Method and device for determining the centre of a hollow shaft rotatably clamped as a workpiece in a machine tool

Abstract

The invention relates to a technical solution for determining the center and the center space run of a hollow shaft, which is rotatably clamped as a workpiece in a machine tool, which is at least sectionally machined on its outer surface. The object of the invention is to provide a corresponding technical solution using a method other than ultrasound. This object is solved by using a sensor which works according to the eddy current principle, wherein the method-technical and device-technical features are described in more detail.

Description

Technical Field

[0001] The present invention relates to a technical solution for determining the center and central spatial orientation of a hollow shaft that is rotatably clamped as a workpiece in a machine tool, the hollow shaft being cut at least in sections on its outer surface. Background Technology

[0002] Determining the center of a drill hole in a workpiece and the orientation of each drill hole or center based on two or more drill hole centers is known. For example, when machining a long hollow shaft to accommodate turbine blades, it is necessary to align the average axis of the inner cavity with the axis of rotation of the machine tool that rotates the hollow shaft. To do this, the inner radii of numerous points within the hollow shaft are measured, and then the alignment of the hollow shaft and the machine tool is achieved by calculating a hypothetically determined average axis. If the inner contour of a drill hole is measured tactilely, problems often arise due to the length of the tactile measuring element used and the vibrations that occur. For this reason, other measurement methods are increasingly being used instead of tactile methods.

[0003] For example, in EP 2 527 084 A2, to reduce imbalance, it is recommended to first perform segmental optical scanning on the hollow shaft to be machined, and to calculate the center of gravity or imbalance segmentally based on the values ​​of these optical records. These points or segments are then milled in a targeted manner to bring the concentricity of the hollow shaft to a substantially optimal level for later use.

[0004] A method for reducing the eccentricity between the inner and outer surfaces of a hollow workpiece rotatably clamped in a machine tool is known from DE 199 58 373 A1. Here, ultrasound is used to determine multiple measurement data depending on the profile of the inner surface. The desired orientation of the outer surface is calculated using these measurement data, and the outer surface is then machined according to the calculated desired orientation using the same workpiece clamping device as during measurement.

[0005] A similar solution is described in EP 2 668 547 B1. However, here, measurement data of the inner surface profile determined by ultrasonic waves are used to calculate a portion of the outer surface, which is at least partially machined in a further machining step. The workpiece is reclamped using a clamping device such as a chuck and center rest through the portion of the surface produced in this way, and then the remaining outer surfaces of the workpiece are machined.

[0006] This method creates new clamping positions for further machining, enabling the optimal machining of hollow shafts. However, using ultrasound to measure the profile within the inner cavity of larger hollow shafts (e.g., those exceeding 2 meters in length) is limited. This is due to the significantly increased cost of the equipment and reduced measurement accuracy. Therefore, there is a need to improve other known measurement methods for such applications, in addition to optical and ultrasonic-based solutions.

[0007] A method for reducing the eccentricity between the inner and outer surfaces of a hollow workpiece rotatably clamped in a machine tool is known in WO 2012 / 100 278 A1. A user-friendly, rapid method for measuring the workpiece wall thickness using an ultrasonic measuring device is described herein. However, it remains unclear whether the method involves sound wave propagation through contact (tactile sensation) or by means of a carrier medium. It is described that the method is performed on the outer surface in the circumferential direction or preferably in the longitudinal direction of the workpiece. Measurement data is recorded using the ultrasonic measuring device, and these measurements are used to create at least one, in this case, two partial surfaces, preferably by a rotary milling pin with parallel axes. With the aid of these partial surfaces, the workpiece is clamped in a new clamping device, but rotated 180 degrees, which requires manual operation by the operator or automation, and is not explicitly stated. The wall thickness determined by the ultrasonic method is affected by both the external and internal contours, and therefore also by the clamping device used. Operator intervention is required during this process.

[0008] Another technical solution for machining workpieces is described in EP 2 572 826 A1. A tool is used here that moves (Zustellung) the tool by means of sensor measurement data, taking into account the deviation of the workpiece's actual axis of rotation from its nominal axis of rotation. The sensor measurement data is recorded by at least two measuring devices of known shapes rotating together. These measuring devices are respectively attached to the end face of a solid workpiece and have known shapes of annular and at least partially spherical. The measurement data is recorded by several inductively operating sensors, which, with the aid of these sensors, improve or reduce existing shape and position deviations by machining with geometrically specific cutting edges to meet the highest geometric requirements. The machining method used is not further described. This method requires workpiece preparation on the end face using the measuring devices to be used. The sensors are aligned with the workpiece through the opening of the clamping device or starting from the tailstock. Summary of the Invention

[0009] The purpose of this invention is to provide a new technical solution for determining the center and spatial orientation of a hollow shaft that is rotatably clamped as a workpiece in a machine tool using methods other than ultrasonics.

