Abstract:
There is described a method for monitoring a drive device for a defective sensor signal from a first sensor of the drive device and to a monitoring device which is suitable for this purpose. Although sensors operate reliably, sensor errors which may give rise to significant damage if they are not detected may arise. Monitoring the sensor makes it possible to increase the reliability of the drive device. The sensor signal from the first sensor is compared with a sensor signal from a second sensor in such a manner that the first sensor is monitored. In this case, the monitoring device is intended, in particular, for a sensor having a sensor disc.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2006/068584, filed Nov. 16, 2006 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2005 060 352.1 DE filed Dec. 16, 2005, German application No. 10 2006 046 283.1 DE filed Sep. 29, 2006 and German application No. 10 2006 046 286.6 DE filed Sep. 29, 2006, all of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a monitoring device for a drive device for detecting faults in a sensor of the drive device. A fault of said kind can occur particularly when the drive device is at rest but also while it is traveling. 
       BACKGROUND OF INVENTION 
       [0003]    There are machine parts, for example angle boards on lathes and hoisting cages in standard material handling systems, that are driven by means of standard electric drive devices and where the “hanging load” state can arise. The electric drive device therein has at least one electric machine that can be motor-operated and in particular also generator-operated. In the “hanging load” state a minimum moment must be exerted by the drive, meaning by the electric machine, in order to counteract the gravitational force pulling the load down. For that purpose the drive has, for example, a power converter for powering the electric machine. However, the electric machine can also be connected as a drive device directly to a supply voltage. 
         [0004]    In the event of an outage or other fault in the electric drive device it will be unable to exert the requisite moment. If no further measures are taken, a hoisting cage, for instance, may drop and put persons and objects at risk. 
         [0005]    As a safeguard against such risks, safety devices such as releasable brakes are known that will engage in the event of faults and power outages and put the hanging load into a safe state. For detecting faults of said kind it is possible to employ, for example, multi-channel, redundant safety systems and components that cause one or more safety devices to trigger. Safety devices of said kind are used advantageously not only when the drive device is at rest but also while it is operating. 
         [0006]    The transition to the safe state can, of course, be initiated only if a fault having occurred is also detected. Depending on the specific implementation and application, the fault therein needs to be detected appropriately quickly. The implementation therein relates in particular to the mechanism of a machine, wherein, for instance, transmission ratios of gears have a possible impact. 
         [0007]    There are faults that cannot be detected directly or whose detection would require complex additional measures. Examples of faults of this kind are:
   breaking of the sensor shaft, meaning of the rotationally fixed link between the drive device and a sensor device (sensor) that registers an actual position or actual rotational speed of the drive device,   malfunctions in the sensor system itself that give rise to apparently correct signals.   
 
         [0010]    Faults of said kind cannot be detected in the case of a single-channel sensor device. Sensor signals can, for example, assume a static state in the event of a fault, meaning that although the signals of the sensor are indeed correct they are following a movement of the drive device because, for instance, there is a fault in the sensor system or a fault in a coupling device between the sensor and the drive device. Breaking of a sensor shaft means, for example, that a frictional connection between a motor shaft and sensor shaft will have been lost. Apart from said possibility of a broken sensor shaft there are, though, other possibilities such as loss of the frictional connection between the sensor shaft and a code disk of the sensor. The sensor&#39;s code disk serves to generate sensor signals and is referred to frequently also as a sensor disk. 
         [0011]    Examples of known sensors are location sensors, speed sensors, and acceleration sensors. For registering location, position, linear speed, and rotational speed, sensors can be used that generate two sinusoidal or square wave signals offset by 90°. The location or rotational speed can be determined from said signals. If said sensor signals become static or the sensor shaft breaks and the drive device, which is to say the electric motor, remains in the active idling state (moment is exerted against the force due to weight, rotational speed is zero), then the sensor signals (sensor variables) will freeze unnoticed. Location and rotational speed regulators would then be in an open loop mode. In particular a control loop for regulating location, speed and/or acceleration would hence be open, so that controlled operation is no longer possible. The drive device will then be in a labile state. The slightest disturbing moments could in the case of, for instance, hoisting gear then cause a load to be dropped. 
