EP2722133B1 - Method for operating a motor-actuated manual injection device and manual injection device - Google Patents

Description

The invention initially relates to a method for operating a motor-operated hand-pressing device according to the features of the preamble of claim 1.

Moreover, the invention also relates to a motor-operated hand-pressing device according to the features of the preamble of claim 10.

Such methods for operating a pressing device or hand-pressing devices are known. For example, be on the WO 99/19947 directed. The pressing device known therefrom is hydraulically driven. In addition, directly driven by electric motor such pressing devices are known. For this purpose, for example, on the DE 203 05 473 U1 to refer. Instead of two compression jaws and only one, be provided against a fixed counter-stop to be moved pressing jaw. See, for example US 5,727,417 ,

It has also already been proposed, see for example the not previously published German patent application 10 2006 026 552 in a release of the pressing jaws, so that they can move back to the open or openable starting position or can be moved (with respect to be moved is to point out that such pressing jaws, although their opening is basically possible, with a spring in a biased position may be biased, see, for example DE 10 2005 028 083 A1 ), to be able to make an interruption of the movement in the starting position, so that a next pressing operation can be started immediately from an intermediate position selected thereby. It saves time when a full movement to the starting position is not required. This interruption must always be made for a special operation.

Furthermore, measures have already been proposed in various respects to allow a check whether a compression was actually carried out. In the EP 1 092 487 A2 For this purpose, a device proposed on the pressing jaws, which allows a reopening only after complete compression. However, this measure for checking the complete compression is relatively expensive.

From the US 5195042 a pressing device is known which has an analog pressure sensor for detecting a low pressure position, a high pressure position and a starting position. For the actual detection and evaluation of an actuator located outside a singular position, the pressure sensor can not be used.

Next is the state of the art on the US 2003/0066324 A1 and the EP 1306939 A2 to refer. The pressure sensors known from the latter documents serve only to measure the press force achieved.

Starting from a state of the art approximately according to US 5195042 A The invention has the object to provide an advantageous method for operating a hand-pressing device and an advantageous hand-pressing device, in which a simple determination of the position of the pressing jaws acting actuator is made or achieved.

This object is procedurally achieved in the subject matter of claim 1, wherein it is pointed out that by means of the detected by the pressure sensor Pressure a position of the one or more pressing jaws acting actuator is detected by a time measured pressure value is converted into a distance value or used as an analog value.

This object is achieved with respect to the hand-held pressing device in the subject matter of claim 10, wherein it is pointed out that a pressure value over time can be measured by means of the pressure sensor and a determination of the piston position by converting a pressure value into a path value or by using as analog value is feasible.

Since the hydraulic fluid pressure due to the friction of the piston in the cylinder and the force of the return spring has an approximately linear pressure increase and pressure drop on the way back and forth of the piston, the actual position of the piston in the cylinder can be determined hereby also with a certain tolerance. In this respect, the pressure value measured over time can be converted into a distance value and to that extent, as explained below with respect to a displacement value, with respect to the position of the piston and thus ultimately the pressing jaws are converted or used as an analog value for this purpose.

In particular, there are a large number of possibilities for concrete implementation. It is advantageous, first, that a first workpiece contact is determined and a path or time mark assigned to this first workpiece contact is detected. The workpiece contact can basically be detected by a pressure sensor arranged, for example, in a pressing jaw. The workpiece contact can continue, for example, by evaluating the motor current. As soon as there is a significant increase in the motor current, this can be interpreted as a workpiece contact. The formation of a pressing device with a pressure sensor also has significance in terms of interrupting the return of the moving part or concretely a hydraulic piston at an intermediate position.

In a known manner, one or more pressing jaws can be moved from an open starting position into a closed pressing position by a switch actuation until a predetermined pressing force has been reached or a predetermined time has elapsed, after which automatically, for example by return of a pressing piston acting on the pressing jaws, a pressing jaw Release occurs, but this release can be interrupted before reaching the start position in an intermediate position to start a next pressing operation from such an intermediate position.

