Methods to reduce residual imbalance in machining spindles

Abstract

To reduce spindle imbalance in numerically controlled machine tools. [Solution] During the data acquisition stage, in two measurement operations, the spindle (10) and the tool (20) are positioned at different angles to each other, and in each measurement operation, the vibration experienced by the spindle as it rotates is measured and values ​​V0,...,V0 representing the intensity are obtained. n It is recorded in the database as V0,...,V n These represent the angle values ​​θ0,...,θ, which are the angles formed between the spindle and the tool during measurement. n A data acquisition stage associated with the above, and a target angular position determination stage in which the target angular position of the spindle relative to the tool is determined from a database constructed by measurement, wherein the target angular position is the minimum V0,...,V n Angular values ​​θ0,...,θ associated with the value n The corresponding target angle value θ x A target angle position determination step having a target angle value θ x The process includes a positioning step of arranging the spindle and the tool to form a shape.

Description

[Technical Field]

[0001] This invention relates to the field of machine tools, and more particularly to the field of numerically controlled machine tools.

[0002] More specifically, the present invention relates to a method for reducing residual unbalance in a machining spindle. [Background technology]

[0003] In particular, spindles are used in numerically controlled machine tools (NCMTs) to process parts, especially through milling. A spindle is a shaft that rotates relative to the frame using bearings, and is configured to house a tool holder to which the tool is fixed. When the spindle rotates, it transmits rotational motion to the tool, and the part is machined.

[0004] Machining and forming a complete part typically requires multiple tools with different shapes and / or dimensional configurations. Therefore, numerically controlled machine tools can be equipped with a tool magazine that stores all the tools and tool holders necessary to produce the complete part. Tools are retrieved from the tool magazine and mounted on the spindle by a manipulator arm. This manipulator arm can also remove tools from the spindle and place them back into the tool magazine.

[0005] In practice, tools are manually attached to the tool holder by an operator located outside the machine, such as on a workbench. Once the tool is secured in the tool holder, the operator manually inserts the tool holder into a groove in the tool magazine on the numerically controlled machine tool. These manual operations performed by the operator can introduce imbalances into the assembly, which can result in an imbalance in the spindle during rotation.

[0006] Furthermore, the assembly of the spindle components and bearings can introduce uncertainty regarding the rotational balance of the tool, tool holder, and spindle assembly. These bearings allow the spindle to be mounted to the frame of the numerically controlled machine tool. Similarly, the balance between the tool and tool holder may be disrupted.

[0007] Furthermore, using tools with asymmetrical shapes is particularly difficult due to their design. This is because the asymmetry of these tools causes the center of inertia to be off the axis of rotation, resulting in an imbalance.

[0008] In summary, there are many factors that cause imbalance during spindle rotation, which effectively leads to a systematic residual imbalance. [Overview of the project] [Problems that the invention aims to solve]

[0009] This invention provides a method for reducing spindle imbalance in numerically controlled machine tools. [Means for solving the problem]

[0010] For this purpose, the present invention relates to a method for reducing residual unbalance of a spindle in a numerically controlled machine tool, wherein the spindle is configured to hold a tool fixed to the spindle by a tool holder. In this document, the assembly formed by the tool and the tool holder is also referred to using the general term "tool," as long as the tool and the tool holder maintain their relative positions without being disassembled throughout the use of the method according to the present invention.

[0011] The method according to the present invention includes a data acquisition stage in which at least two measurement operations are performed. In each of the measurement operations, the spindle and the tool are arranged at different angles to each other. Also, in each of the measurement operations, the spindle rotates at a speed greater than, for example, 10 krpm, and the vibration experienced by the spindle is measured and represented by values V0,...,V n are recorded in a database. The values V0,...,V n are respectively associated with angle values θ0,...,θ n representing the angles formed by the spindle and the tool during measurement.

