Abstract:
A blood sample test device has a continuous strip sensor which is advanced through the device so that multiple blood sample tests can be conducted on a single strip. The device is provided with a sprocket having an encoder which engages sprocket holes on the strip to precisely control the advancement of the strip through the device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention is in the field of blood sample acquisition and testing. In particular, the invention is directed to a sensor strip positioning mechanism used in a device that performs both a lancing operation to acquire a blood sample and a measurement operation on the sample in one user-initiated step. The strip is provided with a plurality of test sites, wound on a supply wheel and fed through the device between the supply wheel and a take-up wheel, so that a single strip may be used to obtain a plurality of measurements. According to the invention, a mechanism is provided to control the advancement of the strip in precise increments for proper alignment of the test sites in the device. 
         [0003]    2. Description of the Related Art 
         [0004]    Self-monitoring of blood glucose generally requires the user to extract a volume of capillary blood and place it on a disposable element for analysis. Devices for lancing a subject at an extraction site to obtain a small quantity of blood for testing on a test strip are known in the prior art. For example, U.S. Pat. No. 6,558,402, which is incorporated by reference, discloses a lancer having mechanisms for piercing a subject&#39;s skin and obtaining a sample. 
         [0005]    Test strip sensing elements using amperometric and other techniques for determining the concentration of blood glucose in a blood sample are known in the prior art. U.S. Pat. Nos. 6,143,164, and 5,437,999, incorporated by reference herein, each disclose examples of test strip construction for electrochemical measurement of blood glucose. 
         [0006]    The integration of lancing and sensing would be a desirable advance in the self-monitoring of blood glucose. U.S. patent application Ser. No. 12/502,594, filed Jul. 14, 2009, which is incorporated by reference, describes such a “two-in-one” device, wherein a single test strip contains a plurality of test sites, which can be advanced automatically through a testing device. Application Ser. No. 12/502,585, also filed Jul. 14, 2009 and incorporated by reference, describes fluid transport features that may be included on a continuous strip to facilitate the movement of a blood sample from the collection site to the test site. U.S. patent application Ser. No. ______, filed concurrently herewith, and incorporated by reference, discloses an electrode layout on a continuous test strip which makes electrical contact with contacts in a device, producing signals which are used to control the advancement of the sensor strip. In this context, it would be desirable to have a mechanism to permit automatic advancement of the strip through the device in precise increments, that would account for changes in the effective diameter of the supply wheel and take-up wheel as the sensor strip is wound from one to the other as the strip is indexed through different stop points in the lancing/sensing process. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the invention is a blood sample test device, comprising: a supply wheel; a take-up wheel; a sensor strip on the supply wheel and the take-up wheel; and a motor engaging the supply wheel or the take up wheel to advance the sensor strip through the device. The sensor strip has a plurality of test sites arranged in series in a travel direction on the strip, such that each test site includes a lancet hole, first electrodes for determining a blood sample volume, and test electrodes for determining a blood sample characteristic. A sprocket with an associated encoder is provided having teeth that engage with sprocket holes in the continuous sensor strip. A processor operatively connected to the first electrodes, the test electrodes, the encoder and the motor controls advancement of the strip through the device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  depicts the strip path in a cartridge according to a preferred embodiment of the invention. 
           [0009]      FIG. 2A  depicts the engagement of sprocket teeth with sprocket holes in the sensor strip according to the invention. 
           [0010]      FIG. 2B  depicts the engagement of sprocket teeth with sprocket holes in the sensor strip according to a comparative example. 
           [0011]      FIG. 3  depicts a sensor strip positioning mechanism in a unitary housing with a supply wheel, take up wheel, lancing mechanism, and power supply, user operated controls, display and processor for controlling different stages of the lancing and sensing operation. 
           [0012]      FIG. 4  depicts a test site on the continuous strip. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    In the embodiment of  FIG. 1 , a cartridge  10  is provided having continuous sensor strip  20  which is wound on supply wheel  30  and take up wheel  40 . As the sensor strip advances, the effective diameter of the wheels changes. Thus, the identical amount of rotation imparted to the wheel by motor  42  would result in a greater or lesser linear distance on the strip being advanced through the device. However, optimal operation of the sensor requires accurate alignment of the test site in the opening  50  of the device, as well as alignment of device contacts (not shown) with electrodes on the sensor strip. 
