EP3003702B1 - Method for controlling a press with a variable gear ratio - Google Patents

Description

The present invention relates to a method for controlling a press. It is a weggebunden working press. The press has an electric drive motor which serves to reciprocate a plunger in a stroke direction between an upper reversal point and a lower reversal point. For this, the electric drive motor is motion-coupled to the ram via a press gear. The transmission has a variable transmission ratio. The gear ratio changes in particular depending on which position the transmission parts have or which position the ram has during its stroke movement. Such press drives can be, for example, eccentric or toggle mechanisms. The gear ratio is very large in these transmissions in the range of the lower reversal point and increases computationally against infinity.

Presses with an electric drive motor are known. For example, describes DE 10 2010 006 120 A1 a press with a servo-pulling device and a joint drive. In this press, it is proposed that overload protection in the form of pressure pads can be provided.

DE 10 2007 026 727 A1 describes a press with servomotors, in which, for example, hydraulic pads can be provided as overload protection.

At the DE 10 2005 040 263 A1 known methods To control a press, the plunger drive is position-controlled during its working movement or its upward movement. When the tool is closed, the position control switches over to a torque or force control.

US 2012/0111207 A1 describes a control device for a servo press and a corresponding control method. In this case, a moment is calculated for the servomotor, which is used to generate the pressing force. Another moment is determined that causes the required positive or negative accelerations of the plunger within the position or speed control of the press ram. The working torque for the pressing force and the control torque in the context of the position or speed control are limited separately.

US 2012/0111207 A1 also discloses a method according to the preamble of claim 1.

Out WO 2013/045105 A1 For example, there is disclosed a method and apparatus for making bales of compressible material, such as agricultural material. When compressing the material, the force of a plunger increases continuously. To avoid this force exceeding a threshold, the counterforce is generated by a previously compressed bale in an exit channel. In this output channel friction elements are provided with which the friction force and thus the counter-holding force can be adjusted for the plunger.

In an engine torque control device for a press according to EP 0922562 A1 is the engine torque by the corresponding Motor current limited. To achieve the pressing force according to a predetermined setpoint, the accelerations of the plunger are taken into account in the control of the engine torque. This should avoid unwanted deviations from the setpoint of the pressing force.

US 2011/0061547 A1 describes a press and a control method for the press, in which a variable capacity control of the press is to take place. For this purpose, a field control of the electric motor is proposed. The engine torque is limited as part of a position or speed control of the plunger of the press. This limitation takes place via correspondingly specified d and q axis currents for the electric motor as part of the field control.

At the JP 2009 208134 A proposed servo press overload to be avoided by excessive heat to avoid damage to components, in particular servo amplifiers. For this purpose, an integral value based on the motor current and the heat generated thereby is determined depending on the engine torque. The heat is compared with a heat threshold. If the heat threshold is exceeded, the motor current is reduced. The heat generated thereby is limited.

DE 10 2011 115 932 A1 describes a method for avoiding high pressing forces. A servomotor is connected via a press gear with variable transmission ratio with a movable in the lifting direction between an upper reversal point and a lower reversal point ram. The drive torque of the servomotor is limited to a work limiting torque.

Based on this, it can be regarded as an object of the present invention to propose an improved method for operating a press, which reliably avoids excessive press force in order to prevent damage to the press.

This object is achieved by a method having the features of claim 1.

As described above, the press has a press drive with at least one electric drive motor and a press gear, which produces a movement coupling between the drive motor and the plunger. The plunger can be reciprocated in a stroke direction between an upper reversal point and a lower reversal point.

In the method according to the invention, a maximum pressing force, which is also referred to as nominal pressing force, is first predetermined for the press. Subsequently, a position-dependent maximum torque for the at least one electric drive motor is determined depending on the maximum pressing force and the variable transmission ratio. The gear ratio depends on the position of the plunger during its stroke movement or from a predetermined for controlling the press press angle. The press angle describes a complete movement of the plunger from its upper reversal point to the lower reversal point and back to the upper reversal point, wherein the press angle changes from 0 ° to 360 °. The lower reversal point can - depending on the kinematics of the press gear - be assigned to a press angle of about 180 °. Since the gear ratio changes during the stroke movement of the plunger, the maximum torque is specified depending on the stroke position or depending on the press angle.

