Abstract:
The invention relates to a device and a method for checking the leak tightness of deformable containers. The device comprises a probe that can be brought in contact with a container in a probing motion, a drive unit for the probe, and a measuring apparatus coupled to the drive unit and/or the probe for determining the container leak tightness by evaluating the probing motion. For said device, according to this disclosure, a sensor element adapted to detect motion of the sensor element is arranged on the probe, and that the measuring apparatus coupled to the sensor element is designed to record a time curve of the probing motion.

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT/EP2013/072733, filed Oct. 30, 2013, which claims priority to DE 10 2012 219 993.4, filed Oct. 31, 2012, both of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The invention relates to a device for checking the leak tightness or leakage testing of containers, in particular, polyethylene terephthalate (PET) bottles under internal pressure, comprising a probe that can be brought into contact with a deformable container in a probing movement, a drive unit for the probe and a measuring device coupled to the drive unit and/or the probe for determining the container leak tightness by evaluating the probing movement. The invention also relates to a corresponding checking method. 
     WO-A 99/15871 discloses a device of the type in question and a method that can be carried out with it, in which a probing member is pressed against a container wall by a predetermined advancement of a sensing unit, the probing member being supported on the sensing unit by way of a compression spring. The end position of the probing member in the advancing movement is then detected as a measure of the gas pressure. Problematic aspects here appear to be the complex mechanical construction and the required positioning accuracy as well as possible influencing of the measuring accuracy by tolerances in the diameters of the bottles. 
     SUMMARY 
     Against this background, this disclosure further improves the checking devices and methods that are known in the prior art and provides a system that can be easily produced and reliably operated, in particular, even with a high container throughput, and has a low space requirement. 
     This disclosure is based on the idea of deriving from the movement profile of the probe a measure of the leak tightness, at least in qualitative terms. It is accordingly proposed by this disclosure that on the probe there is arranged a sensor element adapted for the detection of a movement of the probe itself, and that the measuring device coupled to the sensor element is designed for detecting the course of the probing movement over time. The time-resolved detection of a movement parameter, for which a displacement, speed or acceleration profile can be used, provides a high level of informational content for the evaluation. It is thereby ensured that it is only in the state of contact that a property of the object being measured influences the movement profile. The possibility of a specific evaluation of only one time segment also means that a high level of insensitivity to positioning tolerances can be achieved. Furthermore, it is also possible to dispense with an infeeding movement involving complex mechanics. 
     A preferred refinement of this disclosure provides that the sensor element has a piece of permanent magnet, and that the piece of permanent magnet, which is solidly integrated in the probe, possibly together with a ferromagnetic core, is inductively coupled to a measuring coil of the measuring device. In this way, a movement of the probe itself in relation to the measuring coil can be detected contactlessly, while involving little structural complexity and without appreciably influencing the course of movement. 
     The measuring device advantageously has a signal processor for the time-dependent detection of the movement profile, in particular the displacement covered and/or the speed and/or the acceleration of the probe during the probing movement. 
     In order to derive a qualitative or quantitative test result, an evaluation unit for determining a measure of the container leak tightness from the course of the probing movement over time is advantageously provided. 
     A further particularly advantageous refinement provides that, after an initial acceleration phase, the drive unit is switched off or decoupled from the probe, at least during the contact of the probe with the container, so that the impact behavior can be investigated without being affected by positioning problems. 
     To obtain a significant reduction in mechanical components, it is also of advantage if the drive unit has at least one drive coil for an electromagnetic drive of the probe. A further improvement provides that the drive unit has a first drive coil for an advancement of the probe, directed toward the container, and a second drive coil for a retraction of the probe into its starting position. To realize an electromagnetic actuator, it is advantageous if the probe has a ferromagnetic core that enters a drive coil. 
     The probe is advantageously formed by a linearly guided probe pin, which can be moved with its free end against the container, the actuating and sensing being able to take place by way of the pin shaft. It is also of advantage in this connection if the probe has a non-magnetic guide tube mounted in a sliding guide. 
     Alternatively, it may also be of advantage if the probe is arranged pivotably by way of a pivoting arm in a pivot bearing in the manner of a rocker. The pivot bearing may consequently be arranged outside a region that is susceptible to contamination, while the actual probing member is pivoted against the container at the end of the pivoting arm remote from the bearing. Such a pivot bearing also allows a low-friction movement sequence to be achieved. 