The detection of the position of the pressing jaws acting on the pressing member may subsequently, after pressing, in the course of the release of the pressing jaws, be used to this extent according to the interruption to achieve the intermediate position. Suitably, you will not choose exactly the same place where the device by the increase of the motor current, in the example given, the workpiece touch has detected, but make some addition to this so determined travel, pressure or Zeitmaß to certainly a To reach intermediate position, in which the next grouting without hindrance can be started again. Without hindrance means here in particular that the pressing jaws are a little wider than it would actually be required.

The addition to the travel, pressure or time measure can be between 0 and 50% of the measure, this bandwidth also including all intermediate values, in particular in 1/10% steps. The addition may therefore be between 0 and 40.9% and 0 and 40.8% etc. But also between 0.1 and 50%, 0.2 and 50%, 0.3 and 50% and on the other hand also between 0.1 and 40.9%, 02 and 40.9%, 0.2 and 40.8 % etc. Of these values, 0 to 10% inclusive, in turn, is preferred as indicated.

In practical applications, for example, it is the compression between fittings and pipes by means of a cross-pressing sleeve. To achieve a tight connection between two abutting tubes. If subsequently a plurality of crimping takes place either on the same pipe string or in pipe runs of the same nominal diameter, which in each case do not require the method of pressing jaws in the starting position, but an intermediate position at which the interruption of the release is advantageous, can with a as described herein Design be worked very efficiently. Another application is the compression (crimping) of a cable lug.

For this purpose, it may further be provided that an interruption of an intermediate position assigned and determined in the course of the pressing process Distance and / or time and / or pressure measure is recorded or stored, according to which degree the release can be interrupted at the following intermediate Verpressions automatically at the relevant intermediate position.

In this case, it is first of all essential that the release is not necessarily interrupted in the case of the aforementioned intermediate position even in such a case. But it can be interrupted. In other words, as a result, the pressing device is variably usable, so that it (only) interrupts the release when suitably actuated at the intermediate position. Similar processes can always be carried out starting from the same intermediate position. Suitably, it may be provided in terms of operation technology, which is also explained below, that with regard to the respective interruption at the intermediate position no special operation is required, but if no interruption should take place at the intermediate position, this - more preferably: once - by a special operation of the device can be achieved. Conversely, it is equally possible that only for a particular operation of the device, i. In particular, a special switch operation out, an interruption of the press jaw release at the desired intermediate position, but not otherwise.

In this context, it is further preferred that the storage of said measure or measured value always takes place during each pressing process. Regardless of whether the interruption is applied using this measure or not.

A further possibility for determining the intermediate position is also given by the fact that the time from the workpiece contact to the completion of the compression is measured and the press jaw release after the passage of a measured time corresponding path, since the completion of the compression, is interrupted. The interruption is thus (only) time-dependent, whereby due to the given relationships (in the case of return, there is practically no disturbance to be taken into account, so that a certain time since the beginning of the return corresponds quite accurately to a specific piston travel), the path can be readily determined (for example over a factor applied to the measured time ).

The end of the compression itself will suitably be detected in a conventional manner. For example, due to the pressure drop and / or opening of a return or overload valve. If necessary, also only on the expiry of a certain period of time, for example measured since the beginning of the Verpresszyklus.

In this respect, it is further advantageous that the intermediate position can be stored and, depending on a specific actuation or non-confirmation of the pressing device during the following pressing operations, the return is in each case carried out only up to the intermediate position. This can be achieved, for example, by the fact that the interruption at the intermediate position takes place only as long as it is repeated, as a start key of the device remains pressed continuously. As soon as the start button is no longer pressed, the device then returns to its original start position. Despite the pressed start button can then take place nevertheless a shutdown of the engine, be it the hydraulic motor or the electric motor, after completion of the compression. The - further depressed start button then ensures that at the assigned intermediate position, the interruption of the return or the press jaw release takes place. For example, by brief automatic actuation of the hydraulic pump in the case of the return interruption according to the German patent application mentioned above 10 2006 026 552 , It may then be necessary to start a new injection cycle, release the start button first and then press again. Over this, until the next pressing cycle is triggered by pressing the start button, can basically take an arbitrarily long time. In order to achieve the desired sequence, ie the interruption of the return at the desired position, it is only necessary to then press the button again until the desired interruption of the return. For example, here also the circuit may be provided so that the start button does not need to remain pressed until the actual return interruption, but only a longer period than usual when triggering the pressing process.

