GB2117682A - A glass grinding machine - Google Patents

Abstract

A glass grinding machine for treating the edges of glass panes, comprising a horizontal motor-driven turntable (10) having a releasable workholder (38) operating in dependence on the turntable movement in order periodically to secure a pane (14) for treatment; a peripheral grinding wheel (16) mounted movably at the turntable periphery with its axis of rotation vertical and controlled by a template guide (58) or the like; and a loading and unloading system operating in dependence on the rotary movement of the turntable and comprising a rocker arm (24) which near its free end has two automatically operating releasable retaining devices (42, 44) for supplying a pane for treatment to the turntable and for the removal of a finished pane from the turntable, said arm (24) being pivotable about a vertical axis and having a drive operating independently of the turntable drive, the pivot axis of the rocker arm being so disposed laterally of the turntable that in a loading position the retaining devices (42, 44) are situated in the region of the workholder and in an unloading position the retaining devices are situated in an unloading station disposed laterally of the turntable, the retaining devices being disposed in substantially vertical alignment extending away from one another on the top and bottom of the rocker arm respectively extending away from and towards the workholder; and a vertically adjustable lifting means (52) disposed on a turntable frame above the workholder for lifting a finished pane from the workholder before pivoting of the rocker arm into the loading position and transfer of said pane to the top retaining device of the rocker arm after pivoting of the latter into the loading position. <IMAGE>

Description

SPECIFICATION A glass grinding machine THIS INVENTION relates to a glass grinding machine for treating the edges of glass panes.

German Patent 23 49 871 discloses a glass grinding machine wherein two retaining devices are disposed on a member mounted rotatably on a rocker arm, and the rocker arm and a turntable run periodically in synchronism in response to a drive connected to the turntable drive shaft. The member is pivoted by means of its own motor. Such known glass grinding machines have proved satisfactory in principle, but it has been found that there is a need to raise the cycle speeds and, in particular, to reduce the total expenditure in terms of construction and energy.

In one aspect, the invention provides a glass grinding machine for treating the edges of glass panes, comprising a horizontal motordriven turntable having a releasable workholder operating in dependence on the turntable movement in order periodically to secure a pane for treatment; a peripheral grinding wheel mounted movably at the turntable periphery with its axis of rotation vertical and controlled by a template guide or the like; and a loading and unloading system operating in dependence on the rotary movement of the turntable and comprising a rocker arm which near its free end has two releasable retaining devices for supplying a pane for treatment to the turntable and for the removal of a finished pane from the turntable, said arm being pivotable about a vertical axis and having a drive operating independently of the turntable drive, the pivot axis of the rocker arm being so disposed laterally of the turntable that in a loading position the retaining devices are situated in the region of the workholder and in an unloading position the retaining devices are situated in an unloading station disposed laterally of the turntable, the retaining devices being disposed in substantially vertical alignment extending away from one another on the top and bottom of the rocker respectively extending away from and towards the workholder; and a vertically adjustable lifting means disposed on a turntable frame above the workholder for lifting a finished pane from the workholder before pivoting of the rocker arm into the loading position and transfer of said pane to the top retaining device of the rocker arm after pivoting of the latter into the loading position.

More particularly, the retaining devices, the workholder and the lifting means may have a suction cup or the like to which a vacuum can be controllably applied.

Also, the suction cups may be in vertical alignment when the rocker arm is in the loading position of the rocker arm. In this case the longitudinal centre-line of the suction cups in the loading position of the rocker arm is preferably situated on the axis of rotation of the turntable.

The suction cup of the lifting means may be adapted to be lowered substantially as far as the level of the suction cup of the top retaining device when the rocker arm is in the loading position, and the suction cup of the workholder may be adapted to be raised substantially as far as the level of the suction cup of the bottom retaining device when the rocker arm is in the loading position.

Alternatively, the suction cup of the top retaining device may be adapted to be lifted substantially as far as the level of the suction cup of the lifting means when the rocker arm is in the loading position.

