Process for the automatic machining of edges of glass plates and apparatus for carrying out said process

Abstract: The process for the automatic machining of edges of glass plates includes the steps of: fixing the glass plate onto a work table (3); storing a set of space coordinates along two orthogonal axes X and Y of the edge of the plate (2) to be machined, the coordinates being either detected by means of successive sequences of self-learning movements of a probe along the edge of the plate or being set on a keyboard; processing the coordinates in order to determine the path to be followed by the contour of a grinder (9) in order to produce a contour which is constituted by mutually tangent arcs and straight lines; calculating the successive movements along the axes X and Y which the center of the grinder must perform in order to machine the edge of the plate according to the diameter and/or wear of the grinder being used; controlling, according to the calculated values, the movements of a grinder-supporting machining head along the edge of the plate; actuating the head so as to remove in succession, from a tool magazine (28), the self-learning probe and/or increasingly finer diamondized polishing grinders in order to produce, by successive passes, the polished edge on the edge of the plate.

Description: The present invention relates to a process for the automatic machining of edges of glass plates and to an apparatus for carrying out said process. The edges of glass plates are usually subjected to a process known as "polished-edge machining", which consists in performing in succession various passes with increasingly finer grinders along the edge of the plate while keeping the abrasion region wet with water; said grinders operate with their axis orthogonal to the plane of the plate to be machined. The polished edge machining is currently performed with semiautomatic processes, using apparatuses constituted by a central support with a sucker-fitted table, on which the plate to be machined is fixed, and by a grinder supporting arm which can be turned all around the plate and along which a grinder supporting head can be moved radially; the operator grips the head with his hands and, while keeping it pressed against the plate, moves it tangentially all around said plate, in order to machine its edge; these apparatuses are sometimes equipped with electronic devices and, by using a template, allow to semiautomatically machine parts having a simple contour. This method is generally time consuming and requires expert operators who can optimally measure the pressing effort against the edge of the plate so as to avoid damaging it and also avoid removing excess material; besides, if it is necessary to produce a series of identical parts, said parts will usually be slightly different from one another according to the skill of the operator. Known from GB-A-1,566,443 is a working centre which is programmable for performing automated operations and which has two working heads, each activated by a plurality of stepping motors, having three degrees of freedom, and being controlled by an electronic unit and by a minicomputer. A program unit stores the working centre program and position data defining the path of the working head and process data defining the operations to be performed by the working head at predetermined points along the path of the working head. EP-A3-0,092,021 relates to a drillhole centerline determining device comprising an interposer having a central pocket enabling a robot to probe the interposer to learn the location and orientation of the desired drillhole. EP-A1-0,377,755 relates to a visually controlled robot system having a robot control device for controlling an operation of a robot body, and a vision sensor system for detecting visual information. A common operator panel is also provided which has means for selecting either a first mode for carrying out an operation related to the robot control device, or a second mode for carrying out an operation related to the vision sensor system. Also known from EP-A3-0,155,218 is a process as defined in the precharacterising of claim 1. Also known from EP-A3-0,155,218 is an apparatus as defined in the precharacterizing part of claim 3. The technical aim of the present invention is to obviate the above described disadvantages, i.e. to provide an automatic apparatus which performs polished-edge machining on glass plates having any contour, without requiring expert operators and ensuring that, in case of batch machinings, all the finished plates are identical. According to one aspect of the invention, this aim is achieved by a process for the automatic machining of an edge of a glass plate as defined in claim 1. According to another aspect of the invention, the above-mentioned aim is achieved by an apparatus for the automatic machining of an edge of a glass plate as defined in claim 3. Further peculiarities will become apparent and evident from the detailed description of a preferred but not exclusive embodiment of a process and of an apparatus according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: figure 1 is a schematic elevation view of the apparatus according to the invention; figure 2 is a schematic plan view of the apparatus of figure 1; figure 3 is a sectional enlarged-scale view of a detail of the apparatus of figure 1; figure 4 is a schematic plan view of the table of figure 1 with a glass plate, during various steps of self-learning; figure 5 is a view of the mounting of the self-learning probe; figure 6 is a schematic view of the sequence of the self-learning movements. With particular reference to the above figures, the reference numeral 1 generally indicates the apparatus for carrying out the polished edge machining according to the invention. The apparatus 1 is intended to follow the contour of a glass plate 2 which has the shape of a figure-of-eight in the example illustrated in figure 4. A contour comprising straight portions and curved portions with a blended contour, in that the tangents of the curved portions are blended to the straight portions, can be executed on the plate 2. The apparatus 1 comprises a frame which extends longitudinally in a direction X-X and has a horizontal table 3 and a sort of longitudinal portal which extends upward like a bridge along the table and above it. Said portal has vertical uprights 4, 5 and a horizontal cross-member 6. A horizontal surface 7 is fixed onto the table 3 and is intended to receive the glass 2 so that it rests thereon and is arranged horizontally on appropriate supports 8 which can be arranged