Abstract:
An electronic metering device with a drive comprising an electric drive motor, at least one displacement device comprising a piston fixed to an axle drivable by the drive, for metering the fluid, and an electronic control for the drive motor, with a transducer which converts a feed voltage delivered by an electrical voltage source into a supply voltage for the drive, the supply voltage being matched in size to the respective load of the drive.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electronic metering device. 
     Electronic metering devices are applied in the laboratory for metering fluids. They are known in various embodiments. Metering devices functioning according to the air cushion principle have an integrated piston-cylinder unit, by way of which an air column is displaceable in order to suction sample fluid into a metering syringe and to expel this from the syringe. With this the piston-cylinder unit does not come into contact with the fluid. Only the metering syringe which as a rule consists of plastic is contaminated and may be exchanged after use. 
     With direct displacement metering devices on the other hand a syringe is directly filled with sample fluid. The piston and the cylinder of the syringe are thus contaminated by the fluid so that the syringe before the exchange of the fluid mostly must be replaced by a new syringe or be cleaned. Also this syringe consists as a rule of plastic. 
     Pistonless metering devices may comprise a metering tip with a balloon-like end section which is expanded for suctioning fluid, and for expulsion is compressed. Such metering tips are also already conceived as an exchange part. 
     Micro-metering devices may have a micro-membrane pump and/or a free jet meterer, wherein at least one of these components is designed with micro-system technology, in particularly with silicon, glass and plastic injection molding technology and/or plastic imprinting technology. The metering is achieved by deformation of a wall of a container which is filled with fluid. The electrical drive for the deformation of the wall may be piezoelectric, thermoelectric, electromagnetic, electrostatic, electromechanical, magnetorestrictive, etc. 
     Air cushion, direct displacement, pistonless and micro-metering devices may have an unchangeable or changeable metering volume. A changing of the metering volume is achieved by adjustment of the displacement of the displacement means, i.e. of the displacement path of the piston or of the degree of deformation of the balloon-like end section or of the chamber wall. 
     Dispensers are metering devices which may repetitively dispense an accommodated fluid in small part quantities. 
     Furthermore there are multi-channel metering devices which have several “channels” by way of which it is simultaneously metered. 
     All metering devices may in particular be designed as a hand apparatus and/or stationary apparatus. 
     All previously mentioned metering devices may be electronic metering devices in the meaning of this application. With this they comprise a drive means with an electrical drive for driving a displacement means with which it may be the case of the piston-cylinder unit or the balloon-like end section of a metering tip, or a chamber with a deformable wall. The electrical drive in particular may be an electrical drive motor, electric linear drive or an electrical drive mentioned in the context of the micro-metering devices. Furthermore an electronic control means for the drive and an electrical voltage source for the supply of the control means and the drive is present. Electronic metering devices have in particular the advantage of the high reproducibility of meterings. In particular by way of preset constant metering speed (μl/s) more exact results may be achieved than with manually driven metering devices. Furthermore they have the advantage of a broad area of application since they may fulfill simple pipetting functions as well as dispensing functions. The electrical voltage source may comprise a battery, an accumulator and/or mains electricity part. 
     With conventional electronic metering devices the electrical voltage source is dimensioned such that in the normal condition it makes available a sufficient power for the drive with all operating loads of the drive means. With a battery or an accumulator this requires a suitable number of cells. However with an advanced discharging and thus reducing feed voltage increasingly operating malfunctions occur. With a reducing feed voltage specifically the torque of the drive reduces so that the drive means no longer drives the displacement means with all occurring loads in the desired manner. In particular with the design of the drive as a stepper motor steps may be lost and by way of this metering errors arise. Therefore for a reliable operation over a desired time a complicated battery or accumulator supply with corresponding costs, volume and weight are required. The same applies to the embodiment of the electrical voltage source as a mains electricity part. 
     BRIEF SUMMMARY OF THE INVENTION 
     Proceeding from this it is the object of the invention to provide an electronic metering device with which the cost for the electrical voltage source, in particular its costs, space requirement and weight is reduced and the drive in spite of this at all operational loads is supplied with the required voltage. 
     This object is achieved by an electronic metering device with the features of claim 1. Advantageous formations of the electronic metering device are specified in the dependent claims. 
     The electronic metering device according to the invention has 
     a drive means comprising an electric drive, 
     at least one displacement means drivable by the drive means, for metering the fluid and 
     an electronic control and/or regulating means for the drive with a transducer which converts a feed voltage delivered by an electrical voltage source into a supply voltage for the drive, this supply voltage being matched in size to the respective load of drive means. 
