EP0084504B1 - Apparatus for grinding the edges of glass sheets - Google Patents

Description

The present invention relates to an apparatus for grinding the edges of glass sheets using a grinding tool rotatably mounted on a tool holder which can be moved in a direction perpendicular to the edge of the glass sheet and on which acts a pressure means by which the grinding tool is pressed against the glass sheet under an adjustable force.

There are automatic grinding machines, some in which the glass sheet is placed on a rotating support and the grinding tool kept in contact with the edge of the glass, others in which the grinding tool kept in contact with the glass. glass is carried by a carriage, mobile around the glass sheet by moving in a compound movement resulting from translations in two orthogonal directions; in both types of machines, the grinding pressure can be adjusted.

Thus the document DE-C-19 66 260 (or its French correspondent FR-A-1 588 348) describes an apparatus as above in which the device serving to press the grinding tool against the edges of the glass sheet is constituted by a double-acting cylinder, a modification of the pressure in the cylinder of the cylinder making it possible to adjust the grinding pressure.

It is also thus that document US-A-3 803 772 describes a grinding machine provided with an adjustable pressure device to maintain a constant force of engagement between the grinding wheel and the workpiece, this device comprising a motor constant torque electric.

Pneumatic or hydraulic cylinders used as pressure means require additional lines for the supply of pressurized fluid. In addition, in order to adjust the grinding pressure, additional devices are required. In addition, it has been found that in such machines regulating the grinding pressure using a regulating circuit gives unsatisfactory results because it is not possible to avoid regulating oscillations.

The object of the invention is to improve the grinding apparatuses with adjustable grinding pressure according to document DE-C-1 996 260 in such a way that their structure is simplified, their working method safer, the regulatory oscillations eliminated, finer and more precise grinding pressure regulation.

This object is achieved in accordance with the invention by the fact that the pressure device is formed by a constant torque electric motor which is articulated on the tool holder by means of a crank arm, the pressure exerted by the constant torque motor being transmitted to the tool holder by means of a pressure capsule, the electrical output signal of which is supplied, as a setpoint regulating the grinding pressure, to a regulating amplifier which controls the torque motor constant.

The embodiment according to the invention offers decisive advantages: firstly, it makes it possible to eliminate the additional pressurized fluid lines as well as the expensive mechanical devices for modifying and regulating the pressure of the pressurized fluid. Secondly, and this is particularly important, the grinding pressure can be adjusted and changed much more precisely, and at relatively reduced cost. In the embodiment according to the invention, the oscillations produced by the regulation circuit are several times lower than those produced when a jack is used. The reason for this is that the journal friction is insignificant in the case of the constant torque motor compared to the friction of the piston in the cylinder of the jack in the known apparatus. However, it is precisely this high friction in the cylinder of the cylinder which is the origin of the fact that the piston only detaches from the wall of the cylinder by means of a relatively high tearing force, this high tearing force being responsible for the inevitable oscillations in regulation.

In many cases, it may be desirable to increase or reduce the grinding pressure at specific locations on the glass sheet. Thus, in the case for example, of glass sheets having angular portions, it is advantageous to reduce the grinding pressure in these portions. To this end, in one embodiment of the invention, provision is made to modify the setpoint voltage controlling the grinding pressure, according to a preset program, for example by switching on or on the contrary by deactivating a series of potentiometers.

Fine regulation of the grinding pressure also requires mounting the tool holder with minimal friction. Particularly effective and advantageous construction solutions reside in accordance with the invention in that the tool holder is mounted either sliding on or air cushion, or rotating in bearings using pivoting arms.

• -la figure 1 est une vue schématique d'un appareil de meulage conforme à l'invention muni d'un circuit de régulation pour la pression de meulage;
• -la figure 2 est le schéma électrique d'une régulation préprogrammée de la pression de meulage pour le meulage de pourtour d'une feuille de verre;
• -la figure 3 illustre la structure d'un appareil de meulage dans lequel le porte-outil pour l'outil de meulage est monté sur un coussin d'air;
• -la figure 4 illustre une autre forme d'exécution d'un appareil de meulage dans -lequel le porte-outil pour l'outil de meulage est monté sur des bras coulissants;

Other features and advantages of the invention will emerge clearly from the following description made with reference to the appended drawings in which:

• FIG. 1 is a schematic view of a grinding apparatus according to the invention provided with a regulation circuit for the grinding pressure;
• FIG. 2 is the electrical diagram of a preprogrammed regulation of the grinding pressure for the grinding of the periphery of a glass sheet;
• FIG. 3 illustrates the structure of a grinding apparatus in which the tool holder for the grinding tool is mounted on an air cushion;
• FIG. 4 illustrates another embodiment of a grinding apparatus in which the tool holder for the grinding tool is mounted on sliding arms;

