JP2001108747A - Range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a range finder of high measuring precision capable of conducting range-finding in a close distance, and capable of conducting plural times of measurement at a high speed. SOLUTION: Transmission points of time detected in plural respective conditions different in operation conditions such as a pohot-receiving quantity, a transmitted light quantity and an amplification factor are stored prior to the plural times of measurement, only receive points of time are detected in the measurement of each time, and a flight time is calculated based on the transmission point of time detected in the condition resembling each other closely in the operation conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-of-flight measuring distance measuring apparatus.

[0002]

2. Description of the Related Art A so-called flight time (TOF: ti) from transmission of pulsed light to reception of pulsed light reflected by an object and returned.
By measuring the me of flight, the distance between the objectives can be determined by applying a known light propagation velocity. The transmission time point at which the measurement of the flight time is started may be a time point when a predetermined time has elapsed from the time point at which the light emission control signal is output.However, by monitoring the actual light emission amount and detecting the pulse, Measurement errors due to variations in the characteristics of the light emitting element and the delay amount of the control signal can be eliminated.

[0003] Japanese Patent Application Laid-Open No. 7-63853 describes a distance measuring device that detects a transmission time point by guiding a part of pulse light emitted from a light source to a light receiving unit through an optical fiber. The pulse light that has propagated through the optical fiber (internal optical path) and the pulse light that has been reflected and returned outside are sequentially incident on the light receiving unit. The time of flight is calculated by detecting these incident points.

Japanese Patent Laid-Open Publication No. Hei 10-123250 discloses a distance measuring apparatus in which a light source emits light twice in one measurement. In this conventional example, an internal optical path is provided not for detecting the transmission time point but for eliminating the influence of the detection error at the reception time point. For example, pulse light is emitted to the outside by the first light emission, and the time of reception is detected to determine the flight time. The transmission time is the light emission instruction time. continue,
Pulse light is emitted to the internal optical path in the second light emission, and the time of reception is detected to determine the flight time (propagation time) of the internal optical path.
Then, a difference ΔTa between these flight times is obtained, and L = C ×
An inter-object distance L represented by ΔTa + L ′ (C: light speed, L ′: internal optical path length) is calculated. By calculating the difference ΔTa, it is possible to cancel a detection error caused by a change in circuit characteristics depending on an environmental condition (mainly temperature).

[0005]

The width of pulse light in a general distance measuring device is about 50 to 100 ns. Although it is desirable that the pulse width is close to zero, it is actually limited by the response of the light source and the receiving sensitivity. Therefore, in a conventional device that measures the distance by one light emission, two pulses are superimposed when performing a relatively short distance measurement of about several meters to several tens of meters, and the transmission time and the reception time are different. Becomes indistinguishable, and the distance between the objects cannot be determined.

[0006] As a method for enabling measurement at a short distance,
There is a method of separately detecting the transmission time and the reception time. For example, first, an optical path is set so as to receive only the pulsed light propagated through the internal optical path, and the transmission time point is detected and stored. Next, the optical path is set so as to receive only the pulse light that has been reflected and returned from the outside, and the reception time point is detected. The detection of the transmission time point may be performed for each measurement. However, in this case, pulse light is emitted twice for each measurement, which is disadvantageous in terms of required time and power consumption. Therefore, it is conceivable that the transmission time point is detected only once in a plurality of measurements, and only the reception time point is detected for each measurement. This operation mode is particularly suitable for a case where measurement is continuously performed at many points on an object (for example, measurement of a three-dimensional shape).

However, since the transmission time and the reception time are separately detected, a measurement error occurs due to the difference between the “operation conditions for detecting the transmission time” and the “operation conditions for detecting the reception time”. was there. In some cases, the results of a plurality of measurements may be slightly different even though the measurement target distances are equal.

