Peter E. Orban

Remote Monitoring and Control in a Distributed Manufacturing Environment

Remote monitoring and control are crucial in decentralized manufacturing environments. This is evidenced by today’s distributed shop floors where agility and responsiveness are required to maintain high productivity and flexibility. However, there exists a lack of an effective system architecture that integrates remote condition monitoring and control of automated equipment. Addressing this problem, this chapter introduces a web-based and sensor-driven technique that bridges this missing link. A framework of WISE-SHOPFLOOR (Web-based integrated sensor-driven e-shop floor) was designed to realize such a concept. The conceptulization, architectural design, and system implementation are discussed in detail and two case studies on robot control and remote machining are presented. Enabled by Java and web technologies, WISE-SHOPFLOOR demonstrates significant promise of intelligent distributed manufacturing.

Design of a robot control architecture

A real-time modular control architecture for robot control has been developed for reconfigurable machines. The proliferation of communication buses such as fieldbuses for factory and machine operation has necessitated the need for uniformity and standardization. Although Ethernet stands out as the most ubiquitous, its non-real time property renders it unsuitable for device level communication where real-time is required. Given this challenge, our research imposes traffic management schemes in order to realize a real-time effect. An enabling feature is a switched Ethernet using UDP/IP. Each machine axis is controlled by a real-time Java micro-controller and all the controllers communicate through the Ethernet communication network. The architecture is designed to support reconfiguration of both hardware and software resources by the use of modularity and service-discovery schemes in the software and hardware design. Therefore devices such as axis and sensors may be reorganized, removed or added easily. The underpinnings of the object-oriented software include communication and computation architectures. The architecture can be configured to operate in different group communication schemes, i.e., client-sever, or multi-peer, depending on the task requirements.

Vibration-Based Machine Condition Monitoring with Attention to the Use of Time-Frequency Methods

To enable lightly staffed or fully autonomous machining operations, it is essential that both the condition of the cutter and the health of the machine tool system be known. In this paper, the health of the spindle positioning drive (Z axis) on a Proteo D/94 precision machining center is investigated using time, frequency and time-frequency techniques. Investigated is a cogging phenomenon produced as a result of the DC servomotor brushes sticking due to poor design. This incipient fault reduces the accuracy and controllability of the machine tool, and always leads to total drive failure. Thus, it is important to determine the fault signature of the drive so that corrective action may be taken before failure can occur, permanently damaging both the motor and the workpiece. The vibratory signatures of both a healthy and a faulty spindle during translation are analyzed. It is shown that a spindle under fault conditions behaves differently from a healthy one, and that time and time-frequency domain methods provide useful information on the status of the system. This paper lays the groundwork for the development of a future machine condition monitoring system, which can be easily retrofitted to any machine tool system.

CNC interpolator architecture for on-line error correction

The quality of a work piece is usually related to the machining precision. In order to improve the accuracy of machining, geometric adaptive control is adopted in conventional CNC (Computer Numerical Control) control system. Adjusting machining variables in real-time can compensate for the errors caused by the varying machining condition. This paper briefly introduces the geometric adaptive control system and proposes a new path generator architecture for CNCs, suitable for real-time error correction.

Spiral-Layer Machining for Making Thin-Wall Structures

CNC machining is one of the most widely used manufacturing processes. While possessing good flexibility and fast cycle time, there are some restrictions imposed depending on the geometry of the part to be machined. One challenge often encountered is the machining of thinwall structures. The instability and deflection of the thin-wall causes difficulty for control of the machining condition, affecting the accuracy of the modeling and simulation of the process. This paper presents an alternative machining method called spiral-layer machining that could improve this condition using the concept of layer manufacturing technology and technologies that would reduce the machining force or tool-force variation and divert the force-vector. A case study of machining a turbine blade was conducted to verify the method. The result was successful in terms of stability and feasibility. Error correction techniques are being investigated to ensure good dimensional precision of the part.

