A CHUCK FOR A HIGH PRECISION MACHINE TOOL AND METHOD FOR MAKING A MULTI-CAVITY DIE OR MOULD

Abstract

A chuck for a machine tool having a rotation spindle with a main axis of rotation. The chuck comprises a base plate, a first rotatable plate eccentrically mounted on the base plate, a second rotatable plate eccentrically mounted on the first rotatable plate, balancing means for aligning a principal axis of inertia of the chuck with the main axis of rotation and a holding mechanism. The chuck is provided with an actuating mechanism for angularly displacing the first rotatable plate around a first rotation axis over a first angle of rotation and/or the second rotatable plate around a second rotation axis over a second angle of rotation such that the position of the object with respect to the main axis of rotation can be altered.

Claims

1. A chuck for a machine tool having a rotation spindle with a main axis of rotation, in particular a lathe, the chuck being arranged for positioning an object, such as a work piece, at a relevant position with respect to the main axis of rotation, the chuck being arranged such that the chuck together with the object positioned on it has a principal axis of inertia that can be arranged to coincide with the main axis of rotation, the chuck comprising: a base plate comprising mounting means for mounting the chuck to the spindle; a first rotatable plate eccentrically mounted on the base plate with respect to the main axis of rotation and having a first rotation axis running in parallel to the main axis of rotation such that the first rotational axis is shifted with respect to the main axis of rotation of the spindle; balancing means arranged for balancing the centre of gravity of the chuck together with the object positioned on it with respect to the main axis of rotation such that the principal axis of inertia of the chuck together with the object substantially coincides with the main axis of rotation (19) of the spindle (14); a holding mechanism arranged for securing the first rotatable plate to the base plate; and an actuating mechanism arranged for angularly displacing the first rotatable plate around the first rotation axis over a first angle of rotation such the position of the object with respect to the main axis of rotation can be altered; wherein the chuck comprises a second rotatable plate arranged for receiving the object, the second rotatable plate being eccentrically mounted on the first rotatable plate with respect to the first rotational axis and having a second rotation axis running in parallel to the main axis of rotation and the first axis of rotation such that the second rotation axis is shifted with respect to the first rotation axis, and being secured on the first plate by means of the holding mechanism; and wherein the actuating mechanism is arranged for angularly displacing the second rotatable plate around the second rotation axis over a second angle of rotation such that the position of the object with respect to the main axis of rotation can be altered.

2. A chuck according to claim 1, wherein for at least one angle of rotation of the first rotatable plate the second rotation axis is arranged for substantially coinciding with the main axis of rotation.

3. A chuck according to claim 1, wherein the holding mechanism is arranged for generating a holding force.

4. A chuck according to claim 3, wherein the holding mechanism comprises a magnet arrangement.

5. A chuck according to claim 1, wherein the balancing means comprises a counterweight arrangement, wherein the counterweight arrangement is adjustable, wherein the counterweight arrangement comprises a first part and a second part and wherein the first part of the counterweight arrangement is arranged for being positioned at a first location on the base plate and the second part of the counterweight arrangement is arranged for being positioned at a second location on the first rotatable plate with respect to the location of the first counterweight part.

6-10. (canceled)

11. A chuck according to claim 1, wherein the chuck comprises a pneumatic arrangement, wherein the pneumatic arrangement is arranged for generating a suction force for securing the object on the second rotatable plate, wherein the pneumatic arrangement is arranged for generating a lifting force that exceeds the holding force generated by the holding mechanism such that the first rotatable plate is lifted about the first rotation axis with respect to the base plate and, wherein the pneumatic arrangement is arranged for generating a lifting force that exceeds the holding force generated by the holding mechanism such that the second rotatable plate is lifted about the second rotation axis with respect to the first rotatable plate.

12-18. (canceled)

19. A chuck according to claim 1, wherein the actuating mechanism comprises at least one rotary encoder arranged for monitoring the angular displacement of the first rotatable plate and/or second rotatable plate, wherein the actuating mechanism comprises at least one motor arranged for angularly displacing the first and/or second rotatable plates and, wherein the actuating mechanism comprises a controller arranged for controlling the at least one motor.

