EP2686138B1 - Method for rotating a rotatable part - Google Patents

Description

The invention relates to a method for rotating a rotatable member using a driven by a hydraulic pressure source hydraulic piston cylinder drive with at least one piston and a hydraulic cylinder and a ratchet, wherein during a load stroke, a torque applied to the rotatable member and the piston via a return stroke in a Starting position is moved.

Methods for rotating a rotatable part are known in particular in the operation of hydraulic power wrenches. A method according to the preamble of claim 1 shows the GB 2 449 638 ,

In the operation of hydraulic power wrenches come in practice in particular two methods are used, the so-called torque method and the so-called torque-rotation angle method. Both methods include a method step in which a defined torque is applied to the part to be rotated.

It is known that a torque sensor is provided for measuring the torque applied to the part to be rotated. Such a method is for example from the WO 03/013797 A1 previously known. The provision of additional torque sensors is an additional expense and has the consequence that only certain types of power wrenches are suitable for carrying out the method. In addition, such sensors are arranged on the power wrench itself, which is thereby sensitive to pollution and environmental influences. Since power wrenches are often used on construction sites, the aforementioned sensitivity to environmental influences and contamination is to be regarded as particularly disadvantageous.

It is also known to determine from the piston cylinder unit of a power screw feeding pressure source pressure data and to close by these on the force exerted on the part to be rotated torque. For this purpose, the pressure exerted on the piston of the piston-cylinder unit by the pressure source is converted into a torque from the known geometry of the hydraulic screwdriver.

For example, it is known to manually control such power wrenches by giving the pressure source a maximum pressure which corresponds to the desired torque. An operator must manually initiate the forward and return strokes of the piston. In such a method, however, the system does not recognize whether the pressure exerted by the pressure source is actually applied as torque to the part to be rotated. It may happen that the piston of the piston-cylinder unit is struck at an end stop, and the pressure source further increases the pressure. Therefore, in this method basically a visual inspection by the operating personnel was necessary to determine whether on reaching the preset final pressure previously a rotational movement of the part to be rotated has taken place. Especially with very large power wrenches, in which a very slow angular velocity of the part to be rotated is generated, such visual inspection is very difficult to carry out.

In modern power wrench systems, the power wrenches are automatically controlled by a controller, upon reaching the pressure corresponding to the desired torque, the pressure source is automatically switched off or a phase of the angle-controlled rotation is initiated.

The controller can not recognize that the applied pressure is exerted only on the end stop and not a transfer of the Pressure on the rotatable part takes place. Therefore, even with such an automatic control, a visual inspection by the operator is necessary.

There are therefore known various control methods of hydraulic screwdrivers which provide automatic control of the pressure source DE 102 22 159 A1 For example, describes a method in which the temporal pressure profile of the pressure source is evaluated. From the change in the gradient of the pressure curve, signals for reversing the piston-cylinder unit and for terminating the process are obtained. The process of torque application is then terminated when it is ensured that the required torque has actually been impressed on the fastener. The advantage of this method is that no sensor technology is necessary on the hydraulic wrench itself, since the pressure signals can be measured directly in the pressure source. In this method, there is the problem that the gradient change between on the one hand the gradient of the pressure during pressure build-up at the beginning of a stroke, ie at a time when there is no rotation of the part to be rotated, the gradient of the pressure during the rotational movement and the gradient of Pressure after striking the piston at an end stop at the end of the load stroke is greatly influenced by the volume of the piston-cylinder unit and the volume of the hydraulic hose connecting the pressure source with the hydraulic screwdriver. In particular, since the gradient change between the gradient of the pressure during the rotational movement and the gradient of the pressure after striking the piston at the end of the load stroke is of interest, since it is to determine which torque is actually present before striking the piston at the end stop on the rotatable part Reliable control in this method is only possible if the pressure curve during the gradient change has a discontinuity. Especially with large tools and weak pressure sources, the pressure curve of a gradient change may have a steady course, so that an accurate determination of the before the striking of the Piston at the end stop on the rotatable part acted upon torque is difficult or impossible to determine.

In addition, the gradients to be evaluated become even with identical systems, i. identical hose lengths and volumes of the piston-cylinder units, influenced by parameters of the parts to be rotated, so that a pressure gradient-based control of the pressure source can react unambiguously in different applications.

It is therefore an object of the present invention to provide a method for rotating a rotatable member using a hydraulic piston-cylinder drive and a ratchet, which ensures regardless of the system components used and without the use of additional torque sensors that when switching off the pressure source upon reaching a the end torque corresponding to the desired end torque corresponding pressure has actually been impressed on the rotatable part.

