Open Control Architecture Research Articles

Reconfigurable open architecture control system with integrated digital twin for 3-axis woodworking milling machine

ABSTRACT This study proposes a reconfigurable open architecture control system for the Computer Numerical Control (CNC) woodworking educational machine tool called “EMCO F1 CNC”. On this machine physical hardware reconfiguration (spindle position can be vertical and horizontal) is possible. The idea was to develop a control system that would follow the configuration changes of the machine tool. The educational character of the machine and its reconfigurability demand possibilities for machining programme simulations in order to determine optimal workpiece position in the workspace and programme verification. Those are the reasons for developing a virtual machine tool integrated with the control system as a digital twin. The study presents a novel methodology for the development of control systems, merging the concept of “virtual commissioning” with iterative error-driven processes. The objective was to develop a dynamic control system capable of promptly adjusting to kinematics changes in real time. In a wood machining experiment, a test workpiece for machine tools for both machine configurations verified the operation of the developed control system.

Active Compliance Smart Control Strategy of Hybrid Mechanism for Bonnet Polishing.

Compliance control strategies have been utilised for the ultraprecision polishing process for many years. Most researchers execute active compliance control strategies by employing impedance control law on a robot development platform. However, these methods are limited by the load capacity, positioning accuracy, and repeatability of polishing mechanisms. Moreover, a sophisticated actuator mounted at the end of the end-effector of robots is difficult to maintain in the polishing scenario. In contrast, a hybrid mechanism for polishing that possesses the advantages of serial and parallel mechanisms can mitigate the above problems, especially when an active compliance control strategy is employed. In this research, a high-frequency-impedance robust force control strategy is proposed. It outputs a position adjustment value directly according to a contact pressure adjustment value. An open architecture control system with customised software is developed to respond to external interrupts during the polishing procedure, implementing the active compliance control strategy on a hybrid mechanism. Through this method, the hybrid mechanism can adapt to the external environment with a given contact pressure automatically instead of relying on estimating the environment stiffness. Experimental results show that the proposed strategy adapts the unknown freeform surface without overshooting and improves the surface quality. The average surface roughness value decreases from 0.057 um to 0.027 um.

G-code converter using interface system for a STEP file (ISO 10303)

The STEP file is the “standard for the exchange of product model data,” which is usually used to exchange geometric data in boundary representation (B-rep) between different computer-aided design (CAD) platforms. These data can be fully utilized and integrated into a larger manufacturing organization, such as a computer-aided manufacturing (CAM) environment for computer numerical control (CNC) machining applications based on ISO 6983. The 3D models of 2D machining profiles were created in CAD software and saved as STEP files. The data structure was analyzed by comparing the geometric entities of the CAD model and the STEP file. The algorithm was created using the hypertext preprocessor (PHP) programming language and produced a computer interface system to convert STEP files into G-code format. The machining blocks with profile machining features were simulated using a CNC simulator and PC-based open architecture control (OAC) software. The G-code was validated on a three-axis CNC milling machine, and the result was compared to the CAD model to confirm the machining profile. The integrated interface system I2S demonstrates its ability to interpret all 2D profiles and generate machining tool paths and G-code, allowing data flow between CAD and CAM environments and shortening product development cycles.

Design and Development of 3-Axis Benchtop CNC Milling Machine for Educational Purpose

The main factor in improving learning skills is providing students with hands-on laboratory experience, and the small-scale machine can accomplish academic programs requiring students tolearn machining skills. This paper aims to design and develop a 3-axis CNC milling machine with a PC-based open architecture controller in a vertical position open frame structure. Some technical specifications were randomly selected based on the capabilities of similarly sized machines reviewed in previous work. The designed machine consisted of inexpensive off-the-shelf hardware components capable of machining the sample block with high cutting speed and reasonable precision. The accepted percentage error of circular and straightness test readings is below the set requirements. This machine is not intended for series production and precise machining. It can still effectivelyreplace the high cost of commercial CNC machines and be used in any higher education institution offering technical courses.

