Abstract:
A laboratory microplate incubator ( 10 ) including a housing ( 12 ) having a specially-sized, enclosed incubation chamber ( 24 ) therein and a temperature control assembly ( 14 ) that uniformly maintains the temperature within the incubator in a desired range. The temperature control assembly includes a heater ( 34 ) positioned within the housing for heating the chamber, a temperature sensor ( 38 ) and a controller ( 36 ). Multiple incubation chambers can be electrically controlled by the temperature control assembly in a master incubator. Multiple incubation chambers can be stacked to conserve laboratory space. An externally fillable water reservoir is provided inside the chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to laboratory incubators, and more particularly, to a very small, inexpensive incubator having improved temperature stability, uniformity and temperature recovery response. 
     2. Description of the Prior Art 
     The temperature within a laboratory incubator must be maintained within a certain operating temperature range for specimen treatment and evaluation. Therefore, it is common to provide laboratory incubators with heating devices that are periodically cycled to maintain the interior temperature of the incubators in this range. Temperature control must be very precise, with less than 0.5° C. variation desired in order to provide accurate, repeatable results. 
     Such stable temperature control is difficult to obtain with prior art incubators because they are typically large and hold numerous specimens. This presents a problem because the internal temperature of a large incubator varies from location to location within the incubator. In large incubators, temperature uniformity is poor, with actual individual sample exposure temperatures varying as much as 0.75° C. between specimens in some incubators. Furthermore, when multiple specimens are placed in a large incubator, all the specimens are exposed to temperature variations each time the incubator is opened for access to any specimen. Further, large incubators are not energy efficient when one, or a small number of specimens must be incubated. And, of course, large incubators consume excessive laboratory space. 
     Accordingly, there is a need for an improved incubator that overcomes the limitations of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above-described problems and provides a distinct advance in the art of microplate incubators. More particularly, the present invention provides an improved incubator that offers superior temperature uniformity and stability with a simple construction that reduces individual unit cost and allows for the efficient use of available space. 
     The incubator of the present invention broadly includes a housing having an enclosed incubation chamber therein; a heater positioned within the housing for heating the chamber; and a controller for regulating the operation of the heater to maintain the chamber at a desired temperature. 
     The incubator is optimally sized to hold a single standard microplate sample, providing less than 0.02 cubic feet of internal space. Such constrained size ensures the microplate sample is always in near proximity to the heater. The primary thermal path from the heater to the microplate is conductive and therefore more stable and uniform than the convection thermal path experienced by microplate samples in large incubators. The optimal sizing and conductive heat path also provide for improved temperature control when the chamber is accessed because less cooler ambient air can be admitted into the chamber. 
     In operation, the controller cycles the heater whenever the internal temperature is lower than the set operating temperature of the incubator, thus maintaining the operating temperature of the incubator within a desired range. The construction of the present invention provides improved temperature uniformity and temperature stability by shortening the thermal path between the heater and the specimen, reducing the distance between the heater and the temperature sensor and facilitating the operators&#39; ability to minimize access. The present invention more consistently and uniformly maintains the contained specimen microplate at the set temperature rather than, as in prior art incubators, allowing specimen microplate temperature to suffer temperature fluctuations based on random position and temperature variations within the incubator. 
     The incubator is configured to allow multiple incubators to be stacked vertically so as to provide efficient utilization of laboratory space. This allows laboratory personnel to establish multiple temperature controlled environments in a compact space. 
     The incubator also preferably includes an internal water reservoir that can be used to maintain a high humidity environment, reducing evaporation from the microplate sample. The operator can fill or replenish the reservoir externally. 
     A preferred embodiment of the invention couples a plurality of incubators together wherein secondary microplate incubator units may be electrically linked to a master incubator. The secondary microplate incubator units are simplified and less expensive because the temperature controller and sensor are not required. All units are maintained at the desired temperature based on the controller and sensor in the master incubator. A single control for multiple incubators also simplifies operation. 
     These and other important aspects of the present invention are described more fully in the detailed description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     A preferred embodiment of the present invention is described in detail below with reference to the attached drawing figures, wherein: 
     FIG. 1 is a perspective view of a microplate incubator constructed in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a vertical sectional view of a microplate incubator constructed in accordance with a preferred embodiment of the present invention; 
     FIG. 3 is a schematic diagram of the temperature control assembly of the incubator in accordance with a preferred embodiment of the present invention; 
     FIG. 4 is a perspective view of a microplate incubator constructed in accordance with an alternative embodiment of the present invention; and 
     FIG. 5 is a schematic diagram of the temperature control assembly of the incubator in accordance with an alternative embodiment of the present invention. 
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawing figures, a laboratory incubator  10  constructed in accordance with a preferred embodiment of the invention is illustrated. The incubator includes a housing  12  and a temperature control assembly broadly referred to by the numeral  14 . 
