Patent Description:
There is a device that uses light to measure a distance to an object positioned outside. An example of a technique regarding such a device is disclosed in the following Patent Document <NUM>, for example.

In Patent Document <NUM>, a technique for avoiding saturation of a specific pixel without adversely affecting measurement of other pixels by adjusting power of laser light at a time interval equal to or shorter than a time interval for outputting the laser light is disclosed.

Patent Document <NUM> describes an erroneous detection restraining circuit for a laser range finder in which each reflected light reflected by at least one object of pulsed laser light emitted by a light emitting element reaches a light receiving element, and distance information to the at least one object is acquired based on an amount of time from a light emission starting time for the pulsed laser light to an output starting time from the light receiving element.

Patent Document <NUM> describes a LADAR sensor, with an adaptive controller with at least one control output, which adapts an optoelectronic conversion gain of a detector array of light detecting pixels.

Patent Document <NUM> describes a range imaging apparatus and a range imaging method using a time-of-flight (TOF) system in which distance information of a subject is obtained based on the time difference arising between signal light and reflection light when the signal light is emitted toward, reaches and reflects off the subject, and the reflection light is received.

In the technique of Patent Document <NUM>, light emitted from a light source and light reflected by an external object pass through different optical systems, but in a structure where these light utilize the same optical system, for example, the following problems may occur. That is, when light is emitted from the light source, light reflected by a member inside a device may leak out to a light receiving element side through the optical system, and the light receiving element may be saturated at an unintended timing. In such a case, a light reception timing of light reflected by the external object cannot be accurately grasped.

As a problem to be solved by the present invention, provision of a technique for accurately grasping a light reception timing of light reflected by an object positioned outside in a device for measuring a distance by light may be included as an example, in the device.

The object described above, and other objects, features, and advantages will become more apparent from the preferred embodiments described below and the following figures associated therewith.

In all the drawings, the same components are denoted by the same reference numerals, and the description thereof will not be appropriately repeated.

<FIG> is a block diagram conceptually illustrating a functional configuration of a light scanning device in Embodiment <NUM>. The light scanning device according to the present invention is, for example, a so-called light detecting and ranging (LIDAR) device mounted on a moving object. Here, the expression "being mounted on a moving object" means not only being incorporated into the moving object as a part of the moving object but also installing a separately assembled single device inside the moving object or outside the moving object. In the following, although the description is made on the assumption that the moving object is a vehicle, the moving object is not limited to the vehicle. For example, the moving object may be an airplane, a ship, or a robot (for example a drone) capable of autonomous navigation. As illustrated in <FIG>, a light scanning device <NUM> includes a light source <NUM>, a light receiving circuit <NUM> including a light receiving element (not illustrated), an optical system <NUM>, and a control unit <NUM>. In the example of this figure, the light scanning device <NUM> further includes a signal processing unit <NUM>. In <FIG>, the solid line conceptually represents a connection relation between respective components by wiring and the like, the broken line conceptually represents a path of light (hereinafter also denoted by "emission light") emitted from the light source <NUM>, and the dotted line conceptually represent a path of light (hereinafter also denoted by "external reflection light") reflected from the emission light described above by a certain object positioned outside the light scanning device <NUM>.

The light source <NUM> is configured by a circuit including a light emitting element such as, for example, a laser diode (LD). The light receiving circuit <NUM> is configured to include a light receiving element such as, for example, an avalanche photo diode (APD).

The optical system <NUM> is configured to include a movable reflection portion (for example, a mirror) that changes a traveling direction of light, and a condenser lens. With this configuration, the optical system <NUM> can direct emission light emitted by the light source <NUM> toward the outside of the light scanning device <NUM>. Also, with this configuration, the optical system <NUM> can direct external reflection light by an object positioned outside the light scanning device <NUM> toward the light receiving element of the light receiving circuit <NUM>.

