Abstract:
A floating gearbox includes an outer housing with first and second side walls opposite and spaced apart from each other and an inner gear assembly received within the outer housing. The inner gear assembly comprises an inner housing, a first gear member rotatably received within the inner housing, and a second gear member having an output shaft rotatably supported on the inner housing. A slider plate received within the outer housing has first and second pairs of axially aligned elongate openings, wherein the first and second pairs of elongate openings align with a first axis and a second axis, respectively. Pins on the first sidewall are received in the first pair of elongate openings to allow relative sliding movement between the outer housing and the slider plate along the first axis. The inner housing includes pins received in the second pair of elongate openings, allowing relative sliding movement between the inner housing and the slider plate along the second axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit under 35 U.S.C. §119(e) of U.S. provisional patent application Nos. 61/323,168 filed Apr. 12, 2010, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to a floating gearbox apparatus and method. The present development will be described primarily by way of reference to a gearbox for use in a fluid flow control system such as an intravenous (IV) pump. However, it will be recognized that the present gearbox will find utility in all manner of applications wherein it is desired to couple the output shaft of a gear transmission system to a shaft to be driven. 
         [0003]    Flexible couplings for joining drive shafts exist; however, they only accommodate slight axial and angular misalignment. It would, therefore, be desirable to provide a gear transmission system that can accommodate a large tolerance loop between the location of the output shaft and the location of the driven shaft. 
         [0004]    Additionally, the standard flexible couplings are primarily designed to couple two permanently fixed shafts. It would also be desirable to provide a gear transmission system that couples an output shaft to a snap in driven shaft. 
         [0005]    One disadvantage of flexible shaft couplings is that they induce a torsional flexibility into the system, which can result in an error if the position of the driven shaft is being read by an encoder. It would, therefore, also be desirable to provide a gear transmission system that does not induce torsional flexibility into the system. 
         [0006]    Accordingly, the present disclosure contemplates a floating gearbox that overcomes the above problems and others. The present disclosure also contemplates a fluid control system and method employing the same. 
       SUMMARY 
       [0007]    In one aspect, the present disclosure provides a gearbox for transmitting rotation from an input shaft to an output shaft, wherein the gearbox is movable along two intersecting (and preferably perpendicular) axes lying in a plane that is perpendicular to the axis of rotation of the output shaft. In more limited aspects, a gearbox for adjusting a flow resistor in a flow control system, and a method and flow control system employing the same, are provided. The floating gearbox disclosed herein includes an outer housing, a slider plate, and an inner gearbox assembly. The outer housing comprises a front housing component and a rear housing component. The slider plate comprises a plate having two elongated openings along a first axis and two elongated openings along a second axis. The inner gearbox assembly comprises a front inner housing component, a rear inner housing component, a motor driving a worm, a helical gear driven by the worm, and a rotary encoder for sensing a rotational position of an output shaft of the helical gear. 
         [0008]    The slider plate is placed on the inner gearbox assembly aligning the two pins on the inner gearbox assembly with the corresponding openings on the slider plate, enabling the slider plate to move in a first direction relative to the inner gearbox assembly. The inner gearbox assembly and slider plate combination is then placed into the front outer housing component aligning the two pins on the front outer housing component with the corresponding openings on the slider plate, enabling the slider plate to move in a second direction relative to the front outer housing. 
         [0009]    In exemplary embodiments, the two sets of openings in the slider plate are perpendicular, enabling the inner gearbox assembly to move in two cardinal directions, without causing any coupling or restorative forces when a torque is applied at the output shaft, which extends in the third cardinal direction. In further embodiments, the drive axis may be in line with two axes of movement of the slider plate. However, as shown in the depicted embodiment, the slider plate elongate openings may be offset relative to the drive axis, for example, where space of size limitations of the gearbox dictate, although it is desirable in such instances that the slider plate openings be placed as close as possible to the output axis to reduce any off-axis forces at the output shaft. 
         [0010]    Once the inner gearbox assembly and slider plate have been properly aligned and placed within the front outer housing component, the rear outer housing component is placed over the inner gearbox assembly and slider plate combination and secured via mechanical fasteners. After the floating gearbox is secured, an output drive shaft is inserted into the gear shaft and a tension member is then connected between a spring pin on the rear outer housing and a spring pin on the inner gearbox assembly. The tension member preloads the gearbox into the upper, centered position. The tension member should provide only a relatively small force, i.e., one that is large enough only to ensure that the gearbox is centered, while not imparting any significant force against the driven shaft. 
