GB2329779A - Distance measuring device - Google Patents

Distance measuring device Download PDF

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Publication number
GB2329779A
GB2329779A GB9900624A GB9900624A GB2329779A GB 2329779 A GB2329779 A GB 2329779A GB 9900624 A GB9900624 A GB 9900624A GB 9900624 A GB9900624 A GB 9900624A GB 2329779 A GB2329779 A GB 2329779A
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United Kingdom
Prior art keywords
light
interference
reception signal
level
distance
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Granted
Application number
GB9900624A
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GB2329779B (en
Inventor
Masahira Akasu
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Priority claimed from JP14648094A external-priority patent/JP3185547B2/en
Application filed by Mitsubishi Electric Corp filed Critical Mitsubishi Electric Corp
Publication of GB2329779A publication Critical patent/GB2329779A/en
Application granted granted Critical
Publication of GB2329779B publication Critical patent/GB2329779B/en
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483Details of pulse systems
    • G01S7/486Receivers
    • G01S7/487Extracting wanted echo signals, e.g. pulse detection
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/08Systems determining position data of a target for measuring distance only
    • G01S17/10Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/08Systems determining position data of a target for measuring distance only
    • G01S17/32Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S17/36Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88Lidar systems specially adapted for specific applications
    • G01S17/93Lidar systems specially adapted for specific applications for anti-collision purposes
    • G01S17/931Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/497Means for monitoring or calibrating
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/42Simultaneous measurement of distance and other co-ordinates
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483Details of pulse systems
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/495Counter-measures or counter-counter-measures using electronic or electro-optical means

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

A distance measurement device comprises a light-sending unit (2) for sending pulsed light towards an object 10 whose distance is to be measured. A return signal E from the object 10 to a light receiving unit 3 may be corrupted by interference light S. The device further comprises a light sending output control means 7 which increases and decreases the output of pulsed light from light-sending unit 2. Interference detection means 5 determines whether interference light S exists on the basis of whether the level of the light reception signal changes according to the increase and decrease in level of pulsed light output by light-sending unit 2.

Description

1
DISTANCE MEASUREMENT DEVICE BACKGROUND OF THE INVENTION Field of the Invention
The present invention relates to a distance measurement device which sends pulsed light toward an object of measurement where a distance thereto is measured, receives light reflected by the object, and measures the time required from the sending of light to the receiving of light to obtain the distance to the object.
Description of the Related Art
A distance measurement device of the above kind is shown in FIG. 7. In the figure, the distance measurement device comprises clock pulse generation means 1, light-sending means 2, a pulse drive unit 21, a laser diode 22 that is driven by the pulse drive unit 21, and a light-sending lens 23. Light receiving means 3 consists of a light-receiving lens 31 and a light-rezeiving element 32. And, distance measurement means 4 obtains a distance to an object 10 which is an object of measurement.
Next, the operation of the conventional device thus constructed will be described. The clock pulse generation means 1 generates a clock pulse CP which is a reference. The lightsending means 2 drives the pulse drive unit 21 to generate a drive pulse DP in synchronization with the clock pulse CP that the clock pulse generation means 1 generates, and then drives the laser diode 22 to generate pulsed light A. The pulsed light A generated by the laser diode 22 is irradiated forward as a 2329779 2 pulsed light beam B that is condensed by the light-sending lens 23. This irradiated light beam B will be reflected by the object 10 if the object is within a range of the irradiation. This reflection light E reflected by the object 10 is incident on the light-receiving lens 31 of the light- receiving means 3 as incident light G and is condensed at the light- receiving surface of a light-receiving element 32 as focused light H. The lightreceiving element (a photoelectron converter) 32 converts the focused light H into a light reception signal J.
The above-described distance measurement means 4 compares the light reception signal J from the light-receiving element 32 with a predetermined threshold value and detects the significant light reception signal J based on the reflection light E from the object 10. Further, the distance measurement means 4 measures, from the clock pulse CP, i.e., the time of occurrence (ta) of the drive pulse DP of the laser diode of the light sending means 2 and the time of detection (tb) of the light reception signal i based on the reflection light E from the above-described object 10, the turnaround time to the object 10 (t = tb ta) by using, for example, a high frequency oscillator and a high speed counter, and obtains the distance between the distance measurement device and the object, d, by the following Equation (l):
d = t x c/2 (Equation 1) where c represents the speed of light.
in summary, instead of the drive pulse and the light reception signal which are electric signals, the above-described time, t (= tb - ta), is modified to the time from the sending of 3 the pulsed light A to the incidence of the focused light H and is substituted into Equation (1).
