Abstract:
A regulation structure ( 13 ) for regulating a hydraulic cylinder unit ( 1 ) has an internal regulator ( 15 ) and an external regulator ( 16 ). The external regulator is supplied with a set force (F*) or a set position (s*) for a piston ( 3 ) of the hydraulic cylinder unit and a corresponding actual parameter (F, s) for the piston. The external regulator determines a set status (z*) for the hydraulic cylinder unit and provides the same to the internal regulator as the set value therefor. The regulator structure comprises a status determining unit ( 19 ), provided with both an actual position (s) and an actual force (F) for the piston and which determines an actual status (z) for the hydraulic cylinder unit and provides the same to the internal regulator as the actual value therefor. The internal regulator determines a control parameter (u) for a valve control unit ( 9 ) of the hydraulic cylinder unit ( 1 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2008/061797 filed Sep. 5, 2008, which designates the United States of America, and claims priority to German Application No. 10 2007 050 892.3 filed Oct. 24, 2007, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is based on a controller structure for controlling a hydraulic cylinder unit,
       wherein the controller structure has an external controller, to which a setpoint force or a setpoint position of a piston of the hydraulic cylinder unit is fed as a setpoint value, and to which a corresponding actual variable of the piston is fed,   wherein the external controller determines, on the basis of the setpoint value fed thereto and the actual value fed thereto, a manipulated variable for a valve control unit of the hydraulic cylinder unit and outputs the manipulated variable to the valve control unit.       
 
       BACKGROUND 
       [0005]    Such control structures are generally known. 
         [0006]    When controlling hydraulic systems which are composed of a servovalve (=valve control unit), hydraulic cylinder and hydraulic piston, the shortest possible activation times are aimed at in order to be able to react quickly when implementing newly predefined setpoint values and compensating for disruption. However, in customary position controllers and force controllers, only relatively long activation times may be possible depending on the behavior of the hydraulic cylinder unit. This problem is highly significant, in particular in the case of long stroke cylinders. 
         [0007]    In the prior art an attempt is made to reduce the activation times by applying a force. The application of the force consists in the fact that during the position control the force is connected in a positive feedback arrangement via a DT 1  element. This procedure allows the effective amplification of the position controller to be increased. The activation time therefore becomes shorter. However, a disadvantage with this configuration is that damping of the control process becomes very small. The system therefore tends to oscillate. 
         [0008]    DE 10 2006 028 094 A1 discloses, in conjunction with an injection molding machine, a control structure for controlling a hydraulic cylinder unit which has an internal controller and an external controller which is superimposed on the internal controller. A setpoint position of the piston of the hydraulic cylinder unit can be fed as a setpoint value to the external controller, and the corresponding actual variable of the piston can be fed as an actual value to the external controller. The external controller determines, on the basis of the setpoint value fed thereto and on the basis of the actual value fed thereto, a “setpoint state” of the hydraulic cylinder unit. The setpoint state is here the setpoint force. The external controller feeds the setpoint force determined thereby to the internal controller as the setpoint value of said internal controller. Furthermore, the actual force is always fed to the internal controller. In addition, a travel actual value or speed actual value can be fed to the internal controller. 
       SUMMARY 
       [0009]    According to various embodiments, a controller structure for a hydraulic cylinder unit can be provided which, on the one hand, reacts very dynamically and nevertheless operates in a stable fashion. 
         [0010]    According to an embodiment, a controller structure for controlling a hydraulic cylinder unit may comprise an internal controller and an external controller superimposed on the internal controller, wherein a setpoint force or a setpoint position of a piston of the hydraulic cylinder unit is fed as a setpoint value to the external controller, and a corresponding actual variable of the piston is fed as an actual value to the external controller, wherein the external controller determines, on the basis of the setpoint value fed thereto and the actual value fed thereto, a setpoint state of the hydraulic cylinder unit, wherein the external controller feeds the setpoint state, determined thereby, to the internal controller as the setpoint value of said internal controller, wherein the controller structure has a state-determining unit, to which both an actual position of the piston and an actual force of the piston are fed, wherein the state-determining unit determines, on the basis of the actual position, fed thereto, of the piston and the actual force, fed thereto, of the piston as such, an actual state of the hydraulic cylinder unit and feeds said actual state to the internal controller as the actual value thereof, and wherein the internal controller determines, on the basis of the setpoint value fed thereto and the actual value fed thereto, a manipulated variable for a valve control unit of the hydraulic cylinder unit and outputs said manipulated variable to the valve control unit. 
