Abstract:
The invention relates to a stand having a parallelogram carrier ( 2   b ) and a balancing device, in which, between a support arm ( 60 ) that runs substantially horizontally and a basic part ( 62 ) that can be braked with respect to a basic body ( 12 ), there is arranged at least one measuring unit ( 64 ) to measure and absorb the imbalance forces and moments which arise.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This invention claims priority of the German application 200 19 106.3 filed Nov. 12, 2000 which is incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a stand, capable of being balanced, having a parallelogram carrier that accommodates a load and comprises at least three support arms, of which two parallel support arms are supported with respect to a base, and having a measuring unit in the area of one of the support arms. 
     BACKGROUND OF THE INVENTION 
     Stands with electronic balancing mechanisms have measuring units which measure an imbalance. Such measuring units are, for example, published in U.S. Pat. No. 5,528,417, in DE 4320443 A1 and DE 4334069 A1 and in WO 97/13997 from the applicant. The known measuring units frequently measure bending forces or travel resulting from bending in a braked stand. If appropriate, they use angle sensors, optical position sensors or bending sensors. A braked stand is understood to mean a stand of which at least one support arm is held by means of a brake so that it does not pivot with respect to the uprights. In practice, such brakes are as rule arranged between points fixed to the uprights and parallelogram carriers or between adjacent arms of a parallelogram carrier. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of providing a new generation of measuring units which can be implemented with particularly cost-effective, available sensors and can be mounted as simply as possible and/or integrated into stand components. This object is achieved by the following measures. 
     In the area of one of the parallel support arms of the parallelogram carrier, preferably on one of the two horizontal support arms, a compressive-force, shear force or bending sensor is arranged, which measures forces between a part of the support arm that is connected to the load and a braked part of the stand, and provides the measured values for the balancing control system. 
     In the process, the following criteria are satisfied, or use is made of the following laws: 
     a) The support arm is held in a brake-free manner. It follows from this that, if the load is balanced, it remains at the selected location. However, if the support arm is not balanced, then the load tends to drift away from the selected location. 
     b) Provided parallel to at least one of the supports or on a support belonging to the parallelogram carrier is a sensor which detects this drift. 
     c) The measured drift behavior controls the balancing. 
     As a variant of a different type, a sensor is alternatively incorporated directly in one of the supports of the parallelogram carrier, and measures the bending or shear forces occurring there. As a result of integrating a sensor into a weakened or interrupted point of a support arm in a parallelogram carrier, firstly a good integrated solution is found, which saves space. Secondly, however, the measurement is displaced to a location which is present in any stand with parallelogram carriers. The measuring unit itself can therefore be produced as a standard product, which can be used in any desired parallelogram carrier. 
     This applies equally to the first-named variant, in which the drift behaviour of the carrier is measured on its outside. A shear force sensor is particularly suitable for the application in the sense of the invention, being mounted at the interrupted or weakened point on the support arm, or between the support arm and a support. The use of a shear force sensor is advantageous in as much as it is produced in large numbers for other purposes and can therefore be used extremely cost-effectively. 
     However, the invention is not restricted to the use of a shear force sensor in a parallelogram carrier, but instead also includes the use of a shear force carrier for imbalance measurement in a stand quite generally. This is because the finding relating to the possible use of a shear force sensor for balance measurement can be advantageous even in other stand designs which manage without a parallelogram carrier, particularly since it leads to a considerable reduction in cost and saving in space in the measuring device. 
     The state in which the imbalance forces in a support arm of a parallelogram carrier can best be measured is that in which at least one link of the parallelogram carrier is braked or in which the aforementioned support is braked, but the support arm itself can drift slightly. In particular when the sensor, which then under certain circumstances operates as a bending sensor is arranged in the vicinity of the brake, the imbalance can be measured with good measurement accuracy in the braked state. 
     Furthermore, the use of a platform weighing cell has proven to be particularly cost-effective. 
     The invention can advantageously be used in a new stand corresponding to the commonly-owned and concurrently filed utility patent applications U.S. application Ser. No. 10/010101 (corresponding to German application DE 200 19 105), U.S. application Ser. No. 10/010103 (corresponding to German application DE 200 19 109), and U.S. application Ser. No. 10/007168 (corresponding to German application DE 200 19 107) filed on the same date, Nov. 8, 2001, by the applicant, which copending U.S. applications are hereby incorporated by reference into the present application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     By using the figure description, the present invention will be explained in more detail by way of example. In the figures: 
     FIG. 1 shows a schematic illustration of a parallelogram carrier with incorporated measuring sensor and brake; 
     FIG. 2 shows the mechanical design of a platform weighing cell which can be used according to the invention; 
     FIG. 2 a  shows the schematic use of such a platform weighing cell; 
     FIG. 3 shows the design of a parallelogram carrier in a preferred configuration for a surgical microscope stand, in side view; 
     FIG. 4 shows the lower support arm of the parallelogram carrier from FIG. 3, in side view; 
     FIG. 5 shows the support arm according to FIG. 3 in plan view; 
     FIG. 6 shows a perspective view of the support arm from FIGS. 3 and 4, with the cover plate in the sensor area removed; 
     FIG. 7 shows a variant with a force measuring or strain sensor which, according to the invention, is used a bending sensor; 
     FIG. 8 shows a variant of the design according to FIG. 7; 
     FIG. 9 shows a schematic stand design according to the invention; 
     FIG. 10 shows a schematic overall design of a stand according to the invention having two pressure sensors; and 
     FIG. 11 shows a schematic overall design of a stand according to the invention having a shear force sensor fixed to the support arm. 
    
