DEVICE FOR POLISHING AN OPTICAL LENS OR AN OPTICAL MIRROR AND METHOD FOR POLISHING AN OPTICAL LENS OR AN OPTICAL MIRROR

Description

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. § 119 of European Application No. 24199273.4 filed Sep. 9, 2024, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device for polishing an optical lens or an optical mirror and to a method for polishing an optical lens or an optical mirror.

2. Description of the Related Art

In the following text, the term lenses is used for linguistic simplification; however, optical mirrors having an imaging function are always meant, as well.

In practice, optical lenses are produced from transparent materials, by means of multiple grinding processes or other chip-removing machining methods. The materials can be mineral glass or suitable plastics.

In practice, the optical lenses are produced from blanks, in multiple work processes. Polishing follows the grinding processes, during which polishing the surface is made smooth.

From practice, it is known to form the main body of the polishing tool from a solid material. The main body has a shaping in the work region that approximately corresponds to the negative imprint of the surface to be machined, of the lens to be polished. This region of the polishing tool is provided with the aforementioned polishing film or with a polishing pitch, and this polishing film is very precisely dressed using a dressing tool. After the dressing process, the surface of the polishing pad corresponds very precisely to the negative imprint of the optical lens. Such polishing tools are referred to as shaping tools; however, polishing tools have also become known that have a surface, in the work region, that consists of a material that has the properties of a polishing film, so that an additional polishing film is not necessary.

The polishing tool is attached, as is known from practice, to a tool spindle of a polishing machine, by means of which it is set into rotation. The lens to be polished is situated in a workpiece carrier, also called a lens holder, which in turn is connected to a workpiece spindle and also rotates. The drive required for this arrangement is situated in the workpiece spindle. The tool spindle and the workpiece spindle of the polishing machine can usually be moved in multiple axes. Furthermore, one of the two spindles can be set at a slant, so that the geometric axes of the tool and the lens form an angle relative to one another, and intersect at the center point of the radii of the spherical lens surface to be machined. The tool spindle and the workpiece spindle have the same direction of rotation. They rotate at different speeds. This method is also referred to as the synchro-speed method.

A method for polishing optical lenses or mirrors having imaging properties, using a polishing machine, is part of the prior art (DE 100 44 872 A1).

According to this prior art, the optical lens is mounted in a lens holder, which in turn is mounted resiliently and therefore possesses axial mobility. The polishing pressure between the polishing tool and the lens is applied by springs, after these springs have been biased by means of setting movements of at least one of the machine spindles. The lens is held in place on the lens lining, in the lens holder, by suction, by means of applying a partial vacuum on its rear side. In this regard, the lens lining is previously adapted to the rear side of the lens, by means of dressing in the polishing machine.

During polishing, specific polishing tools are used, which polishing tools consist either of a plastic suitable for polishing, for example, Novotex or Pertinax, or also metal tools covered with a polishing pad suitable for polishing. As is known from practice, the polishing pad can be, for example, a foamed polyurethane (PU) film having a thickness of 0.5 mm to 1.3 mm, depending on the size of the tools, but can also be a polishing pitch having a thickness of a few millimeters. From practice, it is known that the polishing suspension used is usually a polishing agent consisting of rare earths dissolved in water. It is possible to use, for example, Opaline or Cerox (cerium oxide). The particle size of the polishing agent is typically in the range from 0.5 μm to 3.5 μm. It is also possible, however, to use other polishing agents, for example, aluminum oxide (Al₂O₃), or ferrous oxides (iron oxides). Very fine diamond liquids having a particle size in the range from 0.5 μm to 3.0 μm, however, can also be used.

The polishing process has both a mechanical removal function and chemical and thermal mechanisms of action.

For the precise imaging of a ground lens, it is necessary to treat the glass surface by polishing. For one thing, the surface roughness is further reduced. For another thing, final deviations from the required spherical radius, or from the desired sphere, are eliminated.

The polishing is carried out by means of a sliding relative movement between the surface of the workpiece to be machined and a polishing tool, which is designed as a receptacle for a polishing agent carrier. This feature enables, in connection with a polishing agent, the removal of material by polishing and, thus, an adaptation, or a smoothing, of the workpiece surface.

Very high requirements are placed on the polishing agent carrier and the polishing agent. For example, the polishing agent carrier must be malleable in order to be able to assume the necessary workpiece radius. In addition, it must be able to be well connected to the tool carrier and it may not contain impurities, which could cause damage to the glass surface. The following are well suited, as described above: for example, elastomeric films consisting of foamed polyurethane, which largely meet these requirements due to their good mechanical and chemical properties, as well as polishing pitches and other wax-like coatings.

