JP5388928B2 - Time measuring device and distance measuring device - Google Patents

Description

  The present invention relates to a time measuring device and a distance measuring device.

  An apparatus based on the TOF (Time-of-flight) method is known as a distance measuring device that measures the distance to an object (see Patent Documents 1 and 2). A distance measuring device based on the TOF method projects pulsed light from a light source onto an object, receives reflected pulsed light generated by projecting the pulsed light on the object by a light receiving element, and receives light from the light projection timing. By measuring the time to timing, the distance is obtained from that time. That is, the distance measuring device based on the TOF method includes a time measuring device that measures the time from the light projection timing to the light receiving timing.

JP 2005-10133 A Japanese Patent Laid-Open No. 6-18665

  The distance measuring device or time measuring device based on the TOF method may cause an error in the measurement results up to the target object due to differences in the component characteristics depending on the temperature or the actual component characteristics differing from the design values. There is.

  The distance measuring device disclosed in Patent Document 1 is intended to deal with such a problem of error, and uses a measurement result using an optical fiber having a known length, The measurement result of the distance to is corrected. However, this distance measuring device also may cause an error in the measurement result up to the object because the characteristics of the optical fiber depend on the temperature. In addition, since this distance measuring device needs to perform measurement using an optical fiber, the time required for distance measurement becomes long and large.

  The present invention has been made to solve the above problems, and includes a time measuring device capable of measuring time with high accuracy with a simple configuration, and a distance measuring device including such a time measuring device. The purpose is to provide.

The time measuring device according to the present invention includes (1) a constant current source, and (2) J capacitive elements C _{1 to} C _J having a first end and a second end, and the first end is connected to a reference potential. And (3) a switch SW _j provided between the second end of each capacitive element C _j and the constant current source, and (4) from time t ₀ to time t _J based on a signal given from the outside. Of the J switches SW _{1 to} SW _J , the switch SW _j is closed and the other switches are opened in the period from the time t _j−1 to the time t _{j in} the period in which the time T ₀ is known. (5) From time t _j−1 to time t _j based on the potential change amount V _j at the second end of each capacitive element C _j at time t _J with respect to time t ₀ and the known time T ₀ And an operation unit for obtaining any one of the time periods _Tj . However, J is an integer greater than or equal to 2, and j is an integer greater than or equal to 1 and less than or equal to J.

The distance measuring device according to the present invention includes (1) a light source that outputs pulsed light, and (2) a drive unit that drives the light source to emit pulsed light from the light source and outputs a light emission timing signal representing the light emission timing. (3) a light receiving element that receives the reflected pulse light generated by projecting the pulsed light output from the light source onto the object and outputs a current signal corresponding to the received light intensity, and (4) from the light receiving element. An IV converter that converts the output current signal into a voltage signal and outputs the voltage signal; and (5) a timing at which the light receiving element receives the reflected pulse light based on the voltage signal output from the IV converter. represents a determination unit for outputting a light reception timing signal, (6) the time t ₀ the timing of light emission timing signal is representative of the output from the drive unit, the time t ₁ to a timing indicated by the received timing signal output from the determination unit ~t _J- Any _one of the time measurement devices according to the present invention described above for obtaining a time representing a distance to an object is provided.

In the present invention, pulsed light is output from the light source driven by the driving unit. Further, a light emission timing signal representing the light emission timing is output from the drive unit. The reflected pulse light generated by projecting the pulsed light output from the light source onto the object is received by the light receiving element, and a current signal corresponding to the received light intensity is output from the light receiving element. The current signal output from the light receiving element is converted into a voltage signal by the IV converter. Based on the voltage signal, the determination unit outputs a light reception timing signal indicating the timing at which the light receiving element receives the reflected pulse light. In the time measuring device, the timing represented by the light emission timing signal output from the drive unit is defined as time t _0, and the timing represented by the light reception timing signal output from the determination unit is defined as any _one of times t ₁ to t _J−1. A time representing the distance to the object is required.

In the time measuring device, J switches SW are controlled in the period from time t _{j −1} to time t _j among the periods where the time T ₀ from time t ₀ to time t _J is known. _{1 to} SW _J , the switch SW _j is closed, and the other switches are opened, so that the potential of only the capacitive element C _j among the _J capacitive elements C _{1 to} C _J changes. Then, based on the potential change amount V _j of each capacitive element C _j at time t _J with respect to time t ₀ and the known time T ₀ , the time from time t _{j −1} to time t _{j is} calculated by the arithmetic unit. Any one of the times T _j is obtained. From this determined time, the distance to the object is determined.