    
     The figures are described in an overlapping fashion, identical reference symbols signifying identical components, reference symbols with the same numbers but different indices signifying slightly different components with identical tasks and/or similar effects. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The load G—a surgical microscope in the preferred application—is suspended, by means of pivoting supports not specifically illustrated (for example a pivoting support in accordance with the international Patent Application WO 97/47240 from the Applicant) on a stand. The pivoting support and therefore the load G acts on the outermost lower link  58  of a parallelogram carrier designated overall by  2   b . The upper support arm  59  is of conventional design, while the lower support arm  60  has a novel construction. In the area of its pivot  61  on the stand side on a base  12 , it is of weakened material or interrupted design. 
     A basic part  62  is attached to the base  12  via a brake (brakeable coupling)  63 . The basic part  62  can be prevented from pivoting up and down by activating the brake  63 . Rigidly connected to the basic part  62  is a measuring unit  64  which is designed as a platform weighing cell and which, at its other end, rigidly accommodates the support arm part  65  of the support arm  60 . The connection between the basic part  62  and the support arm part  65  via the measuring unit  64  is so stable that, when the brake  63  is released, the lower support arm  60  can pivot up and down parallel to the upper support arm  59 . 
     In the engaged state of the brake  63 , however, the following phenomenon occurs: In the balanced state, which is reached when, for example, a balance weight AGa indicated symbolically produces the numerically equal but opposed torque to that produced by the load G, the lower support arm  60  is loaded only in compression. The single force component acting on the lower support arm  60  therefore extends from the link  58  as far as the pivot  61  along its longitudinal axis  66 . The sensor  64  is insensitive to tensile/compression loading, that is to say no imbalance values are measured on the basis of these forces. 
     In the event of an imbalance, however, transverse forces, which can be measured, occur at the interrupted or weakened point. Transverse forces within the context of this invention are produced by forces or moments which act obliquely or perpendicularly on the longitudinal extent of the support arm  60 —the lower support arm in the present example. 
     If, however, when the brake  63  is engaged, the load G is increased without any simultaneous change in the balance weight AGa, then this leads to a bending or shear loading at the sensor  64 : The force vector acting along the longitudinal axis  66  in a balance state then acts obliquely with respect to the longitudinal axis  66 . However, since the brake  63  is engaged, a bending or shear force arises at the sensor  64 , and can preferably be detected by this sensor  64 . 
     As is familiar to those skilled in the art, such detected forces can be used electronically to control a balance weight. Since an extremely wide range of such control systems are known to those skilled in the art, for example in the Leica OHS(™) from the applicant, and also in the case of other stands on the market with automatic or semi-automatic balancing, the electronic part of the invention will not be discussed in more detail here. The critical factor is that at the sensor  64 , forces are measured when the parallelogram  2   b  enters an unbalanced state. 
     The basic part  62  may possibly be equipped, beyond the fundamental requirement for its function, with further features, which constitute a development of the invention: An upper support arm  67  and a lower support arm  68  project beyond the sensor  64  and reach as far as the support arm part  65 . With respect to the latter, they have a clearance designated by “x”. This clearance provides the sensor  64  with sufficient space to produce its sensor output. However, it is so small that, in the event of a particularly high load or overload, contact between the support parts  67  or  68  and the support arm part  65  occurs, the latter support themselves mutually and, as a result, prevent any damage to the sensor  64 . 
     FIG. 2 reveals the perspective view of a sensor  64  used in accordance with the invention. It has measuring zones  69  and/or  70 , a sealed electronic circuit  71  and connecting cables  72 . Such a sensor is, for example, a PW4F-2 platform weighing cell from HBM Spectris Group/Darmstadt (Germany). 
     Provided at both ends of the sensor  64  are threaded holes  73  and  74 , in order firstly to be screwed to the basic part  62  and secondly to be screwed to the support arm part  65 . The centrally arranged double oblong hole cut-out  75  may vary in its shape from sensor to sensor, but in the form shown for the present application corresponds to a standard design. 
     FIG. 2 a  shows in schematic form the clamping or application of a platform weighing cell selected as a bending or shear force sensor  64 . 
     In the design according to FIG. 3, the outrig of a stand is illustrated in its horizontal rest position. Situated on the base  12  is the brakeable pivot  61  on the stand side, with the brake  63  and a pivot point  76  for the upper support arm  59  of the parallelogram carrier  2   b.  The latter is of telescopic design, so that in principle one can see the upper support arm  59 , which is designed with a U-shaped cross section and in its interior accommodates the upwardly angled part of the lower support arm  60 . The lower support arm  60  is divided into two, as shown schematically in FIG. 1, and comprises the support arm part  65  and the basic part  62 , in which the sensor  64  according to FIG. 6 is integrated. 
     Mounted at the pivoting point  58  is a pivoting carrier  79 , which accommodates the load G or a surgical microscope. 
     The upper support arm  59  is lengthened beyond its pivoting point  76  and forms the balance arm  22  there. Displaceably mounted on the latter is a sliding pad  23 , to which a cable pull  24  is fixed. On the lower area (not shown) of the cable pull  24 , a balance weight AGa is suspended. The sliding pad  23  can preferably be displaced under electronic or electrical control, on the basis of the bending or shear forces determined at the sensor  64  in the basic part  62 . 