One of the operating conditions is the amount of received light that depends on the distance to be measured and the reflectance of the object. When the amount of received light changes, the state of occurrence of shot noise in the light receiving element changes, affecting the waveform of the photoelectric conversion signal. In addition, the emission light amount of the pulse light (transmission light amount) and the amplification factor of the photoelectric conversion signal are also operating conditions. In the detection of the reception time point, an automatic or manual operation setting for adjusting the amount of transmitted light so that the amount of received light is within a proper range or increasing or decreasing the amplification factor so as to be suitable for signal processing can be performed. The drive current supplied to the light emitting element changes due to the adjustment of the transmission light amount, and accordingly, the noise superimposed on the photoelectric conversion signal changes. As the gain increases or decreases, the frequency characteristics of the amplifier change, and the waveform is deformed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a distance measuring apparatus capable of measuring a short distance, performing a plurality of measurements at a high speed, and having high measurement accuracy.

[0010]

In the present invention, prior to the "measurement a plurality of times", transmission time points detected in a plurality of situations having different operating conditions, such as a received light amount, a transmitted light amount, and an amplification factor, are stored. Keep it. In each measurement, only the reception time point is detected, and the flight time is calculated based on the reception time point and the transmission time point detected in a situation where operating conditions are similar.

[0011] Alternatively, as a plurality of measurement operations, transmission and reception for detecting a reception point are performed a plurality of times, and then the transmission point is detected in a situation similar to the transmission and reception for detection of the reception point and operating conditions.

By separately detecting the transmission time and the reception time, it is possible to measure a short distance. By applying the detected transmission point to a plurality of measurements, it is possible to reduce the number of times of detection of the transmission point, increase the speed, and reduce the power consumed for light emission. By using the transmission time point and the reception time point detected in the situation where the operating conditions are similar, it is possible to reduce the error due to the difference in the operating conditions.

"Multiple measurements" means the next measurement. (1) When detecting and storing the transmission time point at the time of shipment from the factory, all distance measurements performed by the user are “multiple measurements”. (2) When detecting and storing the transmission time point immediately after the power is turned on, all the distance measurements until the power is turned off are “multiple measurements”.
Becomes (3) When detecting and storing the transmission time in response to the measurement start instruction, the distance measurement for the set number of times corresponding to one instruction is "multiple measurements". For example, three-dimensional measurement for scanning an object corresponds to this.

The blocking of external light for detecting the transmission time point is as follows:
It is also possible to cover the light receiving window with a suitable light shielding body, so that it is not always necessary to provide light shielding means in the distance measuring device. Environmental conditions represented by temperature can be used as operating conditions. In that case, an environmental condition for detecting the reception point may be detected by an appropriate sensor.

An apparatus according to a first aspect of the present invention includes a transmitting means for emitting pulsed light, and a receiving means for receiving the pulsed light reflected by the object to be measured and based on the transmission time and the reception time. A distance measuring device for measuring a distance to an object to be measured, wherein a storage means for storing data for specifying a transmission time point corresponding to each of a plurality of operating conditions, and the data stored in the storage means Means for selecting data corresponding to the operating condition at the time, and means for detecting the receiving time of the pulse light based on the output of the receiving means, and the transmission time specified by the selected data is detected. The distance is calculated based on the reception time.

In the distance measuring apparatus according to the second aspect of the present invention, the operating condition is an emission light amount of pulse light. In the distance measuring apparatus according to the third aspect of the present invention, the operating condition is an amount of pulsed light received by the receiving unit.

In the distance measuring apparatus according to a fourth aspect of the present invention, the operating condition is an amplification factor for an output of the receiving means. In the distance measuring apparatus according to the fifth aspect of the present invention, the operation of storing data for specifying a transmission time point in the storage means includes:
Before multiple measurements.

In the distance measuring apparatus according to the sixth aspect of the present invention, the operation of storing data for specifying the transmission time point in the storage means is performed after a plurality of measurements. A distance measuring apparatus according to a seventh aspect of the present invention includes a scanning unit that scans the pulse light, and performs measurement at different positions on a measurement target.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is an overall configuration diagram of a distance measuring apparatus, FIG. 2 is a block diagram of a transmission unit, and FIG. 3 is a block diagram of a reception unit.

The distance measuring device 1 includes a transmitting unit 10, a receiving unit 20,
It includes a reception processing circuit 30, a controller 40, a clock generator 50, and a scanning unit 60, and receives the returned pulse light reflected by the external object Q from the emission of the pulse light to the outside (transmission time ts) (the reception time The flight time Ta up to tr) is measured.

