EP1796872B1 - Method for polishing particularly of optically-active surfaces such as lenses - Google Patents

Abstract

A method is disclosed, whereby a reduced wear of the polishing tool and a reduced duration for the polishing process may be achieved and also free form surfaces and non-rotating workpieces may be polished. The above may be achieved whereby the surface of the tool actually in contact with the workpiece lies off the tool axis. The invention further relates to a method for polishing a surface of a workpiece, via a tool rotating about a tool axis, whereby the workpiece, at least in one region of the workpiece surface has a contacted surface which is part region of a surface for machining, which for its part is at least part of a polishing surface of the tool, whereby the tool axis intersects the polishing surface.

Description

The invention relates to a method for polishing a surface of a workpiece by means of a tool rotating about a tool axis, wherein the workpiece in a region of the workpiece surface with a respective currently touching surface, which is at least a portion of a machined surface, which in turn is a portion of a polishing surface of the Tool is, is touched, with the tool axis pierces the polishing surface.

The EP 0 835 722 A1 describes an apparatus and method for making plastic lens substrates by processing a plastic block material. A rotating machining tool, for example for polishing, is moved on an equally rotating workpiece. The machining tool, which rotates axially via a manipulator, is held by a holding device. The holding device is coupled to a drive and acts on the processing tool with respect to an X and / or Y and / or Z direction of movement, a distance of the movement, an on and off operation as well as an inclination of the movement ,

From the DE 101 06 007 For example, a method of polishing finished finished lenses is known. Here, by means of molding tools using polishing machines, which have at least one workpiece spindle and a tool spindle, uses a variable mold. This is brought into firm contact with the lens before the actual polishing process with its resilient work surface, wherein the working surface assumes the contour of the lens as a negative impression. This negative impression is then fixed, whereby the working surface of the variable mold maintains the shape required for the polishing process during polishing.

Furthermore, in the EP 0 727 280 A1 a device and a method for polishing glass lenses described. In this case, a CNC machine tool has a feed drive with a rotationally driven tool spindle for receiving a polishing tool. At a second feed drive at a fixed distance a rotatably mounted tool spindle for receiving a lens and a rotatably mounted parallel to this tool spindle for receiving a dressing tool, such as a pot tool is arranged. In this case, a relative pivoting is executable between the polishing tool and the lens or the dressing tool. The polishing tool has a carrier for receiving a polishing agent carrier, which is preferably a polyurethane film. It is trained microprocessor-controlled before and / or after a polishing operation without position change, wherein polishing tool and dressing tool are moved with the same direction of rotation.

In the following, a working surface is understood as meaning the entirety of all surfaces of a rotating tool that contact a workpiece during one revolution of the tool. The momentarily contacting surface is considered to be the surface of the tool which is in contact with the workpiece at any one time.

For polishing is in the prior art according to FIG. 1 a rotating tool 2 moves on a likewise rotating workpiece 1, wherein the tool 2 consists of a rubber membrane or a plunger with a glued polyurethane membrane, the so-called polishing foil or surface 2.1. The tool rotates about a tool axis 2.2, the workpiece rotates about a workpiece axis 1.2. The polishing film has a curvature and lies during machining with its center of rotation and a circular, working area 2.4 around the center of rotation on the workpiece 1. It is, for example, by compressed air or a deforming Elastomer pressed. The removal of the workpiece 1 is achieved both by the polishing film, as well as by a constantly supplied liquid. The membrane or the plunger is always placed by means of a CNC program perpendicular to the workpiece surface to be polished 1.1 and slowly guided over the workpiece 1 on a radius. The sub-figures a), b) and c) show individual times of such a movement, both in side view as well as in top view. The choice of the speed profile on the radius controls the removal in order to achieve the desired shape of the workpiece 1.

