Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B19/00—Testing; Calibrating; Fault detection or monitoring; Simulation or modelling of fluid-pressure systems or apparatus not otherwise provided for
  • F15B19/005—Fault detection or monitoring
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B20/00—Safety arrangements for fluid actuator systems; Applications of safety devices in fluid actuator systems; Emergency measures for fluid actuator systems
  • F15B20/008—Valve failure

Definitions

• the present invention relates to a fluid power system for safety-oriented control of at least one fluid power actuator, with at least one local control device for controlling the fluid power actuator via control means of the fluid power system, at least one sensor for transmitting at least one item of information about at least one operating state of the fluid power system the local control device is provided
• the invention further relates to a fluid power actuator, a local control device for a fluid power system, a software module for a local control device of a fluid power system, and a method for operating a fluid power system.
• An electrical control device controls the flow of the pressure medium to actuate the fluid power actuator or actuators via control means, for example valves.
• On such an actuator is, for example, a working cylinder.
• the respective operating state of the fluid power system is monitored with the help of a sensor.
• a position sensor system can be attached to the fluid power actuator, which provides the control device with information about the respective position of the actuator, so that it can influence the position of the actuator, for example, based on the information by suitably applying the pressure medium to the actuator.
• a fluid technology system for safety-oriented control of at least one fluid power actuator with at least one local control device for controlling the fluid power actuator via control means of the fluid power system, at least one sensor for transmitting at least one item of information about at least one operating state of the fluid power system is provided to the local control device, characterized in that the local control device is designed such that it can evaluate at least one piece of information for determining at least one safety-critical state and that it carries out at least one predetermined follow-up action when the at least one safety-critical state is present.
• the object is further achieved by a fluid power actuator according to the technical teaching of claim 16, a control device according to the technical teaching of claim 17, a software module according to the technical teaching of claim 18 and a method according to the technical teaching of claim 19.
• the invention is based on the idea of integrating safety functions into the fluid-technical system for controlling the actuator which meet simple and also high so-called requirement classes, for example the European standard EN 941-1.
• the fluid power actuator can be, for example, a valve arrangement, a pneumatic drive or a maintenance unit.
• the control means can consist, for example, of a valve arrangement which is controlled by an electronic control module as a local control device. If a safety-critical malfunction occurs within the control means, the local control device or on the controlled fluid power actuator, the local control device recognizes this problem and triggers a follow-up action to remedy it. The local control device ensures that a safety-critical state does not go undetected.
• the monitoring of the safety function can be optimally matched to the respective fluid technology system, in particular also to the actuator to be controlled. Any existing sensors can also be used for safety functions. However, it is also possible that with the help of some additional sensors, higher security criteria can be met.
• the fluid power system can be used as a complete, compact and prefabricated unit that already has integrated safety functions that can interact, for example, with a higher-level control device. This then does not need to be elaborately coordinated with the locally required safety functions.
• the local control device can also send and receive messages specially designed for reporting safety-related information and for issuing safety-related commands.
• the safety-oriented fluid technology system according to the invention can be designed as part of a fluid technology actuator.
• the fluid power system can be integrated into a locally controlled valve arrangement, which can be a single valve or a valve group, that is to say a so-called valve island.
• the safety-oriented fluid technology system according to the invention can be part of a fluid power drive, for example a pneumatic gripper, a pneumatic cylinder or a pneumatic linear drive.
• a switch-on valve, a maintenance device e.g. an oiler, or a "Pneumatic emergency stop” can be controlled in a safety-oriented manner by means of an external or integrated fluid technology system according to the invention.
• check valves integrated in a pneumatic cylinder can also be controlled in a safety-oriented manner according to the invention.
• the control device can check information provided by a sensor for monitoring the movement speed of the actuator to determine whether a predetermined movement speed of the actuator has been exceeded.
• the sensor can even be used for several functions, on the one hand for controlling the movement speed to a predetermined one and on the other hand for monitoring whether the actuator has exceeded a safety-critical movement speed.
• the local control device After the local control device has determined the presence of a safety-critical state, it can, for example, follow the fluid power actuator as a follow-up action
• Control taking a safe operating state e.g. trigger a so-called "emergency stop” function in which the actuator is stopped.
