EP2228178B1 - Handheld drive device for a press device and method for controlling a handheld drive device for a press device - Google Patents

Description

The invention relates to a handleable drive device for a pressing device and a method for controlling a hand-held drive device for a pressing device.

• die Antriebseinrichtung hat einen Antriebsmotor;
• der Antriebsmotor treibt eine Hydraulikpumpe an;
• die Hydraulikpumpe ist über ein Hydrauliksystem mit einem Hydraulikmotor verbunden;
• die Antriebseinrichtung weist vorzugsweise eine Kupplung für die Anbringung eines Presswerkzeugs zum Verpressen von Werkstücken auf;
• der Hydraulikmotor ist vorzugsweise mit einer Betätigungseinrichtung zur Betätigung des Presswerkzeugs gekoppelt;
• der Hydraulikmotor ist über das Hydrauliksystem mit einem Hydraulikreservoir verbunden;
• in dem Hydrauliksystem befindet sich zumindest ein Überdruckventil;
• das Überdruckventil ist derart ausgelegt, dass es bei Erreichen eines bestimmten Abschaltdruckes im Hydraulikmotor die Verbindung zu dem Hydraulikreservoir öffnet;
• der Hydraulikmotor weist vorzugsweise eine Rückstelleinrichtung auf, die den Hydraulikmotor nach Öffnen des Überdruckventils in seine Ausgangsstellung zurückbewegt und hierdurch Hydraulikflüssigkeit aus dem Hydraulikmotor in das Hydraulikreservoir befördert.

Known handleable drive devices for press devices usually have the following features:

• the drive device has a drive motor;
• the drive motor drives a hydraulic pump;
• the hydraulic pump is connected to a hydraulic motor via a hydraulic system;
• the drive device preferably has a coupling for the attachment of a pressing tool for the pressing of workpieces;
• the hydraulic motor is preferably provided with an actuating device for Actuation of the pressing tool coupled;
• the hydraulic motor is connected via the hydraulic system to a hydraulic reservoir;
• in the hydraulic system is at least one pressure relief valve;
• the pressure relief valve is designed such that it opens the connection to the hydraulic reservoir upon reaching a certain cut-off pressure in the hydraulic motor;
• the hydraulic motor preferably has a return device, which moves the hydraulic motor back to its starting position after opening the pressure relief valve and thereby conveys hydraulic fluid from the hydraulic motor into the hydraulic reservoir.

Furthermore, the present invention relates to a pressing device with such a drive device.

For connecting pipes by means of press fittings and for the attachment of cable lugs to electric cables hand-held pressing devices are known, which consist of a drive device and an end attached via a coupling adapted to the particular application pressing tool. The drive device is formed electrohydraulically in the present type of such pressing devices. In this case, a mains or battery-powered, electric drive motor drives a hydraulic pump, which may be designed as a piston or gear pump. The hydraulic pump acts on an actuating device in the form of a hydraulic motor. As a rule, such a hydraulic motor is designed as a piston-cylinder unit with a hydraulic piston arranged in a hydraulic piston whose piston rod acts on the pressing tool. During movement of the piston rod, one or more pressing jaws are moved in the pressing tool in the pressing direction. In this type of drive Thus, the rotational movement of a drive motor is hydraulically converted into a linear movement of the piston rod to provide a pressing movement of the pressing tool. Examples of such pressing devices can be found in US 5,125,324 A . DE 203 03 877 Ui and DE 20 2004 000 215 Ui ,

To the hydraulic pump includes a hydraulic reservoir, from which the hydraulic pump sucks hydraulic fluid through its suction side and promotes via its pressure side in the pressure chamber of the piston-cylinder unit. The hydraulic system also includes a connection between the pressure side of the hydraulic motor and the hydraulic reservoir.

In the hydraulic system between hydraulic motor and hydraulic reservoir, a pressure relief valve is arranged, which is initially closed during the pressing process and only when reaching a certain maximum pressure, also called cut-off pressure, opens to the hydraulic reservoir. The cut-off pressure is designed so high that in a normal pressing operation opening only takes place when the pressing process is completed, so that the pressing tool has reached its final pressing position.

