Abstract:
A system for check weighing the content of a blister strip which includes a guide adapted to receive a blister strip comprised of at least one blister, a punch aligned with the guide for receiving the at least one blister, an actuator engaged with the punch for driving the punch toward the blister strip, whereby the blister is punched from the blister strip, and a balance adapted to receive the punched blister for weighing the punched blister and generating a weight signal after subtracting a predetermined value representing the weight of an empty blister. An alternative method of determining the content of a blister strip comprises reflecting a beam of energy off of a blister strip and determining the height of the blister from the reflected energy. The measured height is compared to a predetermined height to derive the amount of powder contained therein.

Description:
This application is filed under 35 U.S.C. §371 as the United States National Phase Application of International Application No. PCT/US01/05277 filed Feb. 16, 2001 claiming priority from U.S. Provisional Application No. 60/183,465 filed Feb. 18, 2000, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to blister strips used to deliver powdered medication, and more particularly to a system and method for accurately measuring the content contained in the blisters comprising a blister strip. 
     BACKGROUND ART 
     Powdered medication for use with Multi Dose Powder Inhalers (MDPI) is provided in blister strips comprised of one or more rows of blisters (indents made in an aluminum foil strip wherein each blister is filled with a metered amount of medication and the powder sealed within the blister by a composite lid foil). 
     A device is provided for the user that removes the lid foil, thus releasing the powder for use, so that the user can inhale the powdered medication. A variety of ailments can be treated in this manner, particularly asthma. Also, recent developments in antibiotic medications have proven MDPI to be an effective method of introducing the medication into a user&#39;s system. 
     In any case, irrespective of the medical condition being treated, it is critical that each blister contain the correct metered dose of medication to ensure proper treatment of the ailment and protect the user from over-medication or under-medication. 
     Currently, to ensure that the correct metered dose is being dispensed in each blister, random strips from a production run are tested by weighing each strip, inserting a needle into the individual blisters one at a time, extracting the powder through suction and then re-weighing the strip. Not only is this method time consuming (a strip comprising 120 blisters can typically take up to one hour to test), but the method has within it inherent inaccuracies. For instance, if all the powder is not extracted from each blister, then the weight of the strip after the powder has supposedly been removed will be inaccurate. Moreover, because it is understood and accepted that powder residue is left behind within the blister, a percentage of residual powder is assumed and an additional weight based on that assumed percentage is automatically subtracted from the weight of the empty strip. 
     Accordingly, because it is essential that the powder medication be dispensed in the correct metered dose, it is essential that the powder contained in each blister be accurately measured to ensure proper dosage. 
     SUMMARY OF THE INVENTION 
     This invention results from the realization that a truly effective system and method for accurately measuring a dose of powdered medication contained in a blister for use in a metered dose powder inhaler can be achieved in which the powder filled blister is punched from a blister strip without breaking the blister, to prevent loss of powder weight, and the punched blister is weighed. A predetermined weight, representing the weight of an empty blister, is subtracted from the weight of the punched blister to determine the weight of the powder dose contained in the punched blister. 
     The invention results from the further realization that the correct size of a blister can be verified by measuring the maximum height of the blister and comparing it to a predetermined height to determine whether the blister is the correct size for receiving, and thus dispensing, a predetermined dose of medication. 
     The invention results still further from the realization that a blister can be accurately punched without breaking the blister. This is accomplished by monitoring the profile of the blister whereby the center of the blister is determined. The blister is advanced a predetermined distance based on the blister&#39;s center to the punch such that the blister is accurately aligned beneath the punch. The foil strip or blister strip is then punched from the strip without breaking the blister. 
     This invention features a system for check-weighing a metered dose powder inhaler blister. The system comprises a guide adapted to receive a blister strip having at least one blister, a punch aligned with the guide for receiving the at least one blister, and an actuator engaging the punch for driving the punch toward the blister strip whereby the blister is punched from the blister strip. A balance adapted to receive the punched blister is provided for weighing the punched blister and generating a punched blister weight for the at least one blister. 
     In one embodiment of the present invention there can be a computer controller, responsive to the balance, for subtracting a predetermined weight from the punched blister weight. A drive assembly can be included, responsive to the blister strip, for advancing the at least one blister toward the punch. The drive assembly can include a drive wheel adapted to engage a first side of the blister strip for advancing the at least one blister toward the punch and a friction wheel adapted to engage a second side of the blister strip opposite the first side for urging the blister strip toward the friction wheel to ensure the friction wheel properly engages the blister strip. The drive assembly can include a stepper motor responsive to the computer controller for engaging the drive wheel to advance the at least one blister a predetermined distance toward the punch. 
