Machine for grinding the edges of a lens

A machine for grinding the edges of a spectacle lens, including shaft halves for holding the lens therebetween, a grinding wheel for machining the periphery of the lens, a support for the template that is held by one of the shaft halves, and a measuring head that is connected to a computer and serves for measuring the position of the front and rear sides of the lens at the grinding or contact point, in the vicinity of the periphery of the grinding wheel, relative to a prescribed plane. The measuring head has a fork-like configuration, including fork legs that are disposed parallel to one another and to the prescribed plane, and are spaced from one another by a distance that is greater than the greatest width of the periphery of the lens, whereby the shaft halves with the lens, or the grinding wheel with the measuring head, carries out an oscillating back and forth movement relative to the other.

BACKGROUND OF THE INVENTION 
The present invention relates to a machine for grinding the edges or rim of 
a spectacle lens, including shaft halves for holding the lens 
therebetween, a grinding wheel for machining the periphery of the lens, a 
support means for a template that is held by one of the shaft means, and a 
measuring head that is connected to a computer and serves for measuring 
the position of the front and rear sides of the lens at the grinding or 
contact point, in the vicinity of the periphery of the grinding wheel, 
relative to a prescribed plane. 
U.S. Pat. No. 4,596,091 and the corresponding French Patent No. 2 543 039 
disclose a machine of this general type for grinding the edges of a lens 
that serves for providing a bevel at the edge of the lens. With this known 
machine, the inner and outer sides of the lens are scanned in the vicinity 
of the periphery of the lens by two resiliently mounted, pin-like sensors 
that constantly rest directly against the lens. The axial position of the 
sensors is communicated to potentiometers, with the values and data 
determined by these potentiometers being relayed to a computer or a data 
bank. If the scanning is effected at the same time as the grinding, the 
heretofore known scanning apparatus causes scratches to occur in the 
vicinity of the periphery of the lens as a consequence of the particles of 
the lens that have been ground off. In addition, when the lens is inserted 
between the two pin-like sensors, it is necessary to retract one of the 
sensors against spring force in order to provide a gap between the two 
sensors into which the edge of the lens can be inserted. 
In contrast to the heretofore known apparatus, it is an object of the 
present invention to provide a machine of the aforementioned general type 
for grinding the edges of a lens, with the inventive machine making it 
possible to determine the data concerning the curve of the grinding or 
contact point on the periphery of the grinding wheel, which curve is 
described by the front and rear edge of the lens, without hereby producing 
scratches as occurs with the aforementioned known machine.

SUMMARY OF THE INVENTION 
The inventive machine for grinding the edges of a spectacle lens is 
characterized primarily in that the measuring head has a fork-like 
configuration, including fork legs that are disposed parallel to one 
another and to the prescribed plane, and are spaced from one another by a 
distance that is greater than the greatest width of the periphery of the 
lens, whereby the shaft halves with the lens carry out an oscillating back 
and forth movement relative to the grinding wheel with the measuring head, 
or vice versa. 
In one specific embodiment, this back and forth movement of the shaft 
halves and lens or the grinding wheel and measuring head has a constant 
amplitude of a minimum magnitude that corresponds to the spacing between 
the fork legs. Pursuant to another alternative, the back and forth 
movement has an amplitude of a magnitude that is determined by the 
respective position of the lens on the fork legs, with the duration of the 
back and forth movements of the lens or the grinding wheel being measured 
between the prescribed plane and the reversal points of the back and forth 
movement. 
As a further development of the present invention, it is also desirable, at 
the same time that the data for the spherical curve of the lens edges is 
determined, to be able to utilize the full or nearly full width of the 
grinding wheel. 
In this regard, DE-U 85 29 208 discloses a machine for grinding the edges 
of a lens where the grinding wheel is uniformly used up over its entire 
width by having the lens carry out a back and forth movement over the 
width of the grinding wheel, the sides of which are provided with narrow 
beveled abutment surfaces for the front and rear peripheral edges of the 
lens. In this connection, a reversing gearing is used that is 
load-controlled and effects a reversal of the transverse movement of the 
lens, so that this reversal of the movement is always effected at the same 
axial level of the grinding wheel width. In contrast thereto, pursuant to 
one specific embodiment of the present invention the parts of the scanner 
that effect the reversal of the back and forth movement of the grinding 
wheel or the lens, and that are spaced apart at a distance approximating 
the width of the grinding wheel, are movably disposed, with their movement 
transmitting not only the desired data pulse but also the reversal signal 
for the conclusion of one pass and the beginning of another pass of the 
oscillating movement of the grinding wheel or the lens. 
