A multi-axis collaborative motion control system and method for a skin stretching machine

Abstract

The present invention provides a multi-axis coordinated motion control system and method for a skin stretching machine. The control system includes a controller, a servo valve, and a displacement sensor. The servo valve is installed on the pipeline connecting the stretching branch and the hydraulic station, and the displacement sensor is installed on the stretching branch. The servo valve and the displacement sensor are both electrically connected to the controller. The controller of the present invention obtains an inverse analytical solution for the stretching branch position of the skin stretching machine corresponding to the ideal motion trajectory of the clamp based on an established mathematical model for multi-axis coordinated motion control of the skin stretching machine. After obtaining the ideal displacement trajectory curve of the stretching branch, it sends a command to the servo valve, which then drives each stretching branch hydraulic cylinder to move according to the ideal displacement trajectory curve. During the motion control process, the controller subtracts the real-time data of the displacement sensor from the ideal displacement to obtain a motion control quantity, and sends this motion control quantity to the servo valve to adjust the displacement of the stretching branch, control the motion trajectory of the clamp, and realize multi-axis coordinated motion control of the skin stretching machine.

Description

Technical Field

[0001] The present invention belongs to the technical field of stretching forming, and in particular relates to a multi-axis coordinated motion control system and method for a skin stretching machine. Background Art

[0002] Skin sheet metal parts are key components that define an aircraft's exterior, characterized by a wide variety, small batch sizes, and complex shapes. Skin parts are primarily manufactured using a stretch forming (or simply, stretching) process on a skin stretching machine. Traditional skin stretching machines have a low degree of automation, often employing a point-to-point operation mode. The kinematic relationship between input and output is unclear, and the stretching of the first skin part requires repeated stretching tests before a qualified part can be formed. This process is time-consuming, and the resulting skin parts have poor repeatability. This makes it difficult to guarantee skin quality, and the qualified rate of the finished product is heavily dependent on the operator's experience.

[0003] With the continuous development of modern science and technology, large, complex, three-dimensional curved skin parts are increasingly being used in industries such as aerospace, high-speed rail, and modern architecture. This places higher demands on the quality, shape, and dimensional accuracy of these skin parts, as well as the automation level of skin stretching machines. Traditional motion control methods for skin stretching machines struggle to meet the expected quality, accuracy, and efficiency requirements for these parts. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-axis coordinated motion control system for a skin stretching machine to overcome the technical problems existing in the prior art.

[0005] Another object of the present invention is to provide a multi-axis coordinated motion control method for a skin stretching machine to meet the stretching forming working conditions requirements of skin-type sheet metal parts.

[0006] To this end, the technical solutions provided by the present invention are as follows:

[0007] A multi-axis coordinated motion control system for a skin stretching machine, comprising a stretching unit and a frame, wherein the stretching unit comprises a clamp, a constraint branch, and a plurality of stretching branches, wherein the clamp is connected to the frame via the stretching branch and the constraint branch, and wherein the control system comprises a controller, a servo valve, and a displacement sensor, wherein the servo valve is installed on a pipeline connecting the stretching branch and a hydraulic station, and the displacement sensor is installed on the stretching branch;

[0008] The servo valve and displacement sensor are both connected to the controller by electrical signals. The controller is used to subtract the real-time data of the displacement sensor from the ideal displacement to obtain the motion control quantity, and send this motion control quantity to the servo valve to adjust the stretching branch displacement, control the clamp motion trajectory, and realize multi-axis coordinated motion control of the skin stretching machine.

[0009] There are two stretching units, namely a left stretching unit and a right stretching unit, the left stretching unit and the right stretching unit have the same structure, and the left stretching unit and the right stretching unit are symmetrically connected to the frame;

[0010] The stretching branch includes a horizontal driving branch and a vertical driving branch, and there are two of each of the horizontal driving branch and the vertical driving branch. The vertical driving branch and the constraint branch are arranged longitudinally along the lower end surface of the clamp, and the constraint branch is located between the two vertical driving branches.