The method according to the invention for rotating a rotatable part using a hydraulic piston-cylinder drive operated by a hydraulic pressure source with at least one piston and a ratchet, wherein during a load stroke a torque is applied to the rotatable part and the piston is moved to a starting position during the return stroke, the Features of claim 1 on.

The inventive method is characterized in that the load stroke ends when reaching an end position and then the return stroke is initiated, wherein the end position is a position of the piston before striking the piston to an end stop. In this way it can be ensured that the pressure exerted by the pressure source via the piston cylinder drive and the ratchet always on the rotatable part in the form of a Torque is transmitted. The control of the hydraulic pressure source can thus turn off upon reaching a predetermined pressure, which is determined by the known system component or a previous calibration, and it is ensured that this pressure has actually been impressed in the form of a torque on the rotatable member. The fact that the load stroke is terminated when the piston is not yet struck against the end stop, it is ensured that the increasing pressure generated by the pressure source due to the higher rotational resistance of the rotatable member and not due to the impact of the piston against the end stop. In other words, the pressure would be transmitted to the rotatable part and not to the end stop of the piston.

By the method according to the invention, a control of the hydraulic pressure source in a simplified manner possible, since the problem resulting from the achievement of the end stop of the piston is not present.

Since very high pressures are built up by the pressure source during the load stroke, which lead to a high mechanical load of the piston cylinder drive when striking the piston at the end stop, the inventive method can avoid this mechanical stress in the use of the piston cylinder drive, resulting in a longer service life of Piston cylinder drive leads. The method according to the invention makes possible a control which is independent of the actual chronological course of the pressure during a load stroke. Thus, such control will not be affected by unpredictable pressure gradient changes that may occur during rotation of a rotatable member in the load stroke, for example, by clutches, seating, seizure or changes in friction values. The reliability of the control is thus increased.

The return stroke can be done either by pressurizing the piston with hydraulic fluid or via a return element, for example a spring.

Under a ratchet in the context of the invention is basically understood an element for force or torque transmission, which runs free in one direction and transmits in the opposite direction by force or positive engagement of the force or torque.

In the method according to the invention, provision may be made for an instantaneous position of the piston to be determined via the travel path of the piston during the load stroke. The determination of the instantaneous position of the piston with the travel of the piston is made possible in a simple way to determine the reaching of the end position of the piston and to end the load stroke. The determination of the position can take place continuously or at intervals of time. According to a preferred embodiment of the invention, the travel during the load stroke is determined by the volume of hydraulic fluid supplied to the hydraulic cylinder. This is done by the volume and the known geometry of the hydraulic cylinder can be converted into the travel.

It can be provided that the volume of hydraulic fluid supplied to the hydraulic cylinder during the return stroke is determined. By means of the volume of hydraulic fluid supplied to the hydraulic cylinder during the return stroke, the travel path determined during the preceding load stroke can be checked so that malfunctions in the control of the pressure source can be avoided. Checking the travel path during the load stroke allows the detection of malfunctions in which the piston has been moved past the intended end position and against the end stop. Thus, the inventive method can avoid unnoticed that the controller stops the pressure source, although the predetermined torque has not yet been impressed on the rotatable member.

About a particularly preferred embodiment of the invention it is provided that the volume supplied to the hydraulic cylinder is determined by the temporal pressure curve of the hydraulic pressure source. By calibrating the system, a pressure / volume flow characteristic can be determined, so that over the temporal pressure curve, the currently funded volumes can be summed up to the total volume delivered. Such a method according to the invention has the particular advantage that no further sensor is necessary for carrying out the method according to the invention, since a pressure sensor is already present for determining the impressed torque. In particular, no additional sensor to the piston cylinder drive is necessary, whereby the complexity and susceptibility of the system is reduced. Additionally or alternatively, it may be provided that the volume supplied to the hydraulic cylinder during the load stroke is determined via a volume flow measurement of the hydraulic fluid. A volumetric flow measurement can be carried out by conventional volumetric flow measuring methods, for example in the hydraulic line between the piston cylinder drive and the pressure source. In volumetric flow measurement, the volume supplied to the hydraulic cylinder can be determined in a simple manner.

It may be provided that the volume of hydraulic fluid supplied to the hydraulic cylinder during the return stroke is determined via a volume flow measurement of the hydraulic fluid or over the time profile of the hydraulic pressure source.

