The parallel kinematic machine (PKM), which is applied Exechon mechanism, is efficiently used for manufacturing industry due to its agile movement, flexibility and high rigidity. On-Machine measurement (OMM) in high-dof manufacturing machines such as the PKM and five-axis machine tools has importantly used for processed part measurement, coordinate system set and machine performance evaluation. In this study, measurement and compensation of touch probe offset, which occurs measurement error of the OMM, are carried out for the PKM. A dependent rotational motion is occurred due to kinematic constraint, and causes non-constant offset of a touch probe. The dependent rotational motion is calculated via inverse kinematics analysis. The probe offset is accurately measured using a master ring with considering the analyzed dependent rotational motion angle. In addition, measurement procedure to eliminate the offset induced measurement error is presented. To verify the proposed technique, circular tests using a master ring and commercial touch probe on the PKM were performed. Circularity measurement deviation of a master was reduced 65% without the PKM’s kinematic error calibration.
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Sequential Measurement of Position-independent Geometric Errors in the Rotary and Spindle Axes of a Hybrid Parallel Kinematic Machine Seung-Han Yang, Dong-Mok Lee, Hoon-Hee Lee, Kwang-Il Lee International Journal of Precision Engineering and Manufacturing.2020; 21(12): 2391. CrossRef
The parallel slider system can be configured as a parallel robot by combining with other link devices. Therefore, the degree of positioning of the parallel slider would have considerable influence on the smooth operation of the parallel robot. In order to examine the degree of positioning of each slider, the following trajectory is equally presented, and the possibility of tracking the slider trajectory examined by application of the PD and PND control. From the experimental results, the dynamic characteristics of the slider show different responses to differing equivalent frictional forces acting on the slider. The PND control can make the rise time shorter than the PD control, and the PND control and PD control can smoothly follow the same trajectory given to each slider. It is therefore anticipated that the PND control and the PD control could be successfully implemented to follow the trajectory of a parallel robot based on a parallel slider system. It would then be necessary to fabricate slider experimental equipment capable of generating torque of sufficient magnitude to successfully reduce the trajectory error of the slider.
A fine stage is developed for the 3-DOF error compensation of a linear axis in order to improve the positioning accuracy. This stage is designed as a planar parallel mechanism, and the joints are based on a flexure hinge to achieve ultra-precise positioning. Also, the effect of Abbe’s offsets between the measuring and driving coordinate systems is minimized to ensure an exact error compensation. The mode shapes of the designed stage are analyzed to verify the desired 3-DOF motions, and the workspace and displacement of a piezoelectric actuator (PZT) for compensation are analyzed using forward and inverse kinematics. The 3-DOF error of a linear axis is measured and compensated by using the developed fine stage. A marked improvement is observed compared to the results obtained without error compensation. The peak-to-valley (PV) values of the positional and rotational errors are reduced by 92.6% and 91.3%, respectively.
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A new method to identify the position-independent geometric errors in the rotary axes of five-axis machine tools Seth Osei, Wei Wang, Qicheng Ding Journal of Manufacturing Processes.2023; 87: 46. CrossRef
Development and Performance Evaluation of a Fine Stage for Compensating 6-DOF Motion Errors of an Ultra-Precision Linear Stage Hoon-Hee Lee, In-Seok Lee, Kwang-Il Lee, Seung-Han Yang Journal of the Korean Society for Precision Engineering.2021; 38(2): 123. CrossRef
Optimal On-Machine Measurement of Position-Independent Geometric Errors for Rotary Axes in Five-Axis Machines with a Universal Head Kwang-Il Lee, Jae-Chang Lee, Seung-Han Yang International Journal of Precision Engineering and Manufacturing.2018; 19(4): 545. CrossRef
Error Compensation Using Variable Stiffness in Orbital Grinding Joon Jang, Woo Chun Choi International Journal of Precision Engineering and Manufacturing.2018; 19(3): 317. CrossRef
Face- and Body-Diagonal Length Tests using a Double Ball-Bar for Squareness Errors of Machine Tools Seung-Han Yang, Hoon-Hee Lee, Kwang-Il Lee International Journal of Precision Engineering and Manufacturing.2018; 19(7): 1039. CrossRef
Servo mismatch, which affects positioning accuracy of multi-axis machine tools, is usually estimated via the circular test. However, due to mechanical restrictions in measuring instruments, the circular test using a double ball-bar is difficult to apply in miniaturized or super-large sized machine tools. Laser trackers are widely used to measure the form accuracy of parts and the positioning accuracy of driving systems. In this paper, a technique for the servo mismatch estimation of multi-axis machine tools is proposed via the circular test using a laser tracker. To verify the proposed technique, experiments using a double ball-bar and laser tracker are conducted in a 3-axis machine tool. The difference in the evaluation results is 0.05 msec. The servo mismatch for the miniaturized machine tool is also evaluated using the proposed technique.
The out-of-squareness is one of the error sources that affect the positioning accuracy of machine tools and coordinate measuring machines. Laser interferometer is widely used to measure the position and angular errors, and can measure the squareness using an optical square. However, the squareness measurement using the laser interferometer is difficult, as compared to other errors due to complicated optics setup and Abbe’s error occurrence. The effect of out-of squareness mainly appears at the face-diagonal of the movable plane. The diagonal displacements are also affected by the position dependent geometric errors. In this study, the squareness estimation techniques via diagonal displacement measurement using the laser interferometer without an optical square were proposed. For accurate estimation and measurement time reduction, the errors selected from proposed discriminant were measured. Discrepancy between the proposed technique with the laser interferometer (with an optical square) result was 0.6 μrad.
In this paper, two-DOF parallel manipulator has the sliders which execute a linear reciprocating motion depending on parallel guides and the end-effector which can be adjusted arbitrarily. To investigate the dynamic characteristics of the manipulator, the dynamic performance index is used. The index is able to be obtained by the relation between the Jacobian matrix and the inertia matrix. The kinematic and the dynamic analysis find these matrices. Also, the dynamic model of the manipulator is derived from the Lagrange formula. This model represents complicated nonlinear equations of motion. With the simulation results of the dynamic characteristic of the manipulator, we find that the dynamic performance index is based on the selection of the ranges for the continuous movement of the manipulator and the dynamic model derived can be used to the control algorithm development of the manipulator.
In this research, three degree-of-freedom parallel spherical robot is developed for an artificial eyeball. The proposed system is comprised of a moving and a base plate, three prismatic actuators, and a ball joint for an angular movement of the moving plate. The vector analysis is employed to investigate the relationship between positions of the actuators and a pose of the moving plate. The required ranges for every actuators are calculated using the derived inverse kinematics in regard to the combination of two different levels for the size of the system component. Then the size of every components is determined from the analyzed trend. PI controller is employed for the position control of the moving plate. Finally the proposed system is verified using an arbitrary path of the angular movement.
This paper proposes a new model to compensate for errors of a five-axis machine tool. A matrix with error components, that is, an error matrix, is separated from the error synthesis model of a five-axis machine tool. Based on the kinematics and inversion of the error matrix which can be obtained not by using a numerical method, an error compensation model is established and used to calculate compensation values of joint variables. The proposed compensation model does not need numerical methods to find the compensation values from the error compensation model, which includes nonlinear equations. An experiment using a double ball-bar is implemented to verify the proposed model.
Recently, technologies to help the elderly or disabled people who have difficulty in walking are being developed. In order to develop these technologies, it is necessary to construct a system that gathers the gait data of people and analysis of these data is also important. In this research, we constructed the development of sensor system which consists of pressure sensor, three-axis accelerometer and two-axis gyro sensor. We used k-means clustering algorithm to classify the data for characterization, and then calculated the symmetry index with histogram which was produced from each cluster. We collected gait data from sensors attached on two subjects. The experiment was conducted for two kinds of gait status. One is walking with normal gait; the other is walking with abnormal gait (abnormal gait means that the subject walks by dragging the right leg intentionally). With the result from the analysis of acceleration component, we were able to confirm that the analysis technique of this data could be used to determine gait symmetry. In addition, by adding gyro components in the analysis, we could find that the symmetry index was appropriate to express symmetry better.
In this paper, a parallel manipulator is comprised of two sliders and four links. Sliders execute a linear reciprocating motion depending on parallel guides and make the connected links rotate. A couple of links connected by sliders do coupling motion. The end-effector called a link tip has orientation angle. Through the kinematics analysis of this manipulator, we found displacement, velocity and acceleration using direct and inverse kinematics. We used equations that derived from this analysis and determined five constraint conditions. These conditions had much to do with rotation states of links, the relative relation of link length and coupling motion state. To verify those, we suggest a new algorithm regarding constraint conditions of a manipulator. With the result which performed the algorithm, we found out that operation range of coupled links was limited by relative relation of link length and that manipulator was not able to carry out a series of link motion , in case of being the link vertical between two parallel guides.
The growing need for higher precision and productivity in manufacturing industry has lead to an increased interest in computer numerical control (CNC) systems. It is well known fact that the cross-coupling controller (CCC) is an effective method for contouring applications. In this paper, a multi-axis contour error controller (CEC) based on a contour error vector using parametric curve interpolator is introduced. The contour error vector is a vector from the actual tool position to the nearest point on the desired path. The contour error vector is the closest error model to the contour error. The simulation results show that the CEC is more accurate than the conventional CCC for a biaxial motion system. In addition, the experimental results on 3-axis motion system show that the CEC is simply applied to 3-axis motions and contouring accuracy is significantly improved.
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