Abstract:
A manipulator for positioning a test head is provided with a positioning means by which the test head is three-dimensionally positionable and with a cradle to which the test head is securable and which is connected to the positioning means. The manipulator includes a compensator which can be loaded by the mass of the test head. The positioning means includes a column and at least one lead screw extending in the vertical direction. The compensator is connected to the cradle and can be moved by the lead screw in the vertical direction. The compensator includes a driver cooperating with the lead screw and is guided in the vertical direction on the column. The compensator has a spring element which is biased and supported by the driver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority under 35 USC §119 to previously filed German application 10200724949.9 filed May 30, 2007. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   REFERENCE TO A “SEQUENCE LISTING” 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a manipulator, in particular for positioning a test head on a tester, comprising a positioning means by which the test head is three-dimensionally positionable. The manipulator features furthermore a cradle to which the test head is securable and which is connected to the positioning means. The invention furthermore relates to a compensator for application with one such manipulator and serving to compensate the mass of the test head. 
   A manipulator for positioning a test head normally has a plurality of translational and rotational degrees of freedom which allow for the test head to be precisely positioned three-dimensionally and to be positioned at a desired location. This is why, as a rule, such a manipulator finds application in testing electronic components such as, for instance, integrated circuits (ICs) or wafers. For function or quality testing electronic components it is necessary to precisely locate the relatively heavy test head at a tester. The tester, for example as a device handler or wafer prober, presents the electronic components to the test head for testing. Obtaining a genuine test result when testing electronic components requires precise docking of the test head at the tester. This is why precise, smooth adjustment of the manipulator positioning the test head is a mandatory requirement. 
   2. Description of Related Art 
   Smooth adjustment of the test head is obtained when the manipulator is provided with a compensator which compensates the mass of the test head. The compensator relieving the positioning means of the weight of the test head usually features a counterweight connected to the test head. Manipulators in which the mass of the test head is compensated by a counterweight are described, for instance, in German patents DE 36 17 741 C2 and DE 40 07 011 C2. 
   In addition German patent DE 10 2004 026 031 B3 discloses a manipulator permitting temporary loading of the test head to be docked on a tester to achieve reliable contacting of the tester. A manipulator provided with a fixed counterweight is described in U.S. Pat. No. 6,766,996 B1. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention is based on the object of improving a manipulator for positioning a test head in a compact and reliable operational design. 
   The manipulator in accordance with the invention comprises a positioning means by which the test head is three-dimensionally positionable. The manipulator comprises furthermore a cradle to which the test head can be secured and which is connected to the positioning means. In addition, the manipulator features a compensator loadable by the mass of the test head. The positioning means comprises a column and at least one lead screw extending in the vertical direction. The compensator is connected to the cradle and can be moved by means of the lead screw in the vertical direction. The compensator comprises a driver cooperating with the lead screw and which is guided in the vertical direction on the column. In addition, the compensator comprises a spring element which is biased and supported by the driver. 
   The manipulator, in accordance with the invention, is based on having discovered how to compensate the mass of the test head not by a moveable counterweight but by a counterforce produced by a spring element. Thus, the manipulator may be designed with a relatively low weight in thus making for lower shipping costs. Unlike conventional manipulators in which the moveable counterweight needs to be balanced to the mass of the test head, the manipulator in accordance with the invention also features a universal configuration which now makes it possible to compensate the mass of a variety of test heads. For, now, the counterforce produced by the compensator to compensate the force of the weight of the test head concerned is solely a function of the excursion of the spring element caused by the corresponding force of the weight for a constant spring rate. 
   The force of the weight acting on the compensator materializes mainly from the mass of the test head, the mass of the cradle to which the test head is secured and the mass of a plate to which the cradle is secured. The spring element, which may be composed of a plurality of springs, where necessary, features a spring rate by which a force of the weight is generated which compensates the force of the weight acting on the securement means at least in part. For instance, the spring rate may be selected so that the counterforce generated by the spring element compensates just the component of the force of the weight produced by the mass of the test head. However, the component of the weight force resulting from the mass of the cradle and the mass of the mounting plate is in this case absorbed by the lead screw. It has, however, been discovered to be particularly an advantage to endow the spring element with a spring rate by which a counter force is generated which fully compensates the force of the weight acting on the compensator so that the compensator has smooth freedom of movement. 
   It has furthermore been discovered to particularly advantage to bias the spring element. This bias has the advantage that an excursion of the spring element does not occur until the force acting thereon exceeds the bias. This ensures precise motion of the test head by the positioning means. In addition to this, biasing the spring element permits tweaking the spring rate in thus achieving a compact design of the compensator. 
   Unlike prior art as it reads from U.S. Pat. No. 6,766,996 B1, the manipulator in accordance with the invention is additionally characterized by a reliable motion of the compensator in the vertical direction. This is particularly to be contributed to the fact that the driver cooperating with the lead screw is directly guided at the column, resulting in the compensator permitting precise vertical motion. 