     A sensor can be provided, aligned with the guide and responsive to the at least one blister, for detecting the profile of the at least one blister. The sensor can include an energy source for directing a beam of energy toward the blister strip and a detector for receiving a beam of reflected energy from the blister strip. The energy source can include a light source, which can be a laser. The guide can include a spring for urging the blister trip into the guide to ensure the profile of the blister is accurately detected. The guide can further include a hole through which the beam of energy passes to prevent a beam of reflected energy from being detected in the absence of a blister strip within the guide. The punch can include a clamp such as a stripper plate, responsive to the actuator, for holding the blister strip within the guide as the blister is being punched from the blister strip to ensure a clean punch. The punch can also include a contoured tip for seating the blister within the punch as the blister is being punched from the blister strip to ensure that the blister is not broken when punched, the tip engaging the blister strip at an oblique angle. The actuator can include a fluid driven actuator which can be an air cylinder. 
     The invention also features a method for weighing the content of a blister in a blister strip. The method includes punching a blister containing a metered content from a blister strip, weighing the punched blister to determine a punched blister weight and subtracting from the punched blister weight a predetermined weight and representing the weight of an empty blister to determine a weight representative of the metered content. 
     In one embodiment the step of punching can include punching the blister from the blister strip without breaking the blister. The method can also include the steps of punching a blank from the blister strip and weighing the blank to produce the predetermined weight. The method can also include the step of measuring the height of the blister prior to punching the blister and detecting the center of the blister to facilitate alignment of the blister for punching. The step of detecting the center can include calculating first and second slopes of respective first and second blister sides to generate a blister profile and detecting the midpoint, or center, of the blister profile which represents the center of the blister. 
     The invention further features a method for detecting defects in a blister strip blister. The method includes directing a beam of energy from an energy source toward a blister strip containing at least one blister, moving the blister strip in alignment with the beam of energy such that the at least one blister passes through the beam of energy, and receiving beams of reflected energy from the blister strip. The maximum height of the at least one blister is determined from the reflected beams of energy and compared to a predetermined height. 
     The invention features still further a method for aligning a blister strip blister with a punch. The method includes directing a beam of energy from an energy source toward a blister strip containing at least one blister, moving the blister strip toward a punch in alignment with the beam of energy such that the at least one blister passes through the beam of energy. Reflected beams of energy from the blister strip are received and the center of the blister is detected. The blister is moved, in response to the detected center, a predetermined distance toward the punch so that the blister is accurately aligned with the punch. 
     In one embodiment the step of detecting the center can include calculating first and second slopes of respective first and second sides of the blister to generate a blister profile and detecting the midpoint of the blister profile which represents the center f the blister. The step of detecting the center can also include detecting the maximum height of the blister. 
     Finally, the invention features a system for aligning a blister strip blister with a punch including an energy source for directing a beam of energy toward a blister strip containing at least one blister, a drive assembly for moving the blister strip in alignment with the beam of energy such that the at least one blister passes through the beam of energy and a detector for receiving beams of reflected energy from the blister strip. There are means for detecting the center of the at least one blister from the reflected beams of energy. The drive assembly, in response to the detected center, moves the blister a predetermined distance, the distance from the sensor to a punch, toward the punch so that the blister is aligned with the punch. 
     In one embodiment the means for detecting can include means, responsive to the detector, for calculating first and second slopes of respective first and second sides of the blister and generating a blister profile and means, responsive to the means for calculating, for determining the midpoint of the blister profile which represents the center of the blister. The means for detecting the center can include means, responsive to the detector, for detecting the maximum height of the blister which represents the center of the blister. 
     It is therefore an object of the present invention to provide a system and method that accurately and efficiently weighs the amount of powder contained in a blister strip blister. 
     It is a further object of the present invention to provide such a system and method that detects defects in a blister strip blister. 