     In order to ensure a defined and rapid measuring sequence, it is advantageous if the range of movement of the probe is limited by at least one end stop. 
     With regard to a method, the improvement mentioned above is achieved by a course of the probing movement over time being detected by a sensor element arranged on the probe and a measuring device coupled to the sensor element, and by a measure of the container leak tightness being determined by evaluating the course over time. It is also of particular advantage if the probe is directed against the container without any driving forces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a block diagram of a leak tightness checking system for elastic containers with an electromechanical sensing device; 
         FIG. 2  shows the sensing device with an axially movable probe pin in vertical axial section; 
         FIGS. 3 a  and  b    show the course of the speed of the probe pin when sensing containers with differing internal pressure; and 
         FIG. 4  shows a further embodiment with a pivotable probe pin in plan view. 
     
    
    
     DESCRIPTION 
     The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure. 
     The leak tightness checking system that is shown in the drawings can be used at a testing station at a filling plant, for example for PET beverage bottles, in order to detect leaking bottles as defective and segregate them. For this purpose, the system that is symbolically illustrated in  FIG. 1  comprises a sensing device  10  with a linearly movable probe pin  12  for sensing a container  14  in a probing movement, a measuring device  16  for the real-time processing of the movement signals detected at the probe pin  12  and a computer-aided operator unit  18  for setting the operating parameters and calculating or displaying test results. 
     The sensing device  10  explained in more detail below has in the example shown in  FIG. 2  two drive coils  20 ,  22  for an advancing and retracting movement of the probe pin  12  and a measuring coil  24  for detecting the probing movement. The pressure testing is based on the fact that the measurement of the impact behavior of the probe pin  12  fired against the container  14  in, as it were, a “freely flying” manner provides precise information about the internal pressure of the container  14 , which influences the deformability. 
     The measuring device  16  comprises a signal processor  26  for processing measuring signals and for checking the measuring sequence. The activation of the drive coils  20 ,  22  takes place by way of an I/O unit  28 , while the analog signals detected at the measuring coil  24  or a movement sensor are recorded with a given time increment by way of an A/D converter, so that the course of the probing movement over time is determined by a multiplicity of measured values. 
       FIG. 2  shows a vertical section of the sensing device  10  in the longitudinal axis  32  of the probe pin  12 . A housing  34  on a frame  36  makes stable positioning possible in transverse alignment of the axis  32  in relation to the transporting direction of the containers  14  in the testing station. The drive coils  20 ,  22  and the measuring coil  24  are fixed to the housing coaxially in relation to the axis  32 . A guide tube  38  passing centrally through the coils  20 ,  22 ,  24  forms the casing of the pin shaft  40 . The guide tube  38 , mounted in a linearly movable manner in sliding bearings  39 , includes, as seen from the front to the rear, a non-magnetic first spacer sleeve  42 , a first iron core  44 , mounted in the drive coils  20 ,  22 , and a non-magnetic second spacer sleeve  46 , a second iron core  48 , mounted in the measuring coil  24 , and a proximal stroke limiter  50 . Screwed onto the front end of the first spacer sleeve  42  is a metallic probe head  52 , which with its convexly rounded front face makes it possible to press into a specific point on the container wall without damaging it. The stroke limiter  50 , protruding radially at the rear end of the shaft as a collar, strikes against a stop  54  on the measuring coil  24  to limit the forward movement and against a damper  56  fixed to the housing to limit the retracting movement. 
     In order to be able to detect the movement of the probe pin  12  itself during its probing movement, a piece of permanent magnet  58  is solidly integrated as a sensor element at the rear end portion of the pin shaft  40 , in magnetically conducting connection with the second iron core  48 . During the probing movement, the arrangement comprising the piece of permanent magnet  58  and the iron core  48  moves in the fixed measuring coil  24  and thereby induces an electrical voltage that is proportional to the speed during the probing movement and can be picked up as analog measuring signal. 
