Design, dynamic analysis and experimental evaluation of a hybrid parallel-serial polishing machine with decoupled motions

In this paper, a novel six degrees-of-freedom (DOF) hybrid kinematic machine (HKM) is designed, analyzed and evaluated for precision polishing. The design adopts a three DOF tripod-based parallel manipulator (PM) to locate the workpiece, a two DOF serial manipulator (SM) to orient the polishing tool and a functional extension limb to provide a redundant DOF for the workpiece with an axially symmetrical shape. Compared with the existing HKMs, the most distinctive feature is that the position and orientation adjustments of the tool with respect to the workpiece are decoupled during the synchronous machining, thus allowing the rotational tool center point (RTCP) function to be conveniently realized. For the developed HKM, the kinematics are studied systematically, including position, velocity, acceleration and workspace. The dynamic model of the PM is derived by employing the principle of virtual work. For a pre-defined trajectory, the required driving forces are obtained through dynamic simulation. Based on these analyses, a laboratory prototype of the HKM is designed and developed. Preliminary accuracy assessment of the HKM is implemented with a double ball-bar and a series of polishing experiments are conducted to show the capacity and feasibility of the developed HKM.

A Universal Postprocessor of General Table-Tilting Type of Five-Axis Machine Tools Without Rotational Tool Center Point Function for Actual NC Code Generation

The postprocessor is essential for machining with five-axis machine tools. This paper develops one universal postprocessor for table-tilting type of five-axis machine tools without rotational tool center point (RTCP) function. Firstly, positions of two rotary axes and the workpiece in the machine coordinate system (MCS) are introduced into the kinematic chain of the five-axis machine tools. The uniform product of exponential (POE) formula of the tool relative to the workpiece is established to obtain the universal forward kinematics. On this basis, the postprocessor of table-tilting type of five-axis machine tools is developed. The calculation of rotation angles of rotation axes is proposed in details, including the calculation of double solutions, the determination of rotation angles of C-axis and the selection principle of the shortest path of rotation angles. Movements of linear axes are calculated with rotation angles of rotary axes. The generated movements of all axes are actual positions of all axes relative to their zero positions, which can be used for machining directly. The postprocessor does not rely on RTCP function with positions of rotary axes and the workpiece in MCS. Finally, cutting test in VERICUT and real cutting experiments on SmartCNC500_DRTD five-axis machine tool are carried out to verify the effectiveness of the proposed postprocessor.

Research of RTCP Function for Five-Axis Machine Tools Based on Low-Cost Embedded CNC System

To solve the problem which current research of RTCP function is limited to high-grade CNC system. Based on limited computational resources of the embedded CNC system, analyzes and modeling calculates RTCP function of CA double swing structure, and points out the offset distance is only related to the chord length corresponding to the arc length that the rotating radius crosses, and obtains the calculation formula of compensation. Finally, gives the implementing flow chart of the RTCP algorithm for low-cost embedded CNC system.

Calibration and Optimization for Spindle-Tilting Type Five-Axis Machine Tools with Inclinable Head AB Based on Compensation of Rotation Axis Direction Error

To solve the five-axis machining accuracy problems that caused by assembly precision and direction error of rotary axes of inclinable head in high precision five axis machine tool. By selecting the five axis machine tool with inclinable head AB, GMC1230u, as the research object and analyzing the causes of the inclinable head error, the kinematics relationship of the rotation center position error and axis tilt error is established. By that, the direction vectors of each rotation axis and the position vector of rotation center are calculated based on the regression analysis of on-line measurement of the tool center point position and the calibration of five-axis RTCP function parameters is also accomplished. Finally, the compensation for inclinable head error in five-axis machine tools is fulfilled efficiently and remarkable improvement of RTCP machining accuracy is achieved.

RTCP Function in Five-Axis Machining

Because of the rotate kinematics, the machining of 5-axis brings up the non-linear error. The RTCP (Rotation Tool Center Point) function can always make the interpolated point on the programming track by a real-time linear compensation of CNC system for motion of the rotary axes. Based on detailed analysis of the kinematics principle of 5-axis machine with dual rotary tables, a new design of interpolated algorithm integrated with RTCP function is presented which is simulated in MATLAB, and the result indicates that the algorithm can reduce the non-linear error effectively.