CN115902837A - Calibration method of laser radar, laser radar and calibration system - Google Patents
Calibration method of laser radar, laser radar and calibration system Download PDFInfo
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Abstract
The invention provides a calibration method of a laser radar, wherein the laser radar comprises a rotating mirror and a motor for driving the rotating mirror to rotate, and the calibration method comprises the following steps: s11: acquiring at least one target position of the rotating mirror; s12: adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and S13: and calibrating the laser radar according to the echo pulse information obtained when the rotating mirror is at the at least one target position. According to the technical scheme, the motor can be controlled to stop at the designated position, a more efficient and accurate motor control mode can be provided, the angle of the motor which is not in the working state can be accurately controlled, and the calibration operation efficiency is improved.
Description
Technical Field
The present disclosure relates to the field of photoelectric detection, and in particular, to a calibration method for a laser radar, a computer-readable storage medium, a laser radar, and a calibration system.
Background
In the current mechanical laser radar calibration mode that has a rotating mirror (like distance calibration, reflectivity calibration), calibrate when laser radar has not accomplished the shell assembly yet, through mechanical frock, the rotary part among the fixed laser radar to the fixed laser radar departure beam's direction, and then can keep the stability of product gesture and laser radar echo signal in the calibration process. The specific calibration mode is that target plates with different reflectivities are arranged at one or more fixed distances, so that the laser radar rotates, the laser emitting direction points to different target plates, and the corresponding relation among the pulse width, the front edge and the real distance is established by measuring the pulse width and the front edge of an echo, so that the laser radar calibration is completed.
Because the motor can not lock self direction itself, need the supplementary fixed angle of outside frock in the calibration process, avoid changeing the mirror and rock, influence the calibration result. In order to install an external tool, the laser radar shell is not assembled, and production links such as shell assembly need to be further realized after calibration is completed. The target plate is far away from the laser radar in the calibration process, the space of a production field can be obviously occupied, the laser radar is usually used for completing production in an ultra-clean room, space resources are precious, and the calibration mode has obvious adverse effects on the production line.
Besides being fixed through a mechanical tool, the rotating mirror angle of the laser radar can be fixed through a control motor. The traditional motor control method is from the perspective of a power supply, and a sine wave power supply with adjustable frequency and voltage is generated. In order to continuously rotate the rotor of the motor, a process of converting dc to ac is required in the motor (or in an external drive circuit). For a brush motor, this is achieved by brushes and a commutator, whereas for a brushless motor this is achieved by an inverter circuit. The Brushless Motor includes a Brushless Direct Current Motor (BLDCM) and a Permanent Magnet Synchronous Motor (PMSM). Taking a three-phase dipolar permanent magnet synchronous motor as an example, a rotor of the permanent magnet synchronous motor PMSM is a permanent magnet, a stator is provided with three-phase windings, the three-phase windings are symmetrically distributed by adopting a Y-type connection method, and the three-phase windings are different from each other by 120 degrees in space to form a three-phase static coordinate system ABC of the permanent magnet synchronous motor PMSM. The working principle is as follows: a rotating magnetic field with a constant magnitude is generated in the stator to drive the rotor to rotate continuously. The magnitude of this rotating magnetic field is constant in order to ensure smooth motion performance of the motor. However, the difficulty in controlling the three phase voltages respectively is high, and an efficient and precise control scheme is urgently needed to realize effective control of the motor.
The statements in the background section merely disclose technology known to the inventors and are not necessarily indicative of prior art in the field.
Disclosure of Invention
In view of one or more drawbacks of the prior art, the present invention is directed to a calibration method of a lidar, wherein the lidar includes a rotating mirror and a motor that drives the rotating mirror to rotate, the calibration method comprising:
s11: acquiring at least one target position of the rotating mirror;
s12: adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
s13: and calibrating the laser radar according to the echo pulse information obtained when the rotating mirror is at the at least one target position.
According to an aspect of the invention, said step S12 comprises: and adjusting the vector magnitude and/or the duty ratio of each space vector voltage in the control voltage to obtain the motor torque output in the specified direction, so that the rotating mirror reaches the target position.
According to an aspect of the invention, said step S12 comprises: and adjusting the control voltage of the motor according to the at least one target position and the load information corresponding to the rotating mirrors, so that the rotating mirrors rotate to the at least one target position respectively.
According to one aspect of the invention, the reverse torque is obtained according to the load information of the rotating mirror, and the torque output of the motor is corrected.
According to an aspect of the invention, the step S12 further comprises: and in the rotation process of the motor, acquiring deviation position information of the rotating mirror, and adjusting the control voltage according to the deviation position information until the rotating mirror reaches the target position.
According to an aspect of the present invention, the deviation position information is acquired based on the current position and the target position of the rotating mirror.
According to an aspect of the invention, step S12 further comprises: and in the rotation process of the motor, acquiring current circuit parameter information, and adjusting the control voltage according to the deviation position information and the circuit parameter information until the rotating mirror reaches a target position.
According to one aspect of the invention, the circuit parameter information is determined from current information of the motor.
According to an aspect of the invention, the lidar further comprises an encoder disc, and the calibration method further comprises: and detecting the current position of the rotating mirror through the code disc.
According to an aspect of the invention, the calibration method further comprises: the laser radar transmits a detection laser pulse and acquires echo pulses emitted to a plurality of targets by the detection laser pulse; and determining calibration parameters of the laser radar according to echo pulse information which is obtained when the rotating mirror is at the at least one target position and respectively corresponds to a plurality of target objects.
According to an aspect of the present invention, the plurality of targets may respectively correspond to different measurement information, and the calibration parameters are used for calibrating the corresponding measurement information.