     According to the invention thus the control and/or regulating means makes available to the drive via a transducer a supply voltage which is matched to the respective load of the drive means. Thus for example at the beginning of the drive procedure it may increase the supply voltage in order to overcome start resistances of the displacement means. Thereafter it may reduce the supply voltage to a nominal value which is sufficient for the further drive of the displacement means set in motion. In the case that the metering device can be equipped with various displacement means which represent varying loads for the drive means, for example syringes of differing size, the supply may be matched to the respective displacement means. The control and/or displacement means controls the operation of the metering device, for example according to control commands which may be inputted via a keyboard so that it recognizes the respective operating condition of the metering device. According to predetermined criteria the control and/or regulating means may find a suitable supply voltage for each operating condition and make this available via the transducer. Furthermore information on the respective present displacement means, e.g. a coding of a syringe may be automatically read by the metering device or inputted separately. Furthermore the control and/or regulating means may evaluate the respective load which may be unforeseeably changed by external influences and on account of the evaluation result regulate the supply voltage. Thus the matching of the supply voltage to the respective load may be achieved. 
     The invention is not limited to the application of step-up transducers. Included is also the case in which the supply voltage required by the electrical drive lies below the feed voltage of the voltage supply. Thus for example Lithium Ion (Li-Ion) accumulators are available which deliver a relatively high voltage (approx. 3V per cell), so that by way of series connection of only a few cells a relatively high feed voltage may be made available. In the state of the art, in particular with the application of stepper motors, with a low load of the drive means the high feed voltage is partly converted into waste heat. This is undesirable for various reasons. Within the scope of the invention then in such cases a stepping-up convertion of the feed voltage to the supply voltage at the level required with the respective load may be effected. Also the invention includes the case in which the supply voltage from the transducer is increased as well as also reduced, according to the load of the drive means. 
     The metering device according to the invention has the advantage that the electrical voltage source and the drive may be matched to an average load. With increased loads the transducer makes available an increased supply voltage. Since these only occur for a short time no damage to the drive motor is to be feared. As a result of this the metering device makes do with a lower number of battery or accumulator cells or with a smaller-dimensioned mains electricity part than conventional metering devices. On the part of the electrical supply voltage a cost saving can be achieved which exceeds the additional costs of the transducer. Furthermore by way of this the space requirement for the voltage source is reduced and a weight reduction of the metering device is achieved. A further advantage lies in the fact that this is largely independent on the discharged state of a battery or accumulator. 
     The electrical drive may in particular be an electrical drive motor, an electrical linear drive or one of the electrical drives mentioned in the combination with micro-metering devices. An electrical drive motor may in particular be a stepper motor with which an impulse control favors exactly defined metering quantities or metering steps. 
     Additionally or instead of this, exactly defined metering quantities may also be ensured by end abutments, angle coders or coding strips. 
     Furthermore the drive means may have a gear for converting a rotational movement of a shaft of the drive motor into a linear drive movement for the displacement means. This may in particular be the case if the displacement means comprises a piston-cylinder arrangement. With this it may be the case of the syringe of a direct displacer or displacement unit of an air cushion metering device. 
     The electrical voltage source may comprise at least one battery, at least one accumulator and/or an electrical mains part. In particular NiMH accumulators may be present. Preferably by way of two such accumulators a feed voltage of 2.4 volts may be made available. 
     The transducer may deliver the supply voltage in particular roughly at the level of the feed voltage and above this. Thus the supply voltage at the level of a feed voltage of e.g. 2.4 Volts may be used in order to exert a holding moment onto a stepper moment which is designed for a nominal voltage of e.g. 6 Volts. Without such a holding moment with a stepper motor on braking there is a tendency to oscillate, so that it possibly covers one or more undesired steps. 
     Preferably the transducer may deliver the supply voltage at various discrete or continuous levels. Of these one may serve the production of the holding moment. A further level may be the nominal voltage which the drive motor requires with an average load. Furthermore it may also output an increased voltage level for increased loads. Accordingly the control and/or regulating means may deliver the supply voltage at a low level with the stopping of the drive motor, at the middle level with an average load and with an increased load at the increased level. For example the supply voltage may assume the discrete value 2.4 Volts, 6 Volts and 8 Volts. 
     Preferably the transducer comprises a step-up converter. Step-up converters in supply technology are known circuits with which a constant voltage may be brought to an increased level. Step-up converters may set an output voltage via the input voltage, wherein as a rule these exploit the energy stored in an inductance. 
     Preferably the electronic metering device is designed as a hand device and accordingly is equipped with at least one battery or at least one accumulator. The electronic metering device may in particular be an electronic pipetting device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is hereinafter described in more detail by way of the accompanying drawings of embodiment examples. In the drawings there are shown: 
     FIG. 1 a total block diagram of the electronic pipetting device; 
     FIG. 2 a circuit diagram of the step-up converter of the same pipetting device; 
     FIG. 3 a block diagram of the supply voltage of the drive motor of an electronic pipetting device. 
     FIG. 4 a diagram of a hand pipetting device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to FIG. 1 the electronic pipetting device consists essentially of six function regions, specifically a drive means  1 , a displacement means  2 , an electronic control and/or regulating means  3 , an electrical voltage source  4 , and operating means  5  and a display means  6 . All function regions  1  to  6  are formed in or on a pipette housing—not shown—of a hand pipette. 
