JP2010107212A - Distance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distance measuring device which enables stable distance measurement irrespective of weather conditions and other various disturbance factors. <P>SOLUTION: The device includes a light-projecting part 11 which outputs laser light toward a target 2, a light-receiving part 12 which receives reflected light from the target 2, and an operation part 13 which calculates a distance to the target 2, based on a time difference from the time of output of the laser light by the light-projecting part 11 to the time of reception of the reflected light by the light-receiving part 12. The light-projecting part 11 outputs the laser light in the quantity equal to or larger than the maximum receivable light quantity of a light-receiving element 16, while the light-receiving part 12 is equipped with a light quantity adjusting mechanism 17 which adjusts the quantity of incident light so that the quantity of light incident on the light-receiving element 16 be equal to or smaller than the maximum receivable light quantity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a distance measuring device for measuring a change in distance between a measuring point and a point to be measured, and in particular, a distance measuring device using a laser beam that is used in a place where measurement conditions are bad such as outdoors. About.

  In order to measure the prediction of natural disasters such as earthquakes and landslides and the movement of glaciers, distance measuring devices that regularly measure the distance between two points set on the ground are used. As one of such distance measuring devices, laser light is irradiated from a measuring device body installed at a measurement point (or a fixed point) toward a target such as a mirror installed at a measurement point (or moving point). The distance of the active method that measures the distance between the measurement point and the point to be measured by receiving the light reflected by the target, measuring the time from receiving the laser light to receiving the reflected light A measuring device has been proposed (see Patent Document 1).

  Since such a distance measuring device is installed outdoors, it is easily affected by measurement conditions due to the natural environment such as the weather. For example, when the sky is clear, the attenuation of the laser light in the air is small, so the intensity of the reflected light from the target reaching the light receiving unit is high. On the other hand, in the case of rain or fog, the laser light is scattered by water droplets floating in the air, so the attenuation of the laser light is large, the intensity of the reflected light from the target reaching the light receiving unit is small, And the degree is not constant. Further, when the distance measuring device is left outside for a long time, dust or mud adheres to the window of the light projecting part and the light receiving part of the housing, and the laser light and the reflected light are also attenuated by these adhering substances. In addition, when a mirror or the like cannot be installed at the measurement point, the target object is the rock or tree that originally exists at the measurement point, and the reflected light from the target is received. However, the intensity of the reflected light is reduced.

On the other hand, a light receiving element such as a photodiode for detecting reflected light from a target used in the light receiving unit has a range in which an appropriate signal corresponding to the intensity of the received light can be output. Specifically, when the intensity of light incident on the light receiving element is smaller than the lower limit threshold, the S / N of the output signal extremely decreases due to the influence of dark current. When the intensity of light incident on the light receiving element is larger than the upper limit threshold, the photoelectric conversion capability of the light receiving element is exceeded and an overflow state occurs. Therefore, when the distance measuring device is installed outdoors, the light output from the light projecting unit is set so that the intensity of the reflected light from the target incident on the light receiving element is between the upper limit threshold and the lower limit threshold, for example, on a clear day. The intensity of the laser beam is adjusted. Then, due to the influence of the weather conditions as described above, the intensity of the reflected light of the target incident on the light receiving element may be lower than the lower limit threshold value, and in this case, it is impossible to perform an appropriate distance measurement. Produce.
Japanese Patent No. 2994256

  The present invention has been made to solve the above-described problems of the conventional example, and provides a distance measuring device capable of performing stable distance measurement regardless of weather conditions and other various disturbance factors. Objective.

  In order to achieve the above object, the invention of claim 1 is a distance measuring device, wherein a light projecting unit that outputs laser light toward a target, a light receiving unit that receives reflected light from the target, A calculation unit that calculates a distance to the target based on a time difference from an output time of laser light by the light projecting unit to a reception time of reflected light by the light receiving unit, and the light projecting unit includes the light receiving unit A light amount adjusting means for adjusting the amount of incident light so that the amount of light incident on the light receiving element is less than or equal to the maximum amount of light that can be received. It is characterized by having.