According to an aspect of the invention, the echo pulse information comprises at least one of a leading edge, a pulse width, a slope, and a peak value of the echo pulse, the calibration method further comprises: and on the basis of the calibration parameters, calculating the data of the calibration parameters to establish a calibration table of the laser radar.
The invention also relates to a computer-readable storage medium comprising computer-executable instructions stored thereon, wherein the executable instructions, when executed by a processor, implement the calibration method as described above.
The invention also relates to a laser radar, which comprises a rotating mirror and a motor for driving the rotating mirror to rotate, wherein the laser radar also comprises:
a position sensor configured to detect position information of the rotating mirror; and
a control unit coupled with the motor and the position sensor and configured to:
acquiring at least one target position of the rotating mirror through the position sensor;
adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
and acquiring echo pulse information when the rotating mirror is at the at least one target position so as to calibrate the laser radar.
According to one aspect of the invention, the position sensor is an encoder disc and the position information is an angular position.
According to an aspect of the present invention, the lidar further includes a multi-phase inverter driving circuit, coupled between the control unit and the motor, configured to drive the motor to operate under the control of the control unit.
According to one aspect of the invention, the control voltage is synthesized using a portion of the plurality of space vector voltages.
According to an aspect of the present invention, the multi-phase inverter driving circuit is a three-phase inverter driving circuit, the plurality of space vector voltages is six space vector voltages, and a part of the plurality of space vector voltages is two space vector voltages.
According to one aspect of the invention, the control unit adjusts the vector magnitude and/or the duty ratio of each space vector voltage in the control voltage by controlling the switching state and the duration time of the multiple inverter driving circuits, so as to obtain the motor torque output in a specified direction, so as to control the motor to stop rotating and point to a fixed direction.
According to an aspect of the present invention, during the rotation of the motor, the control unit acquires deviation position information of the rotating mirror, and adjusts the control voltage according to the deviation position information until the rotating mirror reaches the target position.
According to an aspect of the present invention, during the rotation of the motor, the control unit obtains current circuit parameter information, and adjusts the control voltage according to the deviation position information and the circuit parameter information until the rotating mirror reaches a target position.
According to an aspect of the present invention, the calibration system further comprises a transmitting unit and a receiving unit, wherein the transmitting unit is configured to transmit a detection laser pulse, the receiving unit is configured to obtain echo pulses of the detection laser pulse emitted to a plurality of targets, and the control unit is further configured to determine calibration parameters of the laser radar according to echo pulse information, which is obtained when the turning mirror is at the at least one target position and corresponds to the plurality of targets respectively.
According to an aspect of the invention, the plurality of objects may have different distances and/or reflectivities, respectively.
According to one aspect of the invention, the echo pulse information includes at least one of a leading edge, a pulse width, a gradient and a peak value of the echo pulse, and the control unit establishes a calibration table of the laser radar by performing calculation processing on data of the calibration parameter based on the calibration parameter.
According to one aspect of the invention, the lidar further comprises a computer-readable storage medium comprising computer-executable instructions stored thereon that, when executed by the control unit, implement the calibration method as described above.
The invention also relates to a calibration system comprising:
a calibration aid comprising at least one target disposed at different orientations; and
lidar, lidar includes commentaries on classics mirror and drive the rotatory motor of commentaries on classics mirror, lidar still includes:
a position sensor configured to detect position information of the rotating mirror; and
a control unit coupled with the motor and the position sensor and configured to:
acquiring at least one target position of the rotating mirror through the position sensor;
adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
and acquiring echo pulse information when the rotating mirror is at the at least one target position so as to calibrate the laser radar.
Wherein the at least one target location corresponds to the at least one target disposed at a different orientation.
For a rotating mirror scanning radar, the emergent light direction needs to be fixed in the calibration process, and because the motor rotates freely, the calibration process cannot be carried out after the production process is finished, and the calibration must be carried out when a shell is not assembled in the production process, so that the production efficiency and the product production yield control are seriously influenced. According to the invention, by utilizing a space vector voltage modulation technology and a corresponding inverter driving circuit, the motor can be stopped at a specified angle, so that the emergent light direction of the laser radar is fixed, a more efficient and accurate motor control mode is provided, the angle of the motor which is not in a working state can be accurately controlled, and the efficiency of calibration operation is improved. The invention realizes the separation of laser radar hardware production and calibration parameters by combining a more advanced motor driving algorithm and a laser radar calibration technology, and can avoid the ultra-clean room space required in the hardware production process from being occupied by the calibration process because the calibration process usually needs to occupy larger space, thereby improving the space utilization rate, improving the production efficiency, optimizing the production link and being beneficial to reducing the radar production cost.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to be construed as limiting the disclosure. In the drawings:
FIG. 1A shows a laser radar calibration schematic of one embodiment of the present invention;
FIG. 1B shows a schematic diagram of a scanning unit of a lidar;
FIG. 2 shows a flow diagram of a lidar calibration method of one embodiment of the invention;
fig. 3 shows a schematic diagram of a permanent magnet synchronous machine;
FIG. 4 illustrates a trajectory diagram of the phase voltage to control voltage vector conversion for one embodiment of the present invention;
FIG. 5A shows a schematic diagram of a three-phase inverter driver circuit according to one embodiment of the invention;
FIG. 5B shows the vector U of FIG. 5A at the fundamental voltage space 4 (100) An equivalent circuit diagram of states;
FIG. 6 illustrates a schematic diagram of space vector voltages in the ABC and α β coordinate systems, according to one embodiment of the present invention;
FIG. 7A shows a lidar calibration diagram of one embodiment of the invention;
FIG. 7B shows a laser radar calibration schematic of one embodiment of the present invention;
FIG. 7C shows a lidar calibration diagram of one embodiment of the invention;
FIG. 8 shows an overall block diagram of a PID controller;
FIG. 9 shows a PID control schematic of one embodiment of the invention.
