Device for measuring distance of object, process for manufacturing optical fiber used in such device, and method for measuring distance of object

Abstract

To provide a device for measuring a distance of an object on which a laser beam modulated and emitted by the device is reflected.SOLUTION: A device 1 comprises an optical fiber 2 into which laser radiation can be coupled, and a main lens 3 from which laser radiation can be emitted along an optical axis 4 of the main lens. The optical fiber 2 is provided with a decoupling surface 5, and a reflective surface 6, in particular an annular surface, is arranged on the decoupling surface 5.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention is directed to an apparatus for measuring the distance of an object, a process for manufacturing an optical fiber for use in such an apparatus, and a method for measuring the distance of an object.

Background Art

[0002] Optical distance meters based on laser measurement are known from the prior art. Such distance meters use the time-of-flight (TOF) principle or phase modulation as the measurement technique. When used particularly in an industrial environment, such measuring devices are exposed to temperature changes, vibrations, and other problems that can affect the measurement accuracy. In addition, since the light emitting surface and the light incident surface are usually not in the same place, the measuring device does not operate at very short distances. Another problem is that a very small deviation in the measuring device leads to a large measurement error at long distances.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Accordingly, an object of the present invention is to create an apparatus for measuring the distance of an object, a process for manufacturing an optical fiber for use in such an apparatus, and a process for measuring the distance of an object that avoids the disadvantages of the prior art. In particular, an apparatus for measuring distance using a related process that can accurately measure under difficult conditions is created.

Means for Solving the Problems

[0004] The object is solved by an apparatus for measuring distance, a process for manufacturing an optical fiber for use in such an apparatus, and a process for measuring distance according to the independent claims.

[0005] In particular, the object is solved by a device for measuring the distance of an object from which the laser radiation modulated and emitted by the device is reflected. The device comprises an optical fiber capable of coupling the laser radiation and a main lens capable of emitting the laser radiation along the optical axis. The optical fiber comprises a decoupling surface, and a reflecting surface, in particular an annular reflecting surface, is arranged on the decoupling surface.

[0006] This type of device enables the laser radiation used for the measurement to be emitted and received again on the same surface of the optical fiber, so that the measurement can also be carried out over short distances. The calibration is optimized such that the reference channel and the measurement channel are substantially identical. Since the transmission channel and the reception channel are focused simultaneously, no adjustment from the transmission axis to the reception axis is necessary. The adjustment is also temperature-stable since the influence of temperature is the same for the transmission channel and the reception channel. The reflecting surface can be, for example, gold plating.

[0007] Using an annular reflecting surface, the laser radiation can be emitted through the center of the optical fiber and, after being reflected by the object to be measured, can be reflected back through the lens to the reflecting surface.

[0008] The decoupling surface can be arranged at a non-perpendicular angle with respect to the optical axis of the optical fiber. The angle can be in the range of 25° to 65°, in particular in the range of 35° to 55°, in particular substantially 52°, with respect to the optical axis of the main lens. Preferably, the sum of the angle of the optical axis of the optical fiber with respect to the optical axis of the main lens and the angle of the decoupling surface with respect to the optical axis of the optical fiber is substantially 45°.

[0009] This means that the reflected laser light does not have to be arranged within the range of the main lens of the device from the reflecting surface of the decoupling surface and can be directed to a receiver which has to be arranged at different positions within the device depending on the angle of the decoupling surface.

[0010] This enables the device to be manufactured more easily and compactly. The laser radiation can be conducted from the reflecting surface to the receiver, whereby the receiver is, in particular, an avalanche photodiode and is preferably arranged at a distance of 0.01 mm to 2 mm, preferably 0.05 mm to 0.3 mm or 0.4 mm to 1 mm, in particular 0.3 mm to 0.6 mm, from the reflecting surface.

[0011] Such a close arrangement of the receiver relative to the reflecting surface ensures that sufficient reflected laser light can be received and processed by the electronic device.

[0012] The receiver can be provided with a hemispherical lens or a spherical lens. The optical fiber can be a single-mode optical fiber, in particular a polarization-maintaining fiber.

