Temperature Controlled Centrifuge

Abstract

Peltier effect thermoelectric devices are mounted in a rotatable centrifuge head. Thermal conduction paths are attached between the thermoelectric devices and a position adjacent to the specimen being rotated in the centrifuge. A temperature-controlled device responds to the difference between a preselected temperature and the temperature of the specimen for maintaining the fluid at the preselected temperature.

Description

BACKGROUND OF THE INVENTION

1.

This invention pertains to centrifuges, and more particularly, to centrifuges having means for controlling the temperature of the specimen in the centrifuge by temperature control means mounted on the rotating head of the centrifuge.

2. Brief Description of the Prior Art

Centrifuges have become a familiar laboratory tool in many fields of scientific and medical research. It is frequently desirable in work in these areas to centrifuge a specimen while maintaining the specimen at a preselected temperature. The desired centrifuge temperature may either be above or below the ambient room temperature in which the centrifuge operation is to be performed.

There have been many devices that attempt to heat or cool the fluid that is being centrifuged. The most common of these devices is an enclosure around the entire centrifuge, the enclosure being either a refrigerator or an oven which may be temperature controlled. The oven or refrigerator is heated or cooled to the desired temperature. A centrifuge containing the fluid being centrifuged is placed in the temperature controlled enclosure and the entire centrifuge maintained at that temperature during the centrifuge operation.

There are several drawbacks to the total enclosure approach to solving the temperature problem. An excess amount of heating or cooling is required since the entire centrifuge is ether heated or cooled. In addition Such an over or refrigerator is quite bulky because the entire centrifuge must be enclosed. Also due to the increased size and weight of such device, the cost of the device increases. Still further the structural and quality control requirements on a centrifuge that is to be entirely enclosed in a hostile cold or hot atmosphere must be improved. Increased quality control leads in turn to increased costs of manufacture. Still further, precise temperature control is not achieved, if at all, without large temperature transients involving greatly extended times to perform the centrifuge operation. Also, friction of the rotating head in the environment, time to stabilize and initial values all contribute to errors in estimating sample temperature.

One of the reasons for using the completely enclosed refrigerated centrifuge is to avoid the problem of transporting a refrigerant to and from the rotatable head of the centrifuge. Naturally cooling coils cannot be attached directly to the rotating head of the centrifuge without some sort of elaborate coupling that would allow for the flow of refrigerant to and from the head of the centrifuge. Rather than attempt to solve this very difficult problem, most experimentors have followed the enclosed refrigerated space approach.

An invention of interest in this area is "Refrigerated Centrifuge" by W. E. Waye et al. U.S. Pat. No. 3,444,695. Waye's device has a rotor mounted inside a housing. Thermoelectric devices are spaced around the housing as well as having refrigerant coolant flowing through these thermoelectric devices. In the device of Waye neither the thermoelectric devices nor the refrigerant tubes are mounted on any rotating components of the device. It is obviously impossible in the device of Waye and similar devices to have the heat transfer devices in approximate relationship to large portions of the specimen under centrifuge.

SUMMARY OF THE INVENTION

Peltier effect thermoelectric devices are mounted in the rotating head of a centrifuge. Depending upon the particular application any number of thermoelectric devices may be mounted in the rotating head. Heat conduction means are attached between the thermoelectric devices and an area adjacent insulated fluid spaces of the centrifuge head. The heat conduction means serves as a heat path for the transfer of heat to and from the thermoelectric devices and the fluid under centrifuge.

Temperature control means are provided for maintaining the temperature of the fluid under centrifuge at a preselected temperature. If the preselected temperature is below ambient the fluid under centrifuge is cooled and if the desired temperature is above ambient the fluid under centrifuge is heated. The temperature control means is coupled from the rotating head of the centrifuge to stationary portions of the centrifuge such that switching and other logic network need not be rotated with the rotating head of the centrifuge.

It is therefore an object of this invention to provide an improved centrifuge.

It is another object of this invention to provide an improved centrifuge having compact means for heating and cooling the specimen under centrifuge.

It is another object of this invention to provide an improved centrifuge wherein the heating and cooling means are mounted on the rotating head of said centrifuge.

