Abstract:
A device ( 14 ) allows a door of a balance draft shield enclosure ( 12 ) to be activated by a carrier fork ( 4 ) of a robot ( 5 ). The vertically movable draft shield door ( 13 ) sets open an access opening in a raised position and closes the opening in a lowered position. A door-lifter with a force-application element ( 41 ) is connected to the draft shield door for application of an upward-directed vertical force. A transmitting mechanism ( 15 ), standing clear of the balance ( 11 ) includes a force-receiving element ( 20, 21, 26, 27 ) that is moved vertically by the carrier fork, between upper and lower end positions. It further includes at least one direction-reversing element ( 22, 23, 24, 25, 29 ), coupled to the force-receiving element for coupling to the force-application element, a return spring ( 28 ), and a spring-biased locking latch ( 30 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is entitled to benefit of a right of priority under 35 USC §119 from European patent application 14162219.1, filed on 28 Mar. 2014, the content of which is incorporated by reference as if fully recited herein. 
       TECHNICAL FIELD 
       [0002]    The disclosed invention concerns a robot-actuated device serving to open and close the door of a draft shield compartment of an analytical or micro-analytical balance for use in an automated laboratory system. The invention further concerns a method for the opening and closing of a draft shield door that is designed in accordance with the invention. 
       BACKGROUND 
       [0003]    Automated laboratory systems in which weighing processes are performed with the help of robots belong to the known state of the art. Such systems are normally used in situations where weighing operations are performed serially in large numbers, where the automation brings labor cost savings and improved reliability. 
         [0004]    A typical example for an automated serial weighing process occurs in the weighing of filters that are used in air pollution tests, for example in the testing of diesel engines. In these tests, the exhaust gases that are to be tested are sent through a filter which holds back solid particles, in particular soot particles. The filters which are individually marked and traceable are weighed a first time in their new, unused condition, and the initial weight of each filter is registered in a database. The filters are then used for collecting the particles in the equipment under test and are subsequently weighed again. Next, the net weight of the combustion residues collected by the filter is determined by subtracting the initial weight from the end weight. 
         [0005]    A system for the weighing of filters with the help of robots is described for example in U.S. Pat. No. 5,606,153, wherein the flat, circular filters are seated in ring-shaped holders that carry a barcode identification. Arranged on a vibration-isolated weighing table are a swivel-arm robot, a microbalance, an electrostatic discharging device, a carousel tray holding the filters, as well as a device for temporarily parking the ring-shaped holder of the filter that is in the process of being weighed. To carry out a weighing operation, the robot first transports a filter that is seated in a ring-shaped holder from the carousel tray to the temporary parking station, where the filter is separated from the ring-shaped holder device. The robot then moves the filter without the ring-shaped holder through the electrostatic discharging device to the microbalance, where the functions of the balance—opening and closing the door, setting the balance to zero, recording the weighing result and transmitting it to a computer—run automatically and are coordinated with the movements of the robot. The filter is returned to the temporary parking device and inserted into the ring-shaped holder, whereupon the ring-shaped holder with the filter is returned to the carousel tray. 
         [0006]    In the robotic weighing system of the foregoing description, a commercially available microbalance is used in which the aforementioned, normally manual functions can also be executed automatically, i.e. in response to control commands of a computer. However, with this kind of balance, one has to accept that a balance that is designed to satisfy the ergonomic requirements of manual operation and of a wide range of applications will in some respects not be optimally tailored to the needs of automated filter weighing. In particular, a draft shield enclosure in the standard version of a commercially available microbalance has a taller interior space than is necessary for filter weighing. With a lower profile of the draft shield enclosure, the air turbulence associated with the opening and closing of the weighing compartment door could be reduced and the settling time of transient oscillations of the balance could be shortened. In addition, if the balance is operated automatically, the draft shield enclosure does not need to be transparent and can therefore be made of metal, whereby the problem of electrostatic charges is eliminated. 
         [0007]    A filter-weighing system which was developed by the applicant and which is being distributed in Germany by the firm Horiba under the name PWS ONEplus™ includes an XYZ-robot, a microbalance, a rack for holding the filters with several shelves arranged vertically above each other, as well as a computer to control the system and to process and store the data. The flat, circular-shaped filters are individually contained in suitably shaped receptacles which carry a barcode identification, whereby the filter that is currently held by the receptacle is individually identified. The bottoms of the receptacles have a circular opening whose diameter is smaller than the filter diameter, but larger than the weighing-pan diameter of the microbalance. To weigh a filter, the receptacle is moved to a centered position over the weighing pan and lowered onto the floor of the weighing compartment, whereby the filter is transferred to the weighing pan and lifted off the receptacle bottom. Consequently, the filter does not have to be taken out of the receptacle for the weighing. 