[0011] The stretching branch is a hydraulic cylinder, a fixed end of the hydraulic cylinder is connected to the frame, and a movable end is connected to the clamp.

[0012] The constraint branch includes a rotating pair 1, a guide cylinder, a guide shaft, and a rotating pair 2. The guide shaft is sleeved in the guide cylinder. The lower end of the guide cylinder is connected to the frame through the rotating pair 1, and the upper end of the guide shaft is connected to the clamp through the rotating pair 2.

[0013] One end of the horizontal drive branch is connected to the frame through a ball joint, and the other end is connected to the clamp through a universal joint; one end of the vertical drive branch is connected to the frame through a ball joint, and the other end is connected to the clamp through a ball joint.

[0014] A multi-axis coordinated motion control method for a skin stretching machine comprises the following steps:

[0015] Step 1) determining the ideal motion trajectory of the clamp based on the final stretched shape of the skin part and the mold tread shape, and inputting it into the controller;

[0016] Step 2) The controller obtains an inverse analytical solution for the position of the stretching branch of the skin stretching machine corresponding to the ideal motion trajectory of the clamp based on the established mathematical model of multi-axis coordinated motion control of the skin stretching machine, and obtains an ideal displacement trajectory curve of the stretching branch;

[0017] Step 3) The controller sends a command to the servo valve to drive the stretching branch to move according to the ideal displacement trajectory curve;

[0018] Step 4) The displacement sensor feeds back the actual movement displacement of the stretching branch to the controller in real time;

[0019] Step 5) The controller obtains the motion control quantity by subtracting the ideal displacement of the stretching branch from the actual motion displacement, and sends it to the servo valve to adjust the stretching branch displacement. This cycle is repeated to control the motion trajectory of the clamp and realize multi-axis coordinated motion control of the skin stretching machine.

[0020] Step 2) Based on the established mathematical model of multi-axis coordinated motion control of the skin stretching machine, the inverse analytical solution process for the stretching branch position of the skin stretching machine is obtained as follows:

[0021] Establish a fixed coordinate system Ox on the frame o yo z o , establish the motion coordinate system Px on the clamp p y p z p , the motion coordinate system Px at the initial position p y p z p With fixed coordinate system Ox o y o z o The two are parallel to each other. Point O is the hinge point between the constraint branch and the frame, point P is the hinge point between the constraint branch and the clamp, the hinge points between the vertical drive branch and the frame are A1 and A2, the hinge points between the horizontal drive branch and the frame are A3 and A4, the hinge points between the vertical drive branch and the clamp are B1 and B2, and the hinge points between the horizontal drive branch and the clamp frame are B3 and B4.

[0022] When the position of the clamp changes arbitrarily, point B i In the fixed coordinate system Ox o y o z o The middle position can be expressed as

[0023]

[0024] Where, O P=(P x ,P y ,P z ) T is the coordinate of point P in the fixed coordinate system; The moving coordinate system is relative to the fixed coordinate system Ox o y o The rotation transformation matrix of z; i = 1, 2, 3, 4;

[0025] Assume that the clamp first wraps around z p Rotate by angle β and then rotate around the updated y p The axis rotates by an angle of γ and finally rotates around x o The axis rotates by an angle α, then the rotation transformation matrix It can be expressed as

[0026]

[0027] In the formula, sα=sinα, cα=cosα, sβ=sinβ, cβ=cosβ, sγ=sinγ, cγ=cosγ;

[0028] According to the distance formula between two points in the same coordinate system, the position constraint equation of the stretching branch can be obtained as follows:

[0029]

[0030] Where, O E j Point E is in the fixed coordinate system Ox o y o z o The coordinates in ;

[0031] The inverse analytical expression of the tensile branch position can be obtained as

[0032]

[0033] Where l1, l2, l3 and l4 are the lengths of the hydraulic cylinder rods of the two vertical drive branches and the two horizontal drive branches, respectively; l is the distance the clamp moves along the vector OP; a, b, c, d, e, and f are all structural parameters and are constants; θ3 and θ4 are the distances between the vectors E3B3, E4B4 and y p The angle between the axes;

[0034] According to the spatial geometric relationship, we can get

[0035]

[0036] Thus, the inverse analytical solution of the stretching branch position of the skin stretching machine is obtained.

