JP2006329797A - Light wave range finder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control the receiving quantity of reflected light from a target more quickly to a proper value. <P>SOLUTION: Distance measuring light L1 by emission from a light emitting element 14 is transmitted from an optical path switcher 16 toward a target 32, and reference light L2 is transmitted from an optical path switcher 36 toward a reference optical path. When reflected light L3 generated by reflection of the distance measuring light L1 by the target 32 is received by a light emitting element 24, a reverse direction voltage to be applied to the light emitting element 24 corresponding to the light receiving quantity is controlled. On the other hand, when the reference light L2 enters the light emitting element 24 through an optical filter 18, the quantity of the reference light L2 entering the light emitting element 24 is adjusted by driving a motor 20 corresponding to the light receiving quantity and by adjusting the position of a rotary disk 18a, to thereby control each quantity of the reference light L2 and the reflected light L3 in a fixed state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  According to the present invention, the distance measuring light modulated by the modulation signal is emitted toward the target, and the distance to the target is obtained based on the phase difference between the light before the emission and the light reflected by the target and returned. It relates to an optical distance meter that can be used.

  Conventionally, as a phase difference type lightwave distance meter, for example, light whose luminance is modulated by an electric signal having a constant frequency is divided into ranging light and reference light, and the ranging light is emitted toward the target and the reference light is emitted. A distance measurement signal obtained from the reflected light, which is guided to the reference light path, is reflected by the distance measurement light reflected by the target or received from the reference light path by the light receiving element and photoelectrically converted to generate a distance measurement signal. Are known in which the phase difference of the ranging signal obtained from the reference light is obtained, and the distance to the target is obtained based on the phase difference (see Patent Document 1).

  In a phase-difference optical distance meter, when the reflected light and reference light are separately incident on the light receiving element and the phases of the two are compared, the amount of light incident on the light receiving element affects the measurement accuracy. It is desirable that the light intensity level of the reflected light is the same. However, the reference optical path through which the reference light propagates is provided as a reference optical path having a fixed length in the optical distance meter, whereas the optical path through which the distance measuring light propagates changes depending on the distance to the target. If the reflected light and the reference light are simply incident on the light receiving element, the light quantity levels of the two often do not match due to the relationship with the distance.

  In other words, since the laser beam used for ranging light and reference light is not a perfect parallel beam, ranging as the measuring point where the target is placed becomes far away and the propagation distance of the ranging light becomes longer. The light will spread. For this reason, the light intensity of the reflected light incident on the lightwave distance meter decreases as the measurement point becomes far away, and the light intensity of the reflected light and the light intensity of the reference light often do not match.

  Therefore, in the prior art, as shown in FIG. 2, the light emitted from the light transmitting element (laser diode) 50 is converted into light that has been subjected to luminance modulation at a constant frequency by driving the light transmitting drive circuit 52. After being transmitted to the target 56 as the distance measuring light L10, the reference light L12 is transmitted to the reference optical path via the optical path switch 54, and the reference light L12 is received by the light receiving element 58 and reflected by the light receiving element 58. A distance measurement signal or a reference signal is generated by performing photoelectric conversion according to the light L14 or the reference light L12, and the distance measurement signal is amplified by the amplifier 60 and then guided to the received light signal processing circuit 62. Further, an optical filter 64 that reduces the light amount of the reference light L12 with a constant attenuation rate is provided in the middle of the reference light path, and optical that attenuates the light amount of the reflected light L14 on the reflected light path that guides the reflected light L14 to the light receiving element 58. A configuration in which the filter 66 is disposed and the optical filter 66 is rotated by a motor 68 is employed.

  That is, since the distance of the reference light path is constant, the light amount of the reference light L12 that has passed through the optical filter 64 is always constant, and the reference light L12 having a constant light amount enters the light receiving element 58. A constant reverse voltage is applied to the light receiving element 58 by the power supply circuit 70, and when the reference light L12 is incident on the light receiving element 58, a distance measuring signal according to the reference light L12 having a constant light amount can be generated.

