Manually operated press having an overload protection

A manually operated press comprises an actuation lever coupled to a shaft assembly. An actuation of the actuation lever is transformed into a stroke movement of a press ram. A clutch assembly is provided for interrupting a flow of force between the actuation lever and the press ram. The clutch is adapted to separate an input shaft from an output shaft depending on predetermined pressing parameters. The input shaft extends as an inner shaft through the output shaft. The clutch assembly has a first clutch designed as a stroke stop for immobilizing the input shaft with a press housing depending on the pressing parameter, and a second clutch designed as an overload clutch for interrupting a flow of force between the input shaft and the output shaft.

FIELD OF THE INVENTION

The present invention is related to the field of manually operated presses which are conventionally used for pressing workpieces together.

The invention, further, is related to a method for protecting a manually operated press against mechanical overload and for aborting an insufficiently executed pressing operation.

More specifically, the invention is related to a manually operated press comprising an actuation member coupled to a shaft, an actuation of the actuation member being transformed into a stroke movement of a press ram coupled to the shaft and, accordingly, into a change of a relative displacement position of the press ram, and a clutch for interrupting a flow of force between the actuation member and the press ram.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 7,080,595 B2 discloses a manually operated press into which a backstroke inhibitor is electronically implemented, such as known e.g. from U.S. Pat. No. 6,755,124 B2.

Manually operated presses of the kind described above are conventionally used for piece-work workplaces. As in manually operated presses the exerted force increases towards the end of the pressing stroke, some operating persons tend to exert too much force and, thereby, produce pressed workpieces of bad quality or even damaged workpieces.

For many conventional manually operated presses no documentation is produced, in contrast to automatically executed pressing operations for which numerically controlled presses are conventionally used. The lack of documentation, however, is nowadays no longer acceptable for many fields of application, in particular when production processes are to be certified under the ISO 9000 standard.

In order to make sure that one can distinguish between “good” and “bad” parts, European patent specification 0 960 017 B1 teaches to provide a press with a sensor for the pressing stroke (displacement position) as well as with another sensor for the pressing force for generating a displacement-force diagram for any pressing operation being characteristic for a good and for a bad pressing. If a measured displacement-force curve lies within a given tolerance band, then the respective part is identified as well pressed. If not, the part is identified as a bad part that must be disposed of.

In order to be able to determine the pressing force exerted during a pressing operation, e.g. on a Seeger circlip ring, a bearing, a pinion, a sealing etc., a press ram of the press is configured as a force sensor. The force sensor has a force measuring system, for example a strain gauge strip, integrated therein. The strain gauge is connected to a press control unit of the press which, in turn, may be connected with a rotation sensor, for example, for sensing the rotation angle of the actuation lever and, hence, the ram displacement position. The control unit then processes the sensed data to enable the above-mentioned differentiation between good and bad parts once the pressing operation is executed.

If the examination shows that a bad part was pressed, the press may switch off automatically when the bad part is still within the press. This is likewise made upon a respective command from the control unit.

To start with, there is a first problem that during conventional manual pressing operations, in contrast to automatically executed pressing operations, there may unintentionally occur high pressing forces which, for example, are caused by negligence of the operating person. High pressing forces may likewise occur when the parts which are to be pressed together, are already sufficiently joined, however, the mechanical final position of the pressing stroke has not yet been reached. In such a situation, the operating person “feels” that the actuation lever may still be moved further in the pressing direction, and, therefore executes such movement to its end. In such a case a too high pressing force may be executed resulting in a “bad” pressing.

It is, therefore, necessary that the exerted pressing force be measured as precisely as possible in order to be able to optimally execute the quality examination based thereon. For that purpose highly sensitive force measuring systems are used which, however, are destroyed or at least damaged at too high mechanical overloads. Moreover, high overloads may occur from time to time that exceed admissible overload specifications by 100 or 200%.