[0012] This method further includes a target angle position determination stage for determining a target angular position of the spindle with respect to the tool from the database constructed by the measurement. The target angular position has a target angle value θ n corresponding to the angle values θ0,...,θ n associated with the minimum values of V0,...,V x .

[0013] Also, it includes an arrangement stage for arranging the spindle and the tool relative to each other so as to form the target angle value θ x .

[0014] In a particular embodiment, the present invention can further include one or more of the following features, separately or in any technically possible combination.

[0015] In a particular embodiment, in the data acquisition stage, at least three measurement operations are performed, and the spindle and the tool are arranged relative to each other such that the angle values θ0,...,θ n correspond to angles evenly distributed or randomly distributed over a range of 360°, with θ0 = 0° and θ n ≦360°.

[0016] In certain embodiments, the vibrations received by the spindle are measured by an acceleration sensor, and the values of V0, ..., V n each correspond to the displacement, displacement velocity, or acceleration of a point in the tool when the spindle is rotating.

[0017] In certain embodiments, during the data acquisition phase, the spindle is fixed between two consecutive measurements, the tool is removed from the spindle by a manipulator arm, the spindle rotates by an angle corresponding to the difference between two consecutive angular values θ0, ..., θ n and then the tool is engaged with the spindle at the same angular position as when it was removed, according to a reference system linked to the frame of the numerically controlled machine tool.

[0018] In certain embodiments, the data acquisition phase and the determination phase are performed for a plurality of tools, and for each of these tools, an individual target angular value is recorded in memory.

[0019] Other features and advantages of the present invention will become apparent by reading the following detailed description given by way of example with reference to the accompanying drawings.

Brief Description of the Drawings

[0020] [Figure 1] Figs. 1a - 1f schematically show cross-sectional views of a spindle with which a tool is engaged to perform a data acquisition phase in a method for reducing the residual unbalance of a spindle in a numerically controlled machine tool, and for each figure, the spindle and the tool are arranged to form different angles with each other. [Figure 2] A table of the data measured in the data acquisition phase is shown. [Figure 3] A radar chart of the data in the table of Fig. 2 is shown.

Modes for Carrying Out the Invention

[0021] The drawings are not necessarily drawn to scale for the sake of clarity.

[0022] The present invention relates to a method for reducing residual unbalance in a spindle 10 in a numerically controlled machine tool, also referred to hereafter as "NCMT". As is well known, a spindle 10 is configured to hold a tool 20 fixed to the spindle 10 by a tool holder (not shown) for, for example, to perform a machining operation. Such a tool 20 extends along a longitudinal axis and is formed, for example, by a milling cutter. In this document, for the sake of brevity, the assembly formed by the tool 20 and the tool holder will also be simply referred to as the "tool".

[0023] The method according to the present invention includes a plurality of steps, including a first data acquisition step in which at least two measurement operations are performed. In an exemplary embodiment of the present invention shown in the drawings, six measurement operations are performed.

[0024] In each measurement operation, the angles formed by the spindle 10 and the tool 20 relative to each other are different. The origin of this angle of interest lies on the longitudinal axis of the tool 20, and it is clear that this angle lies in a plane perpendicular to this longitudinal axis. That is, as schematically shown in Figures 1a to 1f, a fixed point 21 is provided on the tool 20 and a fixed point 11 is provided on the spindle 10, so that in each measurement operation, the angles formed by the points on the tool 20 and the points on the spindle 10 relative to each other are different.

[0025] In each measurement operation, the spindle 10 rotates at a speed preferably greater than 10krpm, or at a speed of 30krpm or 60krpm, and the vibrations experienced by the spindle 10 are measured and recorded in a database. These vibrations characterize the unbalance of the spindle 10. Specifically, as shown in the table in Figure 2, the vibrations are represented by values ​​V0,...,V0, which represent their intensity. nThese values ​​are recorded as V0,...,V n These are angle values ​​θ0,...,θ, respectively, representing the angle formed between the spindle 10 and the tool 20 during the measurement operation in which the intensity of vibration is recorded. n This is related to the data in Figure 2, which is shown in the radar chart in Figure 3.

