Abstract:
The invention relates to a vacuum generating device ( 1 ) and to a method suitable for the operation thereof. An ejector device ( 27 ) is connected with an inlet ( 29 ) thereof to an air supply conduit ( 32 ) that can be selectively closed or opened by an electronic control unit ( 14 ) in order to selectively turn off or turn on the ejector device ( 27 ). When the ejector device ( 27 ) is turned on, a vacuum is generated in a suction channel ( 35 ). The ejector device ( 27 ) is operated such that the vacuum fluctuates between an upper switching value and a lower switching value. By comparison to a reference time value, the operating period of the ejector device ( 27 ) is determined in order to generate a diagnosis signal that allows a conclusion of the leak that is present.

Description:
This application claims priority based on an International Application filed under the Patent Cooperation Treaty, PCT/EP2008/010057, filed Nov. 27, 2008, which claims priority to DE 102007058114.0, filed Dec. 4, 2007. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method for the operation of a vacuum generating device, having an ejector device, whose inlet is connected with an air supply conduit and whose suction side is connected with a suction channel, which is connected with a suction gripper, and which has a pressure detection device for detecting the vacuum in the suction channel, wherein the vacuum in the suction channel is regulated in that the air supply of the inlet is turned off once the vacuum has reached an upper switching value and is switched on again until the upper switching value has been reached once the vacuum drops to a lower switching value. 
     The invention furthermore relates to a vacuum generating device with an ejector device having an inlet, which is connected with an air supply conduit and has a suction opening, to which a suction channel is connected, which is or can be connected with a suction gripper, furthermore has a pressure detection device used for detecting the vacuum in the suction channel, and has an electronic regulating device for regulating the vacuum prevailing in the suction channel in such a way that the air supply of the inlet is switched off once the vacuum being built up has reached an upper switching value and is again switched on until the upper switching value has been reached if the vacuum has dropped to a lower switching value. 
     Such a vacuum generating device, as well as the method suitable for operating it, of the type mentioned ensue from DE 10 2004 031 924 B4. The vacuum generating device contains an ejector arrangement, whose inlet can be connected via an air supply conduit with a compressed air source for generating a vacuum at a suction opening which defines a suction side. The vacuum is also applied to a connected suction channel, which can be connected with a suction gripper, by means of which an object to be handled can be held and transported by means of the vacuum. 
     For minimizing the use of compressed air, the air supply conduit can be blocked off once a vacuum, which is a function of the situation, exists in the suction channel, and which is capable of securely gripping an object. However, because of the unavoidable leakage, the air supply is again switched on once the underpressure drops to an also preset lower switching value. Once the upper switching value has again been subsequently reached, the air supply is again switched off, and this process can be repeated several times during an operating cycle as a function of the length an object is handled, as well as of the intensity of the occurring leakage. A monitoring device exists in accordance with DE 10 2004 031 924 B4, which detects the number of the above mentioned regulating processes, so that conclusions can be drawn as to whether there is an increased leakage and therefore malfunctions exist in the system. It is furthermore possible for a monitoring device to be provided, by means of which the evacuation time for performing a self-diagnosis can be determined. 
     Although this type of monitoring promises to be very dependable, it makes certain demands on the processor output of the electronic evaluation device and therefore demands comparatively very costly hardware. 
     A control device for a suction element is disclosed in DE 10 2004 047 853 A1, which has a vacuum generation arrangement and contains an electronic module, which is in operational connection with a separate display- and/or operating device. Inter alia, the electronic module is used for monitoring parameters, such as evacuation times and air supply times, and transmits the measured parameters to the display- and/or operating device. 
     DE 42 29 834 C2 describes a method and a device for electrically processing vacuum pressure information, in which measured pressure values are compared with stored ones, and an error determination is made on the basis thereof. 
     U.S. Pat. No. 5,617,898 discloses an arrangement of fluid pressure devices, each of which has its own electronic control unit in order to relieve a connected sequencer. The fluid pressure devices can have displays for showing malfunctions. 
     SUMMARY OF THE INVENTION 
     The goal of the invention is to suggest measures which, with little outlay, make possible the dependable functional monitoring of a vacuum generating device. 
     In connection with a method of the type mentioned at the outset, this object is attained in that the regulating time which has passed between the shutting off of the air supply and either the subsequent restarting, or the renewed shutting off of the air supply, is detected and compared with at least one predetermined reference time value in order to generate an electrical diagnostic signal as a function of the result of the comparison. 