[0037] In the control process of step 5), the specific control formula for the stretching branch movement is:

[0038]

[0039] Where Δu(k) is the deviation between the kth control value and the k-1th control value of the stretching branch, u(k) is the kth stretching branch control value, u(k-1) is the k-1th stretching branch control value, k p is the proportionality coefficient, k T is the integral time constant, k D is the differential time constant, k is the sampling number (k=1, 2, ...), T is the sampling period, e(k), e(k-1), and e(k-2) are the motion control quantities at the kth moment, k-1th moment, and k-2th moment respectively.

[0040] The beneficial effects of the present invention are:

[0041] The multi-axis collaborative motion control system of the skin stretching machine provided by the present invention, the controller obtains the inverse analytical solution of the stretching branch position of the skin stretching machine corresponding to the ideal motion trajectory of the clamp based on the established mathematical model of the multi-axis collaborative motion control of the skin stretching machine, obtains the ideal displacement trajectory curve of the stretching branch, and then sends an instruction to the servo valve to drive each stretching branch hydraulic cylinder to move according to the ideal displacement trajectory curve. During the motion control process, the controller subtracts the real-time data of the displacement sensor from the ideal displacement to obtain the motion control amount, and sends this motion control amount to the servo valve to adjust the stretching branch displacement, control the motion trajectory of the clamp, and realize multi-axis collaborative motion control of the skin stretching machine.

[0042] The method of the present invention enables skin-type sheet metal parts to achieve continuous multi-axis coordinated motion within the entire working space of the skin stretching machine during stretching forming, can collaboratively complete complex process design requirements, effectively improves the shape and dimensional accuracy of skin parts, reduces production costs, saves production time, and improves the level of digital precision forming technology for skin parts.

[0043] The following will provide further detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a three-dimensional structural diagram of the stretching machine;

[0045] Figure 2 This is the main structural view of the stretching machine;

[0046] Figure 3 This is the left side view of the stretching machine structure;

[0047] Figure 4 It is a coordinate diagram of a stretching unit of a stretching machine;

[0048] Figure 5 It is a flow chart of the method of the present invention.

[0049] In the figure: 1. Clamp; 2. Horizontal drive branch; 3. Vertical drive branch; 4. Constraint branch; 5. Frame; 6. Rotational pair 1; 7. Guide cylinder; 8. Guide shaft; 9. Rotational pair 2; 10. Ball joint; 11. Universal joint. DETAILED DESCRIPTION

[0050] The following describes the embodiments of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0051] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided so as to provide a thorough and complete disclosure of the present invention and fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0052] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0053] Example 1:

[0054] This embodiment provides a multi-axis coordinated motion control system for a skin stretching machine. The skin stretching machine includes a stretching unit and a frame 5. The stretching unit includes a clamp 1, a constraint branch 4, and multiple stretching branches. The clamp 1 is connected to the frame 5 via the stretching branch and the constraint branch 4. The control system includes a controller, a servo valve, and a displacement sensor. The servo valve is installed on the pipeline connecting the stretching branch and the hydraulic station, and the displacement sensor is installed on the stretching branch.

[0055] The servo valve and displacement sensor are both connected to the controller electrical signal. The controller is used to subtract the real-time data of the displacement sensor from the ideal displacement to obtain the motion control quantity, and send this motion control quantity to the servo valve to adjust the stretching branch displacement, control the motion trajectory of the clamp 1, and realize multi-axis coordinated motion control of the skin stretching machine.

[0056] The present invention uses a controller to make the difference between the ideal displacement and the actual motion displacement of each stretching branch to obtain a motion control quantity, and sends this motion control quantity to the servo valve to adjust the displacement of each stretching branch. This cycle is repeated to finally control the motion trajectory of the clamp 1, thereby realizing multi-axis coordinated motion control of the skin stretching machine and meeting the stretching forming working conditions of skin-type sheet metal parts.

