JPH01169385A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To always enable accurate measurement of distance, by applying a projection signal of a light emitting element and a reception signal of a light receiving element selectively to a phase difference detection circuit. CONSTITUTION:Light with a modulated intensity is projected to an object with a light emitting element 1 by a projection signal with a specified frequency. A changeover switch 6 applies a projection signal of a light emitting element 1 and a reception signal of a light receiving element 2 selectively to a phase difference detection circuit 10. A correction circuit 20 subtracts a phase difference data obtained from a phase difference detection circuit 10 when the changeover switch 6 selects the projection signal from a phase difference data obtained from the phase difference detection circuit 10 when the changeover switch 6 selects the reception signal and outputs a phase difference data after the correction. An output circuit 30 calculates a distance from the phase difference data to be shown on a display device 32.

Description

[Detailed Description of the Invention] Summary of the Invention Projecting intensity-modulated light onto an object to be measured (object) and receiving the reflected light, detecting the phase difference between the light projection signal and the light reception signal, and detecting the phase difference between the light projection signal and the light reception signal. In a device that measures distance based on , a light emitting signal is applied to one input of a two-phase detection circuit, and a light emitting signal and a light receiving signal are switched and applied to the other input using a changeover switch.

The phase error that occurs in the circuit when both inputs of the phase detection circuit are light emitting signals is measured. This measured phase error is used to correct the phase difference between the projection and reception signals detected by the phase detection circuit.

Background of the Invention This invention projects the output light of a light emitting element whose intensity is modulated by a signal of a predetermined frequency onto a target object, receives the reflected light with a light receiving element, and detects the target object from the phase difference between the light emitting signal and the light receiving signal. This invention relates to a device that measures the distance to an object.

Such a distance measuring device is provided with a phase difference detection circuit that detects a phase difference between a light emitting signal and a light receiving signal. The light projection signal is obtained from a light receiving element that monitors the light projected by the light emitting element, and is applied to one input of the phase difference detection circuit through an amplification circuit. The light reception signal of the light receiving element that receives the reflected light from the object is applied to the other input of the phase difference detection circuit through an AGC (automatic gain control) circuit with an amplitude of 1 [to keep the amplitude 1 constant]. A phase shift occurs in the light emitting signal and the light receiving signal due to variations in the monitor light receiving element, each amplifier circuit, etc., temperature trit, etc., and the amount of phase shift varies depending on the device or varies depending on the temperature. .

In particular, in an AGC amplification circuit, the gain varies depending on the amount of reflected light, so the phase shift of the output signal (light reception signal) is significant and changes. Therefore, there is a problem in that the phase difference between the projection and reception signals detected by the 1-phase detection circuit includes an error.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus that periodically measures one phase error, corrects the detected phase difference thereby, and is capable of always accurately determining the distance 711J.

A distance measuring device according to the present invention includes a light emitting element that projects light whose intensity is modulated by a light projection signal of a predetermined frequency onto an object;
A light-receiving element that receives reflected light from an object 1 A change-over switch that switches between the light-emitting signal of the light-emitting element and the light-receiving signal of the light-receiving element and outputs one of them, and the phase difference between the light-emitting signal and the output signal of the changeover switch. A phase difference detection circuit detects and outputs data representing this phase difference, and controls switching of the changeover switch, and also detects the phase difference from the phase difference data obtained from the phase difference detection circuit when the changeover switch selects the received light signal. The present invention is characterized by comprising a correction circuit that subtracts phase difference data obtained from the phase difference detection circuit when the changeover switch selects the light projection signal and outputs corrected phase difference data.

According to this invention, by controlling the changeover switch, a light emitting signal is periodically selected and the light emitting signal is applied to a phase difference detection circuit through a light receiving circuit (including an AGC amplification circuit, etc.) for a light receiving signal. be able to. At this time, the phase difference detection circuit measures the phase shift occurring in each of the circuits on the transmitting and receiving sides.

By subtracting the above 11-determined phase difference from the detected phase difference of the phase difference detection circuit obtained when the light reception signal is selected by the selector switch, the accurate result that does not include the phase error caused by the amplification circuit, etc. can be obtained. Throw.