The interruption of the return at a desired location has the consequence that the pressing jaws or a movable pressing jaw with fixed counter-stop, only a maximum of such interruption associated, opening, then, when the interruption has occurred. This may mean, for example, that a displacement on the same tubing to a further injection point is possible, but the complete removal of the device from the pipe in question is not possible. In this respect, a security aspect is given that the device, for example, can not fall down.

Further alternatively, it can also be provided that the travel and / or pressure and / or time measurement is detected according to a freely selected interruption. As soon as, for example, by briefly tapping the shutter button for a pressing operation, a break occurs (see above-mentioned German patent application 10 2006 026 552 ) can this associated travel and / or pressure and / or time measurement (time about the time that has passed since the completion of the pressing process) are detected and then take place at a next injection process at the same point the interruption automatically. It then only requires, for example by briefly pressing the start button, an initiation of the next pressing process, which then without any other operation is required, automatically ends at the selected intermediate position again. If you want to return to the starting position, you can this is done, for example, by a long press, double-pressing the start key or the like; depending on which "detection" on the device is preset or preprogrammed.

Further alternatively, the displacement and / or pressure and / or time measurement can be detected according to a change in the operating rhythm. This can be done, for example, that up to the desired intermediate position, now starting with the start position (on the "way out" to a - first - pressing), by repeated short-term pressing a start button of the device, the advancement of the biasing member for the dies takes place. As soon as the desired intermediate position has been reached, the start button can be pressed continuously until the compression is completed. Then the start button can be released and the release of the pressing jaws then takes place automatically only up to the intermediate position. Pressing the start button again, whether with constant holding or only short-term operation, the next Verpressrhythmus runs accordingly in the same way.

With regard to compliance with the predetermined pressing force, by a pressure sensor of the hydraulic fluid detected pressure sensor is given a further use of the pressure sensor. The check can be carried out in detail, for example, by a comparison between a predetermined minimum pressure value and an actually achieved pressure value. If, for example, the compression should have reached at least a pressure value of 500 bar, this value can be preset as a minimum pressure value and compared with a pressure value reached, for example 600 bar or 650 bar. As long as the difference between the actually achieved pressure value and the predetermined pressure value is positive, such a compression can be considered to be in order.

In other respects, such a pressure sensor can also be used to check by means of the pressure detection a desired automatic opening of the return valve. By storing corresponding curves corresponding to a complete pressing operation, the actual setting and function of the automatically opening return valve can be checked for the large pressure drop occurring upon automatic opening of the return valve. In particular, a corresponding value storage can be used during maintenance work to set the return valve without having to actually perform an actual pressurization.

In particular cases, such as tube expansion operations, it is desirable to maintain a certain pressure value, a rupture pressure value, for some time without opening the return valve. In that regard, the provision of the pressure transmitter can be used to that by setting a pressure threshold, which is below a to be reached for the completion of a press cycle maximum pressure, a stop of the moving member is performed to achieve a pressure maintenance. In the case of the automatically opening return valve, the maximum pressure value would correspond to the release pressure set with respect to the return valve. The pressure threshold value is selected correspondingly below the release pressure of the return valve in this case. Upon reaching the pressure threshold then suitably a shutdown of the engine, which actuates the hydraulic fluid pump. The pressure is therefore kept. By predetermined or manually selected repeated actuation of the trigger switch, the pumping operation can then be continued. The predetermined actuation of the trigger switch can proceed accordingly automatically and take place after expiration of a, optionally freely selectable, period of time from stopping the engine after reaching the pressure threshold. In this case, however, it may also be readily provided in a variant that when detecting a repeated actuation below Pressure, so at the approximately predetermined pressure threshold, at the same time with the repeated operation of the opening of the return valve, since then the desired target for this purpose pressurization is reached and it no longer requires a further rise in pressure to the automatic opening of the return valve (in the usual cycle).