[0057] Example 2:

[0058] Based on Example 1, this embodiment provides a multi-axis coordinated motion control system for a skin stretching machine, such as Figure 1 As shown, there are two stretching units, namely a left stretching unit and a right stretching unit. The left stretching unit and the right stretching unit have the same structure and are symmetrically connected to the frame 5.

[0059] The stretching branch includes a horizontal driving branch 2 and a vertical driving branch 3, and there are two horizontal driving branches 2 and two vertical driving branches 3. The vertical driving branch 3 and the constraint branch 4 are arranged longitudinally along the lower end surface of the clamp 1, and the constraint branch 4 is located between the two vertical driving branches 3.

[0060] Working principle:

[0061] The sheet is placed directly above the mold. The stretching machine uses two clamps 1 in the left and right stretching units to clamp the sheet on both sides and pre-stretch it as needed. During stretching, the left and right stretching units respectively use four stretching branches (two horizontal drive branches 2 and two vertical drive branches 3) and one restraining branch 4 to enable the clamps 1 to clamp the sheet along the mold tangential direction and close to the mold. This is mainly used to form curved and shaped parts with small lateral curvature.

[0062] Example 3:

[0063] Based on Example 1, this embodiment provides a multi-axis coordinated motion control system for a skin stretching machine, wherein the stretching branch is a hydraulic cylinder, a fixed end of the hydraulic cylinder is connected to the frame 5, and a movable end is connected to the clamp 1.

[0064] The hydraulic cylinder drive can easily realize stepless speed regulation with a wide speed regulation range, which can make the movement of the clamp 1 uniform and stable, and can prevent reversing shock when the moving parts are reversed. Under the same power conditions, the device is small in size, light in weight, compact in structure, simple in operation, and easy to adjust and control.

[0065] Example 4:

[0066] Based on Example 2, this embodiment provides a multi-axis coordinated motion control system for a skin stretching machine, such as Figure 3 As shown, the constraint branch 4 includes a rotating pair 1 6, a guide cylinder 7, a guide shaft 8, and a rotating pair 2 9. The guide shaft 8 is sleeved in the guide cylinder 7. The lower end of the guide cylinder 7 is connected to the frame 5 through the rotating pair 1 6, and the upper end of the guide shaft 8 is connected to the clamp 1 through the rotating pair 2 9.

[0067] The combination of the first rotational pair 6 , the guide cylinder 7 , the guide shaft 8 and the second rotational pair 9 allows the constraint branch 4 to have four degrees of freedom, thereby constraining the freedom of movement of the clamp 1 along the horizontal and vertical directions of the frame 5 .

[0068] Example 5:

[0069] Based on Example 2, this embodiment provides a multi-axis coordinated motion control system for a skin stretching machine, such as Figure 2As shown, one end of the horizontal drive branch 2 is connected to the frame 5 through a ball joint 10, and the other end is connected to the clamp 1 through a universal joint 11; one end of the vertical drive branch 3 is connected to the frame through a ball joint 10, and the other end is connected to the clamp 1 through a ball joint 10.

[0070] Universal joint 11 comprises a first and second rotational pairs. The movable end of horizontal drive branch 2 is connected to clamp 1 via the second and first rotational pairs, respectively. The first and second rotational pairs cooperate in rotational connection, driving flexible rotation of clamp 1. The axis of the first rotational pair is parallel to the longitudinal axis of clamp 1. The axes of the horizontal drive branch 2, the first and second rotational pairs are perpendicular to each other. The centerline of ball joint 10 is parallel to the transverse axis of frame 5. This arrangement ensures that both horizontal drive branches 2 have six degrees of freedom and do not constrain the movement of clamp 1 in any direction.

[0071] In the two vertical drive branches 3, the centerline of the two ball joints 10 connected to the frame 5 is parallel to the frame's transverse axis, while the centerline of the two ball joints 10 connected to the clamp 1 is parallel to the clamp's longitudinal axis. This arrangement ensures that both vertical drive branches have six degrees of freedom and do not constrain the movement of the clamp 1 in any direction.

