CA1206756A - Front surface grinding machine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:
Each workpiece holder of a grinding machine is reciprocated relative to and turned about an axis parallel to that of a wheelhead spindle. Workpieces carried by the holder are brought from in front of and to the side of an abrasive wheel front working surface into contact with the working surface. To prevent he pieces ground by the abrasive wheel from being scratched, after the workpieces have been ground, the wheelhead spindle is translated from a region where the grinding is performed. Simultaneously the workpiece holder is turned from in front to the side of the abrasive wheel working surface. The grinding machine, for instance, comprises two workpiece holders that are diametrally opposed with respect to the abrasive wheel.
The holders turn in opposite reciprocating directions.
The workpiece holders carry two half-holders for optical fibers having ends to be connected together. The ends of the fibers are simultaneously and coplanarly ground by the machine.

Description

~2~)67S~i BACKGROUND OF THE INVENTION
1 - Field of the Invention This invention relates to a front surface grinding machine, and more particularly to the use of such a grinding machine for grinding down the sides of very small pieces and in particular two pieces to be placed end to end, for instance the end surfaces of optical fibers mounted on connection holders for two multifiber cables.

2 - Description of the Prior Art To butt optical fibers end to end~ several methods are known among which note may be made of the following :
1) bonding fibers end to end by partial fusion of the ends, combined with bringing the fibers together ;
2) cutting fibers by a very slight preliminary break on each fiber, followed by traction : this method affords sufficient surface quality for obtaining a satisfactory connection quality when laying the fibers to be connected end to end and applying an index adaptor agent.

3) cutting fibers with no particular precaution, fixing in a holder generally by bonding, and manual polishing of the end faces constituting the fiber connection plane.
The first two methods are usable usually when the fibers must be connected one by one.
The third method concerns more particularly the invention. When several fibers must be connected such as in the case of numerous fibers in two bundles or cables, advantage can be gained, especially with a view to reducing the individual handling for each pair of fibers and thus the time taken to connect them, by dealing with all the fibers at _ ~ _ ~L2~675~

the same time. This simu]taneity in dealing with the fibers is achieved both for the operations of unsheathing, positioning or bonding and for the operation which consists of simultaneously alining all the fiber tip ends so that they lie in the same plane.
To achieve this alinement 9 it is necessary to resort to a grinding machine usable under good conditions, especially for connecting optical fiber cables in situ. Experience has shown it unnecessary to undertake polishing of the opposite optical fiber ends. One fine grinding run is sufficient whilst doing the utmost to obtain excellent geometric definition.
Front surface grinding machines are described in U.S. patent 3,299,579 and U.K. patent 4~1,022. Such a grinding machine comprises at least an abrasive wheel, a wheelhead spindle, means for driving the spindle in rotation, a single workpiece holder, and mean.s for imparting reciprocating rotational motion to the holder about an axis parallel to that of the spindle and in a circular sector at the ends of which the holder is respectively in front, i.e. at the centre, and to the side of the front working surface of the abrasive wheel.
According to U.S. patent 3,299,579, the workpiece holder is a rotating arm including a workpiece guidance recess. The means for imparting reciprocating rotational motion to the workpiece holder is of the crank arm type. Two superposed and coaxial circular abrasive wheels are provided for simultaneously grinding opposite faces of a workpiece.
Each abrasive wheel is made up three concentric abrasive portions having different grades or hardnesses such that the piece as it passes between the two wheels from their circumference towards their centre is first of all rough ground and then ground ever more finely. Upon each grinding cycle, the workpiece holder recess receives the lowest piece in a stack .~

~67~6 of such pieces in a chute when the holder is on the side of the abrasive wheels ; then the holder pivots towards the centre of the two wheels with a view to progressive grinding of the two faces of the workpiece ;
finally, the piece thus ground falls into a central circular column coaxial with the hollow spindle carrying the lower abrasive wheel towards an endless belt conveyor. During grinding, the piece is not actually carried by the workpiece arm but driven thereby and guided during this ~otation by a guide and then by the opposite working surfaces of the two abrasive wheels. The piece may even rotate on its own axis when it is being "rough" and "intermediate" ground by the outer peripheral and interme~iate abrasive portions. In the other rotational direction, the workpiece holder pivots away from the centre of the abrasive wheels towards the workpiece input stack, without carrying a workpiece.
In U.K~ patent 441,022, the workpiece holder is a swinging arm and is also subject to reciprocating motion between the outer circumference and the centre of two coaxial and superposed abrasive wheels by a connecting rod, pivoted arm and eccentric path cam arrangement. The workpiece holder is in the form of a vise capable of gripping one or more pleces such as bricks. In this case, the pieces are ground during the two reciprocating motions of the workpiece holder. The return motion, from the centre to the edges of the abrasive wheels, scratches the workpieces, which here is of no importance since the workpieces are bricks. If however the workpieces were fragile, such as optical fibers, scratches on the fiber end surfaces give rise to a join between fibers placed end to end that have considerable insertion loss as far as optical signal transmission is concerned.

