Method of operating a handheld pressing unit

Abstract

A method of operating a motor-actuated handheld pressing unit includes actuating a switch to initiate a pressing operation whereby one or more pressing jaws are moved from a starting position to a closed pressing position; automatically releasing the one or more pressing jaws by using a pressing piston when a prescribed pressing force has been reached, the pressing piston being actuated hydraulically by a hydraulic medium; and checking the reaching of the prescribed pressing force by using a pressure sensor to detect the pressure of the hydraulic medium. In an embodiment, the release of the pressing jaws may be interrupted. In an embodiment, a motor moves the jaws from the starting position to the closed pressing position. In an embodiment, the pressing force is continuously measured on intervals of less than one second.

Claims

1. A method of operating a motor-actuated handheld pressing unit comprising: actuating a switch to initiate a pressing operation whereby one or more pressing jaws are moved from a starting position to a closed pressing position; automatically releasing the one or more pressing jaws by using a pressing piston when a prescribed pressing force has been reached, the pressing piston being actuated hydraulically by a hydraulic medium, wherein the pressing force is continuously measured on time intervals of less than one second; and checking the reaching of the prescribed pressing force by using a pressure sensor to detect a pressure of the hydraulic medium.

2. The method according to claim 1, wherein the time intervals are between 1 and 20 milliseconds.

3. The method according to claim 1, wherein contact with a workpiece is determined and an associated measurement of travel, time or pressure is recorded.

4. The method according to claim 3, wherein the one or more pressing jaws are moved from the starting position to the closed pressing position by use of a motor; and the contact with the workpiece is determined by evaluating current within the motor.

5. The method according to claim 1, wherein the one or more pressing jaws are moved from the starting position to the closed pressing position by use of a motor; and a contact with a workpiece is determined by evaluating current within the motor.

6. The method according claim 1, wherein a time is measured from contact with a workpiece to completion of the pressing operation, and a release of the one or more pressing jaws is interrupted after an elapse of a travel distance that corresponds to the time measured.

7. The method according claim 1, further comprising: automatically releasing the one or more pressing jaws during the pressing operation when the prescribed pressing force has been reached or the prescribed amount of time has elapsed, the one or more pressing jaws are moved from the closed pressing position to an intermediate position which is between the closed pressing position and the starting position.

8. The method according to claim 1, wherein the checking of the reaching of the prescribed pressing force is carried out by comparison between a prescribed minimum pressure value and a pressure value actually achieved.

9. A motor-actuated handheld pressing unit configured to perform a pressing operation comprising: one or more pressing jaws; a switch configured to initiate the pressing operation whereby the one or more pressing jaws are moved from a starting position to a closed position; a pressing piston being actuated hydraulically by a hydraulic medium; a timer configured to measure time of a pressing force; and a pressure sensor configured to detect a pressure of the hydraulic medium, wherein the pressing piston is configured to automatically release the one or more pressing jaws when a prescribed pressing force has been reached, wherein the pressing force is continuously measured on time intervals of less than one second by the timer; and wherein the pressure sensor is configured to check the reaching of the prescribed pressing force to detect the pressure of the hydraulic medium.

10. The method according to claim 1, wherein checking the reaching of the prescribed pressing force by using the pressure sensor to detect the pressure of the hydraulic medium is carried out by comparing a prescribed minimum pressure value and a pressure value actually achieved as measured by the pressure sensor.

11. The method according to claim 1, wherein the pressing operation is monitored with regard to different pressure gradients determined by using the pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which:

(2) FIG. 1 shows a partially sectioned representation of a first pressing unit with a pressing jaw in the starting position;

(3) FIG. 2 shows a representation according to FIG. 1, with the pressing jaw in the pressing position;

(4) FIG. 3 shows a representation according to FIG. 1 or FIG. 2 with the pressing jaw in the intermediate position;

(5) FIG. 4 shows a representation according to FIG. 1, but in the case of a configuration with two pressing jaws;

(6) FIG. 5 shows a further sectional representation of a corresponding pressing unit in the region of the pump with a pressure sensor located there;

(7) FIG. 6 shows a section through the subject matter according to FIG. 5, taken in section along the line VI-VI;

(8) FIG. 7 shows a schematic representation of the pressure profile in the case of a pressing cycle in the region up to workpiece contact, plotted against the travel;

(9) FIG. 8 shows a schematic representation of the pressure profile over a pressing cycle, plotted against the travel;

(10) FIG. 9 shows a representation according to FIG. 8, plotted against time;

(11) FIG. 10 shows a first schematic representation of the motor current during pressing, plotted against the travel;

(12) FIG. 11 shows a representation according to FIG. 10, but in the case of a different construction of the pump; and

(13) FIG. 12 shows a circuit used for the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

(14) While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein.