[0072] Example 6:

[0073] This embodiment provides a multi-axis coordinated motion control method for a skin stretching machine, such as Figure 5 As shown, the following steps are included:

[0074] Step 1) determining the ideal motion trajectory of the clamp 1 based on the final stretched shape of the skin part and the mold tread shape, and inputting it into the controller;

[0075] Step 2) The controller obtains an inverse analytical solution for the position of the stretching branch of the skin stretching machine corresponding to the ideal motion trajectory of the clamp 1 based on the established mathematical model of multi-axis coordinated motion control of the skin stretching machine, and obtains an ideal displacement trajectory curve of the stretching branch;

[0076] Step 3) The controller sends a command to the servo valve to drive the stretching branch to move according to the ideal displacement trajectory curve;

[0077] Step 4) The displacement sensor feeds back the actual movement displacement of the stretching branch to the controller in real time;

[0078] Step 5) The controller obtains the motion control quantity by subtracting the ideal displacement of the stretching branch from the actual motion displacement, and sends it to the servo valve to adjust the stretching branch displacement. This cycle is repeated to control the motion trajectory of clamp 1 and realize multi-axis coordinated motion control of the skin stretching machine.

[0079] This method enables skin-type sheet metal parts to achieve continuous multi-axis coordinated motion within the entire working space of the skin stretching machine during stretching forming, can collaboratively complete complex process design requirements, effectively improve the shape and dimensional accuracy of skin parts, reduce production costs, save production time, and improve the level of digital precision forming technology for skin parts.

[0080] Example 7:

[0081] Based on Example 6, this embodiment provides a multi-axis coordinated motion control method for a skin stretching machine. Step 2) based on the established mathematical model for multi-axis coordinated motion control of the skin stretching machine, the inverse solution for the stretching branch position of the skin stretching machine is obtained as follows:

[0082] like Figure 4 As shown, a fixed coordinate system Ox is established on the rack 5. o y o z o , establish motion coordinate system Px on clamp 1 p y p z p , the motion coordinate system Px at the initial position p y p z p With fixed coordinate system Ox o y o z o The two are parallel to each other, point O is the hinge point between the constraint branch 4 and the frame 5, point P is the hinge point between the constraint branch 4 and the clamp 1, the hinge points between the vertical drive branch 3 and the frame 5 are A1 and A2, the hinge points between the horizontal drive branch 2 and the frame 5 are A3 and A4, the hinge points between the vertical drive branch 3 and the clamp 1 are B1 and B2, and the hinge points between the horizontal drive branch 2 and the clamp 1 are B3 and B4;

[0083] When the position of clamp 1 changes arbitrarily, point B i In the fixed coordinate system Ox o y o z o The middle position can be expressed as

[0084]

[0085] Where, O P=(P x ,P y ,P z ) T is the coordinate of point P in the fixed coordinate system; The moving coordinate system is relative to the fixed coordinate system Ox o y o The rotation transformation matrix of z; i = 1, 2, 3, 4;

[0086] Assume that clamp 1 first wraps around z p Rotate by angle β and then rotate around the updated y p The axis rotates by an angle of γ and finally rotates around x o The axis rotates by an angle α, then the rotation transformation matrix It can be expressed as

[0087]

[0088] In the formula, sα=sinα, cα=cosα, sβ=sinβ, cβ=cosβ, sγ=sinγ, cγ=cosγ;

[0089] According to the distance formula between two points in the same coordinate system, the position constraint equation of the stretching branch can be obtained as follows:

[0090]

[0091] Where, O E j Point E is in the fixed coordinate system Ox o y o z o The coordinates in ;

[0092] The inverse analytical expression of the tensile branch position can be obtained as

[0093]

[0094] Where l1, l2, l3 and l4 are the lengths of the hydraulic cylinder rods of the two vertical drive branches 3 and the two horizontal drive branches 2, respectively; l is the distance the clamp 1 moves along the vector OP; a, b, c, d, e, and f are all structural parameters and are constants; θ3 and θ4 are the distances between the vectors E3B3, E4B4 and y p The angle between the axes;

[0095] According to the spatial geometric relationship, we can get

[0096]

[0097] Thus, the inverse analytical solution of the stretching branch position of the skin stretching machine is obtained.

