Abstract:
The syringe pump comprises a receiving position for a syringe. The piston plate of the syringe is moved by a drive head which is fastened to a drive rod. For locking the piston rod prior to fixing the piston plate in the drive head, a braking element is provided on a syringe holding head. The syringe holding head further serves for determining the respective syringe size. After placing the syringe holding head against a syringe cylinder, the brake element is actuated to temporarily engage the piston rod and fix it relatively to the syringe cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This is a divisional application of Ser. No. 10/346,609, which claims priority from German Patent Application No. 202 00 885.1, titled A SYRINGE PUMP HAVING A PISTON BRAKE, filed in Germany on Jan. 22, 2002, the entire contents of which are expressly incorporated hereby by reference as though set forth in full. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a syringe pump having a piston brake for controlled discharge of medical syringes. 
         [0003]    From EP 0 566 825 A1 a syringe pump having a piston brake is known, which comprises a first holder for fixing the cylinder of a syringe and a linearly movable second holder for displacing the piston rod of the syringe. 
         [0004]    A stationary piston brake engages the piston rod and, when the piston cylinder is inserted, blocks the piston rod until the piston rod has been gripped by the second holder. Thereby unintentional displacement of the piston rod caused by suction effect or mechanical movement prior to the start of infusion is prevented. Securing the piston rod after an exchange of syringes is of importance in particular for small syringes having small frictional forces. 
         [0005]    Further, syringe pumps are known which allow an automatic exchange of syringes. For this purpose, a syringe holding head is provided which, after insertion of a syringe, scans said syringe and determines the syringe size. On the basis of the syringe size the displacement velocity and other parameters are automatically adjusted. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the invention to provide a syringe pump having a piston brake, which, in the syringe position, requires only a simplified support. 
         [0007]    In the syringe pump according to the invention the brake element is arranged on the syringe-position side opposite the drive rod, i.e., on the outside. The brake element is movable toward a syringe bearing arranged on the drive-rod side in order to impart the brake effect. Consequently, the syringe bearing is located on the drive-rod side which defines the inside. Against this syringe bearing syringes of various sizes may be placed for assuming a defined position suitable for the discharge process. 
         [0008]    According to a preferred aspect of the present invention, the brake element is provided on a syringe holding head which is movable transversely to a syringe in the syringe position. Such a syringe holding head normally engages only the syringe cylinder. It serves as a holder which secures the syringe cylinder against displacement out of the syringe position. According to the invention, this syringe holding head is additionally provided with a brake element which acts upon the piston rod projecting out of the syringe cylinder. One advantage of this measure is that the piston brake is spatially related to the syringe cylinder, i.e., activation, and deactivation, of the piston brake require only a very small amount of displacement of the brake element. After closing of the syringe holding head and recognition of a proper syringe, the piston brake automatically imparts a braking effect until the motorized drive head has recognized and locked the piston plate of the syringe. Thereafter, the piston brake is released by displacing the brake element, wherein engagement of the syringe holding head with the syringe cylinder is however not released. 
         [0009]    According to a preferred embodiment of the present invention, a linear drive for the brake element extends below the syringe position, wherein a motor is arranged on one side and the syringe holding head on the other side of the drive rod. The linear drive effects adjustment of the brake element from the drive-rod side, wherein the syringe is pulled against the syringe bearing which is also located on the drive-rod side. 
         [0010]    Preferably, the brake element is provided on a syringe holding head, wherein a portion of the syringe holding head engages the syringe cylinder, and the brake element engages the piston rod. In this manner, the functions of syringe holding head and brake element can be combined in one unit. 
         [0011]    According to a preferred aspect of the present invention, an actuating means for the brake element is arranged on a slide which is connected with the syringe holding head, and a sensor detecting the position of the slide is provided for the purpose of determining the syringe size. When the syringe holding head is manually removed to allow the syringe to be inserted, and is then placed against the syringe, the slide carrying the actuating means for the brake element moves together with the syringe holding head. When the syringe is in the syringe position, the sensor provides a position signal indicative of the syringe holding head position and thus the size (diameter) of the inserted syringe. 
         [0012]    Preferably, the slide is connected via a tube with the syringe holding head, through which tube extends an axially movable rod for adjusting the brake element relatively to the syringe holding head. This configuration offers a particularly simple mechanism for adjusting the brake element relatively to the syringe holding head. 
         [0013]    To definedly position the syringe in axial direction when the syringe is inserted into the syringe pump, a positioning means engaging a winglike syringe portion is provided according to a preferred aspect of the present invention, said positioning means being coupled with the syringe holding head such that it presses the winglike syringe portion axially against a stop wall when the syringe holding head radially approaches an inserted syringe. 
