Abstract:
A balance having at least one adjusting device ( 2 , . . . ) having a drive, wherein the drive of the adjusting device is configured as a fluidic drive ( 4 , . . . ), to which pressure can be applied by a pressure source disposed outside the scales via a pressure connection.

Description:
[0001]    This is a Continuation of International Application PCT/EP2008/008702, with an international filing date of Oct. 15, 2008, which was published under PCT Article 21(2) in German, and the complete disclosure of which, including amendments, is incorporated into this application by reference. 
     
    
     FIELD AND BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a set of scales having at least one adjusting device provided with a drive. 
         [0003]    In particular in precision scales or analytical scales, electric motors, usually configured as DC motors, are used for various adjusting functions. 
         [0004]    In some cases, differently dimensioned motors are used for the different adjusting functions. Alternatively, for production or cost reasons, identical motors may be used, but then these motors are not optimally configured for their respective purposes. 
         [0005]    DE 90 06 644 U1discloses a set of scales with a wind shield which is moved by a motor. A wall element of a weighing chamber surrounding the scale pan is moved by an electric motor. A sensor serves to detect the position of the wall element. 
         [0006]    In the case of known automatic weight switching for a set of scales, an adjusting weight lies on a weight support which can be lowered or raised through tilting about a tilt axis. Arranged parallel to the tilt axis is a rotation axis with an eccentrically mounted cam disk. A contact surface of the weight support, which is arranged at a right angle to the cam disk, is pressed by a spring against the cam disk. The rotation axis is driven by a DC motor via a gearbox. In order to fix the position of the eccentrically mounted cam disk or of the weight support, two disks with control cams are arranged on the rotation axis, whereby the control cams actuate switches assigned thereto in their respective predetermined end positions. Although this weight switching system has proved to be essentially effective in practice, the control cams with switches render the system relatively costly and also relatively bulky, due to the electric motor and the gearbox that are used. 
         [0007]    A motor-driven weight switching and locking system is disclosed in, for example, DE 42 35 250 C1. A set of scales with a motor-driven movable contact surface is known, for example, from DE  198   28   515  Al. This set of scales using the principle of electromagnetic force compensation has a vertically movable load support, a position sensor, a variable gain amplifier and a coil in a magnetic field of a permanent magnet, as well as at least one contact surface which delimits the downward movement of the load support, at least one contact surface which delimits the upward movement of the load support and an electronic evaluation unit. At least one of the contact surfaces is movable. The movable contact surface is controlled with the aid of the position sensor such that the load support is held as far as possible in the same position as in normal weighing operation. 
         [0008]    DE 28 41 996 C2 discloses a weight switching system for a beam balance, particularly for an analytical balance, comprising a plurality of cam shafts for lifting/lowering the weights and an electric motor drive that controls the cam shafts via sensors. 
         [0009]    It is common to all the known sets of scales that the electric motors used are relatively bulky and require relatively complex gearboxes. 
         [0010]    A further disadvantage is that due to the power dissipation that occurs from the electric motors, an undesirable level of heat can be generated. The electric motors can also produce undesirably large magnetic fields. The use of electric motors can also give rise to problems in explosion hazard areas. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0011]    It is an object of the present invention to improve upon the known adjusting devices. Preferably, they should be configured as small as possible and should be capable of being used in a set of scales in as versatile a manner as possible. In addition, undesirable heat production by the electric motors should be avoided as far as possible. Gearboxes should also be avoided if and where possible. The construction of such adjusting devices is to be improved overall. 
         [0012]    According to one formulation of the invention, this aim is achieved in that the drive of the adjusting device is configured as a fluid drive to which pressure is applied, via a pressure connection, from a pressure source arranged outside the set of scales. 
         [0013]    Persons skilled in the art have previously striven to provide the scales intended particularly for use in automated systems with adjusting devices each having an individual electric drive. Persons skilled in the art have previously been so wedded to this concept that they strove, at most, to provide adjusting devices with individual drives of types other than electric motors, such as, for example, piezoelectric drives. 
