Patent Application
20220283277
The present application claims priority under 35 U.S.C. § 119 to the Japanese Patent Application No. 2021-035056 filed Mar. 5, 2021. The contents of this application are incorporated herein by reference in their entirely.
The present invention relates to an electro-optical distance meter, and more specifically, to an electro-optical distance meter that measures a distance to a target by emitting distance-measuring light to the target and receiving the distance-measuring light reflected by the target, and a method for calculating an optical noise signal of the electro-optical distance meter.
An electro-optical distance meter that measures a distance to a target by emitting distance-measuring light to the target and receiving the distance-measuring light reflected by the target, as disclosed in Patent Literature 1 has been known.
In the electro-optical distance meter, in some cases, a reference signal and noise generated from various electronic circuits enter a circuit of a light receiving unit side due to electrostatic coupling, electromagnetic coupling, and electromagnetic radiation, etc., without reciprocating to a target, and cause electrical noise, and as a result, an error occurs in a distance value. In the electro-optical distance meter of Patent Literature 1, before a distance measurement, (1) in a state where a diaphragm just before a light receiving element is narrowed most, (2) a light source is caused to emit light, and (3) a multiplication factor of the light receiving element is controlled to a proper value, noise is measured, and an amplitude and an initial phase of the noise are obtained and stored in a storage unit, and at the time of the distance measurement, based on these amplitude and initial phase, a distance from which an error caused by the noise has been removed is calculated (refer to Paragraph [0045]). This can reduce errors without devising components and wirings.
However, noise that causes an error in a distance value in an electro-optical distance meter includes not only electrical noise but also optical noise caused by the distance-measuring light being reflected by the inside of the electro-optical distance meter to enter into the light receiving element. In the electro-optical distance meter disclosed in Patent Literature 1, optical noise reduction is not considered.
The present invention has been made in view of these circumstances, and an object thereof is to provide an electro-optical distance meter in which an error in a distance value caused by noise is further reduced without specially devising components and wirings.
In order to achieve the object described above, an electro-optical distance meter according to an aspect of the present invention includes a first light source configured to emit distance-measuring light toward a measuring object, a first light receiving unit including a first light receiving element configured to receive the distance-measuring light reflected by the measuring object and convert the distance-measuring light into a distance-measuring signal, and a first received light amount adjusting means configured to adjust a light amount entering the first light receiving element, a first objective lens configured to condense the reflected distance-measuring light to the first light receiving unit, a first arithmetic control unit configured to calculate a distance to the measuring object from an initial phase of the distance-measuring signal, and a first storage unit configured to store the distance-measuring signal, distance value data, and an optical noise signal, and configured to measure an electrical noise signal by putting the first received light amount adjusting means into a state where the first received light amount adjusting means completely blocks light and causing the first light source to emit light, measure a distance-measuring signal of the measuring object by putting the first received light amount adjusting means into a proper state, and calculate a distance by subtracting the electrical noise signal and the optical noise signal from the distance-measuring signal, wherein the first arithmetic control unit measures a first noise signal by putting the first received light amount adjusting means into a state where the first received light amount adjusting means completely blocks light and causing the first light source to emit light with a noise measuring jig having a unique jig-derived noise signal attached, the noise measuring jig being attachable to and detachable from the electro-optical distance meter and configured to remove reflected distance-measuring light entering the first light receiving unit when attached, measures a second noise signal by putting the first received light amount adjusting means into a state where the first received light amount adjusting means transmits light most and causing the first light source to emit light in a state where the noise measuring jig is attached, and calculates the optical noise signal by subtracting the first noise signal and the jig-derived noise stores the optical noise signal from the second noise signal, and in the storage unit.
In the aspect described above, it is also preferable that, the jig-derived noise signal is obtained by, by using a second electro-optical distance meter including a second light source configured to emit distance-measuring light toward a measuring object, a second light receiving unit including a second light receiving element configured to receive the distance-measuring light reflected by the measuring object and convert the distance-measuring light into a distance-measuring signal, and a second received light amount adjusting means configured to adjust a light amount entering the second light receiving element, a second objective lens configured to condense the reflected distance-measuring light to the second light receiving unit, a second arithmetic control unit configured to calculate a distance to the measuring object based on the distance-measuring signal, and a second storage unit, in a state where collimation to a night sky is performed, measuring a third noise signal by putting the second received light amount adjusting means into a state where the second received light amount adjusting means completely blocks light and causing the second light source to emit light, measuring a fourth noise signal by putting the second received light amount adjusting means into a state where the second received light amount adjusting means transmits light most and causing the second light source to emit light, and calculating an optical noise signal unique to the second electro-optical distance meter by subtracting the third noise signal from the fourth noise signal, measuring a fifth measurement noise signal by putting the second received light amount adjusting means into a state where the second received light amount adjusting means completely blocks light and causing the second light source to emit light in a state where the noise measuring jig is attached, measuring a sixth measurement noise signal by putting the second received light amount adjusting means into a state where the second received light amount adjusting means transmits light most in a state where the noise measuring jig is attached, and subtracting the fifth measurement noise signal and the unique optical noise signal from the sixth measurement noise signal.