In the distance measuring device according to the present invention, (a) the determination unit outputs a first light reception timing signal indicating a timing at which the value of the voltage signal output from the IV conversion unit transitions from a state less than the threshold to a state exceeding the threshold. And a second light receiving timing signal indicating a timing at which the value of the voltage signal output from the IV conversion unit transitions from a state exceeding the threshold to a state below the threshold, and (b) the time measuring device has a J value of a 3, a timing indicated by the first light receiving timing signal output from the determination unit and the time t _1, as the time t ₂ to a timing indicated by the second light receiving timing signal output from the determination unit, the time T _1, time T Request ₂ or time _{T 3,} it is preferable to.

Further, in the distance measuring device according to the present invention, (a) the determination unit has a timing when the value of the voltage signal output from the IV conversion unit reaches a peak, and the value of the voltage signal output from the IV conversion unit is less than a threshold value. A light receiving timing signal representing any one of a timing of transition from a state to a state exceeding a threshold and a timing of transition from a state where the value of a voltage signal output from the IV converter exceeds a threshold to a state below a threshold (B) The time measuring device preferably has a J value of ₂ and obtains the time T ₁ or the time T ₂ with the timing represented by the light reception timing signal output from the determination unit as the time t _1. .

  According to the present invention, highly accurate time or distance measurement can be performed with a simple configuration.

It is a figure showing composition of distance measuring device 1 concerning a 1st embodiment. It is a figure showing composition of time measuring device 10 contained in distance measuring device 1 concerning a 1st embodiment. It is a timing chart explaining the example of operation of time measuring device 10 concerning a 1st embodiment. It is a figure which shows the structure of 10 A of time measuring devices contained in the distance measuring device which concerns on 2nd Embodiment. It is a timing chart explaining the operation example of 10 A of time measuring devices which concern on 2nd Embodiment. It is a timing chart explaining other examples of operation of time measuring device 10A concerning a 2nd embodiment. It is a timing chart explaining other examples of operation of time measuring device 10A concerning a 2nd embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  (First embodiment)

  FIG. 1 is a diagram illustrating a configuration of a distance measuring device 1 according to the first embodiment. The distance measuring device 1 measures the distance to the object 90 and includes a time measuring device 10, a light source 20, a driving unit 30, a light receiving element 40, an IV converting unit 50, and a determining unit 60.

  The light source 20 is driven by the drive unit 30 and outputs pulsed light toward the object 90. A laser diode is preferably used as the light source 20. The drive unit 30 drives the light source 20 to emit pulsed light from the light source 20 and outputs a light emission timing signal representing the light emission timing to the distance measuring device 10.

  The light receiving element 40 receives reflected pulsed light generated by projecting the pulsed light output from the light source 20 onto the object 90, and outputs a current signal corresponding to the received light intensity to the IV conversion unit 50. An avalanche photodiode is preferably used as the light receiving element 40. The IV conversion unit 50 converts the current signal output from the light receiving element 40 into a voltage signal, and outputs the voltage signal to the determination unit 60. Based on the voltage signal output from the IV conversion unit 50, the determination unit 60 outputs a light reception timing signal representing the timing at which the light receiving element 40 receives the reflected pulse light to the time measuring device 10.

  The time measuring device 10 receives the light emission timing signal output from the drive unit 30 and also receives the light reception timing signal output from the determination unit 60, and the timing represented by the light reception timing signal from the timing represented by the light emission timing signal. Find the time until. The obtained time represents the sum of the distance from the light source 20 to the object 90 and the distance from the object 90 to the light receiving element 40, that is, the distance from the distance measuring device 1 to the object 90. ing.

FIG. 2 is a diagram illustrating a configuration of the time measuring device 10 included in the distance measuring device 1 according to the first embodiment. The time measuring device 10 includes a constant current source 11, a control unit 12, a calculation unit 13, capacitive elements C _{1 to} C ₃ , a resistor R, switches SW _{0 to} SW _3, and switches SW _{11 to} SW ₁₃ . Each of the switches SW _{0 to} SW ₃ and the switches SW _{11 to} SW ₁₃ is composed of a transistor.

