阅读说明：本技术 一种六自由度串并混联数控机床及其后处理方法 (Six-degree-of-freedom serial-parallel hybrid numerical control machine tool and post-processing method thereof ) 是由 宋得宁 陈卓 周超 钟宇光 马建伟 姚建均 于 2021-07-23 设计创作，主要内容包括：本发明提供一种六自由度串并混联数控机床及其后处理方法,本发明属于机器人与高档数控机床领域,涉及一种六自由度串并混联机床的结构,以及针对该结构机床的后处理方法。首先,搭建由具有三个移动自由度的串联机架和具有三个旋转自由度的并联摆头组成的六自由度串并混联数控机床；其次,给出利用刀具位置、姿态计算所搭建六自由度串并混联数控机床各进给轴位置坐标的后处理方法。该机床不仅结合了串联机床工作空间大和并联机床动态性能好的优点,而且由于对刀具位置和姿态的控制分别由串联部分和并联部分完成,可实现刀具位置控制和姿态的解耦控制,后处理计算方法过程简单,计算效率高,适用于高速、高精度加工,具有广阔的应用前景。(The invention provides a six-degree-of-freedom serial-parallel connection numerical control machine tool and a post-processing method thereof, belongs to the field of robots and high-grade numerical control machine tools, and relates to a structure of the six-degree-of-freedom serial-parallel connection numerical control machine tool and a post-processing method for the structural machine tool. Firstly, constructing a six-freedom-degree series-parallel numerical control machine tool consisting of a series rack with three moving degrees of freedom and a parallel oscillating head with three rotating degrees of freedom; and secondly, providing a post-processing method for calculating the position coordinates of each feeding shaft of the established six-freedom-degree series-parallel connection numerical control machine tool by utilizing the position and the posture of the cutter. The machine tool not only combines the advantages of large working space of a series machine tool and good dynamic performance of a parallel machine tool, but also can realize the decoupling control of the position control and the posture of the cutter because the control of the position and the posture of the cutter is respectively completed by the series part and the parallel part, has simple post-processing calculation method process and high calculation efficiency, is suitable for high-speed and high-precision machining, and has wide application prospect.)

1. A six-freedom-degree series-parallel hybrid numerical control machine tool is characterized in that: the device comprises a parallel mechanism and a serial mechanism, wherein the serial mechanism comprises a base, a lathe bed, an X-axis motor, an X-axis lead screw, an X-axis sliding table, an X-axis guide rail, a stand column, a Z-axis motor, a Z-axis lead screw, a Z-axis nut, a cross beam, a Y-axis motor, a Y-axis lead screw, a Y-axis sliding table, a Y-axis guide rail and a parallel mechanism connecting frame; the X-axis is positioned on the base, the X-axis motor drives the X-axis screw rod to rotate, and the X-axis sliding table moves along the X-axis guide rail through the screw rod nut mechanism; the Z axis is positioned on the upright columns on two sides of the machine tool, the Z axis motor drives the Z axis screw rod to rotate, the rotation of the screw rod is converted into the linear motion of the nut through the screw rod nut mechanism, and the nut drives the cross beam to realize the movement of the whole cross beam along the Z axis; the Y axis is positioned on the cross beam, a Y axis motor drives a Y axis screw rod to rotate, a Y axis sliding table moves along a Y axis guide rail through a screw rod nut mechanism, a parallel mechanism is rigidly connected with the Y axis sliding table through a parallel mechanism connecting frame, and the Y axis sliding table drives the parallel mechanism to move while moving; the parallel mechanism comprises an upper platform, a restraint rod, a lower platform, an electric cylinder, a spherical hinge and a Hooke hinge; the upper platform is rigidly connected with the constraint rod, and the constraint rod is connected with the lower platform through the ball hinge to limit the moving freedom degree of the lower platform, so that the lower platform can only rotate around the ball hinge and has three rotational freedom degrees; the electric cylinders are connected with the upper platform through spherical hinges and connected with the lower platform through Hooke hinges, and the inclination angle of the lower platform can be changed by changing the lengths of the three electric cylinders.