In the aspect described above, it is also preferable that the noise measuring jig includes a bottomed cylindrical housing, a glass filter configured to absorb light of a wavelength of the distance-measuring light, and a laser light absorber configured to absorb the distance-measuring light reflected by the glass filter, and the glass filter is installed so that distance-measuring light emitted through the first or second objective lens in an attached state of the noise measuring jig enters the glass filter at a Brewster's angle.
A method for calculating an optical noise according to another aspect of the present invention, uses an electro-optical distance meter including a light source configured to emit distance-measuring light toward a measuring object, a light receiving unit including a light receiving element configured to receive the distance-measuring light reflected by the measuring object and convert the distance-measuring light into a distance-measuring signal, and a received light amount adjusting means configured to adjust a light amount entering the light receiving element, a storage unit configured to store an optical noise signal, and an arithmetic control unit configured to calculate a distance to the measuring object based on the distance-measuring signal, and a noise measuring jig having a unique jig-derived noise signal, attachable to and detachable from the electro-optical distance meter, and configured to remove reflected distance-measuring light entering the light receiving unit when attached, and includes measuring a first noise signal by putting the received light amount adjusting means into a state where the received light amount adjusting means completely blocks light and causing the light source to emit light with the noise measuring jig attached, measuring a second noise signal by putting the received light amount adjusting means into a state where the received light amount adjusting means transmits light most and causing the light source to emit light with the noise measuring jig attached, calculating the optical noise signal by subtracting the first noise signal and the jig-derived noise signal from the second noise signal, measuring an electrical noise signal by putting the received light amount adjusting means into a state where the received light amount adjusting means completely blocks light and causing the light source to emit light, and calculating the distance by subtracting the electrical noise signal and the optical noise signal from the distance-measuring signal of the measuring object measured by putting the received light amount adjusting means into a proper state.
Herein, “true distance-measuring signal” refers to the signal component obtained by removing noise signals from measured distance-measuring signal.
According to the aspects described above, an electro-optical distance meter in which an error in a distance value caused by noise is further reduced without specially devising components and wirings can be provided.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, however, the present invention is not limited to these. In each embodiment, the same components are provided with the same reference sign, and overlapping description will be omitted.
An electro-optical distance meter 100 according to the present embodiment is a so-called phase difference system electro-optical distance meter. As illustrated in
The light transmitting unit 10 includes a light source 11, a light transmitting optical system (not illustrated), a modulator 12, and a reference signal oscillator 13. The light source 11 is, for example, a light emitting element such as a laser diode, and emits distance-measuring light L along a collimation axis toward a target 70 such as a prism placed on a survey point through the light transmitting optical system and an objective lens. The light source 11 is connected to the modulator 12, and the modulator 12 is connected to the reference signal oscillator 13. The reference signal oscillator 13 generates a reference signal K with a constant frequency. The modulator 12 modulates the reference signal K to a modulated signal K1.
The light receiving unit 20 includes a light receiving optical system (not illustrated), received light amount adjusting means 21, 21A, a light receiving element 22, a high frequency amplifier 23, a bandpass filter 24, a frequency converter 25, and a low-pass filter 26.
The received light amount adjusting means 21 is arranged just before the light receiving element 22 and adjusts an amount of light entering the light receiving element. The received light amount adjusting means 21 is, for example, a variable density filter composed of a thin discoid film as illustrated in
The received light amount adjusting means 21 in
The received light amount adjusting means 21 is configured so that the light intensity decay rate is 0% (a state where light is transmitted most) when the opening 21b is at a position matching the light receiving element 22, and the light intensity decay rate reaches 100% (a state where light is blocked most) when the other end portion region 21c reaches a position matching the light receiving element 22. Opening and closing of the received light amount adjusting means 21 (filter) are controlled by controlling motor rotation by the arithmetic control unit 40.