In another alternative arrangement, the suction cup of the bottom retaining device can be adapted to be lowered substantially as far as the level of the suction cup of the workholder when the rocker arm is in the loading position.

More particularly, the rocker arm may be controllably adjustable in that the suction cup of the bottom retaining device in a first vertical position is situated substantially at the level of the suction cup of the workholder, while in a second vertical position it is situated on a level enabling a pane held by the bottom retaining device and a pane held by the suction cup of the top retaining device to be freely swung into and out of the loading position respectively, while in a third vertical position it is situated substantially at the level of the suction cup of the lifting means in the lifting position.

According to another feature of the invention, the bottom retaining device may be rotatable about a vertical axis for adjustment of the relative angular positions of the pane and the template.

The unloading station may comprise a conveyor, disposed substantially at the working level of the workholder, that is adapted for the supply of untreated panes and for the removal of treated panes, for example the conveyor may be a roller table or the like, and a lowering device disposed substantially at the level of the lifting means, to receive a treated pane supplied on the top retaining device of the rocker arm when the latter is in the unloading position, and for depositing this pane on the conveyor after the rocker arm has pivoted out of the unloading position. In this case, the lowering device may comprise a suction cup to which vacuum can be controllably applied. Also, if required, the lowering device may be movable in the longitudinal direction of the conveyor, preferably along its longitudinal centre-line.

In another embodiment of the invention, the lowering device may be provided with a centring means for pre-positioning the pane for treatment in a horizontal position at the unloading station such that the pane can be moved to the turntable and treated by the peripheral grinding wheel without any re-positioning after its transfer to the workholder.

The rocker drive may comprise a hydropneumatic rotary hydraulic unit adapted to be locked in the loading and unloading positions of the rocker arm by means of two opposed linear piston-and-cylinder units. It is particularly desirable in this case that the rocker arm has a mechanical locking member which, in both the loading and unloading positions, is adapted to be brought into engagement with a receiving means, to fix the accurate position of the rocker arm.

According to another feature of the invention, the locking member may comprise a stud which is disposed at the bottom of the rocker arm and which has a substantially circular cross-section, the longitudinal axis of the stud extending radially of the pivot axis of the rocker arm, and the receiving means may comprise a block with a V-shaped groove, which is also disposed radially to the pivot axis of the rocker arm.

Preferably, the turntable is adapted to be driven from a hydraulic unit through a clutch.

The turntable hydraulic unit may include a fine drive which, after a coarse rotation of the hydraulic unit through more than 360 , operates to cause the turntable to be moved back into a desired position. In addition, the fine drive may comprise two rollers offset from one another in the peripheral direction of the turntable at the bottom thereof, the axes of rotation of the rollers being vertical, and a pin being adapted to be introduced between the two rollers. In this case the rollers may have a concave surface and the pin may be substantially conical.

The speed of rotation of the turntable is preferably controlled according to the requirements of the contour of the pane to be treated, by controlling the rate of flow of fluid supplied to the hydraulic unit.

Desirably a control disc which rotates in synchronism with the turntable and which has a peripheral surface shaped according to the requirements of the contour of the pane to be treated, and a cam which by sensing said peripheral surface operates to control the fluid flow to the hydraulic unit. In this case the control disc may be interchangeable for adjustment to different pane formats. Alternatively, the control dic may have a plurality of adjustable segments disposed near the periphery of the control disc for adjustment of this to conform with different pane formats.

In a preferred embodiment, two turntables are arranged in tandem and a tandem arrangement is associated with a single rocker arm and unloading station.

With such an arrangement the fluid displaced during the working stroke by the hydraulic unit of one turntable may be utilized to return the other turntable into its starting position, preferably with the peripheral grinding wheel disengaged.

Desirably, the peripheral grinding wheels of the two turntables are fed with coolant only during the grinding operations in each case.