In the pressing device, a current sensor for detecting the motor current and / or a pressure sensor for detecting the hydraulic fluid pressure in the hydraulic cylinder, as already described, be provided, wherein by means of the pressure and / or current measurement of the relevant hydraulic fluid pressure is used for evaluation and / or derived therefrom distance measure is used for further determination.

In a further preferred embodiment, it is provided that a - suitably preprogrammed - microcontroller for evaluating the signals supplied by the pressure sensor and / or a current sensor and / or a timer and / or a displacement sensor is provided. In particular, it is also preferred that only one pressure sensor, i. no displacement sensor and no current sensor, but a timer, or only a current sensor, that is, no displacement sensor and no pressure sensor, but possibly a timer, are provided. On the other hand, in particular, the pressure sensor may be provided in combination with the current sensor, and a timer.

In a further preferred embodiment, it is provided that an electrical line transmitting the signal of the pressure sensor to a microcontroller is branched and that a branch line is switched unfiltered to an ADC channel of the microcontroller, while the other branch line is provided with an amplification unit and / or a low-pass filter ,

It is furthermore preferred that a pressure prevailing in the hydraulic fluid when a pressing process is activated be measured and compared with a desired value. In this way, it can first be determined whether it is a turning on of the pressing device in a conventional starting position, in which only the bias voltage caused by the return spring, for example (with a certain surcharge) is applied. Or whether it is a reconnection of the pressing device after switching off and pressure, for example, when in the course of a Aufweitvorganges a certain compression pressure over a certain time continuously applied to the workpiece.

In a further preferred embodiment, it can then be provided that an opening of the return valve is performed in dependence on the determined when switching on the pressure of the hydraulic fluid associated with this switching. This procedure is in turn of importance, in particular, in relation to the expansion method already given by way of example. If, on the basis of the comparison with a nominal value, it is ascertained that it is a reconnection under pressure, the desired or predetermined holding time under pressure in the course of the expansion process, for example, has expired at the same time. Thus, with this reconnection then immediately opening the return valve can be performed combined.

In general, it is preferred that the pressure is measured after switching on the device at regular intervals. For example, at intervals of less than a second. More preferably at intervals of between one and twenty milliseconds.

Fig. 1

eine teilweise aufgeschnittene Darstellung eines ersten Verpressgerätes mit einer Pressbacke in der Startposition;

Fig. 2

eine Darstellung gemäß Fig. 1, mit der Pressbacke in der Verpressposition;

Fig. 3

eine Darstellung gemäß Fig. 1 bzw. Fig. 2 mit der Verpressbacke in der Zwischenposition;

Fig. 4

eine Darstellung gemäß Fig. 1, jedoch bei einer Ausführung mit zwei Verpressbacken;

Fig. 5

eine weitere Schnittdarstellung eines entsprechenden Verpressgerätes im Bereich der Pumpe mit angeordnetem Drucksensor;

Fig. 6

einen Schnitt durch den Gegenstand gemäß Fig. 5, geschnitten entlang der Linie VI - VI;

Fig. 7

eine schematische Darstellung des Druckverlaufs bei einem Verpresszyklus im Bereich bis zur Werkstückberührung, aufgetragen über den Weg;

Fig. 8

eine schematische Darstellung des Druckverlaufs über einen Verpresszyklus, aufgetragen über den Weg;

Fig. 9

eine Darstellung gemäß Fig. 8, aufgetragen über die Zeit;

Fig. 10

eine erste schematische Darstellung des Motorstroms bei einer Verpressung, aufgetragen über den Weg;

Fig. 11

eine Darstellung gemäß Fig. 10, jedoch bei anderen konstruktivem Aufbau der Pumpe.

In the following, the invention will be explained further with reference to the attached drawing, which, however, represents only exemplary embodiments. This shows.