     “The drive means  1  comprises an electrical drive motor which is designed as a stepper motor  7 . By way of the stepper motor  7  an axle  8  may be displaced linearly forwards and backwards. Furthermore to the drive means there belongs a motor step in the form of two H-bridges  9  which serve the control of the stepper motor  7 . This in the manner known to the man skilled in the art comprises eight power transistors connected in an H-arrangement, with which the stepper motor  7  via supply leads  10  may be operated in the forwards or backwards direction. It is known to the skilled person that the H-bridge or H-drive is an arrangement for switches, i.e., relays or semiconductors for reversing the direction of current in any load.” 
     The displacement means  2  comprises a piston  11  which is fixed on the axle  8 . The piston  11  is displaceable in a cylinder  12 . This is connected via a channel  13  to a pipette tip  14  which is separable from the device. 
     To the electronic control and/or regulating means  3  there belongs a micro-controller  15  which in particular has integrated a timer, an operating memory and a non-volatile memory. The micro-controller controls the H-bridges via control leads  16 . 
     To this there further belongs a step-up transducer  17  for producing the supply voltage of the stepper motor  7  which via supply leads  18  feeds the H-bridges. Control leads  19  connect the micro-controller  15  to the step-up transducer  17 . 
     A further component of the control and/or regulating means  3  is a further step-up transducer  20  which supplies the micro-controller  15  via further supply leads  21 . 
     To the axle  8  of the stepper motor  7  there is allocated an end bearing switch  22  which via a control lead  23  is monitored by the micro-controller  15  in order to permit a zero-point setting. 
     The electrical voltage source  4  comprises two NiMH accumulators  24  whose feed voltage via feed leads  25  are supplied to the step-up transducer  17  and the further step-up transducer  20 . The feed voltage of the two accumulators  24  are supplied via control leads  26  to the micro-controller  15 . Furthermore to the electrical voltage source  24  there belongs a charging current control  27  which on the one hand via charging contacts  28  can be connected to an external voltage source and on the other hand via charging leads  29  is connected to the accumulators. The charging current control  27  is furthermore via control leads  30  for the charging voltage and via charging current leads  31  in each case connected to the micro-controller  15 . 
     The operating means  5  comprises an input keyboard  32  which via leads  33  is connected to the micro-controller  15 . Furthermore it comprises the trigger button  34  which via leads  35  is connected to the micro-controller  15 . 
     The display means  6  is an LCD display which via leads  36  is connected to the micro-controller  15  which contains a display control. 
     Basically the pipetting device functions as follows: 
     The control software is stored in the micro-controller. Special pipetting parameters may be inputted before the metering procedure by way of an input keyboard  32 . By way of the trigger buttons  34  individual pipetting procedures may be triggered. The display  6  displays inputted pipetting parameters, control commands and operating conditions of the pipetting device. 
     The complete feed voltage of the two accumulator cells  24  is 2.4 Volts. This is regulated by the further step-up transducer  20  to 3.3 Volts supply voltage for the micro-controller  15 . 
     According to the control, via the control lead  19  the step-up transducer  17  connects through the feed voltage of the accumulators  24  as the supply voltage to the supply leads  18  or increases this to 6 or 8 Volts. Since the micro-controller controls the operation of the stepper motor  7  via the control leads  16 , it knows the respective voltage requirement of the stepper motor and correspondingly controls the step-up transducer  17 . 
     The feed voltage is controlled by the micro-controller  15  via the control leads  26 . If it falls below an allowable voltage from the display  6  corresponding information is outputted. By way of connection of the charging contacts  28  to an external mains supply part in the case needed a charging of the accumulators  24  may be effected. Via the charging current control leads  31  the charging current is controlled according to the charged condition of the accumulators  24  evaluated via the control leads  30 . 
     The design of the function regions  1  to  6  and the associated function blocks is known to the man skilled in the art. One embodiment example of the step-up transducer  17  is however to be explained by way of FIG.  2 . The step-up transducer  17  comprises an IC  37  of the type which amongst experts is known as “step-up converter”. For example it is the case of an IC MAX 608 of the company Maxim. The IC  37  is in the usual manner connected to the transistor  38 , resistance  40 , capacitors  45  to  50 , diode  51  and inductance  52 . The IC  37  regulates via the voltage feedback consisting of transistor  39  and resistances  41  to  43 , the switching time of the transistor  38 , by which means the inductance  52  is charged with energy. This energy is outputted as an additional series voltage source during the blocking phase of the transistor  38  to the output capacitors  48  and  49 . With this the voltage feedback can be switched by way of the contact  57 . If the contact  57  is set to “low” the supply voltage is 6V, if it is on “high” it is 8V. 
     Finally by way of the contact  58  the supply voltage may roughly be set to the value of the feed voltage. For this the contact  58  is to be switched from “low” to “high”. 
     Accordingly the feed leads  25  lie at the contacts  53 ,  54  and the supply leads  18  at the contacts  55 ,  56  and the control leads  19  are connected to the contacts  57 ,  58 . 
     The drive motor  7  may thus by way of the electronic control means  3  be operated at three differing voltages: 
     a) the micro-controller  15  sets the contact  58  to “high” and the step-up converter  37  is not active so that the supply voltage corresponds to the feed voltage minus the loss voltage of the diode  51 . 
     b) the micro-controller  15  sets the contact  57  of the step-up converter to “low” so that the transducer  39  is controlled and the IC  37  is activated and the step-up transducer  17  delivers a supply voltage of 6 Volts. 
     c) the micro-controller  15  sets the contact  57  to “high” so that the transistor  39  is blocked and the IC  37  is activated and the step-up transducer  17  makes available a supply voltage of 8 Volts. 
     With this for the step-up transducer there applies: 
     