(15) Presented and described, in first instance with reference to FIGS. 1 to 3, is a hydraulic pressing unit 1 with an electric motor 2, a reservoir 3 for hydraulic medium, a pump assembly 4 and a pressing piston 5, which is connected directly to a pressing jaw 6.

(16) In the case of the exemplary embodiment, the electric motor 2 is operated by means of electrical energy stored in a rechargeable battery 7, which is not specifically represented.

(17) The beginning of a pressing cycle can be triggered by means of a start switch 8.

(18) In the case of the exemplary embodiment represented, in response to the actuation of the switch 8, the electric motor 2 will begin to run and hydraulic medium will be correspondingly pumped by means of the pump assembly 4 out of the hydraulic medium reservoir 3 into the hydraulic cylinder 9, whereupon the hydraulic piston 5 moves, together with the pressing jaw 6, from the starting position, represented in FIG. 1, into the pressing position, represented in FIG. 2.

(19) In a further embodiment, a current sensor may be provided in respect of the current drawn by the electric motor 2, the sensor detecting a current profile over the travel of the hydraulic piston 5, as quantitatively represented in the FIGS. 10 and 11.

(20) FIG. 10 relates here to a hydraulic pump of a conventional type and the qualitatively quite fundamental profile of the current curve. FIG. 11 relates to the profile of the current curve in the case of a two-stage hydraulic pump, here again however not exactly reproduced but represented qualitatively, specifically for such a two-stage hydraulic pump as is known from EP 0 927 305 B1.

(21) In both cases, there is initially a very high current pulse to be seen, associated with the switching-on of the unit. In practice, the value for this is, for example, around 80 amperes. This current value decreases very rapidly as the electric motor 2 runs up to speed, to a value that lies only a little above the idling current of the motor 2. At the beginning of workpiece contact, there is in principle a rise in the motor current. If a certain threshold value is exceeded, this being associated in FIGS. 10 and 11 with the travel S1 (this is likewise also a measurement of time, although it will be appreciated that the travel can only be plotted up until the closing of the pressing jaws), storage of this travel value takes place for instance in a memory chip which is accommodated in the unit and may have for this purpose a volatile memory. It can be seen that the current curve then rises up to a maximum value. This corresponds to the completion of the pressing operation and the triggering of the return valve, after which the hydraulic pressure correspondingly falls abruptly and the hydraulic pump is also automatically switched off.

(22) With regard to the representation in FIG. 11, there is to this extent a characteristic difference when the current curve rises (not yet significantly) after the travel S1. In practice, it may not only remain the same but even initially fall. This is attributable to the fact that at this point, a switch-over of the two-stage reciprocating pump from the first stage to the second stage takes place. Since the second stage operates, as it were, with a much higher transmission ratio, initially the motor current that is required is the same or in some cases even lower.

(23) But also in the case of a qualitative profile of the motor current corresponding to FIG. 11, a significant steep rise in the motor current that takes place after a certain further travel or a certain further time period up to the completion of the pressing operation.

(24) On the basis of the value stored, an interruption of the return of the hydraulic piston 5 after completion of pressing may then take place at this associated travel marker S1. In the case of the qualitative profile of the motor current according to FIG. 11, a computational allowance may then also be made, if for instance in the case of actual units, it is deemed appropriate, depending perhaps also on the power of the unit, to define contact only as from the travel or time S1, that is from the beginning of the actual rise in the motor current.

(25) Interruption may, for example, take place as specifically explained in the aforementioned patent application 10 2006 026 552. The relationship between the motor current and the travel, for instance according to FIG. 10, may be stored in a nonvolatile memory during the production of the unit.

(26) It is also clear from the above that it is possible to work in principle in the same manner with corresponding measurements of time.

(27) Once a certain threshold value has been exceeded with regard to the rise in the motor current, the threshold value being associated with the value of the travel S1 indicated in FIG. 10, storage of this associated travel value takes place, for instance in a memory chip which is accommodated in the unit and may have for this purpose a volatile memory. The travel value may, for example, be obtained by converting the motor current detected over time, since there is a sufficiently accurate (at least with averaging: linear) relationship between the travel of the piston 5 and the motor current (only) required, at least up to first workpiece contact. Interruption of the return of the hydraulic piston 5 after completion of pressing then takes place at this associated travel marker S1. Interruption may take place, for example, as specifically explained in the aforementioned patent application 10 2006 026 552. The relationship between the motor current and the travel, for instance according to FIG. 5, may be stored in a nonvolatile memory during the production of the unit.

