Abstract:
In a computer-aided detection of the jamming of an object, wherein, when adjusting a component of a motor vehicle using an adjusting drive ( 6 ), measurement values related to the adjusting force (F) are compared to a prescribed threshold value (FR), initiating a slowdown, stop, or reversing of the adjusting motion when said value is reached. A spring rate correcting term characterizing the rigidity of the object is determined for correcting the relationship between the adjusting force (F) and the threshold value (FR), and is considered in the comparison.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2009/053424 filed Mar. 24, 2009, which designates the United States of America, and claims priority to German Application No. 10 2008 021 383.7 filed Apr. 29, 2008, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The invention relates to a method and apparatus for the computer-aided detection of the pinching of an object when a component of a motor vehicle is adjusted with the aid of an adjusting drive, with measurement values relating to the adjusting force being compared with a predetermined threshold value, the reaching of which causes a slowing, stopping or reversing of the adjusting movement to be initiated. 
     BACKGROUND 
     When the adjustment of components in motor vehicles is actuated by external forces, for example in the case of electrically operated window raising mechanisms or sunroofs, an anti-pinch protection system is prescribed to limit the excess force generated by the adjusting drive. This anti-pinch protection system ideally recognizes a pinching incident immediately, by comparing adjusting force values currently determined in predetermined positions with a predetermined threshold value during an adjusting process. If the adjusting force applied by the motor rises above this threshold value, this indicates an obstacle in the adjustment path of the component and “pinching” is decided; the movement of the component is then stopped, the motor preferably also being reversed. 
     The anti-pinch protection system acts during the adjusting process at least within a partial region of the adjustment path, e.g. when a sliding window approaches a predetermined distance from the closing position, with current force values or variables correlated therewith, such as values of the window speed, motor speed, motor current etc. being determined at least in this partial region of the adjustment path at predetermined positions in quick succession, and corresponding values being compared as “force values” with the threshold value. 
     If the threshold value is exceeded, in the known systems time delays in the electrical circuit, for example an activation relay switching delay and generally mechanical inertia of the adjusting system and also the mechanical play contained therein mean that the adjusting movement is not stopped or reversed immediately but continues for a short time, in other words the pinching process continues before the adjusting movement is stopped and in some instances a movement reversal is initiated. Depending on the rigidity of the trapped object (e.g. a person&#39;s arm) this continued clamping increases the pinching force. This increase in the pinching force is naturally a function of how quickly the component, e.g. the window or sunroof, was being moved before the clamping process and how long the clamping continues. This increase in the pinching force, also referred to as an overshooting pinching force, is however also a function of the rigidity of the trapped object, as already mentioned above. Such a variation in the clamping force is not desirable. Ideally it should be possible to assume constant clamping forces for an optimally synchronized system, in order on the one hand to comply with the specified safety requirements and on the other hand to ensure the greatest possible safety margin in respect of a potential incorrect stopping and reversing of the movement of the motor vehicle component. Every fluctuation in the clamping force, as mentioned above also as a function of the rigidity of the object, however reduces this safety margin. 
     The reduction of the safety margin was generally accepted in the past and no measures were taken to compensate for the described phenomenon. However it has already been proposed here to adjust the threshold value for compensation purposes by an amount which is a linear function of the supply voltage. This change to the threshold value is based on the knowledge that the change in the adjustment speed of the respective motor vehicle component is initially caused by different vehicle electrical system voltages in the motor vehicle. However even with this procedure only unsatisfactory compensation for the clamping force fluctuations is possible, as the variation in adjustment speed is only partially caused by fluctuations in the vehicle electrical system voltage, in other words the supply voltage. Therefore, because other influencing variables bring about different adjustment speeds, such as for example fluctuations in the sluggishness of the mechanical system, which are in particular also caused by temperature fluctuations, it has also been proposed that such speed changes be taken into account. In principle such fluctuations in the pinching force due to speed changes are also to be compensated for on the basis that the cause, namely speed or voltage, is almost immediately known based on size. However this is not the case for pinching force fluctuations due to objects of differing rigidity (also referred to as differing spring rates). 
     Clamping force measurements for anti-pinch protection systems are often only measured using objects of identical rigidity, in other words identical spring rate, in particular at 10N/mm. The reason for this is that this spring value is specifically required in the European directive 2000/EC. If measurement only takes place with objects of identical rigidity, the problem of different clamping forces does not arise. In practice the trapped objects can be of different rigidity however. Therefore, and also in respect of the increasingly frequently required compliance with the US directive FMVSS 188, section S5, there is increasingly also requirement to cover spring rates of 20N/mm and 65N/mm. 
     In this instance in the past the systems were designed for the hardest object (i.e. for 65N/mm for example) and lower clamping forces were accepted for lower spring rates. However this results in a disadvantageous lower level of stability of the system in respect of incorrect triggering of the anti-pinch protection, also referred to as incorrect reversing. 
     SUMMARY 
