Abstract:
A modular patient care system having a central management unit module and one or more detachable functional units is described. Using unique mechanical and electrical features, the modular patient care system is capable of flexibly, bilaterally, and safely providing electrical power from the central management unit to the attached functional units, with exposed power leads of end units being electrically isolated for safety and security. Functional units are capable of detecting the presence of other functional units more distant from the central management unit for passing power to those units, and for otherwise electrically isolating exposed power leads when no further units are attached. Additionally, the modular patient care system provides for a modular connection arrangement wherein modules are detachably connected to each other in a convenient, flexible, interchangeable, and secure manner by providing a hinge connector pair, a specially located latch mechanism, and a guide means between any pair of modules.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/379,212, filed Aug. 23, 1999, now U.S. Pat. No. 7,074,205, which is a continuation of U.S. application Ser. No. 08/871,307, filed on Jun. 9, 1997, now U.S. Pat. No. 5,941,846, which is a continuation in part of U.S. application Ser. No. 08/403,503, filed on Mar. 13, 1995, now U.S. Pat. No. 5,713,856. The subject matter of U.S. application Ser. No. 08/403,503 is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to modular patient care systems. More specifically, the present invention relates to modular connection arrangement wherein modules are detachably connected to each other in a convenient, flexible, interchangeable, and secure manner. Additionally, the present invention relates to a scheme for flexibly, bilaterally, and safely providing electrical power from a central management unit to attached peripheral units. 
     BACKGROUND OF THE INVENTION 
     Systems containing multiple infusion pumping units, sensing units such as blood pressure monitors and pulse oximeters, and other patient-care units are known in the medical field. For example, Kerns et al (U.S. Pat. No. 4,756,706 “Kerns”) discloses a centrally managed pump system in which pump and monitoring modules are selectively attached to a central management unit. The central management unit controls the internal setup and programming of the attached modules, and receives and displays information from them. Each module is capable of being detached from the central management unit except for the first module, which is permanently attached. Once attached and programmed, a module which is subsequently detached is still capable of operating independently of the management unit. 
     Kerns provides for attachment of the modules in a vertical stacking sequence in a manner similar to that shown in  FIG. 1 . Attachment of an additional unit to the modular patient care system involves a multiple step process. These steps include (1) sliding a support plate  62  of the additional unit into the channel  64  of a previous unit, and (2) turning a knob  120 , causing male connectors  122  and  124  of the additional unit to pop up and mate with corresponding female portions in the previous unit (Kerns FIG. 3 and col. 4 lines 7-16). Thus, achieving mechanical and electrical connectivity in Kerns clearly involves a multi-step, two-handed operation. 
     Further, Kerns provides for distinct, direct electrical connectivity from each stack module to the central management unit. Each module is provided with a separate AC power signal from the central management unit AC+ and AC− leads. Each module also contains its own power supply for autonomous operation when disconnected from the central management unit (Kerns FIG. 6). 
     Kerns has several disadvantages. First, for electrical and mechanical connectivity of an added unit to the central management unit, a multi-step, two-handed operation is needed, which may be cumbersome and time consuming in the medical environment. Second, because each module requires its own set of electrical paths to the central unit, the total number of modules which may be stacked is only one greater than the number of pass-through cables in each module. For example, for the pass-through structure shown in Kerns FIG. 4 f , only four modules total may be accommodated by a system which uses these modules. Third, there is added weight, cost, and complexity due to the multiple cabling structure. For example, each signal of each cable must have its own contact pin in among the pins  122  of the contact structure of Kerns FIG. 3. Finally, the presence of a power supply in each functional module adds weight and cost. 
     Rubalcaba (U.S. Pat. No. 4,898,578) also discloses a drug infusion system which includes a plurality of infusion pump modules selectively attached to a central management unit so as to provide for centralized control. In particular, the central management unit obtains infusion parameters from the user and then performs calculations with the parameters to establish the desired infusion rate. Once this rate is determined, the central management unit may control the infusion accordingly. Rubalcaba, however, provides no solution for the problems related to electrical and mechanical connectivity of units described above with respect to Kerns. 
     Accordingly, it is an object of the present invention to provide a modular patient care system wherein modules are detachably connected to each other in a convenient, flexible, interchangeable, and secure manner. 
     It is another object of the present invention to provide a modular patient care system wherein each functional unit is powered by the central management unit using a common power bus scheme to avoid a multiplicity of power lines. 