The requirements on a polishing agent are not directly due to measurable variables, and so the selection and mixture of the polishing agent is based substantially on empirical values. Primarily, suspensions of finely ground oxides of trivalent and tetravalent metals are used, although they are highly dependent on the material to be machined. A tool often determines the shape of a workpiece during machining; however, such determination does not apply to the polishing of glass materials to the same extent as, for example, to metal processing by machining. In particular when glass lenses are polished, a wear-induced adaptation of the polishing agent carrier to the surface of the workpiece takes place, and so only a few surfaces of the tool radius have changed already after the machining. The target correction of the lens surface quickly lies outside the specified tolerances. This circumstance makes it necessary to dress the polishing agent carrier to the required spherical radius at regular intervals during the polishing process, i.e., to adapt the polishing agent carrier such that the shape accuracy and the traction of the polishing tool are retained.

A polishing tool is frequently dressed outside the polishing machine on specific dressing machines. These machines are, for example, lever machines with diamond pellet-coated surface tools, which can only be empirically adjusted, however. In addition, the polishing correction tool must be ground by means of a special tool to be produced separately, before the actual correction of the polishing tool can be carried out. Multiple post-corrections of the polishing tool and, optionally, also of the fine-grinding tool are often necessary, and so this method is extremely tedious and highly cost-intensive. When dressing using surface tools, a dedicated polishing correction tool must be produced for each radius.

A device and a method for polishing spherical lens surfaces are part of the prior art (EP 0 727 280 A1). This device, which is part of the prior art, is designed as a three-spindle machine. This machine is a computer numerical control (CNC) machine tool, which has a swivel unit of an axis with a rotationally driven tool spindle for accommodating a polishing tool. On a second feed drive, a rotatably mounted workpiece spindle for accommodating a lens, and a tool spindle, which is rotatably mounted parallel to the workpiece spindle, for accommodating a dressing tool, for example, a cup-shaped tool, are provided at a fixed distance. A relative swiveling is executable between the polishing tool and the lens. This prior art is the so-called “synchro-speed method.”

Here, the lenses are held by means of a workpiece chuck. This workpiece chuck consists of a guide ring, a main body, and a diaphragm, to which compressed air is applied via the workpiece spindle to cardanically press on the lens. A tool is situated, on the tool spindle side, opposite the workpiece chuck with the lens in place, which tool is approximately twice as great in diameter than the lens, according to the prior art. This tool has a covering consisting of polishing film, or consists of a material that is suitable for carrying out optical polishing.

The polishing tool is also fixed to the tool spindle of the machine via a mechanical clamping system. In order to provide the polishing tool with the precise radius of the lens to be machined, a second spindle is situated on the triaxial CNC machine parallel to the workpiece spindle, which second spindle is equipped with a dressing tool. As is known from the prior art, this dressing tool is an annular cup-shaped tool, which is also fixed to the dressing spindle via a mechanical system.

This CNC machine, which is part of the prior art, has the disadvantage that it is very expensive. In addition, the receptacle for the lens must be machined on a separate CNC-controlled grinding machine.

Particularly fine surfaces are obtained with optical materials, such as optical glass or crystalline material, by using polishing pitch as the tool covering; however, polishing pitch is thermoplastic and the polishing time is substantially longer than the polishing time is when PU film (thermosetting plastic) is used as the tool covering. Polishing with pitch tends to create low roughness. A short machining time arises when polyurethane film is used as the polishing pad.

Since the manufacture of spherical components must be particularly economical, PU film is predominantly used at this time in practice to polish optical materials.

If a very fine surface quality is required, however, re-polishing is carried out in a second process step using a tool that is covered with polishing pitch.

In tools having polishing film, tools are used in practice that have a surface covering which is calculated such that no changes in shape occur on the tool during machining, even in case of wear of the film. This so-called synchro-speed method is the state of the art nowadays in polishing using polishing films.

A further component of this synchro-speed method is the constant relative speed between the tool and the workpiece.

These methods could only have been used to this day when polishing using polishing pads consisting of polishing film.

The great advantage of using polishing pitch is that optical surfaces can be created with the highest form qualities (up to λ/100 and better), and with the lowest surface roughness (1 to 2 angstrom). Polishing using polishing film is worse by a factor of 10.

Since qualities in the range from λ/50 to λ/100 and in the roughness range from 2 to 3 angstrom are also required nowadays in the spherical range, very expensive and lengthy correction processes usually need to be carried out after the spherical pre-polishing using film.