Also, the distance measurement means 4 is constructed so that it calculates a distance based the first significant light reception signal i and would not calculate a distance even if other significant light reception signals were between the first distance calculation and the next distance calculation.
A distance measurement device such as described above detects the distance to the object 10 by sending the light beam B to the object 10 and receiving the light E reflected from the object 10. However, if interference light S, such as pulsed light from other light sources or pulsed reflection light therefrom, is incident on the light- receiving means 3 as incident light G before the reflection light E from the object 10 is incident, the light-receiving means 3 cannot determine whether the light incident thereon is the reflection light E from the object 10 based on the light beam B sent by the lightreceiving means 3 or the interference light S from other light sources, so the interference light S from other light sources is recoanized as reflection light E by mistake. And, the distance measurement means 4 performs a distance measurement calculation with the light reception signal J based on the interference light S and will calculate a mistaken distance d (Equation 1).
The above-described problem of the incidence of the interference light S from other light sources occurs when a plurality of distance measurement devices of the above kind are used. For example, this kind of distance measurement device is mounted in a vehicle and utilized as a device which measures the 1+ distance]etween vehicles and alarms to maintain a saf e distance between vehicles. And, if two opposite vehicles traveling on two opposite lanes are provided with similar devices, the pulsed light of the distance measurement device of the opposite vehicle will surely be incident on the distance measurement device of a self-vehicle as interference light S.
Since the interference light S from the opposite vehicle is direct light, even if the opposite vehicle were far away, the level (illuminance) of the incident light to the light-receiving means 3 would be far stronger than that of the reflection light E from a normal preceding vehicle. At this time, if the reflection light E from the distance measurement device of a self-vehicle and the pulsed interference light S from the distance measurement device of the opposite vehicle occur at the substantially same time, the interference light S from the opposite vehicle will be detected by mistake, so an alarm is to be given even when there is no preceding vehicle on the same lane as a self-vehicle.
Thus, the mistaken operation caused by receiving the interference light S other than the regular light E reflected from the object 10 becomes an important problem associated with the safety and reliability of a system, when this kind of device is used in a sensor of a system for controlling an alarm occurrence or equipment.
Also, when the interference light S of the distance measurement device of an opposite vehicle is received, conversely the pulsed light A of the distance measurement device of a self-vehicle is also irradiated to the opposite vehicle.
Therefore, since the driver of the opposite vehicle is also subjected to the irradiation of the pulsed light A, the conventional device is undesirable from the standpoint of safety.
SUMMARY OF THE INVENTION
This invention has been made to solve problems such as described above. Accordingly, it is an object of the present invention to provide a distance measurement device which is capable of judging whether interference light exists in the light incident on light-receiving means.
According to this invention, there I's provided a distance measurement device

Claims (2)

  1. comprising the features of Claim 1.
    In this arrangement, the output of the sent pulsed light is in proportion to the intensity of the pulsed reflection light reflected by an object of measurement. Therefore, if the intensity of the incident light changes when the output of the sent pulsed light is changed, the incident light is reflection light. On the other hand, if the intensity of the incident light does not change, the incident light can be determined to be interference light. As a result, whether interference light exists in incident light can be determined based on the intensity of pulsed light to be sent and based on the intensity of reflection light.
    In a preferred form of the invention, the interference detection means determines that interference light does not 7 exist in incident light, when the intensity of the incident light is increased and decreased as the intensity of the pulsed light is increased and decreased.
    In this arrangement, the output of the sent pulsed light is in proportion to the intensity of the pulsed reflection light reflected by an object of measurement. Therefore, if the intensity of incident light is increased when the output of the sent pulsed light is increased, and is decreased when the output of the sent pulsed light is reduced, the incident light is reflection light. On the other hand, if a change in the intensity of the incident light is small when the output of the sent pulsed light is increased and decreased, it can be determined that interference light exists in the incident light.
    "I 8 The present application has been divided from UK patent application no. 9513205.6 which relates to a light-sending distance measurement device which identifies interference light from its intensity.