With the opening of the pressure relief valve and possibly the switching off of the drive motor and thus of the hydraulic pump, the hydraulic piston is moved back to its starting position with a return spring acting on it or the piston rod. As a result, the hydraulic fluid in the pressure chamber is pushed back into the hydraulic reservoir.

From the EP 0 860 220 B1 is a press device is known, which is provided with a fault monitoring function. For this purpose, a physical variable, such as, for example, the electrical current or the force to be applied, is monitored via an actual value pickup and compared with a desired value curve. As soon as the actual value course deviates from the target value course in an inadmissible manner, this is indicated via a signal device or the drive motor is switched off.

Further, the EP 1 230 998 A2 a method for automatic control of electro-hydraulic hand tools and in particular hand presses, in which the drive motor is automatically switched off after completion of the pressing operation. As an indicator of the completion of the pressing process, each current drop is monitored after opening the pressure relief valve.

Furthermore, it is off US 2007/0033984 A1 a hand-held drive device for a pressing device according to the preamble of claim 1 known.

The known monitoring systems have proven themselves in practice quite well. However, efforts are being made to increase reliability.

The object of the invention is to provide a hand-held drive device for pressing devices, in which the reliability is improved. It is another object of the invention to provide a corresponding method for controlling a hand-held drive device for pressing devices.

The object is achieved according to the invention by a handleable drive device according to claim 1 or a method for controlling a handleable drive device according to claim 10.

According to the invention, the manageable drive device for pressing devices on the features according to the characterizing part of claim 1.

At the end of the pressing process, a plausibility check is carried out. The pressing process is terminated in a first control, when the pressure relief valve opens and thus a predetermined pressure, which correlates to the pressing pressure, is constructed. As part of the plausibility check, it is also checked whether the recorded data confirms that the drive motor is also in an operating condition that corresponds to a successful pressing process. An operator is then informed whether or not the pressing operation has been completed properly.

According to the invention it is provided that the Istwertaufnehmer is designed to detect the rotational speed of the drive motor and in the evaluation at least one target load speed range is stored, in which the load speed of the drive motor should be on reaching the cut-off. In other words, the speed of the drive motor at the time of opening the pressure relief valve is monitored as the characteristic value.

The rotational speed correlates directly with the pressing force, with a high speed equal to a low load and a low speed indicative of a high load. Thus, a target load speed can be defined, which must be undercut for reaching a prescribed pressing force. Falling below this predefined target load speed means that the required pressing force has been achieved.

In principle, it may be sufficient to define only one target load speed which must be undershot in order to conclude from this a positive course of the pressing operation. In this case, the setpoint load speed forms the upper limit of a downwardly open setpoint load speed range, which in the Evaluation device is stored. In addition, a lower limit for the permissible target load speed range can also be defined in order to detect overshoots of the permissible pressing force in this way. When the engine speed is within the predetermined target load speed range after opening the relief valve, the operator receives feedback that the pressing operation has been completed successfully. For this purpose, for example, be provided an acoustic and / or optical signaling device.

Depending on the state of charge of the batteries or the voltage level of the power supply as well as the engine condition and the ambient temperature, it can lead to greatly different idling engine speeds and accordingly also come under load. To compensate for these fluctuations, it is provided according to the invention that the evaluation device detects the idling speed before the beginning of a compression and predetermines the target load speed range as a function of the measured idling speed. It is therefore initially measured the idle speed. This is the speed with which the press unit moves without load to a fitting. If the idle speed is low, so will the load speed when opening the pressure relief valve will be lower, and in reverse, the idle speed is high, so the load speed will be higher. Accordingly, the target load speed range is predetermined as a function of the idle speed measured before the pressing process. This can be determined empirically.

In a manner known per se, the drive device according to the present invention can have a control device for influencing the drive motor, wherein the evaluation device is connected to the control device or forms part of it. The control device is preferably designed so that it controls the drive motor in dependence on the actual value, which is detected by the Istwerteaufnehmer. In particular, the control device can switch off the drive motor if the evaluation device detects an increase in the actual rotational speed detected by the actual value pickup after opening the pressure relief valve.