2. A post-processing method of a serial-parallel numerically-controlled machine tool with six degrees of freedom comprising the serial-parallel numerically-controlled machine tool with six degrees of freedom according to claim 1, characterized in that: the method comprises the following steps:

the method comprises the following steps: performing inverse kinematics derivation for the parallel mechanism;

establishing coordinate systems of an upper platform and a lower platform as O respectively₁、O₂The original points of the two coordinate systems are respectively the geometric centers of the two platforms, and the position of the ball hinge of the upper platform is A_i(ii) a The hooke joint position of the lower platform is B_i(ii) a The radiuses of the circumscribed circles of the equilateral triangle formed by connecting the hinge points of the upper platform and the lower platform are a and b respectively; the distance between the center points of the two corresponding hinges is the length of the rod, which is denoted as L_i(ii) a AboutThe length of the beam is l₀；i＝1，2，3；

Pose, i.e. coordinate system O, of the lower platform relative to the upper platform₂Relative to a coordinate system O₁Can be determined by attitude angles theta, gamma, psi and is expressed by Euler angles of Z-Y-X type:

wherein s is sin and c is cos; each row element in the matrix represents a coordinate system O₂X of (2)₂、Y₂、Z₂Axis in coordinate system O₁Direction cosine of the corresponding coordinate axis;

the origin of the lower platform coordinate system is O₂Coordinate system O of upper platform₁The coordinates in (1) are:

O₂＝(0，0，-l₀)

in the formula I₀Is the length of the restraint rod;

in a coordinate system O₁Middle, ball hinge joint A_iIs expressed as:

in a coordinate system O₂Middle and hooke hinge point B_iIs expressed as:

after the lower platform rotates around three euler angles, the coordinates of three hooke joints are expressed as follows:

B_i1＝R·B_i+O₂

length L of electric cylinder between each group of corresponding hinges_i(i ═ 1,2,3) is:

step two: deducing a post-processing matrix of the machine tool;

establishing a machine tool coordinate system O, and arranging the machine tool coordinate system at the center of an upper platform when the cross beam moves to the top end limit and the Y-axis sliding table moves to the center of the cross beam; machine tool coordinate system O and upper platform coordinate system O₁Overlapping; the machine tool coordinate system is fixed, and the upper platform coordinate system and the lower platform coordinate system move along with the movement of the parallel mechanism;

the length of the cutter is given as l, the coordinate D of a cutter point in a workpiece system is defined as (x, y, z), and the coordinate of the center point of the lower platform is O₂＝(x_d，y_d，z_d)；

And obtaining a vector from the tool point to the central point of the movable platform as follows:

will be provided withObtaining the vector after unitization Namely a tool shaft vector in a workpiece coordinate system; i, j and k are components of the cutter axis vector on the X, Y, Z coordinate axis; note q₁、q₂、q₃X, Y, Z axis coordinates q under the machine coordinate system₄、q₅、q₆Respectively is the length coordinate L of the electric cylinder under the machine tool coordinate system₁、L₂、L₃；

Step three: determining X, Y, Z axis coordinates under a machine tool coordinate system for position control;

according to the structure of the machine tool and the calculation method of the vector, the following steps are obtained:

the X, Y, Z axis coordinate q under the machine tool coordinate system used for position control is obtained by the above formula₁、q₂、q₃Comprises the following steps:

step four: determining the length coordinate of an electric cylinder under a machine tool coordinate system for attitude control;

machine tool coordinate system A for attitude control₁And B₁、A₂And B₂、A₃And B₃Length coordinate q of electric cylinder between₄、q₅、q₆The calculation matrix of (2) is as follows:

the relationship of gamma, psi, j, k is obtained according to the rotating posture of the lower platform as follows:

step five: obtaining a coordinate system A of the machine tool for attitude control₁And B₁、A₂And B₂、A₃And B₃Length coordinate q of electric cylinder between₄、q₅、q₆(ii) a Q is to be₁、q₂、q₃、q₄、q₅、q₆Respectively input to X-axis, Y-axis, Z-axis and A₁And B₁Intermittent electric cylinder, A₂And B₂Intermittent electric cylinder, A₃And B₃In the position controller of inter-electric cylinder, the position sum of six-freedom series-parallel connection numerical control machine tool is completedAnd (5) attitude control.

