CN114199281A - Multi-sensor combined calibration method and system based on speed optimization - Google Patents

Multi-sensor combined calibration method and system based on speed optimization Download PDF

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CN114199281A
CN114199281A CN202111521844.7A CN202111521844A CN114199281A CN 114199281 A CN114199281 A CN 114199281A CN 202111521844 A CN202111521844 A CN 202111521844A CN 114199281 A CN114199281 A CN 114199281A
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sensor
sensors
speed
data set
time
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陈智君
郝奇
郑亮
曹雏清
陈双
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Wuhu Robot Technology Research Institute of Harbin Institute of Technology
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    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
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Abstract

The invention discloses a multi-sensor combined calibration method based on speed optimization, which comprises the following steps: s1, acquiring data and timestamps of the mobile robot in the driving process by the m sensors, and calculating the speed of the sensors at the acquisition time; s2, acquiring speed values of m sensors under the same time sequence through an interpolation method, and putting the speed values into a data set Sensor _ list; and S3, converting the speed values of different sensors under the base coordinate system into a least square problem, and solving the least square problem in a nonlinear way to obtain a transformation matrix of each sensor relative to the base coordinate system. The invention has no requirements on the type, performance and quantity of the sensors to be calibrated, and has strong expandability; the method is insensitive to the self accumulated error of the sensor and has high calibration precision.

