Error Prediction in Industrial Robot Machining: Optimization Based on Stiffness and Accuracy Limit

Among the advantages of using industrial robots for machining applications instead of machine tools are flexibility, cost effectiveness, and versatility. Due to the kinematics of the articulated robot, the system behaviour is quite different compared with machine tools. Two major questions arise in implementing robots in machining tasks: one is the robot’s stiffness, and the second is the achievable machined part accuracy, which varies mainly due to the huge variety of robot models. This paper proposes error prediction model in the application of industrial robot for machining tasks, based on stiffness and accuracy limits. The research work includes experimental and theoretical parts. Advanced machining and inspection tools were applied, as well as a theoretical model of the robot structure and stiffness based on the form-shaping function approach. The robot machining performances, from the workpiece accuracy point of view were predicted.

Implementation of a new PC based controller for a PUMA robot

This paper describes the replacement of a controller for a programmable universal machine for assembly (PUMA) 512 robot with a newly designed PC based (open architecture) controller employing a real-time direct control of six joints. The original structure of the PUMA robot is retained. The hardware of the new controller includes such in-house designed parts as pulse width modulation (PWM) amplifiers, digital and analog controllers, I/O cards, signal conditioner cards, and 16-bit A/D and D/A boards. An Intel Pentium IV industrial computer is used as the central controller. The control software is implemented using VC++ programming language. The trajectory tracking performance of all six joints is tested at varying velocities. Experimental results show that it is feasible to implement the suggested open architecture platform for PUMA 500 series robots through the software routines running on a PC. By assembling controller from off-the-shell hardware and software components, the benefits of reduced and improved robustness have been realized.

Base placement optimization of a mobile hybrid machining robot by stiffness analysis considering reachability and nonsingularity constraints

The mobile hybrid machining robot has a very bright application prospect in the field of high-efficiency and high-precision machining of large aerospace structures.However,an inappropriate base placement may make the robot encounter a singular configuration,or even fail to complete the entire machining task due to unreachability.In addition to considering the two constraints of reachability and non-singularity,this paper also optimizes the robot base placement with stiffness as the goal to improve the machining quality.First of all,starting from the structure of the robot,the reachability and nonsingularity constraints are transformed into a simple geometric constraint imposed on the base placement:feasible base placement area.Then,genetic algorithm is used to search for the base placement with near optimal stiffness(near optimal base placement for short)in the feasible base placement area.Finally,multiple controlled experiments were carried out by taking the milling of a protuberance on the spacecraft cabin as an example.It is found that the calculated optimal base placement meets all the constraints and that the machining quality was indeed improved.In addition,compared with simple genetic algorithm,it is proved that the feasible base placement area method can shorten the running time of the whole program.

Path,feedrate and trajectory planning for free-form surface machining:A state-of-the-art review

Nowadays,free-form surfaces have been widely used in various industrial fields.They are usually machined by CNC machine tools,but recently have also begun to be manufactured by industrial robotic arm manipulators,thanks to low cost,large operation reaching space and high machining flexibility of robot.So far,various methodologies have been proposed to improve efficiency and quality of free-form surface machining,thus this paper aims at providing a state-ofthe-art review on research advances in free-form surface machining.In this review,tool path generation,feedrate scheduling in Cartesian space and trajectory planning in joint space are focused for both CNC machining and robot machining,and their research statues,existing difficulties and key issues are discussed in detail.Finally,the feasible routes,breakthrough points and future development trend are also expounded.

A review of recent advances in machining techniques of complex surfaces

Complex surfaces are widely used in aerospace,energy,and national defense industries.As one of the major means of manufacturing such as complex surfaces,the multi-axis numerical control(NC)machining technique makes much contribution.When the size of complex surfaces is large or the machining space is narrow,the multi-axis NC machining may not be a good choice because of its high cost and low dexterity.Robotic machining is a beneficial supplement to the NC machining.Since it has the advantages of large operating space,good dexterity,and easy to realize parallel machining,it is a promising technique to enhance the capability of traditional NC machining.However,whether it is the multi-axis NC machining or the robotic machining,owing to the complex geometric properties and strict machining requirements,high-efficiency and high-accuracy machining of complex surfaces has always been a great challenge and remains a cutting-edge problem in the current manufacturing field.In this paper,by surveying the machining of complex parts and large complex surfaces,the theory and technology of high-efficiency and high-accuracy machining of complex surfaces are reviewed thoroughly.Then,a series of typical applications are introduced to show the state-of-the-art on the machining of complex surfaces,especially the recently developed industrial software and equipment.Finally,the summary and prospect of the machining of complex surfaces are addressed.To the best of our knowledge,this may be the first attempt to systematically review the machining of complex surfaces by the multiaxis NC and robotic machining techniques,in order to promote the further research in related fields.

Machining Robot with Vibrational Motion and 3D Printer-like Data Interface

In this paper, a vibration motion control is proposed and implemented on a foamed polystyrene machining robot to suppress the generation of undesirable cusp marks, and the basic performance of the controller is verified through machining experiments of foamed polystyrene. Then, a 3 dimensional （3D） printer-like data interface is proposed for the machining robot. The 3D data inter- face enables to control the machining robot directly using stereolithography （STL） data without conducting any computer-aided man- ufacturing （CAM） process. This is done by developing a robotic preprocessor that helps to remove the need for the conventional CAM process by directly converting the STL data into cutter location source data called cutter location （CL） or cutter location source （CLS） data. The STL is a file format proposed by 3D systems, and recently is supported by many computer aided design （CAD）/CAM soft- waxes. The STL is widely used for rapid prototyping with a 3D printer which is a typical additive manufacturing system. The STL deals with a triangular representation of a curved surface geometry. The developed 3D printer-like data interface allows to directly control the machining robot through a zigzag path, rectangular spiral path and circular spiral path generated according to the information included in STL data. The effectiveness and usefulness of the developed system are demonstrated through actual machining experiments.