The position-dependent maximum torque describes for each stroke position or for each press angle a drive torque for the electric drive motor, which must not be exceeded in order not to exceed the maximum pressing force in the further course of the lifting movement of the plunger. If the drive torque of the at least one electric drive motor exceeds the maximum torque, it is determined that with continued movement of the plunger and the drive motor with the intended drive torque, the maximum pressing force would be exceeded.

The position-dependent varying transmission ratio and the desired value of the drive torque of the at least one electric drive motor are known. From this it is possible to determine a profile for a maximum torque depending on the press angle or the slide position that is exceeded before the maximum press force is exceeded. This can occur, for example, if accidentally several sheets are inserted into the press or the press operator has made the stroke adjustment - ie the position of the lower reversal point - wrong. If the drive torque exceeds the maximum torque, so the danger is detected in good time and it can be initiated before exceeding the maximum pressing force a suitable measure to safely avoid damage to the press.

When determining the position-dependent maximum torque and at least one of the springing of the Considering the press descriptive parameter. As a result, a maximum torque for the electric drive motor can be defined for each press angle or for each plunger position, the exceeding of which indicates that the maximum pressing force is to be expected if the plunger continues to move from the upper reversal point to the lower reversal point.

For example, the press gear may have an eccentric or a toggle mechanism. In particular, the press gearbox has a gear ratio which increases as the ram approaches the lower reversal point. Due to this changing gear ratio, it is not enough to monitor the engine torque. The increasing transmission ratio increases sharply at the lower reversal point and is mathematically infinitely large at the lower reversal point. Therefore, very low drive torques of the electric drive motor are sufficient to exceed the maximum press force near the lower reversal point. For this reason, the press angle or the plunger position and thus the gear position is included in the determination of a position-dependent maximum torque, so that press damage is effectively avoided.

The position-dependent maximum torque is given in a preferred embodiment for the entire stroke of the plunger or for each press angle between 0 ° and 360 °. Alternatively, it may be sufficient to specify the position-dependent maximum torque at least within a nominal force path in the movement of the plunger from the upper reversal point to the lower reversal point in a movement section until reaching the lower reversal point. The nominal force can be up to a few millimeters one centimeter of the plunger movement measured in the stroke direction.

It is advantageous if the drive torque of the at least one electric drive motor is reduced when it is determined that the risk of exceeding the maximum torque exists. The risk of exceeding the maximum torque is detected in particular by the fact that the current drive torque of the at least one electric drive motor is greater than the determined position-dependent maximum torque. To reduce the drive torque, for example, the motor current can be reduced or switched off completely.

Upon detection of the danger of exceeding the maximum torque, the plunger can also be actively decelerated via the electric drive motor. For example, for this purpose, the at least one electric drive motor can be switched over to its generator mode. Alternatively or additionally, it is also possible to energize the at least one drive motor for generating a braking force. The drive motor is so to speak so controlled that he tries to reverse its direction of rotation and thereby generates a braking force on the plunger.

If the drive torque exceeds the maximum torque, the plunger can be braked with respect to the predetermined plunger movement and, in a preferred embodiment, moved to a reference position. The reference point used is in particular the upper reversal point. As a result, the press is brought into a defined state. Raising the plunger to the reference position or upper reversal point allows access to the workpiece. Of the The operator can then investigate the cause of the impending overshoot of the maximum pressing force and eliminate the problem.

In a preferred embodiment of the method, an optical and / or audible alarm signal is generated when the drive torque exceeds the position-dependent maximum torque.