         [0012]    While a machine is in operation, a drive device assigned thereto will continue being moved, for example, from one position to another. The assumed faults can therein be detected by observing certain controlled variables. As that is a very complex process and the risk that the sensor shaft will break or that the sensor signals will become static is assessed as being at most very slight, such additional measures for monitoring are frequently omitted. 
         [0013]    U.S. Pat. No. 4,115,958 A discloses a monitoring device for a drive device which is provided for monitoring a movement of the drive device. The monitoring device has a first and a second sensor, the second sensor being provided for monitoring the first sensor. 
         [0014]    U.S. Pat. No. 4,807,153 A discloses a monitoring device for a drive device which is provided for monitoring a movement of the drive device. The monitoring device has a sensor. The motor current and the terminal voltage of a motor of the drive device are also recorded. On the basis of the motor current, the terminal voltage and motor-specific characteristic variables (resistance and inductance), an estimated value for a motor velocity is determined so that the motor velocity determined by means of the sensor can be checked with regard to its validity. 
         [0015]    EP 0 658 832 A discloses a sensor which supplies an incremental signal on one hand and an absolute signal on the other hand so that the two signals can be mutually checked with regard to their validity. 
         [0016]    It is known from U.S. Pat. No. 6,071,477 A to connect a stepper motor to a driven shaft by means of a coupling. The rotary position of the shaft is sensed by means of an encoder. 
       SUMMARY OF INVENTION 
       [0017]    To comply with certain safety standards it is, however, no longer adequate to assess outage risks qualitatively. An object of the present invention is therefore to disclose a monitoring device for a drive device by means of which enhanced safety can be achieved, with attention needing to be paid in particular to a simple implementation of these measures. As the probability that the sensor shaft will break or the sensor signals will become static is scarcely calculable and because having to include the sensor itself in a quantifying process is to be avoided for reasons of cost and effort, there is a need also to be able to recognize these highly improbable fault sources. What is also required, for example, by the new IEC 61508 safety standard while safety is being considered is a qualified calculation of breakdown probability which makes it necessary to assess the probability of failure quantitatively. 
         [0018]    The object of the invention can be achieved by means of a monitoring device for a drive device for detecting an erroneous sensor signal having the features as claimed in an independent claim. The dependent claims relate to advantageous inventive developments of the invention. 
         [0019]    The object of the invention can be also achieved by means of a monitoring device for a drive device which is provided for monitoring a movement of the drive device, wherein the monitoring device has a first sensor and a second sensor, the second sensor being provided for the purpose of monitoring the first sensor. The first sensor is mechanically coupled to a motor shaft by means of a coupling. The coupling has a driving side and a driven side. The first sensor is assigned to the driven side and the second sensor to the driving side of the coupling. 
         [0020]    In an advantageous embodiment of the monitoring device the first sensor has a sensor disk which is coupled to a sensor shaft by means of a form-fit link. Faults due to detached connections between the sensor disk and sensor shaft, established, for example, by means only of an adhesive link, can be reduced through the embodiment of the form-fit link. 
         [0021]    The sensor disposed on the driven side is preferably a highly accurate sensor compared with the sensor disposed on the driving side of the coupling. 
         [0022]    To reduce the failure probability of the monitoring device it is furthermore advantageous for the driving side of the coupling to be linked to a motor shaft in a form-fit manner. Said form-fit link can be realized by means of, for instance, a slot-and-key combination. 