  According to a second aspect of the present invention, in the distance measuring device according to the first aspect, the light amount adjusting means includes a light amount reducing element that decreases a light transmission amount.

  According to a third aspect of the present invention, in the distance measuring device according to the second aspect, the light amount reducing element is a liquid crystal element, and the amount of transmitted light is adjusted by adjusting the density of the liquid crystal element.

  According to a fourth aspect of the present invention, in the distance measuring device according to the third aspect, the liquid crystal element has a polarization direction of a polarizing filter on an incident surface side thereof and a polarization direction of reflected light from the target. It is attached.

  According to a fifth aspect of the present invention, in the distance measuring device according to any one of the first to third aspects, the light amount adjusting means receives light when the light projecting unit is not in a state capable of outputting laser light. It is characterized by taking a state where the amount of light incident on the element is minimized.

  The invention of claim 6 is the distance measuring device according to claim 1, wherein the light amount adjusting means includes a condenser lens and a displacement mechanism that changes a relative position of the condenser lens with respect to the light receiving element, The amount of light incident on the light receiving element is adjusted by moving the focal position of the condenser lens with respect to the light receiving surface of the light receiving element in the optical axis direction.

  A seventh aspect of the present invention is the distance measuring device according to any one of the first to sixth aspects, wherein the light amount incident on the light receiving element or the level of the output signal from the light receiving element at the time of past measurement. The apparatus further includes a light quantity value storage means for storing the value.

  According to an eighth aspect of the present invention, in the distance measuring device according to any one of the first to sixth aspects, when the elapsed time from the previous measurement is shorter than a predetermined time, the light amount adjusting means The light quantity adjustment is stopped.

  According to a ninth aspect of the present invention, in the distance measuring device according to any one of the first to sixth aspects, the target is a reflector directed to a location to be measured.

  According to a tenth aspect of the present invention, in the distance measuring device according to any one of the first to ninth aspects, the light amount is not adjusted by the light amount adjusting means, and the reflected light from the target attenuates the light amount. Even when the light is incident on the light receiving element, if the incident light quantity is less than the minimum receivable light quantity of the light receiving element, the light projecting unit is configured so that the incident light quantity is equal to or greater than the minimum receivable light quantity of the light receiving element. Is characterized by increasing the intensity of the output laser beam.

  According to the first aspect of the present invention, the light projecting unit outputs a laser beam having a light quantity equal to or greater than the maximum receivable light quantity of the light receiving element in the light receiving part, but the light receiving part is provided with the light quantity adjusting means. Even if the measurement conditions are good and the reflectance of the surface of the target is high, the amount of light incident on the light receiving element can be adjusted to be less than the maximum receivable light amount, preventing overflow in the light receiving element. Thus, an appropriate distance measurement can be performed. Further, even when the measurement conditions are poor and the reflectance of the surface of the target is low, the amount of light incident on the light receiving element can be selected by appropriately selecting the intensity of the laser light output from the light projecting unit. The minimum amount of light that can be received can be increased. As a result, measurement with a high S / N becomes possible.

  According to the invention of claim 2, since the light amount adjusting means includes the light amount reducing element for reducing the light transmission amount, the light amount distribution is close to the normal distribution, and the light beam is concentrated in the central portion of the light beam. Even for light, the amount of transmitted light can be reduced uniformly by the light amount reducing element. As the light quantity reducing element, for example, an ND filter, a translucent plate, polished glass, a mesh or lattice plate, a half mirror, or the like can be used. Further, these different kinds of light quantity reducing elements may be used in combination.

  According to the third aspect of the present invention, a liquid crystal element is used as the light quantity reducing element, and the transmitted light quantity is adjusted by adjusting the density of the liquid crystal element. In the sense that there is no possibility of failure, it is more advantageous than using an ND filter or the like. In addition, since the ND filter has an advantage that the liquid crystal element does not have, it cannot be determined that either one is superior.

