DE10133923B4 - Method for automatically controlling a screwing operation - Google Patents

Abstract

During a screwdriving process, the torque (MD) and the angle of rotation (α) are measured in a screwdriver. First, tightening a screw in a torque mode while measuring the torque until a mating torque (MF) is achieved. Thereafter, without stopping the rotation, it enters a rotation angle mode (DWM) in which the rotation angle (α) is measured. The rotation angle is increased up to a target rotation angle (αS). Before the setpoint rotation angle is reached, taking into account a correction value (αK) determined in test runs, the measured value (αM) at which the drive must be shut off is determined in order to obtain the desired setpoint torque (MS) and the desired setpoint angle (αS ) within a tolerance range (T).

Description

The invention relates to a method for automatically controlling a screwdriving process of a rotary screwdriver comprising a controllable drive for an output shaft and an integrated control unit ( 32 ) with microprocessor and memory, a torque sensor and a rotation angle sensor.

Rotary screwdrivers are often required to tighten a screw with a specified setpoint torque. The exact observance of the target torque is particularly important in safety-relevant applications such as reactors, power generators or wind turbines or in the offshore area of importance. The targeted achievement of a certain torque to cause the screw is loaded with a predetermined tensile force, so that the parts connected by the screw are pressed against each other with a corresponding force from the screw. However, the torque measured on the output shaft of a screwdriver does not always provide information about the elongation of the screw. It is for example falsified by the fact that the screw thread is dirty or provided with paint or that on the screw thread oil is present. Furthermore, there may be flaws in the screw thread and also in the nut. For this reason, it is not appropriate to let the drive be turned on until a desired torque is reached, and then shut it off abruptly. In addition, in an abrupt shutdown an undefined overshoot due to the inertia of the moving mass and undefined frictional forces u. like.

DE 27 35 594 A1 and US 4,344,216 disclose a method for controlling screwing operations in which tightening parameters are continuously determined from data obtained during the screwing operation. DE 32 05 090 A1 and DE 2 213 549 A disclose methods for controlling screwing operations, in which the drive of a screwdriver rotates the screws to a clamping torque and then the screwdriver is rotated by a rotation angle.

The invention has for its object to provide a method for automatically controlling a screwing of a rotary wrench, which allows a secure achievement of the desired final state of the screw under complete monitoring of the screwing and requires no manual intervention.

• – Aktivieren des Antriebs unter Messung des Drehmoments in einem Drehmomentmodus, bis das Drehmoment ein vorbestimmtes Fügemoment erreicht,
• – bei Erreichen des Fügemoments: Übergang auf einen Drehwinkelmodus, bei dem der von der Ausgangswelle überstrichene Drehwinkel gemessen wird,
• – bei Erreichen des Fügemoments: Übergang auf einen Drehwinkelmodus, bei dem der von der Ausgangswelle überstrichene Drehwinkel gemessen wird,
• – Beenden des Antriebs, wenn der Drehwinkel einen vorgegebenen Endwert erreicht.

The solution of this object is achieved according to the invention with the features specified in claim 1. After that, the method for automatically controlling the screwing process has the following steps:

• Activating the drive while measuring the torque in a torque mode until the torque reaches a predetermined torque,
• Upon reaching the joining moment: transition to a rotation angle mode in which the angle of rotation swept by the output shaft is measured,
• Upon reaching the joining moment: transition to a rotation angle mode in which the angle of rotation swept by the output shaft is measured,
• - End of the drive when the rotation angle reaches a preset final value.

In the method according to the invention, an automatic transition from the torque mode to the rotational angle mode takes place without manual intervention being necessary. The rotation angle mode starts from the joining torque, the further rotation taking place under constant monitoring by the rotation angle sensor. In this case, in each case the assumed actual value of the respective position can be subtracted from the desired value of the rotational angle in order to determine the difference value yet to be swept over. Depending on this difference value, the drive can be controlled, specifically in such a way that it controls the setpoint precisely, whereby a controlled reduction of the speed can already take place beforehand.

According to the invention, it is provided that upon reaching the joining moment the drive remains activated and the control unit goes into torque mode without stopping the output shaft. In this case, it is avoided that, when reaching the joining moment, an overshoot takes place until it stops, as a result of which the joining moment would be falsified. Rather, the rotation angle mode is initiated during the turning process, so that a precisely defined start of the rotation angle mode is present. In addition, the screwing is shortened because no shutdown of the drive is necessary.