When the glass grinding machine comprises a horizontal motor-driven turntable having a releasable workholder system operating automatically in dependence on the turntable movement, for periodically securing a pane for treatment, and a motor-driven peripheral grinding wheel mounted with a vertical axis of rotation at the free end of a grinding arm pivotable about a vertical axis, the said grinding wheel being mechanically coupled to a sensing disc which senses a template corresponding to the contour of the pane for treatment, the peripheral grinding wheel and the sensing disc being adapted to be pressed against the edge of the pane for treatment and against the template respectively by means of a pneumatic piston-and-cylinder unit actuating the grinding arm, the grinding arm preferably has a hermetically sealed cavity connected to the compressed air cylinder of the piston-and-cylinder unit on the working side of the piston thereof via a connecting line.

Preferably, that section of the compressed air cylinder which is situated opposite the working side of the piston of the piston-andcylinder unit is adapted to have compressed air controllably applied to it in order to reduce the force biassing the grinding wheel toward the centre of the turntable.

Desirably, disengagement means enabling the peripheral grinding wheel to be periodically moved away from the position of the pane for treatment without disengaging the sensing disc from the template is provided between the sensing disc and the peripheral grinding wheel.

The disengaging means may comprise a fluid-actuated piston-and-cylinder unit.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, an embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a glass grinding machine according to the invention; Figure 2 is a side elevation, in partial section, of a part of the machine shown in Fig. 1; Figure 3 is a more detailed view of the machine of Fig. 1, again in plan view; Figure 4 is a side elevation, in partial section, of a turntable unit of the glass grinding machine of Fig. 1; Figure 5 is a plan view of a turntable drive control disc; Figure 6 is a vertical section through the longitudinal centre line of a precision locking mechanism for the rocker arm of a glass grinding machine according to the invention;; Figure 7 illustrates the fine drive of a turntable hydraulic unit, viewed radially from the axis of the turntable; and Figure 8 is a vertical section through a pheripheral grinding wheel and sensing disc, and shows the disengaging mechanism for the peripheral grinding wheel.

Referring to Fig. 1, a glass grinding machine according to the invention comprises two turntables 10, 12 disposed in a tandem arrangement with their axes of rotation vertical.

Each of the turntables 10, 12, is adapted to receive a triangular glass pane 14 that is to be treated, and to position the plate such that its edges can be worked upon by one of a pair of motor-driven rotating peripheral grinding wheels 16. Each wheel 16 is supported on a grinding arm 18, which is pivotable about a vertical axis by means of a pneumatic pistonand-cylinder unit 20. The internal volume of the arms 18 is hermetically sealed and is connected, via a line 22, to the cylinder of the unit 20 on that side of the piston thereof which, when subjected to pressure, causes the grinding wheel 16 to be moved towards the glass pane 14. The arrangement of the pistonand-cylinder unit 20 and the line 22 is only illustrated for the right-hand turntable in Fig.

1. However, the left-hand turntable has a like arrangement.

A rocker arm 24, only part of which is shown in Fig. 1, is disposed between the two turntables 10, 12. The rocker arm 24 is pivotable about a vertical axis of rotation, via a central hydropneumatic hydraulic unit 26.

Opposed linear piston-and-cylinder units 28, 30 enable the arm 24 to be locked in any required positions by selectively counter-acting the force of the unit 26. The arm 24, is also vertically adjustable and is so disposed relative to the two turntables 10, 12 that in a loading position, which will be described in detail hereinafter, it can reach both the zone of each of the turntables 10, 12 which receives a glass pane 14 and a loading station 32 that is positioned laterally of the turntables 10, 12. The loading station 32 is passed by a conveyor 34, in the form of a roller table, for supplying glass panes 14 for treatment (from the left in Fig. 1) and for carrying off treated panes 14 (to the right in Fig. 1).

As will be seen from Fig. 1, a centring means 36 consisting of three components is provided at the loading station 32 to enable precise prepositioning of the panes 14 before treatment.