[0013] Using a single-mode fiber results in low signal attenuation, little delay shift, and the possibility of using a high bandwidth. Furthermore, the single-mode fiber has a smaller diameter at the light exit. The single-mode fiber can be used to generate an optimally small laser dot on the target surface. Using a polarization-maintaining fiber, outcoupling reflection can be minimized or intentionally controlled.

[0014] A coupling device for laser coupling can be formed on the coupling surface of the optical fiber. This enables the laser light to be optimally coupled into the optical fiber.

[0015] The coupling device can be provided with a spherical lens and / or a cylindrical lens. The coupling device can also be a tapered optical fiber.

[0016] The device can be provided with a laser source, in particular a laser diode, and its light can be coupled into the optical fiber, thereby preferably generating light having a wavelength in the range of substantially 490 nm to 950 nm. In particular, light of 490 to 575 nm and / or 630 to 680 nm and / or 780 to 950 nm can be generated.

[0017] Using this type of laser source, the laser light required for measurement can be optimally generated and transmitted via an optical fiber.

[0018] Alternatively, a fiber laser can be used instead of a laser diode. Since there are no wavelength jumps within the pulse, the fiber laser is particularly suitable for short pulses of less than 100 ps and high-precision measurements. The fiber laser can then replace the optical fiber and can be provided with an output coupling surface according to the invention. Optionally, an optical fiber with a reflector attached can be joined to the fiber laser in the same way as the optical fiber decoupling surface described above.

[0019] The main lens can be at least partially covered with a dispersion sputter on the side facing the optical fiber so as to be able to reflect diffused light. In particular, the dispersion sputter can be printed thereon with an inkjet printer. As the ink for the dispersion sputter, a UV-curable ink, in particular a white ink, can be used. This means that the dispersion sputter can be applied with good reproducibility and is easy to cure.

[0020] This means that a diffusion calibration signal can be obtained from the lens. In particular, 1% to 20% of the lens surface is covered with the dispersion sputter.

[0021] Alternatively, a diffusion reflection foil or a partial mirror coating can be arranged on the transmission region, i.e., the side of the main lens facing the optical fiber.

[0022] By using the diffusion calibration signal, it is compared with the measurement signal and the measurement signal also diffuses. Thereby, the accuracy is improved.

[0023] The calibration signal also eliminates the delay time and changes in the delay of the measurement electronics and is therefore necessary to achieve accurate measurement results, especially within an accuracy range of 0.1 mm. For this purpose, the measurement signal and the calibration signal should be as identical as possible.

[0024] The main lens can be a spherical lens, particularly an achromatic doublet lens. The transmitter is focused by the spherical lens, and the received signal is defocused by the doublet lens outside the sensor range.

[0025] The double lens can also be used to eliminate chromatic aberration and spherical aberration. This also helps to optimize the accuracy.

[0026] The main lens can be an aspherical lens, particularly an aspherical plastic lens. Different focal lengths can be formed within the aspherical surface so that the lens has different focal lengths at the center and the outer ring. This can also be achieved using a hybrid lens. Alternatively, a film or thin glass with a hole in the center can be adhered. The thin glass can also be placed in front of the lens. The aspherical lens can also have different radii in the transmission beam region and the reception beam region. The plastic lens has low manufacturing costs but defocuses within the temperature range. A combination of a spherical glass lens and an aspherical plastic lens is also conceivable. This combines the accuracy of the glass lens and the advantageous manufacturing cost of the plastic lens. In addition, active focus adjustment within the temperature range is possible using the plastic lens.

[0027] The optical axis of the main lens can be arranged neither coaxial nor parallel to the optical axis of the optical fiber, and can have an angle within the range of 1° to 359°, particularly 1° to 179°, preferably + / - 10° to 30° with respect to each other.

[0028] This means that the optical fiber, particularly the optical axis of the optical fiber, is arranged at an angle with respect to the optical axis of the main lens, and as a result, in combination with the non-vertical angle of the decoupling surface, the positioning of the receiver of the measurement light can be optimized.

