A vehicle speed testing method and device based on optics

Abstract

A vehicle speed test method and device based on optics, belonging to the field of automobile parameter testing. The vehicle speed test method and device include: black and white marking tapes of different lengths Lx (x is 0 or 1), used for reflecting and forming light intensity signals with large differences; a photoelectric sensor, used for generating stable light and sensing the change in light intensity of the light returned by the marking tape; and judging the black and white state of the light intensity signal in the form of a level digital signal; a signal acquisition processor, used for collecting the change process of the digital signal, and recording the change time, and calculating the vehicle speed according to the length corresponding to the marking tape and the time difference of the digital signal change; judging the change direction of the vehicle speed according to the corresponding color code length and the speed estimation trend.

Description

Technical Field

[0001] The invention belongs to automobile measurement technology and relates to an automobile speed testing device and method. Background Art

[0002] The traditional way to obtain the vehicle speed while the car is driving is through the speedometer inside the car. The calculation principle is that the rolling of the wheels drives the movement of the car, and the speed sensor is used to measure the product of the tire speed and the wheel radius to represent the vehicle speed.

[0003] When encountering special scenarios such as accumulated water or icy roads, the road friction coefficient becomes smaller, the wheels produce sliding friction, and the product of the rotation speed and the wheel radius is not equal to the vehicle speed. At this time, the vehicle speed on the dial is not accurate.

[0004] Accurate testing of vehicle speed on special roads helps analyze the vehicle's motion state and the specific analysis of the road friction coefficient, which has safety value and practical research significance. Summary of the invention

[0005] According to the above vehicle speed measurement requirements, the present invention proposes an optical-based vehicle speed testing method and device.

[0006] The vehicle speed test device includes: determining the length L x A black and white (x is 0 or 1) marking photoelectric sensor, comprising a light source generating device, a light receiver and a signal converter; and a signal acquisition and processing device.

[0007] The black and white marking tapes return light of different intensities when exposed to light, generating light intensity signals with large differences. The black and white marking tapes have two lengths, and the length of the long marking tape L1 is stipulated to be at least 5 times the length of the short marking tape L0. The typical recommended length-to-short ratio is 10, i.e., L1=10L0. The laying rule is black and white, and each black (white) mark is adjacent to two white (black) marks of different lengths.

[0008] The light source generating device is used to generate a stable light source, and the light receiver generates an induction pulse at a higher frequency; the intensity change of the induction received light is used to determine the time of the light intensity change;

[0009] The signal converter converts the light intensity signal into a level digital signal. When the light intensity of the black mark band is small, it is converted into a low-level digital signal, recorded as 0. When the light intensity of the white mark band is large, it is converted into a high-level digital signal, recorded as 1. The signal acquisition and processing device is used to collect the change process of the level digital signal and record the moment of signal change.

[0010] The specific steps of the vehicle speed test method are as follows: when the vehicle is moving, the sensor scans the black and white marking tape, and after the level digital changes twice, the time of the two changes (t0 and t1) is recorded, and the time of the two changes (t0 and t1) is recorded. According to the known length L of the marking tape x The speed (v1) at time t1 is obtained by taking the time difference of the digital signal change as the quotient. The formula is as follows:

[0011]

[0012] Where L x To set the length of the marking tape, t0 and t1 are the level change moments. The principle of calculating the level change interval time is the product of the number of induction pulses n between two level changes and the induction pulse period T. In actual calculation, the induction pulse period is set and the number of pulses within the level change time is recorded.

[0013] The specific steps of the speed direction judgment method based on optics are as follows: when the next level digital changes (t2), the number of induction pulses n2 is recorded by the above formula to calculate the movement speed (v2) at the moment t2;

[0014] According to the speed calculation formula, when the next level digital changes (t3), the number of induction pulses n3 is recorded to calculate the movement speed (v3) at t3;

[0015] The speed change trend fitting curve is made based on the three known speeds v1v2v3 to obtain the predicted speed (v 4预 ), and according to the vehicle dynamic parameters and speed change law, determine the reasonable numerical range of the predicted speed, such as [0.5v 4预 ,1.5v 4预 ];

[0016] At the next digital level change moment (t4), the number of induction pulses n4 is recorded by the above formula to calculate the movement speed (v4) at the moment t4;

[0017] Determine whether the speed at time t4 (v4) is within the predicted speed range [0.5v 4预 ,1.5v 4预 ], if it is within the predicted speed range, the vehicle speed direction remains unchanged, otherwise the speed direction is opposite.