   In addition the compensator ensures adequate compliance for docking the test head to, for example, a tester as needed in practice. On top of this, it is possible with the manipulator in accordance with the invention to load the tester temporary with the test head to achieve reliable contacting of the tester as is known from German patent DE 10 2004 026031 B3. For, when the spring rate is selected so that the counterforce generated by the spring element not fully compensates the mass of the test head, then the non-compensated component of the force of the weight of the test head is a load on the tester when the test head is docked. 
   Preferably the spring element is a compression spring, for example, a helical compression spring. Depending on the particular application the spring element may also be engineered as a tension spring. 
   In one preferred aspect the column is provided with at least one guide rail. The driver expediently involving a lead screw nut comprises a carriage guided by the guide rail. Guiding the car can be done by known ways and means, for example, by a linear bearing. 
   It is furthermore of advantage when the positioning means includes a mounting plate to which the cradle is secured. The mounting plate may be vertically guided on the column, if necessary, and provided with a plurality of holes permitting variable securement of the cradle. 
   In another aspect of the manipulator in accordance with the invention at least two lead screws, which are arranged parallel to each other, and at least two compensators are provided. Each lead screw is assigned a compensator. In this way the mass of the test head is compensated by two or more compensators. 
   Preferably, the compensator comprises a housing through which the lead screw extends and in which the spring element is arranged. The housing is expediently provided with an inspection window to permit checking the spring element to ascertain for example, the excursion of the spring element. 
   For simplified assembly it has been discovered to be of an advantage when the housing comprises an inner sleeve and an outer sleeve connected to the inner sleeve. Preferably, the inner sleeve is screwed into the outer sleeve to bias the spring element arranged in the inner sleeve. To facilitate screwing the inner sleeve into the outer sleeve the inner sleeve is expediently provided with a lug preferably configured in the form of a hexagon so that the inner sleeve can be turned by means of a hexagon wrench. To prevent the spring element being torsioned when screwing in the inner sleeve into the outer sleeve the spring element is preferably mounted rotatably in the inner sleeve by means of a thrust bearing. 
   Preferably, shiftably arranged in the housing is a clamping sleeve which is connected to the driver. The spring element engineered for example, as a helical compression spring is expediently supported by one end to the clamping sleeve and by the other end to the thrust bearing. 
   Expediently, the housing comprises at least one boss serving to support the spring element in the housing. In this case it has been discovered to be of advantage when the clamping sleeve comprises a stopper at which the spring element is supported and which in the biased condition of the spring element contacts the boss. Advantageously, the clamping sleeve comprises a connecting portion which connects the stopper and the driver to each other. To simplify assembly of the compensator the stopper and the connecting portion are preferably separate components. But, depending on the particular application the clamping sleeve composed of the stopper and connecting portion may be engineered in one piece. 
   Preferably, the inner sleeve comprises a face provided with a ramp. The ramp serves to center the clamping sleeve in the inner sleeve to prevent, for example, the stopper becoming jammed at the face when screwing the inner sleeve into the outer sleeve. 
   To secure the mounting plate or cradle to the compensator the housing is preferably connected to a securement sleeve. The securement sleeve is expediently fitted on the inner sleeve at the end facing away from the outer sleeve. 
   In another aspect of the manipulator in accordance with the invention the cradle comprises two side arms between which the test head is clampable. The side arms ensure reliable securement of the test head, even when it is relatively heavy. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     Details and further advantages of the invention read from the following description of a preferred aspect. The aspect is shown simply diagrammatically in the drawings in which: 
       FIG. 1  is a view in perspective of a manipulator comprising a cradle to which a test head is secured; 
       FIG. 2  is a view in perspective of a positioning means comprising two lead screws arranged in parallel; 
       FIG. 3  is a side view of the positioning means as shown in  FIG. 2 ; 
       FIG. 4  is a magnified view of the portion identified IV in  FIG. 3 ; 
       FIG. 5   a  is a view in perspective of a compensator; 
       FIG. 5   b  is a side view of the compensator as shown in  FIG. 5   a;    
       FIG. 5   c  is a section taken along the line Vc-Vc in  FIG. 5   b;    
       FIG. 6   a  is a longitudinal section through the compensator showing a spring element unloaded; 
       FIG. 6   b  is a longitudinal section as shown in  FIG. 6   a  showing a spring element biased and 
       FIG. 6   c  is a longitudinal section as shown in  FIG. 6   a  showing a spring element loaded. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1  there is illustrated the manipulator serving to position a test head  40  at a tester (not shown) for electronic components, such as, for example, ICs or wafers. For this purpose the manipulator comprises a positioning means  20  supported on a base  10  and connected to a cradle  30 . The positioning means  20  comprises a vertical column  25  and two lead screws  21  extending parallel to each other in the vertical direction z, which are arranged within the column  25 . The lead screws  21  as evident from  FIG. 2  in particular are rotatably mounted with the aid of bearings  22  and connected with the aid of gears  23  to an electric motor  24 . The electric motor  24  powers the lead screws  21  in synchronism. 
   The lead screws  21  are arranged on a horizontal carriage  28  which can be linearly displaced in a horizontal direction y on the base  10 . Depending on the application a carousel may be arranged on the horizontal carriage  28  making it possible to rotate the lead screw  21  about an axis of rotation extending in the vertical direction z, as is known from German patent DE 101 32 489 B4. The base  10  comprises two supporting beams  11  extending in the horizontal direction y which are supported by cross members  12  extending in a horizontal direction x orthogonal to the horizontal direction y. To ensure safe standing of the manipulator even on an uneven surface the supporting beams  11  and the cross members  12  are mounted on height-adjustable feet plates  13 . Arranged on the supporting beams  11  are guide rails  14  which serve to guide the horizontal carriage  28  in the horizontal direction y. 