As already mentioned above, the prior art teaches to record the force as a function of the displacement position for making a quality evaluation (good/bad) once the pressing operation is finished. As the pressing operation is effected manually, each pressing operation is effected with different pressing force. For that reason some work pieces which shall be pressed together, may already be joined sufficiently “well” before the press ram has reached its mechanical final position, or some work pieces may be sufficiently joined only at the final position. In the event that the sufficient joining has already been achieved prematurely, it would be desirable to abort the pressing operation before the final (mechanical) press ram position has been reached.

SUMMARY OF THE INVENTION

It is, therefore, an object underlying the invention to improve a manually operated press of the type specified at the outset such that the above-discussed problems are avoided. In particular, a manually operated press shall be provided in which admissible overloads can be limited to a predetermined threshold value, and in which a force sensor is protected against overload. Moreover, the pressing operation shall be aborted prematurely in the event that the desired pressing force has been reached prematurely. “Bad” pressings shall be avoided.

In a press of the type specified at the outset, this object is achieved according to the invention in that the lever shaft is at least a two-piece construction, namely configured with an input shaft and an output shaft, and that the clutch is adapted to separate the input shaft from the output shaft depending on the pressing force and/or the relative displacement position of the press ram.

The object underlying the invention is, thereby, entirely solved.

Due to the fact that in contrast to the prior art the shaft of the invention is configured two-piece, one now has, unlike before, the option to interrupt the flow of force between the actuation member and the press ram at will, namely independent from the effective actuation of the actuation member. The prior art until now only teaches to brake or to immobilize a one-piece shaft upon occurrence of a failure, in particular when the back stroke is initiated prematurely.

According to the present invention the flow of force between the press ram and the actuation lever can be interrupted at any moment in time by means of the clutch, namely by separating the shafts from each other. In the event that a desired pressing force is exerted already before a (mechanical) final position of the pressing operation has been reached, the shafts may be separated from each other depending on that event. If an inadmissibly high pressing force is exerted during a pressing operation which would damage a force sensor or would result in a “badly” pressed work piece, the shafts could likewise be separated from each other, again—depending on these events.

For that purpose it is advantageous to additionally provide a first sensor for sensing the pressing force and/or a sensor for sensing the relative position of the press ram.

If only a pressing force sensor is provided, a force measuring system of the press can be protected against overload. Should only a sensor for sensing the relative position of the press ram be provided then one can determine from the executed stroke displacement which pressing force was exerted, provided that all required further parameters as needed therefore are known, as, for example, the transmission of the lever movement into the press stroke, properties of the work pieces to be pressed together, etc.

If both sensors are used in combination, one can record a force vs. displacement curve for each pressing operation so that it is possible to make a good/bad distinction already during the course of the pressing operation. In particular, one may determine when a “good” pressing has occurred. If the force is recorded vs. the displacement, one can, for example, decide by means of a higher level control that the pressing operation shall be aborted already before a (mechanical) final position of the press ram has been reached, because a desired pressing force has been reached. In such a way “bad” pressings are generally avoided.

Preferably, a control unit is provided for that purpose which is coupled to the first and/or the second sensor and also to the clutch for supplying respective clutch signals to the clutch.

The control unit samples the force sensor(s) for outputting clutch signals to the clutch as a response to signals produced by the sensors.

The control unit, preferably, outputs a clutch signal for keeping the clutch closed when the sensed pressing force or the sensed relative displacement position of the press ram is smaller than a predetermined threshold value.

When the clutch is open, no flow of force may occur between the actuation member and the press ram. If the actuation member is not in its predetermined initial position, a pressing operation is not allowed at all due to the open clutch. This enhances pressing safety.

It is, further, preferred, when the control unit supplies a clutch signal for opening the clutch when the pressing force or the relative displacement position of the press ram is greater than or equal to a predetermined threshold value. The threshold value may be an admissible maximum pressing force, at which a force sensor is not damaged, and/or may be a minimum pressing stroke displacement at which a “good” pressing is obtained.

The control unit is, in particular, provided with means for determining whether a predetermined pressing force limit was exceeded or a desired pressing force has been reached. If the limit is exceeded, then a signal for opening the clutch is generated. Thereby, the flow of force between the actuation member and the press ram is interrupted.