so as to allow the machining of the contour of the plate: said supports are of the type constituted by suckers associated with a suction unit, and retracting pneumatic abutments are also provided, constituted by cylinder type elements with a vertical axis, which are slidingly connected to the table and are actuated in an extraction direction to center the plate to be machined and are then actuated into a retracted position during the plate machining steps. The apparatus 1 furthermore comprises a tool supporting head 9 which is supported by the frame in a manner described hereinafter. A carriage 10 is mounted along the cross-member 6 of the frame so that it can slide along appropriate guides 11 connected to the cross-member 6. Said carriage 10 can be moved in the direction X-X under the action of per se conventional actuation means 12, constituted for example by a direct-current motor which actuates a ball bearing nut rigidly associated with the carriage. A truck 13 is mounted below the carriage 12 and can slide with respect to the carriage along appropriate guides 14 which extend in a direction Y-Y which is orthogonal to the direction X-X. Said truck 13 can move in the direction Y-Y under the action of per se conventional actuation means, for example a direct-current motor. A slider 20 is mounted on the truck 13 and can slide along vertical guides 21 in the direction Z-Z. Said slider 20 can move in the direction Z-Z under the action of actuation means which comprise a direct-current electric motor 22 which is mounted on a platform 23 associated with the truck 13, the shaft whereof rotates, by means of a toothed-belt transmission, a vertical screw 24 the thread whereof engages a ball bearing nut 25 which is rigidly associated with the slider. The tool supporting head 9 is fixed to the slider 20 and comprises a grinder support mandrel 26 which can accommodate diamondized polishing grinders or a probe head for self-learning, as described hereinafter. The mandrel 26 is actuated so as to rotate as required by an electric motor 27 which is mounted on the slider 20. The grinders are chosen so that they are suitable for performing, in succession, the roughing, finishing and polishing operations. The apparatus is furthermore provided with means for sprinkling water at the grinding area, such means being of a generally known type. A magazine 28 for the automatic changing of the tools and the loading of the probe is provided on a short side of the apparatus; in the particular case, there is a magazine for five tools plus a self-learning probe 29, but the number of tools might be different. The tools are locked in the seat of the mandrel by means of known devices, advantageously by means of spiral springs which act on a double-action linear pneumatic actuation device in which the pressurized air is used to release the tool. The self-learning probe 29 is advantageously of the type suitable for detecting the three dimensions X, Y and Z and for transmitting the coordinates with infrared-ray pulses; said probe allows to detect the position of the part and thus to define the placement of the tool at the optimum grinding level, and also allows the sensing, placement and machining of any geometrical contour. The infrared-ray transmission of the pulses avoids the presence of transmission cables which would hinder movements. The detection of the level Z occurs by lowering the probe onto the plate; by means of this lowering, the level of the upper surface of the plate is detected, and the thickness of the plate is determined by subtracting the level at which the suckers act. The apparatus according to the invention furthermore comprises a per se conventional numeric control device 30 which can be supplied with the coordinates of the contour of the plate 2: this can be performed either by means of manual programming from the keyboard, for simple contours, or by self-learning, for more complex contours, by means of successive detections of the coordinates of the edge of the plate on the part of the probe. The numeric control device is connected by means of cables to the means for actuating the carriage 10 and to the means for actuating the truck 13 in order to move the head 9 in the directions X-X and Y-Y with continuous contour processing control. Advantageously, the numeric control device is also connected to the means which actuate the slider 20 in order to move the head 9 vertically toward and away from the glass to be contoured, as well as to the other motor means for an appropriate control of all the movements of the apparatus and for tool changing in automatic sequence according to the requirements. Each of the sequences of self-learning movements is shown in figure 6, and consists of a first large and fast movement I away from the plate L, of a second large and fast movement II in a direction which is orthogonal to the first movement, of a third large and fast movement III for approximate approach to the part until abutment therewith occurs, of a fourth small and rapid backoff movement IV, of a fifth slow movement V for precise approach to the part, and of a sixth small and slow movement VI, at the end of which the pulses related to the sensed coordinates X and Y are transmitted to the computer. If the plate is encountered during the second movement, or if the plate is not detected during the third movement, these events indicate a change in the direction of the plate with respect to the preceding sequences; in this case the directions and orientations of the movement of the head are rotated through 90 degrees. For the machining of a glass plate having straight contour portions blended with curved portions, provisions are made so that the straight contour portions extend preferably along the axes X or Y, and in this manner the machining of these portions is performed by moving the grinder only along the direction of the axis X or only along the direction of the axis Y, whereas for the execution of the curved portions or also of the straight inclined portions the grinder is actuated with simultaneous X and Y movements such as to reproduce the required shape. The contour of the plate is followed in succession with increasingly finer grinders, indeed in order to perform first roughing, then finishing and finally polishing. Advantageously, the grinder is arranged halfway along the thickness of the glass plate, and the glass plate is equally touched by the probe halfway along its thickness in order to sense its contour. The polishing grinders are subject to rapid wear, i.e. to rapid variations of their diameter and therefore of their