Dongdong Chen

A micro-adjusting attitude mechanism for autonomous drilling robot end-effector

Drilling end-effector is a key unit in autonomous drilling robot. The perpendicularity of the hole has an important influence on the quality of airplane assembly. Aiming at the robot drilling perpendicularity, a micro-adjusting attitude mechanism and a surface normal measurement algorithm are proposed in this paper. In the mechanism, two rounded eccentric discs are used and the small one is embedded in the big one, which makes the drill’s point static when adjusting the drill’s attitude. Thus, removal of drill’s point position after adjusting the drill attitude can be avoided. Before the micro-adjusting progress, four non-coplanar points in space are used to determine a unique sphere. The normal at the drilling point is measured by four laser ranging sensors. The adjusting angles at which the motors should be rotated to adjust attitude can be calculated by using the deviation between the normal and the drill axis. Finally, the motors will drive the two eccentric discs to achieve micro-adjusting progress. Experiments on drilling robot system and the results demonstrate that the adjusting mechanism and the algorithm for surface normal measurement are effective with high accuracy and efficiency.概要创新点(1)设计一种微型姿态调整机构, 实现对钻头姿态进行调整, 使其沿制孔点法线进行制孔, 提高孔的垂直度. 使得钻头调整前后, 钻头顶点保持不变, 提高制孔效率. (2)利用4个激光测距传感器, 根据空间不共面四点确定唯一球, 测得制孔点处的法线向量, 为钻头的姿态调整做准备.

Perpendicularity adjustment end effector for aeronautical drilling robot

The quality of holes has important influence on the mechanical strength, assembly quality and life of aircraft, and inferior quality holes may even cause airplane crash and casualties. The perpendicular accuracy of holes during drilling is crucial one of all the factors influencing the quality of holes. In order to improve the perpendicular accuracy during drilling, this paper presented an attitude adjustment mechanism and attitude adjustment algorithm for the end effector. For the mechanism, it adjusts the drill bit attitude by using double eccentric discs and a spherical pair. After the surface normal vector at drilling point is obtained, double eccentric discs will rotate define angels calculated by using attitude adjustment algorithm based on the shortest time principle to achieve the coincidence of the surface normal vector and the drill bit axis vector if the angle between the normal vector and drill bit axis vector is greater than 0.5°. To demonstrate the method mentioned above, simulation and experiment are carried out on the aeronautical drilling robot. The results show that the attitude adjustment mechanism and attitude adjustment algorithm can increase the perpendicular accuracy of holes during drilling and satisfy the demand in automatic aircraft assembly.

Movement Planning and Simulation for Attitude Adjustment of a Drilling Robot

A movement planning method for attitude adjustment of a drilling robot is presented in this paper. The double eccentric discs normal adjustment mechanism is used in the robot to adjust the attitude of the drill axis. To improve the adjustment efficiency, the robot should rotate the eccentric discs to the target point in a most effective way. But there are two available directions and attitudes to rotate, while the anti-trigonometric functions also have two solutions, the key problem of the movement planning is how to choose the optimal solutions from these calculated solutions to rotate the eccentric discs to improve the rotary efficiency. The principle of choosing the solutions is that the eccentric discs should rotate in the minimum absolute angle values to move to the target point. Finally, the movement loci from the initial position and a specific attitude to some different points in different quadrants are simulated in Mat lab to verify the feasibility of the rotary angle calculation method.

The study of drilling and countersink technology in robot drilling end-effector

Aiming at the drilling verticality in aircraft assembly, this paper presents a design method of a Double-Eccentricdisc Normal-Adjustment (DENA) mechanism; it can adjust the two rotational degrees of freedom by the interaction of two eccentric discs, and make the drill axis coincide with the normal direction of the drilling point. This method ensures that the position of the drill vertex can be kept static during the attitude adjustment process. In addition, it can avoid position compensation and secondary positioning, and then improve the drilling efficiency. Using pressure sensor, the robot can control the countersink depth by detecting the states of the drill and the pressing force of the cylinder. It can eliminate the influence of the deformation under the compression to the countersink depth precision and make the countersink precision accuracy within 0.05mm. Finally, the experimental results are addressed to verify the rationality of DENA mechanism and the feasibility of using pressure sensor to control the countersink depth.

