K. M. Muditha Dassanayake

Accuracy evaluation method for multi-tasking turning centre

Multi-tasking turning centre has ten inherent deviations which were identified by considering the axis configuration and mutual motions of axes. To estimate all these deviations, in this paper, a new methodology which is based on simultaneous three-axis motion technique is proposed. The effects of deviations on predefined trajectories were investigated by simulations. Five measurements which were extracted by conducting four simultaneous motions were used in the identification algorithm. All the ten inherent deviations were estimated accurately by means of the centre offset values of the trajectory measurement. Furthermore, the effects of setting errors of balls of ball bar and clamp-unclamp process of B-axis on measurement were discussed and eliminating techniques were proposed. All the results were verified by means of simulations and experiments. Based on the results, it can be said that the proposed method can be used as an accuracy evaluation and identification tool for multi-tasking turning centres.

Motion Characteristics of High Performance Rotary Tables for CNC Machines

In this paper, the characteristics of two rotary tables driven by worm gear and roller gear cam are measured and compared. The positioning accuracy and repeatability as specified in ISO 230-2 are measured together with the rotational fluctuation, backlash, friction torque, frequency response of the systems and also the influence of unbalance mass on rotational motion. Two rotary encoders which were attached to motor and output axis were used for measurements. The motor, controller, and the rotary encoders were kept the same for both tables to ignore the effects of these units on results. Furthermore, the simulations were carried out by mathematical models which were proposed by two of the authors and the results were compared with measured results. From the simulation results, the torsional stiffness and friction torque were identified and also compared. The results show that the measured and simulated data have a good agreement and therefore it can be said that the identified parameters from simulations are accurate. The result shows that the performances of the rotary table driven by roller gear cam is better than that of rotary table driven by worm gear.© 2008 ASME

A Methodology for Identifying Inherent Deviations in Universal Spindle Head Type Multi-Axis Machines by Simultaneous Five-Axis Control Motions

In this paper, two different simulataneous five-axis control motions were newly proposed to identify the ten inherent deviations in universal spindle head type multi-axis machines. The ball bar was used as a measuring device. Both of the two motions were carried out bu using a single setup which was a simple extension bar. This leads to reduce non-productive time of the operator within the machine work space. Three measurments were used to estimate the ten deviations in which two measurements were extracted by means of axial direction motion and the other by tangential direction motion. By using the axial direction motion, seven deviations were estiamted in which four deviations were estiamted by means of the observation equation and simple geometric relations were used for other three. Remaining three of the ten deviations was estimated by using tangential direction motion. The validity of the proposed methodology for identifying the ten deviations inherent to universal spindle head type five-axis machining centers is confirmed by simulations.Copyright

Feasibility Study of Using Simultaneous Motion of Two Rotary Axes to Evaluate Machining Center: Simulation

In this paper, a new motion: the two rotary axes simultaneous motion was proposed and the mathematical model which was used to carryout simulations was described. The effect of each deviation on the proposed motion was identified and described one by one. A methodology to estimate all the eight deviations which inherent to tilting rotary table type machining centers was described step by step. This methodology consists of two motions: the proposed motion and C axis radial direction motion. Both the two motions used only the rotary axes. All the motions can be run on one setup. The simulations were carried out by considering that the double ball bar as the measuring device. Furthermore, number of settings which can be used for the new motion were discussed. From this study, it was confirmed that this method can be used for estimate all the eight deviations, accurately.Copyright

Identification of Geometric Deviations Using Simultaneous Five-axis Control Technique in Five-axis Machining Centers with Double Pivot Spindle Head

This study was conducted for developing the testing methods by means of simultaneous five-axis motion in five-axis controlled machining centers with a double pivot spindle head. In this paper, the five axis motion was simulated considering the measurement by a ball bar system and the relative distance change between both balls of the table side and the spindle side was simulated, changing the ten deviations inherent to the five-axis machining centers. Two of the three kinds of simultaneous five-axis motions were introduced for the identification of the deviations inherent to the five axis machining centers. In the first step, the ball bar was set parallel to the A-axis of the spindle head and in the second step the distance between the ball of the spindle side and the center of the A-axis was extended and then the measurement was repeated. In the third step, the ball bar was set tangential to the A-axis rotation. The observation equations and the geometric analysis were applied to the identification. The ten deviations inherent to the machining centers were accurately identified through these three steps. It was confirmed that the proposed five axis motion was effective for valuating the accuracy of the five-axis machining centers compared with our previous proposed method.