The received light amount adjusting means 21 is not limited to the above-described variable density filter, and a publicly known diaphragm to be used for an electro-optical distance meter can be used.
The light receiving element 22 is, for example, an avalanche photodiode (APD), etc. A bias voltage to be applied to the light receiving element 22 can be controlled by a reverse voltage control unit not illustrated. The reverse voltage control unit changes the bias voltage according to a command from the arithmetic control unit 40 to control the light receiving element 22 to a proper multiplication factor according to a surrounding brightness. The light receiving element 22 receives distance-measuring light L reflected by the target 70 through the light receiving optical system and the received light amount adjusting means 21, and converts the received distance-measuring light into a distance-measuring signal as an electric signal.
This electric signal is amplified by the high-frequency amplifier 23, and then, noise is removed from the signal by the bandpass filter 24.
The frequency converter 25 includes a mixer and a local oscillator. By inputting a local oscillation signal generated by the local oscillator and the distance-measuring signal from which noise has been removed into the mixer and multiplying these, the frequency converter generates a frequency component as a difference in frequency between the signals and a frequency component as a sum of the frequencies of the signals. Here, only the distance-measuring signal converted into an intermediate frequency IF as a difference in frequency between the signals is sorted out by the low-pass filter 26.
The distance-measuring signal converted into the intermediate frequency IF is amplified by an intermediate frequency amplifier 27. The amplified distance-measuring signal is converted into a digital signal by the A/D converter 30, and stored in the storage unit 50 through the arithmetic control unit 40. In the following description, a distance-measuring signal that has been converted into an intermediate frequency IF and converted into a digital signal is referred to as a distance-measuring signal M.
The arithmetic control unit 40 is a processing device that realizes processing to calculate a distance based on a distance-measuring signal M obtained by performing a distance measurement by controlling the light transmitting unit 10 and the light receiving unit 20. As the arithmetic control unit 40, for example, at least one processor, such as a CPU (Central Processing Unit), etc., can be applied. The function of the arithmetic control unit 40 described hereinafter can be realized by a program or a circuit, or a combination of these. When the function is realized by a program, the function is realized by reading out the program stored in the storage unit 50 into a main memory and executing the program.
In addition, the arithmetic control unit 40 obtains a true distance-measuring signal MT by removing an optical noise signal IR and an electrical noise signal EL described later from the measured distance-measuring signal M, and calculates a distance value based on an initial phase βT of the true distance-measuring signal MT.
The storage unit 50 is composed of a recording medium that stores, saves, and transmits information in a computer-processable format, and includes a so-called main memory and auxiliary storage device. The storage unit 50 stores sampling data and calculated distance value data. In addition, the storage unit 50 stores an average amplitude aIR and an initial phase ηIR of the optical noise signal IR. Also, the storage unit 50 stores programs for realizing functions of the arithmetic control unit 40 and the electro-optical distance meter 100. As the storage unit 50, for example, a nonvolatile memory such as a flash memory or a ROM (Read Only Memory), a volatile memory such as a RAM (Random Access Memory), etc., can be applied.
Although not illustrated in the drawings, the electro-optical distance meter 100 includes, as user interfaces, an input unit such as button keys and a display unit such as a liquid crystal display. In addition, although not illustrated in the drawings, the electro-optical distance meter 100 includes an external interface, for example, a communication unit, a USB port, etc., that enables external input and output of data stored in the storage unit 50 and data to be arithmetically processed in the arithmetic control unit 40.
(Calculation of Theoretical Distance)
First, measurement of a theoretical distance by the electro-optical distance meter 100 will be described. When the electro-optical distance meter 100 performs a distance measurement, the reference signal oscillator 13 transmits a synchronization signal P to the arithmetic control unit 40 and the A/D converter 30, and transmits a reference signal K to the modulator. The A/D converter performs sampling synchronized with the reference signal K. During the distance measurement, a light amount to be transmitted through the received light amount adjusting means 21 is fixed.
In order to store the sampling data in the storage unit 50, a storage area of the storage unit 50 corresponding to N data of one period of the distance-measuring signal M is prepared, and N sampling data at the same phase position are synchronously added and stored. In this way, as illustrated in
Na sin(θ−β)+Nb (Expression 1)
(Here, N is the number of distance-measuring signals M added, a is an average amplitude of the distance-measuring signal M, b is a bias level, θ is coordinates regulating an angle corresponding to a sampling position, and β is an initial phase.)
The initial phase β is equal to a phase difference between a signal obtained by dividing the frequency of the reference signal K to the same frequency as that of the intermediate frequency signal and the distance-measuring signal M. Based on this initial phase β, a distance D to the target 70 is calculated according to Expression 2.