         [0023]    It is also advantageous, for example, for the first and second sensor to be disposed in a common housing. The fault probability will be reduced thereby and it will require less effort to encapsulate the sensors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0024]    Further advantages and specifics will emerge from the following description of exemplary embodiments in conjunction with the drawings, in which: 
           [0025]      FIG. 1  schematically shows a monitoring device having two sensors, 
           [0026]      FIG. 2  schematically shows a signal flow in the case of a monitoring method for monitoring an erroneous sensor signal of a drive device, and 
           [0027]      FIG. 3  schematically shows an exemplary application for a drive device. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0028]    The schematic according to  FIG. 1  shows a drive device  1 . The drive device  1  has an electric machine of which only the end plate  31  (end plate on the operating side of an electric machine), a bearing  24  constituting a motor bearing, and a motor shaft  21  are shown in  FIG. 1 . The schematic according to  FIG. 1  also shows a first sensor  3  and a second sensor  7 . The first sensor  3  has a sensor shaft  6 , a sensor disk  4  (code disk) and a signal processing device  13 . The signal processing device  13  is provided for processing the signals that can be generated by means of the code disk (sensor disk)  4 . The sensor disk  4  is placed on the sensor shaft  6 , the sensor shaft  6  being mechanically linked to a coupling  15 . The mechanical link is, for example, a snug or press fit. The sensor disk  4  is advantageously mechanically coupled to the sensor shaft  6  by means of a form-fit link (not shown). The coupling  15  has a driving side  17  and a driven side  19 . The driving side  17  and driven side  19  are mutually mechanically coupled by means of an elastic connecting part  18 . The driving side  17  is the coupling part that is mechanically linked on the motor side to the motor shaft  21 . A mechanical link of said type can be realized by means of, for example, a slot-and-key connection. According to the embodiment shown in  FIG. 1  the slot  25  and key  27  of the slot-and-key connection can be integrated in the motor shaft  21 . The driven side  19  of the coupling  15  relates to the coupling part on the sensor side. Said coupling part on the sensor side is mechanically linked to the sensor shaft  6 . A rotational movement or a position of the driven part  19  of the coupling  15  can be registered by means of the first sensor  3 . A movement of the coupling part on the motor side, meaning of the driving side  17  of the coupling  15 , can be registered by means of the second sensor  7 . That can be achieved, for example, economically by means of a magnetic sensor that detects claws of a claw coupling. The second sensor  7  advantageously has a data link to the first sensor  3 . The sensor signal of the first sensor  3  can then be evaluated with reference to the sensor signal of the second sensor  7  in the signal processing device  13 . An evaluation signal can be conveyed by means of, for example, a data cable  33  enabling a data link to a control and/or regulating device  11 . In a further embodiment the signals of the first and second sensor  3 ,  7  are compared in the control and/or regulating device  11  itself, with there being a direct or indirect data link to said control and/or regulating device  11 . That variant is not, though, shown explicitly in  FIG. 1 . 
         [0029]    The gap that exists in the prior art in monitoring the drive device  1  can be closed and hence improved fault monitoring realized by means of a monitoring device shown for a drive device  1 . That is regardless of whether an elastic coupling (for example claw coupling) or a rigid coupling to the motor shaft  21  has been realized as the coupling. 
         [0030]    According to the prior art the sensor disk (code disk)  4  is usually glued to the sensor shaft  6 . According to the invention, however, in one embodiment the sensor disk  4  is linked to the sensor shaft  6  by means of a form-fit connection, since in that way, for example, a frictional connection established between the sensor shaft  6  and sensor disk  4  can be additionally improved by way of a clamping device, a press fit or suchlike. A slot-and-key connection is an example of a form-fit link. 
         [0031]    Three sites can advantageously be improved in terms of their fault characteristics. Those are, firstly, the link between the driving side of the coupling  15  and the motor shaft  21 , secondly, the opposite driven side of the coupling  15 , meaning the link between the first sensor  3  and the coupling  15 , and, thirdly, the link of the sensor disk  4  with reference to the sensor shaft  6 . Links of said type can advantageously be embodied by means of a form-fit connection. The use of form-fit links in said areas is independent of the use of a first and second sensor  3 ,  7 . 
         [0032]    According to the schematic shown in  FIG. 1 , only one form-fit link is provided to connect the motor shaft  21  to the driving side  17  of the coupling  15 . Claws  53  of the coupling part on the driving side are additionally scanned by means of a simple magnetic sensor, in the present example the second sensor  7 . Additional position signals arise as a result. Regarding the position at which said signals are generated there is an expectation in terms of the position generated in the first sensor  3 . If the expectation is not met, it means there is a fault in the form of, for example, a broken sensor shaft or sensor signal that has become static. Whether the expectation has been met can be checked either in the electronics of the first sensor  3 , meaning in the signal processing device  13 , or in the control and/or regulating device  11 . The control and/or regulating device  11  is provided for, for example, regulating the rotational speed or position of the electric machine. The sensor signals can also be checked in the moving state. Depending on how the arrangement has been specifically implemented, a fault will be detected after one revolution at the latest. 