Further specific features of the present invention will be described in 
detail subsequently. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings in detail, in the illustrated embodiment, the 
machine for grinding the edge of a spectacle lens includes a grinding 
wheel S that is fixedly disposed on the shaft 1, which can be shifted 
longitudinally and serves to rotate the grinding wheel. In the embodiment 
of FIGS. 1 to 3, provided on both sides of the grinding wheel S on a 
non-illustrated wall of the machine housing are two parallel rods or bars 
3, 4 that merge with further rods or bars 5, 6 that extend approximately 
perpendicular thereto. Disposed at the end of this second pair of bars 5, 
6 is a fork-like measuring head that is indicated in general by the 
reference numeral 7 and comprises a crossmember 8 and two parallel fork 
legs 9, 10 that in their starting position are spaced from one another by 
a distance "a" that is approximately equal to the width "b" of the 
grinding wheel S. As shown in FIG. 3, the legs 9, 10 have an upper portion 
11 that has a rectangular cross-sectional configuration and to which is 
connected a narrow base portion 12 that extends from the upper portion 11 
in the direction toward the central plane M of the grinding wheel S (see 
FIGS. 4 and 5). The forward edge 13 of the base portion 12 is either 
pointed at an acute angle or is slightly rounded off, with a very small 
gap being left between the base portion and the grinding wheel. 
The spectacle lens B is held in a known manner between two shaft halves 14, 
15 of the machine and is rotated thereby. Fixedly disposed on the shaft 
half 14 is the template 16, which rests upon a support member 17. 
As shown in FIG. 2, the crossmember 8 of the measuring head 7 is provided 
with two short extensions 18, 19 that end in respective inclined edges 20, 
21. Disposed across from each of these edges 20, 21 is a corresponding 
inclined edge 22, 23 of the legs 9, 10, whereby between each of the pairs 
of edges 20, 22 and 21, 23 a respective vertical gap 24 is formed that has 
a triangular cross-sectional configuration. Disposed between the 
extensions 18, 19 and the adjacent end of the legs 9, 10 is a respective 
measuring strip 25. When these measuring strips 25 stretch as a 
consequence of the deflection of the legs 9, 10 in the direction of the 
arrows P and P.sub.1 out of their starting position, in which they are 
parallel to one another, a signal is transmitted via a line 26, 27 to a 
non-illustrated computer and register that are generally known for such 
purposes. 
In the illustrated embodiment, the lens B along with the two shaft halves 
14, 15 carry out a repetitive, uniform oscillating movement in the 
direction of the arrows O and O.sub.1 in FIG. 1. Conversely, the shaft 
halves 14, 15 for the lens can be fixed in a longitudinal direction, and 
the grinding wheel S can carry out oscillating transverse movements, with 
the fork-like measuring head 7 then following this oscillating movement of 
the grinding wheel. These axial oscillating movements of the shaft halves 
or of the grinding wheel can be effected with the aid of means familiar to 
anyone skilled in the art, such as a reversing motor that has a shift dog. 
The rotational movement of the lens B and the oscillating movement of the 
lens or of the grinding wheel, which oscillating movement is carried out 
at a constant speed, are coordinated with one another in such a way that 
the oscillating movements repeat themselves over approximately the width 
of the grinding wheel in conformity with a specific angular rotational 
movement of the shaft halves. This can be effected with a speed-measuring 
device of the lens shaft halves and with the reversing motor for the shaft 
halves or the grinding wheel. At the end of each oscillating transverse 
movement of the lens B over the approximate width of the grinding wheel S, 
the edge of the front or rear side of the lens B contacts one of the legs 
9, 10 and slightly deflects the same in the direction of the arrow P or 
P.sub.1. 
The fork legs 9, 10, which can have a contour that is adapted to the 
periphery of the grinding wheel (FIG. 7), transmit via the measuring 
strips 25 not only the control signal for reversing the oscillating 
movement, but with the aid of these measuring strips spacing data 
concerning the contact points BB of the front or rear edge BR.sub.1 and 
BR.sub.2 (FIG. 1) of the lens edge or rim surface BU with the legs 9, 10 
are also determined. By coordinating this data to the angle values of the 
lens rotation, the shape of the spherical curve of the lens edges BR.sub.1 
and BR.sub.2 of the front and rear sides of the lens can be determined. 