With large lenses in particular, for example from 100 mm in diameter to, for example, 2 m in diameter, this procedure is an enormous problem, since the correction techniques are extremely expensive and also extremely slow.

Very high investments are necessary for this purpose in industrial sectors that require large quantities of spherical, large optical elements.

Since the need for large optical elements with very high accuracies and very low roughness is growing, for example, for laser optics and space optics, the methods and devices that are part of the prior art, for producing these large lenses and mirrors, are uneconomical. The methods that are part of the prior art are too expensive, in particular also for new optical materials, such as SiC components (silicon carbide).

SUMMARY OF THE INVENTION

The technical problem on which the invention is based consists of indicating a device and a method for polishing an optical lens or an optical mirror, with which device and method a polishing process can be economically carried out and with which polishing film or polishing pitch are equally suitable.

This technical problem is solved by means of a device having the features according to one aspect of the invention and by a method having the features according to another aspect of the invention.

The device according to the invention, for polishing an optical lens or an optical mirror using a polishing tool and using a workpiece holding ring for accommodating the optical lens or the optical mirror, wherein the workpiece holding ring is arranged above the tool in a vertical direction, is characterized in that the device has three axes, which are movable during the polishing process, for moving the workpiece holding ring and the polishing tool.

In the device according to the invention, a triaxial polishing process is carried out.

Triaxial, interpolating machining about an axial center point of the polishing tool is advantageously carried out.

Movable means, for one thing, a movement in one direction of a Cartesian coordinate system. For another thing, movable means that a swivel movement can be carried out about an axis.

The polishing tool is advantageously part-spherical and has a center point.

Advantageously, the workpiece holding ring is moved in the x-direction and the z-direction, wherein x and z are coordinates of a Cartesian coordinate system and z represents the vertical direction.

Moreover, the polishing tool is advantageously swiveled about a swivel axis. This swivel movement is combined with the movement of the movable x-axis and of the movable z-axis. This triaxial, interpolating movement is carried out such that the workpiece, i.e., the optical lens or the optical mirror, always rests vertically on the tool coating, i.e., on the polishing tool having the polishing pad.

The polishing tool advantageously swivels through under the workpiece surface of the optical mirror and of the optical lens.

The swivel movement is a part of the calculation for the surface of the polishing pad that is applied on the polishing tool.

By means of the device according to the invention, in particular, large lenses or large mirrors, for example, having a diameter of more than 100 mm and up to, for example, 2 m, can be economically and cost-effectively machined.

According to an advantageous embodiment of the invention, it is provided that the workpiece holding ring having the two movable axes and the polishing tool having the one movable axis are designed to be movable in an interpolating manner during the polishing process, and that a center point of the workpiece holding ring is arranged vertically above a center point of the polishing tool during the polishing process.

The workpiece holding ring moves advantageously cardanically aligned on the polishing tool.

The workpiece holding ring is advantageously moved in the x-direction and the z-direction. The polishing tool is advantageously movably swiveled about an axis. The three movable axes of the polishing tool and of the workpiece holding ring are designed to be interpolatingly movable, so that a center point of the workpiece holding ring is arranged vertically above a center point of the polishing tool during the polishing process.

By means of the device according to the invention, the workpiece holding ring is positioned on the center point of the tool.

The movable axis of the polishing tool is to be understood to mean that the polishing tool is swiveled about the axis. The displacement movement is a swivel movement in this case.

According to a further advantageous embodiment of the invention, it is provided that the workpiece holding ring is arranged so as to rest on the polishing tool by gravity.

This embodiment has the advantage that the workpiece holding ring is positioned on the center point of the tool when the workpiece holding ring rests with its underside on the polishing tool under its own weight.

According to a further advantageous embodiment of the invention, it is provided that the optical lens or the optical mirror is arranged so as to rest on the polishing tool by gravity.

Due to this embodiment, it is ensured that the optical lens or the optical mirror rests cardanically on the polishing tool under its own weight. The workpiece rests cardanically on the polishing pad.

According to a further advantageous embodiment of the invention, it is provided that the workpiece holding ring is mounted for rotation about a longitudinal axis.

The workpiece holding ring is driven via a drive. The workpiece holding ring rotates about its longitudinal axis.

Due to an entrainment effect on the edge between the optical lens or the optical mirror and the workpiece holding ring, a rotational movement of the optical lens or of the optical mirror is generated. This is a friction drive.

This friction drive makes it possible for the optical lens or the optical mirror to rotate at a specified rotational speed and nevertheless rest on the polishing tool due only to gravity.

