Note: Descriptions are shown in the official language in which they were submitted.
67~
- 1 - F.1166
MAGNETIC COUPLING FOR CONTACT LENS MACHINING APPARATUS
This invention relates to an improved machine for
diamond turning and polishing contact lenses and the
like.
Drawbacks experienced with existing known machines
for this purpose are briefly that due to vibration caused
by between relatively moving parts of the machine it
is not always possible to obtaln a good surface finish
to the ienses and to maintain the required accuracy and
geometry thereof.
Also, the production of high quality lenses at present
depends to a great extent upon the skill of operatives
and unless expertly and efficiently carried out breakage
of or damage to both the lenses and the diamond turning
or polishing tools can easily result.
It is known from US 4037496 to provide a machine
for producing optical quality surface finishes and wherein
an eddy current magnetic coupling is provided between
the driv;e motor and workpiece holder. The purpose is
:
t~o avoid vibration. The construction is however complex
and toIerance conscious, and the greater the slip the
higher is the transmitted to~que.
It is an object of this invention to provide a machine
~ ~ ~ 25 with a vibration-free coupling which is of simple construction
: ~
.., ,~
. ,
6~
-- 2
and which eliminates the drawbacks above referred, to
and enables high quality accurate lenses to be obtained
with the risk of breakage both of lenses and tools avoided,
or substantially so.
According to this invention, there is provided a
machine for diamond turning and polishing contact lenses
characterised in that the drive from a prime mover, e.g.
an electric motor, to means for rotatably supporting
a workpiece, is effected through the intermediary of
a coupling comprising inner and outer magnets supported
by adaptors fitted respectively to a driving shaft of
the prime mover and a machine spindle provided or formed
integral with an adaptor for receiving a contact lens,
the magnetic force between the two magnets being such
that the coupling will drive the machine spindle without
physical contact between the machine spindle and the
prime mover when the latter is actuated.
Preferably a predetermined breaking torque is provided
between the magnets such that the machine spindle will
immediately stop if excessive pressure is created between
a workp1ece and the tool.
In addition to the above, vibration is still further
avoided by an arrangement of bearings as will hereinafter
be made apparent.
In this construction breakage is avoided by a
:~ "!J,
~ ~ 76~7~
predetermined breaking torque between the two magnets
of the magnetic coupling resulting in the means rotatably
supporting the workpiece being stopped in the event
of excessive pressure being exerted between the workpiece
and a tool acting thereon. The drive will not
thereafter re-engage unless the motor is stopped and
then restarted.
An advantage also resulting Erom this invention
is that mechanical noise is significantly reduced during
operation of the machine.
To enable the invention to be clearly understood
and readily carried into effect a preferred embodiment
thereof will now be described by way of example with
reference to the accompanying purely diagrammatic drawings
wherein:~
Figure 1 is a part sectional side elevation of
the apparatus and
Figure 2 is a longitudinal section taken through
the casing of the apparatus.
Referring firstly to Figure 1, the apparatus comprises
a shaft 1 driven in both clockwise and anti-clockwise
directlons by a printed armature motor 2, the shaft
1 transmi.tting a drive to the machine spindle 7 by way
of a magnetic coupling comprising inner and outer ceramic
magnets 6 and 3 respectively supported by metal adaptors
7 8
5 and 4. The magnet 6~ by way of its adaptor 5, is
fixed to the drive shaft 1 and the magnet 3, by way
of its adaptor 4 is fixed to the spindle 7. The magnets
3 and 6 are aligned in order that the magnetic force
between the two will drive the spindle 7 without physical
contact between the spindle 7 and the motor 2 when the
latter is activated.
It will be readily appreciated that by means of
the arrangement described above that no vibration is
transmitted by the motor 2 to the machine spindle 7
as would normally occur with known machines due to poor
quality bearings, the use of a belt drive, lack of
stability and excessive machine tolerances generally.
Referring next to Figure 2, the machine spindle
15 7 is hollow and is mounted to rotate in bearings in
a casing 8, said bearings comprising self-aligning
angular contact ball races ~ and 10 having spacers 11
and 12 lnterposed therebetween, and a self-aligning
angular contact ball race 13 mounted in a sleeve 14,
;20 ~a spacer 15 belng interposed between this latter bearing
and the bearing 10. This assembly of bearings, which
ensures stability of rotation of the spindle 7, is held
in position in the casing 8 by retaining rings 16 and
17 at the ends of the casing 8.
The casing 8 is mounted on a metal bed (not shown)
~ ~.
6 ~ 8
-- 5 --
ensuring that the machine is very stable.
A work piece, e.g. a contact lens, is supported
within a tapered adàptor 7a fitted to or formed integral
with, the front end of the machine shaft or spindle
7.
In a further embodimen~ of the invention which;is
not illustrated, the machine spindle is supported by a
minimum total of two bearings. At least one ball race
is provide-d at the end of the spindle adjacent the
workpiece-receiving adaptor and at the end of the spindle
adjacent the magnetic coupling and drive shaft. These
bearings may be separated by a spacer or suitable spacing
means. Suitable bearings in all embodiments include
angular contact ball races which may additionally be
self-aligning.
The provision of the magnetic drive coupling above
described also overcomes the problem of tool breakage
that has previously been experienced with known machines
because a predetermined break1ng torque between the
two magnets 3 and 6 ensures that the spindle 7 will
mmediately stop if the diamond turning tool is plunged
into the workpiece and excessive pressure created between
the latter and the tool. With a conventional belt
or magnetic drive mechanisms a diamond turning tool
would be damaged because of the outgoing inertia in
~i,~,i
!:5~ '~
7 8
the spindle 7.
Preferably the electric motor 2 i5 a D.C. motor
as this has low vibration.
Although this invention is primarily concerned
with the diamond turning and polishing of contact lenses,
it is to be appreciated that it can be adapted to be
used for analogous purposes, such as for ~he diamond
turning and. polishing of lenses or the like for scientific
apparatus such as those for cameras; optical apparatus,
microscopes and the working of any non-ferrous or precious
metal or plastic component par;ts.
:
: ~ ,
: .