     It is a further object to provide a flexible, bilateral power scheme wherein any functional unit may be placed anywhere in a linear array of units and be adequately powered. It is a further object of the present invention to make this powering scheme safe by avoiding active power supply voltages at exposed ends of the power bus. 
     SUMMARY OF THE INVENTION 
     These and other objects of the present invention are provided in a modular patient care system comprising an interface unit for providing a user interface to the system and for providing electrical power to at least one functional unit, the functional unit being capable of removable connection to the interface unit for providing patient therapies or monitoring the condition of the patient, the functional unit being for removable attachment to the interface unit or other functional units so as to form a linear array of units. The linear array of units comprises an originating end and a terminating end, and each unit has an originating side and a terminating side, the originating side of any unit being capable of removable connection to the terminating side of any other unit. In one embodiment, the originating side is the left side, and the terminating side is the right side of the linear array. 
     The interface unit according to the present invention has a left power lead for powering left side functional units and a right power lead for powering right side functional units. Power supply aspects of the left and right sides are substantially symmetric. Using the left side as an example, power supplying aspects of the interface unit are arranged so as to connect power to the left power lead when functional units are attached to the left, but to leave the left power lead electrically isolated when no functional units are attached to the left. This prevents the unsafe and insecure situation of a live voltage existing at an exposed left power lead of the linear array of units, which would be subject to shorting out or otherwise undesirably discharging. To accomplish this objective, the interface unit includes a power source for receiving electrical power from a power supply and providing electrical power, a detecting lead for detecting the presence of a right sense signal, such as a ground signal, from a unit attached to the left, means for coupling the power source to the left power lead in the presence of the right sense signal, and means for decoupling the power source from the left power lead in the absence of the right sense signal. In one embodiment, the detecting lead is connected to a gate of a field effect transistor, the power source is connected to a drain of the field effect transistor, and the left power lead is coupled to a source of the field effect transistor. 
     A flexible, bilateral, and safe powering scheme in the modular patient care system according to the present invention is also provided for by providing an exemplary functional unit having a left lead and a right lead, the left lead for contacting the right lead of a left adjacent functional unit or the right power lead of the left adjacent interface unit in the linear array, the right lead for contacting the left lead of a right adjacent functional unit in the linear array or the right power lead of the right adjacent interface unit in the linear array. The functional unit has a load unidirectionally coupled to the left and right leads and capable of receiving electrical power from either of the leads. The functional unit also has a right sense signal lead for providing a right sense signal to the adjacent right unit, if any, and a left detect lead for detecting the right sense signal from the adjacent left unit, if any. Further, the functional unit also has a left sense signal lead for providing a left sense signal to the adjacent left unit, if any, and a right detect lead for detecting the left sense signal from the adjacent right unit, if any. Finally, the functional unit comprises means for bidirectionally connecting the left power lead to the right power lead only upon detecting both left and right signals. 
     In this manner, a functional unit which is located between two other units in the linear array is capable of powering its load while also passing power, in either direction as needed, to the adjacent unit which is located farther away from the interface unit. However, if the functional unit is located at the left end of the linear array, the left power lead remains electrically isolated because no right sense signal is detected. Likewise, if the functional unit is located at the right end of the linear array, the right power lead remains electrically isolated because no left sense signal is detected. In this manner, the functional units are capable of flexible, bilateral power connection in the linear array of units, and live power contacts are prevented from existing at the leads located at the ends of the linear array of units for safety and security. 
     In another embodiment of the invention, a modular patient care system is provided having an interface module for providing a user interface to the system and at least one functional module capable of removable connection to the interface module. The functional module is for providing patient therapies or monitoring the patient&#39;s condition and is capable of removable attachment to the interface module or other functional modules so as to form a linear array of modules. The linear array of modules comprises an originating end and a terminating end, and each module has an originating side and a terminating side, the originating side of any module being capable of removable connection to the terminating side of any other module. 