The control unit <NUM> transmits a control signal to a light source drive circuit <NUM>, and controls the timing of emitting light from the light source <NUM>. The control unit <NUM> also transmits a control signal to the light receiving circuit <NUM>, and controls an operation of the light receiving circuit <NUM>. The control unit <NUM> also transmits a control signal to an optical system drive circuit <NUM>, and controls an operation of the optical system <NUM>. The control unit <NUM> can also receive a processing result of a signal processing unit <NUM> and output the result to a control device such as an electronic control unit (ECU) that performs operation control of the vehicle.

The signal processing unit <NUM> can generate a measurement result (for example, a distance image) in a scannable range of the light scanning device <NUM> based on a signal output from the light receiving circuit <NUM> using, for example, a time-of-flight (TOF) method or the like. The measurement result generated by the signal processing unit <NUM> is output to a control device (for example, an ECU) (not illustrated) that performs operation control of the vehicle and the like through the control unit <NUM>.

In the example illustrated in <FIG>, a structure in which the emission light and the external reflection light pass through the same optical system <NUM> is adopted. In such a structure, when light is emitted from the light source <NUM>, the emitted emission light is reflected by an internal member (for example, a mirror or a lens of the optical system <NUM>) of the light scanning device <NUM> and unnecessary reflection light (hereinafter, also denoted by "internal reflection light") may occur. Then, there is also a possibility that the light receiving element of the light receiving circuit <NUM> is saturated at an unintended timing (a timing different from the timing at which the external reflection light from the measurement range returns) by incidence of the internal reflection light onto the light receiving surface of the light receiving element of the light receiving circuit <NUM> before the external reflection light. In this case, a problem that a light reception timing of the external reflection light cannot be accurately measured may be generated. For this problem, it is necessary to devise matters that the light receiving element is not saturated until the external reflection light reaches the light receiving surface of the light receiving element.

Accordingly, the control unit <NUM> executes a process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> in a period (hereinafter, also denoted by "first period") determined based on the timing when the emission light from the light source <NUM> is emitted. The first period is defined so as not to overlap a period (hereinafter, also denoted by "second period") during which the light scanning device <NUM> measures the distance. Here, the time taken for the light receiving circuit <NUM> to detect the external reflection light after the light source <NUM> emits the emission light is determined by a distance between the light scanning device <NUM> and an object positioned outside. Thus, if a measurement target range (the upper limit value and the lower limit value of the distance to be measured) of the light scanning device <NUM> is determined, the second period described above can be determined based on the emission timing of the emission light.

Hereinafter, the execution timing of a process by the control unit <NUM> will be described with reference to <FIG> is a diagram for explaining the execution timing of the process by the control unit <NUM>.

The horizontal axis of <FIG> is a time axis. In the example of the figure, the control unit <NUM> transmits a signal (emission timing control signal) for emitting light from the light source <NUM> to the light source drive circuit <NUM> at time t1 and time t2. The light source drive circuit <NUM> operates in accordance with the emission timing control signal, and causes light to be emitted from the light source <NUM>. Hereinafter, light emitted from the light source <NUM> at time t1 is also denoted by "first emission light", and light emitted from the light source <NUM> at time t2 is also referred to as "second emission light". The light source drive circuit <NUM> causes light to be emitted from the light source <NUM> based on the emission timing control signal.

In this case, the time when it is predicted that the external reflection light reflected by the object positioned in the measurement target range of the light scanning device <NUM> is detected by the light receiving element <NUM> can be grasped in advance based on the emission timing of light of the light source <NUM> as described above. In <FIG>, these times are represented as time tLL and time tUL. The time tLL in the figure indicates the timing at which the external reflection light by the object positioned at the lower limit value of the distance to be measured is detected by the light receiving element <NUM>. Further, time tUL in the figure indicates the timing at which the external reflection light by the object positioned at the upper limit value of the distance to be measured is detected by the light receiving element <NUM>.

The period A in the figure corresponds to "a period from when light is irradiated from the light source <NUM> to when the external reflection light by the object positioned at the lower limit value of the measurement target range of the light scanning device <NUM>" returns. The period B in the figure corresponds to "a period during which the light scanning device <NUM> measures a distance". Further, the period C in the figure corresponds to "a period from when external reflection light by the object positioned at the upper limit value of the measurement target range of the light scanning device <NUM> returns to when the light source <NUM> emits the next emission light".

