JP2013092385A - Distance measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measurement apparatus capable of preventing changes in measurement accuracy due to temperature change of a light emitting element.SOLUTION: A light projection means 1 comprises a light emitting element 11 that projects a light beam into a target space. A light receiving means 2 comprises a light receiving element 21 that receives the light from the target space. A control means 3 provides a modulation signal to the light projection means 1 to cause the light emitting element 11 to emit a modulation light, the brightness of which changes as the time passes, and provides a demodulation signal, which is synchronous with the modulation signal, to the light receiving means 2 to extract components of the modulation light from the output of the light receiving element 21. A calculation means 4 measures the time from a point when the modulation light is emitted by the light projection means 1 into the target space up to a point when the same is received by the light receiving means 2 to calculate the distance to an object in the target space. A temperature measurement means 6 measures the temperature of the light emitting element 11. An accuracy maintaining means 7 controls the drive current to the light emitting element 11 so as to be larger in proportion to the temperature measured by the temperature measurement means 6; to thereby prevent the modulation light received by the light receiving element 21 from changing irrespective of the temperature change of the light emitting element 11.

Description

  The present invention relates to a distance measuring device that measures the distance to an object that reflects light using the time from light projection to light reception.

  2. Description of the Related Art Conventionally, an active type distance measuring device that measures the time from light projection to light reception and measures the distance to an object that reflects the projected light is known. This distance measuring device converts a time of flight of light into a distance. In order to measure the time from light projection to light reception, it is necessary to know the time when the received light was projected. However, if it is a short distance of about several meters, a short time measurement of about several tens of ns is required. Therefore, it is difficult to improve the accuracy of distance measurement.

  Therefore, when performing distance measurement using time of flight, in order to accurately measure the time from light projection to light reception, there is a technology that projects light with modulated intensity and detects the intensity change of the received light. It has been proposed (see, for example, Patent Document 1). In the technique described in Patent Document 1, modulated light whose intensity changes in a sine wave shape at a fixed period is projected, and the received light intensity is detected at a plurality of timings synchronized with the modulated light, whereby the received modulated light The phase delay with respect to the projected modulated light is calculated.

That is, the received light intensity is obtained at the timing of 90 ° intervals of the phase of the modulated light, and the phase delay is calculated using the known relationship of the received light intensity at each timing. Specifically, when the received light intensities obtained at timings synchronized with the four phases of modulated light of 0 degree, 90 degrees, 180 degrees, and 270 degrees are A0, A1, A2, and A3, the phase difference φ is φ = Tan ⁻¹ {(A0−A2) / (A1−A3)}. Here, the sign is ignored.

  When the phase difference φ is obtained as described above, the distance L [m] to the object is obtained by using the light beam c [m / s] and the frequency f [Hz] of the modulated light. That is, if the phase difference is φ [rad], L = (φ / 2π) (c / f) / 2.

JP 2004-45304 A

  By the way, the relational expression described above assumes that the modulated light is a sine wave. Even if the timing of detecting the received light intensity is accurate, if the received modulated light waveform is distorted, the phase difference φ Cannot be determined accurately. That is, if the waveform of the received modulated light is distorted, the distance cannot be measured accurately.

  It is considered that the main causes of the distortion of the received modulated light waveform are the influence of ambient light and the characteristics of the light emitting element that projects the modulated light. In particular, when used outdoors, the influence of sunlight, which is ambient light, increases, so it is necessary to remove sunlight and receive light.

  Therefore, in order to reduce the influence of sunlight, a band pass filter that transmits only light near the wavelength of the modulated light is used. For outdoor use, a light emitting element having a larger light output than that for indoor use is employed. By these measures, a decrease in measurement accuracy due to the influence of sunlight is suppressed.

  On the other hand, light emitting diodes or laser diodes are used as light emitting elements for projecting modulated light because of the demand for responsiveness, and this type of light emitting element is known to depend on temperature for light output. Yes. In addition, the wavelength range and peak wavelength of the emission wavelength also change due to the influence of temperature. Further, the response of the light output to the electric input to the light emitting element is also affected by the temperature.

