An on-line measuring and compensating system and method for free bending machining

Abstract

The present application relates to the technical field of numerical control machining, in particular to an online measurement and compensation system and method for free bending machining, which measures the offset of the bending part in real time through a displacement sensor, obtains the curvature and the flexure of the bending part after the shape analysis module processes the offset data, compares the azimuth through an azimuth comparison module after splicing by a shape splicing module, obtains the deviation value, and the feed axis position compensation module gives the feed value and the feed speed of the feed axis, the action execution module calls the process parameters, sends them to the designated internal PLC address of the numerical control system as the input value of the compensation amount of the bending part. The present application detects the outer diameter offset of the bending part at the cross section in real time, realizes the online measurement of the part shape, obtains the deviation through comparative analysis, and then performs compensation, realizes the real-time compensation of the free bending part, improves the iteration speed of the free bending forming process, realizes the rapid optimization of the process parameters, improves the part forming precision, and can be applied to the free bending equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of numerical control machining, in particular to an online measurement and compensation system and method for free bending machining. BACKGROUND

[0002] At present, the forming mode of metal pipes and profiles generally adopts a plane bending mode, mainly including bending around, bending by pulling, bending by pressing, bending by pushing, bending by rolling, etc. These modes can only be used for forming bending pieces with single-axis form and constant bending radius. However, in recent years, the spatial configuration of metal bending pieces is gradually becoming complex, and the axis form of the bending piece gradually evolves from a plane form to a spatial form. For complex bending components with spatial complex axis form or continuously changing bending radius, the traditional pipe bending process has great application limitations. Therefore, free bending forming has gradually become a technical innovation hotspot in the field of plastic forming at home and abroad. This technology not only can realize precise dieless pipe bending, effectively save the mold design and production link, shorten the mold preparation period, and reduce the production cost. However, due to the differences in the performance of different batches of materials, the complexity of the boundary conditions, the precision of the formed parts is poor, and the process parameter adjustment period is long, which affects the application of free bending process in the military, automobile and other fields.

[0003] The existing free bending parts have no precision feedback in the forming process, and can only be measured offline after processing, and then corrected and compensated according to the deviation between the actual part and the theoretical part, which leads to the inability to accurately control the forming precision of the parts during the forming process, and the inability to quickly obtain the target part shape, and the long debugging period. SUMMARY

[0004] (I) Technical problem to be solved

[0005] The embodiment of the present application provides an online measurement and compensation system and method for free bending machining, which solves the technical problem that the existing free bending parts have no precision feedback in the forming process, and can only be measured offline after processing, and then corrected and compensated according to the deviation between the actual part and the theoretical part.

[0006] (II) Technical scheme

[0007] In a first aspect, embodiments of the present application provide an online measurement and compensation system for free bending processing, comprising a real-time displacement measurement module, a shape analysis module, a shape splicing module, an orientation comparison module, a feed shaft position compensation module, and an action execution module; the real-time displacement measurement module is arranged on a bending die of a free bending device, and is configured to collect a displacement of a current segment of a bent part; the shape analysis module is connected to the real-time displacement measurement module, and is configured to calculate curvature κ and torsion τ information of the shape of the current segment of the bent part according to the collected displacement; the shape splicing module is connected to the shape analysis module, and is configured to splice each single segment of the bent part into a complete bent part; the orientation comparison module is connected to the shape splicing module, and is configured to calculate a matching condition of the bent part after splicing and a target part, and to give a deviation value; the feed shaft position compensation module is connected to the orientation comparison module, and is configured to perform optimization according to the deviation value and a target value given by the orientation comparison module, and to give a feed value and a feed speed of the feed shaft; and the action execution module is connected to the feed shaft position compensation module, and is configured to control the free bending device to work, and to perform corresponding compensation on the bending die according to control parameters given by the feed shaft position compensation module.

[0008] Further, the real-time displacement measurement module comprises a displacement sensor, a computer serial port, and a signal calibration module.

