Ultra-precision lathe and method for ultra-precise shaping with it

Abstract

The present invention relates to an ultra-precision lathe (1) for ultra-precise shaping of a workpiece (3), wherein the ultra-precision lathe (1) comprises: - a spindle (7) with a workpiece holder (5) for receiving a workpiece (3) to be machined, wherein the spindle (7) defines an axis of rotation (L) about which the spindle (7) with a workpiece (3) received by means of the workpiece holder (5) is rotatable, - at least one tool (9) that can be dynamically adjusted relative to the spindle (7) for material removal by machining, and - at least one sensor for direct or indirect detection of spindle imbalance (7), characterized by the fact that The ultra-precision lathe (1) further comprises a balancing ring (13) which is detachably attached to the spindle (7) coaxially to the axis of rotation (L), wherein the balancing ring (13) has an inner diameter which is larger than an outer diameter of the workpiece holder (5), wherein material of the balancing ring (13) can be removed rotationally asymmetrically by dynamically adjusting the at least one tool (9) while the spindle (7) is rotating, in order to compensate for an imbalance determined by means of the at least one sensor by machining material of the balancing ring (13).

Description

[0001] The present disclosure relates to an ultra-precision lathe and a method for ultra-precise forming using it. The surfaces of workpieces machined by this machine, whose shape is to be produced in this way, are intended to have a dimensional tolerance of less than 5 µm.

[0002] Ultra-precision lathes are used to machine workpieces, giving them a very precisely defined surface finish. The goal of ultra-precision machining with an ultra-precision lathe is to achieve exceptionally high surface quality with a dimensional tolerance of less than 5 µm across the entire machined surface of the workpiece. A dimensional tolerance of less than 5 µm across the entire machined surface means that the peak-to-valley value (R) across the entire machined surface is very low. † according to DIN EN ISO 4287) of 5 µm is not exceeded.

[0003] Such surface qualities are particularly needed for special optics made of glass, glass-ceramics, or plastic. However, metallic workpieces can also require such surface qualities, for example, when they are intended to define a negative surface of a mold insert for the replicative production of optical surfaces, such as in injection molding or injection compression molding processes.

[0004] Regardless of the workpiece material or the material used for machining, achieving such surface qualities requires precise balancing of the ultra-precision lathe before machining the workpiece. Any imbalances in the spindle of the ultra-precision lathe, such as first-order eccentricity, second-order wobble, or higher-order deformation or vibration, can prevent the required dimensional tolerance of less than 5 µm from being achieved across the entire machined surface.

[0005] Therefore, the spindle of an ultra-precision lathe is typically balanced in a lengthy manual adjustment process before each machining operation on a newly clamped workpiece. This involves manually adjusting small set screws distributed around the circumference of the spindle. For fine-tuning, adhesive strips are even strategically applied to the spindle to compensate for any imbalances. This process is iterative, meaning that after each adjustment, the change in imbalance is measured, and the spindle is readjusted until it is below a tolerable level. This manual balancing process is not only very time-consuming but also requires highly experienced operators who must have in-depth knowledge of a specific ultra-precision lathe model to achieve imbalances below a tolerable level.Due to the complexity of this manual balancing process, readjustment is regularly omitted once material removal from the workpiece has begun.

[0006] DE 10 2020 007 626 A1 discloses a clamping system with a base plate and a slide. DE 102012 110 139 A1 describes a balancing device for balancing a rotating workpiece. DE 2335 542 A1 describes a machining process for the machining of machine parts.

[0007] This results in the task of accelerating and simplifying the manual balancing process on the one hand, so that it no longer depends so heavily on the experience of the operating personnel and readjustment is possible if material has already been removed from the workpiece.

[0008] According to the present invention, an ultra-precision lathe and a method according to the independent claims are provided to solve this problem. Advantageous embodiments of the invention can be found in the dependent claims, the description, and the drawings.

[0009] According to a first aspect of the invention, an ultra-precision lathe is provided for the ultra-precision shaping of a workpiece, wherein the ultra-precision lathe comprises: - a spindle with a workpiece holder for receiving a workpiece to be machined, wherein the spindle defines an axis of rotation about which the spindle with a workpiece received by means of the workpiece holder can be rotated, - at least one tool that can be dynamically adjusted relative to the spindle for material removal by cutting, and - at least one sensor for the direct or indirect detection of spindle imbalance, characterized by the fact that The ultra-precision lathe further comprises a balancing ring which is detachably attached to the spindle coaxially to the axis of rotation, wherein the balancing ring has an inner diameter which is larger than an outer diameter of the workpiece holder, wherein the material of the balancing ring by dynamically adjusting the at least one tool while the spindle is rotating, in order to compensate for an imbalance determined by means of the at least one sensor by machining material from the balancing ring.

