Although initially the only Coordinate Measuring Machine (CMM) sensor available was a touch trigger probe, technological advances in sensors and computing have greatly increased the variety of available inspection sensors. Non-contact laser digitizers and analog scanning touch probes require very well tuned CMM motion control, as well as an extensible, open architecture interface. This paper describes the implementation of a retrofit CMM motion controller designed for open architecture interface to a variety of sensors. The controller is based on an Intel Pentium microcomputer and a Servo To Go motion interface electronics card. Motor amplifiers, safety, and additional interface electronics are housed in a separate enclosure. Host Signal Processing (HSP) is used for the motion control algorithm. Compared to the usual host plus DSP architecture, single CPU HSP simplifies integration with the various sensors, and implementation of software geometric error compensation. Motion control tuning is accomplished using a remote computer via 100BaseTX Ethernet. A Graphical User Interface (GUI) is used to enter geometric error compensation data, and to optimize the motion control tuning parameters. It is shown that this architecture achieves the required real time motion control response, yet is much easier to extend to additional sensors.
General-purpose microprocessors are increasingly being used for control applications due to their widespread availability and software support for non-control functions like networking and operator interfaces. Two classes of real-time operating systems (RTOS) exist for these systems. The traditional RTOS serves as the sole operating system, and provides all OS services. Examples include ETS, LynxOS, QNX, Windows CE and VxWorks. RTOS extensions add real-time scheduling capabilities to non-real-time OSes, and provide minimal services needed for the time-critical portions of an application. Examples include RTAI and RTL for Linux, and HyperKernel, OnTime and RTX for Windows NT. Timing jitter is an issue in these systems, due to hardware effects such as bus locking, caches and pipelines, and software effects from mutual exclusion resource locks, non-preemtible critical sections, disabled interrupts, and multiple code paths in the scheduler. Jitter is typically on the order of a microsecond to a few tens of microseconds for hard real-time operating systems, and ranges from milliseconds to seconds in the worst case for soft real-time operating systems. The question of its significance on the performance of a controller arises. Naturally, the smaller the scheduling period required for a control task, the more significant is the impact of timing jitter. Aside from this intuitive relationship is the greater significance of timing on open-loop control, such as for stepper motors, than for closed-loop control, such as for servo motors. Techniques for measuring timing jitter are discussed, and comparisons between various platforms are presented. Techniques to reduce jitter or mitigate its effects are presented. The impact of jitter on stepper motor control is analyzed.
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 an ideal scenario of intelligent machine tools  the human mechanist was almost replaced by the controller. During the last decade many efforts have been made to get closer to this ideal scenario, but the way of information processing within the CNC did not change too much. The paper summarizes the requirements of an intelligent CNC evaluating the different research efforts done in this field using different artificial intelligence (AI) methods. The need for open CNC architecture was emerging at many places around the world. The second part of the paper introduces and shortly compares these efforts. In the third part a low cost concept for intelligent and open systems named Knowledge Server for Controllers (KSC) is introduced. It allows more devices to solve their intelligent processing needs using the same server that is capable to process intelligent data. In the final part the KSC concept is used in an open CNC environment to build up some elements of an intelligent CNC. The preliminary results of the implementation are also introduced.
In laser materials processing, usually CNC controls come into operation that are fitted to conventional applications of machining, like milling. Because of the flexibility required and the large variety of applications in laser technology the use of an open architecture control is necessary. Open controls based on the OSACA (Open System Architecture for Controls within Automation systems) specification gain an increasing importance when innovative technology is integrated into controls. OSACA defines a uniform system platform that provides services for communication and configuration. The OSACA platform has been developed as a modular system for different operating systems with or without real-time capability and different hardware platforms. The functionality of the control is subdivided into single functional units, which communicate provided by the OSACA platform. Every unit can access the internal control data in a standardized way. The contribution reports about the implementation of an OSACA based control into a laser manufacturing plant. The problems and components concerning a linkage to the laser control and the implementation of some laser specific control units are discussed.
A thermal infrared imager of competitive sensitivity and very simple construction is presented. It is a pyroelectric device of 96 pixels, based on ferroelectric polyvinylidene fluoride (PVDF). It uses a novel charge-dispensing multiplexer based on ordinary light emitting diodes to achieve a noise-equivalent temperature change (NETD) of 0.13 K at a 5 Hz frame rate (2.1 Hz BW). Design information, theory, and measured performance are presented. Achieving such a low total system cost requires the use of the very least expensive optical system, a moulded polyethylene Fresnel lens, whose advantages and limitations are discussed. Several possible improvements, aggregating approximately 30 dB in sensitivity are also discussed, leading to the interesting possibility of few-millikelvin NETD values with an uncooled pyroelectric device of extremely low cost.