  On the other hand, as shown in FIG. 3, the optical filter 66 includes a rotating disk 67, and the center of the rotating disk 67 is connected to the rotating shaft of the motor 68. The rotating disk 67 is divided into a plurality of unit filters F1 to F8, and the light attenuation factors of the unit filters F1 to F8 are set so as to increase sequentially in the order of the numbers. For example, the attenuation factor is sequentially increased by 6 dB so that the unit filter F1 having the smallest attenuation factor is 0 dB and the unit filter F8 having the largest attenuation factor is 42 dB. When the motor drive circuit 72 rotates the motor 68 based on a command from the light reception signal processing circuit 62, the rotating disk 67 rotates with the rotation of the motor 68, and any one of the unit filters F1 to F8. A unit filter is inserted into the optical path of the reflected light L14. In this case, when the light quantity of the reflected light L14 decreases as the distance to the target 56 becomes longer, a unit filter with a small light attenuation factor is selected, and the light quantity of the reference light L12 and the light quantity of the reflected light L14 match. The motor control for making it perform is performed. That is, the light amount of the reflected light L14 transmitted through the unit filter F8 having the largest light attenuation rate is matched with the light amount of the reference light L12, and the light attenuation rate is higher than that of the unit filter F8 as the distance to the target 56 increases. By sequentially selecting small unit filters, the amount of reflected light L14 and the amount of reference light L12 can be matched.

JP-A-8-50178

  In the prior art, in order to make the light quantity of the reference light L12 coincide with the light quantity of the reflected light L14, the received light quantity of the reflected light L14 is measured by the received light signal processing circuit 62, and based on the measurement result, the motor drive circuit 72 Since the drive is controlled, the rotating disk 67 must be rotated until an appropriate amount of light is received, and an operation time is required for the rotation of the rotating disk 67. Moreover, since the distance measuring light L10 propagates in the field, the amount of light may change due to atmospheric fluctuations as shown in FIG. 4 even if the distance to the target 56 is constant. When the amount of the reflected light L14 that passes through the optical filter 66 varies due to fluctuations in the atmosphere and the change in the amount of light is too fast, it takes time to calculate the correct amount of received light so that the specified amount of received light is obtained. It becomes difficult to position the motor 68. That is, when the light quantity of the reflected light L14 changes with the fluctuation of the atmosphere, it is necessary to position the rotary disk 67 so that the light quantity becomes a set value at the center of the fluctuation. It is difficult to determine instantaneously.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to more quickly control the amount of reflected light from the target to an appropriate value.

  In order to achieve the above object, in the optical distance meter according to claim 1, ranging light transmitting means for transmitting the ranging light modulated by the modulation signal toward the target, modulated by the modulation signal. A reference light transmitting means for transmitting the reference light toward the reference optical path, and photoelectric conversion with a received light amount according to an applied voltage when the reflected light from the target or the reference light from the reference optical path is received. A light receiving means for outputting a ranging signal, a voltage control means for controlling a voltage applied to the light receiving means in accordance with the amount of light received when the light receiving means receives the reflected light, and the light receiving means for outputting the reference light. Obtained based on the reflected light from the target among the light amount adjusting means for adjusting the light quantity of the reference light incident on the light receiving means according to the amount of light received when received, and the distance measuring signal output from the light receiving means And configured to include a calculating means for calculating a distance to the target based on the phase difference of the distance measurement signal obtained based and No. 距信 to the reference light.

  (Operation) Distance measurement light is transmitted toward the target and reference light is transmitted toward the reference optical path, and the reflected light from the target or the reference light from the reference optical path is received to perform photoelectric conversion to perform distance measurement. When generating a signal and calculating the distance to the target based on the phase difference between the distance measurement signal obtained based on the reflected light from the target and the distance measurement signal obtained based on the reference light, the light receiving means The voltage applied to the light receiving means is controlled as the applied voltage at the time of photoelectric conversion according to the amount of light received when the distance measuring light is received, and the light receiving means enters the light receiving means according to the amount of light received when the reference light is received. Since the amount of reference light is adjusted, the amount of reflected light received can be controlled to an appropriate value more quickly.