    UK patent application no. 972707.6 has been divided from UK patent application no. 9513205.6. That relates to a light-sending distance measurement device which identifies interference light from the time at which it is received (which implies a distance).
    UK patent application no. 9727072.2 has also been divided from UK patent application no. 9513205.6. That relates to a light-sending distance measurement device which determines that interference is present from light detected while light is not being sent.
    UK patent application no. 9727076.3 has also been divided from UK patent application no. 9513205.6. That relates to a light-sending distance measurement device which alters the timing of light-sending in order to avoid interference light.
    UK patent application no. 9727074.8 has also been divided from UK patent application no. 9513205.6. That relates to a light-sending distance measurement device which detects interference llohi on the basis of direction of incident lieffit.
    UK patent application no. 9727066.4 has also been divided from UK patent application no. 9513205.6. That relates to a light-sending distance measurement device which reduces or stops output of pulsed light in response to detection of interference li!zht.
    UK patent application no. has also been divided from UK patent application no. 9513205,6. That relates to a light-sending distance measurement device which determines whether interference lieffit exists in incident lip-ht based on fluctuations in distance data and intensity of incident light.
    The above and other objects and advantages of the present 9 invention' will become apparent from the following detailed description of the preferred embodiments of the invention when the same is read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a distance measurement device as background to this invention., FIG. 2 is a diagram showing the determination level in a second embodiment of this invention; FIG. 3 is a flowchart showing the operation of a third embodiment of this invention; FIG. 4 is a block diagram showing a distance measurement device of a first embodiment of this invention; FIG. 5 is a diagram used to explain the operation of the distance measurement device of the fifteenth embodiment of this invention; FIG. 6 is a flowchart showing the operation of the fifteenth embodiment of this invention; and FIG. 7 is a block diagram showing a conventional distance measurement device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings.
    FIG. 1 shows a distance measurement device constructed in accordance with background to this invention. In the figure, reference numerals 1, 2, 3, 4 and 10 are the same as the above- described conventional device and therefore a description thereof is omitted by applying the same reference numerals. interference detection means 5 has a display unit 5a, determines that interference light exists, when the level of a light reception signal j from light-receiving means 3 exceeds a mredetermined value, and displays that effect on the display unit 5a and also cenerates interference detection signal AL.
    In the distance measurement device thus constructed, light- 11 sending means 2 sends a light beam B at the timings T1, T2, T3,... 1 and TN of a drive pulse DP synchronized with the clock pulse CP generated by clock pulse generation means 1, and the light beam is reflected by an object 10. The light-receiving means 3 receives incident light G including reflection light E reflected by the object 10 and converts it into a light reception signal J, which is input to distance measurement means 4 and interference detection means 5.
    From the time difference between the timings T1, T2, T3, and TN of the drive pulse DP synchronized with the clock pulse CP input by clock pulse generation means 1 and the timings T1, T2, T3,..., and TN of the first light reception signal J output by the light-receivin.g means 3 after each light beam is sent, the distance measurement means 4 calculates and outputs distances D1, D2, D3,..., and DN based on Equation (1).
    At the same time, the interference detection means 5 compares with a predetermined value ctO (see FIG. 2) the level L of the light reception signal J based on the incident light G that is first incident on the light-receiving means 3 after each light beam is sent. When the level L of the light reception signal J is czO or more, the interference detection means 5 determines that interference light S exists in incident light G, and displays that effect on the display unit 5a and also generates interference detection signal AL.
    That is, each time the distance measurement means 4 calculates a distance based on the light reception signal J first incident on the lightreceiving means 3, the level L of the light reception signal J is compared with a predetermined 12- is value. And, when the level L of the light reception signal i is a predetermined value or more, that effect is displayed on the display unit 5a, so it can be understood that the distance calculated at that time is based on interference light.
    Incidentally, if the light beam B sent by the light-sending means 2 is irradiated on object 10, reflection light E with an intensity corresponding to the reflectivity of the object 10 will be reflected. when the light-sending means 2 sends light beam B with a power po and a radiant solid angle QO, the illuminance Hr on the light-receiving means 3 by the reflection light E reflected by the object 10 having an area St at a point spaced by a distance R, a reflectivity K, and a radiant solid angle 92t is given by the following laser equation Hr = PO x St x K/R4 x f20 x 92t (Equation 2) The level L of the light reception signal i of the lightreceiving means 3 is proportional to the illuminance Hr. Therefore, the level L of the light reception signal J by the reflection light E of the object 10 is inversely proportional to the distance R4.
