WO2000039037A1

WO2000039037A1 - Glass forming apparatus with improved carousel mechanism and method for control thereof

Info

Publication number: WO2000039037A1
Application number: PCT/IB1999/002046
Authority: WO
Inventors: Antonio Cruccu
Original assignee: Antas S.P.A.
Priority date: 1998-12-23
Filing date: 1999-12-22
Publication date: 2000-07-06
Also published as: AU1674900A; ITMI982806A1; IT1304700B1

Abstract

A glass forming apparatus is disclosed, comprising a workpiece-carrying carousel (2) fixed to a rotor (5) rotatable coaxially with respect to a corresponding fixed stator, (6) said rotor and said stator forming part of a direct-drive electric motor.

Description

GLASS FORMING APPARATUS WITH IMPROVED CAROUSEL MECHANISM AND METHOD FOR CONTROL THEREOF

The present invention relates to a glass forming apparatus, provided with an improved carousel mechanism, and to a method for control thereof.

As is known, in the industrial manufacture of glass objects, the apparatus for forming or processing glass parts commonly comprises a carousel mechanism, by means of which the moulds or the mandrels for the parts to be processed are transported, along a circular path, at various workstations where the tools co-operating with the carousel and suitable for performing the various steps for production of the article (moulding, pressing, centrifuging, grinding, chamfering, finishing, etc.) are located.

Normally the carousel mechanism consists of a rotating platform performing a continuous movement or discontinuous movement, also called an "indexed" movement, namely one which is divided up into a plurality of separate displacements .

For historical reasons which have now become firmly established in the field and for the technical reasons which will be discussed further below, the carousel mechanism is currently operated by means of a motor, a mechanical reduction drive, an indexing mechanism and various other secondary accessories.

The reason for the use of this somewhat "heavy" and unsophisticated structure is attributable to the typical operating conditions for this equipment. In fact, the glass forming apparatus always operate in aggressive environments: both the high operating temperature and the constant presence of glass waste and dust (produced by processing) create problems with regard to the preservation and the safeguarding of any delicate components and have always resulted in other systems - other than the well established tried-and-tested mechanical drive systems being disregarded a priori in this field.

Furthermore, it must be underlined that this type of apparatus operates with a continuous cycle - i.e. is never stopped, except for maintenance - since start-up and stoppage are always critical phases when working with glass in the molten or plastic state: it must therefore be robust and reliable.

For all these reasons, the design of the carousel system has never made any significant progress, when compared to the technical evolution which has occurred in other sectors, there also existing a prejudice in this specific field as to the real convenience of finding new solutions other than those which have been fully tested and become firmly established.

Therefore, the function of transmission and indexing has always been assigned to purely mechanical systems which use toothed wheels (for example a pinion/toothed-wheel pair) and/or other kinematic mechanisms which have an established solidity and reliability. The indexing mechanism, for example, in many applications is embodied by a Maltese-cross kinematic mechanism.

However, in contrast to the features of solidity and the widespread use, the mechanical systems which have been used hitherto have certain drawbacks.

First of all, since the stresses are anything but negligible (the torques applied to the carousels most subject to stress are of the order of a few tens of thousands of Nm) , all the components must be designed with dimensions which allow for ample safety tolerances; said components are therefore heavy and produce intense inertia forces, therefore constituting a further limitation for the dimensional design of the apparatus itself.

In view, therefore, of the large masses involved (a carousel may have a diameter as much as 3000 mm and a mass as high as 4000 kg) and the accelerations required (accelerations of up to 3 g may be easily reached) , it is necessary to use reduction units, which do not have a high efficiency, as well as high-power electric motors. Further problems which commonly affect the mechanical drive systems are as follows: a not insignificant degree of wear due to the presence of components which are mutually engaged in relative movement with each other and which impose the need for a series of complex design features as well as major periodic maintenance programmes; impacts generated by the ample play and the elasticity of the coupled components which result in further stressing of the parts in contact; - the positioning precision is poor; moreover, in the case where the drive is provided solely by means of gears, the play and the elasticity which arise are such as to make it impossible to acquire a position feedback signal downstream of the resisting load: it is therefore necessary to use special mechanical centring devices which are able to compensate for these errors; high manufacturing, processing, assembly and maintenance costs.