     In a vacuum generating device of the type mentioned at the outset, the object of the invention is furthermore attained in that the regulating device has regulating time detection means, by means of which the regulating time passing between the shutting off of the air supply and either the subsequent restarting, or the renewed shutting off of the air supply, can be detected, and that furthermore the regulating device has comparing means, with which the detected regulating time can be compared with at least one reference time value stored in memory means, and that the regulating device has output means which, as a function of the result of the comparison by the comparing means, can output an electrical diagnostic signal. 
     In connection with the method, as well as with the vacuum generating device operating in particular in accordance with the method, monitoring is performed as to how long it takes before the air supply, which had been shut off when the upper switching value had been reached, is again switched on, or is switched off again after having been switched on again in the intervening time. This length of time, which can be called regulating time, is a measure of how quickly a vacuum decays and, as a result, how extensive the leakage is in the system section adjoining the suction side of the ejector device. It is possible to store at least one reference time value, based on experimental values, with which the detected regulating time can be compared, in order to then generate an electrical diagnostic signal as a function of the result of the comparison, which provides indications to the user regarding the actual functional state, or which itself directly causes one or several measures, for example the output of a visual and/or acoustic warning report, or the switching of the air supply to continuous operation, in order to prevent an undesired drop of an object which had been held by suction. 
     Advantageous further developments of the invention ensue from the dependent claims. 
     If the regulating time lies below the predetermined reference value, a diagnostic signal is usefully generated. The diagnostic signal can be displayed directly locally at the vacuum generating device. If the vacuum generating device is connected to an external electronic control device, a diagnostic signal can also be put out to this external control device. 
     There is the possibility of classifying the appearing leakage by taking its intensity into consideration. In this connection it is possible to simultaneously store several different reference time values, which are compared with the detected regulating time, in which case the issued electronic diagnostic signal depends on which of the stored reference values corresponds to the detected regulating time. In accordance with this it is possible to generate diagnostic signals in varying diagnostic stages, in which case different follow-up steps are taken. Thus, for example, it is possible in case of a low diagnostic stage to merely issue generate a warning signal, without impairing the function of the vacuum generating device. If the leakage increases and therefore falls under a higher diagnostic stage, it is possible to purposely set operating limits, for example a switch-over to continuous suction up to a controlled shut-down of the installation if an extreme leakage exists. 
     It is of advantage if a check valve is inserted into the suction channel, which prevents an undesired drop of the vacuum in the system section located between the check valve and the suction gripper, when the air supply is shut off. In this case the pressure detection device usefully detects the vacuum in the section of the suction channel extending between the check valve and the suction gripper. 
     A blow-off conduit is usefully connected with the suction channel, which makes possible the feed-in of compressed air which is under atmospheric overpressure into the suction channel if an object which had previously been grasped by suction is to be released. This measure is particularly recommended in connection with a check valve introduced into the suction channel. 
     The upper switching value can be usefully preset in a function-specific manner. Input means can exist, which make a direct input of the upper switching value, based on the experimental value, possible for the user. The possibility for entering a hysteresis value can be provided in the same way, which is considered by the user, based on his experience, as that drop in vacuum which is permissible for continued dependable operation. Then, the lower switching value is usefully generated by adding a safety pressure value, resulting from the difference between the upper switching value and the hysteresis value. 
     It is also possible to provide the possibility to determine the upper switching value and the lower switching value by means of a learning process. This possibility can exist in addition, or alternatively, to the direct input by manually operable input means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In what follows, the invention will be explained in greater detail by means of the attached drawings. Represented in these is in: 
         FIG. 1 , in a schematic representation, a preferred embodiment of the vacuum generating device in accordance with the invention for executing a method in accordance with the invention, and 
         FIG. 2 , a diagram, in which the progression of the vacuum in the suction channel, which takes place in the course of manipulating an object, can be seen. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The vacuum generating device, identified as a whole by the reference numeral  1 , has the particular purpose of grasping objects  5  by means of a vacuum, so that they can be repositioned between different locations. It is, for example, employed in connection with assembly technology or in the packaging industry. A plate-shaped product, here in the shape of a thin plate, is illustrated by way of example in  FIG. 1  as the object  5 . 
     The vacuum generating device  1  contains a vacuum generating unit  2 , to which at least one suction gripper  7  is connected. 
     In principle, the vacuum generating device  1  can also be equipped with several vacuum generating units  2 , which can be combined to form a structural component. 
     The already mentioned suction gripper  7  is connected by means of a suction line  4  to the vacuum generating unit  2 . In this case it can be arranged remote from the vacuum generating unit  2 , so that a rigid structural component exists. 
