Abstract:
A control system and a method for controlling an infant support configurable in a closed configuration in which a canopy contributes to formation of an enclosure about an infant support surface, and an open configuration is disclosed. The controlled infant support includes an air heater, a blower, and duct work communicating with the air heater, blower and enclosure. To facilitate bringing the air temperature within the enclosure quickly to a desired temperature whereby the temperature of an infant in the enclosure is controlled, power is supplied to air heater when infant support is in the open configuration to generate a heat reservoir. Upon the infant support assuming the closed configuration the controller controls power to the blower to increase air flow and infuse heat from the heat reservoir into the enclosure.

Description:
[0001]    The present invention relates to infant supports that provide both incubator and warmer configurations, and, more particularly, to temperature control systems for such infant supports during transition between incubator and warmer configurations.  
           [0002]    Newborns and premature infants often require isolation in a controlled environment for proper development. Incubators provide such an environment by providing a canopy forming an enclosure surrounding an infant support surface. The environment within the enclosure is controlled so that the oxygen content, air temperature, noise levels and other environmental parameters are maintained at levels conducive to infant development. The air temperature within the enclosure is an environmental factors which highly influences an infant&#39;s core temperature as indicated by its skin temperature. Incubators include temperature sensors to provide an indication of the air temperature within the enclosure and an indication of the skin temperature of the infant. The air temperature within the enclosure is adjusted by infusion of warmed air into the enclosure. Warm air infusion is accomplished by a system including a blower or fan for drawing external and/or internal air past a heater for introduction into the enclosure through orifices.  
           [0003]    Often newborns and infants also require various procedures to be performed on them by one or more caregivers. While the canopy and walls of an incubator includes access panels and orifices permitting access to an infant within the enclosure, this access is often too limited to perform all of the necessary procedures. Warmers provide relatively unobstructed access to an infant or newborn. Typically when relatively unobstructed access to an infant in a dedicated incubator is required, the infant is moved from the dedicated incubator to a dedicated warmer. The movement disturbs the infant and often requires the removal of sensors and tubes which further disturbs the infant. The move from the incubator to the warmer typically does not adversely affect the core temperature of the infant. After the procedures are performed on the infant, the infant is typically returned to an incubator. Insertion of the infant into the incubator requires reconfiguration of the access panels in the walls and canopy permitting warmed air to escape from the enclosure. Often the time required for the incubator to stabilize the skin temperature of the infant is unduly long.  
           [0004]    Infant supports having the capability to serve as both incubators and warmers are known and were developed to address sone of the issues arising from the use of dedicated incubators and dedicated warmers. Such infant supports are shown and described in Donnelly et al., U.S. Pat. No. 5,453,077, issued Sep. 26, 1995; Donnelly et al., U.S. Pat. No. 5,817,002, issued Oct. 6, 1998; Moll et al., U.S. Pat. No. 5,817,003, issued Oct. 6, 1998; Goldberg et al., U.S. Pat. No. 5,759,149, issued Jun. 2, 1998; Newkirk et al., U.S. Pat. No. 5,971,913, issued Oct. 26, 1999; Donnelly et al., U.S. Pat. No. 5,971,914, issued Oct. 26, 1999; Goldberg et al., U.S. Pat. No. 6,022,310, issued Feb. 8, 2000, Goldberg et al., U.S. Pat. No. 6,024,694, issued Feb. 15, 2000; Goldberg et al., U.S. Pat. No. 6,036,634, issued Mar. 14, 2000, Prows et al., U.S. Pat. No. 6,049,924, issued Apr. 18, 2000; Speraw et al., U.S. Pat. No. 6,071,228, issued Jun. 6, 2000; Donnelly et al., U.S. Pat. No. 6,270,452, issued Aug. 7, 2001; Goldberg et al., U.S. Pat. No. 6,296,606, issued Oct. 2, 2001; and Prows et al., U.S. Pat. No. 6,345,402, issued Feb. 12, 2002, the complete disclosures of which are hereby expressly incorporated by reference. Such infant supports are also shown and described in U.S. patent application Ser. No. 09/688,528 filed on Oct. 16, 2000 and U.S. patent application Ser. No. 09/571,449, filed on May 16, 2000, assigned to the common assignee of the present application, the complete disclosures of which are hereby expressly incorporated by reference.  
           [0005]    Such incubator/warmers include an infant support surface resting on a housing that incorporates systems similar to standard incubators facilitating control of the environment surrounding the infant when the canopy and walls are configured in a closed state and the incubator/warmer is acting in incubator mode. The incubator/warmer  110  also includes a radiant heater which directly warms the skin of the infant when some or all of the canopy and walls are configured to an open state and the incubator/warmer is in a warmer configuration. Such incubator/warmers are adapted to facilitate a transition from incubator to warmer configuration and from warmer to incubator configuration. During transition from incubator to warmer configuration, the walls and the canopy are configured to provide relatively unobstructed access to the infant and an infrared radiant heater is activated to directly warm the skin of the infant. When the walls and the canopy are configured to provide such free access, the warm air adjacent the infant dissipates throughout the room in which the incubator/warmer is located. Thus, the air adjacent the infant quickly approaches the ambient air temperature of the room allowing convective heat loss from the infant&#39;s skin to the surrounding air. The infrared heater, by directly warming the infant&#39;s skin is able to compensate quickly for the convective heat loss from the infant to maintain the core temperature of the infant at desired levels.  