In a further embodiment it can be provided that the Istwertaufnehmer a held on the output shaft of the drive motor or elsewhere in the drive train signal generator, distributed over the circumference, in particular at equal or unequal intervals contactors, and a device-fixed sensor, which emanates from the contactors Detects contacts and outputs corresponding signals to the control device has, wherein the control device determines the actual speed from the detected signals. Appropriately, in this case, the speed sensor carry at its periphery a magnet or more magnets as a contactor and the sensor detects the emanating from the magnet magnetic fields and emit appropriate signals to the controller. Optical contactors are also possible.

In this embodiment of the invention, the speed sensor receives one or more pulses from the magnets attached to the output shaft of the drive motor or elsewhere in the drive train per engine compartment rotation, which are counted. Due to the design-related pulsating load of a hydraulic piston pump, a smoothing of the speed curve may be necessary. This is done by calculation and is dependent on the structure of the pump and the gear ratio. An advantage of this method is that only counts the pulses and the speed is calculated from the number of pulses. An AD converter as in current or voltage measurements is not required here, which makes the evaluation easy.

The hydraulic motor can be designed in a manner known per se as a piston-cylinder unit with a hydraulic cylinder and a hydraulic piston. In this case, it has proved to be advantageous that the pressure relief valve in the hydraulic piston and / or in a piston rod of the hydraulic piston is arranged (see. DE 203 03 877 UI and DE 20 2004 000 215 U1 ). In this case, a control valve may also be provided in addition, as it DE 20 2004 000 215 Ui can be seen.

Furthermore, the invention relates to a method for controlling a hand-held drive device for a pressing device, wherein the method is preferably carried out with the drive device described above.

According to the method according to the invention, a hydraulic pump via a hydraulic system with to carry out a pressing operation Hydraulic motor of a drive motor, which is in particular an electric motor driven. Upon reaching a certain cut-off pressure in the hydraulic motor, a pressure relief valve is opened, so that the hydraulic medium is in particular returned to a hydraulic reservoir.

Furthermore, with the aid of an actual value sensor, a physical quantity is detected according to the invention, which is correlated with the compression resistance and assigned to the drive motor. The first physical quantity is compared with at least one predetermined setpoint range. In this case, the setpoint range defines the actual value of the physical variable in which it should lie when the cutoff pressure is reached. It also indicates whether the actual value lies within the specified setpoint range.

The actual value sensor detects an actual rotational speed of the drive motor, wherein the drive motor is preferably controlled by means of a control device as a function of the detected actual rotational speed upon reaching the cut-off pressure.

In a preferred embodiment, the detected after opening the pressure relief valve actual speed is compared with a stored target speed range in an evaluation. By means of such a comparison, it can be ensured in the context of the plausibility check that a correct compression has been carried out when the detected actual rotational speed is within the desired rotational speed range. Preferably, it can be displayed by means of a signaling device, whether the actual speed is within the stored target speed range and thus a proper compression was performed.

As explained above with reference to the drive device, the. Before the beginning of the compression Idle speed of the drive motor detected and then specified depending on the measured idle speed of the target speed range.

Figur 1

einen Längsschnitt durch das erfindungsgemäße Pressgerät zum Verpressen von Pressfittings,

Figur 2

den Ausschnitt X aus Figur 1 in vergrößerter Ansicht,

Figur 3

einen vergrößerten Ausschnitt des Mittelbereichs des Pressgerätes aus Figur 1 in einer Ebene, die um die Achse des Pressgerätes um 90° versetzt ist, und

Figur 4

ein Diagramm, das einen möglichen Drehzahlverlauf während eines Pressvorgangs darstellt.

In the drawing, the invention with reference to an embodiment is illustrated in more detail. Show it:

FIG. 1

a longitudinal section through the pressing device according to the invention for pressing press fittings,

FIG. 2

the cutout X out FIG. 1 in an enlarged view,

FIG. 3

an enlarged section of the central region of the pressing device FIG. 1 in a plane which is offset by 90 ° about the axis of the pressing device, and

FIG. 4

a diagram showing a possible speed curve during a pressing process.

The illustrated pressing apparatus 1 has an elongated drive unit 2, at one end of which a pressing tool 3 is coupled, which is suitable for the compression of press fittings, which serve to connect pipe ends.