[0010] Optionally, the balancing ring can have at least one annular end face, and the at least one tool can be configured to remove material from this end face of the balancing ring in a rotationally asymmetric manner by dynamically feeding the tool while the spindle is rotating. This is particularly advantageous because feeding the tool in the direction of the axis of rotation is relatively simple if the workpiece is also being machined on its end face. The tool for removing material from the balancing ring can be the same as the one used for machining the workpiece, or it can be a separate tool. If the balancing ring is made of the same material as the workpiece, it can be advantageous to use the same tool for balancing that is also used for machining the workpiece. If the balancing ring is made of a different material than the workpiece, it can be advantageous to use a different tool for balancing than the one used for machining the workpiece.

[0011] Optionally, the balancing ring can have at least two annular end faces, with the at least two annular end faces being axially spaced apart. This is advantageous for addressing any second-order imbalances, such as wobble, by removing material from the different end faces.

[0012] Optionally, the balancing ring can be designed in multiple parts, with each part providing a material removal surface, preferably on its end face, and the material removal surfaces being axially spaced apart. This is advantageous for making the balancing ring compact on the one hand and achieving the largest possible axial distance between the material removal surfaces on the other, thereby more effectively compensating for any second-order imbalances, such as wobble.

[0013] Optionally, the components of the balancing ring can be detachably mounted on the spindle with an axial distance from each other and coaxial to the axis of rotation. In principle, the greater the axial distance, the better a second-order imbalance, such as wobble, can be compensated. However, both material removal surfaces must be located in a machine area where controlled approach of the tool to the respective material removal surface is possible quickly and efficiently.

[0014] Optionally, the parts of the balancing ring can have different outer diameters. This can be advantageous so that two separate tools are not needed for each part of the balancing ring, but rather all, preferably two, parts of the balancing ring can be machined for balancing with the same tool, especially from one end face.

[0015] Optionally, at least one tool can be suitable for both machining material off the balancing ring and machining material off a workpiece held in the workpiece holder. As mentioned above, this is particularly useful if the balancing ring is made of the same material as the workpiece.

[0016] Optionally, the ultra-precision lathe can also have at least one additional tool that can be dynamically positioned relative to the spindle for machining the workpiece. As mentioned above, this is particularly useful if the balancing ring is not made of the same material as the workpiece.

[0017] Optionally, at least one tool can be configured to remove material from the balancing ring once or several times during or between machining steps of a workpiece held by the workpiece holder by means of dynamic infeed while the spindle is rotating. This is done by dynamically adjusting the tool while the spindle is rotating. Such readjustment is particularly useful when the workpiece is machined with rotational asymmetricity, resulting in an imbalance. This imbalance can then be corrected by removing material from the balancing ring during or between machining steps.

[0018] According to a second aspect of the present invention, a method is provided for ultra-precise shaping of a workpiece using an ultra-precision lathe, wherein the method comprises the following steps: - Rotating a spindle of the ultra-precision lathe about a rotary axis, wherein the spindle has a workpiece holder for receiving a workpiece to be machined, - Direct or indirect determination of an imbalance of the rotated spindle by means of at least one sensor, characterized in that the method further comprises: - Balancing the rotated spindle by machining material from a balancing ring which is detachably attached to the spindle coaxially to the axis of rotation and has an inner diameter that is larger than an outer diameter of the workpiece holder, wherein the material of the balancing ring is machined away in a rotationally asymmetric manner by dynamically feeding at least one tool while the spindle is rotating, in order to compensate for an imbalance determined by means of at least one sensor by machining material from the balancing ring.

[0019] The method according to the invention is preferably carried out on an ultra-precision lathe according to the invention.

[0020] Optionally, the steps of turning, determining the imbalance and balancing can be performed and / or repeated during or between machining steps of a workpiece held by means of the workpiece fixture.

[0021] Optionally, the same tool used for balancing can be used for machining the workpiece. Alternatively, a separate tool, not used for balancing, can be used for machining the workpiece.

[0022] Optionally, during balancing, the material of the balancing ring can be removed by dynamically adjusting at least one tool while the spindle is rotating, in a rotationally asymmetrical manner, from an annular end face of the balancing ring.