Integrated Interface System of STEP Data Models for the Tool Path Generation

The STEP (STandard for the Exchange of Product model data) is a worldwide standard for exchanging products between diverse computer systems and industrial applications. STEP files (ISO 10303) contain 3D data in the universal data format with a boundary representation (B-rep) that allows the exchange of data models between CAD, CAM, and CNC systems. Traditionally, G-code generation relies on CAM software as an add-on, which incurs significant installation costs. The purpose of this paper is to describe the development of an Integrated Interface System (I2S) for Tool Path Generation (TPG) for the CNC milling operations utilizing neutral STEP files.The algorithm was interpreted in Hypertext Preprocessor (PHP) programming and produced a computer interface system that is capable to convert STEP file geometric data to G-code format.The geometric features of the sample block were modeled using a 3D CAD model. The result was validated using machining simulation, and the machining is performed on a three-axis CNC milling machine with a PC-based controller.In modern manufacturing systems based on Open Architecture Controller (OAC), the development of the I2S provides an alternative to generating machining tool paths and G-code by intercepting CAM software.

A unified inner‐/outer‐loop distributed design for task‐space robust cooperative tracking of uncertain networked manipulators under directed graphs

AbstractThis paper investigates task‐space cooperative tracking of networked manipulators with an inner‐/outer‐loop closed control architecture, taking effects of uncertain kinematics, dynamics, disturbances, and unavailable task‐space velocities into account. In the existing related works, the developed distributed cooperative control algorithms require either an open control architecture with torque‐based controllers or the combination of inner/outer loop to be stable with the effects of unknown dynamics being neglected. In contrast, in this work we propose a novel distributed control framework such that a distributed outer‐loop adaptive scheme is developed to achieve task‐space robust cooperative tracking with dynamic effects being considered and without modifying the inner control loop. In particular, a distributed estimator is firstly developed to estimate the desired global task. With this estimated information, distributed cooperative algorithms are presented for two types of inner‐loop controllers to ensure task‐space coordinated tracking asymptotically. If the robot has an open control architecture, the torque‐based distributed controller is provided for task‐space cooperative tracking, which can cover existing related results as a special case. Finally, numerical simulations are provided to show the effectiveness of the proposed designs.

STEP-NC Compliant Intelligent CNC Milling Machine with an Open Architecture Controller

A STEP-NC or ISO 14649 compliant machine controller is developed, using Open Architecture Control technology for a three-axis Computer Numerical Control milling machine in this research. The controller is developed on a Raspberry Pi single-board computer, using C++ language. This new development is proposed as a low-cost alternative to ISO6983 standard, ensuring continuous integration in the CAD/CAM/CNC chain in machining; thus, it broadens the spectrum of problems handled by conventional CNC systems. The new machine controller is intelligent enough to extract geometrical and manufacturing parameters, cutting tool data, and material data from the STEP-NC file. Accordingly, tool paths for machining can be generated in the controller itself. The shop floor level modification of parameters and the possibility of regeneration of new toolpaths is an added advantage of this new controller. The modified or improved version of the STEP-NC file can be sent back to the CAD/CAM system to close the CAD/CAM/CNC chain. Machine condition monitoring can be achieved by connecting sensors through an available slave I/O board. In the present development, the current drawn by each servo motor is fed back to the controller for cutting condition monitoring. A laboratory scale three-axis CNC milling machine is developed to test the performance of the newly developed controller. The accuracy of positioning, perpendicularity of axes and linearity of this machine are experimentally verified through standard tests. The STEP-NC compliance of the controller is tested and verified, using a STEP-NC program derived based on a sample program given in ISO 14649 standard.

A review of G code, STEP, STEP-NC, and open architecture control technologies based embedded CNC systems

Computer Numeric Control (CNC) is a significant pillar of manufacturing for decades. These systems are an essential part of future manufacturing. In the urge towards the development of next-generation manufacturing systems, various technologies have been introduced. Moreover, based on those technologies, numerous systems have been developed all around the world. In order to assist in future research, the related major technologies and developments are discussed in this content. This paper presents the review of basics CN), Computer-Aided Design (CAD), Computer-Aided Process Planning (CAPP), Computer-Aided Manufacturing (CAM), G codes (ISO 6983), Standard for the Exchange of Product (STEP) model data (STEP), STEP-numeric control (STEP-NC), and open architecture control (OAC) technologies. The in-depth discussion on the development and implementation of the STEP and STEP-NC technologies is also addressed. The review also highlights the benefits and role of the open architecture control technology in the CNC system development. Apart from that, the paper also presents the last 17 years of embedded CNC systems development in tabular form, which shows the cocktail of various technologies and ISO data interface models. Finally, the paper concludes with future directions and recommendations.

