Medication delivery system with improved dose accuracy

• US 7,500,959 B2
• Filed: 10/04/2001
• Issued: 03/10/2009
• Est. Priority Date: 10/05/2000
• Status: Expired due to Fees

• Current Assignee: Novo Nordisk A/S
• Original Assignee: Novo Nordisk A/S
• Inventors: Munk, Jens Aage
• Primary Examiner(s): Lucchesi; Nicholas D.
• Assistant Examiner(s): Bhatia; Aarti
• Application Number:
  US09/972,828
• Publication Number:
  US 20020107486A1
• Time in Patent Office: 2,714 Days
• Field of Search: 604/167, 604/155, 604 65- 67, 604/135, 604/134, 604/133, 604/132, 604/131, 604151-154, 604/121, 604/14, 128/DIG.12, 128/DIG.13, 128/DIG.1
• US Class Current: 604/67
• CPC Class Codes: A61M 2005/31518 designed to reduce the overall size of an injection device, e.g. using flexible or pivotally connected chain-like rod members
• CPC Class Codes: A61M 2205/33 Controlling, regulating or measuring
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 5/14566 with a replaceable reservoir for receiving a piston rod of the pump

Abstract

The invention relates to: A medication delivery device (1) for delivering a specific dose comprising a medication cartridge (11) having an outlet (111) and a piston (112), and means (12) for holding said cartridge, and a piston rod (13) being operable to engage and displace said piston, and electrically driven actuating means (15), and driving means (161, 162) for transferring movement from said actuating means to said piston rod, and memory means (17) for storing data, and processing means (18) for evaluating said data and for controlling said actuating means. The object of the present invention is to provide a medication delivery system that combines a relatively high dose accuracy with the use of relatively low quality mechanical components and which enables compensation for built-in non-linearities. The problem is solved in that a first set of data (19) describing the actual movement (130) of said piston rod (13) relative to said medication cartridge (11) as a function of the movement (150) of said actuating means (15) is stored in said memory means (17), and the movement (130) of the piston rod (13) governing the delivered dose is controlled by the processing means (18) on the basis of said first set of data (19). This has the advantage of allowing compensation for mechanical inaccuracies and built-in non-linearities linearities. The invention may e.g. be used in injection or infusion devices for a person'"'"'s self-treatment of a disease such as diabetes.

Claims

1. A method of configuring motorized injection device having a piston rod that pushes a piston in a medication cartridge to expel medication from the cartridge and having an actuator that drives the piston rod, the method comprising the steps of:

a. calculating a relationship between movement of the actuator and expected movement of the piston rod;

b. moving the actuator an amount expected to move the piston rod a predetermined distance;

c. measuring the actual distance the piston rod moves when the actuator is moved in step b;

d. determining the error between actual movement of the piston rod and expected movement when the actuator is moved a predetermined distance, wherein expected movement is a value calculated from design specifications and actual movement is a value measured from a calibration procedure;

e. programming a processor to control the actuator to compensate for the error of step d so that the piston rod is moved by a desired amount even though the actuator is moved by a greater or lesser amount than would be expected to move the piston rod by the desired amount.

2. The method of claim 1, wherein steps a-d are repeated over a range of useable piston rod displacements and wherein the processor does not receive feedback from the device regarding piston rod movement.

3. The method of claim 2, wherein the prograninuing of the processor comprises first calculating an equation describing movement of the piston rod based on movement of the actuator.

4. The method of claim 3 wherein the equation is a linear equation.

5. The method of claim 3, wherein the equation is non-linear.

6. An apparatus for injecting a dose of medication, the apparatus comprising:

a piston rod for expelling medication from a cartridge housed in the apparatus;

an actuator that moves the piston rod by an amount necessary to expel a predetermined dose, wherein movement of the actuator by a given amount is expected to produce a given movement of the piston rod, but wherein actual movement of the actuator by a given amount does not result in the corresponding expected movement of the piston rod;

a processor that is programmed to compensate for the difference between actual piston rod movement and expected actuator movement, the processor adapted to control the actuator to move the actuator an actual distance necessary to achieve the expected piston rod movement,

wherein actual movement is a measured amount of displacement and wherein expected movement is the amount of movement calculated from design specifications.