According to one embodiment of the invention it is provided that the end position of the piston is detected by a sensor. Via a sensor, the end position of the piston can be determined very accurately. The detection over a sensor may alternatively or additionally to the detection of the end position via the travel of the piston. Although the sensor on the piston cylinder drive forms a higher cost and a higher susceptibility to external influences, but also means a higher accuracy of the method according to the invention. Depending on which type of rotatable parts the method according to the invention is used, the provision of a sensor on the piston-cylinder drive can therefore be advantageous.

The sensor may be an electronic sensor, an optical sensor or a Hall sensor. The sensor can be used, for example, as a limit switch.

In a preferred embodiment of the method according to the invention it is provided that the delivery volume of the pressure source for a return stroke is greater than the volume of hydraulic fluid necessary for a piston movement from the end position of the previous load stroke to the starting position. This can ensure that the piston is moved into the starting position during the return stroke, so that a malfunction can be avoided in a subsequent load stroke. The delivery volume of the pressure source for a return stroke can be specified as a function of the volume actually supplied to the hydraulic cylinder in the preceding load stroke or of the volume to be supplied by calibration during a load stroke prior to a single operation.

In a particularly preferred embodiment of the method according to the invention it is provided that the end position of the piston is arranged at a distance D from the initial position of the piston, which is 85% -95%, preferably 90%, of the distance D between the initial position of the piston and the end stop. In other words, the load stroke is only 85% -95% of the maximum achievable with the piston cylinder drive stroke. In this way, there is sufficient security that the load stroke is terminated, without the piston abutting against the end stop, whereby it can be ensured that the pressure of the pressure source determined at the end of the load stroke has been impressed as torque onto the rotatable part.

When using a system with known system components known system properties of a control of the pressure source can be specified. In known system components, such as a known hydraulic line, and a known piston-cylinder drive thus the control of the corresponding volumes and a system behavior can be specified, so that, for example, pressure-dependent volume changes can be considered as correction volumes.

When using a system with at least one unknown system component system properties can be specified by a calibration and a control of the pressure source, the system properties are determined by the repeated performing maximum piston strokes without concern of a load and return strokes, the maximum piston strokes of the starting position of Piston until the piston stops against the end stop. In this way, necessary system properties such as volume of the hydraulic lines and volume of the piston cylinder drive and pressure-dependent volume changes can be determined by stretching the hydraulic lines and taken into account in the control of the pressure source. As a result, the method according to the invention can be used in a particularly advantageous manner, since a pressure source with a controller can be used on different systems, without requiring a complex adaptation of the controller.

The method according to the invention is explained in more detail below with reference to the following drawings.

Figur 1

eine schematische Darstellung einer Schraubvorrichtung mit einem Hydraulikaggregat in einem Kraftschrauber zum Drehen einer Schraube,

Figur 2

eine schematische Darstellung des Kraftschraubers, der den Kolbenzylinderantrieb enthält.

Show it:

FIG. 1

a schematic representation of a screwing device with a hydraulic unit in a power screwdriver for rotating a screw,

FIG. 2

a schematic representation of the power wrench containing the piston cylinder drive.

The method according to the invention for rotating a rotatable part using a hydraulic piston-cylinder drive operated by a hydraulic pressure source can be carried out, for example, with a power screwdriver for turning a screw.

In Fig. 1 and Fig. 2 schematically a power wrench 10 is shown. This has a hydraulic piston cylinder drive 11 with hydraulic cylinder 12 and a piston 13 movable therein. The piston 13 is connected to a piston rod 14 and the end of the piston rod 14 engages a lever 15, which engages with a latching pawl 15 a on the toothing of a ratchet wheel 17. The ratchet wheel 17 is part of a ring piece 18 which has a socket 19 for attaching a key nut or a screw head to be rotated. By reciprocating movement of the piston 13, the ring piece 18 is rotated and with this the screw. The ring piece 18 is mounted in a housing 20 which also contains the piston cylinder drive 11.

The pressure for the piston cylinder drive 11 is supplied by a pressure source 25, which in the in Fig. 1 illustrated embodiment is designed as a hydraulic unit. The hydraulic unit has a positive displacement pump 26 containing a motor and a tank. The pressure source 25 is connected to the pressure line 28 and a return line 29 connected. These two lines are connected via a control valve 30 to the piston-cylinder drive 11. By switching the control valve 30, the piston 13 can be moved either forward or backward.

For controlling the pressure source 25 and the control valve 30, a control unit 31 is provided.