         [0011]    According to a further embodiment, the external controller can be embodied as a PI controller. According to a further embodiment, the PI controller may have a proportional block and an integral extension block, which is arranged downstream of the proportional block and extends a proportional signal, output by the proportional block, by an integral portion. According to a further embodiment, a first switching element can be arranged between the proportional block and the integral extension block, a second switching element can be arranged downstream of the internal controller, and the controller structure may have an actuation unit, by which the two switching elements can be actuated, so that the integral extension block and the internal controller can be bypassed by corresponding actuation of the switching elements. According to a further embodiment, the internal controller can be embodied as a P controller. According to a further embodiment, a switching device, to which the setpoint force, the actual force, the setpoint position and the actual position of the piston are fed, can be arranged upstream of the external controller, and the controller structure may have an actuation unit, by which the switching device can be actuated in such a way that the setpoint force and the actual force or the setpoint position and the actual position of the piston are alternatively fed to the external controller. According to a further embodiment, the state-determining unit may determine the actual state on the basis of the relationship 
         [0000]    
       
      
       z=s+F/c  
      
     
         [0000]    where z is the actual state of the hydraulic cylinder unit, s is the actual position of the piston, F is the actual force of the piston and c is a spring constant of a hydraulic fluid of the hydraulic cylinder unit. According to a further embodiment, the controller structure can be embodied as a software module. 
         [0012]    According to another embodiment, a hydraulic cylinder unit can be used for controlling the positioning of a rolling stand, wherein the hydraulic cylinder is controlled by means of a controller structure as described above. 
         [0013]    According to yet another embodiment, an internal structure for a controller structure for controlling a hydraulic cylinder unit, may comprise an integral extension block which extends a proportional signal, fed to the integral extension block, by an integral portion, wherein the proportional signal which is extended by the integral portion corresponds to a setpoint state which is fed to an internal controller of the internal structure as the setpoint value of said internal controller, wherein the internal structure has a state-determining unit to which both an actual position of a piston of the hydraulic cylinder unit and an actual force of the piston are fed, and which determines, on the basis of the actual position, fed thereto, of the piston and the actual force, fed thereto, of the piston as such, an actual state of the hydraulic cylinder unit and feeds said actual state to the internal controller as the actual value thereof, wherein the internal controller determines, on the basis of the setpoint value fed thereto and the actual value fed thereto, a manipulated variable for a valve control unit of the hydraulic cylinder unit and outputs said manipulated variable to the valve control unit, and wherein the internal structure is embodied as an independent unit which can be connected between an output of a P controller, embodied as a force controller or position controller, for the hydraulic cylinder unit and the valve control unit of the hydraulic cylinder unit into a controller structure which is formed by the P controller and the valve control unit, without having to largely adapt the previously existing controller structure beyond the connection of the internal structure. 
         [0014]    According to a further embodiment of the internal structure, a first switching element can be arranged upstream of the integral extension block, a second switching element can be arranged downstream of the internal controller, and the internal structure may have an actuation unit, by which the two switching elements can be actuated, so that the integral extension block and the internal controller can be bypassed by correspondingly actuating the switching elements. According to a further embodiment of the internal structure, the internal controller is embodied as a P controller. According to a further embodiment of the internal structure, the state-determining unit may determine the actual state on the basis of the relationship 
         [0000]    
       
      
       z=s+F/c,  
      
     
         [0000]    where z is the actual state of the hydraulic cylinder unit, s is the actual position of the piston, F is the actual force of the piston and c is a spring constant of a hydraulic fluid of the hydraulic cylinder unit. According to a further embodiment of the internal structure, the internal structure can be embodied as a software module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Further advantages and details emerge from the following description of exemplary embodiments in conjunction with the drawings and the further claims. In basic illustration 
           [0016]      FIG. 1  shows an overall circuit diagram of a hydraulic cylinder unit and a controller structure, 
           [0017]      FIG. 2  shows the controller structure in  FIG. 1  in detail, and 
           [0018]      FIG. 3  shows an embodiment of the controller structure in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    According to various embodiments, the controller structure has an internal controller and an external controller superimposed on the internal controller. A setpoint force or a setpoint position of a piston of the hydraulic cylinder unit is fed as a setpoint value to the external controller, and a corresponding actual variable of the piston is fed as an actual value to the external controller. 
