JP2011013108A - Lightwave distance meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightwave distance meter dispensing with any variable received-light density filter and allowing a distance measuring light amount to be adjusted at higher speed.SOLUTION: This lightwave distance meter includes a light send-out means 100 for sending out light which is intensity-modulated by a signal superimposed on a carrier of a certain frequency, a light separating means 102 for sending out the light from the send-out means 100 to one chosen between a target reflector 22 disposed at a measurement point and a reference optical path 25, a light receiving means (light receiving element 30) for receiving distance measuring light reflected by the target reflector 22 or reference light having passed along the optical path 25 to output a distance measurement signal and a reference signal, and a distance calculation means (CPU 41) for finding an airline distance to the target reflector 22 based on a phase difference between the measurement signal and the reference signal. The send-out means 100 includes a light amount adjustment means 101.

Description

  The present invention measures the phase difference between ranging light obtained by reflecting light having a predetermined phase that is intensity-modulated to a target reflector, and reference light obtained by emitting the intensity-modulated light to a reference light path. The present invention relates to a light wave rangefinder that measures a linear distance to a target reflector.

  In the conventional optical distance meter, the distance-modulated light obtained by reflecting the intensity-modulated light having a predetermined phase to a target reflector such as a prism or a reflecting mirror arranged at the measurement point, and the intensity-modulated light are referred to Calculates the phase difference between the electrical signal (ranging signal) of the distance measuring light and the electrical signal (reference signal) of the reference light, which are received and output by the light receiving means, respectively. Some measure the linear distance to the target reflector (generally referred to as a phase difference type lightwave distance meter). The phase difference type lightwave distance meter utilizes the fact that the phase difference between the distance measuring light and the reference light changes according to the measurement distance.

  The phase difference Δφ between the distance measuring light and the reference light is expressed by Δφ = 4πfD / C, where D is the distance measured to the target reflector, f is the modulation frequency, and C is the high speed. It is obtained by measuring the phase difference Δφ. In actual measurement, modulated light having two or more different frequencies is used, and each digit of the distance value is determined according to each resolution.

  In such a light wave distance meter, the light amount of the ranging light received when the distance from the light wave distance meter to the target reflector is short becomes strong, and the light amount of the distance measuring light becomes weak when the distance is long. The output level of the ranging signal varies depending on the distance from the target reflector to the target. Therefore, in such a light wave distance meter, for example, as shown in Patent Document 1 below, a variable light reception density filter mechanism that is driven by a motor or the like is provided between a target reflector and a light receiving means, and reflected light (ranging light). ) To adjust the amount of distance measuring light to an optimum state.

Japanese Patent Publication No.51-8340

  The variable light-receiving density filter mechanism used in the conventional lightwave distance meter takes a long time to adjust the light amount as a result of operating the mechanical structure and adjusting the aperture. In particular, in long-distance ranging performed by placing a prism at a measurement point several kilometers away from the optical wave distance meter, the transmitted distance-measuring light has its optical path bent due to atmospheric fluctuations, resulting in a large amount of distance-measuring light. As a result of the change, it took about several seconds to adjust the light amount, and there was a problem that the light amount could not be adjusted within a predetermined distance measurement specification time.

  In view of such problems, the present invention provides a lightwave distance meter that does not require a variable light-receiving density filter and that can adjust the distance-measuring light amount at a higher speed.

  A lightwave distance meter according to claim 1 is a light transmission means for transmitting light whose intensity is modulated by a signal on which a carrier wave having a constant frequency is superimposed, and a target reflector or reference optical path in which the light of the light transmission means is disposed at a measurement point. And a light receiving means for receiving a distance measuring light reflected by the target reflector or a reference light passing through the reference light path and outputting a distance measuring signal and a reference signal. And a distance calculation means for obtaining a linear distance to the target reflector based on a phase difference between the distance measurement signal and the reference signal, and a light amount adjustment means is provided in the light transmission means. That is, in claim 1, instead of adjusting the amount of reflected light received by the mechanical operating means, the lighting amount of the light emitting element is adjusted by the electric means.