(28) As an alternative or in addition, the relative position between the hydraulic cylinder and the hydraulic piston 5, in the case of a piston unit, may, for example, be detected for a travel measurement, for instance by means of one or more (two to four) or a multiplicity of (five or more) proximity switches which are provided in the hydraulic cylinder over the length thereof and can each detect the position of the hydraulic piston 5.

(29) The completion of the pressing operation may be detected, for example, by a sharp drop in the motor current taking place along with the opening of a return valve, which drop is then used for detecting the end of the pressing operation.

(30) Since the time which elapses from workpiece contact up to the completion of the pressing operation is not the same for every pressing, but rather may depend on individual pressing conditions, such as in particular the materials pressed, the time which elapses from first workpiece contact, for instance detected in the manner explained above, up to the completion of the pressing operation, may, in addition or as an alternative, also be measured, and this measurement of time then used correspondingly to trigger the interruption after completion of the pressing operation and the elapse of this amount of time, so thatin the exemplary casethe hydraulic piston 5 assumes the desired intermediate position.

(31) Since a greater travel is generally covered in the same amount of time in the case of unhindered return than in the case of the advancement under pressing conditions, there is at the same time also a generally desired excess, in order to be certain of having achieved the interruption or the release of the pressing jaws before the position (the release position of the pressing jaws) that is required as a minimum to allow the next pressing to be carried out.

(32) With regard to the time measurement, a timer may be provided in the unit, for instance also in the form of a microchip. In the case where a time period is to be detected, this timer will begin to count as from a specific triggering time, and the time period that is thus determined is recorded, at a specific end time, and stored, for example, in the volatile memory.

(33) Specifically for instance whenever the time period from first workpiece contact (for example obtained by detecting the characteristic increase in the motor current) up until the completion of the pressing operation (for example obtained by detecting the drop in the motor current after the return valve has opened) is measured, and this time period is then prescribed for the return of the piston 5 (in the case of a hydraulic unit), up until the interruption takes place at the intermediate position then determined for this, or in that the time from the automatic switching-off of the hydraulic motor 2 after completion of the pressing operation (determination as described above) up until a (short) deliberate renewed switching-on for the interruption of the return is measured and after that, in the following cycle, this interruption takes place automaticallyafter the elapse of the time period thus measured and then stored. This automatic interruption can then take place, as also already described further above, in the case of each cycle as long as a specific mode of actuation is maintained, for instance keeping the start button depressed until the interruption has taken place.

(34) It is generally not important for the return to take place always after reaching the same maximum pressure. If a travel sensor is used, the pressing times and pressing forces are not important. The build-up and release of the pressure may also be controlled by means of solenoid valves.

(35) On the other hand, as also already described at the beginning, it is also possible in this connection to work with specific (mathematical) factors, whether they have the effect of lengthening or shortening the travel. These are generally obtained from empirical knowledge. They are, however, nevertheless prescribed at the factory when the unit is supplied.

(36) Since a greater travel is generally covered in the same amount of time in the case of unhindered return than in the case of advancement under pressing conditions, there is at the same time also a generally desired excess, in order to be certain of having achieved the interruption or the release of the pressing jaws before the position (the release position of the pressing jaws) that is required as a minimum to allow the next pressing to be carried out.

(37) In FIG. 2, the pressing state of the unit according to FIG. 1 is presented.

(38) In FIG. 3, the unit according to FIG. 1 is represented in the intermediate position then assumed in the case of return on the basis of the procedure described.

(39) In FIG. 4, a unit with two pressing jaws is alternatively represented.

(40) With reference to FIG. 5, a pressing unit in which a pressure sensor 10 is located is represented in a partially schematic view. As is evident in conjunction with FIG. 6, the pressure sensor 10 is disposed such that it is associated with the return channel 11 of the hydraulic medium, by which return channel 11 the hydraulic medium flows to the return valve 12 and from there, when the return valve 12 is open, into the storage region 13. Provided from the return channel 11, on the other side of the branch extending to the return valve 12 as seen in the direction of return flow, is a side channel 14, which communicates with a receiving channel 15 of the pressure sensor 10, see FIG. 6. The pressure sensor 10 is therefore disposed such that it is circumferentially offset in relation to the return valve 12 and/or the return channel 11.

(41) With reference to FIG. 7, the pressure measured by a pressure sensor 10 over the piston travel during a pressing operation is qualitatively represented. This already corresponds to a conversion, since the actual pressure detection preferably generally takes place only over time. In principle, however, it is also possible for example to provide an additional travel sensor.

(42) The curve is drawn here only up until the event that there is first significant workpiece contact, and consequently an increase in pressure. Accordingly, the pressure scale is also set out for very low pressures, for instance up to 10 bar, in the illustration. The pressure is preferably measured at regular time intervals, in the case of the embodiment, in intervals of five milliseconds.

