Drive and control device and related process for a grinding machine

Abstract: It is provided a drive and control device for a grinding machine of the type comprising a rotatable abrasive wheel (2), translating members (3) of the wheel (2) with respect to a rotating piece (4) to be ground, and restoring means (5) to reset the wheel (2) comprising a diamond-resetting member (6) and a balancing member (7), the device comprising sensor members (10) adapted to detect the piece roundness and electronic means (19) adapted to generate actuating signals (23) of the restoring means (5), in the presence of a roundness of the piece (4) different from a predetermined roundness. The process consists in grinding the piece and simultaneously measuring the piece diameter until achievement of a predetermined diameter, detecting the piece roundness, and operating said restoring means in interlocked relationship with the detected roundness.

Description: The invention relates to a drive and control device and related process for a grinding machine, defined in the preambles of the accompanying Claims 1 and 3, respectively. It is known that when a grinding machine is used to machine a piece having at least one circular section by means of an abrasive wheel, a margin of uncertainty may exist about the quality of the carried out working, depending on the condition of the abrasive wheel. In fact, when machining of a piece having circular sections is concerned, the maintenance operations of the abrasive wheel are of the greatest importance, in view of achieving the desired qualitative level. These operations particularly consist of balancing interventions carried out on the wheel using appropriate balancing members disposed along the wheel axis, and of interventions for dressing the grinding paste of the wheel by means of appropriate diamond-resetting members adapted to carry out said dressing. Said operations are ideally to be repeated very often to keep high qualitative levels in machinings, but actually they should be avoided if they are not strictly necessary, in that they are time-consuming and in addition involve wear both of the wheel and the diamond-resetting tools, which results in high costs. Practically, in establishing the frequency of the above operations an intermediate choice is done between these opposite requirements, based on the quality to be achieved each time. It should be also noted that the good quality of this choice is ascertained by controls carried out on the already machined pieces, and these controls establish which pieces are to be discarded, which can be used and which need to be possibly machined again. It is apparent that discarding of machined pieces or reinsertion of same in a working cycle involve important economical burdens. Therefore in the management of a grinding machine there is a drawback in that it is necessary to carefully select each time the frequency of the maintenance operations to be executed on the abrasive wheel. Every wrong choice involving a too reduced frequency leads to a decreased working quality of the machine and a too great number of pieces to be discarded. On the contrary, every wrong choice involving a too high frequency brings about high costs and reduced production rates. EP-A-0 566 853 discloses a grinding machine of the type comprising at least one rotatable abrasive wheel, translating members for displacing said abrasive wheel relative to a rotating piece to be ground, restoring means for said abrasive wheel comprising a diamond-resetting member for said wheel, sensor members for detecting the roundness of said piece being machined, and electronic means for processing the detections carried out by said sensor members and generating dressing-actuating signals for operating said diamond-resetting member in the presence of a roundness of said piece different from a predetermined roundness after a predetermined time. In this known apparatus dressing of the grinding wheel is carried out when the desired roundness of the piece being machined is not achieved within a first set time or when a preset number of pieces has been ground. A second time is set which is longer than the first time and when the desired roundness is not achieved within said second time, the occurrence of an abnormal condition is informed on a display to an operator, so indicating that the machine is unable to obtain the desired roundness. This system avoids unnecessary dressing operations but cannot avoid discarding of pieces that have not reached the allowable roundness. EP-A-0 569 774 is illustrative of the general type of apparatus and process as defined in the preambles of claims 1 and 3, although the particular construction of the dressing member is not detailed. Under this situation the technical task underlying the present invention is to devise a drive and control device and related process for a grinding machine capable of substantially obviating the drawbacks of the prior art, and in particular capable of optimizing the frequency of the balancing and diamond-resetting operations on the abrasive wheel, depending on the required quality level, and in addition capable of making the quality controls carried out on the pieces at the end of the machining operations substantially useless. The technical task specified is substantially achieved by a drive and control device for a grinding machine as claimed in the Claims 1 and 3. Preferred embodiments of the invention are specified in Claims 2 and 4. The description of a preferred embodiment of the invention is now given by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the device applied to a grinding machine; Figure 2 shows a portion of the device; and Figure 3 shows the process embodied by the device. With reference to the drawings, the device in accordance with the invention is applied to a grinding machine identified by reference numeral 1. In a manner known per se, the machine 1 comprises at least one rotatable abrasive wheel 2 rotation of which is obtained by an appropriate motor, an electric motor for example. The abrasive wheel 2 is mounted on translating members 3 diagrammatically shown in Fig. 1 and embodied by a wheel slide capable