Method for positioning glass sheets for forming

A method for positioning glass sheets for forming includes positioners (55) that are moved slower than the speed of glass sheet conveyance to provide rotational adjustment of a glass sheet for accurate alignment above a forming mold (52). The forming mold (52) is moved upwardly for the forming in a pressing manner against a downwardly facing upper mold (58). Both preformed and flat glass sheets can be positioned by different embodiments of the apparatus.

TECHNICAL FIELD

This invention relates to a method for positioning glass sheets for forming and also involves forming of glass sheets after the positioning.

BACKGROUND

Glass sheets after heating have previously been formed by conveyance on a lower roll bed to above a forming mold that is moved upwardly to provide the forming, see U.S. Pat. No. 6,543,255. The roll bed can include wheels or, as disclosed in United States Patent Application Publication No. US2011/0247367 entitled PRESS BENDING STATION AND METHOD FOR BENDING HEATED GLASS SHEETS by Dean M. Nitschke et al., can include elongated rollers or wheels and elongated rollers that are selectively attachable and detachable for rotational driving and positioning to provide the required shape for the mold to move vertically from below to above the conveyor for lifting of the heated glass sheet for the forming. The above referenced patent and application are hereby incorporated by reference.

SUMMARY

One object of the present invention is to provide an improved method for positioning a heated glass sheet with respect to a forming mold for forming.

In carrying out the above object, the method for positioning a heated glass sheet with respect to a forming mold for forming is performed by conveying a heated glass sheet horizontally on a roll conveyor at a conveyor speed in a direction of conveyance along a path toward a vertically aligned position above a forming mold. A pair of positioners are moved along the direction of conveyance at laterally spaced locations in the path of the conveyed glass sheet and at a slower speed than the conveyor speed so the conveyed glass sheet contacts the positioners for a sufficient time in order to rotate the glass sheet on the roll conveyor to correct any rotation from a design rotational position with respect to the forming mold. The positioners are then moved along the direction of conveyance at a faster speed than the conveyor speed and the conveyed glass sheet so as to move out of contact therewith in order to permit the glass sheet to move into vertical alignment with the forming mold for forming.

As disclosed, the conveyor speed and the speed of the slower moving positioners are decelerated at the same rate as each other prior to the positioners moving faster than the speed of the conveyor. Also, after the deceleration of the speed of the conveyor and the speed of the positioners at the same rate as each other and before the positioners begin moving faster than the speed of the conveyor, the speed of the conveyor continues to decelerate and the speed of the positioners accelerates until the speed of the conveyor and the speed of the positioners are the same as each other whereupon the positioners move out of contact with the glass sheet as the speed of the conveyor continues to decelerate and the speed of positioners continues to accelerate. Also, the positioners move out of contact with the glass sheet at a location upstream a predetermined distance along the direction of conveyance from the location at which the glass sheet moves into vertical alignment with the forming mold

The forming mold as disclosed is a peripheral forming mold having an open center and includes a downstream portion adjacent which the movement of the positioners takes place within the open center of the peripheral forming mold. After moving out of contact with the glass sheet, the positioners are moved downwardly and the glass sheet moves above the positioners toward a location at which the periphery of the glass sheet moves above and into alignment with the peripheral forming mold. The peripheral forming mold as disclosed is then moved upwardly at a time and speed to lift the moving glass sheet from the roll conveyor for forming of the glass sheet. More specifically, the peripheral forming mold is moved upwardly at a time and speed to lift the glass sheet from the roll conveyor after the glass sheet has been conveyed a predetermined distance along the direction of conveyance subsequent to the positioners moving out of contact with the glass sheet. An upper mold is disclosed as being moved downwardly and the glass sheet is press formed between the forming mold and the upper mold.

In one disclosed practice of the method, the heated glass sheet is preformed prior to being conveyed into alignment with the forming mold, and in another disclosed practice of the method the heated glass sheet is conveyed with a flat shape into alignment with the forming mold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1of the drawings, a system for forming glass sheets is generally indicated by10and includes a forming station12whose construction and method of operation will be described in an integrated manner with the entire system.

With continuing reference toFIG. 1, the system10includes a furnace14having a roll forming station16just upstream along a direction of conveyance C from the press bending station12. Downstream from the press forming station12along the direction of conveyance C, the system10is illustrated as including a final processing station18at which the formed glass sheet can be slowly cooled for annealing or more rapidly cooled by quenching to provide heat strengthening or tempering.

