Abstract:
In order to produce a sawing machine including a plurality of drives and a control unit which is constructed in a simple manner in regard to the control of the drive system, it is proposed that a first drive and a second drive be controlled in such a manner that they are not operable at the same time and that the first drive and the second drive be coupled to a common frequency converter.

Description:
[0001]     The present disclosure relates to the subject matter disclosed in German application No. 103 45 353.9 of Sep. 18, 2003, which is incorporated herein by reference in its entirety and for all purposes.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a sawing machine comprising a plurality of drives and a control unit.  
         [0003]     Furthermore, the invention relates to a method for controlling the drive system of a sawing machine wherein a first drive drives a sawing tool and a second drive drives a work piece carriage.  
         [0004]     Sawing machines of this type are known, for example, those of the HBP type from the company Behringer GmbH.  
       SUMMARY OF THE INVENTION  
       [0005]     In accordance with the present invention, a sawing machine of simple construction in regard to the arrangement for controlling the drive system is provided.  
         [0006]     This is achieved in that a first drive and a second drive are controlled in such a manner that they are not operable at the same time and in that the first drive and the second drive are coupled to a common frequency converter.  
         [0007]     By virtue of the solution in accordance with the invention whereby a common frequency converter is associated with the first drive and the second drive, the number of frequency converters that are needed can be minimized. One achieves cost savings thereby. Furthermore, the space needed in a switchbox or a switchgear cabinet is reduced. This also leads to a reduction in the number of heat sources in the switchgear cabinet whilst the number of electronic interference sources in the switchgear cabinet is reduced.  
         [0008]     The sawing machine in accordance with the invention is thereby of more simple construction and is more trouble-free in operation.  
         [0009]     In accordance with the invention, it is ensured that the first drive and the second drive are not activatable at the same time. This is possible for example, if the first drive is a drive for the saw and the second drive is a drive for a feed carriage for the work-pieces. The effect is thereby achieved that the frequency converter has to control at most one drive at a certain time point. In consequence, this enables a common frequency converter to be associated with the two drives.  
         [0010]     In particular, the rotational speed of the first drive and the rotational speed of the second drive are adjustable by means of the frequency converter. A frequency converter converts the mains frequency, an alternating current of 50 Hz or 60 Hz for example, in order to control the rotational speed of the relevant drive by means of the converted frequency. The torque is thereby frequency-independent over a wide speed range. In accordance with the invention, both the first drive and the second drive—but not both simultaneously—can be controlled by a single frequency converter. In principle hereby, it is also possible to control at least one further drive if this is not operated at the same time as the first drive and the second drive.  
         [0011]     In particular, the first drive and the second drive are activated at different times so that it is ensured that at most just one drive must be controlled by the frequency converter.  
         [0012]     It is most particularly advantageous, if the frequency converter controls the first drive in accordance with a first set of parameters and if it controls the second drive in accordance with a second set of parameters. A functional separation with regard to the control of the drive system can thus be achieved. Usually, different drives have different requirements as regards, inter alia, the rotational speed, the torque (as determined by the frequency and the voltage), and as regards the direction of rotation, the speed or the ramp function. By the use of a first set of parameters and a second set of parameters which are respectively adapted to the first drive and to the second drive, the effect is achieved that the respective drive that is being controlled at a certain time point will run optimally despite being controlled by a common frequency converter. Further sets of parameters could also be provided for further drives.  
         [0013]     In particular, the parameters for the first set of parameters and/or the second set of parameters are stored in the frequency converter, this thereby ensuring that the corresponding drive is controlled by the correct set of parameters. Parameters for further sets of parameters could also be stored in like manner. The parameters (corresponding to the first or second set of parameters) that are needed for a special drive can be activated by the control unit.  
         [0014]     The first set of parameters and the second set of parameters are different. Parallel control of the first drive and the second drive is thereby impossible since even different starting values, such as the voltage and the frequency, have to be set for the different drives. Due to the solution in accordance with the invention whereby it is ensured that the two drives are not operated at the same time, a common frequency converter can nevertheless be used for controlling the first and the second drive (or further drives).  