[0023] Optionally, when determining the imbalance, a wobbling movement of the spindle can be detected, and during balancing, material can be removed from at least two material removal surfaces of the balancing ring, wherein the at least two material removal surfaces have an axial distance from each other.

[0024] Optionally, the at least two material removal surfaces can be located on different end faces of a stepped balancing ring and / or on two different parts of a multi-part balancing ring.

[0025] Optionally, the process can also include a step of smoothing the balancing ring before or after machining a workpiece held by means of the workpiece holder, wherein the balancing ring is smoothed by removing material from the balancing ring by the at least one tool while the spindle is rotating until the balancing ring again has a rotationally symmetrical material distribution.

[0026] An inventive method and / or an inventive ultra-precision lathe can be used to produce optical surfaces in metal for mirrors or molding tools, in infrared materials such as germanium, silicon, or zinc selenide, or directly in plastics, particularly for rotationally symmetric optics. The workpiece to be machined rotates on the spindle, and the tool can be moved by two interpolating linear axes such that a target geometry is established on the workpiece, taking radius correction into account. Non-rotationally symmetric surfaces can also be produced by superimposing a dynamic feed motion synchronized with the spindle rotation onto the cutting edge of the tool.

[0027] This process makes it possible to achieve dimensional accuracy of less than 100 nm over diameters of 50 mm and more, with workpiece roughness of less than 1 nm Ra. To achieve such qualities in this machining process using a tool with a geometrically defined cutting edge, for example made of natural or synthetic monocrystalline diamond, numerous aspects can be taken into account.

[0028] For example, a monocrystalline diamond tool, if correctly oriented, can be lapped to achieve cutting edge radii as low as 50 nm for exceptionally high cutting performance. The tool geometry can also be designed with a radius optimized for minimal residual waviness.

[0029] First and foremost, the material of the workpiece to be machined should exhibit a high degree of homogeneity. Grain boundaries in metals, impurities, or voids can impair the quality of the result.

[0030] Surface description data and routines for calculating machine programs should have a sufficiently high resolution. This applies both to program calculations that determine spindle speeds and tool feed movements, and to subsequent CNC (Computer Numerical Control) processing.

[0031] The machine itself should meet the highest accuracy standards to achieve the surface qualities described above. To this end, the ultra-precision lathe according to the invention can feature mechanically contactless linear axes with fluidic bearings (aerostatic or hydrostatic), a linear direct drive, and a high-resolution optical scale. Due to increased relative speeds in the bearing gap, the spindle can be aerostatically mounted to minimize frictional resistance. Granite can be used as the material for the machine bed to ensure low thermal expansion and, due to the material's open porosity, to allow the relevant guideways to be lapped by hand to flatness levels below 1 µm per meter.

[0032] Furthermore, by actively controlling the temperatures of cooling water, oil in hydrostatics and / or compressed air, temperature fluctuations can be kept within the range of a few tens of millikelvin.

[0033] As explained above, in addition to the workpiece material, the tool, the data and the machine parts, the balance condition has a significant influence on the achievable surface qualities when turning ultra-precise surfaces.

[0034] An imbalance arises when masses are unevenly distributed around the ideal axis of rotation of the spindle. If the center of mass of this distribution is not located on the axis of rotation, a centrifugal force is generated according to the formula ω × ω × r * m, where ω is the angular velocity, r is the radius between the axis of rotation and the center of mass, and m is the eccentrically located mass. This centrifugal force acts as a disturbance on the machine and affects the achievable precision. Due to the limited mechanical stiffness of the machine structure and its individual components, this disturbance force can cause displacements and consequently lead to inaccuracies. In particular, any air gap in the preferably aerostatically mounted spindle, in which the spindle rotor can shift, must be considered. Mechanical structural components in the linear axes, the machine bed, or the spindle mount can also experience displacements.

[0035] Traditionally, machine stiffness is specified in N / µm, with values ​​ranging from 20-30 N / µm for good machines when considering the entire machine structure from the so-called tool center point to the component. However, since stiffness-related deviations of just 50 nm can have a significant impact in the case of ultra-precision machining considered here, even disturbance forces on the order of 1 N can lead to unacceptable quality losses.