When determining the maximum torque occurring changes in the drive torque are taken into account, which are caused by predetermined accelerations of the plunger. Depending on the movement characteristic of the tappet stored in the press control, it may be necessary to make changes in the drive torque during the stroke movement of the tappet in order to adapt the time-dependent or press angle-dependent position and / or speed of the tappet to the predetermined desired values. The acceleration of the ram is considered to be any change in speed, that is to say speed increases and speed reductions. For example, depending on the forming task of the press during a stroke, the speed of the at least one electric drive motor can be varied in order to accelerate the ram in predetermined movement sections. These changes in the drive torque possibly lead to the risk of exceeding the maximum pressing force, because these drive torque changes cause a change in the kinetic energy of the plunger. Such predetermined by the ram movement characteristic or caused drive torque changes are taken into account in the determination of the position-dependent maximum torque. As a result, the accuracy of the method can be increased and erroneous ratings of the occurring pressing force avoided.

The changes in the drive torque occurring as a result of the acceleration of the ram, which can be taken into account in the determination of the maximum torque, are those drive torque changes which occur independently of the forming work of the press. Such changes in the drive torque can be determined, for example, based on the predetermined ram movement characteristic. This ram movement characteristic can be obtained, for example, from the simulation of the pressing process or from the press control.

According to the invention occurring by accelerations of the plunger during its stroke changes in the drive torque can also be determined during a test or Leerhub the plunger without a workpiece. As explained, these changes can be determined on the basis of the ram movement characteristic curve from a simulation or based on an idle stroke before the press is put into operation.

According to the invention, a stroke-number-dependent parameter is additionally taken into account in the determination of the position-dependent maximum torque in addition to the changes in the drive torque, which result from its acceleration of the ram independently of its forming work. As the number of strokes increases, so does the acceleration of the tappet, which is taken into account by the number of stroke-dependent parameters. The stroke-number-dependent parameter can thus form a factor with which the drive torque changes occurring independently of the forming work are multiplied.

• Figur 1 eine schematische blockschaltbildähnliche Darstellung eine Ausführungsbeispiels einer Presse,
• Figur 2 ein schematisches Prinzipbild des Zusammenhangs zwischen einem Pressenwinkel und der Stößelbewegung,
• Figur 3 einen stark schematisierten beispielhaften Verlauf für die Drehzahl des elektrischen Antriebsmotors der Presse sowie das ermittelte Maximaldrehmoment in einem Nennkraftweg,
• Figur 4 eine stark schematisierte, beispielhafte Darstellung des zeitlichen Verlaufs der Drehzahl des elektrischen Antriebsmotors sowie der Stößelbewegung.

Advantageous embodiments of the invention will become apparent from the dependent claims and the description. The description is limited to essential features of the invention. The drawing is to be used as a supplement. Hereinafter, embodiments of the invention will be explained in detail with reference to the accompanying drawings. Show it:

• FIG. 1 1 is a schematic block diagram similar representation of an embodiment of a press,
• FIG. 2 a schematic diagram of the relationship between a press angle and the plunger movement,
• FIG. 3 a highly schematic exemplary course for the rotational speed of the electric drive motor of the press and the determined maximum torque in a nominal force path,
• FIG. 4 a highly schematic, exemplary representation of the time course of the rotational speed of the electric drive motor and the plunger movement.

FIG. 1 shows a weggebunden working press 10 with a press frame 11. At the press frame 11, a plunger 12 is slidably guided guided in a stroke direction R. A press table 13 is arranged on the press frame 11. The plunger 12 carries an upper tool 14 and the press table 13, a lower tool 15 is arranged. The two tools 14, 15 work together for forming a workpiece, not shown. For this purpose, the plunger 12 can be moved with the upper tool 14 to the press table 13 and the lower tool 15 out.

To move the plunger 12 is a press drive 20. The press drive 20 has at least one electric drive motor 21 and a press gear 22. In the following, it is assumed by way of example that a single drive motor 21 is present. The required drive torque for the press 10 can also be achieved by a combination of several drive motors. A control device 23 serves to control or regulate the at least one electric drive motor 21.

The press gear 22 has no constant predetermined, but a variable transmission ratio Ü on. The gear ratio Ü is dependent on the plunger position z of the plunger 12 in the stroke direction R considered or from a press angle α. The press angle α is used to describe a complete stroke of the plunger 12 from an upper reversal point OT to a lower reversal point UT, in which the plunger 12 has the smallest distance to the press table 13, and back to the upper reversal point OT. An exemplary sequence of movements of a complete stroke is in FIG. 4 illustrated by dashed lines. Since the press angle α and the plunger position Z in are a predetermined relationship, the transmission ratio Ü can be specified as a first function f _{1 of} the press angle α or as a second function f ₂ of the plunger position Z.