         [0015]     Hereby, at least one of the variables, voltage, frequency, direction of rotation, speed or ramp function is adapted to be set for the first drive and the second drive by means of the respectively associated sets of parameters.  
         [0016]     It is expedient, if the action of switching between the first set of parameters and the second set of parameters were to be performed by means of the control unit. Switching between control of the first drive and control of the second drive is effected in this manner. The change-over is initiated by the control unit and is effected automatically for example at a suitable time point during a machine cycle.  
         [0017]     For the same reason, it is expedient if provision is made for at least one switch or one circuit which is constructed in such a manner that at most one drive is controlled. The at least one switch or circuit may, for example, comprise a motor contactor. For example, provision is made for a respective motor contactor to be associated with the first drive and the second drive, and for ensuring that at least one of the two motor contactors is always open so that at most one of the two drives is being controlled.  
         [0018]     In particular, provision is made for the first drive to drive a tool. In the case of a sawing machine, the tool is a sawing tool. In the case of a band saw, the tool is an endless strip of saw-blading (endless saw blade). Such a band-saw blade can usually be driven independently of a feed carriage for the work-pieces so that operations of the sawing machine are possible in which the drives for the sawing tool and a feed carriage do not have to be moved together.  
         [0019]     It is expedient, if the second drive drives a carriage and in particular, drives a carriage in a conveyor device for the work-pieces.  
         [0020]     The second drive then preferably drives a feed carriage for one or more work-pieces.  
         [0021]     Furthermore, in accordance with the invention a method is provided with which the process of controlling the drive system of a sawing machine is effected in a more simple manner.  
         [0022]     In accordance with the invention, this is achieved in that the control of the first drive and the control of the second drive is effected by a common frequency converter and in that the first drive and the second drive are operated at different times.  
         [0023]     This solution in accordance with the invention has the advantages that have already been explained in connection with the sawing machine in accordance with the invention.  
         [0024]     It is ensured in a preferable manner that the first drive and the second drive are not activated at the same time. If this is possible, then it is also possible to control the two drives—but not simultaneously—by means of a common frequency converter.  
         [0025]     Further advantageous embodiments of the method in accordance with the invention have already been explained in connection with the sawing machine in accordance with the invention.  
         [0026]     The following description of a preferred embodiment serves, in conjunction with the drawing, for a more detailed explanation of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  shows a side view of an exemplary embodiment of a sawing machine in accordance with the invention and  
         [0028]      FIG. 2  shows an exemplary embodiment of a frequency converter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     An exemplary embodiment of a sawing machine in accordance with the invention, which is shown in  FIG. 1  and bears the general reference  10  therein, comprises the main frame  12  of the machine with the aid of which the sawing machine  10  is set up on a supporting base.  
         [0030]     Two guide columns  14 , which extend in the height direction  16 , are fixed to the main frame  12  of the machine. (Only one column  14  is visible in  FIG. 1 .) The guide columns  14  project above a feed plane  18  for the work-pieces. In particular, the height direction  16  is perpendicular relative to the feed plane  18 .  
         [0031]     At the upper ends thereof, the guide columns  14  are interconnected by means of a connecting element  20  thereby forming a guidance portal  22  on which a sawing framework  24  is guided such as to be displaceable in the height direction  16 . The displacement in the height direction  16  is effected by a sawing framework drive  26 . The sawing framework drive  26  is an electric drive or a hydraulic drive for example.  
         [0032]     The sawing framework  24  comprises a drive  28  for a sawing tool such as a continuous (endless) band-saw blade (which is not visible in  FIG. 1 ). The saw drive  28  drives the band-saw blade on the sawing framework  24  in a circulating (unidirectional) movement in order to enable a saw cut to be made in a work piece.  
         [0033]     Furthermore, a drive  30  for a cleaning brush, which serves to clean sawn shavings off the band-saw blade, is held on the sawing framework  24 .  
