Method of identifying an abrasive tool for removing a coating off a coated sheet of glass, and grinding machine implementing such a method

Abstract: On a machine (1) for removing a coating (3) off a coated sheet (2) of glass, an abrasive tool (6a) for removing the coating (3) is selected from a number of abrasive tools by means of a detecting and control unit (10, 14) for identifying the coating (3) and emitting a corresponding tool selection and pickup signal.

Description: The present invention relates to a method of identifying an abrasive tool for removing a coating off a coated sheet of glass. As is known, a coated sheet of glass is obtained by depositing on an extensive surface of an ordinary sheet of glass a coating material which, depending on what the coated sheet of glass is used for, is selected from a number of coating materials having different characteristics, such as electric conductivity, degree of reflection or refraction, etc. When cutting and/or gluing coated sheets of glass, the coating material along the cutting or gluing lines must be removed. This is done using grinding wheels, which must be selected according to the type of coating material for removal. At present, grinding wheels are selected by the operator who, given the type of coating material on the sheet of glass being worked, consults appropriate tables, for example, to select the wheel best suited to the characteristics of the coating material for removal. The above grinding wheel selection method is unsatisfactory by depending exclusively on the skill, experience, and degree of concentration of the operator. That is, any error on the part of the operator, due simply to overwork or misinformation, results in the wrong type of wheel being selected and inevitably in rejection of the sheet of glass, which in most cases is already partly processed, thus resulting in rejection costs which at times can be considerable. It is an object of the present invention to provide a method of identifying an abrasive tool for removing the coating off a coated sheet of glass, designed to provide a straightforward, low-cost solution to the aforementioned drawbacks. According to the present invention, there is provided a method of identifying an abrasive tool for removing a coating off a coated sheet of glass; the method comprising the steps of identifying the type of material defining the coating on the sheet of glass; and selecting the abrasive tool from a number of abrasive tools as a function of said coating; and being characterized in that identification of the type of coating material and selection of the abrasive tool comprise the steps of memorizing a number of reference quantities, each related to a respective abrasive tool; supplying a test signal to said coating; picking up a corresponding response signal from said coating in response to said test signal; and using said response signal as an input signal by which to select one of the memorized said reference quantities. The present invention also relates to a grinding machine for removing a coating off a coated sheet of glass. According to the present invention, there is provided a grinding machine for removing a coating off a coated sheet of glass; the machine comprising at least one tool spindle; an abrasive tool connected to the tool spindle and selectable from a number of abrasive tools in a tool store; and transfer means for moving said abrasive tools between the tool store and the tool spindle; and being characterized by also comprising identification means for emitting an identification signal identifying said coating; and selection means for selecting an abrasive tool from different said abrasive tools in response to said identification signal. A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a plan view, substantially in block form, of a preferred embodiment of a grinding machine for removing a coating off a coated sheet of glass in accordance with the invention; Figure 2 shows a circuit diagram of a detail of the Figure 1 machine." Number 1 in Figure 1 indicates a grinding machine for machining a coated sheet of glass of the type comprising a sheet of glass 2, and a coating 3 (Figure 2) deposited on an extensive surface 2a of sheet 2 and selectable from a number of coating materials of different characteristics. Machine 1 comprises a frame 4 defining a supporting surface for the sheet of glass 2 and fitted with a slide 5. Slide 5 is moved over sheet 2 by a respective known actuating unit (not shown), and supports a grinding head 6, a grinding wheel 6a of which removes coating 3 along predefined paths indicated A and B. Wheel 6a forms part of a number of different grinding wheels housed in a wheel store 7 and moved between head 6 and store 7 by a known wheel-change device 8 not described in detail. The wheel 6a for use is selected automatically by a detecting device 10 for detecting the type of coating 3 and emitting a corresponding wheel selection and pickup signal. More specifically, detecting device 10 is moved to and from and over the supporting surface by a respective known actuating unit A1, and, in the example described, comprises a first and a second brush-type input electrode 10a, 10b spaced apart and which rest on coating 3; and an output terminal 10c. With reference to Figure 2, detecting device 10 also comprises an amplifying circuit 11, a resistive element 12, and a constant-voltage source 13. More specifically, amplifying circuit 11 has a first and a second input terminal connected respectively to a first and a second terminal of resistive element 12; and an output terminal connected to the output terminal 10c of detecting device 10. The first terminal of resistive element 12 is also connected to a first terminal of constant-voltage source 13, which has a second terminal connected to first input electrode 10a; and the second terminal of resistive element 12 is connected to second input electrode 10b of detecting device 10. Detecting device 10 cooperates with a numeric control unit 14 to which automatic wheel-change device 8, wheel store 7, and the respective actuating units of slide 5 and detecting device 10 are connected. Control unit 14 comprises a memory 15 in which are stored a number of reference quantities, each corresponding to a respective wheel 6a housed in wheel store 7. Operation of machine 1 will now be described as of the condition in which no sheets of glass 2 rest on the supporting surface, and detecting device 10 and automatic wheel-change device 8 are set to their respective withdrawn rest positions. When the sheet of glass 2 is placed on frame 4, known presence sensors (not shown) on machine 1 transmit a sheet-present signal to control unit 14, which, keeping grinding head 6 stationary, performs an identification cycle to identify coating 3 and select wheel 6a. During this cycle, input electrodes 10a, 10b of detecting device 10 - which are located a fixed distance apart and subjected to a given fixed potential difference by constant-voltage source 13 - are brought to rest on coating 3. On contacting coating 3, a current I R , depending on the physical resistance of coating 3, is generated in resistive element 12, so that amplifying circuit 11 generates a response signal related to the amplitude or intensity of current I R . Control unit 14 compares the amplitude of current I R with a number of reference quantities, and generates and transmits a wheel selection signal to automatic wheel-change device 8, which, in response to the selection signal, withdraws a corresponding wheel 6a from wheel store 7 and fits it on to grinding head 6. The same operations are repeated for each sheet or for the first sheet in each lot. Machine 1 described has the following advantages. Firstly, compared with known machines, machine 1 is far more efficient by removing any coating in the best possible operating and output conditions at all times. Machine 1, in fact, involves no decision-making or consent on the part of the operator, and provides for checking each sheet or part of the sheet on the supporting surface according to the set sheet-feed program, and for determining, also according to a predetermined program, the type of coating and the best type of wheel to use. In other words, device 10 enables store 7, device 8 and unit 14 to dialog directly and so eliminate any possibility of the wrong type of wheel being selected. This therefore translates into a net reduction in rejects following the grinding stage or, worse still, after the notching and parting stage which normally follows grinding, and into longer working life of the notching tools which, as is known, undergo severe wear in contact with the coating material. Moreover, device 10 provides for exploiting the full potential of robot-operated wheel-change devices, which in most cases are unwarranted by depending on the operator decision-making element still involved. Clearly, changes may be made to machine 1 as described herein without, however, departing from the scope of the present invention. In particular, detecting device 10 may be of a different type from the one indicated by way of example, and may conveniently be optical to determine, for example, the refraction index or any other optical characteristic of coating 3.

