Method for processing a surface of an optical lens or an optical mirror and device for processing a surface of an optical lens or an optical mirror

Abstract

The invention relates to a method and a device for machining a surface of an optical lens or an optical mirror, comprising the following operations: - rough grinding - fine grinding - ultra-fine grinding, wherein the three operations are carried out on a single device with a single clamping of the workpiece, wherein the operations of rough grinding and fine grinding are carried out with a workpiece support fixed in the direction of a longitudinal axis of a workpiece shaft, and wherein the operation of ultra-fine grinding is carried out with a workpiece support springable in the direction of the longitudinal axis of the workpiece shaft.

Description

[0001] The invention relates to a method for machining a surface of an optical lens or an optical mirror and to a device for machining a surface of an optical lens or an optical mirror.

[0002] The prior art (EP 0 685 298 B2) includes a method and apparatus for producing aspherical lens surfaces. Optical lenses with spherical surfaces are generally manufactured by surface grinding glass blanks, followed by polishing. Spherical lenses are also produced from pre-formed glass pressed parts using a diamond cup wheel, using ball grinding. The feed is achieved either by a tool spindle or by a workpiece spindle, to which the diamond cup wheel is positioned at a defined angle. The sphere radius on the lens is determined by this setting angle, so that, within certain limits, various spherical shapes can be produced using one and the same tool.

[0003] It is known in practice that the rough and fine grinding of optical lenses is carried out in a two-step process on a 3-axis CNC-controlled grinding machine. This grinding machine typically uses two cup grinding tools. If a third step, called ultra-fine grinding or ball honing, is used, this is carried out according to the state of the art on a downstream machine equipped with a special gimbal compensation system. Polishing then follows.

[0004] In ultra-fine grinding, very fine-grained diamond forming tools are typically used, typically with grain sizes of 7 µm to 15 µm (micrometers). A water-based emulsion can be used as a suspension. In polishing, special polishing tools are used, which are either made of a plastic suitable for polishing, for example Novotex or Pertinax, or metal tools covered with a polishing film suitable for polishing. The polishing film can, as is known in practice, be a foamed PU film with a thickness of 0.5 to 1.3 mm, depending on the size of the tools. As is known in practice, a polishing agent made of rare earths dissolved in water is usually used as a polishing suspension. Examples of polishing agents that can be used are Opaline or Cerox (cerium oxide). The grain size of the polishing agent is typically in the range of 0.5 µm to 2.5 µm.However, other polishing agents can also be used, for example aluminum oxide (AL 2 O 3 ) or ferric oxides (iron oxides).

[0005] The polishing process involves both mechanical removal and chemical and thermal effects. In contrast, all upstream processes, such as pre-grinding, fine grinding, and ultra-fine grinding (ball honing), are purely mechanical removal processes. The removal properties of these three removal processes using diamond tools typically exhibit the following removal rates: When pre-grinding with diamond tools in the range of 80 μm to 200 μm diamond particle size, the removal rates are in the 3 mm to 5 mm range. When fine grinding with diamond tools in the range of 10 μm to 20 μm diamond particle size, the removal rates are in the 0.2 mm to 0.3 mm range. When ultra-fine grinding or ball honing with diamond tools in the range of 7 μm to 15 μm diamond particle size, typical removal rates are in the range of 0.01 mm to 0.1 mm.

[0006] The machines used for rough and fine grinding, such as those described in EP 0 685 298 B2, are CNC-controlled machines that typically have three axes (XZ and B). The grinding process is carried out, as described in EP 0 685 298 B2, with a so-called cup grinding tool.

[0007] In practice, it is known to design cup grinding tools with a spherical annular cutting segment (tangential cutting lip). There are also cup grinding tools with a radial cutting lip. Cup grinding tools with radial cutting lips are used for the pre-grinding process. Cup grinding tools with spherical annular cutting segments are used for the fine grinding and ultra-fine grinding processes.

[0008] In practice, CNC machines with four axes (X, Y, and B) are already being used in some cases. The additional Y-axis is used to adjust the optimal center position of the cutting lip. Typically, adjustments of a maximum of 0.1 mm to 0.2 mm are made here. This is an attempt to reduce the so-called "aspherical error." This "aspherical error" occurs when the center cutting line of the grinding tools does not pass 100% precisely through the workpiece's center of rotation.

[0009] For precision grinding and polishing, 3-axis CNC machines (XZB axes) are used in practice. Since the lens must be perfectly aligned with the spherical tool during the process, a chuck capable of spatial gimbal compensation is advantageously used as the tool holder.

[0010] The tool kinematics during rough and fine grinding are significantly different from those during superfine grinding or ball honing. During rough and fine grinding, the tool typically rotates significantly faster than the workpiece. Depending on the tool diameter, the tool speeds range from 10,000 to 100,000 revolutions per minute, and the tool speeds typically range from 100 to 500 revolutions per minute. This process is known in technical terms as surface grinding. Optimal cutting speeds are in the range of 20 to 30 meters per second (m / s).

[0011] During rough and fine grinding, the workpiece is always firmly connected to the workpiece spindle.

[0012] In precision grinding or ball honing, however, gimbal compensation is always necessary, as the workpiece cannot be changed with sufficient reproducibility due to clamping and unclamping from one machine to another. Clamping repeatability accuracies of less than 1 µm are required here. However, this is not technically feasible to date.

