Method for calibrating dressing spindle of machine tool

Abstract

To provide a method for calibrating a dressing spindle of a machine tool with improved calibration accuracy.SOLUTION: In order to determine the inclination angulation Tα of the dressing spindle, the grinding tool mounted on the main spindle is replaced by a touch probe 40 and the dressing tool is replaced by a test mandrel 30 comprising a seat 32 for clamping the test mandrel on the dressing spindle and an elongated body 31 on the seat. The touch probe 40 is positioned near the body 31 of the test mandrel and is controlled by the control unit to contact points Q1, Q2 on the side of the body 31 of the test mandrel. The coordinates of the measured points Q1, Q2, and Q1, Q2 are input into the control unit and the angle of inclination Tα of the test mandrel 30 can be calculated.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for calibrating a dressing spindle of a machine tool. [Background technology]

[0002] A grinding machine is a machine tool used for grinding. The grinding process is usually used to machine a workpiece to achieve high surface quality and high shape accuracy. A machine tool for grinding includes a machine bed for holding the workpiece and a spindle for accommodating the grinding tool inside. The grinding tool is an essential element for shaping the workpiece by removing material from the workpiece. Since the workpiece material is removed by abrasion, the grinding tool must be conditioned periodically to restore its original shape. Therefore, a dressing wheel is placed in the grinding machine near the spindle to reshape the grinding tool. Proper dressing has a direct impact on the quality of the machined part.

[0003] As with all machine tools, the kinematic calibration of the dressing wheel is mandatory. The position of the dressing wheel must be precisely determined. The dressing wheel may not be vertically aligned on the machine tool. For example, on the machine tool "Miron Mill S", the rotation axis of the dressing wheel has an inclination with respect to the vertical. As shown in Figures 3a and 3b, the grinding tool must be dressed laterally to meet the diameter specification and from the bottom to reshape the front face of the grinding tool. If the dressing spindle is mounted without an inclination with respect to the Z axis, it is difficult to reliably reshape the front face of the grinding tool. For this reason, the dressing spindle is mounted at a certain angle with respect to the Z axis. Thus, an angulation occurs between the rotation axis of the dressing wheel and the vertical. This angulation is usually in the range of 5 to 20 degrees. The angular orientation of the dressing wheel makes it difficult to accurately measure the position of the dressing wheel by standard calibration procedures. Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the present invention to provide a method for calibrating a dressing spindle of a machine tool with improved calibration accuracy. It is a further object of the present invention to provide a method for calibrating a dressing spindle of a machine tool with a simple device. [Means for solving the problem]

[0005] According to the invention, these objects are achieved by the features recited in the independent claims, further advantageous embodiments of which emerge from the dependent claims and the description.

[0006] According to the invention, a method for calibrating a dressing spindle of a machine tool is provided, the machine tool having a spindle arranged in the machine head and a dressing spindle arranged in the machining area, 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 in order to dress the grinding tool with the dressing tool. The method includes the steps of providing a test mandrel having an elongated body and a seat; mounting the test mandrel on the dressing spindle by connecting the seat to the dressing spindle such that the axial axis of the body is parallel to the axis of rotation of the dressing spindle; measuring a plurality of positions on the body by contacting the body of the test mandrel with a measuring device at a plurality of positions; and determining, by a processing unit, an inclination angle of the rotation axis of the dressing spindle based on the measured plurality of positions on the test mandrel, the inclination angle being an angulation of the rotation axis of the dressing spindle with respect to a vertical direction; mounting a touch probe on the spindle; and connecting a connection portion and a fixture provided on the top of the connection portion. The method includes the steps of: mounting a calibration sphere having a calibration fixture and a calibration ball on a dressing spindle, the calibration sphere being concentrically disposed on the dressing spindle; measuring a plurality of positions on the fixture by contacting a touch probe with the fixture at a plurality of positions; determining, by a processing unit, a center position of the calibration sphere according to the measured plurality of positions of the calibration sphere; and determining a position of a reference point of the dressing spindle based on the determined center position of the calibration sphere, the inclination angle of the rotation axis of the dressing spindle, and dimensions of the calibration sphere, the reference point being disposed at a center position on a reference surface of the dressing spindle.

