Abstract:
The device for generating a multi-component compound, in particular for dental purposes, by pressing out and mixing its components from cartridges ( 5 ), which open into a mixer ( 10 ), is characterized in that the advance speed of the motor ( 15 ) is regulated by the pressing-out behaviour of the components, which pressing-out behaviour can be determined by sensors (III-VIII).

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a method and a device for generating a multi-component compound, in particular for dental purposes, by pressing its components out from exchangeable cartridges, which are arranged alongside one another and open into a mixer, by jointly advancing their plungers by means of an electric drive, in which the advance speed is regulated. 
   In a known method and a known device of this type (EP 1 010 401 A1), the plungers are at first advanced rapidly. When contact with the components then takes place, the resistance increases, and this is detected. The advance speed is then regulated to a lower constant value in order to ensure that the components are pressed out at a uniform speed. However, it has now been found that in many cases it is not sufficient to regulate the advance speed to a constant value, and instead it is also necessary to select the suitable advance speed. The dentist can of course do this by using already known apparatus. However, in most cases he will not succeed in setting the optimum advance speed. Different types of material have very different viscosities or require particular speeds due to processing factors. A universal adaptation does not take sufficient account of the large number of types of material. Depending on the properties of the material, there is an optimum advance and a good and reproducible result of the work. This is all the more so when the mixer used for the two combined components is not a static mixer, but a dynamic mixer driven by an electric motor. The speed too of this electric motor must then be adapted to the special requirements of the components so that the multi-component compound has the optimum properties. 
   If the advance and/or the speed of the mixer motor is not set optimally, the following problems can arise.
         1. An unsuitable ratio of the speeds of advance and mixer shaft results in a non-optimum mixing of the components. Thus, conditions such as processing times and strengths of the impression are only partly achieved or not adequately achieved.   2. Depending on the viscosity of the material type, a wrong speed of the mixer shaft can result in inadmissibly high shearing, which means that the setting behaviour of the compounds is allowed to increase in an uncontrolled manner.   3. If the components have different flow behaviour, incorrect quantities are dispensed by a rigid speed of rotation. These lead to partial hardening or delays in the impression-taking. This can be compensated for or considerably improved by start and stop ramps.   4. If compounds are dispensed too quickly, a deformation of the pressure vessels or cartridges must be expected. The deformation leads to a change in the volume and thus to an inaccurate dosing of the components. This is all the more problematic if, for example, a container deforms more strongly than the second component. The error can impair the mechanical values of the impression and lead to partial hardening.   5. If compounds are used which have to be placed with precision and accurate dosing, an ideal dispensing speed is helpful. By this means, air inclusions and excess dosing are avoided.       

   SUMMARY OF THE INVENTION 
   The object of the invention is to make available a method and a device with which the advance speed is automatically regulated to a suitable value for the corresponding material. The solution according to the invention lies in the fact that the regulation of the advance speed is effected as a function of the pressing-out behaviour of the components, which behaviour is compared with stored or calculated values for known materials. 
   The pressing-out behaviour is thus measured. If, for example, there is only a relatively low resistance to pressing-out, then the components involved are evidently of low viscosity, which already permits conclusions to be drawn concerning the material used if the measured pressing-out pressure or the force is compared with stored values of various materials. After the material has thus been identified, the advance speed can be set to the optimum value for this material. The force or pressure needed for the pressing-out can be measured via the current consumption or the torque of the electric drive for the advance. 
   In an advantageous embodiment, the pressing-out pressure of one or all of the components is measured. Instead of the pressure, the pressing-out force can of course also be measured if the cross section of the plungers is known. This pressing-out force is very much dependent on the material. The pressing-out force in a particular apparatus is, for example, 283 N for Honigum as the base component and 1124 N as the catalyst component. In the case of the material Silagum, these forces are 1014 N as the base component and 1234 N as the catalyst component. If these forces are measured and compared with the stored values for these materials, it is possible to ascertain automatically which material is to be processed, so that the advance speed and if appropriate also the mixing speed can be optimally set accordingly. 
   If the advance speed is measured together with the current consumption or the torque of the electric drive for the advance, values for the flowability of the materials can be determined from this and can likewise be compared with known stored values and used for the regulating. 
   Moreover, the deformation of one or all of the cartridges or the deformation of the cartridge holder can be measured, which likewise permits conclusions to be drawn regarding the flow behaviour and can thus be used for identifying the material used and for optimum regulation. 
   If a mixer driven by an electric motor is provided, the current consumption or the torque of the electric motor can be measured, which likewise permits conclusions to be drawn regarding the viscosity of the material and thus, by comparison with stored values, regarding which material is involved. The speed of rotation for the electric motor of the mixer can then likewise be regulated to a suitable value. 