The constant current source 11 includes a current source 11a and transistors Tr ₁ and Tr ₂ . One end of the current source 11a is connected to the reference potential _{V ref,} the other end of the current source 11a is connected to the drain terminal of the transistor Tr _1. The drain terminal of the transistor Tr ₁ is connected to the transistors Tr ₁ and the transistor Tr ₂ of the gate terminal. Each of the source terminal transistor Tr ₁ and the transistor Tr ₂ is grounded. The drain terminal of the transistor Tr ₂ is connected to the reference potential _{V ref} via a switch SW ₀ and the resistor R. The constant current source 11 constitutes a current mirror circuit, can flow a constant current between the drain terminal and the source terminal of the transistor Tr _2.

One end of the switch SW ₁ is connected to the drain terminal of the transistor Tr _2. The other end of the switch SW ₁ is connected to the reset potential V _reset via the switch SW ₁₁ and is connected to the ground potential via the capacitive element C ₁ . The potential at the other end of the switch SW ₁ is input to the calculation unit 13.

One end of the switch SW ₂ is connected to the drain terminal of the transistor Tr _2. The other end of the switch SW ₂ is connected to the reset potential _{V reset} via the switch _{SW 12,} also connected to the ground potential through the capacitor _{C 2.} The potential of the other end of the switch SW ₂ is input to the arithmetic unit 13.

One end of the switch SW ₃ is connected to the drain terminal of the transistor Tr _2. The other end of the switch SW ₃ is connected to the reset potential _{V reset} via the switch _{SW 13,} also connected to the ground potential via a capacitor _{C 3.} The potential of the other end of the switch SW ₃ is inputted to the arithmetic unit 13.

The switch SW ₀ is controlled to open and close by a taoff signal given from the control unit 12. Switch SW ₁ is opened and closed controlled by tac1 signal supplied from the control unit 12. Switch SW ₂ is opened and closed controlled by tac2 signal supplied from the control unit 12. Switch SW ₃ is opened and closed controlled by tac3 signal supplied from the control unit 12. The switch SW ₁₁ is controlled to open and close by a reset 1 signal given from the control unit 12. The switch SW ₁₂ is controlled to be opened and closed by a reset2 signal given from the control unit 12. The switch SW ₁₃ is controlled to open and close by a reset3 signal given from the control unit 12.

The control unit 12 receives the light emission timing signal output from the drive unit 30 and also receives the light reception timing signal output from the determination unit 60, and generates the tacoff signal, the tacl signal, the tac2 signal, and the tac3 signal. . Then, the control unit 12 gives these signals to any of the switches SW ₀ to SW ₃ to control the opening / closing operation of these switches. The control unit 12, the emission timing signals outputted from the driving unit 30, generates a reset1 signal, reset2 signal and reset3 signal, giving these signals to one of the switches _SW 11 _{to SW 13,} these Controls the opening and closing of the switch.

The calculation unit 13 includes a potential V _{out1 at} the connection point between the switch SW ₁ and the capacitive element C ₁ , a potential V _{out2 at} the connection point between the switch SW ₂ and the capacitive element C ₂ , and the switch SW ₃ and the capacitive element C ₃ . The potential V _out3 of the connection point is input, a predetermined calculation is performed based on these potentials V _{out1 to} V _out3 , and a time representing the distance to the object 90 is obtained. The calculation unit 13 may perform analog calculation or digital calculation.

Next, operations of the distance measuring device 1 and the time measuring device 10 according to the first embodiment will be described. FIG. 3 is a timing chart for explaining an operation example of the time measuring apparatus 10 according to the first embodiment. In this figure, in order from the top, the light emission timing signal given from the drive unit 30 to the control unit 12 of the time measuring device 10, the voltage signal outputted from the IV conversion unit 50 and inputted to the judgment unit 60, and the time from the judgment unit 60 receiving timing signal supplied to the control unit 12 of the measuring device 10, tacoff signal given from the controller 12 to the switch SW _0, TAC1 signal given from the controller 12 to the switch SW _1, given from the control unit 12 to the switch SW ₂ tac2 signal, TAC3 signal given from the controller 12 to the switch SW _3, the switch SW ₁ and the capacitor _{C 1} and the connection point of the potential _{V out1,} switch SW ₂ and the capacitor _{C 2} and the connection point potential _{V out2,} In addition, a potential V _{out3 at} a connection point between the switch SW ₃ and the capacitive element C ₃ is shown.