[0013] Three-stage machining is too expensive due to small batch sizes and the need for an additional machine. For this reason, in practice, only a two-stage grinding process is used in small-batch production.

[0014] The two-stage grinding process is carried out using cup grinding tools which have a radius-shaped cutting lip for the pre-grinding process and a spherical ring-shaped cutting segment for the fine grinding and ultra-fine grinding process.

[0015] The cup grinding tool is adjusted by the three main axes of the grinding machine via CNC controls so that the corresponding sphere can be created by positioning.

[0016] A major disadvantage of this very hard two-stage machining process, known in practice, is the relatively deep damage (8 µm to 12 µm), but also the fact that a perfect sphere is not created. This is due, on the one hand, to the wear behavior of the tool, but also, on the other, to the inaccuracy of the positioning of the tool's center grinding line at the center of the workpiece.

[0017] These two weak points lead to significantly longer polishing times, for example by a factor of 2 to 3, as well as to constant wear of the polishing tool, especially in the center of the lens. A hump typically develops on the polished lens because the aspherical error of the workpiece is transferred to the polishing tool after fine grinding. The polishing tool then transfers the error to the next workpiece. Highly qualified specialists are required to attempt to minimize the error by modifying the polishing kinematics.

[0018] The technical problem underlying the invention is to provide a method and a device for machining a surface of an optical lens or an optical mirror, with which it is possible to machine the surface of the optical lens or the optical mirror with high precision and which are also inexpensive.

[0019] This technical problem is solved by a method having the features according to claim 1 and by a device having the features according to claim 11.

[0020] The method according to the invention for machining a surface of an optical lens or an optical mirror with the following operations: Pre-grinding, fine grinding, super-fine grinding, in which the optical lens or the optical mirror is arranged in a workpiece carrier as the workpiece, and in which the workpiece carrier is arranged on a workpiece shaft, is characterized in that the three operations are carried out on a single device with a single clamping of the workpiece, that the operations of rough grinding and fine grinding are carried out with a workpiece bearing that is fixed in the direction of a longitudinal axis of the workpiece shaft and that the operation of ultra-fine grinding is carried out with a workpiece bearing that is resilient in the direction of the longitudinal axis of the workpiece shaft.

[0021] In the following, the optical lens or optical mirror refers to the workpiece.

[0022] The device can advantageously be designed as a machine tool.

[0023] Fine grinding is also called ball grinding or hybrid grinding.

[0024] The method according to the invention comprises a three-stage grinding process in which two operations, namely rough grinding and fine grinding, are carried out in such a way that the workpiece shaft is mounted with a fixed workpiece support in the direction of a longitudinal axis of the workpiece shaft. For the ultra-fine grinding or ball honing operation, the workpiece shaft can be spring-mounted in the direction of the longitudinal axis of the workpiece shaft. Because the workpiece shaft enables both fixed workpiece support and switchable spring-loaded workpiece support, the method according to the invention makes it possible to perform the three operations of rough grinding, fine grinding, and ultra-fine grinding on a single device. Furthermore, it is not necessary to clamp the workpiece again for the third operation, namely ultra-fine grinding, i.e., to arrange it in a workpiece carrier.For this reason, three-stage processing is possible with a single device, so that the disadvantages of the prior art with two-stage processing can be avoided.

[0025] The problems that occur with two-stage machining are eliminated with the three-stage diamond grinding process, as cardanic precision grinding, or ball honing, eliminates the center error due to the pivoting kinematics used in the precision grinding machine. Furthermore, this operation significantly reduces damage to the surface (3 µm to 5 µm maximum) because the process is very smooth. Cardanic compensation can be further supported by a diaphragm chuck. This allows the process to be carried out with significantly less vibration. It is vibration-damped grinding.

[0026] According to an advantageous embodiment of the invention, it is provided that the pre-grinding operation is carried out with a cup grinding tool with a radius-shaped cutting lip, and that the fine grinding and ultra-fine grinding operations are carried out one after the other with a cup grinding tool with a spherically shaped annular cutting segment, and that between the fine grinding and ultra-fine grinding operations, the workpiece bearing is switched from the fixed workpiece bearing in the direction of the longitudinal axis of the workpiece shaft to the resilient workpiece bearing in the direction of the longitudinal axis of the workpiece shaft.

[0027] During the third step, namely fine grinding, the rigid pre- and fine-grinding device is transformed into a gimbal-mounted fine-grinding or ball-peening device. At the same time, the surface grinding process of the first and second steps is switched to a synchronized fine-grinding or ball-peening process in the third step.

[0028] According to a further advantageous embodiment of the method according to the invention, the pre-grinding and fine-grinding operations are carried out with tool spindles driven in a speed range of 10,000 to 100,000 revolutions per minute and a workpiece shaft driven in a speed range of 100 to 500 revolutions per minute. According to a further advantageous embodiment of the method according to the invention, the fine-grinding operation is carried out with a tool spindle driven in a speed range of 1,000 to 3,000 revolutions per minute and a workpiece shaft driven in a speed range of 1,000 to 3,000 revolutions per minute.