     In the present invention, the balancing area; that is to say the area to the left of the pivoting points  61  and  76 , is preferably designed in the way specified in U.S. application Ser. No. 10/010101 (corresponding to German application DE 200 19 105) and U.S. application Ser. No. 10/010103 (corresponding to German application DE 200 19 109). It is further preferred, in that event of cable pull  24  being used as specified in the exemplary embodiment according to FIG. 3, to use a cable safeguard corresponding to that disclosed in U.S. application Ser. No. 10/007 168 (corresponding to German application DE 200 19 107). 
     The detailed design of the pivoting carrier  79  will not be discussed in the present text, since it has no significant importance for the design and the fitting of the sensor  64  or for the design of the parallelogram carrier  2   b.    
     The design of the lower support arm  60  shown in FIGS. 4-6 shows an optimally integrated basic part  62  and a single, slat-like support arm part  65 , which is accommodated in an optimum manner by the upper support arm  59  cut out in a U shape. The support arm part  65  can also comprise parallel part-supports for molded tubes. At the outer end of the support arm part  65  there is a lengthened arm segment  77 , which is designed like a fork, to accommodate the vertical support arm  78  of the parallelogram carrier  2   b  and/or to accommodate the pivoting carrier  79 . At the point  80 , a locking means can be arranged between the upper support arm  59  and the lower support arm  60 . 
     The sensor  64  is protected by a cover  81  in the basic part  62 . 
     The designs according to FIGS. 7 and 8 represent variants of the invention, in which, instead of a platform weighing sensor, conventional bending sensors  64   a  and  64   b  are used. These sensors are situated at points at which the lower support arm  60   a  or  60   b  is weakened. The bending values measured by the sensors  64   a  or  64   b  at these points correspond to the shear force values which are measured by the sensor  64 , and therefore likewise permit conclusions to be drawn about the imbalance. 
     In the symbolic design according to FIG. 9, it is possible to see the stand foot  20 , a vertical support column  21  and a balance arm  22   a  projecting from the latter. This balance arm  22   a  can be pivoted about the support column  21 . It carries the base  12 , on which the parallelogram carrier  2   b  is pivotably mounted in the manner described. The cable pull  24  is only indicated, since the load balancing device is preferably designed as in U.S. application Ser. No. 10/010101 (corresponding to German application DE 200 19 105) or, alternatively, as in U.S. application Ser. No. 10/010103 (corresponding to German application DE 200 19 109 or U.S. application Ser. No. 10/007168 (corresponding to German application DE 20019107). 
     FIG. 10 reveals a schematic stand design, in which the lower support is configured as a continuous support arm  60   c.  It reaches from the link  58  as far as the pivot  61  on the stand side, at which not only the support arm  60   c,  but also the substantially fork-like basic part  62   a  is pivotably mounted. The mobility of the basic part  62   a  can be braked by a brake  63 . The mobility of the support arm  60   c  at the pivoting point  61  is consequently restricted to the clearance x. 
     Fitted to the support arms  67  and  68  are pressure sensors  64   c  which, in the balanced state illustrated (and with the brake  63  engaged), have the clearance designated by “x” with respect to the support arm  60   c.  In the event of imbalance, a torque occurs about the link  76 , which leads to the support arm  78  drifting upwards or downwards. The support arm  78  transmits this drift to the support arm  60   c,  so that if the brake  63  is engaged, the clearance x at the lower pressure sensor  64   c  increases or becomes smaller, while at the upper pressure sensor  64   c  the clearance x changes to the same extent in the opposite direction. As soon as one of the two sensors  64   c  is touched, and therefore a compressive force occurs, this is measured and forwarded as an imbalance value. 
     FIG. 11 shows a variant of the design shown in FIG. 10, in which a shear force sensor  64   a  is used instead of the pressure sensors  64   c.  The former is firmly connected at one end to the individual support arm of the basic part  62   a  and at the other end to the support arm  60   c,  and is capable of accommodating and detecting the shear forces that occur when the brake  63  is engaged. 
     As compared with the design according to FIG. 10, the clearance x is dispensed with here. This could also be left out in the design according to FIG. 10, but this would necessary lead to complicated adjustment procedures in the case of the two pressure sensors  64   c.    
     In a manner similar to the design according to FIG. 1, upper and lower support arms  67   a  and  68   a  are provided, in this design the lower support arm  68   a  projecting like a lug from the basic part  62   a.  Alternatively, these parts could also be arranged parallel to each other and connected by bolts or the like, the supporting faces being formed between the bolts or the like and oblong holes, larger bores or the like. 
     The present invention will preferably be used in the case of a standard design according to U.S. Patent Applications DE 200 19 107, DE 200 19 109 and DE 200 19 105 (respectively corresponding to German application nos. DE 200 19 107, DE 200 19 109 and DE 200 19 105) filed on the same date. However, it is not restricted to such designs. 
     The following list of reference symbols is a constituent part of the description. The designs specified in the patent claims likewise count as disclosed in the same way as in the description. Support arms in the sense of the patent claims are to be understood to mean both individual support arms and parallelogram carriers or similar constructions. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  2b 
                 Parallelogram carrier 
               