The light emission timing signal given from the drive unit 30 to the control unit 12 of the time measuring device 10 rises at time t ₀ when the light source 20 emits pulsed light. Further, the light emission timing signal, falls from time t ₀ to time t ₃ when the known time T ₀ has elapsed. That is, the light emitting timing signal is a signal having a pulse width T _0.

  The voltage signal output from the IV conversion unit 50 and input to the determination unit 60 is a signal representing a temporal change in the intensity of the reflected pulsed light that has reached the light receiving element 40.

The light reception timing signal given from the determination unit 60 to the control unit 12 of the time measuring device 10 is a signal representing the timing at which the light receiving element 40 receives the reflected pulse light, and the value of the voltage signal output from the IV conversion unit 50 is rise time t ₁ a transition to a state exceeding the threshold from the state of less than the threshold value, falls at the time t ₂ to transition from a state in which the value of the voltage signal exceeds the threshold value of the state of less than the threshold value.

  Based on the light emission timing signal output from the drive unit 30 and the light reception timing signal output from the determination unit 60, the control unit 12 generates a tacoff signal, a tac1 signal, a tac2 signal, and a tac3 signal. Further, the control unit 12 generates a reset 1 signal, a reset 2 signal, and a reset 3 signal based on the light emission timing signal output from the driving unit 30.

Prior to time t ₀ , the reset 1 signal, the reset 2 signal, and the reset 3 signal have significant values, the switches SW _{11 to} SW ₁₃ are closed, and the potentials V _{out1 to} V _out3 are set to the reset potential V _reset . At time t ₀ , each of the reset 1 signal, reset 2 signal, and reset 3 signal is changed to an insignificant value, and each of the switches SW _{11 to} SW ₁₃ is changed to an open state.

The time _{t 0} before or at time _t after _3, Tacoff signals, TAC1 signal, only Tacoff signal of tac2 signals and tac3 signal is a significant value, only the switch SW ₀ of the switch _SW 0 to SW ₃ are closed.

In the period from time t ₀ to time t ₁ , only the tac 1 signal among the tacoff signal, the tacl signal, the tac 2 signal, and the tac 3 signal has a significant value, and only the switch SW ₁ among the switches SW _{0 to} SW ₃ is closed. .

In the period from time _{t 1} to time _{t 2, tacoff} signal, TAC1 signal, only tac2 signal of tac2 signals and tac3 signal is a significant value, only the switch SW ₂ of the switch _SW 0 to SW ₃ are closed .

In the period from time _{t 2} to time _{t 3, tacoff} signals, TAC1 signal, only tac3 signal of tac2 signals and tac3 signal is a significant value, only the switch SW ₃ of the switch _SW 0 to SW ₃ are closed .

The potential V _out1 changes over a period from time t ₀ to time t _1, and the amount of potential change is V ₁ . Potential _{V out2} changes over a period from time _{t 1} to time _{t 2, the} potential thereof variation becomes _{V 2.} The potential _{V out3} changes over a period from time _{t 2} to time _{t 3,} the potential change amount is _{V 3.}

Here, the period from time _{t 0} to time _{t 1} and _{T 1,} the time from time _{t 1} to time _{t 2} and _{T 2,} the time from time _{t 2} to time _{t 3} and _{T 3.} Assume that the capacitance values of the capacitive elements C _{1 to} C ₃ are equal to each other and C. Also, let I be the current flowing through the constant current source 11. At this time, the following relational expression holds between these parameters.
V ₁ = T ₁ I / C (1)
V ₂ = T ₂ I / C (2)
V ₃ = T ₃ I / C (3)
T ₀ = T ₁ + T ₂ + T ₃ (4)

The following relational expressions are obtained from the above expressions (1) to (4).
T ₁ = T ₀ V ₁ / (V ₁ + V ₂ + V ₃ ) (5)
T ₂ = T ₀ V ₂ / (V ₁ + V ₂ + V ₃ ) (6)
T ₃ = T ₀ V ₃ / (V ₁ + V ₂ + V ₃ ) (7)

The calculation unit 13 can calculate the times T _{1 to} T ₃ by performing the above calculation based on the potential change amounts V _{1 to} V ₃ and the known time T ₀ . Then, time _{T 1,} can be based on time _(T 1 + _{T 2)} or the time _{(T 1 + T 2/2} ), determine the distance to the object 90. In addition, since the peak value of light emission is not necessarily at the center of the light emission time, a lookup table (LUT) or function that relates the magnitude of the light reception timing signal, that is, the amount of reflected pulse light and the peak position of light emission, It may be prepared and the distance may be calculated based on the amount of reflected pulsed light.