[0009] Further, the shape analysis module is based on an independent executable program of a numerical control system interface, and uninterruptedly accesses the computer serial port to obtain sampling data of the displacement sensor; the data packet is subjected to verification, decoding, denoising, mean value, and data processing based on geometric reasoning to obtain the curvature κ and the torsion τ of the workpiece.

[0010] Further, the action execution module comprises the following processing parameters when controlling the free bending device to perform bending: displacement, deflection, feed speed, and rotation speed of the bending die.

[0011] Further, the bending die is moved and rotated in space to bend and shape the bent part, and the movement axes of the bending die are controlled according to a Cartesian coordinate system; the movement axes of the bending die of a three-axis bending device include horizontal X-axis movement and vertical Z-axis movement, and the movement axes of the bending die of a six-axis bending device include horizontal X-axis movement, vertical Z-axis movement, rotation around the X-axis, rotation around the Y-axis, rotation around the Z-axis, and feeding Y-axis movement.

[0012] In a second aspect, an online measurement and compensation method for free bending processing is provided, and the method comprises the following steps:

[0013] S1, collecting a displacement of a bent part at a measurement point in a bending process by a displacement sensor in real time;

[0014] S2, the offset data is read by a computer serial port, and the curvature and the deflection of the bent part are obtained after being processed by a shape analysis module;

[0015] S3, after being spliced by a shape splicing module, the orientation is compared by an orientation comparison module to obtain a deviation value;

[0016] S4, a feed shaft position compensation module gives the feed value and the feed speed of the feed shaft according to the bending part feed rule;

[0017] S5, an action execution module calls process parameters and sends them to a specified numerical control system internal PLC address as input values of the compensation amount of the bent part;

[0018] S6, S1~S5 are repeated, and the process ends when the target shape requirement is met, realizing closed-loop control.

[0019] Further, according to the curvature and the deflection characteristics of the part, the part is divided into a stable section and a transition section, the shape, position and direction of the stable section are ensured by adjusting the movement of the bending die, so that the final shape of the part meets the target shape requirement, and the compensation and control process is performed for each transition section and ends at the start point of the stable section.

[0020] Further, the stable section is a shape formed by keeping the bending die still during the forming process, and the axis thereof is in the form of a diameter, a circular arc and a spiral line; the transition section is a part shape formed during the movement of the bending die during the forming process.

[0021] Further, the bending part is pushed through the fixed die and the bending die by a feeding mechanism, the bending die continuously changes the movement track and posture according to the requirements of the numerical model along the translation of the XZ axis and the rotation around the XYZ axis, so that the bending part is bent and twisted, and the bending part is continuously bent and formed in multiple sections and multiple directions.

[0022] Further, the feed rule of the bending part is the positional relationship between the shape of the bending part and the bending die accumulated in the knowledge base.

[0023] (Three) beneficial effects

[0024] In summary, the displacement sensor is arranged at the outlet of the bending die, the outer diameter offset of the bending part at the cross section is detected in real time, the curvature and the deflection of the bending part are calculated from the offset, the part shape is measured online, the deviation is obtained through comparative analysis, and then compensation is performed, the real-time compensation of the free bending part is realized, the iteration speed of the free bending forming process is improved, the process parameters are quickly optimized, the part forming precision is improved, and the free bending equipment can be applied.

[0025] (1) The forming parameters are corrected in real time through comparison with the corresponding curvature and deflection of the numerical model, the part forming precision is improved, and the process iteration efficiency is improved;

[0026] (2) Real-time record the corresponding relationship between the part shape and the process parameters, improve the accumulation speed of the process knowledge base;

[0027] (3) Good reliability, effectively improve the bending accuracy, make the overall bending pipe accuracy rise by one order of magnitude, and can timely find the waste products and alarm, which is of great significance in multi-bending long pipe and mass production. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0029] Figure 1 is a flowchart of an online measurement and compensation method for free bending processing according to some embodiments of the present application;

[0030] Figure 2 is a schematic diagram of bending processing and detection of a bent part according to some embodiments of the present application;

[0031] Figure 3 is a displacement sensor installation schematic diagram of an online measurement and compensation system for free bending processing according to some embodiments of the present application;

[0032] Figure 4 is a measurement schematic diagram of a displacement sensor according to some embodiments of the present application.