[0036] Furthermore, the disturbance force caused by an imbalance also affects the axis control. A position controller in the CNC machine can receive target position values, for example. The controller preferably attempts to minimize the deviation between a specified target value and the actual achieved position value. The remaining deviation between the target and actual values ​​is called the following error. An external disturbance force, such as an imbalance, is extremely difficult for the controller to compensate for. In a rest state (no spindle rotation), a well-balanced linear axis of an ultra-precision lathe can exhibit following errors of < 1 nm. However, rotation of the spindle with insufficient balance can cause the following error to increase to unacceptable values ​​of > 100 nm and more.

[0037] The phenomenon of imbalance can be considered in several planes. For example, the rotor of an aerostatic spindle of an ultra-precision lathe according to the invention can have a length of 300 mm. At the front end of the rotor, the workpiece holder, for example a clamping system, can be arranged to hold a workpiece. At the rear end of the rotor, the motor with a rotary encoder for determining the angle of rotation can be located. The imbalances at both ends of the spindle rotor can be different, so that the absolute magnitudes of the imbalance vectors as well as their vector orientations can differ. What is purely radial deflection when considering the imbalance in one plane can result in rotor wobble when considering it in two planes.

[0038] Balancing can preferably be performed in at least two planes spaced apart along the axis of rotation when the spindle is initially set up. The process can be iterative, as the spindle rotor may not be considered ideally stiff, and therefore the balance state of the front side may influence that of the back side. An uneven mass distribution around the spindle's axis of rotation may not be directly quantifiable as a mass with eccentricity. Two approaches for the metrological characterization of the imbalance are preferred.

[0039] Firstly, accelerometers can be mounted on the spindle. Additionally, the rotor's angular position and rotational speed can be measured using an optical or electrical sensor. The imbalances can be determined from the synchronously read signals of radial acceleration and angular position. The acceleration signal can be integrated to obtain a vibration velocity or, after a second integration, the rotor displacement as a measured value. Using two accelerometers allows measurements in two planes. Besides the rotor's displacement in one plane, a wobble motion can also be determined by analyzing the phase angles of the two accelerometers. A measurement system consisting of an accelerometer, a rotation sensor, and evaluation electronics with software can be used as a standalone unit, which can be mounted on the spindle for balancing purposes.

[0040] Alternatively or additionally to using accelerometers, integrated position measurement technology can be employed. Instead of an external rotation sensor, a machine-integrated rotary encoder is used to determine the angular position of the spindle. Instead of an accelerometer, a linear encoder on the linear axis, on which the spindle may be mounted, can be read. The spindle's axis of rotation is preferably orthogonal to the direction of travel of the linear axis, so that the radially acting imbalance force of the rotating spindle acts in the direction of the linear axis's drive motor. A following error read out here can be related to the angular position of the spindle rotor and used to determine the actual imbalance.

[0041] According to the invention, the imbalance is not compensated for manually by adjusting screws or applying adhesive strips, but rather the rotating spindle is balanced by rotationally asymmetrical machining of material from a balancing ring. The balancing ring is detachably mounted coaxially to the axis of rotation on the spindle and has an inner diameter that is larger than the outer diameter of the workpiece holder. The balancing ring is therefore a wear part or consumable of the ultra-precision lathe according to the invention. When the balancing ring is worn out, it must be replaced with a new one.

[0042] The workpiece holder can be, for example, a vacuum chuck or another system for mechanical, magnetic or adhesive clamping of a workpiece.

[0043] The balancing method according to the invention can be fully automated. After the automatic determination of an imbalance, a turning program is calculated to create recesses in the balancing ring using a dynamic infeed movement of a tool. The measurement, the calculation of the correction, and the machining of the balancing ring can all be fully automated. The recesses can have different geometries: fine cups, longer indentations, or larger recesses. Fine balancing can be achieved with this approach by reducing the cup depth and width. It is particularly advantageous to machine a circumferential groove or channel into an end face of the balancing ring, wherein the depth of the groove or channel is rotationally asymmetrically distributed; that is, the depth of the groove or channel is calculated to vary over the angle of rotation in order to compensate for a specific imbalance.The groove can vary in shape along the angle of rotation, with the wave amplitude and / or wave frequency varying over this angle. For larger imbalances, two or more such grooves may be advantageous.

[0044] By utilizing the machine's online measurement technology to determine residual imbalance, the workpiece's balance can be checked for quality control purposes during or after intermediate machining steps and corrected if necessary. This is particularly useful for rotationally asymmetrical workpiece geometries, which inherently introduce an imbalance during manufacturing. Therefore, after partial machining of the rotationally asymmetrical workpiece, the imbalance can be measured and corrected to ensure optimal balancing conditions for the final machining cut.