[0098] This embodiment takes a single-side stretching unit (left stretching unit) as an example to introduce the establishment of a mathematical model for multi-axis collaborative motion control of a skin stretching machine, and obtains the inverse analytical solution of the stretching mechanism of the skin stretching machine. The stretching unit on the other side (right stretching unit) is mirror-symmetrical to the side (left stretching unit) and is synchronously controlled by a controller.

[0099] Example 8:

[0100] Based on Example 6, this embodiment provides a multi-axis coordinated motion control method for a skin stretching machine. During the control process of step 5), the specific control formula for the stretching branch motion is:

[0101]

[0102] Where Δu(k) is the deviation between the kth control value and the k-1th control value of the stretching branch, u(k) is the kth stretching branch control value, u(k-1) is the k-1th stretching branch control value, k p is the proportionality coefficient, k T is the integral time constant, k D is the differential time constant, k is the sampling number (k=1, 2, ...), T is the sampling period, e(k), e(k-1), and e(k-2) are the motion control quantities at the kth moment, k-1th moment, and k-2th moment respectively.

[0103] The motion control quantity is the deviation between the ideal displacement of the driving hydraulic cylinder obtained by the multi-axis coordinated motion control mathematical model of the skin stretching machine at different times and the actual displacement of the driving hydraulic cylinder obtained by detection by the displacement sensor.

[0104] The above examples are merely illustrative of the present invention and do not limit the scope of protection of the present invention. Any design that is identical or similar to the present invention falls within the scope of protection of the present invention.

Claims

1. A multi-axis collaborative motion control method for a skin stretching machine, which adopts a multi-axis collaborative motion control system for a skin stretching machine. The skin stretching machine includes a stretching unit and a frame. The stretching unit includes a clamp, a constraint branch and multiple stretching branches. The clamp is connected to the frame through the stretching branch and the constraint branch; the multi-axis collaborative motion control system for the skin stretching machine includes a controller, a servo valve and a displacement sensor. The servo valve is installed on the connecting pipeline between the stretching branch and the hydraulic station, and the displacement sensor is installed on the stretching branch; the servo valve and the displacement sensor are both connected to the controller by electrical signals, and the controller is used to perform a difference between the real-time data of the displacement sensor and the ideal displacement to obtain a motion control amount, and send this motion control amount to the servo valve to adjust the displacement of the stretching branch, control the motion trajectory of the clamp, and realize the multi-axis collaborative motion control of the skin stretching machine, which is characterized in that The following steps are involved: Step 1) Determine the ideal motion trajectory of the clamp based on the final stretched shape of the skin part and the mold tread shape, and input it into the controller; Step 2) The controller obtains the inverse analytical solution for the stretching branch position of the skin stretching machine corresponding to the ideal motion trajectory of the clamp based on the established mathematical model of multi-axis coordinated motion control of the skin stretching machine, and obtains the ideal displacement trajectory curve of the stretching branch; Step 3) The controller sends a command to the servo valve to drive the stretching branch to move according to the ideal displacement trajectory curve; Step 4) The displacement sensor feeds back the actual movement displacement of the stretching branch to the controller in real time; Step 5) The controller calculates the difference between the ideal displacement of the stretching branch and the actual motion displacement to obtain the motion control variable, and sends it to the servo valve to adjust the stretching branch displacement. This cycle is repeated to control the motion trajectory of the clamp and realize multi-axis coordinated motion control of the skin stretching machine.

2. The multi-axis coordinated motion control method of a skin stretching machine according to claim 1, characterized in that: There are two stretching units, namely a left stretching unit and a right stretching unit, the left stretching unit and the right stretching unit have the same structure, and the left stretching unit and the right stretching unit are symmetrically connected to the frame; The stretching branch includes a horizontal driving branch and a vertical driving branch, and there are two of each of the horizontal driving branch and the vertical driving branch. The vertical driving branch and the constraint branch are arranged longitudinally along the lower end surface of the clamp, and the constraint branch is located between the two vertical driving branches.

