JP6911674B2 - Time measuring device, ranging device, mobile device, time measuring method and ranging method - Google Patents

Description

The present invention relates to a time measuring device, a distance measuring device, a moving body device, a time measuring method, and a distance measuring method.

Conventionally, there are known devices that measure the time from the measurement start time to the input of the measurement target signal (see, for example, Patent Documents 1 and 2).

However, in the devices disclosed in Patent Documents 1 and 2, there is room for improvement in improving the measurement accuracy while suppressing the complexity of the configuration.

The present invention uses a delay element array in which a plurality of delay elements that delay an input signal are arranged, and a reference clock having a constant period T longer than the delay time of each delay element in the delay element array, and a measurement start time. A time measuring device that measures the time from when the signal to be measured is input, and the time for inputting noise generated inside and outside the time measuring device into the delay element train to acquire the delay time for each delay element. It is a measuring device.

According to the present invention, it is possible to improve the measurement accuracy while suppressing the complexity of the configuration.

It is a figure which shows the schematic structure of the object detection apparatus of one Embodiment. FIG. 2 (A) is a diagram for explaining a light projecting optical system and a synchronous system, FIG. 2 (B) is a diagram for explaining a light receiving optical system, and FIG. 2 (C) is a diagram for explaining an LD. It is a figure which shows roughly the optical path of the light from the reflection mirror to the reflection mirror, and the optical path of the light from the reflection mirror to the PD for time measurement. It is a timing diagram which shows the synchronization signal and LD drive signal. FIG. 4A is a timing diagram showing an emission light pulse and a reflected light pulse, and FIG. 4B is a timing diagram showing a binarized emission light pulse and a reflected light pulse. It is a figure for demonstrating the TOF method. It is a figure which shows the structural example of the PD output detection part. It is a figure which shows the structure of the general TDC (Time to Digital Controller) apparatus. FIG. 8A is a diagram for explaining a calculation method of a general TDC device, and FIG. 8B is a diagram for explaining an edge detection operation of a general TDC device. It is a figure which shows the structure which calculates the delay time for each delay element in one Embodiment. FIG. 10A is a histogram showing the number of edge detections for each delay element, and FIG. 10B is a diagram for explaining a method of calculating the delay time for each delay element. It is a figure for demonstrating the time measuring apparatus and distance measuring apparatus of Example 1 of one Embodiment. FIG. 12A is a flowchart for explaining the operation flow of the first time measuring means, and FIG. 12B is a flowchart for explaining the operation flow of the second time measuring means. It is a figure for demonstrating operation of a binarization circuit. It is a figure for demonstrating the threshold value control performed by dividing a histogram generation time. It is a figure for demonstrating the threshold value control corresponding to mode switching. It is a figure for demonstrating the operation flow of the time measuring apparatus. It is a figure for demonstrating the sensing apparatus. It is a flowchart for demonstrating distance measurement processing. It is a flowchart for demonstrating the time information acquisition mode for estimation. It is a flowchart for demonstrating the delay time calculation mode. It is a flowchart for demonstrating the measurement target time calculation process.

Hereinafter, the object detection device 100 according to the embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of the object detection device 100 in a block diagram.

As an example, the object detection device 100 is mounted on a vehicle as a moving body, emits light, receives light reflected or scattered by an object (for example, a preceding vehicle, a stopped vehicle, an obstacle, a pedestrian, etc.) and receives the light. It is a scanning laser radar that detects information about an object (hereinafter, also referred to as "object information") such as the presence or absence of an object and the distance to the object. The object detection device 100 receives electric power from, for example, a vehicle battery (storage battery). Laser radar is also called lidar. In addition, LIDAR is an abbreviation for Light Detection and Ranking, or Laser Imaging Detection and Ranking.

As shown in FIG. 1, the object detection device 100 includes a light projection system 10, a light receiving optical system 30, a detection system 40, a time measurement system 45 (time measurement device), a synchronization system 50, a measurement control unit 46, and an object recognition unit. It is equipped with 47 and the like.

The floodlight system 10 includes an LD (laser diode) as a light source, an LD drive unit 12, and a floodlight optical system 20.

The LD is also called an end face emitting laser, and is driven by the LD drive unit 12 to emit laser light. The LD drive unit 12 lights (lights) the LD using the LD drive signal (rectangular pulse signal) output from the measurement control unit 46. As an example, the LD drive unit 12 includes a capacitor connected so as to be able to supply a current to the LD, a transistor for switching conduction / non-conduction between the capacitor and the LD, a charging means capable of charging the capacitor, and the like. .. The measurement control unit 46 receives a measurement control signal from the ECU (electronic control unit) of the automobile to start or stop the measurement.

FIG. 2A schematically shows the projectile optical system 20 and the synchronous system 50. FIG. 2B schematically shows the light receiving optical system 30. Hereinafter, the XYZ three-dimensional Cartesian coordinate system in which the Z-axis direction shown in FIG. 2A or the like is the vertical direction will be described as appropriate.

As shown in FIG. 2A, the projection optical system 20 is arranged on a coupling lens 22 arranged on the optical path of light from the LD and on the optical path of light via the coupling lens 22. The reflection mirror 24 and the rotation mirror 26 as a deflector arranged on the optical path of the light reflected by the reflection mirror 24 are included. Here, in order to reduce the size of the device, a reflection mirror 24 is provided on the optical path between the coupling lens 22 and the rotating mirror 26, and the optical path is folded back.

Therefore, the light emitted from the LD is shaped into light having a predetermined beam profile by the coupling lens 22, then reflected by the reflection mirror 24 and deflected around the Z axis by the rotation mirror 26.

The light deflected to a predetermined deflection range around the Z axis by the rotating mirror 26 is the light projected from the projection optical system 20, that is, the light emitted from the object detection device 100.

The rotating mirror 26 has a plurality of reflecting surfaces around the rotating axis (Z axis), and reflects (deflects) the light from the reflecting mirror 24 while rotating around the rotating axis, so that the light corresponds to the above deflection range. The effective scanning area is scanned one-dimensionally in the horizontal one-axis direction (here, the Y-axis direction). Here, the deflection range and the effective scanning area are on the + X side of the object detection device 100. Hereinafter, the rotation direction of the rotation mirror 26 is also referred to as a “mirror rotation direction”.

As can be seen from FIG. 2A, the rotating mirror 26 has two reflecting surfaces (two opposing surfaces), but the present invention is not limited to this, and may be one surface or three or more surfaces. It is also possible to provide at least two reflecting surfaces and arrange them at different angles with respect to the rotation axis of the rotating mirror to switch the scanning / detecting region in the Z-axis direction.

As shown in FIG. 2B, the light receiving optical system 30 is formed by a rotating mirror 26 that reflects light projected from the light projecting optical system 20 and reflected by an object within the effective scanning region, and the rotating mirror 26. Includes a reflection mirror 24 that reflects the light of the above, and an imaging optical system that is arranged on the optical path of the light from the reflection mirror 24 and forms the light on a time measurement PD 42 described later.

Here, as an example, the floodlight optical system 20 and the light receiving optical system 30 are installed in the same housing. This housing has an opening on the optical path of the emitted light from the projectile optical system 20 and on the optical path of the incident light to the light receiving optical system 30, and the opening is closed by a window (light transmitting window member). It has been. The window can be made of glass or resin, for example.

FIG. 2C shows an optical path from the LD to the reflection mirror 24 and an optical path from the reflection mirror 24 to the PD42 for time measurement.

As can be seen from FIG. 2C, the floodlight optical system 20 and the light receiving optical system 30 are arranged so as to overlap each other in the Z-axis direction, and the rotating mirror 26 and the reflection mirror 24 receive the light receiving optical system 20 and the light receiving optical system 20. It is common to the optical system 30. As a result, the relative positional deviation between the LD irradiation range on the object and the light receiving range of the time measurement PD42 can be reduced, and stable object detection can be realized.

As shown in FIGS. 2B and 1, the detection system 40 receives the light projected from the light projecting optical system 20 and reflected by the object in the effective scanning region via the light receiving optical system 30. It includes a measurement PD 42 (photodiode) and a PD output detection unit 44 that detects a voltage signal (light receiving signal) based on the output current (photocurrent) of the time measurement PD 42.