20-23. (canceled)

24. A machine tool for turning and/or grinding a work piece so as to form at least one cavity on the surface of the work piece, the machine tool comprising a chuck according to claim 1.

25. A work piece formed by a machine tool according to claim 24.

26-28. (canceled)

29. A lens formed in a work piece or a replication piece manufactured from the work piece, the work piece comprising at least one cavity, the at least one cavity being a mould cavity.

30-31. (canceled)

32. A method of using a machine tool comprising a chuck according to claim 1 for positioning the object, such as a work piece, at a relevant position with respect to the main axis of rotation.

33. The method according to claim 32 for turning or grinding a work piece.

34. (canceled)

35. The method according to claim 32, wherein in a further step at least one lens mould cavity is formed on the surface of the work piece, wherein in a further step at least one array of lens mould cavities (24) is formed on the surface of the work piece.

36. (canceled)

37. The method according to claim 32, wherein in a further step a replication piece is created from the work piece.

38. The method according to claim 32, wherein in a further step at least one lens is created.

39. The method according to claim 38, wherein in a further step the lens is mounted in a lens arrangement.

40. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will be further elucidated by means of the following description and the appended figures.

[0034] FIG. 1 shows schematically an example of a chuck according to embodiments of the present invention mounted on a spindle.

[0035] FIG. 2 shows schematically a cross-section of the chuck of FIG. 1.

[0036] FIGS. 3 and 4 show schematically examples of changing the position of the object by angularly displacing the first and/or second rotatable plates.

MODES FOR CARRYING OUT THE INVENTION

[0037] The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the disclosure.

[0038] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the disclosure can operate in other sequences than described or illustrated herein.

[0039] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the disclosure described herein can operate in other orientations than described or illustrated herein.

[0040] Furthermore, the various embodiments, although referred to as preferred are to be construed as exemplary manners in which the disclosure may be implemented rather than as limiting the scope of the disclosure.

[0041] The term comprising, used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression a device comprising A and B should not be limited to devices consisting only of components A and B, rather with respect to the present disclosure, the only enumerated components of the device are A and B, and further the claim should be interpreted as including equivalents of those components.

[0042] The present invention will be elucidated by means of the example embodiments shown in FIGS. 1 to 4, which will be described in more details below.