The drive unit 2 has, at the end opposite the pressing tool 3, a drive motor 4 whose output shaft 5 is coupled to a pump shaft 6 of a hydraulic pump designated as a whole by 7. The pump shaft 6 is guided in the hydraulic pump 7 in two bearings 8, 9 and has between the two bearings an eccentric 10 which acts via a needle bearing 11 on a radially displaceably guided pump piston 12. When the pump shaft 6 is driven, the pump piston 12 is moved radially back and forth.

The housing of the hydraulic pump 7 is surrounded on the outside by an elastomeric hose 13 which encloses a hydraulic reservoir 14 between them and the outside of the hydraulic pump 7 in a liquid-tight manner. For this purpose, the ends of the tube 13 engage in grooves 15, 16 and are held there from the outside by pushed-over fixing rings 17, 18 in position.

The hydraulic pump 7 is flanged in the axial direction on the side facing away from the electric motor 4 to a hydraulic motor in the form of a piston-cylinder unit 19. The piston-cylinder unit 19 has a hydraulic cylinder 20 which is closed on the hydraulic pump side with an end plate 21. In the hydraulic cylinder 20, a hydraulic piston 22 is guided displaceably. He divides the interior of the hydraulic cylinder 20 in an end plate-side pressure chamber 23 and a rear space 24 a.

The hydraulic piston 22 is seated on a piston rod 25 which extends on the side facing away from the end plate 21 in the direction of the pressing tool 3. At the local end of the hydraulic piston 22, a hat-shaped sealing element 26 is inserted, which rests on the inside of the piston rod 25 and thus seals the rear space 24. The sealing element 26 also serves to support a piston spring 25 surrounding the coil spring 27, which is supported at the other end on the side remote from the pressure chamber 23 of the hydraulic piston 22. The coil spring 27 is formed as a compression spring and consequently endeavors to move the hydraulic piston 22 in the direction of the end plate 21.

The hydraulic piston 22 remote from the end of the Kolbentsange 25 is rigidly connected outside of the rear space 24 with a spreader 28. The spreader 28 has a bearing body 29, are mounted on the two spreader rollers 30, 31 transversely to the axis of the pressing device 1 side by side and freely rotatable in mutual contact. Attached to the rear space-side end of the hydraulic cylinder 20 is a holder 32, the two Clutch plates 33, 34 forms, which extend in the axial direction of the pressing device 1. The coupling tabs 33, 34 have such a distance from each other that the spreader 28 can move between them. At the ends of the coupling tabs 33, 34 end coupling bores are provided which extend transversely to the longitudinal axis of the pressing device 1 and are aligned. In the area of these coupling bores and between the coupling tabs 33, 34 in a manner known per se (cf., for example FIG. 1 of the EP 1 157 786 A2 or FIG. 1 of the DE 20 2004 000 215 U1 ) two mutually parallel pressing tool tabs, of which in FIG. 1 only the rear pressing tool tab 35 can be seen. Both press tool tabs 35 also have coupling holes that are aligned with each other and have the same diameter as the coupling holes in the coupling tabs 33, 34. About this coupling hole, the connection between the coupling tabs 33, 34 and thus the drive unit 2 is made by a coupling pin 36 through passed through all four coupling holes and locked for the purpose of its positional fixation. In this way, the pressing tool 3 is pivotally connected to the drive unit 2.

The press tool flaps 35 are of identical construction and are arranged congruently and at a distance. They are connected to each other via two hinge pins 37, 38. In the intermediate space between the press tool tabs 35, mirror-shaped press jaw levers 39, 40 are mounted pivotably on the hinge pins 37, 38. The pressing jaw levers 39, 40 form semicircular pressing jaws 41, 42 at their outer ends, which in the illustrated, closed state of the pressing tool 3 enclose a pressing space 43. A compression spring 44 ensures that the pressing jaw lever 39, 40 take the illustrated closed final pressing position in the idle state. At the opposite ends, the pressing jaw levers 39, 40 form drive surfaces 45, 46, which interact with the cylindrical surfaces of the spreading rollers 30, 31 during the pressing process.