     The suction gripper  7  is for example a suction cup or suction disk. It delimits a work chamber  12  having a work opening  8  and can be displaced in such a way that it comes into contact with its work opening  8  in front with the object  5  to be manipulated. At the moment of contact, the work opening  8  is covered by the object  5  and the suction chamber  12  is closed in the direction toward the atmosphere. This state is indicated by dash-dotted lines in the drawings. 
     The displacement of the suction gripper  7  takes place by displacing an arrangement which supports it, which can be the vacuum generating unit  2  itself, if it is fastened on it. 
     An air supply interface  17  is located at a one- or multiple-piece main housing  3  of the vacuum generating unit  2  and is used for the feeding-in of compressed air made available by an external compressed air source  18 . Furthermore, at least one electro-mechanical interface  22  for exchanging electrical signals and for feeding in electrical energy required for operating the electric components of the vacuum generating unit  2  is located on the main housing  3 . In this connection it is possible to connect an external electronic control device  23 , schematically indicated in  FIG. 1 . 
     The vacuum required for gripping an object  5  is directly generated in the vacuum generating unit  2 . To this end, the latter is equipped with at least one ejector device  27  and contains at least one suction nozzle  26  operating in accordance with the ejector principle, whose inlet  29  is connected via an air supply conduit  32  with the air supply interface  17 . 
     The ejector device  27  furthermore has an outlet  33  leading to the outside air, to which a muffler can be connected when needed. 
     Finally, the ejector device  27  has a suction side or suction opening  34 , which is connected via a suction channel  35  to the suction chamber  12  of the suction gripper  7 . 
     By way of example, a first channel section  35   a  of the suction channel  35  extends through the main housing  3  and ends at a suction line interface  6 , to which the suction line  4  is connected, preferably in a releasable manner, and in which the suction channel  35  continues with a second channel opening  35   b  as far as the suction chamber  12 . 
     An electrically operable control valve  36  has been inserted into the course of the air supply conduit  32 , and usefully has a 2/2-way functionality. It can selectively block or release the passage of air through the air supply conduit  32  in order to selectively cut off or open the air supply to the inlet  29  of the ejector device  27 . 
     A further air supply conduit which, for better distinction, is identified as blow-off conduit  38 , also communicates at one end with the air supply interface  17 , and is connected with its other end at a connecting point  28  to the suction channel  35 . Again, an electrically operable control valve has been inserted into the course of the blow-off conduit  38 , which preferably is of the same type as the already mentioned control valve  36 , but which is called the blow-out valve  37  for better differentiation. The blow-out valve  37  can selectively take up one of two positions, in which it either blocks or releases the air passage through the blow-off conduit  38 . 
     Usefully, a check valve  42  has been inserted into the course of the suction channel  35 , in particular into the first channel section  35   a . It is oriented in such a way that it permits the flow of air from the suction gripper  7  in the direction toward the ejector device  27 , but prevents it in the opposite direction. In other words, it assumes a blocking position when the pressure prevailing on the side of the ejector device  27  is absolutely greater than the pressure prevailing on the side of the suction gripper  7 . 
     The check valve  42  is seated in that section of the suction channel  35  extending between the suction opening  34  and the connecting point  28 . 
     Finally, a pressure detection installation  24  is connected to the suction channel  35 , which makes possible the detection of the pressure prevailing in the suction channel  35 , and therefore also of the vacuum existing therein. In particular, the pressure detection installation  24  is a pressure sensor which converts the pneumatic pressure into electrical pressure signals and sends them, via a signal line  25  indicated in dashed lines, to an electronic regulating device  14 , which is preferably a component of the vacuum generating unit  2 . 
     Usefully, the pressure detection installation  24  is connected to the suction channel  35  at a connecting point  30 , located between the check valve  42  and the suction gripper  7 . In this way the vacuum existing in the suction channel  35  is dependably detected, even if the ejector device  27  is switched off and the suction opening  34  is in connection with the atmosphere via the outlet  33 . The connecting point  30  is preferably located inside the vacuum generating unit  2 , but it can also be placed outside of it, for example in the suction line  4 , or directly in the suction gripper. 
     The control valve  36  and the blow-out valve  37  are usefully magnetic valves, however, their design as piezo-valves is also conceivable. They are usefully of the type “normally closed”, so that in the electrically non-activated state they assume the closed position, blocking the associated channel. However, the control valve  36  can also of the “normally open” type. Also conceivable is the employment of a bi-stable control valve (impulse valve). 
     The control valve  36  and the blow-out valve  37  receive their actuation signals via respectively at least one electrical control line  47 ,  48 , by means of which they are connected to the already mentioned electronic regulating device  14 . 
