Method for determining the mechanical action torque component at the guide point of a cutting blade of a cutting machine

Abstract

The invention relates to a method of determining a mechanical action torque component at a guide point of a cutting blade (L) for a cutting machine, the cutting blade being guided into a presser foot (P) of a cutting head of the cutting machine. The method comprises positioning a five-component force transducer on the presser foot, wherein the five-component force transducer comprises a plurality of sensors capable of determining a normal force, a lateral force, a roll torque, a pitch torque, and a yaw torque of the cutting blade; establishing a calibration matrix of the force transducer; determining forces experienced by the cutting blade in three dimensions based on measurements obtained from the sensors and the calibration matrix.

Description

Technical Field

[0001] This invention relates to the general field of automatically cutting flexible materials placed on a cutting table in single or stacked form using a vibrating blade. More specifically, this invention relates to a method for determining the mechanical torque component at the guide point of such a cutting blade. Background Technology

[0002] One application area of ​​this invention is the automatic cutting of parts in flexible textile or non-textile materials (such as leather), particularly in the clothing, furniture, or automotive interior industries.

[0003] A known method for automatically cutting parts in a flexible material includes placing the material in a single layer or stacked form, forming a mattress shape, on a fixed or movable cutting support of a cutting table, and cutting the parts by a cutting head that moves above the cutting support of the cutting table. Specifically, the cutting head has a vibrating steel blade that vibrates in a direction perpendicular to its cutting edge to cut the material.

[0004] During this vertical vibration and material cutting process, the cutting blade is subjected to numerous forces that affect the quality of the cut edge of the part. In particular, these forces have a direct impact on the cutting quality and the geometry of the cut part across the entire height of the material, especially when the material is formed in layers.

[0005] In addition, in order to be able to apply the cutting parameters and directions to the blade, it is necessary to understand as much as possible the strain that the cutting blade is subjected to.

[0006] For this purpose, it is known that a bending sensor can be positioned on the pressure foot of the cutting head. In this way, the sensor can collect data related to the lateral bending of the cutting blade, thereby influencing the cutting parameters and orientation of the blade for correction. For example, see patent application IT 102017000023745 filed in the name of Morgan Tecnica.

[0007] However, these data are insufficient and do not take into account all the forces that the cutting blade experiences. Summary of the Invention

[0008] The main objective of this invention is to provide a method for determining all the forces exerted on a cutting blade, so as to enable more precise and autonomous control over the cutting process.

[0009] According to the present invention, the above-mentioned objective is achieved by a method for determining the mechanical torque component at the guide point of a cutting blade for a cutting machine, the cutting blade being guided into the pressure foot of the cutting head of the cutting machine. The method includes:

[0010] A six-component force gauge is positioned on the presser foot. The six-component force gauge includes multiple sensors for determining the frontal force, lateral force, roll torque, pitch torque, and yaw torque of the cutting blade.

[0011] Establish the calibration matrix of the force gauge; and

[0012] Based on the measurements obtained by the sensor and the calibration matrix, the force exerted on the cutting blade in three dimensions is determined.

[0013] The method provided by this invention is characterized by the ability to determine the forces acting on the blade in three dimensions based on a force gauge installed in the pressure foot of the cutting head. Specifically, five of the six components of the mechanical torque acting on the blade at the guide point can be determined: frontal force, lateral force, roll moment, pitch moment, and yaw moment (excluding the force along the blade's spindle). Based on this data, highly precise and autonomous control of the cutting parameters can be ensured, thereby correcting defects.

[0014] The step of establishing the calibration matrix of the force gauge preferably includes: establishing the theoretical calibration matrix of the force gauge sensor under various theoretical strains, as a function of the six components of the force gauge.

[0015] The step of establishing the calibration matrix of the force gauge preferably further includes: calculating the response matrix of the force gauge sensor under various actual strains based on the theoretical calibration matrix of the force gauge sensor and the actual response measurement value, as a function of the six components of the force gauge.

[0016] The response matrix of the sensor in the force gauge is calculated using a linear optimization method.

[0017] In one embodiment, the force gauge includes three triaxial piezoelectric sensors mounted in the presser foot and distributed around the longitudinal axis of the cutting blade.

[0018] In the second embodiment, the force gauge includes at least three, preferably six, coupled strain gauge bridges, which are mounted on the arm of the pressure foot and regularly distributed around the longitudinal axis of the cutting blade to form at least three, preferably six, full bridges.

[0019] In the third embodiment, the force gauge includes at least five decoupled strain gauge full bridges mounted in the pressure foot.