As described above, in the present embodiment, the times T _{1 to} T ₃ are obtained by the above equations (5) to (7), and thus are not affected by variations in the current I flowing through the constant current source 11. Further, in the present embodiment, it is not necessary to perform measurement for correction using an optical fiber as in the invention disclosed in Patent Document 1. Therefore, in the present embodiment, highly accurate time measurement and distance measurement can be performed with a simple configuration.

Further, in the present embodiment, by switch SW ₀ and resistor R are provided, since the time t ₀ the current also flows through the constant current source 11 before the time t ₀ stable constant current source 11 since the Operation can be obtained, and also in this respect, highly accurate time measurement and distance measurement can be performed.

  (Second Embodiment)

  Next, a second embodiment will be described. The configuration of the distance measuring apparatus according to the second embodiment is different from the first embodiment in the configuration of the time measuring apparatus. FIG. 4 is a diagram illustrating a configuration of a time measuring device 10A included in the distance measuring device according to the second embodiment.

Time measuring device 10A comprises a constant current source 11, control unit 12A, calculating unit 13A, the capacitive element _C 1, _{C 2,} resistors R, the switch _SW 0 to SW ₂ and switches _SW 11 _{to SW 12.} Each of the switches SW _{0 to} SW ₂ and the switches SW _{11 to} SW ₁₂ includes a transistor.

Compared to the configuration of the time measuring device 10 according to the first embodiment shown in FIG. 2, the time measuring device 10A according to the second embodiment shown in FIG. 4 includes switches SW ₃ and SW ₁₃ and a capacitive element C. ₃ in that the control unit 12A is provided instead of the control unit 12, and the calculation unit 13A is provided instead of the calculation unit 13.

The control unit 12A receives the light emission timing signal output from the drive unit 30, and also receives the light reception timing signal output from the determination unit 60, and generates the tacoff signal, the tacl signal, and the tac2 signal. Then, the control unit 12A gives these signals to any one of the switches SW ₀ to SW ₂ and the switches SW _{11 to} SW ₁₂ to control the opening / closing operation of these switches. The control unit 12A inputs the light emission timing signal output from the driving unit 30, generates a reset1 signal and reset2 signal, giving these signals to one of the switches _SW 11 _{to SW 12,} these Controls the opening and closing operation of the switch.

The calculation unit 13A inputs the potential V _{out1 at} the connection point between the switch SW ₁ and the capacitive element C ₁ and the potential V _out2 at the connection point between the switch SW ₂ and the capacitive element C ₂ and inputs these potentials V _out1. , V _out2 , a predetermined calculation is performed to obtain a time representing the distance to the object 90. The computing unit 13A may perform analog computation or digital computation.

Next, operations of the distance measuring device and the time measuring device 10A according to the second embodiment will be described. FIG. 5 is a timing chart for explaining an operation example of the time measuring apparatus 10A according to the second embodiment. In this figure, in order from the top, the light emission timing signal given from the drive unit 30 to the control unit 12A of the time measuring device 10A, the voltage signal outputted from the IV conversion unit 50 and inputted to the judgment unit 60, and the time from the judgment unit 60 receiving timing signal supplied to the control unit 12A of the measuring apparatus 10A, tacoff signal given from the controller 12A to the switch SW _0, TAC1 signal given from the controller 12A to the switch SW _1, given from the control unit 12A to the switch SW ₂ The tac2 signal, the potential V _{out1 at} the connection point between the switch SW ₁ and the capacitive element C ₁ , and the potential V _{out2 at} the connection point between the switch SW ₂ and the capacitive element C ₂ are shown.

Emission timing signal supplied from the drive unit 30 to the control unit 12A of the time measurement device 10A, rise time t ₀ of the light source 20 emits a pulsed light. Further, the light emission timing signal, falls from time t ₀ to time t ₂ the known time T ₀ has elapsed. That is, the light emitting timing signal is a signal having a pulse width T _0.

