Method and apparatus for spinning a metal sheet

Abstract: To spin a metal sheet around a chuck for forming a product, in a teaching phase involving force control, a product is formed on the chuck by rotating the chuck about the axis of rotation and by moving a forming roller one or several times alongside the chuck with a pre-determined pressure force thereby spinning the intermediate metal sheet. In the teaching phase, measuring data corresponding to the movement of the forming roller during spinning is fixed in a memory of a control unit, and in the production phase the forming roller is controlled with the aid of these measuring data. The control unit determines the position values of the forming roller in axial direction and in transverse direction relative to the chuck from the data fixed in the teaching phase, and the control unit controls the forming roller in the production phase at least during a part of the spinning movement by means of the position values determined in this manner for spinning the metal sheet into the desired product.

Description: The invention relates to a method of spinning a metal sheet around a chuck for forming a product, wherein in a teaching phase by force control, a product is formed on the chuck by rotating the chuck about the axis of rotation and by moving a forming roller one or several times alongside the chuck with a pre-determined pressure force thereby spinning the intermediate metal sheet, and in the teaching phase measuring data corresponding to the movement of the forming roller during spinning is fixed in a memory of a control unit, and in the production phase the forming roller is controlled with the aid of these measuring data. Such a method is known from European patent application 0 125 720 of the same applicant. In this patent application a spinning machine is disclosed in which the forming roller is coupled to a driving member through a spring means having a known spring characteristic in order to displace the forming roller. In this prior art method, the teaching phase involving force control is used to fix position values corresponding to forces exerted by the forming roller, whereafter these position values are used to control the forming roller in the production phase. As a result, the metal sheet will be spun accurately against the chuck with a desired force. Although this prior art method offers good results in practice for most of the products, in which particularly the internal dimensions of the product are reproducible in an accurate manner, there are products which should meet high requirements also in respect of external dimension of the product. Such small tolerances for the external dimensions are not ensured in the prior art method involving force control, since, for example, the forming roller will be deflected in case of variations in the thickness of the metal sheet. US 4,976,126 describes a spinning machine comprising an arrangement which will not only prevent the formation of a gap between the mold (chuck) and the material, but will also make is possible for the forming roller to respond instantly to any change in the hardness and thickness of the material. It is the object of the invention to provide a method of the type mentioned in the preamble in which this disadvantage is removed in an effective way. For this purposed, the method according to the invention is characterized in accordance with claim 1. As a result, there is obtained a method of spinning a metal sheet in which the measuring data obtained during the teaching phase in which force control is used, deliver position data of the forming roller so that in the production phase the control unit is permitted to affect the spinning operation by position control at least in those parts where the external dimensions of the product should meet tight tolerances. The invention further provides an apparatus for spinning a metal sheet using the method according to one of the preceding claims, comprising a forming roller, an upper slide guided on an upper bed and supporting the forming roller, a first driving member for displacing the upper slide, in which the forming roller is coupled to the first driving member by means of a first spring means, a control unit having a memory and at least two detectors for determining the force exerted on the forming roller during the spinning operation, in which the control unit is adapted to store measuring data of the detectors into the memory during a teaching phase and to control the forming roller during a production phase with the aid of the measuring data stored in the memory, said apparatus, in accordance with the invention, is characterized in that an additional detector is provided which delivers additional measuring data to the control unit, said control unit being adapted to determine position values of the forming roller from the measuring data and additional data stored in the memory and for controlling the forming roller with the aid of the thus determined position values during at least a part of the spinning operation in the production phase. The invention will now be explained with reference to the drawing showing an embodiment of the apparatus according to the invention by way of example and in a very schematic fashion. Fig. 1 is a schematic plan