Therefore, the light projected from the projection optical system 20 and reflected or scattered by the object is guided to the imaging optical system via the rotating mirror 26 and the reflecting mirror 24, and is focused on the time measurement PD 42 by the imaging optical system. (See FIG. 2 (B)). In FIG. 2B, in order to reduce the size of the device, a reflection mirror 24 is provided between the rotating mirror 26 and the imaging optical system, and the optical path is folded back. Here, the imaging optical system is composed of two lenses (imaging lenses), but it may be a single lens, three or more lenses, or a mirror optical system. good.

As shown in FIGS. 2A and 1, the synchronous system 50 is light emitted from the LD and reflected by the reflection mirror 24 via the coupling lens 22, and is deflected by the rotating mirror 26 and reflected by the reflection mirror 24. The output current (optical current) of the synchronization lens 52 arranged on the optical path of the light reflected again by, the synchronization detection PD54 arranged on the optical path of the light via the synchronization lens 52, and the synchronization detection PD54. ) Is included in the PD output detection unit 56 that detects a voltage signal (light receiving signal) based on the above.

More specifically, the reflection mirror 24 is arranged on the upstream side in the rotation direction of the rotary mirror 26 with respect to the deflection range, and the light deflected by the rotary mirror 26 on the upstream side of the deflection range is incident. Then, the light deflected by the rotating mirror 26 and reflected by the reflecting mirror 24 is incident on the synchronization detection PD 54 via the synchronization lens 52.

The reflection mirror 24 may be arranged on the downstream side in the rotation direction of the rotation mirror 26 with respect to the deflection range. Then, the synchronization system 50 may be arranged on the optical path of the light deflected by the rotating mirror 26 and reflected by the reflecting mirror 24.

Every time the light reflected by the reflecting surface of the rotating mirror 26 is received by the synchronization detection PD 54, the photocurrent is output from the synchronization detection PD 54 to the PD output detection unit 56. As a result, a signal (synchronous signal) is periodically output from the PD output detection unit 56 (see FIG. 3).

By performing synchronous lighting for irradiating the synchronization detection PD 54 with the light from the rotation mirror 26 in this way, it is possible to obtain the rotation timing of the rotation mirror 26 from the light receiving timing of the synchronization detection PD 54.

Therefore, the effective scanning region can be lightly scanned by lighting the LD in a pulsed manner after a predetermined time has elapsed after the LD is turned on synchronously. That is, the effective scanning region can be light-scanned by pulse-lighting the LD in the period before and after the timing when the PD 54 for synchronization detection is irradiated with light.

Here, as the light receiving element used for time measurement and synchronization detection, in addition to the PD (Photodiode) described above, an APD (Avalanche Photodiode), a Geiger mode APD SPAD (Single Photodiode Dictionary), or the like can be used. Is. Since APD and SPAD have high sensitivity to PD, they are advantageous in terms of detection accuracy and detection distance.

When the PD output detection unit 56 detects a voltage signal (light receiving signal) based on the output current (photocurrent) of the synchronization detection PD 54, the PD output detection unit 56 outputs the synchronization signal to the measurement control unit 46.

The PD output detection unit 56 converts the output current from the synchronization detection PD 54 into a voltage signal with a current-voltage converter, amplifies the voltage signal with a signal amplifier, and uses a comparator such as a comparator to amplify the amplified voltage signal. The voltage is binarized at the threshold value, and the binarized signal (binary digital signal) is output to the measurement control unit 46 as a synchronization signal.

The measurement control unit 46 generates an LD drive signal based on the synchronization signal from the PD output detection unit 56, and outputs the LD drive signal to the LD drive unit 12 and the time measurement system 45.

That is, the LD drive signal is a pulse lighting signal (periodic pulse signal) delayed with respect to the synchronization signal (see FIG. 3).

When the PD output detection unit 44 detects a voltage signal (light receiving signal) based on the output current of the time measurement PD 42, the PD output detection unit 44 outputs the detection signal to the time measurement system 45. Details of the PD output detection unit 44 will be described later.

The time measurement system 45 measures the round-trip time of light to the object based on the timing at which the LD drive signal from the measurement control unit 46 is input and the timing at which the detection signal from the PD output detection unit 44 is input. The round trip time is output to the measurement control unit 46 as a time measurement result.

The measurement control unit 46 calculates the round-trip distance to the object by converting the time measurement result from the time measurement system 45 into a distance, and outputs 1/2 of the round-trip distance as distance data to the object recognition unit 47.

The object recognition unit 47 recognizes where an object is based on a plurality of distance data acquired by one scan or a plurality of scans from the measurement control unit 46, and outputs the object recognition result to the measurement control unit 46. .. The measurement control unit 46 transfers the object recognition result to the ECU.

The ECU performs, for example, steering control (for example, auto-steering), speed control (for example, auto-brake), or the like of an automobile based on the transferred object recognition result.

Here, the LD drive unit 12 drives the LD when the effective scanning region is scanned by the rotating mirror 26, and the pulsed light as shown in FIG. 4A (hereinafter, also referred to as “injection light pulse”). ) Is ejected. Then, the pulsed light emitted from the LD and reflected (scattered) by the object (hereinafter, also referred to as “reflected light pulse”) is used for time measurement PD42 (in FIG. 4A, APD is used instead of PD as a light receiving element. Is detected).

It is possible to calculate the distance to the object by measuring the time t from the time when the LD emits the emitted light pulse to the time when the reflected light pulse is detected by the APD. Regarding time measurement, for example, as shown in FIG. 4 (B), the emitted light pulse is received by a light receiving element such as PD to form a binarized rectangular pulse, and the reflected light pulse is binarized by the PD output detection unit. The time difference t of the rising timing of both rectangular pulses may be measured by a time measurement circuit, or the waveforms of the emitted light pulse and the reflected light pulse are A / D converted and converted into digital data, and the LD It is also possible to measure the time t by performing a correlation calculation between the output signal and the output signal of the APD.

As can be seen from the above description, in the present embodiment, the so-called TOF (Time Of Flight) method is used as the time measurement method (see FIG. 5). That is, in the present embodiment, first, the LD as a light source is made to emit pulse light. The pulse width of this pulsed light is, for example, several ns to several tens of ns. This pulsed light is projected through the light projecting optical system 20, reflected by an object, returned, and is incident on the time measurement PD 42 via the light receiving optical system 30. At this time, the photocurrent is output from the time measurement PD 42 to the PD output detection unit 44.

As shown in FIG. 5, the noise is generally small in the projected waveform, but the reflected light and scattered light from the object are usually weak. Therefore, when the light is greatly amplified by the amplifier, the noise is also large in the received waveform. In this specification, "noise" is also referred to as "noise signal" for convenience.

FIG. 6 shows a block diagram of the configuration of the PD output detection unit 44 of the detection system 40.

As shown in FIG. 6, the PD output detection unit 44 includes a current-voltage converter 44a, a signal amplifier 44b, and a binarization circuit 44d.

The current-voltage converter 44a converts the output current from the time measurement PD 42 into a voltage signal (light receiving signal) and outputs it to the signal amplifier 44b.

The signal amplifier 44b amplifies the input received signal and outputs it to the binarization circuit 44d.

Here, a photodetector is configured including a PD42 for time measurement, a current-voltage converter 44a, and a signal amplifier 44b. The signal amplifier is not indispensable in the "photodetector".

The binarization circuit 44d binarizes the input received light signal with a threshold value, and outputs the binarized signal as a detection signal to the time measurement system 45.

Here, the time measuring system 45 as a time measuring device is based on the TDC (Time to Digital Converter) technology for measuring the time difference between two digital signals with high accuracy and stability.

FIG. 7 shows the configuration of a general time measuring device (hereinafter, also referred to as “TDC device”) using TDC technology. This TDC device has a reference clock generating means, a delay element sequence in which a plurality of delay elements that give a time delay to the input signal are connected in series, and an edge of rising or falling of the signal input to the delay element sequence. It is configured to include an edge detecting means for detecting and a calculation means 1.
In FIG. 7, the time difference between the timings at which the signals generated by the signal sources 1 and 2 are input to the TDC device is the time to be measured. Here, the signal generated by the signal source 2 is used as the measurement start signal, and the time difference between the time when the measurement start signal is input to the TDC device and the time when the measurement target signal 1 generated by the signal source 1 is input to the TDC device. An example of measuring (hereinafter, also referred to as “measurement target time”) will be described. That is, in FIG. 7, the signal generation timing at the signal source 1 is later than the signal generation timing at the signal source 2.