3. The multi-axis coordinated motion control method of a skin stretching machine according to claim 1, characterized in that: The stretching branch is a hydraulic cylinder, a fixed end of the hydraulic cylinder is connected to the frame, and a movable end is connected to the clamp.

4. The multi-axis coordinated motion control method of a skin stretching machine according to claim 2, characterized in that: The constraint branch includes a rotating pair 1, a guide cylinder, a guide shaft, and a rotating pair 2. The guide shaft is sleeved in the guide cylinder. The lower end of the guide cylinder is connected to the frame through the rotating pair 1, and the upper end of the guide shaft is connected to the clamp through the rotating pair 2.

5. The multi-axis coordinated motion control method of a skin stretching machine according to claim 2, characterized in that: One end of the horizontal drive branch is connected to the frame through a ball joint, and the other end is connected to the clamp through a universal joint; one end of the vertical drive branch is connected to the frame through a ball joint, and the other end is connected to the clamp through a ball joint.

6. The multi-axis coordinated motion control method of a skin stretching machine according to claim 2, characterized in that: Step 2) Based on the established mathematical model of multi-axis coordinated motion control of the skin stretching machine, the inverse analytical solution process for the stretching branch position of the skin stretching machine is obtained as follows: Establish a fixed coordinate system on the rack O - x o y o z o , establish the motion coordinate system on the clamp P - x p y p z p , the motion coordinate system at the initial position P - x p y p z p With fixed coordinate system O - x o y o z o The two are parallel to each other. O To constrain the hinge point between the branch and the frame, point P The hinge point between the constraint branch and the clamp is the hinge point between the vertical drive branch and the frame. A 1. A 2. The hinge point between the horizontal drive branch and the frame is A 3. A 4. The hinge point between the vertical drive branch and the clamp is B 1. B 2. The hinge point between the horizontal drive branch and the clamp frame is B 3. B 4; When the position of the clamp changes arbitrarily, click B i In a fixed coordinate system O - x o y o z o The middle position can be expressed as Where, for P The coordinates of the point in a fixed coordinate system; The moving coordinate system is relative to the fixed coordinate system O - x o y o z The rotation transformation matrix; i =1,2,3,4; Set the clamp first around z p Rotation β Angle, then around the updated y p Axis rotation γ Corner, finally around x o Axis rotation α Angle, then the rotation transformation matrix It can be expressed as Where, , , , , , ; According to the distance formula between two points in the same coordinate system, the position constraint equation of the stretching branch can be obtained as follows: i =1,2； j =3,4； Where, for point E In a fixed coordinate system O - x o y o z o The coordinates in ; Then the inverse analytical expression of the tensile branch position can be obtained as Where, l 1. l 2. l 3 and l 4 is the length of the hydraulic cylinder rod of the two vertical drive branches and the length of the hydraulic cylinder rod of the two horizontal drive branches, l For the clamp along the vector OP Distance moved ，a 、 b 、 c 、 d 、 e 、 f are all structural parameters and are constants; θ 3. θ 4 are vectors E 3 B 3. E 4 B 4 and y p The angle between the axes; According to the spatial geometric relationship, we can get Thus, the inverse analytical solution of the stretching branch position of the skin stretching machine is obtained.

7. The multi-axis coordinated motion control method of a skin stretching machine according to claim 1, characterized in that: In the control process of step 5), the specific control formula for the stretching branch movement is: Where, For stretching branch k The second control amount and the k -1 deviation between control quantities, For the k Secondary tensile branch control amount, For the k -1 time each stretching branch measurement, is the proportionality coefficient, is the integral time constant system, is the differential time constant, is the sampling sequence number, k =1,2,……, T is the sampling period, 、 、 Respectively k Time, k -1 moment, k -2 Moment motion control amount.

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