The problems relating to the positioning precision are partially overcome using dividing mechanisms of the Maltese cross type. However, since, in order to limit the torques required for the drive, it is necessary to use a mechanical reduction unit, the positioning precision is often adversely affected. Moreover, the Maltese cross mechanism is affected, to a particularly significant degree, by the problems associated with the limited operational flexibility. In fact, once the configuration of the Maltese cross has been defined, the number of divisions of the carousel for each complete revolution, and hence the number of locations on the carousel able to receive the parts to be processed, is unequivocally determined: in this way not only is it impossible to vary the number of subdivisions (except by replacing entirely the drive mechanism) so as to adapt the apparatus to changed requirements, but it is also a very complex matter to adjust the ratio of movement time to stoppage time at a station. Therefore, one is obliged to equip the carousel on the basis of the fixed configuration of its drive mechanism, negatively affecting the flexibility performance which otherwise would enable optimization of the processing of a wide range of objects to be produced. Despite the abovementioned disadvantages, the person skilled in the art has always been discouraged from seeking alternative solutions and especially from seeking them in different working environments where the conditions might not be as specific and demanding as those described above. Instead, by abandoning the well-established reliability of the mechanical drive systems and overcoming the prejudices existing in this field, in an attempt to overcome all the drawbacks of the known art, the Applicant has sought out new approaches. It was found that, for some time already, electric motors of the direct-drive type have been commercially available. These electric motors, which are usually of the synchronous type, are composed of an annular stator, on which a plurality of coil windings which are designed to produce a magnetic field with several movable poles- are formed, and a corresponding annular rotor, which is provided with a series of permanent magnets facing the surface of the stator and located at a short distance from the latter, so as to establish an air gap.

These motors have an extremely simple constructional design, are modular and may manage to exert very high torques at any speed of rotation, are easily controllable and allow an excellent positioning precision to be obtained.

Applying therefore the operating principles of this type of motor to the sector of glass forming machines, the aim of the Applicant was to solve in an original manner the problems which were present in the known art.

This objective has been achieved by means of a glass forming apparatus provided with a workpiece-carrying carousel mechanism integral with a rotor rotatable coaxially with a respective fixed stator, said rotor and said stator forming part of a direct-drive electric motor.

Further characteristic features and advantages of the apparatus according to the invention will in any case emerge more clearly from the detailed description which follows, provided by way of an example and illustrated in the accompanying drawings, in which:

Fig. 1 is a longitudinal section view of an embodiment of the invention; and

Fig. 2 is a view, similar to that of Fig. 1, of another embodiment of the invention. As can be seen in the Figures, a glass forming apparatus comprises a base 1, a carousel 2 mounted rotatably on the base 1, a series of working tools (not shown) such as mandrels, moulds or the like, mounted on a plate of the carousel 2, and other glass processing devices

(not shown) , such as feeders, pressing devices, grinding wheels and the like, which co-operate with the tools mounted on the carousel 2, for example in suitable workstations.

The carousel 2, in turn, is composed of a carousel body 2a mounted, by means of bearings 3a and 3b, on a support column 4 fixed to the base 1. Preferably, at least one of the two bearings, for example the bottom bearing 3b, is of the inclined type so that a thrust-bearing function is also exerted.

According to the invention, a rotor 5 is fixed to the bottom part of the carousel body 2a and has, on its perimetral surface, a plurality of permanent magnets 5a. Coaxial with this rotor 5 and integral with the base 1, there is a stator 6 of an electric "direct drive" motor provided with coil windings of an electric circuit which are able to form a magnetic field with alternating and movable magnetic poles. Optionally, the coil windings may be of the modular type.