         [0034]     The drives  28 ,  30  on the sawing framework  24  are supplied with control signals and energy via lines, these lines being fed through a flexible tube  32  which enables the sawing framework  24  to be displaced in the height direction  16  on the guidance portal  22 .  
         [0035]     Furthermore, a conveyor device  34  for the work-pieces, which comprises a roller conveyer  36  incorporating spaced rollers  38  for example, is fixed to the main frame of the machine  12 . The rotational axes  40  of these rollers  38  lie in a plane which is parallel to the feed plane  18 . The feed plane  18  is formed by the contact surface between the rollers  38  and a work piece.  
         [0036]     A work piece which is to be sawn, a steel girder for example, can be moved on the roller conveyer  36  by means of the conveyor device  34  to the guidance portal  22  where a saw cut can then be made by moving the sawing framework  24  downwardly whilst driving the band-saw blade therein.  
         [0037]     In the case of the exemplary embodiment shown in  FIG. 1 , there are provided laterally of the roller conveyer  36  e.g. oppositely located strips  42  which serve as lateral stops so that a work piece cannot fall out sideways.  
         [0038]     A chuck jaw device  46 , which is fixed with respect to the feed direction  44  for the work-pieces, is arranged in the vicinity of the guidance portal  22 . A work piece can be clamped between opposite chuck jaws of the chuck jaw device  46  in order to fix it with respect to the main frame of the machine  12  during a sawing process.  
         [0039]     The conveyor device  34  has a carriage  48  which is moveable in the feed direction  44  (and in the opposite direction thereto). For the purposes of moving the carriage  48  in the feed direction  44  (parallel to the feed plane  18 ), there is provided a drive  50  which is arranged below the roller conveyer  36  for example. The drive  50  for the movement of the carriage  48  may be a spindle drive.  
         [0040]     The carriage  48  preferably comprises a chuck jaw device  52  having two facing chuck jaws between which a work piece is adapted to be clamped. By moving the carriage  48  with the work piece clamped thereon, the work piece can then be fed to the guidance portal  22  and, in particular, be fed to the fixed chuck jaw device  46  in order to enable the work piece to be fixed for the purposes of making a saw cut therein.  
         [0041]     It is possible for example, for the sawing process to be carried out in such a manner that a work piece being fed in, such as a steel girder for example, is clamped in the fixed chuck jaw device  46  whilst the sawing framework  24  is displaced upwardly during this feeding process and clamping process so that it is positioned outside the feed area for the work piece. After the work piece has been fixed, the sawing process is carried out by driving the sawing framework  24  downwardly.  
         [0042]     Provision may then be made for the sawing framework  24  to be driven back up when the cut has been completed without moving the work piece itself. However, after completion of the saw cut and prior to the raising of the sawing framework  24 , it is also possible for that part of the work piece that is fixed to the carriage  48  to be moved away from the band-saw blade against the feed direction  44  whereafter the sawing framework  24  is raised.  
         [0043]     The corresponding processes are controlled by a control unit  54  ( FIG. 2 ) such as an SPS control unit (stored-program, programmable control system) which is arranged, in particular, in a switchbox  56 . The switchbox  56  is fixed to the main frame of the machine  12  for example.  
         [0044]     The saw drive  28  forms a first drive and the drive  50  for the carriage  48  (a feed carriage for the work piece) forms a second drive which are adapted to be activated independently of one another. As long as a sawing process is taking place, i.e. as long as the band-saw blade is being driven by the saw drive  28 , the carriage  48  must not be operated. In like manner, the band-saw blade must not be driven whilst the carriage  48  is being moved for the purposes of feeding-in a work piece or for removing a work piece, i.e. the saw drive  28  must not be activated.  
         [0045]     In accordance with the invention, a common frequency converter  58  ( FIG. 2 ) is associated with the drive for the saw  28  and the drive  50  for the carriage  48 . This frequency converter  58  is connected to the control unit  54  and is accommodated in the switchbox  56 .  