[0029] Both the receiver and the main lens have mounts, and each of them has a coefficient of thermal expansion greater than that of the holder connecting the mounts.

[0030] The mount can be made of, for example, aluminum or an aluminum alloy, or magnesium or a zinc alloy. The holder connecting the socket can be, for example, a carbon fiber tube, or a nickel steel alloy, titanium steel, or chromium steel. The decisive factor here is the difference in the coefficient of thermal expansion between the materials.

[0031] The device also includes a signal processing device and signal processing electronics. In particular, the signal processing electronics includes a single-channel receiver chain in which the calibration signal and the measurement signal are sequentially time-shifted. The signal processing electronics must have a high bandwidth especially for short measurement distances.

[0032] The signal processing device enables the detection of multiple reflections. The object is further solved by a process for manufacturing an optical fiber using the device described above. In the process, in particular, the decoupling surface of the optical fiber is ground at a non-perpendicular angle to the optical axis of the optical fiber, the decoupling surface is coated with a reflective layer, and the reflective layer is removed from the decoupling surface within the transmission range around the center of the optical fiber by transmitting UV light into the optical fiber, so that only the intermediate range of the reflective layer is removed again.

[0033] In this way, the decoupling surface of the optical fiber can be coated with an annular reflective layer, but the center remains transparent to the transmission radiation. Preferably, the UV laser is temporarily coupled to the optical fiber by splicing so that the applied reflective layer can be removed by the UV laser. The removed layer has a diameter of substantially about 5 μm. As an alternative to splicing in, a fiber connector can also be provided, through which the UV laser and the red measurement laser can be exchanged.

[0034] A process for measuring the distance of an object from which a modulated and emitted laser beam is reflected by the device described above, whereby a laser source generates modulated laser light as transmitted radiation, the transmitted radiation is coupled into an optical fiber, the transmitted radiation is coupled out of the optical fiber through a transmission region in a decoupling plane, a small portion of the transmitted radiation is coupled out of the optical fiber, in particular, a small portion of the transmitted radiation is reflected by the inside of the main lens, the transmitted radiation passes through the main lens, the transmitted radiation is reflected by the object, the reflected laser light passes through the main lens as received radiation, the received radiation is reflected by a reflective layer of the decoupling plane and is directed towards a receiver.

[0035] This process enables accurate distance measurement with little dependence on environmental factors. The present invention will be described in more detail below with the aid of the figures. It shows the following.

Brief Description of the Drawings

[0036]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0037] Figure 1 shows a diagram of the optical elements of apparatus 1. Apparatus 1 includes an optical fiber 2 and a main lens 3. The optical axes of the main lens 3 and the optical fiber 2 are not identical or coaxial. Both the main lens 3 and the optical fiber 2 are held within respective sockets 11, 12, whereby the socket 11 of the optical fiber 2 also includes a receiver 8. Laser light having a wavelength within the range of 490 nm to 950 nm is emitted from the optical fiber 2 and sent as transmitted radiation 13 through the main lens 3 to an object to be measured. The object reflects the radiation back, whereby the radiation is guided as received radiation 14 through the main lens 3 and returned to the receiver 8 (see Figure 5). The main lens 3 is covered on the side facing the optical fiber 2 with small white dots as a dispersion sputter, so that a small portion of the transmitted radiation 13 is immediately reflected back. This reflected radiation is used as calibration radiation. The dispersion sputter diffuses the calibration radiation. The diffused calibration radiation is also detected by the receiver 8 (see Figure 5) and further processed within the electronics.

[0038] Figure 2 shows the apparatus from Figure 1 having a holder 15 connecting the mount 11 of the receiver 8 and the optical fiber 2 and the mount 12 of the main lens 3. The coefficient of thermal expansion of the mounts 11, 12 is equal to or greater than the coefficient of thermal expansion of the holder 15 of the mounts 11, 12. In this case, the mounts 11, 12 are made of an aluminum alloy and the holder 15 is made of carbon fiber.