[0026] In the method according to the present invention, vibration can be measured using any measuring mechanism capable of evaluating physical quantities, such as an accelerometer, optical sensor, inductive sensor, capacitance sensor, extensometer, or microphone. Preferably, the measurement is performed using an accelerometer during the measurement operation. Therefore, V0,...,V n The values ​​are expressed in mm / s in the table in Figure 2. Alternatively, these V0,...,V n The value can be expressed in any appropriate dimension, such as acceleration (mm / s²) or displacement (mm), depending on the measurement mechanism used.

[0027] In exemplary embodiments of the present invention described herein, the relative angular values ​​θ0,...,θ between the spindle 10 and the tool 20 during two consecutive measurement operations are... n To change the angle, only the spindle 10 is rotated, while the tool 20 remains in a fixed angular position. Specifically, after a measurement operation is completed and before the next measurement operation is started, the tool 20 is removed from the spindle 10 by the manipulator arm in a manner well known to those skilled in the art, and the spindle 10 is rotated by a predetermined angle to prepare the angular values ​​θ0,...,θ for the subsequent measurement operation. n Next, the tool 20 is engaged with the spindle 10 by the manipulator arm in the same orientation as when it was removed, according to a reference system linked to the frame of the numerically controlled machine tool.

[0028] Therefore, the angle values ​​θ0, ..., θ nThis corresponds to a specific angular position of the spindle 10 in a preferred embodiment of the present invention. Alternatively, the tool 20 is rotated only after being removed from the spindle 10, or both the tool 20 and the spindle 10 are rotated so that the tool 20 and the spindle 10 are at angular values ​​θ0,...,θ relative to each other. n It can also be predicted that it will form

[0029] Note that the angle values ​​θ0,...,θ n These steps, i.e., the distance between two selected angular values ​​in two consecutive measurement operations, are predetermined according to the desired level of detail in the vibration measurement. As shown in the table in Figure 2 and the graph in Figure 3, the angular values ​​θ0,...,θ between two consecutive measurement operations are predetermined. n The angle can be 90°, 45°, 22.5°, or any angle from 0° to 360°. The pitch can be the same or different between all the measurements obtained.

[0030] Next, this method includes a target angular position determination step in which the target angular position of the spindle 10 relative to the tool 20 is determined, and this target angular position is the smallest V0,...,V in a database constructed from the acquired measurement results. n Angular values ​​θ0,...,θ associated with the value n The corresponding target angle value θ x It has V0,...,V n The minimum value is identified by comparing the values ​​of the same value, and then the angle values ​​θ0,...,θ associated with the minimum vibration intensity value are determined. n Select this value. This selected angle value is the target value θ. x It represents.

[0031] In the example shown in the table in Figure 2 and the graph in Figure 3, the minimum vibration intensity value was measured in the second measurement, which corresponds to 0.2 mm / s at an angle of 90°. Therefore, the target angular position is 90°. Target angular value θ x This is particularly evident in the graph in Figure 3. Here, the values ​​V0,...,V nThe bolded curves representing the angle have inflection points corresponding to the sections representing 90°.

[0032] This stage is preferably carried out by an IT processing unit in a numerically controlled machine tool. The interaction of such a processing unit, which consists of a microcontroller, a microprocessor, and the various mechanisms in the numerically controlled machine tool, is known to those skilled in the art and will not be described in detail here.

[0033] Then, during the placement stage, the spindle 10 and the tool 20 are positioned at the target angle value θ. x The orientation relative to each other is determined accordingly. Preferably, the manipulator arm removes the tool 20 from the spindle 10, at which point the spindle 10 is set to a target angle value θ. x It is located at the corresponding angular position. Next, the tool 20 is engaged with the spindle 10 by the manipulator arm and becomes available for use in the machining operation.

