Force override rate control for robotic manipulators

The work reported deals with the problem of operating a robot manipulator under a rate control mode while the end effector is not in contact with the external environment, and then switching to a force control mode when contact is made. The paper details how the modal changeover may be accomplished in a manner transparent to the operator, and will allow operator applied forces to be reflected at the robot end effector. A one degree of freedom demonstration system is used to illustrate the concept, which is then applied to a PUMA manipulator. Sample code for the implementation of the control is provided, experimental results show that the optimum setting for the gain is a function of the compliance of the end effector, and the compliance of the external constraint

Local sensory control of a dexterous end effector

A numerical scheme was developed to solve the inverse kinematics for a user-defined manipulator. The scheme was based on a nonlinear least-squares technique which determines the joint variables by minimizing the difference between the target end effector pose and the actual end effector pose. The scheme was adapted to a dexterous hand in which the joints are either prismatic or revolute and the fingers are considered open kinematic chains. Feasible solutions were obtained using a three-fingered dexterous hand. An algorithm to estimate the position and orientation of a pre-grasped object was also developed. The algorithm was based on triangulation using an ideal sensor and a spherical object model. By choosing the object to be a sphere, only the position of the object frame was important. Based on these simplifications, a minimum of three sensors are needed to find the position of a sphere. A two dimensional example to determine the position of a circle coordinate frame using a two-fingered dexterous hand was presented

Analysis of Alternative Rework Strategies for Printed Wiring Assembly Manufacturing Systems

This paper presents a model for predicting the cost of test, diagnosis, and rework activities in the manufacture of printed wiring assemblies (PWA's). Rework is defined as all actions taken to correct or improve the basic assembly process. These actions may include those of inspectors and solder touchup technicians who do not add value to the PWA, but whose actions are required in order to produce acceptable yields from the manufacturing process. Two alternative rework strategies for contemporary PWA manufacturing systems are presented: terminal rework and distributed rework. Rework may occur after all assembly operations have been accomplished (terminal rework) or it may be distributed throughout the assembly process. This paper allalyzes the economic basis for deciding between the two rework strategies. The paper assumes that the only reason for utilizing distributed rework is to reduce the cost of producing acceptable PWA's, otherwise the cost of the distributed rework effort cannot be justified. The paper presents a model of each rework strategy. The effect of each strategy upon first pass yield (FPY) of the manufacturing process is discussed. The effect on FPY is then used to evaluate the economic benefit of each rework strategy as an aid in deciding which strategy to use. The increase in FPY needed to justify distributed rework is calculated

Testing the adequacy of a single-value Monte Carlo simulation for space-time interaction of crime

The goal of this study is to determine the number of iterations (r) required in a Monte Carlo based space-time interaction analysis of crime data sets, in order to test the adequacy of using a single value of 999 iterations. A case study of burglary crime data sets is presented in which Knox test is used for the analysis of space-time interactions. The outcomes of this analysis demonstrate that the use of a single value, such as 999, does not always represent the most appropriate number of iterations especially when multiple ST neighbourhood sizes are involved. This analysis opens further research opportunities into determining the best strategy to defining the expected distribution in a space-time interaction analysis of crime

Distributed Mathematical Model Simulation on a Parallel Architecture

The aim of this article is to discuss the design of distributed mathematical models and suitable parallel architecture of computers. The paper summarises the author’s experience with mathematical modelling of decomposed information systems of a simulator. Conclusions are based on the theory of the design of the computer control systems. The author describes computers that create a distributed computer system of a flight simulator. Modelling of a time precision of mathematical model of the speed of a simulator system is done by describing equations. The qualities of models depend on the architecture of computer systems. Some functions of other sections of POSIX are also analysed including semaphores and scheduling functions. An important part of this article is the implementation of computation speed of aircraft in multicore processor architecture

Determining the number of iterations for Monte Carlo simulations of weapon effectiveness

Many weapon effectiveness tools are implemented using a Monte Carlo simulation approach since closed form solutions are too mathematically intractable to compute. A question that usually arises in connection with such simulations is to ask how many iterations of a particular Monte Carlo simulation are needed. This report proposed the probability-based approach to computing effectiveness measures for better feedback to the user regarding the relationship between the number of iterations executed and confidence measures associated with the result.Approved for public release; distribution is unlimited

Robotic automation in computer controlled polishing

We first present a Case Study – the manufacture of 1.4 m prototype mirror-segments for the European Extremely Large Telescope, undertaken by the National Facility for Ultra Precision Surfaces, at the OpTIC facility operated by Glyndwr University. Scale-up to serial-manufacture demands delivery of a 1.4 m off-axis aspheric hexagonal segment with surface precision < 10 nm RMS every four days, compared with a typical year or more for an one-off part. This requires a radically-new approach to large optics fabrication, which will inevitably propagate into wider industrial optics. We report on how these ambitious requirements have stimulated an investigation into the synergy between robots and computer numerically controlled (‘CNC’) polishing machines for optical fabrication. The objective was not to assess which is superior. Rather, it was to understand for the first time their complementary properties, leading us to operate them together as a unit, integrated in hardware and software. Three key areas are reported. First is the novel use of robots to automate currently-manual operations on CNC polishing machines, to improve work-throughput, mitigate risk of damage to parts, and reduce dependence on highly-skilled staff. Second is the use of robots to pre-process surfaces prior to CNC polishing, to reduce total process time. The third draws the threads together, describing our vision of the automated manufacturing cell, where the operator interacts at cell rather than machine level. This promises to deliver a step-change in end-to-end manufacturing times and costs, compared with either platform used on its own or, indeed, the state-of-the-art used elsewhere

Modeling, optimizing and simulating robot calibration with accuracy improvement

This work describes techniques for modeling, optimizing and simulating calibration processes ofrobots using off-line programming. The identification of geometric parameters of the nominalkinematic model is optimized using techniques of numerical optimization of the mathematicalmodel. The simulation of the actual robot and the measurement system is achieved by introducingrandom errors representing their physical behavior and its statistical repeatability. An evaluationof the corrected nominal kinematic model brings about a clear perception of the influence ofdistinct variables involved in the process for a suitable planning, and indicates a considerableaccuracy improvement when the optimized model is compared to the non-optimized one

An Overview of Kinematic and Calibration Models Using Internal/External Sensors or Constraints to Improve the Behavior of Spatial Parallel Mechanisms

This paper presents an overview of the literature on kinematic and calibration models of parallel mechanisms, the influence of sensors in the mechanism accuracy and parallel mechanisms used as sensors. The most relevant classifications to obtain and solve kinematic models and to identify geometric and non-geometric parameters in the calibration of parallel robots are discussed, examining the advantages and disadvantages of each method, presenting new trends and identifying unsolved problems. This overview tries to answer and show the solutions developed by the most up-to-date research to some of the most frequent questions that appear in the modelling of a parallel mechanism, such as how to measure, the number of sensors and necessary configurations, the type and influence of errors or the number of necessary parameters