  The voltage signal output from the IV conversion unit 50 and input to the determination unit 60 is a signal representing a temporal change in the intensity of the reflected pulsed light that has reached the light receiving element 40.

The light reception timing signal given from the determination unit 60 to the control unit 12A of the time measuring device 10A is a signal indicating the timing at which the light receiving element 40 receives the reflected pulse light, and the value of the voltage signal output from the IV conversion unit 50 is stand up to time _{t 1,} which reaches a peak. In addition, the light-receiving timing signals, falls in time t _2. It should be noted that the timing at which the voltage signal value peaks can be detected by detecting the change in the sign of the time differential value of the voltage signal.

  Based on the light emission timing signal output from the drive unit 30 and the light reception timing signal output from the determination unit 60, the control unit 12A generates a tacoff signal, a tacl signal, and a tac2 signal. Further, the control unit 12A generates a reset1 signal and a reset2 signal based on the light emission timing signal output from the driving unit 30.

Prior to time t ₀ , the reset 1 signal and the reset 2 signal have significant values, the switches SW ₁₁ and SW ₁₂ are closed, and the potentials V _out1 and V _out2 are set to the reset potential V _reset . At time t ₀ , the reset 1 signal and the reset 2 signal each turn to an insignificant value, and each of the switches SW ₁₁ and SW ₁₂ turns to an open state.

The time _{t 0} before or after the time _{t 2,} tacoff signal, only Tacoff signal of tac1 signals and tac2 signal is a significant value, only the switch SW ₀ of the switch _SW 0 to SW ₂ are closed.

During the period from time t ₀ to time t ₁ , only the tac 1 signal among the tacoff signal, the tac 1 signal, and the tac 2 signal has a significant value, and only the switch SW ₁ among the switches SW _{0 to} SW ₂ is closed.

In the period from time _{t 1} to time _{t 2, tacoff} signal, only tac2 signal of tac1 signals and tac2 signal is a significant value, only the switch SW ₂ of the switch _SW 0 to SW ₂ are closed.

The potential V _out1 changes over a period from time t ₀ to time t _1, and the amount of potential change is V ₁ . The potential V _out2 changes over a period from time t ₁ to time t ₂ , and the potential change amount is V ₂ .

Here, the period from time _{t 0} to time _{t 1} and _{T 1,} the time from time _{t 1} to time _{t 2} and _{T 2.} Assume that the capacitance values of the capacitive elements C ₁ and C ₂ are equal to each other and C. Also, let I be the current flowing through the constant current source 11. At this time, the following relational expression holds between these parameters.
V ₁ = T ₁ I / C (8)
V ₂ = T ₂ I / C (9)
T ₀ = T ₁ + T ₂ (10)

The following relational expressions are obtained from the above expressions (8) to (10).
T ₁ = T ₀ V ₁ / (V ₁ + V ₂ ) (11)
T ₂ = T ₀ V ₂ / (V ₁ + V ₂ ) (12)

The calculation unit 13A can calculate the times T ₁ and T ₂ by performing the above calculation based on the potential changes V ₁ and V ₂ and the known time T ₀ . Then, it is possible on the basis of the time T _1, determine the distance to the object 90.

6 and 7 are timing charts for explaining another example of the operation of the time measuring apparatus 10A according to the second embodiment. In the operation example shown in FIG. 6, the light reception timing signal given from the determination unit 60 to the control unit 12A of the time measuring device 10A exceeds the threshold value from the state where the value of the voltage signal output from the IV conversion unit 50 is less than the threshold value. stand up to time t ₁ to transition to the state. In the operation example shown in FIG. 7, the light reception timing signal given from the determination unit 60 to the control unit 12A of the time measurement device 10A is less than the threshold value from the state where the value of the voltage signal output from the IV conversion unit 50 exceeds the threshold value. stand up to time t ₁ to transition to the state. Also in these cases, the calculation unit 13A can obtain the times T ₁ and T ₂ by performing the same calculation based on the potential changes V ₁ and V ₂ and the known time T ₀ . Then, it is possible on the basis of the time T _1, determine the distance to the object 90.

As described above, also in this embodiment, the times T ₁ and T ₂ are obtained by the above equations (11 to (12), and thus are not affected by variations in the current I flowing through the constant current source 11. Even in the embodiment, it is not necessary to perform measurement for correction using an optical fiber as in the invention disclosed in Patent Document 1. Therefore, in this embodiment as well, highly accurate time measurement and distance measurement can be performed with a simple configuration. It can be carried out.