Claims: A method of identifying an abrasive tool (6a) for removing a coating (3) off a coated sheet (2) of glass; the method comprising the steps of identifying the type of material defining the coating (3) on the sheet (2) of glass; and selecting the abrasive tool (6a) from a number of abrasive tools as a function of said coating (3); and being characterized in that identification of the type of coating material and selection of the abrasive tool (6a) comprise the steps of memorizing a number of reference quantities, each related to a respective abrasive tool (6a); supplying a test signal to said coating (3); picking up a corresponding response signal from said coating (3) in response to said test signal; and using said response signal as an input signal by which to select one of the memorized said reference quantities. A method as claimed in Claim 1, characterized in that the steps of supplying said test signal and picking up said response signal comprise the operation of moving electrode means (10a)(10b) of an electric device (10) towards said coating (3), bringing said electrode means (10a)(10b) into contact with said coating (3), and sending the test signal to said coating (3) by means of said electrode means (10a) (10b). A method as claimed in Claim 2, characterized in that sending said test signal comprises the step of bringing two electrodes (10a)(10b) into contact with said coating (3) and at a given distance from each other, and generating a given potential difference between the electrodes (10a)(10b). A grinding machine (1) for removing a coating (3) off a coated sheet (2) of glass; the machine (1) comprising at least one tool spindle (6); an abrasive tool (6a) connected to the tool spindle (6) and selectable from a number of abrasive tools in a tool store (7); and transfer means (8, 14) for moving said abrasive tools between the tool store (7) and the tool spindle (6); and being characterized by also comprising identification means (10, 14) for emitting an identification signal identifying said coating (3); and selection means (14) for selecting an abrasive tool from different said abrasive tools in response to said identification signal. A machine as claimed in Claim 4, characterized in that said identification means (10, 14) for identifying said coating (3) comprise source means (13) supplying a test signal to said coating (3); and emitting means (11) for emitting a corresponding response signal from said coating (3) in response to said test signal; said selection means (14) comprising memory means (15) for memorizing a number of reference quantities, each related to a respective abrasive tool (6a); and detecting means (14) for detecting one of the memorized said reference quantities on the basis of said response signal. A machine as claimed in Claim 5, characterized in that said source means (13) and said emitting means (11) are electric. A machine as claimed in Claim 6, characterized in that said source means comprise electrode means (10a)(10b) which are brought into contact with said coating (3). A machine as claimed in Claim 7, characterized in that said electrode means comprise two electrodes (10a)(10b) positioned a given distance apart; and supply means (13) for bringing and maintaining the electrodes (10a)(10b) to and at a predetermined potential difference. A machine as claimed in Claim 7 or 8, characterized by comprising actuating means for moving said electrode means (10a)(10b); and control means for controlling said actuating means and operating in response to a sheet-present signal.

Inventors: BISOTTO SEBASTIANO, GHINAMO PAOLO, BISOTTO, SEBASTIANO, GHINAMO, PAOLO
Applicants: BOTTERO SPA, BOTTERO S.P.A.
Application year: 2001
Main classification: B24B9
IPC codes: B24B49, B24B9