[0043] FIGS. 1 and 2 show an example of a chuck according to the present invention. The chuck may be arranged for being mounted on a machine tool having a spindle 14, such as a work spindle, arranged for rotating about a main axis of rotation 19. The rotation speed of the spindle 14 may be determined according to the application for which the machine tool is used. For example, the rotation speed of the spindle 14 may be in the range between 100 to 1000 RPM. The chuck may be mounted on the spindle 14 by means of a mounting interface plate 15, which may be arranged for being attached to the spindle 14 by attachment means. For example, the mounting interface plate 15 may be fixed to the spindle 14 by a set of screws or by means of a zero point mounting system or alternatively the mounting interface plate 15 may be part of the spindle 14. The chuck may be arranged for positioning an object 13, such as a work-piece, at a relevant position with respect to the main axis of rotation 19. The chuck may be arranged such that one of its principal axes of inertia substantially coincides, or even coincides, with the main axis of rotation 19 of the spindle 14, preferably after positioning the object 13 on the chuck. The chuck may be provided with a base plate 1 arranged for being mounted on the mounting interface plate 15 by mounting means. For example, the mounting means may comprise a set of screws with corresponding bores provided on the mounting interface plate 15 or any other mounting means known to the skilled person in the art suitable for securing the base plate 1 to the mounting interface plate 15 of the spindle 14. On top of the base plate 1, a first rotatable plate 2 may be eccentrically mounted. The first rotatable plate 2 may be arranged for rotating about a first rotation axis 20, which may be shifted with respect to the main axis of rotation 19 of the spindle 14. The first rotatable plate may be secured on the base plate by means of a holding mechanism 17 and 22, more in particular a first part of the holding mechanism 17 called the first holding mechanism. A second rotatable plate 3 may be eccentrically mounted on top of the first rotatable plate 2 by means of holding mechanism 18 and 23, more in particular a second part of the holding mechanism 18 called the second holding mechanism. The second rotatable plate 3 may be arranged for receiving an object 13, such as a work-piece, and for rotating about a second rotation axis 21. The second rotation axis 21 may be arranged to run in parallel to the first rotation axis 20 and being shifted with respect to the first rotation axis 20 of the first rotatable plate 2. The holding mechanism may comprise set of magnets 17 and 18, for example electromagnets, arranged for generating a holding force on relevant locations of the chuck, as shown in FIG. 2. For example, a set of electromagnets 17 may be positioned on opposing surfaces on the first rotatable plate 2 and the base plate 1 so as to secure the first rotatable plate 2 on the base plate 1, and a second set of electro-magnets 18 may be positioned on opposing surfaces on the first rotatable plate 2 and on the second rotatable plate 3 so as to secure the second rotatable plate 3 on the first rotatable plate 2. Furthermore, it should be understood that the holding mechanism 17 and 18 may comprise other means for providing a desired holding force on the relevant location between the plates of the chuck known to the person skilled in the art. For example, the holding mechanism may be realised by means of a vacuum arranged for generating a suction force so as to secure the first and/or second rotatable plates 2 and 3 on the desired position. It is understood that preferably the first and the second disk can be lifted with respect to each other such as to allow a more easy rotation of the disks with respect to each other. Thereto, for example flexure springs 22, 23 are provided which allow the disks to be moved axially.

[0044] In order to align a principal axis of inertia of the chuck together with the object 13 with respect to the main axis of rotation 19, balancing means may be provided. By providing the balancing means 6 and 11 the principal axis of inertia of the chuck, preferably after positioning the object 13 onto the chuck may be arranged to substantially coincide, or even coincide, with the main axis of rotation 19 of the spindle 14. As a result, the chuck, by means of the balancing means 6 and 11, remains balanced on the main axis of rotation 19 irrespective of the position of the object. For example, the balancing means 6 and 11 may comprise a counterweight arrangement arranged for compensating a shift in the centre of gravity of the chuck caused by the eccentric arrangement of the first and second rotatable plates 2 and 3. The counterweight arrangement may be provided with a first part 6, which may be positioned at a first location on the base plate 1, and a second part 11, which may be positioned at a second location on the first rotatable plate 2 with respect to the location of the first counterweight part 6. By providing the counterweight arrangement, it is ensured that each plate of the chuck is balanced on each respective axis, thereby ensuring that the chuck remains balanced irrespective of the angular displacement of the first and/or second rotatable plates 2 and 3. The counterweight arrangement may further be provided with a third part, which is not shown, arranged for being positioned at a location on the second rotatable plate 3 so as to counterbalance the weight of the object 13, thereby ensuring that the second rotatable plate 3 is balanced on its axis 21 when the object 13 is positioned on its surface. For example, the counterweight arrangement may be adjustable such that the centre of gravity of the chuck can be aligned with the main axis of rotation 19 for objects 13 having different mass distributions. As a result, the chuck can be used with interchangeable objects 13 having different mass distributions without requiring to change the configuration of the rotatable plates in order to balance the chuck on the main axis of rotation 19. According to embodiments of the present invention, the counterweight arrangement may be adjusted by changing the mass of the counterweight of the counterweight arrangement so as to achieve the desired balancing of the chuck together with the object 13. Moreover, the counterweight of the counterweight arrangement may be adjusted by changing the height of the counterweight of the counterweight arrangement. By adjusting the height of the counterweight, the tilting moment resulting from the centrifugal forces when turning the chuck about the main axis of rotation 19 may be compensated. The counterweight arrangement may comprise weights made from a solid material such as metal or the like as counterweight. The counterweight arrangement may be itself actuated in radial and/or height positions. Furthermore, the counterweight arrangement may comprise fluids, such as liquids having a predetermined viscosity as counterweight.

