EP2335830B2 - Laboratory centrifuge with compressor cooler - Google Patents

Description

The present invention relates to a laboratory centrifuge according to the preamble of claim 1.

Laboratory centrifuges of this type are used in biological, chemical and medical laboratories for separating various components in a liquid or for separating solids from a liquid. For this purpose, the centrifugal force, which has different effects with different masses, is used.

In currently used laboratory centrifuges, rotation speeds of up to 16,000 revolutions per minute are usually generated, whereby forces of up to approx. 21 x 9.81 m / s ^{2 are} achieved. However, it has been shown that in such centrifuges no complete or no satisfactory separation of the sample liquid can be achieved. Centrifuges are currently being planned in which segregation is to be improved through higher rotation speeds of up to 25,000 revolutions per minute.

However, this is associated with a sharp increase in heating, since on the one hand the motor of the centrifuge's rotor emits heat. This heat can largely be kept away from the samples treated in the centrifuge by thermal insulation. On the other hand, however, heat also arises from the fact that rapid rotation takes place under the action of air resistance. The heating of the sample caused by this cannot be prevented without further ado, since a rotation in a vacuum is not possible with laboratory centrifuges for cost reasons.

Without appropriate countermeasures, the heat generated in this way causes the centrifuged samples to heat up strongly, which can easily lead to their destruction or uselessness. The samples usually have to be kept at defined temperatures, for example at temperatures of 4 ° C, 22 ° C or 37 ° C depending on the application.

In order to prevent the sample temperature from rising above these values, passive or active cooling devices are usually provided in the laboratory centrifuge, with compressors, namely reciprocating compressors, usually being used for the active cooling. Such cooling devices for laboratory centrifuges are out EP 1 196 247 B1 , DE 28 16 449 A1 , JP 56 017956 U known.

From the JPH 05228400 A a centrifuge with a rotary compressor is known.

The object of the present invention is to provide laboratory centrifuges which enable better separation, that is to say a higher separation rate, of the centrifuged samples.

This object is achieved with a laboratory centrifuge according to claim 1. Advantageous further developments of this laboratory centrifuge are specified in the dependent claims.

The inventors have surprisingly recognized that the demixing rates of the centrifuged samples can be increased by using rotary compressors for active cooling within the laboratory centrifuge.

This knowledge is based on the fact that it is not the centrifuge performance that is decisive for the demixing rate, but the backmixing rate brought about by the laboratory centrifuge.

Up to now, only reciprocating compressors have been used in the centrifuge compressor in laboratory centrifuges due to their relatively small design compared to their performance. In such reciprocating compressors there is a purely linear movement of the compressor body in the compressor chamber. Compressors that work according to such a compression principle are therefore also called linear compressors. Linear compressors have dead points in the movement of the compressor, which lead to strong oscillation of the when the compressor is started and stopped Lead compressor. These vibrations cannot be completely kept away from the rotator of the centrifuge, since in a laboratory centrifuge the compressor and the rotator are housed in a uniform housing.

The inventors have now recognized that these vibrations lead to the high backmixing rates of such laboratory centrifuges.

With the rotary piston compressors provided according to the invention, i.e. compressors in which the compressor is constructed in such a way that the compressor body also executes at least a rotational movement in the compressor chamber, such vibrations can be significantly reduced because a rotational movement is always carried out inside the compressor, so that not in the the same extent as with linear compressors to overcome dead centers.

Such compressors are already known from refrigerator construction, but these devices have completely different specifications than laboratory centrifuges. Firstly, laboratory centrifuges are very small compared to refrigerators, which means that all components have to be accommodated in a very limited installation space: In addition, laboratory centrifuges with the very fast moving rotor have a moving part which, despite this limited installation space, must be able to be operated as unaffected by other components as possible . Secondly, laboratory centrifuges have to cover a very wide temperature spectrum, and frequent temperature changes with high lowering speeds have to be implemented.

In addition, rotary compressors are only now available which, with the same dimensions, allow at least the same compression power as a reciprocating compressor, so that the dimensions of the laboratory centrifuge do not increase when they are used.

