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摘要: 事件相机作为一种新型动态视觉传感器, 通过各个像素点独立检测光照强度变化并异步输出“事件流”信号, 具有数据量小、延迟低、动态范围高等优秀特性, 给机器人控制带来新的可能. 本文主要介绍了近年来涌现的一系列事件相机与无人机、机械臂和人形机器人等机器人感知与运动控制结合的研究成果, 同时聚焦基于事件相机的控制新方法、新原理以及控制效果, 并指出基于事件相机的机器人控制的应用前景和发展趋势.Abstract: As a new type of dynamic vision sensor, the event camera detects the change of illumination intensity independently through each pixel and outputs the “event stream” signal asynchronously. It has excellent characteristics such as small amount of data, low latency and high dynamic range, which brings new possibilities for robot control. In this survey, a series of the latest research results on the combination of event camera and robot perception and motion control, including unmanned aerial vehicles, manipulators and humanoid robots, are introduced. At the same time, the new control methods, new principles and control effects based on event camera are focused, and the application prospect and development trend of robot control based on event camera are pointed out.
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Key words:
- Event camera /
- low latency /
- robot control /
- perception and motion /
- new control algorithm
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图 2 旋转圆盘场景下帧相机与事件相机输出对比[2-3]. 帧相机在每一帧图像中记录全部像素点上的数据, 即使圆盘中大部分区域的信息是无用的; 事件相机仅记录圆盘中的黑点位置, 因此仅对运动的有效信息输出事件
Fig. 2 Comparison of outputs between frame camera and event camera in rotating disc scene[2-3]. The frame camera records the data on all pixels in each frame image, even if the information in most areas of the disc is useless; The event camera only records the position of black spots in the disc, so it only outputs events for the effective information of motion
图 6 无人机躲避高速运动物体的相关实验((a)无人机实验平台[26]; (b)真实无人机躲避两个飞行障碍物, 四旋翼无人机使用EVDodgeNet进行障碍物躲避, 其中无人机左右两侧的弧线轨迹为同时掷向无人机的两个障碍物, 中间的轨迹为无人机闪躲轨迹[27]; (c)神经网络架构图[27], 其中EVDeblurNet: 事件帧去噪网络, 在模拟数据集上进行训练就可推广到真实场景, 无需重新训练或者微调; EVHomographyNet: 单应性估计网络, 用于自我运动估计, 计算相机的自我运动. 第一个使用事件相机的单应性估计方案; EVSegFlowNet: 物体分割与光流计算网络, 该网络可分割场景中的运动物体并获取其光流信息)
Fig. 6 Experiments of UAV avoiding high-speed moving obstacles ((a) UAV experimental platform[26]; (b) The real UAV avoids two flying obstacles, and the quadrotor UAV uses EVDodgeNet to avoid obstacles, in which the arc trajectory on left and right sides of the UAV is two obstacles thrown at the same time, and the middle trajectory is the UAV dodge trajectory[27]; (c) Neural network architecture diagram[27], in which EVDeblurNet: event frame denoising network, which can be extended to real scenes by training on simulated datasets without retraining or fine tuning; EVHomographyNet: homography estimation network, which is used to estimate self-motion and calculate self-motion of camera. The first homography estimation scheme using event camera; EVSegFlowNet: an object segmentation and optical flow computing network, which can segment moving objects in the scene and obtain their optical flow information)