Fig. 1

a partially cutaway view of a first Verpressgerätes with a pressing jaw in the start position;

Fig. 2

a representation according to Fig. 1 , with the pressing jaw in the pressing position;

Fig. 3

a representation according to Fig. 1 respectively. Fig. 2 with the compression jaw in the intermediate position;

Fig. 4

a representation according to Fig. 1 , but in a version with two compression jaws;

Fig. 5

a further sectional view of a corresponding Verpressgerätes in the pump with arranged pressure sensor;

Fig. 6

a section through the article according to Fig. 5 , cut along the line VI - VI;

Fig. 7

a schematic representation of the pressure curve in a Verpresszyklus in the area to the workpiece contact, plotted on the way;

Fig. 8

a schematic representation of the pressure curve over a Verpresszyklus, plotted on the way;

Fig. 9

a representation according to Fig. 8 , plotted over time;

Fig. 10

a first schematic representation of the motor current at a compression, plotted on the way;

Fig. 11

a representation according to Fig. 10 , but with other constructive structure of the pump.

Shown and described, first with reference to the Fig. 1 to 3 , a hydraulic pressing device 1 with an electric motor 2, a hydraulic fluid reservoir 3, a pump assembly 4 and a plunger 5, which is directly connected to a pressing jaw 6.

The electric motor 2 is operated in the embodiment via stored in an accumulator 7, not shown in detail electrical energy.

By means of a start switch 8, the beginning of a Verpresszyklus be triggered.

In the illustrated embodiment, the electric motor 2 will start to run on the operation of the switch 8 back and pumped accordingly by means of the pump 4 from the hydraulic fluid reservoir 3 in the hydraulic cylinder 9 hydraulic fluid, whereupon the hydraulic piston 5 together with the pressing jaw 6 from the in Fig. 1 shown starting position in the in Fig. 2 moved shown pressing position.

In a further embodiment, with respect to the current absorbed by the electric motor 2, a current sensor may be provided, which detects a current profile over the path of the hydraulic piston 5, as it qualitatively in the FIGS. 10, 11 is shown.

The Fig. 10 in this case relates to a hydraulic pump of conventional design or the qualitatively quite fundamental course of the current curve. The Fig. 11 relates to the course of the current curve in a two-stage hydraulic pump, but not exactly reproduced here, but qualitatively represented. Especially such a two-stage hydraulic pump as that from the EP 0 927 305 B1 is known.

Associated with the switching on of the device, in both cases, a very high current pulse is initially detected. A practical value is here, for example, at 80 amps. This current value decays very quickly with the starting up of the electric motor, to a value which is only slightly above the no-load current of the motor. In principle, when the workpiece is touched, the motor current increases. If a certain threshold is exceeded in the FIGS. 10, 11 associated with the path S1 (in the same way this is also a time measurement, whereby the way can understandably be applied only to the closing of the compression jaws), this path value is stored approximately in a memory chip accommodated in the device, which for this purpose has a volatile memory can have. Thereafter, the increase in the current curve up to a maximum value is evident. This corresponds to the completion of the compression or the triggering of the return valve, after which the hydraulic pressure correspondingly drops sharply or even the hydraulic pump is switched off automatically.

Regarding the representation in Fig. 11 This results in a characteristic difference insofar as the current curve increases according to the distance measure S1 (not yet significant). In practice, it can not only remain the same, but so also fall off initially. This is due to the fact that at this point a switching of the two-stage piston pump from the first to the second stage takes place. Since the second stage works with a much higher translation, is initially an equal or sometimes even low motor current only required.

But also in the case of a qualitative course of the motor current accordingly Fig. 11 Then, after a certain further path or a certain further period of time, a significant steep rise in the motor current takes place until the completion of the compression.

Due to the stored value, an interruption of the return of the hydraulic piston 5 can then take place after completion of compression at this associated way mark S1. In the case of the qualitative course of the motor current according to Fig. 11 An arithmetical addition can also be made if, for example, in the case of actually executed devices, depending on the performance of the device as well, it is considered sensible to define a touch only from the path or time dimension S'1, ie at the beginning of the actual increase of the motor current.

The interruption can be carried out, for example, as in the above-mentioned patent application 10 2006 026 552 is explained in detail. The relationship between motor current and path, approximately according to Fig. 10 , can be stored in a non-volatile memory during the manufacture of the device.

