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The geometrical accuracy of a machined feature on a workpiece during machining processes is mainly affected by the kinematic
chain errors of multi-axis CNC machines and robots, locating precision of fixtures, and datum errors on the workpiece. It
is necessary to find a way to minimize the feature errors on the workpiece. In this paper, the kinemati...
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Citations
... In these cases, a significant contribution to the machining error can be made by turns of the workpiece, especially in the directions of the prevailing overall dimensions. The need to take into account angular displacements of workpiece under the action of cutting forces was indicated in [3,[29][30][31][32][33][34][35][36][37][38][39][40][41][42]. They even proposed the simplest analytical relationships for calculating these angular displacements. ...
The article discusses the technology capabilities of multi-purpose CNC machines, and possible options for implementing parallel multi-tool processing. It was revealed that the technological capabilities of these machines are used at best by 50% in factories. This is due to the lack of recommendations for the design and use of such adjustments for these machines. To this end, generalised lattice matrix models of the accuracy of multi-tool machining have been developed in order to fulfill the requirements of algorithmic uniformity models and their structural transparency. The use of lattice matrices greatly simplifies the error in model of multi-tool machining and makes it extremely visual. Also, full-factorial distortion models and scattering fields of the dimensions of multi-tool machining performed on modern multi-purpose CNC lathe machines have been developed to take into account the angular displacements of the workpiece when machining parts with prevailing overall dimensions. They take into account the flexibility of the technological system for all six degrees of freedom to identify the influence degree of complex of technological factors on the machining accuracy (structure of multi-tool adjustment, deformation properties of subsystems of a technological system, cutting conditions). A methodology has been developed for determining the complex characteristics of compliance of a technological system. On the basis of the developed accuracy models in spatial adjustments, it is possible to develop recommendations for the design of adjustments for modern multi-purpose machines in CNC turning group (creation of CAD of multi-tool machining). Thus, it is possible to achieve a number of ways to control multi-tool machining, including improving the structure of multi-tool adjustment, calculating the limiting cutting conditions.
... In these cases, a significant contribution to the machining error can be made by turns of the workpiece, especially in the directions of the prevailing overall dimensions. The need to take into account angular displacements of workpiece under the action of cutting forces was indicated in [3,[29][30][31][32][33][34][35][36][37][38][39][40][41][42]. They even proposed the simplest analytical relationships for calculating these angular displacements. ...
The article discusses the technology capabilities of multi-purpose CNC machines, and possible options for implementing parallel multi-tool processing. It was revealed that the technological capabilities of these machines are used at best by 50% in factories. This is due to the lack of recommendations for the design and use of such adjustments for these machines. To this end, generalised lattice matrix models of the accuracy of multi-tool machining have been developed in order to fulfill the requirements of algorithmic uniformity models and their structural
transparency. The use of lattice matrices greatly simplifies the error in model of multi-tool machining and makes it extremely visual. Also, full-factorial distortion models and scattering fields of the dimensions of multi-tool machining performed on modern multi-purpose CNC lathe machines have been developed to take into account the angular displacements of the workpiece when machining parts with prevailing overall dimensions. They take into account the flexibility of the technological system for all six degrees of freedom to identify the influence degree of complex of technological factors on the machining accuracy (structure of multi-tool adjustment, deformation properties of subsystems of a technological system, cutting conditions). A methodology has been developed for determining the complex characteristics of compliance of a technological system. On the basis of
the developed accuracy models in spatial adjustments, it is possible to develop recommendations for the design of adjustments for modern multi-purpose machines in CNC turning group (creation of CAD of multi-tool machining). Thus, it is possible to achieve a number of ways to control multi-tool machining, including improving the structure of multi-tool adjustment, calculating the limiting cutting conditions.
... Caihua Xiong analyzed the relationship between the kinematic chain errors and the displacements of the position and orientation of the workpiece. An error elimination (EE) method of the machined feature is formulated for improving the accuracy [11] . ...
The industrial robot has already been used for machining tasks in the industry. In order to improve the machining accuracy, a CNC controller is proposed as a control system for the industrial robot. This article concentrates on the performance of the industrial robot motion accuracy guided by a CNC controller. Corner paths are studied in consideration of different running speeds. The path accuracy and the influence of motion acceleration are both thoroughly analyzed. The performance of the same paths running in a conventional controller is evaluated for comparison.
... Through interpolation of CL data and post processing, the online compensation to geometric error can be achieved. Xiong [17] proposed an error elimination approach providing an effective measure of quality control for multi-axis CNC machining and robot manipulation. ...
... Under this motivation, a machining-feature-driven locating scheme is developed with the DOFs of workpiece constrained to satisfy machining requirements. Different numbers of DOFs at different positions need to be constrained in terms of the different machining features as listed in Table 1 [14]. For the purpose of simplifying the description, we refer to these necessarily constrained DOFs corresponding to machining feature as feature degrees of freedom (FDOFs), which are used to design locating schemes. ...