         [0014]    It has proven to be particularly useful, in systems for which a pneumatic or hydraulic pressure source providing pressure as auxiliary energy is available anyway, to connect in sets of scales in which the drive of the adjusting device is configured as a fluid drive. Sets of scales of this type can also be used in laboratory rooms which are connected to a central pressure supply. 
         [0015]    The adjusting devices and their drives can be configured to be relatively small and be adapted to different tasks through use of suitable valves. For the pressure supply, the set of scales requires only a suitable pressure connection. Gearboxes can be largely dispensed with, particularly in the case of straight-line movements such as displacement motion. The familiar heat generation from electric motors in the set of scales is also absent, which is advantageous particularly when used in sets of scales configured as comparators. 
         [0016]    In essence, the adjusting device is also regulable in conjunction with an external position sensor, e.g., together with a microcontroller or control unit which controls the adjusting device. 
         [0017]    According to a preferred embodiment of the invention, the drive is configured as a one-sided pressure cylinder, which works against a spring and has a longitudinally displaceable actuator. This has the dual advantage that, firstly, for displacement in the opposing direction, a second one-sided pressure cylinder can be dispensed with and, secondly, the spring ensures a predetermined position when in a pressure-free state. 
         [0018]    According to a further preferred embodiment of the invention, the drive is configured as a two-sided pressure cylinder having a longitudinally-displaceable actuator. Even in this embodiment, a second pressure cylinder can be dispensed with for displacement in the opposing direction. The working pressure is merely switched from a first chamber to a second chamber, which is situated on the other side of the piston moving the actuator. 
         [0019]    According to a further preferred embodiment, at least one control valve is connected upstream of the drive. The actuator can be moved via the control valve and, provided the control valve is regulable, the speed of the actuator can be regulated or controlled. In order to ensure gentle ramping up and down of the actuator motion, the drive is coupled to a damping member which is configured, for example, as a throttle valve. 
         [0020]    According to a further preferred embodiment of the invention, the adjusting device is configured for moving a wall element of a wind shield. Thus a wall element or a wind shield door can be moved easily and inexpensively. 
         [0021]    According to another preferred embodiment of the invention, the adjusting device is configured for adjusting at least one weight in a weight switching system. The weight which lies on a weight support that can be lowered or raised by the adjusting device is placed and/or raised on a force transmitting point of the set of scales. 
         [0022]    In order to be able to move even relatively heavy weights, the weight support can be lowered or raised through tilting about a tilt axis. Advantageously, this arrangement enables one to dispense with a rotation axis arranged parallel to the tilt axis and having an eccentrically mounted cam disk and a gearbox between the drive and the rotation axis. 
         [0023]    According to a preferred embodiment of the invention, in a washing-down position for washing or rinsing, a load support is pressed by the actuator of the adjusting device with a rearward sealing edge facing toward the scales unit housing against a seal arranged between the load support and the scales unit housing in sealing manner. It is also fundamentally possible to configure the rearward edge of the load support, which is, for example, a scale pan, as a seal and to press this seal in sealing manner against the adjacent scales unit housing with the aid of the actuator. 
         [0024]    This represents a simple and reliable arrangement for preventing cleaning or washing-down fluid from penetrating between the load support and the housing surface into the set of scales or the housing thereof during cleaning or washing-down of the set of scales. 
         [0025]    According to a further preferred embodiment, the load support comprises, at the support axis bearing said load support, a contact surface or pusher against which the actuator rests in the washing-down position, pulling parallel to the support axis, with a contact surface or pusher. 
         [0026]    According to a preferred embodiment, the adjusting device is configured as a transport securing device, which locks the set of scales in a pressure-free condition by spring force. For locking, the actuator of the adjusting device engages in a corresponding aperture of the load support. Additionally, for locking, the load support can also be pressed against a contact surface by the actuator of the adjusting device. 