         [0008]    The microbalance in the filter-weighing system just described is a serial-production model manufactured by the applicant. It has a transparent, cylindrical draft-protection enclosure made of glass, with a cylindrically curved sliding door that opens and closes in a swivel movement about the cylinder axis, driven by a motor that is controlled by command signals from the computer. Due to the concept of the filter-weighing receptacles, the problem of electrostatic charge accumulation on the filter is avoided with this filter, but as in the earlier example, the standard-production draft-protection enclosure is taller than would be necessary for filter-weighing. 
         [0009]    To meet the objections against the use of a standard-production draft shield enclosure, the applicant&#39;s first approach was to develop a low-profile draft shield enclosure that was made of metal and tailored specifically to work with the filter-weighing receptacles, but keeping the electric motor-driven door of the standard-production version. It was found, however, that the control of the door movement cannot be coordinated rigidly enough with the movement flow of the robot and that, as a consequence, the draft shield compartment door occasionally opens too late or not at all, causing the robot arm to collide with the closed draft shield door, whereby the filter-weighing system can become damaged. 
         [0010]    The present invention therefore has the objective of providing a door-opening device for a balance draft shield enclosure that is optimally matched to the conditions imposed by a robotically operated filter-weighing system and which, in comparison to the existing state of the art, is distinguished by a simple, cost-effective design and by its functional reliability. In view of the robot being available for use, the motor drive and electronic control that are used in the standard version can be dispensed with, and the robot can also be put to work for the operation of the door-opening device. 
       SUMMARY 
       [0011]    This task is solved by the door-opening device for a draft shield enclosure in accordance with the features of the independent claim. Advantageous embodiments and details of the draft shield enclosure are presented in the dependent claims. In the following, expressions such as “top”, “bottom”, “horizontal”, “vertical” always relate to the operation-ready position of the draft shield enclosure in the installed state on the balance. 
         [0012]    A door-opening device according to the invention for a balance draft shield enclosure with a vertical, laterally arranged loading access opening and with a vertically movable draft shield door which in the raised position sets the access opening free and in the lowered position closes it up is designed to be operated through mechanical actuation by a carrier fork of a robot. The door-opening device includes on the one hand a door-lifter that is connected to the door and includes a force-application element for an upward-directed vertical force which causes the door to open, and on the other hand a transmitting mechanism that stands clear of the balance and includes a force-receiving element which, through the action of the carrier fork, is vertically movable between an upper and a lower end position. Further parts of the door-opening device are at least one direction-reversing element that is coupled to the force-receiving element and can be coupled to the force-application element, a return spring that pulls the force-receiving element into the upper end position, as well as a spring-biased locking latch which arrests the force-receiving element in the lower end position. 
         [0013]    To open the draft shield door, the force-receiving element is pushed downward by the carrier fork against a resetting force of the return spring, whereby the direction-reversing element is brought into engagement with the force-application element and the upward-directed actuating force is generated which causes the door to be opened. When the fully open position of the door has been attained, the transmitting mechanism is arrested as the spring-biased locking latch snaps shut, so that the draft shield door remains in the open position, while the carrier fork can be removed from the force-receiving element. 
         [0014]    To close the draft shield door, the carrier fork is moved into position above the force-receiving element, and the arrestment of the transmitting mechanism is released by a sideways-directed push of the carrier fork against the spring-biased locking latch. As the force-receiving element is released from arrestment, it is pushed against the carrier fork by the weight of the draft shield door acting on the direction-reversing element, whereupon the draft shield door returns under its own weight to the closed position at a speed that is controlled by the robot. After the draft shield door has reached the closed position, the return spring fully retracts the force-receiving element into the upper end position, whereby the engagement between the direction-reversing element and the force-application element is released. 
         [0015]    In a preferred embodiment of the draft shield enclosure according to the invention, the door lifter which is connected to the draft shield door includes a vertically directed second push rod which is axially guided by second glide bushings in a vertical bore of the draft shield enclosure and which carries at its lower end a second wheel fork with a second roller wheel. 
         [0016]    In a further preferred embodiment, the transmitting mechanism has a chassis base, and the force-receiving element is configured as a vertically oriented first push rod which carries at its upper end a push knob against which the carrier fork can exert a force and at its lower end a first roller wheel mounted in a first wheel fork. The first push rod is axially guided by first glide bushings in a vertical bore of the chassis base. 