     According to various embodiments, this can be remedied and improved anti-pinch protection can be provided in so far as objects of differing rigidity, i.e. different spring rates, are automatically to be taken into account in a pinching incident, so that on the one hand the desired safety margin can be ensured and on the other hand incorrect reversing or stopping can be prevented as far as possible. 
     According to an embodiment, in a method for the computer-aided detection of the trapping of an object when a component of a motor vehicle is adjusted with the aid of an adjusting drive, measurement values relating to the adjusting force being compared with a predetermined threshold value, the reaching of which causes a slowing, stopping or reversing of the adjusting movement to be initiated, wherein a spring rate correction term characteristic of the rigidity of the object is determined to correct the relationship between the adjusting force and the threshold value and taken into account during the comparison. 
     According to a further embodiment, when determining the correction term the rise of the measurement value curve relating to the adjusting force can be used. According to a further embodiment, when determining the correction term the first temporal derivation of the measurement value curve can be calculated and this derivation or a term containing the derivation can be multiplied by a predetermined proportionality factor. According to a further embodiment, the correction term obtained by derivation can be subtracted from the predetermined threshold value to determine a corrected threshold value. According to a further embodiment, the correction term obtained by derivation can be added to the determined measurement values relating to the adjusting force to determine corrected values relating to the adjusting force. According to a further embodiment, when determining the correction term an integrated value can be calculated for the measurement values relating to the adjusting force in a predetermined integration interval. According to a further embodiment, the correction term obtained by integration can be added to the predetermined threshold value to determine a corrected threshold value. According to a further embodiment, also when determining the correction term the first derivation of the measurement value curve can be calculated and this derivation or a term containing the derivation can be multiplied by a predetermined proportionality factor and the correction term is subtracted from the predetermined threshold value to determine a compensated threshold value. 
     According to another embodiment, an apparatus for the computer-aided detection of the trapping of an object when a component of a motor vehicle is adjusted with the aid of an adjusting drive, may comprise computation means for calculating the adjusting force of the adjusting drive or a variable correlated with the force, means for predetermining a threshold value, comparison means for comparing the calculated force or the correlated variable with the threshold value, and correction means for calculating a spring rate correction term characteristic of the rigidity of the object and for correcting the relationship between the adjusting force and the threshold value. 
     According to a further embodiment of the apparatus, the correction means can be set up to determine the correction term based on the gradient of a curve showing the profile of the calculated adjusting force. According to a further embodiment of the apparatus, the correction means may feature a differentiation module for calculating the first temporal derivation of the adjusting force curve and linking means for multiplying the derivation or a term containing said derivation by a predetermined proportionality factor, to determine the correction term. According to a further embodiment of the apparatus, the correction means may feature subtraction means connected to the linking means to subtract the correction term obtained from the predetermined threshold value. According to a further embodiment of the apparatus, the correction means may feature adding means connected to the linking means to add the correction term obtained by the derivation to the calculated force. According to a further embodiment of the apparatus, the correction means may feature an integration module for calculating an integrated value of the calculated force in a predetermined integration interval and linking means for multiplying the integrated value or a term containing said integrated value by a proportionality factor, to determine the correction term. According to a further embodiment of the apparatus, the correction means may feature adding means connected to the linking means to add the correction term to the predetermined threshold value. According to a further embodiment of the apparatus, the correction means may also feature a differentiation module for calculating the first temporal derivation of the adjusting force curve and linking means for multiplying the derivation or a term containing said derivation by a predetermined proportionality factor, to determine the correction term, subtraction means being connected to the linking means to subtract the correction term obtained by the derivation from the predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail below based on exemplary embodiments, to which it should not however be restricted, and with reference to the drawing, in which: 
         FIG. 1  shows a schematic diagram of the force profile of a pinching situation for objects of differing rigidity; 
         FIG. 2  shows a block diagram of the apparatus for detecting the pinching of an object in conjunction with an adjusting drive; 
         FIG. 3  show a block diagram of a part of said apparatus according to  FIG. 2 ; 
         FIGS. 4 and 5  show diagrams with schematically illustrated force profiles,  FIG. 4  showing two threshold value profiles corrected with the aid of differential correction values for two different spring rates and  FIG. 5  showing threshold values corrected with the aid of an integration correction value in this instance for two different spring rates; 
         FIG. 6  shows a block diagram of a different part of the apparatus according to  FIG. 2 , for the provision of a differential correction term during the adjusting force calculation; 
         FIG. 7  shows a diagram to illustrate the profile of an adjusting force during pinching without and respectively with a force value correction with the aid of a differential correction value; and 
         FIG. 8  shows a schematic diagram to illustrate the restriction of compensation or correction to the range between the predetermined softest and hardest objects to be pinched. 
     
