Method for calibrating finishing shaft of machine tool

Abstract

The invention relates to a method for calibrating a dressing shaft of a machine tool having a main shaft and a dressing shaft, a grinding tool that can be mounted on the main shaft and a dressing tool that can be mounted on the dressing shaft being movable relative to each other for dressing the grinding tool by means of the dressing tool. The method includes the steps of: providing a test mandrel having a body and a seat; mounting the test mandrel on the trimming shaft so that the axial axis of the main body is parallel to the rotation axis of the trimming shaft; measuring a plurality of positions on the body; determining, by the processing unit, a tilt angle of the rotation axis of the trimming shaft based on the measured plurality of positions; the calibration ball with the clamp is installed on the finishing shaft; a contact probe is installed on the main shaft; measuring a plurality of positions on the jig; the processing unit determines the center position of the calibration balls according to the positions of the calibration balls; and determining, by the processing unit, a reference point position of the dressing shaft based on the center position of the calibration ball, the tilt angle of the rotation axis of the dressing shaft, and the size of the calibration ball.

Description

Technical Field

[0001] The invention relates to a method for calibrating a dressing axis of a machine tool. Background Art

[0002] A grinding machine is a machine tool used for grinding. This process is usually applied to machine workpieces to achieve high surface quality and high shape accuracy. The machine tool used for grinding includes a machine bed for holding the workpiece and a spindle for receiving a grinding tool therein. The grinding tool is an essential element for shaping the workpiece by removing material from the workpiece. Since the material of the workpiece is removed by wear, the grinding tool must be regularly dressed to restore its original shape. Therefore, a dressing wheel is arranged in a grinding machine close to the spindle for reshaping the grinding tool. Correct dressing has a direct impact on the quality of the machined parts.

[0003] For all machine tools, the kinematic calibration of the dressing wheel is crucial. The position of the dressing wheel must be accurately determined. Sometimes, the dressing wheel is not arranged vertically in the machine tool. For example, in the machine tool Mikron Mill S, the axis of rotation of the dressing wheel has an inclination with respect to the vertical. Figure 3a and Figure 3b As shown in , the grinding tool must be dressed laterally to meet the diameter specifications and dressed from the bottom to reshape the front face of the grinding tool. If the dressing spindle is mounted without tilting relative to the Z axis, it is difficult to reliably reshape the front surface of the grinding tool. For this reason, the dressing spindle is mounted at an angle relative to the Z axis. Therefore, there is an angle between the axis of rotation of the dressing wheel and the vertical direction. This angle is usually in the range of 5 to 20 degrees. The angular orientation of the dressing wheel makes it difficult to accurately measure its position by standard calibration procedures. Summary of the invention

[0004] An object of the present invention is to provide a method for calibrating a dressing axis of a machine tool with improved calibration accuracy.A further object of the present invention is to provide a method for calibrating a dressing axis of a machine tool with simple instrumentation.

[0005] According to the invention, these objects are achieved by the features of the independent claims.In addition, further advantageous embodiments can be derived from the dependent claims and the description.

[0006] In the present invention, a method for calibrating a dressing spindle of a machine tool is provided. The machine tool includes a spindle arranged in a machine head and a dressing spindle arranged in a machining area, wherein a grinding tool is mounted on the spindle, and a dressing tool is mounted on the dressing spindle. The grinding tool and the dressing tool are movable relative to each other for dressing the grinding tool by the dressing tool. The method includes the following steps: providing a test spindle having an elongated body and a seat; mounting the test spindle on the dressing spindle by connecting the seat to the dressing spindle so that the axial axis of the body is parallel to the rotation axis of the dressing spindle; measuring multiple positions on the body by bringing a measuring device into contact with the body of the test spindle at multiple positions; determining, by a processing unit, an inclination angle of the rotation axis of the dressing spindle based on the measured multiple positions on the test spindle, wherein the inclination angle is the angle of the rotation axis of the dressing spindle relative to the vertical direction; mounting a contact probe on the spindle; placing a measuring device having a contact probe on the spindle; A connection portion and a calibration sphere of a fixture on top of the connection portion are mounted on the trimming shaft, wherein the calibration sphere is concentrically arranged on the trimming shaft; a plurality of positions on the fixture are measured by bringing a contact probe into contact with the fixture at a plurality of positions; a center position of the calibration sphere is determined by a processing unit based on the measured plurality of calibration sphere positions; and a position of a reference point of the trimming shaft is determined based on the determined center position of the calibration sphere, the inclination angle of the rotation axis of the trimming shaft, and the size of the calibration sphere, wherein the reference point is located at a center position on a reference surface of the trimming shaft.