  Therefore, when the temperature of the light emitting element changes, the intensity of the modulated light changes, so that the waveform of the received modulated light may be distorted. In addition, as described above, when the modulated light is received through the band pass filter, if the wavelength band or the peak wavelength changes, the transmittance with respect to the band pass filter changes, so the waveform of the received modulated light may be distorted. There is sex. Furthermore, since the response characteristics of the light emitting element are affected by temperature, even if the electrical input to the light emitting element is a sine wave, the light output as modulated light may be distorted.

  When using outdoors, compared to using indoors, the ambient temperature change of the light emitting element is large, and it is considered that the temperature change occurs within a relatively short time. Countermeasures are necessary.

  This invention is made | formed in view of the said reason, The objective is to provide the distance measuring device which suppressed the change of the measurement precision with respect to the temperature change of a light emitting element.

A distance measuring apparatus according to the present invention includes a light projecting unit including a light emitting element that projects light into a target space, a light receiving unit including a light receiving element that receives light from the target space, and a modulation signal to the light projecting unit. The modulated light whose intensity changes with the passage of time is projected from the light emitting element, and the demodulated signal synchronized with the modulated signal is supplied to the light receiving means, and the component of the modulated light is extracted from the output of the light receiving element Control means for measuring, calculating means for measuring the time until modulated light projected from the light projecting means to the target space is received by the light receiving means, and temperature measuring means for measuring the temperature of the light projecting means; ,
And an accuracy maintaining unit that suppresses a change in the modulated light incident on the light receiving element using the temperature measured by the temperature measuring unit.

  In this distance measuring apparatus, it is preferable that the accuracy maintaining unit increases the driving current of the light emitting element as the temperature measured by the temperature measuring unit is higher.

  In this distance measuring apparatus, it is preferable that the accuracy maintaining means delays the timing of driving the light emitting element as the temperature measured by the temperature measuring means is higher.

  In this distance measuring apparatus, the accuracy maintaining unit includes a wavelength selection filter that selects a wavelength of light incident on the light receiving element, and the transmission characteristic of the wavelength selection filter increases as the temperature measured by the temperature measurement unit increases. It is preferable to change to the short wavelength side.

  In this distance measuring apparatus, the light projecting unit includes a plurality of types of the light emitting elements having different emission wavelengths, and the accuracy maintaining unit has a shorter emission wavelength as the temperature measured by the temperature measuring unit is higher. It is preferable to project to the target space using

  In the distance measuring device, the light projecting unit includes a temperature adjusting device that adjusts the temperature of the light emitting element, and the accuracy maintaining unit is configured so that the temperature measured by the temperature measuring unit becomes a specified target temperature. It is preferable to control the temperature control device.

  According to the configuration of the present invention, there is an advantage that a change in measurement accuracy with respect to a temperature change of the light emitting element is suppressed.

It is a block diagram which shows the structural example of embodiment. It is a figure which shows the temperature characteristic of the light emitting diode used for the same as the above. It is a block diagram which shows the other structural example of embodiment. It is a front view which shows the light projection means used for the further another structural example of embodiment. It is a block diagram which shows another structural example of embodiment.

  As shown in FIG. 1, the distance measuring device described below includes a light projecting unit 1 using a light emitting diode as a light emitting element 11 that projects light into a target space, and a light receiving element 21 that receives light from the target space. As a light receiving means 2 using a CCD image pickup device.

  The light emitting diode is preferably a high luminance type having a forward current of 1 to several A, and the light projecting means 1 preferably includes a plurality of light emitting diodes. The light emitting element 11 used in the light projecting unit 1 may be capable of modulating the intensity with a drive signal in the range of about 100 Hz to 1 GHz according to the purpose. Depending on the application, a laser diode or the like may be used instead of the light emitting diode. Good. Moreover, although the light emission wavelength of the light emitting element 11 assumes an infrared region, it may be an ultraviolet region or a visible light region depending on the application. In the case where the light emitting element 11 is a light emitting diode, the light emitting diodes are connected in series, and the energization current is controlled through an energization control element such as a MOSFET.

  As the light receiving element 21, in addition to a CCD image pickup element, a CMOS image pickup element or an image pickup element based thereon can be used. Since the image sensor has a plurality of photoelectric conversion units arranged vertically and horizontally in a grid, when the light receiving element 21 is an image sensor, it is possible to individually measure the distances at a plurality of locations within the field of view of the image sensor. It is. Therefore, a distance image having a pixel value as a distance value is generated. However, it is not essential for the light receiving means 2 to include an image pickup device. When the distance to a specific part in the real space only needs to be measured, the light receiving element 21 such as a photodiode is used to start from the specific part in the real space. A configuration for receiving the light of may be adopted.