[0020] In any embodiment, the transmission of the measured values ​​from the sensor of the force gauge can be performed in a contactless or wired manner. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating a first embodiment of the method according to the present invention;

[0022] Figure 2 This is a schematic diagram illustrating a second embodiment of the method according to the present invention;

[0023] Figure 3 This is a schematic diagram illustrating a third embodiment of the method according to the present invention. Detailed Implementation

[0024] This invention is applicable to the automatic cutting of parts in flexible materials having a single layer or a stacked form.

[0025] Such cutting operations are typically performed by a cutting machine equipped with a horizontal cutting support, on which the flexible material to be cut is placed.

[0026] A cutting head with a vibrating blade is mounted on a gantry. As the cutting head moves along the gantry, the gantry also moves along the cutting support so that it can follow multiple cutting paths calculated by the cutting software.

[0027] Usually, such as Figure 1 As shown, a pressure foot is mounted on the lower part of the cutting head to apply controlled force to the flexible material located on its cutting support during cutting. The position of the pressure foot can be adjusted according to the height of the flexible material placed on the cutting support. Therefore, the pressure foot allows the cutting blade to be guided as close as possible to the flexible material.

[0028] This invention proposes a method for determining the mechanical torque component at the guide point of such a cutting blade.

[0029] The method according to the present invention can have several alternative implementation schemes.

[0030] according to Figure 1 As can be seen from the schematic embodiment shown, the method envisions positioning a five-component piezoelectric force gauge on the pressure foot P of the cutting head.

[0031] More specifically, the piezoelectric force gauge includes three triaxial piezoelectric sensors 1 to 3 mounted on the pressure foot P. Preferably, the three triaxial piezoelectric sensors 1 to 3 are regularly distributed around the longitudinal axis Z of the cutting blade L.

[0032] Piezoelectric sensors 1 to 3 are advantageously distributed equidistant from the center of the force gauge and spaced 120° apart. For example... Figure 1As shown, the Z-axis of piezoelectric sensors 1 to 3 (Z1, Z2 and Z3 respectively) points downward (i.e. towards the cutting bracket), their Y-axis (Y1, Y2 and Y3 respectively) points outward to the force gauge to facilitate cable passage, and their X-axis (X1, X2 and X3 respectively) are parallel to the radius of the force gauge.

[0033] This arrangement allows the sensor to integrate well into the presser foot environment while ensuring good sensor rigidity.

[0034] Upper board ( Figure 1 (Not shown) Near the force gauge integrated into the pressure foot. The upper plate has a hole for a screw to pass through, which can press the sensor between the upper plate and the bottom of the pressure foot, causing the sensor to be biased.

[0035] The first step in determining the force on the cutting blade in 3D according to the method of the present invention is to calibrate a piezoelectric force gauge mounted on the pressure foot.

[0036] The calibration involves establishing a calibration matrix that enables the multiple measured voltages transmitted by piezoelectric sensors 1 to 3 to be interpreted as mechanical forces.

[0037] First, a theoretical calibration matrix or global calibration matrix sensitive to the sensor's orientation and geometry should be created. Then, this theoretical calibration matrix should be refined to derive a response matrix corresponding to the actual calibration matrix.

[0038] The consideration of the theoretical calibration matrix is ​​based on the assumption that all geometries are perfect and without defects, and that the positioning is along ideal axes. It is useful to represent the positioning of the three triaxial sensors in space (X, Y, Z) to facilitate the representation of the torque of the mechanical action applied to these three sensors.

[0039] Each sensor i has an orthogonal reference coordinate system (xi, yi, zi) attached to its center Oi. Therefore, the torque of the mechanical action at Oi can be written as:

[0040] [Mathematical Formula 1]

[0041]

[0042] By transmitting the basic torque of each sensor to the origin of the reference coordinate system of the force gauge O, the contribution of each sensor in each measurement direction to the overall force reading can be determined.

[0043] The theoretical calibration matrix or the global calibration matrix is ​​then calculated based on these different formulas.

[0044] The position of the center Oi of each sensor in the cylindrical coordinate system is defined by the radius R and angle βi corresponding to the distance OOi. Each sensor has its own direct reference coordinate system (Oi, xi, yi, zi), and its x-axis is collinear with the line (OOi).