         [0020]    The external controller determines, on the basis of the setpoint value fed thereto and the actual value fed thereto, a setpoint state of the hydraulic cylinder unit. The external controller feeds the setpoint state to the internal controller as the setpoint value of said internal controller. The controller structure also has a state-determining unit, to which both an actual position of the piston and an actual force of the piston are fed. The state-determining unit determines, on the basis of the actual position, fed thereto, of the piston and the actual force, fed thereto, of the piston as such, an actual state of the hydraulic cylinder unit and feeds the actual state to the internal controller as the actual value thereof. The internal controller determines, on the basis of the setpoint value fed thereto and the actual value fed thereto, a manipulated variable for a valve control unit of the hydraulic cylinder unit and outputs the manipulated variable to the valve control unit. 
         [0021]    According to various embodiments, the hydraulic control system can be constructed as a cascade control system. A state is calculated from the position of the piston and from the force applied thereby and is controlled in an internal control circuit. The position controller and/or force controller are/is superimposed on the internal control circuit. 
         [0022]    Owing to the design according to various embodiments, very good control results are obtained, in particular during position control. To a certain extent, activation times of a few milliseconds (typically less than 30 ms and in some cases even less than 20 ms) can be achieved. The controller structure according to various embodiments is also advantageous for force control. However, despite the improved controller dynamics, the controller structure according to various embodiments does not tend to oscillate. 
         [0023]    In one embodiment, the external controller is embodied as a PI controller. This contrasts with the customary embodiment of controller structures for hydraulic cylinder units in which the force controller or position controller is embodied as a P controller. 
         [0024]    In a further preferred embodiment, the PI controller has a proportional block and an integral extension block which is arranged downstream of the proportional block. The proportional block outputs a proportional signal which is extended by the integral extension block by an integral portion. Owing to this embodiment, it is in particular easily possible to retrofit an already existing controller structure (add: embodied as a P controller) for controlling a hydraulic cylinder unit, so that the retrofitted controller structure is embodied according to various embodiments. 
         [0025]    It is possible that a first switching element is arranged between the proportional block and the integral extension block, and a second switching element is arranged downstream of the internal controller. In this case, the controller structure has an actuation unit, by which the two switching elements can be actuated. In this case, the integral extension block and the internal controller can be bypassed by corresponding actuation of the switching elements. By virtue of this embodiment it is possible to operate the controller structure alternatively in the fashion according to various embodiment(i.e. with two cascaded controllers, with the external controller being embodied as a PI controller) or in a conventional fashion (i.e. as an individual controller which operates as a P controller). 
         [0026]    As already mentioned, the external controller is preferably embodied as a PI controller. The internal controller is, on the other hand, preferably embodied as a P controller. 
         [0027]    It is possible to arrange upstream of the external controller a switching device to which the setpoint force, the actual force, the setpoint position and the actual position of the piston are fed. In this case, the controller structure has an actuation unit, by which the switching device can be actuated in such a way that the setpoint force and the actual force or the setpoint position and the actual position of the piston are alternatively fed to the external controller. This makes it possible to operate the hydraulic cylinder unit alternatively with force control and position control. 
         [0028]    The state-determining unit determines the actual state, preferably on the basis of the relationship 
         [0000]        z=s+F/c   (1) 
         [0000]    where z is the actual state of the hydraulic cylinder unit, s is the actual position of the piston, F is the actual force of the piston and c is a spring constant of a hydraulic fluid of the hydraulic cylinder unit. This procedure produces particularly good controller results. 
         [0029]    It is possible for the controller structure to be embodied using hardware. However, it is preferred to embody it as software. 
         [0030]    The hydraulic cylinder unit can in principle be used for any desired adjustment processes. However, it is preferred to use a hydraulic cylinder unit, controlled by means of a controller structure according to the invention, to control the positioning of a rolling stand. 