As best seen in Fig. 2, the turntable 10 is provided with a workholder system for receiving and securing the panes 14 for treatment.

The workholder system comprises a suction cup 38 to which a vacuum can be applied. As also shown in Fig. 2 a device consisting of two parallel guide units 40 is disposed above the turntable 10 for mounting a vertically adjustable lifting device, (not shown), the purpose of which will be explained hereinafter.

In Fig. 2, the rocker arm 24 is illustrated in position at the loading station 32. The arm 24 has a bottom retaining device 42 and a top retaining device 44, each retaining device having a suction cup to which a vacuum can be applied. A lowering means 46, which is also provided with a suction cup to which a vacuum can be applied, is provided above the top retaining device 44. The lowering means 46 enables a treated pane 14 to be removed from the top retaining device 44 and deposited on the roller table 34, as shown on the right in Fig. 1. The suction cup of the lowering means 46 is vertically adjustable and is adapted to traverse in the longitudinal direction of the roller table along the longitudinal centre-line or longitudinal axis thereof. Before the arm 24 reaches the position shown in Fig.

2, it descends, so that the bottom retaining device 42 is lowered to the level of the roller table 34. Having been positioned by the centering means 36, a pane 14 to be treated is then picked up by the retaining device 42 and rocked into the grinding zone of one of the turntables.

Fig. 3 illustrates the grinding machine of Fig. 1 in greater detail. The reference numerals used in Fig. 3 of course corresponding to those used in Fig. 1.

As shown in Fig. 4, the guide units 40 are mounted on the turntable frame 50 via a support member 48. The guide units 40 carry a lifting device 52 which is vertically adjustable by means of an appropriate piston-andcylinder unit 53 and which has a downwardly extending suction cup 54 positioned to be in vertical alignment with the suction cup of the workholder system 38. Each peripheral grinding wheel 16 is mechanically coupled to a sensing disc 56 which co-operates with a template 58 that corresponds to the required contour of the glass pane 14. A hydropneumatic piston-and-cylinder unit 60 can operate to move the peripheral wheel 16 away from the edge of the pane 14 without it being necessary to break the contact between the sensing disc 56 and the template 58.

As also shown in Fig. 4, the turntable 10 is driven by a hydraulic unit 62 through a clutch 64, which may be an electromagnetic clutch.

The speed of the hydraulic unit 62 is controlled by controlling the flow of liquid in a feed line 66, according to the requirements of the contour of the pane 14 for treatment, and is dependent upon the action of a control unit 70, comprising a mechanical sensor 68 which senses the peripheral surface of a control disc 72 (to be described further below) which rotates in synchronism with the turntable 10.

The hydraulic unit 62 for the turntable 10 provides a coarse drive which operates, ratchet-fashion, to produce forward movement of the turntable through an angle of about 365 . A fine drive, for returning the turntable to an exact starting position, of 360 or 0 , comprises a pair of rollers 74 and a conical pin 76 which is adapted to reciprocate and engage with said rollers. The details of this fine drive will also be explained in detail hereinafter.

Referring now to Fig. 5, the control disc 70 has a number of segments 78 mounted around its periphery (sixteen segments 78 are provided in the example illustrated). The segments 78 are mounted to be both pivotable and radially adjustable, and are lockable in any desired position by means of screws 82 which engage in slots 80 on the surface of the disc 70. In this way the control disc 70 can be given a variable peripheral suface contour such that the speed of the hydraulic unit 62 for the turntable can be controlled in a manner suited to the particular type of glass pane to be treated.

Fig. 6 shows a suitable locking member for the rocker arm 24. The locking member comprises a circular stud 84 which may be secured on the rocker arm 24 at right angles to its length and which is adapted to engage a block 86, having a V-shaped groove 88, so that the arm 24 can be exactly located in the required loading and unloading position. This feature is necessary in order that pre-positioning of a glass pane 14 in the workholder 38 of the turntable 10, 12, which is carried out in the loading station 32, may be exactly reproduced without re-adjustment.