The transmitter 10 is a light emitting device (semiconductor laser)
11, a light emitting driver 12, a pulse circuit 13 for defining a light emitting time, a light emitting lens 14, and a light amount distributor 15
And emits pulse light P having a pulse width of about 100 ns to the scanning unit 60 and the internal optical path 19 in response to the irradiation timing signal SC13 from the controller 40. The ratio of distribution between the scanning unit 60 and the inside by the light amount distributor 15 is, for example, about 100 to 1000: 1. The light emission intensity (transmission light amount) of the light emitting element 11 depends on the drive current supplied by the driver 12, and is set stepwise by the light amount setting signal SC12.

The scanning section 60 comprises a two-way rotating mirror mechanism and its driving source, and deflects the pulse light P going from the transmitting section 10 to the outside in the horizontal and vertical directions. Thus, scanning for projecting the pulsed light P at a number of positions (measurement points) on the external object Q in the arrangement order is performed. Pulse light P
Is reflected by the object Q, returns to the distance measuring device 1, and enters the receiving unit 20 as "measuring pulse light P1". The receiving unit 20
, The pulse light P propagating through the internal optical path 19 enters as “reference pulse light P0” for detecting the transmission time point.

The receiving section 20 includes a light receiving element (for example, a photodiode) 21, a light receiving driver 22, a circuit 23 for converting a photocurrent into a voltage, a light receiving lens 24, and a light receiving element 2.
1, an external light shutter 25A for blocking the incidence of external light R1 (including the measurement pulse light P1), and an internal light shutter 25 for blocking the incidence of the reference pulse light P0 to the light receiving element 21.
B, mirror 2 for guiding reference pulse light P0 to light receiving element 21
6, a shutter drive circuit 27, a filter mechanism 28 for adjusting the amount of received reference pulse light P0, and a filter drive circuit 29.

External light shutter 25A and internal light shutter 25
B is provided to detect the transmission time ts and the reception time tr at different times, and is opened and closed by the shutter drive circuit 27 according to a control signal SC27 from the controller 40. In the detection of the detection at the transmission time point ts, the external light shutter 25A is closed, and the reference pulse light P0 enters the light receiving element 21. In detecting the reception time point tr, the internal light shutter 25B closes, and the measurement pulse light P0 enters the light receiving element 21.

The filter mechanism 28 has a plurality of filters having different densities, and is configured so that the transmittance can be set in m stages. The filter drive circuit 29 changes the filter arrangement state of the filter mechanism 28 according to the control signal SC29. The light receiving level V of the light receiving element 21 at the detection of the transmission time ts is expressed by the following equation.

V = U × k × τ × S × TU U: Transmitted light amount k: Light amount distribution ratio coefficient τ: Transmittance of filter mechanism S: Sensitivity of light receiving element T: Current-voltage conversion coefficient Detection and reception of transmission time point ts In each of the detections at the time point tr, the receiving unit 20 outputs the photoelectric conversion signal S20 corresponding to the amount of light received by the light receiving element 21 to the reception processing circuit 30.

FIG. 4 is a block diagram of the reception processing circuit 30, and FIG. 5 is a conceptual diagram of the time center of gravity. The reception processing circuit 30 includes an amplification unit 31, an A / D converter 32, a memory 33, a center-of-gravity calculation unit 34, and a reception level detection unit 35.

The photoelectric conversion signal S20 from the light receiving section 20 is
The signals are input to the amplification unit 31 and the reception level detection unit 35. The amplifier 31 amplifies the photoelectric conversion signal S20 into a signal S31 of an appropriate level. The amplification factor A is set by the control signal SC31. The reception level detection unit 35 detects the amplitude of the photoelectric conversion signal S20 as the reception level V, and sends reception level data D35 indicating the detection result to the controller 40. The reception level data D35 is used for “selection of transmission time” described later.

