Optoelectronic sensor

Abstract

Optoelectronic sensor (11), in particular laser scanner, with at least one light transmitter (13) for emitting a transmitted light beam (15), a first deflection unit (16) for variably deflecting the transmitted light beam (15) in a first spatial direction and a light receiver for receiving received light, wherein the first deflection unit (16) comprises a tilting mirror (19) which can be tilted about a rotation axis (23) by means of a drive (21), wherein the drive (21) comprises a piezoelectric motor (31, 71, 81) with a stator (33, 83) fixed relative to the rotation axis (23) and a rotor (35, 85) coupled to the tilting mirror (19), wherein the stator (33, 83) and the rotor (35, 85) can be coupled to one another via at least one contact section (47) and the at least one contact section (47) is movable by a deformation of a piezo element of the piezoelectric motor (31, 71, 81).

Description

[0001] The invention relates to an optoelectronic sensor, in particular a laser scanner, having at least one light transmitter for emitting a transmitted light beam, a first deflection unit for variably deflecting the transmitted light beam in a first spatial direction and a light receiver for receiving received light, wherein the first deflection unit comprises a tilting mirror which can be tilted about a rotation axis by means of a drive.

[0002] Such sensors are used, for example, to monitor hazardous areas and to detect and measure objects. The deflection unit ensures that the transmitted light beam covers a specific monitoring area. For this purpose, the drive can be controlled so that the tilting mirror moves periodically between two end positions.

[0003] It has proven difficult to provide deflection units for optoelectronic sensors that meet all the requirements of common applications. For example, conventional electric motors such as DC motors or stepper motors are generally not capable of providing a sufficiently high angular resolution, such as 0.01°. A gearbox can remedy this, but this is accompanied by an undesirable reduction in the tilt frequency and increased wear. Galvanometer drives are relatively fast and accurate, but have high energy requirements. Furthermore, galvanometer drives are comparatively expensive and have a limited service life.

[0004] It is an object of the invention to provide an optoelectronic sensor of the above-mentioned type which, on the one hand, enables fast and precise beam deflection and, on the other hand, has a simple structure and low wear.

[0005] The problem is solved by an optoelectronic sensor having the features of claim 1.

[0006] According to the invention, the drive comprises a piezoelectric motor with a stator fixed relative to the rotation axis and a rotor coupled to the tilting mirror, wherein the stator and the rotor can be coupled to one another via at least one contact section and the at least one contact section is movable by a deformation of a piezo element of the piezoelectric motor.

[0007] A piezoelectric motor or piezomotor is capable of providing a relatively high force per volume with comparatively low energy consumption. This allows the size of an optoelectronic sensor according to the invention to be kept small. In contrast to a direct adjustment of the tilting mirror using a piezoelectric element or a piezo actuator, a piezoelectric motor enables a large travel range. By sequencing individual movement steps using successive contacts between the stator and the rotor, as well as deformations of the piezo element, a piezoelectric motor can, in principle, enable an unlimited travel range.

[0008] A particular advantage of the invention is that the deflection unit can maintain a defined angular position of the tilting mirror even when the drive is de-energized. Due to the high precision, no wear-prone gear is required. Lubricants are also unnecessary. Furthermore, a piezoelectric motor does not generate a magnetic field, so that an optoelectronic sensor according to the invention exhibits only low electromagnetic radiation and can therefore also be used in radiation-sensitive areas.

[0009] Preferably, the stator and the rotor can be frictionally coupled to each other via the contact section. This allows for a simple conversion of the deformation of the piezo element into a translational and / or rotational movement of the rotor. For example, the contact section can be pressed against a surface portion of the stator or the rotor to establish the frictional connection.

[0010] The piezoelectric motor can be designed as an ultrasonic motor, traveling wave motor, inchworm motor, walking motor, or inertial motor. Due to the wide range of design options for piezoelectric motors, there is a high degree of flexibility in adapting the deflection unit to the specific application requirements.

[0011] Preferably, the at least one contact section and the piezo element are arranged on the stator. The rotor can then be designed as a simple mechanical component. In particular, no lines need to be connected to the rotor in this configuration.