     During the operation of the sensing device  10 , the probe pin  12  is accelerated against the container  14  by energizing the drive coil  22 , the iron core  32  being drawn into the center of the coil  22 , where the magnetic flux density is greatest. Even before the contact of the probe head  52  with the container  14 , the coil current is switched off, so that the probe pin  12  covers the remaining distance that is left at a uniform speed without any driving forces. During the subsequent impact, the flexible side wall of the container  14  is pressed inward by the probe pin  12  in dependence on the internal pressure, until the point of reversal is reached and the probing movement is reversed again on account of the elastic force of reaction of the container  14 . The course of this movement process can be recorded by means of the signal processor  26  by using the induction signals of the piece of permanent magnet  58  that are picked up at the measuring coil  24 , and possibly evaluated further by means of the operator unit  18  connected by way of a network  60 , in order to segregate defective containers from the transporting section of the filling plant. For preparation in the starting position, the probe pin can be retracted by switching on the second drive coil  20 , acting in the direction of retraction, until the stroke limiter  50  strikes against the damper  56 . The entire process can be repeated with a high frequency, so that reliable testing operation is ensured even when the containers  14  are transported rapidly. 
       FIG. 3  shows speed diagrams of the probing movement for a container  14  with an internal container pressure of 0.5 bar ( FIG. 3 a   ) and 1.5 bar ( FIG. 3 b   ). Plotted as a measure of the speed of the probe pin  12  is the voltage U picked up at the measuring coil  24  in arbitrary units over the time t in milliseconds, the points in time t 0  to t 6  explained below being marked separately. At t 0 , the beginning of recording takes place with the activation of the first drive coil  22 . At the point in time t 1 , at approximately 10 ms, the coil  22  is switched off again and the probe pin  12  moves further without being driven. Having reached that, at t 2  an evaluation window is opened, and is closed again at the end of the measuring process at t 6 . Within this evaluation window, the impingement on the container  14  or the object being measured is reliably evident from the steep drop of the curve. At the zero crossing at t 4 , the reversal of movement takes place, here too the lifting off of the probe pin  12  from the container  14  being detectable without a problem from the discontinuous transition to the lower speed plateau. As a measure of the internal container pressure, the inverse value of the time interval t 5 -t 3  can be determined. Alternatively, the pressure inside the container can be derived from the slope of the curve, i.e. the deceleration and acceleration of the probe pin  12  at the time interval t 3  to t 5 . It is also conceivable to integrate the course of the speed, in order to gain from the displacement data thus obtained at least a qualitative measure of the internal pressure by way of the depth of penetration of the probe pin  12 . 
     In the case of the embodiment shown in  FIG. 4 , the same or similar parts are provided with the same designations as described above. One particular difference is that the probe pin  12  is not linearly movable, but pivotably movable in a horizontal plane along the circular path  62 . For this, the probe pin  12  is held at one end of a pivoting arm  64 , which is mounted at its other end in a pivot bearing  66 . For a back and forth pin drive, a pole-reversible coil  20  that is fixed to the housing is provided in combination with a magnet carrier  68  fixed to the pin and permanent magnets  70  located in said carrier. Another difference is that, instead of inductive movement detection, an acceleration sensor  72  is used. The sensor  72  is formed by an integrated electronic module, which is fixedly attached to a carrier of the pin  12  and is supplied with operating voltage by way of a line  74 . At the bearing-side end of the pivoting arm  64 , the line  74  is led to the circuit board of the measuring device  16  by way of a flexible cable. In this way, measuring signals can be transmitted even during the movement. When there is a change in movement, the acceleration sensor  72  emits an analog voltage signal, which is recorded in dependence on time. By integration of the measured values, the speed or the pivoting displacement can also be determined time-dependently. 
     In  FIG. 4 , a detail of the peripheral contour of an undeformed container  14 , for example a pressurized PET bottle, is indicated. The container  14  moves on a transporter in the direction of the arrow  76  and is thereby guided peripherally along the guide slope  78  into the arcuate path of movement  62  of the probe pin  12 . The forward probing movement of the latter is thereby initiated by a suitably positioned light barrier (not shown). In this case, the container wall is deformed to an extent dependent on the internal pressure. In the case of a comparatively hard container  14 , a high deceleration over a short time period is detected, while in the case of a softer container the deceleration is less and the probing process up to the time when the pin comes a standstill takes longer. 
     While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.