Sensorless disturbance detection in metering pumps with stepping motor

Abstract

The present invention concerns a method of sensorless detection of functional disturbances of a positive displacement pump ( 1 ), wherein the positive displacement pump ( 1 ) has a moveable positive displacement element ( 5 ) having a boundary surface (A G ) which delimits a metering chamber ( 3 ), wherein the metering chamber ( 3 ) is connected to a suction and a pressure line ( 6, 7 ) by way of valves ( 8, 9 ) so that fluid (F) to be conveyed can alternately be sucked into the metering chamber ( 3 ) by way of the suction line ( 6 ) and pressed out of the metering chamber ( 3 ) by way of the pressure line ( 7 ) by an oscillating movement of the positive displacement element ( 5 ) and wherein there is provided a stepping motor ( 13 ) as a drive for the oscillating movement of the positive displacement element ( 5 ). To provide a method of detecting functional disturbances of a positive displacement pump without additional sensors being required according to the invention it is proposed that a motor moment (M M ) provided by the stepping motor ( 13 ) is ascertained and a warning signal is delivered when the ascertained motor moment (M M ) fulfils a first predetermined criterion.

1 . A method of sensorless detection of functional disturbances of a positive displacement pump ( 1 ), wherein the positive displacement pump ( 1 ) has a moveable positive displacement element ( 5 ) having a boundary surface (A G ) which delimits a metering chamber ( 3 ), wherein the metering chamber ( 3 ) is connected to a suction and a pressure line ( 6 ,  7 ) by way of valves ( 8 ,  9 ) so that fluid (F) to be conveyed can alternately be sucked into the metering chamber ( 3 ) by way of the suction line ( 6 ) and pressed out of the metering chamber ( 3 ) by way of the pressure line ( 7 ) by an oscillating movement of the positive displacement element ( 5 ) and wherein there is provided a stepping motor ( 13 ) as a drive for the oscillating movement of the positive displacement element ( 5 ), characterised in that a motor moment (M M ) provided by the stepping motor ( 13 ) is ascertained and a warning signal is delivered when the ascertained motor moment (M M ) fulfils a first predetermined criterion. 
     
     
         2 . A method as set forth in  claim 1  characterised in that the first predetermined criterion takes account of at least one of the following parameters:
 the proportion of the motor moment (M M ) applied by the stepping motor ( 13 ) to the positive displacement element ( 5 ) as the gross drive force (F b ), 
 the proportion of the gross drive force (F b ) applied to the fluid (F) to be conveyed by the positive displacement element ( 5 ) as the net drive force (F n ), and 
 the conveyor pressure (p F ) acting on the fluid (F) to be conveyed in accordance with the relation p F =F n /A G . 
 
     
     
         3 . A method as set forth in  claim 1  characterised in that in addition at least the gross drive force (F b ), the net drive force (F n ) or in accordance with the relation p F =F n /A G  the conveyor pressure (p F ) is determined. 
     
     
         4 . A method as set forth in  claim 3  characterised in that a warning signal is delivered when the gross drive force (F b ), the net drive force (F n ) or the conveyor pressure (p F ) fulfils the first predetermined criterion. 
     
     
         5 . A method as set forth in  claim 1  characterised in that the respective criterion is so selected that a warning signal is delivered when the corresponding parameter from the group consisting of the motor moment (M M ), the gross drive force (F b ), the net drive force (F n ) and the conveyor pressure (p F ) reaches or exceeds a first predetermined threshold value or the corresponding parameter reaches or falls below a second predetermined threshold value. 
     
     
         6 . A method as set forth in  claim 1  characterised in that the first criterion is so selected that the warning signal is delivered when a weighted sum of the relative deviations of the motor moment (M M ) and at least one further parameter from the group consisting of the gross drive force (F b ), the net drive force (F n ) and the conveyor pressure (p F ) from a respective threshold value reaches or exceeds a predetermined value. 
     