[0045] According to embodiments of the present invention, the mass and height position of the counterweight parts 6 and 11 may be precisely determined during the assembly of the chuck so that the chuck is perfectly balanced with no object or work-piece attached to it. The counterweight parts 6 and 11 may then be adjusted for the mass and geometry of the object or work-piece 13 that is installed onto the second rotatable plate 3. The object or work-piece may be considered to be itself balanced so that the second rotatable plate 3 remains perfectly balanced on the second rotation axis. The required adjustments of the counterweight arrangement may be calculated knowing the exact values of the mass and position of the centre of gravity of the object or work-piece 13 and of the geometry of the system. For example, for frictionless air bearing work-spindles with horizontal axis, the balancing of the system can be verified statically for all angular displacements of the first and/or second rotatable plates around the first rotation axis 20 and the second rotation axis 21. Dynamic balancing using precision field balancing instruments or the analysis of induced vibration on the main axis of rotation 19 of ultra-precision machine tools are state of the art procedures, which may be used to optimise the balancing of the chuck with respect to the operating speed of the work-spindle 14. Using dynamic balancing the residual imbalance may be reduced to as low as 50 g.Math.mm or less. The chuck may be provided with an actuating mechanism arranged for angularly displacing the first rotatable plate 2 around the first rotation axis 20 over a first angle of rotation such that the position of the object 13 with respect to the main axis of rotation 19 can be altered. The actuating means may further be provided for angularly displacing the second rotatable plate 3 around the second rotation axis 21 over a second angle of rotation such that the position of the object 13 with respect to the main axis of rotation 19 can be further altered.

[0046] As shown in FIG. 2, the chuck may be provided with a pneumatic arrangement, which may be arranged for cooperating with an air/vacuum channel 25 provided on the spindle 14. A pneumatic connection between the chuck and the air/vacuum channel 25 of the spindle 14 may be formed via the pneumatic connection 26 provided on the mounting interface plate 15. The pneumatic arrangement may be arranged for generating a suction force so as to secure the object and/or any of the rotatable plates of the chuck. The pneumatic arrangement may be further arranged for generating a positive air pressure, such as a lifting force, that may be configured for exceeding the holding force generated by the holding mechanism 17 and 18. For example, by generating a lifting force between the first rotatable plate 2 and the base plate 1, the first rotatable plate 2 may be lifted, at least slightly, on the first rotation axis with respect to the base plate 1, thereby allowing the actuating mechanism to angularly displace the first rotatable plate 2 around the first rotation axis 20 so as to change the position of the object 13 with respect to the main axis of rotation 19. Similarly, the lifting force generated by the pneumatic arrangement may be used for lifting the second rotatable plate 3 on the second rotation axis 21 with respect to the first rotating plate 2 so as to angularly displace the second rotatable plate around the second rotation axis 21, thereby changing the position of the object 13 with respect to the main axis of rotation 19. For example, the pneumatic arrangement may be provided with least one pump, such as a micro venturi pump or the like, which may be arranged for generating a suction force for securing the object 13 on the second rotatable plate 3. The at least one pump may further be arranged for generating a positive air pressure to air bearing provided on the first and/or second rotatable plate 2 and 3. The air pressure generated may be between 1 and 10 bars, preferably between 3 to 7 bars, and more preferably around 5 bars. For example, the pump may be arranged for directing air to the air bearings provided on the first and/or second rotatable plate 2 and 3 a thin film of pressurized air to provide an exceedingly low friction load-bearing interface between the rotatable plates 2 and 3. The pneumatic arrangement may comprise a set of valves, such as micro electrovalves or the like, arranged for controlling the lifting and/or suction force generated by the pneumatic arrangement. In order to control the operation of the set of valves at least one controller 12, which may be electronically controlled, may be provided. The controller 12 may be arranged for controlling the operation of the valves according to a set of instructions received from a computer device. For example, the computer device may be provided with a computer program product, such as a hard disk drive, a USB or the like, arranged for storing instructions for operating the at least one controller 12 of the chuck so as to electronically control the set of valves of the pneumatic arrangement. The controller 12 may be further arranged to control the operation of the pneumatic arrangement.