According to a preferred embodiment of the invention, the manually operated press is provided with a stroke stop for immobilizing the input shaft, wherein the stroke stop, in particular, comprises a brake disc and a brake magnet.

With a stroke stop so configured the actuation of the actuation member may be immobilized in the forward as well as in the backward direction. The actuation lever is rigidly connected with the input shaft, such that an immobilization of the input shaft results in an immobilization of the actuation lever.

In a preferred configuration of the stroke stop using a brake disc cooperating with a brake magnet, the brake disc is, preferably, secured against rotation to the input shaft, and the brake magnet is secured in a stationary manner to the press. Considering that the stroke stop in that case is an electrically operated brake assembly, the brake assembly may likewise be controlled by the above-mentioned control unit, by sending corresponding signals from the control unit to the stroke stop or its elements.

Further, it is preferred when a third sensor is provided for sensing the relative displacement position of the input shaft, wherein the brake disc may be configured such that the third sensor senses the relative displacement position in cooperation with the brake disc.

By means of the third sensor one can generate a signal according to which the clutch is closed, provided that the actuation member is in its corresponding initial position. The initial position may be sensed by means of the brake disc or a disc flange, being connected to the input shaft for rotation therewith and, hence, also to the actuation member. Thereby it is always guaranteed that the flow of force is only established between the actuation lever and the press ram when the actuation lever is in its initial position. Hence, it is guaranteed that the displacement that can be made by the actuation lever is sufficient to effect the press stroke required for making a sufficient pressing operation. In particular, the clutch is closed only when also the press ram is in its initial position.

Further, it is advantageous when a return assembly, in particular a spring, is provided being coupled to the input shaft.

By this measure one may effect that the actuation member is automatically moved back into its initial position, in particular when the clutch is separated, i.e. the flow of force between the actuation member and the press ram is opened and the operating person may have released the actuation lever. For an automatic return movement of the actuation lever it is, of course, necessary that the stroke stop is not immobilized.

According to another preferred embodiment of the invention, the actuation member is a manually operable lever, the input shaft is an inner manual lever shaft and the output shaft is an outer hollow shaft.

By this measure one can obtain a manually operated press with short dimensions because the input shaft constitutes an inner shaft being arranged coaxially to the outer hollow shaft.

In particular, the second sensor may be a linear incremental displacement position measuring system sensing displacement position marks coupled to the press ram.

By coupling the position marks to the press ram, the measurement of the effected displacement is made on the press ram without any inaccuracies caused e.g. by transmissions, in contrast to the prior art where the displacement is sensed by means of a rotary sensor at the input shaft.

Here, too, it is advantageous when the two shafts are interconnected by the clutch in a form-fitting manner for transforming the stroke movement. By the additional form-fitting connection one can constitute a mechanical overload protection in which spontaneous overloads of (very) high intensity can be absorbed before they destroy a force sensor.

For that purpose one preferably uses a toothing having a latch position being configured such as to open automatically from a closed state at a predetermined torque that is effected via the actuation member. The latch position is, preferably, reached when the shafts are in their respective initial positions.

If, suddenly, an inadmissibly high torque appears at the shafts being coupled by the toothing, an automatic separation of the coupling is effected by this kind of coupling. The closing force exerted by the clutch is no more sufficient for compensating a decoupling force caused by the toothing. In that case the clutch opens spontaneously, i.e. without the intervention of a higher level control, for interrupting the flow of force.

It will be understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the respective combination indicated, but also in other combinations or in isolation, without leaving the scope of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1reference numeral10as a whole designates a manually operated press of essentially known design.

Press10has a base member12standing on an appropriate base, for example a work bench. Posts14extend upwardly from base member12to a head member16, also referred to as shifting member because head member16is adapted to be adjustable in the direction of posts14depending on the desired stroke. An actuation lever18is arranged laterally at head member16and is connected to a shaft22journalled within shifting member16by means of bearings20. Shaft22is adapted to be rotated about its axis24by actuation lever18, as indicated by an arrow26.FIG. 1shows the initial position of lever18.