[0007] The machine tool may be a machine tool for grinding or for milling and grinding. It comprises a machine table, a spindle and a dressing axis. The workpiece may be mounted on a workpiece table arranged on the machine table. The spindle is mounted on a head of the machine tool. A grinding tool may be mounted on the spindle for grinding the workpiece. The machine tool comprises at least three linear axes (X, Y, Z) by which the spindle and the machine table can be moved relative to each other. In particular, the machine tool comprises three linear axes and at least two rotational axes.

[0008] The dressing spindle is also integrated in the machine tool, so that dressing can be performed directly in the same machine tool without the need to install and disassemble the grinding tool to improve machining adequacy. The dressing tool can be mounted on the dressing spindle. When the grinding tool must be dressed, the grinding tool and the dressing tool can be moved relative to each other to position the grinding tool to the desired position near the dressing tool for dressing. During dressing, both the spindle and the dressing spindle rotate in opposite directions or in the same direction, and the grinding tool is in contact with the dressing tool to be dressed.

[0009] Depending on the kinematics of the machine tool, the dressing axis has one or more linear axes. For example, the spindle can move together with the machine head in the Y direction and the Z direction. The machine table can move in the X direction. The dressing axis is mounted on the machine table, in particular, on the side of the machine table and can also move in the X direction.

[0010] In order to be able to properly dress a grinding tool, the axis of rotation of the dressing tool must be slightly tilted compared to the axis of rotation of the spindle holding the grinding tool. Typically, the tilt angle is less than 20 degrees.

[0011] In order to ensure the accurate final geometry of the grinding tool produced by the dressing process, the position and orientation of the axis of rotation of the dressing axis must be accurately determined. The determined position can be specified in the kinematic model of the machine tool. In addition, after the position of the dressing axis is disturbed (for example, replacing the dressing axis), or after the transportation of the machine, geometric control is required. This means that the exact position and inclination angle of the dressing axis must be measured. In order to perform such measurements, a contact probe applied to standard calibration can be used. However, due to the inclination angle of the axis of rotation of the dressing axis, detection directly on the dressing tool is usually not accurate enough. In addition, only a small contact surface on the dressing tool can be used for measurement by a contact probe. This also leads to measurement errors. The present invention provides a solution by replacing the dressing tool with a dedicated test spindle and following a specific calibration procedure to accurately calibrate the dressing axis. A reference point is defined on the dressing axis. The goal is to accurately determine the position of the reference point. In addition, the calibration procedure should be simple because complex calibration procedures are time-consuming.

[0012] In a first step, the inclination angle of the dressing spindle has to be determined. A test spindle with an elongated body and a seat is used. The seat is designed to be able to be easily and accurately mounted on the dressing spindle. The test spindle is designed and manufactured in such a way that, in the mounted state, its axial axis is parallel to the axis of rotation of the dressing spindle. Therefore, if the inclination angle of the body can be determined, the inclination angle of the dressing spindle can be simply derived. A measuring device is mounted on the spindle and moved close to the dressing spindle. At least two positions, in particular two positions with different vertical positions on the body, are measured by the measuring device. The inclination angle of the body can be determined by applying trigonometry.

[0013] The measuring device can be a touch probe or a dial indicator. The touch probe is a preferred variant because the measurement can be performed automatically. When applying a touch probe, an automatic procedure can be programmed. The control unit controls the spindle to move the touch probe to several defined positions of the machine tool, and the measured positions are automatically stored in the control unit of the machine tool. Therefore, the processing unit can be the control unit of the machine tool.

[0014] In a further step, the center position of the calibration sphere is determined. Therefore, the test spindle is replaced by the calibration sphere. The touch probe is controlled by the control unit of the machine tool to touch a plurality of positions for calculation. The positions of the calibration sphere are measured by the touch probe in a defined measurement sequence. The different positions of the calibration sphere are generated by activating a spindle movement to position the touch probe to defined positions. From the measured calibration positions, the center position of the calibration sphere can be determined.

[0015] The determined tilt angle and the center point of the calibration sphere are then entered into a processing unit, in particular the control unit of the machine tool. In addition, in order to calculate the position of the reference point, the diameter of the fixture and the height of the calibration sphere are required, so these two parameters are also entered into the control unit of the machine tool. The height of the calibration sphere provides the distance between the reference point and the center point of the calibration sphere.

[0016] In a preferred variant, the processing unit is a control unit of the machine tool. Alternatively, the processing unit is arranged independently of the control unit of the machine tool. The processing unit may be integrated in the machine tool or external to the machine tool. The processing unit may communicate with the control unit of the machine tool.

