Abstract:
An infant incubator in which the heater for heating the air circulated through the incubator and the speed of the fan which forces air across the heater to circulate through the incubator are controlled to increase the temperature of the heated air and delivery of the heated air to the space in which an infant has been placed for treatment when an access door of the incubator has been opened. The increase in temperature and delivery of the heated air is caused by a sensor which senses when the access door is opened.

Description:
TECHNICAL FIELD 
     The present invention relates, to infant incubators and, in particular, to apparatus for regulating the heating of the air which is circulated through an infant incubator and introducing the heated air into the space in which an infant is placed for treatment. 
     BACKGROUND OF THE INVENTION 
     The most common way for regulating the heating of the air which is circulated through an incubator is to control the power delivered to the heater. An alternative approach, although not as common, is to control the speed of a fan which forces air across the heater and through the incubator. Typically, a temperature sensor, located in the space in which an infant is placed for treatment, and a temperature sensor, attached to the infant, serve as the control for establishing and maintaining the desired temperature of the air to which the infant is exposed. 
     Incubators have access doors which, when opened, permit access to an infant by those attending to the infant. When an access door is opened, the ambient air can enter the incubator space in which the infant has been placed and change the conditions of the air to which the infant is exposed. As a result, incubators have been arranged with openings extending along the access doors through which incubator air passes to develop warm air curtains which are intended to serve as shields to inhibit the ambient air from entering the space in which the infant has been positioned. 
     Some incubators are arranged to sense either the access door being opened or a change in temperature in the space in which the infant has been placed and change the heating and delivery of the air which is circulated through the incubator to compensate for the change in conditions by the entry of the ambient air. 
     SUMMARY OF THE INVENTION 
     An infant incubator, constructed in accordance with the present invention, includes a hood having an access door in a wall thereof and a base upon which the hood is mounted and having a deck which with the hood defines an enclosure. The deck has openings through which air enters and leaves the enclosure. Also included in this incubator are a heater within the base for heating the air and a fan for supplying air to the heater and heated air from said heater into the enclosure through at least one of the openings and for returning air from the enclosure to the heater through at least one of the openings. An infant incubator, constructed in accordance with the present invention, further includes sensing means responsive to movement of the access door for sensing when the access door is opened and control means responsive to the sensing means for increasing the heat generated by the heater and increasing the speed of said fan when the access door is opened. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of an incubator constructed in accordance with the present invention. 
     FIG. 2 is a top view of the heater and fan portions of the FIG. 1 incubator. 
     FIG. 3 is a side view of a sensor unit, constructed in accordance with the present invention, by which opening and closing of an access door of an incubator is sensed. 
     FIG. 4 is a block diagram of the sensor and temperature control portions of an incubator constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an infant incubator, constructed in accordance with the present invention, includes a hood  10  having an access door  12  in a wall  14  thereof. This incubator also has a base  16  upon which hood  10  is mounted and having a deck  18  which with the hood defines an enclosure. 
     Deck  18  has openings through which air enters and leaves the enclosure. For the infant incubator illustrated in FIG.  1  and being described, access door  12  is in a front wall of hood  10  and the hood has a second access door  20  in a rear wall  22  of the hood. Deck  18  has openings  24  and  26  extending along front wall  14  and rear wall  22 , respectively, of hood  10 . As shown by the arrows in FIG. 1, air enters the enclosure defined by hood  10  and deck  18  through openings  24  and  26  and leaves this enclosure through a third opening  28  extending along a third wall  29  of the hood. 
     When access door  12  is opened, the air passing through opening  24  in deck  18  forms a warm air curtain which serves as a barrier and reduces the effect of the ambient temperature outside the incubator on the enclosure defined by hood  10  and deck  18 . Similarly, a warm air curtain is formed at opening  26  in deck  18  when access door  20  is opened. 
     An infant incubator, constructed in accordance with the present invention, preferably includes a first inner wall  30  and a second inner wall  31 , respectively, secured to and movable with front access door  12  and rear access door  20 . Inner walls  30  and  31  reduce radiant heat losses when the respective access doors are closed and serve to carry warm air, introduced through openings  24  and  26  in deck  18 , to the top of hood  10  as indicated by the arrows. 
     An infant incubator, constructed in accordance with the present invention, also includes a heater within base  16  for heating the air circulated through the incubator and a fan for supplying air to the heater and heated air from the heater into the enclosure defined by hood  10  and deck  18  through at least one of the openings in the deck and for returning air from this enclosure to the heater through at least one of the openings in the deck. Referring to FIG. 2, a heater  32  is positioned in a first compartment  34  in the base of an incubator. A fan  36  is positioned in a second compartment  38  in the base of the incubator. As fan  36  turns, air is forced past heater  32  and conducted through suitable ducting into the enclosure defined by hood  10  and deck  18  of FIG.  1  and drawn from this enclosure through suitable ducting to the fan for recirculation. 
     An infant incubator, constructed in accordance with the present invention, also includes sensing means responsive to movements of access doors  12  and  22  for sensing when one or both of these access doors is opened, responsive to the temperature in the enclosure defined by hood  10  and deck  18  for measuring the temperature of this enclosure, and responsive to the skin temperature of an infant being treated in the incubator for measuring the skin temperature of the infant. These sensing means include, as shown in FIG. 3, a magnetic sensor composed of a magnetic reed switch  40  and a magnet  42  responsive to movement of an access door, a first temperature sensor  44 , shown in FIG. 1, responsive to the temperature to which an infant being treated in an incubator is exposed, and a second temperature sensor, identified in FIG. 1 by reference numeral  46 , responsive to the skin temperature of an infant being treated in the incubator. 