of drivingly imparting all necessary displacing movements to the grinding wheel 2 with respect to a piece 4 provided with at least one substantially circular profile to be ground. Piece 4 too is rotated during the machining operation in that it is supported in known manner by a work spindle and set in rotation by a respective motor. The machine 1 further comprises restoring means 5 for the wheel 2 capable of maintaining the wheel itself to optimal conditions. In particular, the restoring means 5 comprises a diamond-resetting member 6 provided with a diamond-resetting tool 6a that can be located in contact with the grinding paste of the wheel 2, so as to dress it and give it the proper shape and abrasive capability again, and a balancing member 7 located close to the wheel axis and capable of, by a suitable arrangement of excentric masses present therein, compensating for any wheel unbalance and the vibrations resulting from said unbalances when the wheel is rotating at high speed. The device in accordance with the invention is generally denoted by 8 and comprises a measuring head 9 disposed close to the piece 4 being machined. The head 9, shown in detail in Fig. 2, is provided with sensor members 10, adapted to detect the roundness of the piece 4 being machined, and feeler members 11 adapted to detect the diameter of the same piece 4. Advantageously, the sensor members 10 and feeler members 11 are combined with each other, i.e. they partly use the same structural elements. In detail, the feeler members 11 detecting the piece 4 diameter, consist of contact elements 12 adapted to slidably engage the piece 4 being machined at diametrically opposite positions, swinging arms 13 each supporting one of the contact elements 12 at one end thereof and rotatably fitted on fixed pins 14 at the other end, and two magnetic-inductive transducers 15 known per se, or transducers of another type, each of which is connected to a respective swinging arm 13 and is adapted to detect the movements of said swinging arm 13. Shown in Fig. 2 are transducers 15 of the magnetic-inductive type, provided with a body 15a fitted to the measurement head 9 and a movable rod 15b capable of following the small oscillations of the swinging arms 13. Each of the transducers 15 transmits diameter-indicative movement signals of the swinging arms 13, via a cable 16. The sensor members 10 detecting the roundness of piece 4, use part of the feeler members 11 and more particularly a contact element 12, a swinging arm 13 and one of the transducers 15, as well as cable 16. In addition, the sensor members 10 comprise a phase sensor 17 adapted to detect the angular position of the piece 4 being machined relative to a reference position and transmit a synchronization signal by a cable 18. The phase sensor 17 can be disposed on the machine spindle to detect the angular position of the spindle itself and consequently that of piece 4. Practically, while the feeler members 11 detect how the distance between two contact elements 12 (and therefore the diameter of piece 4) changes, the sensor members 10 verify the piece roundness, in that they detect how the position of each individual contact element 12 varies depending on the rotation angle of the piece 4, that is with reference to a predetermined zero position. The device 8 further comprises electronic means 19 connected to the sensor members 10 and feeler members 11 by cables 18 and 16, respectively, and capable of generating signals to be utilized to advantage to operate the restoring means 5 intended for resetting the grinding wheel 2. In more detail, the electronic means 19 comprises at least first electronic means 19a processing detections from the sensor members 10 and feeler members 11 and capable of generating at least two types of signals: dimensional signals 20 stating the piece 4 diameter and signals 21 stating an insufficient roundness of the profile being machined, as compared with a predetermined profile. In the embodiment shown in Fig. 1, signals 20 and 21 are transmitted to second electronic means 19b adapted to generate, after processing of the signals themselves, at least stop signals 22 addressed to the translating members 3 of the grinding wheel 2 and actuating signals 23 addressed to the restoring members 5. Said actuating signals 23 consist of dressing-actuating signals 23a addressed to the diamond-resetting member 6 and balancing-actuating signals 23b addressed to the balancing member 7. The stop signals 22 directed to the translating members 3 are in particular capable of causing the distance between the wheel 2 and piece 4 being machined to remain unchanged while the wheel 2 goes on rotating. The dressing-actuating signals 23a operate the diamond-resetting member 6 which carries out dressing of the grinding paste of the wheel 2, by moving the diamond-resetting tool 6a close to said wheel 2 while the latter is rotating. The elements converting signal 23a into movements of the diamond-resetting tool 6a are embodied by electrical actuators known per se. The balancing-actuating signals 23b bring into operation the balancing member 7 which compensates for unbalances of the abrasive wheel 2. Arrangement of a balancing member on the rotation axis of an abrasive wheel is usual and it is known that the balancing members generally are bodies internally provided with excentric masses to be positioned in a manner adapted to balance possible unbalances in the abrasive wheel. Displacement of said excentric masses within the balancing members is achieved by rotators for example, and it is exactly provided that the balancing-actuating signals 23b should actuate said rotators, possibly upon interposition of electrical members known per se, so as to change the position of said excentric masses. It is pointed out that the electronic means 19 according to the invention can be structured in different manners and they can be either disposed separately or arranged in a single unit. In accordance with the drive and control process put into practice by the above described device, the following operating steps are carried out, as shown in Fig. 3. First of all a piece 4 being machined is submitted to a grinding