The starting currents can also advantageously be reduced with the specified rotary piston compressors. So far, certain laboratory centrifuges have been allowed in some Countries such as the USA are not sold due to the 110 V alternating current voltage network used there, as the current peaks generated by powerful reciprocating compressors when starting up would endanger the stability of the electricity networks commonly used in these countries. Alternatively, certain controls had to be provided in the laboratory centrifuges, which ensure that the compressor is only activated in such a way that the starting currents do not exceed the legally required values. With the rotary piston compressors provided according to the invention, such controls can be dispensed with, so that the laboratory centrifuges are simply constructed and therefore more robust and cost-effective and their sale is also permitted in these countries.

In a further preferred embodiment, the rotary piston compressor is an electrically driven compressor (direct and / or alternating current). Such compressors can be built very compact and high-torque and their control is i.a. possible via a regulated switched-mode power supply or frequency converter independent of the mains voltage. In addition, such compressors also make it easier to achieve smaller performance levels.

According to the invention it is provided that at least two compressors are arranged in parallel. Thus, the compressors can be designed to be smaller and with less power overall, so that the installation space that can be used in a laboratory centrifuge can be used more effectively, as a result of which the overall volume required for such a laboratory centrifuge is reduced.

The laboratory centrifuge according to the invention can be designed particularly advantageously as a bench-top laboratory centrifuge and microliter centrifuge and the like, since a very compact design is particularly important in these types of centrifuge.

It is particularly advantageous if the laboratory centrifuge has a backmixing rate of less than or equal to 20%, preferably less than or equal to 17%, in particular less than or equal to 14%. Then the segregation rate is particularly high.

Fig. 1

eine nicht beanspruchte Laborzentrifuge und

Fig. 2

eine Laborzentrifuge des Standes der Technik.

The characteristics and further advantages of the present invention will now be described with reference to a preferred embodiment. Show:

Fig. 1

an unclaimed laboratory centrifuge and

Fig. 2

a prior art laboratory centrifuge.

In Fig. 1 a laboratory centrifuge 1 which is not claimed is shown purely schematically. This laboratory centrifuge 1 has a housing 2 and a centrifuge lid 3. The centrifuge lid 3 is designed to close a centrifuge container 4 in which a rotor 5 is arranged. The rotor 5 can be driven by a motor (not shown), as a result of which samples (not shown) arranged on the rotor 5 can be centrifuged in order to separate them.

To cool the samples, the laboratory centrifuge 1 has an active cooling device which comprises a compressor 6. The compressor 6 is designed as a rotary compressor and has a rotary piston compressor. In the area of the compressor 6, the top of the housing 2 is not shown.

This compressor 6 is very compact and high-torque and its regulation is possible via a regulated switched-mode power supply independent of the mains voltage. With the help of this compressor 6, smaller power gradations of the cooling power can also be easily made possible.

In Figure 2 a laboratory centrifuge 10 is shown purely schematically, as it is the prior art. This laboratory centrifuge 10 differs from the laboratory centrifuge 1 in that a compressor 11 with a reciprocating piston compressor is used as the compressor 11. All other parts are therefore provided with the same reference numerals as in the laboratory centrifuge 1.

From the comparison of the laboratory centrifuge 1 with the known laboratory centrifuge it becomes clear that with modern rotary compressors 6 less installation space is required in the housing 2 with the same output. In this way, either the housing 2 can be made smaller, or the cooling capacity can be increased by installing several compressors 6 in parallel.

A comparative test of the backmixing rates of the laboratory centrifuge 1 in comparison to the conventional laboratory centrifuge 10 with a reciprocating compressor will now be described below. A laboratory centrifuge 1 with the XB357 rotary piston compressor from Mitsubishi was used, and the rotor F-45-24-11 from Eppendorf was used as the rotor 5. For the comparative investigation, the centrifuge 5415 R from Eppendorf (type SN 5426 0023218) was used as laboratory centrifuge 10, which had a reciprocating compressor PL50 from Danfoss and the same rotor F-45-24-11 was used as rotor 5. For pipetting, the Eppendorf Reference 500 - 2500 µl pipette (model SN 475116) and the Eppendorf Research pipette per 5 - 100 µl (model SN 022760) were used. In addition, an Eppendorf biophotometer (type SN 6131 00197) was used.