As clearly shown in the diagrammatic view of FIG. 1, the grinding tool comprising the grinding motor 1 and the grinding wheel 2 mounted on the motor shaft, is carried by a tool holder 4 movable on rails 5 or on an equivalent system allowing a linear displacement. The tool holder 4 is connected via connecting rods 6, 6 'to a crank arm 7 which is fixed on the shaft of a constant torque motor 8. This constant torque motor 8 is mounted on a carriage 10 on which the rails 5 are fixed. The constant torque motor 8 presses the grinding wheel 2 with a predetermined force against the edge of a glass sheet 12. The carriage 10 is for its part movable on rails or sliding bars 14, thanks to a motor 38 fixed on a frame 36 and transmitting its movement by means of a toothed belt 39. The grinding tool is positioned using the carriage 10, that is to say it is brought into the desired position, while the tool holder 4 movable on the rails 5 serves to exert the desired pressure with the grinding tool on the edge of the glass sheet 12.

Between the connecting rods 6, 6 'is mounted a pressure capsule 15 which provides an electrical signal corresponding to the effective grinding pressure. This signal, also called actual voltage, is brought to a control amplifier 17 by line 16, while the setpoint voltage corresponding to the set point of the grinding pressure is brought to the control amplifier 17 by the via potentiometer 18. The constant torque motor 8 is activated via line 19 by the regulation amplifier 17 which compares the setpoint voltage and the actual voltage. Since no electromotive force appears on the constant torque motor 8, an equivalent resistance 20 is inserted between the regulation amplifier 17 and the constant torque motor 8.

In Figure 1 are only shown rails 14 arranged in a single direction of movement. This system can be used as is in the case where the glass sheet is rotated and the carriage 10 carrying the grinding tool moves in one direction to remain in contact with the edge of the glass sheet.

In the case where the glass sheet is fixed and where the grinding means move around the glass sheet, the carriage 10 is, as is known, mobile in two orthogonal directions X and Y. FIG. 1 represents only one only direction defined by the rails 14, but the addition of an additional displacement system in a direction perpendicular to the first does not modify the invention. Provision is also made for mounting the assembly ensuring the regulation of the grinding pressure, namely the grinding wheel 2 and its motor 1, the rails 5, the tool holder 4, the motor 8, the connecting rods 6 and 6 ′, the arm crank 7 and the manometric capsule on a rotating disc not shown and adapted to be oriented so as to hold the rails 5 in a direction perpendicular to the edge of the glass sheet. Thus the grinding head can rotate 360 °.

FIG. 2 illustrates a system for regulating the grinding pressure controlled by a program, this system fitted to a grinding machine having a movement carriage composed in two orthogonal directions X and Y, which carries the grinding tool and which is guided all around the glass sheet, that is to say on the 360 ° of the periphery of the glass sheet, by a guide program. Thanks to the grinding pressure regulation circuit, the grinding pressure of the tool is modified during its path along the edge of the glass sheet, in the sense that it is, for example reduced, when the the tool bypasses the portions of glass sheets having angles. Instead of a pre-established and fixed reference voltage, or uses different reference voltages which vary according to the position of the grinding tool.

The grinding motor 1 is, as described above, mounted on the tool holder 4 which is pressed, by means of the connecting rod 6, the pressure capsule 15 and the connecting rod 6 ', thanks to the constant torque motor 8 , against the edge of the glass sheet. The constant torque motor 8 is activated by the regulation amplifier 17 and between this amplifier and the motor 8 the resistor 20 is interposed.

The most important component of the device for the "programming of the route around the whole periphery" is a digital reverse run counter 24. This digital counter 24 has ten preset switches 25. A relay is associated with each switch. preselection 25. The relays are designated by Z ₁ to Z10 '

The preselection switches 25 of the digital counter 24 make it possible to modify, increase or decrease the grinding pressure at particular points in the path of the grinding tool. These points are advantageously determined empirically.

The counter 24 advances through the two pulse generators 26 and 27, the generator 26 being coupled to the carriage drive mechanism in a direction, for example the axis X and the generator 27 being coupled to the drive mechanism in the other direction, for example the Y axis. At each pulse of one of the two digital signal generators 26, 27 the counter 24 advances by one notch and the number of pulses appears on the table d display 28 As soon as a value set on a preselection switch 25 coincides with the number of pulses appearing on display 28, the associated relay 2 ₁ to Z ₁₀ trips and closes the corresponding contact thus establishing a circuit passing through one of the potentiometers P ₁ to Pe.

