EP3727758B1 - Setting method for threaded connection by means of impact wrench - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to a setting method for expansion anchors, which as

Control method for an impact wrench is implemented.

From the EP 2 985 118 A1 A control method of an impact wrench for tightening a screw connection is known which, in response to an actuation of a button, executes a sequence with successive phases: a first phase in which an impact mechanism of the impact wrench exerts a predetermined number N1 of rotary impacts on the screw connection, a second phase, in which further rotary impacts are exerted on the screw connection, and a third phase in which rotary impacts are exerted again on the screw connection until an angle of rotation corresponds to the final angle of rotation or a speed is reached over a predetermined period of time.

DISCLOSURE OF THE INVENTION

A control method of an impact wrench (1) for tightening a screw connection (52) executes a sequence with the successive phases in response to actuation of a button (9). In a first phase, an impact mechanism (3) of the impact wrench (1) exerts a predetermined number N1 of rotary impacts on the screw connection (52). During the first phase S1, a course of a rotation angle Φ over time (t) is estimated. A pattern is adapted to the curve and, based on the pattern, a target torque M0 is determined for a second phase S2 and a final angle of rotation or a final number of strokes is determined for a third phase S3. During the second phase (S2), rotary impacts are exerted until an estimated torque M reaches the setpoint torque M0. During the third phase S3, rotary impacts are exerted on the screw connection until a number of rotary impacts corresponds to the final number N3 or a rotation angle corresponds to the final rotation angle.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

einen Schlagschrauber

Fig. 2

ein Eingabeelement

Fig. 3

eine Schraubverbindung von zwei Stahlplatten

Fig. 4

eine Schraubverbindung von zwei Stahlplatten

Fig. 5

einen Verlauf eines Drehwinkels

Fig. 6

ein Ablaufdiagramm zu dem Betriebsmodus "Stahlbau"

The following description explains the invention on the basis of exemplary embodiments and figures. In the figures show:

Fig. 1

an impact wrench

Fig. 2

an input element

Fig. 3

a screw connection of two steel plates

Fig. 4

a screw connection of two steel plates

Fig. 5

a course of an angle of rotation

Fig. 6

a flowchart for the "steel construction" operating mode

Identical or functionally identical elements are indicated by the same reference symbols in the figures, unless stated otherwise.

EMBODIMENTS OF THE INVENTION

Fig. 1 schematically illustrates the impact wrench 1. The impact wrench 1 has an electric motor 2, an impact mechanism 3 and an output spindle 4. The impact mechanism 3 is continuously driven by the electric motor 2. As soon as a retroactive torque of the output spindle 4 exceeds a threshold value, the percussion mechanism 3 repeatedly exerts rotary impulses (rotary impacts) on the output spindle 4 with a brief but very high torque. The output spindle 4 accordingly rotates continuously or step by step around a working axis 5. The electric motor 2 can be fed via a battery 6 or can be mains-fed.

The impact wrench 1 has a handle 7 by means of which the user can hold and guide the impact wrench 1 during operation. The handle 7 can be fixed to a machine housing 8 in a rigid manner or by means of damping elements. The electric motor 2 and the hammer mechanism 3 are arranged in the machine housing 8 . The electric motor 2 can be switched on and off by means of a button 9. The button 9 is arranged, for example, directly on the handle 7 and can be actuated by the hand surrounding the handle.

The hammer mechanism 3 , for example, has a hammer 10 and an anvil 11. The hammer 10 has claws 12 which rest against claws 13 of the anvil 11 in the direction of rotation. The hammer 10 can transmit a continuous torque or brief rotary impulses to the anvil 11 via the claws 12 . A coil spring 14 biases the hammer 10 toward the anvil 11 , thereby keeping the hammer 10 engaged with the anvil 11 . If the torque exceeds the threshold value, the hammer 10 moves against the force of the helical spring until the claws 12 are no longer in engagement with the anvil 11 . The electric motor 2 can accelerate the hammer 10 in the direction of rotation until the hammer 10 is again forced into engagement with the anvil 11 by the helical spring 14. The meanwhile gained kinetic energy is transmitted by the hammer 10 to the anvil 11 in a short pulse. One embodiment provides that the hammer 10 is positively guided on a drive spindle 15 along a spiral path 16 . The forced guidance can be implemented, for example, as a spiral recess in the drive spindle 15 and a pin of the hammer 10 engaging in the recess. The drive spindle 15 is driven by the electric motor 2 .

