Force control-based vibration suppression in robotic grinding of large thin-wall shells

Vibration suppression is a major difficulty in the grinding of low-stiffness large thin-wall shells. The paper proposes that effective workpiece vibration control can be performed by a novel force-controlled end-effector integrated into a robotic grinding workcell. First, a dynamics model is built to capture the characteristics and vibration suppression mechanism of force control-based robotic grinding, then a novel force control-based vibration suppression method is designed for grinding large thin-wall shells, and three robotic grinding tests are conducted to validate the effects of the new method and the grinding performance of the force control-based robotic grinding workcell. The results are: 75% reduction in the amplitude of workpiece vibration; effective suppression of non-tool passing frequency; stable grinding of large thin-wall shells remarkably enhancing grinding depth up to 0.3 mm per pass, grinding depth error less than ±0.1 mm, and significant improvement of the workpiece surface quality up to Ra=0.762 μm.     

Generic development methodology for flexible robotic pick-and-place workcells based on Digital Twin

Together with the trends of mass personalization, flexible robotic applications become more and more popular. Although conventional robotic automation of workpiece manipulation seems to be solved, advanced tasks still need great amount of effort to be reached. In most cases, on-site robot programming methods, which are intuitive and easy to use, are not applicable in flexible scenarios. On the other hand, the application of offline programming methods requires careful modeling and planning. Consequently, this paper proposes a generalized development methodology for flexible robotic pick-and-place workcells, in order to provide guidance and thus facilitate the development process. The methodology is based on the Digital Twin (DT) concept, which allows the iterative refinement of the workcell both in the digital and in the physical space. The goal is to speed up the overall commissioning (or reconfiguration) process and reduce the amount of work in the physical workcell. This can be achieved by digitizing and automating the development, and maintaining sufficient twin closeness. With that, the operation of the digital model can be accurately realized in the physical workcell. The methodology is presented through a semi-structured pick-and-place task, realized in an experimental robotic workcell together with a reconfiguration scenario.     

A Workcell for the Development of Robot-Assisted Surgical Procedures

This paper describes a robotic workstation for the development of new robot-assisted surgical procedures. This work is motivated by the difficulties and cost associated to the development of surgical robots, often requiring large investments and several re-designs which limit wider use of this technology. The approach presented here consists of using a general purpose robotic workcell to develop the hardware and the surgical aspects of new robot-based surgical systems, before committing to a completely new system design. The workcell is based on a clean room PUMA 260 manipulator, suitably enhanced to expand and improve its capabilities, and on a vision-based operator interface. Two new robot-assisted surgical procedures have been developed and tested using this set-up: percutaneous discectomy and knee osteoctomy. By using the robotic workcell, engineers and surgeons are able to define many aspects of the two procedures, such as surgical gestures, workspace of the robot, and calibration procedures, without incurring a large, up-front investment. First, the article describes the configuration of the workcell, the enhancements to the PUMA manipulator and the surgical procedures developed with this setup. Then the results of the tests and the lessons learned using the workcell are discussed in some detail.     

Off-line programming motion and process commands for robotic welding of space shuttle main engines

An intelligent, adaptive robotic system is being developed for a low-volume, high precision process: the welding of the Space Shuttle Main Engines (SSMEs). The overall system goals include the development of a workstation-based system to provide flexible, efficient off-line programming of both motion and welding process commands for the robotic workcell. This offline programming system includes: implementation of a user interface for weld engineers, generation of both geometric and process commands for the workcell, development of a weld parameter database system, and display of both run-time and archived data. This article presents details of the off-line programming system, including interfaces, implementation, and limitations. The system will be implemented on the SSME production floor, and will be benchmarked in effectiveness and productivity against commercially available robotic welding systems presently in use. The overall system development is a joint effort between NASA's Marshall Space Flight Center and two divisions of Rockwell International: Rocketdyne and the Science Center.     