The phase difference of the received light signal can be obtained. In this way, according to the present invention, accurate distance measurement is always possible.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 shows output signal waveforms of each block in FIG. In FIG. 2, each waveform is illustrated as an ideal waveform in which there is no phase shift caused by an amplification circuit or the like. Further, the light emitting signal A and the light receiving signal B are shown as having considerably low frequencies for convenience of drawing the figures.

The oscillation circuit 4 generates a sine wave signal with a constant frequency f (intensity modulation frequency, for example, about 8 to IOM Hz), and this signal is used to drive the light emitting element (laser diode) 1 by the APC (automatic power control) circuit 5. The output light of the light emitting element 1 will be intensity-modulated at the frequency fif.This output light will be projected toward the object.
The output light of the light emitting element 1 is directly received by a monitoring light receiving element (photodiode) 3 arranged in close proximity (of course, via a filter or the like as necessary). The output of this light receiving cable 3 represents the light projection signal A.

On the one hand, the light reception signal of the element 3 is given to the APC circuit 5,
The APC circuit 5 controls the peak intensity of the output light of the light emitting element 1 to be always constant. On the other hand, the output of the light receiving element 3 is amplified 111 by the amplification circuit 7 and applied to the phase difference detection circuit 10 and also applied to one input terminal of the changeover switch 6.

The reflected light from the object is received by the light receiving cable 2, and this light receiving signal B is given to the other terminal a of the changeover switch 6. There is a phase difference φ between the light projection signal (projection light) A and the light reception signal (reflected light) B, depending on the distance ML to the object. As shown later, the phase difference φL is detected, and using this phase difference φL, the distance ML is determined by the following equation.

L-(φL/2π)(C/fo) C: When the light speed changeover switch 6 is connected to the terminal a, the light reception signal B is applied to the AGC amplification circuit 8 through the changeover switch 6. The output signal of this amplification circuit 8 is input to a phase difference detection circuit 10. Since the intensity of the reflected light changes depending on the distance to the object, the peak level of the received light signal B also changes depending on the position of the object. The peak level of the received light signal is kept constant by the AGC amplification circuit 8.

When the changeover switch 6 is connected to the b side, the light projection signal A is applied to the phase difference detection circuit IO through the switch 6. In order to simplify the explanation, in the following explanation of the phase difference detection circuit IO, it is assumed that the changeover switch 6 is connected to the a side.

The phase difference detection circuit 10 detects a phase difference using a heterodyne detection method. The oscillation circuit 15 generates a positive OC sinusoidal signal with a frequency f 1 very close to the intensity modulation frequency f 2 , and this oscillation output is given to the beat generation circuit 11.13. Beat generation circuit 11, 1
The above-mentioned light emitting signal A and light receiving signal B are respectively input to 3, and beat signals C and D having a frequency f −f −f which is the difference between one frequency f and f are respectively created. . The phase difference φL between the signals A and B is preserved between these beat signals C and D (
(The phase shift described later is not a concern here.) The frequency f of the beat signal is selected to be, for example, about lOKHz,
Since the phase difference φL can be preserved and the frequency can be lowered in this way, it becomes possible to detect the phase difference using the counter 7, which will be described later.

Comparators 12 and 14 are for level discrimination of the beat signal C1D at zero level (zero cross).
, and their output signals E and F are applied to a gate signal generation circuit IB. The gate signal generation circuit 16 generates a gate signal G that is at H level from the rise of the input signal E to the rise of the signal F. The gate signal G is at H level during the time period of the phase difference φL to be detected.

A high-speed (eg, 5 MHz) clock pulse H is applied to the counter 17, and the counter 17 counts this clock pulse H while the gate signal G is at an H level. The count value of the counter 17 is the phase difference φ1. will represent.