[0029] The speed of the cup grinding tools for precision grinding is particularly advantageous in the range of 2,000 to 3,000 revolutions per minute, and the workpiece speed is also advantageously in the same speed range. The tool spindle and the workpiece shaft operate in a synchronous mode, depending on the workpiece radius and the aperture angle of the lens or mirror. This kinematics, which differs from pre-grinding and fine grinding, produces a significantly finer surface with significantly reduced depth damage, even though the form sizes of the two tools may be identical. For example, the depth damage is 2 to 3 times better than with surface grinding.

[0030] A 10 µm to 12 µm diamond tool produces a depth of damage of 8 µm to 12 µm during surface grinding, but only a depth of damage of 2 µm to 4 µm during ball honing or fine grinding in cardanic or spring synchronous mode.

[0031] As already explained, the method according to the invention comprises a three-stage grinding process. The pre-grinding and fine-grinding steps are carried out using high-speed tool spindles with a speed range of advantageously 10,000 to 100,000 revolutions per minute. The workpiece speed is advantageously between 100 and 500 revolutions per minute. This is the so-called surface grinding process. The pre-grinding and fine-grinding steps are followed by the ultra-fine grinding step, which is carried out on the same device as the third step. Here, the cup grinding tool of the second step, namely fine grinding, is used with a diamond particle size of advantageously 10 µm to 12 µm. However, in the third ultra-fine grinding step, the workpiece shaft is spring-mounted in the direction of the longitudinal axis of the workpiece shaft.This creates a cardanic balance through the additional axis in the workpiece shaft. In the third operation, the rigid roughing and fine grinding machine transforms into a cardanically mounted fine grinding or ball honing machine. At the same time, the surface grinding process in the third operation is switched to a synchronized fine grinding or ball honing process. During this process, the tool spindle and the workpiece shaft are switched to a so-called synchronous mode, in which the speed of the tool and the workpiece is each set in the range of advantageously 1,000 to 3,000 revolutions per minute, preferably 2,000 to 3,000 revolutions per minute, in a relatively synchronized direction of rotation.

[0032] Since the three operations are carried out without changing the workpiece in the fixture, the positioning of the workpieces relative to the tool is so precise that gimbal compensation with a linear axis is sufficient.

[0033] During the third pass, the device switches from the rigid grinding mode to a precision grinding or ball-cutting mode that pivots around the center of the optical lens. This process produces a significantly more precise spherical shape and significantly reduced surface damage. This third pass, in particular, requires the use of a quasi-spherical segment tool. For this reason, the spherical annular cutting segment is designed for the precision grinding process.

[0034] According to a further advantageous embodiment of the method according to the invention, the precision grinding operation is carried out in a synchronous mode with the rotational directions of the workpiece and the cup grinding tool synchronized relative to each other. With simultaneous spring mounting of the workpiece carrier in the direction of the longitudinal axis of the tool spindle, a precision grinding process is achieved that exhibits only very minimal depth damage.

[0035] The two cup grinding tools differ in their cutting edge shape. The cup grinding tool used for the pre-grinding process advantageously features a radius-shaped cutting lip. It is advantageously a universal tool that is independent of the lens radius.

[0036] For fine grinding and ultra-fine grinding, spherical annular segment tools are advantageously used. This tool has a tangential cutting edge. This tool is a segment tool assigned to the lens radius.

[0037] Any cup grinding tool used for a specific lens for an extended period of time will develop into a tangential tool due to wear. This can happen after just 50 to 100 lenses.

[0038] For optimal implementation of the third step of precision grinding, it is important to work with a cup grinding tool that matches the lens radius from the beginning. This cup grinding tool can advantageously have a metallic, ceramic, and / or plastic-based diamond tool segment cutting edge.

[0039] According to a further advantageous embodiment of the method according to the invention, it is provided that after the first pre-grinding operation, which is carried out with the first cup grinding tool, the second cup grinding tool is used, and that after the fine grinding operation, the speed of the workpiece shaft and the speed of the tool spindle are reduced, and that the workpiece is switched from a mounting that is fixed in the direction of the longitudinal axis of the workpiece shaft to a mounting that is resilient in the direction of the longitudinal axis of the workpiece shaft.

[0040] The first pre-grinding step is performed with the first cup grinding tool. This cup grinding tool advantageously has a radius-shaped cutting lip and is a universal tool independent of the lens radius. After this step, the second cup grinding tool is used for the fine grinding and ultra-fine grinding steps. After the fine grinding step, the speed of the tool spindle and the speed of the workpiece shaft are reduced, and the workpiece is switched from a rigid mounting to a spring-loaded mounting on the workpiece carrier.

[0041] A further advantageous embodiment of the method according to the invention provides that the optical lens or the optical mirror is arranged in the workpiece carrier, wherein the workpiece carrier for the optical lens or for the optical mirror is non-positively connected to the workpiece shaft, that the first rough grinding operation is carried out with the first cup grinding tool with a radius-shaped cutting lip and with a workpiece bearing that is fixed in the direction of the longitudinal axis of the workpiece shaft, that the fine grinding operation is carried out with the second cup grinding tool with a spherically designed annular cutting segment and with a workpiece bearing that is fixed in the direction of the longitudinal axis of the workpiece shaft, that before the ultra-fine grinding operation, the workpiece bearing that is fixed in the direction of the longitudinal axis of the workpiece shaft is switched to a spring bearing, and that the speed of the workpiece shaft and the speed of the tool spindle are reduced, that the ultra-fine grinding operation is carried out.