           [0006]    When the incubator/warmer is transited from the warmer configuration to the incubator configuration, the walls and canopy are configured to a closed state forming an enclosure around the infant support surface. During transition to the closed state air at or near ambient room temperature may be trapped within the enclosure. Certain infrared radiant heaters are not very effective in maintaining the infant&#39;s skin temperature when the walls and the canopy are closed because the canopy and walls may be opaque to infrared radiation or the refractive index of the optically transparent walls and canopy may cause reflection of much of the incident infrared radiation. Thus, after transition from warmer configuration to incubator configuration, time is required to raise the temperature of the air within the enclosure from near ambient room temperature to a temperature sufficient to maintain the skin and core temperature of the infant. It has been found that fluctuations in the core temperature of an infant can adversely affect their development.  
           [0007]    The infant support thermal control system disclosed herein controls a convective heater and blower of an infant support during a priming stage when the support is acting as a warmer to reduce the time required for the support to stabilize the temperature of the infant at desired levels after transition to incubator configuration. The control system may also control the radiant heater of an incubator/warmer in warmer configuration and the convective heater and blower of the incubator/warmer after transition between warmer configuration and incubator configuration. The controller operates the blower and convective heater during the priming stage to reduce the time required for the incubator/warmer to stabilize the temperature of the infant at desired levels. The controller may also control infrared heater operation in the warmer configuration to compensate for infant heating attributable to the operation of the blower and convective heater during the primer stage.  
           [0008]    Typically, during the incubator configuration, an infant is isolated from the outside environment by side and end walls cooperating with a canopy that surrounds an infant support surface forming an enclosure. A convective heater and blower are provided in the support to direct warm air into the enclosure for controlling the temperature of the air therein. Such a system typically comprises a blower, a heater and passageways. The passageways communicate between the heater and blower to direct warm air produced by the heater and blower into the enclosure. During the warmer mode, the canopy is raised and the enclosure is opened. A radiant heater is also typically included with the support to direct radiant heat to the infant while exposed to the outside environment.  
           [0009]    Temperature sensors are also provided with the infant support to monitor and control the temperature and relative humidity of the air adjacent the infant. Such sensors are shown and described in U.S. Provisional Patent Application Nos. 60/199,103, entitled Fail Safe Device for Incubator &amp; Warmer, filed on Apr. 21, 2000, and 60/258,011, entitled Humidity Sensor for Incubator, filed on Dec. 22, 2000, the complete disclosures of which are hereby expressly incorporated by reference. Illustratively, the fail-safe device includes a temperature sensor assembly wherein one sensor is associated with a heating element that generates the heat, and a second sensor is associated with at least one of a plurality of air-contacting fins that distributes the heat. The second sensor is a back-up that provides an independent measurement of the temperature that can be correlated with the temperature measurement of the first sensor. A control system is also provided that monitors the sensors to prevent the infant support from becoming too warm.  
           [0010]    The illustrative humidity sensor is an assembly that comprises a first sensor spaced apart from the infant positioned on the support surface. The temperature of the air drawn from the enclosure is measured. In addition, the temperature of the air adjacent a humidity sensor is measured by a second sensor.  
           [0011]    In conventional incubator/warmers, during transition of the infant support from the incubator to warmer configuration, the infrared heater elements typically respond quickly enough to maintain the infant&#39;s core temperature within a reasonable variation. When transiting the infant support from the warmer to incubator configuration, however, the response of the convective heater may be inadequate to maintain the infant&#39;s core temperature within the reasonable variation.  
           [0012]    Conventionally, during the incubator mode, the temperature of the air adjacent the infant maintains the temperature of the infant. During warmer mode, however, the convective heater is often not used. Rather, the radiant heater warms the infant directly. The radiant heater, however, does not warm the surrounding air. Because the incubator/warmer, when in the warmer configuration, does not isolate the infant from the outside environment, a temperature change occurs in the air adjacent the infant. Consequently, during the return transition from warmer to incubator configuration, the initial temperature of the air inside the enclosure is closer to that of the outside environment, which is most often lower than the desired air temperature for the incubator mode. Substantial time may be required for the convective heating system to warm the enclosure to the desired temperature.  
           [0013]    Accordingly, the thermal control system of the present disclosure reduces the time it takes for the enclosure to reach the desired temperature after the support transitions from the warmer to the incubator configuration. During the warmer mode, the infant support illustratively uses a variable priming mechanism to regulate a thermal infusion of a known magnitude at transition. This will allow for a rapid response to the transition, since the convective heater will already be warmed. In addition, heating the surfaces and volumes within the air passages creates a heat reservoir, which may be infused into the enclosure after transition from warmer configuration to incubator configuration to quickly increase the air temperature needed to sustain the core temperature of the infant. Upon transition into incubator configuration, the infant support will adapt the convective PID error for convergence to the targeted temperature set point.  
           [0014]    An incubator/warmer, in accordance with one aspect of the disclosure, includes an infant support, a canopy, a convective heating system, a radiant warmer and a control system. The canopy provides an enclosure about the infant support and an infant residing on the support when the incubator/warmer is in an incubator configuration. The canopy is retractable to place incubator/warmer in a warmer configuration. The convective heater system includes an air heater, a blower and passageways through which air is circulated by the blower to provide heated air to the enclosure. The radiant warmer is positioned to warm the infant on the support when the canopy is retracted and the incubator/warmer is in the warmer configuration. The control system is configured to rapidly bring air in the enclosure to a target temperature when the incubator/warmer transitions from the warmer configuration to the heater configuration. The control system includes a priming stage algorithm that maintains air in the passageways of the convective heater system at a priming temperature by controlling power to the air heater while the incubator/warmer is in the warmer configuration and an infusion stage algorithm that controls the blower to drive air from the passageways into the enclosure to rapidly warm the enclosure after transition of the incubator/warmer to the incubator configuration. The incubator/warmer may also include a convergence stage algorithm that controls the blower to drive warmed air into the enclosure until the target temperature is reached.  