         [0017]    The direction-reversing element is advantageously configured as at least one lever which has its fulcrum in the chassis base and is rotatable in a vertical plane of movement, with a first lever arm being held by the return spring in permanent pressure-transmitting engagement with the first roller wheel, while a second lever arm can be brought into pressure-transmitting engagement with the second roller wheel. 
         [0018]    The direction-reversing element can be realized in particular as a pair of levers that are mounted in the chassis base vertically above each other and are coupled to each other by a coupling member constraining the two levers to swing up and down together, wherein the first lever arm belongs to a first of the two levers and the second lever arm belongs to the second of the two levers. 
         [0019]    The spring-biased locking latch in an advantageous embodiment is configured as a leaf spring element which is fastened to the chassis base in the immediate vicinity of the force-receiving element, wherein the leaf spring element has a catch opening and the force-receiving element has a projecting latch pin which snaps into the catch opening when the force-receiving element arrives at its lower end position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Details of the door-opening device according to the invention will become apparent from the description of the example that is shown in the drawings, wherein: 
           [0021]      FIG. 1  represents an overall view of a filter-weighing system equipped with the door-opening device according to the invention; 
           [0022]      FIG. 1   a  represents a filter-weighing receptacle with a filter in a schematic cross-sectional view 
           [0023]      FIG. 2  shows the balance with the door-opening device in the closed door position; 
           [0024]      FIG. 3  shows the balance with the door-opening device in the open door position; 
           [0025]      FIG. 4  shows an exploded view of the draft shield enclosure designed for automated filter weighing, with the door being movable by the opening device according to the invention; and 
           [0026]      FIG. 5  represents the transmitting mechanism in an exploded view. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 1  shows a three-dimensional overall view of a filter-weighing system  1  that is equipped with the door-opening device according to the invention, wherein the entire system is arranged on a base plate  2  with level-adjusting feet  3 . The robot  4  with the carrier fork  5  which is movable in the x-y-z directions of a Cartesian coordinate system is shown in the right-hand part of the drawing. Arranged opposite the robot is the holding rack  6  for the filter-weighing receptacles  7  containing the filters  8  that are to be weighed (see  FIG. 1   a ). The microbalance  11 , oriented along the diagonal of the base plate  2 , with the draft shield enclosure  12  and the vertically movable draft shield door  13 , can be seen to the left in the foreground. To the right of the microbalance  11  is the transmitting mechanism  15  which represents the main portion of the door-opening device  14  which is shown in detail in  FIGS. 2 to 5 . 
         [0028]      FIG. 1   a  shows a filter-weighing receptacle  7  containing a filter  8 . The receptacle  7  is covered by a lid  9 , and the floor of the receptacle  7  has an opening  10 . The filter  8 , which needs to be weighed a first time in its new condition prior to use and again in the sooted condition after use, is handled for example with a pair of tweezers and laid into the receptacle  7  where, due to the conically shaped inside wall of the receptacle  7 , the filter  8  centres itself over the opening  10 . A holding rack  6  filled with receptacles  7  that have been loaded in this manner with filters  8 , is set into the filter-weighing system  1 . 
         [0029]      FIGS. 2 and 3  show the microbalance  11  with the draft shield enclosure  12  as well as the door-opening device  14  with the transmitting mechanism  15  in the same orientation relative to the robot coordinates x, y, z as in  FIG. 1 . In  FIG. 2 , the draft shield door  13  is in the closed position and in  FIG. 3  in the open position. In  FIG. 2 , the carrier fork  5  can be seen positioned above the knob  20  of the push rod which is held in its upper end position by a spring tension of the transmitting mechanism  15  (for details see  FIG. 5 ), but the carrier fork  5  is not yet applying pressure to the push knob  20 . 
         [0030]    As the carrier fork  5  is being lowered, it pushes the knob  20  of the push rod downward (see  FIG. 3 ), whereby the first lever arm  23  is moved downward and the second lever arm  25  is simultaneously moved upward. The second lever arm  25  comes first into contact with the second roller wheel  41 . With a further lowering of the carrier fork  5 , the knob  20  of the push rod is moved down to its lower end position, where the transmitting mechanism  14  is arrested by a latch pin  32  (see  FIG. 5 ) snapping into a catch opening  34  of the spring-biased locking latch  30 . As a consequence of the downward movement of the push rod knob  20  which is transmitted through the second lever arm  25 , the second roller wheel  41  and the second push rod  42 , the draft shield door  13  is raised to the open position and held there due to the locking arrestment of the transmitting mechanism  15 . 