     Physically, an exemplary functional module according to the present invention comprises a first portion grippable by a user and is configured and dimensioned so as to be capable of being held by a single hand of the user by gripping the first portion. Any pair of modules, including for example the interface module and the exemplary functional module, are easily, flexibly, and interchangeably coupled by including a hinge connector pair for allowing hingeable engagement of the pair, a latch mechanism for securing the pair together, and a guide mechanism located between the hinge connector pair and the latch mechanism for discouraging off-axis engagement of the modules and for providing mechanical stability to the engaged pair. The latch mechanism is designed to automatically secure the pair together, such that engagement of the modules takes place in a single-handed, single step operation, but is designed to require a manual operation by a hand separate from the hand gripping the first portion to unlatch the modules during disengagement. This provides for increased security and prevention of accidental disengagement of modules. Preferably, the latch mechanism springably couples together such that tactile feedback is provided to the user during attachment. An optional fastener for fastening the latching mechanism together may be included, which requires a special tool for unfastening the latching mechanism so as to further increase system security at the option of the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a multi-module electronic system wherein the individual modules are interconnected electrically and structurally in accordance with the present invention; 
         FIG. 2  shows an oblique view of two modules showing structural and electrical features for module connection in accordance with the present invention; 
         FIG. 3   a  shows a front view of the modules shown in  FIG. 2  positioned for subsequent engagement with each other, with portions broken away to reveal the connection scheme according to the present invention and associated electronic components; 
         FIG. 3   b  shows the modules of  FIG. 3   a  after engagement; 
         FIG. 4  shows an exploded perspective view of a single module showing the interconnector parts of the present invention enlarged and out-of-scale; 
         FIG. 5   a  shows a bottom view of a pair of engaged modules in accordance with an embodiment of the present invention; 
         FIG. 5   b  shows a front cut-away view of the modules of  FIG. 5   a  to reveal a latching and locking scheme in accordance with an embodiment of the present invention; 
         FIG. 6  shows a functional diagram of the power provision features of the interface unit according to the present invention; 
         FIG. 7  discloses a functional circuit diagram of the bilateral powering features of a functional unit in accordance with the present invention; and 
         FIG. 8  shows a functional diagram of the unit detection and power features of a modular patient care system in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following embodiments of the present invention will be described in the context of a modular patient care system, although those skilled in the art would recognize that the disclosed methods and structures are readily adaptable for broader application. Note that whenever the same reference numeral is repeated with respect to different figures, it refers to the corresponding structure in each figure. 
       FIG. 1  discloses a modular patient care system  100  in accordance with the present invention. Modular patient care system  100  comprises a plurality of modules or units, including interface unit  102  and functional units  104 , detachably coupled to each other to form a linear array. Shown in  FIG. 1  are exemplary functional units  104 A,  104 B,  104 C, and  104 D coupled to interface unit  102 . While four functional units are shown in  FIG. 1 , a modular patient care system in accordance with the present invention may comprise interface unit  102  coupled to only a single functional unit  104 , or may comprise interface unit  102  coupled to as many as “N” functional units  104 . 
     Interface unit  102  generally performs the functions of (1) providing a physical attachment of the system to structures such as IV poles and bedrails, (2) providing electrical power to the system, (3) providing an interface between the system and external devices, (4) providing a user interface to the system, and (5) providing overall system control, which includes providing information to and receiving information from functional units  104 . Shown in  FIG. 1  are certain user interface aspects of interface unit  102 , which may include an information display  106 , numerical hardkeys  108 , and softkeys  110 . 
     Functional units  104  are generally for providing patient therapies or monitoring responsive to information, at least some of which may be received from interface unit  102 . In many cases, functional units  104  are also for communicating information to interface unit  102 . For example, functional unit  104 A may be an infusion pump unit for delivering fluids to a patient responsive to certain commands received from interface unit  102 , while functional unit  104 B may be a blood pressure monitoring unit for providing patient blood pressure information to the interface unit  102 . The scope of the invention is not so limited, however. 
     For the purposes of the present invention, the specific function of each individual functional unit  104  is not critical. Rather, the present invention is directed toward (1) the mechanical and electromechanical coupling of the functional units  104  to each other and to interface unit  102 , and (2) the electrical powering scheme of the modular patient care system  100 . Thus, for purposes of understanding the present invention, it is important only to recognize that functional units  104  (1) require means for detachably coupling to each other and to interface unit  102 , and (2) require electrical power. 
     In a preferred embodiment of the present invention, interface unit  102  and functional units  104  are laterally interchangeable. By laterally interchangeable, it is meant that the modules may be placed in any order in forming a linear array of modules. Thus, in  FIG. 1 , the modular patient care system  100  may instead have its modules ordered left-to-right in the sequence  104 C,  102 ,  104 B,  104 D,  104 A without affecting its functionality. In order to be laterally interchangeable, the units  102  and  104  of  FIG. 1  should have substantially identical interconnection features on their respective left sides, and should have corresponding substantially identical interconnection features on their right sides. If the units were instead for coupling in a vertical linear array, which is within the scope of the present invention, the interconnection features would have substantially identical interconnection features on their respective top sides, and would have corresponding substantially identical interconnection features on their bottom sides. For clarity of explanation, however, only a left-to-right physical arrangement is described. 