Recognition of free-form objects is a difficult task in a variety of engineering applications such as reverse engineering and product inspection. Most recognition systems can handle polyhedral objects that are defined by a set of primitives such as vertices, edges, or planar faces. However, free-form shapes have curved surfaces and often lack identifiable markers such as corners or sharp discontinuities. This paper presents a novel approach to creating structured representations of free-form surfaces that can be used for object recognition. The proposed method maps the three-dimensional coordinate data acquired by a range sensor onto a spherical self-organizing feature map (SOFM). The adaptation algorithm of the SOFm develops a topological order to the measured coordinate data such that connected nodes on the spherical map represent neighboring points on the object surface. Features are then extracted at each node of the SOFM. The feature vector is computed using a simple function that relates the node's positional vector to each of its neighboring nodes, within a circular are of one unit radius, in the SOFM. The feature vectors are used to establish a correspondence between the spherical map generated by an unknown free-form shape and maps of all the reference models. Any two free-form shapes can be matched for recognition purposes by registering the spherical SOFMs and determining the minimum registration error. This approach enables the unknown object to be in an arbitrary orientation. An experimental study is presented in order to demonstrate the effectiveness of this approach. The spatial coordinate data of a human foot and a toy in the shape of a pelican are used for illustrative purposes.
Industrial lasers are used extensively in modern manufacturing for a variety of applications because these tools provide a highly focused energy source that can be easily transmitted and manipulated for micro-machining. The quantity of material removed and the roughness of the finished surface are a function of the crater geometry formed by a laser pulse with specific energy (power). Laser micro-machining is, however, a complex nonlinear process with numerous stochastic parameters related to the laser apparatus and the material specimen. Consequently, the operator must manually set the process control parameters by trial and error. This paper describes how an artificial neural network can be used to create a nonlinear model of the laser material-removal process in order to automate micro-machining tasks. The multi-layered neural network predicts the pulse energy needed to create a crater of specific depth and average diameter. Laser pulses of different energy levels are impinged on the surface of the test material in order to investigate the effect of pulse energy on the resulting crater geometry and volume of material removed. Experimentally acquired data from several sample materials are used to train and test the network's performance. The key system inputs for the modeler are mean depth of crater and mean diameter of crater, and the system outputs are pulse energy, variance of depth and variance of diameter. The preliminary study using the experimentally acquired data demonstrates that the proposed network can simulate the behavior of the physical process to a high degree of accuracy. Future work involves investigating the effect of different input parameters on the output behavior of the process in hopes that the process performance, and the final product quality, can be improved.
Implementing a reliable condition monitoring system for bearing fault diagnosis and prognosis poses a big challenge to the industry. This challenge stems from the fact that bearing failure is statistical in nature, and thus contains elements of uncertainty and unpredictability. To achieve high accuracy in bearing diagnosis in spite of this inherent variance, reliable data acquisition and analysis techniques are needed. This paper focuses on the vibration analysis of a wireless transmitter module with an integrated sensor that is embedded into the bearing outer raceway for high signal-to-noise ratio data acquisition. A mechatronic design of the sensor module under severe space constraints is presented. The paper also analyses an optimizing scheme for the placement of sensor module substrate supports to reduce vibration transmitted from the bearing to the on-board electronics.
Although using fiber optic refractive index sensor to monitor the resin cure process has long been known as a kind of novel and promising method, there is no further report of the investigation on the in-situ monitoring of composite manufacture process. In this presentation, a kind of fiber optic refractive index sensor is developed and a portable instrument for the optic emission, signal receiving and interrogation are integrated to meet the requirements of on- site application. With it the cure process of resin and fiber reinforced prepreg is monitored. Tests of resin cure process monitoring are carried out with both resin that should be cured under room temperature and resin that should be cured under high temperature. The results of tests with resin cure under temperature are compared with the results of Michelson interferometer tests under similar circumstance, which are in good consistency. Tests are also carried out during composite manufacture, in which the fiber optic refractive index sensors are embedded in prepreg during the cure process. It is proved with the method the key information of the cure process can be extracted out during the process and be used in on-line intelligent control. In conclusion, this technique can be used not only in the establishment of the cure routine but also the in- situ monitoring and control of the composite manufacture process.
This paper presents a method for order reduction of linear structured uncertain systems using L2-optimal pole retention. The four Kharitonov's polynomials associated with the numerators nsI(s),nmI(s) and denominators dsI(s), dmI(s) of the original uncertain system and uncertain reduced model are obtained. By taking all combinations of the nsi(s),nmi(s) and dsj(s),dmj(s) for (i,j=1,2,3,4), respectively, we obtain sixteen Kharitonov's systems and sixteen Kharitonov's reduced models. The L2-optimal sixteen Kharitonov's reduced models retaining a given number of poles of the sixteen Kharitonov's systems are determined in a computationally efficient way. An expression for evaluating the minimum of the impulse response error norm for any choice of retained poles is derived in terms of the sixteen Kharitonov's systems parameters. Then, the corresponding optimal sixteen Kharitonov's reduced models numerators are obtained using an order-recursive procedure. An interesting interpolation property of the sixteen Kharitonov's reduced models is also pointed out. A numerical example is included in order to demonstrate the effectiveness of the proposed method.
