JP6413960B2 - Distance measuring device - Google Patents

Description

  The present invention relates to a technique for measuring a distance from an object using a laser beam.

  Conventionally, if the laser light irradiation level or reflected light amplification gain is adjusted in multiple steps and the waveform obtained at high level or high gain is saturated and no peak can be detected, it can be obtained at low level or low gain. A technique is known in which an accurate distance is measured for both a low reflection object and a high reflection object by detecting a peak using the obtained waveform (see Patent Document 1).

Japanese Patent Laid-Open No. 2007-232381

However, the above-described conventional technique adjusts the signal intensity only on the time axis, and has a problem that the dynamic range in which saturation can be avoided is limited.
The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for expanding a light receiving dynamic range capable of ranging without degrading accuracy.

  The distance measuring device of the present invention includes a light emitting unit, a light receiving unit, and a distance measurement processing unit. The light emitting unit has a plurality of light emission modes that are set so that both the power and the pulse width of the light output increase stepwise. Instead of the pulse width, the pulse rise / fall time may be set to increase stepwise, and as a result, the pulse width only needs to be increased. The light receiving unit has a plurality of light receiving modes that are set so that both the gain and the band of the circuit that receives the reflected light of the optical signal transmitted from the light emitting unit increase stepwise. The distance measurement processing unit repeatedly operates the light emitting unit and the light receiving unit in a plurality of operation modes set by combining the light emission mode and the light reception mode, and the desaturation processing unit extracted from the light reception signal obtained in each of the operation modes. Using the peak waveform, the distance from the object reflecting the optical signal is obtained.

  That is, the light emitting unit and the light receiving unit are operated in cooperation to control not only the component on the time axis (power / gain) but also the component on the frequency axis (pulse width / band). The frequency component included in the light output is determined by the pulse width of the light output. Compared with the conventional technology that controls only the components on the time axis, the dynamic range that represents the range of received light levels that can be processed without saturating the received signal can be expanded, and the non-saturated received signal Accurate ranging can be realized using the.

  In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

It is a block diagram which shows the whole structure of a distance measuring device. It is a circuit diagram which shows the structure of a light emission part. It is a graph which shows the characteristic of a light emission circuit, (a) is the graph which showed the waveform of the optical output for every pulse width of a trigger signal, (b) shows the relationship between the pulse width of a trigger signal and the half value width of optical output. It is a graph. It is explanatory drawing which shows the relationship between an operation mode, the operation | movement of each part, and a waveform. It is a circuit diagram which shows the structure of a light-receiving part. It is a graph which shows the relationship between the trigger signal which a ranging process part produces | generates, operation | movement of a trigger signal and a switching circuit, and also light reception mode. It is a circuit diagram which shows the other structural example of a light-receiving part.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[1. First Embodiment]
[2. overall structure]
The distance measuring device 1 of the present embodiment is used by being mounted on a vehicle such as a passenger car, for example, and includes an optical unit 2, a scanning drive unit 4, and a distance measurement processing unit 5, as shown in FIG.

[3. Optical unit]
The optical unit 2 includes a light emitting unit 20 and a light receiving unit 30.
[3.1. Light emitting part]
The light emitting unit 20 emits laser light according to the pulsed trigger signal St supplied from the distance measurement processing unit 5. The light emitting unit 20 operates in a light emission mode corresponding to the pulse width of the trigger signal St, and here, a first light emission mode with a narrow pulse width and a second light emission mode with a wide pulse width are used. In the first light emission mode, laser light having a low power and a wide bandwidth is irradiated, and in the second light emission mode, laser light having a high power and a narrow band is irradiated. Here, the low power / high power and the narrow band / broadband represent the relative states between the two light emitting modes, and do not represent any absolute values.