[0042] This process enables a three-stage diamond grinding process in which the workpiece can be machined in a single setup using two tools, i.e., two cup grinding tools. It is crucial that the fixed workpiece support is switched to a spring-loaded workpiece support for the precision grinding process.

[0043] Additionally, the device switches from the fixed grinding mode to a precision grinding or ball-honing mode that pivots around the center of the optical lens or mirror. This process produces a more spherically precise shape and significantly reduces surface damage.

[0044] According to a further advantageous embodiment of the method according to the invention, it is provided that during the fine grinding operation, the tool spindle carries out a CNC-controlled, 3-axis pivoting movement around a radius center point of the optical lens or optical mirror to be machined.

[0045] As already explained, this creates the spherically precise shape of the optical lens or optical mirror.

[0046] According to a further advantageous embodiment of the method according to the invention, the frictional connection between the optical lens and the workpiece carrier or between the optical mirror and the workpiece carrier is created by a collet chuck and / or a vacuum fixture and / or an adhesive fixture. For the pre-grinding, fine grinding, and ultra-fine grinding operations, it is necessary that the workpiece is arranged in one and the same position on the workpiece carrier. This can be achieved easily, inexpensively, and reliably using a collet chuck and / or a vacuum fixture and / or an adhesive fixture. In principle, other types of fixture are also possible.

[0047] A further advantageous embodiment of the method according to the invention provides that the fine grinding and ultra-fine grinding operations are carried out with segmented tools having a diamond grain size. It has been found that by arranging the workpiece on the workpiece carrier for both operations and switching from fixed workpiece support to spring-loaded workpiece support in the direction of the longitudinal axis of the tool spindle, it is possible to perform both operations with one and the same diamond grain size.

[0048] By reducing the speed of the tool spindle and workpiece shaft during the third step, the fine grinding step, vibration of the fixture during high-speed operation is reduced or eliminated. This allows a surface with two different roughnesses to be created using a single cup grinding tool (segment tool) with a single diamond grain size, allowing both the fine grinding and the ultra-fine grinding processes to be performed with the same cup grinding tool.

[0049] The device according to the invention for machining an optical lens or an optical mirror with a workpiece carrier for supporting the optical lens or the optical mirror, wherein the workpiece carrier is arranged on a workpiece shaft, is characterized in that that the workpiece shaft is fixable with respect to the direction of its longitudinal axis or that the workpiece shaft is spring-mounted in the direction of its longitudinal axis, that at least two tool spindles are provided, that a cup grinding tool for machining the surface of the optical lens or the optical mirror is arranged on each tool spindle.

[0050] The device according to the invention has the advantage that it can be used in two operating modes: firstly, the workpiece shaft can be fixed along its longitudinal axis, so that a "rigid" workpiece shaft is used for the pre-grinding and fine-grinding operations. Secondly, the workpiece shaft can be spring-mounted along its longitudinal axis. This operating mode is used for the fine-grinding operation.

[0051] The device according to the invention can be switched between both working modes.

[0052] In addition, two tool spindles are provided, each carrying a tool for machining the optical lens or the optical mirror.

[0053] The first cup grinding tool advantageously has a radius-shaped cutting lip. This is a universal tool independent of the lens radius. This tool is used for the pre-grinding process.

[0054] The second cup grinding tool is advantageously a spherically shaped, annular segment tool. This tool has a tangential cutting lip. This cup grinding tool is a segment tool assigned to the lens radius of the optical lens or optical mirror to be machined. This cup grinding tool is used for fine grinding and ultra-fine grinding operations.

[0055] According to a further advantageous embodiment of the invention, it is provided that a switching device is provided for the fixed mounting of the workpiece shaft with respect to the longitudinal axis of the workpiece shaft or for the resilient mounting of the workpiece shaft with respect to the longitudinal axis of the workpiece shaft.

[0056] This is the particular advantage of the device according to the invention. Due to the ability to switch between fixed and spring-loaded mounting, it is possible to perform three work steps—pre-grinding, fine grinding, and ultra-fine grinding—on one and the same device.

[0057] According to a further advantageous embodiment of the invention, the switching device is designed as a pneumatic switching device. A pneumatic switching device has the advantage that it does not cause contamination, unlike an oil-operated switching device. In principle, it is also possible to provide a hydraulic or electromagnetic switching device. However, the pneumatic switching device is particularly advantageous because it is operated solely with compressed air.

[0058] According to a further advantageous embodiment of the invention, it is provided that the cup grinding tools can be arranged on the tool spindle by means of a collet or a hydraulic expansion chuck.

[0059] In principle, other mounting options are also possible. However, the mounting options mentioned are reliable and inexpensive.

[0060] According to a further advantageous embodiment of the invention, it is provided that either two cup grinding tools or one cup grinding tool and one polishing tool are arranged on the tool spindles.

[0061] In principle, the device can be used for the three work steps of pre-grinding, fine grinding and super-fine grinding, as already described in detail.

[0062] However, it is also possible to arrange a cup grinding tool for the fine grinding process and a polishing tool on the second tool spindle for a polishing process. This means that the device according to the invention can also be used as a device for fine grinding and polishing.

