FIELD OF THE INVENTION
[0001] The invention relates to a method for machining an optical surface of an optical
lens, a machining device for machining the optical surface of an optical lens, and
to a computer program product comprising one or more stored sequences of instructions
corresponding to the method of the invention.
BACKGROUND OF THE INVENTION
[0002] An optical lens is typically made of plastic or glass material and generally has
two opposing surfaces which co-operate with one another to converge or diverge light
according to a required corrective prescription.
[0003] During the machining of an optical lens, in addition to the precision in manufacturing
the surfaces, it is also essential for such surfaces to be perfectly aligned with
one another both axially and angularly. Otherwise, the optical lens does not provide
the optical effect for which it was designed, in particular the required corrective
prescription.
[0004] Indeed, the relative positioning and shape of these surfaces has a direct impact
on the effect of the optical lens on light.
[0005] Manufacturing of an optical lens to the required prescription requirements typically
includes machining the surface of a semi-finished lens or lens blank. Typically, a
semi-finished lens has a finished front surface and an unfinished back surface. By
machining the back surface of the lens to remove material, the required shape and
positioning of the back surface with respect to the front surface for the desired
corrective prescription can be generated. Further surfacing operations of an optical
lens can include chamfering, beveling, polishing, or coating the surface of a lens
member in order to modify the optical surface.
[0006] During manufacturing of the lens, it is important that the semi-finished lens is
securely maintained in a correct positioning.
[0007] In the state of the art, in order to hold in position, the semi-finished lens a lens
blocker is used that is applied to the finished front surface at a precise angular
and axial position.
[0008] The lens blocker acts as a gripping interface for the holding system during the manufacturing
of the surface to be manufactured in particular during the cutting step and provides
the semi-finished lens blank with a sufficient strength to counteract the force applied
by the cutting tool.
[0009] During the manufacturing process of an optical lens a desired prism may be introduced.
The desired prism may be either a prescription prism or a thinning prism.
[0010] The prism of the optical lens can be defined by the vector (αf, βf, Zf) which is
perpendicular to the tangential plan at the prism reference point (PRP) of the optical
lens; whereby αf corresponds to the prism amplitude, βf correspondents to the prism
orientation and Zf the vertical position of the PRP.
[0011] The manufacturing of such desired prism requires that the semi-finished lens be oriented
in a desired specific orientation with respect to the manufacturing tools. Such orientation
is usually obtained by using a prismatic blocker enabling the semi-finished lens blank
to be supported at a given inclination or tilt for the machining process.
[0012] Prismatic blockers typically require the use of resins or glues, therefore requiring
long times to allow the adhesive material to set and cool down. Alternatively, the
prism at blocking is applied through a lead-based low melting alloy.
[0013] Therefore, there is a need for a method of machining an optical lens that allows
having a desired prism that would not present the prior art method drawbacks.
[0014] One object of the present invention is to provide such method.
SUMMARY OF THE INVENTION
[0015] To this end, the invention proposes a method for machining an optical surface of
an optical lens, the method comprising:
- a lens blank providing step, during which a lens blank blocked on a lens blocker is
provided,
- a clamping step, during which the lens blocker holding the lens blank is clamped in
a lens machining device,
- a tilting step, during which the lens blank and lens blocker are tilted relative to
the rotation axis of the lens machining device,
- a surface position determining step, during which the position of the surface to be
machined is determined based on the tilt angle of the lens blank and lens blocker
relative to the rotation axis of the lens machining device,
- a machining tool configuration step, during which the operational parameters of the
lens machining tool are configured in order to manufacture the surface to be manufactured
according to the determined surface position so that the desired optical properties
of the optical lens are respected.
[0016] Advantageously, the method of the invention combines a tilting step and a surface
position determining step allowing to machine an optical lens with a desired prism
without the use of a prismatic blocker.
[0017] Therefore, the semi-finished lens blank may be blocked to a simple lens blocker and
the desired prism may be managed entirely during the machining step and in the machining
device.