In order to avoid the influence of the internal reflection light that may be generated by emission of the first emission light, the control unit <NUM> starts the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> at a point in time slightly before the emission timing (time t1) of the first emission light or the emission timing. Then, the control unit <NUM> can determine the timing to end the process of the control unit <NUM>, for example, based on the lower limit value of the distance measured by the light scanning device <NUM>. The control unit <NUM> can end the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> in accordance with an end point (time tLL) of the period A. Further, in consideration of followability of the light receiving element <NUM>, the control unit <NUM> may end the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> at a timing slightly before the end point (time tLL) of the period A.

In order to avoid the influence of the internal reflection light which may be generated by emission of the second emission light (light emitted next to the first emission light), the control unit <NUM> can determine the timing to start the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> based on the emission timing (time t2) of the second emission light. The control unit <NUM> can start the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM>, for example, according to the timing (time t2) at which the second emission light is emitted. For example, the control unit <NUM> may start the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> at a time slightly before the time t2.

The control unit <NUM> may determine the start timing of the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> based on the upper limit value of the distance measured by the light scanning device <NUM>. The control unit <NUM> can start the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> according to an end point (time tUL) of the period B. Further, in order to accurately grasp the light reception timing of the external reflection light by the object positioned at the upper limit value of the measurement target range, the control unit <NUM> may start the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> at a timing slightly after the end point (time tUL) of the period B.

As described above, in this embodiment, the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> is executed at a stage before detecting the external reflection light by the object within the measurement target range positioned outside the light scanning device <NUM>. With this configuration, it is possible to prevent the light receiving element <NUM> from being saturated by the internal reflection light by a member inside the light scanning device <NUM> before the external reflection light by the object within the measurement range reaches the light receiving element <NUM> of the light scanning device <NUM>. With this configuration, it is possible to accurately grasp the light reception timing of the external reflection light by the object present within the measurement target range of the light scanning device <NUM>. As a result, the external reflection light from the object within the measurement target range positioned outside the light scanning device <NUM> can be detected with high accuracy by the light receiving element, and measurement accuracy of the distance to the object positioned outside the light scanning device <NUM> can be enhanced.

Hereinafter, specific processes of the control unit <NUM> will be described by citing some specific examples.

<FIG> is a block diagram illustrating a functional configuration of a light scanning device in a first specific example.

In <FIG>, the optical system <NUM> includes a movable reflection portion <NUM> and a lens portion <NUM>. The movable reflection portion <NUM> includes one mirror configured to be rotatable in each of at least two directions (two axes) of the height direction and the lateral direction. This mirror is, for example, a micro electro mechanical system (MEMS) mirror. The movable reflection portion <NUM> may be configured to be able to scan in each of two directions, for example, by a MEMS mirror capable of scanning in one direction and a motor capable of scanning in a vertical direction to the one direction. In addition, the movable reflection portion <NUM> may be configured by two MEMS mirrors which are disposed to be orthogonal to each other and can be scanned in one direction. With such a configuration, the movable reflection portion <NUM> controls the traveling direction of light emitted from the light source <NUM> and the traveling direction of the external reflection light reflected by the object. The lens portion <NUM> is a condenser lens configured of a single lens or a plurality of lenses.

In <FIG>, the light receiving circuit <NUM> includes a light receiving element <NUM>, an I/V conversion circuit <NUM>, and an amplification factor control unit <NUM>. The light receiving element <NUM> is, for example, an APD. The I/V conversion circuit <NUM> is a circuit that converts the current due to the electric charges accumulated in the light receiving element <NUM> into a voltage. The signal processing unit <NUM> can generate a distance image and the like based on a signal from the I/V conversion circuit <NUM>. The amplification factor control unit <NUM> adjusts the amplification factor of the light receiving element <NUM> by controlling a voltage value to be applied to the light receiving element <NUM> according to a control signal from the control unit <NUM>.