Description

Multi-sensor combined calibration method and system based on speed optimization
Technical Field
The invention belongs to the technical field of robots, and particularly relates to a multi-sensor combined calibration method and system based on speed optimization.
Background
With the development of science and technology, mobile robots are widely applied in the fields of warehouse logistics, intelligent inspection and the like, and the environment perception technology is an important component of the mobile robot technology and is the basis for the mobile robots to execute tasks. Depending on a single sensor to sense the environment, a satisfactory result cannot be obtained, so that a plurality of sensors are installed on the body of the mobile robot, information of various sensors is subjected to complementary and optimized combination processing, and finally an optimal observation result of the environment is generated, such as an IMU, a GPS, a camera, a laser radar and the like. Before a plurality of sensors are comprehensively applied, the relative pose transformation of each sensor needs to be known, namely the calibration of the sensor, and a transformation matrix from each sensor to a base coordinate system needs to be calibrated.
The existing calibration method calculates the positioning results of different sensors to obtain the relative relationship between the sensors, such as the calibration between a laser radar and a odometer or an IMU. However, the above calibration scheme has poor expansibility, cannot adapt to the variation of the type and number of the sensors, and the calibration result is affected by the accumulated error of the measurement of the sensors.
Disclosure of Invention
The invention provides a multi-sensor combined calibration method based on speed optimization, and aims to provide a multi-sensor calibration method with strong expansibility and high calibration precision.
The invention is realized in such a way that a multi-sensor combined calibration method based on speed optimization specifically comprises the following steps:
s1, acquiring data and timestamps of the mobile robot in the driving process by the m sensors, and calculating the speed of the sensors at the acquisition time;
s2, acquiring speed values of m sensors under the same time sequence through an interpolation method, and putting the speed values into a data set Sensor _ list;
and S3, converting the speed values of different sensors under the base coordinate system into a least square problem, and solving the least square problem in a nonlinear way to obtain a transformation matrix of each sensor relative to the base coordinate system.
Further, the speed value obtaining method of the m sensors under the same time sequence is specifically as follows:
s21, putting the Time stamp of each sensor into a Time stamp container Time _ all, arranging the Time stamps in sequence, and deleting redundant Time stamps;
s22, sequentially selecting the data set S of each Sensor in the data set Sensor _ list, interpolating the data set S, and acquiring the speed values of all the sensors under the same time sequence, wherein the data set S of the Sensor iiThe interpolation process of (2) is as follows:
traversing all timestamps t in a timestamp container Time _ all, detecting whether timestamps corresponding to the timestamps t exist in a data set S, and if the detection result is negative, calculating a speed value v of the sensor i under the timestamps t based on an interpolation methodtInserting the data set SiIn (1).
Further, in the data set SiFind two time stamps t adjacent to the time ti、ti+1Wherein t isi<t<ti+1Velocity value v of sensor i at time stamp ttThe calculation formula is as follows:
Figure BDA0003407978430000021
wherein the content of the first and second substances,
Figure BDA0003407978430000022
respectively indicating the time stamp t of the sensor ii、ti+1The lower velocity value.
Further, the formula of the least squares problem is as follows:
Figure BDA0003407978430000023
solving the least square problem through nonlinearity, and calculating to obtain a precise transformation matrix T _ list ═ T of each sensor relative to a base coordinate system1,T2,…,Tm}。
The invention is realized in such a way that a multi-sensor combined calibration system based on speed optimization comprises:
setting m sensors on the same mobile robot, and a processing unit in communication connection with the m sensors, wherein the processing unit calibrates a transformation matrix T _ list ═ T { T } of each sensor relative to a base coordinate system based on the multi-sensor combined calibration method based on speed optimization1,T2,…,Tm}。
The invention has no requirements on the type, performance and quantity of the sensors to be calibrated, and has strong expandability; the method is insensitive to the self accumulated error of the sensor and has high calibration precision.
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FIG. 1 is a flow chart of a multi-sensor joint calibration method based on speed optimization according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a multi-sensor combined calibration system based on speed optimization according to an embodiment of the present invention.
Detailed Description
The following detailed description of the embodiments of the present invention will be given in order to provide those skilled in the art with a more complete, accurate and thorough understanding of the inventive concept and technical solutions of the present invention.
The invention aims to solve the problem that the mobile robot needs to calculate the conversion relation between the coordinate systems of different sensors and a base coordinate system before positioning, navigation and other operations. The sensors in the invention are required to be arranged on the same mobile robot, the base coordinate system is a target coordinate system to which all the sensors are required to be converted, the base coordinate system can be superposed with the coordinate system of a certain sensor, the initial value of the transformation from each sensor to the base coordinate system is required to be calibrated in advance, the accuracy of the initial value is relatively low, and the initial value can be obtained by measurement or estimation on a graph or a real object. Assume a set of m sensors and their initial transformation matrices to the base coordinate system, T _ list ═ T1,T2,…,TmFig. 1 shows a flow of a multi-sensor joint calibration method based on speed optimization, and the method specifically includes the following steps:
s1, acquiring data and timestamps of the mobile robot in the driving process by m sensors, calculating the speed of the sensors at the acquisition time, and storing the timestamps and the corresponding speed in a data set Sensor _ list in pairs;
the IMU and the odometer can obtain the sensor speed through simple integral calculation of original data, the vision (camera) and the laser sensor need to calculate the position and pose of the odometer through a front-end mileage calculation method, and then the speed of the sensor is calculated through the position and pose of continuous time, and the calculation formula of the sensor speed v is as follows:
Figure BDA0003407978430000041
wherein the positioni+1、poseiRepresenting successive time instants ti+1、tiA lower pose;
obtaining a data set of all sensors after completion, wherein the data set is S1,S2,…,SmIn which S isiData set representing sensor i, denoted as
Figure BDA0003407978430000042
Figure BDA0003407978430000043
Indicating sensor i at time tnThe speed of (2).
S2, acquiring speed values of m sensors under the same time sequence through an interpolation method, and putting the speed values into a data set Sensor _ list;
because the data sampling frequencies of the multiple sensors may be different, the acquired data may not be at the same time, and therefore interpolation calculation needs to be performed on the acquired data to obtain data at the same time, and the speed value obtaining method of the m sensors in the same time sequence is specifically as follows:
s21, putting the Time stamp of each sensor into a Time stamp container Time _ all, arranging the Time stamps in sequence, and deleting redundant Time stamps;
s22, sequentially selecting data setsData set S for each Sensor in Sensor _ list, data set S for Sensor iiThe following operations are performed:
traversing all timestamps t in a timestamp container Time _ all, detecting whether timestamps corresponding to the timestamps t exist in a data set S, and if the detection result is negative, calculating a speed value v of the sensor i under the timestamps t based on an interpolation methodtInserting the data set SiPerforming the following steps;
in the embodiment of the invention, in the data set SiFind two time stamps t adjacent to the time ti、ti+1The time stamp satisfies ti<t<ti+1Velocity value v of sensor i at time stamp ttThe calculation formula is as follows:
Figure BDA0003407978430000051
wherein the content of the first and second substances,
Figure BDA0003407978430000052
respectively indicating the time stamp t of the sensor ii、ti+1The lower velocity value.
After the interpolation of all the sensor data sets is completed, the interpolated data sets of all the sensors are obtained
Figure BDA0003407978430000053
Wherein the content of the first and second substances,
Figure BDA0003407978430000054
represents tkTime sensor 1, sensor 2 … …, and sensor m are speed values in their own coordinate system.
S3, constructing a least square problem based on the principle that the speed values of different sensors under the base coordinate system are equal, and obtaining a transformation matrix of each sensor relative to the base coordinate system by solving the least square nonlinearly.
S31, calculating to obtain a data set after interpolation of all sensors, and constructing a least square problem as follows:
Figure BDA0003407978430000055
Vt-irepresenting the speed value, T, of the sensor i in its own coordinates at time TiIs a transformation matrix of sensor i with respect to base coordinates, Vt-jRepresents the velocity value of the sensor j at time T in its own coordinate, TjIs the transformation matrix for sensor j relative to the base coordinate,
taking the coordinate system of one of the sensors as a base coordinate system, that is, the speed values of the sensors at the same time should be equal after being converted to the base coordinate system, solving the least square problem by using step S32, and calculating to obtain a precise transformation matrix T _ list ═ T of each sensor relative to the base coordinate system1,T2,…,Tm}。
S32, solving nonlinear least squares:
1) for a non-linear least squares problem to be solved:
Figure BDA0003407978430000061
Figure BDA0003407978430000062
taylor expansion is performed on F (x), taking the first order linear term approximation into the equation:
Figure BDA0003407978430000063
wherein J (x) is the Jacobian matrix of F (x);
2) the above equation is derived and the reciprocal is made to be 0:
J(x)TJ(x)Δx=-J(x)TF(x)
let A be J (x)TJ(x),B=-J(x)TF (x), the above equation can be simplified to a Δ x ═ B, and the linear equation set is solved, so that the pose increment Δ can be obtainedx;
3) And adding the current pose x to the current pose increment delta x to obtain an optimized pose, judging whether each component of the delta x meets constraint conditions, if so, ending iteration to obtain a final optimized pose, and if not, substituting the optimized pose into the step 3) to continue iterative solution.
Fig. 2 is a schematic structural diagram of a multi-sensor combined calibration system based on speed optimization according to an embodiment of the present invention, which is only shown in relevant parts according to the embodiment of the present invention for convenience of description, and the system includes:
the method comprises the steps that m sensors on the same mobile robot are arranged, a processing unit is in communication connection with the m sensors, and the processing unit calibrates a transformation matrix T _ list ═ T of each sensor relative to a base coordinate system based on data collected by the m sensors1,T2,…,Tm}。
The invention has been described above with reference to the accompanying drawings, it is obvious that the invention is not limited to the specific implementation in the above-described manner, and it is within the scope of the invention to apply the inventive concept and solution to other applications without substantial modification.