[0010] This objective is addressed technically as follows: First, using at least one sensor operating based on the eddy current principle, the radial distance between the sensor and the workpiece profile is detected non-contactly at at least one full angle of the workpiece profile at at least two defined axial positions, within angular relative positions defined between the sensor's rotation axis and the hollow shaft's rotation axis. Then, an arbitrary constant radius is calculated from the detected radial distance, forming a vector from polar coordinates with angular values ​​and radius values ​​with radial distance, and this vector is converted to Cartesian coordinates. A geometric workpiece center point that can be assigned to the corresponding axial position of the hollow shaft is calculated using an averaging method. Then, from at least two such calculated workpiece center points at different axial positions, a central axis in space, close to the workpiece center point, is calculated through regression analysis. Subsequently, starting from the central axis and along the rotation axis of the hollow shaft, an arbitrary number of diameters concentric with the central axis are calculated, and new clamping seats for the hollow shaft are machined using these diameters. These clamping seats re-determine the rotation axis of the hollow shaft concentrically with the central axis. In this case, the radial distance at at least two defined axial positions along the rotation axis of the hollow shaft can be detected sequentially in time by a single sensor. Alternatively, these radial distances can be detected simultaneously or sequentially using at least two sensors.

[0011] To implement this method, an apparatus is proposed that is fixedly or replaceably arranged within the workspace of a machine tool by means of a bracket on a tool carrier, and carries one or more sensors operating according to the eddy current principle, which are oriented and designed in the same or different ways, and the apparatus can be freely positioned within the workspace via at least one machine axis of the tool carrier. Advantageous designs are the subject of the dependent claims, and are explained in more detail in one embodiment.

[0012] The technical solution according to the present invention provides a method and apparatus that enables non-contact measurement over a large measurement range by applying the eddy current principle. Therefore, the center of a borehole can be measured by distance measurement using eddy current technology. Since the center is determined independently of the specific diameter due to the use of virtual diameter calculation, the internal contour can be measured. Vibration damping components ensure high measurement accuracy, even for long workpieces. Therefore, spatially precisely positioned clamping seats and center supports can be created on hollow shafts and similar workpieces for re-clamping the workpiece in an optimal spatial orientation for subsequent cutting. Thus, a technical solution is realized for generating a clamping seat for re-clamping a rotatably clamped workpiece in a machine tool, the workpiece having an internal cavity with free contour sections, the workpiece's outer surface being at least sectionally cut, wherein the center axis is calculated using the proposed method, and the new clamping seat is produced using the proposed apparatus. The measurement process and the subsequent machining process for producing the new clamping seat are performed unattended. Attached Figure Description

[0013] The invention will now be explained in more detail with reference to the accompanying drawings and embodiments. In the drawings:

[0014] Figure 1a The basic structure is shown, demonstrating the efficient connection of components during measurement. Figure 1b This demonstrates the efficient connection of the components when milling a new clamping seat concentrically with the calculated central axis.

[0015] Figure 1c This demonstrates the effective connection of the assembly when the hollow shaft is tensioned.

[0016] Figure 1d This demonstrates the efficient connection of components when milling and turning a new clamping seat for further machining.

[0017] Figure 1e The effective connection of the components under the new clamping condition is shown.

[0018] Figure 2 The basic structure of the device for detecting and measuring values ​​is shown.

[0019] Figure 3 A schematic diagram of the vibration damping component is shown.

[0020] Figure 4 An improved implementation scheme for the device structure is shown. Detailed Implementation

[0021] The device technology components shown in the figure are conceived for performing a method for determining the center and spatial orientation of a workpiece rotatably clamped in a machine tool, the workpiece having free contour sections inside, the workpiece preferably being a hollow shaft, and the outer surface of the workpiece being machined at least in sections.

[0022] according to Figure 1a The workpiece, designed as a hollow shaft 4, is clamped at its end section in a clamping device designed as a chuck 2. Furthermore, the hollow shaft 4 is supported by its outer surface in at least one additional clamping device. However, according to... Figure 1a In this example, the support is not performed in a single additional clamping device, but in two additional clamping devices designed as center supports 5. In the supported position, the hollow shaft 4 rotates about the workpiece rotation axis 1. The direction of rotation is indicated by the arrow shown.