[0017] The method of the invention can improve the accuracy in determining the position of the axis of rotation of the dressing tool. This again enables a more accurate dressing of the grinding tool.

[0018] In some variations, three-dimensional coordinates are measured at all measurement locations.

[0019] In particular, the positions of the determined reference points are added to the kinematic compensation model, in particular the determined reference positions are automatically fed into the kinematic compensation model. Preferably, the kinematic compensation model is generated for calibration of the entire machine tool.

[0020] To further improve the measurement accuracy, a calibration sphere is first applied to determine the main center position of the sphere before determining the tilt angle of the dressing spindle. Therefore, before the test spindle is mounted on the dressing spindle, the calibration sphere is mounted on the dressing spindle and the touch probe measures a plurality of positions for calculating the main center position of the sphere. This allows a rough position to be obtained for the angle measurement by the test spindle. In this variant, the calibration sphere is applied twice, before and after applying the test spindle.

[0021] The core of the invention is to measure the reference point of the sphere as accurately as possible and to measure the angle using the test spindle as accurately as possible. Using these two values ​​and the known values ​​associated with the calibration sphere, the reference position of the dressing wheel can be calculated.

[0022] The present invention relates to a method for grinding a workpiece by a machine tool, the machine tool having a spindle arranged in a machine head and a dressing spindle arranged in a machining area. A grinding tool can be mounted on the spindle for grinding a workpiece mounted on a machine table. A dressing tool can be mounted on the dressing spindle, and the grinding tool and the dressing tool can be moved relative to each other for dressing the grinding tool by the dressing tool. The rotation axis of the dressing spindle has an inclination Tα relative to the vertical direction, comprising the following steps: calibrating the dressing spindle according to the calibration method of the present invention; dressing the grinding tool by the dressing tool; and grinding the workpiece by the dressed grinding tool.

[0023] The invention relates to a machine tool for grinding a workpiece, the machine tool comprising a spindle arranged in a machine head and a dressing spindle arranged in a machining area. A grinding tool can be mounted on the spindle for grinding a workpiece mounted on a machine table. A dressing tool can be mounted on the dressing spindle, and the grinding tool and the dressing tool can be moved relative to each other for dressing the grinding tool by the dressing tool, wherein the axis of rotation of the dressing spindle has an inclination Tα relative to the vertical direction.

[0024] In particular, the machine tool comprises a calibration sphere and a test spindle which can be mounted on a dressing spindle for calibrating the dressing spindle. The calibration sphere comprises a connecting portion and a clamp on top of the connecting portion, wherein the test spindle comprises a seat and an elongated body formed on top of the seat. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the following, a more specific description of the present invention is further described. Embodiments are described and explained in detail with reference to the accompanying drawings, in which: Figure 1 A side view of a machine tool having a main spindle and a dressing spindle is shown; Figure 2 A side view of the machined area with the dressing spindle mounted is shown; Figure 3a schematically illustrates dressing the side surface of a grinding tool; Figure 3b schematically illustrating dressing the bottom surface of a grinding tool; Figure 4 A schematic diagram of a trimming shaft is shown; Figure 5 schematically illustrates a test mandrel having an elongated body and a seat mounted on a dressing shaft; Figure 6 Illustration of the trigonometry used to calculate the angle of inclination; Figure 7 schematically illustrates a calibration sphere mounted on a dressing shaft, the calibration sphere having a clamp and a support element; and Figure 8 The steps of the method of the present invention are illustrated schematically. DETAILED DESCRIPTION

[0026] Figure 1 The illustration applies to grinding machines. In particular, Figure 1 A machine tool for milling and grinding is shown. The machine tool 1 has three linear axes X, Y and Z and two rotation axes B and C. The machine tool comprises a machine table 2 which is linearly movable along the axis X. The linear movements along the Y axis and the Z axis are performed by a machine head 4. A support 3 is mounted on the machine table and is rotatable about an axis of rotation B. The support comprises a workpiece table 6 for mounting a workpiece thereon and which is rotatable about a second axis of rotation C. A spindle 5 is mounted in the machine head for clamping different machining tools therein, such as a grinding tool. A dressing spindle 10 is fixedly mounted on the machine table so that it cannot be moved together with the workpiece table.

[0027] Figure 2 Show Figure 1 The arrangement of the dressing axis as depicted in FIG. The fixture 11 is mounted on the side surface of the machine table. The dressing axis is mounted on the top surface of the fixture. On the top of the dressing axis, a dressing tool 12 can be mounted for dressing the grinding tool. Figure 2 As shown in FIG. 1 , the rotation axis of the trimming shaft 14 is not parallel to the Z direction but has an inclination angle Tα. The reason for the inclination is Figure 3a and Figure 3b Shown in.