The A / D converter 32 outputs the amplified signal S3
1 is periodically sampled and held in synchronization with the clock CLK and digitized. The clock cycle is sufficiently shorter than the pulse width of the pulse light P, specifically, about 10 ns. Time-series received data D obtained by sampling
32 are sequentially sent to the memory 33 and stored in the area of the address number corresponding to the sampling order. That is, the received light waveform is stored by the memory 33.

After sampling over a predetermined length of time corresponding to the maximum measurement distance is completed, a group of received data D32 (referred to as waveform data DW) indicating a received light waveform for the sampling period is read from the memory 33. To the center-of-gravity calculation unit 34. The center-of-gravity calculator 34 performs a center-of-gravity calculation on the waveform data DW, and sends the time center-of-gravity ip obtained thereby to the controller 40.

The time barycenter ip is the barycenter on the time axis in the distribution of the received light data of the sampling number u (u = 30 in the figure), and corresponds to the peak point at which the received light amount (data value) becomes maximum. Received light data 1 to u at each sampling time
With the sampling number. The i-th light reception data is represented by Xi. i is an integer of 1 to u, and corresponds to an address of a memory for storing received light data. The time centroid ip for the 1st to uth light receiving data X1 to Xu is obtained by dividing the sum of i · XiΣi · Xi by the sum of XiΣXi for u light receiving data. That is,

[0032]

(Equation 1)

## EQU1 ## In this embodiment, the reference pulse light P0
Are detected under a plurality of operating conditions and stored as a plurality of transmission times ts. Further, the time centroid ip corresponding to the measurement pulse light P1 is detected as the reception time tr. These detections are performed separately. And
The controller 40 calculates the flight time Ta from the transmission time ts selected from the stored transmission times ts and the reception time tr. The detection of the transmission time will be described later. An inter-object distance is calculated from the flight time Ta and a known light propagation velocity (3 × 10 ⁸ m / s), and the inter-object distances corresponding to the number of measurement points are used as measurement data DL indicating the shape of the object Q by another device. (Display, computer, etc.).

The distance measuring apparatus 1 having the above configuration detects the transmission time ts before scanning the object Q, and detects the reception time tr based on the waveform data DW corresponding to each of a large number of measurement points after scanning. I do. However, it is also possible to detect the reception time tr during scanning.

At the time of scanning, according to the reflectance and the distance of each measurement point (strictly, according to the light receiving level data D35).
The setting of the transmission light amount U and the amplification factor A is appropriately changed. For example, if the amount of the measured pulse light P1 received is insufficient when the pulsed light P is emitted toward a certain measurement point, a change to increase the transmission light amount U is performed, and the pulsed light is again transmitted to the same measurement point. P is injected. That is, the operating conditions may be different for each measurement point.

Therefore, the detection of the transmission time point ts is performed for each of a plurality of operating conditions in which the combination of the set values of the transmission light amount U and the amplification factor A and the reception level V is different. The detected transmission time point ts is stored in the table 90 provided in the RAM 41 inside the controller 40 in association with the operating condition.

FIG. 6 is a diagram showing an example of a table used for selecting a transmission time point. In the illustrated table 90, the transmission light amount U is q steps of U1 to Uq, and the reception level V is V1 to U1.
M stage of Vm, and amplification factor A are n stages of A1 to An,
One transmission time ts for each of the q × m × n conditions
-Abc (a = 1 to q, b = 1 to m, c = 1 to n) are associated with each other.

Flight time Ta for each measurement point of the object Q
In the calculation of the transmission time ts, the reception time tr corresponding to the target measurement point and the transmission time ts closest to the operating condition of the transmission / reception operation are selected and used with reference to the table 90. To enable this selection, the waveform data DW
Operating conditions including the reception level V in conjunction with the storage of
Recorded in M41.

FIG. 7 is a diagram for explaining the point of selection at the time of transmission. Since the transmission light amount U and the amplification factor A among the operation conditions are discrete operation setting values, it is only necessary to select one that matches with reference to the table 90. Regarding the reception level V, the discrete value in the table 90 does not always match the reception level V in the detection of the reception point.
In the example of FIG. 7, the amplitude of the photoelectric conversion signal S20 is V2 ± Vt.
/ 2 (Vt is a level interval) and is closest to the reception level V2 of the q-level reception levels V1 to Vq. Here, assuming that the transmission light amount is V2 and the amplification factor is A2, the transmission time point ts-222 is selected.