step 24 and simultaneously both measurements 25 of the diameter of the piece 4 being machined and comparisons 26 between the gradually achieved diameters and the predetermined final diameter are carried out. Signals signalling a not-yet-achieved final diameter cause the grinding step 24 of piece 4 to go on, while the abrasive wheel 2 gradually continues moving close to piece 4, upon the action of the translating members 3. On achievement of the predetermined diameter, the translating members 3 are stopped and in step 27 the piece roundness is detected at the just-achieved diameter, the piece 4 being still in engagement with the machine 1. The detected roundness is compared at 28 with the desired roundness and if a sufficient roundness has been achieved, stopping of the machine 1, at step 29, is driven. If, on the contrary, signals stating an insufficient roundness occur, first of all a rounding step 30 is carried out in which the grinding wheel 2 is caused to rotate in a grazing relationship with the rotating piece 4, the translating members 3 being still in a stop condition. Simultaneously, measurements of the piece 4 roundness and the duration of the rounding step 30 take place until the predetermined roundness is achieved. In the presence of a prolonged duration of the rounding step exceeding a predetermined time, the rounding step 30 is stopped and the restoring means 5 for the abrasive wheel 2 are operated in step 31 wherein the diamond-resetting member 6 and the balancing member 7 are operated selectively and in succession in the presence of a persisting detection of a roundness different from the predetermined roundness. Usually the diamond-resetting member 6 is operated and only if the latter has not given the desired results, the balancing member 7 is operated as well. The invention achieves important advantages. In particular, an automatic and optimal selection of the frequency of the maintenance and setting operations of the abrasive wheel is possible depending on the required qualitative level. In this manner the work times and maintenance costs of the wheel are optimized and the machine shop rejections are drastically reduced with reference to the required qualitative level. In addition, due to the fact that all geometrical features of the pieces being machined are measured directly on the machine tool and working is interlocked to these measurements, a subsequent quality control is avoided and supply of pieces of a constant quality is ensured.

Claims: A drive and control device for a grinding machine of the type comprising a rotatable abrasive wheel (2), translating members (3) for displacing said wheel (2) relative to a rotating piece (4) to be ground, and restoring means (5) for said wheel (2) comprising a diamond-resetting member (6) adapted to dress said abrasive wheel (2) and a balancing member (7) of said wheel (2), characterized in that it comprises sensor members (10) adapted to detect the roundness of said piece (4) being machined, and electronic means (19) adapted to process the detections carried out by said sensor members (10) and, after a predetermined time in the presence of a roundness of said piece (4) different from a predetermined roundness, generate dressing-actuating signals (23a) for operating said diamond-resetting member (6) and further generate balancing-actuating signals (23b) addressed to said balancing member (7), said dressing-actuating signals (23a) and said balancing-actuating signals (23b) being generated selectively and in succession in the presence of a persisting detection of a roundness different from said predetermined roundness. A device according to claim 1, characterized in that said sensor members (10) are associated with feeler members (11) adapted to detect the diameter of said piece (4) being machined, said feeler members (11) comprising at least two contact elements (12) slidably engaging said piece (4) at diametrically opposite positions, at least two swinging arms (13) each supporting one of said contact elements (12), and at least two transducers (15) each connected to a respective one of said swinging arms (13) and to said electronic means (19) for detecting diameter-indicative movements of said swinging arms (13), and in that said sensor members (10) comprise at least one of said transducers (15) and at least one phase sensor (17) for detecting the angular position of said piece (4) being machined relative to a reference position and for emitting a synchronization signal, said phase sensor (17) being electrically connected with said electronic means (19). A drive and control process for a grinding machine of the type having at least one rotatable abrasive wheel (2), translating members (3) for displacing said wheel (2) relative to a rotating piece (4) to be ground, and restoring means (5) for said wheel (2) comprising at least one diamond-resetting member (6) adapted to dress said grinding wheel (2) and a balancing member (7) of said abrasive wheel (2), the process being characterized in that it consists in: grinding said piece (4) and simultaneously measuring the diameter of said rotating piece (4) until achievement of a predetermined diameter, detecting the roundness of said rotating piece (4) at said predetermined diameter while said piece (4) is in engagement with said machine, and operating said diamond-resetting member (6) in the presence of a roundness of said piece (4) different from a predetermined roundness after a predetermined time, wherein said diamond-resetting member (6) is operated selectively and in succession with the balancing member (7) in the presence of a persisting detection of a roundness different from said predetermined roundness. A process according to claim 3, characterized in that detection of roundness is carried out during a rounding step in which said abrasive wheel (2) is caused to rotate in grazed relationship with said rotating piece (4) and said translating members (3) are in a stop condition.

Inventors: GUIDOTTI ANDREA, TRIONFETTI GIANNI, GUIDOTTI, ANDREA, TRIONFETTI, GIANNI
Applicants: BALANCE SYSTEMS S P A, BALANCE SYSTEMS S.P.A.
Application year: 1996
Main classification: B24B49
IPC codes: B24B49, B24B41