With two tandem-disposed turntables, the panels fed to the grinding zones cannot normally be conveyed in the identical positions relative to the respective templates 58, and consequently the templates 58 must be adjusted appropriately before work starts, adjusting means (not shown in detail in the drawing) being provided for this purpose. Alternatively, if no template adjusting means is provided, the bottom retaining device 42 may be constructed to be rotatable about a vertical axis for controlled adjustment of the relative angular positions of the pane 14 and the template 58. In this way, a pane of glass arriving in any angular position, relative to its vertical axis, can be positioned as required with respect to the templates 58.

Fig. 7 is an enlarged-scale detail of the pair of rollers 74, that cooperate with the conical pin 76 to achieve the fine drive for returning the turntables 10 and 12 to their start positions.

Fig. 8 is a detail of the piston-and-cylinder units 60 which operate to move the grinding wheel 16 away from the edge of the pane 14 without breaking contact between the disc 56 and the template 58. This is particularly im portant since this enables the grinding wheel 16 to be moved away the requisite minimum 30 mm from the edge of the pane to enable a change of panes without the template or the surface of the disc 56 being stressed through frequent engagement and disengagement.

This also serves to protect the turntable mountings as there is no impact between the peripheral surface of the template 58 and the dic 56. Finally, this also enables the dic 56 to be kept in contact with the template during the return of the turntable to its initial position, i.e. on traversing the 360 or 0 position at the beginning and end of the cycle, thus ensuring that the axis of the grinding wheel is always in the correct position relative to the pane.

The glass grinding machine described above operates as follows: A pane of glass 14 for treatment is fed on the roller table 34 and exactly positioned in the loading station 32 (the rocker arm 24 will be in the position shown in Fig. 2, this position being accurately maintained by the positive centring device formed by the stud 84 and the V-groove 88 in the block 86) illustrated in Fig. 6. The arm 24 is then lowered into a bottom position which enables the pane 14 positioned on the roller table 34 to be picked up by the suction cup of the bottom retaining device 42. Before this operation, a finished pane 14 held by the top retaining device 44 of arm 24 is received by the lowering device 46 and moved in the direction of conveyance of the roller table 34 and deposited so that it can be conveyed to a washing station (not shown but situated to the right in Fig. 1).

The rocker arm 24, together with the untreated glass pane 14 suspended from the bottom retaining devicie 42, then rocks, in response to the hydraulic unit 26, in its vertical transport position, into a position, which can be exactly maintained in the man ner already described with reference to load ing station 32, in which the bottom retaining device 42 is situated above the workholder system 38. At this time the turntable 10 has previously been indexed into its exact starting position by means of the hydraulic unit 62 in conjuntion with the fine drive 74, 76. Lower ing of the rocker arm 24 and appropriate change of pressure in the suction cup (this of course applies to all the other described pick up and transfer operations in which suction cups are involved), causes pane 14 to be transferred from the bottom retaining device 42 of the arm 24 to the workholder device 38, where it is fixed in the grinding position.

Prior to this, if a previously finished pane 14 has been positioned in the workholder 38 the pane 14 is lifted from the workholder by the lifting device 52 and held in a waiting posi tion above the level of the top retaining device 44 of the rocker arm 24. Thus while the pane 14 suspended from the bottom retaining de vice 42 is transferred to the workholder 39, the lifting means 52 simultaneously lowers the finished pane 14 suspended in the waiting position on to the top retaining device 44 of the rocker arm 24. Arm 24 then rocks back into the unloading station 32, whereupon the operations described above are repeated. The vacuum-actuated suction cup of the workholder 38 thus enables the pane 14 suspended from the bottom retaining device 42 of the arm 24 to be transferred with accurate positioning.