[0007] The machine tool may be a machine tool for grinding or milling or grinding. The machine tool has a machine table, a spindle and a dressing spindle. The workpiece may be mounted on the workpiece table, which is arranged on the machine table. The spindle is mounted on a machine head of the machine tool. A grinding tool can be mounted on the spindle for grinding the workpiece. The machine tool has at least three linear axes (X, Y, Z), by means of 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 rotary axes.

[0008] The dressing spindle is also integrated into the machine tool, and thus allows conditioning to be performed directly in the same machine tool without removing and attaching the grinding tool, in order to improve machining efficiency. The dressing tool may be mounted on the dressing spindle. When the grinding tool has to be conditioned, the grinding tool and the dressing tool can be moved relative to each other, so that the grinding tool can be positioned in a required position near the dressing tool for conditioning. During conditioning, the main shaft and the dressing spindle both rotate in opposite or the same direction, and the grinding tool comes into contact with the dressing tool to be conditioned.

[0009] Depending on the kinematics of the machine tool, the dressing spindle has one or several linear axes. For example, the spindle can be moved in the Y and Z directions along the machine head. The machine table can be moved in the X direction. The dressing spindle is mounted on the machine table, in particular on the side of the machine table, and can also be moved in the X direction.

[0010] To allow proper dressing of the grinding tool, the axis of rotation of the dressing tool must be slightly inclined relative to the axis of rotation of the spindle holding the grinding tool. Typically, the angle of inclination is less than 20 degrees.

[0011] To guarantee an accurate final geometry of the grinding tool resulting from the dressing process, the position and orientation of the rotation axis of the dressing spindle must be accurately determined. The determined position can be specified in the kinematic model of the machine tool. Furthermore, after a disturbance in the dressing spindle position, such as for example an exchange of the dressing spindle, or after a transport of the machine, a geometric control is required. This means that the exact position and tilt angle of the dressing spindle must be measured. To measure the exact position and tilt angle, a touch probe used for standard calibration can be used. However, direct probing on the dressing tool is generally not accurate enough due to the tilt angle of the rotation axis of the dressing spindle. In addition, only a small contact surface is available on the dressing tool for measurement by the touch probe. This also results in measurement errors. The present invention provides a solution by replacing the dressing tool with a dedicated test mandrel, for accurately calibrating the dressing spindle according to a specific calibration procedure. A reference point is defined on the dressing spindle. The goal is to accurately determine the position of this reference point. Furthermore, it is desirable for the calibration procedure to be simple, since complex calibration procedures are time consuming.

[0012] In the first step, the inclination angle formation of the dressing spindle must be determined. A test mandrel is used, which has an elongated body and a seat. The seat is designed so that it can be easily and accurately mounted on the dressing spindle. The test mandrel is designed and manufactured so that in the mounted state its axial axis is parallel to the axis of rotation of the dressing spindle. Thus, if the inclination angle formation of the body can be determined, the inclination angle formation of the dressing spindle can be determined simply. A measuring device is mounted on the spindle and moved into the vicinity of 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 formation of the body can be determined by using trigonometry.

[0013] The measuring device may be a touch probe or a dial indicator. A touch probe is the preferred variant since the measurements can be performed automatically. If a touch probe is used, an automatic procedure may be programmed. The control unit controls the spindle such that the touch probe is moved to several defined positions of the machine tool, and the measured positions are automatically stored in the control unit of the machine tool. The processing unit may therefore be the control unit of the machine tool.

[0014] In a further step, the position of the center of the calibration sphere is determined. The test mandrel is therefore replaced by the calibration sphere. The touch probe is controlled by the control unit of the machine tool to contact a number of positions for the calculation. The position of the calibration sphere is measured by the touch probe in a defined measurement sequence. The various positions of the calibration sphere are determined by actuating a spindle movement to position the touch probe at the defined positions. From the measured calibration positions, the position of the center of the calibration sphere can be determined.