When light is emitted from the light source <NUM>, a portion of the emission light of the light source <NUM> may be reflected by the movable reflection portion <NUM>, the lens portion <NUM>, or the like of the optical system <NUM> to generate internal reflection light. Then, the internal reflection light may be incident on the light receiving surface of the light receiving element <NUM> earlier than the external reflection light by the object. Depending on the amplification factor of the light receiving element <NUM>, the light receiving element <NUM> is saturated by the internal reflection light, and the external reflection light cannot be detected.

In this specific example, the control unit <NUM> sets the amplification factor of the light receiving element <NUM> in a period determined based on the emission timing of the emission light to one tenth or less of an amplification factor for a period of time while the light scanning device <NUM> measures a distance. For example, when the amplification factor of the light receiving element <NUM> for a period of time while the light scanning device <NUM> measures the distance is "<NUM>", the control unit <NUM> transmits a control signal for setting the amplification factor of the light receiving element <NUM> to "<NUM>" in the period determined based on the emission timing of the emission light to the amplification factor control unit <NUM>. The control unit <NUM> may transmit a control signal for setting the amplification factor of the period determined based on the emission timing of the emission light to "<NUM>" or less to the amplification factor control unit <NUM>. However, in this case, it is assumed that "the amplification factor of the light receiving element <NUM> for a period of time while the light scanning device <NUM> measures the distance" is larger than "<NUM>". The amplification factor control unit <NUM> can adjust the amplification factor of the light receiving element <NUM> by controlling the voltage to be applied to the light receiving element <NUM> according to the control signal from the control unit <NUM>. When the light receiving element <NUM> is made of, for example, indium gallium arsenide (InGaAs) APD or the like, the light receiving element <NUM> may reach a breakdown voltage with an amplification factor of about <NUM> times. In such a case, the control unit <NUM> can operate the light receiving element <NUM> with an appropriate range of amplification factor by storing the amplification factor (in the case of InGaAs APD, the amplification factor is "<NUM>" or less) according to the characteristics of the light receiving element <NUM> in advance in a memory (not illustrated) of the light scanning device <NUM> or the like.

For example, the control unit <NUM> may transmit a control signal for causing a voltage less than the breakdown voltage to be applied to the light receiving element <NUM> to the amplification factor control unit <NUM> so as to operate the light receiving element <NUM> in a so-called linear mode. In addition, the control unit <NUM> may transmit a control signal for causing a voltage near the breakdown voltage (for example, <NUM>% or less of the breakdown voltage) to be applied to the light receiving element <NUM> to the amplification factor control unit <NUM> so that the light receiving element <NUM> operates in a range where the amplification factor is relatively small.

By such a process, the amount of electric charges accumulated in the light receiving element <NUM> is reduced, and the light receiving element <NUM> is less likely to be saturated. With this configuration, the light receiving element <NUM> is prevented from being saturated by the internal reflection light, and the light reception timing of the external reflection light can be accurately grasped.

<FIG> is a block diagram illustrating a functional configuration of a light scanning device in the second specific example. In the second specific example, the light scanning device <NUM> has the same configuration as the configuration described in the first specific example except for the following points.

In this specific example, the light receiving circuit <NUM> further includes a switch element <NUM>. The switch element <NUM> connects one end of the light receiving element <NUM> to a ground point GND. The control unit <NUM> puts the switch element <NUM> in an OFF state while the light scanning device <NUM> measures the distance. In addition, the control unit <NUM> puts the switch element <NUM> in an ON state in a period determined based on the emission timing of the emission light.

When the switch element <NUM> is turned on, the light receiving element <NUM> is grounded. Then, the electric charge generated by light incident on the light receiving surface of the light receiving element <NUM> is not accumulated in the light receiving element <NUM> and flows to the ground point GND. Since the electric charges accumulated in the light receiving element <NUM> is reset by turning on the switch element <NUM>, an amount of electric charges accumulated in the light receiving element <NUM> is reduced, and the light receiving element <NUM> is less likely to be saturated. With this configuration, the light receiving element <NUM> is prevented from being saturated by the internal reflection light, and the light reception timing of the external reflection light can be accurately grasped.