In the illustrated embodiment of the press gear 22, the translation Ü in the movement of the plunger 20 from the upper reversal point OT in the lower reversal point UT steadily increase and go against the limit infinite. The press 10 has in the embodiment according to the FIGS. 1 and 2 an eccentric gear 23 having such a transmission characteristic. Even with a toggle mechanism or a crank gear, the transmission ratio Ü position or distance-dependent and not constant in the course of a stroke.

For detecting the current position of the plunger 12 or for detecting the transmission angle α, the press 10 has a position sensor 25. The position sensor 25 may be associated with the plunger 12 and / or a gear part of the press gear 23 and / or the electric drive motor 21. For example, the position sensor 25 can detect the rotational position of an input shaft 26 of the press gear 22, as shown schematically in FIG FIG. 1 is illustrated.

The concrete structural design of the press gear 22 may be different. For example, the plunger 12 may be pivotally connected via a connecting rod 27 with a ring 28, wherein the ring 28 in turn is rotatably mounted on a driven eccentrically by the input shaft 26 pulley 29. Alternatively to this in FIG. 1 illustrated embodiment, the connecting rod 27 also eccentric be hinged to the disc 29 opposite the input shaft 26 ( FIG. 2 ). In this case, the disc 29 may be arranged concentrically with the input shaft 26 and the rotation axis D, respectively.

In such presses 10 there is the danger that because of the prevailing in certain movement portions of the plunger 12 very large gear ratio Ü too large pressing force is generated, which can damage the press 10. In order to avoid this, a maximum pressing force Fmax is predetermined according to the invention. The maximum pressing force can also be referred to as the nominal force of the press 10. In addition, a nominal force s can be specified, within which the maximum pressing force Fmax may occur. The nominal force path s ends at the lower reversal point UT of the plunger 12 and can be, for example, 5 to 6 mm long, measured in the stroke direction R. The nominal force s and the maximum pressing force Fmax are used to determine the maximum energy of the press 10 during forming can be.

Depending on this maximum pressing force Fmax and the position-dependent gear ratio Ü, a position-dependent maximum torque Mmax is determined or calculated. The maximum torque Mmax represents a limit value for the drive torque M of the electric drive motor 21. In this way it can be determined by monitoring the drive torque M for each plunger position z or for each press angle α, whether there is a risk that the maximum pressing force Fmax at the Continuation of the plunger movement is exceeded according to the predetermined in the control device 23 plunger movement characteristic and the predetermined drive torque M. This ensures that by comparing the drive torque with the maximum torque Mmax already at a press angle α or a plunger position z the danger of exceeding the maximum pressing force Fmax is detected before this is actually the case. In this way, measures can be taken to effectively prevent the force applied by the plunger 12 from exceeding the maximum pressing force Fmax.

In other words, the drive torque M applied by the electric drive motor 21 already exceeds the determined maximum torque Mmax before the force applied by the plunger 12 reaches the maximum pressing force Fmax. This can be determined based on the known gear ratio Ü, the predetermined maximum pressing force Fmax, the known slide movement and preferably additionally from at least one, the springing of the press 10 descriptive Auffederungsparameter. The suspension parameter describes the elastic resilience of the press during the forming of the workpiece. The springing is dependent on the forming path of the plunger 12 from the placement on the workpiece to the lower turning point UT in the path-dependent working press 10.

In FIG. 3 an exemplary highly simplified curve for the maximum torque Mmax is shown. The position-dependent maximum torque Mmax can be given for the entire stroke of the plunger 12 from the top dead center OT to the bottom dead center UT and back to the top dead center OT. At least the course for the maximum torque Mmax in the range of the nominal force path s is determined and monitored. In the simplest case, the maximum torque Mmax is given on the basis of a constant speed n for the electric drive motor 21, as indicated by solid lines in FIG FIG. 3 illustrated schematically is. The maximum torque Mmax rises sharply to a maximum value at the beginning of the nominal force path s and drops again with a smaller absolute slope to the lower reversal point UT. The result is a sawtooth-shaped course in FIG. 3 is shown very heavily schematized.