[0045] Before clamping and balancing a second component, the balancing ring already used for balancing can be continuously turned down and thus reset. This iterative machining of the lost balancing ring for individual balancing and subsequent reset can be carried out until a minimum thickness of the balancing ring is reached. Afterward, the worn balancing ring must be exchanged and replaced.

[0046] If integrated sensors make it possible to measure the balance state in two planes, correction can also be performed in two planes by means of two axially offset separate balancing ring parts mounted in the chuck and a correspondingly extended mathematical calculation of the balance state.

[0047] The disclosure is explained in more detail below with reference to exemplary embodiments shown in the drawings. These show: Fig. 1 a perspective detail view of an exemplary embodiment of an ultra-precision lathe according to the invention; Fig. 2 a perspective view of an exemplary embodiment of a balancing ring according to an ultra-precision lathe according to the invention; Fig. 3 a perspective view of another exemplary embodiment of a balancing ring according to an ultra-precision lathe according to the invention; and Fig. 4 a perspective view of the embodiment of the balancing ring according to Fig. 2 with a schematic detail view of material removal structures; and Fig. 5 a schematic flowchart of an embodiment of the balancing method according to the invention.

[0048] Fig. Figure 1 shows an ultra-precision lathe 1 for the ultra-precise forming of a workpiece 3. The workpiece 3 is held in a workpiece holder 5, here in the form of a vacuum chuck, the workpiece holder 5 being located at one end face of a spindle 7 of the ultra-precision lathe 1. The spindle 7 is rotatably mounted about a rotary axis L. A motor (not shown here) of the ultra-precision lathe 1 is configured to rotate the spindle 7 at a defined speed about the rotary axis L, so that the workpiece 3, held by the workpiece holder 5, also rotates about the rotary axis L.

[0049] The ultra-precision lathe 1 also features a tool 9 for machining material, which can be dynamically positioned relative to the spindle 7. The tool 9 can, for example, be a monocrystalline diamond tool. In the illustrated embodiment, the spindle 7 is mounted on a linear axis 11 oriented horizontally perpendicular to the axis of rotation L. A linear encoder (not shown) of the linear axis 11 can serve as a sensor for indirectly determining an imbalance of the spindle 7, since an imbalance force acting radially to the axis of rotation L from the rotating spindle 7 acts in the direction of a drive motor (not shown) of the linear axis 11. A following error read by the linear encoder can be related to the instantaneous angular position of the spindle 7 and used to determine the actual imbalance.As an alternative to a linear encoder of the linear axis 11, for example at least one acceleration sensor can be arranged on the spindle 7 for the direct determination of an imbalance.

[0050] According to the invention, the ultra-precision lathe 1 has a balancing ring 13 which is detachably attached to the spindle 7 coaxially with the axis of rotation L. The inner diameter of the balancing ring 13 is larger than the outer diameter of the workpiece holder 5, so that the balancing ring 13 can be detachably attached to the spindle 7 in a way that encompasses the workpiece holder 5. The balancing ring 13 serves as a consumable material which can be removed rotationally asymmetrically by dynamically adjusting the tool 9 while the spindle 7 is rotating, in order to compensate for an imbalance determined by the linear encoder of the linear axis 11 by machining material from the balancing ring 13.

[0051] The material of the balancing ring 13 can be removed from an end face 15 of the balancing ring 13 and / or from a cylindrical surface 17 of the balancing ring 13. Material removal from the end face 15 of the balancing ring 13 is preferred, since the workpiece 3 is also machined primarily at its end face. The tool 9 for machining material from the balancing ring 13 can be the same tool 9 used for machining the workpiece 3 or a separate tool 9.

[0052] For better orientation in the figures, a right-handed Cartesian coordinate system is shown in each case, in which the z-axis runs in the direction of the axis of rotation L, the x-axis extends in the direction of the horizontal linear axis 11 of the spindle 7, and the y-axis corresponds to a vertical axis pointing upwards. The tool 9 is preferably arranged in the y-direction at the same vertical height as the axis of rotation L of the spindle 7. If the material removal from the balancing ring 13 takes place from the cylindrical surface 17 of the balancing ring 13, the tool 9 is positioned in the z-direction so that it is next to the balancing ring 13 in the x-direction and is brought into machining engagement with the material of the balancing ring 13 by radial dynamic feeding of the spindle 7 along the linear axis 11. Alternatively or additionally, the tool 9 can be dynamically fed radially onto the cylindrical surface 17 of the balancing ring 13 on a linear axis supported in the x-direction.

