US3452484A - Lens trimming machines - Google Patents

Description

Jul 1, 1969 J. LEVILLAIN ET AL LENS TRIMMING MACHINES Filed June 14, 1966 United States Patent Int. Cl. B24b 7/00, 9/00 U.S. Cl. 51-101 4 Claims ABSTRACT OF THE DISCLOSURE Spectacle lens trimming machine having a grinding wheel and a control follower against which are respectively pressed 2. lens to be trimmed and a template of selected shape. An electrical circuit means is provided for reversing the direction of rotation of the lens and templet upon contact of the follower with the templet.

Machines for automatically trimming lenses, notably spectacle lenses, are already known, wherein a lens carrier rotated at a relatively slow rate and a grinding wheel driven at a relatively high speed are urged against each other, the penetration of the grinding wheel into the lens contour being limited by a fixed follower solid with the wheel mounting and adapted to engaged a templet attached to the lens carrier.

In certain known machines of this type the lens carrier is rotated continuously in the same direction. In this case the lens carrier performs a number of revolutions subordinate to the necessary penetration in front of that point of the final contour which is the deepest one with respect to the initial contour. Thus, the grinding wheel passes again and again on finished circular arcs of the contour, thus retarding the trimming operation.

To avoid this inconvenience trimming machines have been devised wherein the lens rotation is stopped until the templet contacts the roller. Thus this rotation is resumed but it is stopped again when the excess thickness of the follower stops the templet-to-lens contact. This arrangement is advantageous in that it avoids a great number of passes on lens portions requiring a lesser penetration, thus affording a considerable gain of time. On the other hand, in the case of particularly flattened shapes, the penetration of the grinding wheel being relatively deep during the first period of the operation, the stress or torque applied for starting the movement of rotation of the lens is extremely high as the wheel has penetrated the lens material to a substantial depth. This stress produced between the lens and the grinding wheel is frequently attended by a rupture or a rotational shifting of the lens in relation to its templet.

It is a primary object of this invention to provide an automatic trimming machine operating at least as fast as known machines of the second type described hereinabove, but free of the abnormally severe reactions and risks of breakage observed heretofore in machines of this type.

To this end, the trimming machine according to the present invention comprises reversing means adapted to reverse the direction of rotation of the lens carrier as a function of the relative positions of the templet and fixed follower. Thus the machine operates by producing an alternate and relatively fast rotation along each penetration section in a manner similar to a manual machine controlled necessarily by a very skilled operator.

This invention further comprises means for prevent- 3,452,484 Patented July 1, 1969 ing reversals of the direction of rotation of the lens carried in case the excess thickness to be removed by the grinding wheel is too small to develop an excessive resistance to the continuation of the lens rotation in the same direction.

The features and advantages of this invention will appear more completely from the following description given by way of example with reference to the attached drawings in which:

FIGURE 1 is a diagrammatic view showing the lens to be cut and the grinding wheel in an automatic machine of the second type mentioned hereinabove, during a step in which the fixed follower has engaged the templet.

FIGURE 2 shows, on the surface of the lens to be trimmed which is mounted on the machine according to this invention, the path followed by the point of penetration of the grinding wheel into the lens until the trimming of one side ofthe final contour is completed.

FIGURE 3 shows on the same lens the paths followed by the same point of penetration of the grinding wheel during the trimming of the next lens side.

FIGURE 4 is a schematic layout of the whole of a trimming machine according to the invention.

FIGURE 5 shows the paths followed by the point of penetration of the grinding wheel into the lens, in a trimming machine completed by a device for automatically limiting to a maximum angular amplitude the rotation of the lens in one direction.

In the known machine of the second type described hereinabove, the lens carrier remains stationary until the fixed follower carried by the mounting of the grinding Wheel M contacts the templet H rigid with the lens carrier. At this time, as shown in FIGURE 1, the wheel becomes tangent at A to the final contour to be given to the lens V, and an electric contact provided between the roller and the templet re-energizes the means for rotating the lens carrier, whereby the grinding wheel M grinds an arc AB through a relatively great thickness, so that the rotation of the lens carrier is counteracted by an abnormal resistance.

The inconvenience is removed in the trimming machine of this invention which operates in the manner illustrated in FIGURE 2. In this machine the contact between the follower and the templet H controls the reversing of the direction of rotation of the lens carrier and, therefore, of the lens V carried thereby. Under these conditions, the path followed by the point of penetration of the grinding Wheel into the lens, from an initial point 0 on the initial lens contour, describes a series of curvilinear arcs in alternate directions. From this second arc AB each arc starts from a point A of the final contour and leads to another point B of the same contour. The length of these successive arcs AB, BC, CD decreases as well, of course, as the duration of their path. When this duration becomes very moderate, for example in the case of arc CD, it is no more advantageous to impress a rapid to-and-fro motion to the lens, it being obviously more advantageous to continue the rotation in the same direction. This result is obtained as seen in FIG. 4 by completing the pilot electrical circuit controlling the reversing of the templet and lens carrier actuating motor with time-lag means permitting the reversal of the direction of motion of the lens carrier only if the time period elapsing between two successive contacts between the follower and the templet exceeds a predetermined, properly selected lower limit. With this arrangement the lens being trimmed continues to rotate without reversing its direction of rotation when the contact is at D, and thus the wheel enters the zone E where reversals are resumed, the grinding wheel moving in succession to points E, F, G. Thus, the work is performed by successively reducing each one of the larger sides of the lens without causing the grinding wheel to pass several times on the previously ground sections. According to this invention, the machine is completed by an electrical device capable of stopping the machine when a complete uninterrupted rotation has taken place. The reversal may be controlled by using mechanical means or preferably a reversible electric motor, as diagrammatically shown in FIG. 4, the reversing action being simply exerted on the energizing conductors.