  According to the fourth aspect of the present invention, when a liquid crystal element is used as the light quantity reducing element, the polarization direction of the polarizing filter on the incident surface side of the liquid crystal element matches the polarization direction of the reflected light from the target. Therefore, even if the reflected light from the target has polarized light, the component cut off by the polarizing filter can be reduced, and compared with the case where the reflected light from the target does not, the target incident on the liquid crystal element can be reduced. The amount of reflected light from the object can be increased.

  According to the fifth aspect of the present invention, the light amount adjusting means has a minimum amount of light incident on the light receiving element when the light projecting unit is not in a state capable of outputting laser light, that is, when the distance measuring device 1 is not in a measurement posture. Therefore, the amount of natural light incident on the light receiving element through a protective window or the like can be reduced, and deterioration of the light receiving element can be prevented or reduced.

  According to the sixth aspect of the present invention, the relative position of the condenser lens with respect to the light receiving element is changed as the light amount adjusting means, and the focal position of the condenser lens with respect to the light receiving surface of the light receiving element is moved in the optical axis direction. Since the amount of light incident on the light receiving element is adjusted, a light amount reducing element such as the ND filter or the liquid crystal element is not necessary, and the number of components can be reduced. In any optical system, it is necessary to adjust the relative position of the condensing lens with respect to the light receiving element. Therefore, it is possible to realize the light amount adjusting means without complicating the configuration. .

  According to the seventh aspect of the present invention, since the light amount value storage means for storing the light amount value incident on the light receiving element or the level value of the output signal from the light receiving element at the time of past measurement is further provided, When measuring, even if the measurement conditions around the distance measuring device have changed, the amount of light incident on the light receiving element and the amplification level of the output signal can be adjusted by adjusting the light amount with the stored level value as the target value. Is almost constant, the characteristics and noise level of the light receiving element are constant, and the measurement accuracy is stabilized. Note that the level value of the output signal from the light receiving element at the time of past measurement or the light quantity value incident on the light receiving element may be kept as it is at the first measurement in a series of measurement operations, or the measurement operation Each time is performed, it may be replaced with the latest measurement.

  According to the invention of claim 8, when the elapsed time from the previous measurement is shorter than the predetermined time, it is considered that the measurement conditions around the distance measuring device have hardly changed. By stopping the light amount adjustment, the time required for distance measurement can be shortened. Even in this case, the amount of light incident on the light receiving element is maintained within a certain range, and the measurement accuracy is maintained.

  According to the ninth aspect of the present invention, the amount of reflected light from the target incident on the light receiving element is increased by using a reflector directed to the measurement site as the target as compared to the case where the target is not. be able to.

  According to the invention of claim 10, for example, when the measurement conditions are bad and the reflectance of the surface of the target is low, the light amount is not adjusted by the light amount adjusting means, and the reflected light from the target is attenuated. Even if the light is incident on the light receiving element, the laser output from the light projecting unit will make the incident light quantity equal to or greater than the minimum light receiving capacity of the light receiving element when the incident light quantity is less than the minimum light receiving capacity of the light receiving element. Since the light intensity is increased, the ratio of the reflected light component from the target in the light detected by the light receiving element is large under any measurement condition, that is, measurement with a high S / N is possible. Become.

  A distance measuring device according to an embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a block configuration of a distance measuring device 1 according to an embodiment. The distance measuring device 1 receives light from a light projecting unit 11 that outputs laser light toward the target 2, a light receiving unit 12 that receives reflected light from the target 2, and a laser light output time by the light projecting unit 11. Based on the time difference until the light reception time of the reflected light by the unit 12, the calculation unit 13 that calculates the distance to the target 2, the light projecting unit 11, the light receiving unit 12, the housing 14 that houses the calculation unit 13, etc. I have. Since the distance measuring device 1 is installed outdoors, the housing 14 has a waterproof structure and has a protective window 15 that faces the light projecting unit 11 and the light receiving unit 12. In addition, illustration is abbreviate | omitted about the solar cell for power supply, the memory for data recording, the communication apparatus for data transmission, etc.