[0023] Figure 1a It is also shown that the workpiece contour 13 does not have a concentric orientation. Instead, the outer and inner contours of the hollow shaft 4 extend eccentrically to each other. However, in order to perform proper cutting, the center of the hollow interior space of the hollow shaft 4 must first be determined.

[0024] This is set up for this purpose. Figure 1a The device 9 shown on the right side of the middle section has a basic structure that is again in... Figure 2 Shown separately. The device 9 is arranged in the workspace of the machine tool (not shown in more detail here) by means of a bracket 14 on the tool carrier 8. Both fixed and replaceable arrangements are possible, with the replaceable variant having an advantage due to the possibility of using a kassette. The machine axis of the tool carrier 8 is indicated by two arrows 10 shown.

[0025] At least one sensor 6 operating according to the eddy current principle is arranged on the device 9. The axis of rotation associated with the sensor 6 is marked by reference numeral 12. However, the sensor 6 itself does not rotate around this axis of rotation 12. If the device 9 is equipped with multiple sensors 6, sensors 6 of the same or different designs can be arranged for this purpose. Similarly, multiple sensors 6 can be arranged in the same or different defined orientations. Regardless of the specific number, design, or orientation, each sensor 6 can be freely positioned in the working area of ​​the machine tool via at least one machine axis 10 of the tool carrier 8.

[0026] In the illustrated embodiment, only one sensor 6 is provided. Using this sensor 6, which operates based on the eddy current principle, the radial distance between the sensor 6 and the workpiece profile 13 is detected at at least two defined axial positions 7. Figure 1a Three such positions are shown, with sensor 6 exemplarily located in the middle axial position 7. Non-contact detection of radial distance is performed at at least one full angle of the workpiece profile 13 at an angular relative position defined between the rotation axis 12 of sensor 6 and the rotation axis 1 of workpiece 4.

[0027] If only one sensor 6 is used, the radial distance is detected sequentially in time at at least two defined axial positions 7 along the rotation axis 1 of the hollow shaft 4. In contrast, if multiple sensors 6 are used, the radial distance is either detected sequentially in time or advantageously detected simultaneously.

[0028] By equipping device 9 with additional vibration damping elements, high-quality detection of the measured values ​​can be achieved. According to Figure 3 For this purpose, multiple disc-shaped components 15 are structurally integrated into the internal space of the device 9. Each of these components 15 has a resilient member in the circumferential direction, which is radially tensioned with the device 9. The damping components 15 also have concentric and / or eccentrically arranged openings 16 for axially guiding and securing cables and wires. Further configured, at least one damping component 15 is rigidly connected to at least one adjacent damping component 15 and fixed to a bracket 14 for the tool carrier 8. Thus, at least one sensor 6 rotating about the rotation axis 12 can perform very precise movements without deviations affecting the measurement.

[0029] The device 9 can be further designed to best suit the specific application requirements. Thus, the device 9 can be mounted on an extendable sensor carrier for a hollow shaft 4 with a long cavity. Furthermore, the energy required to operate the device 9 can be provided non-contactly or via cable. Here, the non-contact energy supply is designed, for example, as an inductive power source. Additionally, the measurement data detected by the device 9 can be transmitted non-contactly or via cable to a computing unit, which can then transmit the measurement data to another computing unit of the relevant machine tool control device.

[0030] Once the radial distance between sensor 6 and workpiece contour 13 is detected, an arbitrary constant radius is calculated from the detected radial distance, forming a vector with polar coordinates containing both angular and radial distance values. This vector is converted to Cartesian coordinates, and the geometric workpiece center point, which can be assigned to the corresponding axial position 7 of the hollow shaft 4, is calculated by averaging. Then, through regression analysis, a central axis 3 located in space, close to the workpiece center point, is calculated from at least two calculated workpiece center points at different axial positions 7. Subsequently, an arbitrary number of diameters concentric with the central axis 3 are calculated along the rotation axis 1 of the hollow shaft 4, starting from the central axis 3.