Detailed Description
In the following, only certain exemplary embodiments are briefly described. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations or positional relationships based on those shown in the drawings, merely for convenience of description and simplification of the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected" and "connected" are to be construed broadly, e.g., as being fixed or detachable or integral, either mechanically, electrically or communicatively coupled; they may be directly connected or indirectly connected through intervening media, or may be connected through the use of two elements or the interaction of two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless expressly stated or limited otherwise, the recitation of a first feature "on" or "under" a second feature may include the recitation of the first and second features being in direct contact, and may also include the recitation that the first and second features are not in direct contact, but are in contact via another feature between them. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.
The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
Fig. 1A shows a calibration schematic of the lidar and fig. 1B shows a schematic of a scanning unit of the lidar. As shown in fig. 1A and 1B, the laser radar 20 includes a rotating mirror 21 and a motor 22 that drives the rotating mirror 21 to rotate, both constituting a scanning unit of the laser radar 20. As shown in fig. 1B, the turning mirror 21 has a rotation axis O about which it can rotate and/or oscillate reciprocally. The rotating mirror 21 has a reflecting surface on which the laser beam L emitted from the laser of the laser radar 20 is received and the laser beam R is reflected into a three-dimensional space outside the laser radar. As the turning mirror 21 rotates around the rotation axis O, the reflecting surface will reflect the laser beam L in different directions, covering a certain range in three-dimensional space, constituting the field of view FOV of the lidar 20. In addition, the turning mirror 21 may include one or more rotation axes O, for example, a scanning rotation axis in a horizontal direction and a scanning rotation axis in a vertical direction, which are all within the scope of the present invention. In addition, the laser radar 20 further includes a control unit 24 for controlling the rotation of the motor 21. As shown in fig. 1A, when the lidar 20 is calibrated, a plurality of target objects 311, such as the target object 311-1, the target objects 311-2, 8230, the target object 8230, and the target object 311-n shown in fig. 1A, are disposed at different orientations (different angles and/or different positions) around the lidar, the rotation of the motor 24 is controlled to direct the laser emission direction to different target plates, and the pulse width, the leading edge, and the true distance are established by measuring the pulse width and the leading edge of the echo, thereby completing the lidar calibration.
Fig. 2 shows a flow chart of a method 10 for calibrating a lidar according to an embodiment of the invention, which is described in detail below with reference to fig. 2.
At least one target position of the turning mirror is acquired in step S11. Such as externally input target position information in the form of, but not limited to, a target position of a rotating component in the lidar 20, a target position at which a lidar exit beam is directed, or an angular deviation of the optical axis of the lidar 20. The laser radar 20 further includes a control unit 24, and the target angle of the turning mirror is obtained through conversion by a processor in the control unit 24. For calibration of the laser radar 20, as shown in fig. 1A, it is necessary to set a plurality of target objects 311 at different distances (or to sequentially place one target object 311 at different orientations). In the calibration process, the angle of the rotating mirror 21 needs to be controlled, so that the rotating mirror 21 stops at a plurality of target positions, the outgoing laser beams sequentially enter different target objects 311 (such as reflecting plates), and the outgoing light is perpendicular to the plate surface (normal incidence). At each angle, echo information needs to be collected.
Adjusting a control voltage of the motor 22 according to at least one target position of the rotating mirror 21 so that the rotating mirrors 21 are rotated to the at least one target position, respectively, in step S12; the control voltage is obtained by synthesizing a plurality of space vector voltages.
The invention considers the inverter circuit and the motor as a whole based on Space Vector Pulse Width Modulation (SVPWM) technology, and has simple model and convenient real-time control of the processor. According to a preferred embodiment of the present invention, the inverter circuit converts dc to ac, and then the algorithm synthesizes a control voltage from a plurality of space vector voltages, so as to control the brushless motor to drive the rotating mirror 21 to rotate to the target position.
Fig. 3 shows a schematic representation of a permanent magnet synchronous machine. The expression for the three phase voltages (referring to the voltages at points a, B and C at the intermediate connection point N of the three phase windings of the motor) is as follows:
U AN (t)＝U m cosωt
wherein, U AN (t) is A phase voltage, U BN (t) is the B-phase voltage, U CN (t) is C-phase voltage, U m The phase voltage amplitude, ω is the angular velocity of the rotation. Synthesizing three phase voltages, wherein the synthesizing relation is as follows:
converting three phase voltages into a control voltage U by the above formula out The motion trace thereof refers to fig. 4. As can be seen from FIG. 4, the control voltage U out Is a rotating voltage vector which rotates counterclockwise at a constant speed at an angular velocity omega, and the vertex motion locus is a circle. This means that the control of the three phase voltages is equivalent to the control of the voltage U out And U is out The closer the locus of (a) is to a circle, the closer the three phase voltages are to a three-phase symmetrical sine wave, the more constant the electromagnetic torque it generates.
Through the analysis, three phase voltages are equivalent to one control voltage, the motor can stably run by adjusting the control voltage of the motor, the motor torque output in the designated direction can be obtained to fix the motor direction, and the rotating mirror is driven to rotate to the target position. How to synthesize the control voltage by the multiple space vector voltages through the inverter circuit and the algorithm control is continuously analyzed.
Fig. 5A shows a schematic diagram of a three-phase inverter driving circuit according to an embodiment of the present invention. The three-phase inverter driving circuit comprises three groups of half bridges and six switching tubes, and each group of half bridges are divided into an upper bridge arm and a lower bridge arm. For example, when the upper arm of the first half bridge, the lower arm of the second half bridge, and the lower arm of the third half bridge are turned on (short-circuited) and the remaining arms are turned off (open-circuited), the current can flow from the positive electrode of the power supply through the a phase of the motor, then through the B phase and the C phase, and finally back to the negative electrode of the power supply. And controlling the on-off state of the upper bridge arm and the lower bridge arm and continuously circulating to realize the continuous rotation of the motor.