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The grl~ding mçth~d as per U,St p~tent 3,299,579 part~y splves this d~aw~ack si~ce the pie~es a~e o~ly ground during the fi~st rotatlonai ~o~lon~ from the edge towards the centre o~ the tWo abrasive ~heels~ However, such a method cannot be employed for grindi~g the ends of optical fibers fixed onto a holder, Flrs~ of all, such multifiber hol~ers are nok stackab~e an~ cannot fall under gravity onto the centre of ~he abr~sl~e w~eels, as the fibers come from a buIky cable difficult to handle, unlike small indlvidual pieces. Secondly ! the muItifiber holder must be firmiy fixed to the ~orkpiece holder so as to obtain optical fiber alignment faces that are strictly coplanar and ground to a very high de~ree of accuracy.
If such were not the case, this would cause misalignment and lack of parallelism of the optical flber ends to be butted end to end.
OBJECTS OF THE INVENTION
The main object of this invention is to overcome the previously mentioned drawbacks e Another object of this in~ention is to provide a grinding machine ln which the pieces are ground during pivoting of the workpiece holder, from the edge to the centre of the abrasive wheel, and do no longer stay in contact with the abrasive wheel when the workpiece holder pivots in the opposite direction, in order to obviate any scratches on the ground pieces. Such scr~tching must in particular be avoided when khe front working surface of the abrasive wheel comprises concentric circular portions having different structures and/or grades.
Accordingly, the invention is herein broadly claimed as a front surface grinding machine comprising:
an abrasive wheel and a wheelhead spindle~ means for driving said wheelhead spindle in rotation~ a workpiece holder, means for imparting reciprocating rotational motion to said workpiece holder about an axis parallel

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to a longitudinal axis of said wheel head spindle and in a circular sector at the ends of which workpieces carried by said holder are respectively in front and to the side of the front working surface of said abrasive wheel, and means for imparting translational motion to said wheel-head spindle parallel to said longitudinal axis and between a first position where said workpieces are ground by said abrasive wheel working surface, and a second position where said abrasive wheel is disengaged from said workpieces, said abrasive wheel being pulled from said first position to said second position while rotating of said workpiece holder from the front to the side of said abrasive wheel working surface where the ground workpieces are removed. Thus, the rotational path of the workpiece holder towards the centre of the abrasive wheel front surface constitutes the sole grinding run for the workpieces, and the workpiece holder rotational return path to the side of the abrasive wheel, with no contact between the ground workpieces and the abrasive wheel, permits withdrawal of the ground workpieces.
According to another aspect of the invention, such a reciprocating rotational motion of the workpiece holder makes it possible to provide for at least a second workpiece holder which is driven by reciprocating motion imparting means analogous to those of the first workpiece holder. Preferably, the two workpiece holders are substantially diametrally opposed with respect to the centre of the abrasive wheel or, generally speaking, symmetrically arranged with respect to a diametral axis of the abrasive wheel, and have opposite reciprocating motions imparted to them. This enables the edges of two multifiber holders and the end faces of the optical fibers attached to the multifibers holders to be ground simulta-neously, thereby yielding strictly coplanar faces.

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According to a further aspect of the invention, the duration of the grinding operation is reduced still further by the fact that the workpiece holder rotational motion speed in the direction from the side towards the \

- 5a -~2~75-6 front of the f~on.~ wo~ki~g suxfa,ce o~ ~he a,bra,sive wheel for which the woxk~ieces ~re g~ou~ h~ the abra.si~e wheel, is s~ower kha~ that of the workpiece ho~.der in the opposite dlrection from the fron,t tQ the side of the front working surf~ce of the abra.sive wheel for which the ground workpieces are not ln contact with the abrasiv.e wheel, ~ 6 A