           [0015]    According to another aspect of the disclosure, a control system for an infant support of the type capable of assuming and transiting between an incubator configuration wherein an enclosure is defined around an infant support surface and a warmer configuration is disclosed. The infant support has a radiant heater supplied with power in the warmer configuration, a convective heater, a blower and duct work communicating with the enclosure, convective heater and blower. The control system includes a convective heater controller and a blower controller. The convective heater controller controls the power to the convective heater prior to the infant support assuming the incubator configuration so as to prewarm portions of the duct work past which air to be infused into the enclosure will pass. The blower controller controls the power to a blower to provide a slight air flow prior to the infant support assuming the incubator configuration and to provide an increased air flow upon the infant support assuming the incubator configuration.  
           [0016]    According to another aspect of the disclosure, a control system for an infant support of the type capable of assuming and transiting between a closed configuration wherein an enclosure is defined around an infant support surface and an open configuration is provided. The infant support has a convective heater, a blower and duct work communicating with the enclosure, convective heater and blower. The control system includes a convective heater controller and a blower controller. The convective heater controller controls the power to the convective heater prior to the infant support duct work assuming the closed configuration so as to prewarm portions of the duct work past which air to be infused into the enclosure will pass. The blower controller controls the power to the blower to provide a slight air flow prior to the infant support assuming the closed configuration.  
           [0017]    According to yet another aspect of the disclosure a method of controlling the temperature of an infant in an incubator/warmer is provided. The incubator/warmer is of the type having an open configuration for operating as an infant warmer, a closed configuration forming an enclosure for operating as an incubator. The incubator/warmer includes a housing supporting an infant support, an air temperature sensor positioned to be within the enclosure when the incubator/warmer is in the closed configuration, a radiant heater, and an air heating system including an air heater, a blower and duct work located in the housing below the infant support. The duct work is in fluid communication with the enclosure. The method comprises the steps of operating the air heater while the incubator/warmer is in the open configuration to generate a heat reservoir and infusing the heat from the generated heat reservoir into the enclosure upon incubator/warmer attaining the closed configuration.  
           [0018]    Additional features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    In describing the invention, reference is made to the following drawings in which:  
         [0020]    [0020]FIG. 1 is a perspective view of an infant support in a closed configuration conducive to operation of the support in incubator configuration;  
         [0021]    [0021]FIG. 2 is a perspective view of the support of FIG. 1 in an open configuration conducive to operation of the support in warmer configuration;  
         [0022]    [0022]FIG. 3 is a perspective view with parts broken away of the support of FIG. 1 showing a platform assembly supporting a deck, a fixed wall and a mattress supported on a mattress tray;  
         [0023]    [0023]FIG. 4 is a partial exploded view of a portion of the support of FIG. 1 showing a platform assembly supporting a deck, a fixed wall configured to receive a sensor module and hinged walls and also showing a blower and a convective heater located within duct work below the support surface;  
         [0024]    [0024]FIG. 5 is a partial exploded view of a portion of the support of FIG. 1 showing below deck surfaces, a convective heater, a blower, and duct work for circulating air into the enclosure;  
         [0025]    [0025]FIG. 6 is a block diagram of a heater control system and components of the support of FIG. 1;  
         [0026]    [0026]FIG. 7 is a flow diagram of the priming stage algorithm;  
         [0027]    [0027]FIG. 8 is a flow diagram of the algorithm for determining the convective heater control algorithm after transition from warmer to incubator configuration; and  
         [0028]    [0028]FIG. 9 is a flow diagram of a blower speed control algorithm.  
     
    
     DETAILED DESCRIPTION  
       [0029]    Infant support thermal control system  8  disclosed herein controls at least one of a radiant heater  112 , air heater or convective heater  114 , and blower  116  of an incubator/warmer  110  to reduce the time required for incubator/warmer  110  to maintain an infant&#39;s temperature at desired levels upon entry into incubator configuration.  
         [0030]    As shown for example in FIGS.  1 - 6 , and the patents mentioned above, incubator/warmer  110  includes a platform assembly  118 , an infant support surface or deck  120  typically supporting a mattress  122  upon which an infant  123  rests, a canopy  124  configurable to cooperate with hinged walls  125  and fixed walls  127  to form an enclosure  126  surrounding infant support surface  120 , air passages or duct work  128 , air intakes  130  in communication with the interior of enclosure  126  and the exterior  132  and warm air orifices  134  in communication with the interior of enclosure  126 . In the illustrated embodiment, blower  116  draws air from interior and/or exterior air intakes  130  through duct work  128  past convective heater  114  and discharges the air through warm air orifices  134  into enclosure  126 . Air movement is induced by blower  116  which is in fluid communication with duct work  128 . Illustratively, blower  116  and convective heater  114  are coupled to a heater accessory plate  129  mounted in duct work  128 . In the illustrated embodiment, duct work  128 , convective heater  114 , and blower  116  are all located in the platform assembly  118  that supports infant support surface or deck  120 . Thus the surfaces of duct work  128 , blower  116 , and convective heater  114  are referred to as below deck surfaces. Illustratively, incubator/warmer  110  also includes air temperature sensors  136  and skin temperature sensors  138 . Controller  8  is communicatively coupled with air temperature sensor  136 , skin temperature sensor  138 , radiant heater  112 , convective heater  114  and blower  116 .  