[0045] The torque transmission from each sensor to the origin in the reference coordinate system of the force gauge is given by the following formula:

[0046] [Mathematical Formula 2]

[0047]

[0048] The changes in each reference coordinate system are shown below:

[0049] [Mathematical Formula 3]

[0050]

[0051] [Mathematical Formula 4]

[0052]

[0053] [Mathematical Formula 5]

[0054]

[0055] After simplification, the expressions for the torques of each sensor at the origin and in the reference coordinate system of the force gauge can be written as:

[0056] [Mathematical Formula 6]

[0057]

[0058] This calibration matrix is ​​theoretical. It represents the contribution of each axis of the sensor to the force measurement of the force gauge. These measurements depend on the sensitivity K of the piezoelectric sensor used. In practice, despite careful attention to the manufacturing process, geometric imperfections can occur in any manufacturing process, so no element in the matrix is ​​zero. However, the dominant elements must be identifiable.

[0059] Once the theoretical calibration matrix is ​​written, calibration can be performed. This calibration involves correlating the control unit load applied to the force gauge with the various electrical signals transmitted by the triaxial sensors.

[0060] It is useful to apply the identified load at key points where the theoretical response of the force gauge is known. Through linear optimization, the sensor values ​​can be correlated with the expected values. The calibration matrix is ​​determined through testing activities.

[0061] The result of linear optimization can give the following practical calibration matrix:

[0062] [Mathematical Formula 7]

[0063]

[0064] Figure 2 A second embodiment of the invention is shown, wherein the method envisions positioning a force gauge with a coupling plate.

[0065] More specifically, the force gauge includes at least three, preferably six, coupled strain gauge bridges, which are mounted on the arm of the pressure foot P' and distributed around the longitudinal axis Z of the blade L, thereby forming at least three, preferably six, full bridges.

[0066] To ensure accurate force readings, the force gauges are distributed around the axis of the blade and spaced 120° apart. The three strain gauges J1 to J3 forming the six strain gauge bridge are glued together. Preferably, the three strain gauges are located on the inclined surface and are equidistant from the axis of the blade, and their extensions intersect at the point of force application.

[0067] Longitudinal / transverse dual strain gauges J1 to J3 are used and arranged on each face of each arm, so that each half-bridge is opposite. This force gauge requires at least three full bridges in total.

[0068] Calibration involves matching the known applied torque with the strain values ​​measured by the strain gauge bridge.

[0069] Assuming the strain gauge bridges are ideally concentrated on the arms of the test body, the respective centers Oi (i = i:6) of the bridges on each arm coincide. They are then moved away from the sensor's center O by a value r and oriented at an angle α. Finally, the point of force application on the blades is moved -h along the Z-axis to point Q.

[0070] The following known torque [T] is applied at point Q:

[0071] [Mathematical Formula 8]

[0072]

[0073] The shift of this torque [T] at each measuring point of the strain gauge bridge allows us to know the contribution of each axis of the bridge to the force reading.

[0074] To measure the torque Mz, a force is applied along the Y-axis at point Q using a lever arm with a distance l.

[0075] For clarity, the grouped reference coordinate systems are renamed as follows:

[0076] [Mathematical Formula 9]

[0077] (O1_O2, X1_X2, Y1_Y2, Z1_Z2) = R1

[0078] (O3_O4, X3_X4, Y3_Y4, Z3_Z4) = R2

[0079] (O5_O6, X5_X6, Y5_Y6, Z5_Z6) = R3

[0080] These transmissions are then given:

[0081] [Mathematical Formula 10]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] These values ​​give the components of the theoretical calibration matrix. Considering that the strain gauge only responds along its Z-axis, the matrix can be simplified. It can then be written as:

[0089] [Mathematical Formula 11]

[0090]

[0091] Where K represents the sensitivity of each strain gauge bridge (assuming universality here), and Fi represents the strain value measured by strain gauge bridge i.

[0092] The next step in establishing the actual calibration matrix involves applying a known force along a well-defined axis and recording the response of each half-bridge.

[0093] This calibration method provides a large amount of optimized data. Assuming the signal-load relationship is linear, a direct method based on least squares is applied.

[0094] This method aims to minimize the least-squares difference between the applied and measured values ​​based on a linear response model. To this end, we attempt to use n different torques [T] transmitted. j [m] n measurements i ] to represent the calibration matrix [A i，j The formula can be written in the following form:

[0095] [Mathematical Formula 12]

[0096] [T j ] = [Aij ]×[m i ]

[0097] The following format allows for the use of linear optimization methods to solve the matrix [A]. t Item a ij The calculation yields the same solution as the normal equation in the aforementioned formula.

[0098] [Mathematical Formula 13]

[0099] [T j ] t =[m i ] t ×[A ij ] t ,

[0100] [m i ]×[m i ] t ×[A ij ] t =[m i ]×[T j ] t ,

[0101] [A ij ] t =[[m i ]×[m i ] t ] -1 ×[m i ]×[T j ] t .