机器人砂带磨削系统作业精度分析与误差补偿

为了更好地反映及提高工业机器人砂带磨削系统的整体性能,通过分析机器人应用系统的特点,详细 描述了工业机器人应用系统“作业精度”的含义及衡量标准．在此基础上,推导了机器人砂带磨削系统作业精度模 型,设计了机器人砂带磨削系统作业误差测量工具及校准系统,建立了实际的机器人砂带磨削系统．通过实际的机 器人磨削实验验证了方法的有效性．     

Graphic-based analysis of robot motion economy principles

Performance of robotic systems depends on the robot design, its motions and the workcell set-up. Robot motion economy principles can provide important design guidelines to optimize the overall automation in robotic work systems. This work presents graphic-based analysis of the performance of 10 different robots in four classes and three group sizes for 27 different bin locations (positions and orientations). This extensive analysis and evaluation lead to several conclusive results concerning motion economy principles related to design of robotic workcells.     

Feasibility study of robotic fibre placement on intersecting multi-axial revolution surfaces

In this paper, the first steps towards using a robotic workcell for the automated fibre placement (AFP) manufacturing of Y-shaped tubes are proposed. The proposed workcell is constituted of a standard serial manipulator holding the fibre placement toolhead combined to a rotary table on which the part where the fibres must be laid out is attached. The investigations carried out in this work explore the feasibility of this setup and more precisely the path planning aspect. To this aim two novel path planning algorithms are presented generalizing the techniques proposed in the literature for open-contoured and cylindrical surfaces. In the first, the maximal geodesic curvature typically allowed in AFP is disregarded to generate continuous paths with a constant placement angle on the branches without any gaps or overlaps. Subsequently, a second algorithm, taking into account this curvature constraint, is presented. These algorithms were implemented in a software using the MATLAB™ suite. Finally, an algorithm to optimize the motion of the robotic system is presented and simulations are discussed.     

Computer-aided robot modeling,programming and simulation

The use of interactive computer graphics for simulation and off line programming provides a powerful tool in implementing robots. This capability essentially became available with the CAD/CAM system.This paper will present the theory of robot modeling and simulation techniques. An overview of CAD/CAM system in robotic application, such as robot off-line programming, simulation and workcell layout will also be represented.     

工业机器人虚拟样机系统的研究

该文提出将虚拟样机技术应用于工业机器人仿真研究过程，研究与开发工业机器人虚拟样机系统，首先说明虚拟样机技术并分析其关键技术，然后说明了工业机器人虚拟样机系统的构成与样机系统在机器人仿具研究中的研究内容，总结该项技术主要解决以下两方面的问题，即机器人仿真研究中的系统集成及为以机器人为主体的生产线虚拟设计，验证环境提供底层的数字化环境。     

Assembly task execution using visual 3D surface reconstruction: An integrated approach to parts mating

This paper is focused on assembly tasks executed by an industrial robotic manipulator in the presence of uncertainties. The goal is to achieve higher levels of autonomy and flexibility of robotic systems in the execution of such tasks. In particular, as a well-established paradigm of assembly tasks, a Peg-in-Hole task has been considered, where the pose of the target object with respect to the robot is known with uncertainties far larger than the task tolerance, e.g., due to manual positioning of the object in the workcell. The proposed approach is based on the reconstruction of the object surface by means of a number of point clouds provided by a depth sensor. The reconstruction is then compared with a known CAD model of the surface, in order to localize the position and tilt of the holes. Finally, the peg insertion is performed in two steps: a search phase, in which the peg tip gently slides on the surface following a trajectory described by Lissajous functions, and a mechanical coupling phase, in which a compliant behavior is imposed to the peg. Experiments on a collaborative manipulator confirm that the proposed approach allows to achieve a better degree of autonomy and flexibility for a class of robotic tasks in partially structured environments.     

Dynamic tracking line: feasible tracking region of a robot inconveyor systems

The concept of dynamic tracking line is proposed as the feasible tracking region for a robot in a robot-conveyor system, which takes the conveyor speed into consideration. This paper presents an effective method to find the dynamic tracking line in a robotic workcell. The maximum permissible line-speed which is a quantitative measure of the robot capability for conveyor tracking, is defined on the basis of the relation between the end effector speed and the bounds on the joint velocities, accelerations, and torques. This measure is derived in an analytic form using the parameterized dynamics and kinematics of the manipulator, and some of its properties are established mathematically. The problem of finding the dynamic tracking line is then formulated as a root-solving problem for a single-variable equation, and solved by the use of a simple numerical technique. Finally, numerical examples are presented to demonstrate the methodology and its applications in workspace specification.     