[0063] A further advantageous embodiment of the invention provides that the device has an additional axis for the feed movement of the tool spindles. This makes it possible to adjust the feed movement of the tool spindles to achieve the desired material removal rate on the workpiece. At the same time, this axis allows the cup grinding tool, which is used for micro-grinding, to be brought into a perfect tangential position for this operation.

[0064] According to a further advantageous embodiment of the invention, the device is designed as a 4- or 5-axis CNC grinding machine. This CNC machine makes it possible to carry out the method according to the invention. This makes it possible to perform the three work steps of pre-grinding, fine grinding, and ultra-fine grinding on one and the same device, thus eliminating the costly purchase of a second device.

[0065] According to a further advantageous embodiment of the invention, the two tool spindles are designed as frequency-controlled tool spindles. This makes it possible to adjust the speed of the tool spindles and the workpiece shafts depending on the requirements of the respective work process.

[0066] The features of the device according to the invention also apply to the method according to the invention and vice versa.

[0067] Further features and advantages of the invention will become apparent from the accompanying drawings, which illustrate an embodiment of a device according to the invention and various cup grinding tools, without limiting the invention to these embodiments. The drawings show: Fig. 1 shows a device according to the invention in longitudinal section; Fig. 2 shows a cup tool with a tangential grinding lip in longitudinal section; Fig. 3 shows a cup tool with a radius cutting lip in longitudinal section; Fig. 4 shows a cup grinding tool in longitudinal section to illustrate the pivot angle; Fig. 5 shows a cup grinding tool to illustrate the pivot angle.

[0068] Fig. 1 shows a device 1 for machining a surface of an optical lens 2. The lens 2 is mounted in a workpiece carrier 3. The workpiece carrier 3 is releasably fixed to a base part 5 by means of a screw 4. The tool carrier 3 is connected to a workpiece shaft 6. The workpiece shaft 6 rotates about its longitudinal axis L at a rotational speed ω2. It is driven by a drive pin 40 of a workpiece spindle 39.

[0069] The longitudinal axis L is aligned in the Z direction. The spindle 6 is hollow, i.e., a through-bore 7 for compressed air is arranged in the spindle 6. A rotary feedthrough 8 is provided for introducing the compressed air. The compressed air is guided through the bore 7 to the workpiece carrier 3. The workpiece carrier 3 is designed as a collet. The collet is not shown in detail. The workpiece carrier 3 can also be designed as a vacuum fixture. The lens 2 can also be attached to the workpiece carrier 3 by means of an adhesive. If the workpiece carrier 3 is designed as a vacuum fixture, a negative pressure is generated in the bore 7, which continues into a diaphragm chuck 9.

[0070] If the workpiece carrier 3 is designed as a collet chuck, a stroke h2 is generated via a cylinder 10. The stroke h2 closes or opens the collet chuck. For example, when compressed air is introduced through a bore 11, the compressed air is introduced into the cylinder 10. This pushes a piston 12 downward, closing the collet chuck. When the compressed air supply is discontinued, the piston 12 moves upwards again, and the collet chuck releases the lens 2.

[0071] The spindle 6 is mounted by means of ball bearings 13 so that it can rotate around the longitudinal axis 11 at a rotational speed ω2.

[0072] The workpiece shaft 6 can be operated in two operating modes. In the first operating mode, the workpiece shaft is fixed or rigidly mounted in the direction of the longitudinal axis L. This means that the spindle cannot deflect in the Z direction during machining of the optical lens. For this purpose, a pneumatic piston 14 is extended so that it presses against a holding plate 15 with a force F1. The pneumatic device 16 for actuating the piston 14 is attached to a housing part 17 of the device 1. The holding plate 15 and the housing part 17 are arranged at an equidistant, non-variable distance from one another in this operating mode. This means that in this operating mode, the workpiece shaft 6 is fixedly mounted in the direction of the longitudinal axis L of the workpiece shaft 6. Nevertheless, the spindle can rotate about the longitudinal axis L. The fixed mounting refers only to the deflection in the direction of the longitudinal axis L of the workpiece shaft 6.

[0073] In the second operating mode, a force F+ is switched to a force F-, i.e., the force F- is suspended with the spring force FF of a spring 18. In this operating mode, the spring 18 acts between the retaining plate 15 and the housing part 17. The spring 18 is designed as a compression spring. The spring 18 presses the retaining plate 15 downwards from the housing part 17 with the spring force FF. The force F- acting in the opposite direction pulls in the opposite direction. This creates the suspended force. F − − Federkraft FF der Feder 18 = Δ − Kraft .

[0074] This Δ-force is balanced so that the workpiece shaft 6 is moved in a workpiece spindle 39 (weight- and friction-free) in the opposite direction to the spring force FF by the stroke H3. This then represents the working force for fine grinding or ball honing. In the opposite direction to the spring force FF, ΔF, i.e., the Δ-force, becomes positive.

[0075] In this operating mode, the workpiece shaft 6 is spring-mounted. This spring-mounted operation is achieved by the Δ force. The workpiece shaft 6 can now perform the machining of the optical lens 2, i.e., when the Δ force is applied to the optical lens 2 in the Z direction. The workpiece spindle 6 is spring-mounted in this operating mode.

[0076] The piston 14 has a stroke h1.