     Referring to FIG. 3, which shows the sensing means for access door  12  of hood  10 , the sensing means for each door include magnetic reed switch  40  mounted to base  16  and magnet  42  mounted to the access door and movable with the access door into and out of the range of the magnetic reed switch. After access door  12 , with magnet  42 , is moved a predetermined amount, for example 15 degrees, the magnet comes within the range of magnetic reed switch  40  and the magnetic reed switch is actuated. When access door  12  is closed and magnet  42  moves out of the range of magnetic reed switch  40 , the magnetic reed switch opens. 
     It is common practice to measure the temperature of the enclosure defined by hood  10  and deck  18  and the skin temperature of an infant being treated in an incubator and to use such temperature measurements to regulate the temperature in the enclosure. 
     An infant incubator, constructed in accordance with the present invention, also includes control means responsive to the magnetic sensor  40 ,  42  for increasing the heat generated by heater  32  and increasing the speed of fan  36  when an access door is opened. The control means are also responsive to the first temperature sensor  44  and the second temperature sensor  46  for controlling the amount of increased heat generated by heater  32  and the time period over which the increased heat is generated and the amount of increased speed of fan  36  and the time period the fan is operated at the increased speed. 
     Referring to FIG. 4, as one or both of the access doors of an incubator are opened, the magnetic reed switch  42  or  48  associated with the open door or doors closes and signals are supplied to inputs to a heater control processing module  50  and a fan control processing module  52  which, in turn, develop control signals which are supplied from outputs of heater control processing module  50  and a fan control processing module  52  to heater  32  and a fan  36  for increasing the heat generated by heater  32  and increasing the speed of fan  36  when an access door is opened. As one or both of the access doors in opened, there is no immediate effect on the air temperature within hood  10  at the location of temperature sensor  44  nor on the skin temperature of the infant at the location of skin temperature sensor  46 . Yet it is known that the air temperature in the vicinity of the infant drops when one or both of the access doors is opened. Consequently, the magnetic sensors associated with the access doors “over-ride” the usual control function of air temperature sensor  44  and skin temperature sensor  46  to increase the heat generated by heater  32  and to increase the speed of fan  36  when an access door is opened. When the effect of the access door being opened is sensed by air temperature sensor  44  and by skin temperature sensor  46 , control of heater  32  and fan  36  returns to air temperature sensor  44  and skin temperature sensor  46  and the amount of increased heat generated by heater  32  and the time period over which the increased heat is generated and the amount of increased speed of fan  36  and the time period the fan is operated at the increased speed are controlled by air temperature sensor  44  and skin temperature sensor  46  in the usual manner. 
     It is common practice to include in an infant incubator an alarm indicator when either the difference in actual infant skin temperature and a predetermined set point exceeds a predetermined threshold or the difference in actual air temperature within hood  10  and a predetermined set point exceeds a predetermined threshold. Typically, the alarm indication is delayed a prescribed period of time if the difference between the measured effect and the predetermined set point is due, for example, to a change caused by the operator of the incubator. For example, a significant drop in the skin temperature of the infant due to a change in the condition of the infant or a significant drop in the temperature of the air in the hood due to a failure in the air heating unit, each of which would cause the thresholds to be exceeded, should be alarmed immediately. In contrast, for example, opening an access door or raising the predetermined set point for the temperature of the air within the hood or raising the predetermined set point for the skin temperature of the infant, each of which can cause the difference in actual infant skin temperature and a predetermined set point to exceed a predetermined threshold or the difference in actual air temperature within the hood and a predetermined set point to exceed a predetermined threshold, should not be alarmed and would, in the absence of a delay in the alarm indication, indicate an alarm condition. Therefore, sufficient time is provided before an alarm condition is indicated for the incubator to stabilize when a condition, which might otherwise indicate an alarm condition, is created by the operator of the incubator. 
     Preferably, an incubator, constructed in accordance with the present invention, includes a third temperature sensor  52 , shown in FIGS. 1 and 4, for sensing the ambient temperature outside the incubator and controlling the delay, if any, in actuation of an alarm indicator  54 , shown in FIG. 4, when the difference between the actual infant skin temperature and a predetermined set point exceeds a predetermined threshold or the difference in actual air temperature within hood  10  and a predetermined set point exceeds a predetermined threshold. Ambient temperature can be a factor which determines rate at which readings of skin temperature and temperature of the air within the hood recover from readings affected by operator induced changes. Consequently, the control means include an alarm control module  56  which is responsive to ambient temperature sensor  52  for controlling alarm indicator  54  to delay actuation of the alarm indicator depending upon the ambient temperature. For example, the lower the ambient temperature, the longer the delay in actuation of alarm indicator  54  after an open access door is closed. 
     In addition, ambient temperature sensor  52  can be used to control the heater  32  and fan  36  speed and this is indicated in FIG. 4 by the connections between ambient temperature sensor  52  and heater control processing module  48  and fan control processing module  50 . Because ambient temperature can affect the temperature of the air within hood  10 , the ambient temperature, at the time an access door is closed, can be another input to controlling heater  32  and fan  36 . A range of ambient temperatures can be established by which the power delivered to heater  32  and the speed of fan  36  can be set to be dependent upon the particular ambient temperature at the time the access door was closed. 
     While there have been described preferred embodiments of the present invention, it should be obvious to those skilled in the art that various modification and changes can be made without departing from the true spirit and scope of the invention.