The two switching tubes of the same set of half-bridges cannot be turned on or off at the same time, so that there are two states for each leg. The different combinations of the upper bridge arm conduction and the lower bridge arm conduction correspond to space vector voltages in different directions. Defining a switching value S A 、S B 、S C And the switching states of the three bridge arms are represented, wherein 1 represents that the upper bridge arm is conducted, the lower bridge arm is turned off, and 0 represents that the lower bridge arm is conducted, the upper bridge arm is turned off. To simplify the representation, the switching function Sx (x ∈ a, b, c) is defined as:
according to permutation and combination, the switch function has 2 3 =8 combinations, the 8 combinations being referred to as elementary space vector voltages, comprising 6 non-zero vectors: u shape 1 (001)、U 2 (010)、U 3 (011)、U 4 (100)、U 5 (101)、U 6 (110) And 2 zero vectors: u shape 0 (000)、U 7 (111)。
FIG. 5B shows an equivalent circuit diagram of the brushless motor of FIG. 5A, i.e., with a space vector voltage of U 4 (100) In the state, the three load resistors are all R, then U dc The load between is:
the voltage division condition of each resistor can obtain three phase voltages as follows:
here U BN And U CN The resultant vector size of (1/3) U dc And direction is equal to U AN The opposite is true. Synthesized control voltage U out ＝U dc 。
The control voltage U corresponding to other non-zero vectors can be obtained by the same method out 。
By plotting the above 8 space vector voltages on the coordinate axes, the schematic diagrams of the space vector voltages in the ABC coordinate system and the α β coordinate system as shown in fig. 6 can be obtained. It can be seen that 2 zero vectors are located at the origin of the coordinate system, and the end points of the remaining 6 non-zero vectors form a regular hexagon, and the plane is divided into 6 sectors. Taking the 6 space vector voltages as base vectors, any vector can be synthesized, and in each sector, two adjacent space voltage vectors are selected, that is, any voltage vector in each sector can be synthesized according to the volt-second balance principle, wherein the specific synthesis formula is as follows:
wherein, U ref Is the desired voltage vector, T is a Pulse Width Modulation (PWM) period, T x And T y Represents U in one period T x And U y The time taken up.
Wherein the content of the first and second substances,
representing two zero vectors, which may be U 0 Or may be U 7 The selection of the zero vector is flexible, by appropriately configuring the time taken by the zero vector->
The switching of the space vector voltage can be smoother. Here U y And U y As basis vectors, 6 space voltage vectors U are represented in particular 1 、U 2 、U 3 、U 4 、U 5 、U 6 Which two of which, depending on the sector to which the rotor is rotated, e.g. to sector iii, U x And U y The base vector represented is U 2 And U 3 . Assuming that the rotation speed of the motor is ω, the period of one rotation of the motor is 1/ω, and since there are six sectors, the PWM period T =1/6 × 1/ω =1/6 ω in one sector.
For example, if a resultant vector along the direction of the β axis is desired, it is first determined that the direction lies in sector II, which is based on U 2 And U 6 The components are determined. Because the beta direction is positioned at U 2 And U 6 In the middle of (1), therefore, U 2 And U 6 Are each assigned a 50% duty cycle (regardless of the time taken for the zero vector) to obtain the target resultant vector.
Through the above analysis, a voltage vector U exists in the motor ref The direction of the magnetic line of force of the magnetic field and the voltage vector U can be judged according to the right-handed spiral theorem by the characterized voltage ref And (5) the consistency is achieved. Since the rotor permanent magnet tries to rotate until the direction of the inner magnetic line is consistent with that of the outer magnetic field, the vector can represent the direction to which the rotor is expected to rotate, namely the control voltage U synthesized by 6 space vector voltages out . Because the invention controls U out The direction of the motor is fixed, the problem of smooth switching during direction changing does not need to be considered, and therefore, the control voltage U is synthesized out The zero vector may not be considered.
According to a preferred embodiment of the present invention, as shown in fig. 2, the laser radar 20 further includes an inverter driving circuit 25, and the step S12 includes: regulating the control voltage U out The vector magnitude and/or duty ratio of each space vector voltage, and the motor torque output in a specified direction is obtained so that the rotating mirror 21 reaches the target position. The specific implementation process comprises the following steps: determining control voltage U based on target position out The sector where the mobile phone is located; calculating the action time of adjacent space vector voltages to obtain a PWM duty ratio;determining the switching state and the conduction time of each bridge arm of the inverter driving circuit 25 based on the space vector voltage and the duty ratio; the motor 22 is further controlled to output a torque in a predetermined direction to drive the rotary mirror 21 to a target position. That is, based on the above method, only by reasonably combining the magnitudes of 6 vectors and their duty ratios in the process of driving the motor 22 by the inverter circuit, a control voltage can be synthesized, so as to obtain the motor torque output in the designated direction, and if the motor torque vector is kept unchanged, the motor 22 can be stopped and pointed to the fixed direction.
According to a preferred embodiment of the present invention, step S12 includes: according to the at least one target position and the load information corresponding to the turning mirror 21, the control voltage of the motor 22 is adjusted so that the turning mirror 21 is rotated to the at least one target position, respectively. That is, based on the above method, the motor 22 can be stopped and pointed in a fixed direction while keeping the motor torque vector constant. When the motor 22 drives the rotating mirror 21 to rotate, the rotating mirror 21 is the load of the motor 22, and preferably, the reverse torque is obtained according to the load information corresponding to the rotating mirror 21. The torque of the motor is slightly adjusted by combining the reverse torque so as to improve the positioning precision of the target position.