    
    
     DETAILED DESCRIPTION 
     With the present technology a spring rate correction term characteristic of the rigidity of the object is determined to correct the relationship between adjusting force and threshold value and taken into account during the comparison. This correction term is determined in particular as a correction term relating to the gradient of the adjusting force curve. This is based on the fact that when comparatively soft objects are pinched, a relatively flat profile or flat rise is present in the clamping force curve but when the objects are relatively rigid, there is a relatively steep rise in the pinching force, so that overshooting after reaching the threshold value results very quickly here in a high force value, until stopping or reversing intervenes and the clamping force drops again. In order to avoid such a high peak value after the pinching incident has been established, in other words to reduce the “overshoot” to a lower value, the threshold value should therefore be set correspondingly lower; instead the clamping force or adjusting force to be compared with the predetermined threshold value for the comparison can also be increased, so that in this instance too the threshold value is reached earlier. In both instances therefore the adjusting movement can be stopped and a reversal can in some instances be initiated earlier, compared with the situation according to the prior art, in other words without spring rate “compensation”. 
     An extremely favorable procedure is therefore achieved if the first derivation of the measurement value curve is calculated when determining the correction term and the correction term is subtracted from the predetermined threshold value to determine a compensated threshold value. The differential correction term thus obtained can be deducted from the predetermined threshold value so that with a correspondingly steep rise in the clamping force or adjusting force curve the threshold value is reached earlier than with a flatter rise, the rigidity of the object or the spring rate being reflected in this rise (gradient). 
     The abovementioned differential correction term can however also be included directly in the force equation, instead of changing the trigger threshold, in other words the correction term obtained by derivation is added to the initially obtained measurement values relating to the adjusting force to determine “compensated” (corrected) values relating to the adjusting force. 
     Compensation here can be brought about in the respective instance—when calculating a “compensated” threshold value and with a “compensated” force value—by direct addition or subtraction of the correction term or even by taking the derivation term into account in a negative or positive manner with a correction multiplier. In this process a respective predetermined proportionality factor is applied when calculating the correction term. 
     A differential term in the threshold value calculation or force equation can in some instances means that the negative influence of potential synchronization problems of the mechanical system is amplified. It is then also possible to determine the correction term by integrating the adjusting force or values correlated therewith in an integration interval from the start of pinching onward. This alternative embodiment is based on the knowledge that a clamping process up to an established clamping force, e.g. 100N, lasts longer, the softer the clamped object is and the greater the integral. Therefore in the event of a fast rise a lower—compensated or corrected—threshold value is obtained here too and in the event of a relatively soft object a relatively high—corrected—threshold value is obtained. Of course the respective integrated value is also to be multiplied by a predetermined proportionality factor here too. 
     It is also advantageous to combine the above-mentioned integration method with the method in which the first derivation of the adjusting force is used in the period for determining an adjusted threshold value, in which process the detrimental effect due to the tendency of the mechanical system to have synchronization problems can be kept within limits. In this instance comparatively smaller proportionality factors should be predetermined in each instance (namely for the derivation term and for the integration term) to achieve the desired correction result overall. 
     It should be noted that instead of the calculated adjusting or closing force it is of course also possible to use variables correlated therewith, for example motor speed, motor current or values proportional thereto. 
     The present apparatus, which is provided with computation means for calculating the adjusting force of the adjusting drive, means for predetermining the threshold value and comparison means for comparing the calculated force with the threshold value, is correspondingly characterized by correction means for calculating a spring rate correction term characteristic of the rigidity of the object and for correcting the relationship between the adjusting force and the threshold value. The correction means are set up here, for simple correction term calculation, to determine the correction term based on the gradient of a curve showing the profile of the calculated adjusting force. It is also particularly advantageous here for the correction means to feature a differentiation module for calculating the first temporal derivation of the adjusting force curve and linking means for multiplying the derivation or a term containing said derivation by a predetermined proportionality factor, to determine the correction term. The correction means here can feature subtraction means connected in a simple manner to the linking means for subtracting the correction term thus obtained from the predetermined threshold value. This determines a corrected, “compensated” threshold value, which is correspondingly lower, the more markedly the adjusting force curve rises. The computation means, means for predetermining the threshold value, comparison means, and correction means comprise computer instructions stored in non-transitory computer-readable media and executable by at least one processor. 
