Ratchet drive for on body delivery system

Abstract

Ratchet-based drive systems for more reliable and safer drug delivery are provided. The ratchet-based drive systems restrict angular movement and/or linear movement of components that cause a plunger to expel a liquid drug from a drug container. Movement of the components can be restricted to correspond to a predetermined or desired portion of the liquid drug. In the case that control of the drive system is lost or fails, the maximum amount of drug that could be delivered is limited to a known amount, thereby reducing the likelihood of an overdose.

What is claimed is: 
     
         1 . An on-body drug delivery system, comprising:
 a reservoir configured to contain a liquid drug;   a plunger configured to seal an end of the reservoir;   a rack having a plurality of teeth and coupled to the plunger, wherein the rack is configured to move the plunger within the reservoir;   an arm having a pawl configured to engage the rack; and   a power source configured to extend and retract the arm, wherein extending the arm causes the plunger to expel an amount of the liquid drug.   
     
     
         2 . The system of  claim 1 , wherein the arm is sized such that extension of the arm is in a direction parallel to movement of the rack corresponds to the amount of the liquid drug being expelled. 
     
     
         3 . The system of  claim 1 , wherein the arm has a length enabling the amount of the liquid drug expelled by the plunger a desired amount of the liquid drug to be when a corresponding amount of the length of the arm is extended. 
     
     
         4 . The system of  claim 1 , wherein the power source is operable to move the arm backward in a direction away from the plunger. 
     
     
         5 . The system of  claim 4 , wherein the pawl is configured to:
 disengage the rack when the arm is moved backward.   
     
     
         6 . The system of  claim 1 , wherein the pawl is configured to:
 rotate away from when the rack when the arm is moved.   
     
     
         7 . The system of  claim 1 , wherein the plunger is configured to expel a portion of a liquid drug stored in the reservoir when moved in a linear direction. 
     
     
         8 . The system of  claim 1 , further comprising:
 a controller couple to the power source, wherein the controller is operable to control the power source.   
     
     
         9 . The system of  claim 8 , wherein the controller is further operable to:
 track movement of the arm; and   maintain a count of a number of times the arm is moved to expel the liquid drug.   
     
     
         10 . A method, comprising:
 extending an arm coupled to pawl that is engaged with a rack in a first direction, wherein the arm is driven from a first pos from an initial position to a final position;   in response to extending the arm, expelling a dose of a liquid drug from a drug container by a plunger coupled to the rack;   retracting the arm in a second direction, opposite the first direction;   in response to retracting the arm in the second direction, disengaging the pawl from the rack; and   stopping retracting of the arm in the second direction upon return to the initial position in preparation for expelling another dose of the liquid drug.   
     
     
         11 . The method of  claim 10 , further comprising:
 re-engaging the rack by the pawl when the arm stops retracting in the second direction.   
     
     
         12 . The method of  claim 11 , wherein disengaging the pawl from the rack comprises:
 rotating an end of the pawl to disengage the pawl from a tooth on the rack.   
     
     
         13 . The method of  claim 10 , wherein extending the arm in the first direction further comprises:
 advancing the plunger toward an end of the drug container.   
     
     
         14 . The method of  claim 10 , further comprising:
 activating a power source coupled to the arm to deliver the dose of the liquid drug by causing the power source to extend the arm.   
     
     
         15 . The method of  claim 14 , further comprising:
 after returning to the initial position, reactivating the power source to a deliver the other dose of the liquid drug by causing the power source to extend the arm.