  Although not shown in particular, the light projecting unit 11 is a collimator that converts a laser light source such as a semiconductor laser that outputs laser light having a predetermined wavelength and a parallel light beam having a predetermined beam diameter from the laser light output from the laser light source. It consists of a lens. The light receiving unit 12 amplifies the light receiving element 16 such as a photodiode, a light amount adjusting mechanism (light amount adjusting means) 17 provided between the protective window 15 and the light receiving element 16, and an output signal from the light receiving element 16. A signal processing circuit (not shown) and the like. Details of the light amount adjusting mechanism 17 will be described later.

  For example, when the occurrence of a natural disaster such as a landslide is predicted using the distance measuring device 1, a mirror, a white plate, a metal plate, or the like having a high reflectance is measured in advance on a measurement point such as a slope where a landslide is likely to occur. Set the target. Alternatively, if a target such as a mirror cannot be installed at the point to be measured, the target object 2 is the rock or tree originally present at the point to be measured. If possible, the surface has a reflectance such as white. Affix a high sheet or apply a highly reflective paint.

  When a reflector such as a mirror is used as the target, the reflecting surface of the reflector is adjusted so that the laser beam output from the light projecting unit 11 is reflected toward the light receiving unit 12. In that case, since the reflectance at the surface of the target 2 is very high, the intensity of the reflected light incident on the light receiving unit 12 with respect to the intensity of the laser light output from the light projecting unit 11 when the measurement conditions are good such as in fine weather. The percentage of is high. Therefore, in general, by reducing the intensity of the laser light output from the light projecting unit 11, the amount of light incident on the light receiving unit 12 is less than the maximum receivable light amount and greater than the minimum receivable light amount. It is also possible to adjust. However, when the measurement conditions are good, such as in fine weather, the intensity of natural light (noise component) such as sunlight that enters the light receiving unit 12 from the protective window 15 is high, so that if the intensity of the laser light is reduced, the light enters the light receiving unit 12. The ratio of reflected light (signal component) becomes small (S / N becomes small), resulting in a problem that measurement accuracy is lowered. On the other hand, when a target such as a mirror cannot be installed at the point to be measured, only a part of the light irregularly reflected on the surface of the object determined as the target reaches the light receiving unit 12, so that the measurement conditions are good such as in fine weather. However, the ratio of the intensity of the reflected light incident on the light receiving unit 12 to the intensity of the laser light output from the light projecting unit 11 is relatively small. Furthermore, if natural conditions such as rain and fog and dirt on the protective window 15 overlap, the ratio of the intensity of the reflected light incident on the light receiving unit 12 is further reduced. Therefore, it is necessary to increase the intensity of the laser beam output from the light projecting unit 11 as much as possible.

  As described above, the light receiving element 16 outputs an appropriate signal according to the intensity of the received light, so that the upper limit threshold of the amount of light incident on the light receiving element 16, that is, the maximum receivable light amount and the lower limit threshold, that is, the minimum light reception. There is a possible amount of light. In the present embodiment, even when the reflectance on the surface of the target is low and the measurement conditions are bad, the light projecting unit 11 so that the amount of light incident on the light receiving element 16 in the light receiving unit 12 is greater than or equal to the minimum receivable light amount. From the above, a laser beam having a light quantity equal to or larger than the maximum receivable light quantity of the light receiving element 16 in the light receiving unit 12 is output (constant laser light intensity), and the light quantity incident on the light receiving element is the maximum receivable light quantity even when measurement conditions are good The incident light amount to the light receiving element 16 is adjusted by the light amount adjusting mechanism 17 so as to be as follows. Even when the light amount adjustment mechanism 17 does not adjust the light amount and the reflected light from the target 2 enters the light receiving element 16 without attenuation of the light amount, the incident light amount satisfies the minimum receivable light amount of the light receiving element 16. When there is no light, it is preferable that the light projecting unit 11 increases the intensity of the output laser light so that the amount of incident light is greater than or equal to the minimum amount of light that can be received by the light receiving element 16. Thereby, under any measurement condition, the ratio of the reflected light component from the target 2 in the light detected by the light receiving element 16 is large, that is, measurement with a high S / N is possible.

