Zhenyun Shi

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.

The attitude adjustment algorithm in drilling end-effector for aviation

To ensure the perpendicularity of drilling holes in aircraft manufacturing, the attitude of spindle axis must be adjusted to coincide with the normal vector of drilling point before drilling. The double eccentric discs-spherical pair structure was used as attitude adjustment mechanism in drilling end-effector. Therefore, the attitude adjustment algorithm of spindle axis is proposed in this article. There were two attitudes for current and target position, respectively, and the rotation sequence of each eccentric disc would affect the attitude adjustment efficiency. This article presents the path planning and optimal solution choosing from multiple solutions. Finally, the effectiveness and accuracy of the algorithm are verified in simulation and drilling experiment, resulting in a normality tolerance of ±0.5° and precision of H9.

An effective self-adaptive mean filter for mixed noise

The image is usually corrupted by Gauss noise and impulse noise simultaneously, and its quality will be reduced. Thus filtering image is important in image processing. The traditional mean filter cannot remove impulse noise effectively while preserve the details of image well. And the median filter cannot remove Gauss noise effectively. In this paper, we propose the self-adaptive mean filter to remove mixed noise of Gauss noise and impulse noise. Firstly, dividing pixels of image into good pixels and corrupted pixels based on whether there are noises in their small neighborhoods. And the greyscale value of good pixels are output directly. Secondly, for corrupted pixels, removing Gauss noises and impulse noises respectively based on characteristics of different noise. The results demonstrate that the self-adaptive mean filter can eliminate mixed noise of different density better and preserve the details of image better comparing with the mean filter or the median filter for mixed noise.

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.

Application of Universal Kriging for Calibrating Offline-Programming Industrial Robots

The requirement for absolute positioning accuracy has also increased with the increasing use of industrial robots in offline programming. The present study proposed Universal Kriging (UK) for calibrating offline-programming industrial robots. This method was based on the similarities in positional errors. In addition, the method represented the positional errors as a deterministic drift and a residual part, which considered both geometric and non-geometric errors. The semivariogram was designed and the drift was determined to implement UK. Then, the method was applied for predicting positional errors and realizing error compensations. In addition, contrast experiments were performed to verify the practicality and superiority of UK compared with Ordinary Kriging (OK). Experimental results showed that after calibration by UK, the maximum of the original spatial positional errors reduced from 1.3073 mm to 0.2110 mm, that is, by 83.86%. Moreover, the maximum of the spatial positional errors reduced from 1.3073 mm to 0.3148 mm by only 75.92% after calibration using OK. An evident increase was reported in the maximum of the spatial positional errors from 0.3148 mm to 0.2110 mm, with an improvement rate of 32.97%. This is of great significance when accuracy is less than 0.5 mm. Overall, the experimental results proved the effectiveness of UK.

A visual positioning and measurement system for robotic drilling

In order to increase drilling efficiency, it is necessary for robotic drilling system to take advantage of offline programming method to drill a large number of holes automatically. Vision measurement is needed to correct work piece position because of inconformity between actual object and mathematical models. This paper introduces a visual positioning and measurement system for robotic drilling. A calibration board is designed to obtain hand-eye relationship and four laser range sensors are used to measure surface normal. This paper also summarizes workflow of offline programming and correction methods for different parts. Experiments give the result of hand-eye relationship and prove the position accuracy of vision measurement.

Trajectory tracking control method and experiment of AGV

Aiming at the trajectory tracking control of AGV in aeronautical manufacturing and automated warehouse, a novel trajectory tracking control method was proposed. Firstly, the kinematic model and trajectory tracking control model of AGV were established. After analysing the reversing problem of AGV in practical situation and the limitations of classic trajectory tracking control method, and based on the similarity between the forward mode and reversing mode of AGV, a novel trajectory tracking control rule was designed and its stability was proved. The trajectory tracking control rule had simpler, less amount of calculation and improved the flexibility and handling efficiency of AGV. Finally, the trajectory tracking control experiments of sinusoid and path consisting of segments and arcs were done on experimental platform. The experiment results verified that the trajectory tracking control method were effective and feasible. The method could meet the requirements of autonomous handing for AGV in aeronautical manufacturing and automated warehouse.

A compact and stiffer shape memory alloy actuator for surgical instruments

Advances in minimally invasive surgery enable the integration of new micro-systems with a micro actuator, as well as self-sensing ability, in surgical instruments. High energy density, self-sensing ability, and shape flexibility make shape memory alloy (SMA) actuators widely suited for volume-compact required applications. This paper presents a two-degrees-of-freedom instrument driven by SMA triple wires having 8 mm diameter and a rotation range near to ±60°. The actuator drive was constructed by antagonistic SMA triple wires and close-loop controlled by self-sensing. Experiments showed that the hysteresis gap between the phase transformation paths of the strain-resistance curve can be minimized under a fitted interstress. The curves of all the wires were then modeled by fitting polynomials, the collected resistance was converted to strain value and used to determine the control signal, and a feedforward compensator was built as the hysteresis compensation to resist overheating. The control accuracy was verified based on the multistep responding tests, and the results were shown in 3-D space. Under the self-sensing hybrid control scheme, the experimental results showed that the root-mean-square error of the rotation angle around the X and Y axes was about 4.2% and 3.5%, respectively.