The potentiometer P ₁ of the grinding pressure setpoint is associated with the contacts of the relays Z _i , Z ₃ , Z ₅ , Z ₇ , and Z ₃ . The potentiometer P ₁ determines the basic grinding pressure, which must for example be exerted on portions straight edges. Each of the other relays Z ₂ , Z4, Z ₆ , Z ₈ and Z ₁₀ is associated with a potentiometer P ₂ , P ₃ , P ₄ , and P ₆ corresponding to a different set value.

These different set point values are applied at determined locations in the path of the grinding tool where a grinding pressure different from the usual pressure is desired. The potentiometer P _{o is} used, at the end of the grinding process, to eliminate the grinding pressure, that is to say to return the carriage 10 to its rest position.

The device operates as follows. At the start of the grinding machine, the pulse generators 26, 27 are rotated and clock the advancement of the digital counter 24. The preset switches 25 allow the relays Z ₁ to Z ₁₀ to operate at determined points of the path. Before the first relay Z is actuated, a basic grinding pressure determined by the potentiometer P ₁ is exerted. If, at a chosen point in the route, the relay Z ₁ switches, a switchover to the circuit containing the potentiometer P ₂ occurs. When another point in the path of the grinding tool set on the next preset switch is reached, the relay Z ₂ is actuated in turn, which has the effect of switching off the potentiometer P ₂ and by switching back to potentiometer P _i . When the following relay Z ₃ is actuated, a switch to potentiometer P ₃ occurs. The grinding pressure is then the pressure determined by the setpoint voltage resulting from the value of the potentiometer P ₃ . When relay Z ₄ is actuated, a switching return to potentiometer P ₁ occurs again. The switching operation is thus repeated at each point preselected by the preset switches 25.

In order to be able to regulate the grinding pressure in this way, the contact d ₂ is naturally closed when the machine is started and the latter remains closed until the entire periphery to be ground has been covered. At the end of the grinding operation, the contact d ₂ is open and the contact d ₃ is closed. Closing the contact d3 has the effect of activating the servo-amplifier 17 by the set value set by the potentiometer Po, with the consequence that the carriage 10 (FIG. 1) carrying the tool holder 4 is returned to its position of departure. The contact d ₁ which erases the digital counter 24, is closed in turn.

In the drawings, there is shown a preset counter comprising ten preset switches. It goes without saying that it is possible to increase the number of preset switches without modifying the device for the rest.

It is also possible to save the instructions necessary for grinding glass sheets of different shapes on an appropriate medium, so at what points the changes in grinding pressure will have to take place, the switching of the relays to activate the potentiometers P ₁ to P ₆ . These instructions can thus be carried on the magnetic strip which already carries the path information necessary for controlling the drive motors of the carriage 10 carrying the grinding tool, in each of the two orthogonal directions X and Y.

In this way, all the data necessary for grinding a given glass sheet model can be stored on the same information medium, for example a magnetic strip.

In the case where the carriage moves only in one direction to remain in contact with the edge of the molten glass sheet in rotation, a single pulse generator 26 or 27 is necessary.

It is important that the tool holder 4, on which the grinding tool is mounted and which is pressed by the constant torque motor 8 against the edge of the glass sheet, rotates with as little friction as possible. A first embodiment allowing the tool holder 4 to rotate with little friction is illustrated in FIG. 3. The tool holder 4 has the form of a plate with polished surfaces, on which is fixed a bearing 30 which carries the grinding unit formed by the motor 1 and the grinding wheel 2. The constant torque motor 8 acts on the plate 4 by means of the pressure capsule 15 and the crank arm 7. The plate 4 is guided between a plate lower support 31 and an upper support plate 32 which for their part are supported on their two sides by closure plates 33. The set of plates 31, 32, 33 constitutes the carriage 10 which can be moved the along the bars 14 by means of lateral ball bearing bushings 34. The bars 14 are mounted using the yokes 35 on the frame 36 of the machine. This frame 36 also carries the positioning motor 38 which, by means of the toothed belt 39, moves the carriage 10 according to a program recorded in the direction of the arrow double F, so that the grinding wheel 2 is always guided in the position which, upon rotation of the glass sheet 12, is pre-established and determined by the shape of this glass sheet.

On the carriage 10 is also mounted the constant torque motor 8 which acts via the crank arm 7 on the plate 4 and which determines the pressure force with which the grinding wheel is pressed against the edge of the glass sheet.