     
         7 . A method as set forth in  claim 1  characterised in that the motor moment (M M ) of the stepping motor ( 13 ) is detected by ascertaining the phase shift (δ UI ) of the motor voltage (U M ) relative to the motor current (I M ), which is caused by a voltage (U ind ) counter-induced by virtue of the load angle (δ L ) of the stepping motor ( 13 ). 
     
     
         8 . A method as set forth in  claim 2  characterised in that the gross drive force (F b ) applied to the positive displacement element ( 5 ) by the stepping motor ( 13 ) is determined on the basis of a model of the drive kinematics of the stepping motor ( 13 ) and the positive displacement element ( 5 ). 
     
     
         9 . A method as set forth in  claim 1  characterised in that the positive displacement pump ( 1 ), is a metering pump, preferably a diaphragm pump having a positive displacement element ( 5 ) in the form of a metering diaphragm. 
     
     
         10 . A method as set forth in  claim 9  characterised in that the net drive force (F n ) applied to the fluid (F) to be conveyed is determined from the gross drive force (F b ) by subtraction of force components not applied directly to the fluid (F) to be conveyed, in particular by subtraction of the deformation force (F V ) necessary for deformation of the metering diaphragm ( 5 ) and/or the force (F F ) necessary for stressing a spring element ( 12 ), by means of which the metering diaphragm ( 5 ) can be stressed in the direction of the pressure position or in the opposite direction. 
     
     
         11 . A method as set forth in  claim 1  characterised in that a plurality of criteria are predetermined and when a criterion is fulfilled a warning signal characteristic of the respective criterion is delivered. 
     
     
         12 . A method as set forth in  claim 11  characterised in that a fault event is associated with each criterion and when a criterion is fulfilled an associated fault event is diagnosed, in particular an overload and/or a stoppage of the stepping motor ( 13 ). 
     
     
         13 . A method as set forth in  claim 1  characterised in that a delivered warning signal is sent to an automatic shut-down means which shuts down the pump ( 1 ) in response to the receipt of the warning signal. 
     
     
         14 . A method as set forth in  claim 1  characterised in that a delivered warning signal is sent to an output device which outputs an acoustic and/or visual warning indication characteristic of the warning signal in response to the receipt of the warning signal. 
     
     
         15 . A method as set forth in  claim 2  characterised in that in addition at least the gross drive force (F b ), the net drive force (F n ) or in accordance with the relation p F =F n /A G  the conveyor pressure (p F ) is determined. 
     
     
         16 . A method as set forth in  claim 4  characterised in that the respective criterion is so selected that a warning signal is delivered when the corresponding parameter from the group consisting of the motor moment (M M ), the gross drive force (F b ), the net drive force (F n ) and the conveyor pressure (p F ) reaches or exceeds a first predetermined threshold value or the corresponding parameter reaches or falls below a second predetermined threshold value. 
     
     
         17 . A method as set forth in  claim 5  characterised in that the first criterion is so selected that the warning signal is delivered when a weighted sum of the relative deviations of the motor moment (M M ) and at least one further parameter from the group consisting of the gross drive force (F b ), the net drive force (F n ) and the conveyor pressure (p F ) from a respective threshold value reaches or exceeds a predetermined value. 
     
     
         18 . A method as set forth in  claim 6  characterised in that the motor moment (M M ) of the stepping motor ( 13 ) is detected by ascertaining the phase shift (δ UI ) of the motor voltage (U M ) relative to the motor current (I M ), which is caused by a voltage (U ind ) counter-induced by virtue of the load angle (δ L ) of the stepping motor ( 13 ). 
     
     
         19 . A method as set forth in  claim 7  characterised in that the gross drive force (F b ) applied to the positive displacement element ( 5 ) by the stepping motor ( 13 ) is determined on the basis of a model of the drive kinematics of the stepping motor ( 13 ) and the positive displacement element ( 5 ). 
     
     
         20 . A method as set forth in  claim 8  characterised in that the positive displacement pump ( 1 ), is a metering pump, preferably a diaphragm pump having a positive displacement element ( 5 ) in the form of a metering diaphragm.