  That is, when the light receiving means receives the reflected light or the reference light and performs photoelectric conversion with the received light amount according to the applied voltage and outputs a distance measurement signal, the light receiving means receives the reflected light when the reflected light is received. Accordingly, by controlling the applied voltage to the light receiving means as the applied voltage at the time of photoelectric conversion, the applied voltage is controlled in accordance with the change in the amount of light even if the amount of reflected light changes due to the influence of atmospheric fluctuations. Thus, the amount of reflected light received can be controlled more quickly. Moreover, since the reference light propagates through the reference light path and is not affected by fluctuations in the atmosphere, by adjusting the amount of the reference light incident on the light receiving means according to the amount of light received when the light receiving means receives the reference light, The received light amount of the reference light can be matched with the received light amount of the reflected light.

  According to a second aspect of the present invention, in the optical distance meter according to the first aspect, the light receiving unit is configured by an avalanche photodiode, and the voltage control unit is reversely applied as an applied voltage to the avalanche photodiode. A voltage is applied, and the reverse voltage is reduced or increased in accordance with an increase or decrease in the amount of light received when the avalanche photodiode receives reflected light.

  (Operation) When the light receiving means is composed of an avalanche photodiode and a reverse voltage is applied as an applied voltage to the avalanche photodiode, the amplification factor changes according to the applied voltage, and the amount of received light changes according to the amplification factor. By changing the reverse voltage according to the amount of received light, the amount of reflected light can be quickly controlled to an appropriate amount. For example, when the distance to the target is short, the reverse voltage is lowered and the gain is lowered to reduce the amount of received light. Conversely, when the distance to the target is long, the reverse voltage is raised to raise the gain. The amount can be increased. For this reason, by reducing the reverse voltage in accordance with the increase in the amount of light received when receiving reflected light, the noise level is reduced in short-distance measurement, and more stable distance measurement is possible.

  As is clear from the above description, the light wave distance meter according to claim 1 can control the amount of received reflected light to an appropriate value more quickly.

  According to the second aspect, in the short distance measurement, the noise level is reduced, and more stable distance measurement is possible.

  Hereinafter, embodiments of the present invention will be described based on examples. FIG. 1 is a block diagram of a light wave distance meter showing an embodiment of the present invention.

  In FIG. 1, a phase difference type lightwave distance meter 10 includes a light transmission drive circuit 12, a light transmission element 14, an optical path switch 16, an optical filter 18, a motor 20, a motor drive circuit 22, a light receiving element 24, an amplifier 26, a light reception. A signal processing circuit 28 and a power supply circuit 30 are provided. In FIG. 1, optical systems such as a collimating telescope and a transmission / reception objective lens are omitted.

  The light transmission drive circuit 12 includes, for example, a temperature-compensated crystal oscillator, which outputs a reference signal (not shown) as a modulation signal from the crystal oscillator and applies a voltage to both ends of the light transmission element 14. The light emitted from the light transmitting element 14 is modulated by the modulation signal. The phase difference is obtained from the reference signal, the distance measurement signal, and the reference signal. The light transmitting element 14 is configured using, for example, a laser diode, and light accompanying light emission of the light transmitting element 14 is modulated by a modulation signal and transmitted as distance measuring light L1 or reference light L2. ing. The distance measuring light L1 is transmitted toward the target 32 via the optical path switch 16. That is, the light transmission drive circuit 12, the light transmission element 14, and the optical path switch 16 are configured as distance measurement light transmission means for transmitting the distance measurement light L 1 toward the target 32.

