JPS61105417A - Distance measuring instrument - Google Patents

Abstract

PURPOSE:To detect the displacement with high precision by providing a means stopping the detection of a displacement detecting signal when background light becomes more than a specified level in distance measuring instrument measuring the displacement from a datum plane of an object. CONSTITUTION:An object W1 is emitted and worked by laser light 1 for working. Further, a laser emitting source for measurement is provided on a working head 3 and its laser irradiates the working point of the object surface W1 to detect the displacement of height of the datum plane. A reflected beam from that point is made incident on a position detecting element 7 and displacement detection electric currents Ia, Ib are obtained and then, converted into displacement detection voltages Va, Vb with I/V converters 8, 9. At this time, the background light voltage is detected with a comparator 18 and the displacement detecting signal is stopped when the background light voltage is attained to more than the specified level. Accordingly, since the influence of the background light is eliminated from the displacement detecting signal, the displacement of the datum plane of the object can be detected with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distance measuring device that measures the displacement of an object from a reference plane.

[Conventional technology]

Conventionally, the displacement of an object from a reference plane has been measured mechanically. However, in the case of mechanical measurement, there are problems such as time required for setting and measurement, and direct contact with the object, which may damage the object. Therefore, a distance measuring device shown in FIG. 4 was proposed. In FIG. 4, 1 is a processing laser beam, 2 is a processing lens that focuses the processing laser beam 1, 3 is a processing head, 4 is a light source that emits a beam as a measurement laser beam, and 5 is from the light source 4. A light projecting lens that focuses the emitted beam, 6 a light receiving lens that captures a radiation beam image on the surface of the object W1, and 7 a position detection element that generates an electric signal according to the imaging position of the radiation beam image. P S D (Positi.

n 5ensistive Detector), 8
9.9 is the displacement detection current Ta, I output from PSD7
I/V converter that converts b into displacement detection voltages Va and Vb as displacement detection signals and also serves as a preamplifier, l0
11.12 is a V/I converter that inputs a laser drive voltage and outputs a laser drive current 1d, and 11.12 is a displacement detection voltage Va, Vb.
13.14 is a bandpass filter that performs bandpass filtering on the output of the amplifier 8.9. 15 is a displacement detection voltage Va as an analog signal.

an A/D converter that converts Vb into a digital signal; 16 is a D/A converter that converts a laser drive signal as a digital signal into a laser drive voltage Vd as an analog signal;
Reference numeral 17 denotes a high-speed calculation processor, S, which performs setting of the light emission timing of the light source 4, calculation of the displacement ΔH of the surface of the object W1, etc.
1 is a parallel/serial conversion switch that converts the displacement detection voltages Va, Vb as parallel signals into serial signals.

The operation of the device configured in this way will be explained. First, the operation of the optical system will be explained using FIG. 1. The beam emitted from the light source 4 becomes a light spot of an appropriate size by the projection lens 5 and is irradiated onto the surface of the object W1. The light receiving lens 6 images this light spot, and the PSD 7
An image of a light spot is formed on the light receiving surface. The PSD 7 generates an electric signal depending on the imaging position of the optical spot image. That is, the current [a] generated in the two electrodes of the PSD 7.

Based on the rbO value, the imaging position P of the optical spot image is P= (I
a−Ib)/(la+Ib). In the above equation, since the output of the PSD 7 is proportional to the position and intensity of the light spot image, the term (I a + I b), which corresponds to the change in the intensity of the light spot image, is introduced to calculate the light The output is proportional only to the spot position.

Next, the operation of the electrical system will be explained using FIG. Figure 3 (al indicates blinking of the light source 4, Figure 3 (b), ((
Previous displacement detection currents 1a, lb and displacement detection voltages Va,
The waveform of Vb is shown.

First, the operation when the surface of the object Wl is on the reference plane will be explained. The light input to the light receiving lens 6 is irradiated onto the PSD 7 in the form of a spot of light. When the surface of the object W1 is on the reference plane, if the center of gravity of this light is set to be the center P1 of the PSD 7, the displacement detection current 1
a and Tb are equal to each other, and displacement detection voltages Va and Vb
are also equal to each other. The displacement detection voltages Va and Vb are processed by an amplifier 11.12 and a bandpass filter 13.14, and then converted into a serial signal by a parallel/serial conversion switch S1, and converted into a digital signal by an A/D converter 15. The data is then input to the high-speed arithmetic processor 17. The high-speed arithmetic processor 17 calculates the displacement ΔH using the displacement detection voltages Va and Vb converted into digital signals, but in this case, V
Since a=Vb, the displacement ΔH=0.

Next, the operation when the object surface is displaced downward by ΔH will be described. In this case, the light scattered on the surface of the object W1 passes through the light receiving lens 6 and then moves from the center P1 of the PSD 7 to the
The light is incident on a distant point P2 in the form of a spot. Displacement detection currents Ia and Ib are outputted by this incident light, but the displacement detection currents a and Ib have different values. Since ΔH and X are in a proportional relationship, by calculating X, ΔH
can be calculated and output. In response to this output signal, a drive means (not shown) is operated to lower the machining head 3 and make the displacement ΔH zero. In this way, the distance between the processing head 3 and the surface of the object W1 is always kept constant.