• the local control device can signal the presence of the safety-critical state, for example via a light-emitting diode or a loudspeaker, and thus a fault Ease of searching by an operator. Furthermore, the local control device can send a message to a higher-level control device about the presence of the safety-critical state if the local control device acts, for example, as a so-called “slave” on a bus and is controlled and monitored by the higher-level control device working as a “master”. It is also possible for the higher-level control device to instruct the local control device to control the fluid-technical actuator in a safe operating state, that is to say, for example, for the "emergency stop" function already mentioned.
• the fluid power system has shutdown means that can be controlled by the local control device, in particular fluidically and / or electrically actuated shutdown means for turning off the active function of the control means on the fluid power actuator.
• the shutdown means are, for example, check valves connected between the control means and the actuator. It is thus possible for the control means to be switched off and thus decoupled from the actuator if an error occurs in the control means. For example, a valve may be leaking, so that the actuator may be in an undefined, undesired position.
• the local control device can determine such an error, for example, by means of control checking means, for example pressure sensors, which cooperate with it to check the control means.
• the switch-off means make it possible for the local control device to at least partially switch off the active function of the control means with the aid of the switch-off means, and then to check the control means.
• the control means can then be actuated without undesirably influencing the actuator and, for example, run through a test cycle. Such a test cycle is run through, for example, before actuation of the control means, so that the control means are only used to actuate the actuator if they function correctly.
• the control means can also be checked cyclically, so that correct functioning of the control means is ensured if necessary even if they have not been used for a long time.
• the switch-off means are also checked, for example by Sensors are arranged on the switch-off center, record the changes in state of the switch-off means and report them to the local control device.
• the local control device determines whether the reported changes in state correspond to predetermined, expected changes in state or whether there is a malfunction of the shutdown means, possibly a safety-critical one.
• the local control device can then report this malfunction to the higher-level control device, for example, or trigger an "emergency stop" function.
• the control device can also check the switch-off means cyclically or after actuation of the control means or the switch-off means.
• the fluid control system can also be instructed by the higher-level control device with a check instruction to check the control means and also the switch-off means cyclically or in each case per received check instruction.
• FIG. 1 shows a first exemplary embodiment of the invention with a fluid power system that is controlled by a local control device and acts on a working cylinder,
• FIG. 2 shows a table with a test sequence of the exemplary embodiment from FIG. 1 with the working cylinder retracted
• Figure 3 is a table as in Figure 2 with another
• FIG. 4 shows a second exemplary embodiment of the invention, with components that have been partially modified or missing in comparison to FIG. 1.
• FIG. 1 shows a working cylinder 10 as a fluid power actuator with a piston 11 and a piston rod 12, which can move back and forth in a working space 13.
• a fluid as the pressure medium in the present case compressed air, can flow into the working space 13 via a line 14 opening on the bearing cover, the end face of the working space 13 facing the piston rod 12.
• the piston 11 "retracts", ie the piston rod 12 moves into the working space 13 when, on the opposite end facing the piston surface of the piston 11, the end cover of the working space 13 is displaced by the moving piston 11 via a line 15 Air can escape, the work space 13 is vented.
• the piston 11 If compressed air flows into the working space 13 via the line 15, the piston 11 "extends", ie the piston rod 12 moves out of the working space 13, provided that air can escape via the line 14.
• a sensor 16 detects whether the piston 11 is extended and a sensor 17 detects whether the piston 11 is retracted.
• the working cylinder 10 it is also possible, for example, to use a linear drive, a maintenance unit for processing compressed air or a pneumatically controlled valve as the fluid-technical actuator.
• the line 14 can be blocked via a directional valve 20, the line 15 via a directional valve 21, in which case neither compressed air can flow into the working space 13 nor can air displaced by the piston 11 escape from the working space 13.
• the directional control valves 20 and 21 therefore act as switch-off devices and are so-called 2/2-way valves.
• Directional valve has an inlet and an outlet, which are either separated from each other by a blocking position of the respective directional valve or are connected to one another in a passage position of the respective directional valve.