A transmission28shown extremely schematically is provided within shifting member16. Transmission28, in the simplest case, may be a pinion-rack assembly. The assembly is provided for transmitting the rotary movement of shaft22into a vertical stroke movement of a press ram32as indicated by an arrow30.

During a pressing operation, the lower front surface34of press ram32comes to rest on an upper work piece36of a pair of work pieces36,38which shall be pressed together.

Press10is provided with a brake disc40being rigidly connected for rotation with shaft22. Immediately adjacent brake disc40there is provided a second disc42configured as a ring for allowing shaft22to be guided through second disc42. Second disc42is rigidly connected to shifting member16and, therefore, is hereinafter referred to as stationary.

Reference numeral44designates a first clutch having a brake magnet being electrically connected to an electronic control unit46. Control signals may be fed from outside, for example from a numerical control unit, to electronic control unit44via inputs48for constituting an electronic back stroke stop as disclosed in U.S. Pat. No. 7,080,595 B2. This function is likewise possible with the present press10. For further details reference is made to U.S. Pat. No. 7,080,595 incorporated herein by way of reference.

The stroke stop configured by first clutch44is essentially characterized by the magnet clutch effect of electro magnet exerted on clutch discs40and42. This “magnetic brake” may, however, be likewise constituted by a pneumatic or a hydraulic brake interconnecting discs40and42in a frictional manner for preventing a rotation of shaft22about its axis24.

Press ram32may be provided with a force sensor49by which the actually effective pressing force may be sensed. Force sensor49, too, is connected to electronic control unit46. Press ram32may insofar serve as a force sensor for a strain gauge strip integrated therein. Sensor49, however, may likewise be provided at another location, for example at base member12.

Other force measuring systems, for example inductive force sensors or magnetoelastic force sensors or piezo-electric sensors etc. may likewise be used.

In contrast to prior art presses, press10is provided with a second (outer) hollow shaft50being journalled coaxially to shaft22. First shaft22is hereinafter referred to as the inner manual lever shaft because it is guided through outer hollow shaft50. Outer hollow shaft50is directly connected to a toothed wheel or pinion constituting the transmission designated28. Press ram32has corresponding teeth52meshing with the pinion or toothed wheel of outer hollow shaft50. Preferably, the teeth of outer hollow shaft50and of press ram32engage one another directly. However, one could also provide further transmission elements therebetween.

Outer hollow shaft50can be connected to inner manual lever shaft22in a form-fitting or a frictional manner via a second clutch54, preferably an electromagnetic clutch. Second clutch54is also connected to electronic control unit46.

Inner manual lever shaft22constitutes an input shaft that is coupled to outer hollow shaft50via second clutch54.

The operation of press10according to the present invention shall now be explained in further detail.

By means of a third sensor56being, for example, located near brake disk40and cooperating with the latter, one can determine the relative position of manual lever shaft22. For that purpose, sensor56may likewise be connected to electronic control unit46. As actuation lever18is connected to shaft22(for rotation therewith), as is also disc40, one can, therefore, also draw conclusions on the position of lever18.

If it is determined that manual lever shaft22as well as press ram32are in their respective initial positions, from which on a pressing operation may be initiated, a signal is outputted from control unit46to second clutch54, such that second clutch54closes, i.e. inner shaft22and outer shaft50are connected with one another at least frictionally. Thereby, a flow of force is possible between lever18and press ram32.

Thereupon, lever18is rotated in the direction of arrow26for pressing work pieces36and38together.

Under normal conditions, i.e. when no inadmissibly high pressing force occurs, that can be measured with force measuring system49, lever18and, hence, also press ram32eventually reaches its (electronic or mechanical) final position. The mechanical final position is reached when press ram32has run through the maximum possible press stroke, or when lever18has been moved against a corresponding mechanical stop. The electronic final position has been reached when either lever18has been rotated about a predetermined angle or when press ram32has run through a predetermined (stroke) displacement.

The electronic final position could on the one hand be detected by sensor56by configuring brake disc40, for example, in an area corresponding to the final position such that stationary sensor56could detect the final position. If an inductive sensor is used as sensor56, brake disc40in this area could be configured more or less thick in axial direction24.