Technical Field

The invention belongs to the field of robots and high-grade numerical control machines, and relates to a structure of a series-parallel machine tool with six degrees of freedom and a machine tool post-processing method aiming at the structure.

Background

The machine tool is used as an industrial master machine, and the performance level of the machine tool is an important mark for the development of high-end manufacturing industry of China. Therefore, the research on the structural design problem of the numerical control machine tool aiming at improving the machine tool performance has important significance for improving the development level of the hard strength of the heavy machinery in China. The numerical control machine tool can be divided into two types of series machine tools and parallel machine tools according to the structural configuration, the working space of the series machine tool is large, large parts can be machined, the aspects of kinematics and dynamics calculation control are simpler, but the whole rigidity and dynamic performance are poor, the structure is complex, a large number of parts are required for transmission and speed change, and the inertia of each part of the machine tool is larger; the parallel machine tool has a simple structure, adopts a multi-rod parallel mechanical driving device for driving and processing, greatly improves the stability and rigidity of the machine tool, is easy to realize high-speed processing and high-precision processing, has simple inverse kinematics calculation, but is limited by a smaller structural working range. Therefore, it is a trend of machine tool development to combine a series machine tool and a parallel machine tool and design a parallel machine tool that can combine the advantages of the series machine tool and the parallel machine tool.

In the prior art document 1, "structural design, layout design and machining tests of a novel 5-axis hybrid servo-parallel machine tool", Tang et al, Robotics and Computer-Integrated Manufacturing,2020,64, the document constructs a new 5-axis HSPKMT, and the proposed HSPKMT can realize five-axis motion capabilities of three translations and two rotations, and a layered design method is proposed to simplify the design problem of 5-axis high-speed parallel machine tools. Document 2 "Study on the dynamic coupling characteristics of 3PTT-2R numerical control-parallel machine based on single requirements and position coupling factors", Cai et al, Proceedings of the organization of Mechanical Engineers,2017,231(9), which studies the dynamic coupling problem of a self-designed "3 parallel-2 series" hybrid numerical control machine based on singular constraints and position coupling factors in order to ensure that the machine has better dynamic characteristics and higher part quality in the process of machining complex surfaces. However, most of the existing technologies aim to improve the dynamic performance of the machine tool, and the problems of inverse kinematics transformation and post-processing methods of the hybrid machine tool are not considered in the design process. For the hybrid machine tools with different structures, the inverse kinematics transformation complexity is completely different, and the complexity of the inverse kinematics transformation directly determines the difficulty of post-processing and real-time control. Therefore, the inverse kinematics transformation of the hybrid machine tool is considered in the design process of the hybrid machine tool, the hybrid machine tool structure easy to control is provided, and the method has important significance for improving the real-time control effect of the hybrid numerical control machine tool.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, designs a novel position-posture decoupling serial-parallel series-parallel numerical control machine tool structure by taking the aim of reducing the inverse kinematics transformation complexity to the maximum extent on the basis of considering the increase of the working space and simultaneously ensuring the dynamic performance of the machine tool as much as possible, and provides a post-processing method.