[0028] In order to reshape the grinding tool, not only the side surfaces 7a of the grinding tool but also the front surface 7b of the grinding tool must be dressed. Figure 3a The state in which the side surface of the grinding tool is dressed is schematically shown. Figure 3b The state of dressing the front surface of the grinding tool is schematically shown. For dressing, the grinding tool is mounted on the spindle and moved close to the dressing tool to be contacted by the dressing tool. The dressing tool is fixedly mounted on the dressing spindle, but rotates during dressing. It can be clearly seen that the dressing spindle must have an inclination angle so that the dressing tool can also reach the bottom surface.

[0029] Figure 4A schematic diagram of a dressing axis 10 is shown, which includes a dressing axis body 13 and a tool interface 14. The tool interface serves as an interface to clamp a dressing tool thereon and is located on the top surface of the dressing axis body. The connecting surface of the axis body 13 and the tool interface is defined as a reference surface FR. The center point of the reference surface is defined as a reference point R. The goal of the calibration is to accurately determine the coordinates of the position and the inclination angle of the dressing axis. The determined values ​​can be stored in the control unit of the machine tool for calculating the movement of the spindle for dressing. A standard touch probe can only detect in the XY working plane and on the Z axis. Due to the inclination of the dressing axis, it is impossible to determine the position of the reference point by a standard touch probe.

[0030] In order to determine the inclination angle Tα of the dressing spindle, the grinding tool mounted on the spindle is replaced by a touch probe 40 and the dressing tool is replaced by a test spindle 30. Figure 5 As shown in , the test spindle comprises a seat 32 for clamping it on the dressing shaft and an elongated body 31 on the seat. The seat has a cylindrical body and a clamping interface is provided in its inner side for precise mounting on the dressing shaft. The clamping interface is designed so that it can be coupled with the tool interface of the shaft in a simple manner. In particular, in the mounted state, the center axis of the test spindle coincides with the axis of rotation of the dressing shaft. The contact probe is controlled by the control unit of the machine tool to contact different positions on the body and determine the inclination angle based on the measured positions.

[0031] like Figure 5 As shown in FIG. 1 , the touch probe is positioned close to the body and is controlled by the control unit to contact points Q1 and Q2 on, for example, the side surface of the body. The coordinates Q1 (x Q1 ,y Q1 ,z Q1 ) and Q2(x Q2 ,y Q2 ,z Q2 ) is input into the control unit, and the inclination angle Tα of the spindle can be calculated.

[0032] like Figure 6 As shown in , trigonometry must be applied to calculate the tilt angle Tα. The length a is the distance of the measurement position in the Z direction, i.e. z Q1 and z Q2 The length b is the distance of the measurement position in the y direction, that is, y Q1 and Q2 The difference between two values ​​of .

[0033] In a further step, a calibration sphere is applied. The test spindle is replaced by a calibration sphere, which comprises a connecting part 22 for clamping it on the dressing spindle and a clamp 21 formed on top of the connecting part. The connecting part has a cylindrical body and is provided with a clamping interface for precise mounting on the dressing spindle. In particular, the center axis of the calibration sphere coincides with the axis of rotation of the dressing spindle. The touch probe is controlled by the control unit of the machine tool to touch different positions on the clamp and determine the center position of the clamp based on the measured positions, i.e. Figure 7 The coordinates of the point P shown in . The distance A is known from the manufacture of the calibration sphere. The diameter B of the fixture is also known from the manufacturing data. Since the coordinates of the center point P of the fixture are determined, the coordinates of the reference point R can be determined by applying trigonometry.

[0034] Figure 8 The sequence of the method of the present invention is shown. In step S1, a contact probe is mounted on a spindle. In step S2, a test spindle is used to replace the dressing spindle. In step S3, the inclination angle of the axis of rotation of the dressing spindle is determined by contacting the contact probe with the spindle at multiple positions on the spindle. In step S4, a calibration sphere is used to replace the test spindle. In step S5, multiple positions on the calibration sphere are measured by contacting the contact probe with the calibration sphere at multiple positions, and the measured positions are recorded. In step S6, the center position of the calibration sphere is determined by the processing unit based on the multiple calibration sphere positions. In step S7, the center position of the dressing spindle is determined based on the determined center position of the calibration sphere, the inclination angle of the axis of rotation of the dressing spindle, and the size of the contact probe.