It is a still further object of this invention to provide an improved centrifuge wherein the heating and cooling means comprises Peltier effect thermoelectric devices.

It is yet another object of this invention to provide a centrifuge wherein the specimen under centrifuge may be maintained at a hot or cold temperature through temperature controlled means coupled from the rotating components of the centrifuge to stationary components of the centrifuge. A still further object of this invention is to provide a centrifuge that may be maintained at a preselected temperature wherein elaborate coupling between refrigerating means and the rotating part of the centrifuge is eliminated.

These and other objects of this invention will become more apparent in connection with the following drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial cutaway and schematic of the general embodiment of a temperature control centrifuge of the present invention.

FIG. 2 is a cross-sectional view of the temperature controlled centrifuge head having specimen cavities integral with the centrifuge head.

FIG. 3 is a temperature control centrifuge having removable containers for the specimen being centrifuged.

FIG. 4 is an exploded view of an electrical contact between the centrifuge container shown in FIG. 3 and the container support arms in a centrifuge having removable containers.

FIG. 5 is an electrical circuit schematic of the wiring between a Peltier effect thermoelectric device and associated heating and cooling circuits.

FIG. 6 is a schematic representation of a second embodiment circuit for obtaining proper current orientation for use by the Peltier effect thermoelectric device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a centrifuge head 10 on rotatable shaft 12 which is driven by motor 20. The centrifuge head 10 includes a plurality of cavities 11 for holding vials of specimens to be rotated, or centrifuged. Peltier effect thermoelectric device 80 is mounted on thermal sink 19 inside the centrifuge head 10. Thermal sink 19 is integral with the centrifuge head 10 to provide good thermal contact between the Peltier effect thermoelectric device 80 and the thermal sink 19. The centrifuge head 10 and shaft 12 are the rotatable components of the centrifuge. In one embodiment line 30 from the centrifuge head 10 is capacitively coupled to the centrifuge head 10 through concentric ring (see FIG. 2). A signal representing the temperature of the specimen being rotated on line 30 is generated by a sensor (see FIG. 2) that monitors the temperature of the fluid being rotated. The signal provides fluid temperature information to temperature comparator circuit 60.

Temperature comparator 60 compares the temperature of the specimen under centrifuge with a preselected temperature. A signal representing the preselected temperature is received on line 32. The output of temperature comparator 60 provides an input to temperature control 40.

If the temperature of the element, or specimens, under centrifuge exceeds the preselected desired temperature an output signal from temperature control 40 increases the heat absorbing capacity of Peltier effect thermoelectric device 80 causing the fluid temperature to decrease to the preselected temperature value. Conversely if the temperature of the fluid under centrifuge is below the preselected temperature an output signal on line 31 increases the heat producing capacity of device 80 causing the fluid temperature to increase to the preselected value. The output signal from the temperature control 40 controls the current through the thermoelectric device for regulating its cooling capacity. Details, on mean for coupling temperature and control signals to and from the centrifuge head, are described in detail subsequently.

FIG. 2 is a cross-sectional view of an integral head embodiment of a temperature-controlled centrifuge. The centrifuge head 10 mate with the end of shaft 12 such that as shaft 12 rotates the centrifuge head 10 likewise rotates. The centrifuge head 10 is preferably interchangeable with other centrifuge shafts to provide each of use and cleaning. FIG. 3 embodiment is one example of an alternate removable container type of head suitable for use with shaft 12.

The centrifuge head 10 of FIG. 2 defines cavities 11 that are suitable for holding a test tube or vial containing a fluid to be centrifuged. Surrounding the cavities 11 is a layer of metal, substance or other material 81, for instance copper, with good thermal conductivity properties. The good thermal conductivity material 81 of the cavities i connected to a central thermally conducting bus strip 181. Thus all the cavities are in thermal communication.

The cavities 11 are so configured that a test tube or other vial slip snugly inside a cavity. As a result possible damage to the vial or test tube is reduced during the centrifuge operation. The snug fit also provides good contact between the walls of the vial or test tube and the thermally conducting material. Good thermal transfer between the cavity walls and the vial or test tube containing the specimen under centrifuge enables better temperature control of the fluid.