    On the other hand, the illuminance Hd on the lightreceiving means 3 on which interference light is directly incident from a similar distance measurement which is spaced by a distance R and sends pulsed light having the same power and radiant solid angle (PO, QO) as the device of the present invention is given by Hd = PO/R' x 20 (Equation 3) That is, since interference light (pulsed light from an opposite device) is directly incident, very strong light is 1-9 incident on the light-receiving means 3, and accordingly, the level of the light reception signal J that is output by the light-receiving means 3 becomes high.
    A ratio of light reception levels on light-receiving means 3 between interference light S and reflection light E is given by Hd/Hr = R 2 X nt/St X K (Equation 4) Assume now that the object 10 is a reflex reflector that is mounted on the rear reflecting mirror of a vehicle. If the radiant solid angle, reflection area, and reflectivity of the reflector are Rt = 10-3 (sr), St = 2 x 10-3 (M2), and K = 0.3, ratio of light reception levels on the light-receiving means 3 will be given by Hd/Hr = R 2 x 1.67 (Equation 5) According to this ratio, the level of the incident light S from another distance measurement device 50 m (R = 50) ahead is 4000 times as much as that of the reflection light E from the reflex reflector.
    Therefore, when in this kind of distance measurement device an object of measurement 10 is assumed to be the above-described reflex reflector of a vehicle, a value which is, for example, 10 times as much as the reflection light E from the reflex reflector is set as a reference value aO for determining whether interference light exists. In this arrantgement, the level of interference light S is very high like 4000 times, so the interference light S and the normal reflection light E from the object 10 can be distinguished with reliability.
    Thus, interference light S is far stronger than reflection 114- light E. Therefore, even if reference value czO for determining interference light S were set to a value sufficiently greater than the maximum level that light-receiving means 3 receives (in this embodiment, 10 times), it could reliably be determined whether interference light exists.
    In the above arrangement, it has been described that the interference detection means Sa compares the level L of the light reception signal J output by the light-receiving means 3 with a predetermined value aO to detect interference light.
    However, in this arrangement, according to the distance data D calculated by distance measurement means 4, a determination level czv for the level L of the light reception signal of light-receiving means 3 is set to a greater value for a short distance and a smaller value for a long distance so that the incidence of interference light S can be detected more reliably.
    As described above, the reflection light E from object 10 is scattered, the illuminance Hr of the reflection light E on light-receiving means 3 is reduced in inverse proportion to distance R', as shown in Equation 2, and the reflection light E becomes weaker if the object 10 is far away, so the level L of the light reception signal i output by the light-receiving means 3 becomes smaller. on the other hand, the illuminance Hd of interference light S that is incident from other distance measurement devices directly on the light-receiving means 3, is attenuated in inverse proportion to distance R', as shown in Equation 3.
    is Therefore, the determination level av, as shown in FIG. 2, is set to a value which is greater than the level Hr of reflection light E, smaller than the level Hd of interference 2 light S, and reduced in inverse proportion to distance R With this, there can be detected interference light S which is stronger than the reflection light E from the object 10 and is incident from other distance detection means directly on the light-receiving means 3, and other interference light which is weaker than this interference light S and greater than av. As a result, interference light can be detected more reliably.
    is Also, interference detection means 5 stores the levels LI, L2, L3,..., and LN of the light reception signals of lightreceiving means 3 and the distance data D1, D2, D3,..., and DN output by distance measurement means 4, over a plurality of times, i.e., at the timings T1, T2, T3,..., and TN of a drive pulse DP. And, for the respective values, the interference detection means 5 calculates from the stored values a statistical fluctuation value such as a standard deviation or sum of absolute values of differences between continuous data. And, when a fluctuation in the distance data D1 to DN is greater than a predetermined value and a fluctuation in the levels L1 to LN of the light reception signals is smaller than a predetermined value, it can also be determined that interference light exists.