As described above, the light projection signal A is detected by the light receiving element 3, passes through the amplification circuit 7, and is input to the phase difference detection circuit IO. The light reception signal B of the light receiving element 2 is input to the phase difference detection circuit 10 via the AGC amplification circuit 8. In this way, since the light emitting signal A and the light receiving signal B pass through different circuits, a phase shift inherent to these circuits occurs. Further, this phase shift depends on the temperature and the intensity of reflected light (the amount of light incident on the light-receiving probe 2). In particular, since the AGC amplifying circuit 8 has a unique gain-phase characteristic, the phase shift changes as the gain changes.

If the above-mentioned phase shift occurring between the light emitting signal A and the light receiving signal B is expressed as φ, the phase difference detected by the phase difference detection circuit 10 when the changeover switch 6rr is connected to the a side is The sum of the phase difference φ based on the distance of the object and the phase shift φ shown in .

L err It becomes φ + φ.

L err On the other hand, when the changeover switch 6 is switched to the b side, the light emission signal A
is input to the phase difference detection circuit 10 through the AGC amplification circuit 8. Since the two inputs of the phase difference detection circuit 10 are both light projection signals A, the phase difference based on the distance to the object is 0, and the phase difference detected by the 1 phase difference detection circuit 10 is crr of 1 phase shift φ. Become a servant.

Therefore, by subtracting the detected phase difference φ when switching to the b side L crr from the detected phase difference φ +φ when the changeover switch 6 is connected to the a side, the accurate phase difference φ based on the distance of the target object rr can be obtained. , will be obtained.

The correction circuit 20 includes an L err latch circuit 21 that temporally stores the measured phase difference φ +φ when the changeover switch 6 is on the a side, and a L err latch circuit 21 that temporarily stores the measured phase difference φ +φ when the changeover switch 6 is on the b side.
A latch circuit 22 for storing the information is provided.

err These are connected to the output side of the counter 17.

The latch switching circuit 23 controls the switching of the changeover switch 6, and also performs the latch operation of the counter output in the latch circuits 21 and 22 in synchronization with the switching of the switch 6.

As shown in FIG. 3, the changeover switch 6 is switched at a constant period T (for example, 10 m5), and is connected to the a side during a relatively long time t1.

It is connected to the b side in a relatively short time t2 (for example, around 1 ms). These times 1. The phase differences φ +φ and φ measured at 1 are L er
Since r err is stored in the child circuits 21 and 22, the arithmetic circuit 24 performs the calculation (φ +φ) −φ −φ, and L
err err, and as a result φL is temporarily stored.

The data of the corrected phase difference φL stored in the arithmetic circuit 24 is transmitted to the output circuit 3o on the one hand and to the arithmetic circuit 31.
The distance is calculated according to the formula described above.9
It is displayed on the display device 32. On the other hand, data φL is D/
It is converted into an analog quantity by the A conversion circuit 33 and outputted from the analog output circuit 34.

In the embodiment shown in FIG. 1, the oscillation frequencies f and f of the single oscillation circuits 4 and 15 vary due to element variations, temperature Oe, etc., and the single frequency accuracy is ±100 pp11.
That's about it. For example, f -10MHz,
When f = OC 9,99 MHz, the beat frequency is f −10
It is supposed to be KHz, but in reality it is f -10M H
Z±I KHz, f=9.99MHz±IKHz
, fs=IOK Hz±2KHz. For example, the frequency of the clock signal H of the clock generation circuit 18 is set to 5MH.
When z, the phase difference measurement value corresponding to one period of the beat signal varies from 625 counts to 417 counts in terms of the count value of the counter 7. therefore.

An error occurs in the detected phase difference.

The example shown in FIG. 4 solves this problem. This figure shows a part of the circuit shown in FIG. 1. The output of comparator 12.14 represents the beat frequency. The frequency of the output signal of one comparator 12 is P
The signal is multiplied by an integer N by a multiplier circuit 19 such as LL, and the output is given to the counter 17 as a clock signal. By doing this.

If the count number of the counter 17 is n, the phase difference is 2πX
(n/N), and it is possible to eliminate measurement errors due to fluctuations in oscillation frequency due to element variations or temperature changes.