D=(β/2π)(c/F)(1/2)=(βc)/(4πF) (Expression 2)
(Here, β is an initial phase, c is light speed, and F is a modulation frequency of the distance-measuring light L.)
It is also possible that, from the light source 11, the distance-measuring light L is used as reference light R and caused to pass through the received light amount adjusting means 21A having the same configuration as that of the received light amount adjusting means 21 through the inside of the electro-optical distance meter 100, and guided to the light receiving element 22. At the time of a distance measurement, a measurement value is corrected by a publicly known method based on a result of measurement using the reference light R.
(Calculation of Actual Distance)
However, an actually measured distance-measuring signal includes noise. Noise occurring during a distance measurement includes a reference signal, an electrical noise signal EL generated from various electronic circuits, and an optical noise signal IR generated when a distance-measuring light L emitted from the light source 11 is reflected by the inside of the instrument such as an objective lens and unintentionally enters the light receiving element 22.
[Numerical Formula 1]
{right arrow over (MT)}={right arrow over (M)}−({right arrow over (IR)}+{right arrow over (EL)}) (Expression 3)
So, a method for measuring these optical noise signal IR and electrical noise signal EL will be described.
(Method for Measuring Noise)
An electrical noise signal EL can be measured by activating the electro-optical distance meter 100 under, for example, the following condition I.
(1) The received light amount adjusting means 21 is put into a state where it completely blocks light (transmittance: 0%),
(2) the light source 11 is caused to emit light, and
(3) the bias voltage to be applied to the light receiving element is controlled to an optimum value (that is, a multiplication factor is set to an optimum value).
On the other hand, an optical noise signal IR can be measured, for example, as follows. For example, a condition (0) is met. The Condition (0) is that a collimation direction of the electro-optical distance meter 100 is set toward the night sky without obstacles, that is, reflected light of the distance-measuring light L does not enter the objective lens 60. Then, under the condition II, the electro-optical distance meter 100 is activated to measure the signal.
(1a) The received light amount adjusting means 21 is put into a state where it transmits light most (transmittance: 100%),
(2) the light source 11 is caused to emit light, and
(3) the bias voltage to be applied to the light receiving element 22 is set to an optimum value (that is, a multiplication factor is set to an optimum value).
As illustrated in
(Method for Calculating Distance Value)
Hereinafter, a method for calculating a distance value according to the present embodiment will be described. Measurement noise signals NI and NII measured under the condition I and the condition II exhibit the same behavior as the distance-measuring signal M illustrated in
Na·sin(θ−η)+Nb (Expression 4)
(Here, N is the number of noise waves added, a is an average amplitude of noise, b is a bias level, η is an initial phase, and θ is coordinates regulating an angle corresponding to a sampling position.)
Therefore, one wave of the measurement noise signal NI measured by activating the electro-optical distance meter 100 under the condition I is expressed by the following Expression 5:
a
I·sin(θ−ηI)+bI (Expression 5)
(Here, aI is an average amplitude of the measurement noise signal NI, ηI is an initial phase of the measurement noise signal, and bI is a bias level.)
One wave of a measurement noise signal NII measured by activating the electro-optical distance meter 100 under the condition II can be expressed by the following expression 6:
a
II·sin(θ−ηII)+bII (Expression 6)
(Here, aII is an average amplitude of the measurement noise signal NII, ηII is an initial phase of the measurement noise signal, and bII is a bias level.)
The measurement noise signal NII measured under the condition II is a synthetic noise signal of an electrical noise signal EL and an optical noise signal IR, and is expressed vectorially as illustrated in
The noise signal NI measured under the condition I is an electrical noise signal EL. Therefore, an average amplitude aEL and an initial phase ηEL of the electrical noise signal EL are respectively obtained as aEL=aI and ηEL=ηI.
Therefore, from
[Numerical Formula 2]
a
IR=√{square root over ({aII sin(ηII)−aI sin(ηI)}2+{aII cos(ηII)−aI cos(ηI))}}2 (Expression 7)
(Here, aII is an average amplitude of the measurement noise signal NII and ηII is an initial phase of the measurement noise signal NII, and aI is an average amplitude of the measurement noise signal NI and ηI is an initial phase of the measurement noise signal NI.)