   Referring now to  FIG. 2  there is illustrated furthermore how each lead screw  21  is assigned a compensator  50  which can be moved in the vertical direction z by the lead screw  21 . A precise motion of the compensator  50  is ensured by a guide rail  26  arranged on the column  25  guiding the compensator  50  in the vertical direction z. The compensator  50  is connected to a mounting plate  27  to which the cradle  30  is secured. Depending on the particular application the cradle  30  can be arranged rotatable at the mounting plate  27  to permit a twisting motion φ of the test head  40 . The cradle  30  comprises two side arms  31  between which the test head  40  is clamped in place. The test head  40  can be clamped rotatably in place between the side arms  31  to achieve a so-called tumbling motion α of the test head  40 . 
   Referring now to  FIGS. 3 and 4  there is illustrated in particular how the compensator  50  comprises a housing  52  through which the lead screw  21  extends. The housing  52  is composed of an inner sleeve  54  and an outer sleeve  59  as is evident in detail in  FIGS. 5   a  to  5   c . The inner sleeve  54  is provided with a male thread and the outer sleeve  59  with a female thread so that the inner sleeve  54  can be screwed into the outer sleeve  59 . At the end facing away from the outer sleeve  59  the inner sleeve  54  features a boss  55  translating into a lug  58 . As is particularly evident from  FIG. 5   a  the lug  58  takes the form of a hexagon so that a conventional wrench can be used to screw the inner sleeve  54  into the outer sleeve  59 . At the end facing away from the boss  55  the inner sleeve  54  features a face provided with a ramp  56 . The inner sleeve  54  is provided in addition with a plurality of inspection windows  57  distributed along the circumference of the inner sleeve  54 . The outer sleeve  59  comprises at the end facing away from the inner sleeve  54  a boss  60  which limits how far the inner sleeve  54  can be screwed in, as is particularly evident from  FIG. 5   c.    
   Arranged in the interior of the inner sleeve  54  is a spring element  51  engineered as a helical compression spring. The spring element  51  is supported at one end by a thrust bearing  61  in contact with the boss  55  and engineered, for example, as a needle bearing. The thrust bearing  61  results in the spring element  51  being rotatably mounted to prevent it from being torsioned when screwing the inner sleeve  54  into the outer sleeve  59 . At the other end the spring element  51  is supported by a clamping sleeve  62  shiftably arranged in the inner sleeve  54 . The clamping sleeve  62  is composed of a stopper  63  in contact with the spring element  51  and a connecting portion  64  arranged at the side of the stopper  63  facing away from the spring element  51 . The stopper  63  is dimensioned so that it is in contact with the boss  60  of the outer sleeve  59  in the unloaded condition of the spring element  51 . The tubular connecting portion  64 , however, is dimensioned so that it projects through an opening formed in the boss  60  from the outer sleeve  59  and thus from the housing  52 . 
   At the end facing away from the stopper  63  the connecting portion  64  is connected to a driver  65 . The driver  65  comprises—as is evident from FIG.  4 —a lead screw nut  66  which cooperates with the lead screw  21 . The driver  65  in addition features a carriage  67  which cooperates with the guide rail  26  to guide the driver  65  and thus the compensator  50  in the vertical direction z. 
   Mounted on the inner sleeve  54  at the end facing away from the outer sleeve  59  is a securement sleeve  53 . The securement sleeve  53  comprises—as is particularly evident from  FIGS. 5   a  and  5   b —a securement surface  68  to which the mounting plate  27  can be secured. 
   The spring element  51  is biased. Referring now to  FIGS. 6   a  and  6   b  there is illustrated how bias is caused by screwing the inner sleeve  54  into the outer sleeve  59 . Thus, the bias depends on how far screwing in is done so that it can be easily varied. Expediently the spring element  51  is, however, dimensioned so that the wanted bias is achieved when the face of the inner sleeve  54  comes into contact with the boss  60  of the outer sleeve  59 , as is evident from  FIG. 6   b . The ramp  56  of the face of the inner sleeve  54  centers the stopper  63  to thus assure unobstructed motion of the stopper  63  in the inner sleeve  54 . 
   The compensator  50  serves to achieve the compliancy as needed for docking the test head at the tester as required in practice and to compensate the mass of the test head  40  in ensuring smooth adjustment of the test head  40 . Compensating the mass of the test head  40  is done by a counterforce generated by the spring element  51 . As is particularly evident from  FIG. 6   c  the force of the weight of the test head  40  engaging the inner sleeve  54  via the cradle  30 , mounting plate  27  and securement sleeve  53  results in excursion of the spring element  51  by the spring element  51  being compressed in thus shifting the housing  52  in the direction of the driver  65 . But excursion of the spring element  51  does not occur until the force engaging the inner sleeve  54  exceeds the bias of the spring element  51 . 
   As a result of the mass of the test head  40  engaging the inner sleeve  54  excursion of the spring element  51  occurs, i.e. in the present case is compressed as is evident from  FIG. 6   c . The return force materializing in this way represents a counterforce which compensates the force of the weight engaging the compensator  50 . The degree of compensation mainly depends on the spring rate of the spring element  51 . By replacing the spring element  51  the compensator  50  can be adapted to differingly heavy test heads  40 . This is, however, necessary only as an exception since with the spring rate constant any difference in the weight of the test head  40  simply produces a difference in excursion of the spring element  51 . In other words, by suitably selecting the spring rate and the length of the connecting portion  64  dictating excursion a universal configuration is achievable, suitable for compensating the mass of all popular test heads  40 . Last but not least, the manipulator as described above excels by its compact design and low total weight, because of the compensator  50  eliminating the need to provide a movable counterweight to compensate the mass of the test head  40 . 
   