A novel integrating between tool path optimization using an ACO algorithm and interpreter for open architecture CNC system

This article proposes an effective methodology to reduce manufacturing time through the creation of quasi-optimal G command sequences, based on initial machining codes derived from CAD/CAM Service-Oriented Architecture (SOA) software. The optimization steps involved minimizing travel path time for CNC manufacturing machine milling and drilling. Also, identifying the optimal order of operation that enabled the shortest travel path for the cutting tool. These steps resulted in consistent enhancements of approximately 10.41% and 16.58% for milling and drilling machining, respectively. Furthermore, high-performing Ant Colony Optimization (ACO) algorithms were used to optimize the travel path time. In the context of automatic NC program production, the optimization of the cutting tool’s travel path could be achieved by integrating the ACO algorithm and the Open Architecture Control (OAC) into commercial CAD/CAM. In this paper, a new optimized generation of CNC systems, based on combining the Open Architecture Control (OAC) technology supported by the G-code data model and the optimization algorithm are presented.

Virtuelni horizontalni obradni centar LOLA HBG 80 za verifikaciju i monitoring programa

This paper describes configuring the virtual horizontal machining center LOLA HBG80 within the programming and verification system and the open architecture control system. The horizontal machining center LOLA HBG 80 is represented by an equivalent virtual machine in a CAD/CAM environment (PTC Creo and Catia), STEP-NC Machine environment, and the control system. Virtual simulation is essential for machining, and the developed virtual machines are used for program verification and monitoring of the machining process. The virtual machine in the programming system allows the verification of the program before sending it to the real machine and includes verification of the tool path (CLF-Cutter Location File) and G-code. The paper also discusses the possibility of applying a new programming method known as STEP-NC and preparing an adequate environment that includes a virtual machine. The virtual machine in the control system represents the last level for the final program verification and the process monitoring system.

Konfigurisanje nove edukacione mašine alatke na bazi mehanizma sa hibridnom kinematikom

The paper shows the configuration of a new educational machine based on hybrid kinematics mechanism. The concept of a three-axis O-X hybrid mechanism is described, consisting of a single serial translational axis and a two-axis parallel mechanism that can operate in two variants, with extended form O and crossed form X-joints of the parallel mechanism. The virtual prototype of the machine was configured in a CAD/CAM environment, where simulations of the mechanism's operation were performed. A programming system for machine has been prepared that also enables program verification. An open architecture control system based on the LinuxCNC platform has been configured for control of the machine. The trial work of the machine was performed in order to verify the realized prototype and control.

Konfigurisanje virtuelnog prototipa BiSCARA robota

The paper presents the configuring of a virtual prototype BiSCARA robot generated on the basis of a fully developed kinematic model of the robot. The virtual CAD model developed in this way will enable its implementation in the Python graphical environment as an integral part of the open architecture control system developed on the basis of the presented kinematic model. The developed kinematic model included solving the inverse and direct kinematic problem, determining the Jacobian matrix and workspace analysis. Verification of the kinematic model, i.e. the configured virtual prototype of the robot, was performed by simulations of the end-effector tip movement according to the given program in a CAD / CAM environment.

Learning Feedforward Control for Laser Powder Bed Fusion

Additive manufacturing is becoming increasingly important for industrial applications. Especially laser powder bed fusion processes play a decisive role. However, the technology often lacks in reliability and part quality due to complex process interactions and disturbing influences. To counteract these limitations, a flexible and high-dynamic control of relevant process parameters, taking into account the transient process conditions, is indispensable. Currently, the most process parameters are often kept constant, since the used control systems do not offer real-time capable interfaces for intervention. To enable the adjustment of parameters during the process, an open control architecture for galvanometer scanners and laser sources was developed. The architecture is based on an industrial control system in combination with a field-programmable gate array (FPGA) communicating via a real-time fieldbus. The novel control architecture is used to integrate a model-based feedforward control, adjusting the laser power, scan speed and scan strategy based on the current powder bed temperature calculated by a two-dimensional thermal model during run time. An integrated learning algorithm autonomously tunes the process parameters during the manufacturing process and determines the optimal combination of laser power, scan speed and powder bed temperature to achieve a homogeneous melt pool. On average, the standard deviation of the powder bed temperature along the scan path was reduced by 48% for the simulated test cases.