FIG. 8A shows a calculation method performed by the TDC device. First, when the measurement start signal is input, the calculation means 1 increases the count value of the reference clock (counts up the reference clock) in synchronization with the rising or falling edge of the reference clock.
Here, the rising edge is the time or phenomenon when the signal level changes from Low (0) to High (1), and the falling edge is the time or phenomenon when the signal level changes from High (1) to Low (0). Means that.
The calculation means 1 stops increasing the count value of the reference clock when it determines that the measurement target signal 1 is input to the TDC device, and holds _{the count value C clk at that time.} Assuming that the period of the reference clock is T, T × C _clk roughly estimates (approximate) the measurement target time.

In the above calculation, the temporal resolution is determined only by the period T of the reference clock. In the time measuring device, a delay element sequence in which a large number of delay elements are arranged is used in order to calculate this with higher resolution.
Generally, in a delay element sequence in which a large number of delay elements (hereinafter, also simply referred to as "elements") composed of an inverter or a buffer are arranged, each element has a delay time of several to several hundred picoseconds, and an input signal is obtained. On the other hand, a delay is given by the number of elements through which the signal has passed.
For example, when the signal to be measured is a rectangular positive pulse signal, the terminal voltage level of the element through which the pulse signal is passing becomes High (1), and the other elements become Low (0). The number of elements whose terminal voltage levels are set to High (1) at the same time depends on the time width (pulse width) of the generated pulse signal.
In the time difference measurement, it is important which element in the delay element sequence the edge of the signal (specifically, the rising or falling edge) is passing through, so that the signal level is from Low (0) to High ( It is necessary to find an element that switches to 1) or an element that switches from High (1) to Low (0). Therefore, it is preferable to provide an edge detecting means for detecting the edge of the signal in the TDC device.

The operation of the edge detecting means will be described with reference to FIG. 8 (B). In FIG. 8B, a plurality of elements constituting the delay element sequence are numbered 1, 2, 3 ... In order from the side closest to the signal input end, and the falling edge of the third element is 9. An example is shown in which the rising edge is detected in the second element.
The edge detecting means operates in synchronization with the reference clock generated by the reference clock generating means. As an edge detection means, for example, it is desirable to attach a flip-flop circuit to the terminal of each delay element and use a method of monitoring the terminal voltage level of the delay element in synchronization with the reference clock.
Here, for example, when a rising edge is detected in the J-th element, the edge detecting means informs the calculation means 1 that the element in which the edge is detected is the J-th element. The calculation means 1 calculates and holds _{the total delay time T delay} (J) from the first element to the Jth element of the delay element sequence from the known delay time for one element and the information of the Jth element. .. From the above, the measurement target time is output from the calculation means 1 as _{T × C clk} −T _{delay (J).}

In the above description, it is assumed that the delay time of the delay element is uniform from the first to the Jth. However, in reality, there is an individual difference in the delay time for each element due to the difference in wiring length between the delay elements, the process, the power supply variation, and the like. Therefore, assuming that the difference between the assumed delay time of the delay element and the delay time of the kth delay element is ΔT _k , the measurement target time is ΣΔT _{k (k = 1 to} J), that is, ΔT 1 + ΔT ₂ + ... + ΔT. _J-1 + ΔT _J will be superimposed as a measurement error. Therefore, it is possible to reduce the measurement error by grasping the delay time for each delay element and using it in the calculation. In the following, a method for grasping the delay time for each delay element will be described.

Here, a method of inputting a pulse train containing a plurality of pulses to the delay element train and estimating the delay time from the number of times when the edge of the pulse is detected will be described.
Generally, it is known that the number of pulse edge detections and the delay time of the delay element are in a proportional relationship. The principle is that an element with a long delay time has a long pulse stay time and the chance of detecting an edge increases, while an element with a short delay time has a short pulse stay time and a small chance of detecting an edge. Is.

A specific example of edge detection will be described with reference to FIG. In FIG. 9, the measurement target signal 2 generated by the signal source 3 is input to the delay element sequence via the signal input end. Here, it is preferable that the measurement target signal 2 is a pulse train generated stochastically and randomly. When the signal to be measured is input to the delay element train via the signal input end, the edge detecting means detects the rising or falling edge. The edge detecting means sends the information of the element in which the edge is detected to the histogram generating means. The histogram generating means adds (counts up) the number of edge detections for each delay element number, and records and holds the added value (count-up value).

FIG. 10A shows an example of a histogram generated by the histogram generating means of FIG. Here, an example is shown when a total of 100 edges are detected in the delay element numbers 1 to 10. Based on the histogram information generated here, the delay time calculating means calculates the delay time of each delay element.

FIG. 10B is a conceptual diagram when calculating the delay time. The delay time calculating means of FIG. 9 first detects the number of the element whose edge is detected by the nth reference clock and the n + 1th reference clock. FIG. 10B shows an example in which the edge is detected by the first delay element in the nth reference clock and the edge is detected by the eleventh delay element in the n + 1th reference clock. In this case, it can be determined that the number of delay elements corresponding to the time of the period T of the reference clock is 10 from the 1st to the 11th.
Subsequently, since a total of 100 edges are detected in the 1st to 10th delay elements in FIG. 10A, it is extracted how many edges are detected out of 100 times for each delay element. .. This extracted product is the ratio of the delay time for each delay element to one clock. Therefore, the delay time of each delay element is obtained by multiplying the ratio of this delay time by the period T of the reference clock, which is a known time.

A specific calculation example is shown below. Here, the reference clock period T is 5 nanoseconds. Focusing on the delay element of the delay element number 5, the number of edge detections in FIG. 10A is 10 times, and the ratio of the delay time can be calculated as 10/100. Therefore, the delay time of the delay element of the delay element number 5 is calculated to be 500 picoseconds from 5 nanoseconds × (10 ÷ 100). It is possible to calculate the delay time for other delay elements in the same manner.

In the above, the principle of TDC for measuring the time difference between two digital signals and the method for calculating the delay time for each delay element for improving the measurement accuracy of TDC have been described. Hereinafter, an embodiment in which both can be compatible with one device will be described. The time measuring device of each embodiment described below functions as the time measuring system 45 of the object detection device 100.

[Example 1]
As shown in FIG. 11, the time measuring device of the first embodiment includes a light emitting means, a light receiving means, a controlling means, a noise acquiring means, a reference clock generating means, a first time measuring means, a second time measuring means, and a calculation means. 2. Includes delay time calculation means and the like.
Here, the noise control means has the threshold control means, but it is not always necessary to have the threshold control means. The delay time calculating means includes a histogram generating means.
The light projecting means includes a light projecting optical system 20, an LD, and an LD drive unit 12. The light receiving means includes a PD 42 for time measurement and a current / voltage converter 44a. The control means includes a measurement control unit 46.
In the time measuring device of the first embodiment, after the measurement start signal (for example, the LD drive signal which is a trigger signal for driving the light source of the light projecting means) is input, the measurement target signal 1 (for example, the output signal of the light receiving means) is used. It has a function to calculate the elapsed time until a certain received signal) is input.

The operation flow of the first time measuring means will be briefly described below with reference to the flowchart of FIG. 12A.

When the measurement start signal is input (YES in step S1), the clock count-up is started in synchronization with the rising or falling edge of the reference clock (step S2). If the measurement start signal is not input, the state waits (NO in step S1).

After step S2, when it is determined that the measurement target signal 1 is input (YES in step S3), the clock count-up is stopped in synchronization with the rising or falling edge of the next reference clock (step S4). .. If it is determined that the measurement target signal 1 has not been input (NO in step S3), the clock count-up is continued.

After step S4, the count value C _clk of the reference clock is acquired and output to the calculation means 2 (step S5). Using this count value C _clk and the period T of the reference clock, the elapsed time can be roughly estimated (approximate) _{as T × C clk.}

The second time measuring means detects a delay element train in which a plurality of delay elements are connected in series and a change in the signal level at both ends (input end and output end) of each delay element, and the signal level changes at both ends. It has an edge detecting means for detecting the number (delayed element number) of the (different) delay element.

The operation flow of the second time measuring means will be described below with reference to the flowchart of FIG. 12B.
Here, the delay time of each delay element is set shorter than the period of the reference clock. Further, each delay element is composed of a combination of a gate element, a resistor, a capacitor, a coil, and the like.
For the detection of the change in the signal level between the delay elements (change in the terminal voltage level of the delay element), for example, an array of a large number of flip-flops is used, and the operation is performed in synchronization with the reference clock.