view illustrating a part of an embodiment of the apparatus according to the invention. Fig. 2 is a partial schematic sectional view of the apparatus of Fig. 1. Fig. 3 is a partial sectional view along the line III-III of Fig. 2. Now referring to the drawing, Fig. 1 schematically shows a plan view of a part of the exemplary embodiment of the apparatus for spinning the metal sheet, which apparatus comprises a rotatable drivable fixture 1 in which a chuck 2 is provided. A disk-like metal sheet 3 is clamped against the chuck 2 in a conventional manner. The metal sheet 3 has to be deformed into a desired product, such as e.g. a lamp reflector, an expansion vessel or the like, on the chuck 2 by means of a forming roller 4 which is rotatably journalled in a holder 5. For this purpose, the forming roller 4 should follow a pre-determined path of movement and therefore the holder 5 should be supported by a slide assembly which can be constructed in accordance with European patent application 0 125 720 of the same applicant, as mentioned above and the contents of which are incorporated herein by reference thereto. By means of this slide assembly, the forming roller 4 is permitted to be moved both parallel to the axis of the chuck 2 and in transverse direction. Fig. 2 shows the slide assembly very schematically in a view sectioned in the direction of movement of the upper slide 6 which is movably guided on an upper bed 7 which is fixed to an upper slide 8 which is guided movable to-and-fro on a lower bed 9. Fig. 3 shows the slide assembly in a very schematic sectional view along the line III-III of Fig. 2. The holder 5 of the forming roller 4 is attached to one end of the upper slide 6 which, together with the forming roller 4, is displaceable by a first driving member 10 constructed as a cylinder piston unit in the exemplary embodiment as shown. The piston rod 11 of the driving member 10 drives the upper slide 6 through a spring means 12 constructed in this case as a mechanical spring but which may also be constructed as an hydraulic spring or another type of spring means. This spring means 12 has its side facing away from the piston rod 11 supported on a piston rod 13 of a cylinder piston unit 14 which is operative as adjusting member for adjusting the initial spring force of the spring means 12. The apparatus further comprises a position detector 15 measuring the position of the piston rod 11 of the driving member 10 relative to the upper bed 7. For this purpose, a connection pin 16 is attached to the piston rod 11, said connection pin carrying a transmitting element of the position detector 15 not further shown. A second position detector 17 is mounted on the upper slide 6 and measures the position of the piston rod 11 relative to the upper slide 6. The connection pin 16 carries for this purpose a transmitting element (not shown) of the position detector 17. A third position detector 18 is supported by the connection pin 16 and measures the position of the piston rod 13 relative to the piston rod 11. For this purpose, the piston rod 13 comprises a connection pin 19, carrying a transmitting element of the position detector 18. The measuring data of the position detectors 15, 17, 18 are supplied to a control unit 20, including, in a usual manner, a memory in which the measuring data can be stored. Fig. 3 shows that the lower slide 8 is driven by a second driving member 21 constructed as cylinder piston unit of which the piston rod 22 is fixedly mounted in the lower bed 9 and of which a cylinder 23, in which the piston 24 attached on the piston rod 22 is received, is reciprocatingly movable relative to the piston rod 22. The cylinder 23 carries a driving element 25 which is coupled to the lower slide 8 by means of a spring means 26. In the embodiment shown, the spring means 26 consist of mechanical springs positioned on either side of the driving element 25, but also other embodiments are conceivable. The lower bed 9 carries a position detector 27 of which a transmitting element (not shown) is coupled to the lower slide 8 so that the position detector 27 measures the position of the lower slide. Furthermore, two position detectors 28 and 29 are provided which measure the depression of the spring means 26 in the one and other direction, respectively. For this purpose, the cylinder 23 includes a connection pin 30 carrying the transmitting elements (not shown) of the position detectors 28, 29. It is noted that there may be provided means in the lower slide 8 corresponding to the adjusting member 14 for adjusting the initial spring force of the spring means 26 in a manner similar to that of the spring means 12. The position detectors 27-29 are also connected to the control unit 20. The method according to the invention and with use of the apparatus as shown and described is as follows: In a teaching phase, the metal sheet 3 is spun against the chuck 2 on a basis of force control in a usual manner as described e.g. in the above-mentioned European patent application 0 125 720. The advantage of spinning the metal sheet 3 by force control is that the internal dimensions of the metal sheet may be adapted to the shape of the chuck 2 with very tight tolerances. The control unit 20 may adjust the first spring means 12 to a desired spring pre-stress