As illustrated by continuing reference toFIG. 1, the furnace14has entry and exit ends20and22and includes a heating chamber24(FIG. 2) having a conveyor26for conveying glass sheets along the direction of conveyance through the furnace from the entry end to the exit end for heating. The conveyor26on which the glass sheets are heated can be either a conventional gas hearth or a roll conveyor on which the glass sheets are conveyed during heating from ambient temperature to a sufficiently high temperature to permit forming, which is also referred to as bending in the glass sheet industry.

The furnace exit end22includes the roll forming station16which is illustrated inFIG. 2as having horizontally extending conveyor rolls28that are rotatively driven and spaced horizontally within the heating chamber along the direction of conveyance extending laterally with respect thereto to support and convey the heated glass sheets. The roll forming station16also includes a pair of sets30of bending rolls32, with the bending roll sets30spaced laterally with respect to each other within the heating chamber24along the direction of conveyance. Each set of bending rolls30is supported and rotatively driven by a drive mechanism33with the bending rolls at progressively increasing inclinations along the direction of conveyance as illustrated by reference numerals32a,32b,32cand32dinFIG. 2. The conveyance of each heated glass sheet G along the direction of conveyance in cooperation with the bending rolls32provides initial forming of the glass sheet G along a direction transverse to the direction of conveyance as illustrated inFIG. 2. This forming provides the formed shape of the glass sheet with straight line elements that may be parallel to each other in a cylindrical shape or angled with respect to each other in a conical shape. As each location of the glass sheet along the direction of conveyance is bent from its flat shape, this bending also further bends the preceding location such that the net effect is a slightly conical shape.

With combined reference toFIGS. 1 and 3, the press forming station12as previously mentioned is located externally of the furnace14downstream from its exit end22to receive the initially formed glass sheets from the roll forming station16. More specifically, the press forming station12includes a conveyor having a lower wheel or roll bed34of the conveyor for receiving an initially formed glass sheet to be further press formed by press forming apparatus collectively indicated by36. The lower wheel bed34includes a lower base structure38and a plurality of conveyor wheel assemblies40. Each wheel assembly40as is hereinafter more fully described includes a housing42having an upper end including a wheel44and having a lower end including a detachable connection46for detachably connecting the wheel assembly to the base structure38. A drive mechanism provides rotational driving of the wheel44of each wheel assembly40upon connection thereof to the lower base structure38. For a more detailed description of the conveyor and the drive mechanism, refer to U.S. Pat. No. 6,543,255 which has previously been incorporated by reference. Also, it should be noted that the conveyor instead of having only wheel conveyor assemblies can also have elongated roller conveyor assemblies both horizontal and inclined as disclosed by U.S. patent application Ser. No. 12/756,521 filed on Apr. 8, 2010 by Nitschke et al. under the title Press Bending Station And Method For Bending Heated Glass Sheets, the entire disclosure of which has herein been incorporated by reference.

As illustrated inFIG. 3, a lower press ring support50of the press forming apparatus36supports a lower forming mold or press ring52that has an upwardly concave shape and is received within the wheel bed34below the wheels44of the wheel conveyor assemblies40in a ring shape thereof where no wheel assemblies are located. The construction of the lower press ring is hereinafter more fully described. Positioning apparatus54of the system includes positioners55(FIGS. 6-10) that rotate a conveyed glass sheet G to provide alignment with the forming mold52for forming.

As also illustrated inFIG. 3, an upper mount56of the press station12supports an upper press mold58of the press forming apparatus36. This upper press mold58has a downwardly facing convex forming face60complementary to the upwardly concave shape of the lower press ring52.

A mold actuator collectively indicated by62inFIG. 3provides relative vertical movement between the lower press ring52and the wheel bed34and between the lower press ring and the upper press mold58to move the heated glass sheet above the wheel bed and ultimately into pressing engagement between the lower press ring and the upper press mold58to press form the glass sheet as is hereinafter more fully described. As disclosed, the actuator not only moves the lower press ring52upwardly but also moves the upper press mold58downwardly for cooperating with the lower press ring to press form the glass sheet. The actuator62includes a lower mold actuator621, and an upper mold actuator62u, that respectively move the lower forming mold52and the upper mold58upwardly and downwardly. However, it should be appreciated that it is possible to only move the lower forming mold52upwardly and downwardly without any movement of the upper mold.

