Reference trajectory modification based on spatial iterative learning for contour control of 2-axis NC systems

Contour error is a main factor that affects the quality of products in numerical control (NC) machining. This paper presents a contour control strategy based on digital curves for high-precision control of computer numerical control (CNC) machines. A contour error estimation algorithm is presented for digital curves based on a geometrical method. The dynamic model of the motion control system is transformed from time domain to space domain because the contour error is dependent on space instead of time. Spatial iterative learning control (sILC) is developed to reduce the contour error, by modifying the reference trajectory in the form of G code. This allows system improvement without interference of low-level controllers so it is applicable to many commercial controllers where interpolators and feed-drive controllers cannot be altered. The effectiveness of this method is verified by experiments on a NC machine, which have shown good performance not only for smooth trajectories but also for large curvature trajectories

Contour error compensation based on feed rate adjustment

To improve the performance of computer numerical control (CNC) machining, especially for large-curvature trajectories, this paper presents a contour error compensation algorithm based on reference trajectory modification. In order to estimate the contour error accurately and efficiently, a contour error estimation model is established. The reference trajectory is modified on the basis of the estimated contour error and partitioned into different segments, which adopt different feed rates according to a corner detection algorithm. The effectiveness of this contour error compensation algorithm is verified by experiments on a CNC machine tool

Modeling and Contour Control of Multi-Axis Linear Driven Machine Tools

In modern manufacturing industries, many applications require precision motion control of multi-agent systems, like multi-joint robot arms and multi-axis machine tools. Cutter (end effector) should stay as close as possible to the reference trajectory to ensure the quality of the final products. In conventional computer numerical control (CNC), the control unit of each axis is independently designed to achieve the best individual tracking performance. However, this becomes less effective when dealing with multi-axis contour following tasks because of the lack of coordination among axes. This dissertation studies the control of multi-axis machine tools with focus on reducing the contour error. The proposed research explicitly addresses the minimization of contour error and treats the multi-axis machine tool as a multi-input-multi-output (MIMO) system instead of several decoupled single-input-single-output (SISO) systems. New control schemes are developed to achieve superior contour following performance even in the presence of disturbances. This study also extends the applications of the proposed control system from plane contours to regular contours in R3. The effectiveness of the developed control systems is experimentally verified on a micro milling machine

Liquid rocket metal tanks and tank components

Significant guidelines are presented for the successful design of aerospace tanks and tank components, such as expulsion devices, standpipes, and baffles. The state of the art is reviewed, and the design criteria are presented along with recommended practices. Design monographs are listed

ESSE 2017. Proceedings of the International Conference on Environmental Science and Sustainable Energy

Environmental science is an interdisciplinary academic field that integrates physical-, biological-, and information sciences to study and solve environmental problems. ESSE - The International Conference on Environmental Science and Sustainable Energy provides a platform for experts, professionals, and researchers to share updated information and stimulate the communication with each other. In 2017 it was held in Suzhou, China June 23-25, 2017

Characterizing the deformation response of a unidirectional non-crimp fabric for the development of computational draping simulation models

