Pump

Abstract

Provided is a pump and a method of controlling a pump. The pump and method are particularly for use in dispensing reagents, for example in flow chemistry, and more particularly on a laboratory scale. The pump aims to provide a substantially constant output flow of fluid. The pump comprises: a motor; a peristaltic pump having a rotor driven by the motor; a pressure sensor monitoring the pressure of the pumped fluid downstream of the pump; and a control unit which controls the motor by adjusting the standard operating speed of the motor according to the pressure detected by the pressure sensor, such that the pump operates continuously at a rate set by an operator. Embodiments of the pump make use of lookup tables to determine a desired position of the pump rotor at each point in the cycle with the entry point into the lookup table being determined by the feedback from the pressure sensor. Long term changes in the performance of the pump can also be accounted for by changing the entry in the lookup table which is consulted.

What is claimed is: 
     
         1 . A pump for use in dispensing reagents, the pump comprising:
 a motor;   a peristaltic pump having a rotor driven by the motor;   a pressure sensor monitoring the pressure of the pumped fluid downstream of the pump; and   a control unit which controls the motor by adjusting the standard operating speed of the motor according to the pressure detected by the pressure sensor, such that the pump operates continuously at a rate set by an operator.   
     
     
         2 . A pump according to  claim 1  wherein the control unit compares the pressure detected by the pressure sensor with a target pressure and adjusts the speed of the motor accordingly. 
     
     
         3 . A pump according to  claim 1  wherein the control unit receives a measurement of the current position of the rotor and compares that position to a desired position of the rotor, and adjusts the speed of the motor to compensate for any difference between the current position and the desired position. 
     
     
         4 . A pump according to  claim 1  wherein the control unit determines a desired position of the rotor throughout its rotary cycle from a lookup table according to the rate set by the operator. 
     
     
         5 . A pump according to  claim 4  wherein the desired position of the rotor throughout the rotary cycle in the lookup table entries is determined by the position of the rotor required to maintain a constant output pressure. 
     
     
         6 . A pump according to  claim 5  wherein the control unit adjusts the point of entry into the lookup table from which the desired position of the rotor is determined according to a target pressure. 
     
     
         7 . A pump according to  claim 6  wherein, during steady-state operation of the pump, the target pressure is the pressure detected by the pressure sensor and subjected to low-pass filtering. 
     
     
         8 . A pump according to  claim 4  wherein, if the lookup table does not contain an entry for the output pressure in question, the control unit interpolates between adjacent entries in the lookup table to determine the desired position of the rotor throughout the rotary cycle. 
     
     
         9 . A pump according to  claim 4  wherein the control unit monitors the performance of the pump over time using the measured pressure and adjusts the entry in the lookup table which is consulted according to the observed performance of the pump. 
     
     
         10 . A pump according to  claim 1  wherein the motor is a stepper motor. 
     
     
         11 . A pump according to  claim 1  further including a sensor arranged to determine the position of the rotor. 
     
     
         12 . A method of controlling a peristaltic pump having a rotor driven by a motor, the method comprising the steps of:
 receiving a desired operating rate from an operator;   detecting the pressure of the pumped fluid downstream of the pump: and   adjusting the standard operating speed of the motor according to the detected pressure such that the pump operates continuously at the desired operating rate.   
     
     
         13 . A method according to  claim 12  further including the steps of:
 comparing the pressure detected by the pressure sensor with a target pressure; and 
 adjusting the speed of the motor accordingly. 
 
     
     
         14 . A method according to  claim 12  further including the steps of:
 measuring the current position of the rotor; 
 comparing that position to a desired position of the rotor, and 
 adjusting the speed of the motor to compensate for any difference between the current position and the desired position. 
 
     
     
         15 . A method according to  claim 12  further including the step of determining a desired position of the rotor throughout its rotary cycle from a lookup table according to the rate set by the operator. 
     
     
         16 . A method according to  claim 15  wherein the desired position of the rotor throughout the rotary cycle in the lookup table entries is determined by the position of the rotor required to maintain a constant output pressure. 
     
     
         17 . A method according to  claim 16  further including the step of adjusting the point of entry into the lookup table from which the desired position of the rotor is determined according to a target pressure. 
     
     
         18 . A method according to  claim 17  wherein, during steady-state operation of the pump, the target pressure is the detected pressure which is then low-pass filtered. 
     
     
         19 . A method according to  claim 15  further including the step of, if the lookup table does not contain an entry for the output pressure in question, interpolating between adjacent entries in the lookup table to determine the desired position of the rotor throughout the rotary cycle. 
     
     
         20 . A method according to  claim 15  further including the steps of:
 monitoring the performance of the pump over time using the measured pressure; and 
 adjusting the entry into the lookup table which is consulted according to the observed performance of the pump.