The press forming station12as illustrated byFIG. 3and described above has the wheel bed34provided with an upwardly curved shape in a direction transverse to the direction of conveyance C along which the wheel bed receives the heated glass sheet corresponding to the initially formed shape provided by the roll forming station16illustrated inFIGS. 1 and 2. More specifically, the lower base structure38of the wheel bed34includes a plurality of rails64that extend along the direction of conveyance and have different elevations at which they support the wheel assemblies40. This rail height positioning is provided by unshown adjusters to provide the curved shape of the wheel bed along a direction transverse to the direction of conveyance.

As also shown inFIG. 3, the upper press mold58has its forming face60provided with an array of holes61at which a vacuum is provided from a vacuum source66shown inFIG. 1so as to support the formed glass sheet after the press forming and ensure forming of the glass sheet to the shape of the forming face. Upon subsequent operation of the actuator62, the lower press ring52is moved downwardly and the upper press mold58is moved upwardly and a shuttle68of the final processing station18is moved by an actuator70to move a delivery ring72toward the left below the upper mold58. Termination of the vacuum provided by the vacuum source66may then be accompanied by the supply of pressurized gas to the upper mold surface60to release the glass sheet onto the delivery ring72and the shuttle actuator70then moves the shuttle68back toward the right to the position illustrated inFIG. 1such that the delivery ring72and the formed glass sheet thereon are delivered for final processing such as slow cooling for annealing or more rapid cooling by air quenching for heat strengthening or tempering between the lower and upper quench heads74and76.

With reference toFIGS. 4 and 5, another embodiment of the glass sheet forming system10′ is similar to the embodiment ofFIG. 3but operates to provide positioning and forming of flat glass sheets without any preforming as with the previously described embodiment. Thus, like components thereof have the same reference numerals that are primed for the forming station12′, furnace14′, and press forming apparatus36′ as well as the base structure38′.

As illustrated inFIGS. 1 and 4, each embodiment of the system10,10′ includes a controller78connected to the mold actuator62, the shuttle actuator70, a conveyor drive80, and the positioning apparatus54to coordinate the system operation for the positioning and forming cycle. The systems10and10′ each have an unshown sensor like conventional glass sheet forming systems adjacent the junction between the exit end of the roll forming station16and the upstream end of the forming station12or12′ for sensing the location of a downstream extremity at the lateral center of the conveyed glass sheet.

As shown inFIGS. 6 and 7, the upwardly facing lower forming mold52can have curvature both laterally with respect to the direction of conveyance C and along the direction of conveyance C and is mounted on the mold support50by adjusters of any suitable type as schematically illustrated by84so as to provide adjustment to the designed upwardly concave shape to be formed. The pair of laterally spaced positioners55are mounted by a positioner drive86of the positioning apparatus54for movement along the direction of conveyance between the upstream position shown inFIG. 6and the downstream position shown inFIG. 7. The controller78(FIGS. 1 and 4) operates the conveyor drive80and the positioner drive86in a coordinated manner and provides rotational positioning of a conveyed glass sheet G so as to be properly aligned upon conveyance above the mold52for the forming. As the glass sheet is conveyed along the direction of conveyance above the forming mold52, the laterally spaced positioners55are moved along the direction of conveyance from the upstream position ofFIG. 6toward the downstream position ofFIG. 7but at a slower rate than the conveyor such that the positioners contact the glass sheet.

As illustrated inFIG. 10, the glass sheet G as shown by solid line illustration is initially located counterclockwise from the design rotational position and the contact with the slower moving positioners55rotates the glass sheet to the design rotational position illustrated by dash lines so as to be vertically aligned with the forming mold52upon farther conveyance in preparation for the press forming. If the glass sheet is initially located clockwise from the design rotational position, the slower moving positioners55rotate the glass sheet counterclockwise to the design rotation position. Furthermore, the positioners will not rotate the glass sheet if it initially is in the design rotational position and thus does not require any rotation. After any rotation in either direction, the controller moves the positioners55faster than the conveyor speed and the conveyed glass sheet so that the positioners move out of contact with the leading edge of the glass sheet in preparation for the glass sheet moving over and into vertical alignment with the forming mold52.