A Force/Motion Control Approach Based on Trajectory Planning for Industrial Robots With Closed Control Architecture

Most industrial robots are provided by the manufacturer with a controller that cannot be modified by the user (e.g. a standard PID). This arrangement is commonly referred to as closed control architecture, since it is not possible to program arbitrary control laws. For the implementation of novel algorithms, it is on the contrary necessary to employ an open control architecture, which allows programming any control scheme. For that reason, it is customary to have testbeds that are made up of robot manipulators specially designed for this goal. Another disadvantage of the closed control architecture is that the controller provided by the manufacturer usually does not include a force control term since it allows only to program desired motion trajectories. To overcome these drawbacks without physically modifying the closed control architecture, this contribution presents a novel approach to simultaneously follow position and force trajectories by employing only motion planning, i.e. only by choosing the desired position trajectory. The approach is especially well suited for DC motor actuators with large gear reduction ratios as those of many industrial robots. The convergence of the manipulator position and applied force depends exclusively on the performance of the controller provided by the manufacturer. The approach is tested on a dual-arm cooperative manipulation system made up of two ABB IRB-2400 industrial robots with closed control architecture.

Digital twin control of multi-axis wood CNC machining center based on LinuxCNC

This paper presents an application of an open architecture control system implemented on a multi-axis wood computer numerical control milling machining center, as a digital twin control. The development of the digital twin control system was motivated by research and educational requirements, especially in the field of configuring a new control system by “virtual commissioning”, enabling the validation of the developed controls, program verification, and analysis of the machining process and monitoring. The considered wood computer numerical control (CNC) machining system is supported by an equivalent virtual machine in a computer-aided design and computer-aided manufacturing (CAD/CAM) environment, as well as in the control system, as a digital twin. The configured virtual machines are used for the verification of the machining program and programming system via machining simulation, which is extremely important in multi-axis machining. Several test wood workpieces were machined to validate the effectiveness of the developed control system based on LinuxCNC.

A New Methodology for a Retrofitted Self-tuned Controller with Open-Source FPGA.

Servo systems are feedback control systems characterized by position, speed, and/or acceleration outputs. Nowadays, industrial advances make the electronic stages in these systems obsolete compared to the mechanical elements, which generates a recurring problem in technological, commercial and industrial applications. This article presents a methodology for the development of an open-architecture controller that is based on reconfigurable hardware under the open source concept for servo applications. The most outstanding contribution of this paper is the implementation of a Genetic Algorithm for online self tuning with a focus on both high-quality servo control and reduction of vibrations during the positioning of a linear motion system. The proposed techniques have been validated on a real platform and form a novel, effective approach as compared to the conventional tuning methods that employ empirical or analytical solutions and cannot improve their parameter set. The controller was elaborated from the Graphical User Interface to the logical implementation while using free tools. This approach also allows for modification and updates to be made easily, thereby reducing the susceptibility to obsolescence. A comparison of the logical implementation with the manufacturer software was also conducted in order to test the performance of free tools in FPGAs. The Graphical User Interface developed in Python presents features, such as speed profiling, controller auto-tuning, measurement of main parameters, and monitoring of servo system vibrations.

Suppression of robot vibrations using input shaping and learning-based structural models

Industrial robots used in manufacturing processes such as drilling of aerospace structures undergo many rapid positioning motions during each operation. Such aggressive motions excite the structural modes of the robot and cause inertial vibrations at the end-effector, which may damage the part and violate the tolerance requirements. This article presents a vibration avoidance technique based on input shaping combined with a learning-based structural dynamic model. A theoretical dynamic model is first developed for commonly used robotic arms considering the flexibilities of the first three joints of the robot. An artificial neural network is developed and used in conjunction with the dynamic model to predict the natural frequency of the system at any pose in the workspace. Transfer learning techniques are used to extend the trained artificial neural network to account for the mass of the payload with minimal data collection. To reduce the residual vibrations of the robot in rapid motions, zero-vibration derivative shapers are designed and implemented. The effectiveness of the presented methodology has been validated experimentally on a Staubli RX90CR robot with an open-architecture control system developed fully in-house. Experimental results show more than 85% reduction in residual vibrations during aggressive motions of the robot.