Alternatively, changes in the rotational speed n of the drive motor 21 and hence accelerations of the plunger 12 can also be taken into account in the determination of the maximum torque Mmax FIG. 3 is illustrated by the dashed sections. Such changes in rotational speed can be predefined as a function of the forming task by a movement characteristic K for the plunger 12 and stored in the control device 23. The control device controls the drive motor 21, so that the plunger 12 moves according to the predetermined movement characteristic K. A simple motion characteristic K for a constant speed n is exemplified in FIG FIG. 4 shown in dashed lines.

Speed changes of the drive motor 21, which are predetermined by the movement characteristic K for the plunger 12, also lead to the change of the drive torque provided by the electric drive motor M. Such changes, which are independent of the forming work, are taken into account in the determination of the maximum torque Mmax. As a result, erroneous evaluations regarding an imminent exceeding of the maximum pressing force Fmax can be avoided.

In FIG. 3 is assumed only by way of example that at a first press angle α1, the speed n of the electric drive motor reduced to a second press angle α2. The plunger 12 is braked. The amount and / or the direction of the drive torque M of the electric drive motor 21 change accordingly. In order to take account of this acceleration of the plunger 12, in the region between the first press angle α1 and the second press angle α2, the maximum torque Mmax is reduced by the amount by which the drive torque M of the electric drive motor 21 is changed depending on the acceleration of the plunger 12. In FIG. 3 the change in the maximum torque Mmax is shown in dashed lines.

At the in FIG. 3 Example shown is further assumed by way of example that from a third press angle α3 to the lower reversal point UT, the rotational speed n of the electric drive motor 21 is increased. In order to accelerate the plunger 12 in accordance with a magnitude increased drive torque M of the electric drive motor 21 is necessary. The maximum torque Mmax is increased by an amount corresponding to the amount of change of the drive torque M, which is in FIG. 3 also shown in dashed lines.

Thus, changes in the drive torque M, which lead to the acceleration of the plunger 12 and are independent of the forming work, for example, given by a motion characteristic K for the plunger 12, taken into account in determining the position-dependent maximum torque Mmax. The amount and the course of the rotational speed n and the speed changes that occur can vary depending on the forming task of the press 10 and are shown in FIG 3 shown simplified by way of example only. It can also occur non-linear speed characteristics.

• Nennkraftweg s= 8 mm,
• Pressenwinkel zu Beginn des Nennkraftweges α_s = 9°,
• Exzenterradius r = 650 mm,
• maximale Presskraft Fmax = 18.000 kN,
• Übersetzung Ü(α_s) = 17.

For example, the maximum torque Mmax for the plunger position at the beginning of the nominal force path s may be calculated as follows:
assumptions:

• Nominal force s = 8 mm,
• Press angle at the beginning of the nominal force path α _s = 9 °,
• Eccentric radius r = 650 mm,
• maximum pressing force Fmax = 18,000 kN,
• Translation Ü (α _s ) = 17.

The path c, which covers the eccentric at its eccentric radius about the axis of rotation of the eccentric then results in: $$\mathrm{c}=\mathrm{r}*\sin \left({\mathrm{\alpha }}_{\mathrm{s}}\right),$$

The maximum torque Mmax at a press angle α = α _s is then: $$M\mathrm{Max}\left({\alpha }_s\right)=\frac{c*F\mathrm{Max}}{Ü\left({\alpha }_s\right)},$$

With the above numerical values, for example, the maximum torque Mmax = 108,000 Nm results.