     On the other hand the calculated force itself can be “corrected” according to the gradient of the curve, the correction means then featuring adding means connected to the linking means for adding the correction term obtained by the derivation to the calculated force. 
     As mentioned above, in some instances the correction result based on differential correction terms is in some instances detrimentally affected as a result of synchronization problems of the mechanical system and to avoid this it is also favorable if the correction means feature an integration module for calculating an integrated value of the calculated force in a predetermined integration interval and linking means for multiplying the integrated value or a term containing said integrated value by a proportionality factor, to determine the correction term. The linking means can be used to connect adding means for adding the correction term to the predetermined threshold value in a simple manner. 
     It should be noted that as an alternative to integration a low pass filter can also be used, allowing more economical implementation. 
     A further embodiment is obtained, if the correction means also feature a differentiation module for calculating the first temporal derivation of the adjusting force curve and linking means for multiplying the derivation or a term containing the derivation by a predetermined proportionality factor, to determine the correction term, with subtraction means for subtracting the correction term obtained by the derivation from the predetermined threshold value being connected to the linking means. 
       FIG. 1  shows the force profile for three objects of differing rigidity in a pinching situation, the respective force F (in N) being plotted over time t (in ms); specifically the curve  1  shows the force profile for a spring rate of 65N/mm, the curve  2 —which is flatter than curve  1 , with a less steep rise—shows the force profile for a spring rate of 20N/mm and the curve  3 —which has the least steep rise—shows the force profile for a spring rate of 10N/mm. A predetermined, constant threshold value F R  is also shown, with a stop and reverse process for the motor drive bringing about the force, for example for a window raising mechanism or a sunroof of a motor vehicle, being initiated when the respective adjusting force  1 ,  2  or  3  reaches or exceeds this threshold or reference value F R . The switching delay here, for example due to an activation relay or even the mechanical inertia of the system and the mechanical play, however results in the motor drive and therefore the window or sunroof, etc. continuing to move for a short time, before the reversing process actually starts at a peak value, for example 4 for the curve  1  in  FIG. 1 , and the adjusting force drops again, as shown in  FIG. 1 . 
     The three adjusting force curves  1 ,  2  and  3  in  FIG. 1 , which are characteristic of different spring rates, show that this continued clamping, the “overshooting” of the clamping force, is a function of the rigidity of the pinched object, in other words the spring rate, it being clear that the peak value  4 , at which the overshooting of the pinching force is terminated, is higher, the steeper the gradient of the clamping force curve  1 ,  2  or  3 . It is also clear from  FIG. 1  that if the entire system is designed for the most rigid (hardest) object in respect of predetermining the threshold value, in other words for 65N/mm for the instance shown, and therefore the threshold value is set approx. 20N lower, there may be unnecessary reversing, for example with objects having a spring rate of 10N/mm. 
     With the present technology provision is made for “detecting” the spring rate of the pinched object based on the different profile of the force rise and using this information to adapt the threshold value F R  and/or the measured adjusting force F, in other words to correct or “compensate” the relationship between the threshold value and the measured force correspondingly. Therefore in the case of a rigid object clamping detection is triggered earlier in time, to which end either the threshold value is lowered with the aid of a correction term or the measured force is increased with the aid of a correction value for comparison purposes, with a comparable peak value resulting as for softer objects, due to the more marked but earlier starting subsequent force increase in the run out. 
     In order now to achieve a corresponding adjustment of the detection and trigger time t a , it is possible to form for example the first temporal derivation of the rising profile of the force curve and use it to derive a correction term, which is linked linearly to the predetermined threshold value. This link can be as follows: 
                         F     R   ,   corr       ⁡     (   t   )       =         F   R     ⁡     (   t   )       ·     (     1   -         ⅆ     F   ⁡     (   t   )           ⅆ   t       ·     k   1         )         ⁢     
     ⁢   or           (   1   )                   F     R   ,   corr       ⁡     (   t   )       =           F   R     ⁡     (   t   )       ·   1     -         ⅆ     F   ⁡     (   t   )           ⅆ   t       ·     k   1   ′                 (     1   ′     )               
depending on whether compensation is to operate as a factor or just an added term.
 