  (Operation) The lighting amount of light in the light emitting element can be adjusted only by electric means, and does not include a mechanical operation such as a motor by a variable light-receiving density filter at the time of adjustment, so that the time required for adjustment is short. In addition, the optical distance meter does not require an arrangement space for a motor or the like.

  According to a second aspect of the present invention, in the lightwave distance meter according to the first aspect, the light transmitting unit includes a light emitting element, and the light amount adjusting unit is connected to the light emitting element while being supplied with a DC voltage. Control means for the variable resistance means.

  (Operation) By adjusting the resistance value applied to the light emitting element to change the light emission amount of the light emitting element, the light amount of the distance measuring light is adjusted in a very short time.

  According to a third aspect of the present invention, in the optical distance meter of the second aspect, the variable resistance means is constituted by a digital potentiometer.

  (Operation) The digital potentiometer enables fine light amount adjustment of the light emitting element.

  According to the lightwave distance meter of claim 1 or 2, since the light amount adjustment time of the distance measuring light is significantly shortened compared to the conventional one, the number of times of light amount adjustment within the distance measurement specification time can be increased. As a result, even if the adjustment of the amount of light is not completed at one time due to a large fluctuation in the atmosphere between the lightwave distance meter and the target reflector, the number of times is repeated within the distance measurement specification time even if the adjustment is not completed. The possibility that the light intensity adjustment can be completed is increased. In addition, since a mechanism such as a motor for the variable light-receiving density filter is not required, the size of the lightwave distance meter is reduced and the cost is reduced.

  According to the optical distance meter of the third aspect, the distance measurement light quantity can be finely adjusted, so that distance measurement with less error is possible.

It is a block diagram of the Example of a light wave distance meter. It is explanatory drawing of ranging light quantity adjustment in case the ranging light quantity exceeds the appropriate light quantity. It is explanatory drawing in case the ranging light quantity does not exceed the appropriate light quantity.

  Next, an optimal embodiment of the lightwave distance meter will be described with reference to FIG. The lightwave distance meter of the embodiment is composed of the light transmitting means 100, the light amount adjusting means 101 of the light emitting element, the light receiving means (light receiving element 30), the local signal transmitting means 103, the distance calculating means (CPU 41), and the like as described below. Including.

  The oscillator 1, the frequency divider 2, the frequency superimposing circuit 3, the driving circuit 4, and the light emitting element 10 are connected in order as shown in FIG.

  The oscillator 1 generates a reference carrier signal F1 having a predetermined frequency. The frequency divider 2 divides the reference carrier signal F1 to generate reference carrier signals F2 and F3 having different frequencies. The reference carrier signals F1, F2, and F3 are superimposed by the frequency superimposing circuit 3. The drive circuit 4 receiving the voltage supply causes the light emitting element 10 to emit light by an AC signal based on the superimposed reference carrier signal (F1, F2, F3), and the superimposed reference carrier signal (F1, F2, F3) The light whose intensity is modulated by the amplitude is transmitted.

  Connected to the light emitting element 10 are a load resistor 8 and a digital potentiometer 9 (variable resistance means) for loading the light emitting element 10 with a constant resistance. The load resistor 8 is supplied with a DC voltage from a DC power supply 14 via a digital switch 13 that can be switched between conduction and non-conduction. Control means 12 is connected to the digital potentiometer 9. The digital potentiometer 9 is a variable resistor controlled by the control means 12 and changes the resistance loaded on the light emitting element 10. The digital potentiometer 9 constitutes a light amount adjusting means 101 together with the load resistor 8, the control means 12, the digital switch 13 and the DC power supply 14.

  The resistance value loaded on the light emitting element 10 is determined by the combined resistance value of the load resistance 8 and the digital potentiometer 9. When the resistance value of the digital potentiometer 9 is increased by the control means 12 while receiving a direct current voltage, the light emitting element 10 decreases the emitted light amount, and decreasing the resistance value increases the emitted light amount.