• the exit of the Directional control valve 20 is connected to line 14, the output of directional control valve 21 to line 15.
• the directional control valves 20 and 21 can be supplied with compressed air through a line 22 and then move into the open position. In the switching state in FIG. 1, the blocking position, the directional control valves 21 and 22 are not pressurized with compressed air and are each held in the blocking position by an indicated spring.
• the directional control valves 20 and 21 can, for example, also be electrically driven, can be held at rest by compressed air, or can be replaced by other valve arrangements with a shut-off effect.
• the line 22 is pressurized or vented with compressed air via a directional valve 23.
• the directional valve 23 is a 3 / 2-
• Directional control valve with a working outlet for the line 22, an inlet which is connected to a pressure source 24 and a ventilation outlet 25.
• the directional control valve 23 is shown in the ventilation position in FIG. 1 as the rest position, indicated by a spring, in which the line 22 through the ventilation outlet 25 is vented.
• the directional control valve 23 can be brought into the switching position by an electric drive 26, for example a coil drive, in which case compressed air from the pressure source 24 flows into the line 22 and the directional control valves 20 and 21 are moved into the open position.
• a pressure sensor 27 is also connected to line 22 and detects the pressure present on line 22.
• the pressure sensor 27 serves as a shutdown checking means for checking the directional valves 20, 21 and 22 acting as a shutdown means. Instead of the pressure sensor 27, sensors for position detection could also be attached to the directional control valves 20, 21 and 22 as shutdown checking means.
• a control valve 30 which in the present case is a 5/3 directional control valve with three positions, a rest position 31, a (piston) extended position 32 and a (piston) retracted position 33 and a total of five inputs, acts as control means for controlling the working cylinder 10 - / Outputs, of which an input with a pressure source 34 for supply with
• Compressed air is connected, one outlet 35 and 36 each serve for ventilation and an inlet / outlet is connected via a line 37 to the directional valve 20 and an inlet / outlet via a line 38 is connected to the directional valve 21.
• the directional control valves 20 and 22 are in the open position for the following explanation of the function of the directional control valve 30.
• the lines 14 and 37 and the lines 15 and 38 are each connected to one another.
• a drive 39 arranged on the directional control valve 30 is activated, the directional control valve 30 is moved into the extended position 32, at which compressed air flows into the lines 38 and 15 and air can escape via the lines 14 and 37 and the outlet 35.
• the piston rod 12 moves out of the working cylinder 10.
• a drive 40 which is also arranged on the directional control valve 30, is activated, the directional control valve 30 is brought into the retracted position 33, so that compressed air on the one hand flows into the lines 14 and 37 and on the other hand can escape via the lines 38 and 15.
• the piston rod 12 moves into the working cylinder 10.
• a 3/3 directional control valve could be connected to the lines 37 and 38, with each of which a ventilation, a venting and a blocking of the lines 37 and 38 is possible.
• a pressure sensor 41 is connected to line 37 and a further pressure sensor 42 is connected to line 38.
• the pressure sensors 41 and 42 act as control checking means.
• a sensor system for example in the form of limit switches, for monitoring the function of the directional control valve 30 could also be arranged as a control checking means.
• the directional control valves 20, 21 and 23, connected to each other by the line 22 and supplied by the pressure source 24, are
• Switch-off means for switching off the active function of the directional valve 30 acting as a control means.
• the functions of the directional control valves 23 and 30 are controlled by a local control device 50 via the respective drives 26 and 39 and 40.
• the local control device 50 has an input / output module 51, a processor 52, storage means 53 and interface modules 54 and 55 Connection means, which are each connected by connections, not shown.
• the local control device 50 is operated by an operating system and by software modules which are stored in the storage means 53 and whose program code sequences are operated by the
• RAM Random Access Memory
• ROM Read Only Memory
• the local control device 50 Via the interface module 54 connected to a bus 56, the local control device 50 is connected to a higher-level control device 57, from which the control device 50 can receive control commands and to which the control device 50 can send messages.
• AS-i Actor Sensor Interface
• CAN CAN bus
• Profibus a Profibus.