[0015] The determined tilt angle formation and the center point of the calibration sphere are then input to a processing unit, in particular the control unit of the machine tool. Furthermore, the diameter of the fixture and the height of the calibration sphere are required to calculate the position of the reference point, and therefore these two parameters are also input to 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 from the control unit of the machine tool. The processing unit can be integrated into the machine tool or can be integrated outside the machine tool. The processing unit can communicate with the control unit of the machine tool.

[0017] The method according to the invention allows for improved accuracy in determining the position of the rotation axis of the dressing tool, which also allows for more accurate dressing of the grinding tool.

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

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

[0020] To further improve the measurement accuracy, a calibration sphere is first used to determine the initial center position of the sphere before determining the tilt angle formation of the dressing spindle. Therefore, before the test mandrel is mounted on the dressing spindle, a calibration sphere is mounted on the dressing spindle and a touch probe measures multiple positions to calculate the initial center position of the sphere. This provides a rough position for the angle measurement with the test mandrel. In this variant, the calibration sphere is used twice, before and after the use of the test mandrel.

[0021] The gist of the invention is to measure the reference point on the sphere as accurately as possible and then measure the angle using the test mandrel as accurately as possible. Having these two values ​​and a known value related to the calibration sphere, the reference position of the dressing wheel can be calculated.

[0022] The invention relates to a method for grinding a workpiece by means of a machine tool having a spindle arranged on the machine head and a dressing spindle arranged in the machining area, wherein a grinding tool can be mounted on the spindle for grinding a workpiece mounted on the 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 having an inclination Tα with respect to the vertical, the method comprising the steps of calibrating the dressing spindle according to the calibration method of the invention, dressing the grinding tool by the dressing tool and grinding a workpiece by means of the dressed grinding tool.

[0023] The invention relates to a machine tool for grinding workpieces, comprising a main spindle arranged in the machine head and a dressing spindle arranged in the machining area. A grinding tool can be mounted on the main spindle for grinding a workpiece mounted on the 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 to the vertical.

[0024] In particular, the machine tool comprises a calibration sphere and a test mandrel that can be mounted on the dressing spindle to calibrate the dressing spindle, the calibration sphere comprising a connection part and a fixture provided on the top of the connection part, and the test mandrel comprising a seat part and an elongated body formed on the top of the seat part.

[0025] A more specific description of the present invention will be further set forth below. The embodiments are explained and described in detail with reference to the accompanying drawings. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a side view showing a machine tool having a main spindle and a dressing spindle. [Diagram 2] FIG. 2 is a side view showing the machining area where the dressing spindle is mounted. [Figure 3a] FIG. 1 is a schematic diagram showing side dressing of a grinding tool. [Figure 3b] FIG. 1 is a schematic diagram showing dressing of the underside of a grinding tool. [Figure 4] FIG. 2 is a schematic diagram showing a dressing spindle. [Diagram 5] FIG. 1 is a schematic diagram showing a test mandrel having an elongated body and a seat mounted on a dressing spindle. [Figure 6]FIG. 1 illustrates a trigonometric method for the calculation of tilt angle formation. [Figure 7] FIG. 1 is a schematic diagram showing a calibration sphere with a fixture and support elements mounted on a dressing spindle. [Figure 8] FIG. 2 illustrates the steps of the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] FIG. 1 shows a machine tool that can be used for grinding. In particular, FIG. 1 shows a machine tool for milling and grinding. The machine tool 1 has three linear axes X, Y, Z and two rotational axes B, C. The machine tool comprises a machine table 2 that can be moved linearly along the axis X. The linear movements along the Y and Z axes are performed by the machine head 4. A cradle 3 is mounted on the machine table and is rotatable about a rotational axis B. The cradle comprises a workpiece table 6 for mounting a workpiece thereon, the workpiece table being rotatable about a second rotational axis C. A main spindle 5 is mounted in the machine head for clamping various machining tools, for example grinding tools, inside it. The dressing spindle 10 is fixedly mounted on the machine table and is therefore not movable along the workpiece table.