         [0011]    In the depicted preferred embodiment, the floating gearbox is assembled and mounted into a pump assembly. The front and rear outer housing shells of the floating gearbox are rigidly attached to bosses inside the pump housing. When the pump assembly is ready to be used, an administration set is snapped into the pump assembly and the output drive shaft of the floating gearbox assembly is pushed into the correct position to drive the adjustment cap (i.e., the driven shaft) of the fluid flow resistor. When assembled, the slider plate enables the output shaft of the floating gearbox to float freely as it interfaces with the adjustment cap, thereby reducing or minimizing the potential for binding. 
         [0012]    In another aspect, a method for controlling a fluid flow rate in a flow control system using a floating gearbox assembly is provided. Infusion data is input and processing electronics operate the motor under programmed control to rotate the output drive shaft via the floating gear transmission system. The output drive shaft, in turn, drives an adjustment cap of the fluid flow resistor to vary the valve position in a fluid flow resistor to thereby control or adjust the rate of fluid flow to the patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the detailed description herein, serve to explain the principles of the invention. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
           [0014]      FIG. 1A  is a partially exploded isometric view of an exemplary floating gearbox embodiment. 
           [0015]      FIG. 1B  is an isometric view of the exemplary floating gearbox embodiment appearing in  FIG. 1A . 
           [0016]      FIG. 2A  is an exploded side view of the front outer housing and slider plate of the floating gearbox. 
           [0017]      FIG. 2B  is an isometric view of the front outer housing and slider plate of the floating gearbox shown in  FIG. 2A . 
           [0018]      FIG. 3A  is an exploded isometric view of the inner gearbox assembly and slider plate of the floating gearbox. 
           [0019]      FIG. 3B  is an isometric view of the inner gearbox assembly and slider plate of the floating gearbox shown in  FIG. 3A . 
           [0020]      FIG. 4  is an exploded view of the inner gearbox assembly. 
           [0021]      FIG. 5  is an exploded view of the floating gearbox. 
           [0022]      FIG. 6A  is a partially exploded view of the floating gearbox illustrating the means of attachment of the output drive shaft to the floating gearbox. 
           [0023]      FIG. 6B  is an isometric view of the floating gearbox with the output drive shaft attached. 
           [0024]      FIG. 7A  is a partially exploded view of the floating gearbox illustrating the means of attachment of the biasing spring to the floating gearbox. 
           [0025]      FIG. 7B  is an isometric view of the floating gearbox with the biasing spring attached. 
           [0026]      FIG. 8A  is an isometric view of the pump assembly with the floating gearbox mounted into the pump assembly, taken generally from the front and side. 
           [0027]      FIG. 8B  is an isometric view of the pump assembly appearing in  FIG. 8A , with an administration set partially snapped into the pump assembly. 
           [0028]      FIG. 9  is an isometric view of the pump assembly appearing in  FIG. 8B , taken generally from the rear and side. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Referring to the drawings, wherein like reference numerals are used to indicate like or analogous components throughout the several views, and with particular reference to  FIGS. 1A and 1B , there is illustrated an exemplary embodiment floating gearbox  10 , which includes a front outer housing  20 , a slider plate  40 , an inner gearbox assembly  60 , and a rear outer housing  100 . The slider plate  40  and inner gearbox assembly  60  are secured between the front outer housing  20  and rear outer housing  100 . The front housing  20  is secured to the rear housing  100  via mechanical fasteners  12 , such as screws, rivets, clips, dogs, pawls, or the like. 
         [0030]    As best seen in  FIGS. 2A and 2B , the front outer housing  20  contains a front wall  30 , a first side wall  32 , a second side wall  34 , and a third side wall  36 . The front wall  30  has an opening  24  and pins  22  on its interior surface. The slider plate  40  contains elongated openings  42 , which align with and slidably receive the respective aligned pins  22  of the front housing  20 . The long axis of the openings  42  are aligned with the X axis to allow relative sliding movement between the front outer housing shell  20  and the slider plate  40  in the X axial direction. 