  Specifically, as shown in FIG. 2, the light emitting unit 20 includes a driver 21, a protection circuit 22, a light emitting circuit 23, a resistor 24, and noise removing circuits 25 and 26. The driver 21 operates by receiving power from a low voltage (for example, 15 V) signal power source Vs, and converts the trigger signal St supplied from the distance measurement processing unit 5 into a trigger signal Trg having a larger current driving force. The protection circuit 22 includes a pair of Zener diodes connected in series, and is a known circuit that performs a clipping operation so that an excessive voltage is not applied to the driver 21 via the transmission line of the trigger signal Trg. The noise removal circuits 25 and 26 are made of resistors or ferrite beads for suppressing noise. The noise removal circuit 25 is provided on the power supply line of the signal power supply Vs, and the noise removal circuit 26 is provided on the transmission line of the trigger signal Trg from the driver 21 to the light emitting circuit 23.

  The light emitting circuit 23 includes a light emitting element 231, a switching element 232, and a charge storage unit 233. The charge storage unit 233 includes a plurality of capacitors connected in parallel. One end of the charge storage unit 233 is connected to a driving power source Vc having a high voltage (for example, 20 V) via the resistor 24, and the other end is connected to the ground line GND. . The light emitting element 231 is formed of a laser diode, the cathode is connected to the ground GND, and the anode is connected to the drive power supply side of the charge storage unit 233 via the switching element 232. The switching element 232 includes a field effect transistor, and is turned on / off according to a trigger signal Trg output from the driver 21. In the light emitting circuit 23 configured as described above, the capacitor constituting the charge storage unit 233 is charged via the resistor 24 when the switching element 232 is off. Thereafter, when the switching element 232 is turned on, the charge accumulated in the charge accumulation unit 233 is supplied to the light emitting element 231 and irradiated with laser light.

  In the light emitting circuit 23 configured as described above, as shown in FIG. 3A, the light output (hereinafter referred to as “light emission pulse”) increases as the pulse width (4 ns to 80 ns in the figure) of the trigger signal Trg increases. Increases power and pulse width. The peak value of the power of the light emission pulse becomes almost constant when it exceeds 10 ns. Further, as shown in FIG. 3B, the pulse width of the light emission pulse (here, the half width) increases according to the pulse width when the pulse width of the trigger signal Trg is 30 ns or less, and is almost constant when the pulse width exceeds 30 ns. It becomes the size of.

  That is, as shown in FIG. 4, the light emitting circuit 23 irradiates a light emitting pulse having a small power and a narrow pulse width (that is, a wide band) in the first light emitting mode to which the trigger signal Trg having a narrow pulse width is supplied. In the second light emission mode in which the trigger signal Trg having a wide pulse width is supplied, a light emission pulse having a large power and a wide pulse width (that is, a narrow band) is emitted.

[3.2. Light receiving section]
Returning to FIG. 1, the light receiving unit 30 receives reflected light emitted from the light emitting unit 20 and reflected by the object 7, and converts it into a received light signal that is an electrical signal. Here, the light receiving unit 20 includes a first light receiving mode used when the light emitting unit 20 operates in the first light emitting mode, and a second light receiving mode used when the light emitting unit 20 operates in the second light emitting mode. In the first light receiving mode, the circuit forming the light receiving unit 30 has a low gain and a narrow band, and in the second light receiving mode, the circuit forming the light receiving unit 30 has a high gain and a wide band.

Specifically, as shown in FIG. 5, the light receiving unit 30 includes a light receiving element 31, an operational amplifier 32, a first RC circuit 33, a second RC circuit 34, and a switching circuit 35.
The light receiving element 31 is composed of a photodiode (PD) or an avalanche photodiode (APD), and is connected so that a reverse bias is applied. In the operational amplifier 32, the cathode of the light receiving element 31 is connected to the inverting input, the non-inverting input is grounded, and the output is connected to the switching circuit 35. The first RC circuit 33 includes a capacitor C _F1 and a resistor R _F1 connected in parallel. One end is connected to the inverting input of the operational amplifier 32 and the other end is connected to the switching circuit 35. The second RC circuit 34 includes a capacitor C _F2 and a resistor R _F2 connected in parallel. Like the first RC circuit 33, one end is connected to the inverting input of the operational amplifier 32 and the other end is connected to the switching circuit 35. Yes. However, the resistance value and the capacitance value are set such that R _F1 <R _F2 and R _F1 × C _F1 > R _F2 × C _F2 .

