Research on tightly combined positioning method of coal mine robot based on UWB and IMU
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摘要: 针对煤矿井下环境复杂,现有煤矿机器人定位方法受非视距误差等因素影响导致定位精度低、实时性不高等问题,提出了一种基于UWB(超宽带)和IMU(惯性测量单元)的煤矿机器人紧组合定位方法。首先利用UWB模块测量煤矿机器人与UWB基站之间的距离,使用煤矿机器人与UWB基站之间的距离真实值和实测值训练最小二乘支持向量机(LSSVM)模型,得到LSSVM修正模型;然后将煤矿机器人定位过程中UWB模块测得的实测值作为LSSVM修正模型的输入,通过LSSVM修正模型对UWB实测值进行修正,减小非视距误差对定位精度的影响,得到较为准确的距离信息;最后将经过LSSVM修正模型修正后的测距信息作为误差状态卡尔曼滤波(ESKF)的量测输入,与惯性导航解算出的位置信息构成量测方程,使用ESKF对UWB测距修正值与惯性导航解算的距离信息紧组合,完成状态更新,得到更为精确的位置信息,实现煤矿机器人的精确定位。UWB基站不同布置方案下的模拟实验结果表明:使用LSSVM修正模型可使UWB测距信息更为准确,进而提高定位精度。静态定位实验时,当4个UWB基站等高对称布置时,定位的均方根误差由0.146 4 m减小到0.1398 m;当4个UWB基站不等高对称布置时,均方根误差由0.300 8 m减小到0.200 6 m;当4个基站无规律布置时,均方根误差由0.317 5 m减小到0.314 2 m。因此,在实际场景中,应尽可能使UWB基站等高对称布置。动态定位实验时,通过LSSVM修正模型对UWB测距信息进行修正后的融合定位轨迹相较于修正前的融合定位轨迹更接近煤矿机器人的真实轨迹,验证了该紧组合定位方法能够减小非视距误差,提高定位精度。Abstract: The underground coal mine environment is complex. The existing coal mine robot positioning methods have low positioning precision and low real-time performance caused by the non-line-of-sight (NLOS) error and other factors. In order to solve the above problems, a tightly combined positioning method of coal mine robot based on UWB (Ultra Wide Band) and IMU (Inertial Measurement Unit) is proposed. Firstly, the UWB module is used to measure distance between the coal mine robot and UWB base station. The least square support vector machine (LSSVM) model is trained by using real value and measured value of the distance between the coal mine robot and the UWB base station, and the modified LSSVM model is obtained. Secondly, the measured value measured by the UWB module during the positioning process of the coal mine robot is used as the input of the modified LSSVM model. The modified LSSVM model is used to correct the measured value of UWB, reduce the influence of NLOS error on positioning precision, and obtain more accurate distance information. Finally, the range information modified by modified LSSVM model is used as the measurement input of error-state Kalman filter (ESKF). The measurement equation is formed with the position information solved by inertial navigation. The ESKF is used to tightly combine the UWB ranging correction value with the range information calculated by the inertial navigation to complete the state update. The more precise position information of the coal mine robot is obtained, and the precise positioning of the coal mine robot is achieved. The simulation results under different layont schemes of UWB base stations show that using modified LSSVM model can make the UWB range information more accurate, and improve the positioning precision. In the static positioning experiment, when the four UWB base stations are symmetrically distributed at the same height, the root mean square error of the positioning is reduced from 0.146 4 m to 0.139 8 m. When the four UWB base stations are distributed symmetrically with unequal heights, the root mean square error decreases from 0.300 8 m to 0.200 6 m. When the four base stations are distributed irregularly, the root mean square error decreases from 0.317 5 m to 0.314 2 m. Therefore, in actual scenarios, the UWB base stations should be arranged symmetrically at the same height as possible. In the dynamic positioning experiment, the fusion positioning trajectory corrected by the modified LSSVM model is closer to the real trajectory of the coal mine robot than the fusion positioning trajectory before correction. The result verifies that the tightly combined positioning method can reduce the NLOS error and improve positioning precision.
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表 1 UWB基站位置坐标
Table 1. UWB base station layout coordinates
m 方案 位置坐标 基站0 基站1 基站2 基站3 方案1 (4.48,0,2) (−4.48,0,2) (4.15,8.06,2) (−4.15,8.06,2) 方案2 (4.48,0,2) (−4.48,0,2) (4.15,8.06,1) (−4.15,8.06,1) 方案3 (4.48,0,2) (−4.48,0,2) (4.59,7.80,1.44) (−4.5,6.4,1.2) 表 2 3种基站布置方案的实验均方根误差
Table 2. Experimental root mean square error of three base stations layout schemes
m 方案 原始误差 LSSVM模型修正后的误差 方案1 0.146 4 0.139 8 方案2 0.300 8 0.200 6 方案3 0.317 5 0.314 2 -
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