         [0031]    The slider plate  40  also contains an elongated opening  44  and a large, elongated opening  46 . The large opening  46  aligns with opening  24  of the front housing  20  when the slider plate  40  and the inner gearbox assembly  60  are secured within the front and rear housings,  20  and  100  respectively. 
         [0032]    Referring now to  FIGS. 3A and 3B , the inner gearbox assembly  60  includes a front inner gearbox assembly housing  62  and a rear inner gearbox assembly housing  64 . The front inner gearbox assembly housing  62  contains pins  74  and  76 . The pin  74  is slidably received within the elongated opening  44  and the pin  76  is slidably received within the opening  46  when the slider plate  40  is placed on the inner gearbox assembly  60 . The long axis of the openings  44  and  46  are aligned with the Y axis to allow relative sliding movement between the inner gearbox assembly  60  and the slider plate  40  in the Y axial direction. In the depicted embodiment, the X and Y axes are perpendicular to each other and each is perpendicular to the axis of rotation of the output shaft  80 , which is designated the Z axis. 
         [0033]    In the depicted embodiment, the Y axis intersects with the Z axis, which minimizes or reduces the potential for binding by eliminating off-axis forces. In the depicted embodiment, by using one of the pins  74  or  76  ( 76  in the depicted embodiment) as the bearing surface for the helical gear  70 , it is ensured that the output axis Z is aligned with the Y axis of the sliding openings  44  and  46 . It will be recognized, however, space or configuration requirements may require that one of the X or Y axes be displaced or offset from the Z axis, in which case, such offset axis should be placed as close as possible to the Z axis to minimize off-axis forces. For example, in the depicted embodiment, the X axis intersects the Y axis at an offset distance D from the Z axis, as described below. 
         [0034]    As best seen in  FIGS. 4 and 5 , the inner gearbox assembly  60  further includes a motor  66 , such as a DC gearmotor, which drives a worm  68 . The worm  68 , in turn, drives a helical gear or worm wheel  70 . An encoder board  72  including a rotary encoder senses the rotational position of the output shaft  80  of the helical gear  70 . 
         [0035]    The worm  68  has a first end  94 , a second end  96 , and at least one helical tooth  98 . The helical tooth  98  starts at the first end  94  and travels partially down the worm  68  toward the second end  96  in a helical or thread-like fashion. The helical gear  70  has a plurality of teeth  78  and a gear shaft  80  with an opening  122 . The motor shaft  112  of the motor  66  mates with the second end  96  of the worm  68  and the helical tooth  98  of the worm  68  mates with the teeth  78  of the helical gear  70 . The teeth  78  may be inclined or angled to intermesh with the thread  98  of the worm  68 . 
         [0036]    The motor  66 , worm  68 , and helical gear  70  are contained and supported within the inner housing shell defined by the front inner gearbox assembly housing  62  and the rear inner gearbox assembly housing  64  via mechanical fasteners  90 . The gear shaft  80  of the helical gear  70  interacts with the exterior environment via a first opening  82  on the front inner housing  62  and a second opening  84  on the rear inner housing  64 . 
         [0037]    The encoder board  72  is secured to the exterior of the rear inner gearbox assembly housing  64 . The encoder board  72  of the inner gearbox assembly  60  has an opening  88 , which aligns with an alignment pin  73  on the rear inner housing shell  64  to ensure proper alignment of the rotary encoder  72 . A clearance opening  108  is also formed in the rear outer housing  100  to provide a clearance for the pin  73 . 
         [0038]    Referring now to  FIGS. 6A ,  6 B,  7 A, and  7 B and with continued reference to  FIGS. 1-5 , the slider plate  40  is placed on the inner gearbox assembly  60 , with the pins  74  and  76  on the inner gearbox assembly  60  slidably received within the corresponding openings  44  and  46  on the slider plate  40 . The openings  44  and  46  enable the slider plate  40  to move in the Y axial direction relative to the inner gearbox assembly  60 . 
         [0039]    The inner gearbox assembly  60  and slider plate  40  combination is then placed into the front outer housing  20 , with the pins  22  on the front outer housing  20  slidably received within the corresponding aligned openings  42  on the slider plate  40 . The openings  42  enable the slider plate  40  to move in the X axial direction relative to the front outer housing  20 . 
