WO2002054109A1

WO2002054109A1 - Method for detecting emission timing, emission timing detector and distance measuring apparatus

Info

Publication number: WO2002054109A1
Application number: PCT/JP2001/011243
Authority: WO
Inventors: Naoto Inaba; Masaya Nagasawa
Original assignee: Nikon Corporation
Priority date: 2000-12-27
Filing date: 2001-12-21
Publication date: 2002-07-11
Also published as: JP2004053250A

Abstract

A laser distance measuring apparatus (100) comprising a semiconductor laser (112) having such an emission timing as a voltage V being applied to the semiconductor laser (112) reaches a specified level (VTH-VF) at which a constant optical output P01 is produced from the semiconductor laser (112). The timing at which light is emitted at a constant output from a light emitting element can thereby be detected accurately.

Description

Description Light emission timing detection method, light emission timing detection device, and distance measuring device

The present invention relates to a method for detecting a light emission timing of a light emitting element, a light emission timing detection device, and a distance measuring device. And a distance measuring device using the same. Background art

The target object is irradiated with pulsed laser light, and the reflected light is detected. The method is known.

In this laser beam ranging method, if the measurement accuracy of the time difference is low, the measurement accuracy of the distance is reduced.

Here, the time difference between the light emission timing and the light reception timing of the pulsed laser light is counted by the number of sample clock pulses generated therebetween. Therefore, in the laser ranging method, a high-frequency oscillator and a cPU having a high signal processing capability are used in order to improve the measurement accuracy of the distance to the target.

For example, when a transmitter with a sample clock frequency of 80 MHz (the clock period is 12.5 nsec) is used, the minimum unit for detecting the above time difference is 12.5 nsec. Considering the speed of the laser beam, the resolution in the laser ranging method is about 2 m. Incidentally, the light emission timing of the laser light is controlled according to a signal (light emission start signal) synchronized with the clock pulse. For this reason, in the conventional laser ranging method, the time difference is counted using the irradiation timing (light emission timing) of the laser light as the generation timing of the light emission start signal.

However, the present inventor has confirmed that the accuracy of distance measurement is reduced when the above-described light emission start signal is regarded as laser light irradiation timing (light emission timing).

That is, in order to perform laser ranging, a drive current is supplied from a constant current source in the driver circuit to the semiconductor laser based on the above-described light emission start signal synchronized with the clock pulse. It was found that a certain evening lag Δt (a time delay of the order of several nsec) occurs until the value of the drive current exceeds a certain value at which a predetermined light output can be obtained (Fig. 6).

Therefore, as described above, if the generation timing of the light emission start signal synchronized with the clock pulse is the irradiation timing (light emission timing), the above-described delay time Δt causes a distance measurement error, resulting in a highly accurate measurement. I could not distance.

In order to avoid this, for example, a method of subtracting the delay time Δt from receiving the light emission start signal to obtaining a predetermined light output value at the time of the distance measurement calculation can be considered. Fluctuates depending on the environment at the time of use such as temperature fluctuation, so that the correction in consideration of the change becomes complicated.

On the other hand, it is conceivable that a photodetector is separately arranged near the semiconductor laser, the timing at which the semiconductor laser actually emits light is detected, and the time difference is obtained from the detection time.

However, in this case, the number of parts increases. In addition, it is necessary to detect the delay time Δt at a short time interval (about 1 nsec when detecting with a resolution of several tens of cm), and do not prepare an expensive photodetector having a high response speed. The cost of the entire distance measuring device must be increased. Disclosure of the invention

The present invention has been made in view of the above problems, and a first object of the present invention is to provide a light emission timing detection method capable of accurately detecting a timing at which light having a constant light output is emitted from a light emitting element, and An object is to provide a light emission timing detection device.

Further, a second object of the present invention is to provide a distance measuring apparatus in which a delay time is generated from the generation of a signal instructing the start of laser beam irradiation to the actual irradiation of a laser beam having a constant light output. Even so, an object of the present invention is to provide a distance measuring device capable of measuring a distance to a target object with high accuracy.

The light emission timing detection method according to the first invention is to detect a voltage applied to the light emitting element, and use a timing at which the detected voltage reaches a predetermined voltage as a light emission timing of the light emitting element. .

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to detect the light emission timing of a light emitting element with high precision only by monitoring the voltage applied to a light emitting element, without separately providing a photodetector.

According to a second aspect of the present invention, there is provided a light emitting timing detecting device, comprising: a light emitting element; a detecting unit for detecting a voltage applied to the light emitting element; and a timing at which the detected voltage reaches a predetermined voltage. It is provided with a light emission timing detection unit for light emission timing.