From the above it is also clear that in principle the same way with corresponding time measurements can be used.

After a certain threshold is exceeded in terms of the increase of the motor current, assigned to the in Fig. 10 given value of the path S1, a storage of this associated path value takes place approximately in a stored in the device memory chip, which may have a volatile memory for this purpose. The way value can, for example, by converting the over time recorded motor current, since at least up to a first workpiece contact a sufficiently accurate (at least when averaging: linear) relationship between the path of the piston and the (only) required motor current is given. There then takes place an interruption of the return of the hydraulic piston 5 after completion of pressing at this associated way mark S1. The interruption can be carried out, for example, as in the above-mentioned patent application 10 2006 026 552 is explained in detail. The relationship between motor current and path, approximately according to Fig. 5 , can be stored in a non-volatile memory during the manufacture of the device.

For a displacement measurement, alternatively or additionally, the relative position between the hydraulic cylinder and the hydraulic piston, in the case of a piston device, for example, can be detected. About one, several (two to four) or a plurality (five or more) of proximity switches, which are mounted on the length of the hydraulic cylinder in this and each can detect the position of the hydraulic piston.

The completion of the compression can be detected, for example, by the fact that a, accompanied by the opening of a return valve, strong drop in the motor current, which waste is then used to detect the end of the compression.

Since the time that elapses from the workpiece contact to the completion of the pressing is not the same for each pressing, but rather can depend on individual pressing conditions, in particular the pressed materials, the time can additionally or alternatively also be measured, that of the first workpiece contact , as recorded in the manner explained above, passes until the completion of the compression and this time measure then be used accordingly after completion of the compression and elapse of this time measure then trigger the interruption, so that - in the example - the hydraulic piston assumes the desired intermediate position.

As in the same time measurement usually in the unobstructed return a greater way is covered than the flow under Verpressbedingungen, immediately results in a usually desired "oversize" to the interruption or the press jaw release with certainty before the position (the Release position of the pressing jaws) reached, which is minimally required in order to carry out the next pressing can.

With regard to the time measurement can be provided in the device, a timer, such as in the form of a microchip. In the event that a period of time is to be detected, this timer will start to count at a certain triggering time and then at a certain end time point the time interval thus determined will be detected and stored, for example, in the volatile memory.

Specifically, for example, when the time from the first workpiece contact (for example, by detecting the significant increase in motor current) to the completion of the compression (for example, by detecting the drop in motor current after the return valve has opened) is measured, and this time is then used for the return of the piston (in the case of a hydraulic device) is specified until the interruption takes place at the then determined intermediate position. Or, in which the time from the automatic shutdown of the hydraulic motor after completion of the compression (determination as described above) to a (short) will be voluntarily restarted to interrupt the retrace and then, in the following cycle, this interruption - after the measured so and then stored time - automatically. This automatic interruption can then, as already stated above, be carried out for each cycle as long as a certain mode of operation, such as holding down the start button until the interruption has taken place, is maintained.

In general, it does not matter that the return takes place after reaching a constant maximum pressure. When using a displacement sensor, the pressing times and pressing forces are not essential. The control of the pressure build-up and disassembly can also be done with solenoid valves.

On the other hand, as already described in the introduction, certain (mathematical) factors, be they extending the path or shortening the course, can also be used in this context. The latter will usually result from empirical knowledge. But at the same time be factory-set upon delivery of the device.

As in the same time measurement usually in the unobstructed return a greater way is covered than the flow under Verpressbedingungen, immediately results in a usually desired "oversize" to the interruption or the press jaw release with certainty before the position (the Release position of the pressing jaws) reached, which is minimally required in order to carry out the next pressing can.

In Fig. 2 is the injection condition of the device according to Fig. 1 shown.

In Fig. 3 is the device according to Fig. 1 represented in the retracted then then due to the procedure described intermediate position.

In Fig. 4 Alternatively, a device is shown with two pressing jaws.