In the illustrated embodiment the empty suction cup 54 of the lifting means 52 then descends on to the pane 14 to be treated on the workholder 38 and vacuum is applied, whereupon the vacuum applied to the workholder 38 is discontinued. The pane 14 is thus fixed and can be treated by the grinding wheel 16 (which was pivoted out of position during the change of panes by means of the hydraulic unit 60 in the manner described above) as desired. While the pane 14 is being treated to produce the required contour as dictated by the template 58 sensed by the sensing disc 56, the rocker arm 24 can carry out the above-described loading functions for the tandem turntable 12.

On completion of the grinding operation and appropriate removal of the peripheral grinding wheel 16, by the hydraulic unit 60, the finished pane 14 is lifted, by means of the lifting means suction cup 54, so that the rocker arm can again rock into position and deposit on the workholder 38 a new pane 14 held on the bottom retaining device 42, and so on.

As an alternative to the procedure described, it would of course be possible for the workholder 38 to hold a pane 14 during the entire grinding operation, i.e., vacuum could be applied constantly to the suction cup thereof.

Advantageously, the arrangement is also such that the "low-pressure" hydraulic fluid displaced during the working stroke of the hydraulic unit 62 (during which the pane 14 held by the suction cup 54 of the lifting means 52 is treated) is directed to the hydrau lic unit of the second turntable, thus moving the second turntable into its starting position.

In this case the fine drive 74, 76 is disengaged and the peripheral grinding wheel 16 is moved out of the grinding position. Stress is further relieved during this return movement because the grinding arm 18 is subjected to a reduced force pressing the grinding wheel 16 and its associated sensing disc 56 towards the pane 14 and template 58 respectively, the resulting effect being that the operative differential presssure in the unit 20 is reduced by compressed air being correspondingly applied in the opposite direction to the piston.Also, the fact that the hermetically sealed volume of the grinding arm 18 is coupled to the unit 20 via the line 22 means that the pneumatic "suspension" forming the working volume of the unit 20 becomes "softer", so that the arm 18 presses inwards radially towards the centre of the turntable with a particularly soft resilient effect.

The described pick-up and transfer operations in the loading station 32, on the one hand, and above the turntable 10, on the other hand, can of course be modified, in which case the appropriate vertical movements, for exmple, of the lifting means 52 and the lowering means 46, or of the workholder 38, are replaced by vertical adjustment of the rocker arm 24 together with the corresponding retaining devices 42 and 44, or vice-versa, numerous variation options being possible. The important feature is that cooperation between the workholder 38, the retaining devices 42, 44 and the lifting means 52 above the turntable during the pane transfer and deposition can be so carried out that both the untreated and the treated panes 14 are positively held by at least one suction cup in each phase, so that even with relatively unsymmetrical panes there is no risk of tilting etc. If necessary, it is also possible for the workholder 38 so to co-operate with the lifting means 52 during the actual grinding operation that the pane 14 can be held both from below and from above step which may be desirable for grinding of very unsymmetrical panes.

It has been found that, with a grinding machine of this invention, higher cycle speeds can be obtained with reduced expenditure in terms of construction and working energy, and that very small panes of glass can be reliably and accurately treated. A simplified turntable drive is provided combined with a mounting of the peripheral grinding wheel such as to prevent any damage to its associated template or the template sensing disc during operation of the machine.

Claims (34)

1. A glass grinding machine for treating the edges of glass panes, comprising a horizontal motor-driven turntable having a releasable workholder operating in dependence on the turntable movement in order periodically to secure a pane for treatment; a peripheral grinding wheel mounted movably at the turntable periphery with its axis of rotation vertical and controlled by a template guide or the like; and a loading and unloading system operating in dependence on the rotary movement of the turntable and comprising a rocker arm which near its free end has two releasable retaining devices for supplying a pane for treatment to the turntable and for the removal of a finished pane from the turntable, said arm being pivotable about a vertical axis and having a drive operating independently of the turntable drive, the pivot axis of the rocker arm being so disposed laterally of the turntable that in a loading position the retaining devices are situ ated in the region of the workholder and in an unloading position the retaining devices are situated in an unloading station disposed laterally of the turntable, the retaining devices being disposed in substantially vertical alignment extending away from one another on the top and bottom of the rocker arm respectively extending away from and towards the workholder; and a vertically adjustable lifting means disposed on a turntable frame above the workholder for lifting a finished pane from the workholder before pivoting of the rocker arm into the loading position and transfer of said pane to the top retaining device of the rocker arm after pivoting of the latter into the loading position.