Also, in this embodiment, by switch SW ₀ and resistor R are provided, since the time t ₀ the constant current source 11 also before current flows, stable in time t ₀ after the constant current source 11 Operation can be obtained, and also in this respect, highly accurate time measurement and distance measurement can be performed.

  (Modification)

The current I flowing through the constant current source 11 is constant in the above embodiment, but may be variable. The capacitance values of the capacitive elements C _{1 to} C ₃ are equal to each other in the above embodiment, but may be variable or may be different from each other. For example, in the first embodiment, when the time T ₂ compared to the time T ₁ is very short is preferably small capacitance value of the capacitor C ₂ as compared with the capacitance of the capacitor C _1, thus by the potential change amount V ₂ can be detected with high sensitivity. Further, it is preferable to adjust the current I flowing through the constant current source 11 and the capacitance value of the capacitive element according to the measurement range and resolution.

DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 10, 10A ... Time measuring device, 11 ... Constant current source, 11a ... Current source, 12, 12A ... Control part, 13, 13A ... Calculation part, 20 ... Light source, 30 ... Drive part, 40 ... light-receiving element, 50 ... IV converting portion, 60 ... determining _{unit, C} 1 -C 3 _... capacitive element, R ... _{resistors, SW 0 ~SW 3, SW 11} ~SW 13 ... switch, _Tr 1, Tr 2 _... transistor.

Claims (4)

A constant current source;
And the J capacitive element C ₁ -C _J to the first end having a first end and a second end connected to a reference potential,
A switch SW _j provided between the second end of each capacitive element C _j and the constant current source;
Of the period of time _{T 0} from time _{t 0} on the basis of a signal given from the outside to the time _{t J} from the time _{t j-1} of the known time to time _{t j} of J switches _SW 1 to SW _J A control unit for closing the switch SW _j and opening the other switches;
Potential change amount of the second end of the capacitor element _{C j} at time _{t J} against time _{t 0 V j} and known time based on _{T 0,} any time _{T j} from time _{t j-1} to time _{t j} An arithmetic unit for obtaining
(Where J is an integer of 2 or more, j is an integer of 1 or more and J or less). A light source that outputs pulsed light;
A drive unit for driving the light source to emit pulsed light from the light source and outputting a light emission timing signal indicating the light emission timing;
A light receiving element that receives reflected pulse light generated by projecting the pulsed light output from the light source onto an object and outputs a current signal corresponding to the received light intensity;
An IV converter that converts a current signal output from the light receiving element into a voltage signal and outputs the voltage signal;
A determination unit that outputs a light reception timing signal indicating a timing at which the light receiving element receives the reflected pulse light based on a voltage signal output from the IV conversion unit;
The timing represented by the light emission timing signal output from the drive unit is defined as time t _0, and the timing represented by the light reception timing signal output from the determination unit is defined as any _one of times t ₁ to t _J−1 up to the object. The time measuring device according to claim 1 for obtaining a time representing a distance of
A distance measuring device comprising: The determination unit outputs a first light reception timing signal representing a timing at which a value of a voltage signal output from the IV conversion unit transitions from a state less than the threshold to a state exceeding the threshold, and from the IV conversion unit Outputting a second light receiving timing signal representing a timing at which the value of the output voltage signal transitions from a state exceeding the threshold to a state below the threshold;
The time measuring device, J value is 3, the timing of the first light receiving timing signal output from the determination unit represented by the time t _1, the timing indicated by the second light receiving timing signal output from the determination unit As time t ₂ , time T ₁ , time T ₂ or time T ₃ is obtained.
The distance measuring device according to claim 2. The determination unit transitions to a timing at which the value of the voltage signal output from the IV conversion unit reaches a peak, and from a state where the value of the voltage signal output from the IV conversion unit is less than the threshold to a state exceeding the threshold. A light reception timing signal representing any one of timing and a timing at which the value of the voltage signal output from the IV conversion unit transitions from a state exceeding the threshold to a state below the threshold;
The time measuring device calculates a time T ₁ or a time T ₂ with a J value of 2 and a timing represented by a light reception timing signal output from the determination unit as a time t ₁ .
The distance measuring device according to claim 2.

Images