In step S13, the laser radar 20 is calibrated based on the echo pulse information obtained when the mirror is in the at least one target position.
According to a preferred embodiment of the present invention, the calibration method 10 further comprises: the laser radar 20 emits a detection laser pulse (emission pulse), and acquires echo pulses emitted from the detection laser pulse to a plurality of target objects 311 (for example, reflecting plates); then, calibration parameters of the laser radar 20 are determined based on echo pulse information corresponding to each of the plurality of target objects 311 obtained when the rotating mirror 21 is at least one target position. Referring to fig. 1A, 1B, and 2, the laser radar 20 further includes a transmitting unit 26, a receiving unit 27, and a control unit 24. The transmitting unit 26 transmits a detection laser pulse to measure the distance information between the target 311 and the laser radar 20. The receiving unit 27 receives the echo pulse of the probe laser pulse reflected by the target 311. The control unit 24 obtains the flight time according to the time difference between the detection laser pulse and the echo pulse, obtains the calibration reference quantity according to the echo pulse information, and calibrates the flight time according to the calibration curve, thereby calibrating the distance information.
Specifically, the calibration method 10 employs, for example, any one or a combination of three ways:
1) As shown in fig. 7A, a plurality of targets 331 are disposed at different distances, the rotating mirror 21 is controlled to stop at an angular position, a detection laser pulse is emitted and normally enters the target 331-1, and echo pulse information of the target 331-1 is obtained; moving away the target 331-1, emitting a detection laser pulse, and normally entering the target 331-2 to obtain echo pulse information of the target 331-2; and so on until the echo pulse information of the target object 311-n is obtained. And determining calibration parameters of the laser radar 20 at a plurality of different distances according to the actual distance of each target object 311.
2) As shown in fig. 7B, the plurality of targets 331 are disposed in a plurality of orientations, the rotating mirror 21 is controlled to stop at a first angular position, the detection laser pulse is emitted and normally enters the target 331-1, and the echo pulse information of the target 331-1 is obtained; controlling the rotating mirror 21 to stop at the second angle position, emitting a detection laser pulse, normally entering the target 331-2, and obtaining echo pulse information of the target 331-2; and so on until the echo pulse information of the target object 311-n is obtained. And determining calibration parameters of the laser radar 20 at a plurality of different distances according to the actual distance of each azimuth.
3) As shown in fig. 7C, a target 331 is set at a first orientation, the turning mirror 21 is controlled to stop at a first angular position, a detection laser pulse is emitted, the target 331 is normally incident, and echo pulse information of the target 331 at the first orientation is obtained; moving the target 331 to a second position, controlling the turning mirror 21 to stop at a second angle position, emitting a detection laser pulse, and normally injecting the target 331 to obtain echo pulse information of the target 331 in the second position; and so on until the echo pulse information of the target object 311 in the nth azimuth is obtained. And determining calibration parameters of the laser radar 20 at a plurality of different distances according to the actual distance of each azimuth.
Taking the above three methods as an example, calibration parameters of the laser radar 20 in multiple directions are determined through statistics (e.g., averaging errors at the same distance, etc.). The calibration parameters may be an error information table (obtained by looking up a table according to distances) or an error function (obtained by fitting calibration data, and an error may be calculated based on the distances to correct the measured values).
According to a preferred embodiment of the present invention, the echo pulse information includes at least one of a leading edge, a pulse width, a slope, and a peak value of the echo pulse, and the calibration method 10 further includes: and establishing a calibration table of the laser radar 20 by calculating and processing data of the calibration parameters based on the calibration parameters. The leading edge slope value, the pulse width, the gradient and the peak value of the echo pulse are all reference quantities which are monotonously changed along with the intensity change of the echo pulse in a range measurement range, the flight time of the laser radar 20 is calibrated based on the information, for example, a corresponding table is formed through interpolation, fitting or approximation and the like, and the receiving time of the echo pulse is calibrated, so that the flight time is calibrated, and more accurate distance information can be obtained.
Taking the leading edge method as an example, the calibration aims to reduce the error value of the leading edge time of the echo pulse, i.e. the value that the leading edge time needs to be increased or decreased is measured. Taking the triggering time of the emission detection laser pulse as the emission time; extracting the rising edge moment of the echo pulse according to the threshold value of the echo signal as a receiving moment; and obtaining the flight time according to the time difference between the transmitting time and the receiving time. Error information is determined based on the distance between the time of flight and the target 311, and a calibration table is established.
Taking the peak method as an example, the calibration aims to calibrate the peak time of the echo pulse. Taking the triggering time of emitting the detection laser pulse as the emitting time; the time of the peak of the echo signal is used as the receiving time. Then obtaining the flight time according to the time difference between the transmitting time and the receiving time; error information is determined based on the distance between the time of flight and the target 311, and a calibration table is established.
According to a preferred embodiment of the present invention, the plurality of targets 311 may respectively correspond to different measurement information, and the calibration parameters are used for calibrating the corresponding measurement information. The measurement information is, for example, the distance and/or reflectance of the target object. Different measurement information is selected according to requirements, the measured value is compared with the actual value of the target object 311, error information is determined, calibration parameters are formed, and a calibration table of the laser radar 10 is established.
According to yet another preferred embodiment of the present invention, one or more of the targets 311 have different reflectivities. Among them, the plurality of targets 311 set in the calibration process are, for example, target plates of different reflectances; when there is only one target 311, the reflectivity thereof is adjusted, for example, by replacing a sticker on the target board. When the calibration method 10 is implemented according to the above three methods, the turning mirror 21 is controlled to stop at least one angular position in sequence, the reflectivity of the target object 311 is obtained based on the echo pulse information, the error information is determined based on the measured value and the reflectivity of the target object 311, and then the calibration table of the reflectivity is established.