  The present embodiment aims to be usable even outdoors where sunlight is present. Therefore, the light receiving means 2 includes a wavelength selection filter 22 that optically selects a wavelength corresponding to modulated light from incident light. . Since the wavelength selection filter 22 needs to pass only light in a relatively narrow wavelength region centered on the peak wavelength of the modulated light, for example, an optical thin film filter in which thin films are stacked in multiple layers is used. When infrared light is used for the modulated light, the wavelength selection filter 22 is designed to selectively transmit infrared light.

  By using such a wavelength selection filter 22, transmission of visible light region and ultraviolet region of sunlight is blocked, and transmission of unnecessary range is also blocked for infrared region. That is, the incidence of sunlight on the light receiving means 2 is greatly reduced.

  The light projecting means 1 and the light receiving means 2 are controlled by the control means 3. The control means 3 gives a sinusoidal modulation signal to the light projecting means 1 so that the modulated light is projected from the light projecting means 1 and modulates the light receiving means 2 at a timing defined in synchronization with the modulation signal. A demodulated signal is given so as to receive light. The modulation signal supplied to the light projecting means 1 may not be a sine wave, but may be a waveform selected from a rectangular wave, a triangular wave, a sawtooth wave, etc. that change at a constant period.

  The demodulated signal given to the light receiving means 2 instructs the light receiving means 2 to receive light so that the amount of received light at the timing specified for the waveform of the modulation signal can be obtained. For example, when the waveform of the modulation signal is a sine wave, the demodulated signals having different timings at 90-degree intervals in the modulation signal may be given to the light receiving means 2. When the modulation waveform is another waveform, a demodulated signal at an appropriate timing may be given to the light receiving means 2 so that a relational expression for obtaining a time difference from light projection to light reception can be applied according to the waveform. It is easy to determine a relational expression for obtaining a time difference according to the waveform of the modulation signal.

  When receiving the demodulated signal, the light receiving means 2 generates an electric charge corresponding to the received light intensity at the timing when the demodulated signal is given by the photoelectric conversion unit. The demodulated signal has a predetermined time width, and the light receiving means 2 generates a charge corresponding to the amount of light received during that time. When the time width of the demodulated signal is shown as an example using the phase of the modulated signal, the demodulated signal indicates, for example, sections of 0 to 30 degrees, 90 to 120 degrees, 180 to 210 degrees, and 270 to 300 degrees. The light receiving means 2 generates a charge corresponding to the amount of light received for each section. Moreover, the electric charge produced | generated for every area is taken out for every area, without being mixed. Charge generation in the light receiving means 2 is performed over a plurality of cycles (hundreds to tens of thousands of cycles) of the modulation signal, and charges generated in the same section are accumulated for each cycle.

  The technique for controlling the timing for generating the charge can use the same principle as the electronic shutter, but in this case, the charge must be read from the light receiving means 2 every time the charge for each section is accumulated. In other words, if charges in four sections are used for distance measurement, the distance is measured by four imaging operations.

  In addition, by using a dedicated imaging device designed to generate charges by dividing the photoelectric conversion units into a plurality of groups, the number of times of imaging for measuring the distance can be made twice or once. Become. Further, in the case of an image sensor having a light receiving area and an accumulation area (transfer area) such as a field transfer type CCD image sensor, a charge for each section of the modulation signal is generated in the light receiving area, The accumulation region may be configured so that charges can be distinguished and accumulated. If the former configuration is adopted, it is possible to shorten the time required to generate the electric charge that enables the distance to be measured as compared with the case where the imaging is performed four times. In addition, if the latter configuration is adopted, the number of charges read out can be reduced as compared with the case where charges are read out from the image sensor four times. These configurations are already known and will not be described in detail here.

When the charges in the four sections described above are read from the light receiving means 2, they are input to the calculating means 4, and the calculating means 4 calculates the distance using the output of the light receiving means 2. In the present embodiment, since it is assumed that the light receiving unit 2 includes an image sensor, the distance for each pixel is calculated using the unit area defined in the field of view of the image sensor as a pixel. Now, when the waveform of the modulation signal (change waveform of the intensity of the modulated light) is a sine wave and charges are generated in four intervals of 90 degrees in the phase of the modulation signal, the amount of charge generated in each interval Assume that (the output value of the light receiving means 2) is A0, A1, A2, A3. In this case, the relationship between the phase difference φ between the projected modulated light and the received modulated light and the charge amounts A0, A1, A2, A3 is theoretically φ = tan ⁻¹ {(A0−A2 ) / (A1-A3)}.