[Numerical Formula 3]
ηIR=tan−1{aII sin(ηII)−aI sin(ηI)}/{aII cos(ηII)−aI cos(ηI)}} (Expression 8)
(Here, aII is an average amplitude of the measurement noise signal NII and ηII is an initial phase of the measurement noise signal NII, and aI is an average amplitude of the measurement noise signal NI and ηI is an initial phase of the measurement noise signal NI.)
The distance-measuring signal M obtained at the time of a distance measurement is expressed by Expression 1. However, this Expression 1 includes noise signals (optical noise signal IR and electrical noise signal EL). Accordingly, an initial phase βT of a true distance-measuring signal MT from which the noises have been removed from Expression 1 can be obtained from the following Expression 9.
[Numerical Formula 4]
βT=tan−1{A sin(β)−aEL sin(ηEL)−aIR sin(ηIR)}/{A cos(β)−aEL cos(ηEL)−aIR cos(ηIR)}} (Expression 9)
(Here, A is an average amplitude of the distance-measuring signal M, β is an initial phase of the distance-measuring signal M, aEL is an average amplitude of the electrical noise signal, ηEL is an initial phase of the electrical noise signal, aIR is an average amplitude of the optical noise signal IR, and ηIR is an initial phase of the optical noise signal IR.)
Therefore, by Expression 10 obtained by replacing β in Expression 2 with βT in Expression 9, a distance DT in which an error caused by noises has been removed can be obtained.
D
T=(βTc)/(4πF) (Expression 10)
In this way, the initial phase β2 of the true distance-measuring signal MT in which noises have been removed can be calculated by using the average amplitude aEL and the initial phase ηEL of the electrical noise signal EL, and the average amplitude aIR and the initial phase ηIR of the optical noise signal IR, included in the distance-measuring signal M.
(Measurement of Optical Noise by Using Noise Measuring Jig)
For measurement under the condition that the reflected distance-measuring light does not enter the light receiving unit 20, it is necessary on an instrument-to-instrument basis to install the electro-optical distance meter 100 at an outdoor location without obstacles at night. However, this work is very time-consuming. Therefore, a noise measuring jig 80 is attached to the electro-optical distance meter 100 and used to perform a measurement.
The noise measuring jig 80 is detachably attached to a telescope 100a of the electro-optical distance meter 100 so as to close the objective lens 60, and has optical characteristics to remove reflected light by absorbing the distance-measuring light when attached. As an example, one disclosed in Patent Literature 2 can be used.
The noise measuring jig 80 is attached to the electro-optical distance meter 100 so that an axial line C of the housing 81 matches an optical axis B of the distance-measuring light L. The glass filter 83 is disposed so that the distance-measuring light L enters at a Brewster's angle α. In addition, the laser light absorber 84 is disposed so that light reflected by the glass filter 83 enters the laser light absorber 84. The noise measuring jig 80 is configured so that a polarization plane of the distance-measuring light L as linearly polarized light becomes a plane of incidence on the glass filter 83.
With the configuration described above, most of the distance-measuring light L becomes P-wave and is refracted to enter the inside of the glass filter 83, and is absorbed by the glass filter 83. The distance-measuring light L is not perfect linearly polarized light, however, S-wave is reflected by the glass filter 83 and absorbed by the laser light absorber 84.
In this way, it was estimated that, when the noise measuring jig 80 was attached, the distance-measuring light L was almost completely absorbed and light returning to the electro-optical distance meter 100 was removed. However, in actuality, due to diffuse reflection, etc., on a boundary surface of the glass filter 83, a slight amount of returning light that enters the electro-optical distance meter 100 through the objective lens 60 is generated.
(1) The received light amount adjusting means 21 is put into a state where it completely blocks light (transmittance: 0%),
(2) the light source 11 is caused to emit light, and
(3) a bias voltage to be applied to the light receiving element is controlled to an optimum value (that is, a multiplication factor is set to an optimum value).
Hereinafter, this condition (with noise measuring jig+condition I) is referred to as [Condition Ia].
When the light source 11 is caused to emit light, the distance-measuring light L enters the noise measuring jig 80 through the objective lens 60. At this time, a part of the distance-measuring light L advances as internal reflected light La toward the light receiving element 22. In addition, while most of the distance-measuring light L that has entered the noise measuring jig 80 is absorbed by the noise measuring jig 80, a part of the distance-measuring light L advances as returning light Lb toward the light receiving element 22. However, the received light amount adjusting means 21 blocks the internal reflected light La and the returning light Lb, and in the light receiving element 22, as a measurement noise signal NIa, only an electrical noise signal EL is detected.