In summary, the calibration method 10 is implemented by steps S11 to S13 as follows: after the target position information of the rotating mirror 21 is obtained, the control voltage U is adjusted by controlling the on-off state and the on-off time of each bridge arm of the inverter driving circuit 25 out The vector magnitude and the duty ratio of a plurality of space vector voltages, thereby realizing that the motor 22 is controlled to drive the rotating mirror 21 to rotate to a target position; then the laser radar 20 emits the detection laser pulse to obtain the echo pulse information on the target object 311-1, then changes the orientation of the target object 311-1 or for the next target object 311-2, repeats the above steps, determines the calibration parameters corresponding to the measurement information (such as distance and/or reflectivity) of the laser radar 20 based on the obtained multiple sets of echo pulse information, and further establishes the calibration table. When the laser radar works, an accurate measurement result can be obtained by combining a corresponding calibration table according to measurement information.
More preferably, the inverter driving circuit 25 may be selected from three, five, or nine phases, all of which are within the scope of the present invention.
As a preferred solution, the present invention can also combine a Proportional-Integral-Derivative (PID) control technique to stabilize the turning mirror 21 at the target position as soon as possible. The PID controller has the working principle that an output target value is set, the feedback system returns the output value, if the output value is not consistent with the target value, an error exists, and the input value is adjusted according to the error until the output value reaches the target value. Fig. 8 shows an overall block diagram of the PID controller, which superimposes the feedback output value on the input by one or more of proportional, integral and differential operation after obtaining the output value of the system through the measuring element, thereby controlling the output value of the actuator to reach the target value.
According to a preferred embodiment of the present invention, step S12 further comprises: in the process of rotation of the motor 22, deviation position information of the rotating mirror 21 is acquired, and the control voltage is adjusted according to the deviation position information until the rotating mirror 21 reaches the target position. According to a preferred embodiment of the present invention, the deviation position information is acquired based on the current position and the target position of the rotating mirror 21. For example, the control unit 24 includes a PID controller, measures the current position of the turning mirror 21 through the position sensor 23, feeds back to an input terminal of the PID control module, acquires a deviation from the input target position information, and adjusts the control voltage by means of proportional, integral, and differential adjustments based on the deviation until the turning mirror 21 rotates to the target position. This process may be repeated to automatically and quickly fix the turning mirror 21 to the target position.
According to a preferred embodiment of the present invention, referring to fig. 2, the lidar 20 further comprises an encoder disc 23, i.e. a position sensor, for detecting the position of the turning mirror 21. The calibration method 10 further comprises: the current position of the turning mirror 21 is detected by the encoder disk 23.
Above for carrying out automatic closed-loop control to the motor based on a PID controller, probably use three PID controller in the reality, from the inner loop to the outer loop be in proper order: a current loop, a speed loop, and a position loop. That is, the motor current (torque) is controlled by current feedback, then the rotational speed of the motor is controlled by controlling the torque, and finally the motor position is controlled by controlling the rotational speed of the motor.
According to a preferred embodiment of the present invention, step S12 further comprises: during the rotation of the motor 22, the current circuit parameter information is obtained, and the control voltage U is adjusted according to the deviation position information and the circuit parameter information out Until the turning mirror 21 reaches the target position. For calibration of the turning mirror lidar, the angle of the turning mirror 21 needs to be controlled, so that the emergent light points to the target 311 right in front, and the turning mirror 21 can point to and be locked at the required angle through the space vector voltage control, the combination of the position information on the code disc 23 and the closed-loop PID controller. Since in the position control mode, the rotation speed of the motor 22 is very low, and there is a large error in the speed information output by the encoder disc 23 in the average speed measurement mode (the rotor does not move or moves very slowly, at this time, the encoder disc 23 outputs no output or only outputs one or two pulse signals), in order to avoid an error caused by a speed loop, when performing position control, only a double loop formed by positions and currents may be used for control, fig. 9 shows a PID control schematic diagram of an embodiment of the present invention, in which the control unit 24 includes a PID control module, the current position information may be obtained based on the position sensor 23 (e.g., a photosensor on the encoder disc), and the circuit parameter information may be obtained according to the output of the motor 22. According to a preferred embodiment of the present invention, the circuit parameter information is determined based on current information of motor 22. Wherein the current information is used to determine the current power of the motor 22 and reduce the current when the rotating mirror 21 approaches the target position, so as to reduce the power of the rotation of the motor 22. Therefore, current information is input to the current loop of the PID control module, current position information, such as angle position information, is input to the position loop in the PID control module, and the current position information and the target position information are calculated, so that the motor 22 can drive the rotating mirror 21 to rotate to the target angle through feedback control.
Specifically, referring to fig. 9, the control unit 24 includes a PID control module and a space vector voltage control module. First, target position information of the turning mirror 21 externally input is received. Then, the obtained deviation position information is converted into a target current through a position loop in the PID control module by the current position information detected by the position sensor 23, and at the same time, the output phase current of the motor 22 is sampled,the current loop in the PID control module receives the target current and the phase current output by the motor 22, converts the coordinate system, converts the target current into a target voltage, and outputs the target voltage to the space vector voltage control module. Finally, the space vector voltage is converted into a control voltage U by a space vector voltage control module out And thereby controls the drive circuit 25 to output the three-phase voltages of the three-phase winding coordinate system.
The above process can be completed by the controller 24 and the inverter driving circuit 25 of the motor 22, so that the motor 22 can be directly controlled to drive the rotating mirror 21 to be fixed to a target angle without detaching after the radar product is produced. After the angle of the outgoing beam of the radar is fixed, the current echo signal information of the beam can be quickly obtained according to the real distance of the target object 311, so that parameters such as distance calibration and reflectivity calibration can be obtained.
The present invention also relates to a computer-readable storage medium comprising computer-executable instructions stored thereon, wherein the executable instructions, when executed by a processor, implement the calibration method 10 as described above.