     Instead of the calculated closing force F(t), correlated variables, such as motor speed or motor current, can of course also be used in the derivation. 
     In the above equations (1) and (1′) 
     F R,corr (t) is the corrected trigger threshold force, i.e. the corrected threshold value, at time t 
     F R (t) is the uncompensated trigger threshold force, as predetermined in the prior art, at time t (as mentioned above, the trigger threshold can be adapted as a function of voltage fluctuations and speed fluctuations, so that a time dependency can be present)
 
F(t) is the calculated closing force at time t,
 
k 1  is a proportionality factor (weighting parameter), which is system-dependent, can be determined empirically or by measurement in advance and determines the compensation influence, and
 
k 1 ′ is a corresponding proportionality factor for when the correction term is to operate as an “added” (specifically subtracted) term.
 
     The differential correction term contained in the equations (1) and (1′) can result in an amplification of the disadvantageous effect of possible synchronization problems of the respective mechanical system. Therefore an alternative or possibly also supplementary approach is proposed for detecting the spring rate in so far as the respective form of the force rise is taken into account by calculating an integral of the force rise. The softer the clamped object, the longer the clamping process, as shown in  FIG. 1 , and the greater therefore the integral value. The result of the integration is used again to adapt the clamping force or trigger threshold, in other words the predetermined threshold value F R , in this instance however by actually taking into account the correction term additively, in order to raise the threshold value even more, the softer the clamped object. This threshold value adaptation can be written for example using the following equations: 
                         F     R   ,   corr       ⁡     (   t   )       =         F   R     ⁡     (   t   )       ·     (     1   +       k   2     ·       ∫     t   -     t   clamp       t     ⁢         F   ext     ⁢           (   u   )     ⁢     ⅆ   u             )         ⁢     
     ⁢   or           (   2   )                 F     R   ,   corr       =       F   R     +       k   2   ′     ·       ∫     t   -     t   clamp       t     ⁢         F   ext     ⁢           (   u   )     ⁢     ⅆ   u                     (     2   ′     )               
Here the designations F R,corr  and F R  have the meanings given above; k 2  and k 2 ′ again designate system-dependent proportionality factors (weighting parameters); t clamp  designates the respective integration interval (see also  FIG. 5 ); and F ext  designates the difference between the calculated closing force F and the expected closing force at time t. This difference, which is also expressed in the diagram in  FIG. 1 , can also, as shown below based on the block diagram according to  FIG. 2 , be determined later, so that instead of F ext  in the equations (2) and (2′) the calculated closing force F can simply be used.
 