  The switching circuit 35 includes a first path to which the first RC circuit 33 is connected, a second path to which the second RC circuit 34 is connected, one of the first path and the second path as an output terminal of the light receiving unit 30. A pair of switches 351 and 352 are inserted between the outputs of the operational amplifier 32. The switches 351 and 352 are simultaneously switched every time the rising edge of the trigger signal St from the distance measurement processing unit 5 is detected (see FIG. 6). The operation mode in which the first RC circuit 33 is connected by the switching circuit 35 is referred to as a first light reception mode, and the operation mode in the state in which the second RC circuit 34 is connected is referred to as a second light reception mode.

  The RC circuit (one of the first RC circuit 33 and the second RC circuit 34) connected to the output of the operational amplifier 32 by the switching circuit 35 constitutes an integration circuit together with the operational amplifier 32. In this integration circuit, the gain increases as the resistance value of the RC circuit increases, and the cutoff frequency of the low-pass filter formed by the RC circuit decreases as the value obtained by multiplying the resistance value and the capacitance value increases.

  That is, as shown in FIG. 4, the circuit characteristics of the light receiving unit 30 are low gain and narrow band in the first light receiving mode to which the first RC circuit 33 is connected, and in the second light receiving mode to which the second RC circuit 34 is connected. High gain and wide bandwidth. Here, the low gain / high gain and the narrow band / broadband represent relative states between the two light receiving modes, and do not represent any absolute values. Hereinafter, the operation mode in the first light emission mode and the first light reception mode is also referred to as a short distance mode, and the operation mode in the second light emission mode and the second light reception mode is also referred to as a long distance mode.

[4. Scanning drive unit]
The scanning drive unit 4 receives the synchronization signal SY synchronized with the trigger signal St from the distance measurement processing unit 5, and the irradiation direction of the laser light (light emission pulse) emitted from the light emitting unit 20 and the reflected light from the light receiving unit 30. The light receiving direction is changed in the horizontal and vertical directions, and scanning is performed within a preset range. Specifically, for example, a scanning mirror 4 is used in a horizontal direction by rotating the rotating mirror at a timing synchronized with the synchronizing signal SY using a rotating mirror having a plurality of reflecting surfaces that reflect the light emission pulse and the reflected light. Scan with laser light. Also, vertical scanning is realized by setting the angles of the reflecting surfaces to different angles. Note that two-dimensional scanning using a rotating mirror is a well-known technique, and therefore, detailed description thereof is omitted here.

  Also, here, both the irradiation light and the reflected light are configured to scan, but either one is configured so that the irradiation range or the light receiving range covers the entire scanning range, and only the other is scanned. It may be configured. Further, the scanning may be realized by mechanically moving the light emitting unit 20 and the light receiving unit 30 themselves without using a rotating mirror.

[5. Ranging processing unit]
The distance measurement processing unit 5 is configured as a known computer including a CPU 51 and a memory 52 such as a ROM or a RAM. The CPU 51 performs various processes such as a light emission / light reception process and a distance measurement process, which will be described later, according to a program stored in the memory 52. The distance measurement processing unit 5 includes an A / D converter that samples the reception signal Vo from the light receiving unit 30. In the distance measurement processing, the A / D converted digital data is processed. Note that some or all of the functions realized by the distance measurement processing unit 5 may be realized by hardware such as a circuit.

[5.1. Light emission / light reception processing]
The light emission / light reception process is activated by an activation instruction from an input unit (not shown), supplies a trigger signal St to the light emitting unit 20, and supplies a synchronization signal SY to the scanning drive unit 4.

  As shown in FIG. 6, the trigger signal St is composed of two pulse signals having different pulse widths that are generated every preset scanning period of one azimuth. Comparing the pulse widths of both pulse signals, the first is narrower and the latter is wider. Hereinafter, the former is referred to as a narrow pulse and the latter is referred to as a wide pulse. Note that the narrow pulse and the wide pulse are supplied with a predetermined light emission interval.