         [0046]     A frequency converter serves for converting the mains (supply) frequency (which amounts to 50 Hz or 60 Hz for example). The corresponding drives (the drives  28 ,  30 ,  50  in the exemplary embodiment shown) are then fed with this converted frequency so that the rotational speed of the relevant drive and further variables can be set thereby.  
         [0047]     A frequency converter  58  comprises for example, a rectifier, a buffer circuit and an inverter, the supplied alternating voltage being rectified by the rectifier. The buffer circuit then smoothes the DC voltage and the inverter produces a sine-weighted pulse-width modulated voltage from the DC voltage.  
         [0048]     The output voltage and the effective output frequency can then be adjusted, this, in turn, therefore making it possible for the speed of the driving motor being controlled to be adjusted. The torque of the thus controlled drive can thereby be varied over a wide range and essentially independently of the rotational speed.  
         [0049]     The frequency converter  58  is coupled via a feeder  60  to an alternating current supply line  62  over which, in particular, three-phase alternating current is supplied. A main switch  64  is arranged in the supply line  62  for the purposes of interrupting the supply line  62 . Electrical energy is branched off to the frequency converter  58  from this supply line  62 , whereby a protective switch  68  serving as a safety device is arranged upstream thereof in a corresponding branch  66  of the feeder  60 . The frequency converter transforms this input voltage.  
         [0050]     The frequency converter  58  has an output  70  for a current monitoring arrangement.  
         [0051]     Furthermore, there is provided an output  72  for an automatic control arrangement which serves as a function-enabling arrangement for the frequency converter  58  and which incorporates a plurality of series-connected switches  74  in the path thereto. Enabling of the automatic control arrangement is only effected if all the switches  74  are closed. For example, one switch  74  is connected to a sensor which checks as to whether a protective door in the sawing machine  10  is closed. If this door is not closed, then the corresponding switch is opened and the automatic control arrangement is not enabled. A (cumulative) monitoring system for the hardware of the sawing machine  10  can thus be achieved with the aid of the output  72  and the downstream switches  74 .  
         [0052]     The frequency converter  58  is supplied with electrical energy via appropriate connections  76  so that it can accomplish its internal functions.  
         [0053]     The feed speed in the direction of feed  44  is activated via digital inputs  78 ,  80 , i.e. the appropriate speed parameter for the control of the drive  50  is specified. The corresponding inputs  78 ,  80  (as well as the outputs  70 ,  72  and the downstream switches  74 ) are connected to the control unit  54 . (These connections are not shown in  FIG. 2 .)  
         [0054]     Furthermore, a bus module  82  is connected to the frequency converter  58 , said module likewise being connected to the control unit  54 . Process data can thereby be set. For example, reference values can be entered and/or a parameterising process can be carried out. This is described in more detail hereinafter. A change of parameters can also be effected via the bus module  82 . Furthermore, reversal of the direction of rotation can be controlled via the bus module  82 . (Digital inputs could also be provided for the parameter changing process or the reversal of the direction of rotation.) Furthermore, data can be read-out from the frequency converter  58 .  
         [0055]     The frequency converter  58  comprises an output  84  for the frequency converted alternating voltage. In accordance with the invention, provision is made for this output  84  to be connected to the drive for the saw  28  and for it to be connected in parallel to the drive  50  for the carriage  48 .  
         [0056]     A motor contactor  86  for the saw drive  28  is connected downstream of the output  84  and a motor contactor  88  for the drive  50  is also connected downstream thereof.  
         [0057]     However, the two drives  28 ,  50  are not effectively connected—as regards the functioning thereof—in parallel to the output  84 , but rather, are controlled in such a way that either the saw drive  28  will run or the drive  50  will run (or that neither of the two drives  28 ,  50  should run); at most one of the drives  28 ,  50  is activated. An appropriate switch or an appropriate circuit serves for this purpose, said switch or circuit comprising the motor contactors  86  and  88 , and it ensures that both drives  28 ,  50  are not operated at the same time.  