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Preferably, the means for imparting motion to the rotating and sliding members included in the machine frame are pneumatic motors in order to ensure a high degree of safety for the personnal operating the machine. In a further embodiment, when certain driving means are electric motors, the invention provides means for ventilating forced air through the machine frame in order to cool the electric motors as well as remove any water that may seep in via the water-tight seals surrounding the rotatable members protruding from the frame. The pressurized water is sprayed by an auxiliary device for cooling the front working surface of the abrasive wheel and the workpieces being ground.
The feature inherent in utiliæing the front surface grinding machine embodying the invention in order to grind the ends of optical fibers flush with a transverse edge of a multifiber holder with a view to connecting optical fiber cables, is that fixed to each workpiece holder is a vise whose jaw teeth can be semi-cylindrical and intended for enveloping two parallel and longitudinal grooves made in the multifiber holder. The grooves of the multifiber holder serve in taking cylinders for alining two identical multifiber holder and connecting their fibers end to end. Generally speaking, however, the vise and its jaw teeth are matched to the shape of the multifiber holder, i.e. of the workpiece to be ground. The vise is fitted with means for limiting the jaw tightening loads, such as a spring, to prevent damage to the multifiber holder made of relatively fragile material.
BRIEF DESCRIPTION OF THE DRAWING
Other features and advantages of the present invention will become apparent from the following detailed description of preferred i6 embodiments of the grinding machine with reference to the accompanying correspondent drawings in which :
- Figs. 1 and 2 are schematic longitudinal side views of the grinding machine across a section of the frame along the dotted line I-I
in Fig. 3 with an electrical motor and pneumatic motor respectively, for imparting rotation to the abrasive wheel spindle , - Fig. 3 is a schematic front end view of the machine frame with two workpiece holders ;
- Fig. 4 is a schematic plan view of the means for imparting reciprocating motion to the workpiece holders ;
- Fig. 5 is a partial cross-sectional view along the line V-V in Fig. 3 showing the means for adjusting the run depth ;
- Fig. 6 is a schematic axial sectional view of a device for connecting two optical fiber cables ;
- Fig. 7 is a view of a sawn edge to be ground of a multifiber holder equipped with alinement cylinders ;
- Fig. 8 is a partially sectional face view of the upper end of a workpiece holder carrying a vise for clamping a multifiber holder ; and - Figs. 9A to 9C depict various abrasive wheel profiles.

The front surface grinding machine as illustrated in Figs. 1 and 3 comprises in front of the front face 10 of its frame 1, a circular abrasive wheel 2 and two oscillating workpiece holders 3a and 3b.
The abrasive wheel 2 is clamped in a known manner to the outside front end of a wheelhead spindle 20 that is rotatably mounted in a bore 11 of the front face 10 of the frame through annular sealing means 110, such as O-rings or flexible leather, rubber boots or similar. The abrasive wheelhead spindle 20 runs in the upper inside part of the frame s~

1 along a hori~ontal longitudlnal axis Z'Z and is driven at ita other end in rotation by motor means attached to the frame 1. The motor for driving the spindle in rotation can be an electric motor, represented as a whole by the block 21 in Fig. 1, or a compressed air motor 22 associated with a pulley and belt system 23 as depicted in Fig. 2.
The abrasive wheel 2 is surrounded by a protective cowl 24 which ia secured to the front face 10 of the frame and in which two arc-segment slots are made to let the upper oscillating ends 30a, 30b of the two workpiece holders 3a, 3b through which are intended for carrying the workpieces to be ground. As shown in Figs. 1 to 3, the lower ends of the workpiece holders 3a, 3b are secured to front outer ends of two longitudinal shafts 31a, 31b which are rotatably mounted in two bores 12a, 12b of the front face 10 of the frame through water-tight boots 120a, 120b or similar. The rotation axis of shafts 31a, 31b are symmetrical with regard to the vertical diametral plane Y'Y - Z'Z of the abrasive wheel 2 and are at a distance from this plane virtually equal to the average radius of the front working surface of the abrasive wheel 2. The distance between the horizontal plane containing the axes of shaft 31a, 31b and the horizontal diametral plane X'X - Z'Z of abrasive wheel 2 determines the length of the workpiece holders 3a, 3b analogous to oscillating levers 3a 9 3b such that the workpieces attached to the ends 30a, 30b lie substantially in the horizontal plane X'X - Z'Z.
-- The sealed bores 12a and 12b are extended longitudinally inside the frame 1 by two composite long bores 13a, 13b made in two bosses 14a, 15b inside the frame 1. Two ball-bearing units 15a, 15b for example tapered with symmetrical angles are embodied in the bores 13a, 13b and form bearings for the shafts 31a, 31b. Each inside end of a shaft 31a, 31b is engaged with the upper end (said first end) of a vertical longilinear ~t6756 member 40a, 40b by transverse Iceylng or similar indicated at 32a, 32b.
Each pair made up of a shaft 31a, 31b and a member 40a, 40b is held stationary in longitudinal translation by means of two stops on the shaft. One of these stops 33a, 33b comprises a stack of elastic washers for taking up play and is arranged against one of the bearings 15a, 15b while applied against the other bearing is a front shoulder of the shaft. The other stop 34a, 34b is set at the inner end of the shaft 31a, 31b against the rear upper end of the member 40a, 40b and is a locking stop with stop ring and nut.
Referring to Figs. 3 and 4, a roller 41a, 41b is rotatably mounted practically vertical to the inner end (said second end) of the member 40a, 40b. The rollers 41a and 41b can roll against two respective ramps which form the sloped sides of a central longitudinal slide 42 that has an isosceles trapezoid horizontal profile. The sloped sides 42a and 42b form an acute angle with the longitudinal direction Z'Z and thus with the axes of the rotating shafts 31a and 31b. The ends of a helico;dal spring 410 are attached between the first and second ends of members 40a and 40b respectively. The spring 410 draws the rollers 41a and 41b against the respective sloped sides 42as 42b. The slide 42 has a subjacent tongue 420 which slides in the longitudinal groove 160 of a guide 16 that is attached to the inner side of the bottom of the frame 1. The axis along which the slide 42 slides is horizontal and in the vertical diametral plane Y'Y - Z'Z of the abrasive wheel 2~ The vertical ramps 42a and 42b are symmetrical with respect to the sliding axis and diverge in the direction of the frame front face 10. When the slide 42 progressively moves away from the front face 10, the rollers 41a and 41b roll on the vertical ramps 42a, 42b and move away from the sliding axis.
As a result, the upper ends 30a and 30b of the workpiece holders s~

