Patent Application
20060010925
The invention relates to a method and an apparatus for positioning a feeder needle, and to a feeder comprising this needle; the invention also relates to a production line for optical components.
Feeders which have been disclosed hitherto, in particular needle feeders, have long been used for portioning, for example, heated and liquefied glass, and usually have a portioning accuracy of ±3 grammes.
Nowadays, however, even higher portioning accuracies are required for the production of glass engineering items, such as for example gobs for lens manufacture or for the manufacture of optical components.
Patent Abstracts of Japan 11-157847 relating to a “Device and method for supplying molten glass” has disclosed the accurate positioning of a feeder needle with spring assistance. However, one drawback of this holding means is that the fixed spring forces mean that either positioning can only be carried out slowly, in order to avoid mechanical damage to the feeder needle seat, or high levels of wear to the valve have to be accepted. This leads to leaks, which may require intervention on the part of the operator and can lead to apparatus down times. Furthermore, the fixedly set spring has difficulty reacting to thermal changes or any tolerances with the required degree of accuracy.
It is an object of the invention to achieve a higher accuracy of portioning with a needle feeder; in this context, it would be advantageous to achieve a portioning accuracy of ±50 mg or even a higher accuracy without, however, significantly increasing the wear to the needle or having a deleterious influence on its positioning in its seat, which would involve having to accept subsequent inaccurate portioning.
This object is achieved in a surprisingly simple way by the method as claimed in claim 1 and by apparatuses as claimed in claims 22, 30 and 31.
Hitherto, the closing of the valve of a feeder for glass has substantially not been recorded by measurement means, since this was very difficult at the prevailing temperatures, and only the running of the glass was used to establish correct positioning of the feeder needle.
However, the invention can be used to record the closing operation itself, and as a result significantly more accurate closing operations are possible, even with dynamic control.
The invention is described in more detail below with reference to the drawings and on the basis of preferred and particularly preferred embodiments.
In the drawings:
The following detailed description of preferred embodiments refers to the drawings which, however, are not to scale, for the sake of clarity.
Furthermore, reference is made to the reference system shown in
In the context of the present description, the term positioning is to be understood as meaning the movement of the feeder needle 3 into its correct position, in particular its correct operating position.
In this context, the term positioning encompasses
In this context, a feeder needle 3 which adopts a position in the x-y plane in which, as a result of the needle being moved in the z direction, the valve comprising the feeder needle 3 and valve seat 7 opens and closes correctly, and is preferably subject to little wear at the desired portioning accuracy, is regarded as correctly positioned.
The positioning according to the invention takes account of thermal expansion, mechanical wear and any changes in position in the valve comprising feeder needle and its seat which may occur during operation.
The positioning described below can be carried out successfully both for needles of needle feeders that are suspended flexibly, in particular in universally jointed fashion, and for needles of needle feeders which are suspended in a rigid position.
The following text refers to
Furthermore, the apparatus 1 has a reservoir 4 for fluid material 8, which can be heated by means of a heating device 6.
The heating device 6 is used to heat preferably glass sufficiently far above the glass temperature Tg that the glass softens and has a viscosity in a preferred range, for example a range of less than 100 dpas.
As a result of the feeder needle 3 being moved in the opposite z direction, the feeder needle seat 7 can be opened at the lower end of the reservoir 4, which preferably narrows in a funnel shape, with the result that the heated glass 8 is passed from the reservoir 4 into an outflow device which is in particular of tubular configuration, namely the feeder tube 9.
At the lower end of the feeder tube 9 is a detachment device 10 which may comprise a nozzle 11 or forms a defined edge, from which the fluid material is released to a further production facility.
The further production facility (not shown in the figures) may be an optical pressing facility, in particular a precision pressing facility, for the production of gobs, optical components, in particular of lenses, Fresnel lenses and/or plane, in particular plane-parallel, plates.
In an alternative configuration, the detachment device 10 is arranged directly beneath the feeder needle seat 7, and the feeder tube 9 is then absent. As a result, the portioned material is released directly to the further production facility without passing through a further outflow device.
