Dispensing – Automatic control – Motor control
Reexamination Certificate
1999-11-09
2001-11-13
Soohoo, Tony G. (Department: 1723)
Dispensing
Automatic control
Motor control
C222S325000, C366S189000, C366S177100
Reexamination Certificate
active
06315164
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to multi-component dental compounds and is more particularly concerned with a device and method of forming such a material.
BACKGROUND OF THE INVENTION
To produce hardening multi-component impression compounds for use in dentistry, components are employed which are contained in cylindrical cartridges and which are pressed out synchronously and mixed together (EP 87 029 A1, EP-A-492 413, WO98/44860). The cartridges are designed as storage cylinders whose front ends form nozzle openings, which are each connected to an inlet opening of a mixing nozzle, and whose rear ends are open for receiving a plunger which is advanced inside the cylinder in order to press out the compound. To do this, equipment is used into which the cartridges connected to or to be connected to the mixing nozzle are introduced, and which has, for each cartridge, a stamp which acts on its plunger by way of the rear open end of the cartridge. To achieve a constant mixing ratio, the stamps are mechanically connected to one another for synchronous movement and are provided with a common electric drive mechanism. The latter comprises a coupling which can be released so that the stamps can be withdrawn from the cartridges by hand if they are to be changed. This change takes place if the cartridges are empty or if the type of impression compound is to be changed.
The mixers used are usually dynamic mixers. These are oblong, cylindrical or conical containers in which mixer vanes revolve and to whose one end the components to be mixed are delivered, and from whose other end the mixed compound emerges through a nozzle opening. At the delivery end of the container, the mixer shaft is equipped with a coupling part which, with the complementary coupling part of a drive shaft provided in the equipment, forms a coupling which is closed by attachment of the mixer to the equipment. Instead of a dynamic mixer with revolving mixer vanes, it is also possible to use a static mixer which is connected in the same way to the equipment and in which baffle plates are arranged which effect the mixing of the components as they flow through.
Until recently, the production of impression compounds almost exclusively used components of like viscosity. When changing over to compounds whose components have a different viscosity than the conventional components, or in which the viscosities of the components to be mixed differ greatly from one another, a deterioration in mixing quality is observed, and the reaction to this is to use different mixers. The disadvantage of this is that different mixer nozzles have to be kept in stock for different multi-component compounds, and replacement of the mixer nozzles can lead to errors being made. This is not only inconvenient, but also entails the risk that poor mixing will cause uncured material to drip into the patient's pharynx or, as a result of punctiform overheating of the material, the patient may suffer burns.
SUMMARY OF THE INVENTION
The invention is therefore based on the object of ensuring a satisfactory mixing result and of simplifying the overall handling, independently of the type of components to be mixed.
Accordingly, a method for generating a multi-component compound, in particular for dental purposes, is characterized by the fact that the advance speed of the plungers in the storage cylinders containing the components in pressing-out mode is regulated constantly at a predetermined value. The load state of the drive mechanism is ascertained. The drive mechanism is driven at a higher return speed or feed speed in the absence of a load. Thus, on the one hand, there is no need for manual return of the plungers when changing the cartridges, and, on the other hand, the change of cartridges is made considerably quicker and thus handling as a whole is improved This is particularly important when the dental surgeon finds, when mixing impression compound, that the cartridges are empty, before the necessary position is reached. The change of cartridges then has to be done very quickly so that the position can be obtained from the new cartridges within the drip time of the mixture.
The part of the invention concerning the pressing-out mode is based on the recognition that a different viscosity of the components not only has an effect on the rheology conditions in the mixer, but also on the dwell time therein. By constantly regulating the advance speed, a constant mixing time is obtained. In this way, the differences in the mixing result can be largely reduced, and to an extent sufficient for practical purposes. This also compensates for differences which (although the reason for them was not known) were hitherto attributed to randomly different friction ratios of the plungers in the cartridges and to the resultant different advance speeds. In a two-component mixer of similar construction (EP 87029 A1), although the absolute advance speed can admittedly be varied, regulation for maintaining the displacement speed is not provided for. The described effect achieved by the invention is particularly marked when using dynamic mixers; but the constancy of the mixing result is also improved when using static mixers.
For regulating the advance speed, electronic units are available which, used on electric motors, make it possible to measure and maintain the speed of rotation in the pressing-out mode at little cost, for example by regulating the voltage of direct-current motors or modifying the frequency in the case of alternating-current motors. Without any great additional expenditure, this regulating unit can also be designed, in addition to other tasks, for ascertaining, according to the invention, the load state of the electric motor, in which case the latter is run at a higher speed if it is not loaded. This detection of the load state can be done in a simple way by measuring the current consumption. If, in order to return the stamps, the drive mechanism is reversed, the electronic regulating unit ascertains that the drive mechanism is not loaded and ensures that the return movement can take place at high speed. If, conversely, after the cartridges have been changed, the device is switched on again and the stamps advanced, freedom from load is again ascertained as long as the stamps have not yet reached the plungers, and the rapid drive speed is adopted. The result of this is that the withdrawal of the stamps from the plunger before cartridge exchange and their advance movement to the plunger after cartridge exchange each take place in a rapid movement
The return movement of the stamps upon complete emptying of the cartridges can be automatically initiated by the equipment being provided with a sensor which detects the position which the stamps take up when the cartridges are completely empty. This sensor acts on an electronic unit, for example the regulating unit according to the invention, which then reverses the drive mechanism into the return direction.
In known equipment, the coupling mechanism between the mixer shaft and the mixer drive mechanism, provided for the latter in the equipment, is designed such that the mixer shaft has, on the drive side, a polygonal bore into which there engages a corresponding polygonal attachment arranged at the end of the drive shaft on the equipment side. When attaching the mixer nozzle, care must be taken to ensure that the polygonal attachment engages correctly in the polygonal bore. It is only when this has been ensured that the mixer nozzle can be securely connected to the equipment. This demands a certain amount of attention which is deemed inconvenient when—as is generally the case in medical practice—there are more important things to be considered. The invention thus also seeks a possible way of simplifying attachment of the mixer nozzle. It achieves this through the combination of two features. First, one of the two coupling parts is able to deviate from the other in the longitudinal direction counter to a spring force and/or the drive-side coupling part is completely withdrawn in the state in wh
Horth Hans
Muhlbauer Wolfgang
Alix Yale & Ristas, LLP
Ernst Muhlbauer KG
Soohoo Tony G.
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