For high-precision machining, a convenient and accurate detection of motion error for machine tools is significant. Among common detection methods such as the ball-bar method, the laser tracker approach has received much more attention. As a high-accuracy measurement device, laser tracker is capable of long-distance and dynamic measurement, which increases much flexibility during the measurement process. However, existing methods are not so satisfactory in measurement cost, operability or applicability. Currently, a plausible method is called the single-station and time-sharing method, but it needs a large working area all around the machine tool, thus leaving itself not suitable for the machine tools surrounded by a protective cover. In this paper, a novel and convenient positioning error measurement approach by utilizing a single laser tracker is proposed, followed by two corresponding mathematical models including a laser-tracker base-point-coordinate model and a target-mirror-coordinates model. Also, an auxiliary apparatus for target mirrors to be placed on is designed, for which sensitivity analysis and Monte-Carlo simulation are conducted to optimize the dimension. Based on the method proposed, a real experiment using single API TRACKER 3 assisted by the auxiliary apparatus is carried out and a verification experiment using a traditional RENISHAW XL-80 interferometer is conducted under the same condition for comparison. Both results demonstrate a great increase in the Y-axis positioning error of machine tool. Theoretical and experimental studies together verify the feasibility of this method which has a more convenient operation and wider application in various kinds of machine tools.
Dimensional measurement of hot heavy forgings is desirable to permit real-time process control, but usually it is inconvenient because of the difficulty in working with very hot workpieces. We present a new three dimensional (3D) measuring approach based on a two-dimensional laser range sensor (TLRS). First, the measurement system is obtained by assembling a TLRS, an axis of rotation, and a servo motor, which rotates the scan plane of the laser ranger sensor and lets the TLRS scan forgings in different planes. Therefore, the coordinates of forging surface points can be obtained in a sensor coordinate system (SCS). According to the transformation matrix between the SCS and measurement coordinate system (MCS), coordinates of points in different SCSs can be transferred into one fixed MCS. Hence the actual 3D models of hot heavy forgings can be reconstructed by using a triangulated irregular network and be optimized by employing improved Delaunay rules. Different parameters of forgings, such as lengths and diameters, can be measured based on the 3D model. The new method is verified by experiments in both the laboratory and the forging workshop. The experimental results indicate that it is much more practical and convenient for the real-time, onsite measurement of hot heavy forgings.
Geometric motion error measurement has been considered as an important task for accuracy enhancement and quality
assurance of NC machine tools and CMMs. In consideration of the disadvantages of traditional measuring methods，a
new measuring method for motion accuracy of 3-axis NC equipments based on composite trajectory including circle and
non-circle(straight line and/or polygonal line) is proposed. The principles and techniques of the new measuring method
are discussed in detail. 8 feasible measuring strategies based on different measuring groupings are summarized and
optimized. The experiment of the most preferable strategy is carried out on the 3-axis CNC vertical machining center
Cincinnati 750 Arrow by using cross grid encoder. The whole measuring time of 21 error components of the new method
is cut down to 1–2 h because of easy installation, adjustment, operation and the characteristics of non-contact
measurement. Result shows that the new method is suitable for ‘on machine’ measurement and has good prospects of
Dimensional measurement of hot heavy forgings is desirable to permit real-time
process control, but usually is inconvenient because of the difficulty in working with very hot
workpieces. This paper presents an approach based on Two-dimensional Laser Range Sensor
(TLRS). Firstly, the measurement system can be obtained by assembling TLRS, an axis of rotation,
and a servo motor, which rotates and scans forgings in different planes. Then, the coordinates of
points of forging's surface can be obtained in coordinate system in scanning plane. Secondly, the
origin of Measurement Coordinate System (MCS) at the centre of rotation of TLRS can be located.
According to the transformation between Sensor Coordinate System (SCS) and MCS, coordinates
of points in different SCS can be transferred into the fixed MCS. Next, the final points of forging's
surface in MCS can be obtained. Hence models of hot heavy forgings can be reconstructed by
using Triangulated Irregular Network and optimized by employing Delaunay rules. Finally,
different parameters of forgings, such as lengths and diameters, can be measured. In order to
calibrate the measurement system, a pyramid is proposed to compute the transformation matrix
between SCS and MCS based on the projective geometry theory. The new method has been
verified by experiments in both the laboratory and the forging workshop. The experimental results
indicate that it is much more practical for the real time on-site measurement of hot heavy forgings.
This research lays a desirable foundation for the further work.
This paper concerns the study of error modeling and inner parameter identification of 3D laser radar measuring system
(LRMS) equipped with 2D laser sensor and electric servo motor, for the potential application of on-site measurement of
the heavy forging object with temperature as high as 1000°C Firstly the physical and geometric model of 3D laser radar
measuring system is presented. Detail discussion about the deterministic error and random error of the measuring system
is conducted. Consequently the discipline of the deterministic error and the variation laws of random errors are achieved
by the nonlinear equations set through the coordinate transformation. Finally based on the above discuss the
identification method of inner geometrical parameter of the measuring system is presented by using the local
linearization for nonlinear equations with Tailor Series Expansion Formula and the Least Square Algorithm. Therefore
its measuring accuracy has been improved significantly. The results show this calibration method is helpful to the similar
application of other measuring systems.