     The integration interval is advantageously selected so that it corresponds to the clamping time with the lowest spring rate. 
     Again the equations (2) and (2′) show the two options which result from taking the correction term into account as a factor or as an added term. 
     The two correction term determinations set out above can also be combined with one another, as shown in the following equations (3) and (3′): 
     
       
         
           
             
               
                 
                   
                     
                       
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     It should be noted here that in the case of the equations (3) and (3′), in other words in the case of combined correction, the respective correction terms k 1 , k 2  and k 1 ′, k 2 ′ should be selected as smaller than when only one or the other correction term determination takes place, according to the equations (1) and (1′) or according to (2) and (2′). 
     Instead of the threshold value adaptation described above, the adjustment can also take place directly with the pinching force, in other words the calculated clamping force is corrected (“compensated”) correspondingly for the comparison with the threshold value. If 
     F corr  (t) designates the closing force calculated with compensation at time t, 
     F(t) designates the closing force calculated without compensation according to the prior art at time t, and 
     k 3  designates a weighting parameter (proportionality factor), which determines the influence of compensation, then 
     
       
         
           
             
               
                 
                   
                     
                       
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     This approach is similar to the first adjustment, according to the equations (1), (1′). But this similarity only applies for the pinching situation. If account is taken of the fact that the calculated closing force is also used as the basis for other calculations, for example for the algorithm for recognizing a poor road, it can be seen that the effect is different. (“Poor road recognition” is the recognition for example of fluctuations due to poor road conditions, for example the presence of potholes, cobbles, and the like, and these fluctuations are correspondingly recognized and regulated out). 
     Here too there are two options, depending on whether compensation is to operate as a factor or an additive term, according to the equation (4) or (4′). 
       FIG. 2  shows a block diagram of a general example of a facility  5  for limiting the closing force of a component, e.g. a window or window raising mechanism (not shown in detail), of a motor vehicle with the aid of an electric motor  6  provided in the manner of an adjusting drive, referred to in short as a CFL (closing force limiting) facility  5 . Power supply and activation means  7  are assigned to the motor  6 . Means for capturing measurement values relating to the adjusting force are also provided, a current measurement circuit  8  and a voltage measurement circuit  9  for example being present, the outputs of which are applied to a force determination unit  10 , to calculate the closing force F or a value relating thereto. This force determination takes place in a conventional manner per se and if the capturing of motor current I and motor voltage U is shown as a basis for this here, this should only be seen as exemplary, other options for force determination being known and possible, for example on the basis of motor speed; see for example also FR 2 663 798 A or the earlier DE application 10 2006 059 145.3. According to  FIG. 2  the angular speed ω(t) of the motor  6  is also used to calculate the force F(t). To capture the angular speed ω of the electric motor  6 , in particular in conjunction with capturing the position of the electric motor  6 , as shown only schematically in  FIG. 2 , sensors that are standard per se  11 ,  12 , e.g. Hall sensors, are shown schematically, their output signals being applied to a signal processing unit  13 , in order to apply a signal relating to the angular speed ω to the unit  10 , the “force calculation means”. 
     A force value signal F ext  is applied to an input of a comparison unit  14 , which is supplied at its other input with a threshold value F R,corr , which originates from a predetermination unit  15 . When the threshold value is exceeded, the comparison unit  14  emits a corresponding signal to the activation means  7  to slow or stop the electric motor  6  or even reverse its direction of rotation. 
     The force determination unit  10  thus forms computation means for calculating the adjusting force F of the adjusting drive  6 , and the comparison of the adjusting force with a trigger threshold, which is predetermined by the predetermination means  15  in a conventional manner, then takes place in the comparison means  14 . 
     In order then to take into account the different spring rates, i.e. the objects of differing rigidity, which are pinched, correction and compensation means  16  are also provided according to  FIG. 2 , to adjust the relationship between the adjusting force and the threshold value, by adapting at least one of these two variables, to the respective spring rate. 
     In the example shown the correction means  16  specifically contain a threshold value correction unit  17  and also an adjusting force correction unit  18 . The threshold value correction unit  17  here allows adaptation of the threshold value according to the above equations (1), (1′), (2), (2′) and (3), (3′), while the adjusting force correction unit  18  allows adaptation of the adjusting force used for the comparison according to the equations (4) and (4′). 
