Abstract:
The invention relates to a method of handling faults and preventing damage to or from machine tools, production machines, and robots, having individually driven machine elements. Process information is exchanged between the drives (A 1 -A 6 ) via at least one data link (AB 1 , AB 2 , LB, Q), with the result that a drive braking function and/or a system standstill is initiated after detection of a faulty drive (A 1 -A 6 ), and the actual values (G 1 , G 2 , of the faulty drive (A 1 -A 6 ) are transmitted as nominal values to the faultlessly operating drives (A 1 -A 6 ) involved.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a method of handling faults and preventing damage to machine tools, production machines, and robots, hereinafter machines, which have individually driven rotating machine elements.  
         BACKGROUND OF THE INVENTION  
         [0002]    EP 0 687 395 B1 discloses a method of preventing damage on numerically controlled machines in the event of a power failure. It discloses how, in the event of a power failure, a supply voltage for at least one axis drive motor is obtained from the kinetic energy of at least one other axis drive motor to effect a position-controlled, programmed emergency return traverse.  
           [0003]    EP 0 583 487 B1 discloses a method of braking the axis drives of numerically controlled machines optimally in terms of time and without deviating from their path. In these machines, emergency braking of the axis drives is provided for hazardous situations. If this emergency braking is triggered, the drives of the numerically controlled machine are braked linearly in the shortest time by the nominal rotational speed values being correspondingly prescribed. With time-optimal, path-maintaining braking it is intended to avoid collision of the tool with the workpiece or other objects when the machine deviates from the prescribed path.  
           [0004]    If a malfunction of a drive occurs in a technical process, and the drive can no longer control its associated motor, the drive idles until it is at a standstill. Even when other related drives are brought to a system standstill, this generally takes place in an uncontrolled way. Consequently, material produced or transported, or even the involved machine itself, may be damaged by the uncontrolled running down of the faulty drive or other drives.  
         SUMMARY OF THE INVENTION  
         [0005]    The object of the present invention is to initiate a standstill of a system or subsystem (machine) in the event of a drive fault, and to prescribe actual values for the faulty drive that can still be acquired as nominal values to other drives involved. According to the present invention, this object is achieved in accordance with the following method:  
           [0006]    First, an exchange of process information of an associated technical process via at least one data link;  
           [0007]    Second, initiating a drive braking function and/or a system standstill after detection of a faulty drive, and including an impermissible drive state or an unwanted machine state; and  
           [0008]    Third, transmitting, as nominal values to the faultlessly operating drives, actual values of the faulty drive or drive associated with a malfunction, which may be changed by at least one mathematical function according to process requirements.  
           [0009]    The use of this method accomplishes the following:  
           [0010]    the minimizing or avoidance of damage to the machine;  
           [0011]    the minimizing or avoidance of product damage; and  
           [0012]    shorter downtimes on account of shorter repair times.  
           [0013]    These advantages lead to a greater availability of a fully operational system, and a reduced financial burden for the system operator in the event of a fault.  
           [0014]    A preferred aspect of the present invention involves the use of a real-time communication link as the data link. A real-time communication link makes it possible for the remaining operational drives to synchronize themselves in real time with the faulty drive. Consequently, a faster synchronization of all the faultlessly operating drives with the faulty drive is possible, and also a faster response to changes in actual values of the faulty drive.  
           [0015]    A further preferred aspect of the present invention involves the use of a real-time Ethernet as the real-time data link. Consequently, a standardized, universally usable bus protocol can be advantageously used, which moreover facilitates a high transmission capacity. The use of a real-time Ethernet also makes possible short bus cycles, and consequently a rapid detection of measuring parameters, which in turn makes possible a rapid correction of nominal value preselections.  
           [0016]    The preferred application of the present invention is in machine tools, production machines, or robots having at least one individual drive in a coordinated technical process. A specific example of such a preferred application of the method of the present invention is in a printing machine, i.e. production machine, where in the event of a failure of a drive, paper build-ups and jams, as well as damage to the printing machine, are reduced or totally avoided. 
       
    
    
     DRAWINGS  
       [0017]    An exemplary embodiment of the invention is explained in more detail below and in the context of the drawings, in which:  
         [0018]    [0018]FIG. 1 shows a structural overview of various interlinked drive groups; and  
         [0019]    FIGS.  2  to  4  show actual and nominal values of a faulty drive, and also nominal values of involved drives.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    In FIG. 1, major components of a drive A 1  to A 6  are depicted in a rectangle with a broken outline. The drive comprises at least one motor M 1  to M 6 , which is activated by a drive controller AR 1  to AR 6  via power electronics LE 1  to LE 6 . This is identified by a symbol from power electronics, namely an IGBT circuit symbol (Insulated Gate Bipolar Transistor). Furthermore, each motor M 1  to M 6  has an associated sensor G 1  to G 6 . The motor M 1  to M 6  is depicted by a large circle and the sensor G 1  to G 6  is depicted by a small circle in the drive A 1  to A 6 .  