The control device 23 compares the drive torque M currently applied by the electric drive motor 21 with the determined position-dependent maximum torque Mmax. As soon as the drive torque M is the maximum torque Exceeds Mmax, the danger of exceeding the maximum pressing force Fmax is recognized. If the motor torque at the beginning of the nominal force path s exceeds the value of 108,000 Nm in the example shown above, the risk of exceeding the maximum pressing force Fmax is recognized. At this point measures will be taken. In particular, the drive torque M of the electric drive motor 21 is reduced in order to reduce the force applied by the plunger 12. Even if an immediate stop of the plunger 12 due to the inertia and the speed of the plunger 12 is not possible, can be prevented by reducing the drive torque M by a sufficient amount taking into account the position-dependent gear ratio Ü exceeding the maximum pressing force Fmax. The rotational energy stored in the rotation is then converted into a spring-up of the press, which can be calculated on the basis of the rotational energy and the rigidity of the press.

If the calculation indicates that the exceeding of the maximum pressing force Fmax can not be ensured solely by the torque switch-off, a braking means of the press 10 is preferably used to stop or even reverse the continued movement of the plunger 12 faster. For example, the electric drive motor 21 can be switched to its generator mode and serve as a braking means. It may additionally or alternatively, other braking means, such as a friction brake may be provided.

It is thus also possible to switch the electric drive motor 21 in its generator mode, if the risk of exceeding the maximum pressing force Fmax was detected. At the in FIG. 4 shown embodiment is assumed that at a fourth press angle α4 the currently applied drive torque M of the electric drive motor 21 exceeds the predetermined maximum torque Mmax. According to the example, the plunger 12 is first braked by reversing the direction of rotation of the electric drive motor 21 and moved back in the opposite direction. Actually, this is different than in FIG. 4 only schematically illustrates no vertical edge for the speed n on. First, the moving mass must be stopped and accelerated in the opposite direction. The plunger 12 is then moved to a reference position, which corresponds to the upper reversal point OT in the embodiment. The actual movement Z (α) of the plunger 12 (solid line in FIG FIG. 4 ) no longer follows the predetermined motion characteristic K.

Based on the maximum torque of the drive motor 21, the maximum braking power can be calculated depending on speed and from this the average braking power can be determined. For example, half the maximum braking power can be assumed as average braking power. Depending on the rotational energy can then calculate the required braking time and the distance traveled during the braking time angle difference of the press angle α and the distance traveled during the braking time plunger travel.

Once this reference position is reached, the press 10 is stopped. It can also be issued a visual and / or audible alarm. The operator of the press 10 can then search for the cause leading to the danger exceeded the maximum pressing force Fmax. This can be caused, for example, by accidentally placing a plurality of sheets or workpieces in the press 10. Another cause of error may be that the ram stroke and thus the position of the lower reversal point UT adjusted and set too close to the press table 13 and the lower tool 15. This can also lead to inadmissibly high pressing forces.

The accelerations of the plunger 12, which are independent of the forming work, for example, from a predetermined motion characteristic K for the plunger 12, can be determined in various ways. For example, it is possible to obtain these accelerations and thereby caused changes in the driving torque M of the electric drive motor 21 from a simulation of the operation of the press 10. By way of example, when setting up the press 10, an idle stroke is performed without inserting a workpiece. The occurring changes in the drive torque M can be determined and stored. Since no workpiece is present, the changes in the drive torque M are due to the set, predetermined motion characteristic K for the plunger 12 and the resulting accelerations of the plunger 12.

If, in this way, the changes in the drive torque M, which are not caused by deformations but by predetermined desired accelerations of the plunger 12, have been determined, these can be taken into account in the calculation of the position-dependent maximum torque Mmax, as described in connection with FIG FIG. 3 was explained. These changes can also be made at different stroke rates be adapted for the press 10. By way of example, in determining the position-dependent maximum torque Mmax, a stroke-number-dependent parameter is additionally taken into account, which may be, for example, a factor with which the determined change in the drive torque M resulting from the idle stroke is multiplied. As a result, increased magnitude accelerations are taken into account, which result in an increase in the number of strokes of the press 10.