(1a) The received light amount adjusting means 21 is put into a state where it transmits light most (transmittance: 100%),
(2) the light source 11 is caused to emit light, and
(3) the bias voltage to be applied to the light receiving element 22 is set to an optimum value (that is, a multiplication factor is set to an optimum value).
Hereinafter, this condition is referred to as [Condition IIa].
When the light source 11 is caused to emit light, as in
Therefore, by subtracting the jig-derived noise signal IRj and the electrical noise signal EL from the measurement noise signal NIIa, the optical noise signal IR can be obtained.
Here, the electrical noise signal EL can be measured as a measurement noise signal NIa by measurement under the condition Ia. On the other hand, the jig-derived noise signal IRj cannot be directly measured.
The electrical noise signal EL greatly fluctuates due to environmental changes such as changes in surrounding temperature and power supply (battery) voltage, and mechanical deterioration caused by aging. On the other hand, the optical noise signal IR and the jig-derived noise signal IRj are values that do not fluctuate due to measurement conditions, environmental changes and changes caused by aging and are unique to the instrument (electro-optical distance meter 100) or the jig.
Therefore, by using the electro-optical distance meter 100, the optical noise signal IR is known in advance by subtracting the measurement noise signal NI (that is, the electrical noise signal EL) measured under the condition I in a state where collimation to a night sky is performed from the measurement noise signal NII measured under the condition I in a state where collimation to a night sky is performed.
Next, by using the optical noise signal IR obtained in advance by measuring the measurement noise signal NIIa and the measurement noise signal NIa (electrical noise signal EL) by using the same electro-optical distance meter 100, the jig-derived noise signal IRj is obtained from Expression 11.
[Numerical Formula 5]
{right arrow over (IRj)}={right arrow over (NIIa)}−({right arrow over (NIa)}+{right arrow over (IR)}) (Expression 11)
The jig-derived noise signal IRj is a value unique to the jig. The jig-derived noise signal IRj is the same value even when a measurement is performed with another electro-optical distance meter as long as the conditions of the distance-measuring light L such as a laser light wavelength and energy, and a light receiving signal reading method, are the same, that is, as long as the electro-optical distance meter has the same configuration as that of the electro-optical distance meter 100. Therefore, once the value of the jig-derived noise signal is known, by measuring the measurement noise signal NIIa and the measurement noise signal NIa with the noise measuring jig 80 attached to an arbitrary electro-optical distance meter 100, an optical noise signal IR unique to the electro-optical distance meter 100 used for the measurement can be obtained from Expression 12.
[Numerical Formula 6]
{right arrow over (IR)}={right arrow over (NIIa)}−({right arrow over (NIa)}+{right arrow over (IRj)}) (Expression 12)
All of the noise signals described above exhibit the similar behavior as that of the distance-measuring signal M, and a synthetic sine wave obtained by applying a result of synchronous addition of N data of one period of the noise signals to a sine wave is expressed by a general expression of Expression 4. Therefore, by obtaining average amplitudes aIa, aIIa, and aIRj and initial phases ηIa, ηIIa, and ηIRj of the respective noise signals and performing vector addition and subtraction, the average amplitude aIR and the initial phase ηIR of the optical noise signal IR can be expressed as functions of the average amplitudes aIa, aIIa, and aIRj and initial phases ηIa, ηIIa, and ηIRj.
By applying this result to Expression 9, an initial phase βT of a true distance-measuring signal MT is obtained. In addition, by using the obtained initial phase βT, a distance DT from which an error caused by noise has been removed is obtained.
(Operation of Electro-Optical Distance Meter)
An example of operation of the electro-optical distance meter 100 according to the present embodiment will be described with reference to the flowcharts of
For noise measurement before factory shipment, a noise measuring jig 80 whose jig-derived noise signal IRj is known is used. On a surface of the housing 81 of the noise measuring jig 80, values of an average amplitude aj and an initial phase ηj of the jig-derived noise signal IRj are indicated.
First, in Step S01, the average amplitude aj and initial phase 11 of the jig-derived noise signal IRj are input into the arithmetic control unit 40. For example, the arithmetic control unit 40 displays an input screen for the average amplitude aj and initial phase ηj of the jig-derived noise signal IRj on the display unit, and from the input unit, a worker inputs the average amplitude aj and initial phase ηj of the jig-derived noise signal IRj visually read from the noise measuring jig 80. Alternatively, it is also possible that a program for performing a jig-derived noise measurement is called from a general-purpose computer connected by an external interface, and the values can be input from the computer terminal. This general-purpose computer terminal is configured by, for example, a CPU, a RAM, a ROM, a hard disk, an external storage device, and a network interface, etc.