A further advantageous embodiment of the device according to the invention provides that at least one smoothing device for a polishing pad of the polishing tool is arranged on a support surface of the workpiece holding ring arranged in the direction of the polishing pad.

This embodiment has the advantage that this contact surface, which is provided on the support surface and the smoothing device arranged on the support surface, makes it possible to position the workpiece holding ring relative to the polishing tool.

This contact surface is used to continuously smooth the polishing pad. As a result, the function of the continuous polishing process is created.

The at least one smoothing device advantageously consists of glass parts arranged on the support surface of the workpiece holding ring. The glass parts can be designed, for example, in the form of lenses. These glass lenses can be provided prior to the actual polishing operation on an external device having the radius of the workpiece to be machined, i.e., the optical lens or the optical mirror.

Due to the smoothing device, for example, of the glass parts, a continuous smoothing of the polishing pad is advantageously carried out.

The support surface of the workpiece holding ring is advantageously designed in the form of a ring. This ring is used to position the workpiece holding ring relative to the polishing tool.

The glass lenses of the smoothing device are advantageously arranged with the spherical surface in the direction of the polishing tool. With a planar surface, the glass lenses can be arranged on the support surface of the workpiece holding ring.

According to a further advantageous embodiment of the invention, it is provided that the workpiece holding ring is designed to be drivable at a first rotational speed and the polishing tool is designed to be drivable at a second rotational speed, and that the polishing process is executable at two rotational speeds deviating from one another, wherein a direction of rotation of the workpiece holding ring and a direction of rotation of the polishing tool are synchronous.

This arrangement means that the workpiece holding ring, and thus also the optical lens or the optical mirror, which also rotate about their longitudinal axis due to the friction drive, have a first rotational speed and that the polishing tool has a second rotational speed, which is designed deviating from the first rotational speed. The direction of rotation of the workpiece holding ring, and thus, of the optical lens and of the optical mirror, and the direction of rotation of the polishing tool, are synchronous.

As a result, the polishing process is effectively and reliably carried out.

According to a further advantageous embodiment of the invention, it is provided that the workpiece holding ring is exchangeable for a holding ring comprising a drivable tool spindle for machining a surface of the polishing tool.

In order to manufacture the polishing pad of the polishing tool such that no changes to the radius of the polishing tool occur due to the polishing process, the surface of the polishing pad is machined by means of a separate method using the same device according to the invention such that a mathematically predetermined surface arises.

It is advantageously exchanged for a holding ring having a drivable tool spindle to machine the polishing tool of the workpiece holding ring. A surface machining tool, for example, an end-milling cutter, is arranged on the tool spindle. The end-milling cutter can have, for example, a spherical cutting edge.

Next, the process of milling the polishing tool surface can be carried out in the polishing pad.

According to a particularly preferred embodiment of the invention, four movable axes are designed to be movable during the process of machining the surface of the polishing tool. This feature means that, in addition to the two axes in the x-direction and the z-direction and the movable, i.e., swivelable axis B₁ for the polishing tool, there is a fourth axis C₁.

This fourth axis C₁ is a rotation axis, which is arranged on a tool spindle. The rotation axis is positionable and is controllable.

By means of the device according to the invention, it is advantageously possible to polish spherical optical lenses or spherical optical mirrors or planar optical lenses or planar optical mirrors.

The device according to the invention therefore has the advantage that it is universally usable, and thus costs can be reduced.

The method according to the invention for polishing an optical lens or an optical mirror using a polishing tool for polishing the optical lens or the optical mirror, in which the optical lens or the optical mirror is arranged in a workpiece holding ring, wherein the workpiece holding ring is arranged above the polishing tool in a vertical direction, is characterized in that the polishing process is carried out using three movable axes for moving the workpiece holding ring and the polishing tool.

The workpiece holding ring is moved using the two axes, namely the x-axis and the z-axis. The x-axis and the z-axis are axes of a Cartesian coordinate system. The z-axis is the vertical axis.

The polishing tool is moved by means of a further axis. In so doing, the polishing tool does not undergo a linear movement, but rather a swivel movement about the third axis.

Due to this triaxial movement of the workpiece holding ring and the polishing tool, the polishing process is carried out such that the optical lens or the optical mirror is vertically arranged at any point in time. The optical lens or the optical mirror always rest vertically on the polishing tool, i.e., on the tool covering. The polishing tool swivels through under the surface of the optical lens or of the optical mirror.

According to a further advantageous embodiment of the method according to the invention, it is provided that the workpiece holding ring is interpolatingly moved using two movable axes and the polishing tool using one movable axis during the polishing process, such that a center point of the workpiece holding ring is arranged vertically above a center point of the polishing tool during the polishing process.