In this method, only a small removal is achieved. In addition, the polishing tool wears relatively quickly. In addition, the tool for polishing the edge region must at least partially protrude beyond the workpiece as in FIG. 1c) shown. The tool can be very heavily worn, especially at high air pressure and destroyed by the outer lens edge. This method is only suitable for convex or concave rotationally symmetrical workpieces, but not for free-form surfaces and non-rotating workpieces

In another, in FIG. 2 1, a wheel-shaped polishing tool 2 rotating about a tool axis 2.2 is guided over a workpiece surface 2.1 of a workpiece 1 rotating about a workpiece axis 1.2. The polishing surface 2.1 is mounted on the running surface of the wheel-shaped polishing tool 2 in this case. The entire polishing surface 2.1 acts as a working surface 2.4, wherein at any one time only a momentarily contacting surface 2.3 is in contact with the workpiece surface 1.1. However, there is a danger of polishing a hole in the center of the workpiece due to the small machined surface there.

The accuracy of processing is limited in both methods.

The invention is based on the object to provide a method of the type mentioned, in which a lesser wear of the polishing tool or a shorter duration of the polishing process can be achieved, with free-form surfaces and non-rotating workpieces are polished.

The object is achieved by a method which has the features specified in claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims.

With the method according to the invention, it is possible to achieve a lower wear of the polishing tool or to accelerate the polishing process, free-form surfaces and non-rotating workpieces can be polished. This is accomplished by polishing with a polishing tool whose axis of rotation punctures the polishing surface with a portion of the polishing surface remote from the axis of rotation of the tool. The working surface and the currently touching surface are therefore in most cases not identical, but the currently touching surface is a subset of the working surface.

In contrast, in the prior art, the in FIG. 1 shown method polished only with the central portion around the axis of rotation of the polishing tool, which means a minimum machined surface. The working surface and the momentarily contacting surface are identical at all times of polishing.

In the case of the polishing method according to the invention, the center point of the partial area of the polishing surface currently touching the workpiece is preferably located away from the axis of rotation of the tool, whereby an enlarged machining surface is used for polishing. At a greater distance of the center of the currently contacting surface from the axis of rotation, the machined surface is a circular ring on the polishing surface. At a small distance, it is a circle whose diameter increases with distance.

The farther the respective currently touching partial surface is radially away from the axis of rotation, the larger is the working surface in its entirety and the higher, with the same angular velocity of the tool, is the path velocity of the working surface, which determines the duration of the polishing process. At the same rotational frequency as in conventional polishing, so the duration of the polishing process is shortened. If the rotational frequency chosen so that the web speed of the machined surface corresponds approximately to that in the conventional method, the wear is significantly reduced by the increased surface area and thus increases the tool life. The tool requires less downtime because it maintains the required accuracy for a longer period of time and therefore needs to be replaced after a longer period of operation than before, increasing productivity. The longer life of the tool allows a better prediction of the polishing process and thus also a higher accuracy of the same. Furthermore, the method according to the invention makes it possible to effectively polish edge regions of lenses with a reduced risk of destroying the polishing tool.

The extended tool life reduces downtime of the production process.

In addition, the accuracy of polishing is increased by making the velocity distribution across the working surface more uniform, resulting in fewer errors. In the conventional method according to FIG. 1 the center of the polishing surface as a fulcrum is stationary, while the outer edges of the working surface move at opposite speeds, making accurate machining difficult.

Since the rotational frequency of the tool is technically limited, small tools can be used much more effectively or even larger tools, especially for smaller workpieces with mostly strong bends. which achieve a much greater removal than is possible in the previous method.

In the following, any direction parallel to the workpiece axis is regarded as vertical.

For practicing the method, a commercially available polishing machine can be used when the tool is tilted therein, adjusting a relative angle between the tool axis and a local surface normal of the workpiece in the touched area. The method can be used for convex as well as concave workpieces as well as for convex and concave freeform surfaces such as toroids or cylindrical surfaces. There are different types of tools conceivable as spherical and aspherical. The known polishing machines offer only a limited absolute tilt angle to the vertical for tilting the tool, for example, less than 46 °. Work piece surfaces with slopes greater than this maximum angle can not be machined by the conventional method. With the method according to the invention can be polished with sufficiently curved tool at low tilt angle of the tool surfaces with any increase.

According to the invention, a relative angle of more than 0 ° is set, whereby polishing with the center of the polishing surface and the associated disadvantages are avoided.

In an advantageous embodiment, the tool is tilted about an axis perpendicular to the tool axis, which is very easy by means of a CNC program, since tilting in such a direction can be carried out with commercially available polishing machines.