               
                   
                  12 
                 Base and/or basic body 
               
               
                   
                  20 
                 Stand foot 
               
               
                   
                  21 
                 Support column 
               
               
                   
                  22, 22a 
                 Balance arm 
               
               
                   
                  23 
                 Sliding pad 
               
               
                   
                  24 
                 Cable pull 
               
               
                   
                  58 
                 Link 
               
               
                   
                  59 
                 Upper support arm 
               
               
                   
                  60 
                 Lower support arm 
               
               
                   
                  60a, b, c 
                 Variants of the lower support arm 
               
               
                   
                  61 
                 Pivot on the stand side (pivoting axis) 
               
               
                   
                  62a 
                 Basic part and/or measuring arm 
               
               
                   
                  63 
                 Brake (brakeable coupling) 
               
               
                   
                  64 
                 Measuring unit and/or sensor and/or platform 
               
               
                   
                   
                 load cell 
               
               
                   
                  64a, b 
                 Shear force sensor 
               
               
                   
                  64c 
                 Pressure sensor 
               
               
                   
                  65 
                 Support arm part 
               
               
                   
                  66 
                 Axis 
               
               
                   
                  67 
                 Upper support arm 
               
               
                   
                  68 
                 Lower support arm 
               
               
                   
                  69, 70 
                 Measuring zone 
               
               
                   
                  71 
                 Electronic circuit 
               
               
                   
                  72 
                 Connecting cable 
               
               
                   
                  73 
                 Threaded bore 
               
               
                   
                  74 
                 Threaded bores 
               
               
                   
                  75 
                 Double oblong hole cutout 
               
               
                   
                  76 
                 Pivoting point 
               
               
                   
                  77 
                 Arm segment 
               
               
                   
                  78 
                 Vertical support arm 
               
               
                   
                  79 
                 Pivoting carrier 
               
               
                   
                  80 
                 Adjusting mechanism 
               
               
                   
                  81 
                 Cover 
               
               
                   
                 182a, b 
                 Interrupted point in the support arm 60 
               
               
                   
                 AGa 
                 Balance weight 
               
               
                   
                 G 
                 Load and/or weight of the microscope