Distance measuring device for a vehicle

Details Distance measuring device for a vehicle Distance measuring device for a vehicle

2001-10-19

2003-11-18

Buczinski, Stephen C. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

With photodetection

C356S005080, C180S169000, C327S031000

Reexamination Certificate

active

06650403

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical distance measuring device which illuminates an object with a pulsed light beam, receives part of a retroreflection light beam reflected and returned from the object, and measures the delay time to detect the distance to the object and the direction thereof, and more particularly to a device which is to be mounted on an automobile to monitor the periphery of the automobile, and which is to be applied to an obstacle warning device or a cruise controlling device for a vehicle.
2. Description of the Related Art
Conventionally, a device which measures the time period between emission of a pulsed light beam and reception of a light beam reflected from an object, to determine the distance to the object has been used in various fields. Among optical distance measuring devices of this kind, a periphery monitoring device which is to be mounted on a vehicle is used in a larger number. Such a device is used mainly in a vehicle gap controlling device, as a sensor which measures the distance to a preceding vehicle.
An example of a conventional device which measures a distance by such a method will be described with reference to JP-A-8-122437.
FIG. 10
is a diagram of the conventional art example. The reference numeral
10
denotes light transmitting means which is configured by a light emitting element
11
, a light emission driver
12
, an illumination lens
13
, and scanning means
14
for scan-illuminating a transmitted light beam in a predetermined angular range. The reference numeral
20
denotes light receiving means for receiving a reflected pulsed light beam which is reflected and returned from an object. The light receiving means is configured by a photoelectric converting element
21
, an amplifier
22
which converts a photocurrent into a voltage, and a converging lens
23
for receiving light. The amplifier
22
is configured by an STC (Sensitivity Time Control) circuit
22
c
and a variable gain amplifier
22
d
. The reference numeral
30
c
denotes retroreflection time detecting means for detecting a retroreflection time of a reflected pulsed light beam which is reflected by the object and received by the light receiving means
20
. The retroreflection time detecting means is configured by comparing means
34
c
for comparing an output S
20
of the light receiving means
20
with a predetermined value VO, a peak hold circuit
35
c
which detects the peak value of the light reception signal S
20
, and a time measurement circuit
33
c
. The reference numeral
40
b
denotes a calculation unit which controls the illumination direction and timing of the transmitted light beam, and calculates the distance to the object, from an output of the light reception time detecting means
30
c.
Next, the operation of the device will be described with reference to FIG.
11
. The light transmitting means
10
illuminates a transmitted light beam in a predetermined direction on the basis of a signal from the calculation unit
40
b
.
FIG. 11
shows a case where it is assumed that an object QA is a vehicle which is running in front of the device, and an object QB is an article such as a signboard above a road. The light receiving means detects reflected pulsed light beams which are reflected by the objects QA and QB and outputs a reflected pulsed light beam S
20
A from the object QA, and a reflected pulsed light beam S
20
B from the object QB as shown in FIG.
11
. The output S
20
of the light receiving means
20
is supplied to the light reception time detecting means
30
c
, and then compared with the predetermined value by the comparing means
34
c
to supply a signal indicating that the output S
20
is larger than the predetermined value VO, to the time measurement circuit
33
c
. The time measurement circuit
33
c
uses a transmission light signal ST output from the calculation unit
40
b
, as a start signal, and an output of the comparing means
34
c
as a stop signal. Namely, the circuit measures a time difference between illumination and reception of the transmitted light beam. As shown in
FIG. 11
, in the case where reflected pulsed light beams respectively from two objects are detected, the comparing means
34
c
produces two stop signals PA and PB. The time measurement circuit measures time periods ta and tb (indicated in the figure). Each of the time periods ta and tb is a time period when a light beam is reflected and returned from an object. The distance to an object can be calculated from such a time period and the velocity of light by the following expression:
La=
½*(velocity of light)*ta.
As described above, the conventional art example discloses that timings when reflected pulsed light beams due to objects exceed a predetermined value are detected, so that the distances to the objects can be detected. When also a distant object of a low reflectance, such as a dirty preceding vehicle, a vehicle without a reflector, or a laterally-directed vehicle can be detected, it is possible to further enhance safety. In order to attain this, a sensitive photoelectric converting element or an optical system of higher sensitivity may be used. In this case, however, a situation where a plurality of reflected pulsed light beams are detected with respect to one transmitted pulsed light beam often occurs, and troubles such as described below are caused to reduce safety. Specific examples will be described with reference to
FIGS. 12A
to
12
D.
FIGS. 12A
to
12
D show cases where a destination signboard or the like exists in a vertical angular range of the transmitted light beam. Even in the case where the signboard is relatively small, when the sensitivity of the element is enhanced as described above, the device receives not only a reflected pulsed light beam from a vehicle but also that from the signboard.
FIG. 12A
shows a case where the object vehicle QA to be detected is in front of the signboard QB. In the light reception signal S
20
, the reflected pulsed light beam S
20
A from the object vehicle, and the reflected pulsed light beam S
20
B from the signboard QB are separated from each other. Therefore, the retroreflection times ta and tb of the light beams can be detected so that the distances can be measured.
FIG. 12B
shows a state where the object vehicle QA and the signboard QB are close to each other and hence the reflected pulsed light beams from the objects overlap with each other. The occurrence of this overlapping depends on the pulse width of the transmitted pulsed light beam. For example, it is assumed that the transmitted pulsed light beam has a pulse width of 50 nS. When the relative distance between the objects QA and QB is not longer than 7.5 m, overlapping occurs. In such a state where a plurality of reflected pulsed light beams overlap with each other, the conventional art example can detect only the first reflected pulsed light beam. Therefore, only the retroreflection time ta corresponding to the reflected pulsed light beam from the object vehicle QA can be detected, and the detection of the signboard QB is disabled. As a result, only the distance to the object vehicle QA is output.
FIG. 12C
shows a state where the preceding vehicle QA is remoter than the signboard QB but the two reflected pulsed light beams remain to overlap with each other. In this case also, in the same manner as
FIG. 12B
, the two reflected pulsed light beams are detected as one reflected pulsed light beam. Therefore, the reflected pulsed light beam from the object vehicle QA is not detected, and only the time tb corresponding to the reflected pulsed light beam from the signboard QB is detected. As a result, only the distance to the signboard is output.
FIG. 12D
shows a state where the object vehicle QA is advanced to a remoter position, and the reflected pulsed light beam from the signboard QB and that from the object vehicle QA are again separated from each other. Both the distances to the object vehicle QA and the signboard QB are again enabled to be measured. In the states o

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