[0053] In the preferred material removal operation from the end face 15 of the balancing ring 13, the tool 9 is positioned in the z-direction in front of the end face 15 of the balancing ring 13 and is dynamically advanced axially, i.e., in the z-direction, to engage the end face 15 of the balancing ring 13 in a machining action. Regardless of whether the material removal takes place from the end face 15 and / or from the cylindrical surface 17 of the balancing ring 13, the dynamic advancement of the tool 9 utilizes the machine's internal information about the angular position of the spindle 7 at any given moment to perform the material removal in the desired angular range with rotational asymmetricity in order to compensate for an imbalance determined by a linear encoder of the linear axis 11.

[0054] Fig. Figure 2 shows the balancing ring 13 and the workpiece holder 5 for holding the workpiece 3 in more detail. The cylindrical surface 17 of the balancing ring 13 can have two cylindrical surface sections 17a,b, which are arranged offset from each other in the direction of the axis of rotation L, i.e., in the z-direction. The balancing ring 13 can be designed in two parts, wherein a first cylindrical surface section 17a of the balancing ring 13 can belong to a first balancing ring part 13a and a second cylindrical surface section 17b of the balancing ring 13 can belong to a second balancing ring part 13b. In this case, the balancing ring parts 13a,b are arranged offset from each other in the z-direction.The advantage of the cylindrical surface sections 17a,b, offset longitudinally along the axis of rotation L, is that balancing can be performed in different planes offset in the z-direction. This allows for the compensation of second- or higher-order imbalances by selectively removing material from either the first cylindrical surface section 17a and / or the second cylindrical surface section 17b, depending on the current angular position. The balancing ring parts 13a,b preferably have an axial distance A from each other in the z-direction to provide a greater lever for compensating for second- or higher-order imbalances.

[0055] Fig. Figure 3 shows an embodiment of the balancing ring 13, in which the balancing ring 13 is stepped and has two annular end faces 15a,b, wherein the two annular end faces 15a,b have an axial distance A between them. The annular end faces 15a,b can be formed by a single-piece balancing ring 13 that is stepped in a stair-like manner, or they can belong to different balancing ring parts 13a,b, wherein the balancing ring part 13b, which is offset rearward by the axial distance A in the z-direction, has a larger outer diameter than the balancing ring 13a, which is arranged further forward in the z-direction. Regardless of whether the balancing ring 13 is designed as a single piece or in multiple parts, the embodiment according to Figure 3 offers Fig. 3 the advantage that by removing material from either the front face 15a and / or the rear face 15b by means of dynamic feed of the tool 9 in the z-direction, imbalances of the second or higher order can be compensated in different planes offset in the z-direction by the axial distance A.

[0056] In Fig. Figure 4 schematically shows that the dynamic positioning of the tool 9 against the balancing ring 13 can lead to different material removal structures 19 on the balancing ring 13. The geometry of the material removal structures 19 can correspond to fine cups, elongated indentations, or larger recesses. By adjusting the cup depth, width, and / or density, very fine balancing can be achieved automatically without the need for manual adjustments of screws or adhesive strips. It is particularly advantageous to incorporate a circumferential groove or channel 21 into the end face 15 of the balancing ring 13 as the material removal structure 19, wherein a depth T of the groove or channel 21 is rotationally asymmetrically distributed, i.e., the depth T of the groove or channel is calculated to vary over the rotation angle φ in order to compensate for a specific imbalance. The depth T of the groove or channel 21 is determined by the rotation angle φ.The groove 21 varies in a wavy pattern along the rotation angle φ, with the wave amplitude and / or wave frequency also varying over the rotation angle φ. The final groove or slot 21 can be machined in thousands of revolutions. For larger imbalances, two or more such slots or grooves 21 may be advantageous. Additionally, the balance can be readjusted at any time between machining steps on the workpiece 3 by removing material from the balancing ring 13.