   The viscosity or flowability of the materials often critically depends on the temperature. Provision is therefore advantageously made for the temperature also to be measured, specifically either the temperature of the components before mixing or the temperature in the mixer. By measuring the pressing-out behaviour and comparing it with known pressing-out data, the material being used can therefore be identified and the pressing-out speed and if appropriate the speed of rotation of the mixer motor can be optimally set. By means of the method according to the invention and the device according to the invention, transitions from one behaviour to another can also be determined, compared and used for regulation, for example the thixotropy characteristic. The measurements can in this case be used not only for regulation, but can also serve to avoid overloads. In addition, provision can also be made for the dentist to be able to set a speed which he considers to be the optimum speed. If this does not correspond to the optimum advance speed which was determined by the apparatus, either a warning can be displayed or a “compromise” can be reached between the set speed and the automatically determined speed. 
   The speed of rotation for the advance motor and if appropriate for the mixer motor is regulated according to known techniques. Direct-current motors are preferably used which have a voltage range of 12 to 24 volts and whose speed is dependent on the voltage. The speed of the motors can also be influenced by a pulse-width modulation, in which case the torque remains substantially constant. The invention is described below on the basis of advantageous embodiments and with reference to the attached drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below on the basis of advantageous embodiments and with reference to the attached drawings, in which: 
       FIG. 1  shows a previously known apparatus in the opened state, in a perspective view; 
       FIG. 2  shows an apparatus of the type shown in  FIG. 1 , in which measurement means according to the invention are provided, shown in more detail at III to VIII; and 
       FIGS. 3  to  8  show the partial representations III to VIII from  FIG. 2  on an enlarged scale. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A known apparatus (EP 1 010 401 A1) in which the invention can be applied will first be described with reference to FIG.  1 . 
   Rising from a base part  1 , there are support plates  2 ,  3 . A holder  4  is provided on the latter for cartridges  5 , indicated by dot-and-dash lines. In this context it is of no importance whether the cartridges, which are preferably of cylindrical design, are filled directly with the components or receive an optionally exchangeable tubular bag containing the component. 
   The holder  4  comprises a rear holding plate  6  and a front holding plate  7  which are held together by anchors  8 . The cartridges  5  can be fitted between these. Further holding means (not shown) can be provided to act on the lateral positioning of the cartridges  5 . 
   On the front holding plate  7  there is a means (not shown) for arranging a mixer nozzle  10 , indicated by dot-and-dash lines. This has, at its end facing the holding plate  7 , two inlet openings which communicate in a known manner directly or indirectly with the outlet openings of the cartridges  5 . The feature, namely that the cartridges are arranged alongside each other, is intended only to signify that they are arranged such that they can be operated simultaneously and synchronously. A positional restriction going beyond this, for example restriction to a parallel arrangement, in not thereby intended, although this is obviously advantageous. 
   The cartridges  5  contain plungers. These can optionally be omitted if the cartridges contain foil bags. The stamps then take the place of the plungers mentioned in the claim. For advancing the plungers or the rear face of the bags, the apparatus has stamps  11  which, in the drawing, are shown in the state in which they are retracted into the rear holding plate  6  for the purpose of changing the cartridges. They are arranged at the front end of stamp rods  12 , whose rear ends are secured rigidly in a cross bracket  13  which, by means of a threaded spindle  14 , can be advanced in the direction of the mixer nozzle or retracted in the opposite direction. The stamps  11  can optionally be changed if cartridges of different diameter are to be used. Their distance from one another can also be variable. When the cartridges  5  are fitted in the apparatus, the stamps  11  are advanced by advancing the cross bracket  13  until they reach the plungers in the cartridges  5 . This advance movement can be triggered automatically by the insertion of the cartridges or can be triggered manually by switching on the apparatus. 
   For the advance and return of the threaded spindle  14 , a motor  15  with gear  16  is provided, the drive movement of which is transmitted to the threaded spindle  14  via a belt transmission  17 . For mounting the threaded spindle  14  and the annular discs belonging to the belt transmission  17 , means (not shown) are provided which are disposed on the plate  3  and on a further frame plate  20  which is connected rigidly to the plate  3  via columns  21 . 
   A further motor  22  is arranged on the plate  20  and is connected (in a manner not shown) on the drive side to a mixer drive shaft  23  which lies between the plates  3  and  20  coaxially within the threaded spindle  14 , is guided between the cartridges  5  from the rear holding plate  6  to the front holding plate  7 , and is mounted in the latter. It protrudes from the front holding plate  7  in the form of a projection  24  which, for the purpose of rotational connection to the mixer shaft (not shown), is of polygonal design (not shown) for example. The shaft projection  24  can be pushed back counter to a spring force until it no longer protrudes from the front holding plate  7 . It can also be arranged in such a way that when the stamps  11  are completely retracted for the purpose of cartridge exchange, it is likewise retracted into the front holding plate  7  in order to make it easier to attach a new mixer nozzle  10 . 
   An electronic unit  30  is provided and is indicated diagrammatically at  30 . The first function of this electronic unit is to constantly regulate the speed of rotation of the motor at a predetermined value when the motor is in pressing-out mode and loaded. This is the function which guarantees the constant mixing result. 