         [0031]    Incubator/warmer  110  is adapted to assume a warmer configuration, as shown, for example, in FIG. 2, and an incubator configuration, as shown, for example, in FIG. 1, and to transition between the two configurations. In the incubator configuration, walls  125 ,  127  and canopy  124  are configured to form an enclosure  126  surrounding infant support surface  120 . Incubator/warmer  110  includes a plurality of hinged walls and hinged wall panels  125  and a fixed wall  127  the edges of which abut edges of adjacent walls or adjacent wall panels and bottom surfaces of canopy  124  when in the incubator configuration to form the enclosure  126 . Walls  125  and  127  are formed to include a plurality of access ports through which a caregiver can have limited access to infant  123  without compromising the integrity of the enclosure  126 . Hinged wall panels  125  form doors which may be opened when incubator/warmer  110  is in the incubator configuration to provide greater access to infant  123  in enclosure  126 . Incubator/warmer  110  may be provided with entraining curtains of air flowing past doors to reduce loss of heated air while the door is opened. Walls  125  are also configured to fold into a retracted position permitting substantially less restricted access by a caregiver to infant  123  on mattress  122  when incubator/warmer  110  is in warmer configuration. When in warmer configuration canopy  124  is positioned to allow infrared radiation from infrared warmer  112  to impinge upon support surface  120  and infant  123  located on mattress  122 . Illustratively, canopy  124  includes two canopy half portions  140 ,  142  hingedly mounted to an overhead arm assembly  144 .  
         [0032]    It is further contemplated that the infant support  110  may include supplemental heaters, heat reservoirs, ambient temperature sensors, outlet port sensors, head panel sensors, and heat reservoir sensors to provide closed-loop feedback.  
         [0033]    When in incubator configuration, blower  116  pulls air from the interior, and sometimes the exterior, of the enclosure  126  through air intakes  130 . This air is pulled through inlet portions of duct work  128  and across convective ribs  146  thermally coupled to heating element  148  of conductive heater  114  resulting in convective heating of the air. The air is then forced through outlet portions of the duct work  128  to be expelled through orifices  134  into the interior of enclosure  126 . After passing over convective ribs  146  there is some heat transfer between the warmed air and below deck surfaces of duct work  128  and incubator/warmer  110 . During start-up this heat transfer to below deck surfaces continues until below deck surfaces of duct work  128  are warmed to a temperature approaching that of the heated air. Eventually, heat transfer between the warmed air and below deck surfaces is reduced.  
         [0034]    In normal incubator mode, the temperature of infant  123  within enclosure  126  is controlled by regulating the power to the convective heater  114 , speed of the blower  116  or controlling both the power to the convective heater  114  and the speed of the blower  116 . In the illustrated embodiment of incubator/warmer  110 , convective heater power and blower speed may be controlled using various algorithms implemented by a microprocessor  150 . Heater power and blower speed may be controlled by using open loop control implementing algorithms based on certain conditions (e.g. a pre-heat mode or door open mode) or by using closed loop control based on digital feed back received from air temperature sensor  136 , skin temperature sensor  138  or from both air temperature sensor  136  and skin temperature sensor  138 . Open loop control systems to facilitate preheating of an incubator prior to use or for minimizing heat loss when incubator doors are opened are known and are therefore not described in this application. Closed loop controls for controlling the convective heater of an incubator or incubator/warmer  110  during normal incubator mode are also known. All of the power control algorithms mentioned herein use pulse width modulation  152  of the power to the controlled heater  112 ,  114  to regulate power between 0 and 100% of the available power from the heater power supply  154 .  
         [0035]    For purposes of discussion, the following stages are defined for facilitating warmer to incubator transition.  
         [0036]    Priming Stage  
         [0037]    The time spent, before transition, heating the below-deck volume and surfaces while the system remains in a warmer configuration.  
         [0038]    Infusion Stage  
         [0039]    The initial transfer of heat from the below-deck volume and surfaces into the enclosure  126 , which begins when incubator configuration is attained.  
         [0040]    Convergence Stage  
         [0041]    The time from the end of the predominance of thermal infusion to the time when the air temperature is in the neighborhood of the target air temperature.  
         [0042]    In the presently preferred embodiment, when closed loop control of convective heater  114  is implemented in post convergence stage, the microprocessor  150  of incubator/warmer  110  implements a first order PID convective heater controller when the feed back is based on air temperature alone and a dual hierarchy PID convective heater controller when the feed back includes skin temperature information. In skin control mode, the dual hierarchy PID controlled pulse width modulator regulates the percent of line power provided for convective heater operation. The dual hierarchy PID controller provides a scaled signal between 0 and 1 to regulate the duty cycle of the PWM  152  between 0 and 100%. The dual hierarchy PID controller receives skin temperature signals from skin temperature sensor  138 , air temperature signals from air temperature sensor  136  in sensor module  156 , and a skin temperature set point  158  entered through the caregiver interface  160 . The dual hierarchy PID controller includes a first stage proportional-integral (PI) controller and a second stage proportional-differential (PD) controller. The error signal for the first stage PI controller is obtained by comparing the skin temperature to the skin temperature set point. The output of the first stage PI controller is used as the air temperature set point. Thus the error signal for the second stage PD controller is obtained by comparing the PI generated air temperature set point to the air temperature.  
         [0043]    In order to rapidly obtain steady state temperature control of infant  123  in enclosure  126 , the disclosed embodiment of infant support thermal control system  8  operates different control algorithms in different stages of operation prior to and after transition from warmer configuration to incubator configuration. As shown in FIGS.  7 - 9 , infant support thermal control system  8  includes a priming stage convective heater control  10 , a post transition PID convective heater controller  20  including an infusion stage PID convective heater controller  30  and a convergence stage PID convective heater controller  40 , and a blower controller  50  that controls the blower speed during priming, infusion, and convergence stages. While still in warmer configuration, incubator/warmer  110  uses a priming stage control algorithm  10  and  60  to heat the below deck volume and surfaces. This priming stage control algorithm  10  and  60  regulates convective heater  114  and blower  116  until canopy  124  is in incubator configuration forming an enclosure  126  around infant  123  on the support surface  120 . After the canopy  124  has assumed the incubator configuration, incubator/warmer  110  operates an infusion stage control algorithm  30  and  70 . After most of the heat energy has been transferred from the below deck heat reservoir to the air within enclosure  126 , incubator/warmer  110  runs a convergence stage control algorithm  40  and  70  until the air temperature in the enclosure  126  is in the neighborhood of the air temperature set point  162  entered through caregiver interface  160 . Once the air temperature in the enclosure  126  is in the neighborhood of the air temperature set point  162 , the incubator/warmer  110  converts to using known incubator algorithms to control the blower  116  and convective heater  114 .  