  The light emission interval is set to a length obtained by adding a margin to the time required for the light to reciprocate the maximum detection distance in the short distance mode. However, the rotation speed of the rotating mirror is set so that the azimuth error in the irradiation range of both pulses is sufficiently small when a narrow pulse and a wide pulse are output at the light emission interval.

  For example, when the emission interval is 2 μs, the beam width of the emission beam is 0.15 deg, and the rotation speed of the rotating mirror is 1200 rpm, the azimuth error in the irradiation range is 0.0144 deg. In this case, since about 90% of the irradiation range coincides, the narrow pulse and the wide pulse can be regarded as irradiating almost the same place.

The synchronization signal SY only needs to be synchronized with the trigger signal.
With this light emission / light reception processing, as shown in FIG. 4, in the short distance mode in which the light emitting unit 20 operates in the first light emission mode and the light receiving unit 30 operates in the first light reception mode, the power is small and the pulse width is narrow (band width). A wide) emission pulse is irradiated. The reflected light is processed by the light receiving unit 30 with a low gain and a narrow band. As a result, the reception signal Vo taken into the distance measurement processing unit 5 has a waveform in which the signal level is small and the pulse width is widened by limiting the band. In the long distance mode in which the light emitting unit 20 operates in the second light emitting mode and the light receiving unit 30 operates in the second light receiving mode, a light emitting pulse having a large power and a wide pulse width (narrow band) is emitted. The reflected light is processed by the light receiving unit 30 with a high gain and a wide band. As a result, the reception signal Vo captured by the distance measurement processing unit 5 has a waveform in which the pulse width is maintained because the signal level is large and the band is not limited.

[5.2. Ranging process]
The ranging process is started every time the reception signal Vo (sampling data) is acquired in each of the short distance mode and the long distance mode.

  In the distance measurement process, first, the signal level is equal to or higher than the first threshold value from the detection result in the short distance mode, and all pulse signal waveforms are extracted regardless of the presence or absence of saturation. Next, from the detection result in the long-distance mode, all the pulse signal waveforms whose signal level is equal to or higher than the second threshold set below the first threshold and are not saturated are extracted.

  Next, with respect to each extracted pulse signal waveform, the timing at which the maximum value of the pulse signal waveform is obtained is taken as the light reception timing of the reflected light, and the distance to the object reflecting the laser light is obtained by the so-called TOF (time of flight) method. . However, when the pulse signal waveform is detected at almost the same timing in both the short distance mode and the long distance mode, the distance is obtained using the detection result in the long distance mode.

[6. effect]
As explained above, in the short-distance mode, the pulse light with a narrow pulse width is irradiated and the reflected light is band-limited, so that the reflected light from an object with high reflectivity can be processed without saturation. A wide range of received light levels. It should be noted that in TOF distance measurement, it is only necessary to know the timing at which the pulse signal waveform reaches the maximum value in the received light waveform, and therefore the distance can be obtained without problems even if the waveform is blunted by removing the high frequency component. In the long-distance mode, pulse light with a wide pulse width is irradiated and the reflected light is processed so that the band is not limited, so that the reflected light from an object with low reflectivity can be detected. The range can be expanded. As a result, it is possible to expand the light receiving dynamic range that enables accurate ranging as a whole.

  Specifically, in the conventional device that adjusts only the intensity of the transmission signal and the gain of the reception signal, the light receiving dynamic range is about 100 dB, whereas in the distance measuring device 1 that controls by further controlling the band, The reception dynamic range can be expanded to about 140 dB.

[7. Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention can take a various form, without being limited to the said embodiment.