It should be mentioned that the amount of rotation to provide the rotational alignment of the glass sheet G with the forming mold52does not have to be particularly great. More specifically, it has been found that the ability to adjust for a leading amount of about 5 mm or a trailing amount of about 5 mm, for a total range of 10 mm, is sufficient to provide rotational adjustment to the design position to correct for any rotational variance.

As illustrated inFIG. 8, the positioning apparatus54includes cylinders88whose piston connecting rods90are movable vertically and support the positioners55for movement between theFIG. 8upper position where the positioners contact the glass sheet and a lower position shown inFIG. 9for allowing the glass sheet to move over the positioners and into vertical alignment above the forming mold52. More specifically, the forming mold52as shown inFIGS. 6 and 7has an open center92and a peripheral shape that corresponds to the periphery of the glass sheet. A downstream portion94of the forming mold52extends laterally with respect to the direction of conveyance, and the positioners55move toward this downstream portion from the position ofFIG. 6to the position ofFIG. 7during the slower movement of the positioners than the conveyor to provide the glass sheet rotation into rotational alignment with the mold periphery. Prior to the positioners55reaching the downstream mold portion94, the cylinders88move the positioners downwardly so the glass sheet can move over the positioners and over the forming mold52and into vertical alignment with its peripheral shape.

The systems10,10′ each have an unshown electric eye sensor of the electromagnetic wave type like conventional glass sheet forming systems at the lateral center of the conveyed glass sheet adjacent the junction between the exit end of the roll forming system16or furnace14′ and the upstream end of the forming station12or12′. This type of sensor senses the downstream extremity at the lateral center of the conveyed glass as it approaches or moves into the forming station for forming. Such sensors conventionally initiate operation of the associated forming apparatus. Normally there is about one meter, i.e. 1000 mm, of travel from the sensing to the design position at the mold apparatus where the forming takes place. During that amount of travel, the glass sheet lateral midpoint where the sensing normally takes place can vary plus or minus about 3 mm and the lateral extremities due to rotation during the entire conveyance can vary plus or minus about 5 mm from the lateral midpoint, for a total variance in the range of about plus or minus 8 mm.

With the present systems, the electric eye sensor adjacent the junction between the exit end of the roll forming system16or furnace14′ and the upstream end of the forming station12or12′ is connected to the controller78to initiate operation of the positioning apparatus54in coordination with the conveyor and after the positioners complete the positioning and move out of contact with the glass sheet, there is normally less than 100 mm of travel to the design position where the glass sheet is aligned with the forming mold52such that there is then normally only a total variance of the glass position from the design position in the range of about 1.2 mm. More specifically, after the positioners55move out of contact with the glass sheet, the controller78operates the conveyor and the mold actuator62in a coordinated manner that provides more accurate positioning of the glass sheet with respect to the forming mold52as is hereinafter more fully described.

With reference to the timing chart shown inFIG. 11, the X coordinate or abscissa represents the time during a cycle of positioning and forming and the Y coordinate or ordinate represents speed of movement. More specifically, the line C represents the conveyor speed along the horizontal direction of conveyance, the line P represents the speed of the positioners along the horizontal direction of conveyance, and the line M represents the speed of vertical movement of the forming mold52under the operation of the controller78. The conveyor speed C initially moves at a constant index speed during which the electric eye sensor at the time of line S through the operation of the controller78initiates the operation of the positioning apparatus54. Subsequently the conveyor speed C begins to decelerate at a constant rate and the positioners are accelerated until reaching a maximum speed that is slightly less than the conveyor speed and the positioners then begin to decelerate at the same rate as the conveyor. The slower moving positioners contact the glass sheet and provide any required rotational adjustment and also provide any required longitudinal adjustment with respect to the conveyor before reaching the time at phantom line96. If no rotational adjustment is required, both positioners will contact the glass sheet sooner than is the case when the positioners provide the rotational positioning of the glass as previously described. After the phantom line96time, the conveyor speed continues to decelerate and the positioner speed increases until both the conveyor and the positioners have the same speed at the time of intersection98. The positioners55then move out of contact with the conveyed glass sheet as the positioner speed continues to increase and the conveyor speed continues to decrease. After the disengagement of the positioners55from the glass sheet, the positioners move downwardly as previously described and their speed is decelerated until stopping at the locations shown inFIGS. 7 and 9. The conveyor speed and hence the speed of conveyance of the glass sheet then continues to decelerate and the lower mold embodied by the press ring is moved upwardly as shown by the mold line M, with the upward movement initially being relatively rapid to lift the glass sheet from the conveyor whereupon the upward movement is decreased to a relatively slow movement during the pressing with the upper mold and ultimately terminated after completion of the pressing of the glass sheet.