         [0044]    During transition from incubator configuration to warmer configuration, incubator/warmer  110  continues to run the control algorithm used in incubator mode immediately prior to the transition. In the illustrated embodiment, upon reaching warmer configuration, incubator/warmer  110  begins to run priming stage control algorithm  10  and  60  to control power to convective heater  114  and blower  116 , while radiant heater power is controlled using a closed loop PID control based on the error between the skin temperature signal and a skin temperature set point  158 .  
         [0045]    As shown for example in FIGS. 7 and 9, in radiant warmer configuration, priming stage control algorithm  10  and  60  is implemented using priming stage convective heater control  10  and blower control  50 . Priming stage control algorithm  10  and  60  controls the power to convective heater  114  between 0-100% of line power and the speed of blower  116  in priming stage to heat the below deck surfaces of incubator/warmer  110  to maintain a heat reservoir from which thermal energy may be drawn upon transition from warmer configuration to incubator configuration. Thus, in the illustrated embodiment, convective heater  114  and blower  116  continue to operate when incubator/warmer  110  is in warmer configuration. Because there is no enclosure  126  surrounding infant support surface  120 , air warmed by convective heater  114  is discharged into the room  132  in which incubator/warmer  110  is located. As shown for example, in FIG. 9, to minimize the discharge of warmed air, blower speed is reduced to a speed slightly above blower stall speed. In the illustrated embodiment, blower speed is maintained at a constant level during warmer mode. In the illustrated embodiment priming stage blower speed control algorithm  60  maintains blower speed at a constant speed such as  800  RPM throughout priming stage, as shown in FIG. 9.  
         [0046]    While blower speed is illustratively maintained at a constant level during priming stage, as shown in FIG. 9, power to convective heater  114  is not, as shown in FIG. 7. Rather power to convective heater  114  is illustratively controlled by calculating the power requirements  12  to generate a heat reservoir sufficient to rapidly return the air in enclosure  126  to near the temperature set point following transition to incubator configuration. The size of the heat reservoir (and thus the power to convective heater required to generate such heat reservoir) is dependent on the difference between the air temperature set point  162  and the ambient temperature. As shown, for example in FIG. 7, ambient temperature is calculated  14  using the values of the air temperature  16  which is filtered  18 , the convective heater power  22  and the infrared heater power  24  which is also filtered  26  as described hereafter.  
         [0047]    Ideally, the size of the heat reservoir will be sufficient that upon infusion of the heat from the heat reservoir, the temperature in the enclosure  126  will be equal to the set point temperature  162 . However, under certain conditions, generating the ideal size of heat reservoir would require providing convective heater  114  with more power than it is designed to receive, exhausting air at too high of a temperature from the orifices  134 , or overheating the below deck surfaces. Thus the priming stage convective heater control algorithm  10  is bounded to prevent such occurrences. As shown, for example, in FIG. 7, the two illustrated bounds on the priming stage control algorithm are 1) limiting the maximum power to the convective heater  114  to an amount that will not allow the temperature of the air exiting the orifices  134  to exceed 40° C. 28, and 2) eliminating additional heating when the sensed air temperature exceeds 33 ° C. 32.  
         [0048]    The power to convective heater  114  determines the size of the heat reservoir being stored. In order to rapidly transition from warmer configuration to incubator configuration, the capacity of the heat reservoir is controlled as a function of the difference between the ambient temperature and the set point temperature  162  to be reached in incubator mode. Thus, during the priming stage, the power to convective heater  114  is controlled based on the difference between ambient temperature and the set point temperature  162 . As the difference between ambient temperature and the set point temperature  162  increases, more heat must be stored in order to rapidly transition between warmer and incubator configurations and therefore primer algorithm increases the power to convective heater  114 . Thus proper control of power to convective heater  114  in priming stage requires that the ambient temperature be determined  14 .  
         [0049]    The illustrated embodiment of incubator/warmer  110  includes sensors  136 ,  138  providing signals indicative of air temperature  16  entering a sensor module  156  and infant skin temperature but no sensor for ambient room temperature. In warmer configuration, the temperature of air entering sensor module  156  is not the ambient temperature. The temperature of the air entering sensor module  156  is influenced, to varying degrees by multiple parameters. The controller  8  disclosed herein implements an algorithm  14  to estimate the ambient temperature based on the air temperature  16  sensed by air temperature sensor  136  in sensor module  156 . The algorithm assumes that infrared heater power  24  and convective heater power  22  are the two parameters which have the greatest influence on the difference between the air temperature sensed  16  by t air temperature sensor  136  in sensor module  156  and the ambient temperature. It is assumed that the ambient air temperature TA is linearly related to the parameters air temperature T a    16 , infrared heater power P I    24 , and priming power or convective heater power P P    22 . The following discussion indicates the assumptions made in implementing the priming stage convective heater control algorithm  10 .  
         [0050]    One assumption is that by knowing certain parameters, ambient temperature can be calculated  14 . The air temperature  16 , read by air temperature sensor  136  in sensor module  156  while in warmer configuration, is a function of the ambient temperature, the infrared heater power  24  and convective heater power  22 , prime time, the panel configuration, sunlight, building ventilation, the topology, reflectivity and radiation of the infant, the temperature of the mattress and objects on the mattress, and numerous other factors, including care giver activities around and with the infant support  110 . Only a few of these parameters are measured or controlled.  
