George Zhang

Machining with flexible manipulator: toward improving robotic machining performance

This paper presents the critical issues and methodologies to improve robotic machining performance with flexible industrial robots. Compared with CNC machines, the stiffness of industrial robots is significantly lower, resulting in unacceptable quality and lower productivity. The problem is treated with a novel methodology that consists of stiffness modeling, real-time deformation compensation for quality and controlled material removal rate for efficiency. Experimental results show that higher productivity as well as better surface accuracy can be achieved, indicating a promising and practical use of industrial robots for machining applications that is not possible at present

Integrated robotic system for high precision assembly in a semi‐structured environment

Purpose – This paper aims to develop a strategy for high‐precision assembly in a semi‐structured environment based on vision and force control.Design/methodology/approach – The position and orientation of a part are identified using the vision system. The force/torque control algorithm is then applied to perform a tight‐tolerance assembly that is a high‐precision assembly.Findings – The tight tolerance assembly in a semi‐structured environment is successfully implemented using vision guidance and force/torque‐control strategy.Practical implications – The developed methodology can be applied to tight tolerance assembly, such as forward‐clutch assembly, torque‐converter assembly, etc.Originality/value – An industrial assembly methodology has been developed and implemented for high‐precision assembly in a semi‐structured environment. This innovation has many potential applications in automotive manufacturing.

On-Line Path Generation for Robotic Deburring of Cast Aluminum Wheels

Cast aluminum wheels must be deburred and polished before chrome plating operation. Manual deburring and polishing is tedious and monotonous. Industrial robots are attracting more and more attention for the deburring applications. However, Each wheel path program was taking eight to ten weeks to create because the position and orientation of the deburring tool must be accurately identified based on the curvature of the wheel. To solve this problem, we developed a practical 6 DOF robot path generation method using hybrid force and visual servoing methodology. The force servoing keeps the robot tool continuously contacting with the wheel surface and the visual servoing controls the robot tool to follow a marked tool path on the wheel while the position and orientation are controlled and recorded. A robot path is then generated from the recorded data. Experiments are performed and the experimental results demonstrate that the developed algorithm can be used to automatically generate accurate 6 DOF robot paths for deburring aluminum wheels in less than an hour. This significantly reduces the robot programming time. The developed technology can also be used for robot path generation in many other manufacturing applications, such as welding and strip painting

Automated learning for parameter optimization of robotic assembly tasks utilizing genetic algorithms

A challenge for automating mechanical assembly is that cumulative uncertainties typically exceed part clearances, which makes conventional position-based tactics unsuccessful. Force-based assembly strategies offer a potential solution, although such methods are still poorly understood and can be difficult to program. In this paper, we describe a force-based robotic assembly approach that uses fixed strategies with tunable parameters. A generic assembly strategy suitable for execution on an industrial robot is selected by the programmer. Parameters are then self-tuned empirically by the robot using a genetic-algorithm learning process that seeks to minimize assembly time subject to contact-force limits. Results are presented for two automotive part assembly examples using ABB robots with commercial force-control software, showing that the approach is highly effective and suitable for industrial use.

Toward robotizing powertrain assembly

This paper presents the recent progress of using robotics in automotive powertain assembly manufacturing processes. After briefly describing force control and vision-guided robot (VGR), we introduce successful implementation of robotic assembly for transmission torque converters, VGR-based engine head assembly, transmission valve body assembly and engine piston installation. Then we discuss other robotic assembly related technologies such as visual servoing and assembly parameter optimization and followed by discussing assembly production line evolution such as the merging of automated-guided vehicle (AGV). The successful model of collaborative development between Ford Advanced Manufacturing Technology Development (AMTD) and ABB Robotics is also mentioned and reviewed.

Force control technologies for new robotic applications

The long term success of the robotics industry depends on the growth in non-automotive markets. This paper presents the recent efforts in developing force control enabled technologies for a new set of applications that include assembly, polishing, deburring and milling. For each process, a force control based solution was provided to address the specific problem inherent in that process, and verified through experimental results and real life industrial applications.

High-accuracy visual/PSD hybrid servoing of robotic manipulator

This paper presents a new and effective multisensor based control strategy for high-accuracy/precision and high-efficiency automatic robot localization and calibration. The strategy combines both coarsely visual servo and fine position-sensitive detector (PSD) servo control methods. In a large field of view, an image-based visual servo control system is developed to roughly guide the laser beam, which is from a single laser pointer mounted at the end-effector of robot, to project to the high-resolution segmented PSDs. Once the laser spot is projected onto the active area of PSD, the control will be switched to the high-resolution PSD feedback and servoing for fine positioning. The experimental results conducted on an ABB industrial robot IRB1600 verify the effectiveness of the developed visual/PSD hybrid servo controllers as well as demonstrate that the high accuracy 30 mum of robot localization can be approached. The development of the hybrid control system and method will be a major step for achieving high-performance automatic robot calibration.

Robotic wheel loading process in automotive manufacturing automation

The paper aims to develop an automated wheel loading system in the trim-and-final assembly in automotive manufacturing. Currently most of the trim-and-final assemblies are still done manually since the production lines are typically moving randomly. Industrial robots are hardly used to perform any assembly tasks on the randomly changing environments because it is difficult for conventional industrial robots to adjust to any sort of change. Therefore, more intelligent industrial robotic system has to be developed to adopt the random motion of the moving production line for the wheel loading process. This paper presents an intelligent robotics system that performs the wheel loading process while the car is moving randomly with the production line using a synergic combination of visual servoing and force control technology. The developed intelligent robotic technology has been successfully implemented to assembly the wheel onto the car. This practical solution of performing wheel loading on the moving production line, which is not available on the current industrial robot market, can save a lot of money and increase the assembly quality for automotive manufacturing. Since the developed platform is based on the synergic combination of visual servoing and force control technology, it can be used in other areas, such as seam tracking, battery loading and seat loading etc.

An automated method to calibrate industrial robot joint offset using virtual line-based single-point constraint approach

This paper describes an industrial robot joint offset calibration method called the virtual line-based single-point constraint approach. Previous methods such as using CMM, laser trackers or cameras are limited by the cost or the resolution. The proposed method relies mainly upon a laser pointer attached on the end-effector and single position-sensitive detector (PSD) arbitrarily located on the workcell. The automated calibration procedure (about three minutes) involves aiming the laser lines loaded by the robot towards the center of the PSD surface from various robot positions and orientations. The intersections of each pair of laser lines eventually should converge to the same point after compensating the joint offsets. An optimization model and algorithm have been formulated to identify the robot offset. For the highly precise feedback, a segmented PSD with a position resolution of better than 0.1 µm is employed. The mean accuracy of robot localization is up to 0.02 mm, and the mean error of the parameter identification is less than 0.08 degrees. Both simulations and experiments implemented on an ABB industrial robot verify the feasibility of the proposed method and demonstrated the effectiveness of the developed calibration system. The goal of fast, automated, low-cost, and high precision offset calibration are achieved.

Automated Engine Piston Installation Using Industrial Robots

This paper presents engine piston installation using industrial robots. Because the current manual and hard automation engine piston installation systems are either labour intensive or inflexible and costly, the three-robot and two-robot piston installation systems are developed and investigated. The robotic piston installation process is simulated. A robotic piston stuffing gripper with ring detection is designed to perform the sophisticated stuffing process. Robot force control is used in the cylinder bore finding. The piston stuffing is implemented using a search-finding method based on the force control. The searching method and parameters are discussed. Related future research and development are proposed.