[0018] According to further embodiments which can be considered alone or in combination:
- during the surface position determining step the position of the surface to be machined
is determined so that the angle α between the normal of the surface to be machined
at the rotation axis of the lens machining device and the rotation axis of the lens
machining device is smaller than or equal to 3°; and/or
- during the surface position determining step the position of the surface to be machined
is determined so that the normal of the surface to be machined at the rotation axis
of the lens machining device is co-linear with the rotation axis of the lens machining
device; and/or
- during the tilting step the lens blank and lens blocker are tilted of an angle β with
the rotation axis of the lens machining device smaller than or equal to 3°; and/or
- the method further comprises a weight distribution determining step during which a
weight distribution of the lens blank and lens blocker around the rotation axis of
the lens machining device is determined based on the tilt of the lens blank and lens
blocker; and/or
- the tilting step the lens blank and lens blocker are tilted so that the angle α between
the normal of the surface to be machined at the rotation axis of the lens machining
device and the rotation axis of the lens machining device is as small as possible;
and/or
- during the tilting step the lens blank and lens blocker are tilted of an angle β determined
so as the difference with the angle α between the normal of the surface to be machined
at the rotation axis of the lens machining device and the rotation axis of the lens
machining device is as small as possible; and/or
- the clamping and tilting steps are carried out simultaneously by having the clamping
device of the machining device with a predetermined tilt relative to the rotation
axis of the lens machining device; and/or
- the method further comprises a surface machining step during which the surface of
the optical lens blank to be machined is machined based on the operational parameters
of the lens machining tool configured during the machining tool configuration step.
[0019] The invention also relates to a machining device for machining the optical surface
of an optical lens, the machining device comprising:
- a clamp configure to clamp a lens blocker with a tilt angle relative to the rotation
axis of the lens machining device, and
- a processor for:
determining the position of the surface to be machined based on the tilt angle of
the lens blank and lens blocker relative to the rotation axis of the lens machining
device, and
configuring the operational parameters of the lens machining tool in order to manufacture
the surface to be manufactured according to the determined surface position so that
the desired optical properties of the optical lens are respected.
[0020] According to further embodiments which can be considered alone or in combination:
- the clamp has a predetermined tilt angle relative to the rotation axis of the lens
machining device; and/or
- the clamp is configured to tilt the lens blank and lens blocker with an angle β smaller
than or equal to 3°; and/or
- the processor is further configured to determine a weight distribution of the lens
blank and lens blocker around the rotation axis of the lens machining device based
on the tilt of the lens blank and lens blocker.
[0021] The invention further relates to a computer program product comprising one or more
stored sequences of instructions that are stored, for instance, on a non-transitory
computer memory and that are accessible to a processor and which, when executed by
the processor, causes the processor to carry out at least the steps of the method
according to the invention.
[0022] The invention also relates to a computer-readable storage medium having a program
recorded thereon; where the program makes the computer execute at least the steps
of the method of the invention.
[0023] The invention further relates to a device comprising a processor adapted to store
one or more sequence of instructions and to carry out at least steps of the method
according to the invention.
[0024] The invention further relates to a computer readable medium comprising one or more
stored sequences of instruction of a computer program product, wherein the one or
more sequences of instructions are accessible to a processor and which, when executed
by the processor, causes the processor to carry out the steps of the method according
to the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Embodiments of the invention will now be described, by way of example only, and with
reference to the following drawings in which:
- Figure 1 is a flow chart representing a method according to the invention,
- Figure 2 is a perspective view of a lens blank to be machined,
- Figure 3 is a planar view of a preformed surface of a lens blank to be machined,
- Figure 4 is a cross-sectional view of a lens blank blocked on a lens blocker,
- Figure 5 is a cross-sectional view of a lens blank blocked on a lens blocker and clamped
in a lens machining device, and
- Figure 6 is a schematic representation of a machining device adapted to move a machining
tool so that it cooperates in a turning operation with lens blank that is driven in
rotation.
[0026] Elements in the figures are illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the elements in the figure
may be exaggerated relative to other elements to help improve the understanding of
the embodiments of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] The invention relates to a method for machining an optical surface of an optical
lens starting from a lens blank.
[0028] As illustrated on figure 1, the method of the invention comprises at least:
- a lens blank providing step S1,
- a clamping step S2,
- a tilting step S3,
- a surface position determining step S4, and
- a machining tool configuration step S5.
[0029] During the lens blank providing step S1 a lens blank blocked on a lens blocker is
provided.
[0030] The lens blank may be a semi-finished optical lens member. Alternatively, the lens
blank may require that both surfaces be machined.
[0031] As illustrated on figure 2, a semi-finished lens member 10 has a preformed front
surface 11 that, in use of the resulting finished optical lens, is disposed nearest
the object being viewed and an opposing surface 12 to be modified by the manufacturing
process to provide the back surface 13 of the finished optical lens, represented by
the dotted line.
