The main skill of the multi-axis parallel dynamic screw type work lathe tanning system
The control system that is required to be selected has both powerful functions, high reliability, and good openness to facilitate the development and implementation of the above functions. After research and comparison, the architecture of the upper and lower machines is adopted, and the software block diagram is as shown. The software block diagram of the upper computer control system adopts the industrial computer based on Windows operating system to complete the non-real-time control function. The lower computer adopts the open motion controller to complete the real-time control function. The general-purpose functions and special functions can be well realized by the control software developed by the host computer and the secondary development of the motion controller.
The system software is divided into the human-machine interface part of the upper computer and the real-time control part of the lower computer. The two parts exchange information through the TCP/IP protocol of the Ethernet, and its structural block diagram is as shown. Schematic diagram of double motor elimination gap structure 23 Rotation 2 linear five-axis linkage interpolation technology It can be known from the machine tool structure that when using a standard milling head to machine non-overlapping surfaces and special milling heads to process overlapping surfaces, two different accessory milling heads are used respectively. Processing. The standard milling head is processed by X, Z, B1, C1, C2 linkage; the special milling head is processed by X, Z, A2, B2, C2 linkage.
Compared with the general 3 linear 2 rotating machine structure with two oscillating axes, the biggest difference of the machine structure is that the universal table uses the rectangular coordinates of two linear axes to realize the relative movement of the workpiece and the tool. It uses the polar coordinates of a linear axis and a rotating axis to achieve the relative movement of the workpiece and the tool. At the same time, the rotation of the table and the rotation of the tool together change the eccentric angle of the tool in the XOY plane, that is, there are two parallels. The axis of rotation. In this way, the interpolation algorithm can be decomposed into two steps: a standard five-axis linkage interpolation algorithm and a coordinate system projection.
For the sake of simplicity, for standard milling heads, the interpolation methods for special milling heads are basically similar.
The standard five-axis linkage interpolation algorithm is used to find the target space position and normal vector of the tool nose (x1, y1, z1, L1, T1). At this time, the corresponding motor rotation position is (P1, P2, P3, P4, P5) (P1, P2,,, P5 correspond to X, Z, B1, C1, C2 axis motors respectively).
Obviously there is a mapping relationship f such that (x1, y1, z1, L1, T1) f (P1, P2, P3, P4, P5).
(1) If the mapping relationship f can be obtained in real time in each interpolation cycle, the target position coordinates (P1, P2, P3, P4 of the motor for each interpolation cycle can be obtained according to the standard five-axis linkage interpolation result. P5), and then the motion increment of the motor is obtained.
According to the machine structure, {z1, L1}y{P2, P3} is directly mapped, and {x1, y1}y{P1, P5} is equivalent to the mapping of orthogonal coordinates to polar coordinates, {T1}y{P4, P5} is a linear superposition, and considering the influence of the angular change of the rotating shaft on the spatial position, x1-R1cosT1+cosP4=P1cosP5; y1-R1sinT1+sinP4=P1sinP5; P2=z1; P3=L1; P4+P5=T1 In the formula (2), R1 is the projection of the distance from the tool tip to the center of rotation in the XOY plane when the rotary axis moves to the target angle in the standard coordinate system, and can be obtained from the swing radius and angle of the swing axis.
From equation (2), we can find (P1, P2, P3, P4, P5). In order to realize the nonlinear relationship of equation (2), we must be able to read the interpolation result of the standard coordinate system in real time, open motion controller. This possibility is provided. Two coordinate systems are defined in the motion controller: one is the coordinate system of the virtual axis, which can complete the 3-line 2 rotary motion interpolation operation of the standard configuration, but it does not contain the actual motor; the coordinate system of another real axis corresponds to The actual machine tool drives the motor and runs in the background. The interpolation result of the virtual coordinate system is read in each interpolation cycle, and the motion amount of each motor is obtained after the operation of equation (2), and then the actual feed is completed by using the spline instruction. In this way, the standard five-axis linkage interpolation algorithm provided by the motion controller can be used to perform the secondary projection of the interpolation result, and the five-axis linkage interpolation and the online tool compensation function of the three rotations and two lines can be realized, and the universal CAD/CAM system compatible.
The dual-motor clearance-free technology uses a dual-motor drive as shown to achieve the goal of eliminating drive clearance by increasing the reverse pre-tension. To eliminate the transmission gap, it is necessary to ensure that the output torque directions of the two motors are opposite. The difference between the output torques of the two motors determines the rotation direction of the table.
Double motor elimination gap control block diagram system control block diagram as shown: two drivers are working in torque working mode, servo control adopts speed and position double feedback PID+ feedforward control algorithm, and its output is processed to ensure that the worktable is oriented in one direction One motor drives when rotating, and the other motor outputs the opposite direction of tension to ensure that there is no transmission gap when the motor needs to change direction. The calculation formula of the output torque of the two motors is as follows: T1=TT/2+$T/2; T2=-TT/2+$T/2, (3) where: TT is the tension torque to eliminate the gap; $T is the amount of torque control calculated by the position controller. TT should be dynamically selected according to the actual working conditions of the machine tool to minimize the heating of the motor under the premise of ensuring the elimination of the gap. In order to prevent impact, the inertial damping link is necessary.
Define a virtual axis to complete the servo control algorithm. Its position feedback comes from the circular grating of the rotating table. The speed feedback comes from the position feedback signal of the drive system. The processing result is $T, and the servo (3) is used in each servo. The cycle yields T1 and T2, and the two drive systems are controlled directly by D/A conversion.
Since the rotation speed of the table during milling is very low, it is clear that the speed feedback from the encoder of the motor can improve the low speed stability of the system. However, it is necessary to correctly switch the two motor speed feedback signals according to the rotation direction. The position feedback signal of the active motor is always used as the speed feedback source to prevent the mechanical feedback from causing the fluctuation of the speed feedback.
The precision of propeller machining directly affects the ship's operating efficiency and noise. The machining with CNC machine tools can effectively improve its accuracy. The research results of this paper have been successfully used in the control of large-scale propeller milling and milling machine tools, and complete the electromechanical joint adjustment work.
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