A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone

Performance improvement of the LM device and its application to precise measurement of motion trajectories within a small range with a machining centre

In order to apply the LM device previously developed to precisely measuring small motion trajectories located on the different motion planes, three major improvements are successfully performed under the condition of completely maintaining the advantages of the device. These improvements include 1) development of a novel connection mechanism to smoothly attach the device to the spindle of a machining centre; 2) employment of a new data sampling method to achieve a high sampling frequency independent of the operating system of the control computer; and 3) proposal of a set-up method to conveniently install the device on the test machining centre with respect to different motion planes. Practical measurement experiment results with the improved device on a machining centre sufficiently demonstrate the effectiveness of the improvements and confirm several features including a very good response to small displacement close to the resolution of the device, high precision, repeatability and reliance. Moreover, based on the measurement results for a number of trajectories for a wide range of motion conditions, the error characteristics of small size motions are systematically discussed and the effect of the movement size and feed rate on the motion accuracy is verified for the machining centre tested

Evaluation of servo, geometric and dynamic error sources on five axis high-speed machine tool

Many sources of errors exist in the manufacturing process of complex shapes. Some approximations occur at each step from the design geometry to the machined part. The aim of the paper is to present a method to evaluate the effect of high speed and high dynamic load on volumetric errors at the tool center point. The interpolator output signals and the machine encoder signals are recorded and compared to evaluate the contouring errors resulting from each axis follow-up error. The machine encoder signals are also compared to the actual tool center point position as recorded with a non-contact measuring instrument called CapBall to evaluate the total geometric errors. The novelty of the work lies in the method that is proposed to decompose the geometric errors in two categories: the quasi-static geometric errors independent from the speed of the trajectory and the dynamic geometric errors, dependent on the programmed feed rate and resulting from the machine structure deflection during the acceleration of its axes. The evolution of the respective contributions for contouring errors, quasi-static geometric errors and dynamic geomet- ric errors is experimentally evaluated and a relation between programmed feed rate and dynamic errors is highlighted.Comment: 13 pages; International Journal of Machine Tools and Manufacture (2011) pp XX-X

Compensation of a ball end tool trajectory in complex surface milling

This work is consecrated to the minimising of machining errors based on a method for the compensation of the trajectory to be machined in hemispherical milling. This compensation is found to be necessary because of the tool deflection due to the cutting forces. In order to remedy to the machining errors, caused by this deflection, a compensation method has been proposed. The latter is inspired from the mirror method, since the compensated position is going to be determined as being the trajectory reflection, deviated onto the mirror. The advantage of this proposed method is that it takes into account the three deflections dx, dy and dz, respectively to the directions X, Y and Z. After that, two-parallel machinings, separated by a groove and achieved absolutely in the same conditions and with the same tool, are carried out, on the same complex part. The first machining is with compensation, but the second is without compensation. The coordinates of the two obtained surfaces are recorded by a 3D measuring machine. The comparison of the two-surfaces shows the presence of an important correction of the tool trajectory, and reveals a similarity between the part obtained by simulation and the one conceived in CAM

Task Specific Uncertainty in Coordinate Measurement

Task specific uncertainty is the measurement uncertainty associated with the measurement of a specific feature using a specific measurement plan. This paper surveys techniques developed to model and estimate task specific uncertainty for coordinate measuring systems, primarily coordinate measuring machines using contacting probes. Sources of uncertainty are also reviewed

Computer numerical control vertical machining centre feed drive modelling using the transmission line technique

This study presents a novel application of the Transmission Line Matrix Method (TLM) for the modelling of the dynamic behaviour of non-linear hybrid systems for CNC machine tool drives. The application of the TLM technique implies the dividing of the ball-screw shaft into a number of identical elements in order to achieve the synchronisation of events in the simulation, and to provide an acceptable resolution according to the maximum frequency of interest. This entails the use of a high performance computing system with due consideration to the small time steps being applied in the simulation. Generally, the analysis of torsion and axial dynamic effects on a shaft implies the development of independent simulated models. This study presents a new procedure for the modelling of a ball-screw shaft by the synchronisation of the axial and torsion dynamics into the same model. The model parameters were obtained with equipments such as laser interferometer, ball bar, electronic levels, signal acquisition systems etc. The MTLM models for single and two-axis configurations have been simulated and matches well with the measured responses of machines. The new modelling approach designated the Modified Transmission Line Method (MTLM) extends the TLM approach retaining all its inherent qualities but gives improved convergence and processing speeds. Further work since, not the subject of this paper, have identified its potential for real time application