[0012] One embodiment of the invention provides that the at least one contact section is arranged protruding from a base surface of the stator or the rotor and is displaceable and / or pivotable relative to a reference point of the base surface by deformation of the piezoelectric element. For example, in a traveling-wave motor, contact sections can be formed by wave crests of the stator that come into frictional contact with the rotor. In a worm motor or an inertial motor, a displaceable clamping element can form the contact section. In the case of a stepping motor, the contact section can be located at the tip of a bending actuator, which executes pivoting bending movements through selective piezoelectric contractions of sidewall sections.

[0013] A special embodiment of the invention provides that the stator has two separate stator elements, and the rotor is arranged between the two separate stator elements. This allows the motor power to be increased.

[0014] According to a further embodiment of the invention, the rotor is arranged between the stator and a counterbearing. The counterbearing provides a counterforce for the force exerted by the stator on the rotor, thus compensating for manufacturing tolerances, for example.

[0015] The rotor can be a rotor that can be tilted around the rotation axis together with the tilting mirror. This eliminates the need for any transfer devices or gear components, allowing for a particularly simple and compact design.

[0016] Preferably, the rotor is attached to a rear side of the tilting mirror facing away from the light transmitter. This allows the reflective front side of the mirror to be kept free of drive components.

[0017] The rotor can be circularly arc-shaped and interact with a stator that is also circularly arc-shaped. Preferably, the circular-arc rotor and the circular-arc stator are arranged concentrically with respect to the rotation axis. One advantage of this is that the length of the circular arcs can be adjusted to the desired tilt angle range, minimizing the size of the deflection unit.

[0018] The arc angle of the rotor can be greater than the arc angle of the stator by a predetermined maximum tilt angle of the tilting mirror. The rotor can then move past the stator just as far as the maximum tilt angle requires. The length of the area where the rotor and stator overlap can be adjusted to a predetermined drive force.

[0019] According to a further embodiment of the invention, the at least one contact section acts on an adhesion / sliding surface of the circular-arc rotor or the circular-arc stator extending radially or circumferentially with respect to the rotational axis. Depending on the application, an arrangement with radial force application or an arrangement with axial force application can be selected.

[0020] It can be provided that the rotor is linearly displaceable relative to the stator, and the drive has a conversion device for converting a linear displacement of the rotor into a tilting of the tilting mirror. The conversion device can provide a desired transmission ratio. For example, the conversion device can comprise at least one articulated lever.

[0021] According to a further embodiment of the invention, the tilting mirror has a mirror surface which is at least 5 cm 2 , preferably at least 20 cm 2, is large. In this configuration, the tilting mirror can deflect not only a single laser beam, but also, for example, a laser line generated by another deflection unit. For a relatively large mirror, a drive unit with a piezoelectric motor is particularly suitable because, unlike, for example, a microelectromechanical drive unit, such a unit is hardly limited in terms of the achievable deflection.

[0022] The optoelectronic sensor can have a second deflection unit for periodically deflecting the transmitted light beam in a second spatial direction running transversely to the first spatial direction, wherein the first deflection unit is designed and arranged to deflect the transmitted light beam deflected by the second deflection unit. An optoelectronic sensor with two deflection units deflecting in different directions can be used in particular for three-dimensional scanning of objects. It is advantageous if the first deflection unit, which has the piezoelectric motor, is provided after another deflection unit in the beam path, because the requirements for the sweep frequency for a downstream deflection unit are generally lower than for the first deflecting deflection unit. Thus, the advantages of a piezomotor can be particularly well utilized in a downstream deflection unit.The first deflecting deflection unit can be designed, for example, as a rotating polygon mirror.

[0023] The optoelectronic sensor can have an electronic evaluation unit that is in signal communication with the light receiver and is configured to determine the distance to an object reflecting the emitted light beam based on the received light received by the light receiver using a time-of-flight method. Such an optoelectronic sensor is capable, for example, of measuring objects, detecting obstacles, and monitoring safety areas. In particular, an optoelectronic sensor according to the invention can be designed as a lidar scanner, preferably as a three-dimensional lidar scanner.

[0024] The invention also relates to a deflection unit for variably deflecting a transmitted light beam of a laser scanner, comprising a tilting mirror and a drive for tilting the tilting mirror about a rotation axis, wherein the drive comprises a piezoelectric motor with a stator fixed relative to the rotation axis and a rotor coupled to the tilting mirror, wherein the stator and the rotor can be coupled to one another via at least one contact section and the at least one contact section is movable by a deformation of a piezo element of the piezoelectric motor.