[0047] According to embodiments of the present invention, the actuating mechanism may be provided with at least one motor 5 and 9, such as a direct drive or geared DC brushless motor, or any other suitable type of motor arrangement known to the skilled person in the art. The at least one motor 5 and 9 may be arranged for angularly displacing the first and/or second rotatable plate 2 and 3 about their respective rotation axis. For example, each plate may be provided with a respective motor 5 and 9 positioned at a desired location on each rotatable plate 2 and 3. Each motor 5 and 9 being arranged for angularly displacing the respective rotatable plate 2 and 3 around their respective rotation axis 20 and 21, thereby allowing for the position of the object 13 to be altered with respect to the main axis of rotation 19. Each rotatable plate 2 and 3 may be provided with a rotary encoder 4 and 10, which is arranged for detecting the angle of rotation of each respective rotatable plate. The rotary encoders 4 and 10 may be arranged for monitoring the angular displacement of the first rotatable plate 2 and/or second rotatable plate 3 and generate a corresponding analogue or digital output signal indicating the current angle of rotation of the first and/or second rotatable plate 2 and 3 around their respective rotation axis 20 and 21. The rotary encoder may be of any suitable digital or analog type such as an absolute rotary encoder, incremental encoder, resolver and the like. The actuating mechanism may comprise a controller 12 arranged for controlling the angular displacement of the first rotatable plate 2 and/or the second rotatable plate 3. For example the controller 12 may be arranged for controlling the angular displacement of the first and/or second rotatable plate 2 and 3 by providing to the motors 5 and 9 a set of relevant control signals corresponding to a desired angular displacement of the rotatable plates 2 and 3 around their respective rotation axis 20 and 21. The controller 12 may be arranged for controlling the angular displacement of the first and/or second rotatable plates 2 and 3 according to a set of instructions stored in the memory (EPROM or EEPROM or the like) of the controller or received from a computer device. For example, the computer device may be provided with a computer program product, such as a hard disk drive, a USB stick, a CD and the like, arranged for storing instruction for operating the actuator mechanism of the chuck thereby electronically controlling the angular displacement of the first and/or second rotatable plate 2 and 3.

[0048] According to embodiments of the present invention, the mounting interface plate 15 may be provided with a slip-ring 16 arranged for cooperating with a corresponding electrically conducting surface of the chuck so that electrical power may be transmitted from the static part of the ultra precision lathe to the chuck for operating the various electronic parts while rotating. The corresponding electrically conducting surface may comprise a set of brushes, which may be arranged for being retracted during critical machining operations by means of an actuator. As a result, perturbations in the rotating motion of the spindle 14 caused by the friction or pressure of the brushes 16 against the slip-ring may be avoided. Alternatively the electrical power may be supplied to the chuck by means of induction coils or may be provided from batteries installed on the chuck or the mounting interface.

[0049] The chuck according to embodiments of the present invention is arranged for positioning an object, such as a work-piece, at various locations with respect to the main axis 19 of rotation without the need for rebalancing the chuck on the main rotating axis 19 each time the object is shifted to a new position. This is achieved by eccentrically mounting the first and second rotatable plates 2 and 3 so that the position of the object 13 with respect to the main axis may be altered. The necessary rotation angles of the first and second rotatable plates, given a desired cartesian coordinate of a point on the work-piece to align with the rotation axis 19, may be calculated using the following equations or any equivalent transformation:

[00001]$=\arctan (\frac{2.Math.e^2.Math.\sqrt{1-(\frac{x^2+y^2}{2.Math.e^2}-}}{x^2+y^2}.Math..Math.=-\arccos \left(1-\frac{x^2+y^2}{2.Math.e^2}\right).Math..Math.=+$