carrying the workpieces to be ground come closer to the rotation axis Z'Z of the abrasive wheel 2 and describe two circular arcs which are diametrally and respectively opposite those described by the rnember 40a and 40b moving away.
The means for drawing the slide 42 slowly rearwards in translation comprises according to the embodiment shown in Figs. 1 and 4, a rod 43, a system with endless screw 44 and nut 45, means 46 for driving the nut 45 in perpendicular translation to the endless screw 44, and a motor 47.
The two ends of the rod 43 are rotatably mounted at the rear end of the slide 42 and on the nut 45, respectivelyO The nut 45 releasing means 46 comprises an electromagnet, as shown in Fig. 1, or an actuator which makes it possible to wind the nut 45 up or to engage it on the endless screw 44. The motor 47 can be electric and is secured to the inner side of the bottom of the frame 1 and can drive the endless screw 44 in both directions about its longitudinal axis. The motor 47 can also be pneumatic.
The progressive withdrawal of the slide 42 rearwards is achieved by engaging the nut 45 on the endless screw 44, thereby permitting relatively slow grinding of the workpieces by the front surface of the abrasive wheel 2, compared with the rapid return of the ground workpieces, as will be seen hereinafter. The workpiece holder 3a, 3b speeds may be set in both pivoting directions by regulating the speed of the motor 47.
After the grinding run, a motor means is activated to impart rapid translation to the wheelhead spindle 20 and thus the abrasive wheel 2 parallel to axis Z'Z and rearwards and to impart rapid translation to the slide 42 simultaneously forwards thereby moving the abrasive wheel 2 quickly away from the upper ends 30a, 30b of the holders carrying the - 11 ~

ground workpieces as the abrasive wheel withdra~s. The translational motor means i5 illustrated ln Fig. 1 and comprises a pneumatic actuator 50 whose rod 51 is rotatably anchored to the lower arm of a lever 52.
The pivot point 53 of the lever 52 is rotatably mounted about an axis that is parallel to the axis X'X and that is integral with the frame 1 between the spindle 20 and the slide 42 above the internal bosses 14a and 14b ; the upper arm of lever 52 is shorter than the lower one and consequently the withdrawal path taken by the abrasive wheel 2 is shorter than the advantage motion of the slide 42 and the movement of the upper holder ends 30a, 30b towards their initial positions. The lever 52 can oscillate in the vertical plane Y'Y - Z'Z of the abrasive wheel 2 between the internal bosses 14a and 14b. The end 520 of the lever 52 lower arm is designed to push a front upper protrusion 421 of the slide 42 towards the front face 10. The lever 52 upper arm end is rotatably anchored at 521 to a subjacent tongue 200 on the wheelhead spindle 20 which slides in a longitudinal guide 17 made inside the frame 1, above the bosses 14a and 14b. The tongue 200 is in fact part of the housing forming a spindle bearing. It is thrust against the front end of the guide 17 by a compression spring 201.
When the actuator 50 is activated to move the piston rod 51 forwards the front face 10, the slide 42 has withdrawn, the pieces are ground, and the nut 45 disengaged from the endless screw 44 by the electromagnet 46. The wheelhead spindle 20 then slides along the axis Z'Z over a short recoil path and against the spring 201, so as to disengage the abrasive wheel 2 quickly from the circular return paths of the upper ends 30a, 30b of the workpiece holder 3a, 3b carrying the ground workpieces ; simultaneously, the lower arm 520 of the lever 52 rapidly pushes the stop 421 of slide 42 so that the rollers 41a and 41b