     To achieve the lateral interchangeability described above, each of the units  102  and  104  should also have power, unit detection, and communication circuitry which is complementary. By complementary, it is meant that the units  102  and  104  generally have power, unit detection, and communications circuit contacts on a first side and on a second side, and that the first side contacts of one unit may be connected to corresponding second side contacts of any other unit, with the overall linear array of units comprising modular patient care system  100  being fully operational. In  FIG. 1 , for example, the first side of a unit is the left side, and the second side of a unit is the right side. Further to this example, and as further explained later, functional unit  104 C must be capable of receiving electrical power from interface unit  102  to its left and transferring it to unit  104 D to its right; yet, if physically interchanged with functional unit  104 B, unit  104 C must be capable of receiving electrical power from interface unit  102  to its right and transferring it to unit  104 A to its left, and so on. 
     As shown in  FIG. 1 , each functional unit  104  may include a unit ID indicator  112  which identifies a logical address of the functional unit within the linear array. The logical address of a functional unit  104  indicates its position in the linear array relative to other functional units  104 . The logical address of a functional unit  104 , such as unit  104 B, is used by the interface unit  102  to identify and uniquely communicate with functional unit  104 B in a common communications bus environment to be described later. In a preferred embodiment of the invention, the logical address of a functional unit corresponds to its sequential position in the linear array of functional units. Thus, the system shown in  FIG. 1  may illustratively contain functional units  104 A 1041 ) with logical addresses A, B, C, and D, ordered left to right. In this embodiment, the left side of the leftmost unit forms an originating end of the linear array, while the right side of the rightmost unit forms a terminating end of the linear array. 
     In order to provide increased safety, it is preferable that the system be designed such that SELECT key  156  (see  FIG. 1 ) located on the  104  functional unit be depressed in order to select that functional unit. This requirement will help insure that the proper functional unit is selected, in particular when infusion pump units are used for multiple drug infusions. When the desired functional unit is selected, display  102  of the interface unit is configured so as to act as the user interface for the selected functional unit. More specifically, display  102  is configured in accordance with a function specific domain to provide function specific displays and softkeys. 
     Referring now to  FIGS. 2 through 4 , the mechanical and electromechanical aspects of interface unit  102  and functional units  104  as designed in accordance with a first embodiment of the present invention are now described. For purposes of the first embodiment of the present invention, interconnection features of interface unit  102  are substantially identical to interconnection features of functional units  104 . Therefore, only an exemplary unit  104 A will be described. Also, an exemplary unit  104 B, substantially identical to unit  104 A and for connecting thereto, will be described when needed for clarity. 
       FIG. 2  shows an oblique representation of exemplary units  104 A and  104 B positioned before being matably connected, while  FIGS. 3   a  and  3   b  show appropriate cut-away views of units  104 A and  104 B during and after the connection process, respectively. 
     As shown in  FIG. 2 , unit  104 A comprises a chassis  200  having a left side  202 , a front  204 , and a right side  206 . It is to be appreciated that although  FIG. 2  shows numbered components on units  104 A and  104 B according to their visibility in the oblique drawing, the units  104 A and  104 B contain substantially identical numbered components. Unit  104 A further comprises a male connector portion  208  on right side  206 , a female connector portion  210  on left side  202 , a male elevation feature  212  formed on right side  206 , a female recess feature  214  formed in left side  202 , a catch feature  216  formed near the bottom of right side  206 , and a latch  218  near the bottom of left side  202 . Unit  104 A further comprises cover  220  tethered to male connector portion  208  for covering the male connector portion  208  during periods of non-use, and pocket  222  formed in right side  206  near male connector portion  208  for receiving cover  220  otherwise. Unit  104 A further comprises cover  224  tethered to female connector portion  210  for covering female connector portion  210  during periods of non-use, and pocket  226  formed in left side  202  near female connector portion  210  for receiving cover  220  otherwise. 