     It is still a further object of this invention to provide such a system and method that accurately aligns a blister with a punch to punch the blister without breaking the blister. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a detailed three dimensional view of the check-weighing system for accurately weighing the powder contained in the blisters of a blister strip according to the present invention; 
     FIG. 2 is an enlarged three dimensional view of the sensor and the guide of the check-weighing system of FIG. 1; 
     FIG. 3 is an enlarged three dimensional view of the guide of FIG. 2; 
     FIGS. 4A-4D are detailed three dimensional views demonstrating the detection of the peak of the blister according to one aspect of the present invention; 
     FIG. 5 is a side elevational view of the punch and the drive assembly of the check-weighing system of FIG. 1; 
     FIG. 6 is an enlarged three dimensional view of the guide and the punch of the check-weighing system of FIG. 1; 
     FIG. 7 is an enlarged three dimensional view of the punch tip of FIG. 6 in which the tip is contoured to seat an individual blister; 
     FIG. 8 is a three dimensional view, similar to FIG. 1, of the check-weighing system according to the present invention including a hopper for deflecting and catching a punched blister strip; and 
     FIG. 9 is a flow chart of the method of weighing a metered dose of medication within a blister strip blister according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There is shown in FIG. 1 a check-weighing system, generally designated  10 , for check-weighing a metered dose of powder medication according one embodiment of the present invention. Check-weighing system  10  includes a guide  12  for receiving a blister strip  14  and a sensor  16  that detects the height of individual blisters  18  that comprise blister strip  14  and which are filled with a metered content, for example a metered dose of powdered medication. 
     Guide  12  is aligned with a punch generally designated  20 . A drive assembly  22  can be controlled by a computer controller  24 , in response to sensor  16  to advance blister strip  14  through guide  12  toward punch  20 . An actuator  26  drives punch  20  to punch individual blisters  18  from blister strip  14 . Individual punched blisters  18 ′ fall through chutes  28  into respective pans  30 , for example disposable light-weight foil pans, that are placed on respective balances  32 . Balance  32  weighs the punched blisters  18 ′ to provide a punched blister weight. 
     Balance  32 , for example an SAG 245 available from Mettler Toledo, Inc. of Columbus, Ohio, is extremely sensitive and must therefore be permitted to settle before each punched blister weight can be measured This can typically take up to four seconds. Individual punched blisters  18 ′ can be weighed one at a time to determine which, if any, are under weight or over weight for a particular powder dose. Although not a requirement of the present embodiment, balance  32  can be zeroed after each punch weight is measured so that the individual weight of a subsequent punched blister  18 ′ can be accurately measured. However, weighing each punched blister  18 ′ individually and zeroing balance  32  are not necessary limitations of the invention as all the individual blisters  18  can be punched from blister strip  14  before a punched weight is determined. 
     In any case, once the weight of punched blister  18 ′ is measured, computer controller  24 , which may include for example a processor such as, for example, a Pentium® type processor available from Intel Corporation of Santa Clara, Calif., subtracts a predetermined weight (representing the weight of the foil and paper that comprise the blister) from the punched weight to yield the actual weight of the metered dose contained within punched blister  18 ′. The predetermined weight can be determined by first punching a blank from blister strip  14  before the first blister  18  is punched. While this is the most accurate way to determine the powder weight according to the present invention, since the blank is a true representation of the weight of the composite lid foil that comprise blister  18 , this is not a necessary limitation of the invention as a predetermined weight representing an average composite lid foil weight can also be used. 
     System  10  according to the present invention can typically punch a blister strip containing 120 blisters (two rows of 60 blisters) in four minutes, based on a four second settling time for balance  32 . This speed compares favorably to over an hour with the method of the prior art as discussed in the Background Art above. Moreover, the present invention provides a much more accurate measurement and can determine whether individual blisters are under/over weight while the prior art method only measured the powder weight of an entire strip. The system of the present invention can further generate a blister strip profile identifying which blisters, if any, are under or over the required height. 
     As discussed above, the predetermined weight of the composite lid foil can be determined for each strip by punching a blank (not shown) from blister strip  14  before the powder filled blisters  18  are punched, e.g., punching the flat portion of strip  14  that is introduced first into guide  12  which does not contain blisters. In this way, variations in the thickness of the aluminum foil and paper that make up blister strip  14  need not be accounted for and no assumptions that can affect the weight of the metered dose of powder need be made. However, an average weight for a blank can be predetermined and used for all strips although the accuracy of the check-weighing can be affected. 