machining contour: the apparatus automatically compensates this wear by moving the grinder axis toward the part being machined according to the power absorbed by the electric motor 27; when a decrease in absorbed power is detected, indicating that the grinder presses less against the plate since it has a smaller diameter, the path of the grinder axis is moved closer to the plate contour: the rpm rate of the motor is simultaneously changed in order to keep the set cutting speed constant. The main advantage of the apparatus according to the invention resides in the fact that it allows to machine contours on glass plates in a fully automatic manner, with a single positioning of the plate to be machined. Another advantage resides in the fact that the machined contours have unexceptionable and constant quality. It is also possible to achieve a high production rate and a practically complete elimination of breakages or rejects. Finally, the apparatus according to the invention allows to machine complex contours with variable curvatures along said contour also by virtue of the self-learning device, with a reduction in the downtimes for apparatus setup. It has thus been observed that the invention achieves the proposed aim. The invention thus conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept as defined by the claims. In practice, the materials employed, as well as the shapes and dimensions, may be any according to the requirements without thereby abandoning the scope of the protection of the following claims. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: Process for the automatic machining of an edge of a glass plate, comprising the steps of: fixing the glass plate (2) onto a work table (3); storing a set of space coordinates along two orthogonal axes X and Y of the edge of the plate (2) to be machined; providing a numeric control device (30) and processing said coordinates by means of said numeric control device (30) in order to determine the path to be followed by the contour of a grinder in order to produce a contour which is constituted by arcs and straight lines tangent thereto; calculating the successive movements along the axes X and Y which the center of the grinder must perform in order to machine the edge of the plate (2) according to at least one parameter selected from among; a) the diameter of the grinder being used, and; b) the wear of the grinder being used; controlling, by means of said calculated values, the movements of a grinder-supporting machining head (9) along the edge of the plate (2); characterized in that it comprises the steps of; detecting said coordinates by making successive sequences of self-learning movements of an infrared-ray coordinates transmitting probe (29) along the edge of the plate (2); actuating said head (9) so as to remove in succession, from a tool magazine (24); c) said self-learning probe (29), and; d) increasingly finer diamondized polishing grinders, whereby to produce, by means of successive passes, a polished edge on the edge of the plate (2), wherein the sequence of self-learning movements comprises a large and fast movement in a first direction (I) extending away from the plate (2), a large and fast movement in a second direction (II) which is orthogonal to the first direction (I) of movement, a large and fast movement in a third direction (III) of approximate approach to the plate (2) until abutment therewith occurs, a small and rapid back-off movement in a fourth direction (IV) extending away from the plate (2), a slow movement in a fifth direction (V) of precise approach to the plate (2), and a small and slow movement in a sixth direction (VI) opposite to said fifth direction (V) of movement, and wherein abutment with the plate (2) during movement in said second direction (II) or lack of abutment during the movement events indicating a change in the direction of the plate (2) with respect to the preceding sequences, the directions and orientations of motion being in this case rotated through 90 degrees. Process according to claim 1, further comprising the steps of; transmitting coordinates detected by said probe during movement in said first, second, third, fourth, fifth and sixth directions (I, II, III, IV, V, VI) via infrared-ray pulses, and; receiving and processing said infrared-ray pulses transmitted by said probe (29) at said numeric control device (30). Apparatus for the automatic machining of an edge of a glass plate, comprising a substantially horizontal work table (3) provided with fixing and centering means (8) for at least one glass plate (2) and on which a beam (6) is fixed, a carriage (10) being actuated along said beam (6) so as to be movable along two axes X, Y which correspond to the directions of the length and width of said table (3), a slider (20) bearing a machining tool supporting head (9), said machining head comprising a grinder supporting mandrel (26) driven by a motor (27) and having a vertical axis, said apparatus further comprising a numeric control device (30) for storing coordinates of the contour of the edge of the plate (2) to be machined, characterized in that said numerical control device is arranged for controlling movements of the tool supporting head (9) in order to detect the contour with a probe (29), said carriage (10) bears vertical guides (21) along which said slider (20) is mounted and is actuated so as to be movable along a vertical axis Z, a tool magazine (24) being provided for a plurality of grinders and for a probe (29), said numeric control device actuates the head (9) so as to remove in succession, from said tool magazine (24), said self-learning probe (29) and increasingly finer diamondized polishing grinders, means for transmitting detected coordinates by means of infrared-ray pulses being connected to said probe (29) and means for receiving said infrared-ray pulses transmitted by said probe (29) being connected to said numeric control device (30). Edge machining apparatus according to claim 3, further comprising means for automatically compensating for wear of said plurality of grinders for roughing, finishing and polishing operations including means for detecting power absorbed by said motor (27) driving said grinder supporting mandrel (26), and means for increasing speed of said motor (27) upon wear of said plurality of grinders, whereby to maintain constant cutting speed.

Inventors: PACI LUCIANO, SELCI GIANCARLO, TAMBURINI MARCO, PACI, LUCIANO, SELCI, GIANCARLO, TAMBURINI, MARCO
Applicants: INTERMAC SRL, INTERMAC S.R.L.
Application year: 1991
Main classification: B24B9
IPC codes: B24B9, B25J9, G05B19