed. Since the difference in speed also increases rapidly, correction by angle becomes difficult.

In addition, since a small sensing area is formed in this way, the Doppler waves in the sensing area inevitably have more reflected wave components from the top or side of the vehicle than from the reflected waves from the front of the vehicle as the vehicle approaches. As a result, the waveform and phase disturbances become larger.

Therefore, if you want to increase the accuracy of vehicle speed measurement, it is better to measure it at a distance where the observation angle is as close to constant as possible, but setting the speed measurement point far in front of the exterior of the vehicle sensing area is not possible with the same sensor. It's impossible.

In order to determine the presence of a vehicle, it must be confirmed that Doppler waves of a certain amplitude level or higher are continuously incident for a certain period of time, and no matter what judgment method is used, this is true. It doesn't change.

However, during this time, even if the amplitude level is insufficient, a Doppler wave with a sufficient S/N ratio is being received, so there is no problem in speed measurement.

Therefore, speed measurement is always performed every time a Doppler signal with a certain amplitude level or more is received, and the measured value is updated every time a new measurement is made. When it is determined that a vehicle has entered the detection area of the radar based on continuous reception and a presence signal is raised, the latest speed measurement value measured immediately before that is determined as the speed of the vehicle corresponding to this presence signal. This method provides a more reliable speed measurement.

By doing so, it is possible to always measure the speed at the leading edge or outside of the sensing area as the vehicle approaches.

For example, even if the received Doppler wave is ideally clean, if the speed is measured after the presence signal rises, the observed value will change significantly as the vehicle approaches. Considering that measurement accuracy decreases with acceleration, the benefits are extremely large.

According to the method of the present invention, the accuracy of vehicle speed measurement is much greater than the conventional method of repeating speed measurements multiple times in a sensing area and displaying the largest value. Become.

An embodiment of the present invention will be described below.

In the drawing, 1 is an amplification circuit that amplifies the Doppler signal detected by a microwave radar, etc., 2 is a peak hold circuit that holds the peak value of each wave of the Doppler signal, and 3 is a circuit whose amplitude is above a certain level. 4 is a D-type flip-flop circuit that inverts the output of the comparison circuit 3 between gl 14441 and Q 41 in accordance with the rising and falling timing of the Doppler signal.
It creates 11 values.

Reference numeral 5 denotes a vehicle presence determination circuit which raises a presence signal S2 if the human power situation of the Doppler signal satisfies certain conditions.

6 is a Doppler signal shaping circuit which generates a signal S2 such that the Doppler signal inverts between the two values of 6(1↓■(Q ha) with the center level as the boundary.

7 is a gate circuit that allows the S1 signal to pass only when there is a Q11 value.

8 is a counter circuit which uses the S1 signal passed through the gate circuit T as a clock, and when a predetermined number of N is counted, a QN signal is outputted at the rising edge of the tarok.

9 is an inverter, and 10 is an AND gate of Sl and QN.

Reference numeral 11 is a differentiation circuit that differentiates the rise of the output of the AND gate 10 to produce a pulse, and reference numeral 12 is a circuit that applies a slight delay to the output of the differentiation circuit 11 within a range that does not affect other logics.

13 is a counter circuit which counts clocks having a frequency sufficiently higher than the Doppler frequency when 81'=1.

14 is a gate circuit for sending a clock CL to the counter circuit 13 only when 81'=1.

15 is a register circuit for storing the counted value of the counter 13, and 16 is an arithmetic circuit for calculating the speed based on the value of the register 15.

17 is an inverter circuit for creating 82 signals, 1
Reference numeral 8 denotes an inhibit gate for stopping data rewriting of the register 15 in the state 52-1, and stops the rewriting signal from the differentiating circuit 11.

In the frame in the figure, CL indicates a clock input, R8 indicates a reset signal input, PS indicates a data write instruction terminal, J and D indicate a data terminal, and Q indicates a data output terminal.

Next, the operation based on this configuration will be explained.

The peak value of the Doppler signal that has passed through the amplification circuit 1 is held in the peak hold circuit 2, and the output is held constant at a predetermined level. signal is given.

Then, the clock input of the D-type flip-flop circuit 4 is inputted by the shaping circuit 6 to g(l kk ((Q 412 value signal S
The Doppler signal converted to 1 is added, and the Q1 output determines the level of the Doppler signal in synchronization with 81 with a delay of approximately one cycle.