  The calculation means 4 performs the above calculation for each pixel, thereby generating a distance image in which the pixel value is associated with the distance value. The distance image generated by the calculation unit 4 is stored in an image storage unit provided in the output unit 5 and is used. The control means 3, the calculation means 4, and the output means 5 include a processor selected from a microcomputer, a DSP (Digital Signal Processor), an FPGA (Field-Programmable Gate Array), and the processor calculates the distance according to an appropriate program. Do.

  Below, the structure which suppresses the change of the measurement precision of the distance accompanying the temperature change of the light projection means 1 is demonstrated. The light projecting means 1 is provided as the light emitting element 11, and the distance measurement accuracy depends on the temperature change of the light emitting element 11. Therefore, temperature measuring means 6 including a temperature sensor such as a thermistor for measuring the temperature of the light emitting element 11 is provided. The temperature measured by the temperature measuring means 6 is given to the control means 3. The control unit 3 controls the accuracy maintaining unit 7 described below so that the distance measurement result does not change with respect to the temperature change according to the temperature measured by the temperature measuring unit 6. As will be described below in a specific example, the accuracy maintaining unit 7 is realized without using the configuration added only by the operation of the control unit 3, and the configuration added to the light projecting unit 1 and the light receiving unit 2. It may be realized by the control of the control means 3.

In order to realize the accuracy maintaining unit 7 that suppresses the change in the measurement accuracy of the distance according to the temperature of the light projecting unit 1 measured by the temperature measuring unit 6, the present embodiment has the following five types of configurations alone or Use in combination as appropriate.
(1) The drive current of the light emitting element 11 is adjusted.
(2) The timing for driving the light emitting element 11 is adjusted.
(3) The wavelength range incident on the light receiving means 2 is adjusted.
(4) Adjust the emission wavelength of the light emitting element 11.
(5) The temperature change of the light emitting element 11 is suppressed.

  Configuration (1) means that the drive current of the light emitting element 11 is adjusted based on the relationship between the light output (luminance) of the light emitting element 11 and the temperature so that the light output does not change with temperature. That is, if the drive current is constant, it is known that the light output of the light emitting element 11 decreases as the temperature increases. Therefore, the drive current of the light emitting element 11 increases as the temperature detected by the temperature detection unit 6 increases. Is made larger. If the relationship between the temperature and the drive current is appropriately set, the light output can be kept substantially constant regardless of the temperature of the light projecting means 1. Note that when the drive current is increased, the amount of heat generated by the light emitting element 11 is increased, and the drive current has an upper limit. Therefore, the configuration (1) is employed for fine adjustment of the light output with respect to the temperature change. It is desirable to do. When the configuration (1) is adopted, the light projecting unit 1 functions as the accuracy maintaining unit together with the control unit 3.

  Configuration (2) means that the timing for driving the light emitting element 11 is adjusted according to the temperature measured by the temperature measuring means 6. That is, since the demodulated signal is generated in synchronization with the modulation signal, a configuration in which the timing for driving the light emitting element 11 is delayed with respect to the modulation signal is adopted, and the delay time is set to the temperature measured by the temperature measuring means 6. A configuration that adjusts accordingly is adopted. If the configuration (2) is adopted, the distance is corrected in consideration of the variation of the distance value due to the temperature of the light projecting means 1. When the configuration (2) is employed, the light projecting unit 1 functions as the accuracy maintaining unit 7 together with the control unit 3.

  The configuration (3) means that the transmission characteristic of the wavelength selection filter 22 provided in the light receiving unit 2 is adjusted according to the temperature measured by the temperature measuring unit 6. That is, since the light emission wavelength of the light emitting diode used for the light emitting element 11 has temperature dependency, the light receiving means according to the change in the light emission wavelength can be obtained by adjusting the transmission characteristics of the wavelength selection filter 22 according to the temperature of the light emitting element 11. 2 is required to suppress the influence on the output. Specifically, as shown in FIG. 2, in the light emitting diode used as the light emitting element 11, not only the light output decreases as the temperature increases, but also the peak wavelength changes to the long wavelength side. FIG. 2 shows emission wavelengths corresponding to the characteristic X1 of −15 ° C., the characteristic X2 of 25 ° C., and the characteristic X3 of 55 ° C., respectively.