     Furthermore, the electronic regulating device  14  is in connection with the electro-mechanical interface  22  via at least one signal transmission line  43 , and usefully also via an energy-transmitting line  44 , which transmits electrical energy, and can communicate in this way with the external electronic control device  23 . 
     The object  5  grasped by suction, indicated in dash-dotted lines, is held in place as a result of the vacuum created by means of applying suction to the suction chamber  12 . To release it again, the vacuum in the suction chamber  12  is cancelled. This occurs by opening the blow-out valve  37 , in that compressed air, which is under atmospheric overpressure, is fed into the suction channel  35 . The ejector device  27  is bypassed here. 
     In what follows, a preferred mode of operation of the vacuum generating device  1  is described, along with a supplemental description of further functionalities and equipment characteristics of this device. This takes place by making reference to the diagram represented in  FIG. 2  which, making reference to the curve  52  represented in a solid line, represents the time-dependent course of the vacuum p existing in the suction channel  35  at the connecting point  30 . Here, the zero point of the ordinate corresponds to the atmospheric pressure. 
     At an arbitrary time t 0 , atmospheric pressure exists in the suction channel  35 . In this case the ejector device  27  is deactivated, because the control valve  36  assumes the closed position. Here the blow-out valve  37  is also in the closed position. 
     In order to subsequently lift an object  5 , the suction gripper  7  is placed with its work opening  8  against the object  5  and the ejector device  27  is activated. The latter takes place by switching on the air supply of the inlet  29  by switching the control valve  36  into the open position. As a result of this a vacuum is slowly built up in the suction channel  35  in accordance with the first curve section  52   a  in  FIG. 2 . In this case the ejector device  27  remains in operation until the vacuum existing in the suction channel  35  has reached an upper switching value p so . At this time t 1 , the air supply for the ejector device  27  is switched off by closing the control valve  36 . 
     The electronic regulating device  14  contains memory means  53 , in which the upper switching value p so  is stored. It furthermore contains comparison means  54 , in which the vacuum detected in the suction channel  35  is compared with the upper switching value p so  by means of the pressure signals received via the signal line  25  in order to deactivate the ejector device  27  when this upper switching value has been reached. 
     With the ejector device  27  deactivated, the check valve  42  prevents an undesired decay of the vacuum in the suction chamber  12 , because it cuts it off from the ejector device  27 . 
     The pressure detection installation  24  is connected to the channel section of the suction channel  35  extending between the check valve  42  and the suction chamber  12 . To the extent to which the detection of the vacuum existing in the suction channel  35  was mentioned above, this should be understood to be the vacuum in the above mentioned channel section between the check valve  42  and the suction chamber  12 . 
     Switching off the ejector device  27  primarily takes place for saving compressed air, and therefore energy. 
     Because of leakages, which can never be completely prevented, the vacuum prevailing in the suction channel  35  slowly drops after the ejector device  27  has been switched off. This is expressed in  FIG. 2  by a falling second curve section  52   b . This pressure drop is tolerated as long as it does not endanger the holding of the aspirated object  5 . 
     A lower switching value p su  is stored in the memory means  53  of the regulating device  14 . When the pressure detected by the pressure detection installation  24  in the suction channel  35  drops to this lower switching value p su , the regulating device  14  again switches on the air supply for the inlet  29  of the ejector device  27 , so that it again starts its suction operation. In the diagram in  FIG. 2  this is the case at the time t 2 . 
     In accordance with the third curve section  52   c , as a result of this, the vacuum in the suction channel  35  again rises to the upper switching value p so , and when it has been reached, the regulating device  14  again deactivates the ejector device  27 . This is the case at the time t 3 . 
     The interval between the time t 1  and t 3  represents a regulating process. Depending on how strong the leakage is and how long an object  5  must be held, a different number of regulating processes, which follow each other, can occur. The diagram in  FIG. 2  represents two successive regulating processes. 
     The time t 4  identifies the time at which the deposit of the previously held object  5  is initiated. Here, the regulating device  14  maintains the control valve  36  in the closed position and switches the blow-out valve  37  into the open position. In accordance with the last curve section  52   d , this leads to a short-term release of the vacuum in the suction channel  35 . 
     The regulating device  14  has output means  55 , with which it can issue a previously generated electrical diagnostic signal, which provides information relevant to the leakage in the suction chamber  12 . A diagnostic signal is generated and output in particular if a regulating process, which is composed of the second and third curve section  52   b ,  52   c , occurs within a shorter time, called “regulating time” t R , than has been predetermined by a reference time value. The reference time value is stored in the memory means  53 . To make such a diagnosis possible, the regulating device  14  contains electronic regulating time detection means  56 , which detect that time which passes between the times t 1  and t 3 , i.e. the time between two immediately successive switch-off times of the air supply. 