[0039] Figure 3 shows a schematic diagram of the received radiation 14 directed from a main lens (not shown) towards a reflecting surface 6 and from there towards the receiver 8. The receiver 8 is an avalanche photodiode.

[0040] Figure 4 shows a schematic diagram of the received beam 14 on the main lens 3. Figure 5 shows a schematic view of an apparatus 1 having an optical fiber 2 and a main lens 3. The optical fiber 2 has an optical axis 7 that is not the same as the optical axis 4 of the main lens 3. The angle between the optical axes is substantially within the range of 20°, particularly 16° - 20°. The optical fiber 2 also has a coupling surface 9 for laser light. The laser light is generated by a laser source 10 that is a laser diode. The optical fiber 2 has an out-coupling surface 5 having a non-perpendicular angle with respect to the optical axis 7 of the optical fiber and a non-perpendicular angle with respect to the optical axis 4 of the main lens 3. The combination of the two angles substantially results in a 45° angle of the decoupling surface with respect to the optical axis 4 of the main lens 3. The angle between the optical axis 7 of the optical fiber 2 and the optical axis 4 of the main lens is 16°, 29° grinding angle of the optical fiber, i.e., the angle between the optical axis 7 of the optical fiber and the decoupling surface 5, and 45° between the reflecting surface 6 and the optical axis of the main lens 3. Alternatively, a 50° angle between the reflecting surface 6 and the optical axis of the main lens 3 can be considered due to an angle of 18.3° between the optical axis of the optical fiber 2 and the optical axis of the main lens 3 and an angle of 31.7° between the grinding angles of the optical fiber 2. Another alternative is a 52° angle between the reflecting surface 6 and the optical axis of the main lens 3 due to an angle of 19.2° between the optical axis 7 of the optical fiber 2 and the optical axis 4 of the main lens 3 and an angle of 32.8° of the optical fiber 2. At these angles, the components of the receiver 8 are not within the light cone of the received radiation 14 or the transmitted radiation 13. The decoupling surface 5 is also coated annularly with a reflecting surface 6. This means that the radiation generated by the laser diode 10 can pass through the optical fiber 2 and through the intermediate decoupling surface 5 onto the main lens 3. This transmitted radiation 13 (see Figure 1) transmitted through the main lens 3 is then reflected by an object and returns as received radiation 14 (see Figure 1) onto the exit surface 5 through the main lens 3. The reflecting surface 6 of the exit surface 5 (see Figure 7) reflects the light reflected by the object to the receiver 8. In addition, the main lens 3 has small white diffusely reflecting colored dots as a dispersion sputter on the side facing the optical fiber 2, and they immediately reflect the transmitted radiation 13 from the optical fiber 2 and thus send the diffusely reflected light back as a calibration signal. The dispersion sputter reflects 5% - 15% of the emitted laser output. The signal processing device and signal processing electronics are connected to the receiver 8.The signal can be processed by these elements and thus the distance of the object can be determined.

[0041] Figure 6 shows an optical fiber 2 having a decoupling surface 5. The decoupling surface 5 is arranged at a non-perpendicular angle with respect to the optical axis 7 of the optical fiber 2. This means that the reflecting surface 6 on the decoupling surface 5 can reflect the received light and direct the light to the receiver 8 without the need to return the light to the optical fiber 2. The optical fiber 2 also has an input coupling surface 9 which can include an input coupling device.

[0042] Figure 7 shows a cross-section of the optical fiber 2 having a decoupling surface 5. The ring-shaped reflecting surface 6 is arranged on the decoupling surface 5. The transmitted radiation 13 can emerge from the optical fiber 2 within the central circular region, and the received radiation 14 is reflected by the reflecting surface 6 and returned to the receiver 8.

[0043] The transmission and reception of the radiation are not shown in FIGS. 6 and 7.