FIG. 5 shows yet another embodiment. Components that are the same as those shown in FIG. 1 are given the same reference numerals. The amplification circuit 8 shown in FIG.
11 circuit 82 and the resistance divider circuit 4 provided between them.
0 and a switch 41 for selecting the dividing resistance of the dividing circuit 40. When the level of the output signal of the amplifier circuit 81 exceeds a certain level, the amplitude detection circuit 4
2, and this detection signal is given to the gate circuit 44 of the switching control circuit 46. When the gain of the AGC amplification circuit 82 exceeds a certain value, it is detected by the gain detection circuit 43, and this detection signal is given to the gate circuit 45 of the circuit 46.

The selection switch 41 is selected by the outputs of the gate circuits 44 and 45.
is controlled to switch. The gate circuits 44 and 45 are controlled by the switching control signal of the changeover switch 6 mentioned above, and when the changeover switch 6 is connected to the a side, the level of the output signal of the first stage amplifying circuit 81 is used to control the selection switch 41 through the gate circuit 44. Switching control is performed, and when the changeover switch 6 is connected to the b side, the selection switch 41 is controlled by the gain of the AGC amplifier 111 circuit 82 through the gate circuit 45.

As described above with reference to FIG. 3, the time during which the changeover switch 6 is connected to the a side is much longer than the time during which it is switched to the b side. Since the constant of the AGC amplification circuit 82 is relatively large, its gain changes in accordance with the amplitude of the light reception signal of the monitor light reception cable 3 that is input when the changeover switch 6 is connected to the b side. There are almost no A
Basically, the gain of the GC amplification circuit 82 is set by the switch 6.
It changes in accordance with the amplitude of the light reception signal of the light receiving element 2 that is input when the light receiving element 2 is connected to the side. therefore.

When the gain of the AGC amplification circuit 82 is large, the switch 6
is switched to the b side and the output signal of the monitor light receiving element 3 is input to the AGC amplification circuit 82. Since there is a risk that this amplification circuit 82 will be saturated, the selection switch 41 is switched to the d side and the amplification circuit The amplitude of the output signal 81 is resistance-divided and output to the AGC amplification circuit 82. When the light reception signal of the light receiving element 2 is large, this is detected by the amplitude detection circuit 42 when the switch 6 is connected to the a side.
Similarly, when the selection switch 41 is switched to the d side and resistance division is performed, the amplitude [1] is reduced, and the gain of the AGC amplification circuit 82 is prevented from becoming too small.

Although the selection switch 41 switches the resistance of the resistance divider circuit 40 into two stages, it can also be configured to switch into three or more stages depending on the detection amplitude and detection gain.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention. FIG. 2 is a waveform diagram showing output signal waveforms of each block of the circuit of FIG. 1, and FIG. 3 is a time chart showing switching of the changeover switch. FIG. 4 is a block diagram showing a modified example, and FIG. 5 is a block diagram showing another embodiment. 1... Light emitting element, 2... Light receiving element. 3... Light receiving element for monitor. 4...Intensity modulated wave oscillation circuit. 6...Switching circuit, 10...Phase difference detection circuit. 20... Correction circuit. 23... Changeover switch and latch changeover circuit. Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Kenji Ushiku (1 other person) Figure 4

Claims (2)

[Claims] (1) A light-emitting element that projects light whose intensity is modulated by a light-emitting signal of a predetermined frequency onto an object, a light-receiving element that receives reflected light from the object, and switching between the light-emitting signal of the light-emitting element and the light-receiving signal of the light-receiving element. a changeover switch that outputs either one of the output signals of the changeover switch; a phase difference detection circuit that detects the phase difference between the light emission signal and the output signal of the changeover switch and outputs data representing this phase difference; and a phase difference detection circuit that controls switching of the changeover switch. , Subtract the phase difference data obtained from the phase difference detection circuit when the changeover switch selects the light emission signal from the phase difference data obtained from the phase difference detection circuit when the changeover switch selects the light reception signal. and a correction circuit that outputs corrected phase difference data. (2) The light projection signal given to the changeover switch and the phase difference detection circuit is a light reception signal of a monitoring light receiving element that directly receives the light emission output of the light emitting element.
) Distance measuring device described in paragraph 1.