In reference to Fig. 5 is shown in a partially schematic view of a pressing device in which a pressure sensor 10 is arranged. As is clear from the context with Fig. 6 shows, the pressure sensor is associated with the return channel 11 of the hydraulic fluid disposed over which return passage, the hydraulic fluid flows to the return valve 12 and from there, with the return valve open, in the storage area 13. From the return passage 11, seen in return flow beyond the return to the return valve 12th going branch, a branch channel 14 is provided, see Fig. 6 , communicates with a receiving channel 15 of the pressure sensor 10. The pressure sensor is thus arranged circumferentially offset to the return valve 12 and / or the return channel 11.

In reference to Fig. 7 the quality of the pressure measured by a pressure sensor over the piston stroke during compression is shown qualitatively. This already corresponds to a conversion. Because the actual pressure detection is usually preferred only over time. In principle, however, an additional displacement sensor can also be provided, for example.

The curve is drawn here only up to the event that a first significant workpiece contact and thus pressure increase is given. Accordingly, the pressure scale is also designed for very low pressures, for example up to 10 bar, in the illustration. The pressure is preferably measured at regular time intervals. In the embodiment, at intervals of five milliseconds.

It is essential that in the range of low pressures or initial piston stroke, until there is a first significant pressure increase due to a workpiece contact, a linear course results, which is hysteresis-like spaced also with respect to the return. This pressure profile is explained by the fact that the return spring acting on the piston with increasing Compression exerts a higher force. This explains the approximately linear increase of the pressure curve as long as there is no first significant workpiece contact. The fact that, furthermore, the friction of the piston in the cylinder plays a role, but this frictional force acts opposite depending on the direction of movement of the piston, it comes to the different curves in the flow and return. The pressure difference is in the range of 0.5 to 1 bar.

Due to this relationship according to Fig. 7 can also be closed or calculated back to the position of the piston outside a workpiece contact from the measured pressure. This can be exploited, for example, that, by comparing the measured values, that piston position is determined which still corresponds to the linear relationship before a significant pressure increase due to the workpiece contact then occurs. A piston position determined in this way can subsequently be used as an intermediate position or holding position, from which then the next pressing can be started.

At the beginning of the movement of the plunger 5, a pressure jump from zero to, for example, 4 or 5 bar. This pressure jump is due to the preferably given bias of the return spring.

In reference to Fig. 8 is in basically the same representation (pressure over the way) as in Fig. 7 the qualitative pressure curve is shown at a complete compression.

The grouting process begins at point A, here assuming a completely receded compression piston. There is first the slight increase in pressure up to the point B, which represents the workpiece contact and the beginning of a significant compression pressure increase. The compression takes place until the point C is reached, specifically according to a first pressure gradient. After reaching point C, the pressing jaws lie on one another, but the triggering pressure at the end of the pressing or opening of the return valve has not yet been reached. It then comes to an increase in the pressure gradient until the point D is reached. At point D, the return valve opens or the compression is stopped and the pressure drops again to point E, whereupon the return of the piston, in the given case up to the point A in turn, then takes place. The increase in the pressure gradient between the points C and D is due to the fact that the compression then - practically only - against the rigidity of the tool head itself, just when compressed pressing jaws, works. This is significantly higher than the rigidity of the workpiece to be pressed (gradient between B and C).

This difference in the pressure gradient, at least after a first workpiece contact has occurred, which, as explained further above, also due to the pressure sensor, for example, but due to the motor current, can be determined, can also be used for further evaluation. Namely, for the evaluation of whether there really was a complete compression. The fact that the pressure gradient between C and D, which also represents practically a tool constant, is achieved implicitly that the compression jaws abut each other, so the compression has taken place. An incomplete pressing can then also be used, for example, to trigger a signal, for example an acoustic signal. The signal must then be further deleted, for example by a special operation. Furthermore, a light-emitting diode can also be provided in the pressing device as a display means. For example, for the condition "pressing runs".

In Fig. 9 For clarity, the pressure curve (or a current measured at the pressure sensor) is plotted over time. It is in terms of a typical course for a real compression. Again, the above-mentioned points A, B, C, D and E can basically be distinguished.