         [0027]    Additionally or alternatively, the actuator of a further adjusting device can also engage in locking manner in a corresponding aperture of a load transmitting lever of the weighing system. Alternatively, in order to lock the load transmitting lever of the weighing system, the load transmitting lever can be pressed against a contact surface by the actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Further details of the invention are disclosed in the following detailed description and in the attached drawings, illustrating preferred embodiments of the invention by way of example, in which: 
           [0029]      FIG. 1  is a side view of a set of scales including a displaceable wall element of a wind shield in a reduced representation, 
           [0030]      FIG. 2  is a rear view of the displaceable wall element of  FIG. 1  in section and outline, 
           [0031]      FIG. 3  is a plan view of a weight switching system comprising a tiltable weight support, 
           [0032]      FIG. 4  is a side view of the weight support of  FIG. 3  in outline and partially in section, 
           [0033]      FIG. 5  is a schematic side view of a further weight support, 
           [0034]      FIG. 6  is a schematic side view of a set of scales with the load support in the washing-down position, 
           [0035]      FIG. 7  shows a schematic side view of a set of scales in a locked state, 
           [0036]      FIG. 8  shows a schematic representation of an adjusting device with a two-sided pressure cylinder as the drive, and 
           [0037]      FIG. 9  shows a schematic representation of an adjusting device with a one-sided pressure cylinder, acting against a spring, as the drive. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    A set of scales  1  has at least one adjusting device  2 . The adjusting device  2  essentially comprises an actuator  3  which is driven by a fluid drive  4 . 
         [0039]    The drive  4  is constructed from a pressure cylinder  5  in which pressure from a pressure source (not shown) arranged external to the set of scales  1  is applied to a longitudinally displaceable piston  6  via a pressure connection  7 . 
         [0040]    The pressure cylinder  5  can be configured, as per  FIGS. 1 and 8 , as a two-sided pressure cylinder which is divided by the piston  6  into a first chamber  8  and a second chamber  9 . During a forward stroke, pressure is applied to the first chamber  8  and, during a backward stroke, to the second chamber  9 . The piston  6  comprises a piston rod  10  at the free end of which, and remote from the piston  6 , the actuator  3  is arranged. A control valve  19  configured as a multi-way valve  11  (see  FIG. 8 ) optionally connects a pressure line  12  coming from the pressure connection  7  to a first line  13  which leads to the first chamber  8  or to a second line  14  which leads to the second chamber  9 . If the first line  13  is connected to the pressure line  12 , the second line  14  is connected via the multi-way valve  11 , via a return connection  15  to a return line  16 . In the case of a pneumatic drive, the compressed air fed back via the return line  16  can be released to the atmosphere, whereas in the case of a hydraulic drive, the hydraulic fluid fed back via the return line  16  is returned to a hydraulic tank (not shown). 
         [0041]    As shown in  FIGS. 3 to 7  and  9 , in a further embodiment, the pressure cylinder  5 ′,  5 ″,  5 ′″ is configured as a one-sided pressure cylinder  5 ′,  5 ″,  5 ′″ acting against a spring  17 ,  17 ″,  17 ′″,  17 ″″,  18 . 
         [0042]    According to  FIG. 9 , the spring  17  is configured as a compression spring and is arranged in the second chamber  9 ′. According to  FIG. 7 , the spring  17 ″″ is configured as a compression spring and is arranged in the first chamber  8 ″″. 
         [0043]    According to  FIGS. 3 and 4 , the spring  17 ″ can also be arranged outside the pressure cylinder  5 ″, acting against the piston  6 ″ and the actuator  3 ″. 
         [0044]    According to  FIG. 5 , the spring  18  is configured as a tension spring arranged parallel to the pressure cylinder  5 ″, and acting against the piston  6 ″. 