In manufacturing systems, to enhance the accuracy of the machining features, fixture layout planning is the first task to provide a practical and economic scheme of workpiece holding, which maintains a desired position and orientation of the workpiece with respect to the cutting tool. In this paper, a machining-feature requirement-driven workpiece-holding scheme is proposed to constrain the degrees of freedom (DOFs) of the workpiece according to the various machining features. In the proposed scheme, firstly the machining feature on the workpiece is used to determine the DOFs that have to be constrained in machining. Next the practically constrained DOFs are determined in a real locating scheme by using the location model. Finally, an evaluation criterion is given to suggest the extent of satisfaction of the locating scheme. Two examples are presented to verify the new locating procedures.
... In this section, a generic model is derived to describe their relationship. As shown in Fig. 1, a location deviation model proposed in [22,23] is used as follows: ...
Dimensional deviation analysis has been an active and important research topic in mechanical design, manufacturing processes, and manufacturing systems. This paper proposes a comprehensive dimensional deviation evaluation framework for discrete-part manufacturing processes (DMP). A generic, explicit, and transmission model is developed to describe the dimensional deviation accumulation of machining processes by means of kinematic analysis of relationships between fixture error, datum error, machine tool geometric error, fixturing force inducing error and the dimensional quality of the product. The developed modeling technology can deal with general fixture configurations. In addition, the local contact deformations of the workpiece–fixture system are determined by solving a nonlinear programming problem of minimizing the total complementary energy of the frictional workpiece–fixture subsystem in machining system. Moreover, the deviation of an arbitrary point on machining feature can be also evaluated based on a point deviation model with prediction dimension deviation from the transmission model. The dimensional error transmission within the machining process is quantitatively described in this model. A systematic procedure to construct the model is presented and validated. This model can be also applied to process design evaluation for complicated machining processes.
... It is necessary to develop a systemic modeling method to evaluate the machining error. The work described in this paper is development of the resultant deviation model of the tool with respect to the workpiece on the basis of the general fixture error model [24,26]. The resultant deviation is mapped into the locator errors on the fixture. ...
Errors of machine tool, fixture, and datum on workpiece to be machined influence the machining accuracy of the workpiece. The objective of this paper is to provide a framework for abstracting an error model that integrates three types of errors, i.e., machine tool, fixture, and datum errors, into a unified one. Differential motion theory is used to build the evaluation model of three types of errors. The resultant deviation model of the tool with respect to the workpiece is derived by using the model. For the purpose of eliminating the deviation, the resultant geometric variation is mapped into the locator errors on the fixture. Then the position and orientation errors of the tool with respect to the workpiece may be reduced by adjusting the length of locators. Finally, the effectiveness of the resultant deviation model is verified by examples.
... Equation (7) describes the relationship between the position and orientation errors of the workpiece, the position and orientation errors of the th locator, and the local elastic deformation for the general fixturing system. The detailed discussions about all kinds of errors in the workpiece-fixture system can be found in [34], [35]. In summary, we have the following. ...
... Since the local elastic deformations between the workpiece and locators always exist, the goals of fixture design and verification are to guarantee that the position and orientation errors of the workpiece are within the tolerance specification. The influence of all kinds of errors on the localization errors of the workpiece can be found in [34] and [35]. It is usually assumed that the manufacturing errors of the workpiece and locators/clamps can be neglected. ...
... Using the exterior penalty function method [37], the constrained nonlinear programming problem (33) can be transformed into an unconstrained nonlinear programming problem, as shown in (34) at the bottom of the page, where is a positive penalty parameter. The role of the penalty parameter is obvious: As increases, so does the penalty associated with a given choice of that violates one or more of the constraints ( ) and ( ...
This paper presents a new tool orientation optimization approach for multi-axis machining considering up to second order kinematical performance of the multi-axis machine. Different from the traditional optimization approach, tool orientations are optimized with the goal of improving the kinematical performance of the machining process, not only increasing the material removal from purely geometrical aspect. The procedure is to first determine a few key orientations on the part surface along the tool path according to the curvature variation. Key orientations are initially optimized to be able to achieve high material removal by comparing the tool swept curve and the actual part surface. Intermediate orientations between key orientations are interpolated smoothly using rigid body interpolation techniques on SO(3). The time-optimal trajectory planning problem with velocity and acceleration constraints of the multi-axis machine is then solved to adjust the initially determined tool orientations to better exploit the multi-axis machine's motion capacity. Simulation and experiment validate the feasibility and effectiveness of the proposed approach. [DOI: 10.1115/1.4002456]
High speed power chucks are important function units in high speed turning. The gripping force loss is the primary factor
limiting the rotational speed of high-speed power chucks. This paper proposes a piecewise model considering the difference
of wedge transmission’s radial deformation between low-speed stage and medium-to-high-speed stage, the friction forces of
chuck transmission, and the compressibility of hydraulic oil in rotary hydraulic cylinders. A corrected model of gripping
force loss is also established for power chucks with asymmetric stiffness. The model is verified by experiment results. It
is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping
force increases with the rotational speed increasing at medium and high speed stages. Besides, the loss coefficients of gripping
force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed. For wedge
power chucks with small wedge angel (α0>0.06), the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed
stage. For wedge power chucks with larger wedge angel (α>20°) or low friction coefficient (µ0