     Generally, as shown in  FIGS. 3   a  and  3   b , units  104 A and  104 B are designed to be connected using the steps of (1) tilting the units relative to each other while inserting male connector portion  208  into female connector portion  210 , (2) swinging down the units to a nearly parallel position such that male elevation feature  212  is received into female recess feature  214  and latch  218  is received into catch feature  216 , and (3) pressing the units together such that latch  218  is locked into catch feature  216 . 
     Male connector portion  208  of unit  104 A is positioned and formed for hingeable connection with female connector portion  210  of unit  10413  for achieving mechanical and electrical coupling of units  104  and  105 . In a preferred embodiment of the invention, male connector portion  208  and female connector portion  210  also form a 15-pin electrical connector pair for electrically coupling. This electrical connector pair is for electrically coupling electronic components contained in units  104 A and  104 B, these electronic components being shown generally as elements  300  in  FIGS. 3   a  and  3   b . The geometry of male connector portion  208  and female connector portion  210  include lead-in and chamfer to reduce the probability of dropping and off-axis insertion. Advantageously, the geometry of the male-female pair is designed to prevent a unit from falling off if it is hooked but not yet latched. The mechanical characteristics of the male-female pair are detailed in U.S. patent application Ser. No. 08/403,502, cross-referenced above. 
     Male elevation feature  212  is formed on right side  206  of unit  104 A for mating with female recess feature  214  formed in left side  202  of unit  104 B to provide multiple contact surfaces for improved front to back stability during vibration of the connected units. Further, the geometry of male elevation feature  212  includes lead-in and chamfer for mechanical guidance into recess feature  214  such that the probability of off-axis insertion is reduced. 
     Latch  218  is for engaging a catch feature  216  during connection. This keeps the units together mechanically after attachment. In a preferred embodiment, latch  218  is spring loaded with a pre-load force sufficient to positively engage the catch feature  216 , close, and remain latched unless disengaged by an operator. Also in a preferred embodiment, techniques known in the art may be used to shape latch  218  and catch feature  216  such that a small vibration resonates through units  104 A and  104 B upon attachment, to provide tactile feedback to the user. 
     Cover  220  is for covering male connector portions  208  during transport and periods of non-use. In a preferred embodiment of the invention, cover  220  is made of an elastomeric material which is elastic and waterproof. Cover  220  is tethered to male connector portion  208  to reduce the possibility of being lost or misplaced by the user, and is dimensioned and configured to be swung up and over male hook feature  208  for protection. Pocket  222  is formed in right side  206  beneath male connector portion  208  for receiving cover  220 , which nests into pocket  224  when not in use. Cover  220  may be swung up out of pocket  222  to cover male connector portion  208  to protect connector portion  208  from dust or fluids. Similar purpose, material, and configurations apply to cover  224  and pocket  226 . Advantageously, the covers  220  and  224  and pockets  222  and  226  are configured and dimensioned such that the covers recess flush yet are partially compressed when the units  104 A and  104 B are attached, thus providing additional shock cushioning and preventing rattling during vibration or transport. 
     In a preferred embodiment of the invention, the size and geometry of unit  104 A is generally such that it may be held by a single hand of a user, although the invention is not necessarily so limited. This is generally the same user hand which receives the tactile feedback described above upon unit attachment. 
       FIG. 4  shows a view of unit  104 A exploded to more succinctly show male connector portion  208  and female connector portion  210  with respect to a preferred embodiment of the invention. Specifically, male connector portion  208  comprises electrical contacts  400  contained on a curved lip  404  formed on a body portion  406 . Further, female connector portion  210  comprises electrical contacts  408  protruding into an aperture  410  formed in body portion  412 . In a preferred embodiment of the invention, the contact geometry and orientation of electrical contacts  400  and  408  may allow a first set of individual electrical contact pairs formed by joining the connectors to make electrical connection prior to a second set of electrical contacts during connection. A result of this geometry and orientation will be that the first set of contacts will also break after the second set of contacts during disconnection. This ensures, for example, that an electrical ground connection between the units may made first during module attachment, creating a path to dissipate electrostatic discharge. 
     Also in a preferred embodiment of the invention, body portions  406  and  412  are made of a low surface energy/hydrophobic material to shed fluid from exposed surfaces. Also, an a preferred embodiment the electrical contacts  400  and  408  are insert-molded into body portions  406  and  412 , which prevents extraneous fluids from accumulating adjacent to electrical connections. 
