JPS606872A - Optical type ground speed measuring device - Google Patents

Abstract

PURPOSE:To eliminate malfunction caused by an output during a stop and improve precision by constituting a waveform shaping circuit so that the output of a sensor is passed only when an automobile run. CONSTITUTION:The output of the sensor 10 is supplied to the waveform shaping circuit 14 through an amplifier filter 12. This waveform shaping circuit 14 consists of a zero-cross detector 24, comparator 18, integrator 20, comparator 22, and AND gate 26. While the automobile stops, the AND gate 26 is closed and the output of the zero-cross detector 24 is not passed; when the automobile starts running and the input arrives continuously, the output of the zero-cross detector 24 is passed through the AND gate 26 for the first time.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an optical ground speed measuring device using a spatial filter.

Prior Art and Problems The ground speed of an automobile is generally measured by the number of rotations of the axle, but this method cannot be used when the tires slip or knob. If the tire slips or knobs, the car may lose controllability, which could lead to a major accident. Therefore, the ground speed is detected using another method, and this is compared with the axle speed, and the difference between the two is used to detect the slip and knob, and the vehicle is immediately driven. It is desirable to adjust the force or braking force to stop the C-slip and restore maneuverability. Generally speaking, when a slip occurs, the dry nozzle becomes agitated and is often unable to take appropriate treatment, so this type of device (especially an anti-slip gutter device) is important.

Ground speed measurement methods other than axle speed include optical methods that use spatial fill. As shown in FIG. 1, this has a configuration of a sensor, an amplifier filter, a waveform shaping circuit, and a display, and the sensor section includes a lens 28, a three-polar fence-like reticle, etc. as shown in FIG. The road surface 32 has various patterns (distribution of radiant radiance), and when viewed from above the vehicle, the appearance of the patterns differs depending on the speed. This type of ground speed measurement method makes use of the phenomenon of heating.
focuses the radiant glow of the road surface on the surface of the reticle 30,
The reticle (spatial filter) with one-dimensional narrow bandpass characteristics extracts specific spatial frequency components from the road surface radiance distribution. A time frequency fa proportional to the ground speed Vs is obtained as an output, expressed as Vs=2aKfoH/d. where H is the height from the road surface to the lens, d is the height from the lens to the reticle, 2a is the pinch of the shelf element of the reticle, and K is the proportionality constant.

The output waveform of the reticle (sensor) is determined by the narrow band pass characteristics of the spatial filter and the radiance distribution of the road surface, for example, as shown in Figure 2 (
What can be claimed is the frequency (
Ultimately, it is the vehicle speed) and the amplitude component is unnecessary, so
The waveform shaping circuit 14 shapes the waveform. Generally, a Schmitt 1-rigger (hysteresis comparator) is used for waveform shaping, but this causes pulse dropouts where the amplitude drops.

That is, the Schmitt trigger produces an H (high) level output when the amplitude of the input signal exceeds the upper trip point Vu, and the Schmitt trigger outputs an H (high) level output when the amplitude of the input signal exceeds the upper trip point Vu. When the voltage drops to below, it returns to the L (low) level, so it receives the input shown in Figure 2 (a) and produces the output shown in the same figure (Car E). This results in pulse loss as shown in the figure below.

Since the numerical value of the pulse 61 during a certain period indicates the vehicle speed, the speed will decrease during the certain period including part B, resulting in an error.

Furthermore, in an optical ground speed measuring device using a spatial filter, measurement errors may occur due to the influence of external light. For example, when a tree sways due to the wind and its shadow on the road sways, the sensor 10 produces an output, and the amplitude of this is the upper trip point)
- Even though the car is stopped, the waveform shaping circuit 14
A pulse is output and the vehicle speed may be displayed.

OBJECTS OF THE INVENTION The present invention aims to improve the above points and provide a speed measuring device which is free from malfunction and capable of highly accurate measurement.

Structure of the Invention The present invention provides an optical ground speed measuring device for a vehicle that includes a spatial filter and a waveform shaping circuit, and includes a zero-cross detector as the waveform shaping circuit, and a gate that prevents the output of the zero-cross detector from passing through when the vehicle is not stopped. The present invention is characterized in that it uses a circuit, which will be explained next with reference to examples.