Adaptive Monte Carlo applied to uncertainty estimation in a five axis machine tool link errors identification

Knowledge of a machine tool axis to axis location errors allows compensation and correcting actions to be taken to enhance its volumetric accuracy. Several procedures exist, involving either lengthy individual test for each geometric error or faster single tests to identify all errors at once. This study focuses on the closed kinematic Cartesian chain method which uses a single setup test to identify the eight link errors of a five axis machine tool. The identification is based on volumetric error measurements for different poses with a non-contact measuring instrument called CapBall, developed in house. In order to evaluate the uncertainty on each identified error, a multi-output Monte Carlo approach is implemented. Uncertainty sources in the measurement and identification chain - such as sensors output, machine drift and frame transformation uncertainties - can be included in the model and propagated to the identified errors. The estimated uncertainties are finally compared to experimental results to assess the method. It shows that the effect of the drift, a disturbance, must be simulated as a function of time the Monte Carlo approach. The machine drift is found to be an important uncertainty in sources for the machine tested

Thermo Energetic Design of Machine Tools and Requirements for Smart Fluid Power Systems

Modern production systems have to allow high performance cutting processes in a flexible production system environment at a high level of accuracy. The final workpiece accuracy is mainly influenced by the thermo-elastic behavior of the machine tool and can be improved by additional measures, compensation strategies and an optimized machine design. These measures are often implemented as stand-alone solutions. According to the Industry 4.0 all information should be connected in a single model of the actual machine state to increase machining accuracy. It is therefore necessary to integrate upcoming smart fluid power systems into the machine network

Geometric error compensation software in an open architecture, PC-based machine tool controller

A project was initiated at the Oak Ridge Y-12 Plant to implement software geometric error compensation within a PC-based machine tool controller from Manufacturing Data Systems, Inc. This project may be the first in which this type of compensation system was implemented in a commercially available machine tool controller totally in software. Previous implementations typically required using an external computer and hardware to interface through the position feedback loop of the controller because direct access to the controller software was not available. A mathematical error model of the lathe was created using homogeneous matrix transforms to relate the positions of the machine\u27s slides to each other and to a world reference system. Equations describing the effects of the geometric errors were derived from the model. A software architecture was developed to support geometric error compensation for machine tools with up to 3 linear axes. Rotary axes were not supported in this implementation, but the developed architecture would not preclude their support in the future. Specific implementations will be dependent upon the configuration of the machine tool. The test-bed machine for this project was a 2-axis Excello 921 T-base lathe. A laser measuring system from Automated Precision, Inc. was used to characterize the lathe\u27s geometric errors as functions of axis position and direction of motion. Multiple data files generated by the laser system were combined into a single Error File that was read at system startup and used by the compensation system to provide real-time position adjustments to the axis servos. A Renishaw Ballbar was used to evaluate the compensation system. Static positioning tests were conducted in an attempt to observe improved positioning accuracy with the compensation system enabled. These tests gave inconsistent results due to the lathe\u27s inability to position the tool repeatably. The development of the architecture and compensation template will provide a baseline platform for investigating other types of error compensation in the future

Investigation on the sampling size optimisation in gear tooth surface measurement using a Co-ordinate Measuring Machine

Co-ordinate Measuring Machines (CMMs) are widely used in gear manufacturing industry. One of the main issues for contact inspection using a CMM is the sampling technique. In this paper the gear tooth surfaces are expressed by series of parameters and inspection error compensation and initial value optimisation method are presented. The minimum number of measurement points for 3D tooth surfaces are derived. If high precision is required, more points need to be inspected. The sampling size optimisation is obtained from the criterion equation. The surface form deviation and initial values are optimised using the minimum zone method and Genetic Algorithms. A feature based inspection system for spur/helical gears is developed and trials and simulations demonstrated the developed method is very effective and suitable