In several countries around the world, including Canada, government incentives have been put in place to improve the fuel efficiency of vehicles and reduce CO2 emissions. Improvements in composites manufacturing technology, such as high-pressure resin transfer molding and quick curing resins, makes it practical to lightweight through the incorporation of carbon fiber reinforced polymer (CFRP) parts into the body-in-white structure of vehicles. However, the technology has only been realized for small production rates and is currently in the developmental phase towards full automation for high-volume production. Hence, there is a need to developed and calibrate fabric draping simulations models to support this effort and enable the design of CFRP production processes that incorporate cost-effective fabric reinforcement material, such as heavy tow unidirectional non-crimp fabric (UD-NCF). This work aimed to expand the understanding of the forming behaviour of UD-NCFs, within the context of the development of automation capabilities for fabric preforming. The investigation focused on the characterization of the macroscale response of a UD-NCF, including an investigating of associated local deformation mechanisms, to calibrate a macroscale constitutive model and support the development of a computational fabric draping simulation model. The fabric characterization consisted of a series of experimental tests that measured the fabric in-plane and out-of-plane deformation responses reminiscent of draping operations. The tests were conducted with respect to the carbon fiber (CF) tow longitudinal and transverse directions. The experimental tests conducted were the longitudinal, transverse, and off-axis extension tests; the picture frame test (PFT); the cantilever; and friction sliding test in both material directions. The longitudinal extension and bending stiffness were found to be significantly higher than the respective transverse extension and bending stiffnesses. Also, at low strains, the fabric transverse extension stiffness was found to be negligible until crimping in the transverse glass fibers was removed. Regarding the fabric friction response, the coefficients of friction were higher on the stitching fabric side and when sliding occurred in the longitudinal fabric direction. Also, an investigation of the fabric mesoscale deformation mechanisms revealed the generation of CF tow undulations and intertow gapping, mainly generated by deformation of the stitching, when the fabric was subjected to transverse extension and shear deformations. To address difficulties associated with sliding of the glass fibers at the clamps during extension and PFT testing a clamping design was proposed that fully restrained the glass fibers, while at the same time preventing specimen damage at the grips. 2D DIC was used to study the development of strains in the fabric during all in-plane experimental tests. Challenges associated with fabric surface texturization and strain measurements through digital image correlation were investigated and addressed to improve the optical strain analysis. A surface texturization technique with an oil-based paint was implemented in all tests as it created high contrast speckle patterns on the fabric surface and the least amount of fabric deformation interference when compared with two other surface texturization techniques. Using the experimental results, a macroscale material model, chosen from the existing material model library available in the commercial finite element software LS-DYNA® was calibrated to simulate forming operations. The material model was calibrated for in-plane and out-of-plane deformation modes in accordance with the experimental tests conducted. The material model parameters were identified by simulating the experimental tests conducted during the fabric characterization process and an iterative inverse parameter identification approach until a good correlation was obtained between the numerical simulations and the corresponding physical tests. In most cases, piecewise linear functions were used to approximate the experimental test data before entering into the material model. Finally, to validate the calibration of the material model, a single-layer 100-mm diameter hemispherical test with a displacement controlled punch was performed and simulated using the calibrated material model. In addition to the calibrated material model, results from the friction tests were used to define contact boundary conditions in the draping simulation model. A good agreement was obtained between the simulation predictions of macroscopic deformations observed in the fabric, including contour shape and wrinkling, and the experimental results

Motion control and synchronisation of multi-axis drive systems

Motion control and synchronisation of multi-axis drive system

Active and Passive Control of Machine Tool Vibrations for High Speed and Accuracy

High-performance mechatronic systems are widely used in precision manufacturing equipment such as CNC machine tools, 3D-Printers, photolithography systems, industrial robots, and Coordinate Measuring Machines (CMMs). These equipment are utilized in producing parts and components for aviation, semiconductor, optics, and many other emerging industries, with geometric features and surface properties within micrometer-, or even in some cases nanometer-level accuracy. To keep up with the rapidly increasing productivity and accuracy demands, it is crucial that mechatronic systems of these manufacturing equipment deliver high-speed motion with high precision. In this dissertation, motion control strategies are presented to increase dynamic positioning accuracy and productivity of such mechatronic systems. First, a novel trajectory generation method is presented to avoid exciting low frequency structural vibration modes of machine tools and 3D-Printers, without compromising from productivity. The trajectory generation problem is posed as a convex optimization problem, and a practical windowing method is presented to implement the proposed strategy in real-time for long and realistic manufacturing scenarios. The proposed algorithm is validated on an industrial 3-Axis machine tool, and 4-6 times attenuation of the column vibration mode is achieved with 1[g] acceleration commands, without increasing the cycle time compared to state-of-the-art trajectory generation methods. This is followed by proposition of a data-driven trajectory shaping algorithm designed to eliminate dynamic positioning errors induced by flexible motion transmission components (such as ball-screw drives) and nonlinear friction forces typically caused by mechanical bearings and guiding units. The proposed algorithm is used for optimizing trajectory pre-filters through machine-in-the-loop iterations, in a data-driven fashion, and therefore it can be applied on a wide variety of systems without requiring elaborate dynamic modeling. Effectiveness of the proposed technique is validated on a linear-motor-driven planar motion stage and an industrial 3-Axis machine tool, and it is shown that dynamic errors are reduced by 3-5 times compared to industry-standard approaches. Finally, an active tool position control strategy is proposed to mitigate self-excited (chatter) vibrations for improving stability margins of turning processes. Two motion control algorithms are developed to control the dynamic process defined by the interaction of the tool and the workpiece. An industrial lathe (turning center) is utilized for validating the effectiveness of proposed algorithms. A piezo-actuator driven tool-assembly is utilized to control tool position during the machining process, utilizing tool acceleration feedback, and the experiments show that 4-5 times increase in productivity (widths of cut) is achieved by the proposed strategy

Aeronautical engineering, a continuing bibliography with indexes

This bibliography lists 823 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1984