         [0051]    As previously mentioned in implementing the illustrated control system  8 , it is further presumed that the effects of most of these factors are small or negligible. However, those skilled in the art will recognize that the methodology explained herein can be extended to include other parameters within the implementation of the control system within the scope of the disclosure. In the illustrated control system  8 , the factors that are considered to affect the air temperature reading  16  are the infrared heater power  24  and convective heater power  22 , the ambient temperature, the prime time, and the side panel position. The prime time and side panel configuration are considered constants in the illustrated implementation of priming stage convective heater control algorithm  10 .  
         [0052]    Empirical data suggests that a linear approximation can be reasonably used to quantify the relationship of the air temperature reading  16  to each variable independently. Furthermore, the data supports the generalization that this property applies to any pair of these factors. It is presumed that one of these factors can be expressed as some function of the others:  
           R=f ( x, y, z ).  
         [0053]    Since the relationship between R and each variable is known and is essentially linear, it can be written as:  
           R=m   0 ( y, z ) x+b   0 ( y, z ).  
         [0054]    Applying the same logic obtains:  
           R=[m   1 ( z ) y+b   1 ( z )] x+m   2 ( z ) y+b   2 ( z ).  
         [0055]    Performing this operation again, obtains:  
           R=[ ( m   3   z+b   3 ) y+ ( m   4   z+b   4 )] x+ ( m   5   z+b   5 ) y+ ( m   6   z+b   6 ).  
         [0056]    This can be rewritten in the general form:  
           R=k   7   xyz+k   6   xy+k   5   xz+k   4   yz+k   3   x+k   2   y+k   1   z+k   0   Equation 1  
         [0057]    Where k 7 , k 6 , k 5 , k 4 , k 3 , k 2 , k 1 , and k 0  are constants the values of which can be determined through calibration.  
         [0058]    While the illustrated embodiment considers four parameters as being linearly related, those skilled in the art will recognize that additionally parameters can be considered in implementing a control system by extension of the above identified mathematical approach.  
         [0059]    In the illustrated embodiment each system parameter is either measured or calculated as described below. The air temperature sensor  136  in sensor module  156  in warmer, transition and incubator configurations measures the air temperature  16 . The infrared heater power  24  is set by the infrared skin temperature PID controller, the pre-warm timer sequence, or by manual input from the care giver. The presently illustrated embodiment does not include an ambient air temperature sensor and thus calculates the ambient air temperature  14  based upon its linear relationship with air temperature  16 , convective heater power  22 , and infra-red heater power  24 . It is within the scope of the disclosure to measure ambient temperature directly with an infant support warmer temperature sensor interface and thereby eliminate the need for linear approximation of ambient temperature  14 . Until the infant support warmer temperature sensor interface is implemented and filtered for thermal artifact, ambient temperature must be derived  14  from the general form. Thus, the ambient temperature, T A , may be written as follows:  
           T   A   ≅a   7   T   a   P   1   P   P   +a   6   T   a   P   I   +a   5   T   a   P   P   +a   4   P   I   P   P   +a   3   T   a   +a   2   P   I   +a   1   P   P   +a   0   Equation 2  
         [0060]    Where, T A  is the ambient temperature, T a  is the air temperature, P I  is the infrared heater power, P P  is the convective priming power and a 7 , a 6 , a 5 , a 4 , a 3 , a 2 , a 1 , and a 0  are experimentally derived constants. The values of the derived constants are determined during calibration of the incubator/warmer  110 . Those skilled in the art will recognize that various calibration techniques may be used to determine the value of the derived constants. In the illustrated embodiment a 7 , a 6 , a 5 , a 4 , a 3 , a 2 , a 1 , and a 0  are derived experimentally from eight measurements of T A , T a , P P  and P I  using a Gaussian elimination method.  
         [0061]    In order to calculate priming power  12 , a term used for the power to the convective heater  114  when in the priming mode, the priming stage convective heater control system  10  implemented in the disclosed embodiment considers the temperature differential between ambient temperature and the desired temperature  162  within the incubator upon return to incubator configuration. The temperature change ΔT that occurs at the transition without post-transition supplemental heat is calculated as:  
         Δ T=T   Max   −T   a .  Equation 3  
         [0062]    Where, ΔT is the temperature change caused by the thermal infusion, T Max  is the maximum air temperature induced by the thermal infusion, and T a  is the air temperature. Thus, the air temperature differential may be written as follows:  
         Δ T≅b   7   T   A   P   I   P   P   +b   6   T   A   P   I   +b   5   T   A   P   P   +b   4   P   I   P   P   +b   3   T   A   +b   2   P   I   +b   1   P   P   +b   0   Equation 4  
         [0063]    Where, ΔT is the temperature change caused by the thermal infusion, T A  is the ambient temperature, P I  is the infrared heater power and P P  is the convective priming power. b 7 , b 6 , b 5 , b 4 , b 3 , b 2 , b 1 , and b 0  are experimentally derived constants which are derived experimentally from eight measurements of T A , T a , P P  and P I  and a Gaussian elimination.  