2. A glass grinding machine according to claim 1, wherein the retaining devices, the workholder and the lifting means each have a suction cup or the like to which a vacuum can be controllably applied.

3. A glass grinding machine according to claim 2, wherein the suction cups are in vertical alignment when the rocker arm is in the loading position.

4. A glass grinding machine according to claim 3, wherein the longitudinal centreline of the suction cups in the loading position of the rocker arm is situated on the axis of rotation of the turntable.

5. A glass grinding machine according to any one of claims 2 to 4, wherein the suction cup of the lifting means is adapted to be lowered substantially as far as the level of the suction cup of the top retaining device when the rocker arm is in the loading position.

6. A glass grinding machine according to any one of claims 2 to 5, wherein the suction cup of the workholder is adapted to be raised substantially as far as the level of the suction cup of the botton retaining device when the rocker arm is in the loading position.

7. A glass grinding machine according to any one of claims 2 to 4 or according to claim 6 when dependent upon any of claims 2 to 4, wherein the suction cup of the top retaining device is adapted to be lifted substantially as far as the level of the suction cup of the lifting means when the rocker arm is in the loading position.

8. A glass grinding machine according to any one of claims 2 to 5 or according to claim 7 when dependent upon any of claims 2 to 5, wherein the suction cup of the bottom retaining device is adapted to be lowered substantially as far as the level of the suction cup of the workholder when the rocker arm is in the loading position.

9. A glass grinding machine according to claim 7 or claim 8, wherein the rocker arm is controllably adjustable in that the suction cup of the bottom retaining device in a first vertical position is situated substantially at the level of the suction cup of the workholder, while in a second vertical position it is situated on a level enabling a pane held by the bottom retaining device and a pane held by the suction cup of the top retaining device to be freely swung into and out of the loading position respectively, while in a third vertical position it is situated substantially at the level of the suction cup of the lifting means in the lifting position.

10. A glass grinding machine according to any one of the preceding claims, wherein the bottom retaining device is rotatable about a vertical axis for adjustment of the relative angular positions of the pane and the template.

11. A glass grinding machine according to any one of the preceding claims, wherein the unloading station comprises a conveyor, disposed substantially at the working level of the workholder that is adapted for the supply of untreated panes and for the removal of treated panes, and a lowering device disposed substantially at the level of the lifting means, to receive a treated pane supplied on the top retaining device of the rocker arm when the latter is in the unloading position, and for depositing this pane on the conveyor after the rocker arm has pivoted out of the unloading position.

12. A glass grinding machine according to claim 11, wherein the lowering device comprises a suction cup to which vacuum can be controllably applied.

13. A glass grinding machine according to claim 11 or 12, wherein the lowering device is movable in the longitudinal direction of the conveyor.

14. A glass grinding machine according to any one of claims 1 to 13, further comprising centring means for pre-positioning the pane for treatment in a horizontal position at the unloading station such that the pane can be moved to the turntable and treated by the peripheral grinding wheel without any re-positioning after its transfer to the workholder.

15. A glass grinding machine according to any one of claims 1 to 14, wherein the rocker drive comprises a hydropneumatic rotary hy draulic unit adapted to be locked in the load ing positions of the rocker arm by means of two opposed linear piston-and-cylinder units.

16. A glass grinding machine according to any one of claims 1 to 15, wherein the rocker arm has a mechanical locking member which, in both the loading and unloading positions, is adapted to be brought into engagement with a receiving means to fix the accurate position of the rocker arm.