7. A medication delivery device comprising a piston rod, an actuator that moves the piston rod, the movement of the actuator being expected to produce a given unit of movement of the piston rod for a given unit of actuator movement, a processor for controlling the actuator, and a data set comprising data indicative of actual actuator movement versus actual piston rod movement, the processor utilizing the data set to drive the actuator an actual distance necessary to produce a desired piston rod movement, wherein actual movement means the measurable movement that occurs and wherein expected movement refers to a calculated value for movement that should occur and which is calculated from design data.

8. A method of controlling the displacement of a piston rod in a processor controlled medication delivery device, wherein displacement of a piston rod within the device is directly related to the size of a dose of medication delivered by the device and wherein an actuator is used to move the piston rod, the method comprising the steps of:

calculating the relationship between actuator movement and piston rod movement;

creating a data set indicative of actual actuator movement versus actual piston rod displacement and storing that data in the processor;

inputting a predetermined dose of medication to inject;

calculating via the processor the actual distance the actuator must move to drive the piston rod a distance corresponding to the preset dose, wherein the calculating is done by applying the data set to compensate for difference between expected piston rod movement and actual piston rod movement, wherein actual movement is the actual measured distance the piston rod moves and expected movement is the distance that the rod would be expected to move and is calculated from design specifications.

9. A method of configuring a medication delivery device that comprises a piston rod, a piston rod drive, and an actuator, the method comprising the steps of:

a. testing on a test set-up a plurality of piston rods, piston rod drives and actuators;

b. storing data for each piston rod, piston rod drive, and actuator tested in step a, the data indicative of the actual movement of the actuator needed to drive the piston rod a predetermined distance, wherein actual movement corresponds to a measured value for the movement of the actuator;

c. linking the stored data to the individual components;

d. installing one of each component tested in step a into a medication delivery device;

e. downloading the data for each of the components installed in step d into a processor in the delivery device, wherein the processor utilizes the data to control to drive the piston rod a predetermined distance corresponding to a user inputted dose to be delivered by the delivery device.

10. A method for delivering a medication from a drug delivery device that comprises a motorized actuator that drives a piston rod a distance wherein the distance the piston rod moves corresponds to the size of the dose delivered, the method comprising the steps of:

collecting a first set of data that describes a relationship between actual movement of the actuating means and actual movement of the piston rod, wherein the first set of data is taken to mean a set corresponding to isolated values over a range or alternatively an algebraic expression valid in a range and wherein the first set of data is arrived at thru a prerecorded calibration procedure performed on the drug delivery device;

calculating on a processor the movement of the actuator needed to expel a desired dose that is inputted by a user, wherein the calculation is performed by applying the data in the first data set to calculate actual movement of the actuator needed to deliver a set does,

wherein the actual movement needed is different from the calculated movement for that the actuator that is calculated from design specifications for the actuator,

wherein the first data set takes into account differences between a design specification for the actuator and error,

utilizing the data in the first data set so that the actuator is sending a signal from a processor to the actuator to drive the actuator, wherein the signal is computed by the processor on the basis of a desired dose size that is inputted by a user and the first set of data.

11. A drug delivery device comprising:

a motorized actuator;

a piston rod drive by the actuator,

a memory that stores a first set of data or an equation describing the relationship between actual movement of the actuator and actual movement of the piston rod,

wherein the data is collected by performing a calibration procedure on the actuator and/or piston rod, wherein the actual movement is determined by making measurements and the expected movement is made by making calculations using design criteria for the actuator piston, rod, and related components; and

a processor that, based on the first data set, sends a signal that causes the actuator to move an actual distance necessary to drive the piston rod a distance necessary to expel a user selected dose of a drug from the device.