[0028] Figure 2 shows the arrangement of the dressing spindle shown in Figure 1. A fixture 11 is mounted on the side of the machine table. The dressing spindle is mounted on the top surface of the fixture. A dressing tool 12 may be mounted on top of the dressing spindle for conditioning the grinding tool. As shown in Figure 2, the rotation axis of the dressing spindle 10 is not parallel to the Z direction but has an inclination angle Tα. The reason for the inclination is shown in Figures 3a and 3b.

[0029] In order to reshape the grinding tool, not only the side surface 7a of the grinding tool but also the front surface 7b of the grinding tool must be dressed. Fig. 3a shows diagrammatically the dressing of the side surface of the grinding tool. Fig. 3b shows diagrammatically the dressing of the front surface of the grinding tool. For dressing, the grinding tool is mounted on the spindle and moved close to the dressing tool so that it is 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 reach the bottom surface as well.

[0030] FIG. 4 shows a schematic diagram of the dressing spindle 10 with the dressing spindle body 13 and the tool interface 14. The tool interface serves as an interface for clamping the dressing tool thereon and is located on the top surface of the dressing spindle body. The connection surface of the spindle body 13 and the tool interface are defined as the reference plane FR. The center point of the reference plane is defined as the reference point R. The goal of the calibration is to accurately determine the coordinates of this position and the tilt angle formation of the dressing spindle. The determined values ​​can be stored in the control unit of the machine tool in order to calculate the movement of the spindle for dressing. A standard touch probe can only be tested in the XY working plane and the Z axis. Due to the tilt of the dressing spindle, it is not possible to determine the position of the reference point by a standard touch probe.

[0031] To determine the tilt angle formation 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 mandrel 30. As shown in FIG. 5, the test mandrel comprises a seat 32 for clamping the test mandrel on the dressing spindle and an elongated body 31 on the seat. The seat has a cylindrical body and a clamping interface provided on the inner surface of the cylindrical body for accurate mounting on the dressing spindle. The clamping interface is designed in such a way that it can be easily coupled with the tool interface of the spindle. In particular, in the mounted state, the central axis of the test mandrel coincides with the rotation axis of the dressing spindle. The touch probe is controlled by the control unit of the machine tool to contact various positions of the body and determine the tilt angle based on the measured positions.

[0032] As shown in FIG. 5, the touch probe is positioned near the body and is controlled by the control unit to touch points Q1 and Q2 on the side of the body, for example. The coordinates of the measured points Q1 and Q2, Q1(x Q1 ,y Q1 ,z Q1 ) and Q2(x Q2 ,y Q2 ,z Q2 ) is input to the control unit, so that the tilt angle Tα of the mandrel can be calculated.

[0033] As shown in Figure 6, trigonometry must be used to calculate the tilt angle Tα. The length a is the distance of the measured position in the Z direction, i.e. z Q1 and z Q1 The length b is the distance between the measured positions in the Y direction, i.e., y Q1 andy Q2 is the difference between the two values ​​of

[0034] In a further step, a calibration sphere is used. The test mandrel is replaced by the calibration sphere. The calibration sphere is provided with a connection part 22 for clamping on the dressing spindle and a fixture 21 formed at the top of the connection part. The connection part has a cylindrical body and is provided with a clamping interface so that it is accurately mounted on the dressing spindle. In particular, the central axis of the calibration sphere coincides with the axis of rotation of the dressing spindle. The touch probe, controlled by the control unit of the machine tool, contacts various positions on the fixture and determines the center position of the fixture based on the measured positions, i.e. the coordinates of the point P shown in Fig. 7. The distance A is known based on the manufacture of the calibration sphere. The diameter of the fixture B is also known based on the manufacturing data. Since the coordinates of the center point P of the fixture have been determined, the coordinates of the reference point R can be determined using trigonometry.