The hydraulic pump 7, i. their limited by the pump piston 12 pressure chamber has not shown here hydraulic channels on the one hand connection to the hydraulic reservoir 14 and the other to the pressure chamber 23 in the piston-cylinder unit 19. A check valve in the hydraulic line to the hydraulic reservoir 14 ensures that the pump piston 12th Upon movement in one direction, hydraulic oil sucks from the hydraulic reservoir 14 and, when moved in the other direction, conveys the sucked-in hydraulic oil into the pressure chamber 23. As a result, the hydraulic piston 22 and thus also the piston rod 25 and the spreader 28 connected thereto are moved in the direction of the pressing tool 3.

In the region of the connection of hydraulic piston 22 and piston rod 25, a pressure relief valve 47 is formed in the form of a needle valve. For this purpose, the hydraulic piston 22 has a pressure opening 23 open valve opening 48, which serves as a valve seat for a valve body 49 on the inside. This is loaded in the direction of the valve opening 48 by means of a pressure acting on the rear side of the valve body 49 compression spring 50. The compression spring 50 is designed so that it allows a lifting of the valve body 49 only at a certain cut-off pressure in the Druchraum 23. The valve body 49 defines a valve chamber 51, which has a connection to the rear space 24 via a hydraulic channel, not shown here. This in turn is connected via a hydraulic channel, also not shown, with the hydraulic reservoir 14. All above-described hydraulic channels form a total of a hydraulic system.

How only out FIG. 3 can be seen, is located in the housing of the hydraulic pump 7, an emergency valve 52, which is also designed as a needle valve. It has a connecting channel 53 direct connection to the pressure chamber 23. The connecting channel 53 narrows into a valve seat insert 54, which forms a valve seat on the inside, on which a valve needle 55 sealingly abuts. For this purpose, the valve needle 55 with a Compressed spring 56 loaded. This compression spring 56 is designed so that the valve needle 55 only lifts off from the valve seat insert 54 and thus the emergency valve 52 opens when the pressure in the pressure chamber 23 has reached a value which is at least equal to the cut-off, at which the pressure relief valve 47 at normal function opens, but can also lie about it. The valve chamber of the emergency valve 52 has a channel, not shown here, connection to the hydraulic reservoir 14, so that the hydraulic fluid in the pressure chamber 23 can flow into the hydraulic reservoir 14 when opening the emergency valve 50.

In the rear region of the valve needle 55, a manual override device 57 is provided, with the aid of which it is possible to effect an opening of the emergency valve 52 by external action. For this purpose, the manual actuation device 57 has an actuation tappet 58, which is displaceably guided transversely to the axial extension of the valve needle 55 and ends near the tube 13 within the hydraulic reservoir 14. About a compression spring 59, it is held in the starting position shown. A transverse pin 60 passing through the actuating tappet 58 prevents rotation of the actuating tappet 58 and forms a stop for the starting position. At the valve needle end of the actuating plunger 58 is penetrated by the valve needle 55 and forms there an inclined surface 61, against which a contact surface 62 of the valve needle 55 is applied. Due to this coupling, the valve needle 55 is lifted from the valve seat insert 54 against the action of the compression spring 56 when the actuating plunger 58 is moved by applying pressure to the hose 13 in the direction of the valve needle 55. Independently of this, the coupling between actuation tappet 58 and valve needle 55 allows the valve needle 55 to move freely in the opening direction, so that the actuation tappet 58 has no influence on the automatic opening behavior of the emergency valve 52.

As in FIG. 2 can be seen, the output shaft 5 carries a speed sensor 63, on the circumference of the same or unequal distances magnets 64 are distributed. The speed sensor 63 opposite is rotationally fixed Speed sensor 65 is arranged, which is capable of detecting the outgoing magnetic fields from the magnet 64 and emits corresponding signals to a control device not shown here. The signals are counted there, the speed of the drive motor 4 being determined from the number determined. The control device serves to control the course of the press via the drive motor, as is fundamentally understood from US Pat EP 0 860 220 is known. The control device additionally carries out a plausibility check at the end of a pressing operation in order to determine whether a pressing operation has been carried out successfully. Specifically, it is checked whether a measured after opening the pressure relief valve 47 actual load speed of the drive motor 4 is in a predetermined target speed range. The upper limit of the target speed range determines the speed that must be fallen below to ensure that a predetermined pressing force has been reached. In contrast, the lower limit for the allowable target load speed range is defined in order to detect overshoots of the permissible pressing force. When the engine speed when opening the relief valve 47 is in the predetermined target speed range, the operator receives a response that the pressing operation has been completed successfully. For this purpose, for example, an acoustic or optical signaling device may be provided.