         [0031]    According to  FIG. 1 , a hydraulic cylinder unit  1  has a hydraulic cylinder  2 . In the hydraulic cylinder  2 , a piston  3  is mounted in a displaceable fashion. The piston  3  divides two working spaces  4 ,  5  from one another. It has a first working face A on its front side  6 , and a second working face A′ on its rear side  7 . 
         [0032]    Working pressures p, p′ are provided in the working spaces  4 ,  5 . The feeding in and discharging of a hydraulic fluid  8  are carried out via a valve control unit  9 . 
         [0033]    The design explained above and the method of operation of the hydraulic cylinder unit  1  and of the valve control unit  9  as briefly explained above are generally known. No detailed statements will therefore be necessary in this regard. 
         [0034]    The hydraulic cylinder unit  1  can be used for any desired purposes of use. According to  FIG. 1 , the piston  3  acts, for example, via a plunger  10  on a bearing  11  of a roller  12  of a rolling stand (otherwise not illustrated). The hydraulic cylinder unit  1  is therefore used in the present case for controlling the positioning of the rolling stand. The hydraulic cylinder unit  1  is controlled according to  FIG. 1  by means of a controller structure  13  which outputs a manipulated variable u to the valve control unit  9 . An actual position s of the piston  3  and an actual force F which is applied by the piston  3  are fed as actual values s, F to the controller structure  13 . The actual force F is determined here according to the formula 
         [0000]        F=pA−p′A′   (2). 
         [0035]    The determination is carried out according to  FIG. 1  in a force-determining unit  14 , which is not a component of the controller structure  13 . However, the force-determining unit  14  could be integrated into the controller structure  13 . Furthermore, at least one setpoint value s*, F* is fed to the controller structure  13 . This may alternatively be a setpoint position s* of the piston  3  or a setpoint force F* which is to be applied by the piston  3 . It is also possible to feed both setpoint values s*, F* to the controller structure  13 . This will be explained in more detail later in relation to  FIG. 2 . 
         [0036]    Finally, a spring constant c of the hydraulic fluid  8  is fed to the controller structure  13  as a parameter. The spring constant c can be an absolute constant here. Alternatively, it can be determined as a function of the actual position s of the piston  3 , if appropriate with inclusion of the working pressures p, p′ and of the working faces A, A′. 
         [0037]    The embodiment of the controller structure  13  will be explained below in detail in relation to  FIG. 2 . The embodiment of the controller structure  13  is the core concept of the present invention. 
         [0038]    According to  FIG. 2 , the controller structure  13  has an internal controller  15  and an external controller  16 . The external controller  16  is superimposed here on the internal controller  15 . The internal controller  15  is preferably embodied as a P controller. The external controller  16  is preferably embodied as a PI controller. 
         [0039]    The setpoint force F* or the setpoint position s* is alternatively fed as a setpoint value x* to the external controller  16 . The corresponding actual variable s, F of the piston  3  is fed as an actual value x to the external controller  16 . 
         [0040]    It is possible for a switching device  17  to be arranged upstream of the external controller  16 . In this case, the setpoint force F*, the actual force F, the setpoint position s* and the actual position s of the piston  3  are fed to the switching device  17 . The controller structure  13  has, in this case, an actuation unit  18 , by which the switching device  17  can be actuated. Depending on the actuation state of the switching device  17 , the setpoint force F* and the actual force F or the setpoint position s* and the actual position s of the piston  3  are alternatively fed to the external controller  16 , in this case. The external controller  16  can therefore alternatively be operated as a force controller or as a position controller. 
         [0041]    Irrespective of whether the external controller  16  is operated as a force controller or as a position controller, the external controller  16  determines, on the basis of the setpoint value x* fed thereto and the actual value x fed thereto, a setpoint state z* of the hydraulic cylinder unit  1 . The external controller  16  feeds the setpoint state z* determined thereby to the internal controller  15  as the setpoint value z* thereof. 
         [0042]    The controller structure  13  also has a state-determining unit  19 . Both the actual position s and the actual force F of the piston  3  are fed to the state-determining unit  19 . The state-determining unit  19  determines, on the basis of the values s, F fed thereto, an actual state z of the hydraulic cylinder unit  1 . The state-determining unit  19  feeds the actual state z determined thereby to the internal controller  15  as actual value z thereof. 