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come closer together and the ends 30a and 30b of the workpiece holders quickly move away to come back to their initial positions where the ground pieces are removed.
In reference to Fig. 5, the grinding machine comprises means 6 for adjusting the abrasive wheel 2 front surface with respect to the vertical surfaces of the workpieces to be ground, i.e. with respect to the upper ends 30a, 30b of the workpiece holders 3a, 3b. This grinding run depth adjusting means 6 comprises a wedge 60 having a hori~ontal cross-section in the form of a rectangular trape~ium whose long side 61 is slightly inclined to the axis X'X and bears under the effect of the rear spring 201 as it butts up the front vertical side with the same angle 202 of the tongue 200 which slides in the upper guide 17. The other long side 62 of the wedge 60 is perpendicular to the axis Z'Z and slides against the vertical front end wall 170 of the guide 17. One end of the wedge 60 is extended by a threaded stud 63 which is screwed into the closed and tapped hole 64 in the end of a nut 65. The knurled head 66 of the nut 65 is accessible on a longitudinal wall on the outside of the frame 1, as depicted in Fig. 3. The smooth shank of the nut 65 between the head 66 and the closed hole 64 runs through an opening 18 in the aforesaid wall of the frame via an annular seal 67 and is axially held therein by a conventional spacer arrangement using stops rings 680 and 681. The outer stop ring 680 comprises a reference index. A circular scale vernier 69 is integral with the nut 65 and subjacent to the head 66. Rotation of the head 66 and the vernier 69 induces translation motion in the wedge 60 and, consequently, adjusting of the front position of the tongue 200 which butts up against the long sloped side 61 of the wedge 60 during the grinding run. Rotation of the vernier 69 with respect to the reference index thus indicates the depth of the 5~
abrasive wheel 2 run. The adjusting means 6 provide a very fine depthadjustment. Here again, no member slide motion is envisaged outside the machine and the seal is achieved around a cylindrical member such as the smooth shank of the nut 65.
As shown in Figs. 1 and 2, the frame 1 can carry on the top a control console 7 in which are lodged all the knobs and levers controlling the driving means such as 21 or 22, 46, 47 and 50. These driving means can be individually or automatically activated via electromechanical transmission means (not shown) in order to perform a workpiece grinding operation consisting :
- after securing the workpieces to the upper ends 30a, 30b of the holders 3a, 3b and setting the appropriate grinding run depth using adjusting means 6 ;
- of withdrawing the slide 42 by engaging the nut 45 on the rotating endless screw 44 and of simultaneously pivoting the ends 30a and 30b one towards the other in front of the front working surface of the rotating abrasive wheel 2 in order to grind the workpieces, as indicated by the arrows in full in the drawing , - then, after disengaging the nut 45 from the endless screw 44 and activating the actuator 50, of the reverse motion of the spindle 20 and the rotating abrasive wheel 2 and simultaneously the forward motion of the slide 42 to move the ends 30a and 30b and thus the ground workpieces away to their initial positions where the pieces are removed from the workpiece holders 3a, 3b as indicated by the arrows in dashed llnes in the drawing.
As depicted in Figs. l to 3, auxiliary means can be provided for enhancing the grinding operation and are accessible from the control console 7.

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Two no~zles 70a and 70b are carrLed by stirrups fixed to the front face 10 of the frame 1 and on the protective cowl 24 and are symmetrically pointed towards the front working surface of the abrasive wheel 2 in line with the transverse axis X'X. The no7zles 70a and 70b are connected via flexible hosing 71a and 71b to a compressed-air water spray device which sprays water during the grinding operation.
Two small spot-lights 72a and 72b are fed via flexible electrical conductor leads 73a and 73b from a low voltage generator. The two spot-lights 72a and 72b are fixed with stirrups to the outside of the protective cowl 24 and light up the two diametrally opposed working zones on the abrasive wheel 2.
In the particular case of the driving means comprising electric motors, forced air flow is provided inside the frame 1 using a fan 74 that is inserted in an air intake conduit 75 running through the rear of the frame 1 and an air outlet conduit 76 running through the upper wall of the frame 1, as shown in ~ig. 1. The fan 74 cools the electric motors and create an overpressure inside the frame 1 thus eliminating any risk of water infiltration from the nozzles 70a and 70b should the seels such as 110, 120a and 120b not be wholly water-tight.
It will be observed that other embodiments may be deduced by those skilled in the art and be based on the foregoing description relative to a preferred embodiment of the grinding machine.
Hence, instead of the sloped sides 42a and 42b of the slide 42 or ramps for the rollers 41a and 41b being convergent towards the rear of the machine, they could be convergent on the front face 10 of the frame ; in this case, the slide 42 moves towards the front face 10 for grinding the workpieces and moves backwards in the frame for disengaging the ground pieces from the abrasive wheel front surface ; the lever 52 1~06~S~

