Abstract:
Machine for applying threaded caps to containers, comprising: gripping means configured to hold the respective containers, at least one screwing head including a respective gripping member configured to hold a respective cap; at least one electric motor associated with said screwing head and configured to control a rotational movement of said gripping member about a longitudinal axis and a translational movement of said gripping member along said longitudinal axis, the translational movement and the rotational movement being synchronized with each other so as to move said gripping member along a screwing path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of Italian patent application number TO2013A000644, filed Jul. 30, 2013, which is herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a machine for applying threaded caps to containers. 
         [0004]    2. Description of Prior Art 
         [0005]    A common technique for closing containers such as bottles and the like envisages forming an external thread on the neck of the containers and applying caps with an internal thread to the containers. 
         [0006]    The machines usually used for applying threaded caps to containers comprise a carousel structure that picks up the containers to be closed and makes them advance along a circular path. The carousel structure carries a plurality of capping heads each of which is equipped with a respective cap-gripping member. The cap-gripping member is driven with a rotational movement about a respective longitudinal axis and a translational movement. The rotational movement and the translational movement of the gripping member are mutually synchronized so as to apply a screwing movement to the caps. 
         [0007]    In more traditional solutions, the screwing movement of the caps onto the containers stops when a preset torque is reached. The screwing heads limit the maximum torque transmitted to the cap-applying member by means of clutches, for example of the magnetic type, or thanks to a current-limited electric motor. 
         [0008]    These solutions are not entirely satisfactory because the screwing of the caps based on the maximum torque can produce a certain percentage of defectiveness of the closures. 
         [0009]    To overcome these drawbacks, systems have already been proposed for applying threaded caps that apply a screwing stroke of preset angular amplitude starting from a condition of incipient coupling between the thread of the cap and the thread of the container. 
         [0010]    EP-A1-1491490 describes a screwing head equipped with a torque sensor that detects the screwing torque applied to the cap during screwing onto the container. The measured torque rapidly increases in the position wherein the threads of the cap and of the container come into mutual contact, in this way signalling the position of incipient coupling between the thread of the cap and the thread of the container. The cap is rotated by a predetermined angle with reference to the position of incipient coupling. 
         [0011]    US2011/0083405-A1 describes a screwing head that detects the condition of incipient coupling between the cap and the container by measuring the current absorbed by the motor which drives the screwing head. 
         [0012]    In these known solutions the condition of incipient coupling between the threads is detected after the cap is applied onto the container. A part of the working stroke of the screwing head is used for the recognition of the position of incipient coupling between the cap and the container rather than for the actual screwing of the cap. Consequently, in these known solutions a reduced angular stroke is available for the actual screwing of the cap. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention aims to provide a machine for applying threaded caps to containers which overcomes the problems of the prior art. 
         [0014]    According to the present invention, this object is achieved by a machine having the characteristics forming the subject of Claim  1 . 
         [0015]    The claims form an integral part of the disclosure provided in relation to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, wherein: 
           [0017]      FIG. 1  is a schematic side view of a machine for applying threaded caps to containers, and; 
           [0018]      FIGS. 2 and 3  are views in greater detail of the parts indicated by the arrow II in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    With reference to  FIG. 1 , numeral  10  indicates a machine for applying threaded caps to containers C, such as bottles or the like. The machine  10  comprises a central column  12  rotatable about a vertical axis A. The central column  12  carries a turret  14  equipped with a plurality of means for gripping the containers C. The means for gripping the containers C are known per se and can be of various types depending on the type of containers C. In general, the gripping means of the bottles must ensure a radial and axial retention of the bottle and must also have an anti-rotation element which prevents rotation of the bottle about its vertical axis. 
         [0020]    In the illustrated example, the turret  14  is equipped with an external guide  20  and fork elements  22  configured to receive respective necks of the containers C, and equipped with respective anti-rotation elements. It is intended that the system represented in the figures is only an example of a possible gripping means and that the invention is applicable to any other system for gripping the containers C. 
         [0021]    As illustrated in greater detail in  FIGS. 2 and 3 , the containers C are provided with an external thread  16  configured for receiving a threaded cap. At the base of the thread  16  of the containers C a radially projecting rim  18  is formed. 