The purpose of the invention is realized as follows: the six-freedom-degree series-parallel numerical control machine tool structure is a series-parallel structure and is divided into a parallel part and a series part, and the series mechanism mainly comprises: the device comprises a base, a lathe bed, an X-axis motor, an X-axis lead screw, an X-axis sliding table, an X-axis guide rail, a stand column, a Z-axis motor, a Z-axis lead screw, a Z-axis nut, a cross beam, a Y-axis motor, a Y-axis lead screw, a Y-axis sliding table, a Y-axis guide rail and a parallel mechanism connecting frame. The serial part has three degrees of freedom of movement. The X-axis is positioned on the base, the X-axis motor drives the X-axis screw rod to rotate, and the X-axis sliding table moves along the X-axis guide rail through the screw rod nut mechanism. The Z axis is positioned on the stand columns on the two sides of the machine tool, the Z axis motor drives the Z axis screw rod to rotate, the rotation of the screw rod is converted into the linear motion of the nut through the screw rod nut mechanism, and the nut drives the cross beam to realize the movement of the whole cross beam along the Z axis. The Y axis is positioned on the cross beam, a Y axis motor drives a Y axis screw rod to rotate, a Y axis sliding table moves along a Y axis guide rail through a screw rod nut mechanism, a parallel mechanism is rigidly connected with the Y axis sliding table through a parallel mechanism connecting frame, and the Y axis sliding table drives the parallel mechanism to move while moving; the parallel mechanism mainly comprises: the device comprises an upper platform, a restraint rod, a lower platform, an electric cylinder, a spherical hinge and a Hooke hinge. The upper platform is rigidly connected with the constraint rod, the constraint rod is connected with the lower platform through the ball hinge, and the moving freedom degree of the lower platform is limited, so that the lower platform can only rotate around the ball hinge and has three rotating freedom degrees. The electric cylinders are connected with the upper platform through spherical hinges and connected with the lower platform through Hooke hinges, and the inclination angle of the lower platform can be changed by changing the lengths of the three electric cylinders.

Based on the machine tool structure, the post-processing method of the six-degree-of-freedom series-parallel connection numerical control machine tool mainly comprises the following steps of:

after the design of the specific structure of the machine tool is finished, the post-processing method of the machine tool is provided according to the structural characteristics of the machine tool, and the specific steps are as follows:

the method comprises the following steps: an inverse kinematics derivation of the parallel mechanism was performed. Establishing coordinate systems of an upper platform and a lower platform as O respectively₁,O₂(right hand coordinate system). The original points of the two coordinate systems are respectively the geometric centers of the two platforms. The position of the ball hinge of the upper platform is A_i(i ═ 1,2, 3); the hooke joint position of the lower platform is B_i(i ═ 1,2, 3); the radiuses of the circumscribed circles of the equilateral triangle formed by connecting the hinge points of the upper platform and the lower platform are a and b respectively; the distance between the center points of the two corresponding hinges is the length of the rod, which is denoted as L_i(i ═ 1,2, 3); the length of the restraint rod is l₀；

Coordinate system O of upper platform₁In which the X-axis passes through the hinge point A₁Hinge point A₂，A₃Symmetrical about the X axis. In the lower platform coordinate system O₂In which the X-axis passes through the hinge point B₁Hinge point B₂，B₃Symmetrical about the X axis. The Z axes of the two coordinate systems are vertical upwards, and the Y axis direction can be determined by a right-hand rule.

Pose, i.e. coordinate system O, of the lower platform relative to the upper platform₂Relative to a coordinate system O₁Can be determined by attitude angles theta, gamma and psi and is expressed by Euler angles of Z-Y-X type:

wherein s is sin and c is cos; each row element in the matrix represents a coordinate system O₂X of (2)₂、Y₂、Z₂Axis in coordinate system O₁Direction cosine of the corresponding coordinate axis.

The origin of the lower platform coordinate system is O₂Coordinate system O of upper platform₁The coordinates in (1) are:

O₂＝(0，0,-l₀) (2)

in the formula I₀To constrain the length of the rod.

