Method for Determining a Physical Variable in a Positive Displacement Pump

Abstract

The present invention relates to a method for determining at least one physical variable in a positive displacement pump, wherein the positive displacement pump has a movable displacer element which delimits the metering chamber which is connected via valves to a suction and pressure line, with the result that delivery fluid can alternately be sucked into the metering chamber via the suction line and can be pressed out of the metering chamber via the pressure line as a result of an oscillating movement of the displacer element, wherein a drive is provided for the oscillating movement of the displacer element.

1 .- 16 . (canceled) 
     
     
         17 . A method of determining at least one physical variable in a positive displacement pump,
 wherein the positive displacement pump has a moveable displacer element delimiting the metering chamber which is connected by way of valves to a suction and a pressure line so that delivery fluid can alternately be sucked into the metering chamber by way of the suction line and urged out of the metering chamber by way of the pressure line by an oscillating movement of the displacer element,   wherein there is provided a drive for the oscillating movement of the displacer element,   wherein for the displacer element a differential equation is established based on a physical model, at least the position of the displacer element is measured and the physical variable is determined by means of the differential equation,   wherein the fluid pressure p of a delivery fluid in a metering chamber of a positive displacement pump is determined as the physical variable,   characterized in that if the actual fluid pressure reaches or exceeds a predetermined maximum value a warning signal is output and the warning signal is sent to an automatic shut-down arrangement which shuts down the metering pump in response to reception of the warning signal.   
     
     
         18 . A method of determining at least one physical variable in a positive displacement pump,
 wherein the positive displacement pump has a moveable displacer element delimiting the metering chamber which is connected by way of valves to a suction and a pressure line so that delivery fluid can alternately be sucked into the metering chamber by way of the suction line and urged out of the metering chamber by way of the pressure line by an oscillating movement of the displacer element,   wherein there is provided a drive for the oscillating movement of the displacer element,   wherein for the displacer element a differential equation is established based on a physical model, at least the position of the displacer element is measured and the physical variable is determined by means of the differential equation,   wherein the fluid pressure p of a delivery fluid in a metering chamber of a positive displacement pump is determined as the physical variable,   characterized in that for a movement cycle of the displacer element a target fluid pressure curve, a target position curve of the displacer element and/or the target current pattern through the electromagnetic drive is provided and the actual fluid pressure is compared to the target fluid pressure,   the actual position of the displacer element is compared to the target position of the displacer element and/or the actual current through the electromagnetic drive is compared to a target current through the electromagnetic drive and a warning signal is output if the differences between the actual and target values satisfy a predetermined criterion.   
     
     
         19 . A method of determining at least one physical variable in a positive displacement pump,
 wherein the positive displacement pump has a moveable displacer element delimiting the metering chamber which is connected by way of valves to a suction and a pressure line so that delivery fluid can alternately be sucked into the metering chamber by way of the suction line and urged out of the metering chamber by way of the pressure line by an oscillating movement of the displacer element,   wherein there is provided a drive for the oscillating movement of the displacer element,   wherein for the displacer element a differential equation is established based on a physical model, at least the position of the displacer element is measured and the physical variable is determined by means of the differential equation,   characterized in that the mass m of the displacer element, the spring constant k of the spring prestressing the displacer element, the damping d and/or the electrical resistance R Cu  of the electromagnetic drive is determined as the physical variable.   
     
     
         20 . A method as set forth in  claim 17 , characterized in that the positive displacement pump is an electromagnetically driven metering pump. 
     
     
         21 . A method as set forth in  claim 20  characterized in that besides the position of the displacer element the current through the electromagnetic drive is measured and the differential equation uses both the position of the displacer element and also the current through the electromagnetic drive as measurement variables, wherein the differential equation does not have any further measurement variables to be detected. 
     
     
         22 . A method as set forth in  claim 18  characterized in that a weighted sum of the relative deviations from the target value is determined and the criterion is so selected 
     
     
         23 . A method as set forth in  claim 18  characterized in that a plurality of criteria are predetermined, a fault event is associated with each criterion and, if a criterion is fulfilled, the associated fault event is diagnosed. 
     
     
         24 . A method as set forth in  claim 17  characterized in that a model-based closed-loop control is used for the drive. 
     
     
         25 . A method as set forth in  claim 24  characterized in that a non-linear state space model is selected as the model, wherein the non-linear closed-loop control is effected either by way of control-Lyapunov functions, by way of flatness-based closed-loop control methods with flatness-based precontrol, by way of integrator backstepping methods, by way of sliding mode methods or by way of predictive closed-loop control, wherein non-linear closed-loop control by way of control-Lyapunov functions is preferred. 
     
     
         26 . A method as set forth in  claim 24  characterized in that the difference between the detected actual position profile of the displacer element and a predetermined target position profile of the displacer element is detected during a suction-pressure cycle and the difference of at least a part of the detected difference and the predetermined target position profile is used as the target value profile for the next suction-pressure cycle. 
     
     
         27 . A method as set forth in  claim 17  characterized in that hydraulic parameters in the positive displacement pump are determined, for the hydraulic system a physical model is established with hydraulic parameters, the force exerted by the displacer element on the fluid in the metering chamber or the pressure in the metering chamber as well as the position of the displacer element is determined and at least one hydraulic parameter is calculated by means of an optimization calculation. 
     
     
         28 . A method as set forth in  claim 27  characterized in that the density of the fluid in the metering chamber and/or the viscosity of the fluid in the metering chamber is determined as the hydraulic parameter. 
     
     
         29 . A method as set forth in  claim 27  characterized in that the physical model is set up for the situation where the valve to the suction line is opened and the valve to the pressure line is closed and/or for the situation where the valve to the suction line is closed and the valve to the pressure line is opened, wherein if the physical model is set up both for the situation where the valve to the suction line is opened and the valve to the pressure line is closed and also for the situation where the valve to the suction line is closed and the valve to the pressure line is opened, the valve opening times are determined, and the physical model is selected in dependence on the result of determining the valve opening times. 
     
     
         30 . A method as set forth in  claim 28  characterized in that after determination of the hydraulic parameter same and the physical model is used for determining the force exerted by the delivery fluid on the displacer element and the force determined in that way is used in a closed-loop control of the movement of the displacer element. 
     
     
         31 . A method as set forth in  claim 18 , characterized in that the positive displacement pump is an electromagnetically driven metering pump. 
     
     
         32 . A method as set forth in  claim 19 , characterized in that the positive displacement pump is an electromagnetically driven metering pump. 
     
     
         33 . A method as set forth in  claim 18  characterized in that a model-based closed-loop control is used for the drive. 
     
     
         34 . A method as set forth in  claim 19  characterized in that a model-based closed-loop control is used for the drive.