The values in question are stored so that they can later be made available in the form of a graphic. The time profile of the angle of rotation and / or the torque or a relationship between torque and angle of rotation can be transferred from an integrated into the screwdriver control unit to an external disk or fed to an information network. In this way, an accurate and automatic documentation of each screwdriving process is possible. The documentation can, for example, be done on a chip card or another data carrier. Alternatively, it is possible that the integrated in the screwdriver control unit such is designed so that it can communicate with an information network. In this way, the control unit may for example enter data into the Internet and also be dialed from the Internet to retrieve data. This requires a communication capability with the Internet, which can be easily realized via a mobile device or similar communication device.

For each screwdriving case, a data record is created which indicates the characteristic parameters of this screwdriving case. In a learning mode, the drive is switched off when a predetermined torque is reached during a test run, and the excess rotational angle is measured and stored as a correction value. Thereafter, a target rotation angle is set. The drive is then switched off when the measured angle of rotation reaches the value of the setpoint rotation angle minus the correction. As long as the measured rotation angle does not correspond to the desired rotation angle, the correction can be redetermined after an iteration process. The learning phase is ended when the rotation angle measured when the rotary wrench is stationary corresponds to the value of the setpoint rotation angle.

In the following an embodiment of the invention will be explained in more detail with reference to the drawings.

Show it:

1 a side view of the rotary screwdriver,

2 a schematic end view of the rotary screw after 1 from the direction of arrow II,

3 the output shaft with the two sensors, and

4 a diagram for explaining the control of the rotary screwdriver.

The screwdriver has a holding part 10 which can be held by hand. In a housing 12 of the holding part is arranged an electric motor, which over a cable 14 can be connected to the supply network. The holding part 10 is with an output device 20 connected, which includes a reduction gear to the speed of the in the housing 12 located to reduce output device. With the help of a switching ring 22 The reduction gear can be switched to change the degree of reduction. The reduction gear drives a neck nozzle 24 on, on the screw nuts can be plugged. On the case 26 is a support leg 28 provided, which can be set against a stationary abutment to derive the torque generated during the screwing operation to the abutment.

The holding part 10 is opposite the output device 20 rotatable. This is between the holding part 10 and the output device 20 a safety hinge 30 intended. This makes it possible, regardless of the position and the operation of the output device 20 the holding part 10 to rotate in a range of 360 °.

The output device 20 contains a torque sensor 52 that at the output shaft 50 resulting torque measures. This torque sensor is a torsional sensor attached to the output shaft. The signals of this torsion sensor are transmitted via a slip ring arrangement or via a non-contact data transmission to a control unit. In addition, in the output device 20 a rotation angle sensor 54 provided, one at the output shaft 50 attached coding disc 56 and a sensor responsive to code marks of the encoder disk 58 having.

The of the torque sensor 52 and the rotation angle sensor 54 The measured data generated are sent to a control unit integrated in the screwdriver 32 that contains a microprocessor and a memory transfer. Via an interface 34 can the control unit 32 Communicate with other electronic devices and connected, for example, to a modem that has Internet access.

With the control unit 32 is a display device 36 connected, on which the current torque and / or the current rotation angle can be displayed in digital form. Furthermore, the setpoints can be displayed. It is also possible to display data records of different bolting cases, which can be individually selected and thus activated. Via appropriate input elements, a menu selection on the display device 36 respectively. For the menu then different Schraubenanzugsverfahren can be selected. It is also possible to make the screwdriver operational only if a particular code has previously been entered. This can ensure that the screwdriver is not used by unauthorized persons.

The turning on and off of the rotary wrench is done by pressing appropriate switch 18 in the usual way.

On the case 12 is a slot 40 for a chip card 42 intended. The chip card 42 with the chip 44 forms an external one Data carrier that stores the tightening parameters of the tightening operations performed. The chip card 42 For example, it can be taken out at the end of a working day and its contents read into a computer to document every single screwing operation performed on the working day.

The inventive method is based on 3 explains in which the torque M _{D is shown} on the ordinate and the rotation angle α on the abscissa.

In a screwing the drive is first turned on and the screw is rotated at full speed until a predetermined mating torque M _{F is} reached. The joining torque is a defined value, which here is for example 300 Nm. When the joining torque is reached, the screw connection is already tightened so tightly that it can no longer be unintentionally released or unintentionally misaligned. Until reaching the joining moment M _F , the torque mode DMM is performed, in which the torque is measured during the screwing operation with the torque sensor. When the joining torque M _F is reached, a transition into the rotational angle mode DWM takes place, in which with the rotational angle sensor 54 starting from 0 ° the angle of rotation is measured. It is assumed that the target rotational angle α _{S is} reached at the setpoint torque Ms, which is 90 ° here.

