Design of a new fast tool positioning system and systematic study on its positioning stability

The challenge of maintaining good surface quality under high operational frequencies in freeform machining invokes the need for a deterministic error analysis approach and a quantitative understanding on how structural design affects the positioning errors. This paper proposes a novel stiff-support positioning system with a systematic error analysis approach which reveals the contributions of disturbances on the tool positioning errors. The new design reduces the structural complexity and enables the detailed modelling of the closed loop system. Stochastic disturbances are analysed in the frequency domain while the non-stochastic disturbances are simulated in the time domain. The predicted following error spectrum agrees with the measured spectrum across the frequency range and this approach is justified. The real tool positioning error, which is free from sensor noise, is revealed for the first time. The influences of moving mass under various bandwidth settings have been studied both theoretically and experimentally. It is found that a larger moving mass helps combating disturbances except the sensor noises. The influences of cutting force are modelled and experimentally verified in the micro lens array cutting experiments. The origins of the form errors of the lenslet are discussed based on the error analysis model

Reconfigurable software architecture for a hybrid micro machine tool

Hybrid micro machine tools are increasingly in demand for manufacturing microproducts made of hard-to-machine materials, such as ceramic air bearing, bio-implants and power electronics substrates etc. These machines can realize hybrid machining processes which combine one or two non-conventional machining techniques such as EDM, ECM, laser machining, etc. and conventional machining techniques such as turning, grinding, milling on one machine bed. Hybrid machine tool developers tend to mix and match components from multiple vendors for the best value and performance. The system integrity is usually at the second priority at the initial design phase, which generally leads to very complex and inflexible system. This paper proposes a reconfigurable control software, architecture for a hybrid micro machine tool, which combines laser-assisted machining and 5-axis micro-milling as well as incorporating a material handling system and advanced on-machine sensors. The architecture uses finite state machine (FSM) for hardware control and data flow. FSM simplifies the system integration and allows a flexible architecture that can be easily ported to similar applications. Furthermore, component-based technology is employed to encapsulate changes for different modules to realize “plug-and-play”. The benefits of using the software architecture include reduced lead time and lower cost of development

A local tool path smoothening scheme for micromachining

Linear and circular representations are widely used to define tool paths, however, the tangency discontinuity between the linear and circular segments leads to large fluctuations in velocity and acceleration, as a result, the machining accuracy and efficiency are degraded. It becomes the key problem in some micromachining situations where the quality of freeform surfaces is critical, such as moulds and knee implants, etc. This research aims to develop a local tool path smoothening scheme to achieve C2 continuity at the transition positions. This scheme applies to sections consisting of high density of short segments. These segments will be approximated by cubic B-splines. The approximation is carried out within the specific error tolerance. High frequency energy to be injected into the servo loop control system is greatly reduced by the C2 continuity. The proposed scheme is feasible to be implemented in real-time microcontrollers due to the computational efficiency and reliability of B-spline algorithms

A real-time interpolator for parametric curves

Driven by the ever increasing need for the high-speed high-accuracy machining of freeform surfaces, the interpolators for parametric curves become highly desirable, as they can eliminate the feedrate and acceleration fluctuation due to the discontinuity in the first derivatives along the linear tool path. The interpolation for parametric curves is essentially an optimization problem, and it is extremely difficult to get the time-optimal solution. This paper presents a novel real-time interpolator for parametric curves (RTIPC), which provides a near time-optimal solution. It limits the machine dynamics (axial velocities, axial accelerations and jerk) and contour error through feedrate lookahead and acceleration lookahead operations, meanwhile, the feedrate is maintained as high as possible with minimum fluctuation. The lookahead length is dynamically adjusted to minimize the computation load. And the numerical integration error is considered during the lookahead calculation. Two typical parametric curves are selected for both numerical simulation and experimental validation, a cubic phase plate freeform surface is also machined. The numerical simulation is performed using the software (open access information is in the Acknowledgment section) that implements the proposed RTIPC, the results demonstrate the effectiveness of the RTIPC. The real-time performance of the RTIPC is tested on the in-house developed controller, which shows satisfactory efficiency. Finally, machining trials are carried out in comparison with the industrial standard linear interpolator and the state-of-the-art Position-Velocity-Time (PVT) interpolator, the results show the significant advantages of the RTIPC in coding, productivity and motion smoothness

Development of a compact ultra-precision six-axis hybrid micro-machine

High precision miniature and micro products which possess 3D complex structures or free-form surfaces are now widely used in industries. These micro products are usually fabricated by several machining processes in order to apply for various materials such as hard-to-machine steel and ceramic etc. The integration of these machining processes onto one machine becomes necessary since this will help reduce realignment errors and also increase the machining efficiency. In this research, an ultra-precision hybrid micro-machine which is capable of micro milling, micro grinding, micro turning, laser machining and laser assisted micro-machining has been designed and commissioned. Control software for on-machine metrology system (contact probe and dispersed reference interferometry (DRI)) and several plug-in modules including camera and handle system are integrated through a customised human-machine interface (HMI)

A generic control architecture for hybrid micro-machines

Hybrid micro-machining, which integrates several micro-manufacturing processes on one platform, has emerged as a solution to utilize the so-called "1 + 1 = 3" effect to tackle the manufacturing challenges for high value-added 3D micro-products. Hybrid micro-machines tend to integrate multiple functional modules from different vendors for the best value and performance. However, the lack of plug-and-play solutions leads to tremendous difficulty in system integration. This paper proposes a novel three-layer control architecture for the first time for the system integration of hybrid micro-machines. The interaction of hardware is encapsulated into software components, while the data flow among different components is standardized. The proposed control architecture enhances the flexibility of the computer numerical control (CNC) system to accommodate a broad range of functional modules. The component design also improves the scalability and maintainability of the whole system. The effectiveness of the proposed control architecture has been successfully verified through the integration of a six-axis hybrid micro-machine. Thus, it provides invaluable guidelines for the development of next-generation CNC systems for hybrid micro-machines

Design and integration of a high-precision material handling system with a six-axis hybrid micro-machine

Hybrid micro-machines are increasingly in demand for the manufacturing of miniature 3D products made of hard-to-machine materials. A high-precision material handling system for such miniature products can increase the overall efficiency significantly. This paper proposes the design of a machine vision based handling system, which is capable of handling various miniature 3D products. A cloud-based innovative integration method is also developed, a cloud server is deployed to collect and process data from the machine and the material handling system, their actions are coordinated based on the predefined protocol. This method can enhance the reconfigurability of the whole system