The electronic final position could also be defined such that a desired pressing force (depending on the displacement of press ram32) has been reached, i.e. work pieces to be pressed together have been sufficiently “well” be pressed together. For that purpose a distance or displacement measuring system58can be provided depicted schematically inFIG. 1as a dashed line. The displacement measuring system detects displacement position marks59coupled to press ram32.

When the final position has been reached, control unit46—depending on the pressing force and/or the effected stroke displacement—can cause second clutch54to open, whereby the flow of force between lever18and press ram32is interrupted. Ram32can, in particular, be returned to its initial position corresponding to the initial position of lever18, by means of a gas spring not shown inFIG. 1. It is advantageous when press ram32is coupled with displacement mark59for determining the relative position of press ram32because conclusions may be drawn from that information with regard to the pressing force that has been reached. By determining the relative position of press ram32one can, moreover prevent that a subsequent pressing operation is effected before press ram32is in its initial position.

This additional displacement measuring system58could be configured as a linear incremental measuring system having, for example, a resolution of 5 μm. Displacement marks59can be sensed by a measuring head being, preferably, positioned within head member16and being likewise connected to control unit46.

Brake disc40may be connected to a return assembly, in particular a spring57. The spring57is then connected to stationary head member16. In the initial position, the spring57is biased. In the final position it is tensed such that, if an operating person should let lever18loose, lever18is returned automatically into its respective initial position. For that purpose, second clutch54should be open.

As soon as press ram32and lever18have reached their respective initial positions, a new pressing operation can be performed.

In the event that during a pressing operation the admissible pressing force is exceeded so that there is the risk of a damage on the force measuring system49, the invention allows to open second clutch54before the final position of the pressing operation has been reached. In that case the flow of force between lever18and press ram32is interrupted. The force may no more act on force sensor49. Force sensor49is, hence, protected against overload.

Similarly, a prematurely completed pressing operation that has been classified “good”, may be terminated. This means that the flow of force is also interrupted if the pressing operation has been completed before the final position has been reached. The pressing force exerted via actuation lever18can be registered by means of sensor49by (higher level) control46. Control46may, for example, comprise an appropriately prepared microprocessor. In the event that control unit46, on the basis of a force-displacement measurement, determines that the work pieces36and38to be pressed together have actually been combined “well”, control unit46interrupts the flow of force between lever18and ram32by means of an appropriate signal for second clutch54.

The displacement measurement in this case is, preferably, effected via linear incremental displacement measuring system58.

The pressing operation may also be aborted solely depending on the relative position of press ram32without actually measuring the pressing force. For that purpose, however, it is necessary that the force-displacement characteristics of the press be known so that one can determine solely on the basis of the stroke displacement whether or when a “good” pressing has been obtained.

In order to avoid the operating person moving lever18“into emptiness”, which could result in injury to the operating person, the first clutch44is, preferably, actuated first.

More specifically, this is effected as follows: Force sensor49senses the pressing force exerted via lever18; the sensed pressing force is sampled in predetermined time intervals by control unit46; subsequently, control unit46determines, whether there is an inadmissibly high pressing force that would damage force sensor49, by determining, for example, whether the sensed pressing force is greater as or equal to a predetermined threshold value, or, when a “good” pressing of work pieces36and38has occurred (for example a desired pressing force has been reached); if the sensed pressing force exceeds the predetermined threshold value or if the desired pressing force has been reached, control unit46, preferably, first outputs a signal for first clutch40to stop the movement of lever18more or less abruptly; subsequently a clutch signal is outputted by control unit46for second clutch54for opening second clutch54; second clutch54opens; the flow of force between lever8and press ram32is, hence, interrupted; as an option, the brake may be released again.

Similar considerations apply when only the stroke displacement is measured.

Depending on whether the operating person still operates lever18, lever18can be moved further to the mechanical stop, without, however, being in frictional connection with press ram32, so that there is no danger of damaging force sensor49. Or, the operating person has already let lever18go. If the operating person has let lever18go, and if there is the above-mentioned return assembly between brake disc40and head member16, then lever18will automatically return into its initial position.