         [0031]    The carrier fork  5  can now be removed from the push knob  20  and moved, e.g., to the draft shield enclosure  12  in order to take out a filter-weighing receptacle  7  that has just been weighed, or to deliver a filter-weighing receptacle  7  that needs to be weighed (not shown here). 
         [0032]    To close the draft shield door  13 , the carrier fork  5  is first moved into a position slightly above the push knob  20  which is locked in its lower end position. With a brief sideways push of the carrier fork  5  against the spring-biased locking latch  30 , the arrestment is released and the push rod with the knob  20  is pushed upwards against the carrier fork  5  by the weight of the draft shield door  13  as well as the tension force of the return spring  28 . A controlled upward movement of the carrier fork  5  allows the transmitting mechanism  15  to return to the upper end position of the push knob  20 , whereupon the carrier fork  5  is available again for further operations. 
         [0033]      FIG. 4  shows an exploded view of a preferred embodiment of a draft shield enclosure  12  with a removable lid  43  and a draft shield door  13  that is operable with the door-opening device  14  according to the invention. The coordinate axes X, Y, Z defined in  FIG. 1 , are repeated here in order to visualize the orientation of the draft shield enclosure  12 . The draft shield door  13  is vertically movable, guided by lateral track grooves  44  of the draft shield enclosure  12  which also seal out air drafts. In the closed state, the bottom edge  45  of the draft shield door  13  is engaged in a groove  46  which likewise serves to seal out air drafts. The door lifter is constituted by the second push rod  42  which is guided by second glide bushings  47  in a vertical bore of the draft shield enclosure  12 . The upper end of the second push rod  42  is solidly connected to the draft shield door  13 , while the lower end carries the second roller wheel  41  which is mounted in a second wheel fork  40  and serves as force-application element. Illustrated features located inside the draft shield enclosure  12  include the U-shaped supporting ledge  48  for the filter receptacles  7  as well as the passage opening  49  for the weighing pan support (not shown). In order to weigh a filter inside a receptacle  7 , the latter is lowered vertically towards the weighing pan and set down on the supporting ledge  48 , while the filter  8  inside the receptacle  7  is lifted off the receptacle floor by the weighing pan. The filter  8  is not taken out of the receptacle  7  for the weighing (and during the entire time the filter  8  is inside the filter-weighing system  1 ). 
         [0034]      FIG. 5  shows the details of the transmitting mechanism  15  in an exploded view. The coordinate axes X, Y, Z defined in  FIG. 1 , are repeated here once again in order to visualize the orientation of the transmitting mechanism  15 . The first push rod  21 , which is connected to the push knob  20 , is guided in gliding motion in a vertical bore of the chassis base  16  and carries at its lower end the first roller wheel  27  which is mounted in a first wheel fork  26 . The first lever  22  whose fulcrum is supported by the chassis base  16  is biased against the first roller wheel  27  by the return spring which is attached to the chassis base  16 . By way of the coupling member  29 , the first lever  22  is connected to the second lever  24 , which likewise has its fulcrum in the chassis base  16  and is, in turn, actuating the draft shield door  13  through the engagement of the second lever arm  25  with the second roller wheel  41  and further through the second push rod  42 . 
         [0035]    In the illustrated example, the spring-biased locking latch  30  is configured as a leaf spring element  30  that is fastened to the chassis base  16 . As the push knob  20  is pushed downward by the carrier fork  5 , the latch pin  32  which is connected to the first push rod  32  and reaches through the opening  31  of the leaf spring  30  meets the tongue  33  and, through gliding contact with the latter, pushes the leaf spring  30  away from the chassis base  16  and ends up snapping into the catch opening  34 . 
         [0036]    Although the invention has been described through the presentation of the specific example of filter weighing, it will be evident to the reader that the invention can also be used for robotic weighing systems for other applications and that numerous further variant embodiments could be developed from the teachings of the present invention, for example by using only one lever instead of the first and second levers that are connected by a coupling member, or by replacing the lever mechanism for example with a gear mechanism or a Bowden cable. Also, it should be explicitly emphasized that the invention is not limited to a Cartesian robot system. A door-opening device according to the invention can also cooperate for example with a swivel arm robot that is programmable in cylindrical or spherical coordinates. It is considered self-evident that variants of these kinds are to be considered as lying within the scope of the present invention.