         [0014]    The invention further relates to another embodiment of the syringe pump. Here, the brake element defining the piston brake is provided on a syringe holding head which radially presses the syringe cylinder against a syringe bearing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Hereunder an embodiment of the present invention is explained in detail with reference to the drawings in which: 
           [0016]      FIG. 1  shows a plan view of a syringe pump with removed syringe holding head and with the locking means in the release position; 
           [0017]      FIG. 2  shows a section along line II-II of  FIG. 1 ; 
           [0018]      FIG. 3  shows, in a similar representation as that of  FIG. 1 , the condition with properly inserted syringe and closed syringe holding head; 
           [0019]      FIG. 4  shows a section along line IV-IV of  FIG. 3 ; 
           [0020]      FIG. 5  shows a section along line V-V of  FIG. 3  with open arms of the drive head: 
           [0021]      FIG. 6  shows the drive head of  FIG. 5 , wherein the arms are locked with the piston rod; 
           [0022]      FIG. 7  shows a section along line VII-VII of  FIG. 3 ; and 
           [0023]      FIG. 8  shows a detail of  FIG. 1 , wherein the locking means for the syringe holding head is in the locking position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The syringe pump is generally configured like that described in EP 0 566 825 A1 such that a general description of the overall device is omitted here. (EP 0 566 825 A1 was published on Oct. 27, 1993 and is incorporated in its entirety by this reference.) 
         [0025]    The syringe pump serves for discharging a syringe  10  which comprises a syringe cylinder  11  and a piston rod  12 . 
         [0026]    The syringe cylinder  11  is provided at its open end with a projecting winglike syringe portion  13 , and the piston rod comprises at its end a piston plate  14 . The piston rod  12  has a cruciform profile made from ribs arranged perpendicularly to each other. 
         [0027]    In the syringe position P the syringe  10  is placed against a laterally arranged syringe bearing  15  in such a manner that the winglike syringe portion  13  assumes a specified axial position. In this condition, the piston rod  12  is retracted from the syringe cylinder  11 , and the syringe cylinder  11  is filled with a liquid. 
         [0028]    For moving the piston rod  12  a linearly movable drive head  16  is provided on the syringe pump, said drive head  16  being attached to an elongate drive rod  17 . The drive head can be moved toward the piston plate  14  to receive and lock the latter. According to  FIG. 3 , the drive head can be moved to the left for discharging the contents of the syringe  10 . On the drive rod  17  side a supporting bearing  18  is located upon which the piston plate  14  can rest when the piston brake is actuated. 
         [0029]    On the drive rod  17  side a motor  20  having a vertical axis is arranged on a slide  19 . The motor  20  drives, via a worm wheel, a helical gear wheel  21  supported on the slide  19 . The gear wheel  21  is provided with a threaded bore which is in engagement with the thread of a spindle rod  22 . By rotating the gear wheel  21  the spindle rod  22 , which is secured against rotation, is axially displaced. Thus the spindle rod  22  defines a linear drive  23 . 
         [0030]    A tube  24  extends, transversely to the longitudinal direction of the syringe  10  and below the drive rod  17 , from the slide  19 , through which tube  24  the spindle rod  22  extends. On the opposite side of the syringe  10  a syringe holding head  25  is fastened to the end of the tube  24 . On the tube  24  a helical spring  26  is located which is supported on the syringe bearing  15  associated with the housing of the syringe pump, and presses the slide  19  out of the syringe position. Since, on the other hand, the tube  24  is connected with the slide  19 , and at the end of the tube  24  the syringe holding head  25  is located, the syringe holding head is pressed against the syringe  10  which is in the syringe position P, thus pressing the syringe against the syringe bearing  15 . The syringe holding head  25  is rotatable about the axis of the tube  24 . The syringe holding head  25  comprises a handle knob  27  by means of which the syringe holding head  25  can be manually pulled away from the syringe and can be rotated. 
         [0031]    The slide  19  is guided, transversely to the longitudinal direction of the syringe  10  in the syringe position P, in guide rails  28 , 29 . Next to this linear guide a sensor  30  configured as a potentiometer  31  is arranged. The tap  32  of the potentiometer  31  is adjusted by a slider  19   a  connected with the slide  19 . In this manner, the electric resistance of the potentiometer  31  indicates the position of the slide  19  and thus the position of the syringe holding head  25 . The signal of the sensor  30  thus provides information on the syringe size and/or the syringe diameter with closed syringe holding head  25 . 