     Balance  32  rests on a balance surface  34 , for example a marble block, Part Number 2245A44, available from McMaster-Carr of Atlanta, Ga., that is sufficiently heavy so that balance  32 , given its sensitivity, is not unduly affected from external environmental vibrations. To further isolate balance  32  from external vibrations a shock absorbing layer  36 , for example a neoprene rubber pad, Part Number 5996K24, also available from McMaster-Carr of Atlanta, Ga., can be provided between balance surface  34  and frame  38 . To isolate balance  32  from vibrations from punch  20 , neoprene bushings  40  (shown in phantom) can be provided between frame  38  and legs  42 . 
     Guide  12 , as shown in FIG. 2, includes an entry guide  44  for funnelling blister strip  14  into guide  12 . Sensor  16 , for example a Model LB-041 laser micrometer available from Keyence Corporation of Atlanta, Ga., can be used to detect the height of blister  18 . Sensor  16  includes an energy source  46 , shown in phantom, for example a light source, that directs a beam of energy  48 , such as a laser beam, toward blister  18 . Sensor  16  also includes a detector  50 , shown in phantom, that receives a beam of reflected energy  52  from blister strip  14 . However, the sensor described above is not a necessary limitation of the invention as individual energy sources and detectors that include infrared sensors, sonic sensors as well as contact sensors readily apparent to those skilled in the art can also be used without departing from the scope of the present invention. Moreover, while beams  48  and  52  are represented in the drawings as two distinct beams, rather than co-linear beams, this is for illustrative purposes only. The proximity of source  46  and detector  50  will dictate the alignment of beams  48  and  52 , e.g. coplanar or non-coplanar. 
     Using laser micrometer  16 , the slopes of first and second sides, e.g., the front and back sides, of a blister are measured. Computer controller  24  uses the recorded heights to determine the slope of the front and back surfaces of blister  18 . The intercept of the respective slopes and base foil of blister strip  14  are calculated and a blister profile is generated. The blister profile represents a cross section of blister  18  having a blister width defined by the intercepts of the respective slopes with blister strip  14 . The midpoint of the blister profile is determined and represents the center of blister  18 . The center point is then used as the reference point for advancing blister  18  to punch  20 , accurately aligning blister  18  within punch  20 , such that the blister  18  is located under the punch. This eliminates problems due to asymmetrical blisters. Alternatively, the maximum height can be detected as the maximum height is where the slopes change from positive to negative and is typically the center of the blister. 
     In order to ensure that the profile of blister  18  is accurately measured, guide  12  can include a channel  54 , as shown in FIG. 3, for receiving the edges of blister strip  14  to maintain blister strip  14  flat within guide  12 . Guide  12  can further include a spring holder  56 , as shown in FIG. 3, which includes springs  58  (such as, for example, leaf springs) for holding blister strip  14  flat within guide  12 . Individual blisters  18  pass between springs  58  so that blisters  18  will not strike springs and be deformed, which would prevent accurate profile determination. It will be readily apparent to those skilled in the art that as few or as many springs  58  should be used as are required to keep blister strip  14  flat within guide  12 , and thus depends on the number of rows of blisters  18  on blister strip  14 . Guide  12  can be provided with passageways or holes  60  through guide  12  so that energy beam  48 , such as a laser beam, will pass through guide  12  in the absence of blister strip  14 . Accordingly, computer controller  24  can be programmed so that drive assembly  22  remains idle until a beam of reflected energy  52  is detected. Moreover, computer controller  24  can further be programmed to stop system  10  when no more beams of reflected energy  52  are detected after the last blister  18  is punched. 
     Referring now to FIG. 4A, the height of blister  18  is detected by directing beam  48  toward blister strip  14 . As blister strip  14  is advanced through guide  12 , in the direction as indicated by the arrow, a beam of reflected energy  52  is reflected from blister  18  at a point or base  62  and the height at that point is detected. Because base  62  is not a portion of blister  18 , but is instead a flat portion of blister strip  14 , base  62  is a zero reference point. 
     Blister  18  is aligned with and passes through beam  48 , as shown in FIG. 4B, and beam  48  continuously strikes blister  18 , for example at a point  64 . Point  64  is higher than the previously detected height at base  62  indicating that a blister has been detected. The height of blister  18  is continuously measured as blister  18  passes through beam  48 . Computer controller  24  (FIG. 1) determines from the reflected beam the instantaneous height detected from blister  18  and calculates a front slope. 
