Device for measuring the distance of an object, method for using an optical fiber for producing the device and method for measuring the distance of an

Abstract

The invention discloses a device (1) for measuring the distance of an object on which a laser beam modulated and emitted by the device (1) is reflected. The device comprises an optical fiber (2) capable of coupling laser radiation and a main lens (3) through which the laser radiation can be emitted along an optical axis (4). The optical fiber (2) comprises a decoupling surface (5) on which a reflective surface (6), in particular a ring-shaped surface, is arranged.

Description

Technical Field

[0001] The invention relates to a device for measuring the distance of an object, a method for producing an optical fiber used in such a device and a method for measuring the distance of an object. Background Art

[0002] Optical distance meters based on laser measurement are known in the prior art. Such distance meters use the time-of-flight (TOF) principle or phase modulation as the measuring technique. Especially when used in industrial environments, such measuring devices are subject to temperature changes, vibrations and other challenges that affect the measuring accuracy. Furthermore, the optical light output surface and the optical light input surface are usually not provided in the same position, which makes the measuring device unable to work over very short distances. Another challenge is that even very small deviations in the measuring device can lead to large measuring errors over long distances. Summary of the invention

[0003] The object of the present invention is therefore to create a device for measuring the distance of an object, a method for producing an optical fiber used in such a device and a method for measuring the distance of an object which avoid the disadvantages of the prior art. In particular, it is desirable to create a device for measuring distances and a related method which are capable of performing accurate measurements under challenging conditions.

[0004] The objects of the present invention are achieved by a device for measuring distance, a method for producing an optical fiber used in the device and a method for measuring distance.

[0005] In particular, the object of the invention is achieved by a device for measuring the distance of an object on which 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 an optical axis. The optical fiber comprises a decoupling surface, wherein a reflective surface, in particular an annular reflective surface, is arranged on the decoupling surface.

[0006] This type of device can transmit and receive the laser radiation for the measurement again on the same surface of the optical fiber, so that measurements can also be carried out over short distances. Calibration is optimized, because the reference channel and the measuring channel are almost identical. The transmitting and receiving channels are focused simultaneously, so that no adjustment from the transmitting axis to the receiving axis is necessary. This adjustment is also temperature-stable, because the temperature influences are the same for the transmitting and receiving channels. The reflective surface can be, for example, gold-coated.

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

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

[0009] This means that the reflected laser light can be directed from the reflective surface of the decoupling surface to a receiver which does not have to be arranged within the range of the device's main lens, but can be arranged at a different location within the device depending on the angle of the decoupling surface.

[0010] This makes the device easier to manufacture and more compact.

[0011] The laser radiation can be conducted from the reflective surface to a receiver, wherein 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 reflective surface.

[0012] The placement of the receiver so close to the reflecting surface ensures that enough of the reflected laser light is received and can be processed by the electronics.

[0013] The receiver may include a hemispherical lens or a spherical lens.

[0014] The optical fiber may be a single mode optical fiber, in particular a polarization maintaining optical fiber.

[0015] The use of single-mode fiber results in low signal attenuation, virtually no delay offset, and the ability to use a high bandwidth. In addition, single-mode fiber has a smaller diameter of the light exit port. Single-mode fiber can be used to produce an optimally small laser spot on the target surface. Using polarization-maintaining fiber, outcoupling reflections can be minimized or intentionally controlled.

[0016] The coupling device for laser coupling can be formed on the coupling surface of the optical fiber. This allows the laser to be optimally coupled into the optical fiber.

[0017] The coupling device may include a spherical lens and / or a cylindrical lens. The coupling device may also be a tapered optical fiber.

[0018] The device may comprise a laser source, in particular a laser diode, the light of which may be coupled into an optical fiber and thereby preferably generate light having a wavelength substantially in the range of 490 nm to 950 nm. In particular, light having a wavelength of 490-575 nm and / or 630-680 nm and / or 780-950 nm may be generated.

[0019] With this type of laser source, the laser light required for the measurement can be optimally generated and emitted via the optical fiber.

[0020] Alternatively, a fiber laser can be used instead of a laser diode. Fiber lasers are particularly suitable for short pulses of less than 100 ps and for high precision measurements, since there are no wavelength jumps within the pulse. Fiber lasers can therefore replace optical fibers and include decoupling surfaces according to the present invention. Optionally, the optical fiber to which the reflector is connected is fused to the fiber laser, similar to the fiber decoupling surface described above.