(43) It is important that, in the range of low pressures or initial piston travel, up until a first significant increase in pressure occurs as a result of workpiece contact, a linear profile is obtained, which has a hysteresis-like lag with respect to advancement and return. This pressure profile is explained by the fact that the return spring 16 acting on the piston 5 exerts a higher force with increasing compression. This explains the approximately linear rise in the pressure curve, as long as there is no first significant workpiece contact. The fact that furthermore the friction of the piston 5 in the cylinder plays a role, but that this frictional force is opposed, depending on the direction of movement of the piston 5, means that the curves for the advancement and return are different. The pressure difference lies in the range from 0.5 to 1 bar.

(44) On the basis of this relationship according to FIG. 7, when there is no workpiece contact, it is possible to deduce or calculate-back the position of the piston 5 from the pressure measured. This can be used for instance for establishing, by comparison of the measured values, that piston position which still corresponds to the linear relationship before there is then a significant increase in pressure on account of workpiece contact. A piston position thus established can then be used subsequently as an intermediate position or holding position, from which the next pressing operation can then be started.

(45) At the beginning of the movement of the pressing piston 5, a sudden increase in pressure takes place from zero to, for example, 4 or 5 bar. This sudden increase in pressure is attributable to the biasing of the return spring 16 that is preferably provided.

(46) With reference to FIG. 8, the qualitative pressure profile in the case of a completed pressing is represented in an illustration that is fundamentally the same (pressure against travel) as in FIG. 7.

(47) The pressing operation begins at the point A, here with the pressing piston 5 assumed to have returned completely. Initially, the slight rise in pressure takes place up to the point B, which represents the workpiece contact and the beginning of a significant increase in the pressing pressure. The pressing proceeds up until the point C is reached, specifically in a way corresponding to a first pressure gradient. After the point C is reached, the pressing jaws lie on one another, but the triggering pressure for the end of the pressing operation or opening of the return valve has not yet been reached. There is then an increase in the pressure gradient up until the point D is reached.

(48) At the point D, the return valve 12 opens, or the pressing is ended and the pressure falls again until the point E, whereupon the return of the piston 5 occurs, in the given case up until the point A. The increase in the pressure gradient between the points C and D is attributable to the fact that the pressing then works againstvirtually onlythe rigidity of the tool head itself, that is in fact with the pressing tools brought together. This is much greater than the rigidity of the workpiece to be pressed (gradient between B and C).

(49) This difference in the pressure gradients, at least once first workpiece contact has taken place, which can also be established, as explained further above, on the basis for instance of the pressure sensor 10, but also on the basis of the motor current, can also be used for the further evaluation.

(50) To be specific for the evaluation as to whether complete pressing has really been obtained, as a result of the fact that the pressure gradient between C and D, which at the same time also represents a tool constant in practice, is reached, it is implicitly the case that the pressing jaws lie against one another, the pressing operation therefore having taken place. Incomplete pressing may then also be used, for example, for triggering a signal, for example an acoustic signal. The signal must then be cancelled, again for example by specific actuation. Furthermore, a light-emitting diode may be provided in the pressing unit as an indicating means, for instance for the pressing in progress state.

(51) A suitably preprogrammed microcontroller 100, FIG. 5, is provided for the evaluation of the signals supplied by the pressure sensor 10 and/or the current sensor and/or the timer and/or the travel sensor. It is also preferred, in particular, that only the pressure sensor 10, i.e. no travel sensor and no current sensor, but however a timer, are provided, or only a current sensor, that is to say no travel sensor and no pressure sensor 10, but however a timer (if appropriate) are provided. On the other hand, in particular, the pressure sensor 10 may be provided in combination with the current sensor, and with a timer. As shown in FIG. 5, an electrical line transmits the signal of the pressure sensor 10 to the microcontroller 100. The electrical line is branchedone branch line 102 is connected unfiltered to an ADC channel 104 of the microcontroller 100, and the other branch line 106 is provided with a boosting unit with a lowpass filter 108 or is provided with a lowpass filter 110.

(52) In FIG. 9, the pressure profile (or a current measured at the pressure sensor 10) over time is plotted for the purposes of clarification. It is in respect of typical profile for a real pressing operation. Here, too, it is possible in principle to differentiate between the points described above, A, B, C, D and E.

(53) All features disclosed are (in themselves) pertinent to the invention. The disclosure content of the associated/accompanying priority documents (copy of the prior patent application) is also hereby incorporated in full in the disclosure of the application, including for the purpose of incorporating features of these documents in claims of the present application.

(54) While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.