Next, in Step S02, under the condition Ia, the arithmetic control unit 40 activates the electro-optical distance meter 100 and measures a measurement noise signal NIa as a first measurement noise signal.
Next, in Step S03, the arithmetic control unit 40 calculates an average amplitude aIa and an initial phase ηIa of the measurement noise signal NIa, and stores these in the storage unit 50.
Next, in Step S04, under the condition IIa, the arithmetic control unit 40 activates the electro-optical distance meter 100 and measures a measurement noise signal NIIa as a second measurement noise signal.
Next, in Step S05, the arithmetic control unit 40 calculates an average amplitude aII, and an initial phase ηIIa of the measurement noise signal NIIa, and stores these in the storage unit 50.
Next, in Step S06, by using the average amplitudes aIa, aIIa, and aIRj and initial phases ηIa, ηIIa, and ηIRj, the arithmetic control unit 40 calculates an average amplitude aIR and an initial phase ηIR of the optical noise signal IR by subtracting the measurement noise signal NIa and the jig-derived noise signal IRj from the measurement noise signal NIIa, and stores these as an optical noise signal IR in the storage unit 50.
The average amplitude aIa and the initial phase ηIa in Step S02 and the average amplitude aria and the initial phase ηIIa in Step S04 may be discarded or held after being used for calculation of the average amplitude aIR and the initial phase ηIR in Step S05.
Next, when performing a measurement, measurement is performed by collimation to a measuring object (for example, a target).
First, in Step S11, under the condition I, the arithmetic control unit 40 activates the electro-optical distance meter 100 and measures a measurement noise signal NI.
Next, in Step S12, the arithmetic control unit 40 calculates, an average amplitude aI and an initial phase ηI of the measurement noise signal NI, and stores these as an average amplitude aEL and an initial phase ηEL of the electrical noise signal EL in the storage unit 50.
Next, in Step S13, the arithmetic control unit 40 activates the electro-optical distance meter 100 and adjusts the received light amount adjusting means 21 so that the received light amount becomes proper (proper condition), emits distance-measuring light to measure a distance-measuring signal M based on reflected distance-measuring light L by setting a multiplication factor of the light receiving element to an optimum value.
Next, in Step S14, the arithmetic control unit 40 obtains an average amplitude A and an initial phase β of the measured distance-measuring signal M.
Next, in Step S15, the arithmetic control unit 40 reads the average amplitude aIR and the initial phase ηIR of the optical noise signal IR from the storage unit 50.
Next, in Step S16, based on the average amplitudes aIR, aEL, and A and initial phases ηIR, ηEL, and β, an initial phase βT of a true distance-measuring signal MT in which noise has been removed by subtracting the optical noise signal IR and the electrical noise signal EL from the distance-measuring signal M is calculated.
Next, in Step S17, the arithmetic control unit 40 calculates a distance DT in which an error caused by noise has been removed based on the calculated initial phase βT, and ends the processing.
First, in Step S21, in a state where collimation to a night sky is performed, under the condition I, the arithmetic control unit 40x activates the electro-optical distance meter 100x and measures a noise signal NIx as a third noise signal.
Next, in Step S22, the arithmetic control unit 40x calculates an average amplitude aIx and an initial phase ηIx of the noise signal NIx, and stores these in the storage unit 50x.
Next, in Step S23, in a state where collimation to a night sky is performed, under the condition II, the arithmetic control unit 40x activates the electro-optical distance meter 100x, and measures a noise signal NIIx as a fourth noise signal.
Next, in Step S24, the arithmetic control unit 40x calculates an average amplitude aIIx and an initial phase ηIIx of the noise signal NIIx, and stores these in the storage unit 50x.
Next, in Step S25, by using the average amplitudes aIx and aIIx and the initial phases ηIx and ηIIx, the arithmetic control unit 40x calculates an average amplitude aIRx and an initial phase ηIRx of the optical noise signal IRx obtained by subtracting the noise signal NIx from the noise signal NIIx, and stores these as an optical noise signal IRx in the storage unit 50x.
In Step S26, under the condition Ia, the arithmetic control unit 40x activates the electro-optical distance meter 100x, and measures a noise signal NIax as a fifth measurement noise signal.
Next, in Step S27, the arithmetic control unit 40x calculates an average amplitude aIax and an initial phase ηIax of the measurement noise signal NIax, and stores these in the storage unit 50x.