[Problem that the invention seeks to solve]

In a device that operates in this manner, there is a problem in that background light from the measurement laser beam emitted from the light source 4 is incident on the PSD 7, causing an error in displacement measurement. Also, if the background light is large in the form of a spike, the bandpass filter 13
．． 14 causes a large-amplitude damped vibration, which causes it to no longer function as a bandpass filter, which also causes errors.

The present invention has been made in view of these points, and an object of the present invention is to provide a distance measuring device that does not cause errors due to background light in displacement measurement.

[Means for solving problems]

In order to achieve such an object, the present invention provides a distance measuring device that is provided with a stop means that stops the detection of the displacement detection signal when the background light reaches a predetermined level.

[Effect]

In the present invention, the displacement detection signal is detected at a timing that is not affected by background light.

〔Example〕

FIG. 1 shows an embodiment in which a distance measuring device according to the present invention is applied to a laser processing machine. In FIG. 1, 18 is a comparator that outputs a signal when the level of background light exceeds a predetermined first level, and 19 is a timer that starts time measurement based on the signal output from the comparator 18 and outputs a control signal for a certain period of time. , 20.21 are analog switches whose gates are closed by a control signal, and comparators 18. Timer 19. The analog switch 20 constitutes a stopping means. In FIG. 1, the same or equivalent parts as in FIG. 3 are given the same reference numerals.

The operation of the apparatus configured in this way will be explained using FIG. 1 and FIG. 3. The background light emitted from the surface of the object W1 by the irradiation of the processing laser beam 1 is PSD7.
3(d), the PSD 7 outputs a background light signal that gradually attenuates from a large amplitude as shown in FIG. 3(d), and this background light signal is input to the comparator 18. This background optical signal includes displacement detection voltages Va and Vb, but since the displacement detection voltages Va and Vb are so large that they can be ignored, the displacement detection voltages Va and Vb are shown in FIG. 3(d).
'Not shown. The comparator 18 outputs a timer drive signal when the background light signal reaches a first level T111 or higher shown in 3(d). The timer 19 starts measuring time when the timer drive signal rises, and stops the measurement when the set time T is reached. During the time T from the start to the stop of this time measurement, the timer 19 operates as shown in Fig. 3 (
Outputs the gate close signal shown in el and closes the analog switch 2.
0 to the gate closed state. In this case, the set time T is set to the time during which the background light attenuates upward. When background light is generated in this way, by closing the gate of the analog switch 20 and stopping the detection of the displacement detection signal, it is possible to prevent errors in measuring the displacement of the object W1 due to the background light. Also, the time T during which the timer 19 outputs the gate close signal
By making it variable, it is possible to deal with various background lights.

Next, another embodiment is shown in FIG. In Figure 2, 22
is a comparator that outputs a gate close signal from when the background light signal becomes below a predetermined second level until it becomes below a predetermined second level lower than the first level. In FIG. 2, the same or equivalent parts as in FIG. 1 are given the same reference numerals.

The comparator 22 outputs a second level TH from when the background light signal reaches the second level TH1 shown in FIG. 3(d).
The gate close signal is output for the time Tw until the value becomes 2.

This gate close signal causes the analog switch 20 to close the gate. When background light occurs like this,
By closing the gate of the analog switch and stopping detection of the displacement detection signal, it is possible to prevent errors in measuring the displacement of the object due to background light.

〔Effect of the invention〕

As explained above, in the present invention, the background light is blocked by the stopping means that stops the detection of the displacement detection signal for a predetermined time when the background light reaches a predetermined level, so that the displacement measurement accuracy can be improved. There is.

[Brief explanation of the drawing]

Fig. 1 is a block system diagram showing one embodiment in which the distance measuring device according to the present invention is applied to a laser processing machine, Fig. 2 is a program system diagram showing another embodiment, and Fig. 3 is a diagram of these waveforms. 4 are block system diagrams showing a case where a conventional distance measuring device is applied to a laser processing machine. 1... Laser light for processing, 2... Lens for processing,
3... Processing head, 4... Light source, 5... Emitter lens, 6... Light receiving lens, ? -...PSD,
8.9... I/V converter, lO... V/I converter, 11.12... amplifier, 13,14.・・・
・Band leaker, 15... A/D converter, 16...
・D/A converter, 17...high-speed calculation processor, 1
8... Comparator, 19... Timer, 20.
21...Analog switch, SL...Parallel/serial conversion switch.

Claims (3)

[Claims] (1) Background of a distance measuring device that calculates the displacement of an object from a reference plane by irradiating the object with a spot of measurement laser light and determining the center of gravity of the returning scattered light on a position detection element. A distance measuring device characterized by comprising a stop means for stopping detection of a displacement detection signal when light reaches a predetermined first level or higher. (2) The distance measuring device according to claim 1, wherein the stopping means releases the stopping operation after a certain period of time from when the background light becomes equal to or higher than the first level. (3) The distance measuring device according to claim 1, wherein the stopping means releases the stopping operation when the background light becomes equal to or less than a second level.