       
           U   A   ≈U   E ×(1+ t   1 / t   2 ) 
       
     
     wherein U A  is the supply voltage and U E  is the feed voltage. t 1  is the time during which the transistor  38  is conducting and t 2  is the time during which the transistor  38  is blocked. 
     If the transistor  38  conducts just as long as it blocks then there applies U A ≈2×U E . If on the other hand the transistor blocks the whole time then there applies U A ≈U E . 
     The region in which voltages may be stepped up is limited by the resulting current and the applied components. The power balance remains approximately constant: 
     
       
         
           P 
           E 
           =P 
           A 
         
       
     
     i.e. 
     
       
         
           U 
           E 
           ×I 
           E 
           =U 
           a 
           ×I 
           a 
         
       
     
     wherein P E  is the applied power and P A  is the delivered power and I E  is the applied current and I A  is the supply current. Thus the applied current with the voltage step up increases considerably. 
     The increase of the torque of the drive motor  7  results from the fixed motor inner resistance and the increased driving voltage U A . The electrical power which is converted in the motor is also a measure for the available motor torque. 
     By a motor with 2×30 Ohms winding resistance with a supply voltage of 3 Volts a maximum power of 
     
       
           P=U   2 /(1−/2× R )=0.6 Watts 
       
     
     is converted. If on the other hand the voltage is stepped up to 8 Volts the power is increased to 4.3 Watts. The power increased roughly by the factor  7  may of course be converted by the motor only for very short times, since otherwise an overheating of the motor would take place. For overcoming the increased loads which usually with operation of pipetting devices occur only for a short time this is however possible without further ado. 
     FIG. 3 emphasizes the function principle of the invention. An electrical voltage source  24  in the form of a battery, of an accumulator or of a mains supply part delivers a low feed voltage to an step-up transducer  17 . This by way of control leads  19  via a voltage factor Nu is controlled digitally or analog and accordingly delivers a supply voltage according to the product of the voltage factor N u  and the feed voltage. This supply voltage drives via the motor end step  9  the drive motor  7 . Basically also a stepless variation of the voltage factor N u  is possible, in order to achieve a fine adaptation to the power requirement.