  In order not to affect the output of the light receiving means 2 even if the light emission wavelength of the light emitting element 11 is changed due to the temperature change, it is conceivable to use the wavelength selection filter 22 having a wide transmission wavelength range. However, if the wavelength range that transmits the wavelength selection filter 22 is wide, there arises a problem that the effect of removing the influence of sunlight is reduced. Therefore, it is required to make the wavelength range that transmits the wavelength selection filter 22 as narrow as possible. Therefore, it is necessary to adjust the transmission characteristics of the wavelength selection filter 22 according to the temperature measured by the temperature measuring means 6. In order to adjust the transmission characteristics of the wavelength selection filter 22, the arrangement of the wavelength selection filters 22 is changed, or a plurality of wavelength selection filters 22 having different transmission characteristics are used.

  When the arrangement of the wavelength selection filter 22 is changed, the angle of the wavelength selection filter 22 with respect to the light receiving surface of the light receiving unit 2 is changed according to the temperature measured by the temperature measuring unit 6. That is, when an optical thin film filter (especially an interference filter) is used as the wavelength selection filter 22, it is known that a change occurs in the wavelength range of transmission depending on the incident angle of light. is there. When this configuration is employed, an actuator 23 that changes the direction of the wavelength selection filter 22 needs to be added to the light receiving means 2 as shown in FIG. The actuator 23 is displaced in accordance with a voltage provided with a geared motor, an ultrasonic motor, a piezo element, or the like configured to be able to adjust the direction of the wavelength selection filter 22 by a minute angle (several degrees or less). An electrostrictive element whose amount changes is used.

  On the other hand, when the wavelength selection filter 22 having different transmission characteristics is used by being exchanged, a plurality of types of wavelength selection filters 22 having different transmission characteristics are provided in the light receiving means 2 according to the temperature measured by the temperature measurement means 6. An appropriate wavelength selection filter 22 is selected. The wavelength selection filter 22 used in this configuration has substantially the same wavelength band width and different wavelength ranges for transmission. Further, the wavelength selection filter 22 is exchanged by using the actuator 23 as in the configuration shown in FIG. The actuator 23 used in this configuration may be configured such that the wavelength selection filter 22 can be selected by driving a rotary turret having a plurality of wavelength selection filters 22 attached thereto, for example. When the configuration (3) is adopted, the light receiving unit 2 including the wavelength selection filter 22 and the actuator 23 functions as the accuracy maintaining unit 7 together with the control unit 3.

  The configuration (4) uses the fact that the light emission wavelength of the light-emitting diode that is the light-emitting element 11 varies depending on the temperature. It means that one kind of light emitting diode is selected according to the temperature. For example, as shown in FIG. 4, two types of light emitting diodes 111 and 112 having different emission wavelengths at room temperature are arranged, the light emitting diode 111 having a long emission wavelength is used on the low temperature side, and the emission wavelength is short on the high temperature side. A light emitting diode 112 having a wavelength is used. The peak wavelength of the light emitting diode 111 may be, for example, 850 nm (at 25 ° C.), and the peak wavelength of the light emitting diode 112 may be, for example, 820 nm (at 25 ° C.). For example, the light emitting diode 111 is used at -15 to 25 ° C., and the light emitting diode 112 is used at 25 to 55 ° C., for example. When the configuration (4) is employed, the light projecting unit 1 functions as the accuracy maintaining unit 7 together with the control unit 3.

  Since the light emission wavelengths of the light emitting diodes 111 and 112 are longer on the high temperature side than on the low temperature side, if the light emitting diode 112 having a short wavelength is used on the high temperature side, the light emission wavelength approaches the wavelength of the light emitting diode 111 having a long wavelength. Become. On the other hand, when the light emitting diode 111 having a long wavelength is used on the low temperature side, the light emitting wavelength approaches the light emitting diode 112 having a short wavelength. That is, it is possible to suppress a change in the emission wavelength of the light projecting unit 1 due to a temperature change.