<FIG> is a block diagram illustrating a functional configuration of a light scanning device in a third specific example. In the third specific example, the light scanning device <NUM> has the same configuration as the configuration described in the first specific example except for the following points.

In this specific example, the light receiving circuit <NUM> further includes a filter unit <NUM> that prevents light from entering the light receiving surface of the light receiving element <NUM>. The control unit <NUM> operates the filter unit <NUM> in a period determined based on the emission timing of the emission light. For example, the filter unit <NUM> is configured by an optical element whose refractive index is changed by an applied voltage. In this case, the control unit <NUM> can divert the internal reflection light from the light receiving surface of the light receiving element <NUM> by adjusting the voltage value applied to the filter unit <NUM>, in the period determined based on the emission timing of the emission light. The filter unit <NUM> may be realized by a shutter that physically covers the light receiving surface. In this case, the control unit <NUM> can prevent the internal reflection light from entering the light receiving surface of the light receiving element <NUM> by closing the shutter of the filter unit <NUM> in the period determined based on the emission timing of the emission light.

With such processing, the amount of electric charges accumulated in the light receiving element <NUM> is reduced and the light receiving element <NUM> is less likely to be saturated. With this configuration, the light receiving element <NUM> is prevented from being saturated by the internal reflection light, and the light reception timing of the external reflection light can be accurately grasped.

As described above, the control unit <NUM> drives the light receiving element <NUM> during a period in which the reflection light reflected by the object is returned to the light scanning device <NUM>, and prevents the electric charge from accumulating in the light receiving element <NUM> (to release the electric charge by being grounded or to mask the light receiving surface) or makes it difficult for the electric charge to be accumulated in the light receiving element <NUM> (to lower the amplification factor) during a period other than the period. With this configuration, it is possible to prevent the light receiving element <NUM> from being saturated by the internal reflection light generated in the light scanning device <NUM>, and to accurately grasp the light reception timing of the external reflection light by an object present in the surroundings.

<FIG> is a diagram illustrating a hardware configuration of the control unit <NUM> and the signal processing unit <NUM>. In the figure, the control unit <NUM> and the signal processing unit <NUM> are mounted using an integrated circuit <NUM>. The integrated circuit <NUM> is, for example, a system-on-a-chip (SoC).

The integrated circuit <NUM> includes a bus <NUM>, a processor <NUM>, a memory <NUM>, a storage device <NUM>, an input and output interface <NUM>, and a network interface <NUM>. The bus <NUM> is a data transmission path for the processor <NUM>, the memory <NUM>, the storage device <NUM>, the input and output interface <NUM>, and the network interface <NUM> to mutually transmit and receive data. However, a method of connecting the processors <NUM> and the like to one another is not limited to the bus connection. The processor <NUM> is an arithmetic processing unit implemented using a microprocessor or the like. The memory <NUM> is a memory implemented using a random access memory (RAM) or the like. The storage device <NUM> is a storage device realized using a read only memory (ROM), a flash memory, or the like.

The input and output interface <NUM> is an interface for connecting the integrated circuit <NUM> to peripheral devices. In the figure, the light source drive circuit <NUM>, the light receiving circuit <NUM>, and the optical system drive circuit <NUM> are connected to the input and output interface <NUM>.

The network interface <NUM> is an interface for connecting the integrated circuit <NUM> to a communication network. This communication network is, for example, a controller area network (CAN) communication network. The light scanning device <NUM> can be connected to the CAN communication network through the network interface <NUM>, and can communicate with an ECU or the like that controls the operation of the vehicle. A method of connecting the network interface <NUM> to the communication network may be wireless connection or wired connection.