         [0045]    According to  FIG. 6 , the pressure cylinder  5 ′″ is configured so that the piston  6 ′″ comprises a two-sided piston rod  10 ′″, on the second end of which, facing away from the actuator  3 ′″, the spring  18  configured as a tension spring engages, acting against the piston  6 ′″. 
         [0046]    A control valve  19 , which is configured, according to  FIGS. 1 ,  8  and  9 , as a multi-way valve  11 ,  11 ′, is arranged upstream of the fluid drive  4 ,  4 ′,  4 ″,  4 ′″. 
         [0047]    Throttle valves  20  are arranged in the lines  13 ,  14  as damping members. 
         [0048]    According to  FIGS. 1 and 2 , the adjusting device  2  is used for translational movement of a wall element  21  of a wind shield of a set of scales  1 . The wind shield consists of a scale chamber  23  enclosing a scale pan  22  which is accessible by sliding the wall element  21 . At a lower end in the vertical direction, the actuator  3  is linked at the underside  24  of the wall element  21  to the wall element  21 . This wall element  21  is thus displaceable by the adjusting device  2  or the actuator  3  arranged on the piston rod  10 . 
         [0049]    According to the embodiment of  FIGS. 3 and 4  and the embodiment of  FIG. 5 , the adjusting device  2 ″ is configured for adjusting a weight  25  in a weight switching system  26 . The weight  25  lies on a weight support  27  which can be lowered by the adjusting device  2 ″ through tilting about a tilt axis  28  and can be raised by adjustment in the opposite direction. Accordingly, by lowering the weight support  27 , the weight  25  is placed on a force transmitting point  29  or a force transmitting support. The weight support  27  is configured as a fork-shaped elbow lever on the angled end  30  of which, firstly, the actuator  3 ″ of the adjusting device  2 ″ and, secondly, the compression spring  17 ″ engages. According to the embodiment of  FIG. 5 , the actuator thereof  3 ″ and the spring  18  engage on the same side of the weight support  27 . The spring  18  is configured as a compression spring. 
         [0050]    According to the embodiment of  FIG. 6 , the set of scales  1 ′″ comprises a load support  31  which, in a washing-down position, is pressed by the actuator  3 ′″ of the adjusting device  2 ′″ with a rearward sealing edge  33  that faces toward a scale housing  32 , in sealing manner, against a seal  34  arranged between the load support  31  and the scale housing  32 . For this purpose, arranged on the support axis  35  which supports the load support  31  is a contact surface  36 . The actuator  3 ′″ engages, with an actuator contact surface  37 , against this contact surface  36  in the washing-down position, and in pulling manner, parallel to the support axis  35 . In the process, the actuator  3 ′″ actuates an overweight protection system  42  of a weighing system  41 , such that the overweight protection system pulls the contact surface  38  arranged on the support axis  35  out of the stop position thereof in the direction toward the spring  17 ′″. The spring  17 ′″ is configured as a compression spring and acts as an overweight protection spring. For this purpose, the spring  18 , which is configured as a tension spring and acts in pulling manner on the piston rod  10 ′″, must have a greater spring force than the spring  17 ′″ in order that the overweight protection system  42  is actuated in the pressure-free condition of the pressure cylinder  5 ′″. 
         [0051]    According to the exemplary embodiment of  FIG. 7 , the adjusting device  2 ″″ is configured as a transport securing device  39  which locks the set of scales  1 ″″ in a pressure-free condition of the pressure cylinder  5 ″″ by the force of the spring  17 ″″. For the purpose of locking, the actuator  3 ″″ of the adjusting device  2 ″″ engages in a corresponding aperture  40  in the support axis  35 ′ of the load support  31 ′ in locking manner. 
         [0052]    A further transport securing device  39 ′ is correspondingly configured. In this case, in order to lock the actuator ( 3 ″″), the adjusting device ( 2 ″″) engages in a corresponding aperture ( 40 ′) of a load transmitting lever  43  of a weighing system  41 ′ in locking manner. 
         [0053]    The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.