  Next, a specific configuration example of the light amount adjustment mechanism 17 will be described. 2A and 2B show a first configuration example of the light amount adjustment mechanism 17 and a modification thereof. In the first configuration example shown in FIG. 2A, the light amount adjusting mechanism 17 includes a condenser lens 21 for condensing the reflected light incident through the protective window 15 on the light receiving surface of the light receiving element 16, and a plurality of ND filters. (Light quantity reducing element) 22 and a drive mechanism (not shown) that moves the ND filter 22 in a direction orthogonal to the optical axis of the condenser lens 21. In the first configuration example, each ND filter 22 has the same density. On the other hand, in the modification shown in FIG. 2B, each ND filter 22 has a different density. In the latter case, the number of steps of light amount adjustment by the light amount adjustment mechanism 17 can be increased. Needless to say, the drive mechanism can move each ND filter 22 individually. Further, although not shown, the ND filter 22 may be constituted by a single sheet. In that case, the ND filter 22 is preferably formed so that the density partially changes. Thereby, the amount of transmitted light can be changed depending on the position of the ND filter 22 in the direction orthogonal to the optical axis.

  Note that an iris diaphragm used for a photographic lens or the like can be used as the light amount adjusting mechanism 17, but the light amount distribution of the laser light output from a light source such as a laser diode is close to a normal distribution, and a light beam is present at the center of the light beam. Since they are concentrated, an ND filter that can reduce the amount of transmitted light uniformly is more effective than an iris diaphragm. In addition to the ND filter, a translucent plate, frosted glass, a mesh or lattice plate, a half mirror, or the like can be used as the light amount reducing element. Further, these different kinds of light quantity reducing elements may be used in combination. Furthermore, when using a half mirror as the light reduction element, use two light receiving elements to switch between receiving light that has passed through the half mirror and receiving light reflected by the half mirror. Is also possible.

  Next, the measurement operation of the distance measuring device 1 will be described. At the start of the distance measurement, the calculation unit 13 monitors the output from the light receiving element 16 and appropriately adjusts the ND filter 22 so that the output from the light receiving element 16 is equal to or lower than the level of the output signal when the maximum light receivable light amount. It is moved and put on the optical axis of the condenser lens 21. At this time, laser light may be actually output from the light projecting unit 11, or laser light is not output from the light projecting unit 11 and is incident on the light receiving element 16 through the protective window 15 before starting measurement. You may measure the intensity | strength of the natural light which is a noise component. For example, since the intensity of natural light is high when the measurement conditions are good, such as in fine weather, the measurement conditions can be estimated by measuring the intensity of natural light. In the latter case, since a signal of an appropriate level is output from the light receiving element 16 at the same time as the start of measurement, the time required for measurement can be shortened.

  From the light projecting unit 11, for example, a rectangular pulse laser beam is output to the target 2, and the laser beam is reflected by the target 2. The light reflected by the target 2 passes through the light amount adjustment mechanism 17 and is further condensed on the light receiving surface of the light receiving element 16 by the condenser lens 21. When the intensity of the reflected light from the target 2 is predicted to be high when passing through the light amount adjusting mechanism 17, a light amount reducing element such as the ND filter 22 is inserted in the optical path in advance. The amount of incident light is adjusted to be equal to or smaller than the maximum receivable light amount and larger than the minimum receivable light amount. Therefore, the calculation unit 13 can extract a rectangular pulse signal from the output signal from the light receiving element 16, and the time difference from the output time of the laser beam by the light projecting unit 11 to the reception time of the reflected light by the light receiving unit 12 can be calculated. The distance to the target 2 can be calculated based on the time difference. The calculated distance to the target 2 is stored in a memory together with time information such as a measurement start time, or is wirelessly transmitted to a parent device provided at a remote place.