Intelligent surface normal measurement method of end effector for the aeronautical drilling robot

In order to solve the perpendicularity of robotic drilling in the aircraft assembly, this paper proposed a novel surface normal measurement method for the aeronautical drilling robot. Firstly, vision location module is used to mark the drilling point and get the coordinate of drilling point. Meanwhile, four laser range sensors start to measure the distance between the emitting laser points and their subpoints on the workpiece surface. Thus, the coordinates of four subpoints can be obtained. According to the four subpoints and drilling point, line or circle are used to approach two curves through the drilling point on the workpiece surface. Two tangent vectors of the two curves at drilling point can be obtained. Then the normal vector of drilling point can be calculated from the cross product of two tangent vectors. The angle between the normal vector and drill axis vector can be obtained. If the angle is greater than 0.5 degree, the two eccentric discs will rotate definite angles to meet the requirement. Finally, the simulation results and experimental results on the aeronautical drilling robot show that the surface normal measurement method is valid and effective to meet the requirement in aircraft assembly.

AGV System Based on Multi-sensor Information Fusion

This paper proposed hardware and software structure of the AGV system, localization method and tracking control method. In order to achieve long time and high precision localization of the AGV, this paper proposed a multi-sensor information fusion method for localization. The method was based on the characteristics of the used sensors, and adopted Kalman filter to fuse the heading direction data and position data respectively to obtain the best estimate value of AGV posture information. This paper used the control rule designed by Kanayama and the reference velocities and posture of target which were planned in advance and updated continuously for tracking control. This approach realized the tracking control accuracy and stability of the AGV. Some experiment results verified the correctness of localization method and tracking control method of the AGV system on the basis of the differential AGV.

A novel tracking control method based on LADRC for autonomous mobile robot

The trajectory tracking control problem of nonholonomic mobile robots is investigated in the paper. In order to match well the real trajectory and the referenced one which is set in advance, a novel control method is designed. Firstly, velocity and angular velocity of the mobile robot is obtained by kinematic control law using the attitude error. Then the mobile robot will track the referenced kinematic state very well using the dynamic control law based on the control theory of Linear Active Disturbance Rejection Control (LADRC). Finally, the current attitude information would be updated after translation and integration to go on the next calculating circle. Simulation results are given to demonstrate the stability and effectiveness of the proposed controller.

A mapping method based on EKF and point-segment matching for indoor environment

A map construction method based on point-segment (PS) feature with laser scanner is presented in this paper to accomplish the indoor mobile robot SLAM. The preprocessed sensor data is divided into objective set through dynamic threshold segmentation. To fit the feature, improved Hough-transform is adopted to pick out the short segments from the objective set and an incorporating method is applied to merge the segments belonging to the same feature set. Then, a segment phase matching method is used to establish the global map, during which the EKF along with the matching technique is employed to estimate the optimal pose. Finally, experiment is implemented on the robot ATR1 in the given environment. Though the robot deviated from its planning path up to -177.38mm in Y-direction and 124.56mm in X-direction, the constructed map still shows the rationality and effectiveness of the method.

Intelligent Double-Eccentric Disc Normal Adjustment Cell in Robotic Drilling

An intelligent verticality adjustment method named double-eccentric disc normal adjustment (DENA) is presented in precise robotic drilling for aero-structures. The DENA concept is conceived specifically to address the deviation of the spindle from the surface normal at the drilling point. Following the concept of intelligent and accurate normal adjustment, two precise eccentric discs (PEDs) with the identical eccentric radius are adopted. Indispensably, two high-resolution stepper motors are used to provide rotational power for the two PEDs. Once driven to rotate with appropriate angles respectively, two PEDs will carry the spindle to coincide with the surface normal, keeping the vertex of the drill bit still to avoid the repeated adjustment with the help of the spherical plain bearing. Since the center of the spherical plain bearing coincides with the vertex of the drill bit, successful implementation of DENA has been accomplished on an aeronautical drilling robot platform. The experimental results validate that DENA in robotic drilling is attainable in terms of intelligence and accuracy.

A Normal Sensor Calibration Method Based on an Extended Kalman Filter for Robotic Drilling

To enhance the perpendicularity accuracy in the robotic drilling system, a normal sensor calibration method is proposed to identify the errors of the zero point and laser beam direction of laser displacement sensors simultaneously. The procedure of normal adjustment of the robotic drilling system is introduced firstly. Next the measurement model of the zero point and laser beam direction on a datum plane is constructed based on the principle of the distance measurement for laser displacement sensors. An extended Kalman filter algorithm is used to identify the sensor errors. Then the surface normal measurement and attitude adjustments are presented to ensure that the axis of the drill bit coincides with the normal at drilling point. Finally, simulations are conducted to study the performance of the proposed calibration method and experiments are carried out on a robotic drilling system. The simulation and experimental results show that the perpendicularity of the hole is within 0.2°. They also demonstrate that the proposed calibration method has high accuracy of parameter identification and lays a basis for high-precision perpendicularity accuracy of drilling in the robotic drilling system.