Dynamic tracking line: feasible tracking region of a robot inconveyor systems

The concept of dynamic tracking line is proposed as the feasible tracking region for a robot in a robot-conveyor system, which takes the conveyor speed into consideration. This paper presents an effective method to find the dynamic tracking line in a robotic workcell. The maximum permissible line-speed which is a quantitative measure of the robot capability for conveyor tracking, is defined on the basis of the relation between the end-effector speed and the bounds on the joint velocities, accelerations, and torques. This measure is derived in an analytic form using the parameterized dynamics and kinematics of the manipulator, and some of its properties are established mathematically. The problem of finding the dynamic tracking line is then formulated as a root-solving problem for a single-variable equation, and solved by the use of a simple numerical technique. Finally, numerical examples are presented to demonstrate the methodology and its applications in workspace specification.     

PPA-A precise, data driven component tool

This paper outlines the development of a data-driven, fine pitch component placement machine, PPA-A, which is an integrated robotic workcell developed for attaching fine pitch integrated circuit components to printed circuit boards. In particular, the objectives for the machine are reviewed, and an overview of the solution is given. Problems encountered during the development are discussed, and details of the algorithms developed to solve these problems are given. These problems relate to achieving very precise placement of components, and are solved by novel calibration and execution schemes     

Implementing speed and separation monitoring in collaborative robot workcells

We provide an overview and guidance for the speed and separation monitoring methodology as presented in the International Organization of Standardization's technical specification 15066 on collaborative robot safety. Such functionality is provided by external, intelligent observer systems integrated into a robotic workcell. The SSM minimum protective distance function equation is discussed in detail, with consideration for the input values, implementation specifications, and performance expectations. We provide analytical analyses and test results of the current equation, discuss considerations for implementing SSM in human-occupied environments, and provide directions for technological advancements toward standardization.     

Dynamic control of a robot manipulator for high-performance conveyor tracking

A new robot control scheme for the specific application to conveyor tracking is presented. To improve the performance of conveyor tracking, the robot arm dynamics is incorporated into the control scheme. The tracking problem for the workpiece on a variable-speed conveyor is formulated as a stochastic optimal tracking problem with specified criteria. Dividing the conveyor speed into the nominal term and the perturbed term, a two-stage control strategy is employed to cope with the nonlinearity and uncertainty of the robot-conveyor system. Simulation results are given to verify the good tracking performance with fast cycle time and high accuracy obtained in a robotic workcell. © 1995 John Wiley & Sons, Inc.     

Visual servoing and CAD-driven microassembly

The authors describe current research and development on a robotic visual servoing system for assembly of LIGA (lithography galvonoforming abforming) parts. The workcell consists of an AMTI robot, precision stage, long working distance microscope, and LIGA fabricated tweezers for picking up the parts. Fourier optics methods are used to generate synthetic microscope images from CAD drawings. These synthetic images are used off-line to test image processing routines under varying magnifications and depths of field. They also provide reference image features which are used to visually servo the part to the desired position. Currently, we can visually servo a 100 micron outside diameter LIGA gear to a desired x,y reference position as determined from a synthetic image of the gear     

Vision-guided fixtureless assembly of automotive components

Assembly operations in many industries make extensive use of fixtures that are costly and inflexible. The goal of “robotic fixtureless assembly” (RFA) is to replace these fixtures with sensor-guided robots. In this paper, the development of a vision-guided RFA workcell for automotive components is described. Each robot is equipped with a multiple degree-of-freedom programmable gripper, allowing it to hold a wide range of part shapes without tool changing. A 2D computer vision is used to achieve part pickup which is robust to positioning errors. A novel 3D computer vision system is used to align the parts prior to joining them. The actions of the workcell devices are coordinated using a flexible distributed object-oriented approach. Experimental results are presented for the RFA of four automotive body components.     

A timing model for vision-based control of industrial robot manipulators

Visual sensing for robotics has been around for decades, but our understanding of a timing model remains crude. By timing model, we refer to the delays (processing lag and motion lag) between "reality" (when a part is sensed), through data processing (the processing of image data to determine part position and orientation), through control (the computation and initiation of robot motion), through "arrival" (when the robot reaches the commanded goal). In this study, we introduce a timing model where sensing and control operate asynchronously. We apply this model to a robotic workcell consisting of a Sta/spl uml/ubli RX-130 industrial robot manipulator, a network of six cameras for sensing, and an off-the-shelf Adept MV-19 controller. We present experiments to demonstrate how the model can be applied.