  In the above-described example, two types of light emitting diodes 111 and 112 having different emission wavelengths are used, but three or more types of light emitting diodes may be used. Furthermore, in the configuration example described above, a plurality of types of light emitting diodes 111 and 112 having different emission wavelengths are selectively used, but all the light emitting diodes 111 and 112 may be lit. In this case, the currents flowing through the light emitting diodes 111 and 112 may be adjusted so that the light emitting diodes 111 and 112 having convenient wavelengths are mainly used. Further, when the configuration (4) is used, since the change in the light receiving wavelength of the light receiving unit 2 with respect to the temperature change of the light projecting unit 1 is suppressed, the transmission characteristic of the wavelength selection filter 22 is changed as in the configuration (3). It does not have to be. That is, one of the configuration (3) and the configuration (4) may be selected and used.

  In the configuration (5), as shown in FIG. 5, a temperature adjustment device 12 that suppresses a temperature change of the light emitting element 11 is provided. The temperature control device 12 is preferably configured to be capable of controlling heat absorption and heat generation and being small in size. Therefore, a Peltier element is used for the temperature control device 12. In this configuration, the control unit 3 controls the heat absorption amount or the heat generation amount of the temperature adjustment device 12 so that the temperature measured by the temperature measurement unit 6 is maintained at a specified target temperature. Therefore, the temperature of the light emitting element 11 is maintained at a substantially constant temperature regardless of the ambient temperature. Therefore, changes in the light output and emission wavelength of the light emitting element 11 due to temperature changes are suppressed, and as a result, measurement accuracy can be maintained even if there are temperature changes in the surroundings. When the configuration (5) is adopted, the light projecting unit 1 including the temperature control device 12 functions as the accuracy maintaining unit 7 together with the control unit 3.

  When employing the configuration (5), it is not necessary to employ the configurations (1) to (4). That is, when the configuration (5) is not adopted, one of the configuration (3) and the configuration (4), the configuration (1), and the configuration (2) can be used in appropriate combination.

  As described above, by appropriately using the configurations (1) to (5), the change in the distance measurement accuracy due to the change in the ambient temperature is suppressed, and the calibration is performed even if the temperature environment changes. It is possible to measure the distance accurately without any problem.

DESCRIPTION OF SYMBOLS 1 Light projection means 2 Light reception means 3 Control means 4 Calculation means 5 Output means 6 Temperature measurement means 7 Accuracy maintenance means 11 Light emitting element 12 Temperature control device 21 Light receiving element 22 Wavelength selection filter 23 Actuator 111 Light emitting diode 112 Light emitting diode

Claims (6)

A light projecting means including a light emitting element that projects light into a target space;
A light receiving means including a light receiving element for receiving light from the target space;
A modulation signal is given to the light projecting means to emit modulated light whose intensity changes with time, and a demodulated signal synchronized with the modulation signal is given to the light receiving means to output the light receiving element. Control means for extracting the component of the modulated light from
Arithmetic means for measuring time until modulated light projected from the light projecting means to the target space is received by the light receiving means;
Temperature measuring means for measuring the temperature of the light projecting means;
A distance measuring apparatus comprising: an accuracy maintaining unit that suppresses a change in modulated light incident on the light receiving element using the temperature measured by the temperature measuring unit. The distance measuring apparatus according to claim 1, wherein the accuracy maintaining unit increases the drive current of the light emitting element as the temperature measured by the temperature measuring unit increases. The distance measuring apparatus according to claim 1, wherein the accuracy maintaining unit delays the timing of driving the light emitting element as the temperature measured by the temperature measuring unit is higher. The accuracy maintaining means includes a wavelength selection filter that selects a wavelength of light incident on the light receiving element,
The distance measuring apparatus according to claim 1, wherein the transmission characteristic of the wavelength selection filter is changed to a shorter wavelength side as the temperature measured by the temperature measuring unit is higher. The light projecting means includes a plurality of types of the light emitting elements having different emission wavelengths,
The distance measuring apparatus according to claim 1, wherein the accuracy maintaining unit projects the light into the target space using the light emitting element having a shorter emission wavelength as the temperature measured by the temperature measuring unit is higher. The light projecting means includes a temperature control device that adjusts the temperature of the light emitting element,
The distance measuring device according to claim 1, wherein the accuracy maintaining unit controls the temperature adjusting device so that the temperature measured by the temperature measuring unit becomes a specified target temperature.

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