FIG. 8 is a flowchart showing the outline of the operation of the distance measuring apparatus. When measurement start is instructed by an operation input or a command input from an external device, the distance measuring device 1 detects a transmission time point (# 1). After that, scanning starts and 1
The transmission / reception operation of projecting the pulse light P to two measurement points and storing the waveform data DW of the measurement pulse light P0 and the storage of the operation conditions are repeated by changing the measurement points in order (# 2 to #
4). Note that the operations in Steps # 2 to # 4 correspond to the above-described "a plurality of measurements".

When the scanning is completed, the waveform data DW is read from the memory 33 to calculate the time barycenter ip (# 5).
As a result, the operation for detecting a series of reception points including scanning is completed for one measurement point. Subsequently, one of a plurality of transmission times ts in the table 90 is selected according to the operating conditions stored for the target measurement point (# 6). Then, a calculation is performed to determine the inter-object distance from the selected transmission time ts and the calculated time barycenter ip (reception time tr) (# 7). Such data processing is sequentially performed for all measurement points to generate measurement data DL (# 8, # 5).

FIG. 9 is a flowchart showing the detection operation at the time of transmission. The controller 40 includes the external light shutter 25.
A is closed and the internal light shutter 25B is opened (# 11). Then, the setting of the transmission light amount U, the setting of the light receiving level V, and the setting of the amplification factor A are performed (# 12 to # 14). In these settings, the set value is updated by one stage each time the settings are repeated. The setting of the light receiving level V is performed by controlling the filter mechanism 28 according to the stepwise setting value.

The light emitting element 11 emits light to emit the pulse light P0 to the internal optical path 19, and starts to write the reception data D32 into the memory 33 (# 15). When a predetermined length of sampling period (ranging time) obtained by adding a margin to the flight time corresponding to the specified maximum measuring distance has elapsed, the writing is terminated (# 16, # 17). To improve the reliability of detection, transmission and reception are repeated K times (# 18, # 15). K
Read out the waveform data DW in order and calculate the center of gravity,
The K time centroids ip are calculated (# 19). And K
The average value of the time centroids ip is set as the transmission time point ts in the RAM.
41 (# 20).

Thereafter, these settings are changed so as to change the combination of the set values of the transmission light amount U, the light reception level V, and the amplification factor A, and the transmission time ts under each of the q × m × n operating conditions is detected. (# 21 to # 2)
3). [Second Embodiment] FIG. 10 is a flowchart of a distance measuring operation according to a second embodiment.

Scanning is started in response to the measurement start instruction,
The pulse light P is emitted for each measurement point to store the waveform data DW and the operating conditions (# 31 to # 33). After the scanning, the transmission time point is detected (# 34). Thereafter, similarly to the first embodiment, the reception time tr is detected by the centroid calculation, and the transmission time ts is detected.
Is selected and data processing for calculating the distance is performed for all the measurement points (# 35 to # 38).

At the stage of detecting the transmission time ts, the operating conditions relating to the detection of the reception time tr for each measurement point are known. Therefore, the transmission time point ts only needs to be detected for the known operating conditions, and the second embodiment is advantageous in the time required for the detection. Note that the distance measurement operation of the second embodiment can be realized with the same device configuration as the first embodiment.

In the above embodiment, the transmission light amount U,
Although the reception time point ts is detected by changing all of the reception level V and the amplification factor A, the waveform data DW is not affected even if any of these conditions is fixed or the value changes. If no error occurs in the measured value, the transmission time point ts may be detected without changing the condition.

In the above embodiment, the average value of the K transmission times is set as the transmission time ts, but the transmission time obtained by one measurement may be stored. In the above-described embodiment, the detection of the transmission time point ts is performed in response to the measurement start instruction. However, the detection may be performed when the power is turned on. Also, the distance measuring device 1 may be stored in a nonvolatile memory at the final stage of manufacture. Further, the user may be allowed to appropriately detect the transmission time point ts. When the information is stored at the time of manufacturing, the configuration of the internal optical path from the distance measuring device may be omitted.