[0032] Opposing surface 12 is machined by a machining tool so that the back surface 13 is
orientated with respect to and distanced from the front surface 11, according to the
required optical prescription.
[0033] While in this embodiment of the invention, the back surface of the optical lens is
formed by the machining process, it is to be understood, that in alternative embodiments
of the invention both or either surfaces of the lens may be formed by the machining
process.
[0034] Moreover, although the optical surface 13 to be manufactured is represented in Figure
2 as concave, it is to be appreciated that the optical surface 13 could equally well
be convex or any other curved surface
[0035] With reference to Figure 3, reference manufacturing markings 111 may be provided
on the preformed front surface 11 of the semi-finished lens member 10 as reference
features for positioning purposes. The manufacturing markings 111 are visible through
the semi-finished lens member 10 from the opposing side 12 of the lens member 10.
[0036] Referring now to Figure 4 and 5, a lens blocking device 20 for blocking lens member
10 in the correct positioning for manufacturing processes comprises a blocker 21,
a blocking ring 22. A protection film, not represented, may be placed between the
front surface 11 of the lens member 10 and the blocking device 20. Blocking cast material
24 is poured into the cavity defined by the lower front surface 11 of the optical
lens 10, the blocker 21 and the blocking ring 22. The blocking cast material 24 cools
to solidify in order to provide a blocking support for the optical lens 10 at the
desired positioning for machining. The lower surface or bearing surface 241 of blocking
material 241 acts as a reference surface for determining the thickness at the center
of the lens member 10.
[0037] The lens blocking device may also be a vacuum blocking device wherein the semi-finished
lens member is blocked against a blocking device using a vacuum.
[0038] Typically, the blocking device comprises a suction device. Such a device preferably
comprises a first rotary shaft or rear mandrel ending with a suction chamber at the
end intended to come into contact with the front surface of the semi-finished optical
lens member blank. The suction chamber is connected to a suction group for generating
the vacuum and comprises a gasket or other type of sealing elements capable of making
a fluid tight coupling once such sealing elements are rested onto the front surface
of the semi-finished optical lens member.
[0039] During the clamping step S2, the lens blocker holding the lens blank is clamped in
a lens machining device. As illustrated on figure 5, the lens blocker 21 holding the
lens blank 10 may be clamped using a clamping device 30, such as a clamp so as to
allow the rotation of the lens blocker holding the lens blank about a rotation axis
of the machining device.
[0040] As illustrated on figure 6, the lens blank 10 and the lens blocker are tilted relative
to the rotation axis 40 of the lens machining device during the tilting step S3.
[0041] Advantageously, tilting the lens blocker in the lens machining device allows machining
a desired prism without having to carry out a complex blocking process. Indeed, the
lens blank may be blocked without considering a desired prism. Thus, making the blocking
step much easier and allowing an easy use of for example vacuum blocking devices.
[0042] During the tilting step S3, the lens blank and lens blocker are tilted of a tilt
angle β with the rotation axis of the lens machining device. According to an embodiment
of the invention, the angle β is smaller than or equal to 3°.
[0043] The position of the surface 13 to be machined is determined during the surface position
determining step S4. The position of the surface 13 to be machined is determined based
on the tilt angle β of the lens blank and the lens blocker relative to the rotation
axis of the lens machining device.
[0044] According to a preferred embodiment of the invention, during the surface position
determining step S4, the position of the surface to be machined is determined so that
the angle α between the normal of the surface to be machined at the rotation axis
of the lens machining device and the rotation axis of the lens machining device is
smaller than or equal to 3°.
[0045] So as to facilitate the machining of the surface and to increase the quality of the
machined surface, the angle α between the normal of the surface to be machined at
the rotation axis of the lens machining device and the rotation axis of the lens machining
device is to be as small as possible.
[0046] Therefore, according to an embodiment of the invention, during the surface position
determining step the position of the surface to be machined is determined so that
the normal of the surface to be machined at the rotation axis of the lens machining
device is co-linear with the rotation axis of the lens machining device.
[0047] In addition, or alternatively, during the surface position determining step the position
of the surface 13 to be machined is positioned so that the angle β is a small as possible.