[0034] Generally, the spindle 10 and the manipulator arm are driven by electric motors controlled by control signals generated by the processing unit, in a manner known to those skilled in the art.

[0035] The method according to the present invention can be carried out by a machining center equipped with a tool magazine, a manipulator arm, and a numerically controlled machine tool.

[0036] In particular, the tool magazine can contain multiple tools, each of which has its own target angle value recorded in memory. Therefore, before mounting a tool on the spindle 10 to perform a specific machining operation, the spindle 10 is positioned at an angular position relative to the tool to be held such that the imbalance of the spindle 10 on which the tool is mounted is minimized.

[0037] In summary, the method according to the present invention applies a target angular value θ to the spindle 10 before the corresponding tool is mounted. xThis must be done as soon as a new tool is added to the tool magazine, so that it is recorded.

[0038] Advantageously, the method according to the present invention does not need to be performed each time the tool is used, provided that the corresponding target angle value is recorded. Nevertheless, to ensure that the vibration level of the spindle 10 always corresponds to a previously measured optimized equilibrium value, the method according to the present invention can be repeated, for example, after a predetermined period of use of the tool 20.

[0039] More generally, the embodiments and uses described above are merely examples and are not limited to them; other variant forms are also possible. [Explanation of symbols]

[0040] 10 spindles 11, 21 fixed point 20 Tools

Claims

1. A method for reducing residual unbalance of a spindle (10) in a numerically controlled machine tool, The spindle (10) is configured to hold a tool (20) that is fixed to the spindle (10) by a tool holder. The aforementioned method, In a data acquisition stage in which at least two measurement operations are performed, the spindle (10) and the tool (20) are positioned at different angles to each other, the spindle (10) rotates, and the vibration experienced by the spindle (10) is measured to obtain a value V representing the intensity. 0 ,...,V n It is recorded in the database as the value V 0 ,...,V n Each of these represents an angle value θ that indicates the angle formed between the spindle (10) and the tool (20) during measurement. 0 ,...,θ n Related to this, the data acquisition stage, A target angular position determining step of determining a target angular position of the spindle (10) with respect to the tool (20) from a database constructed by the measurement, wherein the target angular position is the minimum V 0 ,..., V n The angular value θ associated with the value of 0 ,..., θ n The target angular value θ corresponding to x Having a target angular position determining step, The aforementioned target angle value θ x Arrangement step of positioning the spindle (10) and the tool (20) relative to each other to form A method that includes this.

2. During the data acquisition stage, at least three measurement operations are performed. The spindle (10) and the tool (20) are related by the angle value θ 0 ,...,θ n However, they are positioned relative to each other so as to correspond to angles that are evenly distributed over a 360° range. θ 0 = 0°, θ n ≤ 360° The method according to claim 1.

3. During the data acquisition stage, at least three measurement operations are performed. The spindle (10) and the tool (20) have an angle value θ 0 ,...,θ n However, they are positioned relative to each other so as to correspond to angles that are randomly distributed over a 360° range. θ 0 = 0°, θ n ≤ 360° The method according to claim 1.

4. The vibrations experienced by the spindle (10) are measured by an acceleration sensor. The aforementioned V 0 ,...,V n The values ​​correspond to the displacement, displacement velocity, or acceleration of a point on the tool (20) when the spindle (10) is rotating. The method according to claim 1.

5. During the data acquisition stage, the spindle (10) is fixed between two consecutive measurements. The tool (20) is removed from the spindle (10) by the manipulator arm. The spindle (10) has two consecutive angular values ​​θ 0 ,...,θ n It rotates by the angle corresponding to the difference, Subsequently, the tool (20) is engaged with the spindle (10) at the same angular position as when it was removed, according to a reference system linked to the frame of the numerically controlled machine tool. The method according to claim 1.

6. The data acquisition and determination steps are performed for multiple tools, and for each of these tools, an individual target angle value is recorded in memory. The method according to claim 1.

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