机械臂倒液任务中透明容器的液位高度视觉检测与控制

Visual detection and control for liquid level height of transparent containers in robotic pouring

针对包含多类透明容器与多种液体的机械臂倒液任务,提出了一种不需要相机标定与标尺辅助的液位相对高度视觉检测方法与闭环控制方案。首先,分析了服务机器人倒液任务的特点,使用计算机视觉中的目标检测方法同时检测液体与容器,利用液体与容器的高度比例关系得到相对液位高度,避免了测量液位绝对高度所需的繁杂标定过程。其次,利用小孔成像模型对所提的相对液位高度检测方案进行几何建模与分析,推理出典型情形下测量的误差规律;再次,采集多种液体、多类容器的图像作为训练集来训练YOLOv5s,用于检测目标物以获得液位相对高度。测试结果验证了所提的液位检测方法的有效性,新方法对于训练集中未出现的新形状容器中的新液体的平均配对检出精度为86.7%;最后,为了避免求解或估计视觉伺服理论中复杂的雅可比矩阵,将求得的相对液位高度与PD控制结合组成液位闭环控制系统。系统使用相同的PD控制器参数在两种倒液平台上的多类倒液任务中均取得成功,验证了液位闭环控制方案的有效性与鲁棒性。

A visual detection method of relative liquid level without camera calibration and liquid level gauge and closed-loop control system are proposed for the robotic pouring task related to multiple types of transparent containers and liquids.Firstly,the characteristics of the service robots′liquid pouring tasks are analyzed and the target detection method in computer vision field is deployed to detect liquids and containers simultaneously.The relative liquid level height is obtained by calculating the height-proportion between the detected container and detected liquid,which avoids the complicated hand-eye calibration processes during the measurement of liquid level′s absolute height.Secondly,the proposed liquid level detection method is geometrically modeled and analyzed by applying the pinhole imaging model,and the laws on measurement errors of relative liquid level height are deduced in typical cases.Thirdly,the images of various liquids and containers are collected to train YOLOv5s,which is deployed to detect target object and obtain the relative height of liquid level.The test results verify the effectiveness of proposed method.The paired average precision of new method is 86.7%for the new types of liquids in new shaped containers that do not appear in the training set.Finally,to avoid solving or estimating corresponding Jacobian matrices in visual servo theory,the detected liquid level height is combined with PD control to get a closed-loop control system.Several kinds of liquid pouring tasks on both manipulator platforms are successful with the same parameters in PD controller,which prove the effectiveness and robustness of proposed closed-loop control method.