         [0040]    In the exemplary illustrated embodiment, the X and Y axes are perpendicular to each other, enabling the inner gearbox assembly  60  to float in two cardinal directions without causing any coupling or restorative forces when a torque is applied at the output shaft  120 . In certain embodiments, the X axis defined by the long axes of the openings  42  may be aligned with the Z axis (output drive axis) to reduce or minimize any off axis forces and is preferable where space permits. In the depicted embodiment, however, the X axis is shown slightly offset by an offset distance D with respect to the Z axis, as may be necessary depending on the space constraints of a given application. In such cases, the X axis defined by the openings  42  should be placed as close to the Z output axis as possible to reduce or minimize off-axis forces. 
         [0041]    Once the inner gearbox assembly  60  and slider plate  40  have been properly aligned and placed within the front outer housing  20 , the rear outer housing  100  is placed over the combination of the inner gearbox assembly  60  and slider plate  40  and secured via mechanical fasteners  12 . An output drive shaft  120  is inserted into the gear shaft  80  via the opening  122 , as best seen in  FIGS. 6A and 6B . 
         [0042]    As best seen in  FIGS. 7A and 7B , a tension member  140  such as a coil spring or the like is connected between a spring pin  106  on the rear outer housing  100  and a spring pin  92  on the inner gearbox assembly  60 . The tension member  140  preloads the gearbox  10  into the upper, centered position. The tension member  140  should provide a force that is sufficient to ensure the gearbox  10  is centered, but not so great as to impart a significant force against the shaft to be driven by the output shaft, such as an adjustment cap  254  of an IV administration set  250  (see  FIGS. 8A ,  8 B, and  9 ) as described below. 
         [0043]    Referring now to  FIGS. 8A ,  8 B, and  9 , the assembled floating gearbox  10  is mounted in a pump assembly  200  by rigidly attaching the front and rear outer housings  20  and  100 , respectively, to the inside of the pump housing  202 . In the depicted embodiment, the floating gearbox  10  is secured within the pump housing  202  via a mounting foot  38  and two snap members  28  and  110  (see, e.g.,  FIG. 5 ). The pump assembly may be as described in U.S. application Ser. No. 12/906,077 filed Oct. 16, 2010, the entire contents of which are incorporated herein by reference. 
         [0044]    The mounting foot  38  of the front outer housing  20  engages the interior of the pump housing  202  and a snap member  28  of the front outer housing  20  is attached to a first boss (not shown) on the interior of the pump housing  202 . A snap member  110  of the rear outer housing  100  is attached to a second boss (not shown) on the interior of the pump housing  202 . Once the gearbox  10  is secured within the pump housing  202 , the output drive shaft  120  protrudes through an opening  208  in the pump housing  202 , thus enabling the drive shaft  120  to interface with the adjustment cap  254 . 
         [0045]    When the pump assembly  200  is ready to be used, an administration set  250  is removably attached into a channel  210  of the pump housing  202 . A latch  214  of the administration set  250  is snapped into a groove  212  of the pump housing  202  and a keyed portion of the output drive shaft  120  is pushed into a complimentary groove or receptacle  260  of the adjustment cap  254  in the correct position to drive the adjustment cap  254  of a fluid flow resistor  252 . 
         [0046]    When assembled, the slider plate  40  enables the output drive shaft  120  of the floating gearbox  10  to float freely in the plane defined by the X and Y axes as it interfaces with the adjustment cap  254 , thus minimizing the potential for binding within the gear transmission system due to misalignment between the axis of rotation of the output shaft  120  (the Z axis) and the axis of rotation of the output cap  254  (the driven shaft). 
         [0047]    In operation, when the pump assembly  200  is removably secured to the pump housing  202 , pneumatic contacts  216  on the pump housing  202  are pneumatically coupled to a corresponding diaphragm of the respectively aligned pumping chambers  264  within the administration set  250 . By using a system of manifolds and valves within the pump housing  202  and check valves within the administration set  250 , positive or negative air pressure can be selectively applied to the diaphragm of one or both of the pumping chambers  264  in the administration set  250  to selectively pump fluid from fluid sources coupled to fluid inlets  256  through the flow resistor and to the vasculature of a patient. 