To guarantee the least possible friction of the plate 4 between the plates 31, 32 it is made so that the corresponding bearing faces do not touch. An introduction of compressed air into the gap separating the plate 4 and the plates 31 and 32, ensures the formation of an air cushion above and below the plate 4. Thus the plate 4 is floating between these two air cushions. To this end, a few lights 42 are provided in the plates 31 and 32 and compressed air lines 43 are connected to it. The compressed air acting below the platform 4 is adjusted so that the total weight of the platform 4, including that of the crew it door, either supported by the air cushion. The compressed air acting above the plate 4 is adjusted to a corresponding lower pressure, for example a pressure equal to one third of that of the compressed air acting on the underside of the plate. The air cushion between the plate 4 and the upper plate 32 is necessary to compensate for the forces which result from the pressure exerted by the grinding wheel placed below the plate 4 on the edge of the glass sheet. The plate 4 is mounted so as to also have little friction on its sides and on its ends.

Rolling balls 45 mounted additionally in the plates 31, 32 are arranged opposite each face of the plate 4 at a height such that the plate 4 does not come into contact with them when the air cushions are present. The rolling balls 45 therefore only fulfill an emergency function and in all cases avoid the friction of the plate 4 against the plates 31 and 32.

FIG. 4 illustrates another embodiment making it possible to obtain low friction of the tool holder. In this case the tool holder comprises a plate 54 mounted oscillating on two pivoting arms 55. The pivoting arms 55 are articulated at one end on pivoting yokes 56 provided on a console 57. The console 57 is for its part fixed to the carriage , here referenced 58, which can be moved by sliding on the sliding bars 14 already present in the previous embodiment.

The constant torque motor 8, fixed on a support 60 belonging to the carriage 58 acts on the carriage 54 via the crank arm 7 and the pressure capsule 15.

The pivoting arms 55 are articulated on the plate 54 by means of pivoting yokes 62. The pivoting yokes 56 and 62 include low friction ball bearings. This oscillating arrangement certainly does not allow a strictly linear movement of the plate 54, but this is of no importance for the present case in which there is simply a regulation of the grinding pressure during which the distances traveled are very small. The motor 38, the frame element 36 and the toothed belt 39, are those already described in FIG. 1.

Claims (10)

1. Apparatus for grinding the edges of glass sheets (12) by means of a grinding tool (1, 2) mounted on a tool carrier (4) which may be displaced perpendicularly to the edge of the glass sheet and on which a pressing device (6-8) acts whereby the grinding tool is pressed with adjustable force against the edge of the glass sheet, characterised in that the pressing device comprises a constant-torque electric motor (8) which is articulated on the tool carrier (4) by the arm of a crank (7), the pressure exercised by the constant torque motor (8) being transmitted to the tool carrier (4) by a manometric cell (15) the output electric signal from which is fed, as the actual grinding pressure value, to a control amplifier (17) which governs the constant torque motor (8).

2. Apparatus according to claim 1, characterised in that an adjustable reference voltage determining the value of the grinding pressure is applied to the control amplifier (17).

3. Apparatus according to claim 2, characterised in that the reference voltage supplied to the control amplifier (17) may be altered according to a predetermined programme.

4. Apparatus according to claim 3, characterised in that it comprises a series of potentiometers for adjusting the reference voltage which are switched on and off by signals stored in an information holder at preselected locations along the periphery of the glass sheet.

5. Apparatus according to claim 3, characterised in that it comprises a series of potentiometers for adjusting the reference voltage (P₁ ... P₆) which are actuated by relays (Z, ... Z_io) associated with a series of preselector switches (25) in the preprogrammed order of the preselector switches (25), the switches (25) being actuated by one or more impulse generators (26, 27) reproducing the path of the grinding tool in the direction or directions of displacement.

6. Apparatus according to any one of claims 1 to 5, characterised in that the tool carrier (4) actuated by the constant torque motor (8) carrying the grinding tool (1, 2) is mounted in such a way as to produce very little friction.

7. Apparatus according to claim 6, characterised in that the tool carrier (4) which is shaped as a plate is mounted on an air cushion.

8. Apparatus according to claim 6, characterised in that the tool carrier (54) is mounted on pivoting arms (55).

9. Apparatus according to one of claims 1 to 8, characterised in that it is incorporated in a grinding machine provided with a carriage displaceable in two orthogonal directions X and Y according to instructions form a programme, said carriage having a tool carrier which comprises a rotatable grinding head which turns through 360° during its path around the glass sheet.

10. Apparatus according to one of claims 1 to 8, characterised in that it is incorporated in a grinding machine having a carriage carrying a grinding tool, said carriage being guided in a linear path in contact with the glass sheet according to a programme, its position on this linear path depending on the angular position of the glass sheet driven in rotation.

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