[0035] FIG. 8 shows the sequence of the method of the present invention. In step S1, a touch probe is mounted on the spindle. In step S2, the dressing spindle is replaced by a test mandrel. In step S3, the inclination angle of the rotation axis of the dressing spindle is determined by contacting the mandrel with the touch probe at multiple positions on the mandrel. In step S4, the test mandrel is replaced by a calibration sphere. In step S5, multiple positions on the calibration sphere are measured by contacting the calibration sphere with the touch probe at multiple positions and the measured positions are recorded. In step S6, the processing unit determines the center position of the calibration sphere 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 rotation axis of the dressing spindle and the dimensions of the touch probe. [Explanation of symbols]

[0036] 1 Machine tools 2 Machine table 3. Cradle 4 Machine Head 5 main axis 6 Workpiece Table 7 Grinding Tools 7a Side of grinding tool 7b Front view of grinding tool 8 Dressing Tools 10 Dressing spindle 11 Mounting fixture 13 Dressing spindle body 14 Tool Interface 20 Calibration sphere 21 Jig 22 Connection 30 Test Mandrel 31 Test mandrel body 32 Seat area 40 Touch Probe

Claims

1. A method for calibrating a dressing spindle (10) of a machine tool (1) having a main spindle (4) arranged in a machine head and a dressing spindle (10) arranged in a machining area, in which a grinding tool can be mounted on the main spindle and a dressing tool can be mounted on the dressing spindle, and in which the grinding tool and the dressing tool can be moved relative to each other in order to dress 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. mounting the test mandrel on the dressing spindle by connecting the seat to the dressing spindle such that the axial axis of the body is parallel to the axis of rotation of the dressing spindle; c. measuring a plurality of locations on the body of the test mandrel by contacting the body with a measurement device at a plurality of locations; d. determining an inclination angle of the rotation axis of the dressing spindle based on the measured positions on the test mandrel by a processing unit, wherein the inclination angle is an angulation of the rotation axis of the dressing spindle with respect to a vertical direction; e. mounting a calibration sphere (20) having a connecting portion (22) and a jig (21) provided at the top of the connecting portion on the dressing spindle, the calibration sphere being concentrically disposed on the dressing spindle; f. Mounting a touch probe (40) on said spindle; g. measuring a plurality of locations on the fixture by contacting the touch probe with the fixture at the plurality of locations; h. determining, by said processing unit, a center position (P) of said calibration sphere according to a plurality of measured positions of said calibration sphere; i. determining by the processing unit a position of a reference point (R) of the dressing spindle based on the determined center position of the calibration sphere, the inclination angle of the rotation axis of the dressing spindle and the dimensions of the calibration sphere, the reference point being located at a center position on a reference plane (FR) of the dressing spindle; The method includes:

2. The method of claim 1 , wherein the measurement device is a touch probe or a dial indicator.

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

4. 4. The method according to claim 1, wherein the determined position of the reference point is added to a kinematic compensation model, in particular the determined reference position is automatically supplied to the kinematic compensation model.

5. 5. The method according to claim 1, wherein the touch probe is controlled by a control unit of the machine tool to perform the measurements.

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

7. 7. The method of claim 1, wherein the calibration sphere is first used to determine an initial center position before mounting the test mandrel on the dressing spindle to determine the tilt angle formation of the dressing spindle.

8. 8. The method according to claim 1, wherein the height of the calibration sphere is taken into account for determining the reference point of the dressing spindle.

9. A method for grinding a workpiece by means of a machine tool having a main spindle (4) arranged in a machine head and a dressing spindle (10) arranged in a machining area, in which a grinding tool can be mounted on the main spindle for grinding the 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 having an inclination Tα to the vertical, a. calibrating the dressing spindle according to any one of claims 1 to 8; b. Dressing the grinding tool with the dressing tool; c) Grinding the workpiece with the dressed grinding tool. The method includes:

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

11. 11. A machine tool according to claim 10, characterized in that the machine tool is provided with a control unit and is used to carry out the steps according to claim 1.

12. 12. The machine tool according to claim 10 or 11, comprising a calibration sphere and a test mandrel, the test mandrel being mountable on the dressing spindle for calibrating the dressing spindle according to claim 1, the calibration sphere comprising a connection portion (22) and a fixture (21) provided on the top of the connection portion, and the test mandrel (30) comprising a seat (32) and an elongated body (31) formed on the top of the seat.

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