Claims (5)

1. A multi-sensor combined calibration method based on speed optimization is characterized by specifically comprising the following steps:
s1, acquiring data and timestamps of the mobile robot in the driving process by the m sensors, and calculating the speed of the sensors at the acquisition time;
s2, acquiring speed values of m sensors under the same time sequence through an interpolation method, and putting the speed values into a data set Sensor _ list;
and S3, converting the speed values of different sensors under the base coordinate system into a least square problem, and solving the least square problem in a nonlinear way to obtain a transformation matrix of each sensor relative to the base coordinate system.
2. The multi-sensor combined calibration method based on speed optimization as claimed in claim 1, wherein the speed value obtaining method of the m sensors under the same time sequence is specifically as follows:
s21, putting the Time stamp of each sensor into a Time stamp container Time _ all, arranging the Time stamps in sequence, and deleting redundant Time stamps;
s22, sequentially selecting the data set S of each Sensor in the data set Sensor _ list, interpolating the data set S, and acquiring the speed values of all the sensors under the same time sequence, wherein the data set S of the Sensor iiThe interpolation value process of (1) is as follows:
traversing all timestamps t in a timestamp container Time _ all, detecting whether timestamps corresponding to the timestamps t exist in a data set S, and if the detection result is negative, calculating a speed value v of the sensor i under the timestamps t based on an interpolation methodtInserting the data set SiIn (1).
3. The method for multi-sensor joint calibration based on speed optimization of claim 1, wherein the data set S is a data setiFind two time stamps t adjacent to the time ti、ti+1Wherein t isi<t<ti+1Velocity value v of sensor i at time stamp ttThe calculation formula is as follows:
Figure FDA0003407978420000011
wherein v isti、vti+1Respectively indicating the time stamp t of the sensor ii、ti+1The lower velocity value.
4. The multi-sensor joint calibration method based on speed optimization as claimed in claim 1, wherein the formula of the least square problem is as follows:
Figure FDA0003407978420000021
solving the least square problem through nonlinearity, and calculating to obtain a precise transformation matrix T _ list ═ T of each sensor relative to a base coordinate system1,T2,…,Tm}。
5. A multi-sensor joint calibration system based on speed optimization, the system comprising:
setting m sensors on the same mobile robot, processing unit connected with the m sensors in communication, the processing unit calibrating the transformation matrix T _ list ═ T of each sensor relative to the base coordinate system based on the multi-sensor combined calibration method based on speed optimization claimed in any one of claims 1 to 41,T2,…,Tm}。
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