Due to this embodiment, the surface of the optical lens or of the optical mirror is highly precisely machined.

This triaxial, interpolating movement is carried out such that the optical lens or the optical mirror always rests vertically on the polishing tool, i.e., on the polishing pad.

According to a further advantageous embodiment of the invention, the optical lens or the optical mirror rests on the polishing tool by gravity. This feature means that the optical lens or the optical mirror is not separately pressed down or held in a separate retaining device.

As a result, the optical lens or the optical mirror rests cardanically on the polishing tool.

In addition, a separate holding device, which is technically complex, for the optical lens or the optical mirror is not necessary.

According to a further advantageous embodiment of the invention, it is provided that the workpiece holding ring rests on the polishing tool by gravity.

This embodiment has the advantage that the workpiece holding ring is positioned on the center point of the polishing tool. The workpiece holding ring advantageously rests with its underside, i.e., with its support surface, on the polishing tool under its own weight.

According to a further advantageous embodiment of the invention, it is provided that the workpiece holding ring is driven so as to be rotatable about its longitudinal axis during the polishing process, and that the optical lens arranged in the workpiece holding ring or the optical mirror arranged in the workpiece holding ring rotates due to friction with the workpiece holding ring about a longitudinal axis of the optical lens or of the optical mirror.

In order to carry out a polishing process, it is necessary for the optical lens or the optical mirror to rotate about its longitudinal axis. Since the optical lens or the optical mirror advantageously rests on the polishing tool due to gravity and is rotated at a deviating rotational speed, i.e., the rotational speed of the polishing tool deviates from the rotational speed of the optical lens or of the optical mirror, the optical lens or the optical mirror is set into a rotational movement due to friction between the edge of the lens and the workpiece holding ring.

According to a further advantageous embodiment of the invention, it is provided that at least one smoothing device, which is arranged on a support surface of the workpiece holding ring arranged in the direction of the polishing tool, smooths the polishing pad during the polishing process.

The workpiece holding ring advantageously rests on the polishing tool due to gravity. At least one smoothing device is advantageously arranged on the support surface of the workpiece holding ring. This smoothing device rests on the polishing pad of the polishing tool during the polishing process.

Advantageously, the smoothing device is formed from glass parts, preferably lenticular glass parts. The glass parts are advantageously formed on an external device having the radius of the workpiece to be machined prior to the actual polishing operation. In the polishing operation, a continuous smoothing of the polishing pad is ensured as a result.

A further advantageous embodiment of the method provides that the workpiece holding ring is driven at a first rotational speed and the polishing tool is rotated at a second rotational speed, and that the polishing process is carried out at two rotational speeds deviating from one another, wherein a direction of rotation of the workpiece holding ring and a direction of rotation of the polishing tool are synchronous.

After the start of the polishing process according to the invention, the polishing tool begins to rotate at a first rotational speed n₁. At the same time, the workpiece holding ring is driven by a drive synchronously with the direction of rotation of the rotational movement n₁ at the rotational speed n₂. The rotational speed ratio n₁ to n₂ is mathematically determined and advantageously set by a CNC controller.

Advantageously, the ratio of the rotational speeds is determined as follows:

n 2 = n 1 · cos ⁢ α 1

• • with n₁ first rotational speed,
  • n₂=second rotational speed,
  • α₁=swivel angle.

According to a further advantageous embodiment, a method for machining a polishing pad of a polishing tool is indicated having a device, which, instead of the workpiece holding ring, has a drivable tool spindle, which method is characterized in that the machining process for machining the surface of the polishing tool is carried out using an interpolating movement with four movable axes.

These are the axes X₁, Z₁, B₁ and C₁. X₁ and Z₁ are the axes of the Cartesian coordinate system and the Z₁ axis is a vertical axis. The axis B₁ extends parallel in the x-direction. The polishing tool is swivelable about the axis B₁.

The axis C₁ extends parallel to the Z₁ axis.

By means of the device according to the invention and the method according to the invention, the pressure force of the optical lens or of the optical mirror on the polishing tool is advantageously generated via gravity.

The device according to the invention and the method according to the invention are suitable both for a planar machining and for a spherical machining of optical lenses or mirrors.

In addition, the device according to the invention can be changed by exchanging the workpiece holding ring for a machining tool such that the surface of the polishing tool can be machined on the device according to the invention such that a polishing tool arises that maintains the form without an additional polishing correction plate. The device can also be used with tools that are covered with polishing pitch.