The output spindle 4 protrudes from the machine housing 8 . The protruding end forms a tool holder 17. The exemplary tool holder 17 has a square cross section. A socket 18 or a similar tool can be plugged onto the tool holder 17 . The socket 18 has a socket 19 with a square, hollow cross-section, the dimensions of which essentially correspond to the tool holder 17. Opposite the socket 19 , the socket 18 has a mouth 20 for receiving the screw head 21, ie the hexagonal nut 22 or an analogous screw. The socket 18 can be secured on the output spindle 4 by means of a tool lock 23. The tool lock 23 is based, for example, on a pin which is inserted both through a bore in the output spindle 4 and in the socket 18.

The impact wrench 1 has a control unit 24. The control unit 24 can be implemented, for example, by a microprocessor and an external or integrated memory 25 . Instead of a microprocessor, the control unit can be implemented from equivalent discrete components, an ASIC, an ASSP, etc.

The impact wrench 1 has an input element 26 via which the user can select an operating mode. The control unit 24 then controls the impact wrench 1 in accordance with the selected operating mode. The control sequences of the various operating modes can be stored in the memory 25.

The input element 26 can include, for example, a display 27 and one or more input buttons 28. The control unit 24 can display the various operating modes stored in the memory 25 and possibly associated connection types. The user can select the operating mode by means of the input buttons 28. In addition, the user can enter specifications such as size, diameter, length, target torque, load capacity or manufacturer designation of a connection type. In an alternative embodiment, the impact wrench 1 has a communication interface 29 which communicates with an external input element 30 . The external input element 30 can be, for example, a mobile phone, a laptop or an analog mobile device. Furthermore, the input element can be an additional module which can be arranged as an adapter between the impact wrench 1 and the battery 6 . Several connection types are stored in an application executed on input element 30 , or the application can query them from a server via a mobile radio interface. The external input element 30 can contain the expansion anchor or relevant information of the connection type on a display 31 . The user selects a connection type via an input button 32 or a touch-sensitive display 31 . The external input element 30 transmits the type designation or parameters relevant to the control method of the selected connection type to the impact wrench 1 via a communication interface 33 to the communication interface 29 of the impact wrench 1. The communication interface 29 is preferably radio-based, e.g. using a Bluetooth standard. As a supplement or alternative, the internal input element 28 or the external input element 30 can be provided with a camera 34 which can capture a bar code on a packaging of the connection type. The input element 28 determines the connection type based on the detected bar code and the bar codes stored in the memory 25. Instead of a camera 34 , a laser-based bar code reader, an RFID reader, etc. can be used to detect a label on the packaging or on the connection type. In a further embodiment, image processing in the input element 28 can recognize the connection type on the basis of an image recorded by the camera 34 , or at least limit a selection of connection types presented to the user based on the image.

Fig. 3 shows schematically a screw connection of two construction elements 50, 51 for steel construction in civil engineering. The two construction elements 50, 51 are to be connected in a load-bearing manner by means of one or more screw connections 52. The construction elements 50, 51 can include, for example, beams, plates, tubes, flanges, etc. The construction elements are made of steel or other metallic materials. The construction elements 50, 51 are reduced to their touching plate-shaped sections in the illustration. One or more eyes 53 are provided in the sections. The eyes 53 of the two construction elements are aligned with one another by the user.

The screw connections 52 can have a typical structure with a screw head 54 on a threaded rod 55 and a screw nut 56 . While the threaded rod 55 has a smaller diameter than the eyes 53 , the screw head 54 and the screw nut 56 have a larger diameter than the eye 53. The threaded rods can already be connected to the first structural element 50 with other screw connections.