[0031] Using the diameter calculated in this way, a new clamping seat is machined for the hollow shaft 4, which re-concentrically determines the rotation axis 1 of the hollow shaft 4 with the central axis 3. The steps of this method are as follows: Figure 1b As shown. The hollow shaft 4 is still clamped in the clamping device designed as a chuck 2 at its end section and rotates about the rotation axis 1. Furthermore, the hollow shaft 4 is still supported by its outer surface in the center frame 5 shown on the right, but no longer in the center frame 5 shown on the left. The new clamping seats 24 are turned orthogonally to the calculated center axis 3. Preferably, each new clamping seat 24 is generated by the turning / drilling / milling unit 20 using a corresponding milling cutter 21. The movement axes of the turning / drilling / milling unit 20 are indicated by the two arrows 19 shown.

[0032] After the new clamping seat 24 is machined, the hollow shaft 4 is tensioned. The steps of this method are as follows: Figure 1c As shown, the arrow marked "A" indicates the tensioning and simultaneous movement of the hollow shaft 4, allowing a new clamping seat to be milled. For this purpose, the tool carrier 8 includes a rotatable clamping device 17, which is selectively designed to be both drivable and lockable. The clamping device 17 is designed for internal or external reception of the hollow shaft 4 and can be operated manually or automatically. The clamping device 17 can be freely positioned within the machine tool's workspace via at least one machine axis 10 of the tool carrier 8. Figure 4 The structure of this device technology is shown separately again.

[0033] according to Figure 1c The hollow shaft 4 is released from the clamping device designed as a chuck 2 and supported at a new clamping position by the clamping device 17 on the center frame 5 shown on the left and the tool carrier 8. The clamping device 17 rotates about the rotation axis 18, thereby causing the hollow shaft 4 to rotate as well. In this clamping condition, the workpiece rotation axis 1, the center axis 3, and the clamping device rotation axis 18 are aligned and overlapped.

[0034] The new clamping seat 24 is then milled and turned for further machining. The steps of this method are as follows: Figure 1d As shown. The hollow shaft 4 remains released from the clamping device designed as chuck 2 and is supported by the center frame 5 shown on the left and the clamping device 17. (Already addressed...) Figure 1b The explained turning / drilling / milling unit 20 is used for machining. For example, now one milling cutter and one turning tool 22 are used instead of two milling cutters 21.

[0035] Figure 1e The clamping configuration after milling and turning the new clamping seat 24 is shown. The hollow shaft 4 is now clamped again in the clamping device designed as a chuck 2 and rotates about the workpiece rotation axis 1, which extends in alignment with the calculated central axis 3. Furthermore, the hollow shaft 4 is supported by its outer surface in the center rest 5 shown on the right, but not in the center rest 5 shown on the left.

[0036] Explanation of reference numerals in the attached figures

[0037] 1. Rotating axis workpiece / hollow shaft

[0038] 2 Clamping device / chuck

[0039] 3. Central axis

[0040] 4. Workpiece / Hollow Shaft

[0041] 5. Clamping device / center frame

[0042] 6 sensors

[0043] 7. Used to determine the axial position of the center point

[0044] 8. Tool Carrier

[0045] 9. Device for recording measured values

[0046] 10. Machine shaft of tool carrier

[0047] 12 Rotary Axis Sensor

[0048] 13. Workpiece outline

[0049] 14 supports

[0050] 15. Disc-shaped components for vibration damping

[0051] 16 Cable, dielectric, and fastening openings

[0052] 17 Clamping device

[0053] 18. Rotary axis clamping device

[0054] 19 Moving axes

[0055] 20 Turning / Drilling / Milling Units

[0056] 21. End Mill

[0057] 22 Lathe tool

[0058] 24 Clamping base

Claims

1. A method for determining the center and spatial orientation of a hollow shaft (4) rotatably clamped as a workpiece in a machine tool, wherein the hollow shaft is at least partially machined on its outer surface, characterized in that, First, using at least one sensor (6) operating based on the eddy current principle, the radial distance between the sensor (6) and the workpiece contour (13) is detected non-contactly at at least one full angle of the workpiece contour (13) at at least two defined axial positions (7) and at angular relative positions defined between the rotation axis (12) of the sensor (6) and the rotation axis (1) of the hollow shaft (4). Then, by calculating an arbitrary constant radius from the detected radial distance, a vector is formed from polar coordinates with angular values ​​and radius values ​​with radial distance, and this vector is converted to Cartesian coordinates. The geometric workpiece center point that can be assigned to the corresponding axial position of the hollow shaft (4) is calculated using the averaging method. Then, from at least two workpiece center points thus calculated at different axial positions (7), a central axis (3) located in space is calculated through regression analysis, said central axis being close to the workpiece center point, and Subsequently, starting from the central axis (3) along the rotation axis (1) of the hollow shaft (4), an arbitrary number of diameters concentric with the central axis (3) are calculated, and new clamping seats (24) of the hollow shaft (4) are machined using these diameters. These clamping seats re-determine the rotation axis (1) of the hollow shaft (4) concentric with the central axis (3).