In a coordinate system O₁Middle, ball hinge joint A_iThe coordinates of (i ═ 1,2,3) can be expressed as:

in a coordinate system O₂Middle and hooke hinge point B_iThe coordinates of (i ═ 1,2,3) can be expressed as:

after the lower platform rotates around three euler angles, the coordinates of three hooke joints can be expressed as follows:

B_i1＝R·B_i+O₂ (5)

obtaining the length L of the electric cylinder between the hinges corresponding to each group_i(i ═ 1,2,3) is:

step two: a post-processing matrix of the machine tool is derived. Building machineAnd a machine tool coordinate system O, which is arranged at the center of the upper platform when the cross beam moves to the top end limit and the Y-axis sliding table moves to the center of the cross beam. At the moment, the machine tool coordinate system O and the upper platform coordinate system O₁And (4) overlapping. The machine tool coordinate system is fixed, and the upper platform coordinate system and the lower platform coordinate system move along with the movement of the parallel mechanism.

Assuming that the length of the tool is l, the coordinate D of the tool point in the workpiece system is defined as (x, y, z), and the coordinate of the center point of the lower platform is defined as O₂＝(x_d，y_d，z_d)。

The vector from the tool point to the center point of the movable platform can be determined according to the coordinates of the two points:

will be provided withObtaining the vector after unitizationNamely the tool axis vector in the workpiece coordinate system.

i, j, k are the components of the cutter axis vector on the X, Y, Z coordinate axis. The purpose of the post-processing is to determine the tool point coordinates x, y, z and the tool axis vector in the workpiece coordinate systemAnd controlling the coordinates (length) of each physical axis in the machine tool coordinate system. Note q₁、q₂、q₃X, Y, Z axis coordinates q under the machine coordinate system₄、q₅、q₆Respectively is the length coordinate L of the electric cylinder under the machine tool coordinate system₁、L₂、L₃。

Step three: x, Y, Z axis coordinates under a machine coordinate system for position control are determined.

According to the calculation method of the machine tool structure and the vector designed in the first step, the following steps can be obtained:

from equation (8), X, Y, Z axis coordinates q in the machine coordinate system for position control can be obtained₁、q₂、q₃Comprises the following steps:

step four: determining the length coordinate of an electric cylinder under a machine tool coordinate system for attitude control;

depending on the configuration of the machine tool designed in the first step, it can be obtained that the tool attitude is independent of the position of the parallel mechanism, i.e. q_iThe calculation results of (i ═ 4, 5, 6) do not contain x, y, z, and relate only to three variables i, j, k.

According to the derivation of equations (1) to (6) about the kinematics of the parallel mechanism, A in the machine coordinate system for attitude control can be obtained₁And B₁、A₂And B₂、A₃And B₃Length coordinate q of electric cylinder between₄、q₅、q₆The calculation matrix of (2) is as follows:

from the rotated attitude of the lower platform, the relationship of γ, ψ, j, k can be calculated as follows:

step five: substituting formula (11) into formula (1), and substituting the calculated result into formula (10) to obtain A in the machine tool coordinate system for attitude control₁And B₁、A₂And B₂、A₃And B₃Length coordinate q of electric cylinder between₄、q₅、q₆；

Q is to be₁、q₂、q₃、q₄、q₅、q₆Respectively input to X-axis, Y-axis, Z-axis and A₁And B₁Intermittent electric cylinder, A₂And B₂Intermittent electric cylinder, A₃And B₃In the position controller of the inter-electric cylinder, the position and the attitude control of the six-freedom-degree series-parallel numerical control machine tool can be completed.

Compared with the prior art, the invention has the beneficial effects that: firstly, the series-parallel hybrid machine tool structure not only combines the advantages of large working space of the series machine tool, high rigidity and good dynamic performance of the parallel machine tool, but also foresight considers the difficulty degree of an inverse kinematics transformation algorithm for post-processing in the design process of the structure, and provides a precondition guarantee for the real-time control of the machine tool; secondly, because the designed machine tool structure realizes three linear motion freedom degrees through the serial part and three rotation freedom degrees through the parallel part, in the post-processing inverse kinematics transformation method, the mutual influence of the point linear motion of the tool tip and the rotation motion of the tool shaft is small, the translation motion of one point on the tool shaft is completely finished by the serial mechanism, and the rotation motion of the tool shaft is completely finished by the parallel mechanism, so that the decoupling control of the position control and the posture of the tool can be realized, and the post-processing calculation method has the advantages of simple process, high calculation efficiency and strong stability.