    Generally speaking, when a distance measurement device continuously detects the same object 10, the fluctuation in the distance data D1 to DN is small and the intensity CK of incident 16 light G is substantially constant, so the fluctuation in the levels Ll to LN of the light reception signals is small. When, on the other hand, the distance measurement device detects a plurality of objects in various positions, the fluctuation in the distance data D1 to DN becomes greater and also the fluctuation in the levels L1 to LN of the light reception signals becomes greater.
    However, since pulsed light which is generated by an opposite distance measurement device and becomes interference light S is not emitted in synchronization with light-sending means 2, the timing at which distance measurement means 4 measures and the timing at which interference pulsed light S is incident on light-receiving means 3 are not synchronized.
    Therefore, the distances D1 to DN calculated by the distance measurement means 4 are not constant and become random values, so the fluctuation becomes very greater.
    Conversely, since the position of a source of interference light is not greatly changed within a plurality of distance measurement times, the levels L1 to LN of the light reception signals of light-receiving means 3 become substantially constant and the fluctuation is small. Interference detection means 5 calculates a fluctuation aD in distance data D1 to DN and a fluctuation al, in light reception signal levels Ll to LN and, when the distance fluctuation aD is great and the level fluctuation aL is small, determines that interference light 5 has been incident. Therefore, whether interference light 5 exists in incident light S can be determined with reliability.
    The above-described operation of the interference detection 1:7 means 5 will be described further in detail with reference to a flowchart of FIG. 3. Nine distance data D1 to D9 were measured with a resolving power of 0.1 m, and the light reception signal levels Ll to L9 were normalized with a maximum value of 1.
    The following process operation is performed once for a single measurement, and the results of measurement for the past nine measurements have been stored in distance data storage registers RD1 to RD9 and signal level storage registers RLI to RL9, respectively.
    First, in step 1 an interference detection flag F for storing a detection result of the incidence of incident light S is cleared (F = 1). In step 2, distance data DO measured this time is stored in the register RDO, and a light reception signal level LO is stored in the register RLO.
    In step 3, an average value Dm of ten consecutive distance data including a current measurement result and the past nine data is obtai.ned. In step 4, a standard deviation cD is obtained by an equation, E(Dm - Dn) 2/9} 111 where Drn represents the average value of distance data DO to D9 obtained in step 3 and Dn represents the measured value of each data.
    Next, in step 5 the standard deviation cD of distance data is compared with a predetermined value KD which is, for example, a value (1 m) ten times greater than a resolving power 0 - 1 m of distance measurement. If aD is less than KD, a fluctuation in distance data DO to D9 will be small and stable, and since this is not the incident of interference light S, step 5 will advance to step 11.
    If, on the other hand, aD is greater than KD, distance data Ps is will have a fluctuation and step 5 will advance to step 6. In step 6, an average value Lm of light reception signal levels LO to L9 is obtained.
    In step 7, a standard deviation aL of light reception signal levels LO to L9 is obtained in the same way as step 4. Further, in step 8 the degree of fluctuation, VL, of the light reception signal levels L is obtained by dividing the standard deviation aL of the light reception signal levels by the average value Lm of the light reception signal levels.
    When in step 9 the degree of fluctuation VI, of the light reception signal levels is greater than or equal to a predetermined value KI, (for example, 0.01), the light reception signal level L has a fluctuation and is not constant. Since this is not the incidence of interference light S, step 9 advances to step 11.
    On the other hand, when in step 9, VL is less than KL (0.01), there is no fluctuation in the light reception signal levels L1 to L9 and step 9 advances to step 10. In step 10, the incidence of interference light S is assumed to exist and the interference detection flag F is set to a 1, because it has been determined in step 5 that distance data DO to D9 has a fluctuation and it has been determined in step 8 that light reception signal levels LO to L9 have no fluctuation.
    In step 11, current distance data and the stored contents of registers RDO to RD8 in which the past eight distance data DO to D8 have been stored are transferred to registers RD1 to RD9, respectively. That is, stored data are transferred so that the content of the register RD8 is transferred to the register RD9 19 and then the content of the register RD7 is transferred to the register RD 8. In step 12, the contents of registers RLO to RL8 in which the data LO to 1.8 of the light reception signal levels have been stored are likewise transferred to registers RL1 to RL9, respectively, and prepared for the interference detection process in the next distance measurement.