In the switched-off condition of press10there is, preferably, no connection between lever18and press ram34which results in a higher process safety. For making a connection, second clutch54must first be energized with current. It goes, however, without saying that second clutch54could operate just the other way round, i.e. second clutch54could also be closed in the non-activated condition, wherein control unit46first interrupts such connection before a pressing operation can be effected and then makes the above-mentioned check on the initial position. In such a way it is always guaranteed that the respective initial positions of lever18and of press ram32are assumed at the beginning of a pressing operation.

Instead of the type of transmission mentioned at the outset in which a rack meshes with a pinion or a toothed wheel, one might also use a planetary gear train, a worm drive, a chain drive, a belt drive a conical wheel drive, a toggle lever, a shoe lever, a hydraulic transmission or the like.

According to another embodiment of the present invention, inner manual lever shaft22and outer hollow shaft50are not only interconnected frictionally but also in a form-fitting manner.

FIG. 2shows a highly schematic cross-sectional view perpendicularly to a coupling plane between inner manual lever shaft22and outer hollow shaft50.

The drawing plane ofFIG. 2corresponds to the plane extending perpendicular to the drawing plane ofFIG. 1. The tooth pair60shown inFIG. 2, preferably, comprises one (latch) tooth62only which, in the embodiment shown is configured with outer hollow shaft50, and a corresponding recess64in inner manual lever shaft22.FIG. 2shows a condition, in which second clutch54(cf.FIG. 1) is open, such that shafts22and50may freely be rotated with respect to each other. Should second clutch54close, shafts22and50will move relatively towards each other along axis24such that tooth62comes into engagement with recess64.

It goes without saying that tooth62, as an alternative, can also be configured with inner manual lever shaft22and recess64at outer hollow shaft50. Instead of one tooth pair only, several such pairs62,64could also be provided. Embodiments with one (latch) tooth, however, are preferred as will be explained further below.

Tooth pair60may, additionally, be used for determining the initial position of press ram32. This means that only if shafts22and50are correctly oriented relative to one another, i.e. if hollow shaft50and, hence, press ram32are in their initial position, then tooth62and recess64may engage. If press ram32is not (yet) in its initial position, no coupling between shafts22and50is possible.

Further, inFIG. 3there are schematically shown forces acting on shafts22,50and their respective tooth, recess62,64, pair along a tooth flange extending parallel to an imaginary line66.

Assuming that for closing second clutch54(cf.FIG. 1), a magnetic force FM(FIG. 3) is required for, for example, moving outer hollow shaft50or its tooth62, in the direction of inner hollow shaft22or its recess64. The (closing) force FMof the clutch magnet may be resolved with the help of a force parallelogram into two force components FEand FS1, wherein FErepresents the coupling force acting along imaginary line66and FS1represents the force acting perpendicularly to the toothing flange.

If both shafts22,50are coupled with each other and actuation lever18is actuated by an operating person, inner manual lever shaft22will transmit a rotary force FDonto outer hollow shaft50as is also shown inFIG. 3. Rotary force FDmay likewise be resolved into two force components FAand FS2, wherein FArepresents the decoupling force and FS2represents the force acting perpendicularly to the tooth flange.

As long as the rotary force does not exceed a certain threshold value, decoupling force component FAis smaller than coupling component FE. If, however, the operating person (spontaneously) exerts a very high force onto shaft22, rotary force FDwill increase abruptly, resulting in an increase of decoupling force FA. If force component FAbecomes greater than force component FE, an opening of tooth pair60results even if clutch54is closed or not yet opened. The force at which tooth pair60opens automatically depends on its design parameters, in particular on the flange angle α. Second clutch54then acts as an overload clutch.

With this measure one can effect that, if a spontaneous torques occur which cannot be compensated for at that speed by the control unit, the coupling between shafts20,50opens automatically. This, in turn, means that the flow of force between actuation lever18and press ram32is separated such that a force sensor is again protected against overload.

Instead of a tooth pair one could likewise use rollers or the like.