The invention also relates to a lidar 20, which, with reference to fig. 2, comprises a turning mirror 21 and a motor 22 for driving the turning mirror to rotate, wherein the lidar 20 further comprises:
a position sensor 23 configured to detect position information of the turning mirror 21; and
a control unit 24, coupled to the motor 22 and the position sensor 23, configured to:
acquiring at least one target position of the turning mirror 21 by the position sensor 23;
adjusting the control voltage U of the motor 22 in dependence on the at least one target position out So that the rotating mirrors 21 are respectively rotated to the at least one target position; wherein the control voltage U out Synthesizing and obtaining a plurality of space vector voltages; and
echo pulse information is acquired when the turning mirror 21 is at the at least one target position to calibrate the laser radar 20.
According to a preferred embodiment of the present invention, the position sensor 23 is a code wheel, and the position information is an angular position.
According to a preferred embodiment of the present invention, the lidar 20 further comprises a multi-phase inverter driving circuit 25, wherein the multi-phase inverter driving circuit 25 is coupled between the control unit 24 and the motor 22, and configured to drive the motor 22 to operate under the control of the control unit 24. The multi-phase inverter driving circuit 25 may be three-phase, five-phase, or nine-phase.
According to a preferred embodiment of the invention, said control voltage U out And synthesizing by using a part of the plurality of space vector voltages. I.e. the control voltage U out All or part of the plurality of space vector voltages may be selected and combined. For example, the plane coordinate system is divided into a plurality of sectors based on a plurality of basic space vector voltages, according to the control voltage U out In the sector, several space vector voltages are selected from a plurality of basic space vector voltages and are combined.
According to a preferred embodiment of the present invention, the multi-phase inverter driving circuit 25 is a three-phase inverter driving circuit, the plurality of space vector voltages is six space vector voltages, and a part of the plurality of space vector voltages is two space vector voltages. For example, the plane coordinate system is divided into six sectors based on six basic space vector voltages, according to the control voltage U out The sector selects two adjacent space vector voltages of six basic space vector voltages to be synthesized.
According to a preferred embodiment of the invention, the control unit 24 regulates the control voltage U out The vector magnitude and/or duty ratio of each space vector voltage in the motor control system, and obtaining motor torque output in a specified direction to control the motor to stop rotating and point to a fixed direction.
According to a preferred embodiment of the present invention, during the rotation of the motor 22, the control unit 24 obtains the deviation position information of the rotating mirror 21, and adjusts the control voltage U according to the deviation position information out Until the rotating mirror 21 arrivesThe target location.
According to a preferred embodiment of the present invention, during the rotation of the motor 22, the control unit 24 obtains the current circuit parameter information, and adjusts the control voltage U according to the deviation position information and the circuit parameter information out Until the turning mirror 21 reaches the target position.
According to a preferred embodiment of the present invention, the laser radar calibration system further comprises a transmitting unit 26 and a receiving unit 27, wherein the transmitting unit 26 is configured to transmit a detection laser pulse, the receiving unit 27 is configured to obtain echo pulses of the detection laser pulse emitted to a plurality of targets 311, and the control unit 24 is further configured to determine calibration parameters of the laser radar 20 according to echo pulse information corresponding to the plurality of targets 311 respectively obtained when the turning mirror 21 is at the at least one target position.
According to a preferred embodiment of the present invention, the plurality of targets 311 may have different distances and/or reflectivities, respectively.
According to a preferred embodiment of the present invention, the echo pulse information includes at least one of a leading edge, a pulse width, a slope and a peak value of the echo pulse, and the control unit 24 establishes a calibration table of the laser radar 20 by performing calculation processing on data of the calibration parameter based on the calibration parameter.
According to a preferred embodiment of the present invention, the lidar further includes a computer-readable storage medium comprising computer-executable instructions stored thereon that, when executed by the control unit 24, implement the calibration method 10.
The invention also relates to a calibration system 30, with reference to fig. 1A, comprising:
a calibration aid 31, said calibration aid 31 comprising at least one target 311 arranged in different orientations; and
a position sensor 23 configured to detect position information of the turning mirror 21; and
a control unit 24, coupled to the motor 22 and the position sensor 23, configured to:
acquiring at least one target position of the turning mirror 21 by the position sensor 23;
adjusting control voltages of the motors 22 according to the at least one target position so that the rotating mirrors 21 are respectively rotated to the at least one target position; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
echo pulse information is acquired when the turning mirror 21 is at the at least one target position to calibrate the laser radar 20.
Wherein the at least one target location corresponds to the at least one target object 311 disposed at a different orientation.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments described above, or equivalents may be substituted for elements thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (26)
1. A calibration method for a lidar, wherein the lidar includes a rotating mirror and a motor that drives the rotating mirror to rotate, the calibration method comprising:
s11: acquiring at least one target position of the rotating mirror;
s12: adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
s13: and calibrating the laser radar according to the echo pulse information obtained when the rotating mirror is at the at least one target position.
2. The calibration method according to claim 1, wherein the step S12 comprises: and adjusting the vector magnitude and/or the duty ratio of each space vector voltage in the control voltage to obtain the motor torque output in the appointed direction, so that the rotating mirror reaches the target position.
3. The calibration method according to claim 1, wherein the step S12 comprises: and adjusting the control voltage of the motor according to the at least one target position and the load information corresponding to the rotating mirrors, so that the rotating mirrors rotate to the at least one target position respectively.
4. The calibration method according to claim 3, wherein a reverse torque is obtained according to the load information corresponding to the rotating mirror, and the torque output of the motor is corrected.
5. The calibration method according to claim 1, wherein the step S12 further comprises: and in the rotation process of the motor, acquiring deviation position information of the rotating mirror, and adjusting the control voltage according to the deviation position information until the rotating mirror reaches the target position.