2. The method according to claim 1, characterized in that, The radial distance at at least two defined axial positions (7) along the hollow shaft (4) rotating axis (1) is detected sequentially in time by a sensor (6).

3. The method according to claim 1, characterized in that, The radial distance at at least two defined axial positions (7) along the hollow shaft (4) rotating axis (1) is detected simultaneously or sequentially in time by at least two sensors (6).

4. The method according to claim 1, characterized in that, The new clamping seat (24) of the hollow shaft (4) is orthogonally turned and milled.

5. An apparatus for performing the method according to claim 1, the method being used to determine the center and spatial orientation of a hollow shaft rotatably clamped as a workpiece in a machine tool, the hollow shaft being machined at least segmentally on its outer surface, wherein, First, using at least one sensor operating based on the eddy current principle, the radial distance between the sensor and the workpiece profile is detected non-contactly at at least two defined axial positions, at angular relative positions defined between the sensor's rotation axis and the hollow shaft's rotation axis, at at least one full angle of the workpiece profile. Then, an arbitrary constant radius is calculated from the detected radial distance, forming a vector from polar coordinates having angular values ​​and radius values ​​having radial distance, and this vector is converted to Cartesian coordinates. A geometric workpiece center point that can be assigned to the corresponding axial position of the hollow shaft is calculated using an averaging method. Then, from at least two such calculated workpiece center points at different axial positions, a central axis in space is calculated through regression analysis, said central axis being close to the workpiece center point. Subsequently, starting from the central axis and along the rotation axis of the hollow shaft, an arbitrary number of diameters concentric with the central axis are calculated. New clamping seats for the hollow shaft are machined using these diameters, these clamping seats re-determine the rotation axis of the hollow shaft concentrically with the central axis. The method is characterized by... The device (9) for recording measurement values ​​is arranged in a fixed or replaceable manner in the working space of the machine tool by means of a bracket (14) on the tool carrier (8), and carries one or more sensors (6) that operate according to the eddy current principle, the sensors being oriented and designed in the same or different ways, and the device for recording measurement values ​​is free to be positioned in the working space by means of at least one machine axis (10) of the tool carrier (8).

6. The apparatus according to claim 5, characterized in that, The tool carrier (8) includes a clamping device (17) that is rotatable about a rotation axis (18), the clamping device being designed to be driven and locked for internal or external housing of the hollow shaft (4), the clamping device being manually or automatically operable and being freely positioned in the workspace of the machine tool via at least one machine axis (10) of the tool carrier (8).

7. The apparatus according to claim 5, characterized in that, Multiple damping components (15) are structurally integrated inside the device (9) for recording measurement values, each of which is designed as a disc and has an elastic component in the circumferential direction, which is radially tensioned with the device (9) for recording measurement values.

8. The apparatus according to claim 7, characterized in that, The vibration damping component (15) has concentric and / or eccentrically arranged openings (16) for axially guiding and securing cables and wires.

9. The apparatus according to claim 7, characterized in that, At least one damping component (15) is rigidly connected to at least one adjacent damping component (15) and rigidly fixed to a bracket (14) for the tool carrier (8).

10. The apparatus according to claim 5, characterized in that, The device (9) for recording the measured values ​​is arranged on a sensor carrier that can extend.

11. The apparatus according to claim 5, characterized in that, The energy required to operate the device (9) for recording measurements can be provided non-contactly or via cable.

12. The apparatus according to claim 11, characterized in that, The contactless power supply is designed as an inductive power source.

13. The apparatus according to claim 5, characterized in that, Measurement data detected by the device (9) for recording measurement values ​​can be transmitted to a computing unit in a non-contact manner or via cable, and the computing unit can transmit the measurement data to another computing unit of the relevant machine tool control device.

14. A method for generating a new clamping seat for rotatably clamping a hollow shaft as a workpiece in a machine tool, wherein the outer surface of the hollow shaft is at least sectionally machined, characterized in that, The central axis (3) is calculated using the method according to any one of claims 1 to 4, and the new clamp (24) is produced using the apparatus according to any one of claims 5 to 13.

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