       FIGS. 5A and 5B  show units  104 A and  104 B with additional features in accordance with a preferred embodiment of the invention.  FIG. 5A  shows a bottom view of coupled units  104 A and  104 B. Unit  104 B comprises latch  218  for engaging catch feature  216  of unit  104 A. In this embodiment however, a fastener  500  may be employed to provide a means for making the attachment of units  104 A and  104 B permanent until the fastener  500  is released by a user using a releasing technique. This releasing technique may employ the use of a special tool (not shown) made available only to specified users.  FIG. 5B  shows a side view of latch  218  engaged to catch feature  216 , further showing a latch tongue  502  of latch  218  which forms a hole  504  in an area which overlaps catch feature  216 . Fastener  500  which is, for example, a screw, is inserted from the bottom of functional unit  104 A near catch feature  216  through hole  504  and into a boss  506  contained in functional unit  104 A near catch feature  216 . The configuration shown advantageously provides for permanent attachment of the units until a user such as a medical technician disengages fastener  500 . In this manner, for example, miscellaneous persons around and in the area of the modular patient care system  100  are prevented either from intentionally or accidentally causing disconnection of units. 
     The unique combination of the module elements described thus far provide for many advantages in stability, safety, security, and ease of use. For example, the attachment of a functional unit may be achieved in a one hand, single step operation, while the presence of latch  218  and catch feature  216  dictate that detachment must take place in a two step operation. This is advantageous in a medical environment where quick, easy attachment of units to the linear array may be necessary, but where detachment of units should be permissible only upon an explicit, reasoned desire of a user and not by accident. This feature is enhanced an a preferred embodiment of the invention employing a fastener  500 , wherein further steps are needed to detach modules. 
     Further, the ease of the one-handed, single step operation in the attachment of units is enhanced where latch  218  and catch feature  216  provide for tactile feedback during the attachment operation. This is advantageous in the medical environment by freeing up the eyes of the user during attachment to pay attention to more sensitive events taking place, such as insuring that needles, lines, fluids, or pumps are not being disturbed during the mechanical movement. Further, the avoidance of the need for visual feedback to the user may save precious moments during medical emergencies when the user&#39;s eyes are more advantageously averted to the emergency at hand. 
     Even further, the presence of male elevation feature  212  mated to recess feature  214  provides for additional front to back stability of the units during handling and abuse. These features also provide guidance during connection to prevent off-axis insertion. Vibration of coupled units is further reduced by the compression of covers  220  and  224  against each other and pockets  222  and  226 . 
     Even further, several means exist to protect the electrical connections from fluid ingress when units are not connected. First, the contact geometry, contact orientation, and hook geometry as shown in  FIG. 4  prevent fluid from accumulating on surfaces of the male connector portion  208 . Similarly, the contact geometry, contact orientation, and contact location of the electrical contacts  408  prevent fluid from accumulating on surfaces of the female connector portion  210 . Use of low surface energy/hydrophobic material for body portions  406  and  412 , insert-molding of the contacts  400  and  408 , and the presence of covers  220  and  224  further  25  discourage unwanted fluid accumulation and ingress. 
     In the modular patient care system  100  of  FIG. 1 , electrical power is supplied to functional modules  104  by interface unit  102 . The interface unit  102 , in turn, may be powered by conventional methods known in the art. At least one electrical power path exists among the electrical contacts  408  and  400  at the connecting point of any two units. 
     The goal of a module powering system designed in accordance with the present invention is, first, for interface unit  102  to provide power to any attached module or set of modules by powering immediately adjacent modules. Thus, in  FIG. 1 , interface unit  102  is to supply electrical power to all functional units  104  by powering functional units  104 B and  104 C, which each use a portion of this power and which, in turn, transfer at least a portion of this power further down the line to units  104 A and  104 D, respectively. 
     Second, the module powering system in accordance with the present invention is to permit lateral interchangeability of the modules, and thus the powering system of any functional unit  104  is to be bilateral. By bilateral, it is meant that the functional unit  104  may receive power from either its first or second side, and may transmit this power, if necessary, to attached units on its second or first side, respectively. 
     Third, it has been found that a module powering system according to the present invention is to comprise an interface unit  102  and functional units  104  which, if they are positioned on the originating or terminating end of a linear array, do not allow a live voltage to exist at the open electrical contacts which will exist at these ends. Such a requirement provides, for example, for added security of the unit from power failure due to accidental or intentional shorting of the exposed power leads. 