A distance measuring apparatus according to a third aspect of the present invention is a distance measuring device comprising: a light emitting element that generates a pulsed optical signal having a constant light output when a supplied voltage exceeds a predetermined value; An irradiating unit that irradiates a target object with a pulsed optical signal having an optical output of the same; a voltage detecting unit that detects a voltage supplied to the light-emitting element; A light receiving element, a time measuring unit for measuring a time from when the voltage detected by the voltage detecting unit reaches a predetermined value until the pulsed optical signal is detected, and a time measuring unit for measuring the time. A distance calculation unit that calculates a distance to the target object based on time and the speed of the pulsed optical signal.

A distance measuring apparatus according to a fourth aspect of the present invention is a distance measuring device, comprising: a light emitting element for generating a pulsed optical signal; an irradiating unit for irradiating the optical signal to a target; A light receiving element for detecting an optical signal reflected from the object; and a point in time when the voltage detected by the voltage section reaches a predetermined value, until a light signal reflected from the object is detected. And a distance calculation unit that calculates a distance to the object based on the time measured by the clock unit and the optical signal. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a laser distance measuring apparatus to which the present invention is applied.

FIG. 2 is a block diagram showing the internal configuration of the laser distance measuring device.

FIG. 3 is a circuit diagram showing a configuration of the light emission detection circuit.

FIG. 4 is a graph showing the relationship between the optical output of the semiconductor laser, the applied voltage, and the constant voltage source.

FIG. 5 is a timing chart showing how light reception timing is measured when obtaining the distance to the target.

FIG. 6 is a timing chart showing a time difference t between the light emission timing and the light reception timing obtained by the conventional laser ranging method. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, among the modes for carrying out the present invention, the best mode will be described, but the scope of the present invention is not limited by these descriptions.

(First Embodiment)

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a perspective view of a laser distance measuring apparatus 100 to which the present invention is applied, and FIG. 2 is a block diagram showing an internal configuration thereof.

As shown in FIG. 1, the laser distance measuring apparatus 100 is provided with a power and measurement start button 101 and a mode change 102 on its upper surface. The mode button 101 is used to change the unit of the distance. Further, a laser irradiation window 103 and a laser receiving window 104 are provided on the front surface thereof, and a finder window (not shown) is provided on the rear surface thereof.

The laser distance measuring device 100 has a collimating lens 111 on the side of the laser irradiation window 103 and a condensing lens 121 on the side of the laser receiving window 104. As shown in Fig. 2 (a), the semiconductor lens (light emitting element) 112, the pulse generation circuit 130, the light emission detection circuit 14 0 is arranged. In addition, a photodiode (light receiving element) 122 and a receiving circuit 150 are arranged on the converging lens 122 side. Here, the irradiation part is constituted by the semiconductor laser 112 and the collimating lens 111.

The control circuit 160 controls the above-described pulse generation circuit 130 and the light emission detection circuit 140 so that a predetermined timing (light emission timing) is output from the semiconductor laser 112. ) To irradiate laser light.

Further, the control circuit 160 detects the timing of receiving the laser beam reflected by the target 1 based on the signal from the receiving circuit 150.

The control circuit 160 detects the time difference between the light emission timing and the light reception timing (t in FIG. 2 (b)) by counting clock pulses (see FIG. 5). The control circuit 160 calculates the distance L from the laser range finder 100 to the object 1 based on the counted time difference t and the speed of the laser light. The control circuit 160 displays this calculation result on the liquid crystal display section 170 in the finder. Here, the control circuit 160 functions as a clock unit, a light emission timing detection unit, and a distance calculation unit.

By the way, in the laser distance measuring apparatus 100 of this embodiment, the light emission detection circuit 140 outputs a signal indicating the irradiation timing (light emission timing) of the laser light.

The light emission detection circuit 140 has a comparator 144 and a constant voltage source 144 as shown in FIG. The comparator 142 functions as a detection unit and a voltage detection unit in the claims.

One terminal of the comparator 140 of the light emission detection circuit 140 is connected to one of the terminals of the constant current source 116 of the semiconductor laser 112, and the other terminal is connected to the constant voltage source 144 of the other terminal. ing.

Here, a current source 116 supplying a current thereto is connected to the semiconductor laser 112 via a switch 113.

Then, the switch 113 is turned on by the light emission start signal S1 from the pulse generation circuit 130. The light emission start signal S1 is generated in synchronization with a clock pulse as shown in FIG.

When the switch 113 is turned on by the light emission start signal S1 and a current flows from the current source 116 to the semiconductor laser 112, one of the semiconductor lasers 112 is turned on. The voltage V at the terminal (current source 1 16 side) becomes a forward voltage corresponding to the current value I flowing through the semiconductor laser 112. At this time, there is a time delay from the timing of the generation of the light emission start signal S1 until this current reaches a predetermined current value.

Now, in FIG. 4, assuming that the optical output P01 is obtained when the predetermined current value is I1, the forward voltage at which the optical output P01 is obtained is V _F丄.

Therefore, if the voltage of one terminal (current source 1 16 side) of the semiconductor laser 112 is V _F丄, the current flowing through the semiconductor laser 112 at this time is I 1, It can be considered that a laser beam having an optical output P01 is generated from the semiconductor laser 112.