     
       
             
           
             
             
           
         
             
                 
             
             
               List of reference signs 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               10 
               base 
             
             
               11 
               supporting beam 
             
             
               12 
               cross member 
             
             
               13 
               feet plate 
             
             
               14 
               guide rail 
             
             
               20. 
               positioning means 
             
             
               21 
               lead screw 
             
             
               22 
               bearings 
             
             
               23 
               gears 
             
             
               24 
               motor 
             
             
               25 
               column 
             
             
               26 
               guide rail 
             
             
               27 
               mounting plate 
             
             
               28 
               horizontal carriage 
             
             
               30 
               cradle 
             
             
               31 
               side arm 
             
             
               40 
               test head 
             
             
               50 
               compensator 
             
             
               51 
               spring element 
             
             
               52 
               housing 
             
             
               53 
               securement sleeve 
             
             
               54 
               inner sleeve 
             
             
               55 
               boss 
             
             
               56 
               ramp 
             
             
               57 
               inspection window 
             
             
               58 
               lug 
             
             
               59 
               outer sleeve 
             
             
               60 
               boss 
             
             
               61 
               thrust bearing 
             
             
               62 
               clamping sleeve 
             
             
               63 
               stopper 
             
             
               64 
               connecting portion 
             
             
               65 
               driver 
             
             
               66 
               lead screw nut 
             
             
               67 
               carriage 
             
             
               68 
               securement surface 
             
             
               x 
               first horizontal direction 
             
             
               y 
               second horizontal direction 
             
             
               z 
               vertical direction 
             
             
               φ 
               twisting motion 
             
             
               α 
               tumbling motion