  The beam splitter 20 constitutes the light extraction means 102 together with the switching shutter 27. The light transmitted from the light emitting element 10 is input to the beam splitter 20 and divided into two in the distance measuring optical path 21 direction and the reference optical path 25 direction, and one of the divided lights is shielded by the switching shutter 27. The split light is transmitted to the optical path that is not shielded by the switching shutter 27 on the distance measuring optical path 21 side or the reference optical path 25 side.

  Since the reference optical path 25 side is shielded by the switching shutter 27, the light transmitted to the distance measuring optical path 21 is reflected to the distance measuring optical path 23 by the target reflector 22 such as a prism disposed at the measurement point. The reflected light (hereinafter referred to as distance measuring light) is collected by the light receiving optical unit 24 (such as a condensing lens) and received by the light receiving element 30 (light receiving unit). On the other hand, by switching the shutter 27 and blocking the distance measuring optical path 21 side, the light transmitted to the reference optical path 25 (hereinafter referred to as reference light) is subjected to constant light amount adjustment by the density filter 26 and then the light receiving element 30. Is received by.

  An amplifier 31 is connected to the light receiving element 30, and a frequency converter (32, 35, 38) and a low-pass filter (33, 36, 39) are connected to the amplifier 31 for each reference carrier signal (F1, F2, F3). The AD converters (34, 37, 40) are connected. The AD converters (34, 37, 40) are connected to the CPU 41. The CPU 41 detects the phase difference between the digital ranging signal and the reference signal and calculates the measuring distance.

  The distance measuring light and the reference light are converted by the light receiving element 30 into electric signals indicating the reference carrier signals (F1, F2, F3), amplified by the amplifier 31, and then electric signals indicating (F1, F2, F3). Each is input to the frequency converter (32, 35, 38).

  On the other hand, a PLL (Phase Locked Loop) 5, a local signal oscillator 6, and a frequency generation circuit 7 constitute a local signal transmission unit 103. The PLL 5 is connected to the oscillator 1, and the local signal oscillator 6 is connected to the PLL 5 through a bidirectional signal line. The frequency generation circuit 7 is connected to the oscillator 1 and the local signal oscillator 6 respectively. The local signal oscillator 6 is connected to the frequency converter 32, and the frequency generation circuit 7 is connected to the frequency converter (35, 38).

  The local signal oscillator 6 receives the reference carrier signal F1 from the oscillator 1 via the PLL 5, and outputs a frequency signal F1 + Δf1 whose frequency is shifted by a minute value Δf1 from the signal F1 to the frequency converter 32. The frequency generation circuit 7 receives the carrier signal F1 from the oscillator 1 and further receives the frequency signal F1 + Δf1 from the local signal oscillator 6. Then, the frequency generation circuit 7 first divides the reference carrier signal F1 into carrier signals F2 and F3, and based on the frequency signal F1 + Δf1, the frequency generation circuit 7 has a frequency that is smaller by the minute values Δf2 and Δf3 than the carrier signals F2 and F3. The shifted frequency signals F2 + Δf2 and F3 + Δf3 are output. The frequency signals (F2 + Δf2, F3 + Δf3) are input to the frequency converters (35, 38), respectively.

  The frequency converter (32, 35, 38) converts the reference carrier signals (F1, F2, F3) input as distance measuring light or reference light into frequency signals (F1 + Δf1, F2 + Δf2, F3 + Δf3) on the local signal transmission means 103 side. ) Is converted into frequency signals (Δf1, Δf2, Δf3) having a lower frequency band and easy to handle. In the frequency signals (Δf1, Δf2, Δf3), the noise generated in the frequency converter (32, 35, 38) is removed by the low-pass filter (33, 36, 39), and the AD converter (34, 37, 40). And is converted from the electrical signal into digital data (Δf1 ′, Δf2 ′, Δf3 ′).