The user inserts the threaded rods 55 through the aligned eyes 53. The screw nut 56 is then put on. With a manual fastening pulls the user turns the screw nut 56 with a torque wrench until a target torque specified for the screw connection is reached. The specification is given by the manufacturer of the screw connection or is specified in the relevant standards for steel construction. The target torque ensures that the screw connection cannot loosen under load, in particular vibrations. On the other hand, the threaded rod 55 should not be unnecessarily stressed or, in the worst case, be permanently damaged while the screw nut 56 is being tightened.

The construction elements 50, 51 occasionally do not lie flat on top of one another, as exemplified in FIG Fig. 4 illustrated. During the tightening of the screw connection 52 , the construction elements 51 deform. The retroactive torque of the screw connection 52 is therefore not only dependent on the screw type, but also on the construction elements 51 and their current pretension. In the case of manual tightening, this generally does not result in any additional difficulties, since the user can see whether the construction elements 50, 51 are already lying flat on one another.

Tightening the screw connections 52 with a torque wrench is a reliable and robust method, but the method is labor intensive. Especially since the screw connection 52 typically contains many screws. The screw connections 52 could in principle be tightened with a conventional electric screwdriver and a corresponding switch-off until the target torque is reached. However, the user cannot apply the necessary holding force for the target torque and there is a considerable risk of injury to the user.

The impact wrench 1 implements a robust setting method for the screw connection 52. The user aligns the structural elements 51 with one another, inserts the threaded rods 55 through the second structural element 51 and puts the screw nuts 56 on. The user can tighten the screw connections 52 with the impact wrench 1. For this purpose, the user selects the “steel construction” operating mode and specifies the type of screw connections 52.

While the torque output of a continuously rotating screwdriver can be measured quite easily via the power consumption of the electric motor and the speed of the output spindle, this is not possible in the impact wrench 1 due to the mechanical decoupling between the output spindle 4 and the electric motor 2. A direct measurement of the output torque by means of a sensor on the output spindle is technically very good due to the high mechanical loads demanding and not suitable for the impact wrench. A further problem arises from the construction elements 50, 51 which deform during the tightening. Their influence on the torque, the rotation progress, etc. is not known a priori.

The setting process makes do with a three-phase tightening of the screw connection 52. A first phase S1 is used to analyze the screw connection 52 and the structural elements 51, 52. Based on the analysis, a target torque M0 and a final angle of rotation ϕ are determined. During a subsequent second phase S2 , the impact wrench 1 exerts blows on the screw connection 52 until an estimated torque M reaches the setpoint torque M. In a final third phase S3 , the screw connection 52 is tightened by the final angle of rotation ϕ.

Each type of screw connection 52 is assigned a number of control parameters which are necessary for the subsequent proper sequence of the setting process. The control parameters are stored in the memory 25 for the type. In response to the input or selection of the screw connection 52 , the control unit 24 reads out the corresponding control parameters. The control parameters are preferably retained until the user selects a different type of screw connection 52. It is not necessary to select the screw connection 52 before each individual setting.

When the button 9 is not actuated, the electric motor 2 is disconnected from the power supply, for example the battery 6, and does not rotate. The impact wrench 1 preferably falls into a standby mode when the button 9 is released. The setting process begins when the button 9 is pressed. In a preparatory phase, it can be checked whether the user has previously selected the type of screw connection 52 by means of one of the input elements 28 . If a corresponding selection has not yet been made and the control parameters are not set, the user is stopped and the impact wrench 1 remains inactive. Otherwise, the electric motor 2 is connected to the power supply.

In response to actuation of the button 9 , the drive spindle 15 is accelerated. The spindle is accelerated to a target speed Do. Initially, the retroactive torque of the screw connection 52 can be so small that the hammer mechanism 3 is not activated. This pre-phase is not described further below.

A first phase S1 of the setting method begins with the first impact of the impact mechanism 3. During the first phase S1 , the impact wrench 1 exerts a predetermined number N1 of impacts. The specified number N1 can be specified by the selected type of screw connection 52 . The screw connection 52 is tightened by the blows by an angle of rotation Φ. In the above example, the screw nut 56 is rotated relative to the threaded rod 55 by the angle of rotation Φ. The angle of rotation Φ is not only dependent on the screw connection 52 but also on the construction elements 50, 51.