17. A glass grinding machine according to claim 16, wherein the locking member con sists of stud which is disposed at the bottom of the rocker arm and which has a substan tially circular cross-section, the longitudinal axis of the stud extending radially of the pivot axis of the rocker arm, and the receiving means comprises a block with a V-shaped groove, which is also disposed radially to the pivot axis of the rocker arm.

18. A glass grinding machine according to any one of claims 1 to 17, wherein the turntable is adapted to be driven from a hydraulic unit through a clutch.

19. A glass grinding machine according to claim 18, wherein the turntable hydraulic unit includes a fine drive which, after a coarse rotation of the hydraulic unit through more than 360 , operates to cause the turntable to be moved back into a desired position.

20. A glass grinding machine according to claim 19, wherein the fine drive comprises two rollers offset from one another in the peripheral direction of the turntable at the bottom thereof, theaxes of rotation of the rollers being vertical, and a pin adapted to be introduced between the two rollers.

21. A glass grinding machine according to claim 20, wherein the rollers have a concave surface and the pin is substantially conical.

22. A glass grinding machine according to any one of claims 18 to 21, wherein the speed of rotation of the turntable is controlled, according to the requirements of the contour of the pane to be treated, by controlling the rate of flow of fluid supplied to the hydraulic unit.

23. A glass grinding machine according to claim 22, further comprising a control disc which rotates in synchronism with the turntable and which has a peripheral surface shaped according to the requirements of the contour of the pane to be treated, and a cam which by sensing said peripheral surface operates to control the fluid flow to the hydraulic unit.

24. A glass grinding machine according to claim 23, wherein the control disc is interchangeable for adjustment to different pane formats.

25. A glass grinding machine according to claim 23, wherein the control disc has a plurality of adjustable segments disposed near the periphery of the control disc for adjustment to different pane formats.

26. A glass grinding machine according to any one of the preceding claims, wherein two turntables together with auxiliaries in a tandem arrangement are associated with a single rocker arm and unloading station.

27. A glass grinding machine according to claim 26 when dependent upon any one of claims 18 to 25, wherein the fluid displaced during the working stroke by the hydraulic unit of one of the turntables is utilised to return the other turntable to its starting position with the peripheral grinding wheel disengaged.

28. A glass grinding machine according to claim 26 or claim 27, wherein the peripheral grinding wheels of the two turntables are fed with coolant only during the grinding operations in each case.

29. A glass grinding machine for treating the edges of panes of glass according to any one of the preceding claims, comprising a horizontal motor-driven turntable having a releasable workholder operating automatically in dependence on the-turntable movement, for periodically securing a pane for treatment, and a motor-driven peripheral grinding wheel mounted with a vertical axis of rotation at the free end of a grinding arm pivotable about a vertical axis, the said grinding wheel being mechanically coupled to a sensing disc which senses a template corresponding to the contour of the pane for treatment, the peripheral grinding wheel and the sensing disc being adapted to be pressed against the edge of the pane for treatment and against the template respectively by means of a pneumatic pistonand-cylinder unit actuating the grinding arm, wherein the grinding arm has a hermetically sealed cavity connected to the compressed air cylinder of the piston-and-cylinder unit on the working side of the piston thereof via a connecting line.

30. A glass grinding machine according to claim 29, wherein that section of the compressed air cylinder which is situated opposite the working side of the piston of the pistonand-cylinder unit is adapted to have compressed air controllably applied to it in order to reduce the force biassing the grinding wheel towards the centre of the turntable.

31. A glass grinding machine according to claim 29 or 30, wherein a disengagement means enabling the peripheral grinding wheel to be periodically moved away from the position of the pane for treatment without disengaging the sensing disc from the template is provided between the sensing disc and the peripheral grinding wheel.

32. A glass grinding machine according to claim 31, wherein the disengaging means comprises a fluid-actuated piston-and-cylinder unit.

33. A glass grinding machine substantially as herein described with reference to and as shown in the accompanying drawings.

34. Any novel feature or combination of features disclosed herein.