[0033] In the figure: 1, bending die fixed seat; 2, sensor fixed seat; 3, displacement sensor; 4, bending die; 5, bent part; 6, measurement section; 7, fixed die; 51, unformed area; 52, formed area; 53, formed part. DETAILED DESCRIPTION

[0034] The embodiments of the present application will be further described in detail below in combination with the drawings and examples. The detailed description of the following embodiments and the drawings are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments, and covers any modification, replacement and improvement of the parts, components and connection modes without departing from the spirit of the present application.

[0035] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0036] Please refer to Figures 1-4The embodiment of the present application provides an on-line measurement and compensation system for free bending processing, which comprises a real-time displacement measurement module, a shape analysis module, a shape splicing module, an orientation comparison module, a feeding shaft position compensation module and an action execution module.

[0037] The real-time displacement measurement module is arranged on a bending die 4 of a free bending device, so that a processed part is in a detection range of the measurement device, target compensation shafts are each motion shaft of the device for controlling the movement of the bending die 4, and the real-time displacement measurement module is used for collecting the offset of the current segment bending part 5. Further, the real-time displacement measurement module comprises a displacement sensor 3, a computer serial port and a signal calibration module.

[0038] The shape analysis module is connected with the real-time displacement measurement module, and is used for calculating the curvature kappa and the torsion tau information of the shape of the current segment bending part 5 according to the collected offset. Further, the shape analysis module is based on an independently executable program of a numerical control system interface, and uninterruptedly accesses the computer serial port to obtain the sampling data of the displacement sensor 3, so that the workpiece curvature kappa and the torsion tau are obtained through a data processing method based on geometry reasoning after the data packet is verified, decoded, denoised and averaged.

[0039] The shape splicing module is connected with the shape analysis module, and is used for splicing each single segment bending part 5 into a complete bending part 5.

[0040] The orientation comparison module is connected with the shape splicing module, and is used for calculating the matching condition of the spliced bending part 5 and a target part, and giving a deviation value.

[0041] The feeding shaft position compensation module is connected with the orientation comparison module, and is used for dynamically adjusting the feeding value and the feeding speed of the feeding shaft according to the feeding rule of the bending part 5, and optimizing according to a target value according to the deviation value given by the orientation comparison module.

[0042] The action execution module is connected with the feeding shaft position compensation module, and is used for controlling the working of the free bending device, and compensating the bending die 4 according to the control parameters given by the feeding shaft position compensation module. Further, the action execution module comprises the following processing parameters when controlling the free bending device to perform bending: the displacement, the deflection, the feeding speed and the rotating speed of the bending die 4.

[0043] In some embodiments, the bending die 4 is the key to free bending forming, which moves in translation and rotation in space so that the bending part 5 is bent and formed. The movement axes of the bending die 4 are controlled according to the number of axes of the device. Taking the feeding direction as an example, the Y axis, according to the Cartesian coordinate system, the movement axes of the bending die 4 of a three-axis bending device include horizontal X axis and vertical Z movement, and the movement axes of the bending die 4 of a six-axis bending device include horizontal X axis, vertical Z movement, rotation of the X axis around the α axis, rotation of the Y axis around the β axis, rotation of the Z axis around the γ axis, and feeding Y axis movement.

[0044] In a second aspect, an online measurement and compensation method for free bending processing is provided, the method comprising:

[0045] S1, the displacement sensor 3 is used to measure the displacement of the bending part 5 at the measuring point in real time during the bending process;

[0046] S2, the displacement data is read by the computer serial port, and the curvature and the flexure of the bending part 5 are obtained after being processed by the shape analysis module;

[0047] S3, after being spliced by the shape splicing module, the azimuth comparison module is used for azimuth comparison to obtain the deviation value;

[0048] S4, the feeding axis position compensation module gives the feeding value and the feeding speed of the feeding axis according to the feeding rule of the bending part 5;

[0049] S5, the action execution module calls the process parameters and sends them to the specified internal PLC address of the numerical control system as the input value of the compensation amount of the bending part 5;

[0050] S6, S1-S5 are repeated, and the process is ended when the target shape requirement is met, realizing closed-loop control.