• the higher-level control device 57 is a bus master in the present example, while the local control device 50 is a bus slave. It is also possible for the local control device 50 to be used without the higher-level control device 57 or for further valves or drives to be connected to the control device 50.
• the higher-level control device 57 can also be omitted entirely.
• the local control device 50 can also be connected to the higher-level control device 57 via digital inputs and outputs.
• the interface module 55 is connected to a display and command input module 59 via connecting lines 58. From the display and command input module 59, the control device 50 can receive control commands entered, for example, via electric hand switches.
• the control device 50 can output to the module 59 messages which the module 59 can display, for example, via light-emitting diodes. It is also possible for the module 59 to be integrated in the control device 50 or to be omitted entirely.
• the input / output module 51 is connected to the drive 39 via a connection 61, to the drive 40 via a connection 62 and to the drive 26 via a connection 63.
• the control device 50 can activate the respectively connected drives via the connections 61, 62 and 63.
• the pressure sensor 41 reports via a connection 64, the pressure sensor 42 via a connection 65 and the pressure sensor 27 via a connection 66 the respectively detected pressure values to the input / output module 51 and thus to the control device 50.
• the sensor 16 also transmits via a Connection 67 and the sensor 17 via a connection 68 to the control device 50 each of the values recorded on the working cylinder 10.
• the (monitoring) connections 64, 65, 66, 67 and 68 and the (control) connections 61, 62 and 63 can be discrete lines or can also run over a bus.
• FIG. 1 An exemplary test cycle for checking the safe functioning of the arrangement from FIG. 1 is shown below with reference to FIGS. 2 and 3.
• Figures 2 and 3 each show a table, in the left, with "ST" column of test or work steps are entered.
• the rest position 31, the extended position 32 and the retracted position 33 of the directional control valve 30 for actuating the working cylinder 10 are shown in the columns labeled "31", “32” and “33".
• "0" in the columns "31", “32” and “33” means that the directional control valve 30 has not assumed the respective position.
• "0-» 1 "in column” 32 means that the drive 39 is activated and the directional valve 30 assumes the extended position 32 and has reached" 1 ".
• Values entered in the column "31" indicate whether the directional control valve 30 has assumed the rest position 31 ("0—» l ”) (" 1 ") due to spring force and not activating the drives 39 or 40 leaves ("l-» 0 ”) or has already left (“ 0 ").
• the columns “20”, “21” and “23” should be read in the same way as the columns “32” and “33".
• the directional control valves 20 and 21, the actuation of which is shown by the compressed air on line 22 in the columns “20” and “21”, are in the rest position, ie in the blocking position ("0"). If the drive 26 is activated by the control device 50 ("0-» l "), the directional control valve 23 goes into the switching position (" 1 "). This also Tile 20 and 21 controlled and go into the open position ("1").
• FIG. 2 shows a test cycle starting with a step 200 with the piston 11 completely “retracted”.
• the sensor 17 gives the signal “1", the sensor 16 the signal “0".
• the pressure sensor 41 is there hence the signal "1” while the pressure sensor connected to the currently vented line 38 outputs "0".
• a step 201 the working cylinder 10 is first separated from the lines 37 and 38 leading to the directional control valve 30 and thus from an undesired pressurization and ventilation.
• the control device 50 controls the directional control valve 23 to take the venting position, so that the line 22 is vented, the pressure sensor 27 reports pressure going to "0" ("1- ⁇ -O") and the directional control valves 20 and 21 move into the blocking position ("1-0").
• pressure sensors 41 and 42 give an undefined signal "X".
• the directional control valves 20 and 21 and the pressure sensors 41 and 42 are then checked in a step 202. Since the directional control valves 20 and 21 are in the blocking position, the directional control valve 30 can now be actuated without influencing the working cylinder 10. For this purpose, the control device 50 activates the drive 39 and deactivates the drive 40, so that the directional control valve switches from the retracted position 33 to the extended position 32, and the pressure sensor 42 flows into the line 38
• the pressure sensor 41 reports a signal changing from “1” to "0" because of the now venting line 37. If this is not the case, there is an error that the control device 50 recognizes and reports, for example, to the higher-level control device 57.