图 18 技术发展脉络图 (横轴为感知技术分类, 负横轴为基于事件帧的图像感知算法, 正横轴为基于异步事件流的感知算法; 纵轴为控制技术分类, 正纵轴为基于目标特征的运动规划与控制的传统方法, 负纵轴为基于异步事件流的新型控制算法,其中使用相似技术路线的文献处于同一象限, 标注是根据机器人类型进行分类并按时间顺序排列, 虚线内文献只涉及基于事件相机的感知技术)
Fig. 18 Development venation map of technology (The horizontal axis is the classification of perception technology, the negative horizontal axis is the image perception algorithm based on event frame, and the positive horizontal axis is the perception algorithm based on asynchronous event stream. The vertical axis is the classification of control technology, the positive vertical axis is the traditional method of motion planning and control based on object features, and the negative vertical axis is a new control algorithm based on asynchronous event stream. The literatures using similar technical routes are in the same quadrant, and the labels are classified according to robot types and arranged in chronological order. The literatures in the dotted line only involve the sensing technology based on event cameras)
表 1 几种事件相机的性能比较表
Table 1 Performance comparison table of several event cameras
文献 事件相机型号 产品年份 分辨率 (pixel) 最高动态范围 (dB) 功耗 (mW) 延迟 (μs) 像素大小 (μm2) [10] DVS128 2008 128×128 120 132 ~ 231 12 40 × 40 [17] DVS1280 2020 1280×960 120 150 — 4.95 × 4.95 [15] ATIS 2011 304×240 143 50 ~ 175 3 30 × 30 [19] DAVIS240 2014 240×180 130 5 ~ 14 12 18.5 × 18.5 [20] DAVIS346 2018 346×260 120 10 ~ 170 20 18.5 × 18.5 [21] CeleX-V 2019 1280×800 120 390 ~ 470 8 9.8 × 9.8 表 2 无人机部分实验场景
Table 2 Experimental scenarios of UAV
文献 无人机型号 事件相机 处理器或控制器 事件流处理方法 备注 基于事件帧 [2] Parrot AR.Drone 2.0 DVS Odroid U2 onboard computer Hough 变换 跟踪速度高达 1200°/s [22] — DVS Standard PC 卡尔曼滤波, Lie-EKF 公式 跟踪速度超过 2.5 m/s,
加速度超过 25.8 g[24] 组装 DAVIS 240C Intel Upboard Lumenier F4
AIO flight controllerHough 变换, 卡尔曼滤波 跟踪速度高达 1600°/s [27] Intel Aero Ready to
Fly DroneDAVIS 240C
DAVIS 240BNVIDIA TX2 CPU+GPU 浅层神经网络 碰撞预测时间 60 ms [37] 定制 MavTec DVS128 Lisa/MX Odroid XU4 聚类, 光流算法 — 基于事件流 [25] 组装 双目 DVS 128 Odroid U3 quad-core computer 高斯核函数, 卡尔曼滤波 碰撞预测时间 250 ms [26] 基于 DJI F330 定制 Insigthness SEEM1 Intel Upboard Lumenier F4
AIO flight controllerDBSCAN 聚类, 光流算法 碰撞预测时间 68 ms (2 m 处)
183 ms (3 m 处)[28] 定制 Insightness SEEM1 Qualcomm Snapdragon Flight
NVIDIA Jetson TX2DBSCAN 聚类, 光流
算法, 卡尔曼滤波碰撞预测时间 3.5 ms [35] 基于 DJI F450 DAVIS 346 PixRacer Khadas VIM3 Hough 变换, 卡尔曼滤波 规划时间 2.95 ms [39] Parrot Bebop2 — Dual-core ARM cortex A9 processor. 脉冲神经网络, 光流算法 神经形态控制器效果良好 表 3 部分基于事件相机的实验设备
Table 3 Experimental equipment based on event camera
文献 使用传感器 机械臂设备 方法 [41] DAVIS240C UR10 事件流 [43] Prophesee Gen3, NeuTouch 7 DOF Franka Emika Panda arm 事件流 + SNN [42] DAVIS240C Baxter robot arm 事件帧 [45] DAVIS240C AX-12A Dynamixel servo motor 事件帧 + DNN [46] DAVIS240C, ATI F/T sensor (Nano17) Baxter robot arm 事件帧 + CNN [47] DAVIS240C, ATI F/T sensor (Nano17) Baxter robot daul-arm 事件帧 [49] DVS128 — 事件帧 -
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