Complementary projector for null-space stiffness control of redundant assembly robot arm

PurposeStiffness control of redundant robot arm, aimed at using extra degrees of freedom (DoF) to shape the robot tool center point (TCP) elastomechanical behavior to be consistent with the essential requirements needed for a successful part mating process, i.e., to mimic part supporting mechanism with selective quasi-isotropic compliance (Remote Center of Compliance – RCC), with additional properties of inherent flexibility.Design/methodology/approachTheoretical analysis and synthesis of the complementary projector for null-space stiffness control of kinematically redundant robot arm. Practical feasibility of the proposed approach was proven by extensive computer simulations and physical experiments, based on commercially available 7 DoF SIA 10 F Yaskawa articulated robot arm, equipped with the open-architecture control system, system for generating excitation force, dedicated sensory system for displacement measurement and a system for real-time acquisition of sensory data.FindingsSimulation experiments demonstrated convergence and stability of the proposed complementary projector. Physical experiments demonstrated that the proposed complementary projector can be implemented on the commercially available anthropomorphic redundant arm upgraded with open-architecture control system and that this projector has the capacity to efficiently affect the task-space TCP stiffness of the robot arm, with a satisfactory degree of consistency with the behavior obtained in the simulation experiments.Originality/valueA novel complementary projector was synthesized based on the adopted objective function. Practical verification was conducted using computer simulations and physical experiments. For the needs of physical experiments, an adequate open-architecture control system was developed and upgraded through the implementation of the proposed complementary projector and an adequate system for generating excitation and measuring displacement of the robot TCP. Experiments demonstrated that the proposed complementary projector for null-space stiffness control is capable of producing the task-space TCP stiffness, which can satisfy the essential requirements needed for a successful part-mating process, thus allowing the redundant robot arm to mimic the RCC supporting mechanism behavior in a programmable manner.

Open Architecture Control for CNC System – An Approach

The Open Architecture concept is gaining more attention because of growing demand from end users. Numerical Control systems are limited in terms of portability because they are dependent on vendor-specific environment, to overcome this limitation Open Architecture Control was introduced. Open Architecture improves portability, interoperability, scalability and ability to reconfigure of an existing CNC machine. Open control system increases the flexibility of CNC machine by allowing vendor-neutral environment. Open Architecture Controller allows the end user to modify the existing system by integrating components from different manufacturers which reduce cost as well as increase extendibility of the system. In this review paper, different initiatives and developments on Open Architecture Controller are presented. This paper also covers the approaches made by researchers in the field of simulation of table movement in CNC machine.

A review of STEP-NC compliant CNC systems and possibilities of closed loop manufacturing

A new programming interface, ISO14649, named STEP-NC, has been introduced recently to overcome the drawbacks of the conventional CNC system. Enhanced machining flexibility, interoperability, and adaptability are the key features of this new programming strategy. STEP-NC technology is based on object-oriented concepts and considers machining processes rather than tool motions as in ISO 6983 for machine tool operation. As such, high level machining features and machining parameters are transferred to the CNC controller, which are eventually used for generating axis movements and other operations. The bidirectional data communication facility of this new strategy enables last minute shop floor level modifications of machining operations at the controller level and establishes a communication pathway to feed major modifications, if required, back to the CAD level as well. Accordingly, the new programming interface allows seamless integration in the CAD/CAM/CNC chain and paves the way for Closed Loop Manufacturing facilities. Most CNC controller vendors have not released STEP-NC compliant controllers yet. Therefore, researchers are developing Open Architecture Control systems to execute STEP-NC and operate CNC machines. This paper reviews research and development of STEP-NC controllers in the last decade and the capabilities of Closed Loop Manufacturing with STEP-NC based systems.