The storage device <NUM> stores a program module for realizing the control unit <NUM> and a program module for realizing the function of the signal processing unit <NUM>. The processor <NUM> reads these program modules into the memory <NUM> and executes the program modules to realize the functions of the control unit <NUM> and the signal processing unit <NUM>.

The hardware configuration of the integrated circuit <NUM> is not limited to the configuration illustrated in this figure. For example, the program modules may be stored in memory <NUM>. In this case, the integrated circuit <NUM> may not include the storage device <NUM>.

In Embodiment <NUM>, the light scanning device <NUM> has the same configuration as the configuration described in Embodiment <NUM> except for the following points. That is, the light scanning device <NUM> according to Embodiment <NUM> determines at least one of the start timing and the end timing of the process executed by the control unit <NUM> according to the distance from the current position to an object (planimetric features) to be measured. In other words, the light scanning device <NUM> described in Embodiment <NUM> changes at least one of the start timing and the end timing of the process executed by the control unit <NUM>, according to the distance from the current position to the object (planimetric features) to be measured.

<FIG> is a block diagram conceptually illustrating a functional configuration of a light scanning device in Embodiment <NUM>. In Embodiment <NUM>, in addition to the configuration described in <FIG>, the light scanning device <NUM> further includes a current position acquisition unit <NUM> that acquires information regarding the current position of the light scanning device <NUM> or a moving object (for example, a vehicle) on which the light scanning device <NUM> is mounted and a map information acquisition unit <NUM> that acquires map information including feature information and the like related to features.

The current position acquisition unit <NUM> is configured to include, for example, a receiver that receives a signal from a positioning satellite system such as a global positioning system (GPS). The current position acquisition unit <NUM> may be configured to acquire information on the current position of the vehicle from other equipment provided with a receiver that receives a signal from the positioning satellite system or a device (for example, a GPS receiver disposed in a vehicle) by communicating with the other equipment or device. Further, the current position acquisition unit <NUM> may be configured to communicate with a control unit in the moving object through the CAN or the like and to acquire current position information of the vehicle from the control unit.

The map information acquisition unit <NUM> acquires map information and the like from a map server device by communicating with, for example, the map server device (not illustrated) that stores and manages map information. In this case, the map information acquisition unit <NUM> may store, for example, the acquired map information in a storage unit (not illustrated) included in the light scanning device <NUM>. The map information acquisition unit <NUM> can communicate with the map server device at any timing. For example, the map information acquisition unit <NUM> can communicate with the map server device according to an instruction input from a user or a predetermined schedule. The map information to be acquired by the map information acquisition unit <NUM> may be stored in advance in a storage unit (not illustrated) included in the light scanning device <NUM>. In this case, the map information acquisition unit <NUM> can read out the map information from the storage unit as needed. The map information includes feature information on features, in addition to information on roads through which the vehicle passes. Examples of planimetric features include, for example, signboards, signs, buildings or markings (for example, lane boundaries and stop lines) drawn on road surfaces. The planimetric feature information includes position information of the planimetric features described above, a planimetric feature ID for identifying the planimetric features, attribute information indicating an attribute of the planimetric features, and the like.

Hereinafter, with reference to <FIG>, a flow of operations when determining timing to start a process to be executed by the control unit <NUM> or timing to end the process will be described. <FIG> is a flowchart illustrating a flow of a process of the control unit <NUM> in Embodiment <NUM>.

The control unit <NUM> identifies a current position of the light scanning device <NUM> or the vehicle from current position information acquired by the current position acquisition unit <NUM> (S102).

Then, with reference to map information (the position information of planimetric features included in the planimetric feature information) acquired by the map information acquisition unit <NUM>, the control unit <NUM> identifies and extracts planimetric features that are presumed to exist around the current position identified in the process of S102 (S104). In this process, the control unit <NUM> may identify and extract, for example, the planimetric features that are presumed to be within a measurable range of the light scanning device <NUM> from the current position. The measurable range of the light scanning device <NUM> is stored in advance in a storage unit (not illustrated) such as a memory or a storage of the light scanning device <NUM>, for example.