         [0058]     The drive  30  for the cleaning brush is connected effectively in parallel with the drive  28  for the band-saw blade so that the cleaning brush is also activated when the saw drive  28  is running.  
         [0059]     The frequency converter  58  also comprises a floating output  90  for conveying error messages from the frequency converter  58 .  
         [0060]     Furthermore, there is provided a first monitoring output  92  for a temperature sensor  93  for the drive  28  and a second output for a temperature sensor  95  for the drive  50 . Hereby, the two temperature sensors  93 ,  95  are connected in series so that an appropriate warning signal is given or the entire device is switched off if at least one of the drives  28 ,  50  exceeds a temperature threshold.  
         [0061]     Provision may also be made for one or more further temperature sensors  96  to be connected in series with the temperature sensors  93 ,  95 , this or these further sensors being associated with special accessories whose temperatures should be monitored.  
         [0062]     The saw drive  28  drives the band-saw blade. It runs at different speeds in dependence on the material of the work piece which is being sawn. It only rotates in one direction and is switched on or off depending upon the operational state.  
         [0063]     The drive  50  for the carriage  48  provides for the feeding of a work piece to the guidance portal  22  and thus for the positioning of the work piece being sawn with respect to the band-saw blade. The carriage  48  can be moved in both the feed direction  44  and in the opposite direction. A plurality of speeds may be envisaged.  
         [0064]     Accordingly, different sets of parameters are provided for the control of the saw drive  28  and the control of the drive  50 , these parameters being stored in the frequency converter  58 . These parameters can be activated for the purposes of selecting a particular set of parameters via the bus module  82  or the inputs of the frequency converter  58  for example. The parameters needed for the drives  28 ,  50  are stored in the frequency converter  58  and the sets of parameters predetermined by the control unit  54  then determine the starting values of the frequency converter  58  at the output  84  from which the appropriate drive  28  or  50  is controlled. In particular, the output voltage and/or the output frequency and/or the direction of rotation and/or the speed and/or the ramp functions are determined in correspondence with the associated set of parameters.  
         [0065]     Hereby, only one set of parameters is effective at a certain time point, namely, the first set of parameters for the first drive  28  or the second set of parameters for the second drive  50  (or further sets of parameters for further drives). Accordingly, the appropriate set of parameters is enabled by a switch or a circuit so as to ensure that at most one of the two drives  28 ,  50  is in operation.  
         [0066]     In principle, it is also possible for the frequency converter  58  to control further drives if these are independent of the drives  28 ,  50  to such an extent that they are not operated at the same time thereas nor at the same time as other further drives.  
         [0067]     By virtue of the solution in accordance with the invention, only one frequency converter, namely, the frequency converter  58  is associated with the drives  28  and  50 . Space savings in the switchbox  56  are thereby achieved; less heat is produced in the switchbox  56  and also fewer sources of electrical interference are present. It is usually the case that the power consumption of the saw-drive  28  is greater than the power consumption of the drive  50  for the carriage  48  (for example, a typical power consumption for the drive  28  is in the region of 3 kW or more for example, whilst a typical power consumption for the drive  50  is in the region of 1.5 kW). Due to the solution in accordance with the invention utilising a frequency converter  58  matched to the power consumption of the drive  28 , the performance of the drive  50  can also be increased as necessary at little expense since the control process is of course being effected by the frequency converter  58  which is matched to the drive  28 .  
         [0068]     In accordance with the invention, control of the drives  28 ,  50  of the sawing machine  10  is effected by the frequency converter  58  which is common to the first drive  28  and the second drive  50 . It is thereby ensured that the first drive and the second drive are operated at different times, i.e. they are not operated at the same time. In the case of a sawing machine  10 , this can be achieved if the first drive  28  is a drive for the saw and the second drive  50  is a drive for a carriage  48  for feeding the work piece. The operational processes for a work piece in the sawing machine can be controlled in such a way that the two drives  28 ,  50  do not have to be operated at the same time.