  Such a distance measuring device 1 periodically measures the distance between two points, that is, a measurement point set on the ground in advance and a point to be measured, and when the distance changes, the distance from the change to the measurement point is measured. The amount of movement and the direction of movement can be measured. Furthermore, it is possible to calculate the moving speed and acceleration of the measurement point from the measurement interval and the moving amount. When the change in distance is small, measurement is performed at preset intervals (for example, every few hours). However, if the change in distance is large, it can be estimated that natural disasters such as landslides are near, so the measurement interval It is preferable to measure continuously (for example, every few minutes) or continuously.

  When the distance change is small and the measurement is performed at relatively long intervals, it is highly possible that the measurement conditions around the distance measuring device 1 have changed. Therefore, it is necessary to adjust the light amount by the light amount adjusting mechanism 17 every time the measurement is performed. There is. As described above, level adjustment is performed on the output signal from the light receiving element 16 by amplification processing or the like, but the characteristics of the light receiving element 16 and noise of the signal are obtained by a combination of light amount adjustment and amplification processing by the light amount adjustment mechanism 17. Levels can change and affect measurement accuracy. Therefore, a memory (light quantity value storage means) is provided in the light receiving section 12 or the calculation section 13 to store the level value of the output signal from the light receiving element 16 in the past measurement, in other words, the light quantity value incident on the light receiving element 16. You may do it. The level of the output signal from the light receiving element 16 is substantially the same as the level value stored in the memory, with the level value stored in the memory as the target value and the amplification degree of the output signal being constant. The light quantity adjustment mechanism 17 may be driven so that By doing so, the amount of light incident on the light receiving element 16 and the amplification degree of the output signal become substantially constant, so that the characteristics and noise level of the light receiving element 16 become constant, and the measurement accuracy is stabilized. The level value of the output signal from the light receiving element 16 at the time of past measurement or the light amount value incident on the light receiving element 16 may be kept as it is at the time of the first measurement in a series of measurement operations. Each time a measurement operation is performed, it may be replaced with the latest measurement.

  On the other hand, when the measurement interval is short or continuously measured, that is, when the elapsed time from the previous measurement is shorter than the predetermined time, the measurement conditions around the distance measuring device 1 are almost changed. It is not considered. In that case, the drive of the light amount adjusting mechanism 17 is stopped on condition that the output signal from the light receiving element 16 is equal to or lower than the level corresponding to the maximum light receivable light level and equal to or higher than the level corresponding to the minimum light receivable light amount. Also good. Thereby, the time required for distance measurement can be shortened. Even in this case, the amount of light incident on the light receiving element 16 is maintained within a certain range, and the measurement accuracy is maintained.

  FIGS. 3A and 3B show a second configuration example of the light amount adjustment mechanism 17 and its modification. In the second configuration example shown in FIG. 3A, the light amount adjusting mechanism 17 includes a condenser lens 21, a transmissive liquid crystal element (light amount reducing element) 31, a drive circuit (not shown), and the like. ing. In addition, in the modification shown in FIG. 3B, the condenser lens 21, a reflective liquid crystal element (light quantity reducing element) 32, a drive circuit (not shown), and the like are included. Since the liquid crystal element can change the transmittance or the reflectance by changing the driving voltage (that is, the density adjustment), it can be used as a light quantity reducing element. The type of liquid crystal element and driving characteristics (relationship between driving voltage and transmittance) are not particularly limited.

  In the first configuration example shown in FIG. 2, the light amount reducing element such as the ND filter 22 is configured to move in a direction orthogonal to the optical axis of the condenser lens 21, so that a mechanical drive mechanism is required. Yes. On the other hand, in the second configuration example shown in FIGS. 3A and 3B, the liquid crystal elements 31 and 32 remain inserted on the optical axis of the condenser lens 21 and require a mechanical drive mechanism. Not in. Therefore, the second configuration example is more advantageous in the sense that there is no possibility of failure of the mechanical drive mechanism.