[0077] To allow the workpiece shaft 6 to move in the direction of its longitudinal axis, guides 10, 20 in the form of sliding bushes are provided. As already explained, the workpiece shaft 6 is rotatably mounted by means of ball bearings 25. The ball bearings 25 are arranged in a spindle sleeve 38.

[0078] The workpiece spindle 39 is driven by a pulley 24 via a toothed belt (not shown).

[0079] In plane AA, the device 1 is shown in sections. The workpiece shaft 6 is significantly longer than in Fig. 1 shown.

[0080] A ball bearing 25 is also shown divided along plane AA. To protect the device 1 from the ingress of dirt particles, a rubber bellows 26 is provided, allowing a stroke h3. The device has a plurality of O-rings 27 for sealing.

[0081] For the processing of lens 2, Fig. 1 a first cup grinding tool 28 is shown. This cup grinding tool is used in Fig. 2 A second cup grinding tool 29 will be described later in Fig. 3 described.

[0082] The cup grinding tool 28 is arranged on a schematically illustrated tool spindle 30. The tool spindle 30 rotates about its longitudinal axis L1 at a rotational speed ω1.

[0083] With the device according to Fig. 1 machining of an optical lens 2 or an optical mirror (not shown) can be carried out with the following three operations: Pre-grinding Fine grinding Ultra-fine grinding (also called ball grinding or hybrid grinding).

[0084] Fig. 2 shows the cup grinding tool 28. The cup grinding tool 28 is a segment tool assigned to the lens radius. The cup grinding tool 28 has a spherically shaped annular cutting segment 31. The annular cutting segment 31 has a tangential cutting lip 32. This cup grinding tool 28 is used for fine grinding and ultra-fine grinding operations.

[0085] The cup grinding tool 28 has an inner diameter Di, a mean diameter DM, and an outer diameter DA. Since the cup grinding tool 28 is a spherically shaped annular cutting segment tool, it has a radius R.

[0086] Fig. 3 shows the cup grinding tool 29, which is arranged on a tool spindle 30. The cup grinding tool 29 has a radius-shaped cutting lip 33. The radius-shaped cutting lip 33 has a radius r. This cup grinding tool also has an inner diameter Di, a mean diameter DM and an outer diameter DA. This cup grinding tool is a universal tool that is independent of the lens radius of the lens 2 to be machined. However, if it is used for a specific lens for an extended period of time, this cup grinding tool will become a tangential tool due to its wear. Fig. 2 This can occur after as little as 50 to 100 lenses. Cup grinding tool 29 is used for the pre-grinding process.

[0087] The implementation of the method according to the invention will now be described with reference to Fig. 1 , 2 und 3 explained.

[0088] The device 1 is intended to perform a grinding process, specifically with the three work steps of pre-grinding, fine grinding, and ultra-fine grinding (also called ball honing or hybrid grinding). For this purpose, the device 1 has two frequency-controlled tool spindles 30, 34 in the upper part on a pivoting B-axis. Cup grinding tools, i.e. one cup grinding tool 28, 29 each, are arranged on these tool spindles 30, 34. The cup grinding tool 29 is intended for the pre-grinding process (first work step). The second cup grinding unit 28 is intended for the second work step of fine grinding and for the third work step of ultra-fine grinding. The cup grinding tools 28, 29 can be attached to the tool spindles 30, 34 using a collet or a hydraulic expansion chuck (not shown).This upper part 35 of the device 1 is arranged on an xy-slide (not shown), which enables the lateral adjustment in the x-direction via the x-slide according to the calculation principle. x = D W ⋅ cos α α = arc sin D W R L ⋅ 2 with D W = Diameter tool R L = radius lens α = swivel angle The additional Y-axis is intended exclusively to eliminate misalignment between the workpiece spindle 38 and the tool spindles 30, 34. This reduces the aspherical error.

[0089] Additionally, a further Z1 axis is arranged in the upper part 35 of the device 1, which carries out the feed movement of the tool spindles 30, 34 with the cup grinding tools 28, 29 in order to perform the desired material removal on the lens 2. At the same time, this axis enables the cup grinding tool 28 to be brought into a perfect tangential position for the third operation of the fine grinding.

[0090] In the lower part 36 of the device according to the invention, which is advantageously designed as a CNC grinding machine, a workpiece spindle 39 is arranged, which enables a further feed movement in the Z direction. In addition to this Z2 axis, a Z3 axis (workpiece shaft 6) is arranged axially in the center of the workpiece spindle 38. This axis, via a pneumatic adjustment with the pneumatic device 16 and the piston 14, switches the workpiece spindle 38 to a spring-loaded mode for the third operation, the so-called fine grinding or ball honing. In this third operation, the workpiece shaft 6 is switched to a gimbal mode.

[0091] The entire production process is as follows: The lens 2 is arranged as a blank on the workpiece carrier 3. According to Fig. 1 The workpiece carrier 3 is designed as a collet. Compressed air actuates the piston 12 and thus the collet, so that the lens 2 is held by the collet.

[0092] It is also possible to not pressurize the bore 7 of the workpiece shaft 6 with compressed air, but to create a vacuum in the bore 7. This causes the lens 2 to be sucked onto a diaphragm chuck 9 and also held in place. Another possibility, not shown, is to attach the lens 2 to the workpiece carrier 3 by means of an adhesive fastening.