The glass sheet moves out of contact with the positioners at the intersection98which is a predetermined distance along the direction of conveyance from the location at lift line L where the lower mold is moved upwardly a sufficient distance to lift the glass sheet from the conveyor and terminate its conveyance. This spacing together with a predetermined speed of the conveyor and the speed of the lifter facilitates correct timing of the actuator62for lifting the glass sheet as it is being conveyed into vertical alignment with the mold in order to provide proper positioning for the lifting that terminates the glass sheet conveyance.

Before time line96shown inFIG. 11, both the conveyor and the positioners55are decelerating at the same rate as each other but the speed of the positioners is slower than the speed of the conveyor, about 100 mm. per second as illustrated. The relevant part of the positioner action starts as the glass sheet approaches the positioners and the positioners have reached their maximum speed, about 100 mm/second slower than the conveyor, and have just started to decelerate with the conveyor at the same rate. Preferably for a glass sheet that has not been rotated and for which the electric eye sensor identified the glass sheet's leading edge correctly and assigned the conveyor's current position to the glass sheet, or registered the glass sheet to the conveyor and for a glass sheet which has not slipped on the conveyor after registration, the glass sheet will have a clearance separation of 10 mm from the positioners at the start of positioning as the positioners just start to decelerate. The positioners will have a 10 mm head start and the ideal glass sheet just discussed will catch up to and contact the slower moving positioners after the positioners have traveled 10 mm less than the conveyor. Typically the relevant part of positioning takes place over a conveyor travel distance of about 200 mm. During that conveyor travel, the positioners travel in the same direction but travel 20 mm less than the conveyor travel distance. Thus, if the positioners were in contact with the glass sheet from the start of their slower movement, they would retard the glass sheet movement 20 mm, but would only retard the ideal glass sheet 10 mm as discussed above.

After the rotational and longitudinal adjustment, the glass sheet will be at the time line96ofFIG. 11when the speed of the positioners accelerates as the speed of the conveyor continues to decelerate. For an additional 1.5 mm of retarding movement of the glass sheet after time line96, the positioners are still going slower than the conveyor, so the glass sheet is still pressed against the positioners. More specifically, at the time point96, the glass sheet is slipping on the conveyor rolls by 100 mm per second and is moving at the speed of the positioners. Between time line96and time point98, the speed of the glass sheet increases to the speed of the conveyor. The coefficient of friction between glass sheet and the conveyor is then initially the dynamic coefficient of friction rather than the static coefficient of friction because of the slippage taking place. So the positioners must be accelerated slowly between time line96and time point98so they do not pull away from the glass sheet until the glass sheet has stopped slipping on the conveyor and its speed of conveyance is the same as the conveyor speed. At time point98, the speed of the positioners and the speed of the conveyor, and hence also the speed of the glass sheet, are the same, so there is no slippage and the conveyor then controls the speed of the glass sheet conveyance. This is important because the positioners have delivered the glass sheet at time point98very accurately under the operation of the controller78in coordination with the conveyor so the glass sheet conveyance to the design position with respect to the forming mold52can be accurately controlled. Also, after point98, the speed of the positioners continues to accelerate for a time but at a greater rate of acceleration than before the positioners move out of contact with the glass sheet.

The conveyor, not the positioner, thus has control of the glass sheet movement for about the last 80 mm before pick-up by the forming mold. This removes the inaccuracy of the positioning provided only by the sensor as previously described and inaccuracy due to slip between the glass sheet and the rolls over the meter or so of travel from the sensor to time point98. Time point98is related very accurately to the mold design position by the controller78and coordinated conveyor operation for electrically controlled delivery of the glass sheet to the design position for the pick-up and forming.

After the positioning and press forming as described above, the forming mold52is moved downwardly and the upper mold58is moved upwardly with the glass sheet thereon by the provision of the vacuum previously discussed so that the delivery ring72can be moved into the forming station to receive the formed glass sheet for final processing, either quenching or annealing as previously discussed.

The total positioning and forming cycle time is less than 2 seconds and specifically is about 1⅔ seconds.