  The laser light has polarization, and the reflected light from the target 2 also has polarization. On the other hand, a polarizing filter is provided on the incident surface side of the liquid crystal element. Here, when the polarization direction of the incident light to the liquid crystal element, that is, the reflected light from the target 2 does not match the polarization direction of the polarizing filter of the liquid crystal element, the incident light to the liquid crystal element is caused by the presence of the polarizing filter. The amount of light is reduced. On the other hand, natural light, which is a noise component, often has no polarization or has a polarization different from that of reflected light. This causes a problem that when the amount of reflected light from the target 2 is small, the amount of reflected light from the target 2 as a signal is further cut off by the polarizing filter, and the S / N is lowered. . Therefore, as shown in FIG. 4, the liquid crystal element 31 or 32 is preferably attached so that the polarization direction of the polarization filter on the incident surface side thereof matches the polarization direction of the reflected light from the target 2. . Thereby, the component cut off by the polarizing filter can be reduced, and the amount of reflected light from the target 2 incident on the liquid crystal element can be increased as compared with the case where it is not.

  FIG. 5 shows a third configuration example of the light amount adjustment mechanism 17. In the third configuration example, the light amount adjustment mechanism 17 includes a condenser lens 21 and a mechanism (not shown) that moves the condenser lens 21 in the optical axis direction. By moving the condenser lens 21 in the optical axis direction, the focal position moves in the optical axis direction. FIG. 6A shows a case where the focal position of the condenser lens 21 is on the light receiving surface of the light receiving element 16 and the amount of light incident on the light receiving surface of the light receiving element 16 is maximized. 6B and 6C, the focal position of the condenser lens is behind and in front of the light receiving surface of the light receiving element 16, respectively, and the incident light beam is expanded in a conical shape and incident on the light receiving surface of the light receiving element 16. The case where only a part of the light beam is incident is shown. In this way, the amount of light incident on the light receiving surface of the light receiving element 16 can also be changed by moving the condenser lens 21 in the optical axis direction.

  In the third configuration example, it is only necessary to change the relative position of the focal position of the condensing lens 21 and the light receiving surface of the light receiving element 16, and the condensing lens 21 is not necessarily moved. For example, the position of the condenser lens 21 may be fixed and the light receiving element 16 may be moved in the optical axis direction. Alternatively, the positions of the condenser lens 21 and the light receiving element 16 may be fixed, and an optical element such as a prism may be inserted between the condenser lens 21 and the light receiving element 16. Alternatively, a plane or curved mirror may be provided in the optical path, and the amount of light incident on the light receiving element 16 may be adjusted by rotating the mirror. Or you may adjust the light quantity which injects into the light receiving element 16 by changing the refractive index of a condensing lens or a prism, or changing the curvature of a condensing lens or a curved mirror. Furthermore, these configurations may be combined.

  By the way, even when the light projecting unit 11 is not in a state capable of outputting laser light, that is, when the distance measuring device 1 is not in a measurement posture, the light receiving element 16 of the light receiving unit 12 always receives natural light or the like through the protective window 15. Incident light is subjected to photoelectric conversion on the light receiving surface of the light receiving element 16, and deterioration of the light receiving element 16 proceeds. In particular, when measurement conditions such as sunny weather are good, the amount of natural light incident on the light receiving element 16 is also large, and the progress of deterioration is accelerated. Therefore, when the light projecting unit 11 is not in a state where laser light can be output, the light amount adjusting mechanism 17 preferably takes a state where the amount of light incident on the light receiving element is minimized. For example, in the first configuration example of the light amount adjusting mechanism 17 shown in FIG. 2, when the ND filter 22 is positioned on the optical axis of the condenser lens 21 when the power is turned off and the distance between the targets 2 is measured. Only if necessary, the drive mechanism may be operated so as to retract the ND filter 22 from the optical axis. In the second configuration example of the light amount adjusting mechanism 17 shown in FIGS. 3A and 3B, a liquid crystal that minimizes the transmittance or reflectance of the liquid crystal element when the power is turned off may be used. Furthermore, in the third configuration example of the light amount adjusting mechanism 17 shown in FIG. 4, the power lens is set so that the focal position of the condenser lens 21 is away from the light receiving surface of the light receiving element 16 at the initial position. That's fine.

