Patent Publication Number: US-2005115305-A1

Title: Leak detection method and devices

Description:
The present invention relates to a method and devices for investigating samples as to leaks.  
      In a multitude of series manufactured products with packagings, encapsulations, housings or alike, there frequently exists the requirement of ensuring their leak tightness. Products, respectively samples of this kind are, for example, packaged products (foodstuffs, pharmaceuticals, sterile items usable only once etc.) be it that the packaging consists of a foil or a bottle, respectively an ampoule with seal. In this instance the leak tightness of the packaging is of interest. Series manufactured products in which the leak tightness plays an important role may also be encapsulated components (electronics components, switches or alike) or other items exhibiting a more or less large hollow chamber (encapsulated machine components, gas cartridges, gas generators . . . ).  
      From DE 196 42 099 A1 it is known to test the packaging of a packaged item as to leak tightness. This test is performed according to the principle of vacuum leak detection in a test chamber being formed by two extensible foils. Introduction into, respectively removal of the sample from the device is performed manually. When employing leak detection devices of this kind in manufacturing processes with short cycle times, leak detection may only performed on random samples for the purpose of being able to detect system malfunctions as early as possible. Disadvantageous here is that the measures for remedying such malfunctions carry the penalty of a considerable time delay. The investigation of as many as possible, or even all samples manufactured with short cycle times is not possible.  
      From U.S. Pat. No. 5,373,729 a device is known with which the packaging of containers, each sealed with a foil, is tested for leak tightness. The test is performed “in-line”, i.e. each of the containers is investigated as to a possibly existing leak. In order to permit this type of test, the containers are introduced to the leak detection device by means of a transport device. The leak detection device itself consists of a lower section and an upper section being movable upwards and downwards. Located between these components is the transport device which is stopped for the period of time during which the leak detection is performed. Leak detection at cycle frequencies in the seconds range is not possible.  
      It is the task of the present invention to create methods and devices of the aforementioned kind which allow for a leak detection on samples at high cycle frequencies so that also for products manufactured at cycle frequencies approximately in the seconds range, an “in-line” leak investigation is possible.  
      This task is solved by the present invention through the measures in accordance with the patent claims.  
      By applying the gymwheel principle it is possible to create test chambers at a relatively high cycle frequency and for a sufficiently long period of time during which the leak detection can be prepared and performed. Here the gymwheel principle is to be understood such that besides the items which are to be analysed for leaks on the transport device there exists a substantially circular rotating device, basically known from other applications, where said device is equipped with the test chambers. Into these, the items are introduced. During a revolution of the system the leak detection process takes place. If the number of test chambers formed per unit of time does not exceed the number of samples manufactured per unit of time, an in-line leak detection may be performed, provided the test chambers can be maintained in the closed state for a sufficiently long period of time. Relevant for the number of test chambers required is here the time interval at which the samples are being manufactured and the time within which a leak detection can be performed. If samples are created at high cycle frequencies, for example one sample per second, and if performing of the leak test takes approximately 10 seconds, then 12 test chambers will be required when the samples can be introduced within one second into a test chamber and removed therefrom. 
    
    
      Further advantages and details of the present invention shall be explained with reference to schematically depicted examples of embodiments in the drawing figure. The drawing figure depicts a solution in which a multitude of test chambers is located on a circular support rotatable about a vertical axis.  
      In the solution according to drawing  FIG. 1 , the samples  13  are introduced to a leak detection device  15  by means of a transport device  14 . Said leak detection device consists of a circular disk-shaped or circular ring-shaped support  16  which is suspended in a manner not depicted in detail rotatable about the vertical axis  17  (arrow  18 ). Located on the support  16  are 12 leak detection chambers  19  arranged in a circle.  1  to  12  designate stations through which each of the leak detection chambers  19  passes. The leak detection chambers  19  of stations  3  to  11  are depicted in the closed state, the chambers of stations  2  and  12  in the half opened state and the chamber of station  1  in the opened state. To each of the leak detection chambers  19  there is assigned a vacuum pump  20 , which is connected through lines with valves, not depicted, to the corresponding leak detection chamber. Two transport devices  21  and  22  serve the purpose of moving the samples  1  detected for leaks away. Transport device  21  serves the purpose of moving leak tight samples  1  away. Samples which exhibit a leak are deposited on the transport device  22 .  
      The leak detection chambers  19  are expediently designed such as detailed in DE-A-196 42 099. The test chamber is formed by two extensible foils which are each clamped into a frame. The sample which is to be tested for leaks is introduced between the foils. Thereafter the intermediate space is evacuated so that a leak detection chamber is created directly encompassing the item. The foils are equipped with means (naps, porous coating or alike) which form a contiguous intermediate chamber between the foils and the area of the item to be tested. This intermediate chamber is connected to a detector sensitive to the test gas. It is not absolutely mandatory that two foils form the test chamber; a foil clamped into a frame and a solid bottom section (or cover section) may also employed for creating a test chamber having a small residual volume.  
      The leak test sequence is performed such that a pick-and-place device  23  grips—with a vacuum suction device, for example—the supplied samples  13  and introduces the samples into the opened leak detection chamber  19  of the station  1 . The chamber  19  dwells at this station  1  for approximately one second. In one second intervals the chambers  19  are transported on to the next respective station. At the level of the station  2  the chamber closes. Immediately thereafter the evacuation commences.  
      It is expedient to commence a gross leak detection already relatively soon after having started the pump down phase. In this manner massive leaks, caused by an air inrush in the instance of a burst sample, for example, may be determined. During the process of precision leak detection (station  11 ) such leaks can no longer be determined, since at this point of time also the test gases contained in the sample have been pumped out. Gross leak detection is performed, for example, in that at the level of the station  5  a sensor sensitive to the test gas is queried, said sensor being connected to the connecting lines between the chambers and their vacuum pumps.  
      The pump down process is continued up to station  10  and there reaches a pressure of approximately 1 mbar. At the level of the station  11 , a sensitive leak detection device  24  is linked to the chamber  19 . Said leak detection device is equipped with a test gas detector being designed by way of a mass spectrometer. With it thus leaks down to 10 −9  mbar l/s can be determined. Through the station  12 , in which opening of the chamber is performed, the chamber reaches the station  1 . The pick-and-place device  23  removes the sample  1  from the chamber  19  and places the sample on one of the two transport devices  21 ,  22 , depending on whether the sample is leaktight or not.  
      In drawing  FIG. 1  also the controller of the leak detection device is depicted by way of block  26 . Due to the multitude of moving parts, communication between the controller  26  and the components to be controlled (transport devices, valves, support  16 , pick-and-place device  23  etc.) on the one hand and the signal sources (gross leak detection, leak detector  24 ) and the controller  26  on the other hand, is effected expediently by means of an infrared data acquisition system.