The reservoir 4 and preferably also the tubular outflow device and the heating device 6 are surrounded by thermally insulating refractory material, and as a result allow very accurate temperature setting of both the reservoir 4, the tubular outflow device and the material 8 located therein.
In addition, both the apparatus 1 shown in
In the first preferred embodiment, illustrated in
The boom 13 has a mast 15, which is held in a mechanically fixed position relative to the reservoir 4 and on which an accurate longitudinal displacement means moving in the z direction 16 is fitted, which displacement means can preferably be actuated and moved by servomotor means via a control device (not shown in the figures). This control device may be a local or linked, in particular central, process control device with which the person skilled in the art will be familiar.
Furthermore, the longitudinal displacement means 16 has displacement sensors which record its precise location in the z direction and transmit this location to a recording and memory device 17.
The universally jointed suspension 14 of the first embodiment is arranged fixedly on an x-y displacement device 18 which can move in a defined manner in the x and y directions and is itself held fixedly on the displacement device 16.
The x-y displacement device 18 also has position indicators, by means of which the x-y device positions can be recorded and transmitted to the recording and memory device 17.
Furthermore, the x-y displacement device 18 preferably has servomotor drive units, and its position can be displaced in a defined way by the control device (not shown in the drawings).
This arrangement allows the feeder needle 3 to be moved in a defined way in both the x, y and z directions and allows its corresponding position to be recorded and stored in the recording device 17.
Furthermore, the velocity and acceleration of the feeder needle can be determined, either without interruption over the course of time or for defined time intervals, by means of a plurality of position measurements which take place at defined time with respect to one another.
This allows excessively high or low velocities of the feeder needle 3 and accelerations which bring with them a risk of danger or wear to be recorded.
In particular the velocity or acceleration of the feeder needle tip 19 in the z direction can be restricted to a maximum value by its velocity value being transmitted to the control device and limited by the latter as a result of the control device acting on the longitudinal displacement means 16.
This allows undesirably high forces to be avoided when the feeder needle tip 19 comes into contact with parts of the reservoir 4, in particular the feeder needle seat 7.
Furthermore, if the location of the feeder needle 3 is known, it is possible to define regions within which very high velocities are permitted in the x, y and z directions and to define regions, for example in the vicinity of the walls of the reservoir 4, within which only low velocities are used, in particular velocities which avoid damage to the feeder needle 3 and the reservoir and seat 7.
The following text refers to
The force-measuring device 2 has a force-measuring device 20 which measures in the z direction and is illustrated, purely by way of example, as a cylindrical piezoelectric element.
Furthermore, the force-measuring device 2 has a force-measuring device 21 which measures forces in the x direction and a force-measuring device 22 which measures forces in the y direction.
The respective force-measuring devices may comprise one or a plurality of force-measuring devices. By way of example, a further force-measuring device 23 in the x direction and a further force-measuring device 24 in the y direction are illustrated in
The respective force-measuring devices may have wire strain gages, piezoelectric measuring devices and other measuring devices.
As an alternative to the illustration presented in
The following text refers to
In the second preferred embodiment of the invention, the feeder needle 3 is mechanically rigidly connected to the x-y displacement device 18, instead of using the universally jointed suspension 4 shown in
This allows undesirable swaying movements of the feeder needle 3, which are produced, for example, by flows in the fluid material 8, to be suppressed to a greater extent than when using the universally jointed suspension.
In this embodiment, it is particularly advantageous for the monitoring of the signals from the force-measuring devices 20 to 24 to be carried out without interruption over the course of time.
Transmission of these signals to the control device and the intervention of the control device on the x-y displacement device 18 and the longitudinal displacement means 16 allows the feeder needle 3 to be stopped or moved in the opposite direction to the instantaneous direction of movement as soon as excessively high forces occur, allowing damage and excessive wear to be avoided.
To provide a better understanding of the forces and force-measuring signals which are to be found in the following description of the method, reference is made to the illustration presented in
This type of arrangement of the feeder needle 3 relative to its valve seat 7, albeit not usually so strongly inclined, may occur if the feeder needle 3 is not correctly positioned as described below.