The rotor 5 and the stator 6 are arranged, facing, at a small distance from each other. The interstice which is established between them forms the air gap 7 of the electric motor. The rotor 5 and the stator 6 may have, for example, opposite cylindrical surfaces (as in the embodiment according to Fig. 1) or flat parallel surfaces, with a radial arrangement of the permanent magnets (as in the embodiment according to Fig. 2). Preferably, the stator 6 and the rotor 5 are enclosed inside a housing 8 which is integral with the base 1 and sealingly closed. The housing 8 may be hermetically closed by means of suitable seals or may be pressurized so as to ensure that a minimum amount of fluid (for example air) escapes externally via sliding seals. Or else the housing may contain a suitable fluid at a controlled pressure. This prevents the waste material, produced by the working environment, from contaminating the motor, adversely affecting operation thereof.

In the glass forming apparatus, advantageously the accessibility from the bottom of the carousel 2 is ensured so as to facilitate the assembly of certain working tools between the base and the carousel itself, for example in the region of the moulds. Moreover, it is necessary to ensure the possibility of performing the operations for maintenance of these processing tools.

Therefore, in the present invention, it is preferred not to use a large thrust bearing, i.e. a so-called fifth wheel, for directly supporting the carousel body 2a on the base, as would be most advantageous in order to obtain an optimum distribution of the load on the bearings and therefore an acceptable stability. On the other hand, it is necessary to ensure a high degree of rigidity of the carousel structure in order to prevent the occurrence of deformations which may modify the spacing of the air gap 7, adversely affecting operation of the electric motor.

Preferably, therefore, the bearings 3a and 3b have small dimensions and are arranged on the column 4 at a distance which is as large as possible, preferably at a distance which is greater than 25% of the radius R of the carousel body 2a.

At the same time it is envisaged that there is a certain distance between the upper surface of the carousel body 2a and the base 1: this has the dual function of keeping the rotor and stator portion as far as possible from the high-temperature working zone and of allowing easy access to the bottom part of the plate of the carousel body 2a.

In order to prevent the stator and the rotor from coming into contact following collapse or anomalous deformations of the rotor support assembly, a safety spacing device (not shown) is envisaged, said device intervening supporting the rotor if necessary. This is particularly desirable in order to prevent the possibility of an excessive reduction in the air gap 7 during operation of the carousel, which would result in sudden magnetic "sticking" of the stator and rotor, causing a sudden and dangerous stoppage of the apparatus.

The adjustment and control of the magnetic field in the stator 6 - and consequently the speed of rotation and angular position of the carousel 2 - may be achieved by means of a control device acting on the current energizing the coil windings, for example in accordance with a signal supplied by a position sensor 9 (such as an encoder) located in the vicinity of the rotor. The parameters necessary for adjustment and control of the magnetic field, which are set so as to optimize the speed profile in accordance with the process requirements, are acquired, stored and processed by the control device, for example, as a matrix. The control device may be provided with calculation algorithms which are especially devised to satisfy the requirements of the processing operations described above.

The same coil windings, in the event of a sudden drop in voltage, may be short-circuited so as to make use of the residual electrical energy flowing in the windings, in order to brake the rotor. This residual energy, being a function of the power used in that moment (and therefore being also proportional to the speed of the carousel) , performs a braking action which undoubtedly provides an advantageous aid for any other external devices, in order to achieve a good passive safety level, even though it cannot have the same efficiency as a braking action obtained by means of a current ramp suitably produced in the windings with an active control device. In addition, it is always possible to provide a safety braking system for stopping the carousel in the event of a voltage drop in the power supply of the motor or the control device. With the apparatus according to the invention, the drawbacks of the known art have therefore been overcome in a satisfactory manner, achieving a significant technical progress for various reasons.

In fact, the mechanical drive components of the known art have been eliminated entirely, thereby reducing the rotating masses and the consequent forces of inertia, so as to allow the use of less driving power; since the overall structure of the carousel may be consequently slimmer and lighter, it is possible to achieve in a synergic manner the advantageous possibility of developing greater acceleration levels (in terms of absolute value), while reducing the overall rotation time of the carousel and consequently increasing the productivity of the apparatus.