When the measurement target signal 1 is input to the second time measurement means, the measurement target signal 1 passes through the delay element sequence. At this time, the signal level is High (1) for the delay element through which the measurement target signal 1 is passing, and Low (0) for the other delay elements.
Then, as in the case described with reference to FIG. 8B, when the portion (delay element number 1) at which the signal level first switches from High to Low in the delay element sequence is read in synchronization with the reference clock. That is, when it is detected that the falling edge of the measurement target signal 1 has entered the delay element train (YES in step S11), with respect to the falling edge position of the reference clock next to the reference clock synchronized with the location. The delay element number J is output as the number of the delay element located closest to the signal input end side (step S12). For example, in FIG. 8A, J = 3.

The delay time calculating means calculates the delay time of each delay element in the second time measuring means. The measurement target signal 2 is used to calculate this delay time. The measurement target signal 2 is a stochastically randomly generated signal acquired by the noise acquisition means.
The measurement target signal 2 is, for example, thermal noise appearing at the resistance end, shot noise derived from light, or the like. Strictly speaking, the measurement target signal 2 is not a “signal” but a “noise”, but here, for convenience, the wording “signal” is used.

Specifically, the measurement target signal 2 is output from a PD (Photo-Diode) or APD (Avalanche Photo-Diode) used as a light-receiving element of the light-receiving means, and binarized (detected) by a binarizing circuit. Shot noise (shot noise) can be used.

Further, as the measurement target signal 2, a wiring may be connected to the resistance end of the circuit inside and outside the time measuring device, and the thermal noise obtained there may be used. Examples of the circuit outside the time measuring device include a circuit after the light receiving element in the photodetector, a circuit in the control means, a circuit in the LD drive unit, and the like.

The delay time calculation means inputs the noise as the measurement target signal 2 as described above into the delay element sequence, and counts the number of edge detections for each delay element.

The delay time calculating means has a histogram generating means for generating a histogram representing the number of edge detections for each delay element, and calculates the delay time of the delay element based on the information of the histogram.
The delay time calculating means calculates the delay time of each delay element. The specific calculation method is the same as the content described with reference to FIGS. 9, 10 (A), and 10 (B).

When an edge is detected in the J-th delay element, the delay time calculation means calculates the total delay time T _delay (J), which is the total delay time from the first (head) delay element to the J-th delay element. It can be calculated and the elapsed time _{can be accurately calculated as in T × C clk} −T _delay (J) (see FIG. 8 (A)).

[Example 2]
Next, Example 2 will be described. In the first embodiment, the measurement target signals 1 and 2 are derived from a light receiving element which is the same signal source. Therefore, in the second embodiment, the signal generation frequency is controlled and only the desired signal is extracted by controlling the threshold value in the binarization circuit for the measurement target signals 1 and 2.

The operation of the binarization circuit will be described below with reference to FIG. As the binarization circuit, it is preferable to use a comparator circuit or the like.
The binarization circuit outputs "1" for an input analog signal that exceeds an arbitrary threshold value, and "0" for other signals.
It is desirable that the binarization circuit is connected immediately after the light receiving means as shown in FIG. 11, and a voltage signal (light receiving signal) based on the above-mentioned PD or APD current may be input, or the light receiving signal may be input. Those that have passed through a filter circuit that allows only those in the desired frequency band to pass through may be used.

In FIG. 13, it is assumed that all analog waveforms on the time axis are noise generated stochastically and randomly. As the threshold value is lowered, the number of pulses of the digital signal generated by the binarization circuit increases. As a result, it is possible to shorten the time required to generate the histogram. On the contrary, by raising the threshold value, it is possible to make the generation of a digital signal based on noise zero. For example, in the sequence in which the TDC device is operated, the S / N ratio of the measurement can be improved by controlling the threshold value so as to extract only the measurement target signal 1 larger than the noise.

As described in the second embodiment, the frequency of digital signal generation can be controlled by controlling the threshold value for binarizing the signal from the signal source. In particular, when the sequence time is limited in the sequence for generating the histogram, it is necessary to efficiently acquire the measurement target signal 2 in FIG.

[Example 3]
Therefore, in the third embodiment, an efficient signal acquisition method will be described. An example of the threshold control method in the histogram generation sequence is shown in FIG.
Here, the histogram generation time is divided into six. During the division time 1 to 5, the threshold value is controlled to be gradually lowered in order to increase the number of noise detections. In the division time 6, since a predetermined number of noises could be acquired (detected) up to the division time 5, the threshold value was not lowered with respect to the division time 5.

In FIG. 14, the threshold value is changed discretely each time the division time is changed, but it may be changed continuously. The change may be linear or non-linear. The method of change may be equal or non-uniform for each division time.

[Example 4]
In the fourth embodiment, the threshold control including the mode switching will be described with reference to FIG. 15 and the like. Here, a mode switching time is provided between the second mode for generating a histogram and calculating the delay time and the first mode for acquiring time information for estimating the elapsed time.
In this case, it is desirable that the measurement target signal 1 and the measurement target signal 2 are output from the same signal source as shown in FIG. By raising or lowering the threshold value, it is possible to efficiently acquire only the desired signal in each mode.

Considering actual use, noise such as the measurement target signal 2 is often mixed with the measurement target signal 1 in FIG. In FIG. 15, two measurement target signals 1 are included in the first mode, but by raising the threshold value, only the measurement target signal 1 can be converted into a digital signal without detecting the noise at the base.
It is preferable to control the threshold value so that there is no noise component exceeding the threshold value at least in the final division time of the mode switching time. The threshold control within the mode switching time may be performed discretely or continuously as shown in FIG. The method of change may be equal or non-uniform for each division time. The continuous change may be linear or non-linear. The threshold value may be constant without changing within the mode switching time.

[Example 5]
In the fifth embodiment, the signal sources of the measurement target signal 1 and the measurement target signal 2 as shown in FIG. 11 are used as the light receiving element of the light receiving means. It is desirable to use PD (Photo-Diode) or APD (Avalanche Photo-Diode) as the light receiving element. The light receiving means may include a filter circuit for passing a desired frequency band. The light receiving means has a means for changing the light receiving sensitivity (ratio of converting light into an electric signal), and may be controlled so that the sensitivity differs between the first mode and the second mode.

The time measuring device of Examples 1 to 5 can be used as a distance measuring device (for example, an object detection device 100) using the TOF method. From the settlement value T × C _clk −T _{delay (J) of the elapsed time, the distance to the object can be calculated by c × {T × C clk} −T _delay (J)} ÷ 2 using the speed of light c. ..
Examples of the light source of the light projecting means include LD, VCSEL, LED and the like. As the light projecting means, the light from the light source may be focused, diffused, and collimated by using a lens or the like, or may be deflected by using a deflecting means such as a mirror.

Examples of the configuration of the distance measuring device including the time measuring device include a configuration in which the light source is fixed and the deflection means for optical scanning is rotated. Due to geometrical optics constraints, the combination of a single light source and deflecting means limits the scanning range of light. Therefore, it is preferable to generate a histogram at a time when the rotation range of the deflection means deviates from the scanning range (effective scanning area).
At this time, it is preferable that the light receiving means can receive light even when the rotation range of the deflection means deviates from the scanning range. This is because the shot noise used for histogram generation can be acquired.
By rotating the deflection means, it is possible to make a configuration in which the scanning time for estimating the elapsed time and the histogram generation time for calculating the delay time are alternately switched.

An example of the operation flow of the time measuring device (time measuring system 45) when such a configuration is adopted will be described with reference to the flowchart of FIG.

In the first step T1, the mode is selected. This mode selection is performed by the mode selection means included in the time measuring device. Specifically, one of the first mode for acquiring the time information for estimating the elapsed time (estimation time information acquisition mode) and the second mode for calculating the delay time (delay time calculation mode) is selected. do.

In the next step T2, it is determined whether or not the first mode is selected. If the judgment here is affirmed, the process proceeds to step T3, and if denied, the process proceeds to step T7.

In the next step T3, scanning is started. Specifically, the measurement control unit 46 is requested to start scanning to start scanning the effective scanning region.

In the next step T4, the first mode is executed. Specifically, the operation flow of FIG. 12A is performed by the first time measuring means, and the operation flow of FIG. 12B is performed by the second time measuring means.