Surrounding the thermal conducting material is a layer of insulation material 15. The insulation material insures minimum heat loss between the thermal conducting material and the centrifuge head 10.

Temperature sensing means 70, such as a thermistor, are located adjacent to each cavity in the thermal conducting layer 181. The temperature-sensing means may, of course, be implemented by other configurations. For example, a thermistor may be maintained in one of the cavities such that the temperature of that cavity can be used to regulate the temperature of the other cavities. However, the use of fewer thermistors, provides relatively less precise control of temperature variations that might occur between the separate cavities.

The output from the temperature sensing means 70 is coupled to converter 71 where it is converted into a signal that is suitable for coupling to the temperature comparator 60. The conventional thermistor, for instance, operates on a change of resistance principle but resistance cannot be capacitively coupled through a rotating member and thus a parameter conversion is required. For example, the converter 71 changes the resistance variations, whether manifested as a voltage or current change, into a capacitance or frequency change, or other measurable parameter that can be coupled through rings such as 73 and 74. In one embodiment, the temperature variations sensed by the thermistor may be converted into a signal having a variable amplitude. This signal could then be capacitively coupled to temperature control 60. If slip rings or other direct contact devices between rotating and nonrotating members are used, the converter may not be necessary.

Capacitive coupling devices 73 is electrically connected to converter 71 and is mounted to the rotating centrifuge head 10. Capacitive coupling ring 74 is mounted to field piece 45 that is mounted on nonrotating components of the centrifuge. Capacitive coupling ring 74 is connected to temperature comparator 60 via line 30 (see FIG. 1). It is pointed out that the temperature control 40 of FIG. 1 is represented by elements designated by numerals 41, 42, 51, 52, 70, 71, 73, 74, in FIG. 2.

In the embodiment of FIG. 2, to generator couplings are provided. Each of armatures 42 and 52 are connected to rectifying and steering diode for the Peltier effect thermoelectric device 80. The diodes of FIG. 2 are illustrative of proper current direction requirements. The Peltier effect thermoelectric device 80 (T.E.D.) is fixedly mounted on the rotating centrifuge head 10 to make good thermal contact with thermal sink 19. Armature 42 is inductively coupled to field coil 41 which for convenience has been selected as the heating field coil. When current is flowing in field coil 41 a current is inductively induced in winding 42 and the induced current direction is such that the thermoelectric device is a heat source.

The use of field and armature notation is convenient in the embodiment of FIG. 2 since the rotating head is readily available. Other electrical coupling schemes are applicable to such a device including AC coupling, direct motor coupling and transformer coupling. When field coil 51 is energized and inductively coupled to winding 52 with current flow through the Peltier effect thermoelectric device 80 is such that the Peltier effect thermoelectric device serves as a heat sink. Thermal energy is thus taken from the thermal specimen under centrifuge by the Peltier effect thermoelectric device 80.

Current flows in the heating or cooling coil circuits as a function of the difference between the measured temperature of the specimen being rotated and a preselected temperature. Switching between the heating and cooling coils is determined by temperature comparator 60. If the temperature of the specimen under centrifuge exceeds the temperature that is desired a signal is generated by temperature comparator 60 to energize the cooling coils of the temperature control 40 (FIG. l) such that the Peltier effect thermoelectric device 80 serves as a heat sink. Conversely, if the temperature of the specimen under centrifuge is below the preselected desired temperature, then the temperature comparator 60 energizes the heating coils and the Peltier effect thermoelectric device 80 acts as a heat source. In the prepared embodiment comparator circuit 60 is not mounted on the rotating components of the centrifuge.

Temperature comparator 60 can be a simple bipolar relay that is responsive to the difference between the preselected temperature and the sensed specimen temperature. A proportional amplifier could be incorporated to provide proportional current regulation to the Peltier effect thermoelectric device. The proportional current regulation would reduce the current to the Peltier effect thermoelectric device as the difference between the preselected temperature and the sensed specimen temperature decreased. The range of accuracy achieved in temperature control is practically limited by self-imposed expense and design limitations and the controls may be as simple or sophisticated as desired.