On the pressure line 28, a pressure sensor 32 is provided, which measures the hydraulic pressure P in the pressure line 28. The pressure sensor 32 is connected via a line 33 to the control unit 31.

During operation of the power wrench 10 hydraulic fluid is conveyed through the pressure line 28 via an inlet 28a into a first space 12a of the hydraulic cylinder 12. As a result, the piston 13 is pressed in the direction of an end stop 16. The piston rod 14 in this case exerts a force on the lever 15, which converts the force into a torque which is impressed on the rotatable part, for example a screw. The piston-cylinder drive 11 thus performs a load stroke, wherein the direction of the load stroke in Fig. 2 is shown by an arrow. During a movement in the direction of the load stroke and the corresponding rotational movement of the lever 15, the ratchet wheel 17 is locked, so that the torque can be transmitted to the rotatable part.

During the load stroke, the hydraulic fluid contained in the second space 12b located in the load lifting direction in front of the piston 13 is forced through an outlet 29a into the return line 29.

Upon reaching an end position of the piston 13, the in Fig. 2 is shown, the controller 31 terminates the load stroke and initiates the return stroke. During the return stroke, hydraulic fluid is conducted via the pressure line 28 through the outlet 29a into the second space 12b, so that the hydraulic fluid in the first space 12a moves from the piston 13 through the inlet 28a into the second chamber 12b Return line 29 is pressed. The piston 13 exerts a movement counter to the load lifting direction, wherein a tensile force is exerted on the piston rod 14. The piston rod 14 pulls during the return stroke the lever 15 with it, the detent pawl 15 a free running.

At the in Fig. 2 illustrated end position of the piston 13, in which the load stroke is terminated and then the return stroke is initiated, the piston is in a position in which the piston is not yet struck at the end stop. In other words, the method according to the invention provides that during normal operation the piston 13 does not abut the end stop 16. It is thereby achieved that the hydraulic pressure P measured by the pressure sensor on the pressure line 28 is completely converted, taking into account the usual correction values, into a torque which is exerted on the rotatable part. In other words, via the measured hydraulic pressure P, the torque impressed in the rotatable part can be determined, wherein it is avoided that the measured hydraulic pressure P is falsified by abutment of the piston 13 against the end stop 16.

The end position of the piston 13 can be determined by determining the instantaneous position of the piston 13 over the travel of the piston during the load stroke. When the end position is reached, the control unit then switches the control valve 30 to initiate the return stroke.

In this case, the travel of the piston 13 can be determined during the load stroke by the hydraulic cylinder 12 supplied volume of hydraulic fluid. The volume of hydraulic fluid supplied to the hydraulic cylinder 12 can be determined, for example, by means of the temporal pressure profile of the hydraulic pressure source 25, wherein the chronological pressure profile of the hydraulic pressure source 25 can be detected with the aid of the pressure sensor 32. For this purpose, a pressure / volume flow characteristic obtained from a calibration of the system is necessary, so that the from the current pressure certain currently funded volumes can be added to the total volume funded. Upon reaching the predetermined total volume, the controller 31 detects that the piston 13 is in the end position.

During the return stroke, in order to check whether the piston 13 has been in the predetermined end position during the preceding load stroke, the volume of hydraulic fluid supplied to the second space 12b can also be determined. When determining the volume of hydraulic fluid during the return stroke, the temporal pressure profile of the hydraulic pressure source 25 can also be used.

Of course, it is also possible that the hydraulic cylinder 12 supplied volume of a hydraulic fluid is determined by a volume flow measurement.

In the method according to the invention, it is also possible that the end position of the piston is detected by a sensor, which is used for example as a limit switch. Via the sensor, the controller 31 receives a signal to end the load stroke and initiate the return stroke. The sensor can be used as an alternative or in addition to the determination of the end position over the travel of the piston 13.

When using the method according to the invention with a power wrench, which has no sensor for detecting the end position of the piston 13, it is advantageous if it can be ensured that before the start of a load stroke of the piston 13 is in a starting position in which it at a second End stop 16a is present. The piston in the starting position is in Fig. 2 indicated by broken lines. This can ensure that there is no residual volume of hydraulic fluid in the first space 12a. A residual volume of hydraulic fluid would cause the piston 13th would proceed with the supply of a predetermined volume beyond the end position. To ensure that the piston 13 at the end of the return stroke and the start of the load stroke in the starting position, it can be provided that during the return stroke, the default of the hydraulic cylinder 12 supplied volume of hydraulic fluid is greater than the hydraulic cylinder supplied volume of the previous load stroke in that the delivery volume setting of the pressure source 25 is set correspondingly higher during the return stroke than during the load stroke. The piston 13 is arranged in the end position at a distance d from the initial position of the piston 13, which is 85% -95% of the distance d between the initial position of the piston 13 and the end stop 16. In other words, the load stroke is only 85% -95% of the maximum stroke that can be carried out with the piston-cylinder drive 11. The maximum stroke of the hydraulic cylinder 12 is a stroke from the initial position of the piston 13 to the approach of the piston 13 to the end stop 16.