         [0032]    The spindle rod  22  extends into the syringe holding head  25  and carries a brake element  33  which is configured as a cutting edge and arranged within the syringe holding head  25 , the tip of the cutting edge facing the syringe cylinder  11 . By operating the motor  20  the brake element  33  is moved between a retraction position ( FIG. 1 ) and an active braking position ( FIG. 3 ). In the braking position the brake element  33 , which moves along the winglike syringe portion  13 , engages the piston rod  12  to block any displacement of the piston rod  12  relative to the syringe cylinder  11 . 
         [0033]    The syringe pump is further provided with an axial positioning means  35  which axially presses the winglike syringe portion  13  against a stop wall  36 . The positioning means  35  comprises a slider  37  which is guided, on two rods  38 , 39 , axially to the syringe  10 . The slider  37  projects into the path of the winglike syringe portion  13 . The slider  37  is fastened to two parallel rods  38 ,  39  which extend parallel to the axis of the syringe  10  and are biased, by a spring  40 , toward the front, i.e., toward the outlet end of the syringe cylinder  11 . The rear ends of the rods  38 , 39  are controlled by a control means  41  connected with the slide  19 , since the control means  41  comprises an inclinded surface  42  acting as a cam. When the slide  19  is moved toward the syringe position P, the control means  41  push the plate  37  toward the rear, i.e., away from the stop wall  36 , such that the winglike syringe portion  13  can be positioned into the space created therebetween. When the syringe holding head  25  is then released, such that it is placed against the syringe cylinder  11 , the plate  37  is pulled forward by the spring  40  action, thereby pressing the winglike syringe portion  13  against the stop wall  36  thus causing the syringe cylinder  11  to assume an exact axial position. 
         [0034]    The drive head  16  contains a piston plate sensor  40  which responds to the presence of a piston plate  14  thus communicating to the device that the drive head  16  has been moved to the piston plate  14  of an inserted syringe. The piston plate sensor  40  is arranged in a recess of the drive head  16 . The recess further contains controlled arms  42 , 43  which are pivotable about a pivot pin  44  and are movable toward each other to lock the piston plate  14  on the drive head. 
         [0035]    For inserting a syringe  10  into the syringe pump the syringe holding head  25  is removed by pulling the handle knob  27 . Simultaneously, the positioning means  35  is brought into the open position. Now the syringe cylinder  11  can be inserted. Then the syringe holding head  25  is placed from outside against the syringe cylinder  11 . The spring  26  causes the syringe holding head  25  to press the syringe cylinder  11  against the syringe bearing  15 . When the syringe holding head  25  is placed against the syringe cylinder  11 , the plate  37  of the positioning means  35  presses the winglike syringe portion  13  against the stop wall  36 . When the syringe holding head  25  is released, the syringe is exactly positioned. The sensor  30  detects, on the basis of the position assumed by the slide  19 , the syringe size and provides a corresponding signal to the control means. When the advance velocity is determined, the syringe size is taken into consideration. 
         [0036]    When the syringe holding head  25  is released, the motor  20  is put into operation such that the tip of the brake element  33  is moved out of the syringe holding head  25  and pressed against the piston rod  12 . Thus the piston rod  12  is fixed relatively to the syringe cylinder  11 . 
         [0037]    Then the drive rod  17  is automatically moved such that the drive head  16  approaches the piston plate  14 . When the piston sensor  40  detects that the piston plate is correctly positioned, the arms  42 ,  43  are actuated to lock the piston plate in the drive head  16 . Then the motor  20  is put into reverse to remove the brake element  33  from, the piston rod  12 . Now the drive head  16  can be moved to discharge the syringe  10 . 
         [0038]    It is further possible to provide a forced limitation of the movement of the slide  19  to secure the inserted syringe on the device. Such securing of the syringe can be particularly appropriate for PCA (patient-controlled analgesia). This is a kind of pain treatment. The securing prevents too high a drug dose from being administered to the patient by his/her own manipulation or manipulation of a third person. Forced limitation is effected by a locking means  47  comprising a shaft  50  which is rotatably supported, parallel to the slide  19 , on housing walls  48 , 49 , the shaft  50  having a rack-type toothing  51  on one side. Said toothing  51  can, by rotating the shaft  50 , be brought into engagement with a tooth segment  52  located on the slide  19 . When the toothed portions are in engagement with each other ( FIG. 8 ), the slide  19  is blocked such that it cannot move. The shaft  50  can be rotated only with the aid of a special wrench which is inserted into a profiled opening (not shown) provided, in the front wall  53 . 
         [0039]    Although a preferred embodiment of the present invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made without departing from the spirit and scope of the present invention, as defined in the appended claims.