For example, the surface 13 to be machined is positioned so that the normal of the
surface to be machined 60 at the rotation axis of the lens machining device is co-linear
with the rotation axis of the lens machining device.
[0048] According to an embodiment of the invention, during the tilting step the lens blank
and lens blocker are tilted of an angle β determined so as the difference with the
angle α between the normal of the surface to be machined at the rotation axis of the
lens machining device and the rotation axis of the lens machining device is as small
as possible.
[0049] The method of the invention may comprise an optimization process so as to determine
the tilt angle and the position of the surface to be machined so that both angles
α and β to be both as small as possible and as close as possible one from the other.
[0050] During the machining tool configuration step, the operational parameters of the lens
machining tool are configured in order to manufacture the surface to be machined according
to the determined surface position so that the desired optical properties of the optical
lens are respected.
[0051] The skilled person may use any know method to determine the operational parameters
depending on the type and shape of the machining tool.
[0052] As illustrated on figure 1, the method according to the invention may further comprise
a surface machining step S6.
[0053] During the surface machining step S6, the surface of the optical lens blank to be
machined is machined based on the operational parameters of the lens machining tool
configured during the machining tool configuration step.
[0054] According to an embodiment of the invention, the clamping and tilting steps may be
carried out simultaneously by having the clamping device of the machining device with
a predetermined tilt relative to the rotation axis of the lens machining device. Advantageously,
such embodiment is easier to implement for the machining operator.
[0055] The desired prism may than be adjusted by positioning the surface 13 to be machined
during the surface positioning step S4.
[0056] As illustrated on figure 1, the method of the invention may further comprise a weight
distribution determining step S31.
[0057] During the weight distribution determining step S31, a weight distribution of the
lens blank and lens blocker around the rotation axis of the lens machining device
is determined based on the tilt of the lens blank and lens blocker. Preferably the
weight distribution is determined so as to reduce the effect of the centrifugal force
that may apply to the lens blank when rotated about the rotation axis 40 when the
weight distribution is not homogeneous.
[0058] According to an embodiment of the invention, during the weight distribution determining
step S31, a weight distribution of the lens blank and lens blocker around the rotation
axis of the lens machining device is determined so as to have a weight distribution
as homogeneous as possible around the rotation axis 40 of the machining device.
[0059] For example, depending on the tilt angle and the surface to be machined, addition
weights may be added to the lens blocker to as to homogenize the weight distribution
around the axis of rotation reducing the stress applied to the rotation axis.
[0060] The invention further relates to a machining device for machining the optical surface
of an optical lens. As illustrated on Figure 6, the machining device comprising at
least a clamp 30, a processor 70 and a machining tool 80.
[0061] The machining device represented diagrammatically in figure 6 is adapted to drive
in rotation about an axis 40 a lens blank 10 that is blocked on a lens blocker. The
lens blocker is hold by a clamp 30 and tilted relative to the axis 40.
[0062] The machining device also drives movement in the directions 81 and 82 of a tool-carrier
80 to which a machining tool 83 is fixed.
[0063] According to an embodiment, the machining device may be adapted to machine with the
tool 83 a surface with a constant depth of pass over the surface 12 of the lens blank.
To this end, the machining device may synchronize the position of the tool 83 and
the angular position of the lens blank in the direction 82 to follow the shape of
the surface 12 and to apply the required depth of pass to it, in addition to its forward
movement in the direction 81.
[0064] The clamp 30 is configure to clamp a lens blocker with a tilt angle relative to the
rotation axis of the lens machining device.
[0065] According to an embodiment, the clamp may have a predetermined tilt angle relative
to the rotation axis of the lens machining device, for example smaller than or equal
to 3°.
[0066] Alternatively, the clamp may be configured to tilt the lens blank and lens blocker
with an angle β, for example smaller than or equal to 3°.
[0067] The processor 70 is configured to determine the position of the surface to be machined
based on the tilt angle of the lens blank and lens blocker relative to the rotation
axis of the lens machining device.
[0068] Furthermore, the processor 70 is configured to determine the operational parameters
of the lens machining tool 80 in order to manufacture the surface to be manufactured
according to the determined surface position so that the desired optical properties
of the optical lens are respected.
[0069] According to an embodiment of the invention, the processor 70 may further be configured
to determine a weight distribution of the lens blank and lens blocker around the rotation
axis of the lens machining device based on the tilt of the lens blank and lens blocker.
[0070] The invention has been described above with the aid of embodiments without limitation
of the general inventive concept.