With correct positioning of the feeder needle 3, the latter will be in an untilted position, i.e. in a position in which the longitudinal axis 26 is oriented parallel to the z direction or to the auxiliary line 27 shown in
The following text describes how this positioning is achieved using the force measurement signals.
If the feeder needle 3 is displaced in the z direction from a position illustrated in
In the process, both a force in the z direction and a force in the y direction act on the feeder needle 3, in particular on its tip 19. These forces are recorded by the force device 20 measuring in the z direction and the force-measuring devices 22 and 24 measuring in the y direction, and by virtue of their simultaneous occurrence make it possible to establish that the feeder needle 3 is incorrectly positioned or has collided with the reservoir 4.
A feeder needle 3 which has been correctly positioned in the x and y directions, on being displaced in the z direction, would substantially only generate a force signal in the force-measuring device 20, i.e. only in the z direction.
Furthermore, it is not only the direction but also the time profile and the strength of the force measurement signals which can be used to ascertain whether the feeder needle 3 has been correctly positioned.
If a feeder needle 3 which has been incorrectly positioned in the lateral direction is displaced in the z direction out of the position illustrated in
The feeder needle tip 19 which has been incorrectly positioned in the lateral direction may deviate laterally in the funnel-shaped lower region of the reservoir 4, which is made possible by the universally jointed suspension 14 and the limited mass of the feeder needle 3. Although a force signal of this nature may show a relatively strong rise, this rise will subsequently decay again relatively quickly, on account of the yielding movement of the feeder needle 3 in the fluid material 8. The extent of the rise is also limited, since the apparatus according to the invention complies with velocity or acceleration limit values, and consequently maximum limits for forces which are active are not exceeded.
However, the lateral deviating movement of the feeder needle 3 described above does not occur if the feeder needle 3 is correctly positioned in the lateral direction and then displaced in the z direction.
If the longitudinal axis 26 of the feeder needle 3 is on the auxiliary line 27, i.e. it is correctly positioned in the x and y directions, the feeder needle tip 19 comes into contact with the feeder needle seat 7 substantially simultaneously over the whole of a front annular region, resulting in an immediate and generally very steep rise in forces in the z direction.
Since there is no possibility of a lateral deviating movement, the level of the force signal in the z direction also does not decrease, as is the case with a tilted needle position, and not only is the increase steeper, but also in some cases the static forces in the z direction are considerably higher.
In particular in the latter case, the force signal in the z direction, in particular when the feeder needle 3 is not moving, can give information as to whether the feeder needle is correctly seated in a sealing position, since these forces in the z direction are also a measure of the closing forces which are acting at the feeder needle tip 19 in the feeder needle seat 7.
The apparatuses as described above and the methods described below can particularly advantageously be used for the production of optical components, such as for example lenses, Fresnel lenses and/or plane, in particular plane-parallel, plates with very accurately defined masses.
This results in significant benefits for the hot-shaping since, in particular in the case of precision pressing, very accurate shapes can be used and it is possible to reliably avoid excessive or insufficient dimensions, which would otherwise lead to incorrect component dimensions.
In the text which follows, the method according to the invention is described in more detail on the basis of preferred embodiments.
At the start of the positioning operation, the feeder needle 3 is advantageously adjusted as accurately as possible in the x-y plane, for example by using the values for a correct positioning stored in the memory device 17 or by optical or mechanical checking of the distances from the walls of the reservoir 4 and from the seat 7.
This adjustment in the x-y plane can be carried out in the cold or unheated state of the fluid material 8 which is to be softened by the supply of heat, while the further positioning can be carried out after the fluid material 8 has been heated and softened.
In a first embodiment of the method according to the invention, the force acting in the x and y directions is measured by the force-measuring device which records in the x and y directions, such as for example wire strain gages or piezoelectric transducers, and while the feeder needle is closing the zero value for the two measured values is searched for by means of a trial-and-error method.
This search may either be carried out randomly or on the basis of intelligent search strategies which recognize the direction of the readjustment on the basis of a change in the measurement signals.
By way of example, first of all the feeder needle can be moved in the x direction, until a local minimum value has been recognized, and then the feeder needle can be held in this x position.