An estimation routine S4 compares the course 59 of the angle of rotation φ over the time t with a pattern 60 ( Fig. 5 ). The pattern 60 is a typical course of the angle of rotation determined from series of tests. The test series are carried out under different boundary conditions, eg different fastening elements, different pretensioning of the fastening elements, etc .. The pattern 60 has four to six degrees of freedom, which prove to be sufficient for classifying the different boundary conditions in steel construction. The patterns 60 can be stored as control parameters for the screw connection 52. A preselection of the possible patterns 60 or a restriction of the degrees of freedom or the values of the parameters for the degrees of freedom depending on the type of screw connection 52 selected in advance can increase the reliability in the selection of the pattern 60 or adaptation of the pattern 60 and the associated computational effort to reduce.

Fig. 5 shows an example of a course 59 in which the construction elements 51 lie flat on top of one another. The estimation routine determines the current boundary condition by adapting the pattern 60 to the previous course 59 of the angle of rotation during the current setting process. The preferred pattern 60 has three sections: a beginning 60, a middle 61 and an end 62. The beginning is linear with a first slope. The end has a linear course with a second slope, which is less than the first slope. The center 61 is described, for example, by an exponential function with a monotonically decreasing slope. Alternatively, the center can be described by other functions with a continuously monotonically decreasing slope, e.g. exponential function, hyperbola. The transitions between the sections are preferably smooth. The pattern has four to six degrees of freedom. The degrees of freedom are or describe, among other things, the slope of the beginning, the slope of the end, the duration of the beginning and the duration of the middle. The comparison of the course with the pattern can be done with a compensation calculation (Fit) in which the numerical values for the degrees of freedom are varied, for example using the least squares method. Since the computing power of the impact wrench 1 is limited, for each type of screw connection 52 value ranges for the two slopes or their associated degrees of freedom. The value ranges are determined by test series and are stored in the specified parameters.

The estimation routine S4 preferably records the angle of rotation φ over time, beginning with the first beat t0 , in order to obtain measurement points for the comparison. A measuring point contains the measured angle of rotation φ and the associated time t. The angle of rotation φ can be estimated based on the angle of rotation of the drive spindle 15 between successive rotary strokes. The angle of rotation φ of the socket 18 differs from the angle of rotation of the drive spindle 15 by the angle between the claws 12 of the hammer 10 multiplied by the number of blows. Time recording can be approximated by chronological recording of the angle of rotation φ. The measuring points can be stored in a buffer.

The estimation routine S4 adapts the pattern 60 according to the predetermined number N1 of rotary strokes. The number is large enough to maintain a good fit. The estimation routine S4 is terminated when a deviation of the pattern 60 from the measuring points lies within a predetermined tolerance. If, after the specified number of rotary strokes or specified duration, a deviation in the pattern is outside a tolerance or if the minimum number of measuring points for the end of the pattern has not been reached, an error message is issued and the setting process is aborted.

A target torque M0 and a final angle of rotation φ are assigned to each of the patterns 60. The target torque M0 and the final angle of rotation ϕ can be stored as a value or can be calculated from the sample 60. The threshold value M0 is typically less than the target torque M9 for the screw connection 52 when this is tightened by hand.

During the second phase S2 , the electric motor 2 rotates the drive spindle 15 preferably at the specified speed Do. The control unit 24 can, for example, determine the speed D of the drive spindle 15 directly with a rotation sensor 45 on the drive spindle 15 or indirectly via a rotation sensor on the electric motor 2 . The rotational speed Do is one of the control parameters assigned to the screw connection 52. The speed has an influence on the torque output by the impact wrench 1. The hammer 10 is released from the anvil 11 after a rotary stroke and is accelerated by the drive spindle 15 up to the next rotary stroke on the anvil 11. The next rotary stroke occurs when the hammer 10 is again aligned with the anvil 11. Due to the largely specified acceleration distance a higher speed of the drive spindle 15 results in a higher angular speed and a higher angular momentum of the hammer 10 in the rotary impact. As a rough approximation, it is assumed that a large part of the angular momentum is transmitted to the anvil 11 and the output spindle 4 in the event of a rotary impact. In a series of tests, the angular momentum or a variable describing the angular momentum can be determined for different speeds and stored in a family of characteristics.