[0093] The device 1 is then moved via its 4-axis positioning to the working position of the first work step, namely pre-grinding. Here, the cup grinding tool 29, which is located in Fig. 3 is shown, the lens is processed. After completion of this operation, the device 1, preferably a CNC-controlled device, moves via its 4-axis positioning to the working position of the second operation, namely fine grinding. For this purpose, the cup grinding tool 28 is used. After completion of this second operation, the device 1 moves by means of its 4-axis positioning to the third working position in order to use the cup grinding tool 28, which is in Fig. 2 The third operation, namely the fine grinding operation, is carried out as shown. The first and second operations are carried out with the piston 14 extended, so that an equidistant distance is maintained between the holding plate 15 and the housing part 17. This fixed distance ensures a rigid or fixed mounting of the workpiece shaft 6.

[0094] For the third machining step, the internal Z-axis of the workpiece shaft 6 is brought into a cardanic state with the stroke h via the piston 14, which is designed as a pneumatic cylinder, on the workpiece shaft 6. At the same time, the cup grinding tool 28 and the workpiece shaft 6 are switched to the low-vibration, slow-running synchronous mode. The pneumatic pressure of the Z-axis Z3 presses the lens 2 against the cup grinding tool 28, and machining is carried out by time control. During this working time, the tool spindle 30 with the cup grinding tool 28 performs a CNC-controlled 3-axis pivoting movement around the radius center of the lens 2 to be machined.

[0095] For the first pre-grinding step and the second fine grinding step, the speeds of the cup grinding tools 28 and 29 range from 10,000 to 100,000 revolutions per minute. The tool speed is typically between 100 and 500 revolutions per minute.

[0096] For the synchronous mode, the cup grinding tools 28, 29 and the workpiece, namely the lens 2, have speeds in the range of 1,000 to 3,000 revolutions per minute.

[0097] By switching to synchronous mode with reduced speeds for the third operation, the vibrations are reduced so that the second operation of fine grinding and the third operation of ultra-fine grinding can be carried out with one and the same cup grinding tool 28.

[0098] In the Fig. 4 und 5 The cup grinding tool 28 is shown in each case. In the Fig. 4 und 5 The swivel range Δα is shown. The swivel range Δα depends on the tool segment width of the cup grinding tool 28. A part of the cup grinding tool 28 should always protrude beyond a center of the lens 2. This means that the cup grinding tool 28 has an outer edge 37, as in Fig. 4 shown, should not swing further to the right over the center line M of lens 2. In Fig. 4 The swivel angle of sin α1 is shown in the outer position. In Fig. 5 The swivel angle sin α2 is shown in the inner position. Fig. 4 und 5 refer only to the spring-loaded state of the workpiece shaft 6.

[0099] The swivel angle is calculated as follows: sin α = D MWZ 2 ⋅ R L sin α 1 = D WZ 1 2 ⋅ R L sin α 2 = D WZ 2 2 ⋅ R L sin Δα = sin α 1 − sin α 2

[0100] Typically, the swivel range should be a relative travel of 2 mm to 4 mm. After the third step, which is performed solely by applying time and pressure, the lens 2 is removed from the fixture 1 and finished in a subsequent CNC polishing machine. Reference numbers

[0101] 1 Fixture 2 Optical lens 3 Workpiece carrier 4 Screw 5 Base part 6 Workpiece shaft 7 O-ring 8 Rotary feedthrough for compressed air 9 Diaphragm chuck 10 Cylinder 11 Bore 12 Piston 13 Ball bearing 14 Piston 15 Retaining plate 16 Pneumatic device 17 Housing part 18 Spring 19 Guides 20 Guides 21 Bearing housing 22 Preload device for ball bearing 23 Screw 24 Pulley 25 Ball bearing 26 Rubber bellows 27 O-rings 28 Cup grinding tool 29 Cup grinding tool 30 Tool spindle 31 Ring cutting segment 32 Tangential cutting lip 33 Radial cutting lip 34 Tool spindle 35 Upper part of the fixture 1 36 Lower part of the fixture 1 37Outer edge of the cup grinding tool 28 38Spindle sleeve 39Workpiece spindle 40Driver pin F1Force FFSpring force F+Force F-Force LLongitudinal axis of the workpiece shaft 6 ω1Rotational speed ω2Rotational speed h1Stroke of the piston 14 h2Stroke H3Stroke hStroke of the workpiece shaft 6 with cardanic bearing L1Longitudinal axis of the tool spindle 30 ΔαSwivel range of the cup grinding tool 28 MCenter axis of the lens DiInner diameter DMMean diameter DAOuter diameter RRadius rRadius

Claims

1. A method for machining a surface of an optical lens (2) or an optical mirror, comprising the following operations: - pre-grinding - fine grinding - super-fine grinding, in which an optical lens (2) or an optical mirror is arranged as a workpiece in a workpiece carrier (3), and in which the workpiece carrier (3) is arranged on a workpiece shaft (6), characterized in that the three operations are carried out on a single device (1) with a single clamping of the workpiece, that the operations of pre-grinding and fine grinding are carried out with a workpiece bearing that is fixed in the direction of a longitudinal axis (L) of the workpiece shaft (6), and that the operation of ultra-fine grinding is carried out with a workpiece bearing that is resilient in the direction of the longitudinal axis (L) of the workpiece shaft (6).