Then, the feeder needle can be moved in the y direction until a local minimum value has been recognized, and the feeder needle can then be held in this y position.
Next, another x and then another y movement can be carried out until the x and/or y value drops below a predetermined limit value or even reaches zero.
When this zero value is found in both directions, the feeder needle 3 does not sway any further during closing, which indicates that then substantially only a perpendicular lifting movement is present.
These or other search strategies can be used in both this embodiment and the embodiments described below.
Furthermore, an x-y position recognized as optimum can be stored at the start of a further positioning operation as a starting value in the recording and memory device 17.
The measurement device 20 which records in the z direction can then reliably and permanently record the closing force of the feeder needle 3 in the seat 7.
This method and the other methods described below can be operated by means of a control loop which is driven by electric servomotor means.
Servomotor drives can perform positioning operations which are fast yet nevertheless permanently accurate, since mechanical acceleration forces which would otherwise have to be applied by the valve seat can be absorbed by the servomotor drive. In particular with the known data relating to the location of the feeder needle, the control device can effect a very fast yet nevertheless reliable movement of the feeder needle.
The time-continuous recording of the forces in the z direction makes it possible to avoid damage to the needle seat at all times, since the forces which occur during the closing operation are always monitored, and it is in this way possible to rule out the possibility of excessively high closing forces.
Furthermore, the actuation by servomotor means allows optimum force profiles to be programmed as fixed values or used as defined set point values within a control loop.
In this context, the universally jointed suspension 14 of the feeder needle 3 is advantageous in order to assist with its free swaying and self-aligning tracking in the event of minor misalignments.
Furthermore, a previously stored value can already predetermine a coarse adjustment for the starting point of the positioning, which then merely requires precision adjustment.
The accurate needle guidance allows shallower valve curves to be realized, which in turn lead to still higher positioning accuracies.
The accurate needle guidance also allows the valve region of both the feeder needle and of the seat of the feeder needle to be more closely matched to one another in terms of shape, so that the opening cross section decreases or increases more quickly in the event of a movement of the feeder needle towards or away from the valve seat.
According to the invention, a wide range of geometries which are matched to one another can be used in this context.
Furthermore, the shape of the z force signal can provide information as to the position of the valve. A signal which rises accurately and quickly can indicate the correct function, while a blurred or more slowly rising signal can represent a misalignment or the occurrence of wear. In this case, the misalignment can be checked with the aid of the x and y signals, and the statement provided by the z signal can be validated.
In a simplified embodiment, the x and y signals are dispensed with, and the shape of the z signal alone provides all the values required.
If the feeder needle has not yet been positioned correctly in the x and y directions, it has to execute a swaying movement which is superimposed on the lifting movement, and first of all the needle has to execute a rubbing movement in the needle seat until it reaches its finally seated position. By means of a movement in the x-y plane in the opposite direction to the preceding movement, it is possible to terminate a rubbing movement after such a movement has been detected.
The feeder needle 3 can be displaced in the x and y directions, and in the process a tilting or swaying movement and a rubbing movement can be recorded in the z force signal, namely as an initially low force in the z direction, which then suddenly rises in the closed position and is recorded by the force measurement signal in the z direction, in particular as a rise in the force in the z direction.
It is possible to use trial-and-error methods or the intelligent search methods described above to find the position of the needle in which a swaying movement no longer occurs, so that the needle is correctly positioned in the x and y directions, with its z force signal correspondingly indicating only a steep rise in the correct closed position.
In general, the shape of the z force signal can also be used to provide information as to the state of the valve comprising the feeder needle 3 and the feeder needle seat 7.
The above description has made reference to a system of Cartesian coordinates with an x-y plane and a z direction; however, the invention is not restricted to this system; by way of example, it is also possible for forces in other coordinate systems, for example in polar coordinate systems or in spherical coordinate systems, to be utilized in accordance with the invention.
Furthermore, it is also possible for a single radial signal, for example the radial signal from a cylindrical piezoelectric transducer, to be measured instead of the force measurement signal measured in the z direction.
List of Designations
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004026932.7 | Jun 2004 | DE | national |