[0051] Please refer to Figure 2 In some embodiments, 51 is an unformed area, 52 is a formed area, and 53 is a formed part. The idea of ensuring the forming accuracy of the free bending part 5 of the free bending device is as follows: according to the curvature and the flexure characteristics of the part, the part is divided into a stable section and a transition section, the movement of the bending die 4 is adjusted to ensure the shape, position and direction of the stable section, so that the final shape of the part meets the target shape requirement, and the compensation and control process is performed for each transition section and ends at the starting point of the stable section. The stable section is a shape formed by keeping the bending die 4 still during the forming process, and its axis is in the form of diameter, circular arc and spiral line; the transition section is a part shape formed by the movement of the bending die 4 during the forming process.

[0052] In some embodiments, the free bending forming principle: the bending part 5 is pushed through the fixed die 7 and the bending die 4 by the feeding mechanism (the feeding device plus the clamping device), and the bending die 4 continuously changes the motion trajectory and posture along the XZ axis translation and rotation around the XYZ axis according to the requirements of the numerical model, so that the bending part 5 is bent and twisted to realize the multi-section and multi-direction continuous bending forming of the bending part 5.

[0053] In some embodiments, the feeding law of the bending part 5 mainly refers to the position relationship between the shape of the bending part 5 accumulated in the knowledge base and the bending die 4.

[0054] Embodiment:

[0055] The variable curvature bending equipment makes the bending part 5 bend and form by controlling the translation and rotation of the bending die 4 in space. The shape of the bending part 5 is measured by an online measurement device such as Figures 2-4 As shown in the figure, including sensor fixing seat 2, displacement sensor 3 and control system (not shown). Two displacement sensors 3 are arranged at the outlet of the bending die 4 with coinciding and mutually perpendicular measurement surfaces. The sensor fixing seat 2 is fastened together with the bending die fixing seat 1 by bolts, so that when the bending die 4 is in the starting position, the center of the bending part 5 is in the center of the measurement position, and the displacement sensor 3 is fastened by screws.

[0056] According to the size of the part and the size of the displacement sensor 3 probe, two displacement sensors 3 are arranged around the fixing seat of the bending die 4. The distance between the displacement sensor 3 and the contact position of the bending die 4 and the bending part 5 is 20mm according to the size of the diameter of the bending part 5 and the size of the displacement sensor 3 entity.

[0057] The displacement sensor 3 can be a laser displacement sensor 3, which needs to have a detection accuracy of 2μm or above. The measurement center of the laser displacement sensor 3 coincides with the center of the bending die 4.

[0058] The laser displacement sensor 3 is electrically connected with the control system to transmit the displacement signals collected by the laser displacement sensor 3. The control system is used to analyze the signals collected by the laser displacement sensor 3.

[0059] The measurement principle assumes that the measurement point is close to the bending position, so it is assumed that the bending part 5 axis between the contact point of the bending die 4 and the bending part 5 and the measurement point is a general spiral, and the bending part 5 at this position is a spiral tube.

[0060] The parameter equation H of the spiral tube is as follows, and the corresponding calculation is performed by selecting the diameter of the bending part 5 as 20.

[0061] ;

[0062] Where R is the radius of the helix axis, r is the radius of the curved part 5, b is the parameter of the pitch h, b = h / 2π, u, v are parameters.

[0063] The general equation of the helix is as follows.

[0064] ;

[0065] The equation can be written as

[0066] F(x, y, z, R, b, r) = 0.

[0067] The parametric equation can be written in the form of a matrix .

[0068] From the parametric equation, the helix above has the Z axis as the axis, and the intersection A0 of the axis and the X axis is (R, 0, 0).

[0069] In order to be consistent with the Frenet frame of the variable-curvature push-bending curved part 5, the following transformation is made.

[0070] (1) The helix rotates by an angle a about the X axis. The tangent line at the point A0 of the helix axis is parallel to the X axis, and the transformation matrix is .