[0018] Continue to calculate the next moment, the speed v5 at time t5, and calculate the predicted speed (v5) at time (t5) based on v2, v3, and v4 5预 ), and reasonable change range, continue to judge, and continue to calculate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a structural block diagram of the vehicle speed measurement device.

[0020] Among them, 1 is a black and white marking tape; 2 is a photoelectric sensor, including 3 a light source generating device, 4 a light receiver and 5 a signal converter; 6 is a connecting cable; and 7 is a signal acquisition and processing device.

[0021] Figure 2 A schematic diagram of state changes.

[0022] A is a diagram showing the length and setting method of the black and white marking tape, as well as the time record; B corresponds to a schematic diagram of the level status at different times, and n1 to n8 are the number of induction pulses recorded each time the level changes, which are used to accurately calculate the time difference between two level digital signal changes;

[0023] Figure 3 The figure is a schematic diagram of the three-point speed fitting curve. The points represent the speed points predicted by the fitting curve, and the black dashed line range represents the reasonable change range of the speed prediction. C indicates that the actual movement speed (v4) at time t4 falls within the predicted speed range, and the speed direction is the same; D indicates that the actual movement speed (v4) at time t4 falls outside the predicted speed range, and the speed direction is opposite.

[0024] Figure 4 Flowchart of vehicle speed calculation and speed direction judgment method DETAILED DESCRIPTION

[0025] The present invention proposes an optical-based vehicle speed testing method and device, and the specific implementation method is as follows, referring to the above schematic diagram.

[0026] Install photoelectric sensors on the side of the vehicle; connect the signal acquisition and processing device to a computer in the vehicle and connect it to the photoelectric sensor via a cable; Figure 2 Arrangement A is laid directly below the photoelectric sensor probe;

[0027] Start the test, the sensor scans the black and white marking tape, after the first level digital change, the pulse count is reset, after the second level digital change, the pulse number n1 is recorded, the time of the two changes (t0 and t1) is recorded, and the time of the two changes (t0 and t1) is recorded. According to the known length L of the marking tape x The speed at time t1 (v1) is obtained by taking the time difference of the digital signal change as the quotient.

[0028] The specific steps of the speed direction judgment method are as follows: when the next level digital changes (t2), the number of induction pulses n2 is recorded by the above formula to calculate the movement speed (v2) at the moment t2;

[0029] According to the speed calculation formula, when the next level digital changes (t3), the number of induction pulses n3 is recorded to calculate the movement speed (v3) at t3;

[0030] The speed change trend fitting curve is made based on the three known speeds v1v2v3 to obtain the predicted speed (v 4预 ), and according to the vehicle dynamic parameters and speed change law, the reasonable value range of the predicted speed is determined to be [0.5v 4预 ,1.5v 4预 ];

[0031] At the next digital level change moment (t4), the number of induction pulses n4 is recorded by the above formula to calculate the movement speed (v4) at the moment t4;

[0032] Determine whether the speed at time t4 (v4) is within the predicted speed range [0.5v 4预 ,1.5v 4预 ], if it is within the predicted speed range, the vehicle speed direction remains unchanged, otherwise the speed direction is opposite;

[0033] Continue to loop the calculation until it ends. Figure 4 The judgment method flow chart is shown.

[0034] In the following actual calculation case, the minimum cycle of the photoelectric sensor is selected as T = 0.02ms, L x The required length of the black and white marking tape (x is 0 or 1) is L1=10L0, and the actual setting is L1=10cm, L0=1cm.

[0035] Start the test, the photoelectric sensor starts to respond, and the vehicle Figure 2 When the direction moves from left to right, the sensor scans the black and white marking tape, and the level changes generated are as follows: Figure 2 As shown in B.