Embodiment of the Invention FIG. 3 shows an embodiment of the invention, in which the same parts as in FIG. 1 are given the same reference numerals. As is clear from comparing both figures, in the present invention, instead of configuring the waveform shaping circuit 14 with a hysteresis comparator, this is replaced with a zero cross detector 24,
Comparator 18, integrator 20, comparator 22, Antoge-1・
It consists of 26 pieces.

Figure 4 shows a specific example of this, where A1-A3 are operational amplifiers whose output stages are open collectors, R1-R14 are resistors, and C1, C
2 is a capacitor, and DI-03 is a diode. D.I.
, D2. R1 and R2 are clamp circuits that connect the power supply V to resistor R1.
', the input voltage Vi is clamped near the voltage Va divided by R2. The operational amplifier AI receives such an input voltage Vi, and receives a voltage Vb (=Va) obtained by dividing the power supply V by resistors R3 and R4 at its reference input, and when Vi>Vb, [to ILz/l.

produces an output of These constitute the zero cross detector 24 as a whole, and as shown in FIG. 2 (C1), the input voltage generates a rectangular wave pulse having an 11 level in the positive part and an L level in the negative part.

With such a pulse, even if the amplitude of the input voltage falls within the hysteresis width V u -V 12, pulse dropout will not occur unlike in a hysteresis comparator, and as long as the input voltage changes from positive to negative, the square wave pulse will not be generated. occurs, and no measurement error occurs. However, in this case, as mentioned above, fluctuations in the shadow of a tree will cause an output, causing malfunctions. Comparator 1
8, the integrator 20 and the comparator 22 prevent this. In Figure 4, the integral N20 is the resistance RIO and the capacitor C2.
The comparator 18 consists of an operational amplifier A2 and a resistor R6~
R8 and comparator z2 are operational amplifier A3 and resistor R11~
It is composed of R14. Fluctuations in the shadow of a tree are intermittent and one-off events that are difficult to pass through the integrator. Therefore, if the amplitude is greater than a certain value through the comparator 18 in the first stage, and the integrated output is passed through the comparator 22 in the second stage if the amplitude is greater than a certain value, there will be no output if the fluctuation of the tree is the same (the comparator 22 will be L /1. (output), there is no output until the car starts running and the input is continuously input (comparator 22
(H level output). In this way, when the car is stopped, the AND gate 26 closes and does not allow the output of the zero-cross detector 24 to pass through, thereby preventing the above-mentioned malfunction.
Jl can be stopped.

In Fig. 4, the AND gate 26 is connected to the resistor R5 and the operational amplifier AI.
, A3, and if the outputs of the operational amplifiers AI and A3 are both + (then the output OUT is also Hl), if any or all of these amplifiers are L, the output also performs the logic of L. The display 16 counts the pulses output from the AND gate 26 and displays the counted value at regular intervals as the vehicle speed.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, it is possible to eliminate pulse dropout during waveform shaping, and it is possible to improve the measurement accuracy of an optical ground speed measuring device using a spatial filter. It also prevents malfunctions caused by ambient light.
It is seriously 9Jt.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the optical ground speed measuring device η, Figure 2 is a waveform diagram for explaining operation, Figures 3 and 4.
The figures are a block diagram and a circuit diagram showing an embodiment of the present invention, and FIG. 5 is an explanatory diagram showing the procedure for optical ground speed measurement. In the drawing, 10 is a sensor equipped with a spatial filter, 14 is a waveform shaping circuit, 24 is a zero cross detector, 18, 22 is a comparator, 20 is an integrator, and 26 is an AND gate. Applicant Fujitsu Ten Co., Ltd. Representative Patent Attorney Minoru Aoyagi Figure 3 14 Figure 5

Claims (1)

[Claims] (11) An optical ground speed measuring device for a motor vehicle equipped with a spatial filter and a waveform shaping circuit, which includes a zero-cross detector as the waveform shaping circuit, and an output of the zero-cross detector that passes through when the vehicle is not stopped. An optical ground speed measuring device characterized by using a gate circuit. (2) The gate circuit includes an integrator, a comparator connected to its input side and output side, the output side comparator and zero cross detection. 2. The optical ground speed measuring device according to claim 1, further comprising an AND gate that receives each output of the device as input.