         [0064]    The convective priming power requirement may be derived similarly using the difference between the targeted air temperature set point  162 , e.g., 33° C., and the air temperature. This is denoted as:  
         Δ T   T   =T   T   −T   a .  Equation 5  
         [0065]    Where, ΔT T  is the temperature change desired by the thermal infusion, T T  is the targeted air temperature set point and T a  is the air temperature. The priming power required to cause a heat infusion of the required magnitude may then be approximated as follows:  
         P P   ≅c   7   T   A   ΔT   T   P   I   +c   6   T   A   ΔT   T   +c   5   T   A   P   I   +c   4   ΔT   T   P   I   +c   3   T   A   +c   2   ΔT   T   +c   I   P   I   +c   0   Equation 6  
         [0066]    Where, P P  is the priming power, T A  is the ambient temperature, ΔT T  is the temperature change desired by the thermal infusion and PI is the infrared heater power. c 7 , c 6 , c 5 , c 4 , c 3 , c 2 , C 1  and c 0  are experimentally derived constants derived experimentally from eight measurements of T A , T a , P P  and P I  and a Gaussian elimination.  
         [0067]    Illustratively, the air temperature at the convective outlet ports  134  shall not exceed 40° C. This will be the limiting factor for priming power.  
         [0068]    Since the relationship between ambient temperature, heater power and outlet port temperature is known to be linear, it may be written as follows:  
           k   2   P   P   +k   1   T   A   +k   0   =T   o   Equation 7  
         [0069]    Where, P P  is the priming power, T A  is the ambient temperature, T o  is the air temperature in warmer configuration and k 2 , k 1 , and k 0  are constants. It is contemplated that k 2 , k 1 , and k 0  may be derived from three measurements of T A , T o  and P P  and a substitution method. Substituting a maximum outlet port temperature of T o =40° C., Equation 7 can be simplified and written as follows:  
           P   PMax   =d   1   T   A   +d   0   Equation 8  
         [0070]    Where, P PMax  is the maximum allowable priming power that meets the specification, T A  is the ambient temperature and d 1  and d 0  are experimentally derived constants. It is contemplated that d 1  and d 0  may be derived from two measurements of T A  and P P  and a substitution method.  
         [0071]    Due to the nature of an air temperature measurement in warmer configuration and infrared heater power outputs, both signals are discretely conditioned using a heavy infinite impulse response filter  18  and  26 , respectively. The air temperature filter  18  is implemented using the following model:  
           T   w ( t )=α 0   T   w ( t− 1)+β 0   T   a ( t )  Equation 9  
         [0072]    Where, T w (t) is the current filtered air temperature in warmer configuration, T w (t−1) is the last filtered air temperature in warmer configuration, T a (t) is the current unfiltered air temperature in warmer configuration and α 0  and β 0  are constants. Similarly, the infrared heater power filter  26  is implemented using the following model:  
           P   I ( t )=α 1   P   I ( t− 1)+β 1   P   IR ( t )  Equation 10  
         [0073]    Where, P I (t) is the current filtered infrared heater power, P I (t−1) is the last filtered infrared heater power, P IR (t) is the current unfiltered infrared heater power and α 1  and β 1  are constants. The value of the above constants are determined through calibration.  
         [0074]    Priming stage convective heater control algorithm  10  is implemented using a microprocessor receiving signals indicative of air temperature  16 , convective heater power  22 , and radiant heater power  24 . As shown for example, in FIG. 7, priming stage convective heater control algorithm  10  is as follows:  
         [0075]    The ambient temperature is calculated  14  using Equation 2 and priming power from the previous iteration and the filtered infrared heater power and filtered air temperature values.  
           T   A   =a   7   T   w ( t ) P   I ( t ) P   P   +a   6   T   w ( t ) P   I ( t )+a 5   T   w ( t ) P   p   +a   4   P   I ( t ) P   P   +a   3   T   w ( t )+ a   2   P   I ( t )+a 1   P   P   +a   0    
         [0076]    The maximum allowable priming power is calculated  34  using Equation 8.  
         
       P 
       PMax 
       =d 
       1 
       T 
       A 
       +d 
       0  
     
         [0077]    If the initial air temperature in warmer configuration exceeds the target temperature, shown illustratively as 33° C. the priming power is set to zero  32 .  
           T   a   ≧T   T             P   P =0%  
         [0078]    Otherwise, the priming power required is calculated  12  using Equation 6 using the calculated value of ambient temperature  14  and the filtered infrared heater power and air temperature signals.  
           P   P   =c   7   T   A ( T   T   −T   w ( t )) P   I ( t )+c 6   T   A ( T   T   −T   w ( t ))+ c   5   T   A   P   I ( t )+ c   4 ( T   T   −T   w ( t )) P   I ( t )+ c   3   T   A   +c   2 ( T   T   −T   w ( t ))+ c   1 P I ( t )+ c   0    
         [0079]    If priming power required exceeds the 40° C. outlet requirement, then the power to the convective heater is limited to the maximum allowable priming power  28 .  
         
       P 
       P 
       &gt;P 
       Pmax 
                 P 
       P 
       =P 
       PMax  
     
         [0080]    Otherwise, the priming power is set to the maximum calculated priming power  36 .  
         [0081]    The priming stage control algorithm  10  and  60  is implemented by the control system  8  until infant support  110  is configured for incubator mode. In the illustrated embodiment, the priming stage control algorithm  10  and  60  is described as functioning from the moment infant support  110  assumes warmer configuration until infant support  110  assumes incubator configuration, however, those skilled in the art will recognize that continuous operation of priming stage control algorithm is not required. Also, the illustrated embodiment considers that the air flow rate and panel configurations during priming stage will be held constant. It is within the teaching of the disclosure for priming stage control algorithm  10  and  60  to be modified to accommodate changes in air flow rate and panel configurations.  
         [0082]    As incubator/warmer  110  begins reconfiguration from warmer configuration to incubator configuration, power to the infrared heater  112  is terminated. The last infrared power reading is stored for use during infusion stage and for the continued operation of priming stage algorithm  10  and  60  until incubator/warmer  110  assumes incubator configuration. Once incubator/warmer  110  assumes incubator configuration, priming stage control algorithm  10  and  60  ceases to control convective heater power and blower speed and convective heater power and blower speed are controlled by infusion stage algorithm  30  and  70  which implements a modified PID controller.  