Claims (15)

1. Method for operating a motor-actuated hand-held pressing device (1), in which one or more pressing jaws (6) are moved from a start position into a closed pressing position on actuation of a switch until a predetermined pressing force is achieved or a predetermined period of time has elapsed, after which the pressing jaw is automatically released, for example by the return of a pressing piston (5), the pressing piston further being hydraulically actuated by means of a hydraulic medium, the pressure of the hydraulic medium being detected by means of a pressure sensor (10), characterised in that a position of an actuator acting on one or more pressing jaws (6) is detected by means of the pressure detected by the pressure sensor (10), by a pressure value measured over time being converted into a stroke value or being used as an analogue value for this purpose.
2. Method according to claim 1, characterised in that the pressure sensor which detects the pressure of the hydraulic medium checks that the predetermined pressing force has been achieved.
3. Method according to either claim 1 or claim 2, characterised in that release of one or more pressing jaws can be interrupted in an intermediate position before said jaws reach the start position in order to initiate the next pressing operation from such an intermediate position; in relation to an interruption, a measure of stroke and/or time and/or pressure associated with the intermediate position and determined during the pressing operation further being detected or stored, as a result of which measure the release can be interrupted automatically in subsequent pressing operations at the relevant intermediate position.
4. Method according to any of the preceding claims, characterised in that a first instance of contact with a workpiece is determined and an associated measure of stroke, time or pressure is detected, the contact with a workpiece preferably being determined by evaluating the motor current.
5. Method according to claim 4, characterised in that the time from the point at which contact is made with a workpiece to the point at which the pressing is completed is measured and the release of the pressing jaws is interrupted after a stroke corresponding to the measured time has been covered since the end of pressing, and/or in that the return is carried out in each case only up to the intermediate position based on a specific actuation of the pressing device in subsequent pressing operations.
6. Method according to either claim 4 or claim 5, characterised in that the measure of stroke and/or time may also be detected in accordance with a freely selected interruption, and/or in that the measure of stroke and/or time is detected in accordance with a change in the actuation rhythm.
7. Method according to any of claims 1 to 6, characterised in that, in order to check that the predetermined pressing force has been achieved, a predetermined minimum pressure value and an actual pressure value are compared, and/or in that the pressing procedure is monitored in relation to different pressure gradients by means of pressure detection, a transition to a steeper pressure increase detected after contact with a workpiece and the corresponding pressing preferably being interpreted as a signal for completed pressing.
8. Method according to any of the preceding claims, characterised in that a desired automatic opening of the return valve is checked by means of the pressure detection.
9. Method according to any of the preceding claims, characterised in that, by predetermining a pressure threshold value that is below a maximum pressure value to be reached for the termination of a pressing cycle, the movable part is stopped in order to maintain the pressure.
10. Motor-actuated hand-held pressing device comprising a stationary part and a movable part (6), the movable part (6) being moved relative to the stationary part by means of a hydraulic piston (5) travelling inside a hydraulic cylinder (9) and being able to be moved back into an initial position by means of a return spring, a pressure sensor (10) being provided which detects the pressure of the hydraulic medium in the hydraulic cylinder (9), characterised in that a pressure value can be measured over time by means of the pressure sensor (10) and the piston position can be determined by converting a pressure value into a stroke value or by using said pressure value as an analogue value for this purpose.
11. Hand-held pressing device according to claim 10, characterised in that an electrical line which transmits the signal from the pressure sensor to a microcontroller is branched and in that one branch line is connected to an ADC channel of the microcontroller in an unfiltered manner, while the other branch line is provided with an amplifier unit and/or a low-pass filter.
12. Hand-held pressing device according to either claim 10 or claim 11, characterised in that a pressure prevailing in the hydraulic medium when a pressing device is activated is measured and compared with a target value.
13. Hand-held pressing device according to claim 12, characterised in that, in association with the activation, the return valve is opened depending on the pressure of the hydraulic medium determined during said activation.
14. Hand-held pressing device according to any of the preceding claims, characterised in that the pressure is measured at a time interval of less than one second.
15. Hand-held pressing device according to claim 14, characterised in that the pressure is measured at a time interval of between one and twenty milliseconds.

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