Claims

1. 1. A device (1) for measuring the distance of an object to which a laser beam modulated and emitted by the device (1) is reflected, the device (1) comprising an optical fiber (2) into which the laser radiation can be coupled and a main lens (3) through which the laser radiation can be emitted along an optical axis (4) of the main lens, characterized in that the optical fiber (2) has an output coupling surface (5) and a reflecting surface (6), in particular an annular surface, is arranged on the output coupling surface (5).

2. 2. The device (1) according to claim 1, characterized in that the decoupling surface (5) has a non-perpendicular angle with respect to the optical axis (7) of the optical fiber.

3. 10. The device (1) according to any one of the preceding claims, characterized in that the laser radiation can be transmitted from the reflecting surface (6) to a receiver (8), the receiver (8) being in particular an avalanche photodiode, preferably arranged within a distance range of 0.01 to 2 mm, preferably 0.05 to 0.3 mm or 0.4 to 1 mm, in particular 0.3 to 0.6 mm from the reflecting surface (6).

4. 10. The device (1) according to any one of the preceding claims, characterized in that the optical fiber (2) is a single-mode optical fiber, in particular a polarization-maintaining fiber.

5. 10. The device (1) according to any one of the preceding claims, characterized in that the optical fiber (2) is provided with a coupling device on its coupling surface (9).

6. The device (1) according to any one of the preceding claims, characterized in that the device (1) comprises a laser source (10), in particular a laser diode, the light of which can be coupled into the optical fiber (2) and which can be generated by preferred light having a wavelength substantially within the range of 490 to 950 nm.

7. 10. The device (1) according to any one of the preceding claims, characterized in that the main lens (3) is at least partially covered with scattered sputters on the side facing the optical fiber (2) so as to be able to reflect diffuse light.

8. 10. Apparatus (1) according to any one of the preceding claims, characterized in that the main lens (3) is a spherical lens, in particular an achromatic doublet lens.

9. Device (1) according to any one of the preceding claims, characterized in that the main lens (3) is an aspheric lens, in particular an aspheric plastic lens.

10. 10. The device (1) according to any one of the preceding claims, characterized in that the optical axis (4) of the main lens is arranged neither coaxially nor parallel to the optical axis (7) of the optical fiber, in particular having an angle relative to one another in the range of 1 to 359°, in particular 1 to 179°, preferably + / - 10° to 30°.

11. 10. The device (1) according to any one of the preceding claims, characterized in that both the receiver (8) and the main lens (3) are held in mounts (11, 12) having a higher coefficient of thermal expansion than the holder (13) connecting the mounts.

12. A process for manufacturing an optical fiber for use in a device (1) according to any one of claims 1 to 8, comprising: in particular, the decoupling surface (5) of said optical fiber (2) is ground at a non-perpendicular angle to said optical axis (7) of said optical fiber (2); - said decoupling surface (5) is coated with a reflective layer (6), - removing the reflective layer from the decoupling surface (5) in a transmission range around the center of the optical fiber (2) by introducing UV light into the optical fiber (2), so that only the central range of the reflective layer (6) is removed again; A process characterized in that

13. A process for measuring the distance of an object to which a laser beam modulated and emitted by a device (1) according to any one of claims 1 to 9 is reflected, comprising: - a laser source (10) generating modulated laser light as transmitted radiation, - said transmission radiation is coupled into said optical fiber (2), - the transmission radiation is coupled out of the optical fiber (2) through the transmission region (5a) in the decoupling region (5), - the transmitted radiation passes through the main lens (3), - the transmitted radiation is reflected by an object, - the reflected laser light passes through the main lens (3) as received radiation, - the received radiation is at least partially reflected at the reflective layer (6) of the decoupling surface (5) and directed towards a receiver (8), process.

14. 1. A device (1) for measuring the distance of an object to which a laser beam modulated and emitted by the device (1) is reflected, the device (1) comprising an optical fiber (2) into which laser radiation can be coupled, and a main lens (3) through which the laser radiation can be emitted along an optical axis (4), characterized in that the laser radiation can be coupled back into the optical fiber (2) through the main lens (3) after reflection at the object, and the reflected light can be detected by a receiver (8) after passing through the optical fiber (2).

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