New optical sensing system applied to taut wire based straightness measurement

In modern manufacturing industry, precision components are typically produced on Computer Numerical Controlled (CNC) machine tools which translate their accuracy onto machined parts. This accuracy is affected by a set of different motion errors caused by inherent imperfections in the design and build of the machine, variations in the local environment such as temperature, the cutting process itself and human factors. The reduction of these effects is achieved primarily through design improvements and error compensation techniques. The latter requires detailed knowledge about the existing errors in order to deal with them effectively. This thesis describes a novel sensor system for measurement of errors caused by deviation in the straightness of Cartesian axes present in the structural loop of most machine tools. Currently there are very few methods available to measure straightness directly, each having advantages and disadvantages when considering simplicity, accuracy and affordability. The proposed system uses a taut wire reference with a novel sensor, a two-point technique for reference error cancellation and software to enable fast and accurate measurement of straightness between any two points of the measured machine’s working volume. The standout features of the sensing system include ultra-low cost and high performance when compared with existing state-of-the-art systems. It is capable of measuring a straightness error as low as 3μm and takes only 2s of dwell time between readings, while laser interferometer requires 4s to perform averaging when measuring the same error. Existing taut wire microscopy is limited by 10-20μm of measured error depending on optics quality and manual reading takes at least 5s to minimise the human error. Setup time is also different – the new system saves 15 minutes time on 2m axis and more on longer lengths compared the laser due to simpler reference alignment procedure. Theoretical analysis and practical implementation are followed by detailed performance evaluation experiments carried out under typical manufacturing conditions comprising different machine tools, different axes, measured errors, environmental effects and alternative measuring equipment. Tests cover aspects of accuracy, repeatability and overall system stability providing a complete picture of the system’s capability and the method’s potential which is also supported by uncertainty analysis. In addition to defining setup and measuring procedures, a user-friendly software interface is described and its main units are explained with respect to overall measurement efficiency and setup fault detection

Aspheric geodesic lenses for an integrated optical spectrum analyser

Abstract available p. xiii-xi

Development of compliant mechanisms for real-time machine tool accuracy enhancement using dual-servo principle

Ph.DDOCTOR OF PHILOSOPH

力制御型スタイラスプローブによる機上形状計測

Tohoku University高偉課

Robust Thermal Error Modeling and Compensation for CNC Machine Tools.

Thermal errors are one of the most significant factors affecting machine tool accuracy. Error compensation has been widely used to reduce the thermal errors, the robustness of the thermal error models, however, still needs to be improvement. Currently, five-axis machine tools are becoming more important and extensively utilized in industry. In this regard, the geometric errors of rotary axis must be properly measured and corrected to assure the accuracy of five-axis machining. Thermal error model, relating temperature variations to thermal errors, is the core of an effective thermal error compensation strategy. Thermal modal analysis, unveiling the essence of thermo-elastic process, is explored for the determination of temperature sensor placement based on the finite element analysis and eigen analysis. Thermal error models are thus derived based on the temperature variations collected from the specified temperature sensors. The robustness of the derived models is investigated in terms of linear extrapolation and frequency sensitivity. Numerical simulation and experiments are conducted to illustrate the existence of thermal modes and validate the robustness of the thermal error models. Thermal loop analysis is developed for the thermal error compensation of an entire machine tool. A machine tool is first decomposed into several thermal links along an identified thermal loop. For each thermal link, the thermal modal analysis is carried out for the derivation of thermal error model. These thermal links are finally reassembled for the thermal error prediction of the entire machine tool. The thermal loop analysis mitigates the inaccurate modeling of machine joints, and extensively facilitates the utilization of the finite element method in the thermal error modeling and compensation. Calibration of rotary axis of five-axis machine tools is usually time-consuming and laborious by using laser interferometer or autocollimator systems. The Telescopic Magnetic Ball Bar is explored to estimate error components induced by the rotational motion of a rotary axis. The calibration algorithm is developed based on the rigorous mathematical derivation. The setup errors, including parameter variation and eccentricity, have been accounted for through the numerical simulation, enabling the practical utilization of this method. This approach shows the advantages of easy setup and quick assessment.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60857/1/zhujie_1.pd

Manufacturing Metrology

Metrology is the science of measurement, which can be divided into three overlapping activities: (1) the definition of units of measurement, (2) the realization of units of measurement, and (3) the traceability of measurement units. Manufacturing metrology originally implicates the measurement of components and inputs for a manufacturing process to assure they are within specification requirements. It can also be extended to indicate the performance measurement of manufacturing equipment. This Special Issue covers papers revealing novel measurement methodologies and instrumentations for manufacturing metrology from the conventional industry to the frontier of the advanced hi-tech industry. Twenty-five papers are included in this Special Issue. These published papers can be categorized into four main groups, as follows: Length measurement: covering new designs, from micro/nanogap measurement with laser triangulation sensors and laser interferometers to very-long-distance, newly developed mode-locked femtosecond lasers. Surface profile and form measurements: covering technologies with new confocal sensors and imagine sensors: in situ and on-machine measurements. Angle measurements: these include a new 2D precision level design, a review of angle measurement with mode-locked femtosecond lasers, and multi-axis machine tool squareness measurement. Other laboratory systems: these include a water cooling temperature control system and a computer-aided inspection framework for CMM performance evaluation

Force sensing enhancement of robot system

At present there is a general industrial need to improve robot performance. Force feedback, which involves sensing and actuation, is one means of improving the relative position between the workpiece and the end-effector. In this research work various causes of errors and poor robot performance are identified. Several methods of improving the performance of robotic systems are discussed. As a result of this research, a system was developed which is interposed between the wrist and the gripper of the manipulator. This system integrates a force sensor with a micro-manipulator, via an electronic control unit, with a micro-computer to enhance a robot system. The force sensor, the micromanipulator and the electronic control unit, were all designed and manufactured at the robotic centre of Middlesex Polytechnic. The force feedback is provided by means of strain gauges and the associated bridge circuitry. Control algorithms which define the relationship between the force detected and the motion required are implemented in the software. The software is capable of performing two specific tasks in real time, these are: 1- Inserting a peg into a hole 2- Following an unknown geometric path A rig was designed and manufactured to enable the robot to follow different geometric shapes and paths in which force control was achieved mainly by control of the micro-manipulator