     A comparison between the stored reference time value and the actually resulting regulation time t R  takes place in the comparison means  54 , whereupon the already mentioned diagnostic signal is generated and output via the output means  55 . 
     The regulating device  14  is in particular embodied in such a way that a diagnostic signal is generated and output if the actual regulating time t R  lies below the predetermined reference time value. Such occurrences are a sign of an excessive leakage, because the ejector device  27  is activated in shorter sequences than would be expected in the course of correct operations. 
     It is alternatively or additionally possible to also use the time span between the times t 1  and t 2  as the regulating time t R  to be compared with the reference time value, i.e. that time which passes between the shut-off of the ejector device  27  and the subsequent restarting of the ejector device  27 . This type of measuring and regulation has the advantage that the actual leakage can be better determined, because the time required for the renewed build-up of the upper switching value is not included in the calculations. 
     For example, the diagnostic signal can be output as an optical and/or acoustic signal. By way of example, for this purpose the vacuum generating device  1  is equipped with output means  55  in the form of a display  55  and a sound generator  55   b . Moreover, the output means  55  also contain an output interface  55   c , through which the diagnostic signal can be output as an electrical signal for further processing, in particular to the signal transmission line  43  and via the latter to the external electronic control device  23 . 
     The reference time value can be fixedly programmed in at the factory. However, the regulating device  14  of the exemplary embodiment also contains manually operable input means  57 , which make a variable input possible at the site, so that the value can be varied, in particular also as a function of the volume of the connected suction chamber  12 . 
     The vacuum generating device  1  can also have different interface means, which permit an external input of the various values, in particular also those which permit wireless communication. 
     The regulating device  14  preferably also offers the option of storing several reference time values simultaneously and independently of each other in the memory means  53 , which are compared with the actually detected regulating time t R . In this case the possibility then exists of generating and issuing different electrical diagnostic signals as a function of the length of the detected regulating time t R . Thus it is possible to display and/or process different diagnostic stages as a function of the intensity of the detected leakage. 
     The exemplary embodiment offers the user the possibility of personally entering the upper switching value p so  and also the lower switching value p su . Input takes place by means of the input means  57 . However, the regulating device  14  is laid out in such a way that only the upper switching value p so  can be directly entered. The lower switching value p su  is determined by the regulating device  14  itself on the basis of an hysteresis value Δp H , which can be entered via the input means  57 . The hysteresis value Δp H  defines an imaginary lower limit value p UG , which is that vacuum which, in the experience of the user, is customarily still sufficient for dependably holding an object  5 . 
     However, the lower limit value p UG  does not constitute the lower switching value p su . The latter only results from the addition of a safety pressure value Δp s  to the lower limit value p UG . 
     The safety pressure value Δp s  is stored in the memory means  53  of the regulating device  14  and is automatically added on by the latter. 
     As a whole, it is assured in this way that, independently of occurring tolerances or also of inaccurate experimental values of the user, the lower switching value p su  is of a sufficient size to dependably prevent the undesired release of the aspirated object  5 . 
     Moreover, in the exemplary embodiment the internal electronics of the regulating device  14  are designed in such a way that the upper switching value p so  and the lower switching value p su  can alternatively also be determined by a learning process, without the exact input of defined pressure values. 
     A preferred sequence of the learning or teaching process provides that initially a first suction channel pressure prevailing in the suction channel  35  is determined when the work opening  8 , and as a result the suction chamber  12  of the suction gripper  7 , are closed. Subsequently, or prior to this, a second suction channel pressure is determined with the suction gripper  7  not covered and open. Alternatively, the second suction channel pressure can also be determined in a state in which the suction gripper  7  is covered by a leaky object  5 , i.e. in particular by a damaged object, which does not tightly close the work opening  8 . Subsequently the mean pressure value is determined from the first and the second suction channel pressure. Then the lower switching value p su  is formed from this mean pressure value and a safety pressure value added to it. The upper switching value p so  is formed from the first suction channel pressure minus a further safety pressure value, which can agree with the previously mentioned safety pressure value Δp s . 
     In principle it would also be possible to set the mean pressure value and the first suction channel pressure as the lower switching value and the upper switching value, without taking a safety pressure value into consideration. 
     The already mentioned input means  57  can be used for initiating the various measurement detecting processes, and a menu guide can be displayed on the display  55   a.    
     The recited steps permit cost-effective monitoring of the leakage behavior of the vacuum generating device  1  without requiring the counting of the number of regulating processes. The number of regulating processes plays no role at all in the evaluation and the determination of the diagnostic signals.