[0071] Many further modifications and variations will suggest themselves to those skilled
in the art upon making reference to the foregoing illustrative embodiments, which
are given by way of example only and which are not intended to limit the scope of
the invention, that being determined solely by the appended claims.
[0072] In the claims, the word "comprising" does not exclude other elements or steps, and
the indefinite article "a" or "an" does not exclude a plurality. The mere fact that
different features are recited in mutually different dependent claims does not indicate
that a combination of these features cannot be advantageously used. Any reference
signs in the claims should not be construed as limiting the scope of the invention.
1. Method for machining an optical surface of an optical lens, the method comprising:
- a lens blank providing step, during which a lens blank blocked on a lens blocker
is provided,
- a clamping step, during which the lens blocker holding the lens blank is clamped
in a lens machining device,
- a tilting step, during which the lens blank and lens blocker are tilted relative
to the rotation axis of the lens machining device,
- a surface position determining step, during which the position of the surface to
be machined is determined based on the tilt angle of the lens blank and lens blocker
relative to the rotation axis of the lens machining device,
- a machining tool configuration step, during which the operational parameters of
the lens machining tool are configured in order to manufacture the surface to be manufactured
according to the determined surface position so that the desired optical properties
of the optical lens are respected.
2. The method according to claim 1, wherein during the surface position determining step
the position of the surface to be machined is determined so that the angle α between
the normal of the surface to be machined at the rotation axis of the lens machining
device and the rotation axis of the lens machining device is smaller than or equal
to 3°.
3. The method according to claim 1 or 2, wherein during the surface position determining
step the position of the surface to be machined is determined so that the normal of
the surface to be machined at the rotation axis of the lens machining device is co-linear
with the rotation axis of the lens machining device.
4. The method according to any of the preceding claims, wherein during the tilting step
the lens blank and lens blocker are tilted of an angle β with the rotation axis of
the lens machining device smaller than or equal to 3°.
5. The method according to any of the preceding claims, wherein the method further comprises
a weight distribution determining step during which a weight distribution of the lens
blank and lens blocker around the rotation axis of the lens machining device is determined
based on the tilt of the lens blank and lens blocker.
6. The method according to any of the preceding claims, wherein during the tilting step
the lens blank and lens blocker are tilted so that the angle α between the normal
of the surface to be machined at the rotation axis of the lens machining device and
the rotation axis of the lens machining device is as small as possible.
7. The method according to any of the preceding claims, wherein during the tilting step
the lens blank and lens blocker are tilted of an angle β determined so as the difference
with the angle α between the normal of the surface to be machined at the rotation
axis of the lens machining device and the rotation axis of the lens machining device
is as small as possible.
8. The method according to any of claims 1 to 5, wherein the clamping and tilting steps
are carried out simultaneously by having the clamping device of the machining device
with a predetermined tilt relative to the rotation axis of the lens machining device.
9. The method according to any of the preceding claims, further comprising a surface
machining step during which the surface of the optical lens blank to be machined is
machined based on the operational parameters of the lens machining tool configured
during the machining tool configuration step.
10. Machining device for machining the optical surface of an optical lens, the machining
device comprising:
- a clamp configure to clamp a lens blocker with a tilt angle relative to the rotation
axis of the lens machining device, and
- a processor for
determining the position of the surface to be machined based on the tilt angle of
the lens blank and lens blocker relative to the rotation axis of the lens machining
device, and
configuring the operational parameters of the lens machining tool in order to manufacture
the surface to be manufactured according to the determined surface position so that
the desired optical properties of the optical lens are respected.
11. The machining device according to claim 10, wherein the clamp has a predetermined
tilt angle relative to the rotation axis of the lens machining device.
12. The machining device according to claim 10, wherein the clamp is configured to tilt
the lens blank and lens blocker with an angle β smaller than or equal to 3°.
13. The machining device according to any of claims 10 to 12, wherein the processor is
further configured to determine a weight distribution of the lens blank and lens blocker
around the rotation axis of the lens machining device based on the tilt of the lens
blank and lens blocker.
14. A computer program product for a data processing device, the computer program product
comprising a set of instructions which, when loaded into the data processing device,
causes the data processing device to perform at least the surface position and machining
steps of the method of any one of claims 1 to 9.
15. A computer readable medium carrying one or more sequences of instructions of the computer
program product of claim 14.