[0057] Fig.Figure 5 shows a flowchart of an embodiment of the balancing method according to the invention. In a first step 501, the spindle 7 is rotated with the workpiece 3 clamped in it. The remaining steps of the method preferably take place with the spindle 7 rotating, so that the ultra-precision lathe 1 does not have to be stopped and restarted for balancing. In a second step, an imbalance is determined as described above, for example, using the linear encoder of the linear axis 11 of the ultra-precision lathe 1, on which the spindle 7 is movably mounted in the x-direction. In the following step 505, it is checked whether a desired balance quality has been achieved, i.e., whether the imbalance just determined is below a predetermined tolerance limit. If this is the case (yes), then the machining of the workpiece 3 follows in step 507.After or during the machining of workpiece 3 in step 507, or after partial machining of workpiece 3 in step 507, an imbalance can again be determined in step 503 and the balance quality checked in step 505. Therefore, if the workpiece is not yet finished in step 509 (no), the process can continue from step 503 to readjust the balance.

[0058] If the required balance quality is not achieved in step 505 (no), a material removal profile is calculated in step 511. This profile defines the desired shape of the balancing ring 13, which is necessary to compensate for the imbalance determined in the previous step 503. The profile can, for example, define one or more grooves or slots 21 whose depth T varies with the rotation angle φ. In the following step 513, the imbalance is then corrected by removing material from the balancing ring 13 according to the calculated profile. Once the required material has been removed, step 505 recursively checks whether the required balance quality has been achieved. If so, the process continues with step 507; if not, steps 511 and 513 are repeated.If the workpiece is finished in step 509 (yes), in a final step 515 the balancing ring can be smoothed for subsequently processed workpieces so that it is rotationally symmetrical again.

[0059] The numbered designations of the components or directions of movement as "first," "second," "third," etc., are purely arbitrary and used here to distinguish between them. They can be chosen differently at will. This designation does not imply any hierarchy. The designation of a component or technical feature as "first" should not be misinterpreted to mean that a second component or technical feature of the same type must exist. Furthermore, unless explicitly stated otherwise or required by law, any process steps can be carried out in any order and / or with partial or complete temporal overlap.

[0060] Equivalent embodiments of the parameters, components, or functions described herein, which appear obvious to a person competent in the field, are hereby covered as if they were explicitly described. Accordingly, the scope of protection of the claims shall encompass such equivalent embodiments. Features designated as optional, advantageous, preferred, desirable, or similar are to be understood as optional and not as limiting the scope of protection.

[0061] The described embodiments are to be understood as illustrative examples and do not constitute an exhaustive list of possible embodiments. Each feature disclosed in connection with an embodiment may be used alone or in combination with one or more other features, regardless of the specific embodiment in which the features were described. While at least one embodiment is described and shown herein, modifications and alternative embodiments that appear obvious to a person skilled in the art in light of this description are also covered by the scope of this disclosure. Furthermore, the term "have" is not intended to exclude additional features or process steps, nor is "a" or "an" intended to exclude multiple embodiments. Reference symbol list: 1 Ultra-precision lathe 3 workpieces 5 Workpiece holder 7 spindles 9 tools 11 Linear axis 13 Balancing ring 13a,b Balancing ring parts 15 Front 15a,b End face sections 17 Surface area 17a,b lateral surface sections 19 material removal structures 21 groove or slot 501 Turning the spindle 503 Determining an imbalance 505 Checking the balance quality 507 Machining the workpiece 509 Check if the workpiece is completely machined 511 Calculating a material removal profile 513 Balancing by material removal from the balancing ring 515 Smoothing the balancing ring Axial distance L axis of rotation T Depth of the groove or slot