The radiator vanes 85 are mounted to the thermoelectric device to facilitate the rapid removal of heat by convective airflow from the Peltier effect thermoelectric device when the device is acting as a heat sink.

Various types of coupling devices and circuits may be used to transmit the temperature data contained in the centrifuge head to nonrotating members of the centrifuge. The embodiments shown feature inductively coupled field coils as well as capacitively coupled rings. An alternate embodiment might use slip rings and sliding communication for direct contact. Yet another embodiment might involve locating substantially all of the components on the centrifuge head or in the rotating shaft and having only a single power output supply coupling between the shaft and nonrotating members. Also a completely self-contained power unit could be located on or in the rotating members and no coupling to nonrotating components would be required at all.

FIG. 3 is an embodiment of the invention as applicable to a removable container type centrifuge. In a container type centrifuge individual containers 90 are supported by arms extending from the centrifuge head 100. The individual container may be easily removed for cleaning and for changing the specimen under centrifuge. This embodiment is desirable for many applications where the integral head centrifuge of FIG. 2 is not applicable.

The container 90 includes a cavity 93. Surrounding cavity 93 is material 94 that has good thermal conductivity characteristics. The material of layer 94 is configured around the cavity 93 so as to provide good thermal contact between the material 94 and the specimen under centrifuge. Surrounding the thermal conductive material 94 is a layer of insulating material 95. The container structure 96 surrounds the insulating material. Material 96 may be any material that is suitable for containers for centrifuge application.

A Peltier effect thermoelectric device (T.E.D.) 91 is mounted on the bottom of the container in good thermal contact with the thermal conducting material 94. The thermal conducting material 94 provides a heat path between the specimen under centrifuge, and the thermoelectric device 91. The thermoelectric device 91 extends through the insulation layer 95 to the adjacent container material 96 where radiating fins 99 assist in heat transfer from the thermoelectric device to the surrounding atmosphere.

Electrical contact 98a is mounted on the curve surface of support arm 181 and electrical contact 98 is mounted on support pin 180 of container 90. These contacts and contacts similarly mounted on the hidden arm and pin are shown more clearly in FIG. 4.

Electrical conductors 191, 192, 193 and 194 lead from the Peltier effect thermoelectric device to the circular contacts mounted on the container 90, support pins 170 (shown in FIG. 4) and 180. In FIG. 3 two of the conductors 191, 192, 193 or 194 would be connected to circular contacts on the support pin that is not shown by FIG. 3, i.e. the support pin 170 (shown in FIG. 4).

The electrical scheme for coupling the temperature-sensing outputs and power for the thermoelectric device of FIG. 3 is the same as described for FIG. 2. Similarly, a thermistor or other temperature-sensing means 140 can be mounted on the centrifuge container for monitoring the temperature of the fluid under centrifuge. In a manner as described for FIG. 2 the temperature-sensing means is utilized by the temperature control circuit for maintaining the desired temperature of the fluid under centrifuge.

Thermistor or other temperature-sensing means 140 is electrically coupled by conductors 141 and 142 to circular contacts 143 and 144 located on support pin 180 (shown in FIG. 4) of the centrifuge container.

Any number of containers may be mounted on a single centrifuge head depending only on the capacity of the centrifuge head. In FIG. 2 it was indicated that either one temperature-sensing means or a variety of temperature-sensing means may be used for determining the temperature of the specimen under centrifuge. If several temperature sensing means are used, the average of the determined temperature of each means will serve as an input to the temperature comparator 60. A similar situation also exists with respect to FIG. 3. That is to say only one container may have a temperature-sensing means circuit or a plurality of containers may have temperature-sensing means circuits.