Depending on the state of charge of the batteries or the voltage level of the power network and the engine condition and the ambient temperature can lead to very different engine speeds at idle and correspondingly under load. To compensate for these fluctuations, it is provided that the control device detects the idling speed before the beginning of a compression and predetermines the target load speed range as a function of the measured idling speed. If the determined idle speed is low, so will the load speed when opening the pressure relief valve will be lower, and in the reverse manner, the idle speed is high, so the load speed will be higher. Accordingly, depending on the before the pressing process measured idle speed of the target load speed range specified. This can be determined empirically, for example, and stored in the control device.

For a pressing operation, the pressing device 1 is attached to the press fitting after previously compressed the two pressing jaw lever 39, 40 by hand to the spreader 28 adjacent ends against the action of the compression spring 44 and thus the pressing jaws 44 are removed from each other so that the end a mouth-like opening results. The pressing tool 3 can then be applied radially to the intended location of the press fitting, wherein the pressing jaws 41, 42 initially come to rest on the press fitting and accordingly the drive surfaces 45, 46 are approximated to each other.

Subsequently, the electric motor 4 is set in motion via a switch not shown here. In this idling operation, first the idling speed is detected, and in dependence on it a target load speed range is defined, in which the speed of the electric motor 4 must be at the end of a successfully completed pressing operation.

By the operation of the electric motor 4, the hydraulic pump 7 sucks hydraulic fluid from the hydraulic reservoir 14 and conveys it into the pressure chamber 23. This leads to a translational movement of the hydraulic piston 22 and via the piston rod 25 of the spreader 28 in the direction of the pressing tool 3. In this case, the lateral surfaces come the spreading rollers 30, 31 on the drive surfaces 45, 46 of the pressing jaw lever 39, 40 for conditioning and spread apart them gradually. This in turn has the consequence that the pressing jaws 41, 42 approach each other and thus ensure a compression of the press fitting radially inward. This continues until the pressing jaws 41, 42 come into mutual contact, so reach their final pressing position. This gradually increases the pressure in the Pressure chamber 23. At the same time the speed of the drive motor 4 decreases continuously, as in the FIG. 4 is recognizable.

Even after reaching the Entpressstellung the pressure in the pressure chamber 23 still increases until the predetermined cut-off pressure is reached at which the pressure relief valve 47 opens by lifting the valve body 49 of the valve port 48. The initially limited to the cross-sectional valve opening 48 pressure effect now detected abruptly the entire surface of the much larger valve body 49, the hydraulic fluid can now flow into the rear chamber 24 and from there into the hydraulic reservoir 14.
The control device detects the rotational speed of the electric motor 4 when opening the pressure relief valve. If the detected speed is within the predetermined target load speed range, the operator is notified via the signaling device that the pressing operation has been completed successfully.

Thereafter, the operator turns off the electric motor 4, so that the hydraulic circulation is interrupted. Alternatively, an automatic shutdown of the electric motor 4 can take place. Like in the FIG. 4 can be seen, the rotational speed of the electric motor 4 increases steeply after the opening of the pressure relief valve 47. This speed increase can be used by the control device as a criterion to turn off the electric motor 4. The coil spring 27 then pushes the hydraulic piston 22 back towards the end plate 21. In this case, a pressure is generated in the pressure chamber 23, which is sufficient to keep the pressure relief valve 47 open during the entire return movement of the hydraulic piston 22 until the hydraulic piston 22 has reached the starting position shown in the figures again. Then the pressure relief valve 47 closes.

