Communication and programming issues in robotic manufacturing cells

The programmable logic unit (PLU) has been proposed to realize a high‐speed operation. The idea is to perform computation obtained by a static data flow scheme using the stepwise arithmetic logics distributed in the memory. This paper describes the configuration of the prototype PLU, the basic concepts of the computation and the synchronization between the PLU and the main control unit (CU). Then theoretical discussions are made on the computation time for the arithmetic and the iterative programs. It is shown that the high‐speed processing is realized by the effects of the parallel computation and of the pipelined computation, mapping many templates of a loop program on the PLU. Furthermore, the multiprogramming for the computer with PLU is proposed to utilize effectively the waiting time for the computation in the PLU. The throughput improvement is indicated by theoertical analysis, comparing the computer using PLU with the traditional sequential computer. Finally, the usefulness of the PLU is demonstrated.

A key to speeding up the processing is how to realize the programmable hardware using both a pipelined processing scheme and a multiprocessor processing scheme for such special hardware as the fast Fourier transform (FFT) unit and the digital filter. This paper proposes a structure for the programmable logic unit (PLU) based on such an idea, where the computing program is mapped on the hardware, and the processing is performed by write/read of the operand data. For the computer using the proposed PLU, three kinds of conceivable processing algorithms are presented. On the other hand, considering the number of pins, the regularity of the circuits, and the recent progress in three‐dimensional VLSI technology, it is highly conceivable that the proposed PLU is realized by VLSI. Thus, from the viewpoint of program execution in the computer using PLU, the program is constructed of the instructions computed by the PLU and the control instructions executed by the main CPU, and the processing mechanism is described using a program example. A discussion is made on the processing time, and it is shown that the computer using the PLU can utilize the parallelism of the computation by PLU to reduce the processing time, compared with the computer not using PLU. Thus, the effectiveness of the computer using PLU is demonstrated.

A robotic cast sand core handling manufacturing cell is composed of two ABB IRB 6600 robotic manipulators and two Loramendi modeling machines. The application Program architecture is anatomized and the program is written in RAPID Language. The program has teach-by-show mode, production mode, and calibration mode. The flow charts for each mode are presented. The effectiveness is shown by the commissioning results.

The methods of modeling and control of discrete event robotic manufacturing cells using Petri nets are considered, and a methodology of decomposition and coordination is presented for hierarchical and distributed control. Based on task specification, a conceptual Petri net model is transformed into the detailed Petri net model, and then decomposed into constituent local Petri net based controller tasks. The local controllers are coordinated by the coordinator through communication between the coordinator and the controllers. Simulation and implementation of the control system for a robotic workcell are described. By the proposed method, modeling, simulation, and control of large and complex manufacturing systems can be performed consistently using Petri nets.

Simulation Program Generators (SPGs) developed using object-oriented environments may be designed to have a number of capabilities not available in traditional SPGs. One such capability is the description of an object's behavior from scratch without any programming when such behavior does not exist in the knowledgebase of the SPG. SmarterSim is an SPG that is currently being developed to provide the user a number of object-oriented tools including libraries of elemental operations, actions/requests, states, and rules and a number of function block templates to create new behavior using the existing primitive elements. The behavior of objects in a robotic manufacturing cell is described using SmarterSim. Like its predecessor SmartSim, SmarterSim supports a hierarchical, modular modeling for building of subsystems (coupled models) from model objects (atomic models) using subsystem management features. The paper also discusses the use of object oriented environments for traditional SPGs and simulation programming languages.

Simulation of local area computer networks

Modern manufacturing systems consist of a sequence of robotic systems, such as robotic cells, which are widely used in the industry. As they become commonplace and play important roles in modern industrial production, efficient modelling and use of robotic cells become a necessity. Robotization brings many measurable benefits. It enables effective utilization of both human resources and the possessed machine park and thus contributing to the improvement of product quality and efficiency. Industrial robots not only increase the growth of productivity, by replacing man in monotonous works, requiring enormous, not achievable for human precision but above all ensure the accuracy and repeatability of the product quality. Appropriate design and modelling of robotic manufacturing systems are crucial in the efficient integration of work cell components and proper maintenance of robotic production systems. Therefore, new solutions for programming environments in industrial applications are sought which not only allow reprogramming of industrial robots but also enable the virtual design of new production lines, which in turn allows the faster introduction of higher quality products. This article presents the modelling and programming of robotic work cells in the Siemens Process Simulate environment.