Moreover, since there is no longer meshing between mechanical components, a great deal of friction has been eliminated to the benefit of the efficiency. Since there is no longer play and uncontrollable deformation in the kinematic chain between the motor and the carousel, it is possible to mount the position sensor in a zone very close to the resisting load. Therefore, the positioning precision is excellent, even without using mechanical centring means. Moreover, in applications where a position precision and repeatability with zero error or a customized subdivision of the rotation is required, it is possible to perform a self-learning operation, during the course of which the control device or the like acquires the values of the real stoppage positions, storing them in numerical form in a suitable look-up table.

The rotor and the stator may also be constructed in several sections so as to provide motors of different sizes, which may be arranged above one another or coaxial, so as to be able to provide the necessary driving torque in any condition, for each specific application, without wasting energy. At the same time it is possible to obtain both continuous operation and indexed operation in accordance with the most varied requirements, determining the number of divisions of the carousel movement as well as the most varied laws of motion, by simply operating an electronic system for regulating the electric power supply to the stator.

This provides, obviously, an operational flexibility without precedent, which allows the whole range of processing devices to be applied to an apparatus provided with a single carousel according to the invention.

The advantageous results achieved are therefore unexpectedly more numerous than those which could have been envisaged, therefore making the new solution described here even more valid and attractive from a technical/commercial point of view.

It is understood, however, that the invention is not limited to the details disclosed in the above specific configuration, but extends to all other technically equivalent constructional variations.

For example, although a carousel in which the coil windings are arranged on the stator has been described, the teachings of the invention also embrace the provision of a _ _

similar carousel in which the functions of the rotor and the stator are reversed, i.e. in which the permanent magnets are located on the stator and the coil windings on the rotor.

The teachings of the invention also include the provision of a similar carousel in which several direct- drive motors are mounted above one another coaxially or arranged concentrically.

Claims

1. Apparatus for processing glass of the type comprising a workpiece-carrying carousel (2), characterized in that said carousel (2) is fixed to at least one rotor (5) rotatable coaxially with respect to at least one fixed stator (6), said rotor (5) and said stator (6) forming part of a direct-drive electric motor.

2. Apparatus as claimed in Claim 1, wherein said rotor (5) and said stator (6) are contained inside a housing (8) isolated from the external environment.

3. Apparatus as claimed in Claim 1, wherein said rotor (5) and said stator (6) are contained inside a housing (8) which is pressurized internally.

4. Apparatus as claimed in Claim 2 or Claim 3, wherein said housing (8) is incorporated in a base (1) of the apparatus.

5. Apparatus as claimed in Claims 1, 2 or 3, wherein said carousel (2) is composed of a carousel body (2a) which is mounted rotatably on a column (4) by means of support bearings (3a, 3b) which are arranged at a distance of not less than 25% of the radius of the carousel body (2a) .

6. Apparatus as claimed in Claim 5, wherein said rotor (5) is integral with the bottom part of said carousel (2) .

7. Apparatus as claimed in any one of the preceding claims, wherein said stator (6) and said rotor (5) are coaxial, contained in respective parallel horizontal planes and arranged above one another.

8. Apparatus as claimed in any one of Claims 1 to 7, wherein said stator (6) and said rotor (5) comprise concentric cylindrical surfaces.

9. Apparatus as claimed in any one of the preceding claims, wherein said rotor (5) and said stator (6) are composed of several sections.

10. Apparatus as claimed in any one of Claims 5 to 9, comprising moreover a safety spacing device designed to support said rotor (5) upon collapse of said support bearings (3a, 3b) such that on air gap between the stator and said rotor is reduced beyond a predetermined threshold.

11. Apparatus as claimed in any one of the preceding claims, wherein said stator (6) comprises coil windings of an electric circuit which are able to create and control a magnetic field and said rotor (5) has permanent magnets.

12. Method for controlling an apparatus as claimed in Claim 11, in which said coil windings of the electric circuit are short-circuited in the event of a voltage drop occurring in a power supply.

13. Method for controlling an apparatus as claimed in any one of the preceding claims, in which the subdivisions and the real stoppage points of the movement of the carousel (2) are self-learned and stored by a control device during a first learning phase.