FIG. 4 shows an exploded view of the contact relationship between the centrifuge containers and the centrifuge support arm. Container 90 has pins 170 and 180 extending therefrom. Contacts 104 and 204 are mounted on the circular surface of support pin 170 and contacts 142, 143, 144 and 98 are mounted on support pin 180. Contacts 104 and 204, along with 98 and 144 are electrically coupled to alternate sides of a Peltier effect thermoelectric device. These contacts provide electrical connection between the container (and the Peltier type thermoelectric device mounted thereon) and control circuits that are inductively coupled to the nonrotating members of the centrifuge. Contacts 142 and 143 are also mounted on support pin 180 and serve as electrical contacts for the temperature-sensing circuit. The thermistor circuit may be completely mounted on either support pin 170 or 180 or one contact on each support pin as preferred. In fact the electrical contacts scheme shown by FIGS. 3 and 4 is but one embodiment of many possible embodiments that might be used to electrically connect the Peltier effect thermoelectric device to associated control circuits.

Support arms 171 and 181 of centrifuge head 100 support container 90 through contact with support pins 170 and 180. Electrical contacts 104a, 204a, 142a, 143a, 144a and 98a are mounted to the circular surface of support arms 171 and 181. These contacts cooperate with similar contacts on the support pins 170 and 180 of container 90.

As the centrifuge speed is increased the container 90 will tend to become oriented so that the cavity is in the plane of rotation. Thus the contacts mounted on the support pins 170 and 180 may not be in contact with the associated contacts on the support arms 171 and 181 when the container is at rest but will come in contact as the centrifuge container is brought up to speed. Of course these contacts might be in continuous contact depending on the size of contacts. Electrical leads 101, 102, 205, 147, 148, and 149 merely connect the respective contacts to the temperature control and switching circuits described in FIG. 2 and FIG. 3. Leads 101, 102, 149 and 205 are the heating and cooling circuit leads between the Peltier effect thermoelectric device and the armature coils. Leads 147 and 148 are temperature-sensing means leads between the temperature-sensing means and the coupling ring.

FIG. 5 shows one embodiment of an electrical arrangement for rectifying and directing current through a Peltier effect thermoelectric device to achieve either heating or cooling. Bridge circuit 110 encloses a Peltier effect thermoelectric device 111 (T.E.D.). The Peltier effect thermoelectric device might be any of the devices 80 or 91 described in FIG. 2 and FIG. 3. with current in the heating field and armature coils 41 and 42 respectively, half-wave rectified current through the thermoelectric device exists as indicated by arrow 300. With current in the cooling field and armature coils 51 nd 52 respectively full-wave rectified current in the Peltier effect thermoelectric device is as shown by arrow 301. The diodes of the circuit insure that current does not flow in unused legs of the bridge when the mutually exclusive heating or cooling coils are energized. It will be noted that FIG. 2 does not show all of the bridge circuit diode to avoid undue confusion of the figure.

FIG. 6 is a schematic representation of an embodiment of a centrifuge device using a single coil for coupling current in the proper direction through the Peltier effect thermoelectric device. In FIG. 6 only one set of generator coils is required for heating and cooling. The arrangement of the coils and the centrifuge head is generally as described in FIG. 2 with the exception that single field and armature coils 131 and 130 are provided. Windings 130 are integral with the rotating head 120 and the field 131 is mounted to the fixed field piece 45. The output of thermistor or other temperature-sensing means converter 71 is capacitively coupled through coupling 73 to nonrotating coupling 74 as described in FIG. 2.

Conductor 149 connects capacitive coupling ring 74 to temperature comparator and switching control 50. Temperature comparator and switching control 50 compares the input temperature signal with the preselected desired temperature and determines if the Peltier effect thermoelectric device should be commanded to heat or cool the fluid under centrifuge. A shaft position signal reactively generated by a pickup on coupling ring 74 is also fed to temperature comparator and switching control 50. Knowledge of the position of the armature on switching will insure proper phase relation in the Peltier effect thermoelectric device circuit since direction of rotation of the centrifuge will not be changed. Switching means 140 (shown as a mechanical configuration for simplicity) directs current in either direction through conducts 132 and 133. If current flowing through 132 to field 131 with return through 133 is the appropriate direction for causing the Peltier effect thermoelectric device to heat, then the switching circuit on the appropriate heating command would cause current to flow in that direction. If current from the switch 140 through conductor 133, field 131 conductor 132, respectively cause Peltier effect thermoelectric device to cool then the switch 140 would be so positioned on a command from the temperature comparator switch control 50 to cool the specimen under centrifuge.