         [0014]    As shown in  FIG. 3 , sprocket  60  is provided in the device with encoder  62  and sprocket teeth  70 . The sprocket and/or encoder may be positioned in the device independently of the cartridge  10 , so that the cartridge containing the sensor strip may be made detachable and removable by the user. The encoder registers the amount of linear distance that the strip advances and appropriate instructions are provided to motor  42  via processor  82 . Because the distance the strip travels is obtained directly from features on the sensor strip, rather than rotation of the supply wheel or the take up wheel, accurate positioning is ensured. 
         [0015]    As shown in  FIG. 4 , a test site on the strip comprises a lancet hole  100 , through which lancet needle passes, and an area between electrodes  110  and  120  where a blood sample accumulates after a lancing operation. When the device is used, the cartridge can be positioned so that the cartridge opening  50  allows the user&#39;s skin to just touch the sensor strip. The lancet hole  100  on the strip lines up with lancet mechanism  90  and a lancing operation is performed. A blood sample accumulates on the sensor strip and when a sufficient volume is obtained, the electrodes  110  and  120  are shorted, signaling the sensor strip to advance in travel direction  130 . As the strip advances, a portion of the blood sample travels along a capillary channel to a test site where a measurement, such as a blood glucose measurement, is conducted at a second pair of electrodes  140 ,  150 . The user may interface with the device through user operable controls and display  63 ,  64 ,  66 . In an alternative embodiment, gears (not shown) are provided that allow the strip to feed forward and backward, so that if an insufficient quantity of blood is obtained, the user can perform the lancing operation again using the same test site on the continuous strip. 
         [0016]    Each test site on the sensor strip comprises a lancet hole, sensing electrodes which sense whether a sufficient volume has been detected, and a capillary channel between the sensing electrodes and the reagent wells where a blood characteristic is determined using a second set of electrodes. Each test site may be about 9 mm to about 19 mm in length, and the distance between the lancet holes of adjacent test sites on the strip may be in a range of about 20 mm to about 40 mm. The distance between sprocket holes is in a range of about 10 mm and about 20 mm, and the diameter of the sprocket should be sized accordingly. An estimate of the sprocket diameter can be calculated by subtracting the strip thickness from the diameter that would be arrived at using simply the hole-to-hole distance on the strip. The strip cannot be considered to have negligible thickness for the teeth to line up in the holes of the strip. 
         [0017]    In  FIG. 2A , the sprocket diameter is calculated taking into account the strip thickness (i.e., according to the invention) so that it is slightly smaller than a comparative example shown in  FIG. 2B . In the comparative example of  FIG. 2B , the sprocket diameter is too large, and the sensor strip slips off the sprocket teeth. In embodiments, the thickness of the sensor strip is in a range of about 10 mils to about 20 mils. The circumferential distance between individual teeth is thus about 9.5 mm to about 19.5 mm. The diameter of the sprocket is established based on the number of teeth, so that a sprocket having 4 teeth, for example, has a diameter in a range of about 12 mm to about 26 mm. 
         [0018]    The sensor tape is made out of the materials conventionally used for this purpose and the method of construction would be known to those of ordinary skill in the art. For example, the substrate and structural layers of the strip defining wells and a capillary may be made from polyethylene terephthalate (PET), while the electrodes may be made from a layer of gold or other conductive material, deposited by sputtering or other known means, and patterned. 
         [0019]    Processor  82  receive signals from the electrodes  110 ,  120 ,  140 , and  150  via contact pads  112 ,  152 ,  122 , and  142 , which make contact with device contacts (not shown) in the device housing. The processor  82  also receives signals from the sprocket encoder, which encodes the distance traveled by the strip and from user-operated controls. The processor coordinates these signals to provide instruction signals to the motor to advance the sensor strip, to the lancing mechanism to perform a lancing operation and to the test electrodes to perform a blood characteristic measurement. Processors which can be adapted for these purposes are commercially available and would be known to those of ordinary skill in the art. 
         [0020]    The foregoing description of the preferred embodiments is not to be deemed limiting of the invention, which is defined by the following claims.