         [0048]    In operation, instructions are provided by a controller such as a processor, microcontroller, or like processing electronics, to operate the motor  66  and drive the worm  68 . As the worm  68  turns, the helical tooth  98  engages the teeth  78  of the helical gear  70 , causing the helical gear  70  and the shaft  80  to rotate. The rotation of the helical gear  70 , in turn, rotates the output drive shaft  120 . When the output drive shaft  120  is interacting with the adjustment cap  254 , the rotation of the output drive shaft  120  rotates the adjustment cap  254 , which may operate a valve to change the resistance of the fluid flow resistor  252 . Because the output drive shaft  120  is able to move or float in the X-Y plane, it is able to accommodate misalignments between the output shaft and the adjustment cap  254 . The rotary encoder  72  takes position readings from the output drive shaft  120  to determine the rotational position of the adjustment cap  254 . Data readings from the encoder  72  are sent to the processer via a data cable  86 . 
         [0049]    In an exemplary embodiment, the fluid inlets  256  are fluidically coupled to one or more fluid sources (not shown), as generally known in the art, e.g., an IV infusion fluid, medication, or the like, e.g., via fluid inlet tubes. A fluid outlet  258  may be fluidically coupled to the vasculature of a patient, e.g., via an IV catheter or cannula (not shown), as generally known in the art. Operation of the pump assembly  200  is controlled and monitored by the processor electronics (not shown) within the pump assembly based on input information. For example, an operator, such as a healthcare provider or the patient, can manually input the desired infusion information via a user input interface, such as a keypad, touch screen, or the like (not shown). Alternatively, the infusion information may be input using an alternative input means, such as a bar code reader, RFID tag, or the like. 
         [0050]    After the infusion data is input, it is desirable to confirm the infusion data before the infusion can begin. Once the infusion information is input and confirmed, the processing electronics will determine the proper setting for the fluid flow resistor  252 . The flow resistor setting may be based on a number of factors, such as a desired or target flow rate, the volume of fluid to be infused, a desired or target infusion time, infusion fluid parameters such as fluid viscosity, temperature, and others. The fluid flow resistor  252  is rotated to the desired position by the output shaft  120  under programmed control via the gearbox  10  as detailed above. During the infusion, further adjustments may be made to the fluid flow resistor  252 , for example, to fine tune flow rate in response to feedback provided by an inline flow sensor  262  or otherwise in accordance with the input infusion information. It will be recognized that valve position within the fluid flow resistor need not be the only means within the flow control system for controlling or adjusting flow rate, and that the flow resistor may be used in combination with other parameters, such as a fluid driving pressure in the pumping chambers  264 , in order to achieve a desired flow rate. 
         [0051]    In the depicted preferred embodiment, the administration set  250  may also include an inline flow sensor  262  for sensing flow rate. In the depicted embodiment, the flow sensor is integrally formed with the fluid flow resistor  252 , although a separately formed flow rate sensor is also contemplated. The flow rate sensor  252  is preferably of a type that includes an moveable inline flow object or element (not shown), the position of which varies as a function of flow rate and the position of which can be monitored optically to determine an actual flow rate of the IV fluid as it passes out of the flow resistor  252  to the patient. 
         [0052]    The flow object may be monitored, for example, by an optical sensor, which includes a light source  204  such as an LED array and an optical detector  206 , which may be a photosensor array, such as a charged-coupled device (CCD) array or the like. The light source  204  and optical detector  206  are preferably disposed on opposite sides of a flow chamber containing the flow object, although other configurations are also contemplated, such as an optical detector  206  positioned to sense light emitted by the light source  204  and reflected by the flow object. The pattern of light is sensed by the detector  206  to determine the position of flow object within the flow resistor  252 . The position information, in turn, is used to determine an actual fluid flow rate. The flow rate information can be sent to the electronic controller to provide feedback, which can in turn, be, used to control fluid flow in accordance with the infusion information. 
         [0053]    The processing unit may also be programmed to shut off flow by rotating the resistor cap  254  to an off or closed position in response to a detected alarm condition, such as an occlusion, a detected an air bubble in the line, etc. In especially preferred embodiments, the fluid flow resistor  252  and/or inline flow rate sensor  262  may be as described in commonly owned International Patent Application No. PCT/US2009/068349 filed Dec. 17, 2009, entitled “Extended Range Fluid Flow Resistor,” which is incorporated herein by reference in its entirety. 
         [0054]    The invention has been described with reference to the preferred embodiments. It will be understood that the architectural and operational embodiments described herein are exemplary of a plurality of possible arrangements to provide the same general features, characteristics, and general system operation. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.