         [0043]    It is possible that the state-determining unit  19  determines the actual state z exclusively on the basis of the actual position s and the actual force F. As a rule, the spring constant c is, however, additionally fed to the state-determining unit  19 . In this case, the state-determining unit  19  preferably determines the actual state z on the basis of the relationship 
         [0000]        z=s+F/c   (3). 
         [0044]    The actual state z therefore corresponds, from the outset to a quantity of hydraulic fluid  8  which is located in the hydraulic cylinder unit  1 . 
         [0045]    The internal controller  15  determines, on the basis of the setpoint value z* fed thereto and the actual value z fed thereto, the manipulated variable u for the valve control unit  9  and outputs the manipulated variable u to the valve control unit  9 . 
         [0046]    It is possible for the controller structure  13  to be implemented by means of circuitry. The controller structure  13  is, however, preferably embodied as a software module  20  according to  FIGS. 1 and 2 . 
         [0047]    A modification of the controller structure  13  in  FIG. 2  will be explained below in relation to  FIG. 3 . In so far as it is possible and appropriate, the same reference symbols as those in  FIG. 2  are used here. In addition, only the differences are emphasized below. The other statements regarding the design and method of functioning of the controller structure  13  largely remain valid. 
         [0048]    According to  FIG. 3 , the external controller  16  has a proportional block  21  and an integral extension block  22 . The integral extension block  22  is arranged downstream of the proportional block  21  here. The proportional block  21  outputs a proportional signal u′. The proportional block  21  therefore corresponds, from the outset, to P controller. The integral extension block  22  extends the proportional signal u′ output by the proportional block  21  by an integral portion. The combination of the proportional block  21  and the integral extension block  22  therefore corresponds to the external controller  16  embodied as a PI controller  16 . 
         [0049]    According to  FIG. 3 , a first switching element  23  is arranged between the proportional block  21  and the integral extension block  22 . Furthermore, a second switching element  23 ′ is arranged downstream of the internal controller  15 . In this case, the controller structure  13  also has an actuation unit  24 , by which the two switching elements  23 ,  23 ′ can be actuated. Depending on the actuation state of the switching elements  23 ,  23 ′ the integral extension block  22  and the internal controller  15  are therefore alternatively active or inactive. Depending on the actuation state of the switching elements  23 ,  23 ′ the controller structure  13  can therefore be operated either as a conventional force controller or position controller or as a cascaded controller according to various embodiments. In the first-mentioned case, the conventional controller is embodied here as P controller, and in the last-mentioned case the external controller  16  is embodied as a PI controller, and the internal controller  15  as P controller. 
         [0050]    The actuation unit  24  is illustrated in  FIG. 3  as a device which is independent of the actuation unit  18 . This embodiment is, of course, possible. Alternatively, the actuation units  18 ,  24  can be combined to form a common unit. 
         [0051]    The integral extension block  22 , the internal controller  15  and the state-determining unit  19  together form an internal structure  25  of the controller structure  13 . The internal structure  25  can be embodied as an independent unit. In particular, according to  FIG. 3 , it is possible, when the controller structure  13  is embodied as a software module  20 , for said internal structure  25  to be embodied as a separate software module  26 . The switching elements  23 ,  23 ′ and the actuation unit  24  for the switching elements  23 ,  23 ′ may here be components of the internal structure  25 . However, they can alternatively not be present or be arranged outside the internal structure  25 . 
         [0052]    Owing to the controller structure  13  which is configured according to various embodiments, shorter actuation times (in some cases below 20 ms, for example 15 ms), than with conventionally configured controller structures can be achieved. This applies even if the conventional controller is operated as a position controller with force-application means. Nevertheless, in the controller structure  13  according to various embodiments the damping is larger, that is to say the tendency to oscillate is smaller. 
         [0053]    In the embodiment according to  FIG. 3 , the internal structure  25  can be implemented as an independent block. This embodiment permits, on the one hand, simple retrofitability of existing conventional controller structures. On the other hand, this embodiment makes it possible to alternatively connect to the internal structure  25  or bypass it. There is no need for more wide-ranging adaptation of superimposed controller structures here. 
         [0054]    The above description serves exclusively to explain the present invention. On the other hand, the scope of protection of the present invention is to be determined exclusively by the appended claims.