  (1) In the above embodiment, in order to adjust the gain and band of the circuit that constitutes the light receiving unit 30, the RC circuit 33 and 34 that constitute the integration circuit together with the operational amplifier 32 are switched. It is not limited to. For example, like the light receiving unit 30a shown in FIG. 7, only one RC circuit 36 is provided, and a variable resistor 371, a variable capacitor 372, and a resistor 373 are provided between the output of the operational amplifier 32 and the output end of the light receiving unit 30a. A configuration having an adjustment circuit 37 added thereto may be used. That is, the gain of the reception signal Vo can be adjusted by a voltage dividing circuit constituted by the variable resistor 371 and the resistor 373, and the reception signal Vo is constituted by a low-pass filter constituted by the variable resistor 371 and the variable capacitor 372. Can be adjusted.

  (2) In the above embodiment, the power and band of the light emission pulse output from the light emitting unit 20 are adjusted by changing the pulse width of the trigger signal St, but the present invention is not limited to this. For example, the voltage may be adjusted by changing the voltage of the driving power supply Vc supplied to the light emitting circuit 23.

  (3) In the above embodiment, the optical unit 2 has two operation modes including a short-distance mode and a long-distance mode. However, the optical unit 2 may have three or more operation modes. In this case, not only can the light receiving dynamic range be further expanded, but also the load on each component used to realize each operation mode can be reduced. Can be configured.

  (4) In the above embodiment, the light emitting unit 20 and the light receiving unit 30 are configured by using one light emitting element 231 and one light receiving element 31, respectively. You may comprise using the light receiving element. In this case, each element may operate in a single operation mode, or each element may operate in a plurality of operation modes.

(5) In the above embodiment, the scanning drive unit 4 is provided and the irradiation light is scanned. However, the present invention is not limited to this, and a configuration in which scanning is not performed may be employed.
(6) The functions of one component in the above embodiment may be distributed to a plurality of components, or the functions of a plurality of components may be integrated into one component. Further, at least a part of the configuration of the above embodiment may be replaced with a known configuration having the same function. Moreover, you may abbreviate | omit a part of structure of the said embodiment. Further, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified only by the wording described in the claim are embodiment of this invention.

  (7) In addition to the distance measuring device described above, the present invention can be realized in various forms such as a system including the distance measuring device as a constituent element and a distance measuring method.

  DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 2 ... Optical unit, 4 ... Scanning drive part, 5 ... Distance measuring process part, 7 ... Object, 20 ... Light emission part, 21 ... Driver, 22 ... Protection circuit, 23 ... Light emission circuit, 24 ... Resistance , 25, 26 ... noise elimination circuit, 30, 30 a ... light receiving unit, 31 ... light receiving element, 32 ... operational amplifier, 33 ... first RC circuit, 34 ... second RC circuit, 35 ... switching circuit, 36 ... RC circuit, 37 ... Adjustment circuit, 51 ... CPU, 52 ... memory, 231 ... light emitting element, 232 ... switching element, 233 ... charge storage unit, 351, 352 ... switch, 371 ... variable resistor, 372 ... variable capacitor, 373 ... resistor

Claims (4)

A light emitting section (20) having a plurality of light emission modes set so that both the power and pulse width of the optical output increase stepwise;
A light receiving section (30) having a plurality of light receiving modes set so that both the gain and the band of the circuit that receives the reflected light of the optical signal transmitted from the light emitting section are increased stepwise;
A plurality of operation modes set by combining the light emitting mode and the light receiving mode, the light emitting unit and the light receiving unit are operated repeatedly, and a non-saturated peak extracted from the light receiving signal obtained in each of the operation modes. A distance measurement processing unit (5) for obtaining a distance from an object reflecting the optical signal using a waveform;
A distance measuring device comprising: The light-emitting unit includes a light-emitting element, a switching element, and a charge storage unit, and is configured using a light-emitting circuit having characteristics that the power and pulse width of the optical output increase as the pulse width of the trigger signal increases. The distance measuring device according to claim 1, wherein:   The light emitting unit is configured by using a plurality of light emitting elements having different characteristics, and each of the light emitting elements is configured to realize one or more of the light emission modes. Or the distance measuring apparatus of Claim 2.   2. The light receiving unit is configured by using a plurality of light receiving elements having different characteristics, and each of the light receiving elements is configured to realize one or more of the light receiving modes. The distance measuring device according to any one of claims 3 to 4.