[0025] The deflection unit can be designed as described above.

[0026] Further developments of the invention can also be found in the dependent claims, the description and the accompanying drawings.

[0027] The invention is described below by way of example with reference to the drawings. Fig. Figure 1 is a simplified representation of an optoelectronic sensor. Fig. 2 is a simplified side view of a deflection unit of an optoelectronic sensor designed according to a first embodiment of the invention. Fig. 3 shows the deflection unit according to Fig. 2 from behind. Fig. 4 shows an alternatively designed deflection unit of an optoelectronic sensor according to the invention from behind. Fig. 5 shows another alternatively designed deflection unit of an optoelectronic sensor according to the invention from behind. Fig. 6 is a simplified side view of a deflection unit of an optoelectronic sensor designed according to a second embodiment of the invention. Fig. 7 is a simplified side view of a deflection unit of an optoelectronic sensor designed according to a third embodiment of the invention.

[0028] The Fig. The optoelectronic sensor 11 shown in Figure 1 comprises a light transmitter 13, for example in the form of a laser diode, which emits a transmitted light beam 15 during operation. The transmitted light beam 15 is variably deflected in a generally known manner by means of a first deflection unit 16 and a second deflection unit 17 in order to scan a monitored area three-dimensionally. The optoelectronic sensor 11 further comprises a Fig. 1 non-visible light receiver for receiving received light, for example a photodiode.

[0029] As shown, the transmitted light beam 15 emitted by the light transmitter 13 first strikes the second deflection unit 17, which is designed, for example, as a rotating polygon mirror, and then the first deflection unit 16, which comprises a tilting mirror 19. The tilting mirror 19 is rotatably mounted with respect to a rotation axis 23 by means of a shaft arrangement 20 and can be tilted about the rotation axis 23 by means of a drive 21. The second deflection unit 17 periodically deflects the transmitted light beam 15 and thereby fans it out, resulting in a light line 25. The light line 25 preferably coincides with the rotation axis 23. The first deflection unit 16 effects a beam deflection perpendicular to the light line 25. In order to be able to assign a received signal to a current measurement position, an angle sensor for detecting the angular position of the tilting mirror 19 can be provided, for example, on the shaft arrangement 20.

[0030] The tilting mirror 19 must be sufficiently long to completely cover the light line 25. For common applications, the mirror surface of the tilting mirror 19 is at least 5 cm 2 , preferably at least 20 cm 2 , large. The length of the tilting mirror 19 can be at least 50 mm and preferably at least 100 mm.

[0031] The optoelectronic sensor 11 also has an electronic evaluation unit (not shown). This unit is in signal communication with the light receiver and is designed to determine the distance to an object reflecting the emitted light beam 15 based on the received light received by the light receiver using a time-of-flight method.

[0032] In Fig. 2, the first deflection unit 16 of an optoelectronic sensor 11 designed according to an embodiment of the invention is shown individually. The drive 21 is a piezoelectric motor 31 with a stator 33 fixed relative to the rotation axis 23 and a rotor 35 coupled to the tilting mirror 19. The rotor 35 is driven by means of a (in Fig. 2) fastening component 36 to the rear side 37 of the tilting mirror 19, while the stator 33 is fastened, for example, to a base plate or to a housing (not shown) of the optoelectronic sensor 11.

[0033] In the Fig. In the embodiment shown in Figure 2, the rotor 35 forms a rotor 39 due to its attachment to the rear side 37 of the tilting mirror 19, which can be tilted together with the tilting mirror 19 about the rotation axis 23. Both the rotor 39 and the stator 33 are circularly arc-shaped and arranged concentrically with respect to the rotation axis 23. The arc angle of the rotor 39 is greater than the arc angle of the stator 33, the difference corresponding to the predetermined maximum tilt angle of the tilting mirror 19. Upon rotation of the rotor 39 relative to the stator 33, a tilt of the tilting mirror 19 about the rotation axis 23 results, and a corresponding change in the beam deflection, as shown in Fig. 2 is shown in dashed lines.