In the method according to the invention, a swiveling of the axis B₁ at an angle Δα is advantageously started after a tool spindle and the workpiece holding ring have begun to rotate. This swivel movement is combined with a movement of the carriage that is movable in the x-direction and of the carriage that is movable in the z-direction. This triaxial, interpolating movement is carried out such that the optical lens or the optical mirror always rests vertically on the polishing pad. The polishing tool swivels through under a workpiece surface of the optical lens or of the optical mirror. This swivel movement is a part of the calculation for the surface of the polishing pad that is applied on the polishing tool.

In order to manufacture the polishing pad such that the radius of the tool is not changed due to the polishing process, the surface of the polishing pad is machined by means of a separate method such that a mathematically predetermined surface arises.

According to an advantageous embodiment of the invention, this surface machining of the polishing pad is generated by means of a milling tool, which surface machining is related to the so-called synchro-speed method.

In order to carry out this operation on the device according to the invention, the workpiece holding ring is removed and exchanged for a further holding ring. A high-speed tool spindle is advantageously arranged in the further holding ring. A milling cutter, for example, an end-milling cutter, is arranged on the lower end of this tool spindle. The end-milling cutter can have a spherical cutting edge.

Then, the process of milling the polishing tool surface is carried out in the polishing pad. The machining is a four-axis process. The axes C₁, X₁, Z₁, B₁ interpolate in this machining.

The machining process has the task of manufacturing a polishing tool surface extending precisely with respect to the first rotational axis n₁.

The machining process has the task of manufacturing a polishing tool surface that is suitable for holding the radius of the polishing tool stable during the actual polishing process.

Polishing pitch can be used in the method according to the invention and in the device according to the invention. It is also possible to use a polishing film.

For example, a pitch can be used that is mixed with plastic particles or wood particles or with a polishing agent or copper particles, or the like.

Once the tool manufacture process has ended, the second holding ring with the tool spindle is removed again. Then, the workpiece holding ring is re-installed and the optical lens or the optical mirror can be arranged in this workpiece holding ring.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

In the drawings,

FIG. 1 shows a device according to the invention in the sectional view;

FIG. 2 shows the mounting of the workpiece holding ring in the longitudinal sectional view;

FIG. 3 shows a representation of the movement of the tool; and

FIG. 4 shows the device according to the invention used to machine the tool, in the longitudinal sectional view.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the device 30 with a base unit 1. The base unit 1 consists preferably of granite plates, which are joined. The base unit 1 can also consist of other materials.

A tool spindle 5 is arranged in the base unit 1 so as to be swivelable about an axis B₁. The tool spindle 5 is swivelable and controllable by ±90° about the axis B₁.

The tool spindle 5 is a rotation axis C₁, which has an entrainment device 31 on the upper end, the rotation axis C₁ is positionable and controllable.

A polishing tool 23 is arranged on the upper end of the tool spindle 5. A polishing pad 24 is applied on the polishing tool 23. An optical lens 19 is arranged perpendicularly on the polishing tool 23. An optical mirror can also be arranged.

The optical lens 19 is pressed against the polishing pad 24 by its own weight.

In order to ensure the vertical position of the optical lens 19 at any point in time, the position of the optical lens is supported by a workpiece holding ring 11 and a holding arm 12.

The workpiece holding ring 11 is in turn positioned by catching rollers 22, 32 (see FIG. 2) precisely centrally relative to the workpiece holding ring 11.

Advantageously, the workpiece holding ring 11 is supported by three rollers. Two rollers are designed as catching rollers 22, 32, the third roller is designed as a drive roller 21.

The workpiece holding ring 11 rotates about a longitudinal axis L_W. The optical lens 19 rotates about a longitudinal axis L_L.

The workpiece holding ring 11 can rotate in the holding arm 12 without friction. The workpiece holding ring 11 has no contact with the holding arm 12. The workpiece holding ring 11 has contact only with the rollers 21, 32, 23.

As is apparent in FIG. 3, a gap 33 is provided between the workpiece holding ring 11 and the holding arm 12, such that the workpiece holding ring 11 and the holding arm 12 are arranged contactlessly with respect to one another.

The drive of the workpiece holding ring 11 is shown in FIG. 2. In order to generate, or to control, the rotational movement and, as a result, a relative speed between the polishing tool 23 and the workpiece holding ring 11, a drive roller 21 is provided, which is driven by a drive motor 25 (FIG. 1).

Displacement axes X₁, Z₁, B₁ and C₁ are shown in FIGS. 1 through 4.

X₁ and Z₁ are axes of a Cartesian coordinate system.

The polishing tool 23 is swiveled about the axis B₁.