[0071] ;

[0072] That is

[0073]

[0074]

[0075] The equation can be written as ;

[0076] (2) The helix moves a distance t along the negative direction of the X axis. t = -R, so that the starting point A of the helix axis becomes the origin in the new coordinate system. That is

[0077] ;

[0078] The equation can be written as ;

[0079] (3) The helix rotates about the Y axis. Due to the need for part forming, the transformed helix also needs to be rotated about the Y axis by β, which is determined by the X axis translation displacement xm and the Z axis translation displacement zm of the bending die 4, and can be obtained from the machine tool control system, . The transformation matrix is .

[0080] ;

[0081] Briefly denoted as ;

[0082] The equation of the spiral tube is

[0083] Let y=S, the curve obtained by the intersection of the spiral tube and the plane y=S is measured as the section 6, i.e. the section where the laser displacement sensor 3 is located.

[0084] See Figure 4 , H1~H4 are the readings of the sensors, and L11, L21, L31, L41 are the offsets calculated from the readings of the sensors; according to the position of the curved part 5 that is blocked, H1, H2, H3 and H4 can be read on the laser displacement sensor 3, and then according to the relative position relationship between the laser displacement sensor 3 and the bending die 4, the outer diameter positions L11, L21, L31, L41 of the curved part 5 at the extreme positions of the curved part 5 can be calculated.

[0085] The general equation of the spiral tube is analyzed as , where y=20. The equation z=P(x, 20, R, b, 10, α, β), x=Q(z, 20, R, b, 10, α, β) can be obtained.

[0086] Using the extreme value formula =0, x11, x12 are obtained, and |x11|≥|x12|; the extreme value formula =0, z21, z22 are obtained, and |z21|≥|z22|. Using the angle β, the extreme values corresponding to x11, x12, z21, z22 are determined. Taking the angle 135 degrees as an example, the following equations can be obtained by simultaneous solution, and R and b are obtained.

[0087] L11=z12=P(x12, 20, R, b, 10, α, β);

[0088] L21=z11=P(x11, 20, R, b, 10, α, β);

[0089] L31=x21=Q(z21, 20, R, b, 10, α, β);

[0090] L41=x22=Q(z22, 20, R, b, 10, α, β);

[0091] For a general spiral:

[0092] ;

[0093] ;

[0094] Thus, the shape of the bent part 5 can be detected in real time, compared with the target value of the numerical model, and then corrected by the numerical control system, so that the shape of the bent part 5 meets the requirements of the numerical model. If the curvature is too small, the translation distance and the corresponding deflection angle of the bending die 4 are increased, so that the subsequent curvature is increased to compensate for the small curvature in the early stage. If the curvature is too large, the opposite is done. If the flexural rigidity is too small, the deflection angle of the bending die 4 is increased, so that the subsequent flexural rigidity is increased to compensate for the small flexural rigidity in the early stage. If the flexural rigidity is too large, the opposite is done.

[0095] It should be noted that each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between the embodiments can be mutually referred to. Each embodiment mainly describes the difference from other embodiments. For the embodiments of the method, the relevant parts can be referred to the description of the device embodiments. The present application is not limited to the specific steps and structures described above and shown in the drawings. Moreover, for the sake of brevity, the detailed description of the known method technology is omitted.