or initial spring force by means of the adjusting member 14, in which the displacement of the piston rod 13 relative to the piston rod 11 is measured by the position detector 18. The force exerted by the forming roller 4 during the spinning operation may be derived from the depression of the spring means 12 by means of the measuring data of the position detector 17. During this teaching phase, the measuring data of the position detector 15 are stored in the memory of the control unit 20. These measuring data correspond to the position of the piston rod 11 of the first driving member 10 relative to the upper bed 7. With the use of these measuring data of the position detector 15 and 17, the control unit 20 may affect the spinning operation using force control, in which the desired force is obtained by bringing the upper slide 6 in a corresponding position, as is further described in the above mentioned European patent application 0 125 720. From the additional measuring data of the position detector 15 and the measuring data of the position detectors 17 and 18 the control unit 20 is able to determine also the actual position of the forming roller 4 in a simple manner so that a position control is possible as well. When the product to be made must have very accurate external dimensions in a part fully along the axial length, the control unit 20 controls the movement of the forming roller 4 in a last spinning movement alongside the chuck 2 by using the position values of the forming roller 4 derived form the measuring data, in which the spring means 12 is made inoperative. As a result, the forming roller 4 may not deflect against the action of the spring means 12 so that also the external dimensions of the product are able to meet very tight tolerances. When the product is produced in the teaching phase and meets the requirements, the production phase is used to form each metal sheet 3 by the control unit 20 using position control by means of the position values determined from the measuring data of the teaching phase. It is noted that in the exemplary embodiment as described, the spring means 12 is made inoperative by fully depressing the spring means 12 by means of the adjusting member 14. However, it is also possible to depress the spring means 12 by the adjusting member 14 to such an extent that the pressure force is sufficiently high to obtain a rigid connection in normal operation but which permits limited deflection of the forming roller 4 in case of unforeseen circumstances or a calamity. Finally it is noted that the spring means 12 may also be made inoperative in another way, e.g. by switching on a mechanical coupling between the piston rod 11 and the upper slide 6. Depending upon the shape of the chuck or the product to be made, respectively, the control unit 20 may be switched between forced control and position control during the spinning operation. Position control is preferably used in those parts of the shape extending substantially axially, whereas force control is preferred in sections extending more or less radially. According to a very favourable embodiment the position values for the forming roller 4 determined by the control unit 20 from the measuring data of the position detector 15, 17 and 18 by means of a path followed by the forming roller 4 in the last spinning step is shown on a display for the user of the apparatus, so that the user may check by means of the graphically illustrated path whether this path corresponds to the desired external shape of the product. If an observation of the screen shows that the path does not fully meet the requirements or needs a correction for another reason, the user may adjust desired position values by means of suitable input means, such as a keyboard or the like, so as to adapt the path of the forming roller. Although the position detector 18 in the embodiment as described is used for determining the additional measuring data by means of which the control unit 20 is able to determine the position values of the forming roller 4 when the spring means 12 is switched off, it is also possible to use a position detector which measures the position values of the forming roller 4 directly to effect the position control. It will be clear that the control of the lower slide 8 by the control unit 20 may take place in a similar manner. A position control with the aid of the measuring data of the position detector 27 is also possible, whereas a force control is possible by using the measuring data of the position detectors 28 and 29. Adjusting a pre-stress is possible again by pre-stressing the spring means 26 by means of a suitable adjusting member such as for example the adjusting member 14. These adjusting members may also be used for switching off the spring means 26, but it is of course also possible to make a fixed mechanical coupling between the driving element 26 and the lower slide 8. It is noted that the apparatus as described comprises one forming roller having a corresponding slide assembly. It is of course also conceivable to equip the apparatus with several forming rollers and slide assemblies. The invention is not restricted to the embodiment described herein before by way of example, which may be varied in different manners within the scope of the claims.