Drawings

FIG. 1 is a schematic structural view of a six-degree-of-freedom series-parallel hybrid numerically-controlled machine tool; in the figure: the automatic cutting machine comprises a base, a bed body, a 3X-axis motor, a 4X-axis lead screw, a 5X-axis guide rail, a 6X-axis sliding table, a 7 upright post, an 8Z-axis motor, a 9Z-axis lead screw, a 10Z-axis nut, a 11Z-axis guide rail, a 12 cross beam, a 13Y-axis motor, a 14Y-axis lead screw, a 15Y-axis sliding table, a 16Y-axis guide rail, a 17 parallel mechanism connecting frame, an 18 parallel mechanism and a 19 cutter.

FIG. 2 is a schematic view of a parallel mechanism; in the figure: 1801 upper platform, 1802 ball hinge, 1803 restraint rod, 1804 electric cylinder, 1805 hook hinge, 1806 lower platform.

Fig. 3 is a schematic diagram of a tool path for actually machining a propeller blade.

Fig. 4 is a control diagram of tool position during machining. Wherein the A axis represents movement time in units ofms, axis B represents position coordinates in mm; q. q.s₁、q₂、q₃The three curves respectively represent the curves of the position coordinates of the X axis, the Y axis and the Z axis in the series structure along with the time change in the processing process.

FIG. 5 is a control diagram of tool pose during machining. Wherein the axis A represents the movement time in ms, and the axis B represents the length of the restraint rod in mm; l is₁、L₂、L₃The three curves represent the length-time variation curves of the three electric cylinders of the parallel mechanism respectively.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic diagram of a six-degree-of-freedom series-parallel numerically-controlled machine tool. The device mainly comprises a base 1, a lathe bed 2, an X-axis motor 3, an X-axis screw 4, an X-axis guide rail 5, an X-axis sliding table 6, an upright post 7, a Z-axis motor 8, a Z-axis screw 9, a Z-axis nut 10, a Z-axis guide rail 11, a cross beam 12, a Y-axis motor 13, a Y-axis screw 14, a Y-axis sliding table 15, a Y-axis guide rail 16, a parallel mechanism connecting frame 17, a parallel mechanism 18 and a cutter 19.

Fig. 2 is a schematic diagram of a parallel mechanism. The parallel mechanism mainly comprises an upper platform 1801, a spherical hinge 1802, a restraint rod 1803, an electric cylinder 1804, a Hooke's hinge 1805 and a lower platform 1806.

The operation mode and post-processing of the machine tool comprise the following specific steps:

first-step six-degree-of-freedom serial-parallel connection numerical control machine tool structure building