[0050] where:

[0051] e is the eccentricity between the rotation axis B, which is the second rotation axis 21, and the rotation axis A, which is the first rotation axis 20

[0052] alpha () is the angle of the rotation axis A (preferably 0 to 360)

[0053] beta () is the angle of the rotation axis B (preferably 0 to 180)

[0054] gamma () is the induced rotation angle further it is assumed that the axis A substantially coincides, or even coincides, with the main axis of rotation 19 for one position of the first rotatable plate. Using the equations above the object 13 can be moved at different locations with respect to the main axis. This is shown schematically on FIGS. 3 and 4. Although any position can be reached using the above mentioned angular ranges for the angles of alpha (preferably 0 to 360) and beta (preferably 0 to 180), these angles may be also continuous over 360. In FIG. 3, the object is positioned, by angularly displacing the first and/or second rotatable plates 2 and 3, such that the main axis 19 substantially coincides, or even coincides, with the second rotation axis 21. At the location of the main rotating axis 19, with the use of a cutting tool, a cavity 24 may be formed. In FIG. 4, the first rotatable plate 2 is rotated around a first angle of rotation, while the second rotatable plate 3 is rotated around a second angle of rotation so that the new object 13 is positioned at a new location with respect to the main axis of rotation 19, at which location and with the use of a cutting tool a new cavity 24 may be formed. By continuously rotating the first and/or second rotatable plates 2 and 3 around a respective angle of rotation the object can be shifted to a new position with respect to the main axis of rotation 19, at which position a new cavity 24 may be formed. Furthermore, by being able to precisely position the object with respect to the main axis, high precision methods, such a diamond turning can be used.

[0055] According to embodiments of the present invention, the second rotatable plate 3 is positioned on the first rotatable plate 2 such that the eccentricity of the two rotatable plates, which is defined as the distance between the first and the second rotating axes 20 and 21 and the distance between the first rotation axis 20 and the main rotation axis 19, is within a predetermined range. For example, the eccentricity may be arranged to be four times shorter than the maximum pitch or centre-to-centre distance (d) between two cavities on a work-piece when for at least one angle of rotation of the first rotatable plate 2 the second rotation axis 21 is arranged for substantially coinciding with the main axis of rotation 19.

[0056] According to embodiments of the present invention, a machine tool for turning and/or grinding a work-piece may be provided. The machine tool may be arranged for forming at least one cavity 24 or an array of cavities 24 on the surface of the work-piece. For example, the at least one cavity may be a mould cavity for the production of lenses. The machine tool may comprise a chuck according to embodiments of the present invention, which may be arranged for positioning the work-piece at a relevant position with respect to the main axis of rotation 19 of the machine spindle, so that machining operations can be performed on the work-piece surface. Using the work-piece manufactured by the machine tool according to embodiments of the present invention, a replication piece may be formed, which may be used for producing moulding products such as lenses. The lens produced either from the work-piece or the replication piece may be subsequently used in a lens arrangement such as the ones provided on mobile phones, cameras, telescopes, microscopes, and the like.

LIST OF REFERENCE NUMBERS

[0057] 1 Base Plate [0058] 2 First rotatable plate [0059] 3 Second rotatable plate [0060] 4 Second encoder [0061] 5 Second motor [0062] 6 First counterweight [0063] 7 First roller bearing [0064] 8 Second roller bearing [0065] 9 First motor [0066] 10 First encoder [0067] 11 Second Counterweight [0068] 12 Controller [0069] 13 Object/work-piece [0070] 14 Spindle [0071] 15 Mounting interface plate [0072] 16 Slip-Ring [0073] 17 First holding mechanism [0074] 18 Second holding mechanism [0075] 19 Main rotating axis [0076] 20 First rotation axis [0077] 21 Second rotation axis [0078] 22 First flexure spring [0079] 23 Second flexure spring [0080] 24 cavity [0081] 25 Air channel [0082] 26 Pneumatic connection