  On the other hand, the reference light L2 transmitted from the light transmitting element 14 is a reference optical path (an optical path of a certain distance connecting the optical path switch 16 and the light receiving element 24 via the optical path switch 16 and is constituted by an optical cable, for example. The light is transmitted to the reference optical path. That is, the light transmission drive circuit 12, the light transmission element 14, and the optical path switch 16 are configured as reference light transmission means for transmitting the reference light L2 toward the reference optical path. An optical filter 18 is provided in the middle of the reference optical path, and the optical filter 18 includes a rotating disk 18a. The center of the rotating disk 18 a is connected to the rotating shaft 20 a of the motor 20 and is rotated by driving the motor 20. A plurality of unit filters (not shown) are arranged on the rotating disk 18a along the circumferential direction about the rotating shaft 20a. The light attenuation factor of each unit filter is set to a different value, and the amount of light is adjusted when the reference light L2 passes through one of the unit filters. That is, when the motor 20 rotates the rotating disk 18a of the optical filter 18 based on the drive signal from the motor drive circuit 22, any unit filter is inserted into the reference optical path and is incident on the light receiving element 24. The amount of light L2 is adjusted. In this case, the optical filter 18, the motor 20, and the motor drive circuit 22 constitute a light amount adjusting means.

  The light receiving element 24 is configured using, for example, an avalanche photodiode, and a reverse voltage is applied from the power supply circuit 30 to both ends (anode and cathode) of the light receiving element 24. The avalanche photodiode that constitutes the light receiving element 24 is configured such that the amplification factor changes in accordance with the magnitude of the reverse voltage, and when the reverse voltage is reduced, the amplification factor also decreases accordingly. When the value is increased, the amplification factor is increased accordingly. For this reason, when the distance to the target 32 is short, the reverse voltage can be reduced and the gain can be reduced to reduce the amount of received light. Conversely, when the distance to the target 32 is long, the reverse voltage is increased. As a result, the gain can be increased and the amount of received light can be increased. The light receiving element 24 is configured as a light receiving unit that performs photoelectric conversion with a received light amount according to an applied voltage, generates a distance measurement signal, and outputs the generated distance measurement signal to the amplifier 26. For example, when the reflected light L3 from the target 32 is received, a distance measuring signal according to the amount of received light of the reflected light L3 is output, and when the reference light L2 is received, a distance measuring signal according to the amount of received light of the reference light L2. Is output.

  The amplifier 26 amplifies the distance measurement signal output from the light receiving element 24 and outputs the amplified distance measurement signal to the light reception signal processing circuit 28. The received light signal processing circuit 28 includes an arithmetic unit such as an A / D converter and a CPU, and converts a distance measurement signal based on an analog signal into digital data. Further, the received light amount of the reference light L2 and the received light amount of the reflected light L3 are obtained, and a control signal according to the received light amount is output to the motor drive circuit 22 and the power supply circuit 30. Further, the light reception signal processing circuit 28 is configured to detect the distance to the target 32 based on the phase difference between the distance measurement signal obtained based on the reflected light L3 from the target 32 and the distance measurement signal obtained based on the reference light L2. It is comprised as a calculating means to calculate. The distance obtained by the received light signal processing circuit 28 is displayed on a display (not shown) as a distance measurement value.

  In the optical distance meter 10 having the above configuration, when the distance measuring light L1 is transmitted from the light transmitting element 14 while the optical path in the optical path switch 16 is switched to the optical path of the distance measuring light L1, the distance measuring light is transmitted. L1 is transmitted toward the target 32 via the optical path switch 16. When this distance measuring light L1 is reflected by the target 32 and received by the light receiving element 24 as reflected light L3, the light receiving element 24 performs photoelectric conversion with the amount of received light according to the applied voltage at that time and outputs a distance measuring signal. To do. When this distance measurement signal is processed by the received light signal processing circuit 28 and the amount of received light when the reflected light is received is obtained, a control signal is output from the received light signal processing circuit 28 to the power supply circuit 30 and the applied voltage of the light receiving element 24 Is controlled as an applied voltage at the time of photoelectric conversion according to the amount of light received when receiving reflected light. At this time, even if the received light amount of the reflected light L3 changes due to the influence of atmospheric fluctuations, the CPU in the received light signal processing circuit 28 performs an operation for estimating the central light amount of the fluctuations, and according to the calculation result. Since the reverse voltage corresponding to the amount of light received by the reflected light L3 is immediately applied to the light receiving element 24, the amount of light received by the reflected light L3 can be quickly controlled to an appropriate value.