In the next step T5, it is determined whether or not the scanning is completed. The determination here is denied before receiving the scanning end notification from the measurement control unit 46, and is affirmed when it is received. If the judgment here is affirmed, the process proceeds to step T6, and if denied, the process returns to step T4 and the first mode is continuously performed.

In step T6, the calculation means 2 calculates an approximate value T × C _clk of the elapsed time. When step T6 is executed, the process proceeds to step T11.

In step T7, the histogram generating means generates a histogram as described above.
Here, it is desirable that the histogram data is stored in the memory and integrated with the previous data each time the histogram generation time is reached. This is because it is considered that the accuracy of the delay time calculation increases as the number of integrations increases.
Further, since there is a limit to the size of data that can be stored in the memory, _{it is preferable to set the upper limit of the edge detection count C total} to a value that can be stored in the memory.

In the next step T8, it is determined whether or not the _{total has reached the specified number.} If the judgment here is affirmed, the process proceeds to step T10, and if denied, the process proceeds to step T9.

In step T9, it is determined whether or not the histogram generation time (the time between one scan and the next scan) has expired. If the judgment here is affirmed, the process proceeds to step T10, and if denied, the process returns to step T7 and the generation of the histogram is continued.

In step T10, the delay time calculating means obtains the delay time for each delay element as described above, and calculates the total value T _delay (J) of the delay times. When step T10 is executed, the process proceeds to step T11.

In step T11, it is determined whether or not the estimated value of the elapsed time and the total value of the delay time have been calculated. If the judgment here is affirmed, the process proceeds to step T12, and if denied, the process returns to step T1.

In step T12, the calculation means 2 corrects the estimated value of the elapsed time with the total value of the delay time. Specifically, the calculation of T × C _clk −T _delay (J) is performed.

In the next step T13, it is determined whether or not the measurement is completed. The determination here is denied before receiving the measurement end notification from the measurement control unit 46, and is affirmed when it is received. If the judgment in step T13 is affirmed, the flow ends, and if it is denied, the process returns to step T1 and the measurement is continued.
When the measurement (loop of steps T1 to T12) is performed a plurality of times, for example, the first mode and the second mode may be alternately selected as the mode selection method in step T1, or the first mode may be selected. May be alternately selected a plurality of times in succession and the second mode may be selected at least once. After the second mode is selected at least once and the _total reaches the specified number (YES in step T8), the effective scanning area is not scanned (when the rotation range of the deflection means deviates from the effective scanning area). It is not necessary to perform the second mode, that is, it is not necessary to select the second mode in step T1.

FIG. 17 shows a sensing device 1000 including an object detection device 100. The sensing device 1000 includes a monitoring control device 300 mounted on a moving body and electrically connected to the object detection device 100 in addition to the object detection device 100. The object detection device 100 is attached near the bumper of the vehicle or near the rear-view mirror. Based on the detection result of the object detection device 100, the monitoring control device 300 performs processing such as estimation of the shape and size of the object, calculation of the position information of the object, calculation of movement information, recognition of the type of the object, and the like. , Judge whether there is a danger. When it is determined that there is a danger, an alarm such as an alarm is issued to alert the operator of the moving body, a command to turn the steering wheel to avoid the danger is issued to the steering control unit of the moving body, and braking is performed. Is issued to the ECU of the moving body. The sensing device 1000 receives electric power from, for example, a vehicle battery.

The monitoring control device 300 may be provided integrally with the object detection device 100, or may be provided separately from the object detection device 100. Further, the monitoring control device 300 may perform at least a part of the control performed by the ECU.

Further, the monitoring control device 300 that obtains object information (at least one of the presence / absence of an object, the position of an object, the moving direction of an object, and the moving speed of an object) based on the object detection device 100 and the output of the object detection device 100. According to the sensing device 1000 including the above, the object information can be stably acquired.

Further, the sensing device 1000 is mounted on the moving body, and the monitoring control device 300 determines the presence or absence of danger based on at least one of the position information and the moving information of the object. Can provide useful information for risk avoidance.

Further, the mobile device including the sensing device 1000 and the moving body on which the sensing device 1000 is mounted is excellent in collision safety.

Hereinafter, an example of the distance measuring process performed by the object detection device 100 of the present embodiment will be described with reference to FIG. The flowchart of FIG. 18 is based on a processing algorithm executed by the measurement control unit 46.

In the first step U1, it is determined whether or not to start scanning the effective scanning area. The judgment here is affirmed when the judgment time is from the time when the synchronization signal from the synchronization system 50 is received to immediately after the reception, and is denied in other cases. If the judgment in step U1 is affirmed, the process proceeds to step U2, and if denied, the process proceeds to step U8.

In step U2, the approximate time information acquisition mode is executed. The details of the approximate time information acquisition mode will be described later. The "time information for estimation" means time information for estimating the measurement target time.

In the next step U3, it is determined whether or not the scanning of the effective scanning area has been completed. The determination here is denied until the rotation mirror 26 rotates by the rotation angle corresponding to the effective scanning region after receiving the synchronization signal from the synchronization system 50, and is affirmed when the rotation mirror 26 rotates. If the judgment in step U3 is affirmed, the process proceeds to step U4, and if denied, the process returns to step U2 and the approximate time information acquisition mode is continuously performed.

In step U4, the delay time calculation mode is executed. In the delay time calculation mode, the delay time for each delay element is calculated. The delay time means the time required for the signal to pass through the delay element. The details of the delay time calculation mode will be described later.

In the next step U5, the “measurement target time calculation process” is executed. The details of the measurement target time calculation process will be described later.

In the next step U6, the distance to the object is calculated from the measurement target time and the speed of light. Specifically, the product of 1/2 of the measurement target time and the speed of light is obtained.

In the next step U7, it is determined whether or not the measurement is completed. The determination here is denied when, for example, the electric system of the vehicle on which the object detection device 100 is mounted is on, and affirmed when it is turned off. If the judgment in step U7 is affirmed, the flow ends, and if it is denied, the process returns to step U1 and distance measurement is continued.

In step U8, the "delay time calculation mode" is executed. The details of the delay time calculation mode will be described later.

In the next step U9, it is determined whether or not to start scanning the effective scanning area. The judgment here is affirmed when the judgment time is from the time when the synchronization signal from the synchronization system 50 is received to immediately after the reception, and is denied in other cases. If the judgment in step U9 is affirmed, the process proceeds to step U10, and if the judgment is denied, the same judgment is made again (that is, the waiting state is reached).

In the next step U10, the "approximate time information acquisition mode" is executed. The details of the approximate time information acquisition mode will be described later.

In the next step U11, it is determined whether or not the effective scanning area has been scanned. The determination here is denied until the rotation mirror 26 rotates by the rotation angle corresponding to the effective scanning region after receiving the synchronization signal from the synchronization system 50, and is affirmed when the rotation mirror 26 rotates. If the judgment here is affirmed, the process proceeds to step U5, and if denied, the process returns to step U10 and the approximate time information acquisition mode is continuously performed.

In FIG. 18, the delay time calculation mode is executed when the effective scanning area is not scanned, that is, between continuous scans, but the delay time calculation mode is at least before or after performing a plurality of scans. It may be executed once.

Subsequently, an example of the approximate time information acquisition mode will be described with reference to the flowchart of FIG. The approximate time information acquisition mode is executed by the time measuring device (time measuring system 45).

In the first step U21, the measurement start signal is output in synchronization with the reference clock, and the clock count-up is started. Specifically, the LD drive signal that triggers the LD lighting is output to the LD drive unit 12 as a measurement start signal in synchronization with the reference clock generated by the reference clock generation means, and the reference clock count-up is started. .. As a result, the object existing in the effective scanning region is irradiated with light, and the reflected light is incident on the photodetector. In a photodetector, shot noise is generated when receiving light.

In the next step U22, the received signal (analog voltage signal) from the photodetector is binarized, and the pulse is input to the delay element sequence.

In the next step U23, the clock count-up is completed when the falling edge of the pulse obtained by binarizing the received signal enters the delay element train, and the clock count value at that time is used as the approximate time information. get. Specifically, when the terminal voltage level at the input end of the first delay element is 0 and the terminal voltage level at the output end is 1 in FIG. 8A, the clock count value C _clk is used as the approximate time information. get.

In the next step U24, the clock count value is initialized to 0. When step U24 is executed, the flow ends.

An example of the delay time calculation mode will be described below with reference to the flowchart of FIG. The delay time calculation mode is executed by the time measuring device (time measuring system 45).