[0035] Reference numerals list 1Machine Tools 2Machine tool table 3 Bracket 4 Head 5 spindles 6 workpiece table 7 Grinding tools 7a Grinding tool side surface 7b Grinding the front surface of the tool 8 Dressing tools 10 Dressing axis 11 Fixer 13. Dressing the shaft body 14 Tool Interface 20 calibration spheres 21 Clamp 22Connection 30 test mandrel 31 Main body of the test mandrel 32 seats 40 contact probes.

Claims

1. A method for calibrating a dressing axis (10) of a machine tool (1), the machine tool (1) having a spindle (4) arranged in a machine head and the dressing axis (10) arranged in a machining area, wherein: A grinding tool can be mounted on the spindle, and a dressing tool can be mounted on the dressing spindle, and the grinding tool and the dressing tool can be moved relative to each other for dressing the grinding tool by the dressing tool, the method comprising: a. Providing a test mandrel (30) having an elongated body (31) and a seat (32); b. by connecting the seat portion with the dressing shaft, mounting the test spindle on the dressing shaft so that the axial axis of the body is parallel to the axis of rotation of the dressing shaft; c. measuring the plurality of locations on the body by contacting the measuring device with the body of the test mandrel at a plurality of locations; d. determining, by a processing unit, an inclination angle of the rotation axis of the dressing shaft based on the plurality of measured positions on the test spindle, wherein the inclination angle is an angle of the rotation axis of the dressing shaft relative to a vertical direction; e. mounting a calibration sphere (20) having a connection portion (22) and a fixture (21) on top of the connection portion on the trimming shaft, wherein the calibration sphere is concentrically arranged on the trimming shaft; f. The contact probe (40) is mounted on the spindle; g. measuring the plurality of positions on the fixture by contacting the contact probe with the fixture at a plurality of positions; h. determining the center position (P) of the calibration sphere according to the measured positions of the plurality of calibration spheres by the processing unit; and i. determining, by the processing unit, a position of a reference point (R) of the dressing axis based on the determined center position of the calibration sphere, the inclination angle of the rotation axis of the dressing axis and the size of the calibration sphere, wherein the reference point is located at the center position on the reference surface (FR) of the dressing axis.

2. The method according to claim 1, wherein: The measuring device is a contact probe or a dial indicator.

3. The method according to claim 1 or 2, wherein: The three-dimensional coordinates are measured at all measurement positions.

4. The method according to any one of claims 1 to 3, wherein: The determined position of the reference point is added to a kinematic compensation model, in particular the determined reference position is automatically fed into the kinematic compensation model.

5. The method according to any one of claims 1 to 4, wherein: The touch probe is controlled by a control unit of the machine tool to perform the measurement.

6. The method according to any one of claims 1 to 5, wherein: The touch probe is calibrated prior to taking the measurement.

7. The method according to any one of claims 1 to 6, wherein: Before mounting the test spindle on the dressing spindle to determine the inclination angle of the dressing spindle, the calibration sphere is first used to determine the principal center position.

8. The method according to any one of claims 1 to 7, wherein: The height of the calibration sphere is taken into account for determining the reference point of the dressing axis.

9. A method for grinding a workpiece by means of a machine tool, the machine tool having a spindle (4) arranged in a machine head and a dressing spindle (10) arranged in a machining area, wherein: A grinding tool can be mounted on the spindle for grinding the workpiece mounted on a machine tool table, wherein a dressing tool can be mounted on the dressing spindle, and the grinding tool and the dressing tool can be moved relative to each other for dressing the grinding tool by the dressing tool, wherein the rotation axis of the dressing spindle has an inclination Tα relative to the vertical direction, and the method comprises: a. Calibration of the dressing axis according to any one of claims 1 to 8; b. Dressing the grinding tool by the dressing tool; and c. Grinding the workpiece by means of the dressed grinding tool.

10. A machine tool (1) for grinding a workpiece, comprising a spindle (4) arranged in a machine head and a dressing spindle (10) arranged in a machining area, wherein: A grinding tool can be mounted on the spindle for grinding the workpiece mounted on the machine tool table, wherein a dressing tool can be mounted on the dressing spindle, and the grinding tool and the dressing tool can be moved relative to each other for dressing the grinding tool by the dressing tool, wherein the rotation axis of the dressing spindle has an inclination Tα relative to the vertical direction.

11. The machine tool according to claim 10, wherein: A control unit is arranged in the machine tool and is adapted to perform the steps according to claim 1 .

12. The machine tool according to claim 10 or 11, wherein: The machine tool comprises a calibration sphere and a test spindle, which can be mounted on the dressing spindle for calibrating The dressing shaft according to claim 1, wherein The calibration sphere comprises a connecting portion (22) and a clamp (21) on top of the connecting portion, wherein the test spindle (30) comprises a seat (32) and an elongated body (31) formed on top of the seat.

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