[0021] The main lens may at least partially cover a diffuse reflection dot on its side facing the optical fiber so that diffuse light can be reflected. In particular, the diffuse reflection dot can be printed with an inkjet printer. Ultraviolet (UV) curable ink, in particular white ink, can be used as the ink for the diffuse reflection dot. This means that the diffuse reflection dot can be applied repeatedly and is easy to cure.

[0022] This means that a diffuse calibration signal can be obtained from the lens. Specifically, 1% to 20% of the lens surface is covered by diffuse reflection points.

[0023] Alternatively, a diffusely reflecting foil or a partially mirrored coating may be arranged in the emission zone, ie the side of the primary lens facing the optical fiber.

[0024] By using a diffuse reflectance calibration signal, the measurement signal, which is also diffuse reflectance, can be compared to improve accuracy.

[0025] The calibration signal is necessary to eliminate the delay times of the measuring electronics and the variations of the delay and thus achieve precise measuring results, in particular within an accuracy range of 0.1 mm. For this purpose, the measuring signal and the calibration signal should be as identical as possible.

[0026] The main lens can be a spherical lens, in particular an achromatic doublet. The emission is focused by the spherical lens and the received signal is defocused outside the sensor range by the doublet.

[0027] The dual lenses can also be used to eliminate chromatic and spherical aberrations. This also helps to optimize accuracy.

[0028] The main lens may be an aspherical lens, in particular an aspherical plastic lens.

[0029] Different focal lengths can be formed in an aspherical lens, so that the center of the lens and the annular area outside the center have different focal lengths. This can also be achieved using a hybrid lens. Alternatively, a film or thin glass with a hole in the center can be glued on. Thin glass can also be placed in front of the lens. Aspherical lenses can also have different radii in the area of ​​the emitted beam and the area of ​​the received beam. Plastic lenses are cheap to manufacture, but they are defocused within the temperature range. A combination of spherical glass lenses and aspherical plastic lenses is also conceivable. This combines the precision of glass lenses with the better manufacturing costs of plastic lenses. In addition, active focusing within the temperature range is also possible with plastic lenses.

[0030] The optical axis of the main lens can be arranged neither coaxially nor parallel to the optical axis of the optical fiber, but can have an angle in the range of 1° to 359°, in particular 1° to 179°, preferably + / -10° to 30° relative to each other.

[0031] This means that the optical fiber, in particular the optical axis of the optical fiber, is arranged at an angle to the optical axis of the main lens, such that, in combination with the non-perpendicular angle of the decoupling surface, the positioning of the receiver of the measurement light can be optimized.

[0032] The receiver and primary lens both have mounts, each of which has a greater coefficient of thermal expansion than a bracket to which the mount is attached.

[0033] The mounting base can be made of aluminum or an aluminum alloy, for example, or a magnesium or zinc alloy. The bracket connecting the support can be, for example, a carbon fiber tube, or a nickel steel alloy, titanium or chrome steel. The decisive factor here is the difference in the thermal expansion coefficients between the materials.

[0034] The device also includes a signal processing device and signal processing electronics. In particular, the signal processing electronics includes a single-channel receiver chain with serial time shifting of the calibration signal and the measurement signal. The signal processing electronics must have a high bandwidth, especially when measuring over short distances.

[0035] Signal processing equipment is capable of detecting multiple reflections.

[0036] The object is further achieved by a method for producing an optical fiber using the above-mentioned device, in particular, grinding the decoupling surface of the optical fiber at a non-perpendicular angle to the optical axis of the optical fiber, the decoupling surface is coated with a reflective layer, and ultraviolet light is irradiated into the optical fiber to remove the reflective layer from the decoupling surface within an emission range around the center of the optical fiber, so that only the middle range of the reflective layer is removed again.

[0037] In this way, the decoupling surface of the optical fiber can be coated with an annular reflective layer, while the center is still transparent for the emitted radiation. Preferably, the UV laser is temporarily coupled into the optical fiber by means of fusion splicing, so that the applied reflective layer can be removed with the UV laser. The removed reflective layer has a diameter of substantially about 5 micrometers. As an alternative to fusion splicing, a fiber connector can also be provided, by means of which the UV laser and the red measuring laser can be exchanged.

[0038] A method for measuring the distance of an object, wherein a modulated and emitted laser beam is reflected by the above-mentioned device, wherein a laser source generates modulated laser light as emission radiation, the emission radiation is coupled into an optical fiber, the emission radiation is coupled out of the optical fiber through an emission region of a decoupling surface, and a small portion of the emission radiation is coupled out of the optical fiber, in particular a small portion of the emission radiation is reflected by the inside of a main lens, the emission radiation passes through the main lens, the emission radiation is reflected by an object, the reflected laser light passes through the main lens as reception radiation, and the reception radiation is reflected at a reflection layer of the decoupling surface and conducted to a receiver.