In the first step U31, the shot noise generated by the photodetector is binarized by the binarization circuit 44d, and the pulse is acquired by the noise acquisition means.

In the next step U32, the pulse obtained by binarizing the shot noise is input to the delay element train. Specifically, the pulse acquired by the noise acquisition means is output to the delay element sequence.

In the next step U33, the histogram generating means histograms the number of times the rising edge or falling edge of the pulse is detected for each delay element.

In the next step U34, the delay time calculating means calculates the delay time for each delay element. Specifically, the delay time of each delay element is obtained from the histogram generated in step U33 as a percentage of one clock (one reference clock), and the delay is multiplied by the reference clock period T. Calculate the time.

In FIG. 20, the noise acquired by the noise acquisition means is the shot noise generated by the light receiving element, but it may be, for example, the thermal noise generated at the resistance end of the circuit inside or outside the time measuring device.

Subsequently, an example of the measurement target time calculation process will be described with reference to the flowchart of FIG. The measurement target time calculation process is executed by the time measuring device (time measuring system 45).

In the first step U41, the calculation means 2 acquires the number J of the delay element closest to the signal input end side with respect to the falling edge of the reference clock next to the reference clock last counted in the approximate time information acquisition mode. do. For example, in FIG. 8A, J = 3.

In the next step U42, the calculation means 2 adds up the delay times of the first to Jth delay elements calculated in the delay time calculation mode.

In the next step U43, the calculation means 2 _{takes the product of the clock count value C clk} acquired in the approximate time information acquisition mode and the period T, and subtracts the total delay time T _{delay from the product T × C clk.} By doing so, the measurement target time is calculated.

The time measuring device that functions as the time measuring system 45 of the present embodiment described above is a time measuring device that measures the time (elapsed time) from the measurement start time to the input of the measurement target signal 1 as the measurement target time. The time information acquisition for acquiring the delay element train in which a plurality of delay elements that delay the input signal are connected in series and the time information for estimation, which is the time information for estimating the measurement target time, is obtained. Delay time acquisition including a system (first time measuring means) and noise acquiring means for acquiring noise generated inside and outside the time measuring device, and inputting the noise into a delay element train to acquire a delay time for each delay element. It is a time measuring device including a system and a calculation means 2 (calculation system) for calculating a measurement target time based on an approximate time information and a delay time.

In this case, since noise that is stochastically and randomly generated is input to the delay element sequence to acquire the delay time for each delay element, it is possible to suppress the acquisition of an unintended delay time. Then, since the approximate value of the elapsed time can be corrected by using the acquired accurate delay time, the elapsed time can be measured accurately.

As a result, according to the time measuring device of the present embodiment, it is possible to improve the measurement accuracy while suppressing the complexity of the configuration.

On the other hand, when a special signal different from the reference clock is input to the delay element sequence to acquire the delay time for each delay element as in the devices disclosed in Patent Documents 1 and 2, a reference clock is generated. In addition to the means, a dedicated signal source for generating the special signal is required. That is, in the conventional device, there is room for improvement in improving the measurement accuracy while suppressing the complexity of the configuration.

Further, the time measuring device of the present embodiment further includes a reference clock generating means for generating a reference clock having a constant period T longer than the delay time of each delay element, and the time information acquisition system is a measurement target from the measurement start time. It is preferable to acquire the count value of the reference clock until the signal 1 is input to the delay element train as the approximate time information. In this case, the approximate time information can be easily obtained.

Instead of the reference clock generating means, a timer that measures the time from the measurement start time to the input of the measurement target signal 1 may be used. In this case, if the time resolution of the delay element sequence is higher than the time resolution of the timer, the estimated time by the timer can be corrected by the delay time for each delay element.

Further, the time measuring device of the present embodiment is an edge detecting means for identifying the delay element in which the measurement target signal 1 input to the delay element sequence or the rising or falling edge of noise is detected in synchronization with the reference clock. It is preferable to further provide.

In this case, it is possible to detect how far the measurement target signal 1 and noise have advanced in the delay element sequence in synchronization with the reference clock.

Further, the total delay time of the delay element train is longer than the period T of the reference clock, and the total number of edges detected by the edge detecting means with K delay elements corresponding to the period T is _Ck , and the signal input in the delay element train is the number of detected edges when the C _L in L th delay element counted from the end side, the delay time of the L-th delay element is determined by T × C _L ÷ C _k.

In this case, since the total delay time of the delay element train is longer than the period T of the reference clock, the edge position is not failed to be detected. Further, a standard of the number of delay elements corresponding to the period T can be set. By providing such a reference, the delay time can be calculated by a simple proportional calculation based on the number of delay elements per clock, the total number of edge detections, and the number of edge detections by a certain delay element.

Further, the delay time acquisition system includes a histogram generating means for generating a histogram showing the number of times an edge is detected for each delay element by the edge detecting means, and a delay time calculating means for calculating the delay time of the delay element based on the histogram. And, preferably.

Further, the delay time acquisition system includes a threshold control means for controlling the threshold value, and the histogram generation means is a binarization circuit that at least binarizes the analog value of noise with the threshold value and outputs the obtained digital signal to the delay element sequence. a set of counting the number of times C _total digital signals are output with rising and falling edges from the threshold control means, when generating the histogram, to control the threshold so C _total counts up one or more Is preferable.
In this case, the output frequency of noise from the binarization circuit can be controlled.

By the way, a sufficient number of sample signals are required to generate a histogram. As long as the signal generation probability is random, if the threshold value is constant, a sufficient number of sample signals may not be acquired within a certain time. By subdividing the histogram generation time and controlling the number of counts and the threshold value within the divided time, it is possible to prevent the sample signal from being at least insufficient for histogram generation.

Therefore, the threshold control means divides the generation time of the histogram into a plurality of time zones, and when the earliest time zone is set as the first time zone, the C _total from the first time zone to the Mth time zone is set. When the predetermined value is not exceeded, it is preferable that the threshold value of the M + 1st time zone is lower than the threshold value of the Mth time zone.

Further, the time measuring device of the present embodiment includes a mode selection system for selecting either a first mode for acquiring approximate time information and a second mode for acquiring delay time, and the mode selection system includes a mode selection system. When switching from the second mode to the first mode, a mode switching time of an arbitrary length is set, and the threshold control means divides the mode switching time into a plurality of time zones, and the mode switching time is divided into a plurality of time zones. out at least in the last time slot controls the threshold so _that C _total no change (e.g., increase) is preferred.
Consider its technical significance.
First, when two signals having different signal levels (measurement target signal and noise signal) are mixed, they can be separated from each other. That is, by setting the threshold value, for example, the noise signal and the measurement target signal can be separated and output.
Further, if the threshold value is kept lowered to generate the histogram, noise other than the desired measurement target signal may be acquired in the first mode. Therefore, a buffer time is provided between the modes, and the threshold value is controlled so that noise is never acquired before the transition from the second mode to the first mode. For example, when the threshold value is gradually increased for each division time, the threshold value can be set to the lowest level at which noise is not acquired but the measurement target signal can be acquired. This makes it possible to measure a longer distance in a distance measuring device using the TOF method. This is because the longer the distance, the weaker the reflected light from the object, making it difficult to distinguish between the signal to be measured and noise.

Further, it is preferable that the measurement target signal and the noise source are the same light receiving means. In this case, the signal component and noise component of light can be acquired as the measurement target signal and noise, respectively.

By the way, in most scanning type ranging devices, there is a time when the light is not scanned. And since that time often occurs repeatedly periodically, it is desirable to utilize it for histogram generation.

Therefore, the object detection device 100 of the present embodiment is projected from a light source (Tatoba LD), a light projecting means including a scanning unit having a rotating mirror 26 for scanning the light from the light source, and the light projecting means. A light receiving means that receives light reflected by an object, a time measuring device that functions as a time measuring system 45 in which the measurement start time coincides with the light emitting timing of the light source and the measurement target signal is an output signal of the light receiving means, and the time. The mode selection system of the time measuring device includes a measurement control unit 46 (distance calculating means) for calculating the distance to the object using the measurement result of the measuring device and the light velocity, and the mode selection system of the time measuring device has a thirth time when the light is scanned. If one mode is selected and the _total does not reach a predetermined value, it can be regarded as a distance measuring device characterized in that the second mode is selected during the time when the light is not scanned.