Incidentally, the peak hold circuit 2 is actually not necessary when performing such a binary determination, but is used for convenience of explanation.

In the apparatus of this embodiment, the speed is determined by the reciprocal of the time obtained by measuring and adding the period at 1 to S for N Doppler waves incident at a certain level or higher.

As is well known, once the installation position of the radar sensor is determined, the distance traveled by the vehicle at a certain position on the road surface is proportional to the Doppler wave number, regardless of the vehicle speed, and the period of a certain number of Doppler waves is proportional to the reciprocal of the vehicle traveling speed. It is.

Therefore, since 81 is a sufficiently amplified and shaped Doppler human power, it is assumed that it can be obtained as a binary signal regardless of the Doppler human power level, and it passes through gate 7 only when Q□ = 1. 8 clock input as 81'.

In addition, Sl controls the clock signal CL applied to the human power of the period measurement counter 13 with the gate 14.
The clock CL is added only when 1'=1.

When the count of counter 8 reaches a predetermined number N, output Q
A level signal appears at N for a period of one clock.

81' becomes 81' in the inverter 9, and is combined with QN in the gate 10 to produce an output at the latter half of QN''1, and output a differentiated pulse through the differentiating circuit 11 at its leading edge.

The differential pulse S2, which is the output of the inverter 17, instructs the register 15 to rewrite only when the value is ((In).

S1 for Doppler waves above a certain level
Only when '=1, the count output of the counter 13 which adds and counts the clocks CL for N clocks is transferred to the register 15 at this time.

Since this transfer is performed immediately after the number becomes 51-0, both counter 8 and counter 13 remain in the same state until S becomes 1 again.

Therefore, during this time, the delay circuit 12 is used to add a slight delay to the rewrite signal and send the reset signal to both counters 8 and 1.
Please send it to 3.

This means that both counters 8 and 13 have finished preparing for new measurement.

When the presence determination circuit 5 finally determines that the vehicle has entered, the presence signal S2 rises, thereby stopping the rewriting of the register 15. At the same time, the arithmetic circuit 16 executes the calculation based on the calculation instruction from the output of the register 15. It will perform calculations and output speed output.

In this embodiment, the period of the Doppler wave is repeatedly measured until the presence signal S2 is outputted, but if sufficient measures have been taken against noise or signal contamination from non-target lanes, The measured period may be stored until the presence signal S2 is generated.

When the presence signal S2 becomes O, the period measurement described above is restarted after the Doppler signal is input again, and the final output of the arithmetic circuit 16 is reset by setting another condition.

In the above embodiments, the speed is measured by calculating the speed from the reciprocal of the time that a certain wave number of the Doppler signal is manually operated, but the speed measurement is performed by calculating the speed by counting Doppler waves with a certain amplitude or more within a certain time. The principles of the present invention can also be applied when using a method of measuring speed.

By doing so, the speed measurement position can be set at a position outside the presence sensing area and closest to the sensing area.

If we closely observe the Doppler signal caused by the reflected wave from the vehicle, we can see that in the sensing area with the largest envelope amplitude, we can obtain the cleanest sinusoidal waveform with a fixed rise time of a series of Doppler signals, and we can also see that the period or frequency changes. Since there is less of a presence sensing area, more accurate speed measurements are easily obtained by applying the principles of the present invention by setting the speed measurement position outside the presence sensing area and closest to the sensing area.

In particular, when one radar sensor is used for both presence detection and speed measurement, the angle between the vehicle's travel vector and the radar antenna's directional vector cannot be made small in order to keep the sensing area small, so the Doppler signal waveform tends to be distorted. Therefore, the effect of adopting the above method is extremely large.

[Brief explanation of the drawing]

The drawing is a block diagram showing a vehicle speed measurement method according to an embodiment of the present invention. 3... Comparison circuit, 4... Flip-flop, 5... Existence determination circuit, 6... Shaping circuit, 8... Counter, 13...
Counter 15...Register 16...
...Arithmetic circuit.

Claims (1)

[Claims] 1 It is detected that the amplitude of the received Doppler signal has reached a certain value or more, and each time it reaches a certain value or more, the speed is measured based on the period or frequency of the Doppler signal, and the When it is detected that a Doppler signal with a certain amplitude continues for a certain number of waves or a certain period of time, and the presence of a vehicle is determined and a presence signal is raised, the measured speed immediately before the presence signal is raised is used as the speed information for the presence signal. A vehicle speed measuring method characterized by outputting.