2. Method according to claim 1, characterized in thatthe rough grinding operation is carried out with a cup grinding tool with a radius-shaped cutting lip (33), and that the fine grinding and ultra-fine grinding operations are carried out one after the other with a cup grinding tool (28) with a spherically shaped annular cutting segment (31), and that between the fine grinding and ultra-fine grinding operations, the workpiece bearing is switched from the workpiece bearing which is fixed in the direction of the longitudinal axis (L) of the workpiece shaft (6) to the workpiece bearing which is resilient in the direction of the longitudinal axis (1) of the workpiece shaft (6).

3. Method according to claim 1 or 2, is characterized in that the pre-grinding and fine grinding operations are carried out with tool spindles (30, 34) which are driven in a speed range of 10,000 to 100,000 revolutions per minute and a workpiece shaft (6) which is driven in a speed range of 100 to 500 revolutions per minute.

4. Method according to one of the preceding claims, characterized in that the fine grinding operation is carried out with a tool spindle (30) which is driven in a speed range of 1,000 to 3,000 revolutions per minute and a workpiece shaft (6) which is driven in a speed range of 1,000 to 3,000 revolutions per minute.

5. Method according to one of the preceding claims, characterized in that the fine grinding operation is carried out in a synchronous mode with the rotational direction of the optical lens (2) or the optical mirror and the workpiece and the cup grinding tool (28) being synchronized relative to one another.

6. Method according to one of the preceding claims, characterized in thatafter the first rough grinding operation, which is carried out with the first cup grinding tool (29), the second cup grinding tool (28) is used, and that after the fine grinding operation the speed of the workpiece shaft (6) and the speed of the tool spindle (30) are reduced, and that the workpiece bearing is switched from the fixed bearing in the direction of the longitudinal axis (L) of the workpiece shaft (6) to a workpiece bearing which is resilient in the direction of the longitudinal axis (L) of the workpiece shaft (6).

7. Method according to one of the preceding claims, characterized by - that the optical lens (2) or the optical mirror is arranged in the workpiece carrier (3), wherein the workpiece carrier (3) for the optical lens (2) or for the optical mirror is non-positively connected to the workpiece shaft (6), - thatthe first pre-grinding operation is carried out with the first cup grinding tool (29) with a radius-shaped cutting lip (33) and with the workpiece bearing fixed in the direction of the longitudinal axis (L) of the workpiece shaft (6), - that the fine grinding operation is carried out with the second cup grinding tool (28) with a spherically shaped annular cutting segment (31) with a workpiece bearing fixed in the direction of the longitudinal axis (L) of the workpiece shaft (6), - that before the fine grinding operation, the workpiece bearing, which is fixed in the direction of the longitudinal axis of the workpiece shaft (6), is switched to a spring-loaded bearing, and the speed of the workpiece shaft (6) and the speed of the tool spindle (30) are reduced, - that the fine grinding operation is carried out.

8. Method according to one of the preceding claims, characterized in thatDuring the fine grinding operation, the tool spindle (30) performs a CNC-controlled 3-axis pivoting movement around a radius center point of the optical lens (2) or the optical mirror to be machined.

9. Method according to claim 7, characterized in that the frictional connection between the optical lens (2) and the workpiece carrier (3) or between the optical mirror and the workpiece carrier (3) is generated by a collet and / or a vacuum fastening and / or an adhesive fastening.

10. Method according to one of the preceding claims, characterized in that all operations of pre-grinding, fine grinding and ultra-fine grinding are carried out with cup grinding tools (28, 29) which have a diamond grain size.

11. Device for machining an optical lens (2) or an optical mirror with a workpiece carrier (3) for supporting the optical lens (2) or the optical mirror, wherein the workpiece carrier (3) is arranged on a workpiece shaft (6), characterized by - that the workpiece shaft (6) is fixable in relation to the direction of its longitudinal axis (L) or that the workpiece shaft (6) is spring-mounted in the direction of its longitudinal axis (L), - that at least two tool spindles (30, 34) are provided, - that a cup grinding tool (28, 29) for machining the surface of the optical lens (2) or the optical mirror is arranged on each tool spindle (30, 34).

12. Device according to claim 11, characterized in thata switching device (16) is provided for the fixed mounting of the workpiece shaft (6) with respect to the longitudinal axis of the workpiece shaft (6) or for the resilient mounting of the workpiece shaft (6) with respect to the longitudinal axis (L) of the workpiece shaft (6).

13. Device according to claim 12, characterized in that the switching device (16) is designed as a pneumatic switching device.

14. Device according to one of claims 11 to 13, characterized in that the cup grinding tools (28, 29) can be arranged on the tool spindle (30, 34) by means of a collet or a hydraulic expansion chuck.

15. Device according to one of claims 11 to 14, characterized in that either two cup grinding tools (28, 29) or one cup grinding tool (28) and one polishing tool are arranged on the tool spindles (30, 34).

16. Device according to one of claims 11 to 15, characterized in thatthe device (1) has an additional axis (Z1) for the feed movement of the tool spindles (30, 34).

17. Device according to one of claims 11 to 16, characterized in that the device (1) is designed as a 4- or 5-axis CNC grinding machine.

18. Device according to one of claims 11 to 17, characterized in that the two tool spindles (30, 34) are designed as frequency-controlled tool spindles (30, 34).

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