pushes the slide 42 and wheelhead spindle 20 to the rear of the frame and the pivot axis ofthe lever 52 comes above the thrust zones 521 and 520.
In another embodiment, in relation to each rotating shaft 31, the respective workpiece holder 3 and member 40 can be not diametrally opposed ; for example, the member 40 can oscillate above the shaft 31 and laterally to the spindle 20, whereas the slide 42 slides in a guide above the spindle 20.
Lastly, in another embodiment, the slide 42 function can be obtained by means of rotatable cam driven by a motoreducer and a free-wheel hub.
It will further be observed that the machine forms a relatively small and light parallelepipedal block unit and is easily portable.
The utilization of a grinding machine embodying t~e invention for grinding the ends of optical fibers in multifibers cables with a view to connecting them is now described.
Referring to Figs. 6 and 7, it is assumed that the ends of fibers Fa and Fb of two multifiber cables Ca and Cb having an axially symmetrical structure are to be connected two by two on a flat holder 8. The grooved cores of the cables around which the fibers are evenly spaced out cirrularly have been sawn after unsheathing the cables and faning out the optical fibers.
The holder 8 is a stretched parallelepipedal substrate one of the plane major faces of which is endowed along the whole length, with parallel longitudinal V-shaped grooves 80 that are each designed to receive the unsheathed ends of two fibers to be placéd end to end Fa and Fb. The longitudinal edges of the holder 8 incorporate parallel grooves 81 which have a wide V-shaped section or a pointed V-shape section and ~L~Q6~S E;

which are intended for acceptillg two callbrated cylinders 82 and forclamping in the vise jaws of the gr~nding machine. The holder 8 also includes one or more small trans~erse grooves 83 in the transverse median plane of the holder. The small groove 83 serves in initiating the break or as sawing poiDt for separating the holder 8 into identical half-holders 8a and 8b~
After sawing the holder 8, tbe fibers Fa and Fb are folded down into the grooves 81 of the respective half-holders 8a and 8b and are held therein by a fast-setting bonding agen~ 84 and/or by application of half-plates 84a, 84b that are also grooved and obtained form a slngle plate 84 and which covers the half-holders. At this stage, the ends of the fibers protrude slightly from the transverse edges of the half-holders 8a and 8b corresponding to the small groove 83.
The edges 83 of the half-holders 8a and 8b are then ground in conjunction with the ends of the optiçal fibers Fa and Fb using the grinding machine embodying the invention.
Fig. ~ gives a detailled view, by way of an example, showin~ the upper end 30b of a workpiece holder such as 3b which is adapted to accept one of the half-holders such as 8b. Incorporated in the top of the end 30b is a notch having a vertical long side 35 that is practically parallel to the plane Y'Y - Z'Z when the half-holder 8b is being ground, as indicated in Fig. 3. The notch is turned away from the abrasive wheel 2. One, 90~ of the jaws of a vis,e 9b has a right-angular vertical cross-section, where said rlght angle is brought up against the long side 35 of the notch and against the horizontal upper side of ~he end 30b by means of a screw 91 screwed into a horizontal tapped hole in the end 30. The other jaw 92 of the vise 9b is parallelepipedal and is pivotable about a horizontal pivot 93 that is parallel to the ~ 17 -., ~067~6 longitudinal axis Z'Z and whlch is attached to the lower portion of theother jaw 90 in fron of the corner of the notch in the end 30b. The vise 9b is equipped wi~h means for limiting the tightening loads, such as a helicoldal traction spring 94, that can be embodied in a jaw and push the clamping tooth thereof towards that of the other or, as illustrated, can be anchored in two holes 95, 96 in jaws 90, 92 and thereby draw the jaw 92 towards the jaw 90. The half-holder 8b is withdrawn from the vise 9b, by acting on the upper portion of the jaw 92 in which a gripping notch 920 is made, and by pivoting the jaw 92 about the pivot 93 against the pull exerted by the spring 94.
The jaw teeth, such as the ~oo~h 97 in the jaw 90 illustrated can both be calibrated semi-cylindrically in shape with the same diameter thereof as the calibrated cylinders 82 (Fig. 7). The fiber ends Fb and the cut edge of the respective half-holder 8b will thus be coplanar and perpendicular to the longitudinal axis of the half-holder after grinding. The geometric provisions are incorporated notably for clamping the grooves 81 with the semi-cylindrical teeth of jaws 90, 92 having a function analogous to the positioning cylinders 82. The tooth 97 of the jaw 90 secured to the end 30b juts out over a small recess 98 above which the V-shaped grooves 81 of the half-holder 8b are enclasped by the semi-cylindrical jaw teeth.
However, as shown in Fig. 8, the semi-cylindrical tooth 99 on the pivotable jaw 92 can be a semi-cylindrical elastomeric buffer that is embodied in the jaw 92 so as to spread the tightening load and dampen, in conjunction with the spring 949 the thrust loads due to abrasive wheel action during the grinding operation.
After clasping the half-holders 8a and 8b in the respective vises 9a and 9b of workpiece holder ends 30a and 30b such that the sawn edges - 18 ~