         [0021]    The drive controllers AR 1  to AR 6  of a respective drive group AG 1 , AG 2  are interlinked with one another in the form of a ring via data lines AB 1 , AB 2 . Two lines of the drive bus respectively lead into each drive controller AR 1  to AR 6 . For the sake of overall clarity, only one data line AB 1 , AB 2  of an annular data network is denoted in each case. Furthermore, a drive group AG 1 , AG 2  is depicted in each case by a large rectangle provided with a broken outline, in which at least one drive A 1  to A 6  is located. Further networking structures, feasible in terms of data technology, are conceivable, for example, a star-shaped connection of the drive controllers AR 1  to AR 6 . In each case, one drive controller AR 1  to AR 6  of a drive group AG 1 , AG 2  has master functionality AR 1 , AR 4 . This is identified in FIG. 1 by the letter M and a more pronounced outline.  
         [0022]    The data network AB 1 , AB 2  close to the drive undertakes the synchronization of the drives A 1  to A 6  of a drive group AG 1 , AG 2 . A cross communication Q makes it possible for the drive controllers with master functionality AR 1 , AR 4  to exchange data close to the drive, which are necessary for the mutual coordination of open-loop or closed-loop control actions.  
         [0023]    For each drive controller with master functionality AR 1 , AR 4 , there is a master computer L 1 , L 2 , which performs a function with higher-level control over the drives. The master computers L 1 , L 2  are connected to a master computer bus LB and can, for example, collect, evaluate and possibly display process data, and hence assume the function of a “human-machine interface”. All the data connections Q, LB, AB 1 , AB 2  may be executed by a real-time data network, such as a real-time Ethernet.  
         [0024]    The power electronics LE 1  to LE 6  of the drives A 1  to A 6  are connected to the power supply system V with the aid of a power distributor EV.  
         [0025]    If the drive A 1  of the drive group AG 1  fails on account of a malfunction, the sensor G 1  continues to transmit its actual values to the drive bus AB 1 . After detection of the malfunction of the drive A 1 , all the other drives A 2 , A 3  involved, synchronize themselves immediately to the actual values of the drive A 1  as transmitted by sensor G 1 . Thereafter, a system or subsystem standstill is initiated.  
         [0026]    The synchronizing function of the faultlessly operating drives A 2 , A 3  to the faulty drive A 1  avoids the drives A 1  to A 3  running in disparity from one another. The faulty drive assumes a master functionality with its actual values being transmitted by the sensor G 1 .  
         [0027]    Since the faulty drive A 1  will inevitably run down, all the fault-free drives A 2 , A 3  follow this rundown to the system or subsystem standstill. The synchronization of all the drives reduces or avoids incalculable states in the machine. Consequently, for example, damage to the machine is advantageously avoided.  
         [0028]    In FIG. 2 to FIG. 4, actual and nominal values of a faulty drive, along with nominal values of involved drives are represented. These are respectively assigned to a drive A 1 , A 2  and A 3  of a drive group AG 1 . An associated nominal rotational speed, is plotted on the respective Y axes, while the X axes represent time with the designation t.  
         [0029]    Up to the depicted time t 1 , the respective drives A 1  to A 3  have a nominal speed, the respective profile of which can be seen in FIG. 2, FIG. 3 and FIG. 4. Up to the time t 1 , the drive A 1  has the nominal speed characteristic A 1 S. A malfunction in the drive A 1  at the time t 1  leads to the drive A 1  running down in an undefined way. The actual speed values of the drive A 1  after failure at the time t 1  are depicted in the representation according to FIG. 2 by A 1 I.  
         [0030]    The malfunction of the drive A 1  is detected in the system at the time t 1  and all the other drives A 2 , A 3  involved immediately convert their nominal speed A 2 S, A 3 S to the actual value characteristic A 1 I of the drive A 1 . This can be seen in the representations according to FIG. 3 and FIG. 4. Since the actual value information of the drive A 1  is available in real time to the drive bus AB 1  through the sensor G 1  and the drive controller AR 1 , the drives A 2 , A 3  can synchronously follow the variations in the actual speed A 1 I of the drive A 1 . At time t 2 , the system or subsystem standstill has been reached.  
         [0031]    This procedure ensures that the drives A 1  to A 6  are synchronously coordinated with one another and consequently reduces an asynchronous running down or idling of the drives A 1  to A 6  in the event of a fault. Damage to the machine and material produced can be reduced or even avoided completely.  
         [0032]    The use of a real-time Ethernet means that a standardized, widespread and universally usable bus protocol is used, making possible a high transmission capacity. On account of short bus cycles, measuring parameters and changes in the system state can be rapidly detected, so that rapid correction of deviations from nominal values can take place.