     According to  FIG. 3  the threshold value correction unit  17  of the correction means  16  contains on the one hand a differentiation module  19  and on the other hand an integration module  20 , to which a predetermination unit  21  for the integration interval t clamp  is assigned. Both modules are supplied in a parallel manner with the pinching force or adjusting force F or F ext  (or a variable correlated therewith), so that said force or variable is on the one hand constantly differentiated and on the other hand integrated in the integration interval t clamp  (see  FIG. 5 ). The differentiated or integrated values obtained are then multiplied with the aid of linking means (multiplier means)  22  and  23  by the respective proportionality factors k 1 ′ and k 2 ′, which are supplied by corresponding predetermination modules  24  and  25 . The outputs of the multiplier means  22 ,  23  thus supply the differential or integral correction terms contained above in the equations (1′) and (2′), which are applied to an inverting (−) input or a + input of summing means  26 ; a further + input of said summing means  26  is supplied with a threshold value F R  predetermined by the predetermination means  15  and determined in the conventional manner. At the output of the summing means  26 , which thus form both subtracting means and adding means, the threshold value F R,corr  adapted according to the gradient of the force curve  1 ,  2  or  3  is obtained. This threshold value F R,corr  is supplied to the comparison means  14  according to  FIG. 2  and compared there with the overshoot force F ext , said overshoot force being above the mechanical response, in other words exceeding the expected value. The normal mechanical response is taken into account according to  FIG. 2  by a reference force predetermination unit  27  by means of subtraction means  28 , to subtract the expected force F ext  from the calculated force F (in some instances from the force F corr  corrected in the unit  18 ). 
     If with the unit  17  according to  FIG. 3  only either the differential correction or the integration correction is desired, this can be achieved in a simple manner by setting the corresponding—other—proportionality factor k 2 ′ or k 1 ′ equal to zero. 
     Before looking in more detail at the unit  18  based on  FIG. 6 , the mode of action of the unit  17  should be explained in more detail with reference to  FIGS. 4 and 5 . 
       FIG. 4  specifically shows two force curves  30 ,  31  for two different spring rates, as may occur in a pinching incident with objects of differing rigidity. The diagram according to  FIG. 4  also shows the uncompensated force threshold F R —as a constant trigger threshold for the sake of simplicity here. 
     The force profiles  30  and  31  already describe the force profile as occurs with a compensated system (the peak values are of identical height for this reason).  FIG. 4  also shows the uncompensated force profiles with two broken lines  30 ′,  31 ′. These both lie above the curves  30  and  31 ; the peak value of the uncompensated 10N/mm curve  30 ′ is below that of the uncompensated 65N/mm curve  31 ′. These broken-line curves  30 ′,  31 ′ would correspond to triggering at times t 1 ′ and t 2 ′. 
     According to the curves  30 ′,  31 ′ the force starts to rise above the expected value assumed to be zero and without compensation the comparison with the threshold value F R  would cause a pinching incident to be detected at time t 1 ′ or t 2 ′, with the adjusting drive (motor  6 ) being stopped or reversed after the described overshoot up to a peak value  4 ′ at a time t 4 , resulting in the falling branch of the curves  30 ′,  31 ′. 
       FIG. 4  specifically shows the correction of the threshold value according to the differentiation method for two different spring rates, namely 10N/mm (curve  30 ) and 65N/mm (curve  31 ) and the associated corrected threshold values  32  (for spring rate=10N/mm) and  33  (for spring rate=65N/mm). 
     The described differential correction, with the aid of the differentiation module  19  and the multiplier means  22 , results in an adjustment or correction, also referred to as compensation, of the threshold value F R,corr  according to the curves  32  and  33  shown in  FIG. 4 , the threshold value F R,corr  in the critical region being lower (due to subtraction of the correction term) than the predetermined threshold value F R , so that the pinching incident is detected and reversal of the motor  6  is triggered at an earlier time, e.g. t 1  for the curve  30  and t 2  for the curve  31 . This results in a lower peak value  4 . 
       FIG. 5  again shows two curves  30  (for a spring rate of 10N/mm) and  31  (for a spring rate=65N/mm) and associated corrected threshold value profiles  34  (for spring rate=10N/mm) and  35  (for spring rate=65N/mm) obtained by integrating the adjusting force. The uncompensated conventional predetermined threshold value F R  is also shown—again as a constant trigger threshold. The integration interval t clamp  used is also shown schematically, over which integration is ongoing, while the force according to the curve  30  or  31  rises. As shown, at trigger time t 2  here there is a higher threshold value  34  for softer pinched objects compared with the lower threshold  35  for harder objects, according to the force curve  31 , at trigger time t 2 , so that the desired comparatively early detection of the pinching situation for high spring rates is achieved here too. 
       FIG. 6  shows the adjusting force correction unit  18  from  FIG. 2  in one possible embodiment, in which the adjusting force F itself is corrected (“compensated”) according to the respective spring rate. The unit  18  in turn contains a differentiation module  19 ′ (which can in theory also be the differentiation module  19  from  FIG. 3 ), with downstream multiplier means  22 ′ (for the realization of which the multiplier means  22  according to  FIG. 3  can also be used); a proportionality factor predetermination unit  24 ′ is also provided to predetermine the factor k 3 ′, so that the differentiated force value 
               ⅆ   F       ⅆ   t           
can be multiplied by this factor k 3 ′ and then added in adding means  26 ′ to the force value F. At the output of said adding means  26 ′ the corrected force value F corr  according to the above equation (4′) (or a variable correlated with this force F corr ) is obtained, which is then subjected, taking into account the expected force value, see  FIG. 2 , to the comparison with the—in this instance for example uncompensated threshold value F R —in the comparison means  14 . (The subtraction of the expected force value, see unit  27  in  FIG. 2 , can also take place before the correction means  16 , for which reason in  FIG. 6  and also in  FIG. 3  both F and also—alternatively—F ext  are given as the input variable).
 