The stored transmission time ts may be data for specifying the transmission time, and may be time lag information measured from the light emission instruction or time information based on another predetermined timing. Good.

Environmental conditions represented by temperature can be used as operating conditions. In that case, an environmental condition for detecting the reception point may be detected by an appropriate sensor. In the above embodiment, the distance is calculated in the distance measuring device. However, the data at the time of transmission and the time of reception are stored,
The data may be used to calculate the distance by an external arithmetic device such as a personal computer.

In the above embodiment, the time centroid ip
Are the transmission time ts and the reception time tr, but the results of the peak detection and the pulse edge detection of the photoelectric conversion signal may be the transmission time ts and the reception time tr.

The present invention can be applied to a distance measuring apparatus having no scanning unit 60. It is also useful when performing multiple measurements on the same measurement point.

[0053]

According to the first to seventh aspects of the present invention,
It is possible to realize a distance measuring device that can perform a short distance measurement, can perform a plurality of measurements at a high speed, and has a high measurement accuracy.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a distance measuring device.

FIG. 2 is a block diagram of a transmission unit.

FIG. 3 is a block diagram of a receiving unit.

FIG. 4 is a block diagram of a reception processing circuit.

FIG. 5 is a conceptual diagram of a time center of gravity.

FIG. 6 is a diagram illustrating an example of a table used for selecting a transmission time point.

FIG. 7 is a diagram for explaining a point of selection at a transmission time point.

FIG. 8 is a flowchart showing an outline of the operation of the distance measuring device.

FIG. 9 is a flowchart showing a detection operation at the time of transmission.

FIG. 10 is a flowchart of a distance measuring operation according to the second embodiment.

[Explanation of symbols]

Reference Signs List 1 distance measuring device 19 internal optical path 10 transmitting unit (transmitting unit) 20 receiving unit (receiving unit) 60 scanning unit (scanning unit) 40 controller 41 RAM DL measurement data ts transmitting time tr receiving time P pulse light Q object 34 center of gravity calculating unit (Means for detecting transmission time and light reception time) 25A External light shutter 25B Internal light shutter

Continuation of the front page (72) Inventor Fumiya Yagi 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. 2F065 AA02 AA06 AA17 DD00 DD03 DD06 FF12 FF33 GG18 JJ18 LL24 LL30 LL46 MM16 NN08 QQ03 QQ06 QQ23 QQ42 2F112 AD01 BA03 BA05 BA06 CA12 DA10 DA40 EA05 FA03 FA07 FA21 FA41 5J084 AA02 AA05 AD01 BA04 BA11 BA36 BB02 BB20 CA03 CA61 CA70 DA09 EA04

Claims (7)

[Claims] A transmitting means for emitting a pulse light; and a receiving means for receiving the pulse light reflected back from the measurement object, wherein a distance to the measurement object is determined based on a transmission time and a reception time. A distance measuring apparatus for measuring, comprising: storage means for storing data for specifying a transmission time point corresponding to each of a plurality of operation conditions; and data stored in the storage means, the data corresponding to the operation conditions at the time of measurement. Means for selecting data, and means for detecting the time of reception of the pulsed light based on the output of the receiving means, based on the transmission time specified by the selected data and the detected reception time A distance measuring device characterized in that a distance is calculated. 2. The distance measuring apparatus according to claim 1, wherein said operating condition is an emission light amount of a pulse light. 3. The distance measuring apparatus according to claim 1, wherein said operating condition is an amount of received pulsed light in said receiving means. 4. The distance measuring apparatus according to claim 1, wherein said operating condition is an amplification factor for an output of said receiving means. 5. The distance measuring apparatus according to claim 1, wherein the operation of storing data for specifying a transmission time point in said storage means is performed before a plurality of measurements. 6. The distance measuring apparatus according to claim 1, wherein the operation of storing data for specifying a transmission time point in said storage means is performed after a plurality of measurements. 7. The distance measuring apparatus according to claim 1, further comprising a scanning unit that scans the pulsed light, and performing measurement at different positions on a measurement object.