The Comparator 1402 has the voltage of one terminal (current source 116 side) of the semiconductor laser 112 and the reference voltage V. (V _TH ≤ V. ^ V _F ). Where reference voltage V. Is a value corresponding to a desired optical output, voltage V _TH is a value at which laser light can be generated from semiconductor laser 112, and voltage V _F is a value at which semiconductor laser 112 cannot be destroyed. It is.

Therefore, the VF i <V _F, V. Is V _{F 1} , the timing at which the output signal of the comparator 14 2 rises indicates the timing at which laser light of a constant light output P _Q i is obtained from the semiconductor laser 112. Become.

The timing at which the output signal of the comparator 142 rises is a timing delayed by the drive current delay time Δt with respect to the light emission start signal S1 (FIG. 5).

Thus, in the comparator 142, the voltage V applied to the semiconductor laser 112 is a constant value V. (V _TH ≤ V. ≤ V _F ) Outputs a signal that turns on when it becomes equal to or greater than to the control circuit 160.

As shown in Fig. 5, the control circuit 160 The timing at which the output signal rises is the irradiation timing (light emission timing) of the semiconductor laser 112. Then, a time difference t from the irradiation timing to the light receiving timing from the receiving circuit 150 is determined, and the distance to the target 1 is calculated based on the time difference t and the speed of the laser light.

When counting the time difference t from the rising of the output signal S2 of the light emission detection circuit to the rising timing (light receiving timing) of the light receiving pulse S3, the time difference t may be directly counted. The time difference t, from the rising edge of the light emission start signal S1 to the rising timing of the light reception pulse S3 (light reception time), is determined. From the rising timing of the light emission start signal S1, the light emission detection circuit 140 The time difference At until the rising timing of the output signal S2 may be obtained, and △ t may be subtracted from t.

As described above, in the laser range finder 100 of the present embodiment, the timing at which a constant light output (P 01) is obtained from the semiconductor laser 112 is detected by the operation of the light emission detection circuit 140. Therefore, the delay time A t between the light emission start signal S 1 from the pulse generation circuit 130 and the light emission timing (equivalent to the rising timing of the output signal) is not included in the measurement of the time difference t. Measurement accuracy is improved.

In other words, the voltage of one terminal of the semiconductor laser 112 is monitored, and the light emission timing of the semiconductor laser 112 is detected using the current-voltage characteristics and the current light output characteristics. Even without detection, the light emission timing can be detected at high speed and with high accuracy.

Therefore, even if there is a time delay between the timing of generation of the light emission start signal and the timing of light emission of the semiconductor laser 112, the measurement of the time difference from the timing of light emission to the timing of light reception should be performed with high accuracy without error. The accuracy of the distance measurement by the laser distance measuring device 100 can be improved.

Note that, in the embodiment of the present invention, specific examples of the drive circuit and the switch are described. Although no specific disclosure is made, it goes without saying that the present invention can be applied to a general driving circuit and a pulse generating circuit used for generating laser light.

Also, in the above-described embodiment, an example has been described in which the laser ranging device 100 detects the light emission timing of the semiconductor laser 112, but other light emitting elements (for example, LEDs) The present invention can be applied to the detection of the light emission timing. Industrial applicability

INDUSTRIAL APPLICABILITY The present invention can be used for a time measuring device for measuring the light emission timing of a light emitting element to measure time, or for distance measurement.

Claims

The scope of the claims

1. A method for detecting a light emission timing of a light emitting element, comprising detecting a voltage applied to the light emitting element, and setting a timing at which the detected voltage reaches a predetermined voltage as a light emission timing of the light emitting element.

2. A light-emitting element, a detection unit that detects a voltage applied to the light-emitting element, and a light-emission timing detection unit that sets a timing at which the detected voltage reaches a predetermined voltage as a light-emission timing of the light-emitting element. An emission timing detector characterized by being provided.

3. A light emitting element that generates a pulsed optical signal with a constant light output when the supplied voltage exceeds a predetermined value, and an irradiation unit that irradiates the target with the pulsed optical signal with a constant light output. A voltage detector that detects a voltage supplied to the light emitting element; a light receiving element that detects a pulsed optical signal reflected from the object; and a voltage detected by the voltage detector that has a predetermined value. A timing unit for measuring a time from when the pulsed optical signal is detected until the pulsed optical signal is detected, and the target object based on the time measured by the timing unit and the speed of the pulsed optical signal. A distance calculating unit for calculating a distance to the distance measuring device.

4. A light emitting element that generates a pulsed optical signal, an irradiator that irradiates the target with the optical signal, a voltage detector that detects a voltage supplied to the light emitting element, and a light that is reflected from the target. A light receiving element for detecting the optical signal that has been detected, and a timer for measuring the time from when the voltage detected by the voltage unit reaches a predetermined value to when the optical signal reflected from the object is detected. A distance calculating unit that calculates a distance to the target object based on the time measured by the timer unit and the optical signal.