     The unit  18  can be provided additionally or instead of the unit  17  according to  FIG. 2 ; both units  17 ,  18  are preferably present and, depending on the situation, in the corresponding proportionality factor predetermination means  24 ,  25  or  24 ′ the proportionality factors k 1 ′, k 2 ′ or k 3 ′ are set to zero, to obtain the desired form of correction. It is also conceivable to combine the units  17  and  18  to form a common unit, having a common summing stage  26 , it being possible to switch the individual signal paths to active or to deactivate them by way of logical values (not shown). This summing stage would then also have to be supplied with the calculated force F at a further input compared with the situation according to  FIG. 3 , and the upper differentiation branch, with the differentiation module  19 , could be used for a correction of either the threshold value or the force, depending on the setting of the proportionality factor with the aid of the means  24  and depending on activation of either the threshold value input or the force input in the summing stage  26 . 
     Where the adjusting force is corrected, as shown in detail in  FIG. 6 , a de facto displacement of the force curve  30 ′ results according to  FIG. 7  (for the uncompensated instance) forward in time, see also the curve  30  for the corrected force F corr . This curve  30  is obtained from the curve  30 ′ by constantly adding the correction term 
                   ⅆ   F       ⅆ   t       ·     k   3       ,         
as shown in  FIG. 7 . As a result the pinching situation is again detected at an earlier time t 1 ′, compared with the time t 1  in the uncompensated instance, resulting in a lower actual adjusting force curve, having a correspondingly lower peak value  4 ′.
 
     The forward displacement of clamping detection in time is greater, the higher the rise of the force curve. A greater drop of the peak point  4  therefore takes place, corresponding to the desired effect. 
     To increase system stability, threshold value compensation is advantageously restricted to the range that occurs generally with clamping situations, see the schematic diagram in  FIG. 8 . The broken line  40  in  FIG. 8  shows the compensation profile corresponding to the apparatus  18  and the line  41  shows the advantageous restriction of compensation to the useful range, in other words for example the range between 65N/mm and 10N/mm.