         [0083]    During normal incubator operation stage, the power to convective heater  114  is controlled using a PID controller. During this stage the convective PID controller error is the difference between the targeted air temperature set point  162  and the air temperature. This can be written as:  
         ε= T   T   −T   a .  Equation 11  
         [0084]    Where, ε is convective PID error, T T  is the targeted air temperature set point  162  and T a  is the air temperature.  
         [0085]    During the post-transition infusion period, the infusion stage convective heater control algorithm  30  illustratively sets the convective PID controller error to the difference between the targeted air temperature set point  162  and the estimated air temperature at the end of the thermal infusion  42  using 33° C. as the control variable for air temperature set point  44 . This modified transition error is represented as:  
         ε T   =T   T −( T   a   −ΔT ).  Equation 12  
         [0086]    Where, ε T  is convective PID error, T T  is the targeted air temperature set point  162 , T a  is the air temperature and ΔT is the temperature change caused by the thermal infusion.  
         [0087]    In the illustrated embodiment, infusion convective heater control algorithm  30  controls convective heater power for a set period, illustratively one minute, following transition to incubator configuration. Those skilled in the art will recognize that it is within the scope of the disclosure for the duration of infusion stage to be increased or decreased.  
         [0088]    In the illustrated embodiment, immediately upon transition from warmer configuration to incubator configuration, the blower speed is increased  70  to increase the air flow. Illustratively, blower speed is increased to 2000 RPM  70  for twenty minutes following the transition. The increased air flow facilitates stabilization of the temperature of infant  123  within the enclosure  126 . Thus, in the illustrated embodiment, blower speed is increased during the infusion stage and the convergence stage. After completion of the high air flow duration, blower speed is ramped down to the level determined by normal incubator mode controller. It is within the scope of the disclosure for the air flow rate to be increased by a greater or lesser amount and for a shorter or longer duration.  
         [0089]    During both infusion stage and convergence stage, convective heater power is regulated using a PID controller  46 . The control system  8  consists of a pre-transition algorithm, the priming stage algorithm  10  and  60 , to control the thermal infusion, and post-transition algorithms that relinquishes control to the convective PID without negatively interfering with the infusion. As shown for example in FIG. 8, during infusion stage, the PID error is adapted  42  to compensate for anticipated thermal infusion. Thus, the anticipated temperature change that will be caused by the thermal infusion is calculated using Equation 4 using the last calculated ambient temperature reading  14 , convective heater power reading  22  and filtered infrared heater power reading  26  from the priming stage.  
         Δ T=b   7   T   A   P   I ( t ) P   P   +b   6   T   A   P   I ( t )+ b   5   T   A   P   P   +b   4   P   I ( t ) P   P   +b   3   T   A   +b   2   P   I ( t )+b 1   P   P   +b   0    
         [0090]    During the infusion duration, the convective PID controller error is set to ε T , using Equation 12.  
         ε T   =T   T −( T   a   −ΔT)    
         [0091]    Illustratively, after one minute, the illustrated duration of infusion stage, convergence stage convective heater algorithm  40  begins to control the power to convective heater. During convergence stage, convective PID controller  46  error is set to ε, using Equation 11.  
         ε= T   T   −T   a    
         [0092]    so that air temperature is used as the process variable  48  and the air temperature set point is used as the control variable  52 .  
         [0093]    It is envisioned that as the air temperature in the enclosure  126  begins to stabilize the temperature of infant  123 , the proportional gain, integral gain, and derivative gains of the PID controller may be adjusted to further facilitate stabilization of the infant.  
         [0094]    Upon the expiration of this high airflow time, and barring intervention by the care giver, the blower speed proportionally decays back to the normal steady state blower speed of 800 rpm  80 .  
         [0095]    Air temperature sensor  136  and skin temperature sensor  138  are of the type commonly available for use in medical equipment. In the illustrated device, signals from air temperature sensor  136  and skin temperature sensor  138  are received by a microprocessor  150  which implements the various filters and control algorithms. Most skin temperature sensors and air temperature sensors provide an analog signal indicative of the parameter being sensed, while most microprocessors manipulate digitized information. Those skilled in the art will recognize that air temperature sensor  136  and skin temperature sensor  138  may be digital sensors or may be analog sensors acting in conjunction with analog to digital converters within the scope of the disclosure.  
         [0096]    In the illustrated embodiment, incubator/warmer  110  includes a microprocessor  150  which runs algorithms implementing the described filters, controllers, and pulse width modulators based on digitized air temperature and skin temperature signals. Microprocessor  150  calculates the ambient temperature and stores values of prior infrared heater power, infrared heater error signals, convective heater error signals, and ambient air temperature readings to allow for appropriate filtering of signals and implementation of the integral and proportional components of the various controllers. It is within the scope of the disclosure for the control algorithms, storage functions and controllers to be implemented using discrete components and or integrated circuits rather than a microprocessor.  
         [0097]    Experimental data showing the rate at which the environment of the infant support increases in temperature indicates that the infant skin temperature is maintained through transition within a ±1° C. band and returns to a neighborhood of the set point temperature within 20 minutes.  
         [0098]    For precision control, those skilled in the art will recognize that infant support  110  may include supplemental heaters and heat reservoirs, ambient temperature sensors, outlet port sensors, head panel sensors, heat reservoir sensors and a closed-loop blower controller within the scope of the disclosure. Those skilled in the art will recognize that while the description has focused on an incubator/warmer, the teachings of this disclosure have applicability to any infant support having an open configuration and a closed configuration in which an enclosure is formed for receipt of an infant therein.  
         [0099]    Although the invention has been described in detail with reference to specific embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.