Referring to fig. 1, the six-degree-of-freedom serial-parallel numerically controlled machine tool mainly includes: the device comprises a base 1, a lathe bed 2, an X-axis motor 3, an X-axis lead screw 4, an X-axis guide rail 5, an X-axis sliding table 6, an upright post 7, a Z-axis motor 8, a Z-axis lead screw 9, a Z-axis nut 10, a Z-axis guide rail 11, a cross beam 12, a Y-axis motor 13, a Y-axis lead screw 14, a Y-axis sliding table 15, a Y-axis guide rail 16, a parallel mechanism connecting frame 17, a parallel mechanism 18 and a cutter 19; the parallel mechanism 17 is rigidly connected with the Y-axis sliding table 14, the Z-axis nut 10 and the cross beam 12 by using a parallel mechanism connecting frame 16; the base 1 and the bed body 2, the X-axis guide rail 5 and the bed body 2, the Y-axis guide rail 16 and the cross beam 12, and the Z-axis guide rail 11 and the upright post 7 are all connected in a welding way; when the X-axis motor 3 rotates, the X-axis screw rod 4 is driven to rotate, and the linear motion of the X-axis sliding table 6 along the X-axis guide rail 5 is realized through the screw rod nut mechanism, so that the degree of freedom of the movement of the cutter along the X axis is realized; the Y-axis motor 13 drives the Y-axis screw 14 to rotate when rotating, the Y-axis sliding table 15 is driven to linearly move along the Y-axis guide rail 16 through the screw nut mechanism, and the parallel mechanism connecting frame 17, the parallel mechanism 18 and the cutter 19 also linearly move along with the Y-axis sliding table 15 because the parallel mechanism connecting frame 17 and the parallel mechanism 18 are rigidly connected with the Y-axis sliding table 15, so that the moving freedom of the cutter along the Y axis is realized; when the Z-axis motor 8 rotates, the Z-axis screw 9 is driven to rotate, the Z-axis nut 10 is driven to linearly move through the ball screw mechanism, the Z-axis nut 10 drives the cross beam 12 to linearly move along the Z-axis guide rail 11, and the Y-axis sliding table 15, the parallel mechanism connecting frame 17, the parallel mechanism 18 and the cutter 19 can be driven to linearly move along the Z-axis guide rail 11, so that the moving freedom of the cutter along the Z axis is realized.

Referring to fig. 2, the parallel mechanism mainly includes: an upper platform 1801, a spherical hinge 1802, a restraint rod 1803, an electric cylinder 1804, a hook hinge 1805 and a lower platform 1806; in fig. 1, the cutter 19 is placed at the center of the lower stage 1806 in fig. 2, and the axis of the cutter 19 coincides with the axis of the lower stage 1806.

Second step, post-processing method of six-freedom-degree series-parallel numerical control machine tool

Recording the coordinates of a tool point in a workpiece coordinate system as x, y and z, and the coordinate of the center point of a lower platform as x_d,y_d,z_dThe length of the cutter is l, and the cutter axis vector can be calculated to beUnitizing it into

Referring to fig. 3, a tool path is planned for machining a propeller blade. Tool nose point coordinate data generated from tool path andthe coordinate data are shown in table 1:

TABLE 1 propeller data post-simulation

The data for the simulated propeller post-processing is 819. for space savings, only the top 10 are shown.

According to the calculation method of the machine tool structure and the vector designed in the first step, the following steps can be obtained:

from equation (1), X, Y, Z axis coordinates q in the machine coordinate system for position control can be obtained₁、q₂、q₃：

Further, determining the length coordinate of the electric cylinder 4 under the machine tool coordinate system for controlling the tool posture; according to the structure of the machine tool designed in the first step, the tool posture which is irrelevant to the position of the parallel mechanism can be obtained, namely the length coordinates q of the three electric cylinders₄、q₅、q₆The calculation result of (2) does not contain x, y and z, and only relates to three variables of i, j and k.

Recording the position of the platform ball hinge 2 as A_i(i is 1,2,3), the lower platform Hooke joint 5 is B_i(i ═ 1,2, 3); the radius of the external circle of the equilateral triangle formed by the connecting lines of the hinge points of the upper platform and the lower platform is a and b respectively, the distance between the central points of the two corresponding hinges is the length of the rod, and the distance is marked as L_i(i ═ 1,2, 3); the length of the restraining bar 3 is l₀；

Coordinate system O of upper platform₁In which the X-axis passes through the hinge point A₁Hinge point A₂，A₃Symmetrical about the X axis. In the lower platform coordinate system O₂In which the X-axis passes through the hinge point B₁Hinge point B₂，B₃Symmetrical about the X axis. The Z axes of the two coordinate systems are vertically upwardThe Y-axis direction can be determined by a right-hand rule;

pose, i.e. coordinate system O, of the lower platform 6 relative to the upper platform 1₂Relative to a coordinate system O₁Can be determined by attitude angles theta, gamma and psi and is expressed by Euler angles of Z-Y-X type:

wherein s is sin and c is cos; each row element in the matrix represents a coordinate system O₂X of (2)₂、Y₂、Z₂Axis in coordinate system O₁Direction cosine of the corresponding coordinate axis.