In the rotation angle mode, the rotation angle of the output shaft of the rotary wrench is determined continuously or at time intervals. In this case, when approaching the target torque, the speed can be reduced in order to avoid an abrupt shutdown of the rotary wrench. For example, according to a predetermined function depending on the angle of rotation, the speed can be controlled down.

Around the coordinate point of the setpoint values M _S and α _S is designated a tolerance zone T, defined by the values M _max , M _min , α _min and α _max , which can be input by the user to an input device of the rotary screwdriver. If the tightening process ends in this tolerance zone T, it is considered acceptable.

The drive of the rotary screwdriver is switched off when the rotational angle α _M measured with the rotational angle sensor has reached the value α _S -α _K , where α _{K is} a correction value. After switching off, the drive is still running, so that it finally comes to a stop at or near the setpoint α _S.

The record, which in a screwing on the smart card 42 is registered, contains the following data in addition to the serial number of the screwdriving process and the date and time information:
Joining moment M _F
Target rotation angle α _S
Correction value rotation angle α _K
Correction value of torque
Torque limit minimum M _min
Torque limit maximum M _max
Rotation angle limit minimum α _min
Rotation angle limit maximum α _max .

In addition, the following data are recorded and stored in the chip card for a graphical representation following the achievement of the joining moment M _F :
Torque actual value
Rotation angle actual value.

This value pair is recorded in each case at time zero, namely the achievement of the joining moment M _F , and thereafter at intervals of 10 ms.

If at the end of a screwing process the tolerance range T in 3 is reached, a signal is generated indicating that the bolting is in order. On the other hand, if the tolerance range T is not met, a corresponding negative signal is generated which indicates that this screwing procedure was not correct and must be discarded. The screwdriver is then disabled and can only be switched on manually.

The correction value α _K is determined in such a way that during a test run the drive is switched off when a predetermined torque is reached and the excess rotational angle is measured and stored as a correction value α _K. As a predetermined torque, first the joining torque M _{F is} selected. The drive then comes to a standstill far below the setpoint torque Ms, so that the setpoint torque is not reached.

Thereafter, in a second test run, the drive is switched off when the measured rotation angle α _{M reaches} the value of the setpoint rotation angle minus the previously determined correction value α _K. The subsequently measured rotational angle at which the output shaft comes to a standstill results in a new correction value α _K , which is smaller than the first correction value. In this way, an iterative approach to the value α _{S takes place} . This approach takes place from below, so that it is ensured that the angle of rotation does not exceed the value α _S. The finally resulting correction value α _K is stored for the relevant screw case and adopted for the subsequent screwing.

The logs of the individual screwdriving processes are saved and are also available for later evaluations. It is also possible to program or query the screwdriver via the Internet or other data connections. In this way, the data of the individual screwdrivers that are used anywhere in the world are available at any time in a central office. It can also be determined whether a screwdriver is in need of repair or maintenance.

Claims (7)

Method for automatically controlling a screwdriving process of a rotary screwdriver, comprising a controllable drive for an output shaft and an integrated control unit ( 32 ) with microprocessor and memory, a torque sensor and a rotation angle sensor, comprising the steps of: - activating the drive while measuring the torque in a torque mode (DMM) until the torque reaches a predetermined mating torque (M _F ), - upon reaching the joining torque ( M _F ): Transition to a rotation angle mode (DWM), in which the rotation angle swept by the output shaft (α _M ) is measured, - Ending the drive, when the rotation angle reaches a predetermined value, when reaching the joining torque (M _F ) to To avoid stopping the drive due to stopping the drive remains activated and the controller goes into the rotation angle mode (DWM) without stopping the output shaft. The method of claim 1, wherein after reaching the joining moment (M _F ), the time course of the rotation angle (α) and / or the torque (M _D ) is measured and stored. Method according to Claim 2, wherein the time profile of the angle of rotation (α) and / or of the torque (M _D ) or a relationship between torque and angle of rotation are integrated by a control unit integrated in the screwdriver ( 32 ) to an external data medium ( 42 ) or fed into an information network. Method according to one of claims 1-3, wherein in a test run the drive is switched off when a predetermined torque is reached and the excess rotational angle is measured and stored as a correction value (α _K ). The method of claim 4, wherein a target rotation angle (α _S ) is set and the drive is turned off when the measured rotation angle (α _M ) reaches the value of the desired rotation angle (α _S ) minus the correction value (α _K ). The method of claim 5, wherein after switching off the drive, the rotation angle is measured and compared with the desired rotation angle (α _S ) and stored at a deviation as a new correction value (α _K ). Method according to one of claims 1-6, characterized in that screwing parameters of different screwing are stored and can be retrieved when needed.

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