Claims

[1] Ultra-precision lathe (1) for ultra-precise shaping of a workpiece (3), wherein the ultra-precision lathe (1) comprises: - a spindle (7) with a workpiece holder (5) for receiving a workpiece (3) to be machined, wherein the spindle (7) defines an axis of rotation (L) about which the spindle (7) with a workpiece (3) received by means of the workpiece holder (5) is rotatable, - at least one tool (9) that can be dynamically adjusted relative to the spindle (7) for material removal by machining, and - at least one sensor for direct or indirect detection of spindle imbalance (7), characterized by, that the ultra-precision lathe (1) further comprises a balancing ring (13) which is detachably attached to the spindle (7) coaxially to the axis of rotation (L), wherein the balancing ring (13) has an inner diameter which is larger than an outer diameter of the workpiece holder (5), wherein material of the balancing ring (13) can be removed rotationally asymmetrically by dynamically adjusting the at least one tool (9) while the spindle (7) is rotating, in order to compensate for an imbalance determined by means of the at least one sensor by machining material of the balancing ring (13). [2] Ultra-precision lathe (1) according to claim 1, wherein the balancing ring (13) has at least one annular end face (15) and the at least one tool (9) is configured to remove rotationally asymmetric material from the at least one end face (15) of the balancing ring (13) by dynamically feeding while the spindle (7) is rotating. [3] Ultra-precision lathe (1) according to claim 1 or 2, wherein the balancing ring (13) has at least two annular end faces (15) in a stepped manner, wherein the at least two annular end faces (15) have an axial distance (A) from each other. [4] Ultra-precision lathe (1) according to one of the preceding claims, wherein the balancing ring (13) is designed in multiple parts, wherein each part (13a,b) of the balancing ring (13) provides a material removal surface (15a,b, 17a,b) preferably on the end face, wherein the material removal surfaces (15a,b, 17a,b) have an axial distance (A) from each other. [5] Ultra-precision lathe (1) according to claim 4, wherein the parts (13a,b) of the balancing ring (13) are detachably attached to the spindle (7) with an axial distance (A) to each other and coaxial to the axis of rotation (L). [6] Ultra-precision lathe (1) according to claim 4 or 5, wherein the parts (13a,b) of the balancing ring (13) have different outer diameters. [7] Ultra-precision lathe (1) according to one of the preceding claims, wherein the at least one tool (9) is suitable both for machining material removal from the balancing ring (13) and for machining material removal from a workpiece (3) held by means of the workpiece holder (5). [8] Ultra-precision lathe (1) according to one of the preceding claims, further comprising at least one additional tool (9) which can be dynamically adjusted relative to the spindle (7) for machining the workpiece (3). [9] Ultra-precision lathe (1) according to one of the preceding claims, wherein the at least one tool (9) is configured to remove rotationally asymmetric material from the balancing ring (13) once or several times during or between machining steps of a workpiece (3) held by means of the workpiece holder (5) by dynamically feeding while the spindle (7) is rotating. [10] Method for ultra-precise shaping of a workpiece (3) using an ultra-precision lathe (1), wherein the method comprises the following steps: - Rotating (501) a spindle (7) of the ultra-precision lathe (1) about a rotary axis (L), wherein the spindle (7) has a workpiece holder (5) for receiving a workpiece (3) to be machined, - Direct or indirect determination (503) of an imbalance of the rotated spindle (7) by means of at least one sensor, characterized by , that the procedure further exhibits: - Balancing (513) of the rotated spindle (7) by machining material from a balancing ring (13) which is detachably attached to the spindle (7) coaxially to the axis of rotation (L) and has an inner diameter that is larger than an outer diameter of the workpiece holder (5), wherein the material of the balancing ring (13) is removed by dynamically adjusting at least one tool (9) while the spindle (7) is rotating in a rotationally asymmetric manner in order to compensate for an imbalance determined by means of the at least one sensor by machining material from the balancing ring (13). [11] Method according to claim 10, wherein the steps of turning (501), determining (503) the imbalance and balancing (513) are performed and / or repeated during or between machining steps (507) of a workpiece (3) held by means of the workpiece holder (5). [12] Method according to claim 10 or 11, wherein the same tool (9) is used for machining (507) the workpiece (3) as for balancing (513). [13] Method according to claim 10 or 11, wherein a separate tool (9) is used for machining (507) the workpiece (3), which is not used for balancing (513). [14] Method according to one of claims 10 to 13, wherein during balancing (513) the material of the balancing ring (13) is removed by dynamically adjusting the at least one tool (9) with a rotating spindle (7) in a rotationally asymmetric manner from an annular end face (15) of the balancing ring (13). [15] Method according to one of claims 10 to 14, wherein when determining (503) the imbalance a wobbling movement of the spindle (7) is detected and when balancing material is removed from at least two material removal surfaces (15a,b, 17a,b) of the balancing ring (13), wherein the at least two material removal surfaces (15a,b, 17a,b) have an axial distance (A) to each other. [16] Method according to claim 15, wherein the at least two material removal surfaces (15a,b, 17a,b) are located on different end faces (15) of a stepped balancing ring (13) and / or on two different parts (13a,b) of a multi-part balancing ring (13). [17] Method according to any one of claims 10 to 16, further comprising a step of smoothing (515) the balancing ring (13) before or after machining (507) a workpiece (3) received by means of the workpiece holder (5), wherein the balancing ring (13) is smoothed by machining the material of the balancing ring (13) by the at least one tool (9) with rotating spindle (7) until the balancing ring (13) again has a rotationally symmetrical material distribution.

Images