A Toolbox for Tripod Design, Simulation, and Monitoring

The paper presents a concept and implementation of a toolbox for the design and application of the tripod-based parallel kinematic machines (PKMs). The toolbox is a suite of design tools to support the users from the conceptual design to the actual application of the tripod-based PKMs. These design tools have been individually developed in different languages and they are integrated seamlessly using a Java-based platform. Users can access all of the design tools through a user-friendly graphical interface. It is the first computer-aided design system specially developed for tripod-based PKMs. The toolbox includes some implementations of our innovative methodologies, such as a forward kinematics solver, the concept of joint workspace analysis, on-line monitoring based on forward kinematics, and the concept of motion purity analysis. The paper gives an overview on the toolbox architecture, GUI, and some key technologies.Copyright

Performance Evaluation of a Distributed Reconfigurable Controller Architecture for Robotic Applications

Recent research in controller architecture has had some focus on reconfigurability and associated concepts such as modularity and openness. These paradigms advocate non-proprietary components such as commercial off-the-shelves (COTS) with standard interconnection interfaces. The tradeoffs of such a controller architecture are performance challenges such as network-induced delays and synchronization problems, especially where non-real time entities such as Ethernet are involved. In our quest to address some of these challenges we have developed a modular control architecture for machine and robotic control as a test platform. The advantage of this architecture is cost-effectiveness and openness, achieved through the use of COTS components. Each machine axis is controlled by a real-time Java micro-controller and all the controllers communicate through a switched-Ethernet communication network. The architecture is designed to support reconfiguration of both hardware and software resources by the use of modularity and service-discovery protocols in the software and hardware design. Therefore devices such as axes and sensors may be reorganized, removed or added easily. Our research presents performance results and applications typical of industrial or real life for our control architecture. The performance criteria analyzed include network delays, synchronization resolutions and error analyses.Copyright

Design and Implementation of a PKM Based 5-Axis Reconfigurable Machine

In this paper we present the design and implementation of a parallel kinematics based reconfigurable machine. The machine utilizes a Tripod based module with 3 degrees-of-freedom combined with a linear X-Y stage and gantry system for 5-axis machining. The tripod module uses a unique passive link mechanism with constant length leg actuators. This architecture offers good stiffness and high accuracy. The gantry system itself is reconfigurable, allowing for changing the working characteristics of the machine. The control system is based on open architecture principles. Corresponding to the mechanical reconfiguration, the control system also needs to be reconfigured to reflect the actual state of the machine. Mechanical reconfiguration also brings with it the need to verify the accuracy of the new configuration. Also discussed in the paper is the calibration methodology that ensures high production quality in each configured mode of the machine.Copyright

Machining process as a subject of automatic control

This report deals with the analysis and the design of a conventional machining system by means of mathematical modeling of the machining process. The paper considers the machining process as a dynamic interaction between the cutting tool and workpiece in space and time that additionally involves the dynamic properties of the machine tool mechanical subsystem, the cutting motions. An ideal machining system provides an accurately controlled tool path. However, machining experience has shown that the geometric qualities of the machined part are not only defined by the uniformity of the too path, but are also influenced by the dynamics of the machine tool and cutting process and by the external and internal disturbances. Developed herein, is a systematic approach tying together the four main factors associated with the dynamic processes that play an important role during machining and influence the quality of the machined workpiece. These factors are (a) the kinematic/dynamic disturbances within the cutting/feed motion subsystem, (b) the dynamics of the machine tool mechanical subsystem, (c) the tool-workpiece interaction as a dynamic process, and (d) the forming of the workpiece surface as a dynamic surface as a dynamic process. The generalized mathematical model of the machining process is developed based on the dynamic relationships between those above-mentioned aspects of the process. The approach performs the dynamic analysis of a machining process for diagnostics, control, and process optimization purposes.

Reliable servo system design with redundant sensors

A reliable servo system design scheme against sensor failures in the speed control loop is proposed. In the proposed reliable control system structure, in addition to the primary output sensor, redundant dissimilar sensors are used to measure different system variables which are more easily accessible and dynamically related to the desired output. In the event of output sensor failure, the measured signal from the redundant sensor can still maintain the system stability and certain performance, such as, tracking ability.