[0034] In the rear view of the first deflection unit 16 according to Fig. 3 shows that the stator 33 comprises an arrangement of actuators 41 that protrude from a flat base surface 43 of the stator 33. Piezo elements (not shown individually) are integrated into the actuators 41 and can be deformed by electrical control via a connection unit 44. The free ends of the actuators 41 form contact sections 47 that selectively contact a flat adhesive / sliding surface 49 of the rotor 39 to establish a frictional coupling between the stator 33 and the rotor 39. By selectively controlling the piezo elements, it is possible to move the contact sections 47 in order to pivot the rotor 39 relative to the stator 33.

[0035] A variety of designs of the actuators 41 are possible, which bring about a pivoting movement of the rotor 39 through deformation of piezo elements. For example, the piezoelectric motor 31 could be designed as a worm motor or inchworm motor, and the arrangement of actuators 41 could accordingly include both feed actuators and clamping actuators. Alternatively, the piezoelectric motor 31 can be a stepping motor with flexible actuators 41. A particularly simple construction results from a design of the piezoelectric motor 31 as an inertial motor or "stick-slip" motor, in which the actuators 41 execute a sequence of fast and slow movements and thus drive the rotor 39 through an alternation of static friction contact and sliding friction contact. The piezoelectric motor 31 can also be designed as an ultrasonic motor or traveling wave motor, wherein the actuators 41 are formed by traveling wave crests.

[0036] Fig. 4 shows an alternative embodiment of the first deflection unit 16, in which, in contrast to the embodiment according to Fig. 3, a counterbearing 51 is provided. The rotor 39 is arranged between the stator 33 and the counterbearing 51, whereby the support compensates for manufacturing tolerances and improves power transmission. The counterbearing 51 can be designed, for example, as a roller bearing.

[0037] A further alternative embodiment of the first deflection unit 16 is shown in Fig. 5. The stator 33 here has two separate stator elements 53, 54, which are arranged on either side of the rotor 39. The rotor 39 is arranged between the two separate stator elements 53, 54 such that the actuators 41 of one stator element 53 act on the rotor 39 in a direction opposite to the actuators 41 of the other stator element 54.

[0038] In the embodiments according to Fig. 2-5, the adhesion / sliding surface 49 extends transversely to the rotation axis 23 and the frictional engagement is achieved by axial forces. In contrast, Fig. 6 shows an embodiment of the first deflection unit 66, in which the adhesion / sliding surface 49 of the rotor 39 extends in the circumferential direction with respect to the rotation axis 23 and the frictional engagement is achieved via radial forces. Furthermore, the piezoelectric drive 71 is the one shown in Fig. 6 is designed as in the previously described embodiments.

[0039] In contrast to the arrangement of the motor components in the middle of the tilting mirror 19 as in the embodiments according to Fig. 2-6, the piezoelectric motor 31 can also be mounted at one end of the shaft assembly 20 as in Fig. 1. It is also possible to mount respective piezoelectric motors 31 at both ends of the shaft assembly 20.

[0040] The rotor 35 does not necessarily have to be a rotor 39, but can also be a rotor as in the Fig. The first deflection unit 76 shown in Figure 7 may be a rotor 85 that is linearly displaceable relative to the stator 83. For example, the linearly displaceable rotor 85 may be rod-shaped as shown and guided in a passage of the stator 83. In this embodiment of a piezoelectric motor 81, a conversion device 52 is provided for converting a linear displacement of the rotor 85 into a tilting of the tilting mirror 19. The conversion device 52 may comprise a lever 55 that is pivotally connected to the tilting mirror 19 and to the rotor 85.

[0041] According to an embodiment not shown, the piezoelectric motor 31, 71 is a fully circular motor which is flanged to one end of the shaft assembly 20.

[0042] Thanks to the piezoelectric motor 31, 71, 81, the first deflection unit 16, 66, 76 is capable of positioning the tilting mirror 19 with high precision without the need for a wear-prone gear. Relative to the size of the drive 21, particularly large drive forces are possible, allowing even comparatively large-area tilting mirrors 19 to be controlled reliably and energy-efficiently. List of reference symbols: 11 optoelectronic sensor 13 light transmitters 15 Transmitted light beam 16 first deflection unit 17 second deflection unit 19 tilting mirrors 20 Shaft arrangement 21 Drive 23 Rotation axis 25 Light line 31 piezoelectric motor 33 Stator 35 runners 36 Fastening component 37 Back 39 Rotor 41 Actuator 43 flat base surface 44 connection unit 47 Contact section 49 Adhesive / sliding surface 51 Counter bearing 52 Transfer device 53 Stator element 54 Stator element 55 levers 66 first deflection unit 71 piezoelectric motor 76 first deflection unit 81 piezoelectric motor 83 Stator 85 linearly movable slider