     Turning now to  FIGS. 6 through 8 , a module powering system according to a second embodiment of the present invention is described.  FIG. 6  shows a functional diagram of the power aspects of interface unit  102  designed in accordance with the present invention. Interface unit  102  comprises a microprocessor  600 , a power source  602 , a left transistor  604 , and a right transistor  606 . Power source  602  is adapted for providing an 8-volt DC voltage by either generating its own power, as from a DC voltage source such as an internal battery, or for adapting power from an external AC or DC source, as is known in the art. The 8 volts DC provided by power source  602  is provided by lead  607  with respect to the ground plane of interface unit  102 , denoted generally by element  608  in  FIG. 6 . Interface unit  102  further comprises left and right power leads  610  and  612 , respectively, for coupling to and providing power to left and right adjacent functional units, respectively, when connected. Power leads  610  and/or  612  will be left open, however, when adjacent units are not connected. Interface unit  102  further comprises left and right module detect leads  614  and  616 , respectively, for detecting the presence of attached functional units on the left and right sides, respectively. Interface unit  102  further comprises ground leads  618  to  620  for providing left and right sense signals, respectively (which in this embodiment are ground signals) to adjacently attached units. It is noted that additional electrical contacts not shown may provide an overall ground plane signal to attached functional units, as is known in the art. 
     As shown in  FIG. 6 , lead  607  of power source  602  is coupled to the source of left transistor  604  and also to the source of right transistor  606 . In the embodiment shown, transistors  604  and  606  are, in this embodiment, P-channel enhancement MOSFETs. The gate of left transistor  604  is coupled to left module detect lead  614 , while the gate of right transistor  606  is coupled to right module detect lead  616 . Finally, the drain of left transistor  604  is coupled to left power lead  610 , while the drain of right transistor  606  is coupled to right power lead  612 . 
     As shown in  FIG. 6 , transistor  604  will conduct (i.e., create a “short” between its drain and source) when its gate is low with respect to the source, and will not conduct (i.e., create an “open”) when its gate is high. Transistor  606  behaves similarly. Thus, if left module detect lead  614  is grounded by attachment to an external signal, such as a signal provided by an attached functional unit to the left, transistor  604  will conduct, and thus power lead  610  will be coupled to power source lead  607  to provide power. When left module detect lead  61 . 4  is left open, as when a unit is not attached to the left, transistor  604  does not conduct and leaves power lead  610  electrically isolated from power source lead  607 . This, of course, is a desired result. Similar characteristics exist for right module detect lead  616 , transistor  606 , and right power lead  612 . 
     It is noted that the coupling of the left module detect lead  614  to microprocessor  600  at pin MODDETL shown in  FIG. 6  does not affect the powering aspects described here, as pin MODDETL is only for detection purposes of the microprocessor for purposes to be described later.—A similar note applies to right module detect lead  616  and pin MODDETR of microprocessor  600 . Finally, it is noted that Schottky diodes  626  and  628  are provided across the drain and source of transistors  604  and  606 , respectively, for protection against reverse voltages, as is known in the art. 
       FIG. 7  shows a functional diagram of the power aspects of an exemplary functional unit  104 A designed in accordance with the present invention. Functional unit  104 A comprises a microprocessor  700  and a load  702  such as an infusion pump motor. It is noted that load  702  may represent any kind of electrical system requiring power, however. Functional unit.  104 A further comprises a left transistor  704  and a right transistor  706 . Load  702  receives electrical power provided between an input node  707  and a ground plane, generally denoted by element  708  in  FIG. 7 . Functional unit  104 A further comprises a left power lead  710 , a right power lead  712 , a left module detect lead  714 , a right module detect lead  716 , a left ground lead  718 , and a right ground lead  720 . 
     As shown in  FIG. 7 , the drain of left transistor  704  is coupled to the drain of right transistor  706 . Transistors  704  and  706  are, in this embodiment, P-channel enhancement MOSFETS. The source of left transistor  704  is coupled to left power lead  710 , while the source of right transistor  706  is coupled to right power lead  712 . Left power lead  710  is also coupled through a resistor  722  to the left module detect lead  714 , which is in turn coupled directly to the gate of right transistor  706 . Correspondingly, right power lead  712  is coupled through a resistor  724  to the right module detect lead  716 , which is in turn coupled directly to the gate of left transistor  704 . Left power lead  710  is coupled to the cathode of a diode  726  whose anode is in turn coupled to input node  701  of load  702 . Likewise, right power lead  712  is coupled to the cathode of a diode  728  whose anode is in turn coupled to the input node  707  of load  702 . In this manner, if a positive power voltage is present at lead  710 , power is supplied to load  702  without being supplied to lead  712  unless both transistors  704  and  706  are conductive. Likewise, if a positive power voltage is present at lead  712 , power is supplied to load  702  without being supplied to lead  710  unless both transistors  704  and  706  are conductive. 