During the second phase S2 , an angle of rotation δΦ by which the output spindle 4 rotates due to the rotary shock is determined. The output torque M corresponds to the transmitted angular momentum and the angle of rotation δΦ by which the output spindle 4 rotates due to the rotary impact. Based on the determined angle of rotation δΦ and the approximate correlation of angular momentum and speed D , the output torque M is estimated. A family of characteristics can be stored in the memory 25 , for example, which assigns a torque M or a variable describing the torque to a pairing of speed D and angle of rotation δΦ.

The angle of rotation δΦ is determined by a sensor system 46 in the impact wrench 1 . The sensor system 46 can, for example, directly detect the rotary movement of the output spindle 4 with a rotary sensor 47. The rotation sensor 47 can scan markings on the output spindle 4 inductively or optically. As an alternative or in addition, the sensor system 46 can estimate the angle of rotation δΦ of the output spindle 4 based on the rotary movement of the drive spindle 15 between two successive rotary strokes. The drive spindle 15 rotates between the two rotary shock to the angular spacing of the claws 12, for example, 180 degrees, and the output spindle is provided the anvil 11 has rotated, in addition to the rotation angle δΦ 4. The rotational impacts are detected by a rotary impact sensor 48th For this purpose, the sensor system 46 detects the angle of rotation of the drive spindle 15 in the time span between two immediately successive rotary strokes. The beginning and the end of the period of time are detected by detecting the rotary impacts by means of a rotary impact sensor 48. The rotary impact sensor 48 can, for example, detect the increased short-term vibration in the impact wrench 1 associated with the rotary impact. The vibration is compared, for example, with a threshold value; the beginning or the end corresponds to the point in time when the threshold value is exceeded. The twist sensor 48 can also be based on an acoustic microphone or infrasound microphone that detects a spike in volume. Another variant of a rotary shock sensor 48 detects the power consumption or a fluctuation in speed of the electric motor 2. The power consumption increases briefly during the rotary shock. The angle of rotation of the drive spindle 15 can, for example, from the speed D or the signals of the Rotation sensor 45 and the time span are calculated. The angle of rotation δΦ of the output spindle 4 is determined as the angle of rotation of the drive spindle 15 minus the angular spacing of the claws 12 .

The second phase S2 ends when the estimated torque M exceeds the setpoint torque M0 previously determined using the pattern 60.

The second phase S2 is followed by a third phase S3 in which the screw connection 52 is still rotated by the final angle of rotation ϕ. The progress of the angle of rotation during the third phase S3 can be estimated. The impact wrench 1 stops tightening when the estimated angle of rotation has reached the final angle of rotation ϕ during the third phase S3. Alternatively, instead of a final angle of rotation, a final number N2 of strokes can also be carried out during the third phase S3.

Claims (3)

1. Control method of an impact wrench (1) for tightening a threaded connection (52), which, in response to actuation of a pushbutton key (9), executes a sequence with the consecutive phases:

   a first phase (S1) in which an impact mechanism (3) of the impact wrench (1) exerts a predefined number (N1) of rotary impacts on the threaded connection (52), and during the first phase (S1) a profile (59) of a rotational angle Φ over time (t) is estimated and a pattern (60) is adapted to the profile (59), and on the basis of the pattern (60) a setpoint torque (M0) is determined for a second phase (S2) and a final rotation angle or a final number of impacts is determined for a third phase (S3),

   the second phase (S2) in which rotary impacts are exerted on the threaded connection (52) until an estimated torque (M) reaches the setpoint torque (M0), and

   the third phase (S3) in which rotary impacts are exerted on the threaded connection (52) until a number of the rotary impacts corresponds to the final number (N3), or a rotational angle corresponds to the final rotational angle.
2. Control method according to Claim 1, characterized in that the pattern (60) has a first section (61) with a first gradient and a second section (63) which follows the first section (61) and has a second gradient, wherein the second gradient is lower than the first gradient.
3. Control method according to Claim 2, characterized in that the pattern (60) has a third section (62) with a continuously decreasing gradient, wherein the third section (62) is arranged between the first section (61) and the second section (63).

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