6. The calibration method according to claim 5, wherein the deviation position information is acquired from a current position and a target position of the rotating mirror.
7. The calibration method according to claim 5, wherein step S12 further comprises: and in the rotation process of the motor, acquiring current circuit parameter information, and adjusting the control voltage according to the deviation position information and the circuit parameter information until the rotating mirror reaches a target position.
8. The calibration method of claim 7, wherein the circuit parameter information is determined from current information of the motor.
9. The calibration method of any one of claims 1-8, wherein the lidar further comprises an encoder disc, the calibration method further comprising: and detecting the current position of the rotating mirror through the code disc.
10. The calibration method of any one of claims 1-8, wherein the calibration method further comprises: the laser radar transmits a detection laser pulse and acquires echo pulses emitted to a plurality of targets by the detection laser pulse; and determining calibration parameters of the laser radar according to echo pulse information which is obtained when the rotating mirror is at the at least one target position and respectively corresponds to a plurality of target objects.
11. The calibration method according to claim 10, wherein the plurality of targets respectively correspond to different measurement information, and the calibration parameters are used for calibrating the corresponding measurement information.
12. The calibration method of any one of claims 1-8, wherein the echo pulse information includes at least one of a leading edge, a pulse width, a slope, and a peak value of the echo pulse, the calibration method further comprising: and on the basis of the calibration parameters, calculating the data of the calibration parameters to establish a calibration table of the laser radar.
13. A computer-readable storage medium comprising computer-executable instructions stored thereon, wherein the executable instructions, when executed by a processor, implement the calibration method of any one of claims 1-12.
14. A lidar comprising a rotatable mirror and a motor for driving the rotatable mirror to rotate, wherein the lidar further comprises:
a position sensor configured to detect position information of the rotating mirror; and
a control unit coupled to the motor and the position sensor and configured to:
acquiring at least one target position of the rotating mirror through the position sensor;
adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
and acquiring echo pulse information when the rotating mirror is at the at least one target position so as to calibrate the laser radar.
15. The lidar according to claim 14, wherein the position sensor is an encoder disc and the position information is an angular position.
16. The lidar of claim 14, wherein the lidar further comprises a multi-phase inverter driving circuit coupled between the control unit and the motor and configured to drive the motor under the control of the control unit.
17. The lidar of claim 16, wherein the control voltage is synthesized using a fraction of the plurality of space vector voltages.
18. The lidar of claim 17, wherein the multi-phase inverter drive circuit is a three-phase inverter drive circuit, the plurality of space vector voltages is six space vector voltages, and a portion of the plurality of space vector voltages is two space vector voltages.
19. The lidar according to claim 16, wherein the control unit obtains a motor torque output in a given direction by controlling the switching state and duration of the multi-phase inverter drive circuit to adjust the vector magnitude and/or duty cycle of each space vector voltage in the control voltage to control the motor to stall and point in a fixed direction.
20. The lidar according to claim 14, wherein during rotation of the motor the control unit obtains offset position information of the turning mirror and adjusts the control voltage in dependence on the offset position information until the turning mirror reaches the target position.
21. The lidar according to claim 20, wherein during rotation of the motor the control unit obtains current circuit parameter information, and adjusts the control voltage in dependence on the deviation position information and the circuit parameter information until the mirror reaches a target position.
22. The lidar according to any of claims 14 to 21, further comprising a transmitting unit and a receiving unit, wherein the transmitting unit is configured to transmit a probing laser probe, the receiving unit is configured to obtain echo pulses of the probing laser pulse emitted onto a plurality of targets, and the control unit is further configured to determine calibration parameters of the lidar based on echo pulse information corresponding to the plurality of targets respectively obtained when the turning mirror is in the at least one target position.
23. The lidar according to claim 22, wherein the plurality of targets may correspond to different measurement information, respectively, and the calibration parameter is used for calibrating the corresponding measurement information.
24. The lidar according to any of claims 14-21, wherein the echo pulse information comprises at least one of a leading edge, a pulse width, a slope and a peak value of the echo pulse, and the control unit establishes a calibration table of the lidar by performing a calculation process on data of the calibration parameters based on the calibration parameters.
25. The lidar according to claim 24, wherein the lidar further comprises a computer-readable storage medium comprising computer-executable instructions stored thereon, which when executed by the control unit implement the calibration method according to any of claims 1-12.
26. A calibration system, comprising:
a calibration aid comprising at least one target disposed at different orientations; and
lidar, lidar includes commentaries on classics mirror and drive the rotatory motor of commentaries on classics mirror, lidar still includes:
a position sensor configured to detect position information of the rotating mirror; and
a control unit coupled to the motor and the position sensor and configured to:
acquiring at least one target position of the rotating mirror through the position sensor;
adjusting control voltage of the motor according to the at least one target position so that the rotating mirrors rotate to the at least one target position respectively; the control voltage is obtained by synthesizing a plurality of space vector voltages; and
and acquiring echo pulse information when the rotating mirror is at the at least one target position so as to calibrate the laser radar.
Wherein the at least one target location corresponds to the at least one target disposed at a different orientation.
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| CN202111159772.6A CN115902837A (en) | 2021-09-30 | 2021-09-30 | Calibration method of laser radar, laser radar and calibration system |
| PCT/CN2022/099753 WO2023050905A1 (en) | 2021-09-30 | 2022-06-20 | Calibration method for laser radar, laser radar, and calibration system |
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| CN117347985B (en) * | 2023-12-06 | 2024-02-02 | 陕西德丞电子科技有限公司 | Laser radar optical calibration device |
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| CN104753430A (en) * | 2015-04-03 | 2015-07-01 | 东南大学 | Electromobile driving system vector control method using double inverters |
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