The invention relates to a method for controlling a press 10. The press 10 has an electric drive motor 21 and a press gear 22 with variable gear ratio Ü on. A plunger 12 of the press 10 is movably mounted in the stroke direction R and connected via the press gear 22 to the electric drive motor 21. The gear ratio Ü can steadily increase during the movement of the plunger from an upper reversal point OT to a lower reversal point UT and increase sharply. In order to avoid exceeding a predetermined maximum pressing force Fmax of the press 10, a position-dependent maximum torque Mmax is predetermined for the electric drive motor 21. The control device compares the respectively applied drive torque M with the position-dependent maximum torque Mmax. As soon as the drive torque M exceeds the position-dependent maximum torque Mmax, the danger is recognized that the force applied by the plunger 12 will exceed the maximum pressing force Fmax in the case of a continued deformation movement. The control device 12 then reduces the drive torque M in order to avoid damaging the press 10.

LIST OF REFERENCE NUMBERS

10

Press

11

press frame

12

tappet

13

press table

14

upper tool

15

lower tool

20

press drive

21

electric drive motor

22

Press gear

23

control device

25

position sensor

26

input shaft

27

pleuel

28

ring

29

disc

α

press angle

α1

first press angle

α2

second press angle

α3

third press angle

α4

fourth press angle

D

axis of rotation

Fmax

maximum press force

K

Movement characteristic for the ram

M

drive torque

Mmax

maximum torque

n

rotation speed

OT

upper reversal point

Ü

gear ratio

UT

lower reversal point

s

Nennkraftweg

Z

ram position

Claims (10)

1. Method for controlling a press (10),
   with an electric drive motor (21) which is connected, via a press gear mechanism (22) with variable gear ratio (U), to a slide (12) which is mounted movably in the stroke direction (R) between an upper reversal point (OT) and a lower reversal point (UT), and with a control device (23) which controls or regulates the electric drive motor (21), with the following steps:

   - definition of a maximum pressing force (Fmax) for the press (10),

   - determination of a position-dependent maximum torque (Mmax) for the electric drive motor (21) depending on the maximum pressing force (Fmax) and the gear ratio (U),

   - control or regulation of the electric drive motor (21) such that the pressing force exerted by the slide (12) over the entire stroke movement is smaller than the maximum pressing force (Fmax),

   characterised in that at least one parameter describing the deflection of the press (10) is taken into account in determining the position-dependent maximum torque (Mmax),
   that changes in the drive moment (M) occurring due to travel-dependent predefined accelerations of the slide (12) are taken into account in determining the position-dependent maximum torque (Mmax),
   that the changes in the drive moment (M) occurring due to accelerations of the slide (12) are determined on an idle stroke of the slide (12),
   and that the position-dependent maximum torque (Mmax) is determined from the changes in drive moment (M) determined on an idle stoke of the slide (12) and a parameter dependent on rotation speed.
2. Method according to claim 1, characterised in that the gear ratio (U) of the press gear mechanism (22) increases when the slide (12) approaches the lower reversal point (UT).
3. Method according to claim 1 or 2, characterised in that the press gear mechanism (22) is or comprises an eccentric gear or a toggle gear.
4. Method according to any of the preceding claims, characterised in that the position-dependent maximum torque (Mmax) is predefined at least within a nominal force travel (s) up to the lower reversal point (UT).
5. Method according to any of the preceding claims, characterised in that the drive moment (M) of the electric drive motor (21) is reduced if it is found that there is a risk of exceeding the maximum pressing force (Fmax).
6. Method according to any of the preceding claims, characterised in that the slide (12) is braked if it is found that there is a risk of exceeding the maximum pressing force (Fmax).
7. Method according to claim 6, characterised in that the electric drive motor (21) is actuated against its current rotation direction in order to brake the slide (12).
8. Method according to any of the preceding claims, characterised in that the electric drive motor (21) is switched to its generator operating mode, or actuated to generate a braking force, if it is found that there is a risk of exceeding the maximum pressing force (Fmax).
9. Method according to any of the preceding claims, characterised in that the slide (12) is moved into a reference position (OT) if it is found that there is a risk of exceeding the maximum pressing force (Fmax).
10. Method according to any of claims 1 to 9, characterised in that the changes in drive moment (M) occurring due to accelerations of the slide (12) are determined using a predefined slide movement curve (K).

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