Next, in Step S28, under the condition IIa, the arithmetic control unit 40x activates the electro-optical distance meter 100x and measures a measurement noise signal NIIax as a sixth measurement noise signal.
Next, in Step S29, the arithmetic control unit 40x calculates an average amplitude aIIax and an initial phase ηIIax of the noise signal NIIax, and stores these in the storage unit 50x.
Next, in Step S30, by using the average amplitudes aIax, aIIax, and aIRx and initial phases ηIax, ηIIax, and ηIRx, the arithmetic control unit 40 calculates an average amplitude aIRj and an initial phase ηIRj of a jig-derived noise signal IRA obtained by subtracting the measurement noise signal NIax and the optical noise signal IRx from the measurement noise signal NIIax, and stores these in the storage unit 50x.
Next, in Step S31, the arithmetic control unit 40x outputs the calculated average amplitude aIRj and initial phase ηIRj of the jig-derived noise signal NIRj. As the output, for example, the values may be displayed on the display unit. Alternatively, the values may be output to a data collector, an external terminal, a USB memory, or the like through an external interface.
The optical noise signal IRx of the electro-optical distance meter 100x can be known through the steps as illustrated in
The electro-optical distance meter 100 configured to execute the operation described above is configured so as to calculate a distance value from a true distance-measuring signal MT obtained by subtracting an optical noise signal IR stored in advance in the storage unit and an electrical noise signal EL measured before a distance measurement from a distance-measuring signal M, so that an error in a distance value caused by noise can be reduced without specially devising components and wirings.
According to the electro-optical distance meter 100 described above, an accurate optical noise signal IR can be obtained by using the noise measuring jig 80. The accuracy in distance calculation is improved. The optical noise signal IR is normally small, and takes time to measure. In the electro-optical distance meter 100, it is not necessary to measure an optical noise signal IR at the time of a distance measurement, so that the time to be taken from the distance measurement to calculation can be shortened. Further, in response to fluctuation of the electrical noise signal EL, the electrical noise signal EL can be removed, and in this regard, more accurate distance calculation can be performed.
In particular, in the electro-optical distance meter 100, a measurement of an optical noise signal IR is enabled by attaching the noise measuring jig 80, so that each measurement of an optical noise signal IR does not need to be performed outdoors at night, and the work load can be reduced.
In addition, after a jig-derived noise signal IRj of the noise measuring jig 80 is known by using the electro-optical distance meter 100x whose optical noise IRx has been known, the noise measuring jig 80 can be used any number of times to measure optical noise signals IR of other electro-optical distance meters 100.
In the present embodiment, as the noise measuring jig 80, the noise measuring jig 80 disclosed in Patent Literature 2 is used. The noise measuring jig 80 is configured to absorb light entering the jig so that the light hardly returns to the electro-optical distance meter 100. The noise measuring jig 80 is not limited to this, and only has to have a unique jig-derived noise signal IRj. For example, it is also possible that, inside a similar cylindrical housing, a deflecting mirror is disposed at 45° with respect to an optical axis of distance-measuring light, and a laser absorber is disposed at a position where reflected light enters. However, with a configuration in which light hardly returns as with the noise measuring jig 80, an absolute value of the jig-derived noise signal IRj becomes small. The jig-derived noise signal IRj is a unique value and rarely fluctuates. But, in actuality, the jig-derived noise signal IRj may slightly fluctuate due to the temperature and changes caused by aging. However, as the absolute value of the jig-derived noise signal becomes small, a fluctuation value is also small, so that more accurate optical noise measurement is possible.
As compared with an optical noise signal IR derived from internal reflection, the jig-derived noise signal IRj is small. For example, when the optical noise signal IR is 4, the jig-derived noise signal is approximately 0.1 to 1. However, under the condition that a distance-measuring signal to be received is small as in a case of non-prism distance measurement and a case where the measuring object is distant, even such a small noise signal is not negligible. In the present embodiment, an optical noise signal IR derived from internal reflection can be accurately calculated, so that a minimum signal can also be used, and measurement accuracy is improved.
A jig-derived noise signal IRj is a smaller value than an optical noise signal IR, so that it takes a longer time to measure. In the present embodiment, a jig-derived noise signal IRj is known in advance, and an optical noise signal IR is calculated, and accordingly, the amount of time-consuming work can be reduced, and the work efficiency can be improved.
Preferred embodiments of the present invention have been described above, and the embodiments described above are examples of the present invention, and these can be combined based on knowledge of those skilled in the art, and such a combined embodiment is also included in the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-035056 | Mar 2021 | JP | national |