[0096] The above only describes the embodiments of the present application and does not limit the present application. The present application can have various modifications and changes without departing from the scope of the present application for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. An on-line measurement and compensation method for free bending machining, characterized by, The online measurement and compensation system for free bending processing is realized, and comprises a real-time displacement measurement module, a shape analysis module, a shape splicing module, an orientation comparison module, a feed shaft position compensation module and an action execution module. The real-time displacement measurement module is arranged on a bending die of a free bending device, and is used for collecting the displacement of the current segment of the bent part. The shape analysis module is connected with the real-time displacement measurement module, and is used for calculating the curvature κ and the torsion τ information of the shape of the current segment of the bent part according to the collected displacement. The shape splicing module is connected with the shape analysis module, and is used for splicing the single segments of the bent part into a complete bent part. The orientation comparison module is connected with the shape splicing module, and is used for calculating the matching condition of the spliced bent part and the target part, and giving a deviation value. The feed shaft position compensation module is connected with the orientation comparison module, and is used for optimizing the deviation value and the target value given by the orientation comparison module, and giving the feed value and the feed speed of the feed shaft. The action execution module is connected with the feed shaft position compensation module, and is used for controlling the free bending device to work, and compensating the bending die according to the control parameters given by the feed shaft position compensation module. The real-time displacement measurement module comprises displacement sensors, two displacement sensors are arranged at the outlet of the bending die with coinciding and mutually perpendicular measurement surfaces, a sensor fixing seat is fastened with a bending die fixing seat through bolts, so that the center of the bent part is in the center of the measurement position when the bending die is in the starting position, and the displacement sensors are fastened through screws. The online measurement and compensation method for free bending processing comprises the following steps: S1, collecting the displacement of the bent part at the measurement point in the bending process through the displacement sensor in real time; S2, reading the displacement data through the computer serial port, and obtaining the curvature and the torsion of the bent part through the shape analysis module; S3, comparing the orientation through the orientation comparison module after splicing through the shape splicing module, and obtaining the deviation value; S4, giving the feed value and the feed speed of the feed shaft according to the feed rule of the bent part through the feed shaft position compensation module; S5, calling the process parameters through the action execution module, and sending the process parameters to the specified internal PLC address of the numerical control system as the input value of the compensation amount of the bent part; S6, repeating S1-S5, and ending when the target shape requirement is met, so as to realize the closed-loop control.

2. The on-line measuring and compensating method for free bending machining according to claim 1, characterized in that: The real-time displacement measurement module further comprises a computer serial port and a signal calibration module.

3. The on-line measuring and compensating method for free bending machining according to claim 2, characterized in that: The shape analysis module is based on the independent executable program of the numerical control system interface, and uninterruptedly accesses the computer serial port to obtain the sampling data of the displacement sensor, and obtains the curvature κ and the torsion τ of the workpiece through the data processing method based on the geometry reasoning after the data packet is verified, decoded, denoised and averaged.

4. The on-line measuring and compensating method for free bending machining according to claim 3, characterized in that: The processing parameters of the action execution module in the control of the free bending device in the bending process include the displacement, deflection, feed speed and rotation speed of the bending die.

5. The on-line measuring and compensating method for free bending machining according to claim 4, characterized in that: The bending die moves in space and rotates, so that the bending part is bent and shaped. The movement axis of the bending die is controlled according to the Cartesian coordinate system. The movement axis of the bending die of the three-axis bending equipment includes horizontal X-axis movement and vertical Z-axis movement. The movement axis of the bending die of the six-axis bending equipment includes horizontal X-axis movement, vertical Z-axis movement, rotation of the bending die around the X-axis, rotation of the bending die around the Y-axis, rotation of the bending die around the Z-axis, and feeding Y-axis movement.

6. The on-line measuring and compensating method for free bending machining according to claim 1, characterized in that: According to the curvature and flexural characteristics of the part, the part is divided into a stable section and a transition section. The movement of the bending die is adjusted to ensure the shape, position and direction of the stable section, so that the final shape of the part meets the target shape requirement. Compensation and control are performed for each transition section, and end at the start of the stable section.

7. The on-line measuring and compensating method for free bending machining according to claim 6, characterized in that: The stable section is a shape formed by keeping the bending die still during the forming process, and its axis is in the form of a diameter, a circular arc and a spiral line. The transition section is a part shape formed by the movement of the bending die during the forming process.

8. The on-line measuring and compensating method for free bending machining according to claim 1, characterized in that: The bending part is pushed through the fixed die and the bending die by the feeding mechanism. The bending die continuously changes the movement trajectory and posture according to the requirements of the numerical model along the XZ-axis movement and the rotation around the XYZ-axis, so that the bending part is bent and twisted, and the bending part is continuously bent and shaped in multiple sections and multiple directions.

9. The on-line measurement and compensation method for free bending machining according to claim 1, characterized in that: The feeding law of the bending part is accumulated in the knowledge base as the relationship between the shape of the bending part and the position of the bending die.

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