The workpiece can be processed quickly in one go by translating the tool along at least part of the workpiece surface.

According to the invention, the relative angle is continuously changed during the movement along the workpiece surface. As a result, the removal can be adapted to the machined surface of the workpiece. In the outdoor area, the relative angle is increased to obtain the largest removal there. As a result, in contrast to the conventional method, there is no danger of polishing a hole in the middle due to the small machined surface. In addition, the tool is consumed evenly in this way.

The method can be optimally adapted to the respective application by determining the relative angle to be set on the basis of data of the workpiece and / or of the tool. In a preferred embodiment, the relative angle is determined based on the respective relative position of the tool to the workpiece, based on a surface normal of the workpiece at this position, based on a polishing surface normal of the currently touching surface of the tool and / or on the basis of a distance to be achieved. This allows a high machining accuracy.

In an advantageous embodiment, the absolute tilt angle of the tool with respect to the vertical during the translational movement is kept constant. In this extreme case, the tool is not tilted at all. For this purpose, the tool must meet the mechanical requirements, in particular sufficiently strong increases at its edge, so that it still touch the workpiece in each increase on the surface of the workpiece can. Thus, the contact surface is well predictable. To program with very little effort is such a method in which the absolute tilt angle of the tool during the translational movement with respect to the vertical is kept at 0 °. This variant is preferably used when workpiece and tool have an identical shape.

In general, the relative angle can also be set variably such that the track radii of the machined surface on the workpiece and the machining surface on the tool always coincide. When a point with a certain radius is machined on the workpiece, the tool is tilted so that the working area of the polishing surface itself has the same radius. This is implicitly the case, for example, if the shape of the workpiece and the tool are the same. Thus, a uniform wear of the tool is made possible and optimally effected by the web speed removal at a rotating workpiece adapted to the machined surface.

For the widest possible machining of concave lenses, it is advantageous to use a convex polishing surface and vice versa.

With conventional polishing machines convex workpieces can be processed by the inventive method, by a tool with a flat polishing surface in response to a surface normal of the workpiece is tilted in the touched area about an axis other than the tool axis, wherein the tool axis of the tool is aligned parallel to the surface normal and the tool is displaced parallel to a workpiece surface in the contacted area.

In an advantageous embodiment, the amount of displacement is determined on the basis of a distance to be achieved, which increases the accuracy of the polishing.

In the case of rotationally symmetrical workpieces, the control of the tool is simple if the workpiece rotates about a workpiece axis. The polishing process can be accelerated if the rotational movements of workpiece and tool are directed opposite. The opposite web speeds of processed and machined surface allow a higher removal.

In order to increase the removal, the tool is expediently pressed against the workpiece surface. In this case, the removal is adjustable when the contact pressure is controllable. In the case of damage to the polishing surface, the workpiece is not damaged when the contact pressure is generated by means of compressed air.

The use of the method according to any one of the preceding claims for the polishing of optically active surfaces allows the use of said advantages for optically effective surfaces, for example of lenses or mirrors.

With very little effort rotationally symmetric lenses are machinable with this method.

The invention will be explained below with reference to exemplary embodiments.

Figur 1

ein Polierverfahren im Stand der Technik mit konstantem relativen Winkel von 0°,

Figur 2

ein Polierverfahren im Stand der Technik mit zur Polierfläche paralleler Werkzeugachse,

Figur 3

Phasen des erfindungsgemäßen Verfahrens bei variablem relativem Winkel sowie schematisch Polierfläche und bearbeitende Fläche in jeweils einer Seitenansicht und einer schematischen Draufsicht,

Figur 4

Phasen des Verfahrens bei konstantem relativem Winkel in Seitenansicht sowie schematisch Polierfläche und bearbeitende Fläche,

Figur 5

Phasen des Verfahrens bei konstantem absolutem Kippwinkel zur Vertikalen in Seitenansicht sowie schematisch Polierfläche und bearbeitende Fläche
und

Figur 6

Phasen des Verfahrens mit ebener Polierfläche bei konstantem relativem Winkel von 0° in Seitenansicht.