The origin of the lower platform coordinate system is O₂Coordinate system O of upper platform₁The coordinates in (1) are:

O₂＝(0，0，-l₀) (4)

in the formula I₀For the length of the upper restraining bar 3, /)₀＝645mm。

In a coordinate system O₁Middle, ball hinge 2 hinge point A_iThe coordinates of (i ═ 1,2,3) can be expressed as:

in this example, the distance between the hinge points of the ball hinge 2

In a coordinate system O₂Middle and hooke joint 5 hinge point B_iThe coordinates of (i ═ 1,2,3) can be expressed as:

in this example, the distance between the 5-joint points of the Hooke's joint

After the lower platform rotates around three euler angles, the coordinates of the three hooke joints 5 can be expressed as follows:

B_i1＝R·B_i+O₂ (7)

the length L of the electric cylinder can be obtained_i(i ═ 1,2,3) is:

L_i＝|A_i-B_i| (8)

electric cylinder length coordinate q under machine tool coordinate system for attitude control₄、q₅、q₆The calculation matrix of (2) is as follows:

from the rotated attitude of the lower platform, the relationship between γ, ψ and i, j, k can be calculated as follows:

substituting the formula (10) into the formula (3) to calculate the result, and substituting the result into the formula (9) to obtain the A in the machine tool coordinate system for attitude control₁And B₁、A₂And B₂、A₃And B₃Length coordinate q of electric cylinder between₄、q₅、q₆；q₁、q₂、q₃、q₄、q₅、q₆The specific values of (b) are shown in table 2:

TABLE 2 q₁、q₂、q₃、q₄、q₅、q₆Specific numerical values of

Q is to be₁、q₂、q₃、q₄、q₅、q₆Respectively input to X-axis, Y-axis, Z-axis and A₁And B₁Intermittent electric cylinder, A₂And B₂Intermittent electric cylinder, A₃And B₃In the position controller of the inter-electric cylinder, the position and the attitude control of the six-freedom-degree series-parallel numerical control machine tool can be completed.

Referring to FIGS. 4 and 5, q in FIG. 4₁、q₂、q₃The three curves respectively represent the curves of the position coordinates of an X axis, a Y axis and a Z axis in the series structure along with the change of time in the processing process; l in FIG. 5₁、L₂、L₃The three curves respectively represent the length change curves of the three electric cylinders of the parallel mechanism along with time, and the tool pose can be controlled by driving the machine tool coordinate change; namely, the position and the posture of the end tool are controlled according to the figures 4 and 5, the tool can be processed according to the tool track in the figure 3, and the correctness of the post-processing method of the serial-parallel numerical control machine tool is proved.

In summary, the invention provides a six-degree-of-freedom serial-parallel connection numerical control machine tool and a post-processing method thereof, belongs to the field of robots and high-grade numerical control machine tools, and relates to a structure of the six-degree-of-freedom serial-parallel connection numerical control machine tool and a post-processing method for the structural machine tool. Firstly, constructing a six-freedom-degree series-parallel numerical control machine tool consisting of a series rack with three moving degrees of freedom and a parallel oscillating head with three rotating degrees of freedom; and secondly, providing a post-processing method for calculating the position coordinates of each feeding shaft of the established six-freedom-degree series-parallel connection numerical control machine tool by utilizing the position and the posture of the cutter. The machine tool not only combines the advantages of large working space of a series machine tool and good dynamic performance of a parallel machine tool, but also can realize the decoupling control of the position control and the posture of the cutter because the control of the position and the posture of the cutter is respectively completed by the series part and the parallel part, has simple post-processing calculation method process and high calculation efficiency, is suitable for high-speed and high-precision machining, and has wide application prospect.