C₁ is a vertical axis parallel to the Z₁ axis. The polishing tool 23 rotates about the axis C₁, as is shown in FIG. 4, when the polishing tool 23 is machined.

As is shown in FIG. 1, the polishing tool 23 rotates at a rotational speed n₁. The optical lens 19 rotates at a rotational speed n₂.

The rotational speeds n₁, n₂ are different rotational speeds. The direction of rotation of the optical lens 19 and of the tool 23 is synchronous.

The workpiece holding ring 11 is set into a rotational movement, as is shown in FIG. 2. The rotational movement of the optical lens 19 is generated by an entrainment effect at an edge between the optical lens 19 and the workpiece holding ring 11. This arrangement is a friction drive.

In order to position the workpiece holding ring 11 on the center point of the tool 23, the workpiece holding ring 11 lies with its underside on the polishing tool 23 under its own weight.

As is shown in FIGS. 2 and 3, glass parts 20 are arranged on a support surface 34 of the workpiece holding ring 11, which glass parts have the function of a smoothing device for the polishing pad 23. The glass parts 20 are provided, prior to the actual polishing operation, on an external device having the radius of the workpiece to be machined, i.e., of the optical lens 19 or of an optical mirror. A contact surface of the support surface 34 is designed in the shape of a ring. This contact surface is used to position the workpiece holding ring 11 in relation to the polishing tool 23. The contact surface is used to continuously smooth the polishing pad 24. As a result, the function of a continuous polishing process is created.

The holding arm 11 is fixed to a carriage 18 and can be controlled and positioned over the axis Z₁ using a motor drive 17. The carriage 18, which is displaceable in the Z₁ direction, is connected via a linear bearing system (not shown) to a carriage 16, which is displaceable in the X₁ direction. The carriage 16, which is displaceable in the X₁ direction, is connected to the base unit via a linear bearing system 14. The carriage 16, which is displaceable in the X₁ direction, is positioned and controlled in the X direction in a motor-driven manner using a drive 15.

The swivel axis B₁ is positioned and controlled via a motor drive 10. A holding arm 9, which accommodates the tool spindle 5, is fastened on the opposite side of the motor drive 10 by means of a cardanically compensating counter bearing 2, 3, 4. As a result, a high rigidity of the B₁ axis position is ensured.

The base unit is fixedly arranged on a base stand 7. As a result, a desired operating height of the device 30 is achieved. In order to cover the work space, a cover 26 is arranged over the work region of the tool 23. The cover 26 can be moved up and down in the direction of a Z₂ axis.

A rotation action 8 is represented in FIG. 1. If the tool spindle 5 needs to be lubricated from below, because lubrication from the outside is no longer sufficient, lubrication is carried out by the rotation action 8.

The base stand 7 has a bore 6. Excess polishing agent can drain through this bore 6.

The carriage 16, which is displaceable in the X₁ direction, is arranged on a transverse carriage 13.

FIG. 2 shows, as described above, the mounting of the holding ring 11. The holding ring 11 is held by two catching rollers 22, 32 and is driven by the drive roller 21, which rotates at a rotational speed n₃. The glass parts 20 are arranged on a support surface 34 of the workpiece holding ring 11.

The glass parts 20 can be designed, for example, as lenses having a spherical surface formed in the direction of the polishing tool 23.

The catching rollers 22, 32 are mounted with ball bearings and have rubber tires.

The optical lens 19, which rotates at a rotational speed n₂, is also shown in FIG. 2. The optical lens 19 rotates since it intermittently rests with its edge on the workpiece holding ring 11 and, due to friction, an entrainment effect arises.

FIG. 3 shows the optical lens 19, which rests on the polishing pad 24. The workpiece holding ring 11 is driven by the drive roller 21, which is set into rotation by a drive motor 25. The drive roller 21 rotates at the rotational speed n₃.

The method according to the invention is carried out, as is shown in FIG. 3. The workpiece holding ring 11 is placed in the holding arm 12. The workpiece holding ring 11 moves cardanically aligned on the polishing tool 23, which is fastened to the tool spindle 5.

The optical lens 19 is placed into the workpiece holding ring 11 and rests, under its own weight, cardanically on the polishing tool 23 with the polishing pad 24.

After the polishing process starts, the tool spindle 5 begins to rotate at a rotational speed n₁. At the same time, the workpiece holding ring 11 is driven at the rotational speed n₂ by the drive 25 and the roller 21 synchronously with the rotational movement of the polishing tool 23 at the rotational speed n₁. The rotational speed ratio n₁ to n₂ is mathematically ascertained using the formula:

n 2 = n 1 · cos ⁢ α 1

• • with n₁ first rotational speed,
  • n₂=second rotational speed,
  • α₁=swivel angle.