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and the ends of optical fiber E'a and Fb extend before the end faces 30a and 30b opposite the front working surface of the abrasive wheel 2, the edges 83 of the half-holders 8a and 8b are alined in a plane parallel to the front surface of the abrasive wheel 2 by means of chocks 980. The abrasive wheel grinding run depth is adjusted by the adjusting means 6 (Fig. 5). Grinding is achieved by bringing the workpiece holder ends 30a and 30b together.
Various forms of abrasive wheel can be employed, as depicted in Figs. 9A to 9C. The abrasive wheel 2 is a diamond-set disc of the flat plate type (Fig. 9a) or, preferably of the plate type with a single conical chamfer (Fig. 9b) or double conical chamfer ~Fig. 9c). The conical-chamfer diamond-set abrasive wheels (Figs. 9B and 9C) advantageously make it possible to commence the machining operation by cutting off at least the ends of the optical fibers Fa, Fb protruding from the sawn edges of the half-holders 8a, 8b. Furthermore, the abrasive wheel structure, i.e. the spacing coefficient of its abrasive grains or the concentration thereof, and its hardness, i.e. the grade or cohesion force maintaining the abrasive grains, can be staggered over several concentric portions of the front working surface of the abrasive wheel. The staggerlng of the various concentric portions is such that, starting from the outer circumference of the abrasive wheel, the abrasive portion structures are tighter and tighter or more and more compact, the sizes of their abrasive grains decrease and their hardness increases. Staggering of this nature in the abrasive procures, in a single grinding run or a single bringing together of the workpiece holder ends 30a and 30b, the roughing and finishing going through intermediate grinding phases on the half-holder 8a and 8b cut edges and optical fiber Fa and Fb ends.

~6';'~6 After the grinding operation on the half-holders 8a and 8b and fibers, then return thereof to their initial positions simultaneously with withdrawal of the abrasive wheel 2, the ground edges of the half-holders are butted together and alined two by two. For these purposes, they are covered with an index adaptation agent which has a refraction index corresponding to that of the optical fiber core so as to reduce the losses due to insertion in from the ends of the fibers.
The fiber Fa and Fb ends on the two half-holders 8a and 8b are then alined by laying the two calibrated alinement cylinders 82 in the V-shaped longitudinal grooves 81, as indicated in Figs. 6 and 7. This application is exerted by at least two flexible attachments or clips 85a and 85b horse-shoe shaped with flat or curvilinear loops. The two S-shaped elbow ends 86 of a clip 85 close around the opposite circumferences of the cylinders 82. As depicted in Fig. 6, the loops 87 of these attachment fittings can come into contact with the inside walls of the box 88 of the connection device in order to dampen any vibrations especially radial on the join in the optical fibers both when connecting them up and laying the cables on site and thereafter.
In lieu of single horse-shoe attachments, the latter can be double horse-shoe rings the symmetrical sections of which with respect to the horizontal median plane of the half-holders are analogous to the attachment shown in Fig. 7.
It will further be noted that the flat half-holders 8a and 8b can be cylindrical half-holders having V-shaped alinement grooves, e.g. 81, diametrally opposed and having small grooves 80 circularly and evenly spaced out above and below the alinement grooves. In this case, if the covering half-plates such as 84a, 84b are utilized, these are made up of two cylindrical half-shells. The latter may be replaced by a layer of ~Z~75~;
fast-setting bonder, equivalent to the layer 84 having a depth practically equal to that of the plates 84a and 84b.

Claims (22)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A front surface grinding machine comprising:
an abrasive wheel and a wheelhead spindle, means for driving said wheelhead spindle in rotation, a workpiece holder, means for imparting reciprocating rotational motion to said workpiece holder about an axis parallel to a longitudinal axis of said wheelhead spindle and in a cir-cular sector at the ends of which workpieces carried by said holder are respectively in front and to the side of a front working surface of said abrasive wheel, and means for imparting translational motion to said wheelhead spindle parallel to said longitudinal axis and between a first position where said workpieces are ground by said abrasive wheel working surface, and a second position where said abrasive wheel is disengaged from said workpieces, said abrasive wheel being pulled from said first position to said second position while rotating of said workpiece holder from the front to the side of said abrasive wheel working surface where the ground work-pieces are removed.