Claims

[1] Optoelectronic sensor (11), in particular laser scanner, with at least one light transmitter (13) for emitting a transmitted light beam (15), a first deflection unit (16) for variably deflecting the transmitted light beam (15) in a first spatial direction and a light receiver for receiving received light, wherein the first deflection unit (16) comprises a tilting mirror (19) which can be tilted about a rotation axis (23) by means of a drive (21), wherein the drive (21) comprises a piezoelectric motor (31, 71, 81) with a stator (33, 83) fixed relative to the rotation axis (23) and a rotor (35, 85) coupled to the tilting mirror (19), wherein the stator (33, 83) and the rotor (35, 85) can be coupled to one another via at least one contact section (47) and the at least one contact section (47) is movable by a deformation of a piezo element of the piezoelectric motor (31, 71, 81). [2] Optoelectronic sensor according to claim 1, wherein the stator (33, 83) and the rotor (35, 85) can be frictionally coupled to one another via the contact section (47). [3] Optoelectronic sensor according to claim 1 or 2, wherein the piezoelectric motor (31, 71, 81) is designed as an ultrasonic motor, traveling wave motor, worm motor, walking motor or inertial motor. [4] Optoelectronic sensor according to one of the preceding claims, wherein the at least one contact section (47) is arranged protruding from a base surface (43) of the stator (33, 83) or the rotor (35, 85) and is displaceable and / or pivotable relative to a reference point of the base surface (43) by a deformation of the piezo element. [5] Optoelectronic sensor according to one of the preceding claims, wherein the stator (33) has two separate stator elements (53, 54) and the rotor (35) is arranged between the two separate stator elements (53, 54). [6] Optoelectronic sensor according to one of the preceding claims, wherein the rotor (35) is arranged between the stator (33) and a counter bearing (51). [7] Optoelectronic sensor according to one of the preceding claims, wherein the rotor (35) is a rotor (39) which can be tilted together with the tilting mirror (19) about the rotation axis (23). [8] Optoelectronic sensor according to claim 7, wherein the rotor (39) is fastened to a rear side (37) of the tilting mirror (19) facing away from the light transmitter (13). [9] Optoelectronic sensor according to claim 7 or 8, wherein the rotor (39) is circular-arc-shaped and cooperates with a likewise circular-arc-shaped stator (33), in particular wherein the rotor (39) and the stator (33) are arranged concentrically with respect to the rotation axis (23). [10] Optoelectronic sensor according to claim 9, wherein the arc angle of the rotor (39) is greater than the arc angle of the stator (33) by a predetermined maximum tilt angle of the tilting mirror (19). [11] Optoelectronic sensor according to claim 9 or 10, wherein the at least one contact section (47) acts on an adhesion / sliding surface (49) of the circular-arc-shaped rotor (39) or of the circular-arc-shaped stator (33) extending radially or in the circumferential direction with respect to the rotation axis (23). [12] Optoelectronic sensor according to one of claims 1 to 6, wherein the rotor (85) is linearly displaceable relative to the stator (83) and the drive (21) has a conversion device (52) for converting a linear displacement of the rotor (85) into a tilting of the tilting mirror (19). [13] Optoelectronic sensor according to one of the preceding claims, wherein the tilting mirror (19) has a mirror surface which is at least 5 cm 2, preferably at least 20 cm 2 , is large. [14] Optoelectronic sensor according to one of the preceding claims, wherein the optoelectronic sensor (11) has a second deflection unit (17) for periodically deflecting the transmitted light beam (15) in a second spatial direction extending transversely to the first spatial direction, wherein the first deflection unit (16) is designed and arranged to deflect the transmitted light beam (15) deflected by the second deflection unit (17). [15] Optoelectronic sensor according to one of the preceding claims, wherein the optoelectronic sensor (11) has an electronic evaluation unit which is in signal connection with the light receiver and is designed to determine the distance to an object remitting the emitted transmitted light beam (15) on the basis of the received light received by the light receiver by means of a light transit time method.

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