         [0033]    It is advantageous to use only a simple additional sensor as the second sensor  7  because account can then be taken both of the requirement for monitoring and of the requirement for a simple structure. Said second sensor  7  can advantageously be embodied such that it only has to supply one signal per revolution. It is not in all cases necessary to detect the direction of rotation. A change of slope will basically suffice for detecting a fault. 
         [0034]    In an advantageous embodiment of the invention the second sensor  7  scans a mechanical part that is already present. That is so in the case of, for instance, a coupling  15  that has claws  53 . The claws  53  are advantageously linked to the motor shaft  21  in a form-fit manner, or the motor shaft  21  has contours that can be detected and scanned by means of the second sensor  7 . A form-fit link between the driving side  17  of the coupling  15  and the motor shaft  21  will not be necessary if the motor shaft  21  is scanned by the second sensor  7  precisely because the motor shaft  21  itself will be scanned by the second sensor  7 . Although not shown in  FIG. 1 , that embodiment variant is easy to understand because appropriate contours in the motor shaft  21  can easily be realized by means of furrows or grooves. 
         [0035]    In a further embodiment variant (not shown) the second sensor  7  is integrated in the electric machine itself. That means that the second sensor  7  is located not, as shown, in the sensor housing  8 , and so subsumed on the driven side in terms of the end plate  31 , but in the housing of the electric machine, with a part of the housing of the electric machine being embodied by the end plate  31 . 
         [0036]    According to the invention a capacitively, inductively, optically, magnetically, etc. operating sensor can be used as the sensor. Wherever the second sensor  7  is positioned in or on the electric machine, it must be insured that it is mounted on a part of the electric machine that has a secure mechanical link to the motor shaft  21 . 
         [0037]    The schematic according to  FIG. 2  shows a signal flow of the sensor signals  5  and  9  generated by the first sensor  3  and second sensor  7  respectively. The sensor signal  5  generated by the first sensor  3  is compared in the signal processing device  13  with the sensor signal  9  generated by the second sensor  7 . If a differential value of the signals  5 ,  9  exceeds a certain threshold, for example, a fault signal  35  can be forwarded to the control and/or regulating device  11 . The comparison can advantageously be performed also within the control and/or regulating device  11  itself if the sensor signals  5  and  9  are conveyed directly to the control and/or regulating device  1 . That is not, though, shown in  FIG. 2 . It is possible depending on the generation of a fault signal  35  to apply a brake, for example, or a pulse inhibitor in the case of a power converter. 
         [0038]    The schematic according to  FIG. 3  shows an exemplary application for a drive device which has a monitoring device  23 . The representation according to  FIG. 3  shows the control and/or regulating device  11  that is used for controlling or regulating an electric machine  41 . The control and/or regulating device  11  is assigned to a power section  51 . An intermediate direct current circuit can be connected by means of the power section  51 , with the electric machine  41  being powered by means of a three-phase alternating current supply  37 . The electric machine  41  is provided for moving a weight  47 , with the weight  47  hanging via a cable  45  from a cable drum  43 . The cable drum  43  is connected via a drive shaft  49  to the electric machine  41 . The rotation of the electric machine  41  is monitored via both the second sensor  7  and the first sensor  3 . Monitoring is necessary in particular because the first sensor  3  is linked via a coupling  15  to the electric machine  41 . The first sensor  3  and second sensor  7  are both linked via a data cable  33 ,  34  to the control and/or regulating device  11 , with a signal processing device  13  being integrated inside the control and/or regulating device  11  by means of which the first sensor  3  can be monitored by the second sensor  7 . 
         [0039]    In an embodiment variant in which, as shown in  FIG. 1 , the first sensor  3  and second sensor  7  are integrated inside a common sensor housing  8  there is the advantage that a separate second sensor will not have to be additionally mounted so that fault sources will be reduced thereby. It is furthermore unnecessary according to an embodiment variant of said kind for any rotational or linear means to be provided by a user of the monitoring method or monitoring device  11  for the second sensor  7  for scanning purposes. A further advantage of the integration inside one sensor housing  8  is that a high degree of protection can be realized in a simple manner or that no additional connecting means will need to be kept ready.