  The distance measuring device according to the present invention is not limited to the configuration of the above embodiment, and various modifications can be made without departing from the scope of the invention. In the above embodiment, a mirror or the like is exemplified as the target, but the target is not limited thereto, and a re-reflection element such as a glass bead, a corner cube, or a prism may be used. Further, the surface of the target is not necessarily a flat surface, and may be a curved surface such as a spherical surface.

  In addition, the light projecting unit 11, the light receiving unit 12, and the calculation unit 13 are not necessarily provided in the same casing 14, and may be provided in different casings and installed at different positions. Good. Alternatively, two of the light projecting unit 11, the light receiving unit 12, and the calculation unit 13 may be provided in a separate housing from the other one.

The figure which shows the block structure of the distance measuring device which concerns on one Embodiment of this invention. (A) is a figure which shows the 1st structural example of the light-receiving part in the said distance measuring device, especially a light quantity adjustment mechanism, (b) is a figure which shows the modification. (A) is a figure which shows the 2nd structural example of the said light quantity adjustment mechanism, (b) is a figure which shows the modification. The figure explaining the attachment direction of the liquid crystal element in the 2nd structural example of the said light quantity adjustment mechanism. The figure which shows the 3rd structural example of the said light quantity adjustment mechanism. (A)-(c) is a figure which shows the relationship between the change of the relative position of a condensing lens and a light receiving element, and the light beam which injects into a light receiving element, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Distance measuring device 2 Target object 11 Light projection part 12 Light receiving part 13 Calculation part 14 Case 15 Protection window 16 Light receiving element 17 Light quantity adjustment mechanism (light quantity adjustment means)
21 Condensing lens 22 ND filter 31, 32 Liquid crystal element

Claims (10)

A light projecting unit that outputs laser light toward a target, a light receiving unit that receives reflected light from the target, and a time from the output of laser light by the light projecting unit to the time of receiving reflected light by the light receiving unit An arithmetic unit that calculates the distance to the target based on the time difference of
The light projecting unit outputs a laser beam having a light quantity greater than or equal to the maximum receivable light quantity of the light receiving element in the light receiving part,
The distance measuring device according to claim 1, wherein the light receiving unit includes a light amount adjusting unit that adjusts an incident light amount so that a light amount incident on the light receiving element is equal to or less than the maximum receivable light amount.   The distance measuring device according to claim 1, wherein the light amount adjusting unit includes a light amount reducing element that reduces a light transmission amount.   The distance measuring device according to claim 2, wherein the light amount reducing element is a liquid crystal element, and the transmitted light amount is adjusted by adjusting the density of the liquid crystal element.   The distance measuring device according to claim 3, wherein the liquid crystal element is attached so that a polarization direction of a polarization filter on an incident surface side thereof coincides with a polarization direction of reflected light from the target. .   4. The light amount adjusting unit according to claim 1, wherein the light amount adjusting unit takes a state in which the light amount incident on the light receiving element is minimized when the light projecting unit is not in a state capable of outputting laser light. The distance measuring device according to one item.   The light amount adjusting means includes a condensing lens and a displacement mechanism that changes a relative position of the condensing lens with respect to the light receiving element, and a focal position of the condensing lens with respect to a light receiving surface of the light receiving element is an optical axis thereof. The distance measuring device according to claim 1, wherein the amount of light incident on the light receiving element is adjusted by moving in the direction.   7. A light amount value storage unit for storing a light amount value incident on the light receiving element or a level value of an output signal from the light receiving element at the time of past measurement. The distance measuring device according to one item.   The distance measurement according to any one of claims 1 to 6, wherein when the elapsed time from the previous measurement is shorter than a predetermined time, the light amount adjustment by the light amount adjusting means is stopped. apparatus.   The distance measuring device according to any one of claims 1 to 6, wherein the target is a reflector directed to a measurement location.   When the amount of incident light is less than the minimum receivable light amount of the light receiving element even when the reflected light from the target is incident on the light receiving element without being attenuated, without adjusting the light amount by the light amount adjusting means. 10. The light projecting unit increases the intensity of the output laser beam so that the incident light amount is equal to or greater than the minimum light receivable amount of the light receiving element. The distance measuring device according to one item.

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