[0102] For illustration, the matrix for each sensor is given by the following formula:

[0103] [Mathematical Formula 14]

[0104]

[0105]

[0106]

[0107] Due to inherent deviations in the strain gauge fabrication and bonding processes, the sensors are all different from each other, making it impossible to obtain identical matrices. However, each sensor responds well to each matrix. A matrix that smooths the behavior of each sensor can be obtained. This matrix, which takes into account all calibrated measurements from the three sensors, is called the merge matrix (see example below).

[0108] [Mathematical Formula 15]

[0109]

[0110] The results showed that the three sensors responded very closely to the matrix, and the measurement deviation was very small.

[0111] Figure 3 A third embodiment of the invention is shown, wherein the method envisions positioning a force gauge with a decoupling plate.

[0112] like Figure 3 As shown, the force gauge comprises five strain gauges mounted as a full-bridge bridge in the pressure foot P”. The strain gauges used are half-bridge strain gauges to ensure force readings in both possible bending directions (for clarity, Figure 3 Only five strain gauge bridges, P1 to P5, are shown in the image.

[0113] The actual calibration matrix is ​​obtained by measuring the strain at the strain gauge locations and calculating related to the bridging line. For example, the results are shown in Table 1 below:

[0114] [Table 1]

[0115] Fx(%) Fy(%) Mx(%) My(%) Mz(%) Bridge 1 - 0.03 0.27 5.61 0.2 Bridge 2 1.53 - 0.36 0.85 0.28 Bridge 3 0 4.48 - 0.15 0.03 Bridge 4 2.49 0.12 0.15 - 2.26 Bridge 5 0.08 4.52 0.02 1.5 -

[0116] The results show that during the application of torque My, the maximum coupling obtained by bridge 1 is 5.61% strain.

[0117] The results also show that this embodiment does not require the prior step of establishing a theoretical calibration matrix.

[0118] It is worth noting that, regardless of the embodiment, the transmission of the strain sensor's measured values ​​is performed in a contactless or wired manner.

[0119] It is also worth noting that, regardless of the embodiment, a set of electronic cards is provided between the piezoelectric sensor or strain gauge bridge and the computer station utilizing the received information. These electronic cards perform the following functions: providing and regulating signals from the sensors (depending on the type of sensors), filtering and amplifying signals suitable for the input range of the analog-to-digital converter, and serializing and transmitting data to the computer station.

Claims

1. A method for determining the mechanical torque component at a guide point of a cutting blade (L) for a cutting machine, the blade being guided into the pressure foot (P; P'; P'') of the cutting head of the cutting machine, the method comprising: A five-component force gauge is positioned on the presser foot. The five-component force gauge includes multiple sensors capable of determining the frontal force, lateral force, roll torque, pitch torque, and yaw torque of the cutting blade. Establish the calibration matrix of the force gauge; as well as Based on the measurements obtained by the sensor and the calibration matrix, the force exerted on the cutting blade in three dimensions is determined.

2. The method according to claim 1, wherein, The step of establishing the calibration matrix of the force gauge includes: establishing the theoretical calibration matrix of the force gauge sensor under various theoretical strains, as a function of the six components of the force gauge.

3. The method according to claim 2, wherein, The step of establishing the calibration matrix of the force gauge further includes: based on the theoretical calibration matrix of the sensor of the force gauge and the actual response measurement value, calculating the response matrix of the sensor of the force gauge under various actual strains, as a function of the six components of the force gauge.

4. The method according to claim 3, wherein, The response matrix of the sensor in the force gauge is calculated using a linear optimization method.

5. The method according to any one of claims 1 to 4, wherein, The force gauge includes three triaxial piezoelectric sensors (1, 2, 3) mounted in the presser foot (P) and distributed around the longitudinal axis (Z) of the cutting blade.

6. The method according to any one of claims 1 to 4, wherein, The force gauge includes at least three coupled strain gauge bridges (J1, J2, J3) mounted on the arm of the pressure foot (P') and regularly distributed around the longitudinal axis (Z) of the cutting blade to form at least three full bridges.

7. The method according to claim 6, wherein, The force gauge includes six strain gauge bridges regularly distributed around the longitudinal axis (Z) of the cutting blade to form six full bridges.

8. The method according to any one of claims 1 to 4, wherein, The force gauge includes at least five decoupled strain gauge bridges (P1, P2, P3, P4, P5) mounted on the pressure foot (P'').

9. The method according to any one of claims 1 to 4, wherein, The transmission of the measured values ​​of the sensor in the force gauge is performed in a contactless or wired manner.

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