To show:

FIG. 1

a polishing method in the prior art with a constant relative angle of 0 °,

FIG. 2

a polishing method in the prior art with a tool axis parallel to the polishing surface,

FIG. 3

Phases of the method according to the invention with variable relative angle and schematically polishing surface and working surface in each case a side view and a schematic plan view,

FIG. 4

Phases of the process at a constant relative angle in side view as well as schematically polishing surface and working surface,

FIG. 5

Phases of the process at constant absolute tilt angle to the vertical in side view and schematically polishing surface and machined surface
and

FIG. 6

Phases of the process with a flat polishing surface at a constant relative angle of 0 ° in side view.

The Figures 1 and 2 have already been described in the prior art.

In FIG. 3 is in the partial figures a), b) and c), which are each shown in a side view and a schematic plan view, a workpiece 1, in this case a lens, with aspheric surface 1.1 polished by a tool 2, which is a tool axis 2.2 rotates. The three subfigures show different times during the polishing process. The workpiece 1 in turn rotates about a workpiece axis 1.2, wherein the rotational directions on the tool 2 side facing the workpiece 1 each other are opposite, the vectors of the angular velocity are thus parallel to each other. The tool 2 contacts the workpiece 1 with a respective momentarily contacting surface 2.3, which is a part of a polishing surface 2.1, wherein the machining surface 2.4 results on the polishing surface 2.1 by the rotation of the tool 2 from the union of all currently touching surfaces 2.3. The shape of the working surface 2.4 depends on the position of the tool 2. The polishing surface 2.1 is acted upon on the side facing away from the workpiece 1 side with an air pressure, whereby it is pressed with a corresponding contact pressure against the workpiece surface 1.1. The air pressure and thus the contact pressure are preferably adjustable, whereby the dependent of the contact pressure removal during polishing is controllable.

The tool 2 is tilted in this example by a relative angle 3 between the respective surface normal 1.3 of the workpiece 1 and the tool axis 2.2 of the tool. The tilting takes place about an unillustrated second axis, which is aligned perpendicular to the tool axis 2.2. The partial images a), b) and c) show three different moments of the polishing process, during which the tool 3 is moved along a radius of the workpiece surface 1.1. The relative angle 3 starts at 0 ° in the center of the workpiece 1 and increases continuously during the movement along the workpiece surface 1.1. The absolute tilt angle 4 of the tool 5 to the vertical 5 also increases during the movement, but remains low compared to conventional polishing methods. With a sufficiently curved polishing surface 2.1, therefore, it is also possible to polish steep rises with the method shown.

At a small distance of the center of the currently touching surface 2.3 of the rotation and tool axis 2.2, the working surface 2.4 is a circle whose diameter increases with the distance. At a greater distance than the radius of the contacting surface 2.3, the machined surface 2.4 represents a circular ring on the polishing surface 2.1.

FIG. 4 shows a method in which the relative angle 3 remains constant during the entire movement along the workpiece surface 1.1, in three sections a), b) and c). In this and in the following figures, in each case the polishing surface 2.1 is shown schematically schematically in a view from below in all figures, the respective working surface 2.4 being shown hatched. In this example, the working surface 2.4 is due to the constant geometric conditions consistently a circular ring. The absolute tilt angle 4 of the tool to the vertical 5 decreases during the movement, it is in the center of the workpiece 1 maximum. Even with this method steep increases are polishable.

The removal by the tool 2 is more uniform in this example during the movement along the workpiece surface 1.1 than in the continuous change of the relative angle. 3

At the in FIG. 5 As shown, the relative angle 3 steadily increases, whereas the absolute tilt angle 4 to the vertical 5 is constantly 0 °. This movement allows a simple position control of the tool 2. The tool 2 is positioned so that the center of the contacting surface has the same orbit radius as the circle touched by it on the workpiece surface 1.1. The working surface 2.4 changes as a result of the variable relative angle 3, similar to that in FIG FIG. 1 shown example. It grows as a function of the distance of the center of the currently touching surface 2.3 from the center of rotation of the polishing surface 2.1.