Then, based on the position information of the planimetric features identified in the process of S104 and the current position information acquired by the current position acquisition unit <NUM>, the control unit <NUM> calculates the distance between the planimetric features identified in the process of S104 and the current position (the distance to the planimetric features) (S106).

Then, the control unit <NUM> determines, according to the distance calculated in S106, the timing to start the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> or the timing to end the process (S108). Hereinafter, the operation of the control unit <NUM> in this embodiment will be specifically illustrated.

As a first example, when the calculated distance to the planimetric features is close to the lower limit value of the measurement target range of the light scanning device <NUM> (in other words, the calculated distance to the planimetric features is relatively short), the control unit <NUM>, similarly as in Embodiment <NUM> described above, the control unit <NUM> determines the timing to start the process to be the emission timing of the first emission light (time t1) in <FIG> or a point in time slightly earlier than the timing. The control unit <NUM> determines the timing to end the process to be the end point (time tLL) of the period A corresponding to "a period from when light is emitted from the light source <NUM> to when the external reflection light by the object positioned at the lower limit value of the measurement target range of the light scanning device <NUM> returns".

As a second example, when the calculated distance to the planimetric features is relatively long, the control unit <NUM> can make the timing to end the process later than the end point (time tLL) of the period A described above. In other words, the control unit <NUM> can delay the timing to end the process as the calculated distance to the planimetric features increases. Furthermore, in other words, as the difference between the calculated distance to the planimetric features and the lower limit value of the measurement target range of the light scanning device <NUM> is larger, the control unit <NUM> can delay the timing to end the process. This is due to the following reason. That is, the longer the calculated distance to the planimetric features (in other words, the more the planimetric features to be measured are present at a position farther than the lower limit value of the measurement target range of the light scanning device <NUM>), the longer the time until the reflection light reflected by the planimetric features returns to the light scanning device <NUM>. Therefore, there is no need to end the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> or the like at the end point (time tLL) of the period A described above. In other words, even if the timing to end the process for reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> or the like is put backward in time, the possibility of adversely affecting reception of the reflection light from the planimetric features becomes low. From this, the control unit <NUM> can put the timing to end the process and the like to be later in time than the end point (time tLL) of the period A. By doing as described above, the control unit <NUM> can execute the process of reducing the electric charges accumulated in the light receiving element of the light receiving circuit <NUM> and the like using a longer period than that of Embodiment <NUM>, and can prevent the light receiving element <NUM> from being saturated more accurately.

Embodiment <NUM> described above be described from another viewpoint. Embodiment <NUM> described above has a concept that the period A in <FIG> is "a period from when light is irradiated from the light source <NUM> to when external reflection light reflected by the object positioned at the lower limit value of the measurement target range of the light scanning device <NUM> returns", and the control unit <NUM> executes a process within the range A. In contrast, Embodiment <NUM> described above has a concept that the period A which is a period during which the control unit <NUM> executes the process is set according to the calculated distance to the planimetric features (that is, the end point of the period A is shifted backward in time).

Claim 1:
A light scanning device (<NUM>) comprising:
a light source (<NUM>) that emits emission light;
a light receiving element (<NUM>) that receives reflection light of the emission light reflected by an object positioned outside;
an optical system (<NUM>) that directs the emission light emitted from the light source (<NUM>) to the outside and directs the reflection light to the light receiving element (<NUM>); and
a control unit (<NUM>) that executes a process of reducing electric charges accumulated in the light receiving element (<NUM>) by internal reflection light generated by emission of the emission light at a time point before the light receiving element (<NUM>) receives the reflected light,
wherein the control unit (<NUM>) determines a timing to end the process according to a lower limit value of a distance to be measured by the light scanning device (<NUM>),
characterized in that
the light receiving element (<NUM>) is connected to a ground point through a switch element (<NUM>), and
the control unit (<NUM>) puts the switch element (<NUM>) in an OFF state while the light scanning device (<NUM>) measures a distance, and, as the process, puts the switch element (<NUM>) in an ON state.