Piezoelectric membrane pump for the infusion of liquids

Abstract

An infusion pump (10) includes a fluid chamber (28) having an outlet valve (34) and a piezo-stack actuator (36) comprising a stack of piezo-electric layers (38). An electronic processor (18) is programmed to operate the outlet valve and the piezo-stack actuator to pump fluid through the fluid chamber at a programmed flow rate.

We claim: 
     
         1 . A method of using an infusion pump with a fluid chamber that is pumped by a pump motor comprising a piezo-stack actuator, the method comprising:
 measuring, with a linear encoder, a displacement of the piezo-stack actuator during operation of the piezo-stack actuator;   comparing, with at least one processor, the measured displacement to a reference value to detect the presence of at least one of bubbles in a fluid chamber of the motor, the presence of occlusions in a tube connected to an outlet valve of the fluid chamber, or the presence of line disconnections of the tube connected to the outlet valve of the fluid chamber; and   outputting, with the at least one processor, a warning indicating the presence of at least one of the bubbles, occlusions and tube disconnections.   
     
     
         2 . The method of  claim 1 , further comprising, with the at least one processor:
 reading the linear encoder during operation of the piezo-stack actuator at a reference electrical bias and with the outlet valve closed; and   detecting bubbles in the fluid chamber based on the measured displacement at the reference electrical bias and with the outlet valve closed being greater than a bubbles detection threshold value.   
     
     
         3 . The method of  claim 1 , further comprising, with the at least one processor:
 reading the linear encoder during operation of the piezo-stack actuator at a reference electrical bias and with the outlet valve open; and   detecting a tube occlusion based on the measured displacement at the reference electrical bias and with the outlet valve open being less than an occlusion threshold value.   
     
     
         4 . The method of  claim 3 , wherein the occlusion threshold value is a function of at least one of: tube resistance, tube length, or tube path of the tube connected to the outlet valve of the fluid chamber. 
     
     
         5 . The method of  claim 1 , further comprising, with the at least one processor:
 reading the linear encoder during operation of the piezo-stack actuator at a reference electrical bias and with the outlet valve open; and   detecting a tube disconnection based on the measured displacement at the reference electrical bias and with the outlet valve open being greater than a disconnect threshold value.   
     
     
         6 . The method of  claim 5 , wherein the disconnect threshold value is a function of at least one of: tube resistance, tube length, or tube path of the tube. 
     
     
         7 . The method of  claim 1 , wherein the warning is at least one of: a textual indication, a graphical indication, or an audible indication. 
     
     
         8 . The method of  claim 1 , wherein the reference value is programmed into the processor. 
     
     
         9 . The method of  claim 1 , wherein the linear encoder is at least one of: an optical linear encoder, a capacitive linear encoder, inductive linear encoder, or a magnetic linear encoder. 
     
     
         10 . The method of  claim 1 , wherein the infusion pump includes no magnetic material. 
     
     
         11 . A non-transitory computer readable medium comprising computer code, that when executed, performs the following method of using an infusion pump with a fluid chamber that is pumped by a pump motor comprising a piezo-stack actuator:
 measuring, with a linear encoder, a displacement of the piezo-stack actuator during operation of the piezo-stack actuator;   comparing, with at least one processor, the measured displacement to a reference value to detect the presence of at least one of bubbles in a fluid chamber of the motor, the presence of occlusions in a tube connected to an outlet valve of the fluid chamber, or the presence of line disconnections of the tube connected to the outlet valve of the fluid chamber; and   outputting, with the at least one processor, a warning indicating the presence of at least one of the bubbles, occlusions and tube disconnections.   
     
     
         12 . The non-transitory computer readable medium of  claim 11 , the method further comprising:
 reading the linear encoder during operation of the piezo-stack actuator at a reference electrical bias and with the outlet valve closed; and   detecting bubbles in the fluid chamber based on the measured displacement at the reference electrical bias and with the outlet valve closed being greater than a bubbles detection threshold value.   
     
     
         13 . The non-transitory computer readable medium of  claim 11 , the method further comprising:
 reading the linear encoder during operation of the piezo-stack actuator at a reference electrical bias and with the outlet valve open; and   detecting a tube occlusion based on the measured displacement at the reference electrical bias and with the outlet valve open being less than an occlusion threshold value.   
     
     
         14 . The non-transitory computer readable medium of  claim 13 , wherein the occlusion threshold value is a function of at least one of: tube resistance, tube length, or tube path of the tube connected to the outlet valve of the fluid chamber. 
     
     
         15 . The non-transitory computer readable medium of  claim 11 , wherein the method further comprises:
 reading the linear encoder during operation of the piezo-stack actuator at a reference electrical bias and with the outlet valve open; and   detecting a tube disconnection based on the measured displacement at the reference electrical bias and with the outlet valve open being greater than a disconnect threshold value.   
     
     
         16 . The non-transitory computer readable medium of  claim 15 , wherein the disconnect threshold value is a function of at least one of: tube resistance, tube length, or tube path of the tube. 
     
     
         17 . The non-transitory computer readable medium of  claim 11 , wherein the warning is at least one of: a textual indication, a graphical indication, or an audible indication. 
     
     
         18 . The non-transitory computer readable medium of  claim 11 , wherein the reference value is programmed into the processor. 
     
     
         19 . The non-transitory computer readable medium of  claim 11 , wherein the linear encoder is at least one of: an optical linear encoder, a capacitive linear encoder, or inductive linear encoder. 
     
     
         20 . The non-transitory computer readable medium of  claim 11 , wherein the infusion pump includes no magnetic material.