     As shown in FIG. 4C, beam  48  strikes blister  18  at a point  66  which is the apex or peak of blister  18 , that is, point  66  is thus higher that any previously measured point. However, thus far computer controller  24  is merely detecting the height of blister  18  continuously and has not yet determined that a peak has been detected. 
     Next, as shown in FIG. 4D, beam  48  strikes blister  18  at a point  68  that is lower than the previously measured point  66 . Thus, computer controller  24  determines that the previous position of blister strip  14  within guide  12  corresponds to the maximum height of blister  18 . 
     The maximum height typically corresponds to the center of blister  18 . Computer controller  24  continues to detect the instaneous height and calculates a back slope. Once the front and back slopes are detected, the points at which the respective slopes intersect with base  62  are determined and a blister profile is generated. Computer controller  24  then calculates the distance halfway between the front and back base/slope intersections which represents the actual center of the blister  18 . 
     The profile and height of blister  18  can serve two purposes. First, in terms of quality assurance, the profile and measured maximum height can be compared to a predetermined height in order to determine whether a defect exists in individual blister  18 . If blister  18  is not the correct height, blister  18  can affect the operation of the inhaler device for which blister strip  14  is intended. Also, a defective blister can prevent the proper dose of powdered medication from being contained within blister  18 , although dispensed properly, if the height of blister  18  is too small. 
     A second purpose for detecting either the profile or maximum height is to advance blister strip  14 , as shown in FIG.  5 . the proper distance to ensure that blister  18  aligned with punch  20  so that it is punched cleanly by punch  20  and is not broken. If blister  18  becomes broken when punched, powder can be lost, adversely affecting the accurate weighing of the powder medication. The distance D between sensor  16  and punch  20  does not change. Thus, when computer controller  24  detects the center of blister  18 , computer controller  24  signals drive assembly  22 , via bus  70 , to advance blister strip  14  through guide  12  such that blister  18  is centered with and in alignment with a punch tip  72 . Drive assembly  22  can include a motor  74  such as a stepper motor, for example a Model Number ST-0171EBA-E7LN-NNN available from American Precision Industries, Inc. of Amherst, N.Y., to precisely advance blister strip  14  such that peak  66  is aligned with punch tip  72 . 
     A drive wheel  76  is mounted on a motor shaft  78  of motor  74  to advance blister strip  14 . There can also be provided a friction wheel  80  that urges blister strip  14 , via spring  82 , into contact with drive wheel  76  to ensure proper engagement of drive wheel  76  and blister strip  14 . Spring  82  can include a number of different type of springs such as bent washer springs, coiled springs, leaf springs and the like, as will be readily apparent to those skilled in the art. Accordingly, blister strip  14  is sandwiched between drive wheel  76  and friction wheel  80  so that every rotation of motor  74  is translated into movement of blister  18  toward punch  20 . Proper translation of blister strip  14  ensures proper alignment of peak  66  with punch tip  72 . Once peak  66  of blister  18  is in alignment with punch tip  72 , computer controller  24  signals punch actuator  26  via bus  84  to drive punch  20  such that punch tip  72  punches blister  18  cleanly from blister strip  14  without breaking blister  18 . 
     Actuator  26  can be a fluid driven actuator such as a hydraulic or air cylinder. In one embodiment of the present invention actuator  26  includes a pneumatic air cylinder, Model Number M-120.5-LS available from Bimba Manufacturing Company, New Britain, Conn. Air for operating actuator  26  is supplied by an air compressor  86  via hose  88 . Actuator  26  could also include a hydraulic actuator. However, a fluid driven actuator is not a necessary limitation to the invention as punch  20  can also be gear driven, for example by worm or tooth gears, or driven by a motor and fly wheel assembly, as will be readily apparent to those skilled in the art. 
     In order to ensure a clean punch, the tolerance between punch tip  72  and a die  90 , shown in FIG. 6, must be tight. If blister  18  is not cleanly punched from blister strip  14 , blister  18  will essentially be torn from blister strip  14  which will vary the foil and paper weight from blister to blister and thus can adversely affect the weight determination of the powder within blister  18 . 