• the directional control valve 30 is then brought into the rest position 31 by the control device 50 also deactivating the drive 39.
• the lines 37 and 38 and thus also the chambers of the working cylinder 10 are then separated from a pressurization or ventilation both by the directional control valves 20 and 21 and by the directional control valve 30.
• the directional control valve 23 and, depending on this, the directional control valves 20 and 21 can be activated in step 204 without any further effect on the working cylinder 10.
• Their respective control signals go from “0" to "1", as does the value measured by pressure sensor 27. If this is not the case, there is an error in the shutdown means, which the control device 50 recognizes.
• sensors connected to the control device 50 are arranged in the directional control valves 23, 20 and 21, the signals of which the control device 50 checks in step 203. If an error occurs during this, the control device 50 can infer a safety-critical state and take a countermeasure, for example preventing further actuation of the directional valve 30.
• step 204 the directional valve 20 goes into the open position, compressed air located in the working cylinder 10 on the bearing cover side and in the line 14 can flow into the line 37, so that the pressure sensor 41 signals changing values from “0” to "1", the values to be expected from the control device 50 are monitored and, if they are not present, the control device 50 determines a safety-critical state. If step 204 has been processed without errors, the control device 50 controls the directional control valve 30 again in the retracted position 33 in a step 205 by activating the drive 40, that is to say by giving an actuating signal which changes from "0” to "1". As a result, line 15 is vented via line 38 and vent outlet 36; pressure sensor 42 reports values that change from "1" to "0” during trouble-free operation.
• test cycle with the "retracted” working cylinder 10 thus ended.
• Such a test cycle can be repeated at any time even when the working cylinder 10 is not moving, for example at fixed time intervals, and also, for example, after the working cylinder 10 has been “retracted” or before the working cylinder 10 is “extended”.
• Such an “extension process” is shown in a step 206.
• the control device 50 activates the drive 39 by giving an actuating signal that changes from "0" to "1".
• the control device 50 deactivates the drive 40, so that the line 14 is vented via the line 37 and the vent outlet 35 and the pressure sensor 41 reports values that change from “1" to "0" during trouble-free operation, while the lines 38 and 15 are pressurized with compressed air, the pressure sensor 42 reports values changing from “0” to "1” and the piston 11 "extends” from the working cylinder 10.
• the sensor 16 reports a signal "1"
• the sensor 17 a signal "0”.
• the extended end position then reached is at the same time the starting position shown in FIG. 3, referred to there as step 300.
• a test cycle can also be run through in the extended end position, as shown below.
• step 301 corresponding to step 201 and having the same effect, first the working cylinder 10 is separated from the lines 37 and 38 leading to the directional control valve 30 and thus from an undesired pressurization and ventilation.
• a step 302 corresponding to step 202 the directional valves 20 and 21 and the pressure sensors 41 and 42 are then checked.
• the directional control valves 20 and 21 are in the blocking position and the directional control valve 30 can therefore be switched by the control device 50 from the extended position 32 into the retracted position 33 without influencing the working cylinder 10.
• the control device 50 activates the drive 40 and deactivates the drive 39, so that the pressure sensor 41 changes from “0" to "1” due to compressed air flowing into the line 37, and the pressure sensor 42 switches from “0" to "1” due to the now venting. 1 "signal changing to" 0 "signals. If this is not the case, there is a safety-critical error which the control device 50 recognizes and, for example, controls a warning light-emitting diode on the display and command input module 59.
• control device 50 also deactivates the drive 40, so that the directional control valve 30 goes into the rest position and the lines 37 and 38 are neither vented nor vented can be pressurized externally. Then, in a step 204, the directional control valve 23 and, depending on this, the directional control valves 20 and 21 can be reactivated and thereby go into the open position, so that there are still in the working cylinder 10 on the end cover side and in the line 15
• Compress compressed air into line 38 and the pressure sensor 42 signals values that change from "0" to "1". These are monitored by the control device 50 as expected values, so that the control device 50 reports a safety-critical error in the event of a fault.
• a step 305 the control device 50 activates the drive 39 again, so that the directional control valve 30 returns to the extended position and compressed air located in the lines 14 and 37 can escape.
