Motor-driven metering pump

Abstract

A metering pump with a rotary drive motor and an oscillating piston, wherein the rotary motion of a drive motor is transformed into an oscillatory motion of a connecting rod by means of a gear arrangement, so that a displacement means activated thereby executes an oscillating linear motion on continuous rotation of the drive motor, that results in transfer of a medium to be metered in a metering head ( 12 ) arranged in the longitudinal axis of the connecting rod ( 19 ) cooperating alternately with an outlet and inlet valve to produce a pump stroke (pressure stroke) and a priming stroke. A reference element ( 35 ) is associated with the connecting rod, the position of which is detected by a positional sensor, wherein the positional sensor provides an actual signal (x I ) that is in a fixed relationship to the position of the reference element and thus to that of the displacement means and that provides information regarding the motion executed by the displacement means, so that the electronic control system of the metering pump can react to the conditions of the metering circuit and pump.

1 . A metering pump with a rotary drive motor and an oscillating piston, wherein the rotary motion of a drive motor ( 2 ) is transformed into an oscillatory motion of a connecting rod ( 19 ) by means of a gear arrangement, so that a displacement means actuated thereby executes an oscillating linear motion on continuous rotation of the drive motor ( 2 ), that results in transfer of a medium to be metered in a metering head ( 12 ) arranged in the longitudinal axis of the connecting rod ( 19 ) cooperating alternately with an outlet and an inlet valve to produce a pump stroke (pressure stroke) and a priming stroke, wherein a reference element ( 35 ) is associated with the connecting rod ( 19 ), the position of which is detected by a positional sensor ( 36 ), wherein a positional sensor provides an actual signal (x I ) that is in a fixed relationship to the position of the reference element and thus to that of the displacement means and that provides information regarding the motion executed by the displacement means, so that the electronic control system of the metering pump can react to the operating conditions of the metering circuit and pump.  
   
   
       2 . A metering pump according to  claim 1  wherein the positional sensor ( 36 ) detects the position of the reference element ( 35 ) in accordance with a touch free principle.  
   
   
       3 . A metering pump according to  claim 1  wherein the reference element ( 35 ) associated with the connecting rod ( 19 ) and the positional sensor ( 36 ) are outside the metering head.  
   
   
       4 . A metering pump according to  claim 1  wherein the reference element ( 35 ) influences the path of a light source ( 33 ) and the positional sensor cooperating therewith ( 36 ), that is fixed in the pump housing or another stationary part, operates in a light-sensitive manner.  
   
   
       5 . A metering pump according to  claim 1  wherein the reference element ( 3 ) is a shadow-producing body or a shadow producing contour and the positional sensor ( 36 ) cooperating therewith that is fixed in the pump housing or another stationary part, consists of an optical receiver ( 32 ) in the form of a series of light sensitive charged coupled devices (CCD).  
   
   
       6 . A metering pump according to  claim 1  wherein the positional sensor ( 36 ) is arranged on its own sensor carrier ( 31 ) that is fixed to the pump housing or another stationary part.  
   
   
       7 . A metering pump according to  claim 4  wherein the light source ( 33 ), the shadow-producing body or shadow-producing contour ( 35 ) and the receiver ( 32 ) constitute a light box-like arrangement and the measured values are continuously or intermittently fed to the electronic control system.  
   
   
       8 . A metering pump according to  claim 5  wherein the optical receiver ( 32 ) of the positional sensor ( 36 ) consists of a number of linearly arranged receivers (pixels), preferably 128 pixels.  
   
   
       9 . A metering pump according to  claim 5  wherein the light source ( 33 ) is a light emitting diode (LED) that is arranged with respect to the optical receiver ( 32 ) of the positional sensor ( 36 ) so that its light beam directed at the receiver is not interrupted by the connecting rod ( 19 ).  
   
   
       10 . A metering pump according to  claim 1  wherein a start value for the positional sensor ( 36 ) is produced by interpolating the brightness of a plurality of pixels in a shadow transition region.  
   
   
       11 . A metering pump according to  claim 1  wherein when processing signals for the positional sensor ( 36 ), filtering is employed.  
   
   
       12 . A metering pump according to  claim 1  wherein zero position errors of the positional sensor ( 36 ) are eliminated by means of a reference memory.  
   
   
       13 . A metering pump according to  claim 1  wherein scaling errors of the positional sensor ( 36 ) are eliminated by using one or more reference positions.  
   
   
       14 . A metering pump according to  claim 5  wherein variations in illumination of the positional sensor ( 36 ) are compensated for by controlling or regulating the light source ( 33 ) using pixel brightness values obtained.  
   
   
       15 . A metering pump according to  claim 14  wherein variations in brightness between individual pixels of the optical receiver ( 32 ) are compensated for by using a reference memory for the sensitivity of each pixel.  
   
   
       16 . A metering pump according to  claim 1  wherein determination of a value to which a stroke adjustment apparatus ( 7 ) for adjusting stroke, should be adjusted is obtained directly by means of the positional sensor ( 36 ) by measurement during metering.  
   
   
       17 . A metering pump according to  claim 1  wherein an electronic control system recognizes a blockage in the displacement means or an incompletely executed stroke by evaluating a signal from the positional sensor ( 36 ).  
   
   
       18 . A metering pump according to  claim 1  wherein the drive motor ( 2 ) operates with slippage and an electronic control system defines a nominal stroke frequency or a nominal stroke period for the displacement means from the nominal rotary speed of the drive motor and the known gear characteristics and additionally determines the actual stroke frequency or the actual stroke period of the displacement means by evaluating the positional sensor signal ( 36 ), wherein by comparing the actual stroke frequency with the nominal stroke frequency or the actual stroke period with the nominal stroke period of the displacement means, the slippage of the drive motor can be calculated and the nominal rotary speed can be changed so that the displacement means moves at the desired stroke frequency.  
   