  The CPU 41 analyzes the amplitude and phase information from the distance measurement light and the reference light frequency signals (Δf1 ′, Δf2 ′, Δf3 ′), which are digital data, and calculates the optical wave based on the phase difference between the distance measurement light and the reference light. The straight line distance from the distance meter to the target reflector 22 is calculated with a small error.

  Next, adjustment of the distance measuring light amount by the digital potentiometer 9 will be described. 1 adjusts the resistance value of the digital potentiometer 9 in accordance with the amplitude (light quantity) of the distance measuring light analyzed by the CPU 41, and adjusts the distance measuring light quantity by changing the output of the light emitting element 10. To do.

  In the optical distance meter, an appropriate light amount and a lower limit light amount are determined according to specifications, and set values of these light amounts are stored in the storage means 43. The CPU 41 compares the numerical value of the light quantity obtained from the amplitude of the distance measurement signal with the set value of the storage means 43 to measure the difference, and sends a resistance value control signal to the digital potentiometer 9. As a result, the light emission amount of the light emitting element 10 at the time of measuring the distance measuring light is adjusted according to the changed resistance value of the digital potentiometer 9.

  The light amount of the reference light changes in the same manner as the distance measuring light with the adjustment of the distance measuring light. When the light amount of the reference light is changed using the light amount adjustment result of the distance measuring light in this manner, the light emitting element 10 is less likely to cause a phase change during light emission. As a result, the reference light can suppress a change in phase due to temperature drift to a minimum.

  Further, the specific adjustment of the distance measuring light amount is performed as follows with the reference light amount adjusted in advance to the appropriate light amount by the digital potentiometer 9. Depending on the distance from the light wave rangefinder to the target reflector 22, the distance measurement light amount may be greater than the appropriate light amount (see FIG. 2) or less than the appropriate light amount (see FIG. 3).

  That is, as a result of the distance measurement from the light wave distance meter to the target reflector 22, as shown in FIG. 2, when the distance light quantity is larger than the appropriate light quantity, the resistance value of the digital potentiometer 9 is increased to increase the distance light quantity. Is reduced to the appropriate light level. At this time, the reference light amount decreases from the appropriate light amount as the distance measuring light decreases. When the reference light amount exceeds the lower limit light amount, distance measurement (distance measurement) is performed, and when the reference light amount falls below the lower limit light amount, the distance measurement is stopped.

  On the other hand, as a result of the distance measurement to the target reflector 22, as shown in FIG. 3, when the distance light quantity is smaller than the reference light quantity, the digital potentiometer 9 does not adjust the distance light quantity. If the distance light quantity exceeds the lower limit light quantity, the distance is measured. If the distance light quantity falls below the lower limit light quantity, the distance measurement is stopped.

9 Digital potentiometer (variable resistance means)
DESCRIPTION OF SYMBOLS 10 Light emitting element 12 Control means 22 Target reflector 25 Reference optical path 30 Light receiving element (light receiving means)
41 CPU (distance calculation means)
DESCRIPTION OF SYMBOLS 100 Light transmission means 101 Light quantity adjustment means 102 Light extraction means

Claims (3)

Light transmitting means for transmitting light whose intensity is modulated by a signal with a carrier wave having a constant frequency superimposed thereon, and light from the light transmitting means is transmitted to a selected one of a target reflector or a reference optical path disposed at a measurement point A light output unit; a light receiving unit that receives the ranging light reflected by the target reflector or the reference light that has passed through the reference optical path; and outputs a ranging signal and a reference signal; and the ranging signal and the reference signal A distance calculation means for obtaining a linear distance to the target reflector by the phase difference of
A light wave distance meter characterized in that a light amount adjusting means is provided in the light sending means. The light sending means has a light emitting element,
2. The light wave distance meter according to claim 1, wherein the light amount adjusting means includes variable resistance means connected to the light emitting element while being supplied with a DC voltage, and control means for the variable resistance means. .   The light wave distance meter according to claim 2, wherein the variable resistance means is a digital potentiometer.

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