[0036] After the level digital changes twice, the entire short black mark tape is scanned, and the times of the two changes (t0 and t1) are recorded as 1.00ms and 2.00ms respectively. The number of induced pulses n1=50 is counted, and the speed v1=10m / s at the moment t1 is calculated.

[0037] At the next digital level change time t2 = 2.80ms, the number of induction pulses n2 = 40 is counted, and the speed v2 = 12.5m / s at time t2 is calculated.

[0038] At the next digital level change time t3 = 8.80ms, the number of induction pulses n3 = 300 is counted, and the speed v3 = 16.67m / s at time t3 is calculated.

[0039] The speed change trend fitting curve is made from the three known speeds v1v2v3 to obtain the predicted speed v at the next level digital change time (t4).4预 =21.50m / s, and according to the vehicle dynamic parameters and speed change law, the reasonable change range of the predicted speed is determined to be [10.75,32.25];

[0040] When the next digital level changes at t4=12.8ms, the number of induced pulses n4=200 is counted, and the speed v4=25.00m / s is calculated. Within the predicted speed change range, the speed direction at t4 is judged to be the same as that at the previous moment. If the next digital level changes at t4=20.8ms, the number of induced pulses n4=600 is counted, and the speed v4=8.33m / s is calculated. Outside the predicted speed change range, the speed direction at t4 is judged to be the same as that at the previous moment.

Claims

1. A vehicle speed test method based on optical brightness change, characterized in that: The device used in the method includes: Marking tape; the marking tape has two kinds of marks, black and white, which return light of different intensities when exposed to light, generating light intensity signals with large differences; the marking tape has two lengths of black and white marks, and it is stipulated that the length of the long marking tape L1 is at least 5 times the length of the short marking tape L0, so the marking tape will include four kinds of marks: black long, black short, white long, and white short, and the laying rule is black and white, and each black mark is adjacent to two white marks of different lengths; each white mark is adjacent to two black marks of different lengths; Photoelectric sensor; including a light source generating device, a light receiver and a signal converter, wherein the light source generating device is used to generate a stable light source; the light receiver generates a sensing pulse at a relatively high frequency, and senses the change in the intensity of the received light to determine the time of the light intensity change; the signal converter converts the light intensity signal into a level digital signal, and converts the light intensity of the received black mark band into a low-level digital signal, which is recorded as 0, and converts the light intensity of the received white mark band into a high-level digital signal, which is recorded as 1; A signal acquisition and processing device; used to acquire the change process of the level digital signal and record the moment of signal change; The method is as follows: when the vehicle is moving, the sensor scans the black and white marking tape, and after the level digital changes twice, the time t0 and t1 of the two changes are recorded. x The speed v1 at time t1 is obtained by taking the time difference of the digital signal change as the quotient. The formula is as follows: Where L x To set the length of the mark tape, t0 and t1 are the recorded level change moments; the level change interval time calculation principle is the product of the number of induction pulses n1 between two level changes and the induction pulse period T. The recording accuracy depends on the light intensity induction frequency of the photoelectric sensor, which is determined by the physical characteristics of the photoelectric sensor; At the next digital level change time t2, the number of induction pulses n2 is recorded by the above formula to calculate the movement speed V2 at time t2; At the next digital level change time t3, record the number of induction pulses n3 and calculate the movement speed v3 at time t3; The speed change trend fitting curve is made from the three known speeds v1v2v3 to obtain the predicted speed v at the next level digital change time t4. 4预 , and according to the vehicle dynamic parameters and speed change law, determine the reasonable numerical range of the predicted speed [0.5v 4预 , 1.5v 4预 ]; At the next digital level change time t4, the number of induction pulses n4 is recorded by the above formula to calculate the movement speed v4 at time t4; Determine whether the speed v4 at time t4 is within the predicted speed range [0.5v 4预 , 1.5v 4预 ], if it is within the predicted speed range, the vehicle speed direction remains unchanged, otherwise the speed direction is opposite; Continue to calculate the next moment, the speed v5 at moment t5, and calculate the predicted speed v at moment t5 based on v2, v3, and v4 5预 , and reasonable change range, continue to judge, and continue to calculate.

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