In a modified form of embodiment the recurrence of the changes in the direction of travel of the grinding wheel is limited by a device controlling these changes only when the excess thickness of the contour in relation to the desired final contour exceeds a predetermined, properly selected limit, In this arrangement shown in FIG- URE 4 the electric contact between the templet H and the fixed follower T is replaced by a contact between the follower T and an auxiliary feeler I. Then the follower T is stationary and carried for example by a resilient blade R mounted on the same structure I as said resilient feeler I. A stop K limits to a value a the permissible movement of follower T against the elastic resistance of spring R. The distance b between the contact feeler I and the inferior to a. Since the reversal is controlled by contact pulses, it cannot take place when the excess thicknesses of the lens during the grinding operation such as S, with respect to the finished contour, are inferior to a-b.

With this device minor extra thicknesses cannot cause the reversal of the direction of movement of the grinding wheel, whereas this reversal is maintained in case of substantial extra thicknesses. Thus, as by the use of the aforementioned time-lag means, an abnormally high rate of recurrence of these reversals, which took place heretofore at the end of trimming operations, are safely avoided.

In the case of special contours wherein the first reversal might take place too late and to increase the machine output, control pulses may be fed to the reversing means in order to alternate the direction of rotation between the initial point and the first actual contact point A. Thus, successive artificial reversals A1, A2, A3, A4 are produced before this first contact A takes place. In this case the removal of glass particles develops in the manner illustrated in FIGURE 5, these reversals accelerating the initial grinding operation. Since these reversals are controlled through electrical means such as timers or capacitor charges they can be adjusted as a function of the type of work to be performed and notably to the abrasion resistance of the lens material.

The slow lens rotation may be obtained by utilizing a reduction gearing of the type already known per se, or better a floating-rotor motor of the steromotor type capable of reversing its motion frequently without inertia What we claim is:

1. A machine for trimming lenses, particularly spectacle lenses, comprising a circular grinding wheel rotating rapidly about its axis a follower having a control surface of circular contour of the same radius as the grinding wheel and coaxial with the grinding wheel, a templet of selected shape fixed with respect to the lens to be trimmed and disposed in front of said follower while the lens to be trimmed is disposed in front of the grinding wheel, means for pressing said lens and said templet toward said grinding wheel and follower and for imparting slow movement of rotation as long as said templet does not contact said follower and electric circuit means for reversing the direction of rotation of said lens and templet upon contact of said follower with said templet.

2. A machine for trimming lenses, particularly spectacle lenses, comprising a circular grinding wheel rotating rapidly about its axis, a follower having an operative portion with a circular contour of the same radius as the grinding wheel, a first elastic and conductive blade carrying said follower, abutment means for stopping said follower carried by said elastic blade in a position in which operative portion of the follower is concentric with said grinding wheel, a second elastic and conductive blade carrying a contact which is separated from said first blade when no force acts on said follower and which engages said first blade when a force acts on said follower to move said follower to said abutment means, a templet fixed relative to the lens to be trimmed and disposed in front of said follower while said lens is disposed in front of the grinding wheel, means for pressing said lens and templet toward said grinding wheel and follower, electric motor means for slowly rotating said lens and templet, means for reversing the direction of rotation of the motor, an electric control circuit for controlling the reversing of said motor, said circuit including said first and second elastic blades and being closed to reverse said motor when said templet engages said follower to move the follower toward said abutment means and thereby make contact between said first and second blades.

3. A lens trimming machine according to claim 2, comprising adjustable time delay means in said electric circuit and permitting reversing of said motor only when a closing of said circuit follows a preceding closing by an interval of time greater than that for which said delay means 1s set.

4. A lens trimming machine according to claim 3, in which the contact between the two elastic blades is maintained when said follower is spaced from said abutment means by a slight amount.

References Cited UNITED STATES PATENTS 1,231,920 7/1917 Lumsden 51-101 X 2,723,501 11/ 1955 Lueck. 2,821,050. 1/ 1958 McCarthy. 3,119,206 1/1964- Baumgartner. 3,210,890 10/ 1965 Lannom.

LESTER M. SWINGLE, Primary Examiner.

D. G. KELLY, Assistant Examiner.

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