Power supply 161 supplies current to the Peltier effect thermoelectric device or devices.

It should be pointed out that the switching schematic of FIG. 6 is but one embodiment of the wide variety of switching circuits that are available for applications as described herein.

Claims

I claim:

1. A centrifuge comprising:

a rotatable head including a plurality of cavities each configured for holding a vial to be centrifuged in good contact with the walls thereof, said walls of said cavities having good thermal conductivity and being thermally insulated from said rotatable head,

temperature-sensing means located in said walls of said cavities for sensing the temperature of the cavity,

thermoelectric means mounted to said rotatable head for regulating the temperature of each of said cavities,

thermal conduction means connecting said walls of said cavities to said thermoelectric means for effecting heat transfer therebetween, and

means responsive to said temperature-sensing means for controlling said thermoelectric means whereby the temperature of each of said cavities is maintained within a preselected range.

2. The combination recited in claim 1 further comprising,

means for comparing the difference between a predetermined temperature and the temperature of a predetermined cavity including means for generating a control signal as a function of said difference,

said thermoelectric means being responsive to said control signal for maintaining said temperature difference within a predetermined range.

3. A centrifuge comprising,

a rotatable head including a plurality of cavities with each of said cavities suitable for holding a vial containing a fluid to be centrifuged,

temperature-sensing means mounted adjacent to each of said cavities for sensing the temperature of each cavity,

thermoelectric means mounted to said rotatable head in thermal contact with each of said cavities and in electrical contact with said temperature-sensing means,

means responsive to the differences between a preselected temperature and the temperature of each of said cavities for controlling said thermoelectric means to effect heat transfer between each of said cavities and said thermoelectric means whereby the temperature of each of said cavities is maintained within a preselected range.

4. The centrifuge of claim further comprising first means for coupling current in the proper direction to said thermoelectric means from said means responsive to the differences between a preselected temperature and the temperature of each of said cavities of the centrifuge to cause said thermoelectric means to heat a specimen contained in said rotatable head and second coil means for coupling current in the proper direction to said thermoelectric device to cause said thermoelectric device to cool a specimen contained in said cavity, said heating and cooling of said cavities effected by heat transfer in heat conduction means attached between each thermoelectric device and an associated cavity.

5. The centrifuge of claim 3 further comprising field coil and armature coil means for coupling current to said thermoelectric means from said means for controlling said thermoelectric means, to cause said thermoelectric device to regulate the temperature of the specimen under centrifuge.

6. The centrifuge of claim 3 wherein said rotatable head is a removable container-type centrifuge head wherein a plurality of removable containers containing said cavities are supported by arms extending from said head.

7. The centrifuge of claim 3 wherein said means for controlling said thermoelectric means is capacitively coupled to a conditioned response from said temperature-sensing means.

8. A centrifuge comprising,

A rotatable head including supports for a plurality of container means, each of said container means rotatably engaged in said supports and including a cavity suitable for holding material to be centrifuged, said cavity thermally isolated from said head,

thermoelectric means mounted to each of said container means for regulating the temperature of said material in said container means,

temperature-sensing means mounted in said container for sensing the temperature of said material in said container, and

temperature control means responsive to the temperature difference between a preselected temperature and the temperature of said material under centrifuge for controlling said thermoelectric means.

9. The centrifuge of claim 8 wherein heat conduction means providing a path for heat transfer therebetween connect said thermoelectric means with the inside of said container means.

10. The centrifuge of claim 8 wherein said temperature control means is mounted to a nonrotating member of said centrifuge, a first output of said temperature control means being inductively coupled to said thermoelectric mean and a second output of said temperature control means being capacitively coupled to a conditioned output of said temperature-sensing means.

11. A method for controlling the temperature of a specimen being rotated by a centrifuge, said method consisting of the steps of,

placing the specimen in a container attached to but thermally isolated from a rotatable head of said centrifuge;

providing thermal paths in said contain adjacent the specimen under centrifuge;

sensing the temperature of said specimen;

causing the flow of thermal energy in said thermal paths; and

regulating said flow of thermal energy to maintain the specimen under centrifuge within a preselected temperature range.