This paper presents a method of reduction for linear structured uncertain system using the integral squared error criterion. The four fixed Kharitonov's polynomials associated with the numerators nsI(s), nmI(s) and denominators dsI(s), dmI(s) of the original uncertain system and uncertain reduced model are obtained. By taking all combinations of the nsk(s), nmk(s) and dsh(s),dsh(s) for (k,h = 1,2,3,4), respectively, we obtain sixteen fixed Kharitonov's systems and sixteen fixed Kharitonov's reduced models. Stability equation method and integral squared error criterion are used together to find the uncertain reduced order model. The stability equation method is used to preserve the stability of the sixteen fixed Kharitonov's systems and original uncertain system by first determining the denominator coefficients of the sixteen fixed Kharitonov's reduced models and uncertain reduced model respectively. The numerators of the sixteen fixed Kharitonov's reduced models are determined so that the integral squared error between the unit step responses of the sixteen fixed Kharitonov's reduced models and the corresponding sixteen fixed Kharitonov's systems are minimum. The sixteen fixed Kharitonov's reduced models tend to approximate the transient portions of the corresponding sixteen fixed Kharitonov's systems in the sense of minimum squared error, while the steady portions of the sixteen fixed Kharitonov's reduced models are matched exactly with that of the corresponding sixteen fixed Kharitonov's systems. Instead of actually evaluating time responses of the sixteen fixed Kharitonov's systems and reduced models, a matrix formulas are used for calculating the integral squared error from the coefficients of the error transfer functions. Finally the lower and upper bounds ci-,ci+ for (i=0,1,...r,-1) and dj-,dj+ for (j=1,2...,r) of the uncertain reduced model are found from the coefficients of the sixteen fixed Kharitonov's reduced models. An illustrative example is included in order to demonstrate the main points.
For the satisfying performance of a control system, design of a controller for the system which meets the required specifications, and the role of its supporting hardware that keeps functioning are equally important. Therefore it is inevitable to keep track of accurate and reliable sensor readings for good controller performance. Among the hardware of a control system sensors are most vulnerable to malfunction. Thus it is necessary to provide physical and analytical redundancy for the sensor measurement outputs to increase reliability against sensor failures. In general the task of detection, identification, and accommodation of sensor failures is widely pursued for this need. In case of sensor faults, they are detected by examining the sensor output values and the correlated or relevant values of the system. And then the types of the faults are identified by the analysis of symptoms of faults. If necessary self-validating sensor values are synthesized according to the types of faults, and then they are used for the controller instead of the raw data. In this paper, a self-validating sensor is applied to the control of a flexible link system with the sensor fault problems in the light sensor module for exact positioning to show the applicability. It is shown that the digital controller can provide a satisfactory loop performance even when the sensor faults occur.
Subpixel imaging is one of the effective ways to increase spatial resolutions of optical imagers by reducing frequency aliasing caused by the sampling process of discrete sensor grid. This paper presents a novel subpixel imaging system with linear CCD sensors. The system is consisted of a specially designed focal-plane-assembly(FPA) with two 2048 pixel linear CCD, a CPLD(Complex-Programmable-Logic-Device)-based controller, analog signal chain, and related image processing software. Firstly, analysis of the relationship between MTF and subpixel displacement is conducted, with quantum results presented, and the design of the FPA are analyzed. Secondly, we reviewed related image deconvolution algorithms, and discussed the precision image registration and improved Wiener filtering algorithm for this system, potentials of wavelet-based image restoration are also invoked. Preliminary pushbroom tests of a prototype subpixel imaging system show that the resolution of the subpixel system is 1.5~1.6 times greater than that of conventional system at Nyquist frequency, considerable resolution improvment has been obtained.
At present, the indirect method is applied to measuring and controlling mechanical compressive stress, which is the measurement and control of rotating torque of screw with torque transducer during screw revolving. Because the friction coefficient between every screw-cap and washer, of screw-thread is different, the compressive stress of every screw may is different when the machinery is equipped. Therefore, the accurate measurement and control of mechanical compressive stress is realized by the direct measurement of mechanical compressive stress. The author introduces the research of contrast between compressive stress and rotating torque in the paper. The structure and work principle of a special washer type transducer is discussed emphatically. The special instrument cooperates with the washer type transducer for measuring and controlling mechanical compressive stress. The control tactics based on the rate of compressive stress is put to realize accurate control of mechanical compressive stress.