     As shown in  FIG. 7 , transistor  704  will conduct (i.e., create a “short” between its drain and source) when its gate is low with respect to the source, and will not conduct (i.e., create an “open”) when its gate is high. Transistor  706  behaves similarly The gate of transistor  704  will be forced low when right module detect lead  716  is grounded by an adjacent attached unit to the right. Correspondingly, the gate of transistor  706  will be forced low when left detect lead  714  is grounded by an adjacent attached unit to the left. It is noted that Schottky diodes  730  and  732  are provided across the drain and source of transistors  704  and ″ 106 , respectively, for protection against reverse voltages, as is known in the art. It is noted that, as described above and as shown in  FIG. 7 , module  104 A forms a laterally symmetric powering arrangement. 
     As described herein, a modular patient care system  100  comprising the interface unit of  FIG. 6  and functional modules according to  FIG. 7  advantageously provides for bilateral power sourcing and transfer through the functional modules  104 , while providing electrical isolation of power leads of units at the originating and terminating ends, respectively. 
       FIG. 8  shows the modules of  FIG. 6  and  FIG. 7  arranged in an exemplary arrangement comprising functional unit  104 A at the originating (left) end, functional unit  104 D at the terminating (right) end, and units  104 B,  102 , and  104 C in the middle, respectively. As shown in  FIG. 8 , the electrical leads between units are arranged according to the following simple scheme. Left power leads ( 610  or  710 ) are coupled to right power leads ( 712  or  612 ) in any pair of adjacent units. Left module detect leads ( 714  or  614 ) are coupled to right ground leads ( 620  or  720 ) in any pair of adjacent units. Finally, left ground leads ( 618  or  718 ) are coupled to right module detect leads ( 716  or  616 ) in any pair of adjacent units. 
     Serving as an example of a system according to the present embodiment of the present invention, the powering configuration of the modular patient care system  100  shown in  FIG. 8  advantageously functions as follows. 
     Looking to the left of interface unit  102 , lead  720  of unit  104 B grounds the gate of left transistor  704  of unit  102  via module detect lead  614 . Transistor  604  is turned on, and power is thus supplied through left power lead  610  of unit  102  to right power lead  712  of unit  104 B, thus powering the load  702  of unit  104 B. Left ground lead  618  of unit  102  grounds the gate of left transistor  704  of unit  104 B through right module detect lead  716 , making transistor  704  conductive. Further, right ground lead  720  of unit  104 A grounds the gate of right transistor  706  of unit  104 B, making transistor  706  conductive. The result is that both of transistors  704  and  706  of unit  104 B are conductive, and thus power lead  712  of unit  104 A will receive power from left power lead  710  of unit  104 B. Therefore, load  702  of unit  104 A will be powered, and thus left side units  104 A and  104 B are fully powered. 
     However, there is no ground signal provided to left module detect lead  714  of unit  104 A because it is the leftmost unit. Thus, right transistor  706  of unit  104 A remains turned off. The result is that left power lead  710  of leftmost unit  104 A is electrically isolated from right power lead  712 , which is the desired result. It should be clear to anyone of ordinary skill on the art, given the lateral symmetry of the powering arrangement described above, that right side units  104 C and  104 D operate in a similar but reflexive fashion to the left side units  104 A and  104 B. Thus, power is provided to both units  104 C and  104 D, but right power lead  712  of rightmost unit  104 D remains electrically isolated from a power source. This, of course, is the desired result. 
     Additionally, it should be clear to anyone of ordinary skill in the art that the units  102  and  104 A through  104 D can be arranged in any order in  FIG. 18  with the desired result of (1) powering of all units, (2) electrical isolation of the left power leads  710  or  610  of the leftmost (originating) unit, and (3) electrical isolation of the right power leads  712  or  612  of the rightmost (terminating) unit. Various embodiments of the invention have been described. The descriptions are intended to be illustrative, not limitative. Thus, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.