The avoidance of the abutment of the piston 13 to the end stop 16 also has the advantage that the piston-cylinder drive 11 is subjected to a lower mechanical load. Since high pressures are generated during the load stroke, a start of the piston 13 at the end stop 16 means a high mechanical load on the piston 13, which is avoided by the method according to the invention. During the return stroke, no such high mechanical loads on the piston 13 arise when it strikes against the second end stop 16a.

If the method according to the invention uses a system which consists exclusively of known system components, such as a previously known power wrench with a previously known hydraulic piston-cylinder drive 11, and a previously known pressure line 28 and a previously known return line 29, the previously known system properties of the control of the pressure source 25 can be predetermined. These may for example already be stored in the control unit 31. The system properties can be, for example, pressure-dependent volume changes of the lines.

When using a system with at least one unknown system component, the system properties can be determined by a calibration and taken into account in the control of the pressure source 25 accordingly. The system properties are determined by repeatedly performing maximum piston strokes without concern of a load and return strokes.

Claims (14)

1. A method for rotating a rotatable part by use of a hydraulic piston-cylinder drive (11) operated by a hydraulic pressure source (25) and having at least one piston (13) as well as a hydraulic cylinder (12) and a ratchet (17), wherein a torque is applied to the rotatable part during a loading stroke and moving the piston (13) into a starting position via a return stroke,
   characterized in that
   the loading stroke is terminated when an end position of the piston (13) is reached, and the return stroke is subsequently started, wherein the end position is a position of the piston (13) before abutment of the piston (13) against an end stop (16).
2. The method according to claim 1, wherein a current position of the piston (13) is determined on the basis of the travel path of the piston during the load stroke.
3. The method according to claim 1 or 2, wherein the travel path of the piston (13) during the load stroke is determined on the basis of a volume of the hydraulic fluid supplied to the hydraulic cylinder (12).
4. The method according to claim 3, wherein the volume of hydraulic fluid supplied to the hydraulic cylinder (12) during the return stroke is determined.
5. The method according to one of claims 1 to 4, wherein the volume supplied to the hydraulic cylinder (12) is determined on the basis of the temporal pressure development of the hydraulic pressure source (25).
6. The method according to one of claims 3 to 5, wherein a volume supplied to the hydraulic cylinder (12) during the load stroke is determined on the basis of a volume flow measurement of the hydraulic liquid.
7. The method according to one of claims 4 to 6, wherein the volume of hydraulic fluid supplied to the hydraulic cylinder (12) during the return stroke is determined on the basis of a volume flow measurement of the hydraulic liquid or on the basis of the temporal development of the hydraulic pressure source (25).
8. The method according to one of claims 1 to 7, wherein the end position of the piston (13) is detected by a sensor.
9. The method according to claim 8, wherein said sensor is an electronic sensor, an optical sensor or a Hall sensor.
10. The method according to claim 8 or 9, wherein said sensor is used as an end position sensor.
11. The method according to one of claims 1 to 10, wherein a target value of the conveying volume of the pressure source (25) for a return stroke is higher than the volume of hydraulic liquid required for a piston movement from the end position of a preceding load stroke to the starting position.
12. The method according to one of claims 1 to 11, wherein the end position of the piston (13) is arranged at a distance (d) from the starting position of the piston that amounts to 85%-95%, preferably 90% of the distance (D) between the starting position of the piston (13) and the end stop (16).
13. The method according to one of claims 1 to 12, wherein, when using a system comprising known system components, known system properties are preset in a control device of the pressure source (25).
14. The method according to one of claims 1 to 12, wherein, when using a system comprising at least one unknown system component, system properties are detected by calibration and are preset in a control of the pressure source (25), the system properties being detected by repeatedly performing maximum piston strokes without application of a load, and return strokes, said maximum piston strokes extending from the starting position of the piston (13) until abutment of the piston on the end stop (16).

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