[0039] This method enables accurate distance measurements that are largely unaffected by environmental factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be explained in more detail below with the help of diagrams. The diagrams show:

[0041] Figure 1 : Representative schematic diagram of the optical components of the device,

[0042] Figure 2 : Representative schematic diagram of the optics of the device with a stand,

[0043] Figure 3 : Representative schematic diagram of the reflection surface and the path of the received beam,

[0044] Figure 4 : Representative schematic diagram of the primary lens and the path of the received beam,

[0045] Figure 5 : Representative schematic diagram of the device,

[0046] Figure 6 : Representative schematic diagram of optical fiber,

[0047] Figure 7 : Representative schematic of the decoupling surface. DETAILED DESCRIPTION

[0048] Figure 1A schematic diagram of the optical elements of the device 1 is shown. The device 1 comprises 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. The main lens 3 and the optical fiber 2 are mounted in supports 11 and 12, respectively, wherein the support 11 of the optical fiber 2 also comprises a receiver 8. Laser light with a wavelength in the range of 490 nm to 950 nm is emitted from the optical fiber 2 and is emitted in the form of emitted radiation 13 via the main lens 3 onto the object to be measured. The object reflects the radiation back, wherein it is guided back to the receiver 8 as received radiation 14 via the main lens 3 (see Figure 5 ). The side of the main lens 3 facing the optical fiber 2 is covered with small white dots, which act as diffuse reflection dots, so that a small part of the emitted radiation 13 is immediately reflected back again. This reflected radiation is used as calibration radiation. The diffuse reflection dots diffuse the calibration radiation. The diffuse calibration radiation is also detected by the receiver 8 (see Figure 5 ) and further processed in electronic devices.

[0049] Figure 2 Shown is a diagram from a Figure 1 The bracket 15 connects the mounting base 11 of the receiver 8 and the mounting base 12 of the optical fiber 2 and the main lens 3. The thermal expansion coefficient of the mounting bases 11 and 12 is greater than or equal to the thermal expansion coefficient of the bracket 15 of the mounting bases 11 and 12. In this case, the mounting bases 11 and 12 are made of aluminum alloy, and the bracket 15 is made of carbon fiber.

[0050] Figure 3 A representative schematic diagram is shown of received radiation 14 directed from a primary lens (not shown) onto a reflective surface 6 and from there onto a receiver 8. The receiver 8 is an avalanche photodiode.

[0051] Figure 4 A representative schematic diagram of the received light beam 14 on the main lens 3 is shown.

[0052] Figure 5A representative schematic diagram of a device 1 with an optical fiber 2 and a main lens 3 is shown. The optical fiber 2 has an optical axis 7 which is not completely identical to the optical axis 4 of the main lens 3. The angle between the optical axes is substantially 20°, in particular in the range of 16° to 20°. The optical fiber 2 also has a coupling surface 9 for laser light. The laser light is generated by a laser source 10 (laser diode). The optical fiber 2 has a decoupling surface 5 which is at a non-perpendicular angle to the optical axis 7 of the optical fiber and at a non-perpendicular angle to the optical axis 4 of the main lens 3. The combination of these two angles is such that the decoupling surface is at a 45° angle 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°, the grinding angle of the optical fiber is 29°, i.e. the angle between the optical axis 7 of the optical fiber and the decoupling surface 5, and the angle between the reflecting surface 6 and the optical axis of the main lens 3 is 45°. Alternatively, it is conceivable that the angle between the reflecting surface 6 and the optical axis of the main lens 3 is 50°, the angle between the optical axis of the optical fiber 2 and the optical axis of the main lens 3 is 18.3°, and the grinding angle is 31.7°. Another alternative is that the angle between the reflecting surface 6 and the optical axis of the main lens 3 is 52°, the angle between the optical axis 7 of the optical fiber 2 and the optical axis 4 of the main lens 3 is 19.2°, and the grinding angle is 32.8°. At these angles, no part of the receiver 8 is within the light cone of the received or emitted radiation 14, 13. The decoupling surface 5 is also coated with a reflecting surface 6 in an annular manner. This means that the radiation generated by the laser diode 10 can be guided through the optical fiber 2 and directed onto the main lens 3 via the decoupling surface 5 in the middle. The emitted radiation 13 emitted by the main lens 3 (see Figure 1 ) is then reflected by the object and is received as radiation 14 (see Figure 1 ) is returned to the output surface 5 through the main lens 3. The reflecting surface 6 of the output surface 5 (see Figure 7 ) reflects the light reflected by the object onto the receiver 8. In addition, the main lens 3 has a diffusely reflecting small white spot on the side facing the optical fiber 2 as a diffuse reflection spot, which immediately reflects the transmitted radiation 13 from the optical fiber 2 and thus emits diffusely reflected light back as a calibration signal. The diffuse reflection spot reflects 5% to 15% of the laser transmission power. The signal processing device and the signal processing electronics are connected to the receiver 8. The signals processed by these elements and thus the distance of the object can be determined.