  On the other hand, when the optical path switch 16 is switched to the optical path for transmitting the reference light L2, the reference light L2 from the light transmitting element 14 is transmitted from the optical path switch 16 toward the reference optical path. The light amount of the reference light L2 propagating in the reference light path is adjusted by the optical filter 18, and the reference light L <b> 2 whose light amount has been adjusted enters the light receiving element 24. At this time, the light receiving element 24 performs photoelectric conversion with the received light amount according to the same applied voltage as when the reflected light is received, and outputs a reference signal. Based on this reference signal, the received light signal processing circuit 28 calculates the received light amount of the reference light L2, and outputs a control signal corresponding to the received light amount of the reference light L2 to the motor drive circuit 22. As a result, the motor 20 is driven, the designated unit filter in the optical filter 18 is inserted into the reference light path, and control is performed to match the received light amount of the reference light L2 and the received light amount of the reflected light L3. In this case, since the reference light L2 is not affected by atmospheric fluctuations, the received light quantity of the reflected light L3 and the received light quantity of the reference light L2 are matched without performing a calculation for estimating the central light quantity of atmospheric fluctuations. The motor control is performed by the light receiving signal processing circuit 28 and the motor driving circuit 22, and the light amount of the reference light L 2 incident on the light receiving element 24 can be adjusted to a specified value.

  According to the present embodiment, when the received light amount of the reflected light L3 is controlled to an appropriate received light amount, the applied voltage applied to the light receiving element 24 is controlled according to the received light amount of the reflected light L3, and the received light amount of the reference light L2 Is adjusted by the rotation of the rotating disk 18a of the optical filter 18, so that the control for making the light quantity of the reflected light L3 and the light quantity of the reference light L2 constant can be performed quickly, and the reflected light L3 is received. By controlling the reverse voltage with respect to the light receiving element 24 according to the amount, an appropriate amount of received light can be obtained.

  Further, in short distance measurement with a large amount of received light, by reducing the reverse voltage with respect to the light receiving element 24, the noise level is reduced and more stable distance measurement is possible.

  As the light receiving element 24, a pin photodiode can be used instead of the avalanche photodiode.

It is a block block diagram of the light wave distance meter which shows one Example of this invention. It is a block block diagram of the conventional lightwave distance meter. FIG. 3 is a perspective view of the optical filter of FIG. 2. It is a wave form diagram for demonstrating the state from which reflected light receives the influence of the fluctuation | variation of air | atmosphere, and the light quantity changes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light wave distance meter 12 Light transmission drive circuit 14 Light transmission element 16 Optical path switch 18 Optical filter 20 Motor 22 Motor drive circuit 24 Light receiving element 28 Light reception signal processing circuit 30 Power supply circuit 32 Target

Claims (2)

  Ranging light transmitting means for transmitting the distance measuring light modulated by the modulation signal toward the target; Reference light transmitting means for transmitting the reference light modulated by the modulation signal toward the reference optical path; A light receiving means for performing photoelectric conversion with a light receiving amount according to an applied voltage when a reflected light from the target or a reference light from the reference light path is received, and outputting a ranging signal; and the light receiving means receives the reflected light. Voltage control means for controlling the voltage applied to the light receiving means according to the amount of light received when received, and the amount of reference light incident on the light receiving means according to the amount of light received when the light receiving means receives the reference light Of the distance adjustment signal obtained based on the reflected light from the target and the distance measurement signal obtained based on the reference light among the distance measurement signals output from the light receiving means. Based on the phase difference Light wave distance meter comprising an arithmetic means for calculating the distance to the serial target.   2. The lightwave distance meter according to claim 1, wherein the light receiving unit includes an avalanche photodiode, and the voltage control unit applies a reverse voltage as an applied voltage to the avalanche photodiode, and A lightwave distance meter characterized in that the reverse voltage is reduced or increased in accordance with an increase or decrease in the amount of light received when receiving reflected light.

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