   
       19 . A metering pump according to  claim 1  wherein the drive motor ( 2 ) operates with slippage and an electronic control system provides a nominal stroke frequency or a nominal stroke period for the displacement means from the nominal rotary speed of the drive motor and the known gear characteristic and additionally defines the actual stroke frequency or the actual stroke period of the displacement means by evaluating the positional sensor signal ( 36 ), wherein by comparing the actual stroke frequency with the nominal stroke frequency or the actual stroke period with the nominal stroke period of the displacement means, the slippage of the drive motor can be calculated and further, the electronic control system can determine the force on the displacement means from the determined slippage of the drive motor and the known gear characteristic and thus reduce the operating pressure of the metering medium.  
   
   
       20 . A metering pump according to  claim 1  wherein the drive motor ( 2 ) operates with slippage and an electronic control system determines a nominal speed for the displacement means from a nominal rotary speed of the drive motor and a known gear characteristic for every instant of the metering procedure and additionally, determines the actual speed of the displacement means by evaluating the positional sensor signal ( 36 ), wherein by comparing the actual instantaneous speed with the nominal speed of the displacement means, the instantaneous slippage of the drive motor can be calculated and, again in connection with the known gear characteristics, the instantaneous force in the displacement means can be deduced therefrom.  
   
   
       21 . A metering pump according to  claim 20  wherein the electronic control system reduces the operating pressure of the metering medium using the observed force profile on the displacement means.  
   
   
       22 . A metering pump according to  claim 19  wherein the electronic control system recognizes operation beyond the specified pressure range from the determined metering medium operating pressure and adjusts metering when a maximum permissible pressure as dictated by the specification for the metering pump or as provided by the operator is exceeded, or when a predetermined minimum pressure is not reached.  
   
   
       23 . A metering pump according to  claim 21  wherein the electronic control system recognizes operation beyond the specified pressure range from the determined metering medium operating pressure and adjusts metering when a maximum permissible pressure as dictated by the specification for the metering pump or as provided by the operator is exceeded, or when a predetermined minimum pressure is not reached.  
   
   
       24 . A metering pump according to  claim 19  wherein the displacement means is a partially elastic diaphragm ( 13 ), wherein the electronic control system determines an expected metering error from the determined operating pressure of the metering medium and the known dependency of the metering performance on the operating pressure and influences the rotary speed of the drive motor ( 2 ) and thus the stroke frequency to work against the expected metering error.  
   
   
       25 . A metering pump according to  claim 21  wherein the displacement means is a partially elastic diaphragm ( 13 ), wherein the electronic control system determines an expected metering error from the determined operating pressure of the metering medium and the known dependency of the metering performance on the operating pressure and influences the rotary speed of the drive motor ( 2 ) and thus the stroke frequency to work against the expected metering error.  
   
   
       26 . A metering pump according to  claim 1  wherein the signal (x I ) for the position of the connecting rod ( 19 ) read from the positional sensor ( 36 ) is fed to a control circuit device in the context of its control accuracy and influences rotary speed of the drive motor ( 2 ) and thus linear motion of the connecting rod and thus of the displacement means so that it follows a predetermined nominal profile ( 38 ).  
   
   
       27 . A metering pump according to  claim 26  wherein the control device alternately influences the position (x I ), speed (v I ) or the acceleration of the displacement means by changing the rotary speed of the drive motor ( 2 ).  
   
   
       28 . A metering pump according to  claim 27  wherein the control device can deliberately decrease v I  for the displacement means during a priming phase and/or in a pressure phase, in order to counteract pressure drops that are caused by resistance to flow, for example the onset of cavitations.  
   
   
       29 . A metering pump according to  claim 27  wherein the desired stroke length is communicated to the control device by an operator and the control device is used to electronically limit motion of the displacement means to the stroke length to be executed, wherein the control device stops the drive motor ( 2 ) after executing the desired stroke length, switches it into reverse and then carries out a priming stroke and the motor then stops or carries out the next pressure stroke.  
   
   
       30 . A metering pump according to  claim 27  wherein the control device distributes forward motion of the displacement means during the pressure phase by driving the drive motor ( 2 ) for the time determined by the repetition rate of the metering stroke, so that the metering medium is dispensed as evenly as possible, even in the case of metering strokes that are very slow, for example of several minutes.  
   
   
       31 . A metering pump according to  claim 20  wherein the displacement means is partially in the form of an elastic diaphragm ( 13 ) and the electronic control system detects the opening of the outlet valve ( 15 ) from the instantaneous force on the diaphragm ( 13 ) and with the aid of said detection measures a dead region that arises because of elastic deformation of the diaphragm ( 13 ).  
   
   
       32 . A metering pump according to  claim 31  wherein the actual stroke is influenced independently of deduced diaphragm deformation, wherein the control device stops the drive motor ( 2 ) after reaching the desired stroke length from opening of the outlet valve ( 15 ), switches it into reverse and then executes the priming stroke and then stops the motor or executes the subsequent pressure stroke, so that error caused by the diaphragm deformation, with respect to the stroke or the metered volume, is eliminated and the dependency of metered quantity on back pressure is substantially reduced.  
   
   
       33 . A metering pump according to  claim 32  wherein actual hub frequency is influenced independently of the deduced diaphragm deformation, wherein the control device determines a correction for the error caused by the diaphragm deformation, with respect to the stroke or the metered volume, and changes nominal rotary speed of the drive motor ( 2 ) with the aid of said correction so that the error caused by the diaphragm deformation is eliminated.