Purpose – The robot offers interesting capabilities, but suffers from a lack of stiffness. The proposed solution is to introduce redundancies for the overall improvement of different capabilities. The management of redundancy associated with the definition of a set of kinematic, mechanical and stiffness criteria enables path planning to be optimized. Design/methodology/approach – The resolution method is based on the projection onto the kernel of the Jacobian matrix of the gradient of an objective function constructed by aggregating kinematic, mechanical and stiffness weighted criteria. Optimized redundancy management is applied to the 11-DoF (degrees of freedom) cells to provide an efficient placement of turntable and track. The final part presents the improvement of the various criteria applied to both 9-DoF and 11-DoF robotic cells. Findings – The first application concerns the optimized placement of a turntable and a linear track using 11-DoF architecture. Improved criteria for two 9-DoF robotic cells, a robot with parallelogram closed loop and a Tricept are also presented. Simulation results present the contributions of redundancies and the leading role of the track. Research limitations/implications – The redundancy-based optimization presented and the associated simulation approach must be completed by the experimental determination of the optimization criteria to take into account each machining strategy. Practical implications – This work in robotics machining relates to milling operations for automotive and aerospace equipment. The study is carried out within the framework of the RobotEx Equipment of Excellence programme. Originality/value – The resolution method to optimized path planning is applied to 9- and 11-DoF robotic cells, including a hybrid robot with a parallelogram closed loop and a Tricept PKM.

This paper deals with the modeling and control of discrete event robotic manufacturing cells using Petri nets, and proposes a methodology of model based design and implementation of hierarchical and distributed control. Hierarchical Petri net models are adopted; conceptual Petri net model and detailed Petri net model. The overall detailed Petri net model is decomposed into local Petri net models which are used by the local machine controllers. The upper level station controller coordinates the distributed local controllers so that the aggregate behavior of decomposed subnets is the same as that of the original Petri net. The overall control system is implemented using multithreaded programming based on Petri net based multitask processing. Simulation experiments show that the distributed Petri net model based control system can perform the overall multitask processing control by coincidence of the behavior of the real system with the local Petri net models.

<div class="htmlview paragraph">Computer technology is allowing previously expensive functions to now be available at low cost - from engineering applications to machine tool programs. This reduction in cost is allowing the computing functions to be distributed (e.g., CNC), which if left alone would be regrettable, since previously centralized, coordinated functions would now be independent, autonomous, redundant, etc. Hence the role of the Local Area Network (LAN) - to recover the loss that would otherwise occur if computing were continuously subdivided into smaller and smaller, more distributed parts.</div> <div class="htmlview paragraph">LANs have evolved during the past ten years to the point where they are now in popular use in many applications. The lack of a single LAN standard, however, has stimulated the development of <u>heterogeneous networks</u> - those comprised of combinations of dissimilar LANs. Heterogeneous LANs and their applications is the subject of this paper.</div>

Parallel Execution of Iterative Computations on Workstation Clusters

In a robot grinding work cell, as uncertain layout of manipulator and machine always results in vibration and complex process of orientation transformation, the optimization of robotic manufacturing cell layout is necessary especially for grinding applications. In this paper, we suggest a practicable approach based on Genetic Algorithm to find an optimum layout design, which reduces vibration and improves manipulability. Two evaluating indicators, vibration restraint characteristics and gripper dexterity, are herein stressed to evaluate the layout configuration. We expatiate the methods of measuring the evaluating indicators. The results are compared to show the method's efficiency.

The paper describes the elements of a flexible assembly system which is being constructed to investigate methods of integrating robots within production systems. Also described are the features of ‘intelligent’ interfaces which have been designed to allow robots and machines to be linked, via a local area network, to supervisory computers. The interfaces are based on the ISO model of open-system connection and include MAP data packets so that they offer a standard and transferable solution to the problem of integrating computer-based shop-floor and management functions.

The paper considers the methods of modeling and control of discrete event robotic manufacturing systems using Petri nets and proposes a methodology of decomposition and coordination for hierarchical and distributed control. First, a task specification is defined as a Petri net model at the conceptual level, and then transformed to the detailed Petri net representation of the subtasks. Finally, the overall Petri net is decomposed and the constituent subnets are assigned to local Petri net based controllers. The coordinator is introduced to coordinate the distributed controllers so that the behavior of the distributed system is the same as that of the original Petri net. A coordination algorithm by two control levels is developed for defining robot and machine activation conditions. Based on the proposed method, a distributed control system has been implemented for a robotic manufacturing cell.

In recent years robots have dramatically improved in functionality, but as a result their designs have also become more complicated. The increase in the complexity of the tasks and the design of the robot result in a challenging and time-consuming robot development cycle. This paper identifies requirements for improving the robot development process, focusing on facilitating a safe and reliable transition process from simulation to real world tests. We propose that, by applying the concept of Mixed Reality (MR) to robot simulation, it is possible to create a realistic, synthetic environment that enables robot software developers to experiment freely and safely. The new simulation approach, named MR simulation, offers the flexibility of creating simulation environments composed of real and virtual objects that seamlessly interact with one another. This paper contributes a generic, conceptual MR framework which is demonstrated to provide a common, standardised simulation environment for experimentation involving real and virtual objects. An MR robot simulator is implemented based on the framework, integrating standardised data interfaces in its design to increase interoperability. Evaluation results demonstrate that the MR robot simulator is reusable in three different applications. It improved simulation reliability, reduced development cost, and increased efficiency.