In this case, it is not necessary to separately provide a time for generating the histogram, and there is almost no time loss. Even if a sufficient number of signals cannot be acquired in one histogram generation time, it is easy to increase the number of acquired signals and improve the accuracy by repeating the process.

Further, the object detection device 100 of the present embodiment has a light projecting means including a light source (for example, LD), a light receiving means for receiving light projected from the light projecting means and reflected by the object, and a measurement start time of the light source. A time measuring device that matches the light emission timing and functions as a time measuring system 45 whose measurement target signal is an output signal of the light receiving means, and a measurement that calculates the distance to an object using the measurement result and the light speed of the time measuring device. It can be regarded as a distance measuring device including a control unit 46 (distance calculating means).
In this case, it is possible to improve the distance measurement accuracy while suppressing the complexity of the configuration.

Further, according to the mobile device including the object detection device 100 of the present embodiment and the vehicle (moving body) on which the object detection device 100 is mounted, the collision safety is improved while suppressing the complexity of the configuration. Can be made to.

Further, in the time measurement method of the present embodiment, the time (elapsed time) from the measurement start time until the measurement target signal 1 is input to the delay element train in which a plurality of delay elements for delaying the input signal are connected in series. It is a time measurement method for measuring as a measurement target time, in which a step of acquiring approximate time information (time information) for estimating the measurement target time and a process of acquiring noise and inputting the noise into a delay element train are input. This is a time measurement method including a step of acquiring a delay time for each delay element and a step of calculating a measurement target time based on approximate time information and a delay time.

In this case, since noise that is stochastically and randomly generated is input to the delay element sequence to acquire the delay time for each delay element, it is possible to suppress the acquisition of an unintended delay time. Then, since the approximate value of the elapsed time can be corrected by using the acquired accurate delay time, the elapsed time can be measured accurately.

As a result, according to the time measurement method of the present embodiment, it is possible to improve the measurement accuracy while suppressing the complexity of the configuration.

Further, in the process of acquiring the approximate time information, a reference clock having a constant cycle longer than the delay time is generated, and the reference clock is counted from the measurement start time until the measurement target signal 1 is input to the delay element train. It is preferable to acquire the value as time information.

Further, in the process of acquiring the approximate time information and the process of acquiring the delay time, the measurement target signal 1 input to the delay element train and the rising or falling edge of the noise were detected in synchronization with the reference clock. It is preferable to specify the delay element.

Further, the total delay time of the delay element train is longer than the period T of the reference clock, and the total number of edges detected by the K delay elements corresponding to the period T is _Ck , and the number of times the edge is detected by the Lth delay element. the When C _L, the delay time of the L-th delay element counted from the signal input terminal side of the delay element array is determined by T × C _L ÷ C _k.

Further, in the step of acquiring the delay time, it is preferable to generate a histogram showing the number of times the edge is detected for each delay element and calculate the delay time of the delay element based on the histogram.

Further, in the process of acquiring the delay time, a sub-process of binarizing noise with a threshold value and outputting a binary digital signal and a digital signal having a set of rising edge and falling edge in the output sub-process are used. It is preferable to include a sub-process for counting the number of output _signals and a sub-process for controlling the threshold so that the counting sub-process counts up by 1 or more when the histogram is generated.

Further, in the sub-step to be controlled, the histogram generation time is divided into a plurality of time zones, and when the earliest time zone is set as the first time zone, the count from the first time zone to the Mth time zone is performed. When the count number ( _Ctotal ) in the sub-step to be performed does not exceed a predetermined value, it is preferable that the threshold value of the M + 1st time zone is lower than the threshold value of the Mth time zone.

Further, the time measurement method of the present embodiment further includes a step of selecting one of a first mode for executing the step of acquiring the approximate time information and a second mode for executing the step of acquiring the delay time. Including, in the selected step, a mode switching time of an arbitrary length is set when switching from the second mode to the first mode, and in the sub-step to be controlled, the mode switching time is set to a plurality of time zones. It is preferable to control the threshold value so _{that the count number (Total} ) in the sub-step to be counted does not change at least in the last time zone among the plurality of time zones.

Further, the distance measuring method of the present embodiment includes a step of generating a reference clock having a constant period T, a step of causing a light source (for example, LD) to emit light in synchronization with the reference clock, and a step of projecting the light. A delay element in which a plurality of delay elements that delay the input signal are connected in series from the process of receiving the light projected by the light and reflected by the object and performing photoelectric conversion, and the measurement start time that coincides with the light emission timing of the light source. The process of acquiring the count value of the reference clock until the measurement target signal (signal) generated by photoelectric conversion is input to the column, and the delay time for each delay element by acquiring the noise and inputting the noise into the delay element array. A distance measuring method including a step of calculating the round-trip time of light to an object from a delay time, a count value and a period T, and a step of calculating a distance to an object from the round-trip time and light speed. Is.

The configurations of the time measuring device, the distance measuring device, and the moving body device of the above embodiment can be changed as appropriate.

Further, for example, the noise to be acquired by the noise acquisition means may be noise such as thermal noise generated in a component other than the time measurement system 45 in the object detection device 100.

For example, the PD output detection unit 44 does not have to have a signal amplifier.

The light projecting system 10 is a scanning type that uses a deflector, but may be a non-scanning type that does not use a deflector. That is, the light projection system may have at least a light source, and may have a lens for adjusting the light projection range after the light source.

Further, in the above embodiment, a single LD (end face emitting laser) is used as the light source, but the present invention is not limited to this. For example, an LD array in which a plurality of LDs are arranged one-dimensionally or two-dimensionally, a VCSEL (surface emitting laser), a VCSEL array in which VCSELs are arranged one-dimensionally or two-dimensionally, a laser other than a semiconductor laser, a light source other than a laser, etc. May be used. Examples of the LD array in which a plurality of LDs are arranged one-dimensionally include a stack type LD array in which a plurality of LDs are stacked and an LD array in which a plurality of LDs are arranged side by side. For example, as a semiconductor laser, if the LD is replaced with a VCSEL, the number of light emitting points in the array can be set to be larger.

Further, the light projecting system 10 (light projecting means) may have a light source that emits millimeter waves or infrared rays.

Further, the projectile optical system may not have a coupling lens or may have another lens.

Further, the light projecting optical system and the light receiving optical system do not have to have a reflection mirror. That is, the light from the LD may be incident on the rotating mirror without folding back the optical path.

Further, the light receiving optical system may not have a light receiving lens, or may have another optical element (for example, a condensing mirror).

Further, as the deflector, for example, another mirror such as a polygon mirror (rotating multifaceted mirror), a galvano mirror, or a MEMS mirror may be used instead of the rotating mirror.

Further, the synchronous system may not have a synchronous lens, or may have another optical element (for example, a condensing mirror).

Further, in the above embodiment, a vehicle has been described as an example of a moving body on which the object detection device is mounted, but the moving body may be, for example, an aircraft, an unmanned aerial vehicle, a ship, a robot, or the like.

Further, it goes without saying that the specific numerical values and shapes used in the above description are examples and can be appropriately changed without departing from the spirit of the present invention.

As is clear from the above description, the time measuring device, the distance measuring device (object detection device 100), the sensing device 1000, the moving body device, the time measuring method, and the distance measuring method of the above-described embodiment include the round-trip time to the object and the distance measuring method. It is a technology that uses the so-called Time of Flight (TOF) method to measure distance, and can be widely used in industrial fields such as motion capture technology, rangefinders, and three-dimensional shape measurement technology, in addition to sensing in moving objects. .. That is, the time measuring device and the distance measuring device of the present invention do not necessarily have to be mounted on the moving body.

The thinking process that led to the inventor's idea of the above embodiment will be described below.
Generally, in order to measure the time difference between two signals with high accuracy, a coarse measurement using a clock and a fine measurement using a delay element sequence are performed in combination.
The delay element sequence is composed of a plurality of delay elements having a reference time (delay time) shorter than the clock period, and a combination of a gate element in an IC, a resistor, a capacitor, a coil, or the like is used. Often.
It is known that the delay time of a delay element varies between elements due to non-uniformity of temperature and voltage, process variation, difference in wiring length between elements, and the like.
In the measurement of the time difference, since the delay time of the delay element corresponds to the time resolution, there is a concern that the measurement accuracy may be lowered due to the variation of these.