• the pressure sensor 41 then reports values changing from "1" to "0". This test cycle, which has now been completed, can also be repeated at any time.
• Step 306 shows how the piston 11 can be "retracted” again.
• the drive 39 is deactivated, the drive 40 activated.
• the pressure sensor 42 reports falling pressure values by venting, the pressure sensor 41 reports rising pressure values by the application of compressed air.
• the sensor 17 outputs the signal "1", the sensor 16 the signal "0".
• the control device 50 can independently carry out the test steps shown in FIG. 2 and FIG. 3 according to predetermined criteria, for example those defined by configuration data. It is also possible that the control device device 50 on the display and command input module 59 or from the higher-level control device 57 a command to carry out the test steps is given. Furthermore, the control device 50 can also receive a safety-oriented command from there, in which the control device 50 is instructed to end a safety-critical state, for example by the control device 50 bringing the directional control valves 20 and 21 into the blocking position.
• FIG. 4 essentially shows the arrangement known from FIG. 1, the same or equivalent components being provided with the same reference symbols.
• the components used as shutdown means in particular the directional control valves 20, 21 and 23 together with lines, and the pressure sensor 27 used as shutdown checking means are no longer included.
• the sensor 17 is also omitted, while the sensor 16 is now designed as a distance sensor which detects the distance of the piston 11 from the bearing cap of the working cylinder 10.
• a pressure sensor 70 is shown, which detects the pressure of the compressed air supplied by the pressure source 34 and led via the line 69 to the directional control valve 30 and reports it to the control device 50 via a connection 71.
• the control device 50 can set the pressure fed into the line 69 from the pressure source 34 via a throttle valve 72 which is connected to the input / output module 51 via a control connection 73.
• the throttle valve 72 is therefore part of the control means.
• the control device 50 determines the movement Direction of the piston 11, by controlling the throttle valve 72, its holding forces and its speed of movement.
• the control device 50 can determine the movement speed on the basis of the distance of the piston 11 from the bearing cover, which distance is measured by the sensor 16 and changes when the piston 11 moves.
• the control device 50 reduces the pressure on the line 69 via the throttle valve 72; if the speed of movement is too low, it increases the pressure.
• a defect can now occur on the throttle valve, so that, for example, compressed air acts on the piston 11 at an unimpeded high pressure and the piston 11 is moved at a destructive speed.
• the control device 50 detects such a safety-critical state with the aid of the sensor 16 and therefore controls the directional control valve 30 into the rest position 31 in an “emergency stop function”, so that the working space 13 is separated from the pressure source 34 and at the same time is prevented from venting and therefore the piston 11 is braked.
• the control device 50 can recognize this and cause a subsequent reaction to remedy it. If, for example, the directional control valve 30 is in the extension division 32, the pressure sensor 42 and the pressure sensor 70 must determine corresponding pressure values which are significantly higher than the values measured by the pressure sensor 41 as a result of the venting of the line 14. If this is not the case, the control device 50 recognizes this problem and signals the problem in a safety warning message to the higher-level control device 57. The latter can then, for example, instruct the control device 50 in a safety emergency command to completely close the throttle valve 72.
• control device 50 may control a subordinate control device (not shown) in a safety-oriented manner in the manner shown and e.g. locks the working cylinder 10 in an "emergency stop function" in response to a warning message sent by the latter.

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• 2000
  • 2000-02-12 DE DE10006367A patent/DE10006367A1/de not_active Withdrawn
• 2001
  • 2001-01-20 WO PCT/EP2001/000624 patent/WO2001059307A1/fr active IP Right Grant
  • 2001-01-20 JP JP2001558617A patent/JP2003522909A/ja active Pending
  • 2001-01-20 DE DE50105536T patent/DE50105536D1/de not_active Expired - Lifetime
  • 2001-01-20 EP EP01923550A patent/EP1266147B1/fr not_active Expired - Lifetime
  • 2001-01-20 US US10/182,489 patent/US6769250B2/en not_active Expired - Fee Related
  • 2001-01-20 AT AT01923550T patent/ATE290654T1/de active

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