Claims: Method of spinning a metal sheet (3) around a chuck (2) for forming a product, wherein in a teaching phase by force control, a product is formed on the chuck (2) by rotating the chuck (2) about the axis of rotation and by moving a forming roller (4) one or several times alongside the chuck (2) with a pre-determined pressure force thereby spinning the intermediate metal sheet (3), and in the teaching phase measuring data corresponding to the movement of the forming roller (4) during spinning is fixed in a memory of a control unit, and in the production phase the forming roller (4) is controlled with the aid of these measuring data, characterized in that the control unit determines the position values of the forming roller (4) in axial direction and in transverse direction relative to the chuck (2) from the data fixed in the teaching phase, and the control unit controls the forming roller (4) in the production phase at least during a part of the spinning movement by means of the position values determined in this manner for spinning the metal sheet (3) into the desired product and wherein the forming roller (4) is moved alongside the chuck (2) by means of a lower and upper slide (8, 6), the forming roller (4) being coupled to a driving member (10) of the upper slide (6) by means of a spring means (12) and during the production phase this spring means (12) is made at least partially inoperative by the control unit. Method according to claim 1, wherein the step of rendering the spring means (12), constructed as a mechanical pressure spring, inoperative is effected by fully depressing the spring. Method according to claim 2, wherein the bed (7) of the upper slide (6) is coupled to a driving member (21) of the lower slide (8) by means of a second spring means (26) which is operative in both directions of movement and wherein during the production phase this second spring means (26) can be rendered at least partially inoperative by the control unit. Method according to claim 3, wherein the step of rendering the second spring means (26) constructed as mechanical pressure spring inoperative is effected by fully depressing the spring. Method according to one of the preceding claims, wherein the control unit determines from the measuring data obtained during the teaching phase the path of the forming roller (4) with the metal sheet (3) abutting the chuck (2) and stores it in the memory, said path being shown graphically and it is permitted to change or correct the path stored in the memory by means of an input means, whereafter, in the production phase, the forming roller (4) is controlled according to the changed/corrected path. Method according to one of the preceding claims, wherein, in the production phase the forming roller (4) is controlled partly by force control and partly by position control, wherein the position control is preferably used with part of the chuck (2) extending substantially axially. Apparatus for spinning a metal sheet using the method according to one of the preceding claims, comprising a forming roller (4), an upper slide (6) guided on an upper bed (7) and supporting the forming roller (4), a first driving member (10) for displacing the upper slide (6), and a Control Unit having a memory, characterized in that the forming roller (4) is coupled to the first driving member (10) by means of a first spring means (12), the control unit having at least two detectors (15, 17) for determining the force exerted on the forming roller (4) during the spinning operation, in which the control unit is adapted to store measuring data of the detectors (15, 17) into the memory during a teaching phase and to control the forming roller (4) during a production phase with the aid of the measuring data stored in the memory, and an additional detector (18) is provided which delivers additional measuring data to the control unit, said control unit being adapted to determine position values of the forming roller (4) from the measuring data and additional data stored in the memory and for controlling the forming roller (4) with the aid of the thus determined position values during at least a part of the spinning operation in the production phase. Apparatus according to claim 7, wherein the first driving member (10) engages the upper slide (6) through a first spring means (12), said upper slide (6) comprising an adjusting member (14) for adjusting the initial spring force of the first spring means (12), wherein there are provided three detectors (15, 17, 18) for measuring respectively the position of the first driving member (10) relative to the upper bed (7), the position of the upper slide (6) relative to the first driving member (10) and the position of the adjusting member (14) relative to the first driving member (10), in which the control unit is adapted to determine the position of the forming roller (4) from these measuring data. Apparatus according to claim 7 or 8, wherein the upper bed (7) is supported on a lower slide (8) movably guided on a lower bed (9) in a direction transverse to the direction of movement of the upper slide (6), said lower slide (8) being driven by a second driving member which is coupled to the lower slide through a second spring means operative in two directions, two detectors being provided for measuring the spring distance of the second spring means in both directions and a position detector being provided for measuring the position of the lower slide.

Inventors: MASSEE JOHAN, MASSEE, JOHAN, Massée, Johan
Applicants: MASSEE JOHAN, MASSEE, JOHAN
Application year: 1996
Main classification: B21D22
IPC codes: B21D22