The samples were placed in 2.0 ml Safe-Lock vessels (model U123342P 2243) and a 10 mM Tris solution and a salt concentrate color solution with a density of 1.2 g / ml were used to prepare the samples. In each case, 1450 μl of Tris solution were pipetted into a 2.0 ml Safe-Lock vessel with the Eppendorf Reference pipette. With the Eppendorf Research pro pipette, 50 μl of the salt concentrate color solution were then placed under the layer, the pipette being set to the lowest aspiration and dilution level.

In this way, four samples each were generated for laboratory centrifuge 1 and laboratory centrifuge 10, which were then centrifuged at 13,200 revolutions per minute and 4 ° C. for 5 minutes.

For a positive control, four 2.0 ml Safe-Lock vessels were also filled in the same way and vigorously mixed immediately. For the negative control, another four 2.0 ml Safe-Lock vessels were filled in the same way, although these samples were not centrifuged or mixed, but were incubated for 5 minutes at room temperature.

After the five-minute centrifugation or diffusion in the vessels for the positive and negative control had ended, the 50 μl layered salt concentrate color solution were removed from the vessels with the Eppendorf Research pipette. The vessels were then closed again and vigorously mixed. The liquid contained in the vessels was then transferred to a cuvette and measured photometrically at an extinction of 562 nm.
The values obtained with the vessels of the positive control serve as maximum values (100% value) and the values obtained with the negative control serve as background (diffusion).

The backmixing rate was then calculated from the following formula: $$\mathrm{Backmix\; rate}=\left(\mathrm{centrifuged}\mathrm{value}-\mathrm{Diffusion\; value}\right)\times 100/100\%-\mathrm{value}.$$

The results obtained are shown in the table below, the right column shows the mean values calculated from the four samples used. With regard to diffusion, the value in brackets was not used as it was considered an outlier. On the basis of the mean values determined, a backmixing rate of 13.44% was determined for the laboratory centrifuge 1, while the backmixing rate of the conventional laboratory centrifuge 10 was 28.26%. With the laboratory centrifuge 1, the backmixing rate could be reduced by around 15% absolute or even by more than 55% in relative terms. <u> Table: </u> Laboratory centrifuge 1 Laboratory centrifuge 10 Mean values diffusion (0.179%) 0.064% 0.092% 0.046% 0.055% centrifuged value 0.145% 0.141% 0.121% 0.138% 0.161% centrifuged value 0.248 0.228% 0.244 0.197 0.222 100% value 0.570% 0.573% 0.584% 0.576% 0.560%

It has become clear from the present description that the laboratory centrifuge 1 can ensure significantly better demixing rates for centrifuged samples, since the provision according to the invention of at least one rotary compressor 6 means that significantly fewer vibrations are introduced into the laboratory centrifuge 1, resulting in significantly lower backmixing rates.

Claims (4)

1. A laboratory centrifuge (1) comprising a rotor (5) driven by a centrifuge motor; and a cooling device including a compressor (6), wherein the compressor is a rotary compressor (6), characterized in that the rotary compressor includes a rotating piston compressor, wherein at least two compressors are arranged in parallel.
2. The laboratory centrifuge (1) according to claim 1, characterized in that the rotary compressor is a compressor (6) that is electrically driven, in particular by direct voltage and/or alternating voltage.
3. The laboratory centrifuge (1) according to one of the preceding claims, characterized in that the laboratory centrifuge is a laboratory table centrifuge (1), a micro liter centrifuge or similar.
4. The laboratory centrifuge (1) according to one of the preceding claims, characterized in that a remix rate is less than or equal to 20%, preferably less than or equal to 17%, particularly preferably less than or equal to 14%.

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