     In more detail, the housing  12  includes spaced-apart outer walls  16 , inner walls  18  and a door  20 . The outer walls  16 , inner walls  18  and door  20  are preferably formed of stainless steel, but may be manufacture from other suitable materials such as aluminum or high temperature plastic as a matter of design choice. The outer walls  16  illustrated in FIG. 1 are specially configured to allow multiple incubators to be safely stacked vertically, while allowing access to each incubator. 
     More specifically, the inner walls  18  define an incubation chamber  24  therein and include a bottom inner wall  22  which supports a microplate. The chamber  24  is specially sized to hold only one microplate, having an internal volume of less than 0.02 cubic feet. The small volume of the incubator ensures improved temperature uniformity by positioning the microplate a consistent, shortened spacing from the inner walls  18 . Thermal insulation  26  is present between the outer walls  16  and the inner walls  18 . 
     As seen in FIG. 1, the door  20  includes an inner door wall  28  and an outer door wall  30 . In the preferred embodiment, a water reservoir  32  is provided in the inner door wall  28 , which can be filled through the outer door wall  30 . Thermal insulation (not shown) is also present between the inner door wall  28  and the outer door wall  30 . 
     The temperature control assembly  14  is operatively coupled with the housing  12  to control the temperature within the chamber  24  so that the temperature remains within a desired range. For example, in one application, the control assembly  14  maintains the temperature within the chamber  24  at approximately 42° C.±0.4° C. As best illustrated in FIG. 3, the temperature control assembly  14  includes a heater  34 , a controller  36  and a temperature sensor  38 . The proximity of the temperature sensor  38  to the heater  34 , in combination with the constrained volume of the chamber  24 , enables the temperature control assembly  14  to maintain a uniform temperature within 0.2° C. within the chamber  24 . 
     The heater  34  is positioned between the outer walls  16  and the inner walls  18  of the housing  12  and is operable for heating the incubation chamber  24  when the internal temperature in the incubator  10  is below the incubator&#39;s desired operating temperature. The heater  34  may be any conventional heating device, but preferably includes a low watt density, high surface area, contact resistive heater. Thermal insulation  26  is present between the heater  34  and the outer walls  16 , but not between the heater  34  and the innerwalls  18 . In the preferred embodiment the heater is bonded with the bottom inner wall  22 . 
     The controller  36  directs electrical power from a power supply (not shown) to cycle the heater  34 . The controller  36  may be any conventional programmable microprocessor device. The controller  36  allows the operator to adjust thermal conditions in the chamber  24 . 
     As illustrated in FIG. 2, the temperature sensor  38  is mounted within the housing  12  for monitoring the temperature within the incubation chamber  24 . More specifically, the temperature sensor  38  is preferably positioned inside the inner walls  18  of the housing  12  so that it monitors the temperature within the incubation chamber  24 . Alternatively, the temperature sensor  38  may be in contact with the bottom inner wall  22  so as to detect inner wall temperature. As illustrated in FIG. 3, the temperature sensor  38  is coupled with the controller  36  for delivering signals representative of the sensed temperature thereto. 
     In operation, an operator preferably establishes the desired temperature of the incubator  10  prior to the insertion of the specimen microplate. The operator adjusts the controller  36  of the temperature control assembly  14  to the required temperature, ensuring that power is available to the assembly  14 . The temperature control assembly  14  functions to establish and maintain the temperature within the incubation chamber  24 . Specifically, whenever the internal temperature in the chamber  24  is lower than the desired operating temperature of the incubator  10 , the controller  36  cycles power to the heater  34  to maintain the operating temperature of the chamber  24  within a desired range. 
     Due to the limited chamber  24  size, the present invention quickly establishes the required temperature in a uniform pattern. If the specimen requires a saturated water vapor atmosphere, the operator should fill the reservoir and maintain it by filling as necessary. The operator then may place the microplate specimen in the chamber  24 . The temperature senor will provide a temperature signal to the controller, which will cycle the heater as necessary to maintain the operator selected temperature. 
     FIG. 5 illustrates an alternative embodiment, wherein the incubator  100  is identical to the embodiment described above except that it does not include a temperature sensor and temperature controller. The alternative embodiment must be coupled with a master incubator that practices these features. 
     The incubator  100  broadly includes a housing  102  and a heater  104 . In the preferred embodiment, the heater  104  is of the same make and style as the heater in the master incubator. The heater  104  is provided with power in response to the temperature control assembly of the master incubator. 
     As illustrated in FIG. 5, an operator may electrically link the heaters  104  of a desired number of secondary incubators to the temperature control assembly  14  of a master incubator. The temperature control assembly  14  is then set to establish and maintain the temperature within the master incubator  10  and the secondary incubator  100 . The heater  104  maintains the temperature in each secondary incubator at substantially the identical temperature of the master incubator. When a saturated water vapor atmosphere is desired, the operator must fill the reservoir of each incubator. 
     Although the invention has been described with reference to the preferred embodiment illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.