     To further assist in obtaining a clean punch, punch  20  can include a hold down clamp  92 . As actuator  26  drives punch top  94 , containing punch tip  72 , toward blister strip  14  along punch guide supports  96 , hold-down clamp  92 , for example a stripper plate, engages blister strip  14  within guide  12  to firmly hold blister strip  14  in place as punch tip  72  punches blister  18  from blister strip  14 . Hold-down clamp  92  slides on a pair of clamp guides  98  extending downwardly from punch top  94 . Springs  100  about clamp guides  98  urge hold down clamp  92  away from punch top  94  so that hold down clamp  92  engages bliste strip  14  before punch tip  72 . Punch tip  72  can also be slightly angled, for example one half degree, so that tip  72  does not engage blister strip  14  all at once as is well known in the art. 
     Actuator  26 , such as the air cylinder described above, typically includes internal return springs, not shown, such that when power to system  10  is interrupted, for example in the event of an emergency, punch  20  will return to a neutral position. However, return springs  102  can also be provided to return punch  20  to a neutral position, i.e., in the retracted or up position. 
     In order to assist in proper alignment of peak  66  of blister  18  with punch tip  72 , punch tip  72 , as shown in FIG. 7, can include a contour  104 . For example, contour  104  can include a concave surface for receiving blister  18  to properly seat blister  18  within punch tip  72 . Moreover, by adjusting the point in time at which hold down clamp  92 , FIG. 6, engages blister  18  and exerts pressure on blister strip  14 , contour  104  can properly seat a slightly misaligned blister  18  within punch tip  72  before blister strip  14  is firmly held within guide  12 . Punch tip  72  can be removably mounted within punch top  94 , for example with threaded bolt  106 , so that when punch tip  72  becomes dull it can easily be replaced. The ability to remove punch tip  72  from punch top  94  can also be useful to enable the selection of differently shaped punch tips  72  to accommodate differently profiled blisters  18 . 
     As shown in FIG. 8, there is a hopper  108  for receiving punched blister strips  14 ′. Deflector  110  directs punched blister strip  14 ′ into hopper  108  as motor  74  continues to advance blister strip  14  through guide  12 . 
     While computer controller  24  can precisely integrate sensor  16 , drive assembly  22 , actuator  26 , punch  20  and balance  32 , the novelty of the present invention is also realized in the method in which computer controller  24  check-weighs medical powder blister strip blisters. Referring now to FIG. 9, there is represented the method in which computer controller  24  carries out the check-weighing procedure of the present invention. 
     As shown in FIG. 9, a series of incremental heights over the profile of a blister  18  are measured by sensor  16  (Block  112 ) by directing a beam of energy  48  at blister strip  14  and receiving reflected energy  52  as blister  18  passes through beam  48 . These measurements are used to define the profile of blister  18 , and can also be used to determine the maximum height of blister  18 . 
     The incremental heights are used to calculate the front and back slopes of blister  18 , and the point where the slopes intersect base  62  are determined. The midpoint between the respective intersections connotes the center of blister  18 . Alternatively, while less reliable, the maximum height of blister  18  can be detected and used to connote the center of blister  18 . The detected maximum height can also be compared to a predetermined height to detect defects in blister  18 . If the height is greater or less than the predetermined height, the blister is defective. Drive assembly  22  then moves blister strip  14  a predetermined distance toward punch  20  (Block  114 ) based on the detected center of blister  18 . Where blister  18  is the first blister detected on blister strip  14 , drive assembly  22  stops blister strip  14  (Block  116 ) and punches a blank from blister strip  14  (Block  118 ). The blank is weighed by balance  32  (Block  120 ) to get the predetermined weight representing the composite foil material containing blister  18 . Once the blank has been weighed, drive assembly  22  moves blister strip  14  toward punch  20 , aligning blister  18  with punch tip  72  (Block  122 ). Blister  18  is punched from blister strip  14  (Block  124 ) by punch tip  72  and balance  32  is allowed to settle (Block  126 ). Once balance  32  has settled punched blister  18 ′ is weighed (Block  128 ). After punched blister  18 ′ is weighed, the predetermined weight is subtracted from the punched blister weight (Block  130 ) to yield an accurate measurement of the powder contained within blister  18 . 
     Thus, the method and system according to the present invention provide an effective way to very accurately check-weigh powdered medication blister strips without having to make assumptions or otherwise account for lost percentages of powder as in the prior art method. Also, individual blisters can be weighed to determine at what point in a processing run the dosage became inaccurate. 
     It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.