The rotational speed ratio is set by a CNC controller.

Once the rotational movement of the tool spindle 5 and the workpiece holding ring 11 begins, a swiveling about the axis B₁ at the angle Δα is started. This swiveling movement is combined with the movement of the X₁ carriage 16 and of the Z₁ carriage 18. This triaxial, interpolating movement is carried out such that the optical lens 19 rests exclusively vertically on the polishing pad 24 during the polishing process. The polishing tool 23 swivels through under the workpiece surface of the optical lens 19.

The swivel movement is a part of the calculation for the surface of the polishing pad 24, which is arranged on the polishing tool 23.

The angle Δα is composed of the difference between α₁ and α₂. α₁ and α₂ are swivel angles. They are also referred to as pitch angles.

The polishing pad has a radius R₁ and the polishing tool has a radius R₂.

In FIG. 3, OW_W designates the opening angle of the tool and OW_L designates the opening angle of the optical lens 19. The opening angles are the overall aperture of the tool or the overall aperture of the optical lens 19.

The manufacture of the polishing pad 24 is shown in FIG. 4.

The device 30 can also be used to manufacture the polishing pad.

The same parts are labeled using the same reference numbers.

In order to manufacture the polishing pad 24 such that the polishing process does not result in a change to the radius of the polishing tool 23, the surface of the polishing pad 24 is machined, by means of a separate method, such that a mathematically predetermined surface arises.

This surface of the polishing pad 24, which is related to so-called synchro-speed method, is generated by means of a milling tool 35.

In order to be able to carry out the operation of machining the polishing pad 24 on the device 30, the workpiece holding ring 11 is removed from the holding arm 12 and replaced by a second holding ring 27. A high-speed tool spindle 29 is arranged in the second holding ring 27. The milling tool 35, for example, in the form of an end-milling cutter, is arranged on the lower end of this tool spindle 29. The milling tool 35 can have a spherical cutting edge. The second holding ring 27 is fixedly attached to the holding arm 12 using holding pieces 28.

Then, the process of milling the surface of the polishing tool 23 begins in the polishing pad 24. The machining is a four-axis process. The axes C₁/X₁/Z₁/B₁ interpolate during this machining.

The machining process has two tasks:

• • a) manufacturing a polishing pad 24 extending precisely with respect to the axis of rotation of the polishing tool 23
  • b) manufacturing a surface of the polishing pad 24 that is suitable for holding the radius of the polishing tool 23 stable during the actual polishing process.

Once the tool manufacturing process has ended, the second holding ring 27 with the tool spindle 29 is removed again.

Then, the workpiece holding ring 11, with the optical lens 19 or the optical mirror, is re-installed into the holding arm 12.

Then, the polishing process can begin.

The milling tool 35 rotates at a rotational speed n₄.

Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.

NUMBERED REFERENCES

• • 1 base unit
  • 2 cardanically compensating counter bearing
  • 3 cardanically compensating counter bearing
  • 4 cardanically compensating counter bearing
  • 5 tool spindle
  • 6 bore as discharge for polishing agent
  • 7 base stand
  • 8 rotation action
  • 9 holding arm
  • 10 motor drive
  • 11 workpiece holding ring
  • 12 holding arm
  • 13 transverse carriage
  • 14 linear bearing system
  • 15 drive for x-direction
  • 16 carriage movable in X₁ direction
  • 17 motor drive
  • 18 carriage movable in Z₁ direction
  • 19 optical lens
  • 20 glass parts
  • 21 drive roller
  • 22 catching roller
  • 23 polishing tool
  • 24 polishing pad
  • 25 drive motor
  • 26 cover
  • 27 second holding ring
  • 28 holding pieces
  • 29 tool spindle
  • 30 device
  • 31 entrainment device
  • 32 catching roller
  • 33 gap
  • 34 support surface
  • 35 milling tool
  • Z₁ axis
  • Z₂ axis
  • X₁ axis
  • B₁ axis
  • C₁ axis
  • L_W longitudinal axis of workpiece holding ring
  • L_L longitudinal axis of optical lens or optical mirror
  • n₁ rotational speed
  • n₂ rotational speed
  • n₃ rotational speed
  • n₄ rotational speed
  • R₁ radius
  • R₂ radius
  • α₁ angle
  • α₂ angle
  • OW_W opening angle of polishing tool
  • OW_L opening angle of lens
  • Δα angular difference