2. The front surface grinding machine as claimed in claim 1, wherein the rotation speed of said workpiece holder in the direction from the side to the front of said abrasive wheel front working surface for which said work-pieces are ground by said abrasive wheel, is slower than that of said workpiece holder in the opposite direction from the front to the side of said abrasive wheel front working surface for which said ground workpieces are not in contact with said abrasive wheel.

3. The front surface grinding machine as claimed in claim 1, wherein said workpiece holder rotational motion imparting means comprises a member having a first end fixed transversely to the rotation shaft of said workpiece holder, a slide having one side sloped with respect to said rotation shaft, means for drawing the second end of said member against said sloped side of said slide, and means for imparting translational motion to said slide parallel to said rotation shaft.

4 - The front surface grinding machine as claimed in claim 3 wherein said second end of said member is a roller.

5 - The front surface grinding machine as claimed in claim 3 wherein said wheelhead spindle translational motion imparting means simultaneously imparts translational motion to said slide and said wheelhead spindle.

6 - The front surface grinding machine as claimed in claim 5 wherein the path followed by said slide is longer than that of said wheelhead spindle.

7 - The front surface grinding machine as claimed in claim 5 wherein said wheelhead spindle and slide simultaneous translational motion imparting means comprises an actuator acting on a lever having a stationary pivotable point and pushing said wheelhead spindle and said slide.

8 - The front surface grinding machine as claimed in claim 3 wherein said slide translational motion imparting means imparts reciprocal motion.

9 - The front surface grinding machine as claimed in claim 3 wherein said means for imparting translational motion to said slide in the direction corresponding to the workpiece holder rotation direction from the side to the front of said abrasive wheel front working surface comprises an endless screw, means for driving the endless screw in rotation, and a nut linked to said slide and running on said endless screw.

10 - A front surface grinding machine as claimed in claim 9 comprising means for driving said nut in translation off said endless screw upon translational motion of said wheelhead spindle away from the circular rotation of said ground workpiece from the front to the side of said abrasive wheel front working surface.

11 - The front surface grinding machine as claimed in claim 1 wherein said wheelhead spindle slides parallel to its axis in a guide, and wherein provided are elastic means for pulling said wheelhead spindle in the direction of said workpiece holder and against one end of said guide, and means for adjusting the grinding run depth by positoning said wheelhead spindle in said guide.

12 - The front surface grinding machine as claimed in claim 11 wherein said grinding run depth adjusting means comprises means equipped with a vernier for translationally moving a wedge one side of which is inclined to the axis of said guide, between the portion of said spindle sliding in said guide and an end of said guide.

13 - The front surface grinding machine as claimed in claim 1 wherein its frame incorporates forced air flow means.

14 - A front surface grinding machine as claimed in claim 1 comprising another workpiece holder that is driven by reciprocating rotational motion imparting means analogous to those of the aforesaid workpiece holder.

15 - The front surface grinding machine as claimed in claim 14 wherein said two workpiece holders are substantially diametrally opposed with respect to said abrasive wheel and are excited in opposite rotational movements.

16 - The front surface grinding machine as claimed in claim 15 wherein said two workpiece holder rotational imparting means comprise :
each a respective member having a first end fixed transversely to the rotation shaft of the respective workpiece holder, and together, a common slide having two sides symmetrically sloped with respect to the sliding axis of said slide that is parallel to said rotation shafts, common means for drawing the second ends of said respective members against said two sloped sides of said slide respectively, and means for imparting translational motion to said slide parallel to said rotation shafts.

17 - The front surface grinding machine as claimed in claim 1 wherein said abrasive wheel is of the conical chamfer type.

18 - The front surface grinding machine as claimed in claim 17 wherein said front working surface of said abrasive wheel comprises concentric circular portoins having structures, grades and grain sizes different respectively.

19 - A workpiece holder of the front surface grinding machine as claimed in claim 1, used for grinding the ends of optical fibers flush with a transverse edge of a multifiber holder with a view to connecting optical fiber cables, said workpiece holder comprising a vise whose jaw teeth are semi-cylindrical and intended for enveloping two parallel and longitudinal grooves in said multifiber holder, said grooves serving in taking cylinders for alining two identical multifiber holders and connected their fibers end to end.

20 - The workpiece holder as claimed in claim 19 wherein the vise is equipped with means for limiting the jaw tightening loads.

21 - The workpiece holder as claimed in claim 19 wherein one of said jaws is pivotable with respect to the other and drawn back thereto by a spring.

22 - A workpiece holder as claimed in claim 19 wherein one of said jaw teeth is an elastic buffer.