Claims (13)

1. Handheld drive device for a press device (1) comprising
   a drive motor (4) comprising a hydraulic pump (7) connected with a hydraulic motor (19) via a hydraulic system,
   the hydraulic motor (19) being connected with a hydraulic tank (14) via said hydraulic system in which at least one pressure relief valve (47) is provided,
   the pressure relief valve (47) being designed such that it opens the connection to the hydraulic tank (14) when a defined cut-off pressure is reached in the hydraulic motor (19),
   an actual value sensor,
   an evaluation means to which the actual value sensor is connected and which stores at least one set value range in which the actual value of the physical quantity should be upon reaching the cut-off pressure,
   the evaluation means comprising a comparison means checking whether the actual value detected by the actual value sensor is within the predetermined set value range, and
   a signaling means for indicating whether the actual value is within the predetermined set value range,
   characterized in that
   the actual value sensor is designed to detect the rotary speed of the drive motor (4), and at least one set load speed range is stored in the evaluation means within which the load speed of the drive motor (4) should be upon reaching the cut-off pressure,
   the evaluation means detecting the idle speed prior to a pressing operation and predetermines the set load speed range as a function of the measured idle speed.
2. Drive device of claim 1, characterized in that the actual set value sensor comprises a signal transmitter (63) held at output shaft (5) of the drive motor (4), contactors (64) being distributed over the transmitter circumference, in particular at equal or varying intervals, and comprising a sensor (65) fixed to the device that detects the contacts transmitted from the contactors (64) and supplies corresponding signals to a control device, said control device determining the actual rotational speed from the detected signals.
3. Drive device of claim 2, characterized in that the signal transmitter (63) is configured as a rotational speed sensor and carries a magnet (64) as a contactor on its circumference, and the sensor (65) detects the magnetic fields emanating from the magnet (64) and supplies corresponding signals to the control device.
4. Drive device of one of the preceding claims, characterized in that a control device is provided for influencing the drive motor (4), and the evaluation means is connected to the control device or is a part of the same.
5. Drive device of claim 4, characterized in that the control device controls the drive motor (4) depending on the actual value detected by the actual value sensor.
6. Drive device of claim 5 and one of claims 2 to 5, characterized in that the control device turns off the drive motor (4) if the evaluation means detects an increase in the actual rotational speed detected by the actual value sensor after the opening of the pressure relief valve (47).
7. Drive device of one of claims 1-6, characterized in that the drive device (2) comprises a coupling (32) for attaching a pressing tool (3) used to press workpieces, and the hydraulic motor (19) is coupled with an actuation means (28) for actuating the pressing tool (3).
8. Drive device of one of claims 1-7, characterized in that the hydraulic motor (19) comprises a restoring means (27) returning the hydraulic motor (19) to its initial position after the pressure relief valve (47) has been opened, and thereby conveying hydraulic liquid from the hydraulic motor (19) into the hydraulic tank (14).
9. Press device comprising a drive device (2) and a pressing tool (3) for pressing workpieces, said pressing tool being coupled with the drive device (2), characterized in that the drive device (2) is designed according to one of claims 1-8.
10. Method for controlling a handheld drive device for a press device (1), wherein
    for performing a pressing operation, a hydraulic motor (19) is driven by a drive motor (4) through a hydraulic system including a hydraulic pump (7),
    upon reaching a defined cut-off pressure in the hydraulic motor (19), a pressure relief valve (47) is opened,
    an actual value sensor detecting the rotational speed of the drive motor, and an evaluation means storing at least one set load speed range within which the load speed of the drive motor should be upon reaching the cut-off pressure,
    the idle speed being detected prior to the beginning of a pressing operation, and the set load speed range being predetermined as a function of the measured idle speed,
    a comparison is made as to whether the actual value of the rotational speed of the drive motor is within the at least one predefined set value range, and
    it is indicated, whether the actual value is within the predefined set value range.
11. Method for controlling a handheld drive device for a press device (1) of claim 10, wherein said at least one set value range is stored in an evaluation means that preferably includes a comparison means for checking, whether the actual value detected is within the predefined set value range.
12. Method for controlling a handheld drive device for a press device (1) of claim 10 or 11, wherein the drive motor (4) is preferably controlled by means of a control device, the control being made depending on the actual value detected.
13. Method for controlling a handheld drive device for a press device (1) of claim 12, wherein the drive motor (4) is turned off, if, after the opening of the pressure relief valve, an increase is determined in the actual rotational speed detected by the actual speed sensor.

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