FIG. 4 schematically illustrates the path of individual contact points BB 
of the rim surface BU of the lens with the grinding wheel periphery (which 
is unrolled or laid flat in the plane of the drawing), and hence 
illustrates the path of this contact point over the approximate width "b" 
of the grinding wheel S. FIG. 4 is based on the contact point of the front 
side of the lens B with the grinding wheel S first covering the path 50 
over the grinding wheel S and thereafter, prior to reversing the 
oscillating movement to the path 52, covering the path portion 51 which, 
to facilitate illustration, is greatly enlarged in the drawing. After 
conclusion of the path 52, the back side of the lens abuts against the 
fork leg 10, deflecting the same out of its starting position. After 
covering the path portion 53, the contact point BB of the lens B moves on 
the grinding wheel S over the path 54 and the further path portion 55, 
etc. The contact point now moves over the paths 56, 58, 60, 62, and the 
path portions 57, 59, 61, etc. 
The data relating to the spherical curve of the front and rear edge of the 
lens can be determined and stored in various ways. In a first possibility, 
the distances s.sub.1 to s.sub.7 (in conformity with the paths 50, 52, 54, 
56, 58, 60, 62) of the lens contact point with the wheel S from a central 
line M, which is disposed in the central plane of the grinding wheel S, is 
kept uniform and constant, i.e. the reversal of the oscillating movement 
is always effected at the same level on the wheel periphery in the 
vicinity of the two edges 40, 41 of the grinding wheel (FIGS. 1, 3, and 
4). Upon contact and start of the deflection movement of the fork legs 9, 
10, a control signal is transmitted to the computer. The computer stores 
the period of time that the contact point BB of the lens B needs with the 
grinding wheel S (FIG. 1) over each individual path 50 to 62, i.e. the 
distances s.sub.1 to s.sub.7, and calculates therefrom the position of the 
successive contact points, which are the points of the spherical curve of 
the front and rear edges BR.sub.1 and BR.sub.2 of the lens, which curve is 
to be determined. In FIG. 5, the paths s.sub.1 to s.sub.7, and the times 
t.sub.1 to t.sub.7 associated therewith, are illustrated. The 
thus-obtained time curves Z.sub.1 and Z.sub.2 symbolize the spherical 
curves of the edges BR.sub.1 and BR.sub.2 of the front and rear sides of 
the lens. From the above it is clear that it makes no difference for the 
relative movement between the lens and the grinding wheel which of these 
two components carries out the oscillating movement. 
Another possibility for obtaining and storing data relative to the 
spherical curves of the edges of the lens relates to determining the 
amount of deflection of the measuring strips 25. In this instance, the 
various path magnitudes of the deflection of the measuring strips 25 yield 
the spherical curve values without the need to convert the time. In this 
connection, the reversal of the oscillating movement is effected via a 
timing relay at periodic intervals after the first contact of the fork 
legs 9, 10, i.e. after the first deflection pulse of the legs and after 
the deflection of the fork leg has been completely carried out and 
terminated. 
In the embodiment of the measuring head 7a illustrated in FIG. 6, the fork 
legs 9a, 10a of the measuring head are rigidly disposed on a crossmember 
30 of the head that is pivotable about a pin 31 which, along with the fork 
legs, is always returned to the starting position via two springs 32, 33 
that are disposed between the portions 34, 35 and a stationary part 36. 
FIG. 7 once again illustrates the preferred curved configuration 37 of the 
fork legs 9, 10 in adaptation to the periphery of the grinding wheel S. 
Here also the spherical curve of the lens periphery can be determined over 
time or the path of the deflection. 
FIG. 8 shows a further specific embodiment of a measuring head 7b, the 
crossmember 30 of which has the same configuration and arrangement as in 
the embodiment of FIG. 6, while the fork legs 9b, 10b are rigidly 
interconnected by a crosspiece 70. 
The present invention is, of course, in no way restricted to the specific 
disclosure of the specification and drawings, but also encompasses any 
modifications within the scope of the appended claims.