    With the above-described operation, the interference detection flag F is set to a 1 when there is a fluctuation in distance data DO to D9 and there is no fluctuation in light reception signal levels Ll to Lg. Therefore, when distance data is used, whether interference light exists can be detected by monitoring this interference detection flag F. Also, depending on the state of this interference detection flag F, that effect can be displayed on the display unit 5a and also the interference detection signal AL can be generated.
    FIGS. 4, 5, and 6 illustrate a distance measurement device constructed in accordance with a first embodiment of this invention. FIG. 4 is a block diagram showing the structure of 11 is the device, FIG. 5 is a diagram used to explain the operation of the device, and FIG. 6 is a flowchart showing the operation of the device. FIG. 5(a) shows the timing of a clock pulse Cp, FIG 5(b) shows the output control value P of the light-sending output W of light-sending means 2, FIG. 5(c) shows a light reception signal L based on the reflection light E from an object 10, and FIG. 5(d) shows a light reception signal as incident light G is interference light S.
    In FIG. 4, light-sending output control means 7 increases and decreases the output of pulsed light A that is generated by light-sending means 2. when detecting a distance, interference detection means 5 stores the light-sending output W of the light-sending means 2 or the output control value P of the light-sending output control means 7, and also stores the level L of a light reception signal J that is output by lightreceiving means 3. The interference detection means 5 determines whether interference light S exists, by whether the level L of the light reception signal i changes according to the increase and decrease in the light-sending output W at the time of measurement.
    The intensity of the reflection light E from the object 10 is proportional to the intensity of a light beam B sent by the light-sending means 2, that is, the light-sending output W. Therefore, the level L of the light reception signal J is proportional to the intensity of the light beam B. Note that the output control value P of the light-sending output control means 7 is used instead of the light-sending output W.
    22 Then, the output control value P1 of the light-sending output control means 7 at the time of a previous measurement and the level L of the light reception signal J at that time are stored, and for example, at the time of a current measurement the output control value is increased from P1 to PO, as shown in FIG. 5(b) And, the rate of change in the level of the light reception signal J is obtained from the absolute value (1LO - L11) of a difference between the level LO of the current light reception signal J and the level Ll of the previous light reception signal J (FIG. 5(c)) by the following equation RL = (JLO - L11)/L1 And, whether that value exceeds a predetermined value is determined.
    when the light reception signal J is based on interference is light S, a change is very small as shown in L11 and L10 of FIG.
    5(d). Therefore, when the change rate is less than a predetermined value, it is determined that the light reception signal J output by the lightreceiving means 3 is not based on the reflection light E from the object 10, so it can be determined that the light reception signal J is based on interference light S. In this way, in this embodiment, whether interference light S exists is detected.
    Further, the operation of the first embodiment will be described in detail with respect to the flowchart of FIG. 6.
    The following process operation is performed once for a single measurement, and the control value P1 of the light sending output proportional to the light-sending output Wl at the time of a previous measurement has been stored in a register 23 RP1, and the level Ll of the light reception signal has been stored in a register RLI.
    In step 21, an interference detection flag F for storing a result of the incidence of incident light S is cleared (F = 0). In step 22, the level LO of a current light reception signal is stored in a register RLO. In step 23, the change rate of the current signal level LO to the previous signal level Ll is obtained by dividing the absolute value of the difference between the level LO of the current light reception signal J and the level L1 of the previous light reception signal J by the previous signal level Ll. That is, the change rate is obtained by the following equation RL = (1LO - L11)/L1 In step 24, the change rate RL of the level L of the light reception signal J is compared with a predetermined value KL sufficiently smaller than the rate of increase, Kp (= PO/P1 1), of the control value P of the light-sending output. When RL is greater than KL, the level L of the light reception signal changes and it is determined that the light reception signal is not based an interference light S. Step 24 then advances to step 26. Note that KI, is set to 0.05 which is 1/4 the rate of increase (Kp = 0.2 (20%)).
    When, on the other hand, RL is less than KL, the level L of the light reception signal does not change, the light reception signal is based on interference light, and step 24 advances to step 25. In step 25, since it was determined that the level L of the light reception signal does not change although the control value P of the light-sending output was changed, the i 2,t incidence of interference light S is determined and the abovedescribed interference detection flag F is set to a 1.
    In step 26, data in the register RLO where the level LO of the current light reception signal has been stored is transferred to the register RL1.