   A second function of the electronic unit  30  is to measure the current consumption of the motor  15  in order to ascertain whether the latter is loaded or unloaded. In the former case, it is to be assumed that the stamps  11  are bearing on the cylinders of the cartridges  5  and the pressing-out resistance of the cartridges is causing the high current consumption measured by the unit  30 . In this case, the electronic unit  30  ensures that the motor  15  is operated at the predetermined advance speed. 
   If, by contrast, the electronic unit ascertains that the current consumption lies below a value which is normally achieved only when the drive is loaded, it ensures that the motor  15  is operated at a higher speed (for example ten times faster). This applies independently of the direction of rotation of the motor  15 . 
   In the third place, the electronic unit  30  ensures that the motor  22  is operated at a high mixing speed if the drive  15  is loaded. Conversely, it ensures that the motor  22  is operated at a substantially lower speed (for example at a tenth or a twentieth of the mixing speed) if the motor  15  is not loaded in the advance mode. In reverse mode, the drive of the mixer is automatically stopped. 
   A sensor (not shown) is arranged in such a way that it responds when the advance stamps  11  reach their furthest advanced position, which corresponds to complete emptying of the cartridges  5 . If the sensor responds in this position, it causes the electronic unit  30  to reverse the direction of rotation of the motor  15  so that the stamps  11  are drawn back from the cartridges, and in a rapid movement, because they are not loaded at that time. A second sensor (not shown) ascertains when the stamps  11  have reached their completely retracted position shown in the figure. It then causes the motor  15  to stop. The withdrawal of the stamps  11  can also be triggered manually with the aid of a switch (not shown) if cartridges are to be changed before they are empty. 
   When the stamps  11  are retracted, the cartridges  5  can be changed. The motor  15  is started up again automatically after the insertion of the new cartridges or by manual means. Since the stamps  11  are at first not loaded, they advance in a rapid movement until they reach the plungers of the cartridges  5 . The current consumption then increases and the electronic unit  30  switches the motor  15  to its low rotational speed, which is to be kept constant. 
   When the stamps  11  are retracted, the projection  24  of the mixer drive shaft  23  is also preferably retracted so that the mixer nozzle  10  can be easily changed. When the advance movement of the stamps  11  commences after the cartridges have been changed, the motor  22  is also started up again, initially at a low speed as long as the electronic unit  30  does not detect any load state. The shaft projection  24  of the mixer drive shaft  23  then has sufficient time to find the appropriate engagement position in relation to the coupling part of the mixer shaft and, as a result of the spring pressure loading it, to mesh into the coupling position. Only when the stamps  11  have reached the plungers of the cartridges  5  and the electronic unit  30  accordingly detects the load state is the motor  22  accelerated to the high speed of rotation which corresponds to the mixer mode. At the end of an application, the advance is stopped by pressing a button, and in this way a slight return movement of the motor  15  is triggered at the same time, which relieves the load on the system. 
     FIG. 2  shows an apparatus which is fitted according to the invention with sensors. A relatively large number of sensors is shown here, but this does not mean that all sensors must always be present. Simply for the sake of clarity, these sensors are shown in a single drawing. The details of the sensor arrangements indicated at III to VIII are shown on a larger scale in  FIGS. 3  to  8 . A crucial feature, however, is the central electronic unit  30  in which data concerning the pressing-out behaviour of known components are stored and which compares these stored data with measured data, and if appropriate also carries out calculations to take account of various parameters and then regulates the speed of the advance motor and/or of the mixer motor in a favourable manner. 
     FIG. 3  shows a thermocouple  31  which is applied on the outer wall of the mixer nozzle  10  and measures the temperature of the multi-component compound. 
     FIG. 4  shows a tachometer disc  32  with slits and a light barrier  33  with which the speed of rotation of the advance motor  15  is measured. Also shown is a torque measurement cell  37  for measuring the drive moment applied by the advance motor  15 . 
     FIG. 5  shows a strain gauge  34  which extends radially about the cartridge  5  in order to measure the deformation of the cartridge in the circumferential direction. 
   In  FIG. 6 , the strain gauge  34  is applied in the axial direction in order to measure the expansion in this direction. 
     FIG. 7  shows pressure measurement cells  35  which measure the pressure with which the stamps  11  are acted upon via the stamp rods  12 . In the lower part of  FIG. 7 , a view is shown from the side parallel to the plane of the drawing of the upper part of FIG.  7 . 
   Finally,  FIG. 8  shows a measurement cell  36  with which the torque of the mixer drive shaft  23  is measured. 
   The measurement sensors in  FIGS. 3  to  8 , insofar as they are provided, are connected in a manner not shown to the central electronic unit  30  in order to deliver signals concerning the pressing-out behaviour to the unit  30 , which then regulates the drive speeds of the motors  15  and  22 .