[0053] Figure 6 An optical fiber 2 is shown with a decoupling surface 5. The decoupling surface 5 is arranged at a non-perpendicular angle to the optical axis 7 of the optical fiber 2. This means that the reflective surface 6 on the decoupling surface 5 can reflect received light and guide it to the receiver 8 without the light returning to the optical fiber 2. The optical fiber 2 also has an input coupling surface 9, which may include an input coupling device.

[0054] Figure 7A cross section of an optical fiber 2 is shown with a decoupling surface 5. An annular reflecting surface 6 is arranged on the decoupling surface 5. Transmitted radiation 13 may emerge from the optical fiber 2 in a central circular area and received radiation 14 is reflected back onto the reflecting surface 6 on the receiver 8.

[0055] Figure 6 and Figure 7 The transmitted and received radiation is not shown.

Claims

1. A device (1) for measuring the distance of an object, wherein a laser beam modulated and emitted by the device (1) is reflected on the object, the device comprising a light-guiding optical fiber (2) capable of coupling the laser radiation and a main lens (3), through which the laser radiation can be emitted along the optical axis (4) of the main lens, characterized in that The optical fiber (2) comprises a decoupling surface (5), wherein a reflecting surface (6), in particular a toroidal surface, is arranged on the decoupling surface (5).

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

3. The device (1) according to one of the preceding claims, characterized in that The laser radiation can be conducted from the reflective surface (6) to a receiver (8), wherein the receiver (8) is in particular an avalanche photodiode and is preferably arranged at a distance from the reflective surface (6) in the range of 0.01-2 mm, preferably 0.05-0.3 mm or 0.4-1 mm, in particular 0.3-0.6 mm.

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

5. The device (1) according to one of the preceding claims, characterized in that The optical fiber (2) comprises a coupling device on a coupling surface (9).

6. Device (1) according to 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 preferably generate light having a wavelength substantially in the range of 490 to 950 nanometers.

7. Device (1) according to one of the preceding claims, characterized in that The side of the main lens (3) facing the optical fiber (2) at least partially covers the diffuse reflection point, so that diffuse light can be reflected.

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

9. The device (1) according to any one of the preceding claims 1 to 7, characterized in that The main lens (3) is an aspherical lens, in particular an aspherical plastic lens.

10. The device (1) according to one of the preceding claims, characterized in that The optical axis (4) of the main lens is neither coaxially nor parallelly arranged relative to the optical axis (7) of the light-guiding optical fiber, but in particular has an angle in the range of 1-359°, in particular 1-179°, preferably + / -10° to 30° relative to each other.

11. The device (1) according to one of the preceding claims, characterized in that Both the receiver (8) and the primary lens (3) are held in mounts (11, 12) having a greater coefficient of thermal expansion than a bracket (13) to which they are connected.

12. Method for producing an optical fiber for use in the device (1) according to any one of claims 1 to 8, characterized in that The decoupling surface (5) of the optical fiber (2) is at a non-perpendicular angle to the optical axis (7) of the optical fiber (2), The decoupling surface (5) is coated with a reflective layer, By introducing UV light into the optical fiber (2), the reflective layer is removed from the decoupling surface (5) in an emission range around the center of the optical fiber (2), so that only the central range of the reflective layer is removed again.

13. Method for measuring the distance of an object, on which a laser beam modulated and emitted by a device (1) according to any one of claims 1 to 9 is reflected, wherein The laser source (10) generates modulated laser light as emission radiation, coupling the emitted radiation into the optical fiber (2), The emitted radiation is coupled to the outside of the optical fiber (2) through the emission region (5a) in the decoupling region (5). The emitted radiation passes through the primary lens (3), The emitted radiation is reflected by the object, The reflected laser light passes through the primary lens (3) as received radiation. The received radiation is at least partially reflected at the reflective layer of the decoupling surface (5) and conducted to a receiver (8).

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

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