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.
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.
While the basic principles of Numerical Controllers (NC) have not changed much during the years, the implementation of NCs' has changed tremendously. NC equipment has evolved from yesterday's hard-wired specialty control apparatus to today's graphics intensive, networked, increasingly PC based open systems, controlling a wide variety of industrial equipment with positioning needs. One of the newest trends in NC technology is the distributed implementation of the controllers. Distributed implementation promises to offer robustness, lower implementation costs, and a scalable architecture. Historically partitioning has been done along the hierarchical levels, moving individual modules into self contained units. The paper discusses various NC architectures, the underlying technology for distributed implementation, and relevant design issues. First the functional requirements of individual NC modules are analyzed. Module functionality, cycle times, and data requirements are examined. Next the infrastructure for distributed node implementation is reviewed. Various communication protocols and distributed real-time operating system issues are investigated and compared. Finally, a different, vertical system partitioning, offering true scalability and reconfigurability is presented.
In this paper, an analysis of the dynamic characteristics of machine tool spindle-bearing systems is presented. The research utilized the force impact-response testing method. The results are applied to the analysis and modeling of the dynamic performance of machine tool spindle-bearing systems. As an indicator of dynamic performance, the impulse response matrices are experimentally obtained. Two types of impulse response matrices are considered: (1) with respect to (wrt) acceleration; which describes the space-coupled relationship between the vectors of the force (impact) and measured acceleration (response) and (2) wrt displacement; which describes the space-coupled relationship between vectors of the force and simulated displacement. The results indicate an interrelation between different directions of displacements, and lay a foundation for the dynamic modeling of spindle-bearing systems in view of the transfer matrix with nonzero non-diagonal elements. From an engineering point of view, the transfer function matrix can be considered a `dynamic imprint', or `signature' of system performance. As a practical example, the dynamic properties (the impulse and frequency response matrices) of the spindle-bearing system of a Barer-Proteo D/94 high precision machining center are obtained, identified and investigated. The developed approach for modeling and parameter identification appears promising for a wide range of industrial applications, including rotary systems.
KEYWORDS: Process control, Control systems, Modeling, Mathematical modeling, Process modeling, Automatic control, Diagnostics, Control systems design, Spindles, Kinematics
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.
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.
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