Therefore, there is a technique for measuring and correcting the variation in the delay time of the delay element.
Generally, a signal having periodicity is input separately from the signal to be measured, and the number of times the edge of the signal is detected is integrated and histogramd for each delay element. At this time, the longer the delay time, the larger the number of edge detections tends to be.
That is, it is possible to grasp the variation in the delay time from the number of edge detections.
This technique is also commonly referred to as the "code density test".

In Patent Document 1, a test clock signal is input separately from the signal to be measured to generate a histogram. The time measurement configuration is such that the phase difference of the edge of the signal to be measured with respect to the edge of the reference clock is obtained from the delay element sequence. The test clock signal used has no correlation with the period of the reference clock.

In Patent Document 2, a calibration trigger signal is input to a delay element to generate a histogram. The calibration trigger signal is a signal having a frequency that is distributed with equal probability to the delay elements of the delay element sequence.

In order to generate a histogram accurately using a periodic signal, the periodic signal must be uncorrelated with the reference clock, and the frequency of the periodic signal must be a frequency that is probabilistically equally distributed to the delay elements. , Must be satisfied. The former is disclosed in Patent Document 1, and the latter is disclosed in Patent Document 2.

However, if a periodic signal that is uncorrelated with the reference clock is used, it is necessary to use a crystal oscillator or the like separately from the source of the reference clock, so that there is a concern that the configuration becomes complicated.
Further, when generating a periodic signal that is stochastically and equally distributed to the delay elements, it is necessary to use a frequency divider or a delay generator, but desired characteristics due to frequency jitter and frequency changes due to the ambient temperature. There is a possibility that the configuration will be complicated.

That is, in Patent Documents 1 and 2, there is room for improvement in improving the measurement accuracy while suppressing the complexity of the configuration.

Therefore, the inventor has come up with the above-mentioned embodiment in order to solve this problem.

10 ... Light projecting system (light emitting means), 42 ... PD for time measurement (part of light receiving means), 44a ... Current / voltage converter (part of light receiving means), 44b ... Signal amplifier (part of light receiving means) , 44d ... binarization circuit, 45 ... time measurement system (time measurement device), 46 ... measurement control unit (distance calculation means), 100 ... object detection device (distance measuring device).

Japanese Patent No. 5106583 Japanese Patent No. 5055471

Claims (18)

A signal to be measured from the measurement start time using a delay element array in which a plurality of delay elements that delay the input signal are arranged and a reference clock having a constant period T longer than the delay time of each delay element in the delay element array. It is a time measuring device that measures the time until is input.
A time measuring device that inputs noise generated inside and outside the time measuring device to the delay element train to acquire the delay time for each delay element. It is further provided with an edge detecting means for identifying the delay element in which the rising or falling edge of the measurement target signal or the noise input to the delay element train is detected in synchronization with the reference clock. The time measuring device according to claim 1. The total delay time of the delay element train is longer than the period T.
By the edge detection means, the total number of detection of the edge at the K delay elements corresponding to the period T C _k, and detects the edges in L th of the delay elements counted from the input end side of the delay element array When the number of times the C _L, the delay time of the L-th delay element, the time measuring device according to claim 2, characterized in that a T × C _L ÷ C _k. A histogram generating means for generating a histogram representing the number of times the edge is detected for each delay element by the edge detecting means, and a histogram generating means.
The time measuring apparatus according to claim 2 or 3, further comprising a delay time calculating means for calculating the delay time of the delay element based on the histogram. The histogram generating means is a digital signal having a set of rising edge and falling edge from a binarizing circuit that binarizes at least the analog value of the noise with a threshold value and outputs the obtained digital signal to the delay element train. Counts the number of times C _{total is output and}
The time measuring device according to any one of claims 1 to 4, wherein the threshold control means for controlling the threshold value is included so that the _capital counts up by 1 or more when the histogram is generated. Said threshold control means, the generation time of the histogram is divided into a plurality of time zones, the C _total of the earliest time period from the first time period when the first time period to the M-th time slot The time measuring device according to claim 5, wherein when the value does not exceed a predetermined value, the threshold value of the M + 1st time zone is made lower than the threshold value of the Mth time zone. A mode selection system for selecting either a first mode for acquiring the time from the measurement start time to the input of the measurement target signal and a second mode for acquiring the delay time is provided.
The mode selection system sets a mode switching time of an arbitrary length when switching from the second mode to the first mode.
The threshold control means is characterized in that the mode switching time is divided into a plurality of time zones, and the threshold value is controlled so that the _{capital does not change at least in the last time zone of the plurality of time zones.} The time measuring device according to claim 5 or 6. Light projection means including a light source and
A light receiving means that receives light projected from the light projecting means and reflected by an object, and a light receiving means.
The time measuring device according to any one of claims 1 to 7, wherein the measurement start time coincides with the light emission timing of the light source, and the measurement target signal is an output signal of the light receiving means.
A distance measuring device including a distance calculating means for calculating a distance to the object using the measurement result of the time measuring device and the speed of light. A light source and a light projecting means including a scanning unit that scans light from the light source.
A light receiving means that receives light projected from the light projecting means and reflected by an object, and a light receiving means.
The time measuring device according to claim 7, wherein the measurement start time coincides with the light emission timing of the light source, and the measurement target signal is an output signal of the light receiving means.
It is provided with a distance calculating means for calculating the distance to the object using the measurement result by the time measuring device and the speed of light.
Mode selection system of the time measurement device, time during which the light is scanned selects the first mode, when the C _{total does} not reach the predetermined value, the time that the light is not scanned first A distance measuring device characterized by selecting two modes. The distance measuring device according to claim 8 or 9,
A mobile device including a mobile body on which the distance measuring device is mounted. A signal to be measured from the measurement start time using a delay element array in which a plurality of delay elements that delay the input signal are arranged and a reference clock having a constant period T longer than the delay time of each delay element in the delay element array. It is a time measurement method that measures the time until is input.
A time measurement method including a step of inputting noise into the delay element sequence and acquiring a delay time for each delay element. The step of acquiring the delay time is characterized in that the delay element in which the rising or falling edge of the noise input to the delay element train is detected is specified in synchronization with the reference clock. Item 10. The time measuring method according to Item 11. The total delay time of the delay element sequence is longer than the period T of the reference clock.
When the total number of detection of the edge at the K of said delay elements corresponding to the period T C _k, the number of times of detecting the edge in the L-th of the delay elements and C _L, from the input end side of the delay element array The time measuring method according to claim 12, wherein the delay time of the L-th delay element is T × C _L ÷ C _k. 12. The step of acquiring the delay time is characterized in that a histogram representing the number of times the edge is detected for each delay element is generated, and the delay time of the delay element is calculated based on the histogram. Or the time measuring method according to 13. The step of acquiring the delay time is
A sub-process that binarizes the noise with a threshold value and outputs a binary digital signal,
A substep of counting the number of times C _total digital signals are output with a pair of rising and falling edges in the sub-step of the output,
The time measurement method according to claim 14, further comprising a sub-step of controlling the threshold value so that the _capital counts up by 1 or more when the histogram is generated. In the sub-step of the control, the generation time of the histogram is divided into a plurality of time zones, the earliest time period from the first time period when the first time period to the M-th time slot C _total The time measurement method according to claim 15, wherein when the value does not exceed a predetermined value, the threshold value of the M + 1st time zone is made lower than the threshold value of the Mth time zone. A step of selecting one of a first mode for executing the step of acquiring the time from the measurement start time to the input of the measurement target signal and a second mode for executing the step of acquiring the delay time. Including
In the selection step, a mode switching time of an arbitrary length is set when switching from the second mode to the first mode.
The control sub-step is characterized in that the mode switching time is divided into a plurality of time zones, and the threshold value is controlled so that the _{capital does not change at least in the last time zone of the plurality of time zones.} The time measuring method according to claim 15 or 16. The process of generating a reference clock with a fixed cycle and
The process of causing the light source to emit light and projecting light in synchronization with the reference clock,
In the step of projecting light, the step of receiving the light reflected by the object and converting it into photoelectric
The count value of the reference clock from the measurement start time that coincides with the light emission timing of the light source until the signal generated by the photoelectric conversion is input to the delay element array in which a plurality of delay elements that delay the input signal are arranged. The process to acquire and
A step of acquiring noise, inputting the noise into the delay element train, and calculating the delay time for each delay element.
A step of calculating the round-trip time of light from the delay time, the count value, and the period to the object, and
A distance measuring method including a step of calculating a distance to an object from the round trip time and the speed of light.

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