    Next, in step 27 the next control value P of the lightsending output is calculated by multiplying the current control val-ue PO by a predetermined increase coefficient Kp, for example, a value of 1.2 (if the output is increased by 20%).
    In step 28, it is determined if the control value P of the light-sending output calculated in step 27 does not exceed the maximum output Pmax of the device. when the control value P does not exceed Pmax, the operation is ended. when the control value P exceeds Pmax, step 28 advances to step 29. In step 29 the control value P is set to a control minimum value Pmin, and the operation is ended.
    In the above-described operation, when the level L of the light reception signal does not change although the control value P of the light-sending output was changed, the incidence of interference light S is determined and the above-described interference detection flag F is set to a 1. Therefore, when the distance data is used, the existence of interference light can be detected by monitoring this interference detection flag The above-described interference detection means 5 calculates, from the previous and current control values P1 and PO of the light-sendina output, an increase rate RP thereof, and likewise calculates, from the previous and current levels L1 and 25- is LO of the light reception signal, an increase rate RL thereof. And, when the difference between the increase rate RP of the control value of the light-sending output and the increase rate RL of the level of the light reception signal is less than a predetermined value, it can determined that the light reception signal J output by light-receiving means 3 is based on the reflection light E from object 10. This is because, when interference light S does not exist in incident light G and only reflection light E is incident, the control value P of the light-sending output is substantially proportional to the level L of the light reception signal.
    When it is detected, in this way, that there is no incidence of interference light, there is no interference light during measurement, and distance data is obtained correctly. The distance data output by the distance measurement means 4 can be considered as data having high reliability.
    While in the above embodiment the control value P of the light-sending output has been increased to detect whether interference light exists, the existence of interference light can be detected even if the control value P is decreased or changed in both increasing and decreasing directions.
    Also, it is a matter of course that the light-sending output W may be used instead of the control value P of the light-sending output.
    26 While the subject invention has been described with reference to the preferred embodiments thereof, it will be appreciated by those skilled in the art that numerous variations, modifications, and embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the spirit and scope of the invention.
    27 CLAIMS:
    A distance measurement device comprising:
    light-sending means for sending pulsed light toward an object of measurement where a distance thereto is measured., light-sending output control means for controlling the intensity of an output of said pulsed light., light-receiving means for receiving incident light including pulsed reflection light reflected by said object; distance measurement means for measuring the time from the sending of said pulsed light to the receiving of said incident light and calculating the distance to said object; and interference detection means for storing, the intensity of said pulsed light and the intensity of said incident light as intensity data of said pulsed light and intensity data of sid incident light, and for determining whether interference light originating from a al 1 1 1 1 1 1 1 W source other than the light-sending means exists in said incident light, based on said intensity data of said pulsed light and said intensity data of said incident light as the intensity of the output of said pulsed light is changed by said light-sending output control means.
  2. 2. The distance measurement device as set forth in claim 1, wherein said interference detection means determines that interference light does notexist in incident lieht, when the intensity of the incident light is increased and decreased as the intensity W of the pulsed light is increased and decreased.
GB9900624A 1994-06-28 1995-06-27 Distance measurement device Expired - Fee Related GB2329779B (en)

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JP14648094A JP3185547B2 (en) 1994-06-28 1994-06-28 Distance measuring device
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GB9727070A Expired - Fee Related GB2318239B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9727072A Expired - Fee Related GB2318240B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9727074A Expired - Fee Related GB2318241B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9900625A Expired - Fee Related GB2329780B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9727066A Expired - Fee Related GB2318238B (en) 1994-06-28 1995-06-27 Distance measurement device
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GB9727072A Expired - Fee Related GB2318240B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9727074A Expired - Fee Related GB2318241B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9900625A Expired - Fee Related GB2329780B (en) 1994-06-28 1995-06-27 Distance measurement device
GB9727066A Expired - Fee Related GB2318238B (en) 1994-06-28 1995-06-27 Distance measurement device

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GB9727066D0 (en) 1998-02-18
GB2318241A (en) 1998-04-15
GB2318242A (en) 1998-04-15
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GB2329780B (en) 1999-05-12
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GB2318238A (en) 1998-04-15
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GB9727072D0 (en) 1998-02-18
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GB2318239B (en) 1999-03-03
GB2318238B (en) 1999-03-03

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