In FIG. 6 a variant of the method is shown, in which a tool 2 is used with a flat polishing surface 2.1. The position of the tool 2 is adjusted as in conventional polishing method depending on the position of the tool 2 so that the relative angle 3 between the tool axis 2.2 and the local surface normal 1.3 is constant 0 ° and the polishing surface 2.1 thus aligned tangentially to the workpiece surface 1.1 is. As a touching surface 2.4, however, the center of the polishing surface is used only in the center of the workpiece 1, in the outer regions, the tool 2 is moved tangentially to the workpiece surface 1.1, whereby the polishing process is accelerated depending on the rotational speed of the tool 2 or the life of the tool. 2 is increased. Also, the polishing is possible with higher accuracy.

LIST OF REFERENCE NUMBERS

1

workpiece

1.1

Workpiece surface

1.2

Workpiece axis

1.3

surface normal

2

Tool

2.1

polishing surface

2.2

tool axis

2.3

Currently touching area

2.4

Processing area

3

Relative angle

4

Absolute tilt angle

5

vertical

Claims (16)

1. Procedure for polishing the surface of a workpiece (1) using a tool (2) rotating around a workpiece axis (2.2) where the workpiece (1) is touched in one area of a workpiece surface (1.1) by a surface (2.3) contacting instantaneously at a given time which is at least a partial area of a machining surface (2.4) which itself is a partial area of a polishing surface (2.1) of the tool (2), with the tool axis (2.2) passing through the polishing surface (2.1) while the position of the tool (2) is adjusted such that the centre point of the surface (2.3) which touches the workpiece (1) instantaneously at a given time and belongs to the tool (2) is off the tool axis (2.2), characterized in that the tool (2) is tilted around an axis different from the tool axis (2.2) where a relative angle (3) is set between the tool axis (2.2) and a local surface normal (1.3) of the tool (1) in the touched area, that the tool (2) is translated at least along a part of the workpiece surface (1.1), and that the relative angle (3) is changed continuously at least by sections in the course of the translation movement along the workpiece surface (1.1).
2. Procedure as claimed in claim 1, characterized in that the tool (2) is tilted around an axis perpendicular to the tool axis (2.2).
3. Procedure as claimed in any preceding claim, characterized in that the relative angle (3) to be set is determined using data of the workpiece (1) and/or of the tool (2).
4. Procedure as claimed in claim 3, characterized in that the relative angle (3) is determined using the corresponding relative position of the tool (2) relative to the workpiece (1).
5. Procedure as claimed in claim 4, characterized in that the relative angle (3) is determined using a surface normal (1.3) of the workpiece (1) in the area of the workpiece surface (1.1) contacted in this position.
6. Procedure as claimed in any claim 3 through 5, characterized in that the relative angle (3) is determined using a polishing surface normal of the surface area (2.3) of the tool (2) contacting the workpiece surface (1) instantenously from time to time.
7. Procedure as claimed in any claim 3 through 6, characterized in that the relative angle (3) is determined using a removal to be achieved from the workpiece surface (1.1).
8. Procedure as claimed in claim 1, characterized in that one tool (2) having a level polishing surface (2.4) is tilted around an axis different from the tool axis (2.2) in the contacted area as a function of a surface normal of the workpiece (1), while the tool axis (2.2) is aligned in parallel to the surface normal (1.3) and the tool (2) is displaced in parallel to a workpiece surface (1.1) in the contacted area.
9. Procedure as claimed in claim 8, characterized in that the amount of displacement is determined using a removal to be achieved.
10. Procedure as claimed in any preceding claim, characterized in that the workpiece (1) rotates around a workpiece axis (1.2).
11. Procedure as claimed in claim 10, characterized in that the rotational movements of workpiece (1) and tool (2) are directed opposite such that the relative velocity between workpiece surface (1.1) and polishing surface (2.1) is increased in the area (2.3) which is contacting from time to time.
12. Procedure as claimed in any preceding claim, characterized in that the tool (2) is pressed against the workpiece surface (1.1).
13. Procedure as claimed in claim 12, characterized in that the contact pressure is controllable.
14. Procedure as claimed in claim 12 or 13, characterized in that the contact pressure is generated using compressed air.
15. Use of the procedure as claimed in any claim 1 through 14 for polishing optical surfaces.
16. Use of the procedure as claimed in any claim 1 through 14 for machining rotationally symmetric lenses.

Images