• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.10 no.4
• /
• pp.70-75
• /
• 2001

In metal cutting, the machining accuracy is more affected by thermal errors than by geometric errors. This paper models of the thermal errors for error analysis and develops on-the-machine measurement system by which the volumetric error are measured and compensated. The thermal error is modeled by means of angularity errors of a column and thermal drift error of the spindel unit which are measured by the touch probe unit with a star type styluses, a designed spherical ball arti-fact, and five gap sensors. In order to analyze the thermal characteristics under several operating conditions, experiments performed with the touch probe unit and five gap sensors on the vertical and horizontal machining centers.

• Journal of the Korean Society for Precision Engineering
• /
• v.30 no.10
• /
• pp.1087-1093
• /
• 2013

In this study, a measurement method of double ball-bar is proposed to measure the geometric errors of an ultra-precision roll mold machine tool. A volumetric error model of the machine tool is established to investigate the effects of the geometric errors to a radius error and a cylindricity of the roll mold. A measurement path is suggested for the geometric errors, and a ball-bar equation is derived to represent the relation between the geometric errors and a measured data of the double ball-bar. Set-up errors, which are inevitable at the double ball-bar installation, also are analyzed and are removed mathematically for the measurement accuracy. In addition, standard uncertainty of the measured geometric errors is analyzed to determine the experimental condition. Finally, the proposed method is tested and verified through simulation.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.11
• /
• pp.98-105
• /
• 2010

In this paper, double ball-bar is used to estimate the geometric errors of a rotary table, which includes one-axial motion, two-radial motions and two-tilt motions, except the angular positioning error. To simplify the measurement procedures, three measurement steps have been designed and developed. At each measurement step, one end of the double ball-bar is fixed at the nose of spindle and the other end is located on the rotary table. And specific circular test path is planned to keep the distance between two balls as constant at ideal case. The relationship including the geometric errors of a rotary table and the measured distance between two balls which is distorted by the geometric errors is defined by using ball-bar equation. Each geometric error is modeled as $4^{th}$ order polynomial considering $C^1$-continuity. Finally the coefficients of polynomial are calculated by least-square method. Simulation is done to check the validation of the suggested method considering set-up errors and measurement noise. Suggested method is applied to estimate geometric errors of a rotary table of a 5-axis machine tool.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.1
• /
• pp.120-128
• /
• 2000

One of the major limitations of productivity and quality in metal cutting is the machining accuracy of machine tools. The machining accuracy is affected by geometric errors, thermally-induced errors, and the deterioration of the machine tools. Geometric and thermal errors of machine tools should be measured and compensated to manufacture high quality products. In metal cutting, the machining accuracy is more affected by thermal errors than by geometric errors. This paper models of the thermal errors for error analysis and develops on-the-machine measurement system by which the volumetric error are measured and compensated. The thermal error is modeled by means of angularity errors of a column and thermal drift error of the spindle unit which are measured by the touch probe unit with a star type styluses and a designed spherical ball artifact (SBA). Experiments, performed with the developed measurement system, show that the system provides a high measuring accuracy, with repeatability of $\pm$2${\mu}{\textrm}{m}$ in X, Y and Z directions. It is believed that the developed measurement system can be also applied to the machine tools with CNC controller. In addition, machining accuracy and product quality can be improved by using the developed measurement system when the spherical ball artifact is mounted on the modular fixture.

• The Journal of Korean Association of Computer Education
• /
• v.11 no.4
• /
• pp.85-93
• /
• 2008

This paper proposes a method for generating low-level geometric models with retaining salient features during decimation. Our method employs feature extraction technique for extracting feature lines defined via curvature derivatives on the model (we divide features into ridges and valleys). We add the extraction method to simplification technique (Feature Quadric Error Metric) for making coarse model with features. This paper clearly shows that experimental results have better quality and smaller geometric error than previous methods.

• 제어로봇시스템학회:학술대회논문집
• /
• 1992.10b
• /
• pp.1-6
• /
• 1992

A principle of "orthogonalization" is proposed as an extended notion of hybrid (force and position) control for robot manipulators under geometric endpoint constraints. The principle realizes the hybrid control in a strict sense by letting position and velocity feedback signals be orthogonal in joint space to the contact force vector whose components are exerted at corresponding joints. This orthogonalization is executed via a projection matrix computed in real-time from a gradient of the equation of the surface in joint coordinates and hence both projected position and velocity feedback signals become perpendicular to the force vector that is normal to the surface at the contact point in joint space. To show the important role of the principle in control of robot manipulators, three basic problems are analyzed, the first is a hybrid trajectory tracking problem by means of a "modified hybrid computed torque method", the second is a model-based adaptive control problem for robot manipulators under geometric endpoint constraints, and the third is an iterative learning control problem. It is shown that the passivity of residual error dynamics of robots follows from the orthogonalization principle and it plays a crucial role in convergence properties of both positional and force error signals.force error signals.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.1
• /
• pp.163-172
• /
• 1988

An off-line Geometric Adaptive Control Scheme is applied to the milling machine to identify its guideway errors. In the milling process, the workpiece fixed on the bed travels along the guideway while the tool and spindle system is fixed onto the machine. The scheme is based on the exponential smoothing of post-process measurements of relative machining errors due to the tool, workpiece and bed deflections. The guideway error identification system consists of a gap sensor, a, not necessarily accurate, straightedge, and the numerical control unit. Without a priori knowledge of the variations of the cutting parameters, the time-varying parameters are also estimated by an exponentially weighted recursive least squares method. Experimental results show that the guideway error is well identified within the range of RMS values of geometric error changes between machining passes disregarding the machining conditions.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.11
• /
• pp.2655-2663
• /
• 1993

In order to evaluate the relative significance of tolerance management of various elements in a VHS VTR tape transport system, the effect of geometric variations of the elements from standard design values on the tape traveling path is studied. The tape is modeled as a string and each element in the tape transport system is modeled as a cylinder whose radius, position vector and orientation vector are specified. An numerical algorithm is proposed to find the coordinates of tape entry points and tape exit points for the elements from which the tape traveling path can be completely described. By using the suggested algorithm, an error sensitivity analysis of tape traveling path due to the geometric variations of tape transport elements is performed for a particular model in the market and the elements demanding relatively strict tolerance management are identified.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.11
• /
• pp.94-100
• /
• 2000

This paper proposes a method of geometric error calibration for a parallel using only sensor of length measurement without additional sensors. The concept is generalized which creates measurement residuals by exploring conflicting information provided with external length sensing. Although this calibration method requires many configurations, it has an advantage of using relatively simple length measurements. This method is shown to provide good calibration results, especially when there exist smaller measurement noises and more configurations are measured.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.15 no.1
• /
• pp.1-7
• /
• 2006

A method of the volumetric error measurement and calibration of NC machine tools is studied using an artifact method. In this study, a hole-pate is designed and machined using stainless steel. We tested and applied the hole-plate artifact in a commercial CMM(Coordinate Measuring Machine), after calibration of the hole-plate using a precise CMM. It has been shown that not only the measurement of geometric error components but also the 2D length error calculation in a working volume is available using the hole-pate artifact method. The results of study can also be used in NC machine with touch probe as the same method in CMM.