         [0022]    With reference to  FIG. 1 , the machine  10  comprises a plurality of screwing heads  24 . Each screwing head  24  is located above a respective gripping means of the containers C. Each screwing head  24  comprises a spindle  26  carrying a cap-gripping member  28  at its lower end. Each screwing head  24  has a respective electric motor  30  which imparts a rotational movement to the spindle  26  about a respective longitudinal axis B. The cap-gripping member  28  is equipped with a rotational movement about the axis B and a translational movement in the direction of the axis B. The rotational movement and the translational movement are synchronized with each other, so that during operation the caps held by the gripping members  28  are equipped with a screwing movement. The linear movement in the direction of the axis B of the cap-gripping member  28  can be obtained by means of a mechanical or electronic cam. The structure and operation of the screwing heads  24  are known per se and do not require a more detailed description as they are beyond the scope of the present invention. The maximum torque applied to the cap-gripping member  28  is limited by the current supplied to the motor  30 . 
         [0023]    With reference to  FIGS. 2 and 3 , the cap-gripping member  28  of each screwing head  24  has a frusto-conical seat  32  configured for receiving and retaining a respective cap  34 . The cap  34  has a respective internal thread  36  which is designed to couple with the external thread  16  of the respective container C. 
         [0024]    The machine  10  according to the present invention comprises a vision system  38  which is used for detecting the angular position of the threads  16  of the containers C and the angular position of the threads  36  of the caps  34 . More precisely, the vision system  38  is used to detect the angular position of the start points of the threads  16  and  36 . 
         [0025]    The vision system  38  can comprise a first viewing device  40  ( FIG. 2 ) for detecting the angular position of the start point of the external thread  16  of a container C, and a second vision device  42  ( FIG. 3 ) for detecting the angular position of the start point of the internal thread  36  of a cap  34  held by the gripping member  28 . Each vision device  40 ,  42  can be associated with a respective illuminator  44 ,  46  arranged to illuminate the respective area of vision. 
         [0026]    As illustrated in  FIGS. 2 and 3 , the vision devices  40 ,  42  and the respective illuminators  44  and  46  may be arranged outside of the turret  14 . Alternatively, the vision devices  40 ,  42  can be axially aligned with the caps  34  and containers C. 
         [0027]    The vision system  38  is in a fixed position and detects images of the threads  16 ,  36  of the containers C and the caps  34  which, from time to time, pass in front of the vision system  38 . The images recorded by the vision system  28  are sent to an electronic control unit schematically indicated with numeral  48  in  FIG. 1 . The electronic control unit  48  has an algorithm that analyses the images detected by the vision devices  40 ,  42  and determines the angular position with respect to a reference system of the start point of the external thread  16  of the container C and the start point of the internal thread  36  of the corresponding cap  34 . 
         [0028]    The electronic control unit  48  is configured to control the electric motors  30  of the screwing heads  24  in order to make an adjustment of the angular position of the caps  34  according to the information on the detected angular position of the threads  16 ,  36 . The adjustment of the angular position of the caps  34  consists in a rotation about the axis B of the gripping members  28 . This adjustment can be carried out before applying the caps  34  to the respective containers C. 
         [0029]    Alternatively, the adjustment of the angular position of the caps can be carried out after the caps  34  have been placed on the threads  16  of the respective containers C. In this case, an angular stroke equal to the sum of the screwing angle of the caps and the displacement angle between the thread of the cap and the thread of the container is applied to each cap  34 . 
         [0030]    The purpose of the adjustment movement is to arrange the caps  34  with respect to the containers C so that the threads  36  of the caps  34  are in a preset angular position with respect to the threads  16  of the respective containers C. 
         [0031]    Starting from the position in which the caps  34  are juxtaposed to the containers C with the threads  36 ,  16  in a predetermined angular position, the motors  30  apply an angular rotation about the axis B, with a predetermined amplitude, to the respective gripping members  28 . In this way, the screwing stroke of the caps  34  is determined on the basis of a geometric criterion rather than as a function of the screwing torque. This allows a greater precision of screwing to be obtained and the avoidance of defects in the closing of the containers due to an excessive or insufficient closing torque. 
         [0032]    In parallel to the control of the motors  30  on the basis of a predetermined screwing stroke, the electronic control unit  48  can also carry out a detection of the screwing torque applied to the caps  34  by any known method for torque detection. The electronic control unit  48  may be programmed to vary the screwing stroke with respect to the established preset value in case the measured closing torque is insufficient or excessive. 
         [0033]    The vision system  38  is able to recognize the threads  36  of caps with different sizes, different colours and different numbers of thread elements (from 1 to n elements). The vision system  38  is also able to recognize interruptions of the threads and the thread sectors with zero slope. The vision system  38  is also able to detect the thread of transparent glass or plastic containers. 
         [0034]    Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated without departing from the scope of the invention as defined by the claims that follow.