Tracking Error Transform in Parallel Kinematic Machining

2010 ◽  
Vol 450 ◽  
pp. 585-588
Author(s):  
Ghasem Amirian ◽  
Christian Schenck ◽  
Bernd Kuhfuss
Keyword(s):  
Machine Tools ◽  
High Speed ◽  
Tracking Error ◽  
Contour Error ◽  
Machining Accuracy ◽  
Tracking Errors ◽  
High Productivity ◽  
Machine Errors ◽  
Parallel Kinematic ◽  
Servo Tracking

Parallel kinematic machine tools (PKM) are developed to increase dynamic parameters for high speed and high accuracy machining to gain short lead times and high productivity. One of the most important components of machine tools is the numerical controller (NC). Most NCs are organized in a cascaded structure, comprising the position, velocity and current loops. Commonly applied servo controllers generate tracking errors in each axis. These tracking errors are a significant factor that affects machining accuracy, beside geometric machine errors, vibrations, temperature changes and tool errors. In this paper the contour error originated from servo tracking controller in Cartesian kinematic machine tools (CKM) with perpendicular arranged machine axes and PKM is presented. The effects of the forward transformation of the tracking errors in PKM are addressed with experiment and simulation results. The servo tracking effect on trace accuracy is discussed by a tripod mechanism and radial deviations are measured with double ball bar method (DBB).

Improving Contour Accuracy of Machine Tools Using an Integral-Gain Scheduler

2005 ◽  
Vol 219 (7) ◽  
pp. 511-518 ◽  
Author(s):  
R C Ko ◽  
M C Good
Keyword(s):  
Machine Tools ◽  
High Performance ◽  
Pulse Width Modulation ◽  
Tracking Error ◽  
Contour Error ◽  
Current Loop ◽  
Pwm Inverter ◽  
Current Controller ◽  
Reversal Error ◽  
Grinding Machine

In high-precision machine tools, contour error at axis reversal can significantly reduce the quality of products. Resulting from non-linear friction behaviour, the reversal error is traditionally handled by the velocity controller, which highly relies on a high-performance current servo. However, the widely employed pulse width modulation (PWM) inverter in the power stage of the current servo operates with a severe non-linearity known as deadband. The deadband effect degrades the current-loop tracking performance and consequently hinders the velocity controller in responding to friction disturbances. The result is a significant and oscillatory tracking error, or contour error in a multiaxis system. Unlike other approaches where the deadband is compensated via measurement or estimation, a control system approach is proposed in this paper where the deadband is treated as a voltage perturbation in the current loop. The proposed scheme incorporates a feedforward signal from the current command and schedules the integral action in the current controller accordingly. The proposed scheme was implemented in digital servo drives of a commercial grinding machine. Experiments show that the proposed scheme is an effective and practical solution for this type of problem.

Research on Servo Controller for High Speed Tracking System

2011 ◽  
Vol 65 ◽  
pp. 88-91
Author(s):  
Miao Li ◽  
Hui Bin Gao
Keyword(s):  
High Speed ◽  
Tracking System ◽  
Tracking Error ◽  
Engineering Practice ◽  
Mechanical Working ◽  
Loop Control ◽  
Accuracy Requirement ◽  
Servo Tracking ◽  
Servo Controller ◽  
Tracking Measurement

To meet requirement of swiftness and minimization for the tracking system as well as realize horizontal high accuracy tracking measurement, the automatic servo tracking measurement system has been designed. The two closed loop control, bisection method and compound control have been applied into the system. Experimental results show that the maximum tracking error can be limited to less than 0.5°and the regulator time can be 0.04s. The control project resonance frequency should be more than 200Hz and the sample frequency should be more than 400Hz to meet the control accuracy requirement. And these specific mechanical properties indexes are useful to mechanical working to make sure the design can be realization. So the research in this paper has important value to the engineering practice.

scholarly journals An attempt to relate dynamic tracking error to occurring situation based on additional rectilinear motion for five-axis machine tools

2020 ◽  
Vol 12 (10) ◽  
pp. 168781402096757
Author(s):  
Qicheng Ding ◽  
Jiexiong Ding ◽  
Jing Zhang ◽  
Li Du
Keyword(s):  
Machine Tools ◽  
High Speed ◽  
Dynamic Performance ◽  
Tracking Error ◽  
Cnc Machining ◽  
Rectilinear Motion ◽  
Nc System ◽  
Dynamic Tracking ◽  
Five Axis ◽  
Test Process

During five-axis CNC machining, the dynamic tracking error of the five-axis machine tool caused by imperfect servo dynamic performance is the major factor affecting the accuracy during high-speed and high-precision manufacturing. Rotation tool center point (RTCP) test has become a typical kinematic test for the dynamic tracking error of five-axis machine tools. According to the mechanism and characteristics of dynamic tracking error, during the RTCP test, relating the measured dynamic tracking error to corresponding occurring situation is helpful for the research of calibration or reduction of dynamic tracking error. In this paper, a new method to relate dynamic tracking error to occurring situation based on additional rectilinear motion is attempted. During this method, rectilinear motions are added into the RTCP test process, and the dynamic tracking error and corresponding occurring position can be calculated from the scale of rectilinear motion. By six tests with rectilinear motions in and against X, Y and Z directions, the additional error and uncertainty of the test process can be offset by calculation. This method can be implemented without any addition or modification to the instrument or NC system.

Failure Mode Analysis for High-Speed Motorized Spindle of NC Machine Tools

2014 ◽  
Vol 623 ◽  
pp. 85-89
Author(s):  
Yu An He ◽  
Yan Ming He
Keyword(s):  
Machine Tools ◽  
High Speed ◽  
Failure Modes ◽  
Fault Tree ◽  
Mode Analysis ◽  
Machining Accuracy ◽  
High Speed Machining ◽  
Motorized Spindle ◽  
Nc Machine ◽  
Nc Machine Tools

High-speed motorized spindle of NC machine tools is the core component for high speed machining. Production efficiency, machining accuracy, processing quality are greatly improved, and production cost is reduced by high speed machining. The paper describes the common failure modes of high-speed motorized spindle. By the fault tree analysis method, failure modes of motorized spindle are modeled, and the main fault reasons of motorized spindle for NC machine tools are gotten. Qualitative analysis is performed for the fault tree by the mean of the structure function. At the end of this paper, the minimal cut sets which are the main sets of failure modes are all obtained. It has laid a good foundation for further study of quantitative analysis of motorized spindle failure modes.

Research on Subdivision Interpolation for High Speed CNC Applications

2011 ◽  
Vol 141 ◽  
pp. 449-454
Author(s):  
Jing Chuan Dong ◽  
Qing Jian Liu ◽  
Tai Yong Wang
Keyword(s):  
High Speed ◽  
Tool Path ◽  
Tracking Error ◽  
Linear Interpolation ◽  
Cnc Machining ◽  
Contour Error ◽  
Interpolation Scheme ◽  
Simulation Results ◽  
Cnc Controller ◽  
Better Than

High speed CNC machining relies on the smooth interpolation of tool path in order to prevent impact and vibration. We present a new interpolation scheme for CNC controller based on 6-point subdivision. The subdivision interpolation improves the smoothness of the original trajectory, while maintaining the accuracy. The algorithm is simple and effective, and therefore it is suitable for real-time execution in CNC controllers. Simulation results show that the proposed method performs better than linear interpolation, since the tracking error and contour error is reduced.

Trajectory Preshaping for High-Speed Articulated Systems

1995 ◽  
Vol 117 (3) ◽  
pp. 304-310 ◽  
Author(s):  
Zvi Shiller ◽  
Hai Chang
Keyword(s):  
High Speed ◽  
Industrial Robot ◽  
Correction Term ◽  
Tracking Error ◽  
Feedback Controller ◽  
Reference Trajectory ◽  
Direct Drive ◽  
Unknown Parameters ◽  
Tracking Errors ◽  
Articulated Systems

This paper presents a method for reducing the tracking errors of articulated systems, moving along specified paths at high speeds. It consists of preshaping the reference trajectory to account for the dynamics of the feedback controller. The trajectory is assumed to be feasible, satisfying the known manipulator dynamics and the actuator constraints. The correction term, added to the nominal trajectory, is computed by filtering the nominal control inputs through the inverse of the feedback controller. A learning procedure is also presented to account for unknown parameters of the feedback controller and for unmodeled dynamics. It consists of an iterative parameter optimization that minimizes the tracking error along the path at each joint. The initial guesses for this optimization are selected to ensure that the tracking error is not worse than the error with no preshaping. The method is demonstrated experimentally for the UCLA Direct Drive Arm and for the AdeptOne industrial robot, achieving mean tracking errors as low as 0.11 mm at top speeds of 1.8 m/s.

Smooth Cornering Strategy for High Speed CNC Machine Tools With Confined Contour Error

2016 ◽  
Author(s):  
Shingo Tajima ◽  
Burak Sencer
Keyword(s):  
Machine Tools ◽  
High Speed ◽  
Cnc Machine Tools ◽  
Contour Error ◽  
Smoothing Algorithm ◽  
Cnc Machine ◽  
Computationally Efficient ◽  
Positioning Systems ◽  
Tool Paths ◽  
Time Optimal

Conventional tool-paths for CNC (computer numerical controlled) machine tools or NC positioning systems are mainly composed of linear motion segments, or so called the G1 commands. Interpolating along linear tool-paths exhibits serious limitations in terms of achieving the desired part geometry and productivity in high-speed machining. Velocity and acceleration discontinuities occur at the junction points of consecutive segments. In order to generate smooth and continuous feed motion, a kinematic corner smoothing algorithm is proposed in this paper, which plans smooth acceleration and jerk profiles around the segment junction to realize continuous velocity transition between consecutive linear segments. The proposed corner-smoothing algorithm eliminates the need for geometry based corner-blending techniques and presents a computationally efficient interpolation scheme. The cornering error is controlled analytically allowing the end-user to control the cornering